Explosive charge

Abstract

Container (10) is generally cylindrical except for a longitudinal concave groove (11) extending along its entire length. Upon explosion, the contour of this groove (11) results in a focussing effect on the wall material due to the oblique angle at which the expanding cylindrical detonation wave front impacts upon its inner wall. This produces the forging of a rough rod-like projectile (11.sub.1) which, being coherent, maintains its velocity and consequently travels much further than the randomly shaped projectiles (10.sub.1).

Claims

1. An explosive charge comprising a tubular container, said container being generally square shaped and containing an explosive material within said container, said container consisting of four walls, said four walls being equally radially spaced, said container consisting of four web-portion wall portions, said walls being linked by said web-portion wall portions, each of said four walls being a concave longitudinal flute of substantially uniform thickness, each of said flutes being straight and each of said flutes having a longitudinal axis substantially parallel to the longitudinal axis of said tubular container, each of said concave longitudinal flutes extending along substantially the entire length of said container and upon detonation of said explosive material, each of said flutes producing a coherent linear projectile, said linear projectiles providing a cutting effect applied in four equally spaced directions.

2. The charge according to claim 1, wherein said web-portion wall portions are rounded.

3. The charge according to claim 1, wherein said concave longitudinal flutes are rounded grooves.

4. The charge according to claim 1, wherein said concave longitudinal flutes each have a mid-line and are each symmetrical to said mid-line.

5. The charge according to claim 1, wherein said longitudinal flutes have a contour that, upon detonation, produce a focusing effect such that most of the material forming said longitudinal flutes form said coherent linear projectiles.

6. The charge according to claim 1, wherein the tubular container is formed from a material selected from the group consisting of plastic, ceramic, aluminium, magnesium, zirconium, and alloys of aluminium, magnesium and zirconium.

7. A linear explosively formed projectile charge for producing projectiles, the charge comprising an elongate casing being generally square shaped and having a compartment portion containing explosive material, said elongate casing consisting of four equally radially spaced longitudinal flutes which extend along substantially the entire length of said elongate casing, said flutes having substantially uniform thickness and being approximately spherical or hyperbolic, said elongate casing consisting of four web-portion flute portions, said flutes being linked by said web-portion flute portions, each of said flutes producing coherent linear explosively formed projectiles upon detonation of said explosive material, whereby in use no jet is formed in said coherent linear projectiles.

8. A tubular charge comprising a container, said container being generally square-shaped and containing an explosive material within said container, said container consisting of four concave longitudinal flutes which extend along substantially the entire length of said container, each of the concave longitudinal flutes having wall material of substantially uniform thickness, said container consisting of four web-portion flute portions, said flutes being linked by said web-portion flute portions, and upon detonation of said explosive material, each of the flutes forming a coherent linear projectile in which about 90% of the wall material in each of said flutes constitutes each said linear projectile.

9. A tubular container configured to hold an explosive material within said tubular container for use in an explosive charge, said tubular container consisting of four walls, said four walls being equally radially spaced, said container consisting of four web-portion wall portions, said walls being linked by said web-portion wall portions, each of said four walls being a concave longitudinal flute of substantially uniform thickness, each of said flutes being straight and each of said flutes having a longitudinal axis substantially parallel to the longitudinal axis of said tubular container, each of said concave longitudinal flutes extending along substantially the entire length of said container, each of said flutes being configured to produce a coherent linear projectile upon detonation of explosive material within said tubular container.

Description

BRIEF DESCRIPTION OF THE INVENTION

(1) The invention will be more particularly described with reference to the accompanying drawings in which:

(2) FIG. 1 is a transverse section of a simple prior art cylindrical tubular container, filled with explosive;

(3) FIG. 2 is a transverse section of a square sectioned tubular container, filled with explosive;

(4) FIG. 3 is a generally cylindrical tubular container according to the present invention provided with an elongate straight, rounded (in cross-section), groove;

(5) FIG. 4 is a transverse section of a second embodiment of the present invention being a tubular charge which is provided with four equally radially spaced, longitudinal, rounded grooves;

(6) FIG. 5 is a transverse section of a third embodiment of the present invention being a tubular charge which is provided with four equally radially spaced angled grooves;

(7) FIG. 6 is a transverse section of a forth embodiment of the present invention being a tubular charge which is provided with five equally radially spaced angled grooves;

(8) FIG. 7 is a transverse section of a fifth embodiment of the present invention being a tubular charge which is provided with four equally radially spaced faces;

(9) FIG. 8 is a sixth embodiment of the present invention being an array of elongate projectile elements joined along their edges by engagement with corner strips;

(10) FIG. 9 is a transverse section of a seventh embodiment of the present invention, being a charge element for combination with five other such elements.

