U.S. patent application number 10/677649 was filed with the patent office on 2005-04-28 for ordnance device for launching failure prone fragments.
Invention is credited to Forsyth, Colin, Grudza, Maurice E., Jann, David C., Lacy, E. Willis, Waggener, Samuel S..
Application Number | 20050087088 10/677649 |
Document ID | / |
Family ID | 34520515 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087088 |
Kind Code |
A1 |
Lacy, E. Willis ; et
al. |
April 28, 2005 |
Ordnance device for launching failure prone fragments
Abstract
The present invention is an ordnance device capable of launching
discrete failure prone fragments in a coherent, controllable
fashion. The described device is comprised of an explosive charge,
a buffer element, a plurality of preformed failure prone fragments,
and a wrap element in the described order. Buffer element separates
failure prone fragments from the explosive charge so as to protect
the fragments from damage by explosive detonation products and to
reduce an incident pressure wave communicated into the fragments by
the detonation. Wrap element further reduces the pressure within
fragments by imparting a compressive pulse into the fragments
thereby offsetting the negative phase of the incident pressure
wave.
Inventors: |
Lacy, E. Willis;
(Fredericksburg, VA) ; Waggener, Samuel S.; (King
George, VA) ; Grudza, Maurice E.; (Langhorne, PA)
; Jann, David C.; (Bensalem, PA) ; Forsyth,
Colin; (Havertown, PA) |
Correspondence
Address: |
Matthew J. Bussan, Esq.
NSWCDD (XDC1)
Dahlgren
VA
22448-5100
US
|
Family ID: |
34520515 |
Appl. No.: |
10/677649 |
Filed: |
September 30, 2003 |
Current U.S.
Class: |
102/495 |
Current CPC
Class: |
F42B 12/32 20130101;
F42B 12/24 20130101 |
Class at
Publication: |
102/495 |
International
Class: |
F42B 012/22 |
Goverment Interests
[0001] The invention described herein may be manufactured and used
by and for the Government of the United States of America for
Governmental purposes without the payment of any royalties thereon
and therefore.
Claims
1. An ordnance device comprising: (a) an explosive charge; (b) a
fragment layer including a plurality of preformed failure prone
fragments; (c) a metal buffer element disposed between said
explosive charge and said fragment layer, said metal buffer element
configured to attenuate an incident shock communicated into said
fragment layer after detonation of said explosive charge, said
preformed failure prone fragments of said fragment layer being
arranged in a continuous fashion along said buffer element; and (d)
a wrap element having a first layer and a second layer, said first
layer disposed between said second layer and said fragment layer
opposite of said buffer element, said first layer composed of a
compressible material of lower density than said second layer, said
second layer configured to communicate a shock into said fragment
layer to further attenuate said incident shock.
2. The ordnance device of claim 1, wherein said fragment layer
further comprises a plurality of preformed inert fragments
interspersed with said preformed failure prone fragments.
3. The ordnance device of claim 1, wherein said ordnance device is
cylindrically shaped.
4. The ordnance device of claim 3, wherein said fragment layer
further comprises a plurality of preformed inert fragments
interspersed with said preformed failure prone fragments.
5. The ordnance device of claim 1, further comprising: (e) a second
buffer element disposed between said buffer element and said
explosive charge, said second buffer element compressible and less
dense than said buffer element.
6. The ordnance device of claim 5, wherein said ordnance device is
cylindrically shaped.
7. The ordnance device of claim 6, further comprising a plurality
of preformed inert fragments interspersed with said preformed
failure prone fragments.
8. The ordnance device of claim 5, further comprising: (f) a
polymer-based intermediate layer disposed between and contacting
said preformed failure prone fragments and said wrap element; and
(g) a polymer-based outer cover disposed along and contacting said
second layer opposite of said first layer.
9. The ordnance device of claim 8, wherein said ordnance device is
cylindrically shaped.
10. The ordnance device of claim 9, further comprising a plurality
of preformed inert fragments interspersed with said preformed
failure prone fragments.
11. The ordnance device of claim 9, wherein said preformed failure
prone fragments have a width-to-charge-diameter ratio of
approximately 0.07.
12. The ordnance device of claim 9, wherein said preformed failure
prone fragments have a location dependent dimensional
variability.
