High-temperature large strain viscoelastic behavior of polypropylene modeled using an inhomogeneously strained network

The effects of microstructural rearrangements during the stretching of semi crystalline polymers and the resultant inhomogeneous strains are modeled by rigid spheres embedded in a polymer network. This results in strain concen trations in the network, which is then caused to yield at realistic overall strains. To simulate the collapse of the original spherulitic morphology, the radii of the spheres decrease at a rate dependent on the shear stress i mposed on them by the surrounding network. This results in time-dependent b ehavior. The resultant large strain viscoelastic model is implemented in a commercial finite element code and used to predict shapes of necking polypr opylene sheet specimens at 150 degrees C. Rate dependence of stress and str ess relaxation are also predicted, and the model is shown to be generally e ffective in its predictions of shapes and forces up to large deformations. (C) 1999 John Wiley & Sons, Inc.