A framework for three-dimensional finite element analysis of unidirectional and cross-ply composite layups through localized microstructures under hygromechanical conditions

Fiber-reinforced polymers (FRPs) are sensitive to moisture diffusion. Deterioration caused by moisture can limit their service lives considerably. In this work, a three-dimensional finite element modeling and analysis framework is presented to investigate the moisture diffusion kinetics inside fiber-reinforced inside polymer matrix composites by considering different angle and cross-ply orientations. A small localized representative volume element considering a few fibers in the neighborhood of three-layer stacks has been analyzed. The emphasis is on the effect of different fiber orientations over moisture saturation time and diffusion-induced stresses. Stresses induced due to moisture diffusion in FRPs are evaluated on the free fiber ends. The numerical results from finite element approximations are compared with theories of composite micromechanics such as rule of mixtures, Halpin–Tsai model and concentric cylinder assemblage framework. It is observed that the orientation of fiber layers can greatly influence the moisture ingress inside the matrix and resulting stresses. At intermediate time durations of moisture progression, the cross-ply orientation had ~ 25% lower weight gain in comparison with the unidirectional ply orientations. The overall von Mises stresses at the fiber matrix interface were also lower in cross-ply orientations by ~ 40% in comparison with the other orientations with similar fiber volume fraction. The three-layered cross-ply, 90/90/90 orientation took almost 50% more time to fully saturate with moisture in comparison with the unidirectional, 0/0/0 orientation. The interpretations from the smaller local microstructural models presented in this work can be extended to study and design the structure scale composite layups for the improved moisture durability.