AbstractThe tensile behaviors of drawn polystyrene (PS) and high‐impact polystyrene (HIPS) were examined systematically in the wide range of strain rate, 1.7 × 10−4–13.1 m/s, without changing the mode of deformation and the shape of the test pieces. It was found for both PS and HIPS that the flexion points of birefringence with increase of draw ratio are intimately correlated with the tensile properties. Especially, the breaking strain and energy of undrawn and drawn HIPS were assigned to the contributions of the following three toughening mechanisms: (a) the generation of large numbers of microcrazes from the equatorial zone of the dispersed rubber particles; (b) the extension of interfacial rubber phase around the circumpolar zone of the dispersed rubber particles and its disintegration from the matrix component; and (c) the shear band formation of the matrix component followed by cold drawing. These mechanisms were discussed in connection with the factors of stress concentration to the rubber particles, hydrostatic pressure effect arising from the difference in Poisson's ratio of rubber and matrix components, and heat generation due to the adiabatic defor
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