{"text_format":"1","workbook":"xlsx","n_sheets":4,"sheets":["검색","2017년","2018년","2019년"],"not_rendered":{"charts":0,"images":1,"macros":1,"external_links":0,"defined_names":513,"comments":0,"pivot_tables":0},"unopened":[],"bounds":{"document_bytes":16777216,"sheet_cells":100000,"rows_first":2000,"rows_last":500,"rows_between":2000,"halvings":0,"cell_chars":16384,"cell_head_chars":4096},"cells_cut":0,"cells_raw":0,"read":"whole","date_system":"1900"}

{"sheet":"검색","index":0,"n_rows":4,"n_cols":8,"rows_kept":4,"cut":false,"hidden":false,"merged":[]}
["필드선택","검색값"]
["권호","35권5호","☜ 필드선택 - 검색값 입력 후 Enter (첫 글자 대소문자 구분)"]
[]
["시트","권호","제목","토픽","초록","키워드","저자","DOI"]

{"sheet":"2017년","index":1,"n_rows":41,"n_cols":7,"rows_kept":41,"cut":false,"hidden":false,"merged":[]}
["권호","제목","토픽","초록","키워드","저자","DOI"]
["33권1호\npp.1-8","파형 습식클러치의 드래그 토크 저감을 위한 파형내 유로 위치 설정 설계 연구         \n(A Study on the Flow Path Position Design of Waviness Friction Pad for Drag Torque Reduction in Wet Type DCT)","Automotive Tribology ","Drag torque reduction in a wet clutch pack is a key aspect of the design process of the dual clutch transmission (DCT) system. In order to reduce the drag torque caused by lubricant shear resistance, recently developed wet clutch pack systems of DCT, as well as automatic transmission and other four-wheel drive (4WD) couplings, frequently utilize wavy wet clutch pads. Therefore, wavy shape of friction pad are made on the groove patterns like waffle pattern for the reduction of drag torque. Additionally, the groove patterns are designed with larger channels at several locations on the friction pad to facilitate faster outflow of lubricant. However, channel performance is a function of the waviness of the friction pad at the location of the particular channel. This is because the discharge sectional area varies according to the waviness amplitude at the location of the particular channel. The higher location of the additional channel on the friction pad results in a larger cross-sectional area, which allows for a larger flow discharge rate. This results in reduction of the drag torque caused by the shear resistance of DCTF, because of marginal volume fraction of fluid (VOF) in the space between the friction pad and separator. This study computes the VOF in the space between the friction pad and separator, the hydrodynamic pressure developed, and the shear resistance of friction torque, by using CFD software (FLUENT). In addition, the study investigates the dependence of these parameters on the location and waviness amplitude of the channel pattern on the friction pad. The paper presents design guidelines on the proper location of high waviness amplitude on wavy friction pads.\n","DCT(듀얼 클러치 트랜스미션), clutch pack(클러치 팩), wave clutch(웨이브 클러치), drag torque(드래그 토크), flow path(유로), engagement(체결), disengagement(풀림)","조정희1·한준열1·김우정3·장시열2†\n1국민대학교 자동차공학 전문대학원, 2국민대학교 자동차공학과, 3현대파워텍㈜ ","https://doi.org/10.9725/kstle.2017.33.1.1"]
["33권1호\npp.9-14","초임계 CO2 발전용 파워 터빈의 회전체 동역학 해석 및 구동 시험   \n(Rotordynamic Performance Analysis and Operation Test of a Power Turbine for the Super critical CO2 Cycle Application)","Lubrication (Lubricants & Additives)","This paper presents a rotordynamic analysis and the operation of a power turbine applied to a 250 kW super-critical CO2 cycle. The power turbine consists of a turbine wheel and a shaft supported by two fluid film bearings. We use a tilting pad bearing for the power turbine owing to the high speed operation, and employ copper backing pads to improve the thermal management of the bearing. We conduct a rotordynamic analysis based on the design parameters of the power turbine. The dynamic coefficients of the tilting pad bearings were calculated based on the iso-thermal lubrication theory and turbine wheel was modeled as equivalent inertia. The predicted Cambell diagram showed that there are two critical speeds, namely the conical and bending critical speeds under the rated speed. However, the unbalance response prediction showed that vibration levels are controlled within 10 mm for all speed ranges owing to the high damping ratio of the modes. Additionally, the predicted logarithmic decrement indicates that there is no unstable mode. The power turbine uses compressed air at a temperature of 250°C in its operation, and we monitor the shaft vibration and temperature of the lubricant during the test. In the steady state, we record a temperature rise of 40°C between the inlet and outlet lubricant and the measured shaft vibration shows good agreement with the prediction.","super critical CO2(초임계 CO2), tilting pad bearing(틸팅 패드 베어링)","이동현1†·김병옥1·선경호1·임형수2\n1한국기계연구원 시스템다이나믹스 연구실, 2한국기계연구원 극한에너지기계 연구실 ","https://doi.org/10.9725/kstle.2017.33.1.9"]
["33권1호\npp.15-22","탄소섬유가 혼합된 세라믹 복합재 제동마찰재의 마찰·마모 특성     \n(Tribological Properties of Ceramic Composite Friction Materials Reinforced by Carbon Fibers)","Tribology in Transportation (Railway / Road) ","Because the running speed of vehicles is increasing and a shorter braking distance is required, high heat-resistant brake pads are needed to satisfy the requirements of customers and car makers. In the near future, hazardous materials such as Cu, Cr, Zn, and Sb will be restricted from use in friction materials. Ceramic composites reinforced by carbon fibers are good candidates for eco-friendly friction materials. In this study, we develop ceramic composite friction materials. The friction materials are composed of carbon fibers, Si, SiC, graphite, and phenol resin and are prepared by hot forming and heat treatment at high temperatures. The density, void ratio, and compressive strength are 1.59-1.66 g/cm3, 16.6-20, and 70-90 MPa, respectively. Friction and wear tests are performed using a pin-on-plate-type reciprocating friction tester at 25, 100, and 200 °C. The counterpart material is a CrMoV steel extracted from a KTX brake disc. Friction coefficient, wear amount, and wear mechanism are measured and examined. We determine that the friction coefficients depend on the temperature and the fluctuation of the friction coefficients is larger at higher temperatures. The amount of wear increases with the surface temperatures of the specimens. The tribological properties of the developed composites are similar to those of a Cu-based sintered friction material. Through this study, it is confirmed that ceramic composite materials can be used as friction materials.","carbon fiber(탄소섬유), composite(복합재), friction coefficient(마찰계수), friction material(마찰재), SiC(탄화규소), wear(마모)","구병춘1†·김민수2\n1한국철도기술연구원 신교통연구본부, 2한국철도기술연구원 광역도시교통연구본부 ","https://doi.org/10.9725/kstle.2017.33.1.15"]
["33권1호\npp.23-30","탄성유체윤활해석에 의한 연료 펌프 저널베어링 최적간극 선정 연구           \n(A Study on the Optimum Clearance Selection of Fuel Pump Journal Bearing with Elasto-hydrodynamic Lubrication Analysis)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The electric controlled marine diesel engine has fuel pump generating the high pressurized fuel for fuel injection to combustion chamber via a common rail. Fuel pump consists of a cam-roller system. Journal bearing installed between a roller and a cam-roller pin is subjected to fluctuating heavy and instant loads by cam lift. First, Kinematic analysis is carried out to predict bearing loads during one cycle acting on the journal bearing. Second, flexible multi-body dynamic analysis and transient elasto-hydrodynamic(EHD) lubrication analysis for journal bearing considering elastic deformation of cam-roller pin, roller and bearing are conducted using AVL EXCITE/PU software to predict lubrication performance. The clearance ratio and journal groove shape providing lubrication oil are important parameter in bearing design having good performance and can be changed easier than other design parameters such as diameter, width, oil supply pressure and bearing material grade. Generally, journal bearing performance is represented by the minimum oil film thickness(MOFT) and peak oil film pressure(POFP). As well as the traditional design parameters(MOFT, POFP), in this study, temperature rise of lubrication oil is also evaluated through the side leakage flow of supplied oil. By the evaluating MOFT, POFP and temperature rise, the optimum bearing clearance ratio is decided.","clearance ratio(간극비), EHD(elasto-hydrodynamic, 탄성유체윤활), peak oil film pressure(POFP, 최대유막압력), minimum oil film thickness(MOFT, 최소유막두께), oil temperature rise(윤활유 온도 상승)","안성찬1†·이상돈1·손정호1·조용주2\n1현대중공업㈜ 엔진기계사업본부 엔진기계연구소, 2부산대학교 기계공학부 ","https://doi.org/10.9725/kstle.2017.33.1.23"]
["33권1호\npp.31-35","오일샌드 플랜트용 금속소재의 마모 특성에 대한 실험적 연구                        \n(Experimental Study on Wear Characteristics of Metallic Materials used in Oil Sands Plants)","Wear Phenomena & Mechanisms","Recently, international attention has been focused on the development of non-traditional energy resources such as shale gas and oil sands, due to the steep increase in the demand for natural resources. The materials incorporated in an oil gas plant module experience extreme environments, and are prone to various problem such as fracture, corrosion and abrasion due to low-temperature brittleness. In order to improve the plant life, it is necessary to perform characteristics study and performance evaluation of the materials. In particular, this paper explains the main set of materials which are most frequently used in oil sands plant project. In order to investigate wear characteristics, the authors carried out abrasive wear tests of TP 316, stainless steel and SS 400, structural rolled steel. For the analysis of the abrasive wear resistance of an oil sands plant, the authors carried out the test according to ASTM G 105 “Standard Test Method for Conducting Wet Sand/Rubber Wheel Abrasion Test” standard guidelines. The authors have derived the results from the data associated with the loss of mass with respect to wear rate. During the test, for a given wear length for 10,000 revolutions, the rotational speed and applied force of the rubber wheel were varied.","wet abrasive wear(습식 연삭 마모), material(소재), oil sands plant(오일샌드 플랜트)","원성재†·조승현·강대경·허중식\n한국기계전기전자시험연구원  ","https://doi.org/10.9725/kstle.2017.33.1.31"]
["33권2호\npp.37-44","프로세스 압축기 틸팅패드 저널베어링의 비정상 고온거동 트러블슈팅                  \n(Abnormal High-Temperature Behavior Troubleshooting of Process Compressor Tilting Pad Journal Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","A DE-side LBP tilting pad journal bearing of a 1-stage overhung heat-pump compressor in a propylene process exhibited abnormal high-temperature behavior. Its temperature had been relatively high at 78 °C from the beginning of operation. In 2014, after three years of operation, it increased suddenly and reached 103 °C. Installing a varnish removal equipment and others managed to stabilize the temperature at 95 °C. We undertook a troubleshooting approach for reviewing the comprehensive status and integrity of the temperature design of the bearing. We performed lubrication and heat-balance analysis, based on the design engineering data and documents supplied by the OEM. For the base design data of DE-side TPJB, evaluating the effects of key design variables on bearing metal temperature showed that firstly, increasing the bearing clearance and supply oil flow-rate, and next, changing the oil type, and finally, increasing the machined pad clearance and offset, are more effective in reducing the bearing metal temperature. Furthermore, a clarification meeting with the OEM revealed that an incorrect decision had been made to decrease the bearing clearance to eliminate the SSV harshness issue, while not maintaining a sufficient oil flow-rate. We conducted a detailed retrofit design analysis, wherein we increased the oil flow-rate and bearing clearance by decreasing the preload. We predicted that the bearing temperature would decrease to 63 °C from 75.7 °C even at the rerate condition. Finally, after installing and operating a retrofit replacement bearing in 2015, the bearing temperature stabilized at a low temperature of 65 °C. Currently (January. 2017), two year later, the bearing metal temperature remains at 65 °C. Therefore, we can conclude that the abnormal high-temperature behavior of the bearing has been resolved completely.","process compressor(프로세스 압축기), tilting pad journal bearing(틸팅패드 저널베어링), abnormal high-temperature(비정상 고온), troubleshooting(트러블슈팅), design approach(설계 접근)","이안성1†·이운실2·최동훈3\n1한국기계연구원 시스템다이나믹스연구실, 2현대오일뱅크㈜ 대산 엔지니어링팀, 3한양대학교 기계공학부","https://doi.org/10.9725/kstle.2017.33.2.37"]
["33권2호\npp.45-51","경유 혼입에 의한 엔진오일 물성 변화   \n(Change in Physical Properties of Engine oil Contaminated with Diesel)","Automotive Tribology ","Engine oil is a substance used for the lubrication of internal combustion systems. However, in some case, defects in engine systems may contaminate engine oil with fuel. Contaminated engine oil can cause problems in the normal functioning of a vehicle. In this study, we investigate the functional properties of engine oil contaminated with diesel fuel. The test results indicate that the engine oil contaminated with diesel fuel has low flash point, pour point, density, kinematic viscosity and cold cranking simulator value. The contaminated engine oil which has low plash point can cause fire and explosion accident. Furthermore, a four ball test indicates that the contaminated engine oil increases wear scar to poor lubricity. Moreover, we investigate the GC pattern using SIMDIST (simulated distillation) for determination of diesel in engine oil. The SIMDIST analytic result, diesel was detected at earlier retention time than engine oil in chromatogram. Thus the SIMDIST method can define whether engine oil is contaminated by diesel fuel or not. We can use the SIMDIST method for the diagnosis of oil condition instead of analyzing other physical properties that require many analytic instruments, large volume of oil sample and long analysis time."," engine oil(엔진오일), fuel mixing(연료 혼입), vehicle defect(차량 결함), physical property(물성), lubricity(윤활성), SIMDIST(고온시뮬레이션 증류시험)","임영관†·이종은·나용규·김종렬·하종한\n한국석유관리원 석유기술연구소 ","https://doi.org/10.9725/kstle.2017.33.2.45"]
["33권2호\npp.52-58","형광체 함유 용액 고속 토출 조건에서의 듀얼 압전 디스펜서 공이와 노즐의 마모 특성 평가                                 \n(Wear Characteristics for Rod and Nozzle of Jetting Dispenser Driven by Dual Piezoelectric Actuators Under High Frequency with Phosphor-containing Liquid)","Tribology Applications (Industrial Case Studies) ","An ultra-high precise ejection process is essential in a dispensing system for fabricating various precision parts such as a semiconductor, LED, and camera module. The size of such parts has been decreasing, which implies that a precise ejecting technique is required. A phosphor-containing liquid is ejected via a dispenser using dual piezoelectric actuators that are used for generating a high-speed dispensing mechanism. The rod and nozzle continuously contact in high speed to eject the liquid. However, the high-strength filler or phosphor in the liquid causes wear on the surfaces of the rod and nozzle during the dispensing process. As a result, the ejection reliability decreases as the wear on the surfaces increases. Therefore, it is necessary to estimate the wear characteristics of the rod and nozzle via an experiment and FE analysis. Reliability rests up to 1,000 cycles are conducted under relatively severe conditions. The flow rate and surfaces roughness of the rod and nozzle are measured in each ejection cycle. The surface images and wear volume are obtained before and after the tests and the ejection reliability is confirmed by measuring the flow rate of the liquid. The experimental results show that the ejection reliability is maintained up to 1,000k cycles; these results are validated by the simulation results.\n","jetting dispenser(젯팅 디스펜서), wear(마모), phosphor(형광체)","하명우1·이광희1·안준욱2·이철희1†\n1인하대학교 기계공학과, 2인하대학교 건설기계공학과","https://doi.org/10.9725/kstle.2017.33.2.52"]
["33권2호\npp.59-64","양극산화 알루미늄 합금6061의 초순수 물 윤활에서의 트라이볼로지적 특성 \n(Tribological Characteristics of Anodized Al 6061 Under Deinoized Water Lubricated Reciprocating Condition)","Micro/Nano-Tribology ,Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)"," This study investigates friction and wear characteristics of anodized aluminum (Al) alloy 6061 by using a reciprocating tribotester. The diameter and height of the specimen are 30 mm and 10 mm, respectively. The surface roughness of the mirrored-surface is approximately 0.01~0.02 μm, and it is used throughout the current study. As a result of anodizing, the depth and diameter of the nanopore are approximately 25 μm and 30-40 nm, respectively. The testing conditions are as follows: loads of 1, 3, and 5 N; a frequency of 1 Hz; a stoke of 3 mm; and a duration of 1800 s. We use deionized water with a volume of approximately 25 μl, as the lubricant. Micro Vickers hardness measurements show that mirrored-surface specimens had lower hardness values than anodized specimens. Further, their coefficients of friction are lower than those of the anodized samples, and the width of their wear track increases with load, as expected. The anodized specimens' coefficients of friction increase with stable frictional behavior and exhibit insignificant load dependence. Further, we observe that the width of the wear track is less than that of the mirrored-surface specimens, and micro cracks are present near it. Moreover, the anodizing process increases the hardness of the samples, improving their wear resistance. These results indicate that nanoporous structures are not effective in lowering friction under the water-lubricated condition.","AAO(anodic aluminum oxide), friction, wear, reciprocating test","정준호1·조민행2†\n1중앙대학교 대학원 기계시스템엔지니어링학과, 2중앙대학교 기계공학부 ","https://doi.org/10.9725/kstle.2017.33.2.59"]
["33권2호\npp.65-70","수력 원통형 터빈 가이드 베어링의 저부하/저편심 성능향상 설계 – 패드 선단  테이퍼의 도입                              \n(Low-Load/Low-Eccentricity Performance Improvement Designs for Hydro Power Application of Cylindrical Turbine Guide Bearings – Introduction of Pad Leading-Edge Tapers)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In vertical hydro/hydraulic power turbine-generator applications, traditionally, cylindrical turbine guide bearings (TGBs) are widely used to provide turbine runner shafts with smooth rotation guides and supports. All existing cylindrical TGBs with simple plain pads have drawbacks such as having no pressure generation and film stiffness at the no-load condition and in addition, at the low-load/low eccentricity condition, having very low film stiffness values and lacking design credibility in the stiffness values themselves. In this paper, in order to fundamentally improve the low-load/low-eccentricity performance of conventional cylindrical TGBs and thus enhance their design-application availability and usefulness, we propose to introduce a rotation-directional leading-edge taper to each partitioned pad, i.e., a pad leading-edge taper. We perform a design analysis of lubrication performance on 4-Pad×4-Row cylindrical TGBs to verify an engineering/technical usefulness of the proposed pad leading-edge taper. Analysis results show that by introducing the leading-edge taper to each pad of the cylindrical TGB one can expect a constant high average direct stiffness with a high degree of design credibility, regardless of load value, even at the low-load/low-eccentricity condition and also control the average direct stiffness value by exploring the taper height as a design parameter. Therefore, we conclude that the proposed pad leading-edge tapers are greatly effective in more accurately predicting and controlling rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems to which cylindrical TGBs are applied.","hydro power turbine-generator(수력 터빈-발전기), cylindrical turbine guide bearing(원통형 터빈 가이드 베어링), pad leading-edge taper(패드 선단 테이퍼), low-load/low-eccentricity(저부하/저편심)","이안성1†·장선용2\n1한국기계연구원 시스템다이나믹스연구실, 2대동메탈공업㈜ 기술연구소 ","https://doi.org/10.9725/kstle.2017.33.2.65"]
["33권2호\npp.71-78","습식 DCT의 드래그 토크 저감을 위한 클러치 패드 유로 설계                       \n(A Study on the Wet Clutch Pattern Design for the Drag Torque Reduction in Wet DCT System)","Lubrication (Lubricants & Additives) ,Automotive Tribology","The drag torque in the wet clutch system of a dual clutch transmission system is investigated because it is relatively high, up to 10 of the total output torque of the engine, even when the clutch is in the disengagement state with zero torque transfer. Drag torque results from the shear resistance of the DCTF between the friction pad and separator plate. To reduce the drag torque for ensuring fuel economy, the groove pattern of the wet clutch friction pad is designed to have a high flow rate through the pattern groove. In this study, four types of groove patterns on the friction pad are designed. The volume fraction of the DCTF (VOF) and hydrodynamic pressure developments in the gap between the friction pad and separator plate are computed to correlate with the computation of the drag torque. From the computational results, it is found that a high VOF and hydrodynamics increase the drag torque resulting from the shear resistance of the DCTF. Therefore, a patterned groove design should be used for increasing the flow rate to have more air parts in the gap to reduce the drag torque. In this study, ANSYS FLUENT is used to solve the flow analysis.","DCT(듀얼 클러치 트랜스미션), clutch pack(클러치 팩), friction material(마찰재), drag torque(드래그 토크), flow path(유로), engagement(체결), disengagement(풀림)","조정희1·한준열1·김우정3·장시열2†\n1국민대학교 자동차공학 전문대학원, 2국민대학교 자동차공학과, 3현대파워텍㈜ ","https://doi.org/10.9725/kstle.2017.33.2.71"]
["33권3호\npp.85-91","습식 DCT(Dual Clutch Transmission) 클러치 팩 내부에서의 체결 동작에 따른 변속기유 거동 연구                   \n(Study on the Lubricant Flow Behaviors in the Wet Clutch Pack System of Dual Clutch Transmission)","Automotive Tribology ","This work studies the flow behaviors in the gap between the friction pad and separator in wet-clutch systems. The fluid volume of the lubricant is modeled using the entire system of wet-clutch pack of a dual clutch transmission that has larger outer radius of odd gear shifts and smaller inner radius of even gear shifts. Flow behaviors in the gap of the clutch pad are computed using the gear shift modes that consider the real relative velocities between the friction pad and separator. Flow behaviors in the gap of the disengaged clutch pad are mainly investigated for the wet-clutch system, whereas the engaged clutch pad is modeled with no fluid rate through the contacting surfaces. The developed hydrodynamic fluid pressures and velocity fields in the clutch pad gap are computed to obtain the relevant information for managing flow rates in wet-clutch packs under dual operating conditions during gear shifts. These hydrodynamic pressures and velocity fields are compared on the basis of each gear level and gap location, which is necessary to determine the effects of groove patterns on the friction pad. Shear stresses in the gap locations are also computed on the basis of the gear level for the inner and outer clutch pads. The computed results are compared and used for the design of cooling capacity against frictional heat generation in wet-clutch pack systems.","dual clutch transmission(듀얼 클러치 변속기, DCT), clutch pack(클러치 팩), wet clutch(습식 클러치), engagement(체결), disengagement(이탈), flow behaviors(유동), clutch friction pad(클러치 마찰패드), separator(분리판)","김우정1·이상호1·장시열2†\n1현대파워텍㈜, 2국민대학교 자동차공학과 ","https://doi.org/10.9725/kstle.2017.33.3.85"]
["33권3호\npp.92-97","서브 마이크로 구조를 가진 실리콘 표면의 마찰 특성 연구                    \n(Study on Frictional Characteristics of Sub-micro Structured Silicon Surfaces)","Micro/Nano-Tribology","The understanding of the friction characteristics of micro-textured surface is of great importance to enhance the tribological properties of nano- and micro-devices. We fabricate rectangular patterns with submicron-scale structures on a Si wafer surface with various pitches and heights by using a focused ion beam (FIB). In addition, we fabricate tilted rectangular patterns to identify the influence of the tilt angle (45o and 135o) on friction behaviour. We perform the friction test using lateral force microscopy (LFM) employing a colloidal probe. We fabricate the colloidal probe by attaching a 10±1-μm-diameter borosilicate glass sphere to a tipless silicon cantilever by using a ultraviolet cure adhesive. The applied normal loads range between 200 nN and 1100 nN and the sliding speed was set to 12 μm/s. The test results show that the friction behavior varied depending on the pitch, height, and tilt angle of the microstructure. The friction forces were relatively lower for narrower and deeper pitches. The comparison of friction force between the sub-micro-structured surfaces and the original Si surface indicate an improvement of the friction property at a low load range. The current study provides a better understanding of the influence of pitch, height, and tilt angle of the microstructure on their tribological properties, enabling the design of sub-micro- and micro-structured Si surfaces to improve their mechanical durability."," focused ion beam(집속이온빔), lateral force microscopy(마찰력현미경), colloidal probe(콜로이드 탐침), sub-micro pattern(서브 마이크로 패턴), silicon surface(실리콘 표면)","한지희1·한규범2·장동영3·안효석3†\n1서울과학기술대학교 대학원 스마트생산융합시스템공학과, 2위스콘신 대학교 대학원 기계공학과, 3서울과학기술대학교 기술경영융합대","https://doi.org/10.9725/kstle.2017.33.3.92"]
["33권3호\npp.98-105","Ductile Cast Iron (DCI) 롤의 마모 특성 고찰 및 마모계수 도출을 위한 실험적  연구                                   \n(Experimental Study to Examine Wear Characteristics and Determine the Wear Coefficient of Ductile Cast Iron (DCI) Roll)","Tribology in Design & Manufacturing (Metalworking / Machining)","A pin-on-disk test is performed to measure the wear volume of a ductile cast iron (DCI) roll when it wears down using a high carbon steel and two alloy steels at different sliding velocities between the roll and the material (steel). Normal pressure is set as constant and test temperatures are 400, 500 and 600 oC. In addition, thermal softening behavior of the DCI roll is examined using a high-temperature micro-hardness tester and the surface hardness variation of the DCI roll is expressed in terms of temperature and heating time. Based on experimental data, a wear coefficient used in Archard’s wear model for each material is obtained. The wear volume is clearly observed when the test temperature is 400 oC and sliding velocity varies. However, it is not measured at temperatures of 500 oC and 600oC even with variations in sliding velocity. From the optical photographs of the pin and disk, the abrasive wear is observed at 400 oC clearly, but no at 500 oC and 600 oC. At higher temperatures, the pin surface is not smooth and has many tiny caves distributed on it. It is found that wear volume is dependent on the carbon contents rather than alloy contents. Results also reveal that the variations of wear coefficients are almost linearly proportional to the carbon contents of the material.","wear coefficient(마모 계수), archard wear model(아차드 마모모델), thermal softening(열적 연화), wear volume(마모 부피), ductile cast iron roll(구상 흑연 주철롤)","변상민†\n동아대학교 기계공학과 ","https://doi.org/10.9725/kstle.2017.33.3.98"]
