Prediction of probabilistic ignition behavior of polymer-bonded explosives from microstructural stochasticity

Abstract

Random variations in constituent properties, constituent distribution, microstructural morphology, and loading cause the ignition of explosives to be inherently stochastic. An approach is developed to computationally predict and quantify the stochasticity of the ignition process in polymer-bonded explosives (PBXs) under impact loading. The method, the computational equivalent of carrying out multiple experiments under the same conditions, involves subjecting sets of statistically similar microstructure samples to identical overall loading and characterizing the statistical distribution of the ignition response of the samples. Specific quantities predicted based on basic material properties and microstructure attributes include the critical time to ignition at given load intensity and the critical impact velocity below which no ignition occurs. The analyses carried out focus on the influence of random microstructure geometry variations on the critical time to ignition at given load intensity and the critical impact velocity below which no ignition occurs. Results show that the probability distribution of the time to criticality (tc) follows the Weibull distribution. This probability distribution is quantified as a function of microstructural attributes including grain volume fraction, grain size, specific binder-grain interface area, and the stochastic variations of these attributes. The relations reveal that the specific binder-grain interface area and its stochastic variation have the most influence on the critical time to ignition and the critical impact velocity below which no ignition is observed. For a PBX with 95% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine content, the computationally predicted minimum impact velocity for ignition is in the range of 54–63 ms−1 depending on microstructure. This range is comparable to values measured experimentally for PBX9501 (53 ms−1 by Chidester et al., “Low amplitude impact testing and analysis of pristine and aged solid high explosives,” in Eleventh (International) Symposium on Detonation, ONR (1998), 33300. 60–84 ms−1 by Gruau et al., “Ignition of a confined high explosive under low velocity impact,” Int. J. Impact Eng. 36, 537–550 (2009)).