EP0329530B1 - Method for creating a fin-stabilised penetrating jet, and its use in a war head - Google Patents

Abstract

The technical sector of the invention is that of methods making it possible, after the deformation of a covering, to obtain as a result of the detonation of an explosive charge a core which possesses stabilising fins. The method according to the invention is characterised in that there are arranged within the explosive charge means such that the detonation wave front (11) propagated between said means and the covering (3) is not a surface of revolution, but has a rotational symmetry of an order N, at least equal to three, about the axis (7) of the charge. The invention is used for core-producing military charges. <IMAGE>

Description

The present invention provides a method, which is applied to a military charge generating a nucleus, consisting of a coating, an explosive charge and an initiator, and which makes it possible to obtain a nucleus comprising stabilizing fins.

The core-generating charges, from the family of flat charges, were developed for attacking armored vehicles at large distances (greater than 100 meters). These charges are carried by a vector, self-propelled or not, (missile, rocket), and are initiated at a distance from their target of the order of 1000 times the caliber of the charge. They include a coating, an explosive charge and an initiator; the geometry of the coating is concave, approximately spherical, in all cases having a relatively large radius of curvature (of the order of size). This coating will be deformed, following the detonation of the explosive charge, into a core, the approximate shape of which is that of a bar, of elongation between 3 and 5 and of high initial speed, generally between 2000 and 2500 m / s.

To maintain all its perforating efficiency at the target, such a core must have certain aerodynamic qualities which will allow it to remain stable on its trajectory and reach the target with all the desired precision.

We have thus sought to provide these cores with a stabilizing rear zone in the form of a skirt which allows, by increasing the static margin of the core (distance from the center of gravity to the focus of aerodynamic forces), to improve its stability. .

Such skirting is easily obtained by reducing the peripheral thickness of the coating of the load; however, such a solution is not yet entirely satisfactory. Indeed, the skirt obtained has an irregular profile which decreases the precision obtained for the core.

To improve the latter, we sought to give the skirt a shape with fins.

US-A-4,590,861 describes means for obtaining such a result and constitutes the state of the art. This document proposes to play on the geometry of the coating so that its deformation reveals fins at the rear of the core. Thus thinner areas are arranged on the periphery of the coating, the arrival of the detonation wave at these will cause folds, which will give the core a profile with the desired stabilizing fins.

Such a coating is very delicate to produce because it requires complex machining, therefore costly; the slightest dimensional defect in this coating risks damaging the geometry of the core obtained and therefore its precision and stability.

Patent FR-A-2 380 530 relates to a method for directing the detonation wave in the explosive substances of hollow charges. According to this process, the wavefront is given a shape such that it comes into contact with the coating at the same instant over its entire surface. To this end, an annular-shaped recess is provided inside the explosive material in which the detonation wave progresses faster than in the explosive mass itself. This document aims at a problem entirely different from the problem posed in the invention.

Patent EP-A-255,131 describes a charge generating a core, like the invention, but which includes means ensuring the formation of secondary projectiles ejected radially. The problem of stabilizing the forged core is not mentioned in this patent.

It is the object of the invention to propose a method making it possible to obtain a core comprising stabilizing fins, without imposing any particular machining on the coating. the invention also proposes a military charge cleaning this process.

Thus, the subject of the invention is a method, applied to a military charge generating a nucleus constituted by a coating, an explosive charge and an initiator, and making it possible to obtain a nucleus comprising stabilizing fins, method characterized in that there is available inside the explosive charge means such as the detonation wavefront propagating between said means and the coating, is not a surface of revolution but has a rotation symmetry of an order N, at least equal three, around the axis of the load.

A military charge implementing the method according to the invention will comprise means which will consist of at least one insert, the geometry of all the inserts having rotational symmetry of order N around the axis of the charge.

According to an alternative embodiment, the load comprises N identical inserts, each insert can be a disc.

According to another variant, the load comprises a single cylindrical insert carrying N identical holes.

The diameter of the insert may be between 30% and 70% of the diameter of the explosive charge.

The holes may be cylindrical, or else will be lights oriented in radial directions of the insert.

In particular, the insert may carry four lights extending radially between a first circle whose radius is between 20% and 90% of the radius of the insert and a second circle whose radius is between 30% and 100% of the radius of the insert, the radius of the first circle being chosen always less than the radius of the second circle.

