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
PRESSURE WAVE MEASUREMENTS IN CYLINDERS OF
DETONATING LX-17*
J. W. Forbes, P. C. Souers, P. A. Urtiew, K. S. Vandersall,
F. Garcia, D.W. Greenwood, and LeRoy Green
Energetic Materials Center, Lawrence Livermore National Laboratory,
P. O. Box 808, L-282, Livermore, CA 94551
Abstract: Manganin gauges with temporal resolution of less than 75 ns were used to measure the
detonation wave pressure profile in a right cylinder of LX-17 (TATB/Kel-F: 92.5/7.5 wt.%). Three
gauges at different Lagrange locations were on the centerline of the 5.08 cm diameter cylinder at
distances greater than four times its diameter from the boosted end. At the last gauge plane, seven
gauges were placed at the same Lagrange position but spaced radially across the cylinder diameter.
Wave curvature and effects of lateral strain in these gauges were measured.
INTRODUCTION
5.08 cm diameter and 23.4 cm long. Three gauges
were placed on the centerline at distances of 20.0,
20.8, and 22.4 cm, respectively, from the
originally boosted LX-17 surface. To measure the
wave curvature a set of seven manganin gauges are
equally spaced across the diameter of the cylinder at
22.4 cm from the boosted surface as given in Fig. 2.
In-situ gauges have the advantage over other
techniques for measuring detonation properties
because of the minimum disturbance to the flow. In
cylinders of HE with steady detonation waves, insitu gauges can provide 2-D hydrodynamic state
data for validation of 2-D flow theories of
detonation such as Wood-Kirkwood[l] and other
curved front theories[2]. Another reason for this
research is the general need to develop 2-D flow insitu gauge experimentation. Improvements of the
temporal resolution, survivability, and signal
fidelity[3] of the manganin foil gauge in detonations
has allowed us to begin this research project.
The active gauge elements are different in size for
the standard gauge, the mini gauge, and the multiple
gauges. The standard gauge has a rectangular
element of 0.7 mm wide by 2.0 mm long, the minigauge has an element 0.3 by 0.5 mm and the six
multiple gauges each have elements of 0.3 by
0.7 mm. The temporal resolution is determined by
calculating the shock transit time for 3.5 wave
transits through the gauge package. The gauges
20.0 and 20.8 cm from the boosted face had 0.05
mm thick Teflon sheets in front and back of the
0.025 mm thick manganin foil while the gauges at
22.4 cm had 0.07 mm thick Teflon sheets in front
and back of the foil.
The level of difficulty of gauging 2-D flow
experiments is an order of magnitude greater than
difficult 1-D experiments. This is because stress and
particle motion are a function of two spatial
variables and lateral strain exists in the gauges.
EXPERIMENTAL DESCRIPTION
RESULTS AND DISCUSSION
The schematic of the cylindrical charge of LX-17
boosted by a LX-10 cylindrical disc is given in
Fig. 1. This experiment was designed to measure a
steady detonation wave. The cylinder of LX-17 was
Manganin foils were used to measure longitudinal
pressure along the axis of a steady detonating
cylinder of LX-17. The lateral flow at the centerline
902
of the cylinder is zero due to symmetry. Note that
the four lead gauges will be affected by strain due to
the lateral flow in the detonating cylinder.
SE-1 detonator
LX-17 NONE MPACT
Tetryi pellet ?'
FAST GAUGE
H EXPERIMENT
34mm'-
Even with this 75 ns temporal resolution, the
measured peak pressures were near 30 Gpa.
Figure 3 gives all the gauge results as analyzed
without correction for lateral strain. Two
experiments were done with identical LX-17
cylinders. Micro-coaxial cables were used to
eliminate gauge lead length (see Fig. 1) for the
MGNT 30 experiment but not for MGNT 54.
