Shock Initiation in RDX Crystals from Nanovoid Collapse

Area of Science:

• Computational materials science
• Chemical kinetics
• Shock physics

Background:

• Shock initiation in energetic crystals involves complex pressure-shear fields coupling mechanics and chemistry.
• Understanding these non-equilibrium processes is crucial for materials safety and performance.

Purpose of the Study:

• To develop and apply a first-principles neural network potential (NNP) for high-fidelity nanoscale shock simulations of RDX.
• To elucidate the earliest chemical reactions triggered by nanovoid collapse under shock.

Main Methods:

• Development of a first-principles neural network potential (NNP) for RDX.
• Nanometer-scale shock simulations of RDX nanovoid collapse.
• Analysis of reaction front dynamics, vortex structures, and high-pressure reaction pathways.

Main Results:

• The NNP predicts a thinner, coherent reaction front stabilized by a counter-rotating vortex pair, delaying bulk conversion but intensifying rim mechanochemistry.
• Increasing piston speed enhances shear localization and accelerates downstream conversion.
• High-pressure analysis reveals pressure-reordered reaction pathways, favoring N-NO2 scission and intermolecular O-transfer over HONO elimination.

Conclusions:

• Establishes a mechanistic link between vortex-controlled shear localization and pressure-dependent reaction pathways in shock initiation.
• Highlights the capability of first-principles NNPs for predictive modeling of shock-induced chemistry in energetic materials.