EP0084007B1 - Dual stage penetrator bomb - Google Patents

Description

The present invention relates to a penetration bomb, that is to say a bomb intended to be used against an objective having a resistant wall and of great thickness. The term "bomb must be interpreted as designating any projectile of significant mass subsonic at impact and as therefore covering in particular planing bombs, possibly with propulsion engines, and accelerated bombs, as well as bombs falling in free fall, guided or not.

The invention finds a particularly important, although not exclusive, application in the field of guided bombs intended for attacking precise objectives. Mention may in particular be made of planing bombs intended for attacking objectives having significant vertical development and accelerated bombs intended, on the contrary, for attacking an objective having significant horizontal development, such as armored tracks and bridges of ships.

In some cases, it is necessary that the bomb completely ruins the wall and dismantles it. In others, it is sufficient that it digs a crater of notable dimensions and, at the same time, shakes and cracks the objective. Penetration bombs intended to achieve these results are already known. These bombs generally have a shape close to that of a large caliber shell for destroying armored targets, that is to say with a front warhead and cylindrical body, with a very resistant shell and a relatively low explosive content. The penetration effect is mainly due to the kinetic energy and the bombs have, compared to the shells, the serious disadvantage of a clearly lower speed.

We also know that the penetration of a resistant projectile into a target is greater the smaller its diameter. This observation was used in particular in under-calibrated shells or "darts", but it is difficult to transpose to the case of bombs, whose speeds are much lower and whose kinetic energy is generally insufficient. It also led to the proposal to provide the front of the shell with a massive extension of small diameter forming a chisel (DE-A-2 036 897). These solutions, transposed to bombs, have only reduced effectiveness.

The invention aims to provide a penetration bomb with greatly increased efficiency. To this end, the invention provides a penetrating bomb comprising a body and an explosive charge, the body of which has a front part with a thick wall and a rear part with a diameter greater than that of the front wall, with a high explosive content, characterized in that the front part contains explosive, has a loading coefficient much lower than that of the rear part, and is connected to the rear part by an intermediate zone capable of transmitting to the front part the kinetic energy of the rear part upon impact.

We see that this constitution of a completely different approach from those previously adopted. It allows a hole to be drilled in the lens over a significant depth due to the small diameter of the front part, which constitutes a dart or chisel, to which the intermediate part transmits kinetic energy which is much greater than it would be in the case where the rear part would have the same diameter as the front part, since the mass is greatly increased, and because of the load contained in the front part. There is thus damage to the wall by the front part in an entire area whose diameter is of the order of 1.4 times the diameter of the front part. When the firing will take place, with a delay which will be chosen according to the characteristics of the bomb, the rear part of it will come to lodge in the area damaged by the front part, so that its explosion will have a maximum effects.

In practice, the front part will generally be given a diameter between 0.2 and 0.8 times, generally 0.4 to 0.6 times, that of the rear part. A half diameter will generally be close to the optimum. The length of the front part and the connection area will be chosen according to the thickness of the lens wall. at least when it is necessary to pierce it. In practice, a length of half the thickness to be drilled will be satisfactory. Finally, very different values will be adopted for the filling coefficient in the front and rear part, typically about 0.15 for the front part and more than 0.75 for the rear part.

The intermediate part can be designed to transmit the driving forces of the front part, while having a certain flexibility to absorb the impact shock: in general, an approximately conical shape having an angle at the top of between 60 ° and 90 ° gives satisfactory results.