["33권3호\npp.106-111","사파이어 화학기계적 연마에서 결정 방향이 재료제거 특성에 미치는 영향    \n(Effect of Crystal Orientation on Material Removal Characteristics in Sapphire Chemical Mechanical Polishing)\n","Chemical Mechanical Polishing","Sapphire is an anisotropic material with excellent physical and chemical properties and is used as a substrate material in various fields such as LED (light emitting diode), power semiconductor, superconductor, sensor, and optical devices. Sapphire is processed into the final substrate through multi-wire saw, double-side lapping, heat treatment, diamond mechanical polishing, and chemical mechanical polishing. Among these, chemical mechanical polishing is the key process that determines the final surface quality of the substrate. Recent studies have reported that the material removal characteristics during chemical mechanical polishing changes according to the crystal orientations, however, detailed analysis of this phenomenon has not reported. In this work, we carried out chemical mechanical polishing of C(0001), R(1 02), and A(11 0) substrates with different sapphire crystal planes, and analyzed the effect of crystal orientation on the material removal characteristics and their correlations. We measured the material removal rate and frictional force to determine the material removal phenomenon, and performed nano-indentation to evaluate the material characteristics before and after the reaction. Our findings show that the material removal rate and frictional force depend on the crystal orientation, and the chemical reaction between the sapphire substrate and the slurry accelerates the material removal rate during chemical mechanical polishing.","crystal orientation(결정 방향), chemical mechanical polishing(화학기계적 연마), friction force(마찰력), material removal Rate(재료 제거율), sapphire(사파이어)","이상진1,2·이상직1†·김형재1·박철진1·손근용2\n1한국생산기술연구원 정밀가공제어그룹, 2인제대학교 나노융합공학부, 나노매뉴팩처링연구소 ","https://doi.org/10.9725/kstle.2017.33.3.106"]
["33권3호\npp.112-118","터빈 시뮬레이터용 틸팅패드 저널베어링의 열윤활 해석 및 패드 온도 측정  \n(Thermohydrodynamic Analysis and Pad Temperature Measurement of a Tilting Pad Journal Bearing for a Turbine Simulator)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Tilting pad journal bearings(TPJBs) are widely used for high speed rotating machinery owing to their rotordynamic stability and thermal management feature. With increase in the rotating speed of such machinery, an increasingly important aspect of TPJB design is the prediction of their thermal behaviors. Researchers have conducted detailed investigations in the last two decades, which provided design tools for the TPJBs. Based on these previous studies, this paper presents a thermohydrodynamic(THD) analysis model for TPJBs. To calculate pressure distribution, we solve the generalized Reynolds equation and to predict the lubricant temperature, we solve the 3D energy equation. We employ the oil mixing theory to calculate pad inlet temperature; further, to consider heat conduction via the pad, we solve the heat conduction equation for the pads. We assume the shaft temperature as the averaged oil film temperature and apply natural convection boundary conditions to the pad side and back surfaces. To validate the analysis model, we compare the predicted pad temperatures with those from previous research. The results show good agreement with previous research. In addition, we conduct parametric studies on a TPJB which was used in a gas turbine simulator system. The predicted results show that film temperature largely depends on the rotating speed and oil supply condition."," tilting pad bearing(틸팅패드 베어링), thermohydrodynamic analysis(열윤활 해석)","이동현†·선경호\n한국기계연구원 시스템다이나믹스 연구실 ","https://doi.org/10.9725/kstle.2017.33.3.112"]
["33권3호\npp.119-125","윤활유 부족 상태에서의 볼 베어링 유막 두께 변화에 대한 연구                  \n(A Study on the Change in the Film Thickness of Ball Bearing in Starved EHL)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ,Tribology Applications (Industrial Case Studies)","A numerical analysis was carried out to predict the film thickness and lubrication regions for thrust ball bearing according to operating conditions. The film thickness in starved lubrication is affected by film thinning and replenishment. As the inlet meniscus position is brought to the edge of the Hertz contact, the thin film thickness is calculated as starved equation. A film replenishment model is used to figure out the recovery film thickness between rolling elements. To describe film recovery, as a result of the effects of surface tension, a hydrodynamic is used. In this model, the surface tension gradient in a fluid depression is considered the driving force for fluid recovery. A Fourier transform method is used to find the time-dependent depth of depressed oil. Make use of the recovery equation, change of the central film thickness is calculated graphically in starved elastohydrodynamic lubrication(EHL) according to operating conditions which includes numbers of balls, sliding velocity, applied force and ambient film thickness. The degree of starvation is evaluated by the distance from center of contact area to the meniscus position. At the severe condition the film decreases consistently, which is called parched lubrication. We find optimal values with respect to numbers of balls, and sliding velocity. The investigation is expected to contribute to design operating conditions for proper lubrication.","ball bearing(볼 베어링), film replenishment(유막 보충), film thickness(유막 두께), meniscus(미니스커스), starvation(윤활유가 부족한 상태)","정순비·이보라·유용훈·조용주†\n부산대학교 기계공학부 ","https://doi.org/10.9725/kstle.2017.33.3.119"]
["33권4호\npp.127-133","스크래치 시험을 통한 DLC 박막 파손과 밀착 특성 평가                       \n(Evaluation of Failure Modes and Adhesion of DLC Films by Scratch Test)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","In order to characterize the adhesive properties and failure mechanisms of diamond-like carbon (DLC) films of two different thicknesses (130 nm and 1.2 μm), deposited by plasma-enhanced chemical vapor deposition on a Si substrate, scratch testing with a micro-indenter (12.5 μm tip radius) was performed under a linearly increasing load. These scratch tests were conducted under the same test conditions for both films. The critical load of each film was estimated from the scratch test results, based on a sharp increase in the coefficient of friction and a clear distinction of failure modes. The critical load was the basis for evaluating the adhesion strength of the films, and the 1.2 μm-thick DLC film had superior adhesion strength. For better understanding of the failure modes, the following analyses were conducted: friction behavior and scratch tracks analysis using scanning electron microscopy, energy-dispersive spectroscopy, and 3-D profilometry. The scratch test results showed that failure modes were related to the thickness of the films. The 130 nm-thick DLC film underwent cohesive failure modes (cracks and chipping) before reaching to a gross failure stage. On the other hand, the thicker DLC film (1.2 μm-thick) did not exhibit micro cracks before a sudden gross failure of the film together with the evidence of cracking and chipping of the Si substrate.","DLC film, scratch test, critical load, failure mode","김주희1·박찬형1·안효석2†\n1서울과학기술대학교 대학원 스마트생산융합시스템공학과, 2서울과학기술대학교 기술경영융합대학 MSDE전공 ","https://doi.org/10.9725/kstle.2017.33.4.127"]
["33권4호\npp.134-140","표면이 마모된 틸팅 패드 저널베어링의 열윤활 해석 및 온도 측정  \n(Thermohydrodynamic Analysis and Pad Temperature Measurement of Tilting Pad Journal Bearing with Worn Pad)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","With the increase in adoption of tilting pad journal bearings (TPJBs), various failure mechanisms related to TPJBs have been reported, of which pad wear is a frequently reported one. Pad wear causes change in geometry of the bearing, which can sometimes result in the failure of the entire system. The objective of this research is to investigate the influence of pad wear on the pad temperature, which is one of the widely used condition monitoring methods for TPJBs. For the theoretical investigation, thermohydrodynamic (THD) analysis was conducted by solving the generalized Reynolds equation and the 3D energy equation. The results of the analysis show that the temperature of the loaded pad increases while that of the unloaded pad decreases, when there is wear on the loaded pads. In addition, the minimum film thickness decreases with an increase in the wear depth. A validation test was conducted with a test rig, which mimics the axial turbine when a test rotor is supported by two TPJBs. The test bearing consists of five pads with a diameter of 60 mm, and a resistance temperature detector (RTD) is installed in the pad for temperature monitoring. The test was performed by replacing the two loaded pads with the worn pad. The test result for the TPJB with wear depth of 30 μm show that the temperatures of the loaded pads are 8 °C higher and that of the unloaded pad is 2.5 °C lower than that of the normal TPJB. In addition, the predicted pad temperature shows good agreement with the measured pad temperatures.","tilting pad bearing, wear, thermohydrodynamic analysis","이동현†·선경호·김병옥·강동혁\n한국기계연구원 시스템다이나믹스 연구실 ","https://doi.org/10.9725/kstle.2017.33.4.134"]
["33권4호\npp.141-147","볼 베어링의 마멸 상태에 따른 진동 특성의 변화                              \n(Vibration Characteristics According to Wear Progress of Ball Bearings)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ,Condition Monitoring & Maintenance System (System Reliability) ","The vibration data of bearings are very useful for monitoring and determining the condition of the bearings. The defect frequencies of ball bearings have been used for monitoring there condition. However, it is not easy to verify the defect frequencies as the wear progress. Therefore there is a need for an easy method to monitor the damages of bearings in real-time and to observe the variations in vibration characteristics as the wear progress. In this study, a bearing test equipment is constructed to diagnose the damage of bearings. The friction coefficient and vibration data are measured by using a torque sensor and an acceleration sensor, and the correlation between the measured data is analyzed to diagnose the condition of the bearing. We reached the following conclusions from the results. When the ball surface, inner and outer rings of a ball bearing are damaged, the friction coefficient increases to over 0.02 with an adhesion on the surface. Moreover this damage occurs more quickly with an increase in the number of revolutions. In the vibration characteristics, the amplitude of vibration wave appears high with an increase in the friction coefficient. In the high frequency range between 1000 and 2000 Hz, a wide range of frequency components with high amplitude occurs continuously irrespective of the number of revolutions.","ball bearing, condition monitoring, vibration characteristics, frequency spectrum, friction coefficient","조상경·박정우·조연상†\n동아대학교 기계공학과","https://doi.org/10.9725/kstle.2017.33.4.141"]
["33권4호\npp.148-152","필기구 마찰의 주파수 특성 분석     \n(Analysis of Frequency Characteristics of Writing Instruments Due to Friction)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","The feel of writing is important to customers when they buy smart devices with stylus such as smartphones and tablet computers. With an aim to reproduce the tactile sensibility of writing instruments when people write on the glass display using a stylus, this study focuses on the frequency characteristics of writing instruments that can describe the vibrations of writing instruments sliding over counter surfaces. In addition, this study includes the effect of various factors influencing the friction of writing instruments such as lubricant, nib material, and contact type. We perform sliding experiments with six types of writing instruments and a sheet of paper to understand the relation between the friction conditions of the nib and the frequency characteristics. As this research focuses on the tactile perception of human skin when people use a writing instrument, the analysis of frequency characteristics is performed in the perceptible frequency range of mechanoreceptors in the human skin. As a result, three types of frequency characteristics are identified. Low frequency peaks are observed for a metal nib with ink; high frequency peaks are observed for a nib without ink; and, middle frequency peaks with a wide range of distribution occurs for fabric nibs with ink. Therefore, to implement the proper feel of writing, at least three types of vibrations have to be made.","feel of writing, tactile sensibility, sliding friction, friction-induced vibration, frequency characteristics","신재운1·박진확1·이영제2†\n1성균관대학교 대학원 기계공학과, 2성균관대학교 기계공학과 ","https://doi.org/10.9725/kstle.2017.33.4.148"]
["33권4호\npp.153-167","모터링 시동 및 시동정지 사이클에서 경사진 축을 갖는 저어널베어링의 마모 해석 – Part I: 마모발생 가능영역에서의 유막 변화 연구\n(Wear Analysis of Journal Bearings in a Misaligned Shaft During Motoring Start-up and Coast-down Cycles – Part I: Study on the Change in Oil Film Thickness at Potential Wear Regions)","Wear Phenomena & Mechanisms ,Automotive Tribology","The aim of this study is to find the change in trend in the eccentricities of two journal bearings supporting the crankshaft of a single cylinder engine and the degree of misalignment of the shaft. We analyze the change in oil film thickness considering the wear scar under mixed-elasto-hydrodynamic lubrication regime at potential wear regions. For this, we first calculate the central eccentricities of the two journal bearings by using the mobility method. Then we calculate the outer end eccentricity by using the geometry of the bearings. Further, the tilting angle and degree of misalignment of the shaft are calculated by using the eccentricities of the two bearings. We show that the eccentricity of bearing #1, on which higher load is applied, increases at the beginning of the start-up cycle and during the coast-down cycle. However, the eccentricity of bearing #2, on which lower load is applied, decreases at the beginning of the start-up cycle and increases during the coast-down cycle. From the results of the analysis of oil film thickness, we show that the mixed-elasto-hydrodynamic lubrication regime for a misaligned shaft is at the initial stages of the start-up cycle for both bearing #1 and #2 and at the final stage of the coast-down cycle for only bearing #1.","misaligned shaft, degree of misalignment, tilting angle of a shaft, central and outer-end eccentricities, mixed-elasto-hydrodynamic lubrication, start-up and coast-down cycle","전상명† \n호서대학교 기계공학부 자동차공학전공 ","https://doi.org/10.9725/kstle.2017.33.4.153"]
["33권4호\npp.168-186","모터링 시동 및 시동정지 사이클에서   경사진 축을 갖는 저어널베어링의 마모 해석 - Part II: 경사진 지지하는 두 저어널베어링의 마모해석\n(Wear Analysis of Journal Bearings Operating in a Shaft During Motoring Start-up and Coast-down Cycles – Part II: Wear Analysis of two Journal Bearings Supporting a Misaligned Shaft","Wear Phenomena & Mechanisms ,Automotive Tribology","This paper presents a wear analysis procedure for calculating the wear of journal bearings during the start-up and coast-down cycles of a motoring stripped-down single cylinder engine operating with a tilted shaft. In order to decide whether the lubrication state of a journal bearing is in the mixed-elasto-hydrodynamic lubrication regime, we utilize lift-off speed and MOFT (most oil film thickness) under mixed-elasto-hydrodynamic lubrication regime at the corresponding aligned shaft. We formulate an equation for the modified film thickness in a misaligned journal bearing considering the additional wear volume described in Part I of this study. For this, we use the calculation results of the degree of misalignment and tilting angle obtained after finding the eccentricities of the two bearings supporting the crankshaft of a single cylinder engine. In this Part II, we calculate the wear of journal bearings using the fractional film defect coefficient, the asperity load sharing factor, and the modified specific wear rate for the application of mixed-elasto-hydrodynamic lubrication regime. We show that the accumulated wear volume after turning the ignition switch on and off once, increases to σ = 39 μm and then decreases from σ = 39 μm with increasing in surface roughness.","misaligned shaft, asperity contact, lift-off speed, mixed-elasto-hydrodynamic lubrication, start-up and coast-down cycle, wear volume","전상명†\n호서대학교 기계공학부 자동차공학전공 ","https://doi.org/10.9725/kstle.2017.33.4.168"]
["33권5호\npp.187-201","Performance of Hydrostatic/hybrid Journal Symmetric/asymmetric Bearings using Slot-entry Restrictor Under Couple Stress Lubricants","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ,Tribology Applications (Industrial Case Studies)","This paper presents the impact of couple stress lubricant on performance of slot-entry hydrostatic/ hybrid journal symmetric/asymmetric bearings. Reynolds Equation using Finite Element Technique has been solved for the flow of couple stress and Newtonian lubricants in bearings. The results have been computed for concentric design pressure ratio , slot width ratio (SWR = 0.25) and chosen parameters of couple stress lubricant . It is observed that numerically simulated outcomes for slot-entry journal bearings, considering the influence of couple stress lubricant indicate a substantial improvement in the performance of the bearing.","Non-recessed journal bearings, couple stress lubricants, slot-entry restrictor, finite element method","Nathi Ram1†, Saurabh Kumar Yadav2 and Satish C. Sharma3\n1Indira Gandhi Delhi Technical University for Women (IGDTUW), 2Graphic Era University, 3IIT Roorkee","https://doi.org/10.9725/kstle.2017.33.5.187"]
["33권5호\npp.202-206","Simulation for Contact Angle of Droplet on Riblet Surface","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In this study, the hydrophobicity properties for riblet surfaces that replicate shark skin are simulated. Riblet surfaces with surface roughness on riblets are generated numerically based on the measured data of real shark skin. We assumed that a rib on a scale is hemi-elliptical surface. The surface used in the simulation for the calculation of contact angle is composed of 9 scales like checkerboard type with a roughness. The contact angle of a water droplet can be calculated using the Wenzel equation and Cassie-Baxter equation for the generated riblet surfaces. The variation of contact angles with a fractional depth of penetration for the generated shark skin surfaces without and with coatings is demonstrated in the condition of solid-air-water. The results show that the contact angle for the surface without coating decreases with an increase of the fractional depth of penetration more drastically than that for the surface with coating. We compared the experimental and simulated results. It is shown that the measured contact angles of the shark skin template and the shark skin replica are within the simulated results. Therefore the contact angle of water droplet for rough surfaces can be estimated by the developed numerical method in this study.","tilting pad bearing, wear, thermohydrodynamic analysis","김태완† \n부경대학교 기계공학과","https://doi.org/10.9725/kstle.2017.33.5.202"]
["33권5호\npp.207-213","유막온도경계조건이 평행 슬라이더 베어링의 윤활성능에 미치는 영향              \n(Effect of Film-Temperature Boundary Conditions on the Lubrication Performance of Parallel Slider Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In sliding bearings, viscous friction due to high shear acting on the bearing surface raises the oil temperature. One of the mechanisms responsible for generating the load-carrying capacity in parallel surfaces is known as the viscosity wedge effect. In this paper, we investigate the effect of film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of parallel slider bearings. For this purpose, the continuity equation, Navier-Stokes equation, and the energy equation with temperature-viscosity-density relations are numerically analyzed using the commercial computational fluid dynamics (CFD) code FLUENT. Two different film-temperature boundary conditions are adopted to investigate the pressure generation mechanism. The temperature and viscosity distributions in the film thickness and flow directions were obtained, and the factors related to the pressure generation in the equation of motion were examined in detail. It was confirmed that the temperature gradients in the film and flow directions contribute heavily to the thermal wedge effect, due to which parallel slider bearing can not only support a considerable load but also reduce the frictional force, and its effect is significantly changed with the film-temperature boundary conditions. The present results can be used as basic data for THD analysis of surface-textured sliding bearings; however, further studies on various film-temperature boundary conditions are required.\n","computational fluid dynamics (CFD)(전산유체역학), film-temperature boundary condition(유막온도경계조건), parallel slider bearing(평행 슬라이더 베어링), thermohydrodynamic lubrication(열유체 윤활), thermal wedge(열쐐기)","박태조1†·김민규2 \n1경상대학교 기계공학부, 2경상대학교 대학원 기계항공공학부 ","https://doi.org/10.9725/kstle.2017.33.5.207"]
["33권5호\npp.214-219","폴리아세탈의 입자유동베드 가공에서 회전속도와 공기 유량이 재료제거 특성에 미치는 영향                            \n(Effect of Rotating Speed and Air Flow Rate on Material Removal Characteristics in Abrasive Fluidized Bed Machining of Polyacetal)","Others ","Abrasive fluidized bed machining (AFBM) is similar to general abrasive fluidized machining (AFM) in that it can perform polishing of the outer and inner surfaces of a 3-dimensional shape by the flow of particles. However, in the case of AFM, the shear force generated by the flow of the particles causes material removal, while in AFBM, the abrasive particles are suspended in the chamber to form a bed. AFBM can be used for deburring, polishing, edge contouring, shot peening, and cleaning of mechanical parts. Most studies on AFBM are limited to metals, and research on application of AFBM to plastic materials has not been performed yet. Therefore, in this study, we investigate the effect of rotating speed of the specimen and the air flow rate on the material removal characteristics during AFBM of polyacetal with a horizontal AFBM machine. The material removal rate (MRR) increases linearly with increase of the rotating speed of the main shaft because of the shear force between the particles of the fluidized bed and the rotation of the workpiece. The reduction in surface roughness tends to increase as the rotating speed of the main shaft increases. As the air flow rate increases, the MRR tends to decrease. At a flow rate of 70 L/min or more, the MRR remains almost constant. The reduction of the surface roughness of the specimen is found to decrease with increasing air flow rate.","abrasive fluidized bed machining(입자유동베드가공), rotating speed(회전속도), air flow rate(공기유량), material removal rate(재료제거량), surface roughness(표면거칠기)","장양제1·김태경2·황현덕2·서준영2·이다솔3·이현섭2,4†\n1동명대학교 대학원 기계시스템공학과, 2동명대학교 기계공학부, 3부산대학교 기계공학부, 4동명대학교 융합기계기술연구소 ","https://doi.org/10.9725/kstle.2017.33.5.214"]
["33권5호\npp.220-227","카본 나노튜브 및 알루미나 첨가제가 윤활 및 마모특성에 미치는 영향에 대한 연구                                   \n(Study on Influence of Carbon Nanotubes and Alumina Additives to Lubrication and Wear Characteristics)","Lubrication (Lubricants & Additives)","In this work, carbon nanotube and nano-size alumina particle are exploited as additive for lubrication experiment. We used pin-on-disk type tribometer to investigate the tribological characteristics of lubricants with respect to additives and rotational speed. We conducted more than 15 trials of tribotests for two hours for each specimen to obtain stable and accurate frictional force and to create measurable wear track on the substrate. We conducted tests at the boundary/mixed lubrication regime to evaluate the influence of additives on the tribological characteristics. We found that the friction coefficient decreased as the rotational speed increased and as additives were added. In particular, the reduction of friction by adding additives was more significant at low rotational speed than at high rotational speed. We speculate that the additives helped to separate and protect the two contacting surfaces at low speed, while the influence of additives was not significant at high speed since sufficiently thick lubricant film was formed. The wear of the substrate was also reduced by adding additives to the lubricant. However, in contrast to friction, the amount of wear at high rotational speed was less when alumina particles were added to the lubricant than the amount of wear at low speed. We speculate that the increased wear at low rotational speed is as a result of the intermittent abrasive wear caused by alumina particles with uneven shape, while the reduced wear at high speed is as a result of sufficient film thickness which prevented the abrasive wear.","lubrication(윤활), additives(첨가제), carbon nanotube(탄소 나노튜브), alumina particle(알루미나 입자)","윤창석1·오대산2·김현준1†\n1경북대학교 정밀기계공학과, 2국방기술품질원 기동화력2팀","https://doi.org/10.9725/kstle.2017.33.5.220"]
