SDT Behavior of Functionally Graded Energetic Materials (FGEM)

The behavior of energetic materials is significantly influenced by the spatial distributions of microstructure heterogeneities and voids. We propose the concept of Functionally Graded Energetic Materials (FGEM) whose microstructure features (grain size, grain volume fraction, void size, and void volume fraction) change spatially such that they may allow the behavior of the materials to be tailored. Here, we use gradients in the density of voids to alter the detonation behavior of a polymer-bonded explosive with attributes echoing those of PBX9501. Three-dimensional mesoscale simulations are carried out. Microstructures are designed to have different void densities and void density gradients. The analyses focus on the shock-to-detonation transition (SDT) behavior and the run distance. Four cases with different graded microstructures are considered. An HVRB model is used to account for the decomposition of the HMX crystals. The calculations show that the gradient of the void density significantly affects the run distance, the propagation of the shock and reaction fronts, and the rate at which the SDT transition is achieved. Overall, the findings point out that microstructure feature gradients can be viable variable for manipulating the behavior of energetic materials.