Effects of internal stress on the yielding of oriented poly(vinyl chloride)

Abstract

AbstractPoly(vinyl chloride) sheet was oriented by hot stretching at 80°C. Yield stresses in simple tension and compression were measured at 20°C and at a strain rate of 100% min−1 as a function of the angle between the test‐piece axis and the hot‐stretch direction. Simple tensile and compressive yield stresses were also measured in the temperature range −40°C to +80°C, in the hot‐stretch direction at strain rates of 100% min−1 and 1% min−1, and in the unstretched sheet at 100% min−1. The results are discussed in terms of a yield criterion based on that of von Mises but modified to allow for the effects of anisotropy, internal stress and mean normal stress, and are held to justify the inclusion of the internal stress term. By making specified assumptions, the magnitude of the internal stress term is separated from that of the normal stress term and shown to rise slightly with testing temperature and to be only two‐thirds as great at the lower strain rate. A reason is given for thinking that the strain‐rate effect may have been overestimated.