GB2251482A

GB2251482A - Explosive device

Info

Publication number: GB2251482A
Application number: GB8713476A
Authority: GB
Inventors: Peter Raymond Lee; Clifford Robert Allen
Original assignee: Royal Ordnance PLC
Current assignee: BAE Systems Global Combat Systems Munitions Ltd
Priority date: 1987-06-09
Filing date: 1987-06-09
Publication date: 1992-07-08
Anticipated expiration: 2007-06-09
Also published as: GB2251482B; DE3843443A1; FR2674620A1

Abstract

An explosive device which comprises a charge 5 of high explosive material, incorporated within the explosive material an internal zone or wall 7 of a material comprising a metallic fuel, and means 17, 15, 13, 11 for initiating the explosive material on opposite sides of the zone or wall, the explosive material on at least one side of the zone or wall containing or being in contact with further material comprising a metallic fuel. The wall 7 may comprise boron, beryllium, lithium, magnesium, titanium or zirconium. The high explosive material on one or both sides of the wail may incorporate powdered aluminium and the casing 1 may be made of foamed aluminium. <IMAGE>

Description

22514-32 Explosive Devices The present invention relates to explosive

devices Munitions employing blast as the damage agent have been used for many years. They range from bombs used to cause external and internal damage to soft targets, warheads to attack ships and aircraft, to high explosive shell.

However such munitions have well known limitations, the principal one being that the overpressure caused by blast decays very rapidly from the point of detonation, thus making accurate delivery essential unless a blanket attack is possible as in the case of bombs and shell. Additionally, there is a severe loss of effectiveness at high altitude. Very often the fragmenting metal casing around a warhead contributes more to target damage than the blast itself.

Nevertheless, blast has a role to play in future weapon systems particularly if effectiveness can be improved without an increase in overall mass.

Conventionally, the magnitude and duration of a blast wave i.e. over pressure, from a munition filled with high explosive e.g. RDX/Wax, is enhanced by the addition of about 20% by mass of aluminium powder. Additions beyond 20% are not practical for two reasons. Firstly, the reduction in 2- detonation velocity caused by the addition of inert, i.e non explosive, aluminium reduces the effectiveness of the explosive with respect to brisance and case fragmentation. Secondly, the oxidation of the aluminium involves secondary reactions with the detonation products, some of which result in a reduction in the overall volume of gas produced in the explosion. Thus although the heat of explosion, Q, increases with the proportion of aluminium the gas volume, V, decreases so that the "characteristics product", QxV, on which the power or work capacity depends, reaches a maximum at about 20% aluminium.

According to the present invention there is provided an explosive device which comprises a charge of high explosive material, incorporated within the explosive material an internal zone or wall of a material comprising a metallic fuel, and means for initiating the explosive material on opposite sides of the zone or wall, the explosive material on at least one side of the zone or wall containing or being in contact with further material comprising a metallic fuel.

The zone or wall may be in the form of a plate or grid. However it is preferably an enclosure around a cylindrical zone, or in the form of series of portions which together approximate to an enclosure around a cylindrical shape, thereby dividing the explosive material inside and outside the enclosure into inner and outer zones constituting the said sides of the zone or wall.

The said further material may be powdered metallic fuel dispersed within the explosive material and/or an outer casing, in which the explosive material is contained, made of material comDrising a metallic fuel.

The device according to the present invention may conveniently comprise a plurality of substantially cylindrical zones or walls incorporated within the explosive material.

-3 The manner in which the device according to the present invention operates is as follows. When the explosive material on each side of the said zone or wall is initiated an explosive blast is effected against the said zone or wall. The basic shockwave associated with explosion of a high explosive material usually propagates through the material in typically a few microseconds. However, ignition and combustion of metallic fuel in contact with the charge allows the pressure wave to be maintained for up to several milliseconds. The said further metallic fuel thus allows an implosion pressure wave produced upon initiation of the charge to be maintained upon the said zone or wall causing the metallic fuel of the said zone or wall to be ignited thereby providing a concentrated internal source of burning metallic fuel thereby enhancing the overall blast effect of the charge.

This configuration has a number of advantages. The detonation properties of the high explosive are unaffected by the addition of the metal in the said zone or wall; the metal is subjected to high temperatures and pressures by implosion which should ensure successful initiation of combustion; and, should an oxidant be desired it will be possible to introduce it as a separate component, relying on the implosion process to effect mixing and reaction, thus avoiding the need to manufacture intimately mixed explosive/fuel/oxidant mixtures.

The metallic fuel of the material of the said zone or wall may be aluminium but is preferably a metal or mixture of metals having a higher heat of combustion, e.g. selected from one or more of boron, beryllium and lithium. The metallic material may also be selected from magnesium, titanium, zirconium and mixtures thereof.

