A general critical-strain criterion for crazing in amorphous glassy polymers

Abstract

The critical stress for craze formation in four different grades of polystyrene has been investigated under conditions of biaxial stress with one principal stress compressive. The results are consistent with the suggestion of Sternstein and Ongchin (1969) that for crazes to form the hydrostatic component of the stress tensor must be tensile. It has further been shown that a convenient way to express the criterion for the formation of crazes is in terms of a critical tensile strain, ε_c, which is a function of the hydrostatic component of the stress tensor. This critical-strain criterion can readily be applied to predict the onset of crazing under a general triaxial state of stress, and it may be possible to interpret the variation of the two parameters in the criterion in terms of two distinct critical processes in the formation of a craze, one process pressure-dependent the other not.