Yield Behavior of Rigid Plastics

Abstract

The yield behavior of polycarbonate and polyvinyl chloride was investigated by several static load tests: tension test and torsion tests of hollow cylinders having various ratios of the inside to the outside diameter. Particular attention was given to the effect of the macroscopic stress distribution in the specimen on the yield behavior.
Close observation in tension test and torsion tests of thin-walled cylinders revealed that there are two processes in yield of plastics: the initiation process of yield accompanying load drop and the progressive process of yield under constant load. The observed yield behavior suggests that the relation between stress and strain of plastics can be represented by two characteristic curves: the first goes up to the point where yield starts, and the second goes up to the failure after the progressive process of yield appears.
From the yield behavior mentioned above, two kinds of yield stresses were found to exist: the stress at the yield point and the stress at the progressive process of yield.
By applying the above interpretation to the torsion tests of hollow cylinders, it is possible to determine the relation between the torsional moment and shear strain quantitatively. The calculated results were confirmed by the experiments.