96 K. Sakaue and S. Higuchi Fig. 13.1 Stress-displacement curve in tensile test for a large polycarbonate specimen Fig. 13.2 Image of the large specimen after tensile test evaluate the plastic deformation-induced anisotropy. The size of the large specimen is about 190 mm length and 150 mm width, and the size of the small specimen is about 45 mm length and 12 mm width. A uniaxial tensile test for the large specimen is performed by a tensile testing machine with a thermostatic-chamber. In order to reduce the tensile force to create the necking part in the large specimen, the tensile test is carried out at a temperature of 120 ◦C and at a crosshead displacement speed of 2 mm/min. Figure 13.1 shows the typical nominal stress-displacement curves of the large specimen. The stress reaches the maximum value of about 32 MPa subsequently rapidly and decreases to about 23 MPa. Then, the stress increases gradually with the propagation of the necking part. Figure 13.2 is the image of the large specimen after the uniaxial tensile test. A 5 mm×5 mm grid pattern was drawn before the tensile test. It is observed large plastic deformation by the propagation of the necking part. The small tensile specimens are cut off from the necking part in the large specimens by using an NC milling machine. The small specimens are cut from the area enclosed by dashed line in Fig. 13.2. The cutting direction from the necking part changes by 15-degree increments from the tensile direction (0 degree) of the large specimen to the perpendicular direction to the tensile direction (90 degrees). The uniaxial tensile test for the small specimen is carried out in a thermostatic chamber. The temperature condition is 25◦C, and the crosshead displacement speed is 1 mm/min. The displacement and strain on the specimen surface is measured by digital image correlation, DIC. The images are taken with a monochromatic CCD camera at an interval of 1 s. 13.3 Results In the present study, the nominal stress and the nominal strain are used to evaluate for the stress-strain curve. Figure 13.3 shows the stress-strain curves evaluated from the small specimens cut off in various directions from the necking part in the large specimens. The stress-strain curves of the cutting angles of 0, 15, and 30 degrees show the typical stress-strain curve of
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