A strain-rate-dependent damage model for evaluating the low velocity impact induced damage of composite laminates

Low velocity impact (LVI) has always been a potential threaten to composite structures. This out-of-plane dynamic impact load easily leads to a dramatic increase of the strain state in the material transverse plane, which can affect the dynamic stress state and damage evolution of the composite laminate, especially for LVI with a relatively high energy. However, the strain rate effect was always neglected in existing investigations, thus introducing inevitable errors in numerical predictions for engineering practices. To accurately capture the failure process of composite laminates under LVI, a three-dimensional strain-rate-dependent damage model was proposed. This model was composed of three parts: a modified stress-strain relationship for composites under a dynamic stress state; a strain-rate-dependent progressive damage model to evaluate the intra-laminar damage; and a cohesive zone model to examine the inter-laminar delamination. LVI tests with different impact energies were conducted to provide validating data. It is shown that the numerical results from the strain-rate-dependent damage model are highly consistent with the experimental outcomes. The contact force history curves, intra- and inter-laminar damage evolution process are found to be strain rate dependent, and thus the numerical errors predicted by the strain-rate-independent damage model significantly increase with the increment of the applied impact energy, which is unacceptable in practice for LVI with relatively high impact energies.