Finite element modeling of silicon nitride under coupled thermal shock–oxidation–creep: damage assessment and life prediction

Silicon nitride ceramics in aerospace applications are exposed to complex service environments involving thermal shock, oxidation, and creep. Therefore, it is essential to establish a coupled damage model to enable accurate failure analysis and lifetime prediction. This paper presents a unified damage model for silicon nitride under thermal shock, oxidation, and creep, developed using continuum damage mechanics and implemented in finite element analysis via UMAT. Simulation results indicate that thermal shock significantly accelerates oxidation and reduces creep life, with the specimen’s lifetime decreasing from 6300 min under pure creep to 2482 min under coupled conditions. The maximum damage is concentrated at the oxide–matrix interface, identifying it as the most vulnerable region. Furthermore, during the coupled loading cycles, thermal shock dominates the early-stage damage evolution, while creep becomes the primary contributor in the later stages. The proposed model enables life prediction under coupled conditions by leveraging individual experimental data from thermal shock, oxidation, and creep, thereby reducing the need for complex multi-field experiments.