A correlation of Young's modulus with yield stress in oriented poly(vinyl chloride)

The variations of tensile and compressive yield stresses and of Young's modulus of oriented poly(vinyl chloride) sheet with direction and with degree of orientation, represented by birefringence, are shown. Young's modulus was calculated from elastic stiffness constants measured by an ultrasonic pulse method at 5MHz with estimated strain and strain rate amplitudes of 2 × 10^?5 and 100s^?1. Yield strains were about 5 × 10^?2 measured at strain rates of about 2 × 10^?2s^?1. Although the measuring conditions were so different there was found to be a close correlation between tensile yield stress and Young's modulus, the two quantities being connected by a simple linear relationship, as direction of measurement and degree of orientation were varied. Compressive yield stress did not correlate with Young's modulus, and changed little with direction or degree of orientation by comparison with tensile yield stress. The empirical linear relationship between tensile yield stress and Young's modulus, difficult to account for theoretically, might form the basis of a method for determining tensile yield stress ultrasonically.