["33권5호\npp.228-233","염화칼륨 농도에 따른 사파이어 기판 CMP에 관한 연구                        \n(Study on Effect of KCl Concentration on Removal Rate in Chemical Mechanical Polishing of Sapphire)"," Chemical Mechanical Polishing ","Chemical Mechanical Polishing of chemically stable sapphire substrates is dominantly affected by the mechanical processing of abrasives, in terms of the material removal rate. In this study, we investigated the effect of electrostatic force between the abrasives and substrate, on the polishing. If potassium chloride (KCl) is added to slurry, water molecules are decomposed into H+ and OH− ions, and the amount of ions in the slurry changes. The zeta potential of the abrasives decreases with an increase in the amount of H+ ions in the stern layer; consequently, the electrostatic force between the abrasives and substrate decreases. The change in zeta potential of abrasives in the slurry is affected by the slurry pH. In acidic zones, the amount of ions bound to the abrasives increases if the amount of H+ ions is increased by adding KCl. However, in basic zones, there is no change in the corresponding amount. In acidic zones, zeta potential decreases as molar concentration of potassium increases; however, it does not change significantly in basic zones. The removal rate tends to decrease with increase in molar amount of potassium in acidic zones, where zeta potential changes significantly. However, in basic zones, the removal rate does not change with zeta potential. The tendencies of zeta potential and that of the frictional force generated during polishing show strong correlation. Through experiments, it is confirmed that the contact probability of abrasives changes according to the electrostatic force generated between the abrasives and substrate, and variation in removal rate.","chemical mechanical polishing(화학기계적 연마), removal rate(연마율), zeta potential(제타 포텐셜), contact probability(접촉 확률), potassium chloride(염화칼륨)","박철진1·김형재†1·정해도2\n1한국생산기술연구원, 2부산대학교 기계공학부 ","https://doi.org/10.9725/kstle.2017.33.5.228"]
["33권6호\npp.245-250","기판 종류에 따른 물 윤활 특성 및 나노 입자의 영향                                    \n(Water Lubrication Characteristics and Effect of Nano Particles based on the Substrate)","Eco/Green Tribology (Renewable / Alternative Energies) ","In this work, we examine pure water and water with nanoparticles to investigate water lubrication characteristics and the effect of nanoparticles as lubricant additives for different substrates. We test carbon-based coatings and metals such as high-speed steel and stainless steel in pure deionized (DI) water and DI water with nanoparticles. We investigate water lubrication characteristics and the effect of nanoparticles based on the friction coefficient and wear rate for different substrates. The investigation reveals that nanoparticles enhance the friction and wear properties of high-speed steel and stainless steel. The friction coefficient and wear rate of both highspeed steel and stainless steel decreases in DI water with nanoparticles compared with the results in pure DI water. The presence of nanoparticles in water show good lubricating effect at the contact area for both high-speed steel and stainless steel. However, for carbon-based coatings, nanoparticles do not improve friction and wear properties. Rather, the friction coefficient and wear rate increases with an increase in the concentration of nanoparticles in case of water lubrication. Because carbon-based coatings already have good tribological properties in a water environment, nanoparticles in water do not contribute toward improving the friction and wear properties of carbon-based coatings."," carbon-based coating(탄소막 코팅), friction(마찰), nanoparticle(나노 입자), water lubrication(수중 윤활), wear(마모)","김혜균1·김태형1·김종국2·장영준2·강용진2·김대은1†\n1연세대학교 대학원 기계공학과, 무한내마모연구단, 2재료연구소 실용화사업단 표면공정연구실 ","https://doi.org/10.9725/kstle.2017.33.6.245"]
["33권6호\npp.251-255","벼 잎 표면에서 액적의 이방성 흐름 특성에 관한 연구                                  \n(A Study on the Anisotropic Flow Characteristics of Droplets on Rice Leaf Surface)","Bio-Tribology/Biomimetics ","In this study, we aimed to clarify the wettability and anisotropic flow characteristics of rice leaves as a basic study for engineering applications of anisotropic flow characteristics of rice leaf surface. To investigate the surface structure of rice leaf, the micro grooves and asperities of rice leaves were analyzed and quantified by scanning electron microscope, Confocal laser scanning microscopy, and stylus profilometer. The analysis of the structure of rice leaf surface confirmed that asymmetrical cone - like protrusions in leaf veins were inclined toward the leaf tip. The static contact angle test showed that the contact angle at the midline vein or leaf vein location where the micropapilla is concentrated is about 20° higher than the leaf blade position. The contact angles of fresh and dried rice leave were also compared. The dried rice leaves showed a contact angle of about 5° to 15° higher than that of fresh leaves, suggesting that the volume of the protrusions decreased as the water was removed, thus reducing the contact area with the droplet. In the contact angle history test the hysteresis in the leaf tip direction was found to be much lower than that in the leaf petiole direction. This results can be explained that asymmetrical cone - like protrusions had a significant effect on the droplet flow characteristics through contact angle hysteresis experiment.","rice leaf(벼 잎), anisotropic flow(이방성 흐름), contact angle hysteresis(접촉각 이력)","김태완†\n부경대학교 기계공학과 ","https://doi.org/10.9725/kstle.2017.33.6.251"]
["33권6호\npp.256-262","도금액의 내부 유입 방지를 위한 래버린스 시일 설계                                   \n(Labyrinth Seal Design for Preventing Internal Inflow of Plating Solution)","Others ","Molten zinc plating is a process in which zinc is thinly coated over a metallic or non-metallic surface. It is used in various industrial fields for corrosion resistance and decoration. During the process, a steel sheet is passed through a roll that rotates inside the molten zinc liquid in the temperature range of 460 °C to 680 °C, and the plating liquid flows into the roll causing abrasion and erosion of the roll surface. This problem is known to accelerate the replacement cycle of the roll and cause considerable economic loss owing to production line stoppage. Here, we propose a mechanism that operates at high temperature and pressure with a labyrinth type seal design to resolve this problem. We theoretically investigate the flow of the plating solution inside the seal and compute the minimum rotation speed required to prevent the plating solution from entering the seal chamber. In addition, we calculate the thermal deformation of the seal during operation and display thermally deformed dimensions at high temperatures. To verify the theoretical results, we perform experiments using pilot test equipment working in the actual plating environment. The experimental results are in good agreement with theoretical results. We expect our results to contribute towards the extension of the roll's life span and thereby reduce the economic losses.\n"," labyrinth seal(래버린스 시일), plating (도금), molten zinc(용융 아연) , thermal expansion(열 팽창)","이덕규·김완두†\n한국기계연구원 나노자연모사연구실 ","https://doi.org/10.9725/kstle.2017.33.6.256"]
["33권6호\npp.263-268","오염토양 내 석유제품 판별을 위한 TPH 및 BTEX 분석                                    \n(Combined TPH and BTEX Analytic Method to Identify Domestic Petroleum Products in Contaminated Soil)","Others ","The significance of maintaining the soil environment is gradually increasing owing to soil and underground water contamination by petroleum leak accidents. However, the purification of soil is an expensive and more time-consuming process than the purification of contaminated water and air. Moreover, determining the source and people responsible for soil pollution gets often embroiled in legal conflicts, further delaying the cleanup process of the contaminate site. Generally, TPH (total petroleum hydrocarbon) pattern analysis is used to determine the petroleum species and polluter responsible for soil contamination. However, this process has limited application for petroleum products with a similar TPH pattern. In this study, we analyze the TPH pattern and specific sectional ratio (~C10, C10 - C12, C12 - C36, and C36~) of various domestic petroleum products to identify the petroleum product responsible for soil contamination. Also, we perform BTEX (benzene, toluene, ethyl benzene, xylene) quantitative analysis and determine B:T:E:X ratio using GC-MS. The results show that gasoline grade 1 and 2 have a similar TPH pattern but different BTEX values and ratios. This means that BTEX analysis can be used as a new method to purify soil pollution. This complementary TPH and BTEX method proposed in this study can be used to identify the petroleum species and polluters present in the contaminated soil.","soil contamination(토양오염), petroleum(석유), BTEX (benzene, toluene, ethylbenzene, xylene)(벤젠, 톨루엔, 에틸벤젠, 자일렌), TPH (total petroleum hydrocarbon)(석유계 총탄화수소)","임영관†·나용규·김정민·김종렬·하종한\n한국석유관리원 석유기술연구소  ","https://doi.org/10.9725/kstle.2017.33.6.263"]
["33권6호\npp.269-274","습식 클러치 드래그 토크 특성의 실험적 평가                                             \n(Experimental Assessment of Drag Torque of Wet Clutch)","Automotive Tribology ","Currently, fuel efficiency becomes one of critical issues for automotive industries as concerns about environmental and energy problems grow. In an automatic transmission of an automobile, a drag torque due to a viscous drag of a fluid between friction and clutch plates is one of factors that degrade fuel economy. In this work, the drag torque characteristics of a wet clutch was experimentally investigated with respect to rotational speed, temperature of automatic transmission fluid (ATF), and gap between friction and clutch plates. The experimental results showed that drag torque increases to a certain level, and then decrease to the steady state value with increasing rotational speed. This behavior may be associated with two-phase flow of air and ATF at gap between friction and clutch plates. Also, it was found that the maximum drag torque value decreased as ATF viscosity decreases with increasing temperature. However, it was shown that the point at which the maximum drag torque occurs was not significantly affected by the ATF temperature. In addition, maximum drag torque was found to decrease as the gap between friction and clutch plates increased from 0.1 mm to 0.2 mm. Furthermore, it was observed that the generation of maximum drag torque was delayed as the gap increased. The outcomes of this work are expected to be helpful to gain a better understanding of drag torque characteristic of a wet clutch, and may therefore be useful in the design of wet clutch systems with improved performance.","drag torque (드래그 토크), gap(간극), rotating speed (회전 속도), temperature(온도), wet clutch(습식 클러치)","김한솔·정구현† \n울산대학교 기계공학부 ","https://doi.org/10.9725/kstle.2017.33.6.269"]
["33권6호\npp.275-281","다공성 산화알루미늄의 표면코팅에 따른 트라이볼로지적 특성연구                     \n(Study on Tribological Behavior of Porous Anodic Aluminum Oxide with respect to Surface Coating)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)"," In this work, we have fabricated anodic aluminum oxide (AAO) with ordered nanoscale porosity through an anodization process. We deposited gold and nano-organic thin films on the porous AAO surface to protect its structure and reduce friction. We investigated the tribological characteristics of the porous AAO with respect to the protective surface coatings using tribometers. While investigating the frictional characteristics of the samples by applying normal forces of the order of micro-Newton, we observed that AAO without a protective coating exhibits the highest friction coefficient. In the presence of protective surface coatings, the friction coefficient decreases significantly. We applied normal forces of the order of milli-Newton during the tribotests to investigate the wear characteristics of AAO, and observed that AAO without protective surface coatings experiences severe damage due to the brittle nature of the oxide layer. We observed the presence of several pieces of fractured particles in the wear track; these fractured particles lead to an increase in the friction. However, by using surface coatings such as gold thin films and nano-organic thin films, we confirmed that the thin films with nanoscale thickness protect the AAO surface without exhibiting significant wear tracks and maintain a stable friction coefficient for the duration of the tribotests."," anodic aluminum oxide(양극산화 알루미늄), coating(코팅), friction(마찰), wear(마모)","김영진·김현준†\n경북대학교 과학기술대학 정밀기계공학과","https://doi.org/10.9725/kstle.2017.33.6.275"]
["33권6호\npp.282-287","Effect of Pressure on Edge Delamination in Chemical Mechanical Polishing of SU-8 Film on Silicon Wafer                              \n(실리콘 기판 위 SU-8의 화학기계적연마에서 압력이 가장자리 박리에 미치는 영향)","Chemical Mechanical Polishing ","SU-8 is an epoxy-type photoresist widely used for the fabrication of high-aspect-ratio (HAR) microstructures in micro-electro-mechanical systems (MEMS). To fabricate highly integrated structures, chemical mechanical polishing (CMP) has emerged as the preferred manufacturing process for planarizing the MEMS structure. In SU-8 CMP, an oxidizer decomposes organic impurities and particles in the CMP slurry remove the chemically reacted surface of SU-8. To fabricate HAR microstructures using the CMP process, the adhesion between SU-8 and substrate material is important to avoid the delamination of the SU-8 film caused by the mechanical-dominant material removal characteristic. In this study, the friction force during the CMP process is measured with a CMP monitoring system to detect the delamination phenomenon and investigate the delamination of the SU-8 film from the silicon substrate under various pressure conditions. The increase in applied pressure causes an increase in the frictional force and wafer-edge stress concentration. The frictional force measurement shows that the friction force changes according to the delamination phenomenon of the SU-8 film, and that it is possible to monitor the delamination phenomenon during the SU-8 CMP process. The delamination at a high applied pressure is explained by the effect of stress distribution and pad deformation. Consequently, it is necessary to control the pressure of polishing, which can avoid the delamination in SU-8 CMP.","delamination, SU-8, chemical mechanical polishing(CMP), applied pressure","박선준1·임석연2,4·이현섭3,4†\n1DMS Inc., 2Department of Automotive Engineering, Tongmyong University, 3School of Mechanical Engineering, Tongmyong University, 4Center for Mechanical Convergence Engineering, Tongmyong University","https://doi.org/10.9725/kstle.2017.33.6.282"]
["33권6호\npp.288-295","Surface Texturing한 평행 슬라이더 베어링의 열유체윤활 해석: 딤플 깊이의 영향                                             \n(Thermohydrodynamic Lubrication Analysis of Surface-Textured Parallel Slider Bearing: Effect of Dimple Depth)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","In order to improve the efficiency and reliability of the machine, the friction should be minimized. The most widely used method to minimize friction is to maintain the fluid lubrication state. However, we can reduce friction only up to a certain limit because of viscosity. As a result of several recent studies, surface texturing has significantly reduced the friction in highly sliding machine elements, such as mechanical seals and thrust bearings. Thus far, theoretical studies have mainly focused on isothermal/iso-viscous conditions and have not taken into account the heat generation, caused by high viscous shear, and the temperature conditions on the bearing surface. In this study, we investigate the effect of dimple depth and film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of textured parallel slider bearings. We analyzed the continuity equation, the Navier-Stokes equation, the energy equation, and the temperature-viscosity and temperature-density relations using a computational fluid dynamics (CFD) code, FLUENT. We compare the temperature and pressure distributions at various dimple depths. The increase in oil temperature caused by viscous shear was higher in the dimple than in the bearing outlet because of the action of the strong vortex generated in the dimple. The lubrication characteristics significantly change with variations in the dimple depths and film-temperature boundary conditions. We can use the current results as basic data for optimum surface texturing; however, further studies are required for various temperature boundary conditions.","dimple(딤플), friction reduction(마찰저감), parallel slider bearing(평행 슬라이더 베어링), surface texturing(표면조직가공), thermohydrodynamic lubrication(열유체윤활), thermal wedge(열쐐기)","박태조1†·김민규2 \n1경상대학교 기계공학부, 2경상대학교 대학원 기계항공공학부 ","https://doi.org/10.9725/kstle.2017.33.6.288"]
["33권6호\npp.296-302","Ni-Al계 금속간화합물의 고주파 연소 합성코팅에 미치는 볼 밀링의 영향                \n(Effects of Ball Milling for Elemental Powders on Ni-Al based Intermetallics Coating on Mild Steel through Induction Heating Process)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Ball milling of elemental powders in advance and using an induction heating system for intermetallic coatings are known to enhance the reactivity of combustion synthesis. In this work, the effects of simultaneously applying these two incentive methods on the properties of intermetallic coatings are studied. Ni–Al powder compacts ball-milled with three different ball-to-powder weight ratio mixtures are synthesized and coated on mild steel by combustion synthesis in an induction heating system. Consequently, similar to an electrical heating system, the positive effects of ball milling on the combustion synthesis are confirmed in the induction heating system. The enhancement in synthetic reactivity achieved by applying the two incentive methods at the same time is greater than that by applying each incentive method separately. In particular, the enhancement is remarkable at low reaction temperature. However, there are limitations to improving the reactivity by simultaneously applying the two incentive methods to the combustion synthesis, unlike the reaction temperature. The microstructure and hardness of the coating layer are both influenced by the ball-charging ratio employed in the ball-milling process."," ball-milling(볼 밀링), combustion synthesis(연소 합성), induction heating(유도 가열), intermetallics(금속간화합물), reactivity(반응성)","이한영1†·박원규2\n1계명대학교 신소재공학과, 2계명대학교 대학원 재료공학과 ","https://doi.org/10.9725/kstle.2017.33.6.296"]
["33권6호\npp.303-308","노면 표면거칠기 특성의 대표값 정량화와 타이어 접촉력 해석 기법에 대한 고찰                                            \n(Representative Evaluation of Topographical Characteristics of Road Surface for Tire Contact Force Analysis)","Modeling & Simulation in Tribology ,Wear Phenomena & Mechanisms ","Most automobile tire companies have not yet considered the geometric information of a road at the design stage of a tire because the topographical characterization of a road surface is very difficult owing to its vastness and randomness. A road surface shows variable surface roughness values according to magnification, and thus, the contact force between the road and tire significantly fluctuates with respect to the scale. In this study, we make an attempt to define a representative value for surface topographical information at multi-scale levels. To represent surface topography, we use a statistical method called power spectral density (PSD). We use the fast Fourier transform (FFT) and PSD to analyze the height profiles of a random surface. The FFT and PSD of a surface help in obtaining a fractal dimension, which is a representative value of surface topography at all length scales. We develop three surfaces with different fractal dimensions. We use finite element analysis (FEA) to observe the contact forces between a tire and the road surfaces with three different fractal dimensions. The results from FEA reveal that an increase in the fractal dimension decreases the contact length between the tire and road surfaces. On the contrary, the average contact force increases. This result indicates that designing and manufacturing a tire considering the fractal dimension of a road makes safe driving possible, owing to the improvement in service life and braking performance of the tire.","fractal surface, surface topography, frequency analysis, power spectral density","서범교·성인하† \n한남대학교 기계공학과 ","https://doi.org/10.9725/kstle.2017.33.6.303"]
["33권6호\npp.309-314","닫힌 그루브를 갖는 외부가압 공기 패드 베어링의 동특성 해석                         \n(Dynamic Characteristics of Externally Pressurized Air Pad Bearings with Closed Loop Grooves)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This paper presents a theoretical investigation of the dynamic characteristics of externally pressurized air pad bearings with closed loop grooves. These grooves are engraved on the surface of bearings to reduce the number of supply holes so that manufacturing costs can be reduced. The semi-implicit method is applied to calculate the time varying pressure profile on the air bearing surface owing to the advantages of numerical stability and fast time tracing characteristics. The static pressure of the groove bearings is much higher than that without grooves, so the groove bearings can provide high load carrying capacity. The equations of motion considering vertical motion and tilting motion are also solved using the Runge-Kutta 4th order method. By combining the semi-implicit method and the Runge-Kutta method, fast calculations of the dynamic behavior of the air bearing can be achieved. The variations of bearing reaction force, air film reaction moment, height, and tilting angle are investigated for the step force input, which is 20% higher than the bearing reaction, when the nominal clearance is 6 m. The effect of the groove width and the groove depth are investigated by calculating the dynamic behavior. The possibility of the air hammering with the depth of the groove is found and discussed.","externally pressurized air pad bearing(외부가압공기 패드 베어링), bearing instability(베어링 불안정), surface groove (표면 그루브), dynamic analysis(동특성 해석), semi-implicit method(반음함수 방법)","박광원1·박상신2†\n1SL(주) 샤시설계1팀, 2영남대학교 기계공학부 ","https://doi.org/10.9725/kstle.2017.33.6.309"]

{"sheet":"2018년","index":2,"n_rows":43,"n_cols":7,"rows_kept":43,"cut":false,"hidden":false,"merged":[]}
["권호","제목","토픽","초록","키워드","저자","DOI"]
["34권1호\npp.1-8","대변형 접촉을 고려한 고무 마찰 예측 연구                                 \n(Predictive Study of Rubber Friction Considering Large Deformation Contact)","Contact Mechanics & Friction","This paper presents the analysis of friction master curves for a sliding elastomer on rough granite. The hysteresis friction is calculated using an analytical model that considers the energy spent during the local deformation of the rubber due to surface asperities. The adhesion friction is also considered for dry friction prediction. The viscoelastic modulus of the rubber compound and the large-strain effective modulus are obtained from dynamic mechanical analysis (DMA). We accurately demonstrate the large strain of rubber that contacts with road substrate using the GW theory. We found that the rubber block deforms approximately to 40% strain. In addition, the viscoelastic master curve considering nonlinearity (at 40% strain) is derived based on the above finding. As viscoelasticity strongly depends on temperature, it can be assumed that the influence of velocity on friction is connected to the viscoelastic shift factors gained from DMA using the time–temperature superposition. In this study, we apply these shift factors to measure friction on dry granite over a velocity range for various temperatures. The measurements are compared to simulated hysteresis and adhesion friction using the Kluppel friction theory. Although friction results in the low-speed band match well with the simulation results, there are differences in the predicted and experimental results as the velocity increases. Thus, additional research is required for a more precise explanation of the viscoelastic material properties for better prediction of rubber friction characteristics.","Rubber friction(고무 마찰), Fractal dimension(프랙탈 차원), Contact mechanics(접촉역학), Hysteresis(히스테리시스), Self affine(자기 아파인), Viscoelasticity(점탄성)","남승국† \n한국타이어 테크노돔 ","http://dx.doi.org/10.9725/kts.2018.34.1.1"]
["34권1호\npp.9-15","볼 베어링과 스퀴즈 필름 댐퍼로 지지되는 차량용 터보차저의 회전체동역학 해석: 스퀴즈 필름 댐퍼 설계 인자와 회전체 불균형 질량의 영향\n(Rotordynamic Analysis of Automotive Turbochargers Supported on Ball Bearings and Squeeze Film Dampers in Series: Effect of Squeeze Film Damper Design Parameters and Rotor Imbalances)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","Modern high-performance automotive turbochargers (TCs) implement ceramic hybrid angular contact ball bearings in series with squeeze film dampers (SFDs) to enhance transient responses, thereby reducing the overall emission levels. The current study predicts the rotordynamic responses of the commercial automotive TCs (compressor wheel diameter = ~53 mm, turbine wheel diameter = ~43 mm, and shaft diameter at the bearing locations = ~7 mm) supported on ball bearings and SFDs for various design parameters of SFDs, including radial clearance, axial length, lubricant viscosity, and rotor imbalance conditions (i.e., amplitudes and phase angles) while increasing rotor speed up to 150 krpm. This study validates the predictive rotor finite element model against measurements of mass, polar and transverse moments of inertia, and free-free mode natural frequencies and mode shapes. A nonlinear rotordynamic model integrates nonlinear force coefficients of SFDs to calculate the transient responses of the TC rotor-bearing system. The predicted results show that SFD radial clearances, as well as phase angles of rotor imbalances, have the paramount effect on the dynamic responses of TC shaft motions.","automotive turbochargers(차량용 터보차저), ball bearings(볼 베어링), squeeze film dampers(스퀴즈 필름 댐퍼), rotordynamics(회전체동역학), imbalance(불균형질량)","김규만1·류근2† \n1한양대학교 대학원 기계설계공학과, 2한양대학교 기계공학과 ","http://dx.doi.org/10.9725/kts.2018.34.1.9"]
