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a All-Russian Research Institute of Optical and Physical
Measurements (VNIIOFI), BIFO Company, Ozernaya st. 46, 119361
Moscow, Russia.
b
Russian Federal Nuclear Center - All-Russian Research Institute of
Experimental Physics, Mira av. 37, 607190 Sarov, Nizhnii Novgorod Reg.,
Russia. Tel: (831-30) 446-27, Fax: (831-30) 459-58, E-mail:
root@gdd.vniief.ru
Introduction
In
May 2001 the K008 camera /1,2/ being a part of a laser Doppler
velocity meter (LDVM) experimental complex of the Russian Federation
Nuclear Center, the All-Russian Research Institute of Experimental
Physics (RFNC-VNIIEF), was tested under real conditions of
gas-dynamic experiments. Some tasks typical to explosion physics
were solved during these experiments: the record of velocities of
the plates thrown by an explosion; the record of shock and
detonation wave fronts; the record of elastic-plastic properties of
constructional materials. At the same time the following camera’s
characteristics were checked: resistance to electromagnetic,
acoustic and light interference; conformity of real characteristics
to Documentation data; convenience in operation and reliability.
The results of tests and
experiments
The camera
has two modes of operation: a single-frame mode and a streak mode (a mode of
linear sweep). A range of linear sweep coefficients provided by two
interchangeable control units is from 1ns/cm to 300μs/cm (a sweep length is
2cm, a limiting temporal resolution is 20 ps). In so doing, in the
single-frame mode frame duration is ranging from 10ns to 600μs (maximum
frame dimensions are 15 x 20mm2). A spatial resolution is not
less than 15 l.p./mm, a spectral range is from 400 to 800nm.
The camera
without an additional external electromagnetic screen was placed directly
near (~10cm) the high current circuits of a solid-state ruby laser and 2m
apart from a blasting chamber in which initiation of detonators is performed
by a spark discharge with a voltage greater than 30kV. There was neither
false triggering and nor worsening of image quality.
Thanks to
correction, by means of software, of all the geometrical and photometrical
distortions in both single-frame and streak modes including the light-signal
characteristics and sweep nonlinearity, the accuracy of the interference
lines displacement detection was essentially increased in these experiments.
As a result of correction, the geometrical distortions were decreased from
4%max down to not more than 1% and sweep nonlinearity was
decreased from 10%max down to not more than 1%. Conversion
coefficient nonuniformity across an image field was decreased from 30%max
down to not more than 5%.
More than 50
gas-dynamic experiments were performed. The diagrams of mass velocity of
various metallic plates thrown by an explosion were received (see Fig. 1).
Fig. 1. A typical recorded
interferogram and a diagram of a mass velocity
of the aluminum plate thrown by explosion.
After
these successful tests the RFNC-VNIIEF has acquired several K008 cameras.
Three of them are used in the measuring complex, where investigations in the
field of physics of shock and detonation waves are performed with use of a
Fabry-Perot laser interferometer /3-5/. In particular, parameters
of detonation of high dense explosives (HE) were recorded at arrival of a
detonation wave to the interface “HE-transparent window”. A thin aluminum
foil (»10μm)
was placed between HE and the window. This foil reflected laser radiation,
which underwent a Doppler frequency shift due to foil motion. Figure 2
presents an interferogram of the test and the time dependence of the
HE-window interface velocity for HE as trinitrotoluene (TNT) (r=1.633g/cm3,
D=6.93km/s) and the window made of LiF.
Fig. 2. Interferogram and
graph U(t) in a test with TNT.
In a test
with TNT, the value of a particle velocity spike U=1.73km/s was recorded at
the HE-LiF interface. Using the known adiabat of non-reacted TNT
D=2.57+1.88U and recalculating the spike state in LiF for the spike state in
TNT, it is possible to determine the value of
Neumann spike that is equal
to P=24.5GPa, U=2.21km/s in TNT.
The known values of Chapman-Jouguet
state (C-J) for TNT obtained by various methods are within the range
17.9…19.35GPa. We take the average value
Ð=18.6GPa.
In this case, the value of the Neumann
spike, which we recorded, is 1.32 times higher than the C-J state. In
the graph of Figure 2, a drop of the velocity U(t) ends as a shelf. Duration
of U(t) drop was Dt=320ns.