• La figure 1 montre schématiquement la constitution d'une bombe planante constituant un premier mode de réalisation, en coupe suivant un plan passant par l'axe ;
• Les figures 2, 2A et 2B sont des schémas montrant la destruction de la paroi d'un objectif par une bombe du genre montré en figure 1 ;
• La figure 3 montre schématiquement, en tirets, la déformation de la zone intermédiaire de la bombe à l'impact ;
• La figure 4, similaire à la figure 2A, montre la pénétration d'une bombe suivant l'invention dans une paroi d'épaisseur pratiquement infinie ;
• La figure 5 donne l'allure de la variation de la vitesse en fonction du temps à partir de l'impact dans le cas d'une bombe classique et d'une bombe suivant les figures 1 et 2 ;

The invention will be better understood on reading the following description of particular embodiments of the invention, given by way of non-limiting examples. The description refers to the accompanying drawings, in which:

• Figure 1 schematically shows the constitution of a planing bomb constituting a first embodiment, in section along a plane passing through the axis;
• Figures 2, 2A and 2B are diagrams showing the destruction of the wall of a target by a bomb of the kind shown in Figure 1;
• FIG. 3 schematically shows, in dashed lines, the deformation of the intermediate zone of the bomb on impact;
• FIG. 4, similar to FIG. 2A, shows the penetration of a bomb according to the invention into a wall of practically infinite thickness;
• Figure 5 gives the appearance of the variation in speed as a function of time from impact in the case of a conventional bomb and a bomb according to FIGS. 1 and 2;

Figures 5 and 10 are diagrams of alternative embodiments.

We will first describe, with reference to FIG. 1, a bomb whose constitution is such that it is particularly usable for destroying, and not only for damaging, point targets exhibiting vertical development, such as stacks of bridge. The bomb 10 shown comprises a body in which an explosive charge is contained. The body consists of a thick-walled front part 11 and a thin-walled rear part 12, connected by an intermediate zone 13. The explosive charge of the front part will be relatively low, this part having to have a strong structural resistance so as to act as a punch upon impact. The filling coefficient c / m (ratio of the mass of explosive to the total mass) will be between 0.1 and 0.3 and typically of the order of 0.15.

In the case where the bomb is intended to arrive on the objective at moderate speed, for example 150 m / sec, which is the case of a planing bomb, and with an incidence which will not be normal, but rather of the '' 60 °, the nose of the front part must be drawn to limit the risk of ricochets. One can in particular use a nose having a central part in the shape of a point or warhead provided with an edge 14 with a sharp edge. To improve the aerodynamic qualities of the bomb, the body can be wrapped in a cap 15 made of light material. The length 1 of the front part is chosen according to the thickness e of the lens wall: in practice, we will give 1 a value of about half e to get the most out of the destruction mechanism that will be exposed further.

The rear part, whose diameter d ₂ will generally be of the order of twice the diameter d _i of the front part, has a much higher c / m ratio than the front part, which will generally exceed 0.75 and will be frequently understood between 0.8 and 1. As will be seen below, this rear part is subjected to moderate stresses due to the damping effect of the impact shock by the intermediate part. Consequently, the rear part can be thin-walled without however falling apart upon the impact of the nose of the bomb.

The intermediate zone 13 fulfills a double function. It must be stiff enough to transmit the forces and flexible enough to absorb shocks and impact vibrations. This result is achieved by giving the intermediate zone a backward, generally approximately conical shape, which may have a decreasing thickness from front to rear, with an angle at the top of between 60 and 120 °. However, other evolving forms are possible, in particular with a curved generator having an inflection point and connecting to the right generator of the front and rear parts.

The bomb may be supplemented by a firing device, which will generally be introduced from the rear. This device will generally include a delay rocket, causing firing after a delay which will depend on the nature of the objective. It is also possible, in certain cases, to use a firing detecting the peak of deceleration on impact and causing the ignition when the deceleration has stopped and therefore that the front part has finished engaging in the objective.

Furthermore, the bomb may include ancillary elements, for example a rear compartment 16 containing electronics, a rocket engine, etc. and a front guide part. This device can in particular be constituted by a passive infrared guidance device directing the bomb on the objective designated by a laser illuminator.

The process of destruction by a bomb of the kind which has just been described can be explained in the following manner, the accuracy of which however should not be considered as a condition of the validity of the patent.