["34권1호\npp.16-22","패드 선단 테이퍼를 갖는 수력 수직 원통형 터빈 가이드 베어링의 성능향상 - 테이퍼 각도와 길이의 영향         \n(Performance Improvement of Cylindrical Turbine Guide Bearings with Pad Leading-Edge Tapers for Vertical Hydro-Power Application: Effects of Taper Angle and Length)","Nuclear Tribology ,Tribology Applications (Industrial Case Studies)","Cylindrical turbine guide bearings (TGBs) with simple plain pads have conventionally been used in vertical hydro-power turbine-generator applications in order to provide turbine runner shafts with smooth rotation guides and supports. To overcome low-load/low-eccentricity performance drawbacks, such as very low film stiffness and lack of design credibility in the stiffness values themselves, of conventional cylindrical TGBs, the introduction of a rotational-directional leading-edge taper to each partitioned pad, simply pad leading-edge taper, has been found to be very effective in enhancing their design-application availability and usefulness. In this study, we investigate the effects of taper angle and length for given taper heights in detail in order to systematically establish the effectiveness of design on the performance improvement of vertical hydro-power application cylindrical TGBs with pad leading-edge tapers. The analysis results with 4-Pad×1-Row cylindrical TGBs show that the lubrication performance of the cylindrical TGBs is optimized with an approximate taper angle ratio of 0.8 and taper length ratio of 0.9. We conclude that the introduction of pad leading-edge tapers along with the optimization of taper designs can be very effective in improving the overall operation reliability of cylindrical TGBs and the rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems as well, to which the TGBs are applied.","cylindrical turbine guide bearing(원통형 터빈 가이드 베어링), pad leading-edge taper(패드 선단테이퍼), taper angle(테이퍼 각도), taper length(테이퍼 길이), performance improvement(성능향상)","이안성1·장선용2·박수만3†\n1한국기계연구원 시스템다이나믹스연구실, 2대동메탈공업㈜ 기술연구소, 3전력연구원 창의미래연구소 ","http://dx.doi.org/10.9725/kts.2018.34.1.16"]
["34권1호\npp.23-32","곡률 커플링 접촉각에 따른 접촉 강성 및 굽힘 강성해석                     \n(Analysis of Contact Stiffness and Bending Stiffness according to Contact Angle of Curvic Coupling)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Coupling is a mechanical component that transmits rotational force by connecting two shafts. Curvic coupling is widely used in high-performance systems because of its excellent power transmission efficiency and easy machining. However, coupling applications change dynamic behavior by reducing the stiffness of an entire system. Contact surface stiffness is an important parameter that determines the dynamic behavior of a system. In addition, the roughness profile of a contact surface is the most important parameter for obtaining contact stiffness. In this study, we theoretically establish the process of contact and bending stiffness analysis by considering the rough surface contact at Curvic coupling. Surface roughness parameters are obtained from Nayak's random process, and the normal contact stiffness of a contact surface is calculated using the Greenwood and Williamson model in the elastic region and the Jackson and Green model in the elastic–plastic region. The shape of the Curvic coupling contact surface is obtained by modeling a machined shape through an actual machining tool. Based on this modeling, we find the maximum number of gear teeth that can be machined according to the contact angle. Curvic coupling stiffness is calculated by considering the contact angle, and the calculation process is divided into stick and slip conditions. Based on this process, we investigate the stiffness characteristics according to the contact angle.","GW model(GW 모델), Curvic coupling(곡률 커플링), contact stiffness(접촉 강성), bending stiffness(굽힘 강성), surface roughness(표면거칠기) ","유용훈1·조용주1·이동현2·김영철2†\n1부산대학교 기계공학부, 2한국기계연구원 시스템다이나믹스 연구실","http://dx.doi.org/10.9725/kts.2018.34.1.23"]
["34권1호\npp.33-41","자동차 터보차저 베어링 시스템에 적용되는 스퀴즈 필름 댐퍼의 동적계수 측정을 위한 실험장치 개발                       \n(Test Rig Development for Identification of Rotordynamic Force Coefficients of Squeeze Film Dampers in Automotive Turbocharger Bearing Systems)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This paper describes a new test rig for identification of rotordynamic force coefficients of squeeze film dampers (SFDs) in automotive turbochargers (TCs). Prior studies have mainly concentrated on relatively large-sized SFDs used in aircraft engines, turbocompressors, and turbopumps. The main objective of the current study is to propose a test rig for identification of dynamic force coefficients of small-sized SFDs (a journal diameter of ~11 mm). The current test rig consists of a journal, a SFD cartridge, four support rods, an upper structure, a data acquisition (DAQ) system, and an oil circulation unit. The annular gaps between the journal outer surface and SFD cartridge inner surface create SFD film lands. The damper has two parallel film lands separated by a central groove, having an axial length and depth of 3 mm. Each film land has a length of 4 mm with a 40 μm radial clearance. The static load and dynamic impact tests identify the structural characteristics (i.e., stiffness and natural frequency) of the journal and assembled test rig. The measurements show good agreement with predictions. The SFD performance data from this test rig will be used to develop innovative TC rotor systems with improved NVH and reliability characteristics incorporating advanced SFD technology.","squeeze film dampers(스퀴즈 필름 댐퍼), dynamic force coefficients(동적 계수), parameter identification(파라미터 규명), frequency response function(주파수 응답 함수) ","황지수1·류근2†·정승화3\n1한양대학교 대학원 융합시스템학과, 2한양대학교 기계공학과, 3Compressor Technology and Development, Ingersoll Ran","http://dx.doi.org/10.9725/kts.2018.34.1.33"]
["34권2호\npp.43-48","초임계 CO2 발전용 파워터빈을 지지하는 틸팅패드 베어링의 열윤활 해석 및 패드 온도 측정\n(Thermal Analysis and Temperature Measurement of Tilting Pad Bearings Supporting a Power Turbine for the Supercritical CO2 Cycle Application)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This paper presents the thermohydrodynamic analysis of tilting journal pad bearings supporting a power turbine rotor applied to a 250 kW super-critical CO2 cycle. In the analysis, the generalized Reynolds equation and 3D energy equation are solved to predict oil film temperature and the 3D heat conduction equation is solved for pad temperature. The power turbine rotor is supported by two tilting pad bearings consisting of five pads with an oil supply block between the pads. Copper backing pads with higher thermal conductivity compared to steel backing pads are adopted to improve thermal management. The predicted maximum pad temperature is around 55 °C which is approximately 15 °C higher than oil supply temperature. In addition, the predicted minimum film thickness is 50 mm at a rotating speed of 5,000 rpm. These results indicate that there is no issue in the thermal behavior of the bearing. An operation test is performed with a power turbine module consisting of a power turbine, a reduction gear and a generator. Thermocouples are installed at the 75% position from the leading edge of the pad to monitor pad temperature. The power turbine uses compressed air at a temperature of 250 °C in its operation. The steady state pad temperatures measured in the test show good agreement with the predicted temperatures.","super critical CO2(초임계 CO2), tilting pad bearing(틸팅 패드 베어링)","이동현1†·김병옥1·임형수2\n1한국기계연구원 시스템다이나믹스 연구실, 2한국기계연구원 에너지변환기계 연구실","http://dx.doi.org/10.9725/kts.2018.34.2.43"]
["34권2호\npp.49-54","미끄럼 속도 변화에 따른 폴리우레탄 씰의 마모 특성\n(Effect of Sliding Speed on Wear Characteristics of Polyurethane Seal)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","Hydraulic reciprocating seal has been widely used to prevent fluid leakage in hydraulic systems. Also, hydraulic reciprocating seal plays a significant role to provide lubricant film at contacting interface to minimize tribological problems due to sliding with counter material. To predict lifetime of hydraulic reciprocating seal, quantitative understanding of wear characteristics with respect to operating conditions such as normal force and sliding speed is needed. In this work, effect of sliding speed on wear of polyurethane (PU) hydraulic reciprocating seal were experimentally investigated using a pin-on-disk tribo-tester. The wear characteristics of PU specimens were quantitatively determined by comparing the confocal microscope data before and after test. It was found that the wear rate of PU specimens decreased from 4.9×10−11 mm3 to 1.1×10−11 mm3/Nm as sliding speed increased from 120 mm/s to 940 mm/s. Also, it was observed that the friction decreased slightly as the sliding speed increased. Improvement of lubrication state with increasing sliding speed was likely to be responsible for this enhanced friction and wear characteristics. This result also suggests that decrease in sliding distance between PU elastomer and counter materials at lower sliding speed is preferred. Furthermore, the quantitative assessment of wear characteristics of PU specimen may be useful in prediction of lifetime of PU hydraulic reciprocating seal if the allowed degree of wear for failure of the seal is provided.","abrasive wear(연삭 마모), sliding speed(미끄럼 속도), polyurethane(폴리우레탄), wear(마모)","김한솔1·전홍규2·정구현1†\n1울산대학교 기계공학부, 2현대건설기계 신뢰성평가부","http://dx.doi.org/10.9725/kts.2018.34.2.49"]
["34권2호\npp.55-59","브레이크 마찰력 증가를 위한 상용차용 전기- 기계식 브레이크의 쐐기 설계\n(Design of Wedge in the Electro-Mechanical Brakes for Commercial Vehicles to Boost Braking Friction Forces)","Automotive Tribology ","This paper proposes a new type of electro-mechanical wedge brake for commercial vehicles. The brake operates on a novel mechanism for self-boosting braking friction forces using eccentric shafts, and involves wedges that are inserted between the rampbridge and traverse; this self-boosting mechanism is explained herein. A dynamic analysis using ADAMS was conducted, and the findings are reported. The constraint and contact conditions are explained to verify the precision of the dynamic analysis. The dynamic analysis shows that in the proposed mechanism, the self-boosting effect occurs as desired. However, it is also noted that the system has a limitation in terms of the production of unlimited braking forces that can jam the roller inside the wedges. After demonstrating the self-boosting effect, dynamic analyses are performed for several values of the wedge angles and friction coefficients between the brake pads and disks. Conventionally, a lower wedge angle has been suggested owing to its provision of a larger clamping force for given friction coefficients. However, it is noted that lower wedge angles can lead to a higher probability of occurrence of undesirable high braking forces, which can jam the roller into the wedge; thus, a larger wedge angle is preferable for avoiding the undesirable jamming phenomena. These analysis results are presented and discussed herein.\n","electro-mechanical wedge brake(전기-기계식 쐐기 브레이크), self-boosting(자기배력), clamping force(브레이크력), wedge angle(쐐기각), friction coefficient(마찰계수)","이상민1·박정훈1·남강현2·유창희3·박상신2†\n1영남대학교 대학원 기계공학과, 2영남대학교 기계공학부, 3상신브레이크 상용개발부","http://dx.doi.org/10.9725/kts.2018.34.2.55"]
["34권2호\npp.60-66","전사 방법에 따른 그래핀의 물 접촉각 변화\n(Water Contact Angles of Graphene Transferred by Wet and Dry Transfer Methods)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Graphene is a monolayer of carbon atoms (approximately 0.34 nm), arranged in a honeycomb network. It has been hailed as a next-generation flexible and transparent material because it has high electrical and thermal conductivities, excellent mechanical properties, as well as flexible and transparent properties. The wettability of graphene alters its adhesion or surface energy, and it is therefore an important parameter influencing its application in the fabrication of next-generation flexible and transparent electronics. Studies on the wettability of graphene are numerous and various opinions exist. However, almost all of these studies use the wet transfer method to transfer the graphene. In this study, therefore, we investigated the effect of wet and dry transfer methods on water contact angles of graphene on a substrate. The contact angles of substrates vary depending on the type of substrate. It was found that after graphene is transferred to the substrate, regardless of transfer method, the graphene/substrate contact angle increases to a value. The contact angle of graphene transferred using the dry transfer method is higher than the contact angle of graphene transferred using wet transfer methods. The wet transferred graphene is affected by the poly(methyl methacrylate) (PMMA) residue and the polar surface of substrate. The dry transferred graphene is influenced by the conformal contact between graphene and substrate.","contact angles(접촉각), graphene(그래핀), wet transfer(습식 전사), dry transfer(건식 전사)","윤민아1,2·김찬1,2·정현준3·김재현1,2·김광섭1,2†\n1과학기술연합대학원대학교 나노메카트로닉스학과, 2한국기계연구원 나노융합기계연구본부, 3파동에너지극한제어연구단","http://dx.doi.org/10.9725/kts.2018.34.2.60"]
["34권2호\npp.67-73","알루미늄 기판 위 반응합성 Coating 된 Ni-Al계 금속간화합물의 미끄럼마모 특성 해석\n(Sliding Wear Properties of Ni-Al based Intermetallics Layer coated on Aluminum through Reaction Synthesis Process)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials) "," Ni–Al intermetallic coating technology is an available method for the strengthening of aluminum substrate. In this study, Ni–Al intermetallics were coated on an aluminum substrate through a reaction synthesis process at a temperature lower than melting point of aluminum. And the sliding wear properties of the coatings have been investigated to verify their usability and compared the wear properties with those of a cast Al-12.5%Si alloy and an anodizing layer on aluminum. Results show that the wear rate of the coating layer greatly increased at 1 m/s and 1.5 m/s when compared with that of the cast Al-12.5%Si alloy. Much pitting damages were observed on the worn surfaces at these sliding speeds, unlike at other sliding speeds. The wear of the intermetallic coating layer at these sliding speeds seems to be increased by pitting as a consequence of adhesion. In contrast, wear of the coating layer at other speeds hardly occurs, regardless of wear periods. Nevertheless, the wear properties of the intermetallic coating layer on the aluminum substrate through the reaction synthesis process are more stable than those of anodized aluminum and are superior to those of the cast Al-12.5%Si alloy in a steady-state wear period.","intermetallics(금속간화합물), coating(코팅), aluminum(알루미늄) reaction synthesis(반응합성), wear property(마모특성)","이한영†\n계명대학교 신소재공학과 ","http://dx.doi.org/10.9725/kts.2018.34.2.67"]
["34권3호\npp.75-83","범프로 지지되는 다엽 포일을 갖는 가스 포일 베어링의 성능 해석\n(Performance Predictions of Gas Foil Bearing with Leaf Foils Supported on Bumps)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","Microturbomachinery (< 250 kW) using gas foil bearings can function without oil lubricants, simplify rotor-bearing systems, and demonstrate excellent rotordynamic stability at high speeds. State-of-the-art technologies generally use bump foil bearings or leaf foil bearings due to the specific advantages of each of the two types. Although these two types of bearings have been studied extensively, there are very few studies on leaf–bump foil bearings, which are a combination of the two aforementioned bearings. In this work, we illustrate a simple mathematical model of the leaf–bump foil bearing with leaf foils supported on bumps, and predict its static and dynamic performances. The analysis uses the simple elastic model for bumps that was previously developed and verified using experimental data, adds a leaf foil model, and solves the Reynolds equation for isothermal, isoviscous, and ideal gas fluid flow. The model predicts that the drag torques of the leaf–bump foil bearings are not affected significantly by static load and bearing clearance. Due to the preload effect of the leaf foils, rotor spinning, even under null static load, generates significant hydrodynamic pressure with its peak near the trailing edge of each leaf foil. A parametric study reveals that, while the journal eccentricity and minimum film thickness decrease, the drag torque, direct stiffness, and direct damping increase with increasing bump stiffness. The journal attitude angle and cross-coupled stiffness remain nearly constant with increasing bump stiffness. Interestingly, they are significantly smaller compared to the corresponding values obtained for bump foil bearings, thus, implying favorable rotor stability performance.","gas foil bearing(가스 포일 베어링), leaf foil(다엽 포일), bump foil(범프 포일), static performance(정적성능), dynamic performance(동적성능)","김태호1†ㆍ문형욱2\n1국민대학교 기계공학부, 2국민대학교 대학원 기계설계학과","http://dx.doi.org/10.9725/kts.2018.34.3.75"]
["34권3호\npp.84-92","원심주조방식과 레이저 클래딩 증착법을 통한 화이트메탈의 기계 및 마찰특성 비교\n(Comparison of Mechanical properties and Surface Friction of White Metals Produced by Centrifugal and Laser Cladded on SCM440)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Bearings are essential for reducing vibration and wear, in order to achieve high durability and increase longevity. White metal treatment of tilting pads via centrifugal casting method has the possibility of increasing durability. However, this manufacturing method has drawbacks such as long processing time, high defect rate, and harmful health effects. Laser cladding deposition technique is a powerful method that can address these issues by decreasing the processing time and providing good adhesion. In this study, we suggest optimum conditions for laser cladding deposition that can be used in industrial applications. We deposited a soft white metal layer on SCM440 that is primarily used in shafts to minimize wear of bearing pads. During the laser deposition process, we controlled factors such as laser power, powder feed rate, and laser head speed to determine the optimum conditions. In addition, we measured the hardness using micro Vickers, and performed field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and friction tests to\ninvestigate the mechanical properties and surface characteristics for different parameters. Based on the experimental results, we suggest that laser power, powder feed rate, and laser head speed of 1.3 kW, 2.5 rpm, and 10 mm/s, respectively, constitute the optimum conditions for producing white metals using laser cladding.","bearing(베어링), laser cladding(레이저 클래딩), mechanical properties(기계적 성질), surface friction(표면 마찰), white metal(화이트메탈)","정재일1·김동혁1·박진영1·오주영1·최시근1·김석삼2·조영태3·이호4·함승식4·김종형1†\n1한국생산기술연구원, 2말레이시아 사바대학교 기계공학과, 3창원대학교 기계공학과, 4경북대학교 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.3.84"]
["34권3호\npp.93-106","파이어링 상태의 일정 축 각속도에서 엔진 베어링의 마모 해석 – Part I: 베어링 마모발생 부위 파악\n(Wear Analysis of Engine Bearings at Constant Shaft Angular Speed on a Firing State – Part I: Understanding of Bearing Wear Region)","Automotive Tribology","The purpose of Part I of this study is to find the potential region of wear scarring on engine journal bearings operating at a constant angular crank shaft velocity under firing conditions. To do this, we calculate the applied loads and eccentricities of a big-end journal bearing installed on a four-stroke and four-cylinder engine at every crank angle. Then, we find potential wear regions, such as a minimum oil film thickness, at every crank angle below most oil film thickness scarring wear (MOFTSW) obtained based on the concept of the centerline average surface roughness. Thus, the wear region is defined as a set of each film thickness below the MOFTSW at every crank angle. In this region, the wear volume changes according to the wear depth and wear angle, depending on the minimum oil film thickness at every crank angle. The total wear volume is the summation during one cycle. Graphical views of the region in the two-dimensional coordinates show the crank angle and bearing angle along the journal center path, indicating the position of the minimum oil film thickness. The results of wear analysis show that the possible wear region is located at a few tens of angles behind the upper center of a big-end bearing at maximum power rpm.","firing operating condition(파이어링 운전조건), bearing loads of a four-cylinder-engine(4실린더 엔진의 베어링 하중), constant angular velocity of a crank-shaft(일정 크랭크-축 각속도), relative angular velocity of a crank-pin(크랭크-핀의 상대 각속도), most oil film thickness scaring wear(마모유발 최대유막두께)","전상명†\n호서대학교 기계공학부 자동차공학전공","http://dx.doi.org/10.9725/kts.2018.34.3.93"]
["34권3호\npp.107-114","심포일을 갖는 가스 포일 저널 베어링의 성능 예측\n(Performance Predictions of Gas Foil Journal Bearing with Shim Foils)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This paper presents a computational model of a gas foil journal bearing with shim foils between\nthe top foil and bumps, and predicts its static and dynamic performance. The analysis takes the previously\ndeveloped simple elastic foundation model for the top foil-bump structure and advances it by adding foil models\nfor the “shim foil” and “outer top foil.” The outer top foil is installed between the (inner) top foil and\nbumps, and the shim foil is installed between the inner top foil and outer top foil. Both the inner and outer\ntop foils have an arc length of 360°, but the arc length of the shim foil is shorter, which causes a ramp near\nits leading edge in the bearing clearance profile. The Reynolds equation for isothermal and isoviscous ideal\ngas solves the hydrodynamic pressure that develops within the bearing clearance with preloads due to the\nramp. The centerline pressure and film thickness predictions show that the shim foil mitigates the peak pressure\noccurring at the loading direction, and broadens the positive pressure as well as minimum film thickness\nzones except for the shortest shim foil arc length of 180°. In general, the shim foil decreases the journal eccentricity,\nand increases the power loss, direct stiffness, and damping coefficients. As the shim foil arc length\nincreases, the journal eccentricity decreases while the attitude angle, minimum film thickness, and direct stiffness/\ndamping coefficients in the horizontal direction increase.","bmp foil(범프포일), dnamic performance(동적성능), gas foil journal bearing(가스 포일 저널 베어링), shim foil(심포일), satic performance(정적성능)","황성호1·문창국1·이종성2·김태호3†\n1국민대학교 대학원 기계설계학과, 2한온시스템 선행부품개발팀, 3국민대학교 기계공학부","http://dx.doi.org/10.9725/kts.2018.34.3.107"]
["34권3호\npp.115-122","화학기계적 연마(CMP) 공정에서의 트라이볼로지 연구 동향\n(Tribology Research Trends in Chemical Mechanical Polishing (CMP) Process)","Chemical Mechanical Polishing","Chemical mechanical polishing (CMP) is a hybrid processing method in which the surface of a wafer is planarized by chemical and mechanical material removal. Since mechanical material removal in CMP is caused by the rolling or sliding of abrasive particles, interfacial friction during processing greatly influences the CMP results. In this paper, the trend of tribology research on CMP process is discussed. First, various friction force monitoring methods are introduced, and three elements in the CMP tribo-system are defined based on the\nmaterial removal mechanism of the CMP process. Tribological studies on the CMP process include studies of interfacial friction due to changes in consumables such as slurry and polishing pad, modeling of material removal rate using contact mechanics, and stick-slip friction and scratches. The real area of contact (RCA) between the polishing pad and wafer also has a significant influence on the polishing result in the CMP process, and many researchers have studied RCA control and prediction. Despite the fact that the CMP process is a hybrid process using chemical reactions and mechanical material removal, tribological studies to date have yet to clarify the effects of chemical reactions on interfacial friction. In addition, it is necessary to clarify the relationship between the interface friction phenomenon and physical surface defects in CMP, and the cause of their occurrence.","chemical mechanical polishing(화학기계적 연마), tribology(트라이볼로지), friction force(마찰), wear(마모), stick-slip(스틱-슬립), real area of contact(실접촉면적)","이현섭1,2†\n1동명대학교 기계공학부, 2동명대학교 융합기계기술연구소","http://dx.doi.org/10.9725/kts.2018.34.3.115"]
["34권4호\npp.125-131","정밀 마찰측정을 위한 이중 캔틸레버 구조 마찰시험기의 설계에 관한 연구\n(A Study on the Design of a Double Cantilever Structure Friction Tester for Precision Friction Measurement)","Tribo-Testing / Measurement & Instruments","A precision tribometer consisting of a cantilever was designed to measure frictional forces in the micro-Newton range. As frictional forces are measured based on the bending of the cantilever, vibration of the cantilever is the most significant factor affecting the quality of the friction measurement. Therefore, improved design of the tribometer with double cantilevers and a connecting plate that united the two cantilevers mechanically was suggested. For the verification of the modified design of the tribometer, numerical analysis and experiments\nwere conducted. Examination using the finite element method revealed that the tribometer with a double cantilever and a connecting plate exhibited faster damping characteristics than the tribometer with a single cantilever. In the experiment, effectiveness of the double cantilever and connecting plate for vibration reduction was also confirmed. Vibration of the tribometer with double cantilever decreased eight times faster than that of the tribometer with a single cantilever. The faster damping of the double cantilever design is attributed to the mechanical interaction at the contacting surfaces between the cantilever and the connecting plate. Tribotesting using the tribometer with a single cantilever resulted in random fluctuation of frictional forces due to the stickslip behavior. However, using the tribometer with a double cantilever and connecting plate for the tribotest gave relatively uniform and steady measurement of frictional forces. Increased stiffness owing to using a double cantilever and mechanical damping of the connecting plate were responsible for the stable friction signal.","precision tribometer(정밀 마찰시험기), cantilever(외팔보), vibration analysis(진동 분석), finite element analysis(유한요소해석), Stick-slip(스틱슬립)","강원빈·김현준†\n경북대학교 정밀기계공학과","http://dx.doi.org/10.9725/kts.2018.34.4.125"]
