Modeling of moisture-induced stress in PMMA: A simple approach to consider sorption behavior in FEM

Moisture-induced stresses in amorphous thermoplastics are studied in detail using the finite element method (FEM). The approach is based on the coefficient of moisture expansion which is derived from the sorption behavior (i.e., changes of mass, density and elastic properties). The required model parameters were obtained by isothermal diffusion and swelling experiments at different levels of relative humidity at room temperature. In the analysis, the evolutions of moisture-induced stresses in a model system have been analyzed, i.e., drying sheets of poly(- methyl methacrylate). The calculated stresses during drying are discussed with regards to the sorption models. Results indicate that these computational models are essential in capturing the accurate moisture-induced stress. Finally, the simulation results were verified by three-point bending. The implemented method shows the potential to predict environmental stress cracking due to humidity by FEM. This is important for the improved design of plastics parts