Sensitization and desensitization of PBXs stemming from microcrack and microvoid in responses to pressure-time loading

Comprehensively understanding the main differences exhibited in the ignition stage of high-intensity shock and low-intensity impact initiation processes of polymer bonded explosives (PBXs), including defect-related hotspot formation, ignition threshold, and sensitization or desensitization, is necessary for the safety evaluation of PBXs. The roles of shear-crack and void-collapse hotspots in the ignition for single-impacted PBXs are first studied using a physically based thermomechanical model. The variations of sensitivity for pre-impacted PBXs are further reported. Results show that a crack hotspot dominates in a low pressure range (90-200 MPa) with a relatively long ramp time (∼1.0 μs). High pressure will cause a friction-locked crack, while low pressure will lead to the insufficient frictional heating, thus resulting in a slight increase in hotspot temperature. Moreover, a long duration (∼10.0 μs) is required for satisfying the hotspot temperature-size criterion of ignition. The void hotspot dominates in high pressure (≥350 MPa) with a short ramp time (<0.1 μs). The dominant range of crack hotspots is extended (70-240 MPa) after a pre-impact load, while that of the void hotspot reduces (≥550 MPa). If the secondary loading is high-intensity shock, the explosives are desensitized due to the pre-elimination of voids. In contrast, if the secondary loading is low-intensity impact, the explosives are sensitized due to the pre-increase in crack-related damage.