APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016;
Baltimore, Maryland
Session L21: Materials in Extremes: Energetic Materials
11:15 AM–2:15 PM,
Wednesday, March 16, 2016
Room: 320
Sponsoring
Units:
GSCCM DCOMP DMP
Chair: Tariq Aslam, Los Alamos National Laboratory
Abstract ID: BAPS.2016.MAR.L21.1
Abstract: L21.00001 : Modeling the anisotropic shock response of single-crystal RDX
11:15 AM–11:51 AM
Preview Abstract
Abstract
Author:
Darby Luscher
(Los Alamos National Laboratory)
Explosives initiate under impacts whose energy, if distributed homogeneously
throughout the material, translates to temperature increases that are
insufficient to drive the rapid chemistry observed. Heterogeneous
thermomechanical interactions at the meso-scale (i.e. between single-crystal
and macroscale) leads to the formation of localized hot spots. Direct
numerical simulations of mesoscale response can contribute to our
understanding of hot spots if they include the relevant deformation
mechanisms that are essential to the nonlinear thermomechanical response of
explosive molecular crystals.
We have developed a single-crystal model for the finite deformation
thermomechanical response of cyclotrimethylene trinitramine (RDX). Because
of the low symmetry of RDX, a complete description of nonlinear
thermoelasticity requires a careful decomposition of free energy into
components that represent the pressure-volume-temperature (PVT) response and
the coupling between isochoric deformation and both deviatoric and
hydrostatic stresses. An equation-of-state (EOS) based on Debye theory that
defines the PVT response was constructed using experimental data and density
functional theory calculations. This EOS replicates the equilibrium states
of phase transformation from alpha to gamma polymorphs observed in static
high-pressure experiments. Lattice thermoelastic parameters defining the
coupled isochoric free energy were obtained from molecular dynamics
calculations and previous experimental data. Anisotropic crystal plasticity
is modeled using Orowan's expression relating slip rate to dislocation
density and velocity.
Details of the theory will be presented followed by discussion of
simulations of flyer plate impact experiments, including recent experiments
diagnosed with in situ X-ray diffraction at the Advanced Photon Source.
Impact conditions explored within the experimental effort have spanned shock
pressures ranging from 1-10 GPa for several crystallographic orientations.
Simulation results will be used to motivate conclusions about the nature of
dislocation-mediated plasticity in RDX, as well as, future directions to
improve these models and quantitatively compare them to the average lattice
response recorded with in situ X-ray diffraction.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.MAR.L21.1