Is fatigue testing of impact damaged laminates necessary?

A major long-term objective in the evolution of advanced fibre composites as aircraft structural materials must be the establishment of a damage tolerance methodology. The availability of this methodology would greatly aid the design of safe, efficient composite structures as well as their management in service. There are, however, many difficulties in meeting this objective, including the multiplicity of failure modes in the composites, the numerous types of potentially significant defects which may arise during manufacture or in service and sensitivity to moisture and temperature. This paper discusses the necessity of fatigue testing of impact damaged composite laminates. Selected experimental studies in the literature are briefly discussed. It is shown that uniaxial S-N curves for damaged laminates have a generic shape with a pronounced threshold level. Indeed, it is clear that further research is needed to understand the physical reasons for such a threshold value.