Physical Considerations behind Viscoplastic Modelling

Recent work involving the detailed analysis of macroscopic stress-strain-strain rate behaviour of polymers has led to re-examination of the physical origin of strain hardening. Sweeney et al. [123], working with initially isotropic ultra-high molecular weight 

A similar experimental finding, using pre-oriented polypropylene tapes, is that the strain rate dependence of stress is a function of the level of pre-orientation [121,126]. In this case, it was concluded that strain hardening could be viewed as originating entirely from a 

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