SynopsisPoly(viny1 chloride) sheet was oriented by hot drawing. The yield behavior of the oriented sheet was then investigated under uniaxial tension a t room temperature as a function of the angle between the tensile axis and the molecular alignment direction. The onset of yield was localized in deformation bands. The variation of yield stress with direction and the direction in which the deformation bands formed were found to be satisfactorily accounted for in terms of a yield criterion based on that of von Mises, provided that a term representing internal compressive stress in the molecular alignment direction was included. The internal stress was found to increase from zero with increasing draw ratio of the prior hot drawing. It is pointed out that other workers have found polymers to obey the yield criterion of Coulomb rather than that of von Alises.

This paper reports measurements of the variations of residual optical birefringence and extinction direction with residual strain occurring in tensile test pieces cut from oriented polyvinyl chloride strip and extended in simple tension. The strips were oriented by prior extension and both the degree of orientation and the angle between the orientation direction of the strips and the direction of subsequent extension of the test pieces were varied.The experimental results are discussed in terms of a molecular orientation model due to Kuhn and Grün and developed in this paper to apply to cases such as described here, in which the transverse contraction accompanying the longitudinal extension of the test pieces is anisotropic. Agreement between experiment and theory is reasonable in view of the simple assumptions made.