SUMMARY

The proposed research aims at understanding the conditions that lead to reaction initiation of energetic composites as they undergo mechanical and thermal processes subsequent to impact. Simulations will be carried out which will quantify the thermomechanical response of polymer-bonded explosives (PBX). The first part of this research focuses on developing a finite deformation framework, which will incorporate the effects of large deformation, thermomechanical coupling, failure in the forms of micro-cracks in both bulk constituents and along grain/matrix interfaces, and frictional heating. The cohesive finite element method (CFEM) framework involves embedding cohesive elements at all finite element interfaces to capture arbitrary fracture initiation and crack propagation. For the polymer matrix, a thermo-elasto-viscoelastic constitutive formulation shall be used which accounts for temperature dependence, strain rate sensitivity and strain hardening. In the loading regime of interest (non-shock impact loading), the HMX crystals undergo very little plastic dissipation and are hence assumed to be elastic. The second part of the proposed research focuses on the study of two phase HMX/Estane PBXs. Digitized micrographs of actual PBX materials and idealized microstructures shall be used. The research aims to understand the evolution of the various failure mechanisms as a function of microstructural attributes and loading conditions. Loading conditions that may influence the performance of PBXs are initial temperature, strain-rate, degree of confinement, angle of impact, etc. Microstructural attributes are volume fractions of different constituents, grain morphology and defects such as voids or imperfect bonding. Finally, the research will extend this framework to study microstructure with third phase aluminium particles. The framework shall serve as a useful tool for the design of energetic composites and the results can be used to establish microstructure-response relations that can be used to assess the ignition sensitivity energetic composites. Ultimately, better understanding of the initiation mechanisms will help build predictive models that will enable the efficient development of new energetic composites with desired property attributes.