13. The ordnance device of claim 1, wherein said ordnance device is
linearly shaped.
14. The ordnance device of claim 13, further comprising a plurality
of preformed inert fragments interspersed with said preformed
failure prone fragments.
15. The ordnance device of claim 13, further comprising: (e) a
confinement structure, said explosive charge, said buffer element,
said preformed failure prone fragments and said wrap element
disposed within said confinement structure in referenced order so
as to allow launch of said preformed failure prone fragments
unimpeded by said confinement structure.
16. The ordnance device of claim 15, wherein said preformed failure
prone fragments have a location dependent dimensional
variability.
17. The ordnance device of claim 15, further comprising a plurality
of preformed inert fragments interspersed with said preformed
failure prone fragments.
18. A method for launching a preformed failure prone fragments
comprising the steps of: (a) attenuating a first shock along a
first surface of said preformed failure prone fragments; (b)
communicating a second shock into a second surface along said
preformed failure prone fragments; and (c) coupling said first
shock and said second shock so as to reduce pressure and stress
within said preformed failure prone fragments thereby avoiding
mechanical failure.
19. The ordnance device of claim 2 wherein said preformed failure
prone fragments have a width-to-charge-diameter ratio of
approximately 0.07.
20. The ordnance device of claim 3 wherein: said metal buffer
element comprises a copper buffer element having a thickness of at
least 0.064 inches; and said explosive charge has a diameter of at
least 4.85 inches.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0002] None.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention generally relates to an ordnance
device for launching failure prone fragments in a coherent fashion.
Specifically, the invention described herein mitigates
launch-induced conditions within and along such fragments.
[0005] 2. Background
[0006] A typical ordnance device explosively launches a plurality
of inert fragments in a controlled fashion so as to insure impact
between one or more fragments and a target. Inert fragments are
typically composed of a strong, non-brittle material to insure
coherent launch. Fragment strength limits the deposition of kinetic
energy within a target to a small volume immediately surrounding
the penetration path of the fragment.
[0007] In comparison, failure prone fragments produce a large
damage volume within a target thereby increasing the likelihood of
catastrophic damage. A failure prone fragment, for example a
fluorine-based polymer matrix with metal powder disposed therein,
may deposit both kinetic and chemical energies into a target to
achieve a large damage volume. Likewise, a failure prone fragment
may be composed of a brittle, inert composition, for example a
tungsten/metal matrix composite, which fractures and disperses upon
impact to achieve a large damage volume. Lethality enhancements are
achieved by avoiding fracture and/or reaction during launch in
favor of rapid mechanical failures and/or chemical reactions upon
impact.
[0008] The mechanical properties of non-brittle, inert fragments
resist damage associated with the harsh conditions of an explosive
launch. Upon ignition of an explosive, a detonation wave expands
through an explosive charge sweeping across the fragments and
imparting a shock wave into each fragment. Thereafter, individual
fragments are accelerated as the shock traverses the fragment.
Reflected shocks and rarefactions are imparted into the fragment
after the shock reaches surfaces along the fragment and thereafter
superimposed on the incident shock creating a complex pressure
state wherein tensile and compressive forces coexist.
[0009] Failure prone fragments are inherently more difficult to
explosively launch in a coherent fashion making their application
problematic in practical ordnance systems. Polymer-based fragments
in particular are less mechanically robust than homogeneous metals.
For example, PTFE-metal compositions are reported to have a yield
strength at least one order of magnitude lower than metals, thereby
susceptible to stress related failures. Additionally, such
materials are less dense than metals and occupy a larger volume
resulting in greater divergent forces.
[0010] Failure prone fragments exhibit three launch-induced failure
modes, namely spall, lateral fracture, and explosive induced
damage. Spall is manifested as one or more fractures perpendicular
to the flight direction of the fragment. Spall is a consequence of
excessive negative pressures within the material caused by the
rarefaction of strong compressive waves communicated into the
fragment during the detonation process. Lateral fracture is
manifested as one or more failures parallel to the flight direction
of the fragment. Lateral fractures are a consequence of excessive
non-uniform velocity gradients along the fragment width caused by
rarefactions within the detonation gases. Explosive induced damage
is manifested as deformations and fractures along the fragment
adjacent to the explosive charge. Explosive induced damage is a
consequence of high-pressure, explosive products interacting with a
low-strength fragment.