["34권4호\npp.132-137","초음파 진동이 알루미늄 합금의 마찰 마모 특성에 미치는 영향\n(Effect of Ultrasonic Vibration on the Friction and Wear Characteristics of Aluminum Alloy)","Contact Mechanics & Friction ,Wear Phenomena & Mechanisms ","Ultrasonic waves are used in various applications in multiple devices, sensors, and high-power machinery, such as processing machines, welders, and cleaners, because the acoustic vibration frequencies are above the human audible frequency range. In ultrasonic machining, electrical energy at a high frequency of 20 kHz or more is converted into mechanical vibration by a vibrator and an amplifier. This technique allows instantaneous separation between a tool and a workpiece during machining, machining by pulse impulse force at the\ntime of re-contact and minimizes the minute elastic deformations of the workpiece and machine tools due to the cutting effect. The Al7075 alloy used in this study is a typical aluminum alloy with superior strength that is mainly used in aircrafts, automobiles, and sporting goods. To investigate the optimal conditions for machining aluminum alloy using ultrasonic vibration, the present experiment utilized the Taguchi orthogonal array method, and the coefficient of friction was analyzed using the characteristics of the Taguchi technique. In ultrasonic friction and abrasion tests, the changes in the friction coefficient were measured in the absence of ultrasonic vibrations and at 28 kHz and 40 kHz. As a result, the most considerable influence on the friction coefficient was found to be the normal load, and the frequency of ultrasonic vibrations increases, the coefficient of friction increases. It was thus confirmed that the amount of wear increases when ultrasonic vibration is applied.","ultrasonic machining(초음파 가공), coefficient of friction(마찰계수), wear(마모), taguchi method(다구찌 방법)","박재남·이철희†\n인하대학교 건설기계공학과","http://dx.doi.org/10.9725/kts.2018.34.4.132"]
["34권4호\npp.138-145","오일공급 방향에 따른 타원형 베어링 손실 및 온도 특성\n(Effect of Oil Supply Direction on Power Loss and Bearing Temperature of Elliptical Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","Elliptical bearings are widely used for large steam turbines owing to their excellent load carrying capacity and good dynamic stability. Power loss in bearings is an extremely important parameter, especially for high turbine capacities. Optimization of operation conditions and design variables such as bearing clearance and bearing length can reduce the power loss in elliptical bearings. Although changes in the oil supply method have served to increase the efficiency of the tilting pad journal bearing, it has not explicitly improved elliptical bearings. In this study, we verify the static characteristics of an elliptical bearing by changing the direction of oil supply. We evaluate the bearing power loss and bearing metal temperature, and compare the bearing performance and reliability in different test cases. The direction of oil supply is 90° (9 o'clock) and 270° (3 o'clock) when the rotor rotates in a counterclockwise direction. We use an elliptical bearing with an inner diameter and active length of 220.30 and 110.00 mm, respectively. Bearing power loss and bearing metal temperatures are measured and evaluated by rotor rotational speed, oil flow rate, and bearing load. The results reveal a 20 reduction in the power loss when the direction of oil supply is 90. Furthermore, the oil film on the upper part of the bearing has a high temperature when the direction of oil supply is 90°. In contrast, when the direction of oil supply is 270°, the oil film on the upper part of the bearing is relatively cold.","elliptical bearing(타원형 베어링), power loss(동력손실), temperature(온도), oil supply direction(오일 공급 방향)","방경보1†·최용훈1·조용주2\n1두산중공업 터빈발전기그룹, 2부산대학교 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.4.138"]
["34권4호\npp.146-159","파이어링 상태의 일정 축 각속도에서 엔진베어링의 마모 해석 − Part II: 저어널베어링 마모 계산\n(Wear Analysis of Engine Bearings at Constant Shaft Angular Speed during Firing State – Part II: Calculation of the Wear on Journal Bearings)","Automotive Tribology ","This paper presents a wear analysis procedure for calculating the wear of journal bearings of a fourstrokes and four-cylinder engine operating at a constant angular crank shaft speed during firing conditions. To decide whether the lubrication state of a journal bearing is in the possible region of wear scar, we utilize the concept of the centerline average surface roughness to define the most oil film thickness scarring wear (MOFTSW) on two rough surfaces. The wear volume is calculated from the wear depth and wear angle, determined by the magnitude of each film thickness on a set of oil films with thicknesses lower than the MOFTSW at every crank angle. To calculate the wear volume at one contact, the wear range ratio during one cycle is used. The total wear volume is then determined by accumulating the wear volume at every contact. The fractional film defect coefficient, asperity load sharing factor, and modified specific wear rate for the application of the mixed-elasto-hydrodynamic lubrication regime are used. The results of this study show that wear occurs only at the connecting-rod big-end bearing. Thus, simulation results of only the big-end bearing are illustrated and analyzed. It is shown that\nthe wear volume of each wear scar group occurs consecutively as the crank angle changes, resulting in the total accumulated wear volume.","firing operating condition(파이어링 운전조건), constant angular velocity of a crank shaft(크랭크 축의 일정 각속도), asperity contact(돌기접촉), most oil film thickness scarring wear(마모유발최대유막두께), mixedelasto-\nhydrodynamic lubrication(혼합탄성유체윤활), wear volume(마모체적)","전상명†\n호서대학교 기계공학부 자동차공학전공","http://dx.doi.org/10.9725/kts.2018.34.4.146"]
["34권4호\npp.160-167","ZnDTP를 첨가한 혼합윤활유(광유/식물성 오일)의 마모, 산화 및 전단 특성\n(Wear, Oxidation and Shear Characteristics of Mixed Lubricating Oil(Mineral/Vegetable oil) with ZnDTP)","Bio-Tribology/Biomimetics ","Vegetable oils can contribute to the goal of energy independence and security owing to their naturally renewable resources. One of the representative vegetable oils is biodiesel, which is being used in domestic and European markets as a blended fuel with automotive diesel. Vegetable oils are promising candidates as base fluids to replace petroleum lubricants because of their excellent lubricity and biodegradability. We prepared biodiesel with a purity of 99.9% via the esterification of waste cooking oil. Blended biodiesel and Petro-lube base oil were mixed to produce five types of mixed lubricating oil. We analyzed the various characteristics of the blended biodiesel with Petro-lube base oil for different blending ratios. The lubricity of the vegetable lubricant improves as the content of biodiesel increases. In addition, since zinc dialkyldithiophosphates (ZnDTPs) are widely used as multifunctional additives in petroleum-based lubricants, we optimized the blending ratio for lubricity, oxidation stability, and shear stability by adding ZnDTP as a performance additive to improve the biodiesel properties, such as oxidation stability and hydrolysis. The optimized lubricants improve by approximately 25% in lubricity and by 20 times in oxidation stability and shear stability after the addition of ZnDTP.","biodiesel(바이오디젤), lubricity(윤활성), oxidation stability(산화안정성), shear stability(전단안정성), mixed lubricant(혼합윤활유)","임태윤1,2·김양회1·나병기2†\n1현대오일뱅크 윤활유연구소, 2충북대학교 화학공학과","http://dx.doi.org/10.9725/kts.2018.34.4.160"]
["34권5호\npp.169-174","증속 기어 압축기용 스러스트 칼라의 윤활 성능 해석\n(Performance Analysis of Oil-lubricated Thrust Collars in Integrally Geared Compressors)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","A multi-stage compressor (MSC) is comprised of several impellers installed in the pinion gear shaft driven by a main bull gear. In the pinion shaft, a thrust collar (TC) is installed to support the thrust load. The TC makes the lubrication system simpler in the MSC; therefore, it is widely used in similar kinds of machinery. Typically, TCs are installed on both sides of the bull gear and pressure is developed in the lubricated area by creating a taper angle on the TC and bull gear surface. In the current study, we developed a numerical analysis model to evaluate the performance of the TC considering its design parameters. We sloved the Reynolds equation using the finite element method and applied the half Sommerfeld condition to consider cavitation. Based on the pressure calculated in the lubricated area, we calculated the power loss and minimum film thickness. In addition, we calculated stiffness and damping using perturbation method. We performed parametric studies using the developed model. The results of the analysis show that the maximum pressure presents in the center area of the TC and it increases with the taper angle. The area over which pressure is developed decreases with the taper angle. The results also show that there is an optimum taper angle providing minimum power loss and maximum film thickness. Additionally, the stiffness and damping decrease with the taper angle. As the applied load increases, the power loss increases and the minimum film thickness decreases. However, the stiffness and damping increase with the applied load.","multi-stage compressor (다단 압축기), thrust collar (스러스트 칼라)","이동현†·김병옥·선경호\n한국기계연구원 시스템다이나믹스 연구실","http://dx.doi.org/10.9725/kts.2018.34.5.169"]
["34권5호\npp.175-182","침식 해석을 이용한 월 블로워 노즐의 성능 예측\n(Performance Evaluation of Wall Blower Nozzle using Erosion Analysis)","Tribology Applications (Industrial Case Studies) ","Accumulation of coal ash at the boiler wall reduces combustion and fuel efficiency. The design of a wall blower is important to effectively remove coal ash. We present numerical results for the removal of coal ash from boiler walls of domestic coal-fired power plants, associated with the computational fluid dynamics for the flow from spray nozzle to boiler wall. The numerical model simulates an erosion process in which the multiphase fluid comprising saturated vapor and fluid water is sprayed from the nozzle, and the water particles\nimpact the boiler wall. We adopt the Finnie erosion model for water particles. We obtain the erosion rate density as a function of nozzle angle and its injection angle. As excessive coal ash removal usually induces damage to the boiler wall, the removal operation typically focuses on a large area with uniform depth rather than the maximum removal of coal ash at a specific location. In order to estimate the removal performance of the wall blower nozzle considering several functionality and reliability factors, we evaluate the optimal injection and nozzle angles with respect to the biggest cumulative and highest erosion rates, as well as the widest range and lowest standard deviation of the erosion rate distribution.","wall blower(월 블로워), erosion rate density(침식률 밀도), computational fluid dynamics(전산유체역학), furnace wall(노 벽면), nozzle jet(노즐 분사)","백재호·장일광·장용훈†\n연세대학교 대학원 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.5.175"]
["34권5호\npp.183-190","씰 투스 간극이 틸팅 패드 저어널 베어링 손실과 온도에 미치는 영향\n(Effect on Seal Tooth Clearance on Power Loss and Temperature of Tilting Pad Journal Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","Tilting pad journal bearing is widely used for steam turbines because of its excellent dynamic stability. As the turbine capacity increases, power loss in the bearings becomes a matter of concern. Power loss in tilting pad journal bearings can be reduced by increasing the bearing clearance and reducing the pad arc length. In this study, the tilting pad journal bearing is tested by changing the seal tooth clearance to verify the static characteristics of the bearing. Bearing power loss and bearing metal temperature are evaluated to compare the bearing's performance and reliability for several test cases. The test bearing is a tilting pad journal bearing with 300.62mm inner diameter and 120.00mm active length. The bearing power loss, its metal temperature, and oil film thickness are measured and evaluated based on the rotor's rotational speed, oil flow rate, and bearing load. Test results show that a tilting pad journal bearing with large seal tooth clearance has 40% lower power loss compared with a bearing with a small seal tooth clearance. As the seal tooth clearance is increased, the power loss of the tilting pad journal bearing decreases. However, with respect to the bearing metal temperatures, a detuning point is observed that makes the minimum bearing metal temperature. Moreover, as the seal tooth clearance is increased, the oil film thickness increases due to high viscosity.","tilting pad journal bearing(틸팅 패드 저어널 베어링), power loss(동력 손실), temperature(온도), end seal(엔드 씰), seal tooth(씰 투스)","방경보1†·최용훈1·조용주2\n1두산중공업 터빈발전기그룹, 2부산대학교 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.5.183"]
["34권5호\npp.191-196","폐윤활유 불법혼입 C중유 물성 분석\n(Analysis of Illegally Mixed Used Lube Oil in Bunker C)","Lubrication (Lubricants & Additives) ,Condition Monitoring & Maintenance System (System Reliability) ","Bunker C is used in heavy-lift ships, furnaces, and boilers for generating heat, and power. Bunker C has only four regulations for quality standards and is rarely inspected in Korea. For these reasons, other oils such as used lubricant oil are commonly blended with Bunker C. This illegal mixture of fuel can damage the boilers, engines and affect the environment adversely. In this study, we investigate the fuel properties and perform atomic analysis of illegal Bunker C blended with used lube oil. The test results show that higher quantities of\nused lube oil in Bunker C have higher flash points, total acid numbers, copper corruption, solid contamination, and metal components. Further, increasing quantities of used lube oil in Bunker C cause lower viscosity, sulfur, and V content. However, adequate sample (approximately 1 L) is needed to evaluate presence of adulterants in Bunker C, we attempted the SIMDIST analysis. In the SIMDIST chromatogram, the used engine oils are detected for longer retention times than Bunker C owing to the high boiling point. We also quantitatively analyzed the lube oil content using SIMDIST.","bunker C(C중유), used lube oil(폐윤활유), illegal mixing(불법 혼입), SIMDIST(고온시뮬레이션증류시험)","임영관1†·이재민1,2·김완식1·이정민1\n1한국석유관리원 석유기술연구소, 2충북대학교 화학공학과","http://dx.doi.org/10.9725/kts.2018.34.5.191"]
["34권5호\npp.197-207","장기 저장연료의 열안정성 및 연료접촉 고무오링의 수명예측 연구\n(A Study on the Thermal Stability of Long-Term Fuel Storage and Lifetime Estimation of Rubber O-ring in Contacted with Fuel)","Others","Thermal deterioration of fuel due to long-term storage influences engine performance and causes malfunctions. Fuel stability is usually evaluated via heat resistance and thermal stability during a brief heat shock at high temperature; storage stability in this scenario means that there is very little change in the quality of the fuel during long-term storage. In addition, rubber-based products such as oil seals, O-rings, and rubber hoses can influence the quality of the fuel. When these rubber products are in contact with fuel, they can swell, mechanically weaken, and occasionally crack, thus leaking low molar weight rubber and additives including plasticizer and antioxidant into the fuel to degrade its properties and shorten its useful lifetime. This study determines the thermal stabilities of three kinds of synthetic fuels by evaluating their low temperature kinematic viscosities, chemical composition changes via GC analyses, gross heat of combustion, and color changes. We evaluate the compression set of O-rings by immersing one NBR and two FKM rubber O-rings in the three synthetic fuel samples in airtight containers at variable storage temperatures for six months; from this, we estimate the lifetimes of the O-rings using the Power law model. There were very little changes in the chemical compositions and gross heat of combustion after six months of the experiment. The lifetimes are thus dependent on the materials of the rubber products, and in particular, the FKM O-ring was calculated to have a theoretical lifetime of 200 to 5,700 years. These results indicate that the synthetic fuels maintain their physical properties even after long-term storage at high temperatures, and the FKM O-ring is suitable for long-term sealing of these fuels.","synthetic fuel (합성연료), thermal stability (열안정성), rubber O-ring (고무 오링), compression set (압축영구줄음율), lifetime prediction (수명 예측)","정근우1†·홍진숙1·김영운1·한정식2·정병훈2·권태수3·서동욱3·성민준3·권영일4\n1한국화학연구원 환경자원연구센타, 2국방과학연구소, 3㈜풍산 기술연구소, 4청주대학교 산업공학과","http://dx.doi.org/10.9725/kts.2018.34.5.197"]
["34권6호\npp.209-216","Effect of Free Abrasives on Material Removal in Lap Grinding of Sapphire Substrate","Chemical Mechanical Polishing","Sapphire is a substrate material that is widely used in optical and electronic devices. However, the processing of sapphire into a substrate takes a long time owing to its high hardness and chemical inertness. In order to process the sapphire ingot into a substrate, ingot growth, multiwire sawing, lapping, and polishing are required. The lap grinding process using pellets is known as one of the ways to improve the efficiency of sapphire substrate processing. The lap grinding process ensures high processing efficiency while utilizing two-body abrasion,\nunlike the lapping process which utilizes three-body abrasion by particles. However, the lap grinding process has a high material removal rate (MRR), while its weakness is in obtaining the required surface roughness for the final polishing process. In this study, we examine the effects of free abrasives in lap grinding on the material removal characteristics of sapphire substrate. Before conducting the lap grinding experiments, it was confirmed that the addition of free abrasives changed the friction force through the pin-on-disk wear test. The MRR\nand roughness reduction rate are experimentally studied to verify the effects of free abrasive concentration on deionized water. The addition of free abrasives (colloidal silica) in the lap grinding process can improve surface roughness by three-body abrasion along with two-body abrasion by diamond grits.","lap grinding, free abrasive, material removal rate (MRR), surface roughness, sapphire","Junyoung Seo1, Taekyoung Kim1 and Hyunseop Lee2,3†\n1Department of Mechanical System Engineering, Tongmyong University, 2School of Mechanical Engineering, Tongmyong University, 3Center for Mechanical Convergence Engineering, Tongmyong University","http://dx.doi.org/10.9725/kts.2018.34.6.209"]
["34권6호\npp.217-225","Tribological Performance of Ni-Cr Composite Coating Sprayed onto AISI 4340 (SNCM439) Steel by High Velocity Oxygen Fuel","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ","In this study, we spray a Ni-Cr composite powder onto AISI 4340 steel using the high velocity oxygen fuel method. We subsequently subject the Ni-Cr coating (as-sprayed) to ultrasonic nanocrystal surface modification (UNSM) process to improve the tribological performance. This study aims at increasing the wear resistance and durability of the Ni-Cr coating by altering the surface integrity and microstructure via the UNSM process. The UNSM process reduces the surface roughness of the as-sprayed coating by about 64%, which is\nexplained by observing the elimination of high peaks and valleys and filling up micro-pores. Furthermore, a change in the microstructure of the coating due to continuous high-frequency strikes to the surface by a tip can lead to an increase in hardness from about 48 to 60 HRC. Furthermore, we investigate the characterization of the friction and wear behavior of Ni-Cr coating by a ball-on-disc tribometer in the dry conditions. We determine that after the UNSM process, there is a significant reduction in the friction coefficient of the as-sprayed coating from approximately 1.1 to 0.75. This is owing to the increased hardness and smoothed surface roughness. In addition, we investigate the surface morphology and wear track of the coatings before and after the UNSM process using a scanning electron microscope, energy dispersive spectrometer, and three-dimensional laser scanning microscope. We observe that the wear track of the Ni-Cr coating after the UNSM process is lower than that of the as-sprayed one. Thus, we confirm that the UNSM process has a significant influence on the improvement of the tribological performance of the Ni-Cr composite coating.","coating, surface roughness, surface hardness, friction, wear","Rakhmatjon Umarov, Young-Sik Pyun and Auezhan Amanov†\nDept. of Mechanical Engineering, Sun Moon University","http://dx.doi.org/10.9725/kts.2018.34.6.217"]
["34권6호\npp.226-234","Effect of Citric Acid in Cu Chemical Mechanical Planarization Slurry on Frictional Characteristics and\nStep Height Reduction of Cu Pattern","Chemical Mechanical Polishing ","Copper chemical mechanical planarization (CMP) has become a key process in integrated circuit (IC) technology. The results of copper CMP depend not only on the mechanical abrasion, but also on the slurry chemistry. The slurry used for Cu CMP is known to have greater chemical reactivity than mechanical material removal. The Cu CMP slurry is composed of abrasive particles, an oxidizing agent, a complexing agent, and a corrosion inhibitor. Citric acid can be used as the complexing agent in Cu CMP slurries, and is widely used for\npost-CMP cleaning. Although many studies have investigated the effect of citric acid on Cu CMP, no studies have yet been conducted on the interfacial friction characteristics and step height reduction in CMP patterns. In this study, the effect of citric acid on the friction characteristics and step height reduction in a copper wafer with varying pattern densities during CMP are investigated. The prepared slurry consists of citric acid (C6H8O7), hydrogen peroxide (H2O2), and colloidal silica. The friction force is found to depend on the concentration of citric acid in the copper CMP slurry. The step heights of the patterns decrease rapidly with decreasing citric acid concentration in the copper CMP slurry. The step height of the copper pattern decreases more slowly in high-density regions than in low-density regions.","chemical mechanical planarization (CMP), copper, citric acid, step height reduction, friction force","Hyunseop Lee†\nSchool of Mechanical Engineering, Tongmyong University","http://dx.doi.org/10.9725/kts.2018.34.6.226"]
["34권6호\npp.235-240","인산을 이용한 법랑 코팅의 초윤활성 및 초기 시간에 대한 연구\n(Study on the Superlubricity and Running-in Period of Vitreous Enamel Coating using Phosphoric Acid)","Lubrication (Lubricants & Additives) ,Tribochemistry ","Superlubricity refers to the lubrication phenomenon that occurs when the friction coefficient is lower than 0.01. In recent years, this phenomenon has received a significant amount of attention because it can greatly contribute to the reduction of economic and environmental losses caused by friction and wear. In the case of acid lubricants, only ceramic materials can be used for superlubricity, and it takes a long running-in period to enter the superlubricity regime. In this work, we investigated the superlubricity effect of vitreous enamel coating on SUS304. We also examined the running-in period of vitreous enamel coating under phosphoric acid lubricant condition with respect to surface treatments. Drying and polishing methods were used to treat the vitreous enamel coating on the specimen. The friction experimental results revealed that superlubricity could be achieved with vitreous enamel coating. It was also found that the drying and polishing methods can significantly reduce the running-in period and improve the wear properties of vitreous enamel coating. In particular, the polishing method shortened the running-in period by approximately 99% and reduced the wear rate by approximately 99%, compared to nontreated vitreous enamel coating.","superlubricity(초윤활성), vitreous enamel coating(법랑 코팅), running-in period(초기 시간), friction coefficient(마찰계수), wear rate(마모율)","한도렬·김태형·김대은†\n연세대학교 대학원 기계공학과, 무한내마모연구단","http://dx.doi.org/10.9725/kts.2018.34.6.235"]
["34권6호\npp.241-246","A Study on Friction and Wear Properties of Tetrahedral Amorphous Carbon Coatings on Various Counterpart Materials","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","This research addresses the improvement of tribo-systems, specifically regarding the reduction of friction and wear through tribo-coupling between tetrahedral amorphous carbon (ta-C) with different types of counterpart materials, namely bearing steel (SUJ2), tungsten carbide (WC), stainless steel (SUS304), and alumina (Al2O3). A second variable in this project is the utilization of different values of duct bias voltage in the deposition of the ta-C coating – 0, 5, 10, 15, and 20 V. The results of this research are expected to determine the optimum\nduct bias and best counter materials associated with ta-C to produce the lowest friction and wear. Results obtained reveal that the tribo-couple between the ta-C coating and SUJ2 balls produces the lowest friction coefficient and wear rate. In terms of duct bias changes, deposition using 5 V produces the most optimum tribological behavior with lowest friction and wear on the tribo-system. In contrast, the tribo-couple between ta-C with a WC ball causes penetration through the coating surface layer and hence high surface delamination. This study demonstrates that the most effective ta-C coating duct bias is 5 V associated with SUJ2 counter material to produce the lowest friction and wear.","filtered cathodic vacuum arc (FCVA), friction, wear, ta-C coating, tribo-coupling","Min Szan Lim1, Young-Jun Jang2†, Jong-Kuk Kim2†, Jong-Hyoung Kim3† and Seock-Sam Kim1‡\n1Dept. of Mechanical Engineering, Universiti Malaysia Sabah, Malaysia, 2Tribology Laboratory, Aerospace Materials Center, Materials Processing Innovation Research Division, Korea Institute of Materials Science, 3Extreme Fabrication Technology Group, Daegyeong Division, Korea Institute of Industrial Technology","http://dx.doi.org/10.9725/kts.2018.34.6.241"]