According to an alternative embodiment, the holes will be filled with an explosive or inert material whose physical characteristics are such that the speed of detonation or shock at this material is different from that at the level of the insert.

The invention will be better understood on reading the description which follows of particular embodiments, description made with reference to the appended drawings in which:

Figure 1 shows schematically, and in section, a first embodiment of a military charge implementing the method according to the invention.

Figure 2 is a section of the previous one along the plane X-X.

Figures 3 to 6 show variants of the military charge according to the invention.

Referring to FIGS. 1 and 2, a military charge 1 comprises a containment envelope 2, which contains an explosive charge constituted by a priming relay 5, in contact with an initiator 12 of known type, and an explosive composition 4 in contact with a coating 3. The priming relay is for example an explosive composition Hexogen-plastic binder, and the explosive composition an Octogenous-tolite composition. The detonation rates of the two compositions are chosen so as to ensure optimum detonate functioning for the charge.

An insert 6 is placed between the two compositions 4 and 5; it consists of a disc (made of metal or organic or composite material), whose axis coincides with axis 7 of the load, and whose mechanical and geometric characteristics are determined according to criteria which will be specified below .

The insert carries four holes 8 (see FIG. 2), which are here lights, regularly distributed, whose width is a few mm, and which extend radially between a first circle 10 and a second circle 9. The radii of these circles will advantageously be between 20% and 90% of the radius of the insert for the first circle and between 30% and 100% of the radius of the insert for the second circle, the radii of the first and second circle are located at inside these ranges and have values chosen in such a way that the order relation "radius of the first circle less than the radius of the second circle" is always respected.

The diameter of the insert is here less than the diameter of the explosive composition 4, it will advantageously be between 30% and 70% of this diameter. The insert 6 thus has a symmetry of rotation of order four around the axis 7 of the charge.

The functioning of the military charge is as follows:

The initiator 12 generates a detonation wave in the ignition relay 5, this wave meets the insert 6 at its surface in contact with said relay.

The material and the thickness of the insert will be chosen so that the explosive composition 4 is initiated directly by the shock wave which propagates through the insert 6; one could for example associate with a priming relay and with an explosive composition whose detonation speeds are respectively 8200 m / s and 8700 m / s, a material whose compressibility is less than or equal to 50% under a pressure of 50 Gigapascals, (for example an aluminum alloy), and whose thickness is of the order of a few mm.

The lights contain air here, so the speed of propagation of the shock wave is more reduced through them than through the insert.

It therefore follows, downstream of the insert, a modified wavefront (shown schematically at 11 in FIG. 1), which has disturbances, which are delay zones corresponding to the passage of the initial wave through the lights. Because of the symmetry of rotation of order four of the insert 6 around the axis 7 of the load, the wave front 11 is a surface which also presents a symmetry of rotation of order four around the load axis. Such a front, no longer exhibiting symmetry of revolution, will therefore come into contact with the coating 3 first in preferred directions (13 and 14 in FIG. 2), corresponding to the most advanced areas of the front, this will have the effect of causing a folding of the coating along these preferred directions, and therefore a final geometry of the core generated by the detonation comprising four undulations which will constitute stabilizing fins for the core obtained.

It can thus be seen that the invention, by proposing to have means inside the explosive charge such as the detonation wavefront propagating between said means and the coating, is not a surface of revolution but has symmetry of rotation of an order N, at least equal to three, around the axis of the load, proposes a new method making it possible to obtain a core comprising stabilizing fins. (N will be chosen greater than or equal to three because it is essential, for there to be effective stabilization of the core, that the latter has at least three undulations).

We also see that it is much easier to produce such means in the form of an insert pierced with lights, than to produce a coating with a particular profile such as that described in the preamble.

It will thus be possible to obtain aerodynamically stable and precise cores from coatings having a symmetry of revolution, therefore easy to achieve with all the guarantees of geometric precision desired. Precision which is, as has already been said in the preamble, an absolute necessity for obtaining stable nuclei whose flight path can be controlled.

