CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
EXPERIMENTAL STUDY OF EXPLOSIVE
FRAGMENTATION OF METALS MELTS
A.K. Zhiembetov, A.L. Mikhaylov, G.S. Smirnov
RFNC-VNIIEF, IPhE, Sarov, Nizhni Novgorod region, 37 Mira ave.
Russia, 607190
Abstract. The authors describe the device, techniques and results of study of explosive
fragmentation and dispersion of metallic shells after their melting under shock-release wave loading. It
was revealed that structures of dispersed and fragmented shells of melted metals (lead and indium) are
large-mesh foam structures similar to structures formed at extension of real (low-viscous) liquids. The
process of fragmentation and dispersion of shells of melted metals is qualitatively described by the
cavitational model of liquid medium fracture with formation of a gas-drop cloud. It is shown that at
absence of metals melting in the used tested devices, the shells destruction occurs according to
commonly known regularities revealed at high-velocity destruction.
Indeterminacy in solidus-liquidus temperatures,
lack of knowledge on the metals melt fragmentation
process - all these problems can cause errors in
determination of fragments parameters for important
practical situations, and they require obtaining new
experimental data with expansion of the methodical
approaches.
INTRODUCTION
Experimental study of fragmentation and
dispersion of metals melts at volume strain rates of
104-106 s"1 has prominent practical and scientific
value. Information on fracture of such media is
required for creation of a generalized model of
dynamic fracture of condensed media, including
peculiarities of liquids and solids fracture.
The traditional thermodynamic approach based
on analysis of the phase diagrams of equilibrium
states causes indeterminacy of solidus-liquidus
temperatures range in some cases. So, for example,
for widely studied lead, this range is 20-120 GPa
[1,2].
It is shown in [3-8] that liquid layer fragmentation
under pulse loading differs significantly from the
process of solid fracture and fragmentation.
It is revealed that at explosive fracture, depending
on value of specific energy release, the cavitational
mechanism of fracture or growth of hydrodynamic
perturbations (of Rayleigh-Taylor instability type)
can be implemented in a liquid on outside and inside
surfaces of liquid volume. The spall type of fracture
is also possible.
EXPERIMENTAL
The scheme of experimental set-ups is similar to
the scheme used by many researchers
[9-14], and it is shown in Fig. 1.
Cylindrical charges of HE based on HMX of the
PBX-9501 type or plastic HE of the XTX8003 type
with radius Ro=30 mm were inserted coaxially in
rings made of lead, indium or soft steel. HE charges
lengths were: for indium rings -30 mm, for rings
made of lead and soft steel - 20 mm. Thickness of
metal rings was chosen basing on equilibrium of the
relation between linear masses of HE charge and
ring. The relative thickness of rings walls was 6-9%.
HE charge initiation was performed along axis at
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Analysis of data of the optical recording allowed
to choose stages of interest for determination of
times of pulse X-ray recording, distances of targets
and CD arrangement.
The X-ray photos of the process allowed to trace
dynamics of the interior state, explosive
fragmentation and dispersion of rings made of
indium and lead melts at expansion degrees up
to 30 RQ.
The X-ray photos of consecutive growth of
cavitation up to foam structure, fragmentation and
dispersion in tested device with use of
PBX-9501-type HE charge are presented in Fig. 2
and 3 for lead and indium, respectively.
X-ray recording was performed perpendicularly to
the device symmetry axis (Fig. 2 a, b and Fig. 3),
and along the symmetry axis of the tested device
(from an end face) (Fig. 2 c and Fig.3) with time of
the process recording up to 300 (is from time of HE
charge detonation initiation.
one end face with use of an extra initiator. Density
/
^
1 - additional initiator
2 - HE charge
3 - metal shell
FIGURE 1. Scheme of testing device.
of rings made of lead and indium was 0.999 of the
maximum theoretical density. No any alien inserts
and voids were revealed by y-defectoscopy of rings.
According to estimations, pressure at the internal
boundary of rings has the following values:
for lead rings - 50GPa (for PBX-9501) and
<30GPa (for XTX8003);
for indium rings - 50.5GPa (for PBX-9501).
