Dynamic Responses and Initial Decomposition under Shock Loading: A DFTB Calculation Combined with MSST Method for...

Area of Science:

• Materials Science
• Chemistry
• Computational Physics

Background:

• The decomposition mechanism of high melting explosive (HMX) under extreme conditions remains incompletely understood.
• An intrinsic understanding of the mechanical and chemical processes initiating HMX decomposition is lacking.

Purpose of the Study:

• To explore the microscopic dynamic response and initial decomposition of beta-HMX under shock conditions.
• To elucidate the initial reaction mechanism of HMX by analyzing bond length and charge transfer evolutions.

Main Methods:

• Utilized the self-consistent-charge density-functional tight-binding method (SCC-DFTB).
• Employed the multiscale shock technique (MSST) to simulate shock conditions.
• Analyzed bond length changes, charge transfer, and molecular dynamics.

Main Results:

• The C-N bond near major axes exhibits lower compression sensitivity and higher stretch activity.
• Charge transfer occurs from N-NO2 groups and H atoms to C atoms during initial compression.
• The primary reaction initiates with the fission of the molecular ring at the C-N bond near major axes.
• Subsequent ring breaking promotes intermolecular interactions and cleavage of C-H and N-NO2 bonds.
• Dynamic response is significantly influenced by the angle between chemical bonds and shock direction.

Conclusions:

• The initial decomposition of beta-HMX under shock is governed by the C-N bond's response near major axes.
• Molecular vacancy and surface effects influence the shock-induced decomposition pathway.
• Understanding bond-angle-dependent dynamic response is key to predicting HMX behavior under extreme conditions.