This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Polymers are often used as a protective or energy-absorbing material in impact applications, including athletic equipment, consumer electronics, wearable devices, automotive structures, and medical devices. The molecular structure of polymers makes their response inherently strain-rate dependent. Experimentally capturing the rate-dependence of polymers is difficult due to the low stiffness and wave speed of materials, so specialized test techniques are needed. We have developed multiple test methods to test polymers in multiple loading modes up to 2000 1/s. These high strain rate test methods enable engineers to measure material response for impact applications and design at these strain rates.



Polymers also exhibit complicated material behavior including viscoplasticity, creep and relaxation, pressure dependent yield and failure, temperature dependence, and anisotropy. Accurately capturing these effects requires the use of advanced constitutive models and advanced methods to calibrate material parameters to the proposed constitutive models. We have developed advanced nonlinear optimization techniques to select and calibrate constitutive models to experimental data. This enables engineers select appropriate constitutive models and calibrate constitutive models that capture all effects for FE simulation.



We demonstrate these test and constitutive modeling capabilities with a case study on a high density polyethylene (HDPE) material. We collect and present test data at impact strain rates and large strains, discussing the impact test methods. We then select and calibrate the Three Network Viscoplastic (TNV) constitutive model to the experimental data. This model can capture the finite strain, viscoplastic response of the material, including creep and stress relaxation. The constitutive model matches the experimental data and validation experiment well.