[0011] While metal-polymer materials in devices are disclosed in
the related arts, the attenuation of launch-related failures by the
invention described herein is neither described nor claimed in the
related arts.
[0012] Kuhns et al. discloses one such related art device in U.S.
Pat. No. 6,484,642 having a prescribed pattern of internal grooves
or recesses partially traversing the thickness of a shell structure
composed of steel thereby defining a plurality of inert fragments.
An undefined energetic or reactive material occupies the recesses
forming a continuous or nearly continuous web. An optional thin
liner of metal, plastic, or ceramic is coated, adhered, or
mechanically fastened over the reactive material to aid in fragment
retention. The described confinement of reactive material serves no
other purpose than to produce a high-pressure region within the
recesses, via a compression of and/or reaction by the reactive
material, so as to facilitate a controlled fragmentation of the
shell. The rapid release of this high pressure within the reactive
material, after fragmentation of the shell is completed, allows the
uncontrolled particulation and dispersion of the same. In contrast,
the present invention attenuates pressures within a fragment via a
buffer-wrap system about the fragments so as to prevent mechanical
failures and uncontrolled dispersion.
[0013] Hornig discloses an enhanced blast device in U.S. Pat. No.
5,852,256 comprised of a unitary casing of reactive material
surrounding and contacting an explosive charge. Also described is a
unitary liner of reactive material disposed between and contacting
a hardened steel casing and an explosive charge. The steel casing
facilitates penetration, protects the munition during penetration,
and increases compression of the reactive material to enhance its
dispersion and reactivity. In an alternate embodiment, larger
fragments of reactive metal are dispersed within a polymer binder
matrix therein having a finer reactive metal powder. The device
disperses reactive material in a finely divided form over a
relatively large space so as to enhance reactivity with the medium
immediately surrounding the device. Dispersal is achieved by
maximizing pressure and divergent forces within the reactive
material. In contrast, the present invention attenuates high
pressures within a fragment via a buffer-wrap system thereby
preventing reaction during launch and minimizing divergent
forces.
[0014] Cuadros discloses another device in U.S. Pat. No. 5,313,890
having a fabric liner woven from high-strength fibers located
between and intimately contacting an explosive charge and preformed
fragments, namely reactive-fluid filled fragments, as an
improvement over ductile metal liners. The fabric liner softens the
explosive launch of fragments via the controlled expansion and
delayed venting of detonation products. Fragments are disposed
between folds in a fabric liner that unfold as the explosive
products expand thereby projecting fragments in an outward radial
direction. Fragments are retained by an outer casing or enclosure,
such as a tubular metal or plastic casing, or tape spirally wound
around and contacting the fragments. In contrast, the present
invention provides a coupled arrangement between buffer and wrap so
as to attenuate the pressure state in a failure prone fragment. An
inner buffer of sufficient density and thickness attenuates the
shock communicated into fragments from the detonation event. An
outer wrap communicates a shock into the fragment via impact
between wrap and partially accelerated fragment further attenuating
the negative phase of the incident shock.
[0015] What is required is an ordnance device capable of launching
failure prone fragments in a coherent, controllable fashion. It is
desired that the device attenuate the incident shock communicated
into a fragment via a detonation event and/or attenuate the
negative phase of the incident shock within a fragment and/or
mitigate explosive induced damage thereon.
SUMMARY OF THE INVENTION
[0016] An object of the present invention is an ordnance device
capable of launching low-strength, brittle fragments so as to avoid
one or more damage modes inherent to such projectiles.
[0017] The present invention is comprised of an explosive charge, a
buffer element, a plurality of preformed failure prone fragments,
and a wrap element arranged in the order described. Formulations of
failure prone materials are composed of, but not limited to,
aluminum, magnesium, and zirconium powders within a matrix of one
or more fluorine rich polymers. Likewise, failure prone materials
may be comprised of brittle, chemically active or inert materials.
