Craze yielding and stress-strain characteristics of crazes in polystyrene

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Abstract
The crazing behaviour of a grade of polystyrene which crazes profusely when tested in tension has been studied at 293°K using quantitative optical, electron and electron scanning microscopy. Tensile tests on this material showed that a high density of crazes was produced at room temperature. The crazes formed in a zone which spread progressively down the specimen. The plastic strain associated with crazing was sufficient to cause craze yielding and the phenomenon is compared with discontinuous yield in mild steel. Craze-yielded specimens were used to determine the stress—strain curve of craze material. Microstrain techniques were developed for this work and the total volume of craze was determined from the density, distribution and thickness of the crazes. It was found that the stress—strain characteristics of polystyrene crazes are similar to those observed by Kambour and Kopp (1969) for solvent-induced crazes in polycarbonate.