Thermomechanical fracture behaviour of interacting microdefects in thermal barrier coatings

The build-up to spallation failure of the ceramic top coat in thermal barrier coating (TBC) often involves the propagation of a dominant (main) crack interacting with nearby microdefects. To evaluate this, we used micromechanics-based analytical and numerical techniques to establish the effect of the presence of microdefects on the stress intensity factor (SIF) of the main crack. Additionally, we developed an adaptive finite element model with automatic geometry reconstruction and adaptive remeshing algorithm to study the shielding and amplification effect of microdefects have on a propagating semi-infinite crack. We tracked the main crack propagation path using both maximum strain energy release rate and maximum-minimum stress crack tracking criteria. We extended the work and determined the conditions necessary for the main crack to coalesce with a typical microporosity found in TBC processed by atmospheric plasma spray. Our work reveals that unless the main crack and microcrack are collinear, the main crack does not coalesce with a microcrack in a self-similar manner. Furthermore, we showed that thermal stresses induced by mixed oxides inhomogeneities can amplify the main crack SIF and alter its propagation path.

Automated summary

The interaction between the main crack and microdefects in thermal barrier coating is crucial for the spallation failure of the ceramic top coat. We investigated the effect of microdefects on the stress intensity factor of the main crack using micromechanics-based analytical and numerical techniques. Additionally, we studied the shielding and amplification effect of microdefects on the propagation of a semi-infinite crack. Our findings provide insights into the performance and failure mechanism of thermal barrier coatings.