PERIODIC CRACKING OF FUNCTIONALLY GRADED COATINGS

The antiplane elasticity problem for a functionally; graded coating bo nded to a homogeneous half space is considered, The coating is assumed to contain periodic cracks perpendicular to the surface. The problem is formulated in terms of an integral equation with strongly singular kernels. Three dimensionless parameters representing the crack depth, the material nonhomogeneity and the crack periodicity are identified. In addition to the mode III stress intensity factor calculated by vary ing these three parameters, the results presented include a qualitativ e discussion of the question of fracture instability, the effect of pe riodic cracking on the relaxation of stresses on the coating surface, and the comparison of the total strain energy released as a result of surface cracking with that assumed in a simple stress relaxation model .