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Fracture Processes in Ductile Polymer. II. Morphological Analysis of the Localized Plastic Deformation of Polycarbonate Film

The plastic deformation behavior of an artificially induced crack tip in polycarbonate films has been studied morphologically. It is shown that the plastic-zone ahead of the crack tip consists of crazes, shear bands and their intersections.While the craze initiation is restricted to the immediate vicinity of the crack tip, the shear bands extend to a region some distance from the initial crack tip and their intersections closely relate to the local reduction in thickness of the specimen.The structure of the shear bands and their intersections which are associated with the biaxial stresses at the plastic-zone tip causes biaxial orientation of molecular chains.The plastic strain in the intersection of the shear bands is discussed on the basis of the concept of the strain ellipsoid, and it is suggested that deformation caused by the intersection of the shear bands results from reorientation of the molecular chains initially oriented by the first shear rather than the duplication of simple shear deformations.