Study on the possibility of increasing the maximum allowable stresses in fibre-reinforced plastics

This article presents the results of a study aimed at investigating the possibility of increasing the maximum allowable stresses in fibre-reinforced plastics compared to current practice. The study consisted of a comparison between the maximum allowable stresses of a group of cross-ply laminates, determined by deterministic analyses with safety and model factors as stated in design rules, and their probabilistic responses estimated with a fracture mechanics based model that accounted for material degradation. The results suggest that for the studied cases, the maximum allowable stresses do not provide the desired reliability; thus, their increase cannot be motivated. More importantly, the investigation shows that a better understanding of the effects of matrix cracks, and therefore, the maximum allowable crack density in a composite laminate, would lead to better and safer composite structures.