Boron is preferred for use as the metallic fuel of the said zone or wall. The boron may be provided in elemental form but may also be provided in the form of an alloy or compound with other elements. It may be provided in the form of a pyrotechnic composition with other,exothermic materials, e.g. one or more of the other metals specified above. The metallic fuel-containing material, e.g. boron-containing material, is preferably provided as a powder. This may for example be provided as a filling directly in the explosive charge, e.g. as powdered or sintered boron, or it may be provided in a suitable solid casing located within the explosive charge or it may be embedded in a binder, e.g. plastics material which may be an energetic combustible binder such as nitrocellulose.

An oxidant, e.g. an inorganic nitrate, such as potassium nitrate may optionally be added e.g. in a quantity of up to 20 per cent by weight to the material comprising the metallic fuel of the zone or wall.

Where the metallic fuel is boron the present invention provides an especially beneficial way of using boron as metallic fuel. Boron is known to be very reactive and has a long term incompatability with high explosives and imparts a high sensitivity to high explosives. It is also very difficult to initiate. Consequently boron may not be used as a metallic fuel by intimate mixture with high explosives in the same way that powdered aluminium is used in such applications.

The present invention allows the aforementioned problems of using boron in high explosives to be overcome. The said zone or wall, when comprising boron, allows the boron to separated from the explosive material. Furthermore, the heat generated by combustion of the said further material comprising a metallic fuel, allows the boron to be initiated by the implosion mechanism described hereinbefore.

The metallic fuel of the said further material comprising metallic fuel is preferably aluminium, e.g. in elemental, or compound form. The high explosive material on 1 one or both sides of the said zone or wall may for example incorporate powdered aluminium. The charge may conveniently be enclosed in an outer aluminium casing. For example, such a casing desirably comprises low density foamed aluminium.

The explosive device according to the present invention may be one of any of the types of devices in which high explosive is detonated to give a blast, e.g. munitions such as bombs, warheads, shells, projectiles, bomblets, mines and the like.

Depending upon its construction and method of use the device according to the present invention may be detonated in the open air or underwater as required. In general, metallic fuels will burn in air or in the products of detonation or in water or steam.

The material of the explosive charge in the explosive device according to the present invention may be any suitable high explosive well known to those skilled in the art. For example. the material may be provided in a melt cast or a moulded, pressed, rolled, or extruded form but preferably comprises a powdered or sintered material containing a finely divided metallic fuel comprising aluminium. It may for example comprise a composition comprising one or more of TNT (2,4,6-trinitrotoluene), RDX (cyclo-1,3,5-trimethylene-2,4,6-trinitramine), HM (cyclo-1,3,5,7tetramethylene-2,4,6,8-tetranitramine) ammonium perchlorate, or ammonium nitrate, optionally together with other oxidisers, binders, fillers or plasticisers such as polymers, plastics, waxes and organic liquids as conventionally used in high explosive compositions.

Preferably, the said zone or wall is formed as a cupshaped structure inside the charge dividing it into an inner and outer region inside. The cup-shaped structure and charge may be located inside a cup-shaped container. Conveniently, the outer end of the said cup-shaped structure 6- substantially coincides with the outer surface of the inner and outer regions of the charge inside the container.

The inner and outer regions of the charge may be initiated by a ring of explosive material, e.g. a known plastic sheet-explosive material, deposited on the end of the said cup shaped structure and making contact with the charge inner and outer regions. The ring of sheet explosive material may be initiated by a series of tracks of explosive material, e. g. plastic sheet explosive material, each of the tracks being located outside the container and making contact with one of a series of circumferentially equidistant positions on the said ring. The tracks may be initiated by a common exploder pellet which may be initiated by an adjacent detonator, e.g. of the known exploding bridgewire type. The pellet and the detonator may conveniently be located as plugs in a cavity formed through a cap fitted over the explosive ring and tracks and one end of the container.

The sheet explosive material of the said ring and tracks may be a known plastic bonded material, e.g. a known material comprising the ingredients:

RDX PIB (polyisobutylene) DEHS (diethyl hexyl sebacate) and containing about 90 per cent by weight of RDX.

The said explosive pellet may comprise a known RDX/wax mixture, e.g. comprising 96 per cent by weight RDX and 4 per cent wax.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional side elevation of an enhanced blast warhead embodying the present invention.

Figure 2 is a plan view of the warhead shown in Figure 1 (shown with its cap removed).

