Synchrotron-based high-pressure research in materials science Page: 3 of 5
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Target Plate
Explosive
Sample /
Impactor
Lexan
Voltage = BLap Projectile
G auge P atka go
Magnetic Field
_ ___J I ,' Gun Barrel
FIGURE 1. Experimental setup. Explosive sample installed in
gun target chamber and magnetic field.
Lexan projectile is faced with an impactor disk
made of Kel-F, a high-density plastic, and coinci-
dentally, the binder material for the explosives stud-
ied. Because of our problem with projectiles disin-
tegrating when launched, we have till now been re-
luctant to use impactors made of anything but plas-
tic.
In all but one of the experiments, the projectile
velocity was measured using optical methods. We
must confess, however, that the optical method
changed from one experiment to the next as "im-
provements" were made. Nevertheless, all the
methods we used gave standard errors in the veloc-
ity of < 10 m/s.
When the impactor strikes the explosive sample,
a planar shock wave is generated which begins the
initiation process. The stress of the initial shock is
determined using the impact velocity, the Hugoniot
of the Kel-F impactor,8 the Hugoniot of the explo-
sive,9 and standard impedance matching techniques.
Electromagnetic particle velocity gauges are em-
bedded in the explosive sample at ten or eleven dif-
ferent depths. These vary from the impact surface
to about 11 mm into the sample. These, of course,
produce voltages proportional to the local mass
(particle) velocity at the Lagrangian position of the
gauge. Three "shock trackers" also allow construc-
tion of distance - time (x-t) plots of the position of
the shock front with time as it moves through the
sample. These x-t trajectories are used to determine
the position and time where detonation is achieved.
EXPERIMENTAL RESULTS
Wave profiles of particle velocity vs. time and
x-t plots of the shock trajectories were successfully
obtained for eight experiments on PBX 9502 andthree experiments on LX-17. In addition, there
were many additional experiments that failed for
one reason or another. Impact stresses of 10.8 to
15.4 Gpa were created with projectile velocities of
2.4 to 3 km/s. This produced run distances of 4.4 to
over 14 mm.
Figure 2 shows wave-profiles from shot 2S-47
where LX-17 was impacted with a Kel-F impactor at
a velocity of 2.951 0.004 km/s producing an input
of 14.96 GPa. The data quality is seen to be ex-
ceptional in this figure. Surprisingly, this quality
was typical for experiments that worked. Experi-
ments that didn't work failed in an unmistakable
fashion. Nine good wave profiles from gauges lo-
cated at depths of 0.0 through 6.7 mm were re-
corded. The first profile is from a gauge on the
front of the sample and the remaining 8 from em-
bedded gauges. The input particle velocity is 1.45
km/s and this grows to a full detonation well before
the wave reaches the last gauge.
All wave profiles other than the first show that
the amplitude of the wave at the shock front is in-
creasing as the wave travels into the sample. This is
observed in all heterogeneous explosives. Addi-
tionally, there is a small hump behind the shock
front. This is consistent with some delay between
the shock passing through un-shocked material and
the release of energy.
Additionally, as observed by Wackerle, Stacy
and Seitz,6 the slope of the particle velocity imme-
diately behind the shock front is positive. This per-2 25
2 00
1 75
1 50Y
01 25
1 00
0 75
0 500 25 -
0 00w--
N
N N-s
C
000 025 050 75 100 125 150
Time ( s)FIGURE 2. Particle velocity wave profiles from shot 2S-47 on
LX-17. The input is 14.96 GPa and was created by impacting
Kel-F on the LX-17 at 2.951 km/s.'C
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Synchrotron-based high-pressure research in materials science, article, Date Unknown; [Los Alamos, New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc927377/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.