Retonation Wave upon Shock-Wave Initiation of Detonation of Solid Explosives, CHEMIA I PIROTECHNIKA, Chemia i ...

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Combustion, Explosion, and Shock Waves, Vol. 38, No. 4, pp. 470{472, 2002
Retonation Wave upon Shock-Wave Initiation
of Detonation of Solid Explosives
A. N. Afanasenkov
1
UDC 622.235.21,622.215
Translated from Fizika Goreniya i Vzryva, Vol. 38, No. 4, pp. 103{105, July{August, 2002.
Original article submitted February 29, 2000.
An original photograph of a retonation wave is presented; the wave arose sponta-
neously in a charge of a 20/80 nitroglycerine/ammonium nitrate mixture with a den-
sity of 0.9 g/cm
3
at a distance of 0.8 of the charge length and went back half of the
charge length toward the place of initiation. The velocity of the forward wave was
2300 m/sec, and the velocity of the retonation wave was 1700 m/sec. The retonation
wave was registered only in one, unique experiment.
Key words: initiation, detonation, retonation wave, velocity, nitroglycerine, am-
monium nitrate.
The problem of emergence of retonation detona-
tion waves in solid high explosives (HE) (powdered and
pressed) being initiated by shock waves through an inert
obstacle or air has been extensively discussed in the lit-
erature. The existence of these waves has been usually
proved by traces on photographic lms, which were ob-
tained by means of optical registration of luminescence
of explosion products (by a high-speed photorecorder)
in the case where the detonation wave arrives on the side
surface of the charge. A typical photograph is shown in
Fig. 1. The shock wave enters the HE charge (pressed
RDX) at the point A, and luminescence of air in charge
pores is observed. At the point B, detonation moves to
the charge surface with a certain delay (the distance
between the points A and B along the t axis) and at
a certain depth h (the distance between the points A
and B along the x axis). These quantities depend both
on the pressure in the shock wave (SW) and on the
charge diameter. With increasing charge diameter and
decreasing pressure in the initiating SW, the values of
and h generally increase; however, the proportionality
is violated near the limits of initiation [1]. Some au-
thors used the dependence of on the critical pressure
to determine the kinetic parameters of HE decomposi-
tion. The detonation trace has two sectors. The rst
one is directed (from the point B) toward the free end
of the charge. Its slope on the photograph corresponds
to the detonation velocity of the HE examined. The
second sector of the trace is directed toward the obsta-
cle but does not reach it. It is the second sector that is
associated with retonation-wave luminescence.
The rst explanation of the \retonation"-wave phe-
nomenon seems to be proposed in [2], where the deto-
nation velocity was measured both on the surface of the
initiated charge and inside it (at the charge axis), which
B
A
x
t
1
Institute of Problems of Chemical Physics,
Russian Academy of Sciences, Chernogolovka 142432;
ilmaslov@mail.ru.
Fig. 1. Typical photograph of shock-wave excitation
of detonation in a solid HE charge.
470
0010-5082/02/3804-0470 $27.00
c
2002
Plenum Publishing Corporation
Retonation Wave upon Shock-Wave Initiation of Detonation of Solid Explosives
471
Fig. 2. Schematic of the process of shock-wave exci-
tation of detonation in a solid HE charge.
Fig. 3. Retonation wave in an explosive 20/80
NG/AN mixture.
was ensured by drilling orices 3 mm in diameter spaced
by 10 mm from each other along the charge generatrix
up to its center. The measurement results suggested
the following pattern of propagation of the detonation
front over the charge in time (Fig. 2). Detonation arises
at the center of the charge at the charge{obstacle inter-
face with a delay and propagates inside the charge.
Figure 2 (left part) shows the wave-front positions at
dierent times. At the time t
4
, the front arrives on the
side surface of the charge (point B in Fig. 1) and then is
\separated." Conventional detonation with an approx-
imately constant velocity propagates upward over the
charge, and an explosive process with a variable velocity
propagates downward, toward the obstacle (right part
in Fig. 2). The latter was called the retonation wave.
The distance covered by this wave is not large.
It follows from this explanation that the parame-
ters h and , which were commonly accepted to be the
depth and delay of detonation, are ctitious. In reality,
there is no detonation depth, it is equal to zero, and the
real delay of detonation is smaller than the value, which
is measured in experiments using photographs similar to
that in Fig. 1, by (t
4
{t
0
).
This idea was later conrmed by Dremin et al. [3].
No retonation waves were observed in numerous exper-
iments with measurement of mass velocity inside the
charge by an electromagnetic method. Dremin et al. [3]
also assumed that the second sector of the trace is as-
sociated with the arrival of the curved detonation front
on the side surface of the charge.
