No abstract

The paper is concerned with the measurement by an ultrasonic pulse technique (Markham 1970) of the elastic stiffness constants of oriented polyvinyl chloride sheet over a range of degrees of orientation produced by drawing. The technique involved immersing the sample in a tank of water containing an ultrasonic transmitter and receiver, and measuring the difference in transit time between the two, with and without the sample. In general, two types of wave were propagated through the sample, and their velocities were determined, from which the stiffness constants were deduced. The frequency was 5 MHz. Measurements of the optical birefringence were also made.The effect of drawing the initially elastically isotropic sheet was most marked in the case of c33 (axis 3 being the draw direction) which increased from 6·3 to 11·8 GN m−2, and least marked in the case of c44 which decreased from 1·8 to 1·6 GN m−2. The material was found to have transverse elastic isotropy about the draw direction, and the other three stiffness constants changed by intermediate percentages.The variation of stiffness constants with draw ratio was fitted quite well by a theory of Ward (1962), except for a discrepancy in the case of the unoriented material.

SYNOPSISPoly(viny1 chloride) sheet was oriented by hot stretching at 8OOC. Yield stresses in simple tension and compression were measured at 2OoC and at a strain rate of 100% min-' 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 -4OOC to +8OoC, in the hot-stretch direction at strain rates of 100% min-' and 1% rnin-l, and in the unstretched sheet at 100% min-'. 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.(1) Wo,, -ovy)' + F(oyy -oZz)' +G(ozz -oXxI2 + 2N7*,, + 2Lr2,, + 2M72zx = 1 87 0 1 9 7 1 by John Wiley i t Sons, Inc.