As shown in Figure 1 and 2 a warhead comprises a cupshaped container 1 defining a substantially cylindrical - region therein, the container 1 being made of foamed aluminium having a closed end 3. The container 1 is filled with a charge 5 of high explosive material comprising an oxidising material intimately mixed together with an aluminium powder metallic fuel. An internal cup 7 inside the container 1 and charge 5 is made of material comprising boron optionally mixed with other metallic fuel such as zirconium. The internal cup 7 divides charge 5 into an inner region 5a and an outer region 5b. The open end of the internal cup 7 substantially coincides with a surface 9 of the charge 5 facing outward from the cylinder 1. The surface 9 is inside the container 1. A ring 11 of annular cross-section formed of a sheet explosive is deposited on the surface 9 and covers the outer end of the cup 7 and makes contact with the charge 5 inner region 5a and outer region 5b. A series of explosive tracks 13 (shown also in Figure 2) of sheet explosive run to different points on the ring 11 from a single exploder pellet 15 located outside the container 1. The pellet 15 is initiated by an adjacent bridgewire type detonator 17 which may be controlled by a known fuse (not shown). The thickness of the ring 11 is substantially the same as the length of the container 1 projecting beyond the surface 9 of the charge 5. A further ring 19 is fitted between the ring 11 and container 1 to fill the gap between them. Finally, a metallic outer cap 21 shown in Figure 1 but removed in Figure 2 is fitted over the tracks 13, the rings 11, 19 and the open end of the container 1. The cup 21 has a cavity therethrough in which the pellet 15 and detonator 17 are conveniently located.

In operation, the detonator 17 energises the pellet 15 causing an initiation shock wave to run along the tracks 13 reaching both the inner and outer regions 5a and 5b of the charge 5 via the ring 11 at substantially the same 8_ instant in time. initiation of the charge 5 then takes place and causes implosion upon the inner cup 7 which implosion is fueled by the aluminium contained in the explosive material of the charge 5 and the container 1. The inner cup 7 acting as a concentrated source of boron is thereby ignited and the highly exothermic combustion of the boron enhances the overall blast effect of the warhead.

In an alternative embodiment of the present invention there may be a plurality of inner cups comprising boron within the charge 5 dividing the charge into more than two regions. In this case the ring of sheet explosive covers both cups and contacts all regions of the charge.

/2505J 9

Claims

1. An explosive device which comprises a charge of high explosive material, incorporated within the explosive material an internal zone or wall of a material comprising a metallic fuel, and means for initiating the explosive material on opposite sides of the zone or wall, the explosive material on at least one side of the zone or wall containing or being in contact with further material comprising a metallic fuel.

2. An explosive device as claimed in claim 1 and wherein the said zone or wall is an enclosure around a cylindrical zone, or in the form of series of portions which together approximate to an enclosure around a cylindrical shape, thereby dividing the explosive material inside and outside the enclosure into inner and outer zones constituting the said sides of the zone or wall.

3. An explosive device as claimed in claim 1 or claim 2 and wherein the said further material is powdered metallic fuel dispersed within the explosive material and/or an outer casing, in which the explosive material is contained, made of material comprising a metallic fuel.

4. An explosive device as claimed in any one of the preceding claims and which comprises a plurality of substantially cylindrical zones or walls incorporated within the explosive material.

5. An explosive device as claimed in any one of the preceding claims and wherein the metallic fuel of the material of the said zone or wall is selected from a metal or mixture of metals selected from one or more of boron, beryllium, lithium, magnesium, titanium and zirconium.

6. An explosive device as claimed in claim 5 and wherein the metallic fuel of the said zone or wall comprises boron provided in elemental form or in the form of an alloy or compound with other elements.

10- 7. An explosive device as claimed in claim 6 and wherein the said boron is in the form of a pyrotechnic composition with other exothermic materials. 8. An explosive device as claimed in claim 6 and wherein the boron containing material is provided as a powder. 9. An explosive device as claimed in claim 6 and wherein the boron containing material is embedded in a binder. 10. An explosive device as claimed in any one of the preceding claims and wherein an oxidant is added in a quantity of up to 20 per cent by weight to the material comprising the metallic fuel of the zone or wall. 11. An explosive device as claimed in claim 10 and wherein the oxidant comprises an inorganic nitrate. 12. An explosive device as claimed in any one of the preceding claims and wherein the metallic fuel of the said further material comprising metallic fuel is aluminium. 13. An explosive device as claimed in claim 12 and wherein the high explosive material on one or both sides of I- the said zone or wall incorporates powdered aluminium. 14. An explosive device as claimed in claim 12 and wherein the charge is enclosed in an outer aluminium casing. 15. An explosive device as claimed in claim 14 and wherein the casing comprises low density foamed aluminium. 16. An explosive device as claimed in any one of the preceding claims and wherein the said zone or wall is formed as a cup-shaped structure inside the charge dividing the charge into an inner and outer region. 17. An explosive device as claimed in claim 16 and wherein the charge is located inside a cup-shaped container and the outer end of the cup shaped structure substantially coincides with the outer surface of the inner and outer regions of the charge inside the container. 18. An explosive device as claimed in claim 17 and wherein the inner and outer regions of the charge are initiated by a ring of explosive material deposited on the end of the said cup shaped structure and making contact with the charge inner and outer regions.

