The mechanism for craze-tip advance in glassy polymers

Abstract

Stereo electron microscopy of the craze tip in glassy polymers shows unequivocally that the tip breaks up into a series of fingers, as predicted by the meniscus instability mechanism. As the fingers propagate, the familiar fibril structure is developed at the webs of polymer between the fingers. Although there is a region of plastic deformation located in the two surfaces of the polymer film ahead of the tip, no large-scale yielding is observed and no isolated voids are formed. It is possible to construct a simple theoretical model for the critical wavelength of this instability. From this model a range of values, 16–33 nm, is obtained depending on the thickness of the craze behind the craze tip. These values are in agreement with the observed interfibrillar spacing along the craze of 20–30 nm.