The ductile-brittle transition in a polyethylene copolymer

Abstract

The ductile-brittle transition of an ethylene-hexene copolymer was measured from 80 to 24° C. The basic curves of stress against time to failure could all be unified in terms of a single equation based on normalizing the stress relative to the transition stress between the ductile and brittle regions and using a single thermal activation parameter. This unity is based on the observations which show that the ductile and brittle failure processes are both associated with a shear process. The unifying equation is

$$\left( {\frac{\sigma }{{\sigma _{\text{c}} }}} \right)^n = \left( {\frac{{t_{\text{R}} }}{{t_{\text{f}} }}} \right){\text{ exp }}\left[ {{\text{85 500/}}R\left( {\frac{1}{T} - \frac{1}{{T_{\text{R}} }}} \right)} \right]$$

where σ _c is the minimum stress for ductile failure at an arbitrary temperature, T _R; t _R is the time to failure at an arbitrary reference temperature T _R; n equals 34 and 3.3 for the ductile and brittle regions, respectively and R is in J mol⁻¹ K⁻¹.