-II 19. An explosive device as claimed in claim 18 and wherein the ring of explosive material is initiated by a series of tracks of explosive material, each of the tracks being located outside the container and making contact with one of a series of circumferentially equidistant positions on the said ring.

20. An explosive device as claimed in claim 19 and wherein the said tracks are initiated by a common exploder pellet which is arranged to be initiated by an adjacent detonator.

21. An explosive device as claimed in claim 20 and wherein the pellet and the detonator are located as plugs in a cavity formed through a cap fitted over the explosive ring and tracks and one end of the container.

22. An explosive device substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows m -- 1. An explosive device which comprises a charge of high explosive material, incorporated within the explosive material an Internal zone or wall of a material comprising a metallic fuel, the zone or wall dividing the explosive material Into adjacent regions on opposite sides of the zone or wall and means for Initiating the explosive material simultaneously on opposite sides of the zone or wall whereby pressure waves from both sides of the zone or wall provide implosion upon the zone or wall, the explosive material on at least one side of the zone or wall containing or being in contact with further material comprising a metallic fuel whereby the Implosion upon the zone or wall is maintained to permit Ignition of the metallic fuel In the wall or zone. 2. An explosive device as claimed in claim 1 and wherein the said zone or wall Is an enclosure around a cylindrical zone, or In the form of series of portions which together approximate to an enclosure around acylindrical shape, thereby dividing the explosive material inside and outside the enclosure into Inner and outer zones constituting the said sides of the zone or wall. 3. An explosive device as claimed In claim 1 or claim 2 and wherein the said further material Is powdered metallic fuel dispersed within the explosive material and/or an outer casing, in which the explosive material Is contained, made of material comprising a metallic fuel. 4. An explosive device as claimed in any one of the preceding claims and which comprises a plurality of substantially cylindrical zones or walls Incorporated within the explosive material. 5. An explosive device as claimed in any one of the preceding claims and wherein the metallic fuel of the material of the said zone or wall is selected from a metal or mixture of metals selected from one or more of boron, beryllium, lithium, magnesium, titanium and zirconium. 6. An explosive device as claimed In claim 5 and wherein the metallic fuel of the said zone or wall comprises boron provided in elemental form or in the form of an alloy with other elements.

11 7. An explosive device as claimed in claim 6 and wherein the said boron is in the form of a pyrotechnic composition with other exothermic materials.

8. An explosive device as claimed in claim 6 and wherein the boron containing material is provided as a powder.

9. An explosive device as claimed in claim 6 and wherein the boron containing material is embedded in a binder.

10. An explosive device as claimed in any one of the preceding claims and wherein an oxidant is added in a quantity of up to 20 per cent by weight to the material comprising the metallic fuel of the zone or wall.

11. An explosive device as claimed in claim 10 and wherein the oxidant comprises an inorganic nitrate.

12. An explosive device as claimed in any one of the preceding claims and wherein the metallic fuel of the said further material comprising metallic fuel is aluminium.

13. An explosive device as claimed in claim 12 and wherein the high explosive material on one or both sides of the said zone or wall incorporates powdered aluminium.

14. An explosive device as claimed in claim 12 and wherein the charge is enclosed in an outer aluminium casing.

15. An explosive device as claimed in claim 14 and wherein the casing comprises low density foamed aluminium.

16. An explosive device as claimed in any one of the preceding claims and wherein the said zone or wall is formed as a cup-shaped structure inside the charge dividing the charge into an inner and outer region.

17. An explosive device as claimed in claim 16 and wherein the charge is located inside a cup-shaped container and the outer end of the cup shaped structure substantially coincides with the outer surface_of the inner and outer regions of the charge inside the container.

18. An explosive device as claimed in claim 17 and wherein the inner and outer regions of the charge are initiated by a ring of explosive material deposited on the end of the said cup shaped structure and making contact with the charge inner and outer regions.

1M.

19. An explosive device as claimed in claim 18 and wherein the ring of explosive material is initiated by a series of tracks of explosive material, each of the tracks being located outside the container and making contact with one of a series of circumferentially equidistant positions on the said ring.