A CONSTITUTIVE MODEL FOR THERMOPLASTICS WITH SOME APPLICATIONS

A constitutive model for thermoplastics is outlined in this paper. The model consists of two parts: A hyperelastic-viscoplastic response due to in ermolecular resistance denoted Part A, and an entropic hyperelastic response due to re-ori ntation of molecular chains called Part B. Both parts are developed within a framework for finite strains. The main constituents are the Neo-Hookean model describing large elastic deformations, the pressure-sensitive Raghava yield function, a non-associated visco-plas tic flow potential and Anand’s stressstretch relation representing the intramolecular st iffness. The 11 non-zero coefficients of the model are identified from uniaxial tension and comp ression tests on two materials, HDPE and PVC, which are respectively semi-crystalline an d amorphous thermoplastics. Subsequently, it is employed in numerical simulatio ns f three-point bending tests on the same materials. The model gives satisfactory predictions when compared to experimental behaviour.