On the relationship between failure mechanism and compression after impact (CAI) strength in composites

Abstract

This work explores the relationship between different failure mechanisms and compression after impact (CAI) strength through an advanced finite element analysis. A Continuum Damage Mechanics (CDM) approach is used to model intra-laminar failure and Cohesive Zone Modelling (CZM) for inter-laminar failure. The FE progressive failure analysis is performed in two consecutive steps. The first is a low-velocity impact analysis in which the induced damage maps are obtained. In the second step, the boundary conditions are modified and an analysis of CAI is performed. The effect of change in ply layup sequence, sub-laminate scaling and ply blocking are investigated and a link between failure and CAI strength is established. Results suggest that changes in ply layup sequence affect delamination sizes, positions and shapes during impact, which in turn result in either global or sub-laminate buckling failure during compression. A global buckling mode results in higher CAI strength compared to failure by sub-laminate buckling for quasi-isotropic laminates of the same thickness. Ply-blocking increases tendency towards delamination, causing a decrease in CAI strength. Sub-laminate scaling causes a transition in failure mode from out-of-plane buckling to in-plane compressive fiber failure. These results suggest a strong correlation between failure mechanism and CAI strength.