However, the invention also makes it possible, by playing on the geometry of the insert and on the coupling characteristics of the insert with the explosive charge, to vary the final characteristics of the nucleus obtained in a simple manner, without affecting the geometry. of the coating, which is a factor, on the one hand of savings in terms of manufacturing, and on the other hand of good reproducibility of the characteristics of the filler.

It is possible, for example, to provide an insert whose holes 8 will no longer be filled with air but filled with a third explosive composition or else with an inert material (gas, metal or organic material), the physical characteristics of which (speed detonation, or compressibility for the inert material) will be chosen so as to obtain a different impact speed at the level of the holes and at the level of the insert, and therefore a wavefront having, after passage of the insert, disturbances giving it a rotation symmetry of order four. It is thus possible to very precisely modulate the profile of the wavefront 11. It is possible to play on the dimensions of the holes, and in particular on the circles 9 and 10 limiting the lights; it is also possible to have a greater number (N) of holes, on the sole condition that the geometry of the insert then has symmetry of order N around the axis 7 of the load, which will guarantee obtaining of a wave front having a similar symmetry.

Other variants are thus conceivable, Figures 3 to 7 show some possible types of embodiment.

Referring to Figures 3 and 4 (Figure 4 is a section of the previous along the plane X′-X ′), the insert 6 is here placed inside the explosive composition 4, it is the same diameter that envelope 2 and carries four cylindrical holes 8 filled with a third explosive composition 16. The insert 6 also carries an axial cylindrical hole 15 filled with composition 4.

We can also give the insert any overall shape having a symmetry of revolution, and then having the effect of bringing a wavefront simultaneously on the periphery and on the axis of the coating; the holes made on such an insert will bring symmetry of order N around the axis which will cause the formation of stabilization fins on the core.

Other forms of inserts are possible.

Referring to FIGS. 5 and 6, (FIG. 6 is a section through the previous one along the plane X˝-X˝), the military charge 1 carries, inside the explosive composition 4, four identical inserts 6, having here the form of discs, and regularly distributed. The geometry of all of these inserts thus presents a symmetry of rotation of order four around the axis of the load.

The dimensions and the material constituting these inserts will be chosen so as to create zones of delays of the detonation wave at the level of the inserts. Thus between the inserts and the coating, the detonation wavefront will not be a surface of revolution but will present a rotation symmetry of order four, which will make it possible to obtain stabilizing fins on the core. It will of course be possible to have any number of inserts N greater than three, provided that the geometry of all of them has rotational symmetry of order N around the axis of the load, which will ensure the symmetry of the same order of the wave front and therefore the formation of a nucleus having stabilizing fins.

Claims (10)

1. Process, applied to a penetrating slug generating warhead (1) consisting of a liner (3), an explosive charge (4, 5) and a detonator (12), for producing a penetrating slug having stabilisation fins, characterised by the fact that means are devised inside the explosive charge such that the detonation wavefront propagating between the said means and the liner is not a surface of revolution but has rotational symmetry of order N, equal to at least three, about the axis of the charge.
2. Warhead implementing the process according to claim 1, characterised by the fact that the means consist of at least one insert (6), the overall geometry of the inserts having rotational symmetry of order N about the axis of the charge.
3. Warhead according to claim 2, characterised by the fact that it comprises N identical inserts (6).
4. Warhead according to claim 3, characterised by the fact that each insert (6) is a disk.
5. Warhead according to claim 2, characterised by the fact that it has a single cylindrical insert (6) having N identical holes (8).
6. Warhead according to claim 5, characterised by the fact that the diameter of the insert (6) is between 30% and 70% of the diameter of the explosive charge.
7. Warhead according to one of the claims 5 or 6, characterised by the fact that the holes (8) are cylindrical.
8. Warhead according to one of the claims 5 or 6, characterised by the fact that the holes (8) are apertures orientated along the radial directions of the insert (6).
9. Warhead according to claim 8, characterised by the fact that the insert (6) is provided with four apertures extending radially between a first circle (10) whose radius is between 20% and 90% of the radius of the insert and a second circle (9) whose radius is between 30% and 100% of the radius of the insert, the radius of the first circle being chosen to be always less than the radius of the second circle.
10. Warhead according to one of the claims 5 to 9, characterised by the fact that the holes (8) are filled with an explosive or inert material whose physical characteristics are such that the detonation or shock velocity in this material is different from that in the insert (6).

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