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박준목,이은호,김재호,김석삼,Park, Jun-Ho,Park, Eun-Ho,Kim, Chae-Ho,Kim, Seock-Sam 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.10
In this paper, to examine the propagation of inclined surface crack due to frictional heating, analytic model is considered as the semi-infinite elastic body subjected to the thermo-mechanical loading of an asperity moving with a high speed. Considering the moving of frictional heat source and convection on a semi-infinite surface having inclined crack, theoretical analysis was carried out to estimate the propagation characteristics of thermo-mechanical crack. Numerical results showed that stress intensity factor $K_\prod/P_0\sqrt{c}$ is increasing with increasing velocity and frictional coefficient, inclined degree, decreasing crack length and the maximum value of it is positioned at the trailing edge. So it is shown that the propagation probability of surface crack is high at the trailing edge of contact area as increasing velocity and frictional coefficient, inclined degree, as decreasing crack length.
Slat 형 장애물이 부착된 이차원 채널유동에서의 난류열전달실험(亂流熱傳達實驗)
최영돈,박준목 고려대학교 공학기술연구소 1985 고려대학교 생산기술연구소 생기연논문집 Vol.21 No.1
Experiments were performed in order to measure the velocity profiles, pressure distributions and heat transfer coefficients of turbulent two-dimensional channel flow with slat type blockage. Air was used for working fluid in experiments. In experiments, blockage way positioned at the center between inlet and outlet sectors. Reynolds number ranged from 20,000 to 50,000 and height of blockage was varied ¼, ⅓, ½, ¾ of channel height. Velocity and pressure were measured at the inlet and outlet sections. However heat transfer coefficients were measured only at the outlet section under the constant heat flux condition. Results showed that blockage induced the variation of flow patterns arc heat transfer coefficient on the wall near blockage, Increasing the height of ,blockage and Reynolds number, recirculating region and pressure drop increased. Pressure. suddenly dropped at the just back of blockage. At the reatteching region after blockage, Nusselt numbers had maximum values. increasing the height of blockage at constant Reynolds number and decreasing the Reynolds number at constant height of blockage, the ratio of local Nusselt number to the Nusselt number of fully developed flaw increased.
플라즈마 코팅한 주조용 알루미늄합금의 마찰 및 마멸특성
채영훈,임정일,박준목,김석삼,Chae, Young-Hun,Ren, Jing-Ri,Park, Jun-Mock,Kim, Seock-Sam 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.5
The wear characteristics and wear mechanisms of plasma sprayed Al/sub 2/ O/sub 3/-40%TiO/sub 2/ and Cr/sub 2/O/sub 3/ deposited on casting aluminum alloy(AC4C) were investigated. Specimens were processed for various coating thicknesses. Ball on disk type wear tester was used for wear test. The scratch test on plasma sprayed coating surface showed that critical load to break the coating layer was greater than 40 N. The critical load increase with the increase of coating thickness of specimens. The friction coefficient of Cr/sub 2/O/sub 3/ coating layer was less than that of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer. The wear resistance of Cr/sub 2/O/sub 3/ coating layer was greater than that of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer. Microscopic observation of worn surfaces was made by SEM. SEM observation showed that the main mechanism of wear for Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer was abrasive wear under 50 N. For the case of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer, as the surface cracks perpendicular to sliding direction propagated, the wear debris was generated in wear track. However, the main mechanism of wear for Cr/sub 2/O/sub 3/ coating layer was brittle fracture under 150 N.
김석삼,서창민,박준목 대한기계학회 1995 대한기계학회논문집 Vol.19 No.3
The wear characteristics and wear mechanisms in TiN coating deposited on high speed steel and alloy tool steel by ion plating were investigated. Pin on V-block wear tester was used for a wear test method. The specimen was composed of three kinds of high speed steel and alloy tool steel which had different hardness by changing the heat treating condition. Three kinds of coating thickness were also applied to each specimen. Microscopic observation of worn surfaces was made by SEM. The scratch test of coating surface by the ion plating showed that critical load to break the coating interface was greater than 50N. The critical load increased with both substrate hardness and coating thickness. The wear resistance of TiN coated high speed steel became 10 times greater than that of non-coated ones. SEM observation showed that leading edge of contact was compressive and trailing edge was under maximum tensile stress and then surface cracking broke out perpendicular to sliding direction.