["34권6호\npp.247-253","베어링의 열전도율이 평행 슬라이더 베어링의 윤활성능에 미치는 영향\n(Effect of Thermal Conductivity of Bearing on the Lubrication Performance of Parallel Slider Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Temperature rise due to viscous shear of the lubricating oil generates hydrodynamic pressure, even if the lubricating surfaces are parallel. This effect, known as the thermal wedge effect, varies significantly with film-temperature boundary conditions. The bearing conducts a part of the heat generated; hence, the oil temperature varies with the thermal conductivity of the bearing. In this study, we analyze the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. We numerically analyze the continuity equation, Navier-Stokes equation, energy equation including the temperature-viscosity and temperature-density relations for lubricants, and the heat conduction equation for bearing by creating a 2D model of the micro-bearing using the commercial computational fluid dynamics (CFD) code FLUENT. We then compare the variation in temperature, viscosity, and pressure distributions with the thermal conductivity. The results demonstrate that the thermal conductivity has a significant influence on THD lubrication characteristics of parallel\nslider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect resulting in a higher load-carrying capacity and smaller frictional force. The present results can function as the basic data for optimum bearing design; however, the applicability requires further studies on various operating conditions.","parallel slider bearing(평행 슬라이더 베어링), temperature boundary condition(온도경계조건), thermal conductivity(열전도율), thermal wedge(열쐐기), thermohydrodynamic lubrication(THD)(열유체 윤활)","박태조1†·이원석2·박지빈2\n1경상대학교 기계공학부·항공기부품기술연구소, 2경상대학교 기계항공정보융합공학부 학부생","http://dx.doi.org/10.9725/kts.2018.34.6.247"]
["34권6호\npp.254-261","고탄소크롬 베어링강 2종(SUJ2) 베어링강에 증착된 저마찰 코팅의 트라이볼로지적 특성 연구\n(A Study on the Tribological Characteristics of Low Friction Coating Deposited on SUJ2 Bearing Steel)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In order to reduce resistance torque and energy loss, minimizing friction between race surface and rolling elements of a bearing is necessary. Recently, to reduce friction in bearing element, solid lubricant coating for the bearing raceway surface has been receiving much attention. Considering the operating conditions of real bearings, verifying the effect of solid lubricant coatings under extreme conditions of high load that is more than 1 GPa is necessary. In this study, we evaluated the friction and wear characteristics of SUJ2 bearing steels deposited by carbon-based coatings (Si-DLC, ta-C), MoS2 and graphite. In case of MoS2 and graphite coatings, different surface treatments were applied to the coatings to verify the effect of surface treatment. A pin-on-disc type tribotester was used to evaluate the tribological characteristics of the coatings. It was possible to quantitatively estimate the friction and wear characteristics of solid lubricant under dry and lubrication conditions. The carbonbased coatings improved the friction and wear properties of SUJ2 bearing steels under the high load condition, but MoS2 and graphite coatings were not suitable for high load conditions due to its low hardness. Different friction and wear behaviors were found for different substrate surface treatment method. Also, it was confirmed that solid lubricant coatings had a more positive effect than just applying the lubricant for improving the tribological characteristics.","sliding friction(미끄럼 마찰), high load(고하중), SUJ2 bearing steel(SUJ2 베어링강), carbon-based coatings(탄소기반 코팅), wear(마모)","강경모1·신동갑1·박영훈2·김세웅2·김대은1†\n1연세대학교 대학원 기계공학과, 2일진그룹 선행재료연구센터 재료이노베이션팀","http://dx.doi.org/10.9725/kts.2018.34.6.254"]
["34권6호\npp.262-269","브로칭 가공된 회주철 소재 표면의 마찰 및 마모 특성\n(Friction and Wear Characteristics of Gray Cast Iron Surface Processed by Broaching Method)","Tribology in Design & Manufacturing (Metalworking / Machining)","In this work the friction and wear characteristics of the gray cast iron surface processed by broaching method, which is widely used in the machinery industry, were investigated. The broaching process is mainly used for mass production because it has high dimensional accuracy and processing speed, but the defects on surface can be easily generated. In order to improve the tribological characteristics, the approach was to reduce the roughness and hardness of the surface by adding a machining process to the broaching specimen. The secondary machining process using abrasive grains produces low roughness and hardness than broaching because it has high tool accuracy and removes the work hardened surface. The friction coefficient and the wear rate were assessed using a reciprocating-type tribotester to analyze the effects of surface finishing on the tribological properties. The friction tests were conducted under dry and lubricated conditions. The test results showed that the reduction of surface roughness and hardness through secondary machining process in lubricated condition improved the friction and wear characteristics. The reason why the same results did not appear in a dry condition was that wear occurred more rapidly than in lubricated condition. Thus, the positive effect of roughness and hardness\nof the surface obtained through the secondary machining process was not observed.","compressor(압축기), friction(마찰), hardness(경도), roughness(거칠기), wear(마모)","권문성1,2·강경희1,2·김대은1,2†\n1연세대학교 기계공학과, 2연세대학교 무한내마모연구단","http://dx.doi.org/10.9725/kts.2018.34.6.262"]
["34권6호\npp.270-278","SLM 방식으로 출력된 STS 316L의 기계적 및 마찰 · 마모 특성에 미치는 UNSM처리 후 영향에 관한 연구\n(A Study on the Effect of UNSM Treatment on the Mechanical and Tribological Properties of STS 316L Printed by Selective Laser Melting)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","STS 316L prepared by additive manufacturing (AM) exhibits deterioration of mechanical properties and wear resistance due to the presence of defects such as black-of-fusion defects, internal porosity, residual stress, and anisotropy. In addition, high surface roughness (integrity) of AM products remains an issue. This study aimed to apply ultrasonic nanocrystal surface modification (UNSM) technology to STS 316L prepared by AM to increase the surface hardness, to reduce the surface roughness, and to improve the friction and wear\nbehavior to the level achieved by bulk material manufactured using traditional processes. Herein, the as-received and polished specimens were treated by UNSM technology and their resulting properties were compared and discussed. The results showed that UNSM technology increased the surface hardness and reduced the surface roughness of the as-received and polished specimens. These results can be attributed to grain size refinement and pore elimination from the surface. Moreover, the friction of the as-received and polished specimens after UNSM technology was lower compared to those of the as-received and polished specimens, but no significant differences in wear resistance were found.","friction and wear behavior (마찰마모 거동), hardness (경도), STS 316L (스테인리스강 316L), SLM (선택적 레이저 용융), UNSM (초음파나노표면개질)","노준석1·산성충호1·우마로프 라크마트전1·편영식2·아마노프 아웨즈한2†\n1선문대학교 대학원 기계공학과, 2선문대학교 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.6.270"]
["34권6호\npp.279-283","다수의 연마입자를 고려한 CMP 공정의 Stick-Slip 고찰\n(Stick-slip in Chemical Mechanical Polishing Using Multi-Particle Simulation Models)","Tribology in Design & Manufacturing (Metalworking / Machining)","In this study, we investigate the behavior of abrasive particles and change of the stick-slip pattern according to chemical mechanical polishing (CMP) process parameters when a large number of abrasive particles are fixed on a pad. The CMP process is simulated using the finite element method. In the simulation, the abrasive grains are composed of those used in the actual CMP process. Considering the cohesion of the abrasive grains with the start of the CMP process, abrasive particles with various sizes are fixed onto the pad at different intervals so that stick-slip could occur. In this analysis, we determine that when the abrasive particle size is relatively large, the stick-slip period does not change as the pressure increases while the moving speed is constant. However, if the size of the abrasive grains is relatively small, the amount of deformation of the grains increases due to the elasticity of the pad. Therefore, the stick-slip pattern may not be observed. As the number of abrasive particles increases, the stick-slip period and displacement decrease. This is consistent with the decrease in the von Mises yield stress value on the surface of the wafer as the number of abrasive grains increases. We determine that when the number of the abrasive grains increases, the polishing rate, and characteristics are improved, and scratches are reduced. Moreover, we establish that the period of stick-slip increases and the change of the stick-slip size was not large when the abrasive particle size was relatively small.","chemical-mechanical-polishing(기계화학적 연마), stick-slip(스틱-슬립), surface defect(표면결함)","정소영·성인하†\n한남대학교 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.6.279"]
["34권6호\npp.284-291","고주파 연소합성 코팅된 Ni-Al계 금속간화합물의 미끄럼 마모 특성에 미치는 볼 밀링의 영향\n(Effects of Ball Milling on Sliding Wear Behavior of Ni-Al Intermetallics Coated on Mild Steel through Induction Heating Process)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials) ,Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Ball-milling for reactant powders in advance and using an induction heating system for Ni-Al intermetallic coating process are known to enhance the reactivity of combustion synthesis. In this work, the effects of the charging weight ratio of ball to powder in ball-milling for reactant Ni-Al powders and the synthesizing temperature in induction heating on sliding wear behavior of the coating layers are investigated. Sliding wear behavior of the coating layers is examined against a tool steel using a pin-on-disc type sliding wear machine.\nAs results, wear of the coating layer ball-milled without ball was severely worn out at the sliding speed of 2m/s, regardless of the synthesizing temperature in induction heating. However, the wear rate of the coating layers at the sliding speed was remarkably decreased with increasing the charging weight ratio of ball in ball-milling for reactant powders. This can be explained by the fact that the void in the coating layer is disappeared and the coating layer is densified by the ball-milling. The evidence showed that pitting damages were disappeared on the worn surface of ball-milled coating layer. Consequentially, the Ni-Al intermetallic coating layer could have better wear resistance at all sliding speed ranges with the ball-milling for reactant powders in advance.","ball milling (볼 밀링), induction heating (고주파유도가열), coating layer (코팅층), intermetallics (금속간화합물), wear behavior (마모거동)","이한영†\n계명대학교 신소재공학과","http://dx.doi.org/10.9725/kts.2018.34.6.284"]
["34권6호\npp.292-299","경유엔진용 윤활유의 성상 및 열화가 배출가스 및 후처리 장치에 미치는 영향 연구\n(Effect of the Properties of Diesel Engine Oil and Aging on Exhaust Gases and DPF)","Lubrication (Lubricants & Additives)","The objective of this research is to investigate the impact of engine oil aging on PM(Particulate Matter), exhaust gases, and DPF. It is widely known that the specification of a lubricant and its consumption in an ICE considerably influences the release of regulated harmful emissions under normal engine operating conditions. Considering DPF clogging phenomena associated with lubricant-derived soot/ash components, a simulated aging mode is designed for DPF to facilitate engine dynamometer testing. A PM/ash accumulation cycle is developed by considering real-world engine operating conditions for the increment of engine oil consumption and natural DPF regeneration for ash accumulation. The test duration for DPF aging is approximately 300 h with high- and low-SAPs engine oils. Detailed engine lubricant properties of new and aged oils are analyzed to evaluate the effect of engine oil degradation on vehicle mileage. Furthermore, physical and chemical analyses are performed using X-CT, ICP, and TGA/DSC to quantify the engine oil contribution on the PM composition. This is achieved by sampling with various filters using specially designed PM sampling equipment. Using high SAPs\nengine oil causes more PM/ash accumulation compared with low SAPs engine oils and this could accelerate fouling of the EGR in the engine, which results in an increase in harmful exhaust gas emissions. These test results on engine lubricants under operating conditions will assist in the establishment of regulated and unregulated toxic emissions policies and lubricant quality standards.","engine oil(자동차용 윤활유), DPF (후처리장치), exhaust gases(배출가스), EGR (배출가스 순환장치), soots(매연)","김정환†·김기호·이정민\n한국석유관리원 석유기술연구소","http://dx.doi.org/10.9725/kts.2018.34.6.292"]
["34권6호\npp.300-306","Testing of Load Capacity of a Foil Thrust Bearing","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In this study, the performance of foil thrust bearings was investigated by performing bearing takeoff and load capacity tests, using an in-house designed and manufactured vertical bearing test rig. The mean takeoff rotational speed and maximum load capacity of the bearing specimen were ~18,000 rpm and ~80 kPa, respectively. The vertical bearing test rig was observed to yield higher coefficients of friction and frictional torques than a horizontal bearing test rig under identical test conditions. This was a result of its structural characteristics, in\nthat the bearing specimen is placed atop the thrust runner, which keeps it from being separated from the runner after the bearing take-off. In addition, bearing take-off was observed at a higher runner rotational speed as this structure keeps air from flowing between the top foil and runner surfaces, which requires a higher runner speed. The parallel alignment between the bearing specimen and runner surfaces can be maintained within a certain range more easily in a vertical test rig than in a horizontal test rig. Because of these advantages, Korean Industrial Standard, KS B 2060, recommends a vertical bearing test rig as the standard test device for foil thrust bearings.","foil thrust bearing, vertical bearing test rig, take-off, bearing torque, load capacity","Choong Hyun Kim† and Jisu Park\nCenter for Bionics, Bionics Research Institute, Korea Institute of Science and Technology","http://dx.doi.org/10.9725/kts.2018.34.6.300"]
["34권6호\npp.307-312","스프링 보강 정적 실의 스프링 강성에 따른 기밀 성능 해석\n(Analysis of Sealing Effectiveness Based on Spring Stiffness of a Spring-Energized Static Seal)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Unlike a typical static seals, spring-energized static seals exhibit improvement in leak-tightness by reinforcing the spring inside the aluminum lining. Thus, spring-energized static seals are widely used in various industrial fields, such as aerospace, semiconductors, and petrochemical industries. The primary objective of this study is to develop design guidelines for spring-energized static seals in a wide range of temperatures, including that of cryogenic environments, by analyzing the required performance and influence of design variables through simulations. There are various parameters that can be controlled to design a leak-tight seal. In this study, the finite element analysis (FEA) is performed by controlling the parameters related to the spring and the thickness of the aluminum lining, and the result of the leakage between the seal and the casing is confirmed. Considering the influence of each parameters, all of them are found to be important. However, it is observed that the springrelated variables are more important than the aluminum lining or other variables when complexity is considered. We can identify the threshold value of spring stiffness that changes leak-tight performance of the seal by performing FEA. Simulation results, under the conditions that are considered in this study, show that spring stiffness should be at least 3.6 N/m to maintain leak-tightness caused by the sufficient contact force between the aluminum lining and the upper and lower casings.","finite element analysis(유한요소해석), leakage(누설), static seal(정적 실)","장수연·성인하†\n한남대학교 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.6.307"]
["34권6호\npp.313-317","전기 분사 증착 방식을 이용한 탄소 나노 튜브 박막의 트라이볼로지적 특성에 관한 연구\n(Tribological Properties of Carbon Nanotube Thin Films by using Electrodynamic Spraying Method)","Lubrication (Lubricants & Additives)","Carbon-based coatings, including carbon nanotubes (CNTs), graphene, and buckyball (C60), receive much interest because of their outstanding mechanical and electrical properties for a wide range of electromechanical component-based applications. Previous experimental results demonstrate that these carbon-based coatings are promising solid lubricants because of their superior tribological properties, and thus help prolong the lifetime of silicon-based applications. In this study, CNT coatings are deposited on a bare silicon (100) substrate by electrodynamic spraying under different deposition conditions. During the coating deposition, the applied voltage, CNT concentration of the solution, distance between the injecting nozzle and the substrate and diameter of the injecting nozzle are optimized to control the thickness and surface roughness of the CNT coatings. The surface morphology and thickness of the coatings are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The friction and wear properties of the coatings are investigated by using a pin-on-reciprocating-type tribotester under various experimental conditions. The friction coefficient\nof the CNT coating is as low as 0.15 under high normal loads. The overall results reveal that CNT coatings\ndeposited by electrodynamic spraying provide relatively uniform with superior lubrication performance.","solid lubricants(고체 윤활), carbon nanotube(탄소나노튜브), friction(마찰), wear(마모)","김창래1·김대은2·김해진3†\n1조선대학교 기계공학부, 2연세대학교 기계공학부, 3경상대학교 기계항공공학부","http://dx.doi.org/10.9725/kts.2018.34.6.313"]
["34권6호\npp.318-324","SEM 내부에 설치된 트라이보 시험기를 통한 금속 코팅의 실시간 마찰/마모 특성 분석\n(Real Time Analysis of Friction/Wear Characteristics of Metal Coatings with a Tribo-tester Installed in an SEM)","Wear Phenomena & Mechanisms ,Tribo-Testing / Measurement & Instruments ,Micro/Nano-Tribology","This study aims to visualize the friction and wear behaviors of metal coatings in real time. The main mechanism of wear is identified by observing all the processes in which wear occurs. The friction coefficients of the moments are monitored to confirm the relationship between the friction and wear characteristics of the coating. Thin Ag coatings, which are several hundred nanometers in thickness, are prepared by depositing Ag atoms on silicon substrates through a sputtering method. A pin-on-disk-type tribo-tester is installed inside a scanning electron microscope (SEM) to evaluate the friction and wear characteristics of the Ag coating. A fine diamond pin is brought into contact with the Ag coating surface, and a load of 20 mN is applied. The contact pressure is calculated to be approximately 15 GPa. The moments of wear caused by the sliding motion are visualized, and the changes in the friction characteristics according to each step of wear generation are monitored. The Ag coating can be confirmed to exhibit a wear phenomenon by gradually peeling off the surface of the coating on observing the friction and wear characteristics of the coating in real time inside the SEM. This can be explained by a typical plowing-type wear mechanism.","friction(마찰), real time(실시간), silver coating(은코팅), visualization(가시화), wear(마모)","김해진1·김대은2·김창래3†\n1경상대학교 기계항공공학부, 2연세대학교 기계공학과, 3조선대학교 기계공학과","http://dx.doi.org/10.9725/kts.2018.34.6.318"]
["34권6호\npp.325-331","ZI 및 ZA형 웜기어의 치합전달오차 해석\n(Transmission Error Analysis of ZI and ZA Profile Worm Gears)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Automobiles and systems requiring high gear ratios and high power densities generally use worm gears. In particular, as worm gears have a small volume and self-locking function, home appliances such as refrigerators and washers consist of worm gears. We can classify worm gears into cylindrical worms and rectangular worms. According to the AGMA standard, there are four types of cylindrical worms, ZA, ZN, ZK and ZI, depending on the machining of the worm shaft. It is preferable to use a ZI-type worm shaft, which is a combination of a worm wheel having an involute helical tooth surface and a conjugate tooth surface. However, in many cases, industries mostly use ZK, ZN, and ZA worm shafts because of the ease of processing. This paper presents numerical approaches to produce ZI and ZA worm surfaces and worm wheel. For the analysis of the transmission error of a worm gear system, this study (1) generates surface profile functions of ZI profile worm gear and worm shaft based on the common rack theory, (2) adopts the Newton-Raphson method for the analysis of the gear surface contact condition, and (3) presents and compares the corresponding transmission errors of ZI and ZA worm gears.","worm gear system(웜기어시스템), ZI worm(ZI웜), ZA worm (ZA웜), gear transmission error (기어 치합전달오차)","이태훈1·서준호2†·박노길2\n1부산대학교 대학원 기계공학부, 2부산대학교 기계공학부","http://dx.doi.org/10.9725/kts.2018.34.6.325"]

{"sheet":"2019년","index":3,"n_rows":34,"n_cols":7,"rows_kept":34,"cut":false,"hidden":false,"merged":[]}
["권호","제목","토픽","초록","키워드","저자","DOI"]
["35권1호\npp.1-8","플라스틱 기어의 트라이볼로지적 특성 향상을 위한 DLC 코팅 적용                              \n(Evaluation of Tribological Characteristics of Diamond-Like Carbon (DLC) Coated Plastic Gear)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Demand for plastic gears are increasing in many industries due to their low production cost, light weight, applicability without lubricant, corrosion resistance and high resilience. Despite these benefits, utilizing plastic gears is limited due to their poor material properties. In this work, DLC coating was applied to improve the tribological properties of polyamide66 gear. 0 V, 40 V, and 70 V of negative bias voltages were selected as a deposition parameter in DC magnetron sputtering system. Pin-on-disk experiment was performed in order to investigate the wear characteristics of the gears. The results of the pin-on-disk experiment showed that DLC coated polyamide66 with 40 V of negative bias voltage had the lowest friction coefficient value (0.134) and DLC coated PA66 with 0 V of negative bias voltage showed the best wear resistance (9.83×10-10 mm3/N·mm) among all the specimens. Based on these results, durability tests were conducted for DLC coated polyamide66 gears with 0 V of negative bias voltage. The tests showed that the temperature of the uncoated polyamide66 gear increased to about 37oC while the DLC coated gear saturated at about 25oC. Also, the power transmission efficiency of the DLC coated gear increased by about 6% compared to those without coating. Weight loss of the polyamide66 gears were reduced by about 73%.","plastic gear (플라스틱 기어), friction (마찰), wear (마모), diamond-like carbon (다이아몬드상 카본), coating (코팅), tribology (트라이볼로지), sputtering (스퍼터링)","배수민1,2·마디 카뎀1,2·서국진1,2·김대은1,2†\n1연세대학교 기계공학부, 2연세대학교 무한내마모연구단 1Department of Mechanical Engineering, Yonsei University, 2Center for Nano-Wear, Yonsei University ","https://doi.org/10.9725/kts.2019.35.1.1"]
["35권1호\npp.9-15","전사 방법에 따른 그래핀의 표면 에너지 변화\n(Surface Energy of Graphene Transferred by Wet and Dry Transfer Methods)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Graphene is a fascinating material for fabricating flexible and transparent devices owing to its thickness and mechanical properties. To utilize graphene as a core material for devices, the transfer process of graphene is an inevitable step. The transfer process can be classified into wet and dry methods depending on the surrounding environment. The adhesion between graphene and a target substrate determines the success or failure of the transfer process. As the surface energy of graphene is an important parameter that provides adhesion, it is useful to estimate the surface energy to understand the mechanisms of the transfer process. However, the exact surface energy of graphene is still disputed because the wetting transparency of graphene depends on the polarity of the liquid and target substrate. Previously reported results use graphene transferred by the wet method. However, there are few reports on the surface energy of graphene transferred by the dry method. In this study, the surface energy of graphene transferred by the wet and dry methods is estimated. Wetting transparency occurs for certain combinations of liquids and substrates. For graphene on a polar substrate, the surface energy decreases by 25 and 35% for the wet and dry transfer methods, respectively. However, the surface energy of graphene on dispersive substrates decreases by ~10% regardless of the transfer method. In conclusion, the surface energy of graphene is 36~38 mJ/m2, and differs depending on the transfer method and polarity of the substrate.","contact angles (접촉각), surface energy (표면 에너지), graphene (그래핀), wet transfer (습식 전사), dry transfer (건식 전사)","윤민아1,2·김찬1,2·원세정3·정현준3·김재현1,2·김광섭1,2†\n1과학기술연합대학원대학교 나노메카트로닉스학과, 2한국기계연구원 나노융합기계연구본부, 3파동에너지극한제어연구단","https://doi.org/10.9725/kts.2019.35.1.9"]
["35권1호\npp.16-23","표면막과 표면거칠기가 접촉 저항에 미치는 영향\n(Effect of Surface Film and Surface Roughness on Contact Resistance)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification), Contact Mechanics & Friction","In this study, we aim to analyze the effects of both contact layer properties and surface roughness on contact resistance. The contact has a great influence on performance in terms of electrical conduction and heat transfer. The two biggest factors determining contact resistance are the presence of surface roughness and the surface layer. For this reason we calculated the contact resistance by considering both factors simultaneously. The model of this study to calculate contact resistance is as follows. First, the three representative surface parameters for the GW model are obtained by Nayak's random process. Then, the apparent contact area, real contact area, and contact number of asperities are calculated using the GW model with the surface parameters. The contact resistance of a single surface layer is calculated using Mikic's constriction equation. The total contact resistance is approximated by the parallel connection between the same asperity contact resistances. The results of this study are as follows. The appropriate thickness with reduction effect for contact resistance is determined according to the difference in conductivity between the base layer and surface layer. It was confirmed that the standard deviation of surface roughness has the greatest influence on surface roughness parameters. The results of this study will be useful for selecting the surface material and surface roughness when the design considering the contact resistance is needed.","surface film (표면막), surface roughness (표면거칠기), GW model (GW모델), contact resistance (접촉 저항), constriction resistance (수축 저항)","이현철·이보라·유용훈·조용주†\n부산대학교 기계공학부","https://doi.org/10.9725/kts.2019.35.1.16"]
