RATE-DEPENDENT DEFORMATION OF SEMICRYSTALLINE POLYPROPYLENE NEAR ROOM-TEMPERATURE

We examine the strain rate dependent, large plastic deformation in iso tropic semi-crystalline polypropylene at room temperature. Constant st rain rate uniaxial compression tests on cylindrical polypropylene spec imens show very little true strain softening under quasi-static condit ions. At high strain rates very large amounts (38 percent) of apparent strain softening accompanied by temperature rises are recorded. We ex amine the capability of a recently proposed constitutive model for pla stic deformation in semi-crystalline polymers to predict this behavior . We neglect the contribution of the amorphous phase to the plastic de formation response and include the effects of adiabatic heating at hig h strain rates. Attention is focused on the ability to predict rate de pendent yielding, strain softening, strain hardening, and adiabatic te mperature rises with this approach. Comparison of simulations and expe rimental results show good agreement and provide insight into the meri ts of using a polycrystalline modeling assumption versus incorporating the amorphous contribution. discrepancies between experiments and mod el predictions are explained in terms of expectations associated with neglecting the amorphous deformation.