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
RE-SHOCK EXPERIMENTS IN LX-17 TO INVESTIGATE REACTED
EQUATION OF STATE
Kevin S. Vandersall, Jerry W. Forbes, Craig M. Tarver,
Paul A. Urtiew, and Frank Garcia
Lawrence Livermore National Laboratory, Energetic Materials Center, 7000 East Avenue, L-282, Livermore,
CA 94550
Abstract. Experimental data from measurements of the reacted state of an energetic material are
desired to incorporate reacted states in modeling by computer codes. In a case such as LX-17, where the
time dependent kinetics of reaction is still not fully understood and the reacted state may evolve over
time, this information becomes even more vital. Experiments were performed utilizing a 101 mm gun to
measure the reacted state of LX-17 using a re-shock method. This method involves backing the
energetic material with thin plates (of a known equation of state) that reflect a shock back into the
detonated material. Thus, by measuring the parameters of this reflected wave, information on the
reacted state can be obtained. The experiments were driven by a projectile to near the CJ state ensuring
a quick transition to detonation near the front of the sample. Embedded manganin piezoresistive gauges
were used to measure the pressure profiles at different Lagrange positions during the event. A
discussion of this work will include the experimental setup utilized, pressure gauge profiles, data
interpretation, and future experiments.
INTRODUCTION
reacted products, which can then be incorporated
into the computer codes for improved models.
The main question posed by this research is: what
role does kinetics play in the reacted state of an
energetic material? A TATB based energetic
material, LX-17 (92.5% TATB/ 7.5% Kel-F), was
selected to help answer this question, because
TATB-based explosives are considered somewhat
non-ideal due to the presence of a 3-4 mm reaction
zone. The re-shock technique was chosen because it
provides a method for gaining a measure of the
reacted state via the re-shock wave speed and
pressure profiles. If the reaction in the initial shock
is fast and complete, then the measured re-shock
velocity should be equal to the isentropic (sound)
wave speed in the material [1]. However, if reaction
is incomplete, interpretation is necessary to
correlate the re-shock wave speed to the true
isentropic wave speed in the material. This data will
be used to provide an accurate isentrope of LX-17
Previous reflected wave experiments have been
performed by McQueen and Fritz [2-4], in which
they characterized the point at which the rarefaction
release wave catches up with the reacting energetic
material using an optical technique. Transient
effects and structure in the release profiles were
observed and a ratio of the shock wave velocity to
the rarefaction velocity was obtained. Some
reflected wave experiments have also been
performed above the Chapman-Jouguet (CJ)
pressure (referred to as "supracompression" or
"overdriven") [5-6]. Additional work by Tarver et.
al. investigated the initiation of energetic material
by reflected shocks at pressures driven below the CJ
pressure [7-8]. This work, however, focuses on the
region at or near the CJ pressure in the energetic
material. This paper will discuss experimental setup
153
performed with just SiC plates backed by a A12C>3
reflector material to show the feasibility of the reshock method, however, the results are not included
here for brevity.
used, pressure gauge profiles, data interpretation,
and future work.
EXPERIMENTAL PROCEDURE
Experiments were performed using the 101 mm
diameter propellant driven gas gun at Lawrence
Livermore National Laboratory (LLNL). Figure 1
shows a schematic of the rear reflector re-shock
setup that was used. The projectile consisted of a
polycarbonate sabot with a 15 mm thick silicon
carbide (SiC) flyer plate. The target included a
3.2 mm thick SiC buffer plate in contact with
13 mm of LX-17 (TATB based high explosive) next
to another 5 mm thick plate of SiC with 5 mm of
A12O3 at the rear. Manganin gauges were placed (2
at each level) at the buffer interface (0 mm), 4, 7, 9,
11, and 13 mm within the LX-17 sample with
125 fim Teflon insulation on each side of the gauge.
The SiC plates were SiC-'B' produced by Cercom,
Inc. and the A12O3 plate was AD998 produced by
Coors Ceramics. In the experiment, the first SiC
plate at the back of the LX-17 acts as the first
reflector plate since it has shock impedance
(product of the shock wave speed at pressure and
the density) higher than the LX-17, and the A12O3
will act as a second reflector material since it has a
slightly higher shock impedance than the SiC plate.
Because of this, the manganin gauges will measure
the initial increase in pressure from the initial shock
traveling through the target and then both
reflections from the LX-17/SiC and SiC/Al2O3
interfaces respectively. Using two reflector
materials ensures that a double re-shock is observed
and enables two measurements to be made in the
same experiment.
