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
STRESS GROWTH MEASUREMENTS FOR THE EXPLOSIVE IRX-4
Gerrit T. Sutherland
Naval Surface Warfare Center, Indian Head Division, Indian Head, MD 20640
Embedded gauge experiments were performed to measure the shock reactivity of IRX-4, a plastic-bonded
explosive that contains HMX, Al, AP and HTPB binder. The pressure-time profiles obtained are similar to
those obtained for similar composite explosives. Hugoniot points obtained are in agreement with those obtained with mixture theory.
INTRODUCTION
A series of mono-modal research explosives denoted IRX-1 (independent research explosive one),
IRX-3A, and IRX-4 were formulated to elucidate
the roles of HMX, aluminum (Al), and ammonium
perchlorate (AP) in shock reactivity and detonation
property experiments. All three explosives contain
mono-modal HMX and a polyurethane binder
(HTPB). IRX-3A also contains aluminum, and
IRX-4 contains both Al and AP.
Shock reactivity and detonation property experiments for IRX-1 and IRX-3A have been published. [1-4] In this paper, we present shock reactivity results for IRX-4.
The shock reactivity experiments performed
were embedded gauge experiments, which will be
used to obtain reaction kinetics. Pressure-time or
particle velocity-time records are used to adjust
parameters in reactive rate models such as the LeeTarver [5] model. In this model, the rate at which
unreacted explosive is converted into detonation
products is expressed as a function of the: mass
fraction of explosive reacted, pressure and density.
When inserted in a hydrocode, the Lee-Tarver
model has been successful in simulating [6-7] the
results of shock sensitivity and detonation property
experiments. Our intent is to further refine the LeeTarver model parameters until computer simulations predict the results of tests such as modified
gap, wave curvature, detonation velocity decrement
and the embedded gauge experiments. When reac-
tive rate model parameters are obtained for all of
the IRX series explosives, the differences in global
reaction kinetics between the explosives will be
determined. The roles that each constituent (HMX,
Al, AP) plays in shock reactivity and detonation
properties will be quantified.
EXPERIMENT
IRX-4 consists (by weight) of 30% HMX, 16%
Al, 24% AP and 30% HTPB binder. The HMX was
sieved and had a average particle size of 124 urn.
The Al and AP particle sizes were estimated to be
about 3 and 200 urn respectively. In our experiments, the sample density was taken as the casting
density of 1.46 g cm"3.
A schematic representation of our embedded
gauge experiments appears in Fig. 1 and experimental parameters appear in Table 1. The nominal
diameters of the explosive disks were 70 mm. Impactors and cover plates were constructed from
OFHC copper (Cu) for experiments 3 and 5, and
from 6061T6 Aluminum for the remaining experiments. The Dynasen Corporation manufactured
Manganin gauges from manganin foil supplied by
NSWC. The gauges (MN10-.050 type S) [8] had an
electrical impedance of 0.050 ohms, used a fourwire terminal configuration and incorporated Teflon® encapsulation resulting in gauges of either
0.25 or 0.50 mm nominal total thickness. All ex-
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periments were performed using a 100-mm diameter light gas gun.
TABLE 1. Experimental Parameters________________
Exp. Thickness Thickness Impact
Calculated
Layer 1 Layer 2
Velocity
Impact
(mm)
(mm)
(mm/iisec) Pressure
(GPa)
5.982
6.007
0.639
1
2.18
5.994
5.009
0.756
2
2.68
7.023
4.44
7.010
0.965
3
5.982
5.956
4.12
1.066
4
7.008
3.92
7.023
0.881
5
Time (jisec)
Figure 2. Pressure-time profiles for experiment 1. The calculated impact pressure is 2.18 GPa.
L
10.0
J
\tt
Impactor
5.0
Manganin
Gauges
I
-~A|,_;
Ga.2 !
7mm)\|
Ga. 1
(Omni
\
i
i Ga.3
i
i 14mm)
i
i
^J
- —————
-~^f^^
1
\
ao
Figure 1. Schematic representation of an embedded gauge
experiment.
c1
1
''" *^-'"~-'v,
2
3
4
5
TIME (Useri
Figure 3. Pressure-time profiles for experiment 5. The calculated impact pressure is 3.92 GPa.
RESULTS
15.0
Pressure -Time Profiles
C3
Experimental results for the IRX-4 experiments
appear in Figs. 2-4. In these records, considerable
electrical noise, which will be discussed later, was
observed, so the records were smoothed with a
smoothing routine with a 150 nsec time span. For
each record, the relative resistance change (AR/Ro)
was calculated and the stress determined from an
empirical calibration of Vantine et al.[9]
6
10.0
5.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Time (usec)
The pressure-time profiles show a response similar to a composite explosive [3] containing a nitramine (ie. HMX, RDX), Al, AP and binder. The
similarity includes the square-wave shape in pres-
Figure 4. Pressure-time profiles for experiment 3. The calculated
impact pressure is 4.44 GPa.
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sure-time profile for gauge 1 on experiment 3 and
gauge 3 of experiment 5. The record for our lowest
pressure experiment indicated a modest level of
reaction, something not seen for a similar composite
explosive.[3] This reaction is likely due to the fact
that the composition, although a composite explosive, contains almost 24% volume percent of coarse
HMX. A detonation wave was observed at gauge 2
in the pressure-time profile in Fig. 4. It is believed
that the peak pressure was slightly higher as the
original voltage digitizer record was clipped. Comparison of Figs.3-4 shows that IRX-4 is an insensitive explosive; it takes 3.9-4.5 GPa impact pressure
to produce a detonation at a run distance of 14 mm.
