1987 年 53 巻 489 号 p. 980-985
Polymers can be considered 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 between a pair of opposing punches. Various rates of biaxial drawing were achieved by changing the aspect ratios of the rectangular specimens. In the previous paper, they were subsequentry subjected to tension tests in the direction of principal strain, and the coefficients of anisotropic yield condition were determined for various amounts of principal strains. In the present paper, on the other hand, the test directions were angled 22.5°, 45°, and 67.5° to the principal strain direction. One of the anisotropic coefficients left unknown in the previous study was thus obtained.