Optical Properties and Structure of Crazes in Transparent Glassy Polymers

Abstract

IT has been known for about a year that a large fraction of what appear to be planar reflective cracks in transparent polymers such as polystyrene, polymethyl methacrylate, and polycarbonate are not true cracks at all but rather are thin, abruptly bounded regions of material having different optical properties from the bulk polymer¹. This material connects to the surrounding bulk polymer so that the pseudo-crack (henceforth termed a craze) will bear a tensile load in contrast to the true crack. Furthermore, such things as growth-rates under stress and ability to ‘heal’ under heat are quite different for the craze and the crack. Nevertheless, crazing produces stress heterogeneities, and for this reason at least is a precursor of cracking and fracture.