Mechanism of plastic deformation for polycarbonate under compression by a laser extensometer technique

The large strain behavior of a glassy polymer was studied in terms of compr ession tests at various rates, while the local deformation was evaluated wi th a noncontact laser extensometer. The main features of yield and postyiel ding were described with a constitutive model from nonlinear viscoelasticit y, combined with a kinematic formulation for the separation of total deform ation into a viscoelastic and a plastic part, respectively. The concept of plastic shear transformations introduced Elsewhere was used to develop a ma thematical model for the rate of plastic deformation. The entire experiment al true stress-strain curves (including strain hardening and strain softeni ng) could, through this model, be identified in a self-consistent manner. ( C) 2001 John Wiley & Sons, Inc.