["35권1호\npp.24-29","고온 환경에서 합금의 마모 및 마찰 특성에 관한 연구\n(A Study on Wear Properties of Alloys in High Temperature Condition)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","In this work we investigated the friction and wear characteristics of a magnesium alloy, which has been receiving much attention as a light metal in industrial applications such as automobiles and aerospace. Magnesium is one of the lightest structural material that has high specific strength, lightweight, low density and good formability. However, current issue of using magnesium alloy is that magnesium has weakness against temperature. As the temperature increases, magnesium undergoes poor creep resistance and ease of softening, and therefore, its mechanical strength decreases sharply. To solve this issue, a new type of magnesium alloy that retains high strength at high temperature has been proposed. The tribological behavior of this alloy was investigated using a tribotester with reciprocating motion and heating plate. A stainless steel ball was used as a counter surface. Results showed that extrusion process has similar wear behavior to the commonly used casting process but retains good mechanical strength and durability. The presence of an alloying element enhanced the wear properties especially in high temperature. This study is expected to be utilized as fundamental data for the replacement of high density materials currently used in mechanical industries to a much lighter and durable heatresistant materials.","alloy (합금), friction (마찰), high temperature condition (고온 환경), lubrication (윤활), wear (마모)","최승윤1·Narguess Nemati1·김대은2†\n1연세대학교 대학원 기계공학부, 2연세대학교기계공학과","https://doi.org/10.9725/kts.2019.35.1.24"]
["35권1호\npp.30-36","하중 및 온도에 따른 습식 클러치 마찰재의 트라이볼로지 특성\n(Effect of Normal Force and Temperature on Tribological Properties of Wet Clutch Friction Material)","Wear Phenomena & Mechanisms, Automotive Tribology","The tribological properties of paper-based friction materials are crucial to the performance of a wet clutch system. In this work, the friction and wear characteristics of a paper-based friction material in boundary lubrication state was experimentally investigated using a pin-on-reciprocating tribotester under various normal forces and temperatures. It was found that the wear rate of the friction material increased from 5.8×10-6 mm3/N/cycle to 5.5×10-5 mm3/N/cycle after 1,700 cycles of testing at 80°C as normal force increased from 2 N to 7 N. The friction coefficient was also found to increase from 0.135 to 0.155 with increasing normal force from 2 N to 7 N. The increase in contact pressure with increasing normal force may be responsible for these results. In addition, as temperature increased from 20°C to 80°C, the wear rate of the friction materials increased from 2.0×10-5 mm3/N/cycle to 3.6×10-5 mm3/N/cycle while the friction coefficient decreased from 0.163 to 0.146. This result may be associated with the decrease in the hardness of friction materials with increasing temperature. Furthermore, plastic deformation on the friction materials was mainly observed after the test. The outcome of this work may be useful to gain a better understanding of the tribological properties of friction materials, and therefore can contribute to the development of friction materials with enhanced performance for wet clutch systems.","friction (마찰), friction material (마찰재), wear rate (마모율), wet clutch (습식 클러치)","박혜선·정구현†\n울산대학교 기계공학부","https://doi.org/10.9725/kts.2019.35.1.30"]
["35권1호\npp.37-43","볼 베어링의 무차원 형상변수를 이용한 최적 턱 높이 설계\n(Optimum Shoulder Height Design using Non-dimensional Shape Variables of Ball Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)"," This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.","ball bearing (볼 베어링), contact analysis (접촉해석), shoulder height (턱 높이), edge effect (모서리 효과)","최동철1·김태완2†\n1(주)디에스시 기술연구소, 2부경대학교 기계공학과","https://doi.org/10.9725/kts.2019.35.1.37"]
["35권1호\npp.44-51","가스 포일 베어링으로 지지되는 연료전지 전기자동차용 공기압축기의 회전체동역학적 성능 측정 및 예측\n(Rotordynamic Performance Measurements and Predictions of a FCEV Air Compressor Supported on Gas Foil Bearings)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The paper presents the rotordynamic performance measurements and model predictions of a fuel cell electric vehicle (FCEV) air compressor supported on gas foil bearings (GFBs). The rotor has an impeller on one end and a thrust runner on the other end. The front (impeller side) and rear (thrust side) gas foil journal bearings (GFJBs) are located between the impeller and thrust runner to support the radial loads, and a pair of gas foil thrust bearings are located on both sides of the thrust runner to support the axial loads. The test GFJBs have a partial arc shim foil installed between the top foil and bump strip layers to enhance hydrodynamic pressure generation. During the rotordynamic performance tests, two sets of orthogonally installed eddy-current displacement sensors measure the rotor radial motions at the rotor impeller and thrust ends. A series of speed-up and coast-down tests to 100k rpm demonstrates the dominant synchronous (1X) rotor responses to imbalance masses without noticeable subsynchronous motions, which indicates a rotordynamically stable rotor–GFB system. Finite element analysis of the rotor determines the rotor free-free (bending) natural modes and frequencies well beyond the maximum rotating frequency. The predicted damped natural frequencies and damping ratios of the rotor–GFB system reveal rotordynamic stability over the speeds of interest. The imbalance response predictions show that the predicted critical speeds and rotor amplitudes strongly agree with the test measurements, thus validating the developed rotordynamic model.","gas foil bearing (가스 포일 베어링), mass imbalance response (질량 불균형 응답), rotordynamic (회전체동역학), shim foil (심포일), air compressor (공기압축기)","황성호1·문창국1·김태호1†·이종성2·조경석2·하경구3·이창하3\n1국민대학교 대학원 기계설계학과, 2한온시스템 선행부품개발팀, 3현대자동차 연료전지설계팀","https://doi.org/10.9725/kts.2019.35.1.44"]
["35권1호\npp.52-58","자동차 전장 커넥터 방수 시일의 유한요소해석\n(FEM Analysis of a Waterproof Seal of Automotive Electrical Connectors)","Modeling & Simulation in Tribology","In the case of high-voltage connectors applied to automobiles, waterproofing has become an important issue for the safety of automobiles. In this study, structural analysis is performed on silicone rubber- type waterproof seals used in the voltage connector. For the structural analysis, the tensile properties of the actual rubber seal are evaluated using a miniaturized tensile testing machine. The Mooney-Rivlin material constants of the rubber seal are determined as follows; D1=0, C01=0.241, C10=0.0142. The analysis shows that the contact pressure at the top of the seal where the seal and male connector are in contact is approximately three times higher than that at the bottom of the seal where the seal and female connector are in contact. It is confirmed that the waterproofing performance of the rubber seal depends on the contact pressure of the seal bottom where the seal and female connector are in contact. The contact pressure for waterproofing is found to be 4.7 bar. The strain concentration of the curved part is attributed to excessive initial tension. Therefore, a redesign is recommended for uniform stress or strain distribution in the curved section of the seal in response to the stress relaxation problem due to permanent deformation.","connector seal (커넥터 시일), rubber properties (고무 물성치), waterproof seal (방수 시일), contact pressure (접촉 압력)","한정진1·황원태1·김호경2†\n1서울과학기술대학교 일반대학원 자동차공학과, 2서울과학기술대학교 기계·자동차공학과","https://doi.org/10.9725/kts.2019.35.1.52"]
["35권1호\npp.59-64","자동차 헤드램프내 체결부품사이의 마찰계수 실험장치 개발\n(Development of a Measuring Device for Coefficient of Friction between Connection Parts in Vehicle Head Lamps)","Contact Mechanics & Friction","When slipping occurs between two materials, the coefficients of friction must be considered because these values determine the overall efficiency of the machine or slip characteristics. Therefore, it is important to find the coefficient of friction between two materials. This paper focuses on obtaining the coefficient of friction between an aiming bolt and a retainer located in the headlamps of a vehicle. This bolt supports the headlamp, and if the bolt is loosened by external vibration, the angle of the light will change and block the vision of pedestrians or other drivers. In order to study these situations, the coefficient of friction between aiming bolts and retainers needs to be measured. In addition, the coefficient of friction of materials used in the headlamp should be obtained. To determine these two factors, a new device is designed for two cases: surface-surface contact and surface-line contact. To increase reliability of the results, the device is designed using an air-bearing stage which uses compressed air as lubricant to eliminate the friction of the stage itself. Experiments were carried out by applying various vertical forces, and the results show that the coefficient of friction can be measured consistently. The procedure for designing the device and the results are discussed.","aiming bolt (에이밍 볼트), air bearing stage (공기베어링 스테이지), coefficient of friction (마찰계수), retainer (리테이너), head lamp (헤드램프)","백홍1·문지승1·박상신2†·박종명3\n1영남대학교 대학원 기계공학과, 2영남대학교 기계공학부, 3(주)SL","https://doi.org/10.9725/kts.2019.35.1.59"]
["35권1호\npp.65-70","자동차 헤드램프 내의 에이밍 볼트의 풀림 해석 및 실험\n(Analysis of Self Loosening of Aiming Bolts in Vehicle Head Lamp)","Contact Mechanics & Friction","Self-loosening of bolts owing to external forces occurs in several machines that are clamped by bolts and nuts. This study focuses on the self-loosening of the aiming bolt of the head lamp in a vehicle. It is important to prevent the aiming bolt from self-loosening as it has a decisive effect on the angle of the head lamp. A nut clamped with a bolt, known as a retainer, is made of plastic and has a partial screw thread. In addition, a transverse load has a considerable impact on the self-loosening of a bolt. We concentrate on the self-loosening of a bolt by a transverse load. The aim of this study is to define the limits of the external force that loosen the bolt. Based on the above conditions, we derive a theoretical equation and develop a numerical analysis program that can calculate the limiting forces for self-loosening. To verify the developed program, we design a test device that can measure the self-loosening by applying sliding forces to the aiming bolt. Using this method, we can draw the following conclusions. First, the developed testing device is suitable to prove the theory for calculating the self-loosening force. Second, the equation confirms the relationship of bolt self-loosening between resistance torque and shear force. Finally, the equation obtains the minimum value of the resistance torque required to decrease the change in the angle of the head lamp, thereby improving the possibility of increasing the stability of the head lamp.","aiming bolt(에이밍 볼트), headlamp(헤드램프), resistance torque(저항 토크), self-loosening(풀림)","문지승1·백홍1·박상신2†·박종명3\n1영남대학교 대학원 기계공학과, 2영남대학교 기계공학부, 3(주)SL","https://doi.org/10.9725/kts.2019.35.1.65"]
["35권1호\npp.71-76","콘크리트 믹서 감속기의 진동 평가\n(Vibration Evaluation of Concrete Mixer Reducer)","Condition Monitoring & Maintenance System (System Reliability), Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The differential planetary gear reducer as a main component of the concrete mixer driving mechanism requires a strong torque to mix concrete compounds. As this component is currently dependent on imports, it is necessary to develop it by conducting a study on vibration analysis and the resonance problem. The noise and vibration of a concrete mixer reducer increase owing to the transmission error of planetary gears, and the damage of components occurs owing to the problems in design and production. In this study, the tooth-passing frequency is calculated to evaluate the noise and vibration of a mixer reducer, and a fast Fourier transform (FFT) analysis is conducted through a vibration test using an acceleration sensor. The vibration of the reducer is measured at three points of input and output of the shaft and planetary gear housing with fixed and variable revolutions per minute. The operating conditions of gears and bearings are evaluated by performing the FFT analysis, and the resonance problem is verified. The results show that No. 1 pinion and ring gears revolve disproportionately. The amplitude values appear high, and the wear of tooth faces occur in tooth-passing frequencies and harmonic components of No. 1 and No. 2 pinion-ring gears. Therefore, we conclude that design changes in the reducer and a correction of tooth profiles are required.","mixer reducer (믹서 감속기), FFT analysis (FFT분석), differential planetary gear (차동유성기어), noise and vibration (소음 진동)","조연상1†·배명호2\n1동아대학교 기계공학과, 2창원문성대학교 항공정비학부","https://doi.org/10.9725/kts.2019.35.1.71"]
["35권1호\npp.77-86","모튼이펙트 해석을 위한 동역학-구조-유체-열전달 시간과도응답 연성해석 시차적분법에서 시상수 효과 분석\n(Analysis of Integration Factor Effect in Dynamic-Structure-Fluid-Heat Coupled Time Transient Staggered Integration Scheme for Morton Effect Analysis)","Tribology Applications (Industrial Case Studies)","The present study focuses on the effect of staggered integration factor (SIF) on Morton effect simulation results. The Morton effect is a synchronous rotordynamic instability problem caused by the temperature differential across the journal in fluid film bearings. Convection and conduction of heat in the thin film displaces the hot spot, which is the hottest circumferential position in the thin film, from -20 to 40 degrees ahead of the high spot, where the minimum film clearance is experienced. The temperature differential across the journal causes a bending moment and the corresponding thermal bow in the rotating frame acts like a distributed synchronous excitation in the fixed frame. This thermal bow may cause increased vibrations and continued growth of the synchronous orbit into a limit cycle. The SIF is developed assuming that the response of the rotor-lubricant-bearing dynamic system is much quicker than that of the bearing-journal thermal system, and it is defined as the ratio between the simulation time of the thermal system and the rotor-spinning period. The use of the SIF is unavoidable for efficient computing. The value of the SIF is chosen empirically by the software users as a value between 100 and 400. However, the effect of the SIF on Morton effect simulation results has not been investigated. This research produces simulation results with different values of SIF.","staggered integration scheme(시차적분법), multi-physics system(다중물리 시스템), morton effect(모튼이펙트), tilting pad journal bearing (틸팅패드 저널베어링)","서준호1†·정승화2\n1부산대학교 대학원 기계공학부, 2잉거솔랜드 압축기 연구개발본부","https://doi.org/10.9725/kts.2019.35.1.77"]
["35권2호\npp.87-93","오일리스 부시용 고체윤활제 개발\n(Development of Solid Lubricants for Oil-less Bush)","Lubrication (Lubricants & Additives)","This work aims to develop a dry lubricant for oilless bush, especially a solid lubricant, thereby creating a coating method with improved properties of anti-friction and load-carrying capacity without oil lubrication. In this work, spherical-shaped powders of thermosetting resin such as polyimide (PI) are mixed with a binder matrix obtained by mixing a fluorocarbon compound resin such as Polytetrafluoroethylene (PTFE) or Ethylene tetra fluoro ethylene (ETFE) with itself or with a non-fluorocarbon thermoplastic resin such as Polyether ether ketone (PEEK). And these dry lubricant mixtures are thickly coated (200-300 mm in the thickness) on the inner surface of the bush by using a wet-typed air-spray deposition method. It was found that the load-carrying capacity of the solid lubricant for excavator bush (60 mm in diameter) that operates under a high load condition (at 40 MPa) is greatly improved owing to the spherical-shaped powders of thermosetting resin. In addition, the coefficient of friction at the sliding surface is also reduced less than 0.1. Thick coating also lowers the contact stress at the edge of a bush that results in better tribological performances. The result suggests that the lubrication performance and durability life of the bush can be remarkably improved even without lubrication (oil or grease).","oil-less bush(오일리스 부시), friction(마찰), wear life(내구수명), PTFE(불화탄소수지), solid lubrication(고체윤활)","공호성1†·한흥구1·김진욱2·김경석2·박종식3\n1한국과학기술연구원 책임연구원/연구원, 2㈜대금지오웰 본부장/선임연구원, 3J.S. Chem 대표이사","https://doi.org/10.9725/kts.2019.35.2.87"]
["35권2호\npp.94-98","리블렛 표면에서 유적의 젖음성에 대한 수치 해석\n(Wettability Simulation of Oil Droplet on Riblet Surface)","Bio-Tribology/Biomimetics","The riblet structure like shark skin has been widely studied owing to its drag reduction and antifouling properties. In this study we simulated the wettability of an oil droplet on a riblet surface. We developed a numerical analysis method using the Wenzel equation and Cassie–Baxter equation that can estimate the contact angle with a penetrated depth of the droplet on rough surfaces. Riblet surfaces with nine scales composed of five hemi-elliptical ribs are generated numerically. The variation of contact angles with fractional depth of penetration for the generated riblet surfaces with and without coatings is demonstrated in the condition of solid-air-oil and solid-water-oil interfaces. The contact angle for the uncoated surface decreases with increasing fractional depth of penetration more drastically than that for the coated surface. For the effect of surface roughness on the contact angle of the droplet, the oleophilic surface gives lower contact angle when the surface is rougher, whereas the oleoophobic surface gives higher contact angle with higher roughness To verify the analysis results, the wetting angle was measured in the solid-air-oil interface and solid-water-oil interface for the shark-skin template and shark-skin replica. The effects of teflon coating were also evaluated. It is shown that the simulation results cover the experimental ones.","oil droplet (유적), riblet (리블렛), wettability (젖음성), oleophobicty (소유성)","김태완†\n부경대학교 기계공학과 교수","https://doi.org/10.9725/kts.2019.35.2.94"]
["35권2호\npp.99-105","DN 250만 250℃고온 스팀환경에서 운전되는 단열 브러쉬 실 마모효과에 관한 실험적 연구\n(Experimental Study on the Wear Effects of a Brush Seal in DN 2.5million in a 250℃ High - temperature Steam Environment)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This study presents an experimental investigation of the wear and oxidation of the bristles of a brush seal in a super-heated steam environment. We construct a model reflecting normal force and radial interference to predict the amount of wear. To monitor the volume loss of the bristle induced by the swirl phenomenon of the rotor, we measure the clearance between the rotor and the brush seal by using a non-contact 3-D device. We calculate the area by using the area-wise measurement method. Considering the obvious brush seal wear variables, we use two disks with different roughness(Ra = 0.1μm and 100μm) to determine the effect of roughness on wear. Considering an actual steam turbine, we utilize a steam generator and super-heater to generate a working fluid (0.95MPa, 523.15K) that has high kinetic energy. We observe the abrasion of the bristles in the hot steam environment through a scanning electron microscope image. This study also conducted energy dispersive X-ray (EDX) analysis for a qualitative evaluation of local chemistry. The results indicate that the wear and elimination of bristles occur on the disk with high roughness, and the weight increases due to oxidation. Furthermore these results, reveal that the bristle oxidation is accelerated more under super-heated steam conditions than under conditions without steam.","brush seal(브러쉬 실), wear(마모), Bristle(강모), Surface roughness(표면거칠기), super-heated steam(과열증기)","하윤석1·하태웅2†·이용복3†\n1연합기술대학원대학교(UST) 에너지-환경융합학과 학생연구원, 2가천대학교 기계공학과 교수, 3한국과학기술연구원 국가기반기술연구본부 책임연구원","https://doi.org/10.9725/kts.2019.35.2.99"]
["35권2호\npp.106-113","몰드성형용 렌즈를 위한 ta-C coating의 응용\n(Application of ta-C Coating on WC Mold to Molded Glass Lens)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","We investigated the application of tetrahedral amorphous carbon (ta-C) coatings to fabricate a glass lens manufactured using a glass molding process (GMP). In this work, ta-C coatings with different thickness (50, 100, 150 and 200 nm) were deposited on a tungsten carbide (WC-Co) mold using the X-bend filter of a filtered cathode vacuum arc. The effects of thickness on mechanical and tribological properties of the coating were studied. These ta-C coatings were characterized by atomic force microscopy, scanning electron microscopy, nano-indentation measurements, Raman spectrometry, Rockwell-C tests, scratch tests and ball on disc tribometer tests. The nano-indentation measurements showed that hardness increased with an increase in coating thickness. In addition, the G-peak position in the Raman spectra analysis was right shifted from 1520 to 1586 cm−1, indicating that the sp3 content increased with increasing thickness of ta-C coatings. The scratch test showed that, compared to other coatings, the 100-nm-thick ta-C coating displayed excellent adhesion strength without delamination. The friction test was carried out in a nitrogen environment using a ball-on-disk tribometer. The 100-nm-thick ta-C coating showed a low friction coefficient of 0.078. When this coating was applied to a GMP, the life time, i.e., shot counts, dramatically increased up to 2,500 counts, in comparison with Ir-Re coating.","FCVA, ta-C, hardness, adhesion, CoF, glass molding process, optical lens","Woo-Young Lee1† and Ju-hyun Cho2\n1Researcher, Advanced Materials and Manufacturing Laboratory, Department of Mechanical Science and Engineering, Nagoya University, Japan, 2Director, Photonics & ICT Convergence Research Division, Korea Photonics Technology Institute (KOPTI), Korea","https://doi.org/10.9725/kts.2019.35.2.106"]
["35권2호\npp.114-122","볼 베어링 및 가스 포일 베어링으로 지지되는 소형 고속 전동기의 진동 특성\n(Vibrational Characteristics of High-Speed Motors with Ball Bearings and Gas Foil Bearings Supports)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This study characterizes the coastdown performances of two small electric motors supported on high- speed ball bearings (BBs) and gas foil bearings (GFBs), and it predicts their acceleration performances. The two motors have identical permanent magnetic rotors and mating stators. However, the shaft of the GFBs has a larger mass and polar/transverse moments of inertia than that of the BBs. Motor coastdown tests demonstrate that the rotor speed decreases linearly with the BBs and nonlinearly with the GFBs. A simple model for the BBs predicts a constant drag torque and linear decay of speed with time. The test data validate the model predictions. For the GFBs, the hydrodynamic lubrication model predictions reveal that the drag torque increases linearly with speed, and the speed decreases exponentially with time. The predictions agree very well with the test data in the speed range of 100–30 krpm. The boundary lubrication model predicts a constant drag torque and linear decay of speed with time. The predictions agree well with the test data below 15 krpm. Mixed lubrication occurs in the speed range of 30–15 krpm. Rotor acceleration performances are predicted based on the characteristics of deceleration performances. The GFBs require more time to reach 100,000 krpm than the BBs because of their larger shaft polar moment of inertia. However, predictions for the assumed identical polar moment of inertia reveal that the GFBs have a nearly identical acceleration performance to that of the BBs with a motor torque greater than 0.03 N·m.","high speed motor(고속 전동기), gas foil bearing(가스 포일 베어링), ball bearing(볼 베어링), coastdown(관성정지), acceleration(가속)","서정화1·김태호2†\n1국민대학교 대학원 기계설계학과 연구조교, 2국민대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.2.114"]
["35권2호\npp.123-131","볼 베어링 및 가스 포일 베어링으로 지지되는 고속 전동기의 회전체 관성정지 및 가속 성능 연구\n(Rotor Coastdown and Acceleration Performances of High-speed Motors Supported on Ball Bearings and Gas Foil Bearings)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.","ball bearing (볼 베어링), contact analysis (접촉해석), shoulder height (턱 높이), edge effect (모서리 효과)","문형욱1·서정화1·김태호2†\n1국민대학교 대학원 기계설계학과 연구조교, 2국민대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.2.123"]
["35권2호\npp.132-138","염기 처리된 montmorillonite를 이용한 다이머산 메틸에스테르의 합성\n(Synthesis of Dimer Acid Methyl Ester Using Base-treated Montmorillonite)","Lubrication (Lubricants & Additives)","In this study, we demonstrate the effects of the acidic properties of montmorillonite (MMT), which is commonly used as a catalyst, on the conversion and selectivity of the dimer acid methyl ester (DAME) synthesis. We synthesize DAME by the dimerization of conjugated linoleic acid methyl ester (CLAME) and oleic acid methyl ester using MMT KSF. Incidentally, trimer acid methyl ester was formed as a by-product during the DAME synthesis. There is a necessity to adequately adjust the strength and quantity of the acid site to control the selectivity of DAME. Therefore, we vary the pH of the MMT acid by using various metal hydroxides. The purpose of this study is to increase the yield of monocyclic dimer acid methyl ester, which is a substance with adequate physical properties for industrial applications (e.g., lubricant and adhesive, etc.), using a heterogeneous catalyst. We report the dimerization of fatty acid methyl ester by using base treated-KSF, and apply it to conjugated soybean oil methyl ester. Then, we transmute the acid site properties of KSF, such as pH of 5 wt.% slurry KSF and various alkali metals (Li, Na, K, Ca). Characterization of base treated-KSF using a pH meter, x-ray diffraction, inductively coupled plasma-atomic emission spectrometer, Brunauer–Emmett–Teller surface analysis, and temperature-programmed desorption. We conduct an analysis of CLAME and DAME using nuclear magnetic resonance spectroscopy, gas chromatography, and gel permeation chromatography. Through these experiments, we demonstrate the effects of the acidic properties of KSF on the conversion and selectivity of the DAME synthesis, and evaluate its industrial potential by application to waste vegetable oil.","dimer acid methyl ester (다이머산 메틸에스테르), conjugated linoleic acid methyl ester (공액 리놀레산 메틸에스테르), waste vegetable oil (폐 식물유), acid clay (산성 백토), base-treated clay (염기 처리된 백토)","육정숙·신지훈·김영운†\n한국화학연구원 탄소자원화연구소 연구원/책임연구원","https://doi.org/10.9725/kts.2019.35.2.132"]
