A modified state variable polymer model implementation in LS-DYNA

摘要

A previously developed constitutive model has been modified in order to incorporate the unloading behavior into the nonlinear, strain rate dependent deformation analysis of polymer. 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 unloading behavior is approximated linearly with a simple damage model with decreasing unloading young’s modulus, in which the damage parameter is increasing with the increment of inelastic strain. This nonlinear, rate dependent polymer model is then implemented into LS-DYNA, an explicit transient dynamic finite element code, through the use of the user defined materials option (UMATs). Experimental and computed stress-strain curves under different strain rates are compared for one representative polymer under shear and tensile loading.