Analysis of Temperature and Strain Rate-Dependent Mechanical Behavior of Thermoplastics: a Comparative Study of Multilinear Kinematic Hardening and the Three-Network Material Models

Abstract This paper investigates the modeling of temperature-dependent mechanical behavior of thermoplastics through the experimental tension-compression and stress relaxation data of HDPE at three different temperatures. J-2-based plasticity models are used extensively for modeling thermoplastics. However, recent advancements in material models based on viscoplasticity formulations, such as the three-network model (TNM), are gaining prominence due to their enhanced capability to predict strain-rate-dependent, temperature-dependent, and non-linear behaviors of thermoplastics with better accuracy and reliability. This study uses temperature-dependent multilinear kinematic hardening (MKIN) and a three-network model (TNM) to predict thermoplastic material mechanical response. Both material models are calibrated based on experimental data. The stress-strain response of cyclic behavior of both material models is compared at different temperatures and strain rates. Further, a parametric study of TNM material model parameters is undertaken to understand the sensitivity and their influence on the material model behavior. Finally, an application use-case simulation of grommet loading-unloading force prediction is performed using both material models at different temperatures. Through grommet simulations, the ability of both material models to predict the mechanical response and permanent deformation of thermoplastics is compared. Overall, the TNM material model demonstrates a significant fidelity gain in predicting the strain rate and temperature-dependent plastic deformations in thermoplastics due to its viscoplastic formulation, in contrast to the J-2 plasticity-based MKIN material model.