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조민행(Minhaeng Cho),Shyam Bahadur,박혜영(Hye-Young Park),김윤준(YoonJun Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
The role of transfer films formed during sliding of polymer composites against steel counterfaces was studied in terms of the tribological behaviors of composites. Four kinds of composites were included in this study: (1) unfilled PPS, (2) PPS+2%CuO, (3) PPS+2%CuO+5% carbon fiber (CF), and (4) PPS+2%CuO+15%Kevlar. The filler material CuO was in nanoscale particulate form and the reinforcing material was in the form of short fibers. The composites were prepared by compression molding at 310℃ and sliding tests were run in the pin-on-disk sliding configuration. The counterface was made of tool steel hardened to 55-60 HRC and finished to a surface roughness of 0.09-0.10 ㎛ Ra. Wear tests were run for 6 hrs at the sliding speed of 1 ㎧ and contact pressure of 0.65 MPa. Transfer films formed on the counterfaces during sliding were investigated using AFM and SEM. The results showed that as the transfer film became smooth and uniform, wear rate decreased. PPS+2%CuO+15%Kevlar composite showed the lowest steady state wear rate in this study and its transfer film showed the smoothest and the most uniform characteristics. The examination of worn surfaces of PPS+2%CuO composite using X-ray area scanning (dot mapping) showed back-transfer of steel counterface material to the polymer pin surface. This behavior is believed to strengthen the polymer pin surface during sliding thereby contributing to the decrease in wear rate.
마이크로 공동의 고분자 마찰 및 마모에 대한 영향 연구
조민행(Minhaeng Cho),이재봉(Jaebong Lee),이성혁(Seonghyuk Lee),박상일(Sangil Park) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Micro-cavities manufactured by laser surface texturing technique were studied in terms of their effect on friction and wear of polyoxymethylene (POM). As a preliminary study, a number of attempts to reduce refilling phenomenon of a cavity by melting and flow of POM were made in this study. As a result, it revealed that a strong jet of air applied during laser irradiation is significantly effective in removing the refilling behavior. Cavities with a number of different concentrations, which are the ratio of the total cavity opening area to the total specimen surface area, were then fabricated and tested in ball-on-disk sliding configuration in dry contact. Surfaces after each test were examined by SEM to investigate the correlation between the cavity concentration and tribological behavior of POM. Also, correlation between wear and friction of POM and failure of cavities caused during sliding contact is provided in this study.
미세 딤플의 밀도에 따른 SCM415강의 마찰 거동 연구
조민행(Minhaeng Cho),이성혁(Seung Hyuk Lee),박상일(Sangil Park),여인웅(In Woong Lyo) 한국트라이볼로지학회 2010 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.26 No.6
Surface texturing of micro dimple or pore-shaped pattern was prepared using a fiber laser system. Surface texturing was designed to have a square pattern with a particular pitch distance for each corresponding density of 5, 10, 20, and 30%. Thermal damages such as bulges and burrs formed during laser irradiation were observed around the dimples. Thermal damages were later removed by lapping using alumina particles of 0.3 ㎛ in diameter. Oscillating friction tests were performed against heat-treated high speed steels under lubricated condition. The lubricant used was SAE 5W-30 automotive engine oil. Normal contact pressure and oscillating frequency was 0.28 ㎫ and 20 ㎐, respectively. The tests were continued for 20 minutes, and friction plots were recorded for examination. Results revealed that the coefficient of friction was lowered regardless of texturing density. Moreover, the lowest coefficient of friction was obtained for 10% density texturing. It is attributed to increased lubricity due to the introduction of surface texturing. In addition, it is concluded that the optimum texturing density and pattern must be found for the best lubricity and low friction.