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Talk Abstract:
Modeling
Energetic Materials that Change from Solid to Liquid to Gas
to Burnt Vapor
D.
Scott Stewart
Theoretical and Applied Mechanics
University of Illinois, Urbanaa 61801
dss@uiuc.edu
The ignition of energetic materials, such as explosives and
propellants, when subjected to low speed impacts at velocities
on the order of 100-200~m/sec, requires the study of models
that fully take into account the solid nature of the materials.
Unlike the hydrodynamic models that describe shock-to-detonation
transition and are appropriate for higher impact speeds, the
models for lower speed impact exhibit a much greater degree
of complexity due to the large number of mechanisms available
within the material by which energy can be transformed and localized.
The simplest hydrodynamic models have energy advection, potential
energy storage in the pressure, and energy release by virtue
of chemical reaction. In contrast, a model for an energetic
material that begins as a solid must account for the same mechanisms
and for dissipative processes associated with more complex stress
distributions, phase transformations, heat conduction, and other
localized processes. Such a model is intrinsically more complex
with many more distinct length and time scales than its simple
hydrodynamic counterpart.
In a recent effort with G. A. Ruderman and Eliot Fried we have
applied the tools of continuum thermomechanics to develop a
thermodynamically consistent model of an energetic material
like HMX, that has three states, solid, liquid and gas and can
undergo chemical reaction. This model describes the phase transitions
with phase-field modeling in the sense of Gurtin and Fried's
prior works. Thermomechanically consistent rate laws are obtained
for chemical reaction and phase transitions and these evolution
equations are solved simultaneously with the standard balance
laws.
In work with Ruderman and J. Yoh, we have started to explore
the behavior of this model in various limiting cases when the
equations of motion can be reduced to time dependent equations
with one space dimension. This includes one-dimensional shear
loading (representative of shear bands), and one-dimensional
longitudinal compression loading (piston impact), and spherical
geometries as well such as the ignition of HMX by expanding
hot inert gases from initiating center. We will also talk briefly
about issues associated with the numerical simulation of multi-material
interactions in the context of studies of igniton.
Back to Workshop Schedule
Back to High-Speed Combustion in Gaseous and Condensed-Phase
Energetic Materials
1999-2000
Reactive Flow and Transport Phenomena
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