Combustion, Explosion, and Shock Waves, Vol. 37, No. 5, pp. 567 571, 2001
Shock-Wave Initiation of Detonation
of Double-Base Propellants
A. N. Afanasenkov1 UDC 532. 593
Translated from Fizika Goreniya i Vzryva, Vol. 37, No. 5, pp. 85 89, September October, 2001.
Original article submitted July 19, 1999.
In the known experimental system  active charge target HE charge to be tested ,
critical pressures of shock waves initiating detonation of double-base propellant
charges are determined. TNT charges of various density were used as active HE,
and copper plates 5 mm thick were used as targets. The pressure of the shock wave
acting on the propellant versus the TNT density was constructed; this dependence
being known the critical pressure can be readily determined with only the density of
the active charge available. It was found that double-base propellants are close to liq-
uid HE in terms of sensitivity to shock waves; the critical pressure is 6.0 9.0 GPa for
a charge diameter of 40 mm and decreases with increasing diameter. By an example
of the NDT-2 propellant, it is shown that the use of factory-packed propellants in line
charges may lead to failure in transfer of detonation from one propellant charge to
another.
Along with characteristics of high explosives (HE) rials (ammunition) [5]. This direction of propellant uti-
such as the detonation velocity and pressure, strength, lization is optimum, since commercial HE have a stable
etc., an important factor is the critical pressure of ini- market, the need in them is high (approximately a mil-
tiation of HE detonation by a shock wave (pcr). Know- lion tons per year), and there is a deficit in water-proof
ing this characteristic is necessary in designing contain- HE [6]. The use of propellants as commercial HE con-
ers for HE transportation, calculating storage facilities, ditions a necessity of development of appropriate firing
studying detonation transfer from one charge to an- charges (intermediate detonators) capable of initiation
other, calculating parameters of firing charges necessary of reliable detonation of propellant charges. The solu-
for reliable initiation of deep-hole charges, etc. How- tion of this problem is facilitated if the sensitivity of
ever, the results of experimental determination of pcr the propellant to the shock wave, i.e., the value of pcr
for the same HE are often different, since the test con- is known.
ditions are different (different HE densities and disper- Results of determining pcr for a number of double-
sions, charge diameters, etc.) [1]. Shock-wave initiation base propellants are described in the present paper (we
of detonation of brisant HE is discussed in many pa- did not study pyroxylin compositions). The experi-
pers (see the review in [2]), and only scattered data are ments were conducted using the known scheme: ac-
available for colloidal propellants [3, 4]. tive charge metal target propellant charge to be tested
Because of conversion of the defence industry, a (Fig. 1). TNT charges of different density were used as
considerable amount of colloidal (artillery or rocket) active charges, and copper plates 5 mm thick were used
propellants has been set free for the last decade. One as targets. Propellant specimens were continuous uni-
method of utilization of these propellants is their use in form cylinders of different diameters 80 mm high. The
blasting industry as water-proof HE or as components pressure of shock waves in the double-base propellant
of new commercial HE. It is assumed that they will be was calculated by the reflection method (Fig. 1b). Af-
used both in a pure form and in the form of raw mate- ter the explosion of the active charge, a shock wave
O1 with a mass velocity u1 enters the target (see
1 curve I). Reaching the boundary with the propellant,
Institute of Problems of Chemical Physics,
this shock wave is reflected, and the shock wave O2
Russian Academy of Sciences, Chernogolovka 142432.
0010-5082/01/3705-0567 $25.00 © 2001 Plenum Publishing Corporation 567
568 Afanasenkov
Fig. 1. Layout of the experiment on determining
pcr (a) and graphical interpretation of the experi-
ment (b): 1) HE tested; 2) target; 3) active charge;
Fig. 3. Pressure of the initiating shock wave in
4) lens forming a plane detonation front; 5) detona-
the propellant versus the density of the active TNT
tor; curves I and II are the shock adiabats for the
charge.
target material and propellant; point 1 refers to the
state in the shock wave in the target and point 2
shows the state in the shock wave in the propellant;
u1 is the mass velocity and w is the velocity of the
free surface of the target.
shows the shock adiabat for nitroglycerin and exper-
imental data on shock compressibility of double-base
propellants N [8], NB-40 [9], and RSI-12K (our data),
as well as for nitroglycerin itself [10]. All the data are
described by one curve. The single shock adiabat for
double-base propellants is apparently explained by the
fact that they consist of almost identical components
and, hence, have an identical dynamic compressibility.
These propellants contain 56 60% colloxylin, 25 35%
nitroglycerin, 5 12% dinitrotoluene, and 3% centralite,
i.e., 95% of the composition is the same on the average.
The presence of a small amount of technological addi-
tives (2 5%) has no effect on propellant compressibility
in the experiment. Compositions of some double-base
propellants can be found in [11].
