Rheological constitutive model for thermoplastic resin based on viscoplastic-viscoelastic multiplicative decomposition of deformation gradient

Abstract

We propose a rheology-based viscoelastic-viscoplastic constitutive model in which the deformation gradient is mutiplicatively decomposed into viscoelastic and viscoplastic components. The viscoelastic and viscoplastic rheology elements are connected in series, and the stress is determined only in the former element, which is modified by the back stress introduced in the latter one to represent the hardening due to orientation of molecular chains. The standard generalized Maxwell model is used to characterize the viscoelastic material behavior at small or moderate strain regime, while a proven finite strain viscoplastic model is employed to realize the transient creep deformations due to frictional resistance of molecular chains. After identifying the material parameters with reference to experimental data and verifying the fundamental performance of the proposed model in reproducing typical material behavior of resin, we carry out two kinds of numerical analyses for simple structures to demonstrate its applicability for practical use.