DEFORMATION MECHANISMS AND PLASTIC RESISTANCE IN SINGLE-CRYSTAL-TEXTURED HIGH-DENSITY POLYETHYLENE

Highly textured high-density polyethylene (HDPE) prepared by plane strain compression in a channel die was used as a macroscopic approximation to a single crystalline material to study the plastic deformation mechanisms. Samples cut out of the textured rectangular bars were subjected to tensile, compressive, and simple shear deformation in different crystallographic orientations, specifically chosen to probe the deformation resistances of specific crystallographic mechanisms of deformation. The degree of dominance of specific mechanisms in certain ranges of crystal orientation was ascertained by WAXS and SAXS measurements together with measurements of incremental shape changes of deformed samples. Through these studies it was determined that in deformation orientations requiring chain slip the most dominant mechanism was (100)[001] chain slip, with (010)[001] chain slip being a frequent alternative. Only scant evidence was found for the activity of (110)[001] chain slip. In deformation orientations requiring transverse slip evidence was found for the presence of (100)[010] transverse slip. In such orientations, however, very clear evidence was found also for deformation twinning on (110) planes. Martensitic transformations were not detected in any of the experiments. In compression experiments with the compression axis making a small angle with the chain axis and in tension experiments with the tensile axis making a large angle with the chain axis, chain slip often manifested itself in the formation of prominent kink bands. Shear resistances of the prominent slip systems and twinning systems together with their normal stress dependences at room temperature are reported together with considerably detailed descriptions of the observed kinematical modes of the specific deformation mechanisms.