SiC Flyer
LX-17 HE Sample
Tilt Crystal Pins
AI203
Reflector
Plate
SiC
Reflector
Plate
SiC Buffer Plate
(round with flat edges)
Velocity Crystal Pins
FIGURE 1. Schematic of rear reflector re-shock
experiment setup.
[Modeling Results. EXPT 4557 |
so -. - - - Model, Gauge 1 (0 mm)
Model. Gauge 2 (4 mm)
Model. Gauge 3 (7 mm)
-Model. Gauge 4 (9 mm)
- - - Model, Gauge5 (11 mm) .........
- - - Model, Gauge 6 (13 mm)
In this experiment, the impact velocity was
chosen to result in a pressure at or very near to the
CJ pressure for the LX-17 sample. Therefore, with
the LX-17 driven near CJ state and the 15 mm thick
SiC flyer acting as a piston, a supported shock
propagates through the sample. As shown in
Figure 1, PZT Crystal pins were used to measure the
projectile velocity and tilt (planarity of impact). The
measured impact velocity was 2.33 mm/us with the
crystal pins located at the impact surface and at a
15 mm standoff. The manganin gauges were
analyzed using a hysterisis corrected fit published
elsewhere [9,10]. An experiment was first
-It-
10
time, MS
11
FIGURE 2. Modeling results of LX-17 rear reflector reshock experiment.
RESULTS AND DISCUSSION
Figure 2 displays the modeling results (shown as
dashed lines). The initiation and growth model [8]
was used along with a model developed by
Steinberg [11] for SiC. In short, the re-shock wave
speeds are determined from the travel time between
154
Impacting future experiments at a slightly higher
velocity than was used in this experiment to allow
steady state to be reached faster would be beneficial
to allow measurement where time dependent flow is
not occurring.
the reflected shock peaks at the gauge locations.
The modeling was performed before the experiment
to ensure that the reflected re-shock states could be
measured before any release waves arrive. The
Teflon gauge packages were inserted into the
model.
(a)
Figure 3 (a) shows the results from the
experiment (solid lines) and modeling (dashed lines)
combined together in one trace with only the gauges
at 7, 9, 11, and 13 mm shown in Figure 3 (b) for
clarity of the region of interest. It can be observed
that the model and experiment do not match exactly,
but the main features are reproduced reasonably
well. The model predicts earlier initiation and faster
detonation than the experiment. This is most likely
due to the interference of the teflon gauge packages
with the developing reactive flow [12]. Thinner and
fewer gauge packages and longer LX-17 charges
will be used in future experiments. Aligning the
initial wave arrival times in Fig. 3 (b) shows that the
calculated and measured reflected shock velocities
—— EXPT, Gauge 1 (0 mm)
EX FT, Gauge 2 (4 mm)
EXPT. Gauge 3 (7 mm)
—— EXPT. Gauge4 (9 mm)
—— EXPT, Gauge S (11 mm)
—— EXPT, Gauge 6 (13 mm)
•
-r
-- Model. Gauge 1 (Omm)
Model, Gauge 2 (4 mm)
Model, Gauge 3 (7 mm)
-- Model.Guage4(9mm)
-- Model, Gauge 5 (11 mm)
-- Model. Guage6(13mm>
are in good agreement.
EXPT, Gauge 3 (7 mm)
EXPT. Gauge 4 (9 mm)
EXPT. Gauge 5 (11 mm)
EXPT. Gauge 6 (13 mm)
Model, Gauge 3 (7 mm)
Model,Guage4(9mm)
Model, Gauge 5 (11 mm)
Model,Guage6(13mm)
The re-shock wave speeds were calculated for
both the modeling and experimental results from
travel time between reflected shock peaks in gauge
traces. To be consistent, the wave speed was
calculated from the times at 1/2 the maximum time
from the toe to peak of the increase in pressure the
re-shock event provides. The propagation time
through the Teflon insulation was subtracted using
the insulation thickness and shock wave speed at
pressure. The average pressure value from the first
re-shock peak value to the second re-shock peak
was used. The re-shock wave speeds and pressures
from the modeling are 6.63 mm/|Lis at 31.5 GPa,
6.74 mm/^s at 32.3 GPa, 7.24 mm/^s at 35.5 GPa
from gauges located from 7 mm to 9 mm, 9 mm to
11 mm, and 11 mm to 13 mm, respectively. From
the experiment, the calculated wave speeds from 7
mm to 9 mm and 9 mm to 11 mm respectively are
6.9±0.2 mm/^is at 31.9±0.2 GPa and 7.8±0.2 mm/^s
at 39.4±0.1 GPa. A complete analysis of the errors
associated with the experiment will be done later. It
will include factors such as gauge performance
during the re-shock environment and effects of the
FIGURE 3. Results of LX-17 rear reflector re-shock
experiment showing experiment with (a) all of the gauge
levels and (b) the gauges in the region of interest showing
the reflected shock characteristics.
