Influence of anisotropy on the transient hygroscopic stresses in polymer matrix composites with cyclic environmental conditions

The transient residual stresses in polymer matrix composites induced by cyclic variations in temperature and moisture are very important and must be taken into account in the design of composite materials, particularly aerospace structures e.g. aircraft. Aiming to reduce these stresses, we have studied the influence of anisotropy on the hygrothermal behaviour of the laminated plates. The objective, here, is to contribute to the optimal design of composite structures. The anisotropy is evaluated using the degree of anisotropy introduced from polar representation of tensors , , , and . Various laminates, with controlled and random stacking sequences, were analysed under typical boundary conditions and with the same hygrothermal loading. The results show that the thermal and hygroscopic stresses vary differently with the degree of anisotropy in such a way that their superposition does not lead to a growth of the intern resulting stresses. The other obtained results show that the knowledge of the degree of anisotropy of the laminate permits us to predict the state of different stresses in the ply frame.