A thermodynamically consistent imperfect interface model with damage for hygrothermally aged bonded joints

A computational mechanics model for joints subjected to hygrothermal aging is proposed. The formulation is based on an imperfect interface approach coupled with a damage evolution law, in which aging effects are introduced through time-dependent constitutive parameters governing interface stiffness, damage activation and viscous dissipation. The model is expressed in terms of internal state variables and derived within a thermodynamically consistent framework, ensuring a stable and robust numerical implementation. The governing equations are implemented in a finite element environment and validated by simulating tests on single-lap joints with different adhesives and conditioning media. Numerical results show excellent agreement with experimental load–displacement responses, demonstrating the capability of the model to predict aging-induced degradation mechanisms in bonded composite interfaces.