CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
COMPUTATIONAL CHARACTERIZATION OF THREE-STAGE GUN
FLIER PLATE LAUNCH
Daniel E. Carroll1, Lalit C. Chhabildas1, William D. Reinhart1, Nancy A. Winfree2,
Gerald I. Kerley3
1
Sandia National Laboratories0, Albuquerque, NM 87185
2
Dominca. Albuquerque, NM
3
Kerley Technical Services, Appomattox, VA
Abstract. In three-stage gun experimental situations, a flier-plate can be launched using graded-densiry
impact of stationary target plates. In such cases, the launch plate's velocity and state can be obtained from
highly resolved computational simulations of the launch of the flier plate. The computational tools used for
simulation must be validated for such a use by comparing predictions of launch plate velocity with
measurements of the flier from experiments dedicated to such a measurement. This work reports the results
of several simulations of the launch of Ti6-Al-4V plates at velocities from 7 km/s to 11 km/s. The
experimental configuration for measurements of flier-plate velocity is briefly described. The computed
velocity of the flier is compared to velocity interferometer measurements. Excellent agreement is noted.
Calculational results can therefore be used if the velocity and state of a launch plate can not be measured
simultaneously with experimental measurements of a target.
10 km/s (5) emphasized the need to implement
experimental techniques that required a much higher
degree of precision in support of equation of state
(EOS) studies. Recent experiments at Sandia have
used the HVL to determine the EOS of composite
materials. The accurate knowledge of the initial
condition of the Titanium alloy flier plate prior to
impact with a test sample is critical to the analysis of
experimental results. Since the experimental
configuration precludes the direct measurement of
the flier plate velocity when a test sample is present,
we used computer simulations to determine the state
of the flier prior to impact. This paper describes
these simulations and their validation.
INTRODUCTION
The three stage-light gas-gun, also referred to as
the hypervelocity launcher (HVL), was developed in
the early 1990's(l). Since then, its capabilities have
been enhanced to achieve higher engagement
velocities up to 16 km/s (2). These capabilities were
applied for use with applications such as shockinduced vaporization studies (3) and to assess
impact damage to substructures (4). In these early
investigations, experimental transit times were in the
range of 1 to over 100 microseconds after impact.
These investigations did not require a high degree of
precision in time resolution to obtain high accuracy.
Earlier shock loading and release studies on
aluminum and titanium alloys at impact velocities of
" Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department
of Energy under Contract DE-AC04-94AL85000.
307
Two-stage projectile
^
Tantalum
Titanium
Copper \
J
/ /Magn!S«m
l/^
(c)
FIGURE 1. Configuration of the three-stage impactor showing guard ring and graded-density impactor. (a) Two-stage projectile and third
stage flier plate configuration, (b) Graded density impactor with TPX facing impacting the stationary flier plate. (TPX is a trademark for
poly 4-methyl-l-pentene.) (c) X-ray radiograph of typical three-stage flier plate traveling at 11.1 km/s.
DESCRIPTION OF THE HVL
technique is now routinely used to launch 17-19 mm
diameter, 0.6 mm to 1.0 mm thick titanium fliers to
better than 12 km/s. A typical flier plate radiograph
is shown in Figure l(c). flier plate velocity
determination
The Sandia hypervelocity launcher, a three-stage
gun, is briefly described here.
A two-stage
projectile is accelerated and impacts a stationary
flier plate, Figure l(a), causing it to be launched at
velocities from 8 km/s to greater than 11 km/s
depending on the impact velocity of the two-stage
light-gas gun (TSLGG) projectile. If the two-stage
projectile were made of a single material, the flier
plate would melt or vaporize because a great deal of
mechanical energy would be dissipated as heat
across the single strong shock that the projectile
would induce in the flier.
To decrease the
dissipation and thus prevent the melting or
vaporization of the flier plate, the loading pressure
pulse on the flier plate must be uniform and timedependent.
To accomplish this, the TSLGG
projectile is carefully designed as a stack of layers of
materials so that the density of the projectile is
graded along its length (6,7). A layer of TPX
material is also placed between the TSLGG
projectile and the Ti alloy (Ti6A14V) flier plate.
