1 Crack Opening Displacement as a Criterion for Crack Propagation in Thermal Barrier Coatings

Finite element methods have been used to simulate and understand the physical basis behind surface cracks leading to interface delamination in thermal barrier coatings. Traditionally energy release rate has been used as a criterion for crack propagation in thermal barrier coatings. There have been some conceptual difficulties in using this approach when the coating is modeled as an inelastic material. In this study the possibility of using crack opening displacement behind the crack tip as a surface crack propagation criterion has been explored. It is seen that for a surface crack opening displacement criterion of 6 microns from 0.1mm from the crack tip, the crack propagates to about 65 % of the top coat thickness which matches with final crack lengths obtained from experiments. Nomenclature A = experimental constant J = strain energy release rate R = universal gas constant T = absolute temperature Y = yield strength h = thickness n = experimental constant S11 = stress in the local x-direction S22 = stress in the local y-direction u = crack opening displacement cd dt ξ = creep strain rate HΔ = activation energy mσ = von mises equivalent stres