Simulating the Effects of Grain Surface Morphology on Hot Spots in HMX with Surrogate Model Development

Abstract

There have been several numerical studies on the collapse of internal voids in energetic grains but fewer investigations have probed grain-grain interface effects. In this study, we examine the effects of grain surface morphology and binder conditions on hot spot mechanisms during shock loading using the multi-physics hydrocode, ALE3D, coupled with the thermochemical code, Cheetah. To improve the accuracy of our grain-scale simulations, the HMX material models have been updated from previous studies to incorporate new property predictions from molecular dynamics simulations. In our simulations of the interface between two neighboring energetic grains, the upstream grain surface is described by a single sinusoid with amplitude (0.5-2 μm) and wavelength (0.5-2 μm). The effects of grain surface coating, i. e., no binder, partially coated, and fully coated with binder, is also explored. A range of shock loading pressures (10-30 GPa) is considered. Bind-er coating reduces hot spots at grain-grain interfaces by limiting plastic deformation and heating of upstream grain surfaces as well as preventing transmission of localized deformation modes (e. g., jetting) to the downstream grain. More plastic work and heating is observed with new HMX material models versus the previous models because the strength does not thermally soften as much as a result of the higher melt temperature; this also reduces vortical flow and jetting mechanisms with the new HMX material models. A surrogate model based on neural networks is developed for the early stage reaction rate. Physics-based input features improve the performance of the neural networks over basic input features alone with a root mean squared error = 1.05 μs À 1 and R 2 = 0.98. Accurate and fast-running surrogate models can effectively serve as structure-property-sensitivity relationships.

Predicted Viscosity of Liquid HMX up to 40 GPa

“…It is widely accepted that "heterogeneous" hot spot formation mechanisms that arise due to interactions between shock waves and microstructural defects such as pores are the primary driver for explosive initiation [3]. Microstructure-aware computational models that either implicitly or explicitly account for hot spots are an attractive physicsmotivated tool for component-level design and assessments [12][13][14], but parameterizing these models depends on expensive experiments and/or accurate simulations that explicitly resolve the details of hot spot physics.…”

Predicted viscosity of liquid HMX up to 40 GPa

“…It is widely accepted that “heterogeneous” hot spot formation mechanisms that arise due to interactions between shock waves and microstructural defects such as pores are the primary driver for explosive initiation [3]. Microstructure‐aware computational models that either implicitly or explicitly account for hot spots are an attractive physics‐motivated tool for component‐level design and assessments [12–14], but parameterizing these models depends on expensive experiments and/or accurate simulations that explicitly resolve the details of hot spot physics.…”