Theoretical models of evolution of the initiating
SW to the detonation wave deny the formation of ret-
onation waves altogether [4, 5]. The initiating SW, the
ux of matter, and the detonation wave always move in
the same direction: from the place of initiation (from
the obstacle) to the free end face. It is assumed that all
the matter behind the detonation wave burns out.
Thus, if we assume that the retonation wave ex-
ists, we have to accept another condition: the mat-
ter does not completely decompose behind the front
of the primary initiating wave, part of the matter re-
mains unchanged, and it is over this unreacted mat-
ter that the reverse wave can propagate. An explosive
process where the matter does not completely decom-
pose is observed in nitroglycerine and in powdered and
coarsely dispersed HE (low-velocity detonation). One
direct proof of partial HE decomposition in the regime
of low-velocity detonation (30%) can be the experi-
ment of [6]. Dubovik and Bobolev [6] blasted a verti-
cally located nitroglycerine (NG) charge in a plexiglass
shell by a weak initiator from above, which caused the
low-velocity detonation regime. In 20{30 sec, initi-
ation was performed by a powerful initiator, and the
low-velocity detonation wave was followed by a normal
detonation wave, which overtook the low-velocity front
and entered the initial NG almost without any changes
in velocity.
Nevertheless, in studying detonation of NG{
ammonium nitrate (AN) mixtures, we really observed
a retonation wave in one mixture. The test conditions
were as follows. We studied a 20/80 NG/AN mixture
with a density of 0.9 g/cm
3
; the ammonium-nitrate
472
Afanasenkov
grain size was 0.16{0.32 mm. The mixture was placed
into a plexiglass shell 20 mm in diameter and 160 mm
long; the thickness of the walls was 2 mm. One end
of the shell was glued by a plexiglass plate 2 mm thick
through which the mixture was initiated by a 45/55
TNT/NaCl charge 20 mm in diameter and 30 mm long;
the charge density was 1.0 g/cm
3
. The detonation ve-
locity of the initiator was 2000 m/sec. Detonation lu-
minescence was registered by a ZhFR-2 photorecorder.
The photograph of the experiment is shown in Fig. 3.
A short trace directed toward the plate is observed at
the bottom of the gure. Then, two traces directed from
the place of initiation to the open end of the charge are
observed; the second trace is soon terminated. The det-
onation velocity calculated by the slope of the rst trace
is 2300 m/sec. The second trace appears again at a dis-
tance approximately equal to 0.8 of the charge length,
and a retonation wave, which covers more than half of
the charge length toward the point of initiation, also
emerges. The retonation-wave velocity is 1700 m/sec.
Since the trace of the retonation wave is rather long and
very bright, we can assume that the pressure in the for-
ward wave is not very high (no more than 10 kbar); thus,
the shell is not destroyed and retains transparency dur-
ing 0:1 msec. Possibly, the NG lm, which covers AN
grains, detonates in the forward wave, whereas AN and
the remaining NG react in the retonation wave (wide
blurred trace). The detonation velocity of this mixture
within the 40-mm charge diameter is 3500 m/sec. The
experiment is unique and was not reproduced.
It should also be noted that a double trace is often
registered on photographic lms in the case of detona-
tion of powdered solid HE [7, 8].
REFERENCES
1. M. A. Cook, The Science of High Explosives, Reinhold,
New York (1958).
2. A. Persson, \The transmission of detonation from
charges of TNT to LFB-dynamite, nitrolite, or TNT,"
Appl. Sci. Res., 6, Nos. 5{6 (1956).
3. A. N. Dremin, S. D. Savrov, V. S. Tromov, and
K. K. Shvedov, Detonation Waves in Condensed Media
[in Russian], Nauka, Moscow (1970).
4. G. I. Kanel', A. V. Utkin, and V. E. Fortov, \Equations
of state and macrokinetics of decomposition of solid ex-
plosives in shock and detonation waves," Preprint, Joint
Institute of Chemical Physics, Acad. of Sci. of the USSR,
Chernogolovka (1989).
5. B. A. Khasainov, A. V. Attetkov, and A. A. Borisov,
\Shock-wave initiation of porous energy materials and
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53{123 (1996).
6. A. V. Dubovik and V. K. Bobolev, \Investigation of
low-velocity detonation in nitroglycerine," in: Explo-
sive Engineering (collected scientic papers) [in Rus-
sian], No. 63/20, Nedra, Moscow (1967), pp. 275{278.
7. A. V. Dubovik, A. A. Denisaev, and V. K. Bobolev,
\Eect of the casing of the charge on the stability of
low-velocity detonation in powdered Trotyl," Combust.
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8. I. A. Karpukhin, Yu. M. Balinets, V. K. Bobolev, and
B. P. Stepashkin, \Initiation of fast chemical reactions
in solid composite HE by an elastic wave in a cylindrical
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