Continuum Mechanical and Micromechanical Fundamentals of Mechanochemistry of Energetic Materials
Shear stress and shear banding are suggested by many investigators as possible sources of ignition in energetic materials and explosives. A three-year program is proposed to develop continuum mechanical and micromechanical fundamentals of mechanochemistry of energetic materials, new analytical and computational methods, and to investigate and systematize possible new reasons for shear stress and strain initiation of explosives. We will concentrate on plastic bonded explosives (e.g. PBX-9501) which consist of HMX energetic crystals connected by a polymer binder. The objectives of the research proposed are as follows:
1. To develop a systematic multiscale continuum thermodynamic, kinetic and micromechanical theory for stress- and strain-induced chemical reactions (CR) and phase transformations (PT) in energetic materials allowing for thermodynamic and kinetic coupling between CR, shear stress and large plastic strains, temperature and pressure. New analytical and numerical methods for CR and PT in inelastic materials will be developed.
2. To study analytically and numerically some typical problems for modeling of PT and CR at the microscale and mesoscale under various prescribed stress tensors. These problems include: a) Nucleation and growth of the d phase inside of the b phase matrix; b) Nucleation of the gas phase during sublimation and CR inside the HMX crystal or at the boundary with the binder, as well as in existing and collapsing voids; c) Multistage PT and CR.
3. To investigate analytically and numerically reaction-induced plasticity and transformation-induced plasticity phenomena in the shear band at micro-, meso-, and macroscales, and their effect on the thermodynamics and kinetics of CR and PT (as positive mechanochemical feedback), as well as on the mechanical behavior of energetic materials (as the new deformation mechanism).
4. To conduct multiscale finite element modeling and description of experiments on combined shear-pressure ignition and initial post-ignition processes in explosives. Material parameters and loading conditions responsible for shear sensitivity of explosives will be found.
