Characteristics of Fragment Impacting Steel Cover at High Speed to Initiate Heated Explosives

The temperature of the explosive has a great influence on its shock initiation sensitivity. The response characteristics of the heated explosive under fragment impact is a concern for the safety of the explosive. In order to study the initiation characteristics of heated explosives subjected to fragment impact, an experimental device that uses the shaped charge to generate the high-velocity fragment (2599 m/s) to impact the cover to initiate the heated explosive was designed in this paper. This method achieves uniform temperature control of explosives via heating the upper and lower ends and preserves heat on the side of the explosive charge. We experimentally tested the method on hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)-based aluminized explosives (61 wt.% RDX, 30 wt.% Al, 9 wt.% binder) at different temperatures. The fragment impact behavior and explosive detonation wave growth were observed via X-ray photography. A numerical model of fragment initiating explosive, which considered the temperature change of the explosive, was set up, a numerical simulation of the explosive charge initiated by fragment impacting the cover was carried out, and the reaction degree of explosive impacted by fragment and its change with temperature were analyzed. The study found that the precursor shock wave formed by the fragment impacting the cover initiated the explosive, and the explosive temperature greatly influences the fragment initiation process. Through the numerical simulation calculation of the explosive charge initiated by fragment impact under different cover thicknesses and temperatures, the relationship among the critical cover thickness, the run-to-detonation distance and explosive temperature was given. In the temperature range of 25 °C–111 °C, the shock sensitivity of RDX-based aluminized explosives under fragment impact decreases with the increase of explosive temperature, while in the temperature range of 111 °C–170 °C, the sensitivity increases with the increase of explosive temperature.