Effect of draw rate on the stress-strain behaviour of polymers

Abstract

Abstract A new phenomenon has been observed in the tensile deformation of polymers, including polypropylene, poly(ethylene terephthalate) and polyethylene. It has been seen that when draw rate is larger than a critical value, Young's modulus, yield stress and other parameters associated with the drawing response of these polymers decrease rapidly with the increasing draw rate; the normal time-temperature superposition principle does not appear to hold in this case. Further it can be shown that this decrease in modulus and yield stress is not caused by a temperature rise during drawing; the tensile deformation process before yield is largely isothermal. As an alternative, a change in the yield mechanism is suggested as a reason for the decrease in modulus and yield stress. This decrease may arise from void formation and crazing, which is relatively uniform throughout the sample, and dominates at these high draw rates.