Plastic Deformation Bands in Glassy Polystyrene

Abstract
Plastic deformation bands nearly parallel to planes of maximum shear stress have been observed in unoriented glassy polystryene in compression and in preoriented polystyrene in tension and torsion. In the temperature range 77°–375°K, the shear stress for homogeneous nucleation of deformation bands is of the order of a few percent of the shear modulus, and while this shear stress is only moderately dependent on temperature and independent of strain rate, it shows considerable pressure dependence compared to metals. The shear strain of order unity inside the bands, the positive dilatation observed during deformation, and the stress and temperature conditions of band nucleation and propagation suggest a model in which ``rough'' molecules slide through each other in an initially unordered but closely packed molecular tangle.

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