Creep and recovery behavior of a linear high density polyethylene and an ethylene-hexene copolymer in the region of small uniaxial deformations

The results of creep and recovery experiments are reported for two types of polyethylene—one a linear high density homopolymer, and the other an ethylene‐hexene copolymer. Data were obtained at temperatures in the range 23°C to 57°C and creep times of 10 s to 4.33 × 105 s. In order to approximate constant true stress conditions, all of the experiments were carried out at the same value of applied stress (4 MPa) and the change in strain during creep was in all cases less than 2 percent. Comparison of these results with the results from earlier work on an ultra high molecular weight polyethylene shows that there is a great similarity in the behavior of all three materials, and the behavior of all three can be described quite well by a one‐dimensional equation consisting of two terms—one a hereditary term and the other a plasticity term. It is further shown that to a very good approximation the idea of time‐temperature superposition can be applied to the description of the hereditary term.