This is duration of the zone of chemical reaction. Its value is in good
agreement with data of the other authors /6/.
The
K008 camera is used in the laser measuring complex for recording
elastic-plastic and strength properties of metals. Figure 3 shows a typical
interferogram and a corresponding characteristic profile of velocity of free
surface of an elastic-plastic body at arrival of spall pulse to it. Due to
elastic-plastic behavior of the material, unloading of the spall layer has
two-stage character (an elastic precursor followed by a plastic wave).
Fig. 3. A typical
interferogram and a corresponding characteristic profile of the velocity of
a free surface during spall fracture in an elastic-plastic body.
The formulas for determination of spall strength and the
value of the elastic precursor in an elastic-plastic body are as follows /7/:
The following
designations are taken in formulas (1-4):
r0
- material density; c0, cl ‑ respectively, volumetric and
longitudinal sound velocities in material;
sHEL
- value of elastic precursor;
sspall
- spall strength;
DW
- difference between the first maximum and the minimum of velocity
of free surface of spall layer (the pullback amplitude); Wpl -
amplitude value of plastic wave velocity; Wel - amplitude value of
elastic wave velocity;
Dt
‑ time of occurrence of extending pulse,
dW
- correction, which takes account for difference between velocities
of propagation of the unloading part of falling pulse and the front
of spall pulse; h - thickness of spall plate;
‑
gradients of velocity of free surface, respectively, in falling
rarefaction wave and in front of spall pulse (see Fig. 3).
Conclusion
So, using the
Fabry-Perot laser interferometer
and the K008 camera it is possible to record the following parameters in one
test: amplitude values of elastic and plastic waves velocities (Wel
and Wpl);
DW
-
difference between the first maximum and the minimum of velocity of free
surface on the dependence W(t); time of occurrence of extending pulse (Dt
). The values of elastic precursor (sHEL),
spall strength (sspall)
and thickness of spall plate (h) are calculated from relations (1-4). So,
for example, these values obtained in the test (see Fig.3) were the
following for Armco-iron:
Wel=64m/s;
Wpl=590m/s;
sHEL
=
1.5GPa; sspall
=
2.67GPa; Dt
= 0.22μs;
h = 0.58mm.
The K008
camera is also used within the laser measuring complex to measure velocity
of acceleration of liners and plates; to determine launching capabilities of
various HE, changes of the refractive index during compression of a
transparent material by shock waves, etc.
The camera is
very convenient in operation due to its extremely small overall dimensions
and weight. It can be easily built-in practically into any optical system of
already existing measuring setups without complication of their optical
systems. It can be easily fastened in any position and practically in any
place of both a big measuring complex and small setup. And convenience of
its carrying over and transportation (what is often very important) is
evident and is not to be proved. Fig. 4 shows the participants of the tests
and the K008 camera in the setup of the laboratory LDVM where it was
preliminarily tested. For comparison the K008 camera is set over the FER-7
camera with dimensions of a typical image converter camera. FER-7 protection
against false triggering under operation conditions within the LDVM complex
turned out to be a very difficult problem.
Fig. 4. The participants of the
tests the K008 and FER-7 cameras.
The authors are grateful to G.M. Reitblat for development
of K008 camera software.
REFERENSES
1.
V.B. Lebedev, G.G. Feldman, Super small single
streak and single frame image converter camera, SPIE, Vol. 3516, pp. 85-91.
2.
K008 Streak and Uniframe Camera
3.
A.V. Fedorov et al. Detonation front in
homogenous and heterogeneous HE// Proceedings of APS Conference "Shock
Compression of Condensed Matter", Snowbird, USA, 1999, pp.801-804.
4.
A.V. Fedorov, A.V. Menshikh, N.B. Yagodin. //Chem
Phys. Reports, 2000, vol.18 (10-11), pp.2129-2138.
5.
A.V. Fedorov, A.V. Menshikh, N.B. Yagodin. //
Chemical Physics (in Russian), # 11, 1999, pp.64-68.
6.
S.N. Lubyatinsky, B.G. Loboiko. Detonation
reaction zones of solid explosives. // Proceedings of 11 Symposium on
Detonation, Snowmass, USA, 1998, pp. 836-844.
7.
Kanel' G.I., Razorenov S.V., Utkin A.V., Fortov
V.E. Shock-wave phenomena in condensed matter. M.: "Yanus-K", 1996, p.408.
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