Determination of mixed-mode interfacial fracture toughness for thermal barrier coatings

In this work,a test method was developed to determine the interfacial fracture toughness of the air plasma sprayed (APS) thermal barrier coatings (TBCs) over a wide range of mode mixities.For this mixed-mode test method,the analytical expressions for the energy release rate and stress intensity factors were derived based on the energy theory and the concept of "equivalence".The fidelity of these expressions was affirmed by selected finite element analysis.The experimental results showed that the critical energy release rate increased with the increase of the positive mode mixity,which was mainly due to the increase in contact/friction effect and plastic work dissipation with increasing shear mode loading.Furthermore,an elliptical interfacial failure criterion in terms of the stress intensity factors was proposed.The agreement between the experimental results in the literature and those in our work indicated that our test method and the corresponding analytical solutions can well determine the interfacial fracture toughness of the TBCs over a wide range of mode mixities.