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Mechanics and Modeling of Cold Rolling of Polymeric Films at Large Strains -- A Rate-Independent Approach

We analyze plane strain cold rolling processes, at large strains but slow strain rates, by finite element modeling. At low temperatures, slow strain rates, and moderate thickness reductions during rolling (at which Bauschinger effect can be neglected for the particular class of polymeric films studied here), the task of material modeling is greatly simplified, and enables us to deploy a computationally efficient, yet accurate, finite deformation rate-independent elastic-plastic material behavior (with inclusion of isotropic-hardening). The finite deformation elastic-plastic material behavior based on (i) hypoelasticity, and ii) multiplicative plasticity, are programmed and carried out for cold rolling within Abaqus Explicit. Predictions from both the formulations, i.e., hypoelastic and multiplicative decomposition, exhibit a close match with the experimentally observed rolling loads. We find that no specialized hyperlastic/visco-plastic material model is required to describe the behavior of the particular blend of polymeric films, under the conditions described here, thereby significantly speeding up the computation for steady-state rolling simulations. Moreover, the use of classical rigid-plastic modeling (which is often applicable to metals) is found to greatly underestimate the rolling loads for polymers, due to large elastic stretches in the polymer films at large strains.