0.2
0.4
0.6
0.8
1.0
Particle Velocity (mm/^sec)
Figure 5. Hugoniot points plotted against the results of the
mixture theory. The open triangles represent shock velocities
obtained between gauges 1 and 2; the crosses represent shock
velocities obtained between gauges 2 and 3.
Hugoniot measurements
Reactive rate modeling of our experiments requires a Hugoniot for IRX-4. Minimal reaction at
the shock front allowed Hugoniot points to be obtained from transit time measurements between the
two gauge planes. A correction was made for the
transit time through the Teflon® encapsulation of
the gauge planes. The Hugoniot points obtained are
plotted with a Hugoniot obtained from mixture theory in Figure 5. For our mixture theory calculation,
we used Hugoniots for the HTPB binder from
Grady,[10] and for all other components Hugoniots
from Bernecker[ll-12] were used. The agreement
between the experimental points and mixture theory
implies that mixture theory Hugoniot can be used in
the computer simulations. Hugoniot points were not
determined from front surface gauge pressures; the
gauge calibration is not accurate for low pressures. [13]
Electrical Noise Observed
-l.Q,
1.0
2.0
3.0
4.0
5.0
6.0
Time (isec)
Figure 6. Pressure-time profiles showing electrical noise
observed for experiment 1.
Figure 6 shows the substantial amount of electrical noise that we observed for experiment 1. Other
experiments showed similar noise levels. We have
observed the high frequency noise component for
another composite explosive but we have not always observed the lower frequency noise component (« lMhz).[3] The gauges are susceptible to
noise since a pressure change of 2 GPa represents a
voltage change of only 20 millivolts. The lower
frequency noise may be present due to a different
method of connecting the gauge leads to the coax
cable leading to the instrumentation. Thin copper
strips, twisted hookup wire, and circuit boards in-
corporating strip lines have each been used to make
this connection. Circuit board type connections
were most likely used for these experiments.
FUTURE WORK
The pressure-time profiles will be used to determine parameters for the Lee-Tarver reactive rate
model. The parameter set will be refined by further
adjusting the parameters until the results of all IRX4 experiments such as wave curvature and detonation decrement are predicted.
1057
4.
To reduce the 1MHz electrical noise observed
for the gauge records, the method used to make the
electrical connection between the gauge leads and
the coax cable will be optimized.
5.
ACKNOWLEDGEMENTS
6.
John O'Connor, Paul Gustavson, Bob Baker,
Carl Groves, Dale Ashwell, and Ray Lemar are
thanked for their help in constructing and performing the experiments. Jerry Forbes and Charles Dickinson are thanked for his support and encouragement of this work. This work was supported by
Independent Research Program of the Naval Surface Warfare Center.
7.
8.
REFERENCES
1.
2.
3.
9.
Sutherland, G.T., Lemar, E.R., Forbes, J.W., Anderson, E.W., Ashwell, K.D., and Baker, R.N., in Proceedings of the JANNAF PSHS Meeting, May 1113, 1993, Fort Lewis, WA.
Sutherland, G.T., Forbes, J.W., Lemar, E.R, Ashwell, K.D, and Baker, R.N., and Liddiard, T.P.,
"Shock Wave and Detonation Wave Response of Selected HMX Based Research Explosives with HTPB
binder systems" in High Pressure Science and Technology-1993, Woodbury, NY, AIP, 1994, pp. 14131416.
Sutherland, G.T., Ashwell, K.D., O'Connor, J.H.,
Barker, R.N., and Lemar, E.R., "Shock Response of
Several Plastic Bonded Explosives, in Shock Compression of Condensed Matter-1995, edited by S.C.
Schmidt et al., AIP Conference Proceedings 370,
New York, 1996.pp. 763-766.
10.
11.
12.
13.
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Lemar, E.R, Forbes, J.W., Sutherland, G.T., Detonation Wave Curvature of IRX-4 and PBXN-110",
in Shock Compression of Condensed Matter-1995,
edited by S.C. Schmidt et al., AIP Conference Proceedings 370, New York, 1996.pp. 791-794.
Lee E.L., Tarver, C.M., Phys. Fluids 23, 2362-2372
(1980).
Miller, P.J., Sutherland, G.T., Reaction Rate Modeling of PBXN-110, Shock Waves in Condensed Matter-1995, editors Schmidt, S.C., and Tao, W.C., AIP,
Woodbury, NY
Murphy, M.J., Simpson, R.L., Breithaupt, R D.,
Tarver, C.M., "Reactive Flow Measurements and
Calculations for ZrH2 Based Composite Explosives,
in Proceedings of Ninth Symposium (International)
on Detonation, Office of the Chief of Naval Research, OCNR 113291-7, pg. 525.
Information of the Dynasin pressure gauges can be
found at www.dynasin.com.
Vantine, H.C, Erickson. L.M., Janzen, J.A., J. Appl.
Phys. 51 (1979) 1957.
Grady, D.E., Private Communication
Bernecker R.R.., "Observations on the Hugoniot for
HMX", in Shock Compression of Condensed Matter-1995, edited by S.C. Schmidt et al., AIP Conference Proceedings 370, New York, 1996.pp. 137140.
Bernecker R.R.., "Observations on the Hugoniot for
HMX", in Shock Compression of Condensed Matter-1995, edited by S.C. Schmidt et al., AIP Conference Proceedings 370, New York, 1996.pp. 137140.
Forbes, J.W. Private Communication. Work on a
revised manganin gauge calibration for low pressures is underway at the Lawrence Livermore National Laboratory.