| Hot spot formation and failure mechanisms, such as dynamic fracture and shear strain localization, for RDX (cyclotrimethylene trinitramine)-polymer binder aggregates were investigated for dynamic thermo-mechanical loading conditions. A formulation based on a dislocation-density based crystalline plasticity and a finite viscoelasticity framework was coupled to a microstructurally-based dynamic fracture nucleation and propagation method, and it was used to investigate interrelated high strain-rate failure modes in RDX-polymer binder energetic aggregates. The effects of grain boundary (GB) misorientations, porosity, grain morphologies, dislocation densities, and crystal-binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, thermal conduction, and dissipated heat to predict and understand hot spot formation for a PCTFE (Polychlorotrifluoroethylene) polymer binder. The validated predictions indicate that hot spots were induced by inelastic deformation modes, which resulted in unbounded temperatures due to localized plasticity and thermal decomposition at the peripheries of the voids.;Viscous dissipation, due to the estane polymer binder, where the operating temperatures were above the glass transition temperature, resulted in RDX crystal interactions due to hydrostatic compression of the polymer binder. This hydrostatic compression constrained the polymer binder interfaces, which enhanced RDX inelastic deformation modes and resulted in and accelerated hot spot formation at the RDX crystal peripheries in the interfacial regions between the estane binder and the RDX crystals.;The effects of dynamic crack nucleation and propagation were also investigated in energetic aggregates subjected to high strain rate loading conditions. The fracture approach was based on an overlapping elements method, and cracks were nucleated on preferential cleavage planes. Cracks nucleated from the peripheries of the voids and propagated towards the RDX-estane interfaces, where they were arrested. Large accumulations of plasticity occurred, at the RDX-estane interfaces, where the cracks were arrested, and this subsequently resulted in hot spot formation. Bicrystals with random low and high angle grain boundary (GB) misorientations were also investigated to further understand dynamic crack propagation and arrest at RDX-estane interfaces. For low angle GB misorientations, a pre-existing crack propagated towards the binder and was arrested at the interface due to low stresses in the binder, with little inelastic deformation occurring near the crack front. For high angle GB misorientations, the pre-existing crack propagated towards the interface, but was arrested due to crack front plasticity and dislocation-density accumulation.;The analyses, from this study, have been used to predict hot spot formation, shear strain localization, dynamic crack nucleation, propagation, and arrest in RDX-estane energetic aggregates, which have been subjected to dynamic, thermo-mechanical loading conditions. These predictions indicate that hot spot formation and dynamic failure nucleation, propagation, and arrest can be controlled through the optimization of dominant microstructural characteristics, such as RDX crystal and GB orientations, estane interfaces and distributions, and porosity. |
