This paper reviews findings on the type, morphology and constitutive behaviour of impact damage zones during loading after impact and their effect on the laminate strength and stability. The paper is limited to tape prepreg based monolithic laminates, although some similarities exist with impact damage in textile based laminates. Damage zones have a complex geometry with several damage types, which results in an interaction and competition between different failure mechanisms, e.g. local and global buckling, compressive failure, and delamination growth. Hence, simplified damage models may provide incorrect predictions of the failure load and failure mechanisms after impact. The constitutive behaviour of damage zones has been studied experimentally in tension and compression using an inverse method, and the results have been compared with detailed FE models of a generic impact damage. The paper is concluded with a discussion on analytical and computational models to predict the resulting strength of impacted laminates.

A numerical model is developed for predicting low-velocity impact damage in laminated composites. Stacked shell elements are employed to model laminate plies with discrete interface elements in pre-determined zones to model the onset and propagation of matrix cracks and delamination. These interface elements are governed by a bi-linear cohesive failure law. Cohesive element zone size is determined by a separate finite element analysis using solid elements to identify the stress concentration sites. In order to save the computational effort, low-velocity impact load is modelled by quasi-static loading. Influence of contact force induced friction on shear driven mode II delamination is modelled by a friction model. For a clustered cross-ply laminate, calculated impact force and damage area are in good agreement with the test results. It is shown that matrix cracks should be included in the model in order to simulate delamination in adjacent interface. The practical outcome of this research is a validated modelling approach that can be further improved for predicting low-velocity impact damage in other stacking sequences.