A study of the biaxial forming of polymers. (3rd report Application of the energy method to backward extrusion and tube extrusion-expansion of high-density polyethylene)

Abstract

Polymers are isotropic when they have not been cold worked, but they become highly anisotropic when plastically deformed. Biaxially drawn high density polyethylene (HDPE) sheets were prepared by forging them in compression between a pair of opposing punches. Various degrees and types of biaxial drawings were achieved by changing the aspect ratios of the rectangular specimens. They were subsequenty subjected to tension tests in the direction of compression. The yield strength remaining assumed in the previous study was thus determined. The energy method was applied to the backward extrusion and tube previous extrusion-expansion of HDPE with various extrusion ratios at room temperature. A good agreement was obtained between the theory and the experiments. It is concluded that anisotropy should be taken into consideration when applying the energy method to polymer forming.