Durability analysis of polymer matrix composites for structural applications

Polymer matrix composites have time dependent properties with response times function of the fibre orientations, the volume fraction of the fibres and the stacking sequence for laminates. This viscoelastic–viscoplastic behaviour is also influenced by the type of mechanical loading history and the environmental variations. This time dependent evolution concerns not only the stiffness properties but also the strength characteristics. The durability analysis of such composite systems can be based on strength criteria with time dependent coefficients or on a damage analysis. After an overview of the most important prediction methodologies available today, a combined nonlinear viscoelastic–plastic damage model is described. Results from this model on some specific graphite-epoxy systems are presented for a viscoelastic–viscoplastic behaviour. Extensions for damage development are discussed. Local time dependent effects resulting from the stress transfers between viscoelastic and elastic components are presented in relation to the degree of adhesion between those components