Johnson–Cook yield functions for cyclotetramethylene-tetranitramine (HMX) and cyclotrimethylene-trinitramine (RDX) derived from single crystal plasticity models
Journal of Applied Physics,
Journal Year:
2024,
Volume and Issue:
135(14)
Published: April 8, 2024
High-fidelity
constitutive
models
are
critical
for
accurate
meso-scale
continuum
modeling
and
prediction
of
shock
initiation
crystalline
energetic
materials
(EMs).
While
empirically
calibrated
or
atomistic-guided
anisotropic
elastoplastic
EM
such
as
cyclotetramethylene-tetranitramine
(HMX)
cyclotrimethylene-trinitramine
(RDX)
capture
important
micromechanical
phenomena
(such
dislocation
evolution,
slip-resistance,
elasticity),
the
computational
cost
using
single-crystal
plasticity
can
become
prohibitive
computations
void-collapse
hotspot
formation
in
microstructures.
Thermo-mechanically
representative,
isotropic,
pressure,
temperature,
rate-dependent
material
practical
alternatives
simulations
response
To
this
end,
work
constructs
physically
consistent
isotropic
from
HMX
RDX.
State-of-the-art
crystal
RDX
used
to
compute
stress
states
single
crystals
oriented
three
different
directions
relative
shocks
generated
by
impact
at
velocities
ranging
100
1000
m/s.
Post-shock
von
Mises
fields
orientations
then
calibrate
strain-rate
hardening
coefficient
reference
strain
rate
a
Johnson–Cook
(JC)
yield
surface
model.
We
compare
pressures
post-shock
stresses
between
JC
show
that
closely
approximate
averaged
deformation
orientations.
model
interaction
500
m/s
with
0.5
μm
void
deviatoric
obtained
match
those
computed
both
The
resulting
J2
plastic
flow
be
employed
perform
energy
localization
due
shear
bands
collapse
two
materials.
Language: Английский
Length scale and grid resolution effects in the simulation of shear and energy localization during pore collapse in shocked energetic crystals
Journal of Applied Physics,
Journal Year:
2025,
Volume and Issue:
137(12)
Published: March 26, 2025
Previous
works
[Herrin
et
al.,
J.
Appl.
Phys.
136(13),
135901
(2024),
Nguyen
136(11),
114902
(2024)]
obtained
atomistics-consistent
material
models
for
two
common
energetic
crystals,
HMX
(1,3,5,7-Tetranitro-1,3,5,7-tetrazocane)
and
RDX
(1,3,5-Trinitro-1,3,5-triazinane)
such
that
pore
collapse
calculations
adhered
closely
to
molecular
dynamics
(MD)
results
on
key
features
of
energy
localization,
particularly
the
appearance
shear
bands,
shapes
collapsing
pores,
transition
from
viscoplastic
hydrodynamic
collapse.
However,
only
one
size
(of
50
nm
diameter)
was
studied
some
important
aspects
as
temperature
distributions
in
hotspot
were
found
be
inconsistent
with
atomistic
models.
One
potential
issue
noted
but
not
resolved
adequately
those
works,
namely,
grid
resolution
should
employed
meso-scale
various
sizes
shock
strengths.
Conventional
computational
mechanics
guidelines
selecting
meshes
fine
possible,
balancing
effort,
accuracy,
independence,
shown
produce
physically
consistent
associated
localization.
Here,
we
examine
physics
collapse,
band
evolution
structure,
formation
both
RDX;
then
evaluate
under
what
conditions
yield
“physically
correct”
(considering
MD
“ground
truth”)
hotspots
a
range
diameters,
micrometers,
wide
The
study
provides
insights
into
effects
strength
hotspots,
identifying
size-independent
behaviors,
proportion
contained
opposed
jet
impact-heated
regions
hotspot.
Language: Английский