Dent Initiated Spall Formation in EHL Rolling/Sliding Contact

Abstract

Dents in elasto-hydrodynamic lubricated (EHL) contacts will initiate spalls and shorten the fatigue life significantly. Experimental results are provided from a ball-on-rod rolling contact fatigue tester with the rod predented with a single large dent. The results indicate that the spall usually initiated at the trailing edge of the dent on the driving surface. These cracks and spalls can also be created in the absence of lubricant. Based on the accumulated plastic strain and damage mechanics concept, a line contact spall initiation model was developed to investigate the dent effects on spall initiation and propagation. The near surface volume of the contact solid was divided into many small metal cells and for each cell the damage law was applied to determine whether the cell is undergoing damage or not. If the cell on the surface is damaged, then it is removed from the surface and a spall will be formed. If the damaged cell occurs below the surface, then a subsurface void is generated, this void could grow to the surface depending on the running conditions. The spall will further modify the surface geometry and initiate a new spall, hence, the spall will propagate. The results indicate that the location of spall initiation depends on the EHL and dent condition. Spalls can initiate at either the leading or trailing edge of the dent depending on the surface traction.