Effects of dynamic loading and temperature on NEPE propellant: damage and ignition analysis

We investigate herein the thermo-mechanical behavior of nitrate ester plasticized polyether (NEPE) propellants under dynamic, nonshock loading scenarios, such as impacts and drops, which are vital for assessing the safety of solid rocket motors. Using a split Hopkinson pressure bar (SHPB) apparatus, we performed dynamic loading tests on NEPE propellant samples at high strain rates (4000, 5100, and 6000 s-1) and various temperatures (228, 298, and 318 K). High-speed cameras captured the deformation, fracture, ignition, and combustion stages under these conditions. Results indicate that both the mechanical properties and ignition behavior of the propellant are significantly affected by strain rate and temperature. The propellant demonstrated nonlinear elastic deformation, with both ultimate stress and strain increasing with strain rate and decreasing with temperature. During dynamic loading, samples underwent stages of uniform and nonuniform deformation, fragmentation, and for some, ignition, which was more prompt and intense at higher strain rates and temperatures. High-speed footage, along with optical and scanning electron microscopy, revealed friction among ammonium perchlorate particles as the primary ignition catalyst, presenting as shear flow on a macroscopic level. This investigation underscores the complex interplay between strain rate, temperature, and mechanical integrity in the safety and performance of high-energy propellants.