Abstract: Ceramic thermal barrier coatings (TBCs) are a very important technology for protecting the hot parts of gas turbines (GTs) from a high-temperature environment. The coating stress generated in the operation of GTs brings cracking and peeling damage to the TBCs. Thus, it is necessary to evaluate precisely such coating stress in a TBC system. We have obtained a stress-strain curve for a freestanding ceramic coat specimen peeled from a TBC coated substrate by conducting the bending test. The test results have revealed that the ceramic coating deforms nonlinearly with the applied loading. In this study, an inelastic constitutive equation for the ceramic thermal barrier coatings deposited by APS is developed. The obtained results are as follows: (1) the micromechanics-based constitutive equation was formulated with micro crack density formed at splat boundary, and (2) it was shown that the numerical results for a nonlinearly deformed beam simulated by the developed constitutive equation agreed with the experimental results obtained by cantilever bending tests.

Key words:
Inelastic constitutive equation, Thermal barrier coating, Gas turbine, Micromechanics