(11) FIGS. 10 to 12 show further embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(12) FIG. 1 shows the cross-section of a cylindrical container 1 constituting an explosive charge indicating, in broken lines, the resultant fragmentation after detonation of the explosive in the container.

(13) Referring now to FIG. 1, it will be seen that such container or tube 1, being radially symmetrical, expands radially as a result of the shockwave and gas pressure generated by the detonation passing along its length. This will progressively expand the wall of the tube until its elasticity is exceeded and it will suffer many longitudinal fractures.

(14) Since there is misalignment between the longitudinal fractures in adjacent longitudinal increments of tube, many transverse failures will also result and few, if any, long lengths of projectile material 1.sub.1, 1.sub.2 and so on will survive beyond a distance exceeding the diameter of the tube 1. This is the mode of fracture of conventional Bangalore Torpedoes.

(15) FIG. 2 shows a container with four flat sides 3 to 6 so that, upon explosion, the material will tend to be torn along the corner edges and their radially distributed component increments will diverge more gradually than is the case of the equivalent-sized cylinder 1 shown in FIG. 1. This leads to a greater concentration of projected fragments (3.sub.1, 3.sub.2, and so on) in each of the four planes passing through the long axis of the charge and parallel to the flat sides prior to explosion. The fragments 3.1, 3.2, 3.2, etc, follow paths which are closer than those that the same pieces of metal would follow had the tube 5 been circular in section rather than square. In other words, the rate of separation of the elongate fragments in FIG. 2 is lower, so the metal constituting these (potentially separate) fragments tends to break up less and it thus forms larger fragments.

(16) FIG. 3 shows a container 10 which is generally cylindrical except for a longitudinal concave groove 11 extending along its entire length.

(17) Most of the wall material derived from explosion of the container or charge 10 shown in FIG. 3 will be distributed with approximate radial symmetry in similar manner to that as shown in FIG. 1 and resulting in fragments 10.sub.1, and so on, with the exception of the exploded fragments resulting from the longitudinal groove 11. Upon explosion, the contour of this groove 11 results in a focussing effect on the wall material from which it is constituted, as a result of the oblique angle at which the expanding cylindrical detonation wave front impacts upon its inner wall. This effect produces the forging of a rough rod-like projectile 11.sub.1 which, being coherent, and having a much smaller surface area than the randomly shaped projectiles 10.sub.1 and so on impelled in other directions, maintains its velocity to a significantly greater extent and consequently travels much further than the latter.

(18) Advantageously, the groove 11 in container 10 is should be straight and not caused to spiral along the tube, since rotation of the groove about the long axis of the charge would cause adjacent increments of the projectile to travel along rotationally-spaced radii. This may produce continuous stretching of the spiral projectile which could result in it breaking up into a large number of short pieces to the detriment of any useful cutting power.

(19) Typically, container 10 has a conical shape at one end to enable the end to be readily stuck in the ground, if appropriate. The container may have, at the other end, some form of connection to another similar container or standard tube, for example a screw-thread portion. In this way, an extensive length of explosive charge can be provided to be effective against a long fence or other obstacle with barbed wire.

(20) The container 20 of FIG. 4 comprises four concave longitudinal flutes 21 to 24 shown in cross-section as being linked by web-portion wall portions 25 to 28.

(21) Much greater use is made of the focussing effect in the charge shown in FIG. 4, in which almost all the exploded wall material 21.sub.1, 22.sub.1, 23.sub.1, 24.sub.1 is constrained within one or other of the four flutes 21 to 24 in its wall. In the previous Figure (FIG. 3), no more than a quarter of the metal constituted the grooved portion and was thus destined to be formed into a coherent linear projectile: in the shape shown in FIG. 4, about 90% of the metal ultimately constitutes linear fragment projectiles. Such an arrangement has the advantage that a cutting effect will be applied in four equally spaced directions, thereby increasing the probability of a strike. By way of example, were a charge unit to be thrown or dragged without regard to its radial orientation beneath a parked aircraft, upon detonation of the charge that aircraft would nevertheless be struck by at least one upwardly directed projectile. In the extreme case of the charge being passed through a loop in a helical wire fence, then the wire constituting that loop is likely to be cut in four places.

(22) The container 30 of FIG. 5 has four longitudinal flutes 31 to 34, each of two flat walls 35, 36 angled at about 145°.

