Journal of Materials Processing Technology 85 (1999) 52 55
Non-ideal detonation of emulsion explosives
a, a a b b
K. Takahashi *, K. Murata , Y. Kato , M. Fujita , S. Itoh
a
Research and De elopment Department, NOF Corporation, 61-1 Kitakomatsutani, Taketoyo-cho, Chita-gun, Aichi 470-23, Japan
b
Faculty of Engineering, Kumamoto Uni ersity, 2-39-1 Kurokami, Kumamoto 860, Japan
Abstract
In order to obtain a better understanding of the underwater explosion phenomena related to emulsion explosives, optical
measurements using the water tank technique and cylinder expansion test were carried out. Streak photographs were taken using
an image converter camera with a usual shadow graph system. Four kinds of emulsion explosives differing in aluminium contents
were used in the experiments. These emulsion explosives were placed into copper and PMMA pipes. From the results obtained
with the water tank technique, it is recognized that the maximum velocity of underwater shock wave in the case of a copper pipe
is about 10% faster than that in the case of a PMMA pipe. From the cylinder expansion test, it is found that the degree of radial
displacement of a copper case (Uexp) increases with increased aluminium content and that in the range of more than 10 wt.%, Uexp
decreases with increased aluminium content. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Emulsion explosives; Underwater shock wave; Optical measurements; Cylinder expansion test
1. Introduction order to investigate the effects of confinement on un-
derwater shock wave properties, four kinds of emulsion
Underwater shock waves generated by underwater explosives charged into copper and PMMA pipes were
explosions have been utilized for metal forming, pow- used in experiments and optical measurements using the
der compression, etc. It is well known that commercial water tank technique and cylinder expansion test [2]
explosives are used in explosive working and represent were carried out.
the non-ideal detonation properties. The non-ideal det-
onation properties are constant, but detonation proper-
ties depend on the conditions. The detonation wave 2. Experiments
propagates with lower pressure and lower velocity than
the ideal values, which calculated on the diameter of Four kinds of emulsion explosives, EMX1 EMX4
explosive are assumed infinite [1]. The conditions which (manufactured by NOF), which differ in aluminium
affect the non-ideal detonation properties are mainly content, were used in the experiments. EMX1 is com-
the diameter of explosives and the strength of the posed of 95 wt.% emulsion and 5 wt.% glass micro
confining vessel. Therefore, in order to enhance the balloons. To EMX2, EMX3 and EMX4 is added 5, 10
efficiency of the explosion, it is necessary to elucidate and 15% aluminium powder, respectively. EMX1 does
the basic properties of underwater shock waves gener- not contain aluminium powder. The loading densities
ated by underwater explosions with non-ideal detona- of EMX1 EMX4 are 1100, 1150, 1190 and 1230 kg
tion properties. However, non-ideal detonation m- 3, respectively. The detonation velocities (Dv) of
behavior has not been sufficiently investigated. Emul- EMX1 EMX4 charged into a copper pipe are 5015,
sion explosives are very safe to handle and show non- 5235, 5225 and 5185 m s- 1, respectively, while those of
ideal detonation properties which could be changed by EMX1 EMX4 when charged into a PMMA pipe are
a loading density, addition of metal powder, etc. In 4520, 4570, 4610 and 4610 m s- 1, respectively. The
external diameter, thickness and length of these pipes
are 40, 5 and 160 mm, respectively; Dv was measured
* Corresponding author. Fax: [phone]; e-mail:
[e-mail] via the ion gap method.
0924-0136/99/$  see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII S0924-0136(98)00254-4
K. Takahashi et al. / Journal of Materials Processing Technology 85 (1999) 52 55
K. Takahashi et al. / Journal of Materials Processing Technology 85 (1999) 52 55 53
The experimental apparatus of the water tank tech-
nique [3] is shown in Fig. 1. Emulsion explosives were
charged into copper and PMMA pipes (the external
diameter, thickness and length of these pipe being 40, 5
and 30, respectively) and connected to the explosive
lens, which was composed of SEP (Dv 6970 m s- 1;
loading density 1310 kg m- 3) and HABW (Dv 4970 m
s- 1; loading density 2200 kg m- 3). This apparatus was
sunk into the water and the explosion was initiated by
the no. 6 electric detonator. In order to obtain the
propagation process of the underwater shock wave,
streak and framing photographs were taken by an
image converter camera (Hadland Photonics, Imacon
790) using an usual shadow graph system [4]. The
streak photographs were taken with the streak slit as
shown in Fig. 1 and underwater shock waves were
observed.
In order to conduct the cylinder expansion tests,
EMX1 EMX4 were charged into a copper pipe (the
diameter, thickness and length being 25.4, 2 and 120
mm, respectively) and connected to SEP as a booster.