Buffer elements are composed of a polymer or a metal or a composite
of sufficient density and thickness to attenuate an incident shock
communicated into the failure prone fragments after detonation of
an explosive charge. Failure prone fragments are arranged in a
continuous fashion along the buffer element. A wrap element having
a first layer and a second layer is provided of sufficient density
and thickness so as to communicate a shock into the preformed
fragments to further attenuate the incident shock. The first layer
is composed of a compressible material of lower density than the
second layer. The second layer is composed of a polymer or a metal
or a composite. Cylindrical and linear shaped embodiments are
described and claimed. Confined and unconfined embodiments are also
provided.
[0018] Alternate embodiments of the present invention include an
optional second buffer element between explosive charge and buffer
element. Additional embodiments include an optional thin
polymer-based intermediate layer between fragments and wrap, as
well as a thin polymer-based outer cover over the wrap element. In
yet other embodiments, fragment length may vary with location and
preformed inert fragments may be interspersed with failure prone
fragments.
[0019] The present invention facilitates the exploitation of
failure prone materials within ordnance systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention will now be described in more detail, by way
of example only, with reference to the accompanying drawings, in
which:
[0021] FIG. 1 is a schematic diagram of an exemplary ordnance
device having a single buffer element disposed between explosive
charge and fragments with a layered outer wrap.
[0022] FIG. 2 is a schematic diagram of an exemplary ordnance
device having dually arranged buffer elements disposed between
explosive charge and fragments with a layered outer wrap.
[0023] FIG. 3 is a schematic diagram of a preferred embodiment
having dually arranged buffer elements and intermediate layer
disposed between fragments and layered outer wrap and an outer
cover over the outer wrap.
[0024] FIG. 4 is a perspective view of an exemplary embodiment of a
cylindrically shaped device having fragments of fixed
dimensions.
[0025] FIG. 5 is a section view of a cylindrical shaped embodiment
having variable length fragments with outer wrap not shown.
[0026] FIG. 6 is a perspective view of an exemplary embodiment of a
linearly shaped device having fragments of fixed dimensions.
[0027] FIG. 7 is a section view of a linearly shaped embodiment
showing arrangement of explosive, buffer, variable length
fragments, and wrap within a confinement structure.
REFERENCE NUMERALS
[0028] 1 Ordnance device
[0029] 2 Explosive charge
[0030] 3 Buffer element
[0031] 4 Fragment
[0032] 5 Wrap element
[0033] 6 First Layer
[0034] 7 Second layer
[0035] 8 Second buffer element
[0036] 9 Intermediate layer
[0037] 10 Outer cover
[0038] 11 Cylindrically shaped device
[0039] 12 Length
[0040] 13 Width
[0041] 14 Thickness
[0042] 15 Diameter
[0043] 17 Linearly shaped device
[0044] 18 Confinement structure
[0045] 19 Explosive-buffer interface
[0046] 20 Central axis
[0047] 21 Lateral member.
DESCRIPTION OF THE INVENTION
[0048] Referring now to FIG. 1, an exemplary arrangement of the
present invention, referred herein as an ordnance device 1, is
shown having an explosive charge 2 immediately adjacent to and
contacting a buffer element 3 immediately adjacent to and
contacting a plurality of fragments 4 immediately adjacent to and
contacting a wrap element 5. The term fragment 4 refers to
preformed projectiles composed of a failure prone composition
unless otherwise indicated. Components are assembled and
mechanically fastened or adhered via methods and techniques
understood in the art. For example, buffer element 3 and wrap
element 5 may be planar disposed sheets that are conformally
applied over explosive charge 2 and fragments 4, respectively,
thereby confining and supporting the fragments 4. It is likewise
possible of secure a cylindrically shaped buffer element 3 and wrap
element 5 over explosive charge 2 and fragments 4,
respectively.
[0049] The explosive charge 2 projects fragments 4 to a desired
velocity via the rapid release of energy during chemical
decomposition of the explosive. Explosive compositions known within
the art are applicable to the present invention. A variety of
shapes are possible for the explosive charge 2 shown in FIGS. 1-3,
including but not limited to rectangular, triangular, square,
polygonal, hemispherical, elliptical and combinations thereof.
Likewise, the linear explosive-buffer interface 19 shown in FIG. 1
may be concave, convex or combinations thereof.
