Hygro-coupled viscoelastic viscoplastic material model of paper

Paper is a versatile material, which is known of being very sensitive to moisture changes that make the mechanical behavior hard to predict. To close this gap, we propose a mechanical model that captures the transient behavior during the interaction with water. Since the diffusion of water within the paper network happens on a similar time scale as the mechanical relaxation phenomena, a fully coupled theory is motivated. Furthermore, the absorbed water induces a large increase in volume which motivates the application of finite strain theory. The model is derived in a thermodynamically consistent manner and its parameters are estimated with experiments available in the literature. The model shows a good agreement applied to paper curl experiments and provides further insights into complex multi-physics problems.