Rate-Dependent Shell Element Composite Material Model Implementation in LS-DYNA

Abstract

A previously developed constitutive model has been modified in order to incorporate the rate dependence of elastic modulus of the polymer matrix constituent into the nonlinear, strain-rate-dependent deformation analysis of polymer matrix composites. To compute the inelastic strains in the polymer matrix, state-variable-based viscoplastic equations originally developed for metals are modified in order to account for the effects of hydrostatic stresses, which are significant in polymers. The polymer constitutive equations are implemented within the strength of a material-based micromechanics method in order to predict the nonlinear, strain-rate-dependent deformation of the polymer matrix composite. The polymer and the composite models are implemented into a commercially available explicit finite-element code, LS-DYNA, as user defined materials (UMATs). The deformation behaviors of several representative polymers and two polymer matrix composites of various fiber configurations are simulated in LS-DYNA with the UMATs for a wide range of strain rates, and the numerical results agree well with the experimental data. UMAT is applied for simulations of braiding/weaving composites using the modified through-thickness integration points method.