The mass velocity u1 at the exit from a copper
target 5 mm thick (point 1 in Fig. 1) as a function of
Fig. 2. Generalized shock adiabat of double-base
the density of the active TNT charge is given in [12].
propellants: the curve is the calculated adiabat of ni-
The pressure of shock waves acting on the propel-
troglycerin (D = 1.73+2u-0.1u2/1.73 [km/sec] [1]);
lant (point 2 in Fig. 1) in explosion of TNT charges of
the points show experimental data.
different density was calculated using the data of [12]
and the generalized shock adiabat for propellants (see
enters the propellant (see curve II). It is assumed that Fig. 2). The results are plotted in Fig. 3. These data
the isentrope of metal unloading 1  2  w is symmetric being available, the measurement of the pressure pcr re-
to its shock adiabat (I). The shock adiabat of copper duces to experimental determination (usually, in three
is known; in the coordinates p and u, it is written as parallel experiments) of the minimum density of the
D = 4.0 + 1.5u [km/sec] [7]. For nitroglycerin propel- TNT charge at which the propellant explodes (Á+) and
lants, we used a single shock adiabat, which was the ni- the maximum density at which it fails to explode (Á-).
troglycerin adiabat calculated by the generalized depen- The value of pcr itself is found from Fig. 3. The critical
dence D = c0 + 2u - 0.1u2/c0, where c0 is the adiabatic value is assumed to be either the detonation pressure
velocity of sound [1]. For nitroglycerin, the calculation (p+) or the detonation failure pressure (p-) (we believe
by the Rao rule yields c0 = 1730 m/sec [1]. Figure 2 the first definition is preferable).
Shock-Wave Initiation of Detonation of Double-Base Propellants 569
TABLE 1
Propellant Á+/Á-, g/cm3 p+/p-, GPa dcr, mm
RST-4K 1.41/1.40 5.8/5.7 2.0
RNDSI 1.46/1.44 6.5/6.2 5.0
RSI-12K 1.51/1.48 7.1/6.7 5.0
NB-40 1.61/1.58 8.6/8.1 10"
RAM-10 1.60/1.58 8.4/8.1 14
N 1.59/1.58 8.2/8.1 28""
Note. One and two asterisks indicate the data of [13] and
[14], respectively.
Fig. 5. Dependences pcr (d/dcr) for double-base pro-
pellants: points 1 6 refer to propellants stored for
H"10 months and points 1 refer to the freshly pre-
pared RST-4K.
(H"4.1 km/sec). Then, the velocity decreased, but the
explosion process covered the entire charge length. As
the charge diameter increases, the dependence pcr tends
to become more flat. At the same time, it is known
that the detonation velocity of continuous homogeneous
double-base propellants is independent of the charge di-
ameter [13]. It follows from the data obtained that the
value of p+ of the shock wave exciting propellant deto-
nation under critical conditions (d/dcr = 1) is twice as
small as the pressure of propellant detonation. For the
N propellant, the detonation pressure is 20.4 GPa [14]
(25.0 GPa for pure nitroglycerin [10]).
Fig. 4. Dependence of pcr on the charge diameter for
NB-40 (I) and RST-4K (II) propellant: the points ć%, An attempt was made to generalize experimental
" , and refer to explosion, failure, and transitional
results for obtaining a single dependence for all pro-
regime, respectively.
pellants. The results are plotted in Fig. 5. For all
propellants that have been stored for an identical time
The results of the present paper are shown in Ta- (H"10 months), the results can be described by a single
ble 1 and Figs. 4 and 5. The values of pcr corresponding curve p = 11.2(d/dcr)-0.25 [GPa]. Using this depen-
to propellant explosions and failures, and also the den- dence, one can evaluate the pressure pcr of a propellant
sities of active charges are listed in Table 1. The charge charge if its critical diameter of detonation is known.
size was identical for all propellants: diameter 40 mm, At the same time, the freshly prepared RST-4K pro-
height 80 mm, the density of propellants was assumed pellant (storage time of 1 month) is more sensitive to
to be equal to 1.60 g/cm3; the active charge had a di- shock waves. Possibly, the reason is the evaporation
ameter of 40 mm and a height (together with the plane of the solvent from the propellant during its storage.
front lens) of 60 mm. Table 1 also gives the critical di- Nevertheless, there is another explanation. The RST-
ameter of propellant detonation (dcr). Propellants with 4K propellant contains up to 5% of powdered oxides of
a storage time of H"10 months were used. Figure 4 shows heavy metals whose particles may play the role of  hot
pcr versus the charge diameter d for the NB-40 propel- spots facilitating excitation of detonation [2].
