A plasticity model for predicting the rheological behavior of paperboard

The sorption of water into the paperboard exposes a container to reversible and irreversible deformations under relative humidity variations. In this study, an elasto-plastic material model is used to demonstrate how through-thickness dry solids content gradients can generate permanent inplane strains in paperboard. The measurements presented in this paper indicate that in consecutive loading-unloading cycles, the yield stress either remains roughly constant or decreases, and an additional permanent set of strain is obtained even when the maximum tension of repetitions stays constant. Two modified approaches concerning elasto-plastic hardening behaviour based on the measurements of this work and the observations of previous studies are introduced. The simulated results exhibit some shared features of the frequently observed shrinkage behavior of paperboard exposed to cyclic relative humidity changes. The results suggest that with the use of a suitable hardening approach, the plastic deformations arising from through-thickness dry solids content gradients may be considered as a time-independent component for simulations of phenomena such as moisture-accelerated creep and release of dried-in stresses.