The onset of plastic yielding in a coated sphere compressed by a rigid flat

The onset of plastic yielding in a system of a sphere with a hard coating layer loaded by a rigid flat is studied using finite element analysis. The effect of coating thickness and material properties of both coating and substrate on the critical normal load, critical contact area and critical interference at the onset of plasticity is investigated. Three different locations where plastic yielding first occurs are found. A dimensionless coating parameter is defined, which allows optimization in terms of highest critical load. A possible weakening effect caused by using an ultra thin coating layer is revealed.