A constitutive model of cold drawing in polycarbonates

This paper presents a set of constitutive equations to model cold-drawing ( necking) in polycarbonates (PC). The model is based on a representation of cold drawing asa double glass transition, i.e., a transition from a glass i nto a rubbery state, when a certain yield surface in the stress space is re ached, and a transition back to the glassy state upon unloading or when a c ertain molecular orientation (draw ratio) is achieved. The stretching proce ss in the rubbery state is modeled by a hyperelastic extension of the J(2)- flow theory to the finite strain range. An appropriate yield surface and an associative flow rule (defined via the Kuhn-Tucker optimality conditions) are presented to simulate this process in polycarbonates. The isochoric con straint during double glass transition is treated via an exact multiplicati ve decomposition of the deformation gradient into volume preserving and sph erical parts. Numerical constitutive integration algorithm is based on an o perator splitting technique where constraint/consistency during inelastic d eformation is enforced via return mapping algorithm. Numerical results are presented to demonstrate the correspondence with the experimental data. (C) 1999 Elsevier Science Ltd. All rights reserved.