Local failure initiation mechanisms, such as the nucleation and propagation of multiple cracks, have been investigated in energetic aggregates with a viscoelastic estane binder and crystalline RDX grains that have been subjected to dynamic thermo-mechanical loading conditions. A dislocation density-based crystalline plasticity, finite viscoelasticity, dynamic fracture nucleation and propagation, and non-linear finite-element formulations were used to study crack nucleation and propagation due to dynamic, tensile mechanical strain-rate loading conditions in RDX-Estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal-binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, and viscous dissipation heating to fundamentally understand and predict aggregate behavior and local failure initiation mechanisms. The predictions indicate that local failure occurs when cracks nucleate at the peripheries of internal porosity and subsequently propagate toward the viscoelastic estane binder where crack arrest occurs at the interface, which results in large inelastic deformations and temperature accumulations at the interfaces.