Probing the mechanism underlying preshock desensitization of heterogeneous explosives via meso-resolved simulations

To analyze the mechanism underlying preshock desensitization of heterogeneous explosives, two-dimensional, meso-resolved simulations were conducted to capture the shock-to-detonation transition (SDT) process in mixtures of liquid nitromethane (NM) with air-filled cavities. These simulations explicitly consider temperature-dependent Arrhenius chemical kinetics and a statistically significant number of heterogeneities, without relying on phenomenological models to account for the meso-scale effects of these heterogeneities. The simulations successfully capture the preshock desensitization phenomenon in heterogeneous explosives. For a weak preshock (where the timescale of cavity collapse is similar to the characteristic time that the preshock sweeps through the cavity), the double-shocked heterogeneous NM mixture exhibits a significantly longer SDT time (i.e., quantified as detonation overtake time tot) than in the single-shock scenario with the same post-shock pressure, indicating preshock desensitization occurs. The fact that the cavities are collapsed by the preshock and the lower post-shock temperature indicates that preshock desensitization is governed by a combined mechanism of mesoscale heterogeneity removal and a lower post-shock temperature. Both partially and fully desensitized effects are observed. In the partially desensitized case, no hot spots are formed behind the preshock, and the SDT process is initiated by the second shock. In contrast, the fully desensitized effect exhibits minimal occurrence of strong chemical reactions behind the second shock, with an SDT being triggered after the shock coalescence. There is critical threshold of post-shock temperature behind the second shock that can achieve SDT before shock coalescence under a weak preshock, distinguishing partially vs fully desensitized effects. The critical threshold value mentioned above is likely to be equal to the critical initiation temperature (rather than pressure) in homogeneous NM under single-shock scenarios.