Combustion crack-network reaction evolution model for highly-confined explosives

The evolution behavior of combustion crack reaction of highly confined solid explosives after non-shock ignition is governed by multiple dynamic processes, including intrinsic combustion of explosives, crack propagation, and rapid growth of combustion surface area. Here, the pressure increase can accelerate the combustion rate of explosives, and the crack propagation can enlarge the combustion surface area. The coupling between these two effects leads to the self-enhanced combustion of explosive charge system, which is the key mechanism for the reaction development after ignition. In this study, combustion crack-network (CCN) model is established to describe the evolution of combustion crack reaction of highly confined solid explosives after non-shock ignition and quantify the reaction violence. The feasibility of the model is verified by comparing the computational and experimental results. The results reveal that an increase in charge structure size causes an increase in the time of crack pressurization and extension of cracks due to the high temperature-generated gas flow and surface combustion during the initial stage of explosive reaction, but when the casing is fractured, the larger the charge structure, the more violent the late reaction and the larger the charge reaction degree. The input pressure has no obvious influence on the final reaction violence. Further, a larger venting hole area leads to better pressure relief effect, which causes slower pressure growth inside casing. Larger reserved ullage volume causes longer low-pressure induction stage, which further restrains the internal pressure growth. Furthermore, the stronger the casing constraint, the more rapid the self-enhanced combustion of the high temperature-generated gas, which results in more violent charge reaction and larger charge reaction degree during casing break. Overall, the proposed model can clarify the effects of intrinsic combustion rate of explosives, charge structure size, input pressure, relief area, ullage volume, and constraint strength on the reaction evolution, which can provide theoretical basis for violence evaluation and safety design for ammunition under accident stimulus.