SUMMARY AND FUTURE WORK
The re-shock method was used to measure reshock wave speeds in LX-17. Further analysis is
needed to analyze and minimize the errors involved
and correlate the re-shock wave speeds with the
isentropic (sound) speed in the reacted products.
gauge insulation thickness.
155
2.
R.G. McQueen, J.W. Hopson, and J.N. Fritz, Rev.
Sci. Instrum. 53 (2), Feb. 1982, pp. 245-250.
3. Joseph N. Fritz, "Waves at High-Pressure and
Explosive-Products Equation of State," Shock
Compressrion of Condensed Matter-1999, M.D.
Furnish, L.C. Chhabildas, and R.S. Hixson eds., AIP
Press, New York, 2000, pp. 239-244.
4. J.N. Fritz, R.S. Hixson, M.S. Shaw, C.E. Morris, and
R.G. McQueen, J. Appl. Phys. 80 (11), December
1996.
5. L. Green, E. Lee, A. Mitchell, and C. Tarver, in
Figure 4 outlines a schematic design of a future
experiment in which the re-shock is directed from
the rear of the flyer plate instead of reflecting off the
rear of the sample. Ongoing work to validate the
current research is in progress to conduct a similar
set of experiments using electromagnetic velocity
(EMV) gauges.
LX-17 HE Sample
SiC Flyer Plate
Tilt Crystal Pins
Eighth Symposium (International) on Detonation,
Office of Naval Research NSWC MP 86-194, edited
by J.M. Short (Naval Surface Weapons Center,
6.
Symposium (International) on Detonation, Office of
Naval Research OCNR 113291-7, edited by W.J.
Morat (office of Naval Research, Arlington,
SABOT
Velocity
Crystal
Pins
7.
SiC Buffer Plate
(round with flat edges)
Air Gap
White Oak, Maryland, 1985), pp. 587-595.
L.G. Green, C.M. Tarver, and DJ. Erskine, in Ninth
8.
AI2O3 Reflector Plate
Virginia, 1989), pp. 670-682.
Craig M. Tarver, Paul A. Urtiew, and William C.
Tao, Effects of Tandem and Colliding Shock Waves
on the Initiation of Triaminotrinitrobenzene," J.
Appl. Phys. 78 (5), 1 September 1995.
C.M. Tarver, T.M. Cook, P.A. Urtiew, and W.C.
Tao, "Multiple Shock Initiation of LX-17," Tenth
Symposium (International) on Detonation, ONR
33395-12, (Boston, MA, 1993), pp. 696-703.
FIGURE 4. Schematic of experiment for future work
9. Vantine, H.C., Erickson, L.M. and Janzen, J.,
"Hysteresis-Corrected Calibration of Manganin
where the shock is reflected from the front behind the
flyer plate.
under Shock Loading", J. Appl. Phys., 51 (4), April
1980.
ACKNOWLEDGEMENTS
10. Vantine H., Chan J., Erickson L. M., Janzen J., Lee
R. and Weingart R. C., "Precision Stress
Measurements in Severe Shock-Wave Environments
with Low Impedance Manganin Gauges," Rev. Sci.
Dan Greenwood is greatly acknowledged for
implementing the data acquisition system and
playing a key role in research to reduce noise in
manganin gauge recording. Ernie Urquidez, Gary
Steinhour, and Mike Martin assisted with the
experiments. Funding was provided through LLNL
by the Chemistry and Materials Science Directorate
WR&D and Postdoctoral (for KSV) programs. This
work was performed under the auspices of the
United States Department of Energy by the
Lawrence Livermore National Laboratory under
Contract No. W-7405-ENG-48.
Instr., 51. pp. 116-122 (1980).
11. Daniel Steinberg, "Computer Studies of the Dynamic
Strength of Ceramics," Lawrence Livermore
National Laboratory Report, UCRL-ID-106004,
September, 24, 1990.
12. A. W. Campbell and Ray Engelke, "The Diameter
Effect in High Density Heterogeneous Explosives,"
Sixth Symposium (International) on Detonation,
Office of Naval Research ACR-2221, (Coronado,
CA, August 24-27,1976), pp. 642-652.
REFERENCES
W. Fickett and W.C. Davis, Detonation, Los Alamos
Series in Basic and Applies Sciences, edited by
David J. Sharp and L.M. Simmons, Jr. (University of
California Press, Berkeley, California, 1979).
156