Three-dimensional elasto plastic behaviors of cracks in TiN coatings under the cyclically indenting and sliding contacts of an elastic sphere are studied using finite element method. The stress distributions in the coating and substrate, and the fracture intensity,J integral, of cracks at the surface and interface are calculated. It is shown that the maximum stress is near the contact boundary, where the fatigue cracks will be easily initiated under the cyclic loadings. The parameters, such as thickness of coatings, substrate material, shape and obliquity of crack, have obvious influence on J-integrals of surface and interface cracks.
