Numerical modeling of short crack behavior in a thermal barrier coating upon thermal shock loading

The behavior of microstructurally short inherent cracks within a preoxidized thermal barrier coating system upon thermal shock loading is considered. A thin alumina oxide layer holding residual stresses was induced at the ceramic/metal interface to simulate thermally grown oxide on the bond coat. Undulation of the oxidized bond coat was modeled as a sinusoidal surface. The variations of the stress-intensity factors of inherent centrally located cracks and of edge cracks were calculated during the thermal cycling. The instant crack shapes during the first thermal cycle and at steady state were investigated. It was found that oxide layer thickness, crack tip location, as well as interfacial undulation are factors influencing the risk of crack propagation. It was also found that an edge crack constitutes a greater threat to the coating durability than a central crack. The propagation of an edge crack, if it occurs, will take place during the first load cycle, whereas for a central crack, crack tip position decides the risk of crack propagation.