["35권2호\npp.139-147","상대재 내식성이 철강재료의 미끄럼마모 특성에 미치는 영향\n(Effects of Corrosion Resistance Characteristics of OpponentMaterials in relative Motion on Sliding Wear Behaviorof Mild Carbon Steel)","Tribochemistry","This study investigates the effects of corrosion resistance characteristics of opponent materials in relative motion on the sliding wear behavior of mild carbon steel. Pin specimens made of mild carbon steel are tested at several sliding speeds against mating discs made of two types of alloyed steels, such as type D2 tool steel (STD11) and type 420 stainless steel (STS420J2), with different corrosion resistance characteristics in a pin-on-disc type sliding wear test machine. The results clearly show that the sliding wear behavior of mild carbon steel is influenced by the corrosion resistance characteristics of the mating disc materials at low sliding speeds. However, the sliding wear behavior at high sliding speeds is irrelevant to the characteristics because of the rising temperature. During the steady state wear period, the sliding wear rate of mild carbon steel against the type 420 stainless steel at a sliding speed of 0.5 m/s increases considerably unlike against the type D2 tool steel. This may be because the better corrosion resistance characteristics achieve a worse tribochemical reactivity. However, during the running-in wear period at low sliding speeds, the wear behavior of mild carbon steel is influenced by the microstructure after heat treatment of the mating disc materials rather than by their corrosion resistance characteristics.","corrosion resistance (내식성), opponent material (상대재), mild carbon steel (탄소강), tribochemical reaction (트라이보케미칼 반응), sliding wear behavior (마모거동)","이한영\n계명대학교 신소재공학과 교수","https://doi.org/10.9725/kts.2019.35.2.139"]
["35권3호\npp.151-157","UV-Vis 분광분석에 의한 전기변압기 내 절연지 열화도 측정\n(Application of UV-Vis Spectroscopic Analysis forTransformer Insulating Paper Degradation)","Condition Monitoring & Maintenance System (System Reliability)","Insulated oil degradation produces charged by-products, such as acids and hydro-peroxides, which tend to reduce the insulating properties of the oil. In this study, UV-vis spectroscopy measurement technology is developed and experimentally compared with other measurement methods, such as the titration method and IR spectroscopy, to validate its ability to monitor the degradation of electrical insulating paper. The degradation characteristics of the insulating paper are appropriately represented through various types of measurement methods, such as the Tan (delta) method, CO2 gas production measurement, the titration method, and IR spectroscopy. The results are demonstrated to be well comparable to a change in the fluorescence emission ratio (FER), which is defined as the shift in fluorescence intensity in the measured wavelength range, and also to the chromatic ratio, which is defined as a color shift to longer wavelength ranges. The results also show that, by using UV-vis spectroscopy, it is possible to detect the degradation of the insulating paper. This study suggests that UV-vis spectroscopy can be applied as an alternative to high-performance liquid chromatography, which is the internationally recognized measurement technology for cellulose paper degradation. The FER detector is also verified to be useful as an effective condition-monitoring device for power transformers.","electrical insulating oil(전기절연유), insulating paper(절연지), degradation(열화), UV-Vis spectroscopy(자외선-가시광선 광분광분석기), monitoring(모니터링)","공호성1†·한흥구2\n1한국과학기술연구원 트라이볼로지연구팀 책임연구원, 2한국과학기술연구원 트라이볼로지연구팀 연구원","https://doi.org/10.9725/kts.2019.35.3.151"]
["35권3호\npp.158-168","2.2 kW급 유도전동기의 회전자 적층구조를 고려한 회전체 동역학 해석모델 개발 및 베어링 간극의 영향 분석\n(Rotordynamic Model Development with Consideration of Rotor Core Laminations for 2.2 kW-Class Squirrel-Cage Type Induction Motors and Influence Investigation of Bearing Clearance)"," Modeling & Simulation in Tribology","This paper presents the investigation of two types of rotordynamic modeling issues for 2.2 kW-class, rated speed of 1,800 rpm, squirrel-cage type induction motors. These issues include the lamination structure of rotor cores, and the radial clearance of ball bearings that support the shaft of the motor. Firstly, we focus on identifying the effects of rotor core lamination on the rotordynamic analysis via a 2D prediction model. The influence of lamination is considered as the change in the elastic modulus of the rotor core, which is determined by a modification factor ranging from 0 to 1.0. The analysis results show that the unbalanced response of the rotor-bearing system significantly varies depending on the value of the modification factor. Through modal testing of the system, the modification factor of 0.079 is proven to be appropriate to consider the effects of lamination. Next, we investigate the influence of ball bearing clearance on the rotordynamic analysis by establishing a bearing analysis model based on Hertz's contact theory. The analysis results indicate that negative clearance greatly changes the bearing static behavior. Rotordynamic analysis using predicted bearing stiffness with various clearances from -0.005 mm to 0.010 mm reveals that variations in clearance result in a slight difference in the displacement of the system up to 18.18. Thus, considering lamination in rotordynamic analysis is necessary as it can cause serious analysis errors in unbalanced response. However, considering the effect of the bearing clearance is optional because of its relatively weak impact.","rotordynamics(회전체동역학), induction motors(유도전동기), laminations of rotor cores(회전자 코어 적층), ball bearing clearance(볼 베어링 간극)","박지수1·심규호2†·이성호3\n1서울과학기술대학교 기계시스템디자인공학과 대학원생, 2서울과학기술대학교 기계시스템디자인공학과 부교수, 3한국생산기술연구원 서남지역본부 수석연구원","https://doi.org/10.9725/kts.2019.35.3.158"]
["35권3호\npp.169-175","Colloidal Probe 원자현미경을 이용한 2차전지 전극용 폴리머 바인더의 응착 및 마찰 특성 평가\n(Assessment of Adhesion and Frictional Properties of Polymer Binders for Secondary Cells using Colloidal Probe Atomic Force Microscope)"," Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","In lithium-ion batteries (LIBs), the stress induced by the volume change of an electrode during charge–discharge processes may often cause the mechanical integrity of the electrode to degrade. Polymer binders with enhanced mechanical properties are preferred for improved mechanical integrity and cycling stability of the electrode. In addition, given that sliding and shearing between the polymer binder and components in the electrode may readily occur, frictional and adhesion characteristics of the polymer binder may play a critical role in the mechanical integrity of the electrode. In this study, frictional and adhesion characteristics of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) were investigated using a colloidal probe atomic force microscope. Friction loops were obtained under various normal forces ranging from 0 to 159 nN in air and electrolyte and then the interfacial shear strengths of PAN and PVDF in air were calculated to be 1.4 ± 0.5 and 1.3 ± 0.3 MPa, respectively. The results show that in electrolyte, interfacial shear strength of PAN decreased slightly (1.2 ± 0.2 MPa), whereas that of PVDF decreased drastically (0.06 ± 0.01 MPa). Decreases in mechanical properties and adhesion in electrolyte may be responsible for the decrease in interfacial shear strength in electrolyte. The findings from this study may be helpful in developing polymer binders to improve the mechanical integrity of electrodes in LIBs.","adhesion (응착), atomic force microscopy (원자현미경), friction (마찰), electrolyte (전해질), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF)","웬당쾅1·정구현2†\n1울산대학교 기계공학부 학생연구원, 2울산대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.3.169"]
["35권3호\npp.176-182","단결정 실리콘 웨이퍼의 내마모성 및 내식성 향상에 관한 연구\n(Enhancement of Wear and Corrosion Resistances of Monocrystalline Silicon Wafer)"," Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","The primary objective of this study is to treat a monocrystalline silicon (Si) wafer having a thickness of 279 μm by employing the ultrasonic nanocrystal surface modification (UNSM) technology for improving the efficiency and service life of nano-electromechanical systems (NEMSs) and micro-electromechanical systems (MEMSs) by enhancing of wear and corrosion resistances. The wear and corrosion resistances of the Si wafer were systematically investigated before and after UNSM treatment, wherein abrasive, oxidative and spalling wear mechanisms were applied to the as-received and subsequently UNSM-treated Si wafer. Compared to the as-received state, the wear and corrosion resistances of the UNSM-treated Si wafer are found to be enhanced by about 23% and 14%, respectively. The enhancement in wear and corrosion resistances after UNSM treatment may be attributed to grain size refinement (confirmed by Raman spectroscopy) and modified surface integrity. Furthermore, it is observed that the Raman intensity reduced significantly after UNSM treatment, whereas neither the Raman shift nor new phases were found on the surface of the UNSM-treated Si wafer. In addition, the friction coefficient values of the as-received and UNSM-treated Si wafers are found to be about 0.54 and 0.39, respectively. Hence, UNSM technology can be effectively incorporated as an alternative mechanical surface treatment for NEMSs and MEMSs comprising Si wafers.","silicon wafer (실리콘 웨이퍼), friction and wear behavior (마찰마모 거동), corrosion (부식), ultrasonic nanocrystal surface modification technology (초음파나노표면개질기술)","우르마노프 바흐티요르1·노준석1·편영식2·아마노프 아웨즈한3†\n1선문대학교 대학원 기계공학과 석사과정생, 2선문대학교 기계공학과 교수, 3선문대학교 기계공학과 조교수","https://doi.org/10.9725/kts.2019.35.3.176"]
["35권3호\npp.183-189","윤활제 특성에 따른 시트 리클라이너 부품의 마찰 및 마모 특성\n(The Friction and Wear Characteristics of the Seat Recliner Parts Based on Lubricant Characteristics)"," Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The driver seat of an automobile is in direct contact with the driver and provides the driver with a safe and comfortable ride. The seat consists of a frame, a rail, and many recliners. In recent years, strength and operating force measurement testing of the recliner have become vital for designing car seats. However, performance evaluation requires expensive testing equipment, numerous seat products, and considerable time. Therefore, the trend is to reduce experimentation through interpretation. This study examines the lubrication of solid lubricant for automotive seat recliners and confirms the friction and wear performance. In this study, the lubrication behavior of solid lubricants for car seat recliners is investigated to ascertain the friction and wear performance and to provide accurate values for the strength analysis. The friction material consists of a pin and a plate made from steel, which is widely used in recliners. The friction and wear under lubrication conditions are measured by a reciprocating friction wear tester. The friction coefficient is obtained according to the load and speed. Based on the obtained results, it is possible to achieve a reduction in the error of the test value and the analysis by providing the friction coefficient and wear of the lubricant. The results can be applied to the analysis of automobile seat design.","car seats(자동차 시트), recliner(리클라이너), wear(마모), sliding friction(미끄럼 마찰) friction coefficient(마찰 계수)","홍석준1·이광희2·임현우3·김재웅4·이철희5†\n1인하대학교 대학원 건설기계공학과 석사과정생, 2인하대학교 대학원 기계공학과 박사과정생, 3현대트랜시스㈜ 시트구조설계팀 책임연구원, 4현대트랜시스㈜ 시트구조설계팀 연구원, 5인하대학교 대학원 기계공학과 정교수","https://doi.org/10.9725/kts.2019.35.3.183"]
["35권3호\npp.190-198","난류 유동을 갖는 가스 포일 저널 베어링의 성능 예측\n(Performance Predictions of Gas Foil Journal Bearingswith Turbulent Flows)"," Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Gas foil bearings (GFBs) enable small- to medium-sized turbomachinery to operate at ultra-high speeds in a compact design by using ambient air or process gas as a lubricant. When using air or process gas, which have lower viscosity than lubricant oil, the turbomachinery has the advantage of reduced power loss from bearing friction drag. However, GFBs may have high Reynolds number, which causes turbulent flows due to process gas with low viscosity and high density. This paper analyzes gas foil journal bearings (GFJBs) with high Reynolds numbers and studies the effects of turbulent flows on the static and dynamic performance of bearings. For comparison purposes, air and R-134a gas lubricants are applied to the GFJBs. For the air lubricant, turbulence is dominant only at rotor speeds higher than 200 krpm. At those speeds, the journal eccentricity decreases, but the film thickness, power loss, and direct stiffness and damping coefficients increase. On the other hand, the R-134a gas lubricant, which that has much higher density than air, causes dominant turbulence at rotor speeds greater than 10 krpm. The turbulent flow model predicts decreased journal eccentricity but increased film thickness and power loss when compared with the lamina flow model predictions. The vertical direct stiffness and damping coefficients are lower at speeds below 100 krpm, but higher beyond that speeds for the turbulent model. The present results indicate that turbulent flow effects should be considered for accurate performance predictions of GFJBs with high Reynolds number.","gas foil bearing(가스 포일 베어링), turbulent flow(난류), laminar flow(층류), stiffness(강성), damping(감쇠)","문진혁1·김태호2†\n1LG전자 L&A연구센터 연구원, 2국민대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.3.190"]
["35권4호\npp.199-205","구형 및 평면 원자현미경 탐침에 대한 2차원 소재의 마찰 특성\n(Frictional Properties of Two-dimensional Materials against Spherical and Flat AFM Tips)","Micro/Nano-Tribology","Two-dimensional materials such as graphene, h-BN, and MoS2 have attracted increased interest as solid lubricant and protective coating layer for nanoscale devices owing to their superior mechanical properties and low friction characteristics. In this work, the frictional properties of single-layer graphene, h-BN, and MoS2 are experimentally investigated under various normal forces using atomic force microscope (AFM) tips with a spherical and flat end, with the aim to gain a better understanding of frictional behaviors. The nonlinear relationship between friction and normal force friction was clearly observed for single-layer graphene, h-BN, MoS2 specimens slid against the spherical and flat AFM tips. The results also indicate that single-layer graphene, h-BN, MoS2 exhibit low frictional properties (e.g., friction coefficient below 0.1 under 70~100 nN normal force). In particular, graphene is found to be superior to h-BN and MoS2 in terms of frictional properties. However, the friction of single-layer graphene, h-BN, MoS2 against the flat tip is larger than that against the spherical tip, which may be attributed to the relatively large adhesion. Furthermore, it is shown that the fluctuation of friction is more significant for the flat tip than the spherical tip. The resutls of this study may be helpful to elucidate the feasibility of using two-dimensional materials as solid lubricant and protective coating layer for nanoscale devices.","adhesion (점착), atomic force microscopy (원자현미경), friction (마찰), graphene (그래핀), h-BN (육방정계 질화붕소), MoS2 (이황화몰리브덴)","Tran-Khac Bien-Cuong1ㆍ정구현2†\n1울산대학교 기계공학부 연구원, 2울산대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.4.199"]
["35권4호\npp.206-214","차량용 에어컨에 사용되는 냉매 및 냉동기유의 기술 동향\n(Development Trends of Refrigerant and Refrigerant Oil for Automotive Air-conditioner)","Lubrication (Lubricants & Additives) ,Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This study investigates alternative refrigerants and refrigerant oils as well as the tendency of protecting the global environment in view of automobile air-conditioning systems. Since decades, the R12 refrigerant is not used in automobile air-conditioners because of the ozone depletion potential (ODP) problem, and for the last 20 years, the ODP-free R134a refrigerant is leading the new automotive air-conditioning market. However, owing to its high global warming potential (GWP), the R134a refrigerant use in automobile air-conditioning\nsystem is also prohibited by law, and alternative refrigerants with a low GWP need to be proposed. Therefore, recently, the application of R1234yf, R152a, or other alternative refrigerants has started worldwide. By contrast, natural refrigerant R744 was introduced in the market several years ago by VDA (Verband Der Automobilindustrie), which is a German association in the automotive industry. This study also deals with refrigerant oils. For a long time, polyalkylene glycol (PAG) oil has been traditionally used with automobile air-conditioners, and\npolyolester (POE) oil is suitable for HEV, PHEV, and EV air-conditioning systems, where it is used by the electrically driven compressor owing to its excellent electrical insulation properties. Finally, PAG is an excellent lubricant for all the R134a, R152a, R1234yf, and R744 refrigerants, and has the advantage that it can be applied rapidly to alternative refrigerant air-conditioning systems.","air-conditioning system(에어컨 시스템), automobile(자동차), GWP(지구 온난화 지수), DP(오존층파괴 지수), refrigerant(냉매), refrigerant oil(냉동 윤활유)","이대웅ㆍ황승용†\n한온시스템 연구본부 APIC, 책임연구원","https://doi.org/10.9725/kts.2019.35.4.206"]
["35권4호\npp.215-221","이중 제로터의 설계 및 응용 가능성에 대한 연구\n(Design and Feasibility Study of Double Gerotor)"," Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","A gerotor set consists of two elements, an inner rotor and an outer rotor. The outer rotor has one more tooth than the inner rotor and has its centerline positioned at a fixed eccentricity from the centerline of the inner rotor. Although gerotors come in a variety of geometric configurations, all gerotor sets share the basic principle of having generated tooth profiles that provide continuous tight sealing during operation. The size of the gerotor is proportional to the number of teeth and the amount of eccentricity. The interior of an inner rotor with a large number of teeth has an enough space to include other machine elements. In this paper, the double gerotor mechanism, constructed by putting a small gerotor in the interior of a large inner rotor, is conceptualized. The double gerotor set is composed of an inner rotor, a planetary rotor, and an outer rotor. The inside profile of the planetary rotor corresponds to the outer rotor profile of the small gerotor, and the outside profile is the inner rotor profile of the large gerotor. In the double gerotor, the centers of the inner and the outer rotor are coincident because the eccentricities of two gerotors are balanced. The operation of a double gerotor is examined by analyzing the planetary motion, and a feasibility study for application of the double gerotor for hydraulic motors and pumps is performed.\nThe double gerotor set has much application potential as a component of hydraulic systems.","double gerotor(이중제로터), hydraulic motor(유압모터), hydraulic pump(유압펌프), planetary rotor(유성로터)","이성철†\n인하공업전문대학 기계과 교수","https://doi.org/10.9725/kts.2019.35.4.215"]
["35권4호\npp.222-228","가속노화조건 하 연료접촉 고무오링의 수명예측 및 누유시험 연구\n(A Study on the Lifetime Estimation and Leakage Test of Rubber O-ring in Contacted with Fuel at Accelerated Thermal Aging Conditions)"," Others","As rubber products such as O-rings, which are also known as packings or toric joints, come in regular, long term contact with liquid fuel, they can eventually swell, become mechanically weakened, and occasionally crack; this diminishes both their usefulness and intrinsic lifetime and could cause leaks during the steady-state flow condition of the fuel. In this study, we evaluate the lifetime of such products through compression set tests of FKM, a family of fluorocarbon elastomer materials defined by the ASTM international standard D141; these materials have great compression, sunlight, and ozone resistance as well as a low gas absorption rate. In this process, O-rings are immersed in the liquid fuel of airtight containers that can be expressed as a compression set, and the liquid fuel leakage in a flow rig tester at variable temperatures over 12 months is investigated. Using the Power Law model, our study determined a theoretical O-ring lifetime of 2,647 years, i.e. a semi-permanent lifespan, by confirming the absence of liquid fuel leakage around the O-ring assembled fittings. These results indicate that the FKM O-rings are significantly compatible for fuel tests to evaluate long-term sealing conditions.","liquid fuel (액체연료), rubber O-ring (고무 오링), compression set (압축영구줄음율), lifetime prediction (수명 예측), leakage test(누유시험)","정근우1†ㆍ홍진숙2ㆍ김영운1ㆍ한정식3ㆍ정병훈3ㆍ권영일4\n1한국화학연구원 환경자원연구센터 책임연구원, 2한국화학연구원 환경자원연구센터 연구원, 3국방과학연구소 책임연구원, 4청주대학교 산업공학과 교수","https://doi.org/10.9725/kts.2019.35.4.222"]
["35권4호\npp.229-236","세 물체 간 마찰 완전 접촉 문제의 응력 특이성 거동\n(Stress Singularity Behaviour in the Frictional Complete Contact Problem of Three Bodies)"," Contact Mechanics & Friction","This study investigates the stress singularity that occurs at the contact edge of three bodies in a frictional complete contact. We use the asymptotic analysis method, wherein we constitute an eigenvalue problem and observe the eigenvalue behavior, which we use to obtain the order of the stress singularity. For the present geometry of three bodies in contact, a contact between a cracked indenter and half plane is considered. This is a typical geometry of the PCMI problem of a nuclear fuel rod. Thus, this paper, specifically presents the characteristics of the PCMI problem from the perspective of stress singularity. Consequently, it is noted that the behavior of the stress singularity varies with the difference in the crack angle, coefficient of friction, and material dissimilarity, as is observed in a frictional complete contact of two bodies. In addition, we find that the stress singularity changes essentially linearly with respect to the coefficient of friction, regardless of the variation in the crack angle and material dissimilarity. Concurrently, we find the order of singularity to be 0.5 at a certain coefficient of friction, irrespective of the crack angle, which we also observe in the crack problem of a homogeneous and isotropic body. The order of singularity can also exceed 0.5 in the frictional complete contact problem of three bodies. This implies that the propensity for failure when three bodies are in frictional complete contact can be even worse than that in case of a failure induced by a crack.","frictional complete contact of three bodies(세 물체 마찰 완전접촉), asymptotic analysis(점근 해석), eigenvalue problem(고유치 문제), order of stress singularity(응력 특이성 지수)","김형규1†\n1한국원자력연구원 ATF기술개발부 책임연구원","https://doi.org/10.9725/kts.2019.35.4.229"]
["35권4호\npp.237-243","니들 롤러 베어링의 피로 수명 향상에 대한 연구\n(Improvement in Fatigue Life of Needle Roller Bearing)"," Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Through this study, we investigate the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings. The fatigue life of untreated and UNSM-treated needle roller bearings is evaluated using a roller fatigue tester at various contact stress levels under oil-lubricated conditions. We can ascertain that the fatigue life of an UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with an untreated one, where the effectiveness of UNSM technology diminishes with increasing contact stress. The surface roughness and surface hardness of needle roller bearings before and after being treated by UNSM technology are compared and discussed to understand the role of UNSM technology in improving the fatigue life of needle roller bearings. In addition, a fractograph of the damaged bearings is observed using a scanning electron microscopy to shed light on the fracture mechanisms of bearings under different contact stress levels. We can therefore conclude that the application of UNSM technology to the needle roller bearings improves the fatigue life by reducing the friction coefficient and increasing the wear resistance; this may be attributed to a reduction in surface roughness from 0.5 to 0.149 μm and an increase in surface hardness from 58 to 62 HRc.","needle roller bearing(니들 롤러 베어링), surface roughness(표면 거칠기), surface hardness(표면 경도), rolling contact fatigue(RCF, 구름 접촉 피로), ultrasonic nanocrystal surface modification(UNSM)(초음파나노표면개질)","다리스렝 스르멩닥와1ㆍ아마노프 아웨즈한2ㆍ편영식3†\n1선문대학교 기계공학과 박사과정, 2선문대학교 기계공학과 조교수, 3선문대학교 기계공학과 교수","https://doi.org/10.9725/kts.2019.35.4.237"]
["35권4호\npp.244-266","파이어링 시동 사이클 초기에서의 엔진 베어링 마모 시뮬레이션\n(Wear Simulation of Engine Bearings in the Beginning)"," Automotive Tribology","The purpose of this study is to estimate the wear volumes of engine journal bearings operating at variable angular velocity of a shaft in the beginning of firing start-up cycle. To do this, first we find the potential region of wear scar on engine journal bearings where the applied bearing load and crank shaft velocity are variable. The potential wear regions are discovered by finding minimum oil film thickness at every crank angle existing below most oil film thickness scaring wear (MOFTSW) obtained based on the concept of the centerline\naverage surface roughness. Then we calculate the wear volume from the wear depth and two wear angles decided by the magnitude of each film thickness lower than MOFTSW at every crank angle. The results show that the expected wear region is located at a few bearing angles after and/or behind the upper center of a big-end bearing and the lower center of a main bearing. And the real wear region is similar to the estimated wear region. Further we find that the wear scar on an engine journal bearing may occur at re-starting time after switch-off of a start motor especially under the condition of high oil temperature.","firing start-up cycle(파이어링 시동 사이클), variable angular velocity and dynamic loads(변동 각 속도 및 동적 하중), most oil film thickness scaring wear(마모유발최대유막두께), asperity contact(돌기접촉),\nwear volume(마모체적)","전상명†\n호서대학교 기계공학부 자동차공학전공 교수","https://doi.org/10.9725/kts.2019.35.4.244"]