Shock compression and spallation of polyamides 6 and 66

Abstract

Polyamide 6 (PA6) and polyamide 66 (PA66) are widely used engineering polymers for high-speed applications, and yet their behaviors under extreme impact loading remain unclear. We systematically investigate their dynamic responses through plate impact experiments, and measure their Hugoniot equations of state (shock adiabats) and free-surface velocity histories up to peak shock stress of $\sim$1.6 GPa. The postmortem samples are characterized with synchrotron X-ray computed tomography. Quadratic and linear shock velocity–particle velocity relations are obtained for PA6 and PA66, respectively. Spall strength remains nearly constant for both PA6 and PA66 (approximately 0.18 GPa and 0.23 GPa, respectively) up to peak shock stress of 1.1 GPa. PA6 and PA66 demonstrate ductile and brittle fracture characteristics under high strain rate tension, respectively. The influences of chain conformations and hydrogen bond density on the dynamic mechanical properties and underlying damage mechanisms are elucidated. These differences in dynamic responses of PA6 and PA66 can be attributed to rearrangement and breakage of polymer chains, significantly influenced by varying hydrogen bond frequencies. This study contributes to understanding the connections between hydrogen bond density, chain conformation, and bulk mechanical properties in polyamides, and can be useful for advancing their applications in protective and structural materials.