(23) Container 30 produces projectile material 31, consisting of angular rather than rounded grooves with higher velocities. To some extent, the velocity of the projectile could be increased by decreasing the angle of the groove. This would, however, decrease the volume available for containing the explosive so, beyond an optimally small angle, the reduced amount of available energy would cause a loss of velocity of the projectiles 31, 32, and so on.

(24) FIG. 6 shows a transverse section of a container or charge 40 which is provided with five equally radially spaced angled grooves 41 to 45, resulting in generally similar properties to container 30 illustrated by FIG. 5 except that the probability of impact on a particular target or target component is correspondingly augmented. The diminution of width of each projectile element is somewhat balanced by an increase in internal volume and, hence, of explosive load for a given charge diameter.

(25) It will be understood that both round and square-sectioned steel and aluminium tubes are common articles of commerce. Thus the bodies of charges based upon the shapes shown in FIGS. 1 & 2 could be bought in items. Containers shaped as shown in FIGS. 3, 4, 5 and 6, however, would need to be made for the purpose.

(26) Containers shaped as shown in FIGS. 3 and 6 can be readily formed by rolling or pressing round tubes, and those of FIGS. 4 and 5 by rolling or pressing square tubes.

(27) FIG. 7 shows container 50 which, in cross-section, has an external profile generally square in shape with rounded corners and a slight concave aperture to the exterior side walls; however the interior surfaces of the container have greatly pronounced aperture of the side walls, as shown.

(28) The container 50 shown in FIG. 7 cannot readily be formed from commercially available tubes since the wall thickness varies radially as shown in FIG. 7. Whereas extrusion of the shapes illustrated in FIGS. 1-6 is a feasible alternative to pressing round or square tubes in such metals as aluminium or magnesium, it is the only practicable production method for tubes having varying wall thickness.

(29) Container 50 has four walls 51 to 54 which produces projectiles 51.sub.1, 52.sub.1, 53.sub.1, 54.sub.1 and so on each with a lens-shaped transverse section. The thickness of an increment of projectile material determines its inertia and, thence, its velocity as the detonation wave of the explosive strikes it. Variation of the thickness of increments of a projectile therefore modifies the velocity at which these increments are projected. A tendency for the projectile to disintegrate as it travels because its individual component increments are travelling at different velocities, or in different directions, can therefore be largely mitigated by causing all increments projected in approximately the same direction to be travelling at approximately the same velocity. The strength of the material can therefore suffice to hold the increments together in a coherent mass. Lens shapes are commonly used to achieve this incremental velocity adjustment, which can be optimised for the production of compact elongate masses of maximum stability in flight.

(30) Aluminium based alloys are ideal for precise and rapid manufacture and the advantage in the present case of more rapid deceleration in flight than heavier metals which implies smaller danger zones.

(31) FIG. 8 shows container 60 which is fabricated by joining separate projectile components 61 to 64 along their edges using any known means of joining such as welding, brazing, the application of adhesive or the engagement of interlocking edges. Such interlocking edges might engage directly with each other or with additional corner pieces 65. Alternatively, or additionally, such elongate projectiles may be constrained together, edge to edge, by a surrounding frame or tube of plastics or metal.

(32) FIG. 9 shows a transverse section of a charge 70 which may be used alone, or as a component of an array of such charges to form a charge of equivalent shape and effect as that of FIG. 6. Thus FIG. 9 illustrates the use of charge 70 in the assembly of a radially symmetrical assembly which propels explosively formed projectiles in five equally spaced directions. It will be understood that an outward facing array of charges with a variable number of such charge units could be arranged according to the perceived requirement at the time of use.

(33) The intended effects of conventional Bangalore torpedoes are the blast and fragment damage to adjacent structures. In many applications the, concomitant starting of fires would be disadvantageous in an already dangerous environment. In those instances in which an incendiary effect might be advantageous, however, the use of such incendiary metals as magnesium and its alloys, titanium or zirconium would be advantageous. Incendiary effect might also be obtained or augmented by the use of aluminised plastic or plastic-bonded explosive as the main fill. It will be understood that aluminium, when used for substantial parts of the cases of explosive charges, is little oxidised so makes little contribution to any incendiary effect: when the powdered metal is incorporated in explosive materials, however, it reacts exothermically with both endogenous oxygen of the explosive and with the surrounding air or water.

(34) Alternatively, to a torpedo whose body is made from relatively non-incendiary materials, may be applied additional components made from incendiary materials.

(35) Thus, by way of example, the incendiary effect of such a container as that illustrated in FIG. 7, itself made from aluminium or steel, may be applied an external tube of magnesium or, alternatively, strips of magnesium may be applied, by mechanically interlocking grooves and ribs, or by adhesive or sticky tape.

