Continuum Modeling of Energetic Materials to Interpret Atomistic and Molecular Simulations for Advanced Design
Abstract
It is proposed to develop and use continuum models in order to directly interpret the results of atomistic simulations of energetic materials. The underlying assumption and point of view taken will be that the atomistic simulations represent the exact physical system and that a continuum theory represents averages of that system. The physical and temporal scales of interest are the near-atomic scales, that for purposes of averaging atomistic (molecular dynamic or dissipative particle dynamic) simulations, are such that the stress tensor and temperature are in equilibrium. But on these scales, chemical reaction and phase transformation and other non-equilibrium processes may not be in equilibrium. Hence very small, near atomic scales on the orders of fraction of nanometers and time intervals on the scale of picoseconds or less, can be used effectively to generate the appropriate continuum averages. The recently ONR funded effort at UIUC has led to the development of a very powerful, and consistently formulated continuum model for multi-component, reacting mixtures, that assumes that all the components of reactants and decomposition products can be represented by Gibbs potentials. The UIUC model can simultaneously simulate phase transitions, chemical reaction, species diffusion, and is formulated in a three-dimensional, frame-invariant (tensoral) fashion. Thus it can be used to model known anisotropic properties of solid crystalline reactants. Work was also carried out to show how such a model could employ reduced kinetics and can be used to describe averaged atomistic simulations in a consistent way. The UIUC focus on using continuum modeling, with atomistics as the exact physical system, should lead to a new modeling tool for understanding the results of atomistic simulations, and thus enable molecular design of advanced energetic materials that meet specified requirements. The current implementation of the UIUC continuum model will be modified by making direct comparisons of the results of the model simulations to results obtained by averaging of atomistic simulation, with no model. Thus the current UIUC model can be regarded as a first approximation to a near-atomic scale continuum model, and the modification will lead to adding a stochastic component. Previous work at UIUC, generated sub-models and simulation codes that will be used to great effect in the next phase of the proposed effort. The new 3-year effort focuses on three types of energetic materials that are representative and span the Navy s needs and interests: A sensitive high performance explosive like RDX, an insensitive high performance explosive like TATB or FOX-7 with strong anisotropic properties, and a new energetic high performance high oxygen material, Nitryl Cyanide (recently synthesized by the Christie group at University of Southern California. The effort at UIUC will mainly focus on continuum modeling but will also include atomistic simulations carried out with Dr. Sanatanu Chaudhuri of the UIUC Applied Research Institute. In addition UIUC plans on extensive collaboration with other atomistic simulation research groups. The UIUC effort is described in brief by three principle tasks. I) Continued development of a continuum model that faithfully reproduces the averages of atomistic simulations. II) Continuum and atomistic simulations that study the effects of mechanical and thermal initiation of chemistry. III) Macroscopic simulations of the continuum model on dimensions that are at least on the order of microns.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 10, 2016
- Source ID
- N000141612057
Entities
People
- D. Scott Stewart
Organizations
- Office of Naval Research
- United States Navy
- University of Illinois Urbana–Champaign