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In the present paper an effort is made to model the time-dependent behavior of high-density polyethylene (HDPE) with a one-dimensional integral representation. Owing to the plasto-viscoelastic behavior of the material, we assume that the total strain can be decomposed into a recoverable viscoelastic strain and an irrecoverable plastic strain. The viscoelastic deformation is represented by the Schapery thermodynamic theory. The plastic deformation is assumed to be accumulated during the loading history. An effective time concept is introduced for the plastic deformation, so that the response due to complex loading can be accounted for.The present representation gives a very good prediction of the responses of creep and recovery, two-step creep, and constant stress rate loading and unloading. I t is also applied successfully to describe the process of preconditioning of semicrystalline polymers.

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A numerical study of crack-tip plasticity in glassy polymers Lai, J.; van der Giessen, E. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. AbstractThis paper reports on a finite element analysis of the crack-tip plastic zone and near-tip fields in viscoplastic glassy 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. "lhus, 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.

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