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
SOUND VELOCITY DOPPLER LASER INTERFEROMETRY
MEASUREMENTS ON TIN
E. Martinez - J-M. Servas
Commissariat a I 'Energie Atomique
Centre d'Etudes de BRUYERES-LE-CHATEL
B.P. 12 - 91 680 - BRUYERESLE CHATEL - France
Abstract. Measurement of the sound velocity behind shock waves can be used as a sensitive probe
for detecting phase transition. In order to validate an experimental set-up and to verify the
evolution of the sound velocity versus pressure, we performed an experimental program on tin. By
use of Doppler Laser Interferometry (D.L.I.) measurements, we have measured the sound velocity
in shocked tin at twelve points along its Hugoniot in the pressure range 2 to 33GPa. The shock
generator is a 60mm diameter powder gun.
INTRODUCTION
PRINCIPLE
The sound velocity is an important physical
parameter which evolves with changes in structural
properties. The velocity increases with pressure
until shock heating causes phase transition. The
break occurring in the sound velocity versus
pressure is attributed to structural change. Thus,
phase transitions along the Hugoniot can be
observed
through
sound wave velocity
measurements.
To generate the shock, a flyer plate, accelerated in
a powder gun to velocities up to 1600m/s, hits a tin
target. After the plate impact, a shock propagates
forward in the target and backward in the flyer. A
rarefaction wave originating at the back surface of
the projectile overtakes the shock wave. The sound
velocity CL is defined as the velocity of the leading
release wave (Fig. 1).
In order to validate an experimental set-up and to
verify the evolution of sound velocity versus
pressure, we performed an experimental program
on tin. By use of D.L.I, measurements, we have
measured the sound velocity in shocked tin at
twelve points along its Hugoniot in the pressure
range 2 to 33GPa.
flyer
In this paper, we describe our experimental set-up
using D.L.I, measurements and we give the
experimental results on the tin sample.
,;
target
Figure 1 : Lagrangian diagram. The impactor and
the target are of the same material
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For a symmetrical impact, the impactor and the
target are of the same material, and the sound
velocity CL is calculated taking into account:
At
- the flyer thickness e,
- the shock velocity D,
At2
- and the overtake distance H.
At3
CL=D.(H+e)/(H-e)
and
CEL = CL.p/po
——*———h,
i
V*(m)
Fig. 3 : Determination of the overtake distance H.
where D, shock velocity,
e, flyer thickness
Po, initial density,
p, density after impact.
EXPERIMENTAL SET-UP AND
DIAGNOSTICS
From this expression, we note that the
determination of the sound velocity relies on the
overtake distance measurement. Then, to
determine the overtake distance H, we have
adapted and applied a shock and rarefaction
overtake method described by McQUEEN, FRITZ,
MORRIS (1.) and AS AY, CHHABILDAS (2.).
The time between the shock and the arrival of the
release wave is proportional to the target thickness
(Fig.2). Then, using a stepped-target, the
determination of the overtake distance can be
realised (Fig.3).
Considering that tin presents a phase transition
solid-solid under shock loading in the range 5 to
lOGPa (3.) and the maximum velocity of the flyer
is 1600m/s, we have developed two set-ups to fulfil
our requirements :
- a symmetrical set-up : both impactor and target
are of the same material . It enables us to reach
pressures up to 20GPa. (Fig. 4)
- an unsymmetrical set-up : to reach pressures up
to 33GPa, we used tantalum impactors.(Fig. 5, 6)
The launcher diameter is 60mm and the target has
three steps of different thicknesses. A window
material, the Lithium fluoride (LiF) is attached to
these steps.
The measured experimental parameters are :
- the particle velocity,
- the impactor velocity,
D
- and the shock velocity.
projectile
target
LiF
The velocity histories at the interface between the
sample and the transparent window are measured
using D.L.I, technique. Shock pressure is
established by measuring the projectile velocity
with D.L.I., and piezoelectrics gauges. Shock
velocity is determined using piezoelectric gauges
Figure 2 : Lagrangian diagram
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velocity is deduced from projectile velocity
measurement.
LJ
For unsymmetrical impact, the particle
velocity is calculated from measurement of
shock velocity in tin and HUGONIOT of
impactors. the sound velocity is calculated as
follows :
'LSn
Figure 4 : Schematic representation of the
symmetrical set-up.
and
^ei
H-D Sn .At 0
H-D S n At 0
where DSn, shock velocity in tin
USn, particle velocity
Ato, transit time on the base plate
H, overtake distance in tin.
projectile
Ta
Ta
Sn
Figure 5 : Schematic representation of
unsymmetrical set-up.
EXPERIMENTAL RESULTS
Twelve experiments were performed in the range
pressure 2 to 33GPa: seven, using symmetrical
impact and five, using unsymmetrical set-up.
Calculations were performed using RANKINEHUGONIOT relations.
- For symmetrical impact, H is determined from
overtake method, D is measured and the particle
Figure 6 : Lagrangian diagram using
unsymmetrical set-up
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Tables 1 and 2 summarizes the results obtained.
Ul
1145
8,4
21,3
4222
1270
4,7
25,6
4372
1458
6,8
28,1
4269
1524
10,6
32,1
4411
1476
9,46
33,1
4207
Ta/Ta
225
SI
15,2
U2
3605
2,4
S2
434
15,2
5,0
3861
S3
574
13,4
6,6
3775
S4
620
17,0
6,9
3658
S5
972
15,8
11,3
3963
S6
1180
11,2
14,2
3939
S7
1490
11,1
19,8
4207
Ta/Ta
U3
Ta/Ta
U4
Ta/Ta
U5
W/W
Table 2 : Results obtained using unsymmetrical
set-up.
Table 1: Results obtained using symmetrical
set-up.
CONCLUSION
The experimental results are presented in figure 7.
The realized measurements validate the
experimental method. We observed a break in the
sound velocity versus pressure in the 5-10GPa
pressure range. The accuracy of the sound velocity
measurements is approximately 5%. This precision
depends on the number of step and on the
uncertainly in determining transit times (overtake
distance H). In order to determine the phase
transition, this experimental program requires
some more experiments, especially in the pressure
range (5-10 GPa).
5000 T
4750
4500 -F
4250
4000 i
3750
3500
3250
REFERENCES
1. Me Queen, R.G., Fritz, IN. and Morris, C.E.
« The velocity of sound behind strong shock in
2024 Al» in Shock waves in condensed matter 1983
^ symetrical
H unsymetrical
:
3000
0
10
20
30
2. Asay, J.R., and Chhabildas, L.C.
Shock waves and high strain rate phenomena in
metals. Meyer and Murr Eds, Plenum Publishers
1981
40
Pressure (GPa)
Figure 7 : Diagram (Pchoc ,Cei)
3. Elias, P., Chapron, P., Laurent, B.
«Detection of melting in release for a shockloaded tin sample using the reflectivity
measurement method. ». Opt. Comm., Vol.66, Nber
2,3 (15 April 1988), pp. 100-106.
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