Experimental Characterization and Modeling of Intermediate Strain-Rate Tensile Behavior in Automotive Thermoplastics

Abstract Thermoplastic polymers are increasingly adopted in automotive applications due to their compatibility with high-volume manufacturing, reduced weight, and improved processing efficiency. However, their mechanical response at intermediate strain rates (1-100 s−1), representative of crash conditions, remains insufficiently understood. In particular, large pre-yield deformations and post-yield instabilities limit the applicability of conventional test methods, resulting in a lack of reliable tensile data and constitutive models for accurate impact simulations. To address this gap, a symmetric, double-acting drop-weight impact apparatus was employed to characterize the intermediate strain-rate tensile behavior of five automotive-grade thermoplastics. Baseline rate sensitivity was established through quasi-static testing at four strain rates, followed by dynamic tests conducted at drop heights of 10, 20, and 25 inches. Drop height was selected as the control parameter, as the achieved strain rate varied with polymer morphology. Digital image correlation confirmed a homogeneous strain field across the gauge length for all materials, demonstrating the reliability of the test configuration. The results indicate increasing tensile strength and decreasing failure strain with increasing strain rate, with material-specific trends governed by microstructural differences. Strain-rate sensitivity was quantified using strain-averaged power-law relationships calibrated directly from experimental data. Together, the experimental methodology and constitutive modeling provide a robust framework for incorporating intermediate strain-rate effects of thermoplastics into impact-critical design and simulation tools.