When the graded-density assembly, shown in Figure
l(b), impacts a flier plate, it introduces a series of
small shocks rather than one large shock into the
flier. Taken together, these produce a nearly
shockless, time-dependent megabar pressure pulse
into the flier plate (6,7). The dissipation caused by
this chain of small shocks is considerably less than
the dissipation caused by an equivalent single shock
that launches the flier to the same velocity, and is
insufficient to melt or vaporize the flier. This
The HVL flier plate impacts the test material,
buffered by a layer of TPX. Equation of state
information about the sample is obtained by
examining the shocked state of the test material.
This is done by measuring particle velocity on the
back of the test sample with a velocity
interferometer (VISAR) and using the RankineHugoniot relations, along with an accurate
knowledge of the impact velocity to obtain the EOS
data. The determination of the flier plate impact
velocity is crucial for obtaining accurate EOS
measurements for the target material.
With a test sample present, it is often not
possible to directly measure the velocity of the
HVL-launched flier plate. The value of the plate's
velocity can be obtained from a computer
simulation, if the computer code has been validated
for use in this application. To perform this
validation, a series of experiments were conducted
to map the acceleration history of the flier plate
using a VISAR (8). In addition, flash radiography
was used to determine the terminal velocity over
propagation distances of about 250mm. Typical
velocity profiles obtained from the VISAR map the
entire acceleration history before achieving terminal
velocity. These flier plate velocity measurements
using VISAR and radiography are listed in Table 1.
308
TABLE 1. Comparison of calculated and experimental flier plate velocity.
Graded Density Impactor Dimensions
TwoTest
Stage
(TPX / Mg / Al / Ti / Cu / Ta )
(mm)
Projectile
Velocity
(km/s)
1 .021 / 0.609 / 0.483 / 0.376 / 0.3 12 / 1 .089
6.33
HVLTi-2
6.74
0.842 / 0.479 / 0.404 / 0.323 / 0.254 / 0.744
HVLTi-3
7.22
HVLTi-4
0.807 / 0.445 / 0.414 / 0.3 15 / 0.264 / 0.757
7.32
0.513 / 0.310 / 0.480 / 0.226 / 0.152 / 0.528
HVLTi-5
Based on the fringe sensitivity used in the
velocity interferometer, the terminal flier plate
velocity is determined to a precision better than
0.6%. The X-ray measurements over the distances
previously mentioned indicate a precision in velocity
measurements to better than 0.2%.
VISAR
Flierplate
Velocity
(km/s)
9.80
10.23
11.04
11.15
Xray
Flier-plate
Velocity
(km/s)
Flier-plate
Velocity
(km/s)
No data
10.50
11.05
11.24
9.71
10.49
11.13
11.25
CTH
specified for each model were the yield strength, the
Poisson's ratio and the melt temperature. The
equations of state for the materials in the graded
impactor and the Ti alloy flier were all taken from
the standard CTH material library. All materials but
TPX and Aluminum used the Aneos analytic EOS
model. Sesame EOS tables were used for the
Aluminum and TPX materials.
In these experiments, the exact dimension of the
graded-density material is known. In addition, the
TSLGG projectile velocity is measured to precision
better than 0.2%. The impact velocity, dimensions of
the graded density assembly on the projectile and the
flier plate dimensions were input into the finite
difference hydrodynamic code, CTH (9), to calculate
the flier plate velocity.
For material temperatures above the melt
temperature, the elastic-plastic model is inactivated.
Due to the large value of the pressures in these
simulations, material strength did not play a large
role, but it was modeled. The multi-material
property model used in the simulations was the
"MMP1" variant. This model uses compressibility
weighting for the fluxing of materials after the
Lagrangian step of a cycle. Such a treatment
contrasts to the default (MMP) advection-volume
fraction. Simulations were run both with and
without material fracture being modeled. Some
materials did feel the effect of a release wave and
the presence of fracture pressure allowed the
simulation to run in a more robust fashion.
