On the determination of ignition thresholds of HMX-based cast-cured PBX at non-shock loads

The safety assessment of high explosive (HE) filled ammunition at critical loading conditions during gun launch or impact is based on the experimental testing of the ignition behavior at comparable conditions. The Steven test was introduced to stimulate the reaction by low-velocity impact conditions, clearly below typical shock loads. In order to reduce the number of required tests and to predict the behavior at other more complex loading scenarios ignition criteria based on continuum mechanical quantities like stress and strain rate histories can be formulated, which are then calibrated by experimentally determining a consistent ignition threshold value. This work describes the experimental setup of a modified Steven test, denoted as Safety Threshold Testing (STT), the experimental results obtained for slightly different PBX formulations and the evaluation of the reaction threshold through numerical simulations. In particular, the HMX-based cast-cured formulations HX 497, HX 522 and HX 538 were investigated. Additionally, the work critically reviews first tests to reduce the amount of PBX used in the test and presents improvements obtained through the experimental campaigns.