NONLINEAR MECHANICAL RESPONSE OF HIGH-DENSITY POLYETHYLENE .2. UNIAXIAL CONSTITUTIVE MODELING

Based on the experimental data presented in Part I, two uniaxial const itutive models are constructed. The first, a nonlinear viscoelastlc (N VE) model, is formulated using the mechanical analogy consisting of on e independent spring and six Kelvin elements in series. Creep data are used to determine the model parameters. The second model, a viscoplas tic (VP) formulation, is developed using the viscoplastic theory propo sed by Bodner to characterize the uniaxial viscoplastic behavior of me tals. Inelastic strain rate is introduced into the state variable in a ddition to inelastic work to depict the strong rate dependent behavior of HDPE. Experimental data from constant strain rate tests are employ ed to construct the material functions of the model, Limitations in th e application of each model are discussed in conjunction with possibil ities for future works.