The Development of a Confined Impact Test for Evaluating the Safety of Polymer-Bonded Explosives during Warhead Penetration

During warhead penetration, which lasts several milliseconds, warheads undertake moderate pressures reaching hundreds of MPa. Previous methods have been unable to mimic such stimuli to evaluate the safety of ammunitions. Hence, new safety evaluation methods with moderate pressures and long durations to assess the stability of the explosive charges during actual penetrations are needed. Based on existing explosives safety estimation technologies and preliminary understanding of overload environments during penetration, a confined impact model was developed. The peak stimuli pressure is more than 0.3 GPa and the duration of the pressure is between 1 to 3 milliseconds. Various scales of a polymer-bonded explosive (PBX-9) were subjected to this confined impact test to study the response characteristics. The ignition mechanism of PBX-9 was obtained by synthesizing results from X-ray photoelectron spectroscopy (XPS), computed tomography (CT) scanning, differential scanning calorimetry (DSC) and thermalgravimetric analysis (TG). It was found that cracks formed on the surface during impact and the initial ignition of PBX-9 is mainly due to the decomposition of Ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB) on the interface at low temperature. Our study indicates that the designers of the PBX formulation should try to control the early decomposition of AP and HTPB in order to let the PBX survive the penetration.