For lead and indium rings with PBX-9501-type
HE charge, a frame-by-frame optical high-speed
recording of the initial stage of process was
performed with use of explosive illumination in the
plane passing through the devices symmetry axis.
No axial and radial breaks of rings and explosion
products (EP) releases were revealed for the
recording time at expansion degrees <15R0.
Basing on data of optical recording, the
dependence of radial velocity, V, of motions of the
rings outside boundary on expansion radius was
determined. Accuracy of velocity determination by
these techniques was estimated as 5-10%.
The results for the above-mentioned devices
showed V > 2 km/s at expansion < 15 RO, and 1.5
km/s at expansion > 20 RO.
As it is mentioned in [15], the free ring boundary
keeps high value of particle velocity for rather long
time that is a typical characteristic of growth of
cavitational process.
It is shown that gas-drop cloud (GDC) stops at =70
RO as a result of deceleration at interaction with the
environments.
Interior structure of cavitating ring made of indium
or lead melt, which is inaccessible to optical
recording, and its fragmentation were studied by the
method of pulse X-ray recording, parameters of
biphase flow - by targets and catching devices (CD).
the symmetry axis is perpendicularity to the figure plane
and displace to the left
FIGURE 2. X-ray records of cavitation (a, b), fragmentation
and dispersion (c) of ring made of lead melt.
axis of symmetry
FIGURE 3. X-ray records of cavitation, fragmentation and
dispersion of ring made of indium melt.
X-ray images obtained in tests were digitized by
microdensitometer FEAG-200. Then segmentation
of discretized images was carried out with
determination of distribution of medium material
density, parameters of fragments and aerosols. Using
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The second stage comes to an end, when the
volume concentration of foam structure reaches the
critical value >60%, at which there is a complete
fragmentation of cavitating shell into fragments with
6-10 times smaller densities and with the mentioned
diameters up to 7 mm. Duration of the second stage
is about several hundreds of microseconds after that
the inverse process occurs, namely, bubble liquid
transits into aerosol state.
The third stage with duration of about several
milliseconds is formation of a non-stationary
polydisperse cloud of aerosols with the characteristic
size of = 30 urn due to dispersion of fragments,
effect of turbulent diffusion and intermixing.
To verify that the results are caused not by features
of the used tested device design, tests with a ring
made of soft steel or a ring made of lead, but with
replacement of HE charge for less energetic HE of
XTX8003 type were carried out.
Figure 4 a, b illustrates the initial state of tested
device (a) (the same for all X-ray tests),
X-ray records of the test with ring made of soft
steel (b) with HE of PBX-9501 type and X-ray
records of the test with lead ring using HE of
the processing results, histograms were made for
distribution of meshes crosspieces thicknesses,
uncavitational "crust" in the cavitation area,
fragments sizes and masses.
Targets made of soft alloy of aluminum and CD
mounted at various distances from a tested device
were used in order to determine space distribution of
biphase flows, parameters of fragments and aerosols.
As CD filler, silica-alumina spheres having
diameters of 100 um with wall thickness of
4 um and bulk density of 0.4 g/cm3 were used.
States and structures of the targets surfaces were
studied by profilometry, optical and electronic
microscopy, micro X—ray spectral analysis at facility
JCMA-733.
After tests the silica-alumina microsphere were
separated by the flotation method in order to
perform granulometric analysis with use of
microscope DIP-1. Basing on the processing results,
histograms of aerosols distributions in sizes and
masses were prepared.
DISCUSSION
The experimental data show that the process of
explosive fragmentation and dispersion of rings
made of metal melted under shock-release process
differs significantly from those for rings made of
solid materials, but it proceeds within the frames of
a general physical model, and it is qualitatively
agreed with the process of explosive fragmentation
and dispersion of real liquids.
The process of explosive fragmentation and
dispersion of rings made of such metals and
formation of aerosol cloud can be divided into the
following stages (steps).
The first stage having duration of about several
microseconds is shock wave (SW) propagation from
HE detonation in metal ring, and subsequent
transition of it into the liquid state. When
propagating SW reaches the free boundary of ring,
the next (second) stage of the process occurs.
