Ignition criterion and safety prediction of explosives under low velocity impact

Abstract

Due to the complexity of impact-induced reaction, it is difficult to predict and evaluate the ignition and safety of explosives under low velocity impact. Plastic deformation is very important to explosive ignition under impact loading. At low strain rates, plastic deformation can be treated as an isothermal process. The deformation under high-strain-rate is usually seen as an adiabatic process, and the deformation work is transformed into heat with the attendant temperature increase of the explosive. In this paper, we proposed an ignition criterion in terms of effective plastic work and specific plastic power to predict the ignition of explosives under low velocity impact. The plastic work begins to accumulate, when the specific plastic power (i.e., the plastic strain rate) in a local region meets a threshold value; and when the plastic work is sufficient enough, the ignition occurs. The criterion parameters are determined by numerical simulation using LS-DYNA. Numerical simulation is compared with experimental data in order to calibrate the numerical model. The threshold values of this ignition criterion for different configurations are determined. In order to evaluate the validity of the criterion, the predictions of the ignition time, ignition zone, threshold velocities in Steven test with different PBX size designs and various projectiles, as well as the ignition threshold conditions in a modified drop weight test, Susan test, and Spigot test, are carried out. The predicted results show a good agreement with experimental results, and the errors of the ignition threshold are less than 15% for all the experimental configurations.

Non‐Shock Ignition Probability of Octahydro‐1,3,5,7‐Tetranitro‐Tetrazocine‐Based Polymer Bonded Explosives Based on Microcrack Stochastic Distribution

“…Experiments have shown how sample size affects ignition in the Steven test [14][15]38]. Here, we discuss how the sample radius and thickness affect ignition.…”

“…However, if we consider the ignition probability from 5 % to 99 %, the impact velocity ranges from 42 to 44.6 m/s, which is comparable to the experimental result (43 to 45 m/s). Some researchers have pointed out that the plastic work rate is critical for ignition proposed an ignition criterion involving plastic work and a high plastic work rate. The threshold of the plastic work rate was considered as upper and lower values, which gave a range of ignition impact velocity.…”

“…The test focuses on the impact velocity threshold of ignition. Gruau et al [16] and Ma et al [15] found that, in view of experiments, the velocity threshold was not unique but covered a range spanning from the highest nonreactive velocity to the lowest reaction velocity. Moreover, Ma et al [14] demonstrated that, even for different sample sizes, the velocity threshold still covered a certain range.…”

“…Moreover, Ma et al [14] demonstrated that, even for different sample sizes, the velocity threshold still covered a certain range. Although Ma et al [15] developed a dual criterion for ignition based on work with plastics to predict the velocity range, they could not determine the intrinsic mechanism behind the uncertainty in velocity. Thus, the confined Steven test is an effective tool to validate our current work of developing a framework for predicting the ignition probability and to determine the relationship between ignition probability and the stochastic microcrack distribution.…”

“…Experimental velocity (m/s) [15] ϕ98 mm × 13 mm 41-45 crack is given in millimeters. Note that the real distribution of the initial microcrack size is unknown and is beyond the scope of the present discussion.…”