A numerical study of crack-tip plasticity in glassy polymers

This paper reports on a finite element analysis of the crack-tip plastic zone and near-tip fields in viscoplastic grassy amorphous polymers. The constitutive model employed in this study accounts for the typical shear yielding behavior of glassy polymers, i.e., the intrinsic softening upon yielding and the subsequent orientational strain hardening. The small scale yielding, boundary layer approach is adopted to model the local finite-strain deformation processes in front of a crack with a blunt notch. Numerical results show that the shape of the plastic zone near the tip of a Mode I crack in a glassy polymer depends sensitively on the combined effect of softening and strain hardening. Softening tends to intensify the plastic deformation, while the subsequent hardening tends to depress plastic flow and gives rise to continuous propagation of the current plastic zone. Thus, the plastic zone in typical amorphous polymers is found to be quite different from the HRR solution for yielding in hardening metals. It is also found that the distribution of hydrostatic stress, which is probably responsible for crazing, is intimately related to the pattern of the plastic deformation in front of the crack tip.