ABSTRACT
In this study the axisymetric crack problem for thermal barrier coatings (TBC) under a uniform temperature change is considered. It is assumed that the disk-shaped specimen consists of a nickel-based super alloy substrate, NiCrAlY bond coat and the TBC. The TBC itself is a two phase metal/ceramic functionally graded material (FGM). The metal phase is NiCrAlY and the ceramic is partially stabilized zirconia (PSZ). The composition of TBC varies from zero percent ceramic on the bond coat/TBC interface to hundred percent on the surface. The crack is a plane edge crack, starts at r=r 0 and propagates in a plane perpendicular to the axis of the cylinder, r 0 being the radius of the disk. Modes I and II stress intensity factors and the strain energy release rate are calculated for various sizes and locations of the crack. The main variables in the problem are the inhomogeneity parameter of the FGM coating, the size and the location of the crack and the relative dimensions of the specimen. The finite element method is used to solve the problem. The material property grading is accounted for by developing special inhomogeneous elements and the stress intensity factors are calculated by using enriched crack tip elements.
