Cooling-flow-induced interlayer fracture in thermal barrier coatings

Interlayer separation around film-cooling holes is a critical failure in thermal barrier coating (TBC) systems. It is primarily driven by concentrated stress fields that result from geometric discontinuities, thermal gradients, and cooling-induced pressure. Existing analytical models often neglect the combined effects of free-edge deformation and cooling-flow-induced transverse loading, limiting their ability to predict mixed-mode crack driving forces at the interface. This work develops a mechanical model that captures the coupled thermomechanical cracking behavior near cooling holes in multilayered TBCs. The model explicitly incorporates free-edge effects and pressure-induced deformation to derive stress fields, effective peeling moments and forces, and partitioned mode-I and mode-II energy release rates. Validation against finite element simulations shows strong agreement. Results reveal that cooling pressure amplifies bending deflection but suppresses opening-mode interfacial crack, leading to a transition toward shear-dominated fracture beyond a critical threshold. Additionally, increasing top coat thickness and incorporating through-thickness gradients in temperature or stiffness significantly modulates, driven by the need to improve thermal efficiency and power output, interfacial fracture behavior. This work facilitates TBC design optimization by controlling fracture-mode transitions via cooling parameters and geometric adjustments.