Continuum and molecular dynamics simulations of pore collapse in shocked β-tetramethylene tetranitramine (β-HMX) single crystals

Abstract

The collapse of pores plays an essential role in the shock initiation of high energy (HE) materials. When these materials are subjected to shock loading, energy is localized in hot-spots due to various mechanisms, including void collapse. Depending on the void size and shock strength, the resulting hot-spots may quench or evolve into a self-sustained deflagration wave that consequently can cause detonation. We compare finite element (FE) and non-reactive molecular dynamic (MD) simulations to study the formation of hot-spots during the collapse of an 80 nm size void in a β-tetramethylene tetranitramine energetic crystal. The crystal is shocked normal to the crystallographic plane (010), applying boundary velocities of 0.5 km/s, 1.0 km/s, and 2.0 km/s. The FE simulations capture the transition from viscoelastic collapse for relatively weak shocks to a hydrodynamic regime, the overall temperature distributions, especially at scales relevant for the initiation of HE materials, and the rate of pore collapse. A detailed comparison of velocity and temperature fields shows that the MD simulations exhibit more localization of plastic deformation, which results in higher temperature spikes but localized to small volumes. The void collapse rate and temperature field are strongly dependent on the plasticity model in the FE results, and we quantify these effects.

Strongly Anisotropic Thermomechanical Response to Shock Wave Loading in Oriented Samples of the Triclinic Molecular Crystal 1,3,5-Triamino-2,4,6-trinitrobenzene

“…By contrast, in many single-crystal shock experiments, the impact planes correspond to lower-index surfaces. − Therefore, understanding the anisotropic single-crystal shock response along a generalized direction is critical for connecting atomistic simulations to experiments. It is also highly important for the reliable formulation and parameterization of continuum mesoscale models which increasingly are being used to simulate the single-crystal and grain-scale response of pressed powder aggregates and polymer composites. − The recently reported generalized crystal-cutting method (GCCM) enables the construction, in principle, of two-dimensionally (2D) periodic cells suitable for MD simulations of shock wave propagation normal to any desired plane in crystals with an arbitrary space group and asymmetric unit.…”

Predicted Melt Curve and Liquid Shear Viscosity of RDX up to 30 GPa

“…[a] M. P. Kroonblawd length and time scales has recently been used to calibrate and validate grain scale model terms through direct comparison [25][26][27][28][29][30][31]. Despite the promise of a one-and-done approach to calibration through scalebridging simulations, it is often more advantageous to gradually increase grain scale model complexity and independently determine physics terms due to the highly coupled and nonlinear nature of dynamic material response [24,28,29].…”

A Hotspot’s Better Half: Non-Equilibrium Intra-Molecular Strain in Shock Physics

“…The pore collapse simulation resulted in a hydrodynamic collapse and significant energy localization, as is expected for strong shocks with a particle velocity of 2 km/s. 23,28,41,42 Hotspot formation from pore collapse involves the expansion of the material near the upstream surface of the pore, followed by reshock against the opposite surface until complete volumetric collapse at time t 0 . Recompression and shear deformation results in substantial local heating and loss of crystalline order.…”