Assessment of TBC systems failure mechanisms using a fracture mechanics approach

Failure of thermal barrier coating (TBC) systems under thermomechanical loading is very complicated, as it is influenced by many factors, such as thermal mismatch, oxidation, interface roughness, creep, sintering, which have to be more or less taken into account. Determination of the residual stress fields induced yields information about the critical areas for crack nucleation in a first step and may help interpret the experimental observations of the cracking behavior. The calculated residual stresses relevant to failure are highly localized and may be sufficient for crack nucleation, but not for crack propagation and failure. Therefore, a fracture mechanics approach was developed, by means of which cracks are modeled in the critical areas of the TBC system and assessed using the modified crack closure integral method for determining the mode-dependent crack loading. The crack propagation capability is then predicted using a mixed mode failure criterion implemented recently and proper fracture toughness data. Applying this approach, different failure mechanisms observed experimentally for TBC systems are investigated.