Fretting contact with finite friction of a functionally graded coating with arbitrarily varying elastic modulus Part 2: Tangential loading

Fretting is a major cause of surface damage, with fretting fatigue crack initiation at the contact surface subjected to a small-scale oscillatory tangential motion. In the present paper, which is part 2 of the series, the fretting contact between a functionally graded coated half-space and a rigid cylindrical punch is considered for the case where, first, a constant normal load is applied, and then a cyclically varying tangential load, which is less than that necessary to cause complete sliding, is applied. The functionally graded coated half-space is under conditions of plane strain deformation. The whole contact region is composed of an inner stick region and two outer slip regions in which Coulomb's friction law is assumed to apply. Owing to the mismatch in material constants of the punch and half-space, the problem is fully coupled and can be reduced to two coupled Cauchy singular integral equations. Based on the analyses of normal loading in part 1, contact tractions and in-plane stresses associated with tangential loading are calculated in the whole contact region. The results show that appropriate gradual variation in the shear modulus can significantly alter the contact tractions and in-plane stresses. This may lead to suppression of crack initiation at the edges of the contact region and thus modify the fretting contact damage. Therefore, it is believed that functionally graded material coatings would have potential applications in improving the resistance to fretting contact damage at the contact surfaces.