Criterion for craze nucleation in polycarbonate

Plastic deformation and crazes were initiated in polycarbonate bars containing a round notch by three‐point bending. Morphological observations revealed that internal crazes are nucleated by a hydrostatic stress component caused by plastic constraint ahead of the fully developed plastic deformation zone. The characteristics of the deformation bands for quenched and slowly cooled materials are in good agreement with the logarithmic spiral curves predicted from a slip‐line theory. The distribution of the stress components in the plastic deformation zone was analyzed using this theory. The critical hydrostatic stress is 87 MN/m 2 for slowly cooled polycarbonate and 89 MN/m 2 for quenched material. These results are compared with those of the craze nucleation models of Gent and Argon.