2 - Damage tolerance of composite structures under low-velocity impact

Abstract

Low-velocity impact is one of the most critical load factors for composite laminates. Indeed, for structures submitted to low-energy impacts or small-object drops, such as tools during assembly or maintenance operations, composite laminates reveal a brittle behaviour and can undergo significant damage in terms of matrix cracks, fibre breakage, or delamination. This damage is particularly dangerous because it drastically reduces the residual mechanical characteristics of the structure and at the same time can leave very limited visible marks on the impacted surface. Impact damage tolerance is therefore an important design consideration for aircraft composite structures. The objective is to prove that the composite structure can withstand the required loading, even with impact damage, and in particular if the impact is undetectable. The complexity of this design consideration is that it is necessary to consider, on the one hand, the impact damage, or more precisely the loss of residual strength due to the impact, and, on the other hand, the impact detectability, or more precisely the permanent indentation left by the impact. The goal of this chapter was to present the concept of impact damage tolerance applied to aircraft composite structures.