COATING CRACKS IN MATERIALS WITH GENERAL ANISOTROPY

The problem of a straight crack lying in the coating of a semi-infinit e substrate is considered. The most general case of anisotropy is assu med for both materials (coating and substrate). The solution of Atkins on and Eftaxiopoulos [2] for a dislocation in an anisotropic bimateria l is modified to solve the fundamental problem of a dislocation in the coating, by including a corrective solution that accounts for the add itional boundary conditions at the free surface. The coating crack is modelled as a continuous distribution of such dislocations. The result ing system of singular integral equations is solved by applying an inv ersion theorem and then using numerical integration. The stress intens ity factors for modes I, II and III can be directly obtained from the dislocation densities. Numerical results are presented to compare the present analysis with existing solutions for some particular geometrie s and material models. For the general anisotropic case, results are p resented showing the influence of a number of geometric and material p arameters.