Study on multimodal crack growth of FG-TBCs and its influence on interface cracking

Functionally graded thermal barrier coatings (FG-TBCs) face cracking challenges under extreme thermal shocks, yet the failure mechanisms involving multimodal surface cracks remain unclear. This study investigates the interaction between vertical, branching, and cruciform cracks and their role in interface delamination using laser thermal shock experiments and finite element modeling. A cohesive zone model (CZM) simulates crack evolution under transient thermal loads across eight structural models with varying gradient indices (P). Results reveal that vertical cracks mitigate interfacial stress concentration (108 MPa at P = 1), while branching/cruciform cracks amplify localized stress (218 MPa at P = 0.5) and accelerate crack opening. Higher gradient indices (P = 2) reduce interfacial stress to 88 MPa and lower energy release rates, enhancing coating durability. The synergistic effect of crack morphology and gradient design significantly improves delamination resistance, highlighting the critical role of optimized P-values in balancing stress redistribution and extending FG-TBCs' service life.