The effects of manufacturing techniques on viscoelastic and viscoplastic behavior of high density polyethylene (HDPE)

High density polyethylene (HDPE) has been widely used in the piping industry as a raw material. Even though there are large numbers of experimental and analytical investigations on HDPE, few of them have examined the effects of manufacturing techniques on the small and finite deformation behaviors of HDPE. Since HDPE is a semi-crystalline polymeric material, the rate of crystallinity, molecular morphologies and molecular structure extensively influence its mechanical behaviors. Different manufacturing methods result in different molecular morphologies and molecular structure at final product. In this study, the mechanical behaviors of HDPE associated with manufacturing methods are investigated. The nonlinear mechanical behavior of HDPE is investigated using samples obtained from extruded HDPE pipe and compression molded sheet. Extruded and compression molded specimens are constituted the same raw materials. Extensive experimental work has been performed to characterize the nonlinear time dependent response of the material. The tensile loading-unloading behaviors with three different strain rates are investigated. In addition, creep and relaxation behavior of HDPE at the beginning of elastic, viscoelastic and viscoplastic regions are investigated so that these results can be used in finite element analyses to determine the material parameters for viscoelastic and viscoplastic material models.