2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session H11: Focus Session: Simulations of Matter at Extreme Conditions II
8:00 AM–11:00 AM,
Tuesday, March 22, 2005
LACC
Room: 153C
Sponsoring
Units:
DCOMP DMP GSCCM
Chair: Stephane Mazevet, LANL
Abstract ID: BAPS.2005.MAR.H11.13
Abstract: H11.00013 : Anharmonic Materials and Thermoelasticity at High Temperatures and Pressures
10:48 AM–11:00 AM
Preview Abstract
Abstract
Authors:
Daniel Orlikowski
Randolf Q. Hood
Per Soderlind
John A. Moriarty
(LLNL, Livermore, Ca 94551)
For large-scale constitutive strength models, the shear modulus
is typically
assumed to be linearly dependent on temperature.
However, for materials compressed along or beyond the Hugoniot
into high pressure and temperature regimes where there is
no experimental measurement or very little, accurate and validated
models must be used. To this end, we have investigated and compared,
as a function of temperature ($<$26,000 K) and pressure ($<$10 Mbar),
the anharmonic and quasi-harmonic thermoelasticity
accounting for both the electron-thermal and ion-thermal
contributions for bcc tantalum and bcc molybdenum.
In this approach, the full potential linear muffin-tin
orbital (FP-LMTO) method for the cold and electron-thermal
contributions is closely coupled with ion-thermal contributions. For
the ion contribution two separate approaches are used. In one
approach, the quasi-harmonic ion contribution is obtained through a
Brillouin zone sum of strain derivatives of the phonons, and in the
other the anharmonic ion contribution is obtained directly through
Monte Carlo (MC) canonical distribution averages of strain
derivatives
on the multi-ion potential itself. Both methods for the
ion-contribution use quantum-based interatomic potentials derived
from
model generalized pseudopotential theory (MGPT). The resulting
elastic moduli are compared to available ultrasonic measurements and
diamond-anvil-cell compression experiments, as well as to sound
speeds
along the Hugoniot. Over this range of temperature and pressure, the
results are then used in a polycrystalline averaging for a comparison
to larger-scale shear models like the Steinberg-Guinan strength
model. These results give an indication that
anharmonic effects are negligible in tantalum but not in
molybdenum for
high pressures and temperatures up to melt.
This work was performed under the auspices of the U.S. Department of
Energy by the University of California Lawrence Livermore National
Laboratory under contract W-7405-Eng-48.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.H11.13