[SY-E3] Role of cracks, voids and interfaces in hot spot formation and initiation of energetic materials
Invited
The chemical initiation of high-energy (HE) materials following mechanical insults requires the excitation of chemical bonds with lengths of a few angstroms and sub-picosecond vibrational periods. This would be a nearly impossible task were it not for: i) the materials’ microstructure that localizes the input energy into hotspots, and ii) the equilibration of inter- and intra-molecular degrees of freedom that transfers input energy to the high-frequency bond vibrations responsible for chemistry. Thus, a predictive understanding of the response of HE to strong mechanical insults requires identifying, characterizing and modeling coupled processes at the microstructural level (interfacial friction, cracks, void collapse), crystal level (dislocations and shear bands) and the molecular/electronic level (inter- and intra-molecular energy transfer and chemical reactions).
While our large-scale molecular dynamics (MD) simulations recently provided an atomic picture of the formation of a steady deflagration wave following shock loading of a defective HE crystal, such simulations cannot capture the complex microstructure of the materials of interest nor the size of the hot spots of interest in real applications. Thus, we developed a multiscale model that combines large-scale reactive and non-reactive MD simulations with a continuum model capable of describing dynamical loading, plastic deformation, fracture and friction, together with thermal transport and chemistry. The MD simulations provide insight and parameters to characterize energy localization as shock waves interact with several pre-existing defects, including cracks and voids as well as interfaces. In addition, reactive MD simulations are used to characterize thermal transport and develop chemical kinetics models. These results inform the continuum model that is used to predict energy localization in microstructurally complex systems of plastic bonded energetic formulations. These simulations enable us to characterize the relative potency of various microstructural features to general hot spots that can result in sustained chemistry. Both the atomistic and continuum simulations are validated against experiments capable of capturing the physics of interest at scales matching those of the simulations.
While our large-scale molecular dynamics (MD) simulations recently provided an atomic picture of the formation of a steady deflagration wave following shock loading of a defective HE crystal, such simulations cannot capture the complex microstructure of the materials of interest nor the size of the hot spots of interest in real applications. Thus, we developed a multiscale model that combines large-scale reactive and non-reactive MD simulations with a continuum model capable of describing dynamical loading, plastic deformation, fracture and friction, together with thermal transport and chemistry. The MD simulations provide insight and parameters to characterize energy localization as shock waves interact with several pre-existing defects, including cracks and voids as well as interfaces. In addition, reactive MD simulations are used to characterize thermal transport and develop chemical kinetics models. These results inform the continuum model that is used to predict energy localization in microstructurally complex systems of plastic bonded energetic formulations. These simulations enable us to characterize the relative potency of various microstructural features to general hot spots that can result in sustained chemistry. Both the atomistic and continuum simulations are validated against experiments capable of capturing the physics of interest at scales matching those of the simulations.