[0050] The buffer element 3 attenuates the shock communicated into
the fragments 4 by the explosive charge 2, as well as mitigates
explosive induced damage on the fragments 4. The buffer element 3
may be composed of a metal, non-limiting examples including steel,
copper and aluminum, a polymer, non-limiting examples including
polyethylene, plexiglas, and nylon, an elastomer, a non-limiting
example being neoprene, or a composite, non-limiting examples
including fiber-reinforced plastic, glass-reinforced plastic, and
rigid woven fiber compositions, or laminates thereof.
[0051] Shock attenuation and damage mitigation are achieved via
buffer element 3 design, namely thickness and density. For example,
a buffer element 3 composed of copper having a thickness of
0.064-inches was sufficient to mitigate the deleterious effects on
fragments 4 composed of PTFE-metal formulations by an explosive
charge 2 having a diameter 15 of 4.85-inches.
[0052] Fragments 4 may be arranged in a column-like formation, as
shown in FIGS. 1-3, between buffer element 3 and wrap element 5.
While a variety of fragment shapes are possible, it is preferred
that fragments 4 align in a continuous fashion so as to minimize
gaps or voids there between. Fragment size is performance and
system dependent.
[0053] Fragments 4 may be composed of formulations of one or more
fluoropolymers and one or more oxidation metals. Exemplary
fluoropolymers include polychlorotrifluoroethylene (PCTFE),
ethylene-tetrafluoroethylene (ETFE), fluorinated ethylene-propylene
copolymer (FEP), polyvinylidene fluoride (PVDF), and
perfluoroalkyl-tetrafluoroethylene copolymer (PFA), homopolymers
and copolymers of fluorocarbon resins having analogs of ethylene
such as polytetrafluoroethylene (PTFE), polymers of
chloro-trifluoroethylene, and fluorinated ethylene, and
homopolymers and copolymers of fluoroelastomers such as
polyfluorocilicones. Exemplary oxidation metals include aluminum,
titanium, magnesium, and zirconium. Solid compositions of the above
may be manufactured by the method described by Joshi in U.S. Pat.
No. 6,547,993. It is likewise possible to have fragments 4 composed
of a chemically active or inert powder, preferably a metal, within
a brittle or weak matrix composed of a polymer or ductile
metal.
[0054] The wrap element 5 is comprised of a first layer 6 and a
second layer 7. The first layer 6 is disposed between and
contacting both fragments 4 and second layer 7 either mechanically
attached or adhered thereon via methods understood in the art. The
second layer 7 is preferably composed of a metal, non-limiting
examples including steel, copper, and aluminum. However, alternate
embodiments may be composed of a polymer, non-limiting examples
including polyethylene and nylon, or a composite, non-limiting
examples including fiber-reinforced plastic, glass-reinforced
plastic, and rigid woven fiber compositions, or laminates
thereof.
[0055] The wrap element 5 communicates a shock into the fragments 4
of sufficient magnitude to reduce the negative pressures therein.
The first layer 6, both compressible and less dense than the second
layer 7, allows the fragments 4 to accelerate prior to contacting
the second layer 7. The interaction between fragments 4 and second
layer 7 communicates a second shock into each fragment 4. The first
layer 6 may be composed of a foam, non-limiting examples including
open-cell and closed-cell polymers, a non-porous polymer,
non-limiting examples including polyethyelene and plexiglass, or an
elastomer, a non-limiting example being neoprene. Rigid yet
compressible foams were preferred. For example, a wrap element 5
composed of a 0.187-inch thick expanded, closed-cell polyethyelene
foam having a density of 4 pounds-per-cubic-foot and a 0.030-inch
thick aluminum was sufficient to adequately shock a 1.2-inch thick
PTFE-metal fragment launched from a cylindrically shaped explosive
charge 2 having an approximate diameter 15 of 10-inches.
[0056] In some embodiments, it may be preferred to provide a second
buffer element 8. Referring now of FIG. 2, a second buffer element
8 is shown disposed between the explosive charge 2 and the buffer
element 3. The second buffer element 8 is preferred to be less
dense than the buffer element 3 described above. For example, the
second buffer element 8 may be a gas-filled cavity, one example
being air, allowing the explosive charge 2 to expand prior to
contact with the buffer element 3. Alternately, the second buffer
element 8 may be a compressible material as described above for the
first layer 6. In yet other embodiments, if may be preferred to
provide a pair of dually arranged layers about the wrap element 5.