In this series of tests, experiments and
calculations agreed remarkably well. As listed in
Table 1, the overall agreement is about 1%, similar
to the accuracy of the plate-velocity measurements.
CTH SIMULATIONS
All simulations performed for this work were
done with the CTH computer code. CTH was used
in its one-dimensional mode to model the HVL flier
launch. A mesh resolution of 0.001 cm was used.
This very small value ensures that the simulation is
not resolution limited and has converged. In any
type of calculation other than one-dimensional, such
a small zone size would result in a prohibitively long
computational time, but in one dimension this is not
a detriment for modern workstations.
Comparison of the flier plate velocities from the
launch simulations with the Ti alloy flier plate
velocities measured by the VISAR are presented in
Figures 2 to 5. These figures demonstrate that CTH
simulations can be used to determine the HVL flier
plate velocity to 1% accuracy and thus enable
accurate analysis in the absence of direct flier plate
measurements.
All simulations used the simple elastic-plastic
model for material strength. The parameters
309
VISAR Data^
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CTH Jimulal ion
-I
2
0.2
0.4
#^r*
>
VISAR Data
HVLTI5V
HVLTI2V
0.6
^.._ __
r*
r-fc
4 -
0.0
CTH Simula tionxs •^T^-tr: •Urrt^ _^
~^-^
0.8
1.0
1.2
.0
1.4
Time (microsec)
0.2
0.4
0.6
0.8
1.0
1.2
1.
Time (microseconds)
FIGURE 2. Comparison of VISAR data and CTH simulation for
test HVLTi2V.
FIGURE 5. Comparison of VISAR data and CTH simulation for
testHVLTiSV.
REFERENCES
0
0.2
0.4
0.6
0.8
1
1.2
1. Chhabildas, L. C, and Barker, L. M., Asay, J. R.,
Trucano, T. G., Kerley, G. L, Dunn, J. E., "Launch
capabilities to over 10 km/s," in Shock Waves in
Condensed Matter, edited by S.C. Schmidt, R. D.
Dick, J. W. Forbes, and D. G. Tasker, Elsevier Science
Publishers, 1991, pp. 1025-1031.
2. Chhabildas, L. C., Kmetyk, L. N., Reinhart, W. D.,
and Hall, C. A., International Journal of Impact
Engineering, 17, 183-194 (1995).
3. Brannon, R. M., Chhabildas, L. C., International
Journal of Impact Engineering, 17, 109-120 (1995).
4. Boslough, M. B., et al., International Journal of
Impact Engineering, 14, 95-106 (1993).
5. Furnish, M. D., Chhabildas , L. C., Reinhart, W. D.,
International Journal of Impact Technology 23, 261270 (1999).
6. Barker, L. M., "High Pressure, Quasi-Isentropic
Impact Experiments," in Shock Waves in Condensed
Matter, edited by J. R. Asay, G. Straub, and R. A.
Graham, 1983.
7. Chhabildas, L. C., Asay, J. R., "Dynamic Yield
Strength and Spall Strength Measurements Under
Quasi-Isentropic Loading," in Shock Waves and High
Strain-Rate Phenomena in Materials, edited by M. A.
Myers, L. E. Murr and K. P. Staudhammer, New
York: Marcel Decker, 1992, pp. 947-955.
8. Reinhart, W. D., Chhabildas, L. C., Carroll, D.E.,
Bergstresser, T.K., Thornhill, T.F., and Winfree, N.A.,
International Journal of Impact Engineering 26,
(2001).
9. Hertel, E. S., et al., "CTH: A Software Family for
Multi-Dimensional Shock Physics Analysis," in
Proceedings of the 19th International Symposium on
Shock Waves, VI, Marseille, France, edited by R. Brun,
and L. D. Dumitresce, 1998, pp. 377-382.
1.4
Time (microseconds)
FIGURE 3. Comparison of VISAR data and CTH simulation for
testHVLTiSV.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Time (microseconds)
FIGURE 4. Comparison of VISAR data and CTH simulation for
testHVLTi4V.
510