The effect of strain rate, temperature, and molecular mass on the tensile deformation of polyethylene

Conventional tensile testing applied to high density polyethylene can lead to erroneous impressions of the tensile response of the material due to a l ocal reduction in cross section of the sample. Several workers have develop ed novel tensile testing techniques to measure the response of a small elem ent as it deforms. The true stress true strain curve that results describes tensile deformation of the material in a geometry-independent manner. Here , results from previous workers, together with some of our own, are interpr eted in terms of the Haward-Thackray spring-dashpot model, in which the spr ing defines a strain hardening process according to the theories of high el asticity and the dashpot describes a strain-independent viscous process. Th e effects that temperature, strain rate, and molecular mass have on each pr ocess are investigated. For a pipe-grade, modified high density ethylene co polymer, sufficient data have been measured to interpret the effects of str ain rate and temperature in accordance with an Eyring flow process, where t he parameters for the two mechanisms are found to be similar.