This apparatus was set in air and explosion was ini- Fig. 2. Framing photographs obtained using the water tank technique
(EMX1 charged into a PMMA pipe).
tiated by the no. 6 electric detonator. The streak slit
was located at the middle of the explosives and streak
of the underwater shock wave becomes spherical imme-
photographs of the radial expansion process of a cop-
diately, owing to the effects of the expansion wave
per pipe were taken by the image converter camera.
brought about by the expansion of the detonation
Both the water tank test and the cylinder expansion test
product gas.
were carried out in the High Energy Rate Laboratory
Fig. 3 shows a streak photograph of EMX1 charged
in Kumamoto University.
into a copper pipe obtained with the water tank tech-
nique. The horizontal axis indicates the time (100 ns
mm- 1) and the vertical axis indicates the distance from
3. Results and discussion
the top of the explosives. From the streak photograph,
the relationship between the distance travelled by the
Fig. 2 shows framing photographs of EMX1 ob-
underwater shock wave and the time was read and
tained using the water tank technique. From these
recorded by a computer, after which an approximate
photographs, it can be confirmed that the configuration
curve (Eq. (1)) of the distance time history of the
underwater shock wave was determined by means of
nonlinear curve fitting method [5].
y/D=A1{1-exp(B1t)}+A2{1-exp(B2t)}
+A3{1-exp(B3t)}+c0t/D (1)
U=c0+sup, P= Uup,
0
Pcj=( U+ D)P/(2 U) (2)
0 e 0
where y is the distance of the underwater shock wave
form the top of the explosives, t is time, D is the
detonation velocity of explosives, c0 is the sound veloc-
ity of water, U is the velocity of the underwater shock
wave, s is a constant, up is the particle velocity of water,
P is the pressure of the underwater shock wave, is
0
the density of water, Pcj is the calculated detonation
pressure and is the loading density of the explosives;
e
Fig. 1. Schematic of the apparatus for the water tank technique. A1, A2, A3, B1, B2 and B3 are parameters.
54 K. Takahashi et al. / Journal of Materials Processing Technology 85 (1999) 52 55
K. Takahashi et al. / Journal of Materials Processing Technology 85 (1999) 52 55
Fig. 3. A streak photograph obtained using the water tank technique (EMX1 charged into a PMMA pipe).
velocity of the underwater shock wave rises to its
maximum velocity immediately and then decreases
gradually, finally reaching the sound velocity of water.
The maximum velocity (Umax) of the underwater shock
wave and the detonation pressure (Pcj) are summarized
in Fig. 5. Here, Umax and Pcj are calculated using the
velocity time history curve of the underwater shock
wave and Eq. (2), respectively. In the case of the copper
pipe, Umax of EMX1 EMX4 is about 4.08, 4.25, 4.21
and 4.25 km s- 1 , respectively and that of emulsion
explosive involving aluminium powder is about 200 m
s-1 faster than that of EMX1. However, in the range
Fig. 4. The distance time and velocity time history curves of under- of the experiments, Umax of emulsion explosives involv-
water shock wave generated by the underwater explosion of EMX1
ing aluminium powder is almost constant with increase
charged into a PMMA pipe.
of aluminium content in emulsion explosives. In con-
trast, in the case of the PMMA pipe, Umax of emulsion
Differentiating Eq. (1), the velocity of the underwater
explosives involving aluminium powder (EMX2
shock wave is obtained. Experimental and curve fitting
EMX4) is about 100 m s- 1 faster than that of EMX1,
results of the distance time and the velocity time his-
whose Umax is about 3.8 km s- 1. It is shown that the
tory of the underwater shock wave are plotted in Fig. 4.
Umax generated by emulsion explosives charged into a
When the detonation wave impinges on the water, the
copper pipe is about 10% faster than that generated by
emulsion explosives charged into a PMMA pipe. From
these results, it is recognized that the strength of the
confining vessel affects the velocity of the underwater
shock wave, the detonation pressure of emulsion explo-
sives and the reactivity of aluminium.
Fig. 5. Variations of the maximim velocity (Umax) of underwater
shock wave and the calculated detonation pressure (Pcj) with alu-
minium contents. Open circles, open squares, Umax and Pcj of explo-
Fig. 6. Radial displacement of a copper pipe: time history curves of
sives charged into a PMMA pipe; closed circles, closed squares, Umax
aluminized emulsion explosives obtained in cylinder expansion tests.
and Pcj of explosives charged into a copper pipe.
K. Takahashi et al. / Journal of Materials Processing Technology 85 (1999) 52 55
K. Takahashi et al. / Journal of Materials Processing Technology 85 (1999) 52 55 55
Fig. 6 shows radial displacement time history curves From the results obtained using the water tank tech-
of a copper pipe of EMX1 EMX4, which were mea- nique, it is shown that the maximum velocity of the
sured by streak photographs obtained in the cylinder underwater shock wave (Umax) in the case of a copper
expansion test. It is found that the degree of radial pipe is about 10% faster than that in the case of a
displacement increases with increased aluminium con- PMMA pipe. From the cylinder expansion test, it is
tent and then, in the range of more than 10 wt.%, the found that the degree of the radial displacement of a
degree of the radial displacement decreases with in- copper pipe (Uexp) increases with increase in aluminium
creased aluminium content. content and that in the range with more than 10 wt.%,
Uexp decreases as aluminium content increases.
4. Conclusions
References
In order to investigate the effects of confinement on
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[2] H. Hornberg, Propellants Explos. Pyrotech. 11 (1986) 23 31.
plosives, optical measurement using the water tank
[3] K. Sasa, I. Itoh, J. Jpn. Explos. Soc. 27 (1966) 228 233.
technique and cylinder explosion test were carried out.
[4] S. Itoh, S. Kubota, A. Kira, M. Fujita, J. Jpn. Explos. Soc. 55
Four kinds of emulsion explosives with differing alu-
(1994) 202 208.
minium contents, charged into copper and PMMA
[5] P.R. Bervington, Analysis for the Physical Sciences, Ch.11, Mc-
pipes were used in the experiments. Graw-Hill, New York, 1969.
.