Low velocity impact experiments - On the determination of non-shock ignition thresholds of cast-cured PBX-formulations

High Explosive (HE) filled ammunition, during gun launch or impact, is subjected to intense loading scenarios which can become critical and cause unintended reaction. To experimentally investigate the sensitivity at comparable loadings the Steven test was introduced to stimulate the reaction by low-velocity impact, clearly below typical shock loads. This work describes a modified version of the test, denoted as Safety Threshold Test (STT), which is used to systematically observe the ignition start of different PBX formulations at varying impact velocities. In particular, the HMX-based cast-cured formulations HX 497, HX 522 and HX 538 were investigated. Additionally, critical test conditions and improvements obtained through the experimental campaigns are discussed. By applying an ignition criterion based on macroscopic quantities like stress and strain rate histories numerical simulations of the experiments are used to extract the critical loading condition at ignition start which is said to be the ignition threshold. By comparing the critical conditions extracted from different impact velocities the ignition threshold is validated. It can then be applied to relevant loading scenarios of ammunition to assess its safety.