A Modified Strain-Rate-Dependent Spring-Mass Model for Response Prediction of Composite Laminates Subjected to Low-Velocity Impact

A modified strain-rate dependent (SRD) spring-mass model was first developed to capture the strain rate effect on response prediction of fiber-reinforced polymer (FRP) laminates subjected to low-velocity impact (LVI). The constitutive relations of FRP material were modified with the impact-induced strain rate using Yen-Caiazzo's function in space and time dimensions simultaneously. The stiffness coefficients of the spring-mass model were updated step-by-step during solving the Bubnov-Galerkin equation by the variational method, allowing the SRD contact history to be obtained via recursive integration. The SRD expressions of stiffness coefficients under four typical boundary conditions were presented. Drop-weight tests on FRP laminates and corresponding VUMAT-based LVI simulation with the finite element method (FEM) were provided to prove the validity of the proposed SRD model in evaluating the strain rate effect on the LVI response of composites. Further parameter studies were carried out to investigate the reliability of the proposed SRD model for evaluating the influence of reinforced fibers with different strain rate dependency on impact response. The proposed lumped parameter model has been proven to be more efficient than the traditional FEM, which can be combined with some existing damage models to accurately analyze the delamination evolution process of FRP laminates under LVI in further studies.