Multiscale Modeling of HMX: Calibration of Mesoscale Model Parameters using Molecular Scale Modeling and Simulation Project
Abstract
Energetic materials are compounds which, when subjected to shock loading or/and elevated temperatures decompose releasing important amounts of energy. Developing new formulations of such materials as well as gaining control over the sensitivity of existing materials requires performing multiscale modeling that links physics taking place of multiple scales. In particular, the prediction of hot spots requires accounting for nanoscale processes and for the complexity of the mesoscale structure of the material. The proposed work aims to establish the link between models of nanoscale processes and crystals plasticity models that are used to represent crystal mechanics at the mesoscale. This will fill the gap in our current understanding of the physics that controls various parameters entering the constitutive description used in mesoscale models and of the actual magnitude of these parameters, and will improve the accuracy and reliability of such models. These, in turn, can be used to predict hot spot formation which would allow controlling the sensitivity of polymer bound explosives. The proposed work focuses on the most important polymorphs of HMX, the and phases. Specifically, we will use atomistic simulations to identify: (i) the active slip systems and the critical resolved shear stress required to move dislocations in these systems, (ii) the dependence of the critical stress on temperature, (iii) the energetic barrier for slip system activity and its dependence on the applied stress, (iv) presence of non-Schmid effects, (v) the likelihood and critical conditions for cross-slip of dislocations, (vi) the effect of RDX impurities in HMX on bulk material properties and on dislocation mobility and critical stress, (vii) the critical conditions for twinning including the required stress and activation energy, as well as the interaction of dislocations with twins. The proposal outlines how this information can be used to calibrate crystal plasticity models. It should be observed that the same information also allows calibrating dislocation dynamics models, which are defined on scales between that of atomistic simulations and the scale at which crystal plasticity is relevant. As an extension of the main proposed work and in the limit of time, we will also develop coarse grained models of the atomistic HMX models which will allow modeling larger systems for longer physical times. The entire proposed work emerges from our preliminary work on similar issues in -RDX. The methods and computational tools developed in that project will be available for the proposed project. The atomistic results will be verified against ab-initio models (density functional theory) in specific cases. Also, the various material parameters evaluated with these models will be validated against results from available experiments, including plate impact and indentation.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 25, 2016
- Source ID
- FA86511610004
Entities
People
- Catalin Picu
Organizations
- Air Force Research Laboratory
- Rensselaer Polytechnic Institute
- United States Air Force