MGNT-30
SOmri
AIGasSNelds
LX-T7
SOmri
50mm
Angle cut IX-17 is 60*
Level C
The average steady detonation velocity from the
two experiments was 7.64 mm/us for an initial
density of p0=1.90 g/cm3. Note that the first gauge
in MGNT 30 broke down immediately when the
shock wave arrived as seen in Fig. 3. Therefore, the
arrival time of this gauge was not used for
determining detonation velocity. Impedance
matching using initial density, steady detonation
velocity, and published JWL products EOS[4,5],
gives a CJ pressure of 27.0 GPa. The three gauges
near the centerline of the cylinder gave nominal
results of 29-30 GPa peaks and pulse widths 70 90 ns at PCJ for experiment MGNT 30 and 2830 GPa peaks and pulse widths 130-210 ns at PCj for
MGNT 54. The reasons for the difference in the
pulse widths at 27 GPa are not known. More
experiments are required to determine the reasons
for this difference.
NOT TO SCALE
FIGURE 1. Schematic of LX-17 cylinder experiment
0.05mm thick Teflon/glue
on both sides of manganin
Six multiple gauges were placed symmetrically
from the centerline (one mini-gauge was at the
Level A & B
Irnm
1mm
—— gauge 1 (37.408(43)
gauge 2 (38.444us)
gauge 3 (40.556ps)
4 (40.584us)
—— gauge 5 (40.64us)
—— gauge6(40.56us)
—— gauge 7 (40.592us)
—— gauge 8 (40.656ps)
gauge 9 (40.552Ms)
Mini Gauge
HH—
Level C
I
0.07mm Teflon/glue
on both sides
;mm
10 -
0.07mm Teflon/glue
on both skies
6mm
Time (MS)
FIGURE 2. Gauge details for LX-17 cylinder experiment
FIGURE 3. Manganin gauge records for experiment MGNT 30
903
——gauge3(40.556M8)
— gauge4(40.584Ms)
— gauge5(40.64MS)
_——gauge6(40.56MS)
—— gauge7(40.592ps)
—— gauge8(406S6ps)
—— gaise9(40.552ps)
0
•20
40.4
-10
0
Distance (mm)
10
20
FIGURE 5. Profile of detonation waves in 5.0 cm diameter LX17 cylinders
FIGURE 4. Records for gauges across diameter of plane at
22.4 cm from the boosted LX-17 surface
The manganin gauges are accurate to 4% (i.e.
twice the standard
deviation of errors)
for compression and release states in inert
materials[8]. The accuracy of the present data has
not been determined because of lack of adequate
information on gauge accuracy with the gauge
strain effects in the detonation environment.
center) on a plane 22.4 cm from the boosted
surface. Figure 4 gives the results from the seven
gauges located across the diameter. The gauges
not on the centerline gave voltage signals with
greater peak values than those at the center.
Corrections for the increased voltage signals due to
lateral strain in the gauge were not done.
Analyzing the data without the strain correction
results in apparent higher peak pressures the further
away from the centerline. This apparent result is
contrary to oblique shock theory[6] which gives the
highest pressure at the center and lower pressure as
a function of distance from the centerline.
CONCLUSIONS
The feasibility of using in-situ pressure gauges for
determining CJ states at the center of cylinders has
been demonstrated in experiments with small
divergent flow. Pressures exceeding the PCJ of
27 GPa in LX-17 were measured. However,
accurate Von Neuman spike pressure and pulse
widths were not determined because of insufficient
temporal resolution and accuracy of the gauge
packages used here.
The lateral strain is affecting these results and
needs to be compensated for. Two-dimensional
code calculations could be used to determine the
strain as a function of time for these gauges.
However, the best solution would be to directly
measure this lateral strain as a function of time and
correct the manganin voltage[7]. This is a subject
for future work.
In future experiments the temporal resolution of
the manganin foil gauge package will be reduced to
less than 30 ns. This will allow for a more accurate
measurement of the spike pressure at the detonation
front in cylinders of LX-17. In addition, constantan
strain elements located symmetrically at the same
spatial location will be used to measure lateral strain
in the gauges. Correcting manganin pressure gauges
for lateral strain[6] will provide the first step for
obtaining accurate stress gauge records in these type
of experiments with small divergent flow.
