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 mechanical deformation response of high impact polystyrene (HIPS) under the condition of uni-axial tensile loading processes which include both loading and unloading stages with different constant strain rates. A damage variable, which is defined by the volume dilatation due to crazing, is used to characterize the effect of craze damage on the true stress and further on the visco-plastic mechanical response of HIPS. The damage variable and the plastic strain have been determined from the experimental data. The results also show that the effect of strain rate on the maximum tensile strength and the viscosity coefficient is very significant. A visco-elasto-plastic constitutive equation of polymeric material that takes account of the effect of craze damage, has been established. The solution of this constitutive equation can be used to simulate the non-linear stress-strain curves in tensile loading-unloading process, which agree well with those obtained experimentally.