Reflection from the free surface results in rarefaction
wave formation. Radial tensions occur behind the
front of this wave. The tensions cause intensive
growth of microvoids that is the cavitation
phenomenon, beginning of fragmentation and
dispersion of the meshes crosspieces under effect of
axial tensions*.
FIGURE 4. Preliminary X - ray photo (a), X - ray records of
fracture of rings made of steel (b) and lead (c).
XTX8003 type at X-ray recording times equal to
times, when the X-ray records of Fig. 2 a and 3 a are
obtained. X-ray records of these tests show that,
contrary to X-ray records of Fig. 2 a, b and 3 a,
there is no foam structure of rings, complete
*) For the majority of metals with normal melting curve Pmd\.(T),
transition into the initial state occurs in rarefaction wave already
at subcritical (for melting) values of SW amplitude (T, P temperature and pressure, respectively).
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ACKNOWLEDGEMENT
fracture of ring made of soft steel into fragments
and breaks along radial stresses for lead ring are
observed.
Analysis of the results shows that explosive
fragmentation of rings made of solid metals in used
tested device occurs according to well-known laws
revealed at explosive tension and fragmentation of
thin-wall rings made of solid materials [9-14].
Basing on results of X-ray images processing,
comparative analysis of parameters of dispersed
fragments at melting and with no melting of metal
rings is performed. Figure 5 and Fig. 6 present
histograms of fragments masses in the tests with
lead at melting and with no melting, respectively.
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This work was supported by SNL due to Contract
N°BG-1446. The authors would like to thank
Richard Smith and Paul Yarrington from SNL for
real interest and fiscal support. We wish thank also
all VNIIEF employees who participated in this
work.
REFERENCES
1.
Bat'kosv Yu.V., German V.N., Osipov R.S.,
Novikov S.A., Tsyganov V.A., PMTF, 1, 149-151
(1988).
2. Mineev V.N., Savinov E.V., ZhETF, vol.52, issue 3,
629-636(1967).
3. Kedrinsky V.K., PMTF, 3, 74-93 (1993).
4. Stebnovsky S.V., Chernobaev N.N., PMTF, 1, 57-61
(1986).
5. Sultanov F.M, Yarin A.L., PMTF, 5, 48-54 (1990).
6. S.V. Stebnovsky, "Dynamics of formation of gasdrop flow at explosive dispersion of liquid volume in
Mechanics of liquid fracture", Siberian Branch ofRAS,
Institute of Hydrodynamics, issue 104, 1992, pp. 40-75.
7. Stebnovsky S.V. "Disperse analysis of gas-drop
systems formed as result of explosive fracture of liquid
volumes", Mechanics of liquid fracture. Siberian
Branch of RAS, Institute of Hydrodynamics, issue 104,
1992, pp. 76-95.
8. Aksenov R.M., Zverev A.A.,. Kovalenko O.V,.
Sirotkin V.K, Sumin E.V., PMTF, 6, 103-111 (1992).
9. Allison F.E., Watson R.W., ].App,. Phys.* voI40, 1,
110-113(1969).
10. Kuznetsov V.M., FGV, 4, 567-571 (1973).
11. Ivanov A.G., Kochkin L.I., V.F. Novikov,.
Folomeeva T.M, PMTF, 1, 112-117 (1983).
12. Koshelev E.A., Kuznetsov V.M, Sofronov ST.,
Chernikov A.G., PMTF, 2, 87-100 (1971).
13. Odintsov V.A., Shkalyabin I.O., FGV, 3, 147-150
(1994).
14. Held M, Propellants, Explosives, Pyrotechnics, 15,
254-260(1990).
15. Kedrinsky V.K., Chernobaev N.N., PMTF, 2, 90-96
(1992).
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M,g
FIGURE 5. Histogram of masses of melted lead fragments.
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M,g
FIGURE 6. Histogram of masses of unmelted lead fragments.
Analysis of the obtained data shows that average
mass of melted fragments is -2.5 times less than
average mass of unmelted lead fragments at the
specified distance of dispersion.
CONCLUSIONS
So, the obtained physical results allow to make the
basic conclusion of these studies: the process of
explosive fragmentation arid dispersion of metallic
rings after their melting under shock-release wave
loading has cavitational character, and it differs in
principle from that for rings of solid metals.
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