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. Afanasenkov1 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/cm3 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- of the charge. Its slope on the photograph corresponds
tion waves in solid high explosives (HE) (powdered and to the detonation velocity of the HE examined. The
pressed) being initiated by shock waves through an inert second sector of the trace is directed toward the obsta-
obstacle or air has been extensively discussed in the lit- cle but does not reach it. It is the second sector that is
erature. The existence of these waves has been usually associated with retonation-wave luminescence.
proved by traces on photographic films, which were ob- The first explanation of the  retonation -wave phe-
tained by means of optical registration of luminescence nomenon seems to be proposed in [2], where the deto-
of explosion products (by a high-speed photorecorder) nation velocity was measured both on the surface of the
in the case where the detonation wave arrives on the side initiated charge and inside it (at the charge axis), which
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 Ä (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
B
charge diameter. With increasing charge diameter and
decreasing pressure in the initiating SW, the values of Ä
A
and h generally increase; however, the proportionality
is violated near the limits of initiation [1]. Some au-
thors used the dependence of Ä on the critical pressure
x
to determine the kinetic parameters of HE decomposi-
tion. The detonation trace has two sectors. The first
t
one is directed (from the point B) toward the free end
Fig. 1. Typical photograph of shock-wave excitation
1
Institute of Problems of Chemical Physics,
of detonation in a solid HE charge.
Russian Academy of Sciences, Chernogolovka 142432;
[e-mail].
470 0010-5082/02/3804-0470 $27.00 © 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 orifices 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 flux of matter, and the detonation wave always move in
at the center of the charge at the charge obstacle inter- the same direction: from the place of initiation (from
face with a delay Ä and propagates inside the charge. the obstacle) to the free end face. It is assumed that all
Figure 2 (left part) shows the wave-front positions at the matter behind the detonation wave burns out.
different times. At the time t4, the front arrives on the Thus, if we assume that the retonation wave ex-
side surface of the charge (point B in Fig. 1) and then is ists, we have to accept another condition: the mat-
 separated. Conventional detonation with an approx- ter does not completely decompose behind the front
imately constant velocity propagates upward over the of the primary initiating wave, part of the matter re-
charge, and an explosive process with a variable velocity mains unchanged, and it is over this unreacted mat-
propagates downward, toward the obstacle (right part ter that the reverse wave can propagate. An explosive
in Fig. 2). The latter was called the retonation wave. process where the matter does not completely decom-
The distance covered by this wave is not large. pose is observed in nitroglycerine and in powdered and
It follows from this explanation that the parame- coarsely dispersed HE (low-velocity detonation). One
ters h and Ä, which were commonly accepted to be the direct proof of partial HE decomposition in the regime
depth and delay of detonation, are fictitious. In reality, of low-velocity detonation (H"30%) can be the experi-
there is no detonation depth, it is equal to zero, and the ment of [6]. Dubovik and Bobolev [6] blasted a verti-
real delay of detonation is smaller than the value, which cally located nitroglycerine (NG) charge in a plexiglass
is measured in experiments using photographs similar to shell by a weak initiator from above, which caused the
that in Fig. 1, by (t4 t0). low-velocity detonation regime. In 20 30 µsec, initi-
This idea was later confirmed by Dremin et al. [3]. ation was performed by a powerful initiator, and the
No retonation waves were observed in numerous exper- low-velocity detonation wave was followed by a normal
iments with measurement of mass velocity inside the detonation wave, which overtook the low-velocity front
charge by an electromagnetic method. Dremin et al. [3] and entered the initial NG almost without any changes
also assumed that the second sector of the trace is as- in velocity.
sociated with the arrival of the curved detonation front Nevertheless, in studying detonation of NG
on the side surface of the charge. ammonium nitrate (AN) mixtures, we really observed
Theoretical models of evolution of the initiating a retonation wave in one mixture. The test conditions
SW to the detonation wave deny the formation of ret- were as follows. We studied a 20/80 NG/AN mixture
onation waves altogether [4, 5]. The initiating SW, the with a density of 0.9 g/cm3; the ammonium-nitrate
472 Afanasenkov
grain size was 0.16 0.32 mm. The mixture was placed REFERENCES
into a plexiglass shell 20 mm in diameter and 160 mm
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3. A. N. Dremin, S. D. Savrov, V. S. Trofimov, and
locity of the initiator was 2000 m/sec. Detonation lu-
K. K. Shvedov, Detonation Waves in Condensed Media
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[in Russian], Nauka, Moscow (1970).
The photograph of the experiment is shown in Fig. 3.
4. G. I. Kanel , A. V. Utkin, and V. E. Fortov,  Equations
A short trace directed toward the plate is observed at
of state and macrokinetics of decomposition of solid ex-
the bottom of the figure. Then, two traces directed from
plosives in shock and detonation waves, Preprint, Joint
the place of initiation to the open end of the charge are
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observed; the second trace is soon terminated. The det-
Chernogolovka (1989).
onation velocity calculated by the slope of the first trace
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is 2300 m/sec. The second trace appears again at a dis-
 Shock-wave initiation of porous energy materials and
tance approximately equal to 0.8 of the charge length,
viscoplastic model of hot points, Khim. Fiz., 15, No. 7,
and a retonation wave, which covers more than half of
53 123 (1996).
the charge length toward the point of initiation, also
6. A. V. Dubovik and V. K. Bobolev,  Investigation of
emerges. The retonation-wave velocity is H"1700 m/sec.
low-velocity detonation in nitroglycerine, in: Explo-
Since the trace of the retonation wave is rather long and
sive Engineering (collected scientific papers) [in Rus-
very bright, we can assume that the pressure in the for-
sian], No. 63/20, Nedra, Moscow (1967), pp. 275 278.
ward wave is not very high (no more than 10 kbar); thus,
7. A. V. Dubovik, A. A. Denisaev, and V. K. Bobolev,
the shell is not destroyed and retains transparency dur-
 Effect of the casing of the charge on the stability of
ing H"0.1 msec. Possibly, the NG film, which covers AN
low-velocity detonation in powdered Trotyl, Combust.
grains, detonates in the forward wave, whereas AN and
Expl. Shock Waves, 9, No. 3, 374 377 (1973).
the remaining NG react in the retonation wave (wide
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within the 40-mm charge diameter is 3500 m/sec. The
in solid composite HE by an elastic wave in a cylindrical
experiment is unique and was not reproduced.
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It should also be noted that a double trace is often
sion Processes. Detonation [in Russian], Chernogolovka
registered on photographic films in the case of detona-
(1977), pp. 83 85.
tion of powdered solid HE [7, 8].