LARGE-SCALE MOLECULAR DYNAMICS SIMULATIONS OF SHOCK-INDUCED PLASTICITY, PHASE TRANSFORMATIONS, AND DETONATION Page: 4 of 7
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FIGURE 1: Measured Hugoniot (shock velocity vs. par-
ticle velocity) for the 2-D AB crystal.
elastic wave is maintained, but soon thereafter one
finds split elastic-plastic structure (Fig. 2) followed
by a fluid region due to the extremely low melting
point of the AB model. For piston velocities greater
than ~1.6 km/s, a steady-state detonation is initi-
ated. Velocities just above this threshold clearly in-
dicate that initiation takes place by homogeneneous
nucleation far behind an intial compressive wave,
which is subsequently overtaken by the detonation
wave. The detonation velocity is nearly constant,
~9.5 km/s, until for up > 4.5 km/s an overdriven
detonation wave exists.
STUDIES OF ISOLATED DEFECTS
Our simulations indicate that point defects such
as vacancies are insufficiently strong stress concen-
trators to initiate plastic deformation  or phase
transformations below the perfect single-crystal
threshold. Similarly, replacing an AB molecule in
the molecular solid by an A- radical leads to a few
localized reactions for up < 1.6 km/s, but does not
seem to lower the detonation threshold appreciably
(a few percent at most).
However, more extended defects or grain bound-
aries may readily act as heterogeneous nucleation
2-D supported piston simulations
- - --. - - - - - - - - - -
e * --
r... * *. -- l
a -* ~ ..* - *C .*
.- .+ ..-..*
.. -..t7. .
FIGURE 2: Shockwave in a 2D AB molecular crystal
with nu, = 0.49 km/s (i.e., below the detonation thresh-
old), with molecules colored by their orientation. The un-
shocked herringbone lattice is at the top, and at the bottom
is the shocked state corresponding to a (highly defective)
9O0 rotation of the original lattice. An intermediate elastic
precursor consists of diagonal lines of single molecules
which have rotated by varying amounts, but return to the
original configuration upon release.
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GERMANN, T. C. LARGE-SCALE MOLECULAR DYNAMICS SIMULATIONS OF SHOCK-INDUCED PLASTICITY, PHASE TRANSFORMATIONS, AND DETONATION, article, June 1, 2001; New Mexico. (digital.library.unt.edu/ark:/67531/metadc715793/m1/4/: accessed November 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.