Abstract
A study of the ductile-brittle transition in the tensile behaviour of linear polyethylene is presented. Equipment for the simultaneous measurement of stress, strain and optical birefringence over a broad range of deformation rates and loading times is described. Low strain birefringence measurements showed that the total molecular orientation increased with decreasing test speed. High pressure polyethylene, which is not ‘brittle’ over the range of investigated test speeds, shows no time-dependent birefringence. Further, X-ray measurements show the same sequences of polymer chain orientation for both cold-drawn and brittle-fractured material. A detailed theory is advanced for explaining the low strain behaviour, the cold-drawing process and the mechanism of the ductile-brittle transition.
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