硬質塩化ビニールのクリープ破断性

Abstract

Tensile creep-rupture tests of unplasticized polyvinylchloride were made on test pieces taken from pipes, up to 100 hours, under several temperatures below the second order transition temperature.It was found that the Larson-Miller method developed in the research of metals could be applied to that of this material. With the rupture time-temperature as parameter, T (50+logt), we obtained a considerably fair line, i.e., so called master rupture curve.A discussion was given on the fracture mechanism, especially on the deformation and fracture processes. We presented a significant temperature-stress diagram, having four characteristic regions divided by three straight lines started from 80°C. Each region indicates a different fracture mechanism. This diagram stands also for use in selecting the materials in design. It may be suggested that the similar relationship will be applied for other polymers.So far as the deformation process is concerned, this material flows perfectly in the shoulder of a neck, within certain stress-temperature regions. This region corresponds to a characteristic creep curve-at the end of the 3rd stage, the creep rate apts to decrease-and a fracture marking.The necking mechanism was studied by using X-ray diffraction pattern, electron microscope, density measurement and hardness test. Above all, electron micrographic studies by replica method revealed the fine direct evidence of a marked orientation of the material.The effect of residual stresses before and after a heat treatment, was also discussed.