Modeling the mechanical behavior and impact properties of polypropylene and copolymer polypropylene

We present a general internal state variable (ISV) elastic-viscoplastic constitutive model that was initially applied to amorphous polymers (Bouvard et al J Eng Mater Technol 131(4), 041206, 2013) but has been extended to apply to semi-crystalline polymers along with a fracture criterion. In this work, we experimentally calibrated and validated the mechanical behavior of two semi-crystalline polymers (a polypropylene (PP) and a copolymer polypropylene (co-PP)) under different stress states, temperatures, and nominal strain rates. The experiments included compression, tension, impact, and three point bending tests with the notion of capturing the time, temperature, stress state dependence, and failure mechanisms under large strains. The ISV model was integrated into a finite element (FE) code and the FE simulations agreed very well with the PP and co-PP mechanical behavior under compression, impact, and three point bending thus exercising the model under different nominal strain rates, temperatures, and stress states. Two failure criteria were determined from the numerical simulations to build failure criteria maps that distinguished brittle and ductile failure as validated by the experimental observations. This study illustrates the generality of the Bouvard et al. (J Eng Mater Technol 131(4), 041206, 2013), which was previously employed to analyze an amorphous polycarbonate polymer.