The Eight Modes of Long-Term Failure

The modes of deterioration leading to long-term laminate damage and failure fall into two broad categories: the load-dependent and the load-independent. This chapter introduces the eight modes of laminate long-term failure in industrial service, identifies the critical plies, and discusses the failure criteria in each case. The eight modes of long-term failure defining the durability of industrial laminates are: chemical failure, infiltration failure, weep failure, stiffness failure, fiber rupture failure, laminate strain-corrosion failure, abrasion failure, and anomalous failure. The failure criteria, separating the acceptable from the non-acceptable laminates, depend on the failure mode. The failure criteria for the load-dependent modes of failure—infiltration, weeping, stiffness, and rupture—are the equality of the long-term ply strengths and the applied loads. The crack density increases under cyclic loads until it reaches the critical value defining the ply durability and, by extension, the laminate durability. The micro-crack densities and damage developing in the critical plies are difficult, if not impossible, to see and measure.