Hydraulic-based testing and material modelling to investigate uniaxial compression of thermoset and thermoplastic polymers in quasistatic-to-dynamic regime

Abstract

The strain rate dependence of thermoplastics and thermosets in the range 10-3–102 s−1 is still unclear due to experimental difficulties. This interval cannot be fully treated using a quasistatic-based electromechanical machine nor a high-speed test relying on the Kolsky bar method. This paper presents a uniaxial compression test set-up to cover the aforementioned range providing robust stress–strain measurements up to 100 s−1. This set-up is assessed at room temperature with a semi-crystalline polymer (SCP) polyether-ether-ketone (PEEK) KT880-NT and a toughened thermoset epoxy PR520. High-speed 3D stereo digital image correlation (DIC) and an infra-red camera are used for data acquisition. The macroscopical true stress–strain curves demonstrate the importance of the thermal softening effect taking place in this range, accompanied with a temperature rise. In terms of characterization, an advanced unified SCP (USCP) model is employed to quantify the rate- and temperature-dependence for both polymers. A straightforward FEM-based parameter identification procedure is proposed requiring only two compressive stress–strain curves. The USCP model is further applied to PEEK 450G from literature to highlight the features of SCPs. The comparison of PEEK and PR520 is discussed pointing out the characterization challenges due to the transitional quasistatic-to-dynamic testing regime.

Keywords

• Dynamic compression
• Strain-rate dependence
• PEEK
• Epoxy
• Thermomechanical modelling
• Self-heating