Spall initiation and propagation due to debris denting

Abstract

An analytical model has been developed to investigate the effects of dent on spall initiation and propagation in lubricated contacts. The model is based on the damage mechanics concept that the fatigue spall initiation and propagation is due to the accumulated plastic strain process rather than the stress intensity at the tip of the crack. The contact surface layer was divided into small metal matrix (cell) and for each cell a damage law was applied to determine whether the cell is undergoing damage or not. In this model, spall will be formed when a cell is damaged. A dent profile from finite element analysis for a spherical debris denting the contact surface was used in a point EHL model. The pressure and traction profiles were then used to obtain the internal stresses and accumulated plastic strain for each cell. A damage variable was calculated for each cell based on the accumulated plastic strain. When the damage in a cell reaches a certain level, the cell is damaged and is assumed to fall off the contact surface layer, hence, spall is generated. The spall will further modify the contact surface resulting in new pressure and traction profiles. The accumulated plastic strain and damage are calculated again based on which new spalls may be generated. The entire procedure is repeated which allows the spall to propagate. Spall size and growth rate versus cycle number are presented. The results indicate that spall will always initiate at the dent edge.