Experimental and analytical investigation on surface crack initiation under contact fatigue.

摘要

Contact fatigue tests were made with lubricated rollers containing furrows and dents produced by electric discharge machining (EDM), scratching and denting for studying surface crack initiation. The furrow made by the EDM method did not have edge buildup, which makes further analytical procedure simple. The results show that the cycles for crack initiation increase with hardness and decrease with surface roughness and temperature. Only longitudinal cracks were initiated under pure rolling condition. Size and shape of furrows does not have a significant influence on initiation life and this is confirmed by micro-EHL analysis. For tests under heavy load, severe plastic deformation was found in front of the edge of the defects. The elastic-perfectly plastic contact simulation is performed to determine the pressure distribution near the furrow with a deformed geometry.; A contact fatigue crack initiation model is developed based on the dislocation pileup theory by Mura. For the two-body contact system the slip boundary condition is used for prediction near surface crack initiation. For surface crack initiation, the free boundary condition is used. The substrate crack initiation is modeled as in an infinite body. Initiation life for surface cracks is much shorter than that of subsurface cracks. The new model can include the influence parameters such as the hardness, temperature, irreversibility of the plastic deformation, grain size, residual stress, etc. The Coffin-Manson Law is derived by the model is an analytical approach. The model is consistent with the contact fatigue experiments about surface and near surface crack initiation.