lant and for the freshly prepared RST-4K propellant. From the equation for the dependence that de-
For the NB-40 propellant, the transitional regime was scribes experimental data, it follows that the pressure
observed near d = dcr, with the velocity at the initial of the shock wave exciting propellant detonation un-
section equal to the velocity of the initiating shock wave der critical conditions (d/dcr = 1) does not exceed
570 Afanasenkov
11.2 GPa, which is approximately 1.8 times smaller four boxes were exploded. One box was opened, the free
than the detonation pressure in a continuous propel- space in the metal box above the propellant packed as
lant (H"20.4 GPa [14]). Possibly, this is the limiting a honeycomb was filled by 20 22 kg of powdered RDX,
value of pressure in shock-wave initiation of detonation two T-400 TNT pellets equipped by electric detonators
of double-base propellants. were placed there, the box was closed, turned by its
Note that, to excite propellant detonation by an side surface down, and exploded. In the case of one or
impact of a flying fragment, i.e., to generate a shock two boxes of the propellant (the second box was placed
wave of intensity p+ (point 2 in Fig. 1b), the flight with its side surface against the bottom of the first box),
velocity of the fragment should be greater than w = 2u1. complete detonation of propellant was observed, and no
To ensure wide usage of converted double-base pro- leavings of the propellant were found. In the case of
pellants as water-proof commercial HE, it is necessary three boxes, leavings of unburned propellant elements
to provide reliable initiation of their detonation. For were found; in the case of four boxes, the last one was
this purpose, it is recommended [15] to use firing charges simply destroyed, and the propellant was scattered over
(intermediate detonators) from cartridges of powdered the ground surface.
Amatol (79/21 AN/TNT) or standard T-400 TNT pel- Bearing in mind the above said and taking into
lets. The pressure psh of the shock wave entering a con- account the results of [4], we can offer the following
tinuous propellant charge was evaluated in the case of explanation to the results obtained. The first charge
contact explosion of these firing charges on the charge of the propellant detonates completely, since the pro-
surface. Isentropes of explosion products of Amatol of pellant experiences a powerful initiating pulse from the
density 1.0 g/cm3 and TNT of density 1.55 g/cm3 were contact explosion of the RDX charge. Hitting the target
calculated; in accordance with Fig. 1b, the value of psh (metal wood), the detonation wave generates a shock
was calculated using the point of intersection of isen- wave that moves into the second charge. This shock
tropes with the shock adiabat for the propellant. We wave initiates a strong explosive process in the second
obtained psh = 11.5 GPa for Amatol and 16.0 GPa for charge, which may either decay or transform to low-
TNT (in water-filled propellants, the values of psh are velocity detonation near the boundary with the third
slightly smaller  10.8 and 15.0 GPa, respectively). charge. The third charge experiences the action of a less
A comparison with the data of Table 1 shows that powerful pulse (which is no longer detonation) than the
psh > pcr, i.e., these firing charges in contact provide second charge (the amount of exploded HE was more
reliable initiation of detonation of double-base propel- than 90 kg in the first box and 72 kg in the second
lant charges in holes 40 mm in diameter or more. box). Passing through the next target (package walls),
We note one more circumstance. In contact explo- this pulse is attenuated, and the third charge experi-
sion of a T-400 TNT pellet, a shock wave with a pressure ences the action of a shock wave of lower intensity than
of 16.0 GPa enters the propellant, whereas its pressure the second charge. Either low-velocity detonation or a
is only 7.5 GPa if there is a copper target 5 mm thick weak explosive process similar to that observed in [4]
between the TNT and propellant charges (see Fig. 3), emerges in the third charge. In both processes, the pro-
i.e., the target considerably decreases the value of the pellant elements adjacent to the box wall at the bound-
initiating pulse. This should be taken into account in ary with the fourth charge do not have enough time
the case of discontinuity of the deep-hole charge. We to burn in the reaction zone and are scattered into the
encountered the effect of the shell (package walls) on ambient medium during expansion of explosion prod-
detonation transfer between propellant charges when we ucts (propellant elements near the boundary with the
studied the possibility of using the packed NDT-2 pro- second charge burn completely in explosion products).
pellant for blasting works (construction of channels, col- The decaying mode or low-velocity detonation gener-
lectors, etc.). An industrially packed propellant charge ate a weak shock wave into the fourth charge, which is
is a zinc box located in a wooden box and containing not capable of generating an explosive reaction in the
72 kg of a tubular NDT-2 propellant (tubes 5 mm in propellant, and the propellant is scattered around.
diameter and 180 500 mm long). It was assumed that The results of the present studies show that the
the boxes are butt-jointed to one another in a specially sensitivity of examined double-base propellants in a
prepared trench (3 m deep and approximately 0.8 m continuous state to the shock wave is noticeably lower
wide), and an extended charge (10 15 boxes and more) than that of pressed brisant HE for which pcr =
is exploded from one or both ends. Nevertheless, pre- 0.5 3.0 GPa [1] but is close to the sensitivity of liq-
liminary experiments showed that detonation decays in uid HE. For charge diameters d < 40 mm, we have
such charges, and failures are observed. Four series of pcr = 6.0 9.0 GPa.
experiments were performed: one, two, three, and then
Shock-Wave Initiation of Detonation of Double-Base Propellants 571
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