(36) In a container assembled according to FIG. 8, the projectile components 61 to 64 might be made in steel or aluminium while the joining edge members 65 are made in magnesium.

(37) In such applications as may require a minimal amount of projectile damage, then the tubular components of the container of the invention may be made from plastics or ceramic materials whose effective range is limited by stretching and tearing, giving a very large surface to mass ratio, and by extreme comminution respectively.

(38) By Way of Example:

(39) A strip of aluminium, 25 mm wide and 5 mm thick, was bent along its long axis to an angle of 170° and to its convex surface were stuck three strips of plastic explosive SX2, each 25 mm wide and 3 mm thick. This gave a calculated explosive load equivalent to 480 g/meter. This charge was fired at a distance of 1000 mm from a length of razor wire and a 5 mm thick plate of 43 A grade steel. Both the wire and the plate were cut. The projectile was not projected in a direction exactly normal to the long axis of the charge but was inclined forwards an angle of approximately 40.

(40) It has been shown previously how the randomly shaped and distributed fragments of a metal cylinder filled with detonating explosive can be made cohesive and thus form elongate projectiles by forming the sides of the tube into concave or lens-sectioned longitudinal elements which remain intact and therefore act as longitudinal self-forging fragment projectiles. These maintain more consistent cutting properties at greater stand-off distances than do the fragments derived from explosive-filled tubes of uniform wall thickness.

(41) Then follows an alternative means of mitigating the random fracture of explosive-filled metal tubes and thus producing similar elongate projectile elements.

(42) Referring to FIG. 10, a square-sectioned metal tube 101 is substantially filled with a detonating explosive 104. Between each flat face 102 of the tube 1 is placed a shock wave refracting element 102. This is essentially lens sectioned or prismatic and the material used for its confection, and its shape, are determined according to its shock wave propagation velocity. Since the velocity of shock wave propagation will be lower than that of the detonation velocity of the explosive 104, the shock front will be refracted in the manner of light passing through a prism. The consequence of this refraction is that the otherwise divergent loci imparted to longitudinal elements of the tube 101 will be made parallel with, or even convergent towards, the longitudinal plane passing through the midline of each flat side 105 and normal to its surface.

(43) The consequence of this mitigation of radial expansion of longitudinal elements of the tube 101 is that each side of the tube 101 remains largely coherent and constitutes a longitudinal projectile 103.

(44) It will be understood that this principle is not limited to tubes having four sides.

(45) An alternative configuration is illustrated in FIG. 11 in which shock wave refracting elements 107 are applied to the inner wall of a cylindrical tube 106 containing explosive 105. The inner surface of the elements 107 may be flat or convex. An elongate projectile 108 is produced by each refracting element 107.

(46) The greater the curvature of the inner surfaces of the wave shaping elements 102 and 107, and the slower the velocity of shock wave propagation therein, the greater the degree of convergence of the elements of the projectile material constituting the walls of the tubes 101 and 106.

(47) FIG. 12 shows a charge in which a metal tube 110 contains four refracting elements 110 which are joined by thin-walled sections 111. The refracting elements 110 and the joining elements 111 thus constitute a flexible lining element 112. This element 112 may be made either with flexible joining elements 111 or may be made from elastic material. This facilitates the insertion of the element 112 in the tube 109 before filling with explosive 113. Tamping or injection of explosive into the lumen of the element 12 inflates the element and urges its outer wall against the inner wall of the tube 109.

(48) The use of a flexible or elastic lining element 113 has the further advantage of facilitating the filling of the charge with explosives which are initially made in the form of a paste but which set to form solids. Such explosives are typified by plastic bonded explosives in which a finely divided particulate explosive material, such as cyclo-tetramethylene tetranitramine (HMX), is dispersed in a viscous liquid matrix, such as hydroxyl terminated polbutadiene, which is mixed with a cross-linking substance, such as an organic diisocyanate, immediately before filling. Interaction of the last two components converts the viscous liquid into a rubbery solid. Such an explosive is typified by the composition PBXN-110.

(49) Difficulty is frequently experienced in the filling of munitions with explosives having such a constituency because of the difficulty of excluding bubbles of air. By connecting a reservoir of such an explosive to the end of an evacuated, blind ended and inflatable element 112, flow of explosive into the tube 109 can be induced by the application of a vacuum to the space 114 between the inner wall of the metal tube 9 and the outer surface of the inflatable element 112. Simultaneous application of positive pressure to the open end of the element 112 assists the filling process and, in so doing, urges the outer surface of the element 12 against the inner surface of the tube 109.