Constitutive and Dynamic Behavior of Nylon 66 Polymer Under Quasi and High Rate of Loading

The Two-Stage Light Gas Gun (TSLGG) heavily relies on nylon 66 polymer for crucial components like pistons, rupture disks, sabots, and plastic bullets, subjecting them to high-strain rate loading in experiments and impact situations. However, researchers on the dynamic sensitivity of nylon 66 polymer is scarce, leading to a significant knowledge gap. It is essential to comprehend how variables such as the L/d ratio and cross-sectional shape affect nylon 66 specimens. Therefore, investigating the dynamic behavior of nylon 66 polymers becomes a top priority. This study investigates the dynamic behavior of nylon 66 polymer focusing on energy absorption and strain rate sensitivity using the dynamic increase factor (DIF).

The methodology is used in this study based on one-dimensional elastic wave propagation, which is used to analyze elastic waves obtained from the experiments and computational results. Utilizing Ls-Dyna finite element software, numerical simulations with the calibrated Cowper-Symonds material model accurately reproduce nylon 66 polymer responses under different loading conditions, thereby confirming the validity of the model.

Quasi-static tests consistently demonstrate a compressive yield strength of 64 MPa across various L/d ratios (L/d = 1, 2, and 3), suggesting minimal effects on material strength. The nylon 66 polymer's maximum dynamic strength at an L/d ratio of 0.19 is 139.73 MPa at a strain rate of 1333 s⁻¹, indicating a 2.2 times increase compared to quasi-static strength. Results highlight that, for a given L/d ratio, nylon 66 polymer’s dynamic impact factor (DIF) increases with rising strain rates. However, for strain rates exceeding 500 s⁻¹, this trend reverses, leading to decreased properties.

Energy absorption per unit volume remains constant with increasing L/d ratio but increases at a constant L/d ratio. Various cross-sectional shapes exhibit differing sensitivities, with the pentagonal shape being the most sensitive and the square shape the least sensitive in terms of energy absorption and DIF.