When the bomb arrives at impact, as shown in FIG. 1, the front part 11 bursts the wall and penetrates this wall to a depth which corresponds substantially to its length. As shown in FIG. 2A, there is not only the formation of a hole having an inlet cone, but also damage to the structure in an annular zone whose diameter is of the order of 1.4 d _i . In the damaged region, if it is concrete, it loses all cohesion and only constitutes a disintegrated mass which only resists displacement by its mass. At the same time there is cracking of the wall. When the latter is made of concrete, it cracks approximately along the generatrices of a cone 18 and practically detaches a block of concrete 19 as soon as the penetration is of the order of e / 2.

The low value of d ₁ results in several advantages: on the one hand, the shear surface along which the cracks 18 are formed is much smaller than it would be for a bomb of constant diameter having the same mass ; block 19 is of lower mass; and the kinetic energy of the rear part 12 is transmitted to the front part, where it is exerted on a much more limited action surface than if the bomb were of constant diameter.

The transmission of kinetic energy takes place through the intermediate zone 13, which deforms as indicated schematically, in a very exaggerated manner, in FIG. 3.

The explosive contained in the front part 11 drives out the plug 19, opens a breach right through the wall and cracks the latter (FIG. 2B). The explosion of the rear part housed in the hole (caused for example by the shock wave of the explosion from the front) causes, by blast effect, the dislocation and dismantling of the wall in a large volume and the ruin by chasing the split blocks. When the bomb is intended to cause explosion damage in the area beyond the wall, its characteristics will be chosen so that the full insertion of the front part into the wall consumes only a fraction, typically l order of a third, kinetic energy. This depression further damages the wall over a diameter significantly greater than the diameter of the front part. In the case of a reinforced concrete wall, the latter loses all cohesion in a volume whose diameter is approximately 1.4 times that of the front part. In addition, there is chipping of the exit face of the wall and, as soon as the depression of the front part reaches about half the thickness, cracking of the concrete up to the exit face. Chipping is further favored if the bomb nose is given a flat shape which creates an intense compressive stress in the concrete which is reflected in the form of a wave causing tensile stresses.

The bomb then continues its penetration, the rear part chasing the disintegrated concrete and the fragments of the cracked part. The firing delay is then provided for the explosion of the rear part to occur beyond the wall.

Finally, in the case where the bomb is intended to attack a wall of thickness such that it cannot be shaken or damaged, the front part will generally be given a shape of an elongated warhead so that it plugs into the wall and remains anchored there after absorption of all the kinetic energy. The destruction process is then as follows. After entering the wall and weakening the area surrounding it (Figure 4), the front part is ignited (igniter placed at point A for example). This explosion causes cracking of the material of the wall at 18 and a first tearing of fragments. The subsequent explosion of the rear part creates a pressure wave towards the entry face and a blast effect which disperses the fragments of the objective which have remained in place and shakes the wall in depth.

Comparative tests carried out with bombs of the same mass, one in accordance with the invention, the other of cylindrical shape with ogival nose, with the same impact speed V _o , have shown that the penetration of the bomb according to l he invention was much stronger, which is understandable perfectly if we refer to Figure 5 which shows the variation over time of the speed from the moment of impact. The reduction in speed is much faster in the case of the conventional form (dashed curve) than in the case of the invention (curve in solid line). The inflection 20 in the case of the invention corresponds to the rupture of the concrete wall.

The invention is susceptible of numerous variant embodiments, some of which will now be described.

In the case illustrated in FIG. 6, the bomb 10 is made up of two assembled parts, the rear part 12 and the intermediate zone being formed by the body of a conventional bomb, while the front part 11 is formed by a perforating element. reported, for example in place of the usual priming rocket.

In the case shown in FIG. 7, the shell of the bomb 10 has two internal belts 26 and 27 at the junction of the intermediate zone with the front and rear parts 11 and 12. These belts in particular absorb the radial component (f,) of the forces (f) and allow the intermediate zone to work in traction-compression rather than in bending.

