Abstract
Polyvinyl chloride (PVC) was oriented by uniaxial hot drawing; the resulting anisotropic mechanical properties were then investigated. The molecular weight, density and glass transition temperature were determined to provide material characterisation data of the as-received PVC. The degree of orientation in the PVC was evaluated by draw ratio and birefringence measurements. The symmetry state was determined by reference to geometry changes, x-ray and ultra-sonic velocity data. The mechanical properties examined included the tensile and compressive yield stresses, which were examined as a function of orientation angle and degree of orientation. A modified form of the Hill-von Mises yield criterion was used to explain the experimentally observed yield stresses. The difference between the tensile and compressive yield stresses in the oriented polymer were explained by the hypothesis of a 'frozen-in' stress introduced into the polymer during the drawing process. The variations of the 'frozen-in' stress with temperature and strain rate were examined. The differences between the tensile and compressive yield stresses of the as-received polymer were explained by the hypothesis that the yield stress was affected by hydrostatic pressure. The velocities of propagation of pulsed ultrasonic waves passing through the oriented PVC were measured by a transmission technique. From this data, by applying the elastic wave theory developed by Musgrave, the elastic constants and compliances were calculated. The variations of the elastic constants with orientation were compared with that of an aggregate model. The correlation of the ultrasonic modulus with the yield stress results has been discussed. Some aspects of fracture, yield-fracture transitions tests and impact tests, that were affected by orientation, have also been discussed.