The ignition of polymer-bonded explosives (PBXs) is a topic of great interest in the shock physics community. Major challenges in the development of PBXs involve determining how their microstructures affect sensitivity to ignition. Since PBX is inherently heterogeneous, a multitude of factors contribute to heat generation in the microstructure as a direct result of shock loading, including fracture, friction, viscoplastic deformation, bulk compression and pore collapse. The resulting heat generation influences the time scale of chemical reaction and influences whether the chemical reaction becomes self-sustaining, thereby leading to ignition. High-performance computing is used to analyze the effects of microstructure at the mesoscale level. A multitude of microstructures (including grains, voids, aluminum additives, Estane binder and pressed HMX) are studied in both 2-D and 3-D space. The computational framework uses a Lagrangian-based cohesive finite element model (CFEM) approach to analyze the effect of fracture and friction, as well as an Eulerian-based approach to study the effect of void collapse and detonation.
The goal of this work is to delineate the relative importance of each mechanism as it relates to ignition sensitivity. Specifically, the effects of incorporating aluminum particles as well as other microstructural changes (varying grain size, material type, constitutive behavior, etc.) is discussed. By testing a large quantity of stochastically similar samples, the effect of microstructure is analyzed from a probabilistic perspective. Finally, the thermomechanical transition from heat generation into the evolution of temperature hotspots, and eventually into the onset of chemistry, is analyzed. The results of this research provides a new understanding regarding the importance of microstructure as well as the interaction among physical mechanisms during shock loading, and will guide the future direction of PBX experiments.