Wave curvature was obtained from the
detonation wave arrival times at the seven gauges
located across a diameter in one Lagrange plane.
The arrival times and the steady detonation velocity
allowed calculation of the relative position of wave
front elements along the axis of the cylinder. The
wave front position along the cylinder axis versus
charge diameter is given in Fig. 5. The data points
are connected with straight-line segments.
To complete an accurate gauge calibration
requires applying the theory of piezoeresistance
904
3. D. Greenwood, J. Forbes, F. Garcia, K. Vandersall,
LeRoy Green, and Leroy Erickson "Improvements in the
Signal Fidelity of the Manganin Stress Gauge,"
Proceedings of 12th Biennial APS Conference on Shock
Compression of Condensed Matter, Atlanta, GA, June 2429,2001.
4. C. M. Tarver, J. W. Kury, and R. D. Breithaupt,
"Detonation Waves in Triaminotrinitrobenzene," J. Appl.
Phys. 82, (8), 1997.
5. R. L. Gustavsen, S. A. Sheffield, R. R. Alcon, J. W.
Forbes, C. M. Tarver, and F. Garcia, "Embedded
Electromagnetic Gauge Measurements and Modeling of
Shock Initiation in the TATB Based Explosives PBX 950
and LX-17," Proceedings of 12th Biennial APS
Conference on Shock Compression of Condensed Matter,
Atlanta, GA, June 24-29, 2001.
6. E. R. Lemar, J. W. Forbes, and M.
Cowperthwaite,"Oblique Shockwave Calculations for
Detonation Waves in Brass Confined and Bare PBXN-111
Cylindrical Charges," p. 385, Shock Compression of
Condensed Matter, eds. Schmidt, Dandekar, Forbes, AIP
Conference Proceedings 429,1977.
7. J. A. Charest, "Development of a Strain-Compensated
Shock Pressure Gauge," Dynasen TR-005, February
1979.
8. H. S. Vantine, L. M. Erickson, and J. Janzen,
"Hysteresis Corrected Calibration of Manganin under
Shock Loading," J. Appl. Phys., 51, (4), 1980.
9. S. C. Gupta and Y. M. Gupta, "Experimental
Measurements and Analysis of the Loading and Unloading
Response of Longitudinal and Lateral Manganin Gauges
Shocked to 90 kbar," J. Appl. Phys. 62, (7), 1987.
response of the manganin foil to shock loading and
unloading[9] measurements of compression and
release at pressures near 30 GPa in inert materials
with similar mechanical properties as detonating
HE.
The gauge accuracy needs to be at least 3 % for
compression and release pressure states near
30 GPa for the data to be discriminating for
hydrodynamic models.
The search for gauges to use in the detonation
environment that are not sensitive to lateral strain
and have ns time response with less than 3%
pressure errors continues to be a challenge.
ACKNOWLEDGEMENTS
Mike Martin, Gary Steinhour, and Ernie
Urquidez fired these experiments for us. Dave
Zevely provided the machined HE parts. Paul
Marples machined the inert parts. The authors
acknowledge useful discussions with J. Charest on
strain compensation of manganin gauges and
general discussions on 2-D gauge measurement
techniques with Y. M. Gupta.
REFERENCES
1. W. W. Wood and J. G. Kirkwood, "Diameter Effect
in Condensed Explosives. The Relation Between
Velocity and Radius of Curvature of the Detonation
Wave, "J. Chem. Phys., 22, p. 1920, (1954).
2. D. S. Stewart and J. B. Bdzil, "Examples of
Detonation Shock Dynamics for Wave Spread
Applications," Proceedings of Ninth Symposium
(International) on Detonation, Coronado, CA, Aug. 2427, pp. 773-783, 1976.
*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
No.W-7405-Eng-48.
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