A moisture diffusion coupled model for composite materials

• A moisture diffusion coupled model for composite materials is proposed.
• The diffusion process is considered dependent on the stress state.
• The model is firstly established for homogeneous isotropic materials.
• The model is extended to UD composites with impermeable or permeable fibres.

In this study, a coupled diffusive behaviour model for a polymer matrix composite is proposed. Within this model, the diffusion of moisture depends upon the stress state experienced by the material. The model constitutive equations are based on a thermo-dynamical approach. The model is, firstly, established for a homogeneous isotropic matrix. It is, thereafter, extended to impermeable unidirectional composites. The stress–diffusion relation has been treated through a two steps procedure. In a first step, only the coupling between the maximum moisture absorption capacity and the stresses is assumed to occur. This implicitly involves that the diffusivity remains independent upon the mechanical states. In a second step, both the diffusivities and maximum moisture absorption capacity were expressed as functions of the mechanical states.