Ignition criterion and safety prediction of explosives under low velocity impact

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.