Discussion: “A Mathematical Model for Frictional Elastic-Plastic Sphere-on-Flat Contacts at Sliding Incipient” (Chang, L., and Zhang, H., 2007, ASME J. Appl. Mech., 74, pp. 100–106)

Abstract

The authors presented a model for sliding inception that is essentially based on the 1949 Mindlin approach (see Ref. 1) for frictional contact with extension to elastic-plastic normal loading. According to this concept the interfacial shear stress is assumed to be proportional to the contact pressure until it reaches a limiting value that is related to the shear strength of the sphere bulk (see Eq. (1)). In other words, the Mindlin approach assumes a “local Coulomb friction law” that requires an input of a certain proportionality constant that relates the shear stress distribution to the normal pressure distribution in the contact interface. It may lead to unrealistic situations in which the local equivalent von Mises stress can exceed the yield strength of the sphere material. Another shortcoming of this concept is that sliding inception always occurs in the contact interface regardless of the level of normal loading. This would contradict the well known phenomenon of material transfer, which is associated with high normal loading of adhesive frictional contacts and requires slip below the contact interface.