Hybrid phase-field modelling of hygro-thermo-mechanical fracture in PVC foam-cored CFRP sandwich structures

Carbon fiber reinforced polymer (CFRP) sandwich structures used in aerospace, marine, and wind energy applications are frequently exposed to coupled moisture, temperature, and mechanical loading, which significantly influences their structural integrity and fracture behavior. In this study, a coupled hygro–thermo–mechanical phase-field framework based on a computationally efficient hybrid formulation combined with orthogonal strain decomposition is developed to investigate crack initiation and propagation in a PVC foam-cored AS4/PEEK CFRP sandwich structure. The model incorporates temperature-dependent moisture diffusion via an Arrhenius relation and accounts for thermal and hygroscopic expansion effects in a multi-layered orthotropic system. The proposed formulation is validated against experimentally reported hygroscopic fracture results and subsequently applied to examine three discontinuity scenarios: intact configuration, pre-existing interfacial cracks, and geometrical holes. Comparative analyses are performed under six environmental conditions, including mechanical, hygro-mechanical, thermo-mechanical (heating/cooling), and coupled hygro–thermo–mechanical (heating/cooling) loading. Results indicate that moisture exposure leads to earlier crack initiation and reduced load-bearing and energy absorption capacities, with more pronounced degradation under heating due to enhanced diffusion. The developed framework provides a robust and efficient tool for multi-physics fracture assessment of composite sandwich structures subjected to realistic environmental conditions.