Unified fracture modeling for brittle film interfaces under complex stress conditions

This study introduces a unified fracture criterion for brittle coating-substrate interfaces. The model involves stress decomposition at the interface, with stress triaxiality and the Lode angle computed using finite element analysis. A modified strain energy density function, incorporating volumetric changes and distortion work, is proposed as the interfacial failure criterion under mixed stress conditions, addressing stress concentration near bimaterial system edges. The model is validated through three different interfacial strength tests—uniform out-of-plane tensile, in-plane tensile, and scratch tests—conducted on inkjet-printed SiC films. The results demonstrate a strong correlation between predicted and experimental outcomes in complex stress states, surpassing traditional strength criteria. The study further discusses the model's broad applicability to various coating-substrate systems, offering a comprehensive understanding of interfacial failure and providing a unified framework for characterizing interfacial strength across diverse testing methodologies.