Effect of General Uni- and Bi-axial Stretch on Tensile Property of Rigid Polyvinyl Chloride Sheet

Tensile tests were carried out of bi-axially stretched rigid PVC sheets. Test pieces were prepared from a sheet material for thermoforming use by the technique and the apparatus for thermoforming. The stretch ratios λ and μ along their two main axes were 0.5-6. Effect of stretch ratios was studied by a graphic analysis, and the following results were obtained. i) The yield stress values are almost independentof the stretch ratios both for notched or unnotched pieces. ii) The breakage and yield energy of notched pieces comparatively depend on the stretch ratios. iii) The product and the ratio of a set of these longitudinal and transverse characteristic values have correlations with the product λμ and the ratio μ/λ of the strech ratios respectively. These correlations are easily understood from the plot of the data in logarithmic scale. iv) In the case of uni-axially stretching the reinforcement is induced only along the stretch axis. Along the direction perpendicular to this axis rather significant weakening occurs. The bi-axial reinforcement seems to be due to the superposition of such uni-axial effects, and occurs only within a certain limited range of stretch ratios.