ABSTRACT: Classical plasticity theories for amorphous polymers often assume a flow rule in which the direction of plastic flow is co-directional with the stress deviator, a Mises-type flow rule. Although this is a reasonable approximation at the macro-scale, careful comparison between numerical simulation of plastic strain fields and experiments show that the shear-yielding micro-mechanism of plastic flow in which plasticity occurs by closely spaced bands of intense shearing is not accurately captured by a theory employing a Mises-type flow rule. Following, recent formulations by Anand and co-workers of plasticity theories for granular materials and metallic glasses which employ a double-shearing Mohr-Coulomb-type flow rule, in this study we develop a corresponding theory for large-deformations of amorphous polymers. The theory is implemented in a finite element package. The material parameters appearing in the theory were determined for the amorphous polymer polycarbonate from data obtained from axi-symmetric tension, compression, and cyclic loading experiments. In order to validate the numerical simulation capability a suite of experiments, which include plane strain tension, bending of a notched plate, and tension of a notched compact tension specimen, were performed. Comparison of the results from corresponding numerical simulations against those from the validation experiments show that the predictions from our double-shearing plasticity theory agree well with the experimentally-observed response of polycarbonate.

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