Referring now to FIG. 3, a thin intermediate layer 9, preferably a
polymer, is shown between and contacting fragments 4 and wrap
element 5. A thin outer cover 10, preferably a polymer, is also
shown contacting the wrap element 5 oppositely disposed from the
intermediate layer 9. Both intermediate layer 9 and outer cover 10
are mechanically fastened to, adhered to, or coated onto the wrap
element 5 via methods understood in the art.
[0057] Referring now to FIG. 4, a cylindrically shaped device 11 is
described having a cylinder-shaped explosive charge 2 surrounded by
a plurality of layers about a central axis 20. Material
arrangements shown in FIGS. 1-3 are equally appropriate. The
explosive charge 2 may consist of an unconfined mass of either cast
or pressed explosive material. Alternatively, the explosive charge
2 may be comprised of an explosive filled container as understood
in the art. The cylindrically shaped device 11 is secured to an
ordnance system via means understood in the art.
[0058] A variety of detonation schemes may be employed within the
cylindrically shaped device 11 via methods and devices understood
in the art. For example, one or more detonation points may be
positioned along or within the explosive charge 2. Alternatively,
an initiation scheme forming a toroidal or planar detonation wave
may be employed so as to minimize explosive loading onto the
fragments 4.
[0059] Referring again to FIG. 4, likewise dimensioned
rectangular-shaped fragments 4 are shown of prescribed length 12,
width 13, and thickness 14. However, other shapes are equally
applicable including but not limited to cubes, spheres, and solid
polygons. When the explosive charge 2 is cylindrically shaped, it
is desired to have a slight tapering of the width 13 along the
thickness 14 of the fragment 4 so as to accommodate circumference
differentials. Preformed or individual fragments 4 are arranged in
a contacting fashion to form a desired geometric arrangement, as
shown in FIG. 4.
[0060] Fragments 4 are dimensioned so as to deliver an optimal mass
onto the target, to achieve a desired hit probability, and in some
applications to minimize divergent forces along the fragments 4
during their acceleration by the explosive charge 2. For example, a
fragment 4 having an approximate length-to-width ratio of 1.84 and
an approximate thickness-to-width ratio of 1.75 adequately balanced
design considerations. Furthermore, a width-to-diameter ratio
approximately equal to 0.07 minimized divergent forces.
[0061] Referring now to FIG. 5 shows a sectioned cylindrically
shaped device 11 having a plurality of fragments 4 with differing
length 12. In other embodiments, it may be desired to have
fragments 4 of differing length 12 and/or width 13 and/or thickness
14.
[0062] In yet other alternate embodiments, it may be desired to
intersperse preformed fragments 4 composed of such inert materials
as steel or tungsten with the present invention. For example,
fragments 4 composed of inert materials may be aligned in row or
column formation with fragments 4 composed of failure prone
materials. It is also possible to position a single fragment 4 of
inert material with fragments 4 composed of failure prone materials
disposed thereabout in a repeating pattern.
[0063] Referring now to FIG. 6, an exemplary embodiment of a
linearly shaped device 17 is shown having an optional confinement
structure 18. Explosive charge 2, buffer element 3, fragments 4,
and wrap element 5 are disposed within, mechanically fastened
and/or adhered via techniques understood in the art, and thereby
surrounded by the confinement structure 18, as shown in FIG. 7.
[0064] A typical confinement structure 18 is a box-like device
having several lateral members 21 formed, fastened, attached, or
adhered as is understood in the art. Exemplary lateral members 21
are planar shaped elements composed of a metal, plastic, or
composite. Fragments 4 are disposed within the confinement
structure 18 so as to avoid their contact with lateral members 21
during explosive launch.
[0065] Detonation schemes, fragment 4 variations, and mixed
fragment 4 arrangements as described above for FIGS. 4-5 are
equally applicable to the linearly shaped device 17.
[0066] The description above indicates that a great degree of
flexibility is offered in terms of the present invention. Although
the present invention has been described in considerable detail
with reference to certain preferred versions thereof, other
versions are possible. Therefore, the spirit and scope of the
appended claims should not be limited to the description of the
preferred versions contained herein.
* * * * *