Simulation of impact and residual strength of thick laminate composites

Abstract

Test and simulation of low-velocity impact and residual strength of composite structures is usually limited to relatively thin laminates. However, numerous applications in the aerospace and automotive industry exist, such as high-lift devices and pressure vessels that have thick laminates with notably different damage mechanisms to thin laminate. This paper investigates the influence that laminate thickness has on damage initiation and propagation during low-velocity impact, and on residual strength after impact.An enhanced cohesive zone model is presented that accounts for i) internal friction, ii) crack surface enlargement due to through-the-thickness compression, iii) strain rate effects and iv) different damage initiation stresses in the traction separation law of undamaged and damaged delamination layers. The effect of each feature is discussed and the model is validated on 2 mm–12 mm thick laminates. For residual strength prediction after impact, a strategy is proposed that maps impact damage and residual deformations to a new residual strength model, to avoid mesh distortions and improve computational costs while retaining a high level of accuracy. The mapping strategy is validated through compression after impact simulations and these studies are accompanied by an exploratory study of tension after impact for 2 mm thick laminates. The results show that the proposed modelling improvements are necessary to enable accurate prediction impact damage in thick laminates. Prediction of tensile and compressive residual strength, as well as deformation and failure modes, are also shown to closely agree with test measurements for the range of laminate thicknesses investigated.