Papers by Author: Tae Kun Lee

Abstract: Shot peening generate compressive residual stress, which reduces repeatedly assessed tension stress and increase fatigue life. In this paper, the fatigue characteristics are evaluated according to shot peening condition for the real differential gear. The specimen is a straight bevel gear which transmits rotation of engine to running wheel and it is caburized. The bending fatigue test was done by the jig of our own making. The peening time was changed to find the best condition for the long fatigue life time. Fractography of specimen was analyzed by SEM to detect the location of initial crack. The experimental results show that the optimum peening condition is at 65m/s of shot ball speed and 8min of shot peening time. From the SEM image, the location of initial defect and direction of crack propagation were found

Abstract: In this paper the fatigue life of spur gear was investigated by changing the shot peening condition. From bending fatigue test depending on various shot peening intensity, fatigue characteristics were investigated. The causes of reduction in fatigue life were analyzed by observing the surface of gear with Scanning Electron Microscope(SEM), and impact of residual stress to fatigue characteristics was identified by measuring compressive residual stress depending peening intensity by depth. The results show that the optimum shot ball velocity is 65 m/s and optimum peening time is 8 minutes. From SEM image, the micro-crack was observed at the surface in case of over peening. This seems to be the factor which reduces fatigue life by decreasing compressive residual stress of surface.

Abstract: In this paper the life extension of automobile drive plates will be investigated. The material of specimen is a high carbon steel treated by shot peening, which is most important in the manufacturing process of drive plates. The optimum shot peening condition was investigated by changing the feeding speed and exposure time. The fatigue crack was observed at the fracturing surface of specimens by using scanning electron microscopy (SEM). The distribution of compressive residual stress induced by shot peening process was investigated by using X-ray diffraction. The number of cycles to failure increases at the beginning of exposure. The life cycle decreases after passing some interval of exposure, which will be called as optimum peening zone. Experimental results show that the residual stress distribution and the number of cycles to failure of a drive plate are greatly affected by peening process.