Stress analysis of the thermal barrier coating system near a cooling hole considering the free-edge effect

Abstract

Due to the thermal mismatch between layers and the free-edge effect, interfacial peeling and shear stresses are generated locally around the edges of cooling holes in a thermal barrier coating (TBC)–film cooling system. These interfacial peeling and shear stresses may lead to modes I and II edge delamination, resulting in TBC spallation around the cooling hole. In this study, analytical and numerical models were built to study the stress and interfacial cracking behaviors of TBCs near the cooling hole. Analytical solutions for interfacial peeling moment and shear force at each layer were obtained to analyze the free-edge effect on the stress distributions in TBCs, and they were verified by the finite element calculations. The results showed that interfacial peeling moment and shear force were functions of the hole radius and thicknesses of top coat and oxide layer. The increase of interfacial peeling moment and shear force raised the likelihood of edge cracking around the hole. Derived by the local stresses, the interfacial cracks in TBCs initiated and propagated from the hole edge upon cooling.