SURFACE CRACK INITIATION UNDER CONTACT FATIGUE - EXPERIMENTAL-OBSERVATION AND CONTACT ANALYSIS

An experimental study of surface crack initiation was performed by means of a transverse furrow manufactured by the electric discharge machining (EDM) method. Since there is no built-up edge and plastic zone associated with an EDM furrow, the associated stress analysis is relatively simple and provides a reliable means of comparison with experiment. The test results showed that the crack initiation life was not sensitive to the size of the furrow. This phenomenon was explained by means of a micro-elastohydrodynamic lubrication (MEHL) analysis. The calculated results indicated that the pressure peak, P(max), near the furrow was not sensitive to the depth and width of the furrow, and P(max) could be estimated from the Hertzian contact pressure P0. The more heavily loaded tests showed a newly deformed plastic zone (bump) near the furrow. Two methods were used for the con tact simulation. The elastic-plastic contact analysis was selected for the case when a bump was present; otherwise, the MEHL analysis was used. The stress analysis illustrates that the value and the location of the maximum Mises stress was influenced by the friction coefficient and the geometry of the deformed surface profile.