A comparative study on the failure resistance of thermal barrier coatings

Abstract

A bi-material structure, representing a single layer thermal barrier coating, containing an interfacial crack and subjected to a cooling shock, is investigated using the finite element method. Numerical tests are performed to study the effect of material properties mismatch, between the coating and the substrate, on the failure resistance of the cracked structure, represented by the strain energy release rate. No special care is taken for taking into consideration the singular nature of near tip temperature and displacement fields. The parametric study is based on a quasi-static uncoupled thermo-elasticity assumption and a crack opening displacement formula for obtaining the strain energy release rate. The methodology that is followed has been validated in a previous article by comparison to an analytic solution. Computational results indicate that the strain energy release rate peak, experienced during the thermal shock, is highly dependent on the thermal conductivity and thermal expansion coefficient mismatch, but almost independent from the Young’s modulus mismatch between the two materials. It is concluded that, the failure resistance of the thermal barrier coating decreases, as the insulation provided by the coating and its thermal expansion coefficient increase in relation to the substrate.