Void Collapse in Shocked ‐HMX Single Crystals: Simulations and Experiments

Abstract

Heat generation in the vicinity of a void during shock compression plays a key role in the initiation of energetic materials. The shock response of a single β ‐HMX crystal with a single void is studied with simulations that include plasticity and heat transport. The numerical results are validated with an experiment in which a 500 μ m void is machined in an HMX single crystal and impacted. Experiments and simulations of the dynamical evolution of the morphology of the void during the collapse and the rate of the area are in very good agreement for weak shocks.

Complete Equations of State for Cyclotetramethylene Tetranitramine

“…Owing to the clear dependences between structure and sensitivity in explosives [6], it is highly desirable to be able to simulate the thermomechanical responses of explosives under impact conditions, particularly in the case of weak shocks where material strength plays an important role [7][8][9]. Such simulations could allow us to understand and quantify which characteristic features of the microstructures control the localization of deformation and heat generation [10][11][12]. The length and time scales most pertinent to hot spot formation and the interaction between shock waves and microstructure are beyond those accessible to atomic-scale molecular dynamics simulations.…”

Plastic Dissipation and Hot‐Spot Formation in HMX‐Based PBXs Subjected to Low Velocity Impact

“…Rapid gas compression is compensated by thermal conduction and the first endothermic reaction of the HMX [4, 13]. Observed for impact velocities of 1 km/s [4, 11, 14], the phenomenon of “jetting” is unlikely at low velocities due to the small pore size [15].…”

“…The role of friction is also addressed by a third approach based on a damage phase field to describe the appearance and evolution of cracks [13,15,16,27,28]. This method allows (1) to replicate the damage observed during impacts on single crystals [18,28] and (2) to reproduce the initiation threshold of the β-HMX single crystal observed at 445 m/s [16,29].…”

“…This literature review shows that two mechanisms contribute to the appearance of hot spots: friction and plastic strain. Studies on PBX 9501 show that (1) plasticity alone, within a polycrystal, would not be effective in initiating chemical decomposition [20] and that (2) friction in cracks would allow thermal initiation of the material [15,24,25,28]. However, data obtained on X1 during low speed impacts show that the material first deforms by plastic yielding.…”

“…Similarly, the simulation of the plastic collapse of a pore in a single crystal with anisotropic behavior allows to find strain localization phenomena, such as shear bands, and strong heating for impact speeds greater than 1 km/s [11, 14]. Anisotropic crystal plasticity models reveal the crystal directions that promote plastic dissipation [9, 13, 15, 17]. They explain the threshold variations observed as a function of the orientation of the single crystal β‐HMX during impacts [18].…”