Dynamic Tensile Behavior of Polyamide 6 at Different Strain Rates: Experiments and Constitutive Model

This work studies the tensile behavior of polyamide 6 (PA6) at different strain rates using both experimental and numerical methods. Quasi-static and dynamic tensile tests are performed using a universal testing machine and a split Hopkinson tensile bar (SHTB). The stress-strain curves and specimen morphologies are obtained over a wide range of strain rates from 2.6 x 10(-4) s(-1) to 900 s(-1). The tensile behavior of PA6 is sensitive to strain rate, and the yield strength and yield strain both increase with an increase of strain rate. The plastic stage of PA6 exhibits strain hardening characteristics under quasi-static loading, but strain softening characteristics under dynamic loading. The strain softening characteristics become more significant with an increase of strain rate. The quasi-static tensile mechanical responses of PA6 are analyzed by a ZWT viscoelastic constitutive model, while the dynamic ones are analyzed by a ZWT model with a damage factor. The experimental stress-strain curves are well described by the constitutive model. Three-dimensional incremental expressions of the constitutive model are given, and a user-defined constitutive subroutine is written. Numerical simulations on the stress wave propagation process and the stress-strain curves of PA6 under SHTB loading are conducted, with results that are consistent with the experiments.