On the tensile behavior of high density polyethylene subjected to cold rolling

Abstract

High density polyethylene was cold rolled to produce a series of specimens having from zero to 50% cold work. For those worked beyond 20%, the absolute thickness recovery was relatively constant. X-Ray diffraction studies indicated that significant changes in the original structure also occurred in specimens cold worked beyond 20% and that increasing c-axis orientation was coincident with greater cold work. From the fully recovered specimens, tensile behavior was studied for two strain rates. The early portions of the true stress-true strain curves vary as the degree of initial cold rolling increases; this is reflected in different values of the elastic modulus which exhibits a minimum with material cold rolled about 25%. Tensile instability or necking is delayed as the degree of initial cold working increases but little variation was observed in regard to the tensile strength. The findings pertain for both strain rates. Regarding specimens of similar “structural” condition, say for example 15% cold work, higher strain rates correlate with greater strength and lower strain at instability. In a qualitative manner, comparative behavior between this polymer and ductile metals is discussed.