Modelling of non-linear stress-strain behaviour of HIPS with craze damage in tensile loading-unloading process

Experimental and theoretical works have been done to study the nonlinear me chanical deformation response of high impact polystyrene (HIPS) under the c ondition of uni-axial tensile loading processes which include both loading and unloading stages with different constant strain rates. A damage variabl e, which is defined by the volume dilatation due to crazing, is used to cha racterize the effect of craze damage on the true stress and further on the visco-plastic mechanical response of HIPS. The damage variable and the plas tic strain have been determined from the experimental data. The results als o show that the effect of strain rate on the maximum tensile strength and t he viscosity coefficient is very significant. A visco-elasto-plastic consti tutive equation of polymeric material that takes account of the effect of c raze damage, has been established. The solution of this constitutive equati on can be used to simulate the non-linear stress-strain curves in tensile l oading-unloading process, which agree well with those obtained experimental ly. (C) 2000 Elsevier Science Ltd. All rights reserved.