The variant embodiment shown in FIGS. 8A and 8B (the latter being a partial section along line B in FIG. 8A) still has two belts 26 and 27. But the belt 27 is reduced to a series of external teeth (fig. 8B ) in extra thickness which also have the role of reducing the risk of ricochet: in case of arrival under oblique incidence, the attack is carried out by one of the teeth 28 provided at the front and separated by evacuation passages debris, avoiding jams. If the attachment by this tooth 28 is insufficient and the bomb slides, the attachment of one of the teeth 27 tends to cause the bomb to tip in a direction promoting its penetration.

The front part 11a, of diameter d, approximately half the maximum diameter d ₂ of the rear part, is connected to the latter by a curved zone 13a, of decreasing thickness from the internal belt 26. This decrease continues along the rear, cylindrical from about half the length of the bomb.

The bomb which has just been described, fitted with a delay priming rocket 31, will generally be equipped with accessories the nature of which depends on the mission. In FIG. 8A, the bomb is equipped to be self-guided on a target illuminated by a laser designator. It comprises at the front, in the fairing 32, the steering mechanism comprising servo-motors for orienting the control surfaces 33. The mechanism receives input signals coming from a detector 34 carried by a ball valve 35 allowing to correct the inclination of the bomb under its trajectory. This ball joint is carried by a pole 36 extending the fairing 32. A hollow or flat charge 37 with instantaneous ignition can be placed in the nose of the bomb to flake the target, form a pilot hole therein and facilitate the attachment of the bomb on impact. To keep the penetration of the load 37 at all of its penetrating force, the load is advantageously placed obliquely. Thus, the stinger does not have to cross the pole. A 10 ° angle will generally be sufficient.

Finally, the bomb is provided at the rear with a deployable stabilizer stabilizer conventional, retracted in a bomb extension during the carriage, coming to deploy as shown in phantom after release.

In the variant shown in Figure 9 there is a pole 24 which is added to the front part 11 b. In addition, this front part 11b carries annular hollow charges 25 making it possible to increase the power of penetration and truction. The pole can be finished with an insert constituting a cutting tool. This part can in particular be made of ablative material, for example ceramic, which disappears as the attack progresses.

Finally, as indicated in FIG. 10, your bomber 10c can no longer comprise only two parts, but three, of successive stepped diameters, 11c. 12c and 26 or even more, although the additional complication is not justified by an appreciable advantage. An additional load (hollow or flat load for example) can also be provided at the front to create a pilot hole and / or destroy a protection in front of the objective. This charge will be instant fired.

The shell of the bomb can be made of the same material for all the parts, for example steel or light alloy. But one can also use, for the rear part which does not have to directly undergo the impact force and does not have to perforate the concrete, a material of less mechanical resistance than for the front part. One can for example use at the rear a light alloy or even a composite material based on carbon fiber, glass or boron for example, possibly wound.

By way of example, a bomb of the kind shown in FIGS. 8A and 8B with a steel shell can be produced, with a total mass of approximately 1000 kg, arriving at 150 m / s, to destroy objectives such as barrages or bridge piers. The total length being approximately 1900 mm, the front part can be approximately 500 mm in length and a diameter d ₁ half that of the rear. The thickness of the shell can decrease from 50 mm at the start of the connection zone to 40 mm at the end of this zone and to 25 mm at the end of the rear part, which has a c / m of about 0.9 . The internal diameter d ₃ of the belt 26 can be approximately equal to d _l / 2.

The constitution which has just been defined can also be adopted for producing braked-accelerated bombs intended for digging craters in concrete tracks. In this case, a much lower mass, of the order of 60 kg, can be used. Thanks to the increased penetration power, due to the reduced diameter of the front part, results are then obtained equivalent to those which require a much greater mass in the case of a conventional accelerated bomb. In addition, we gain not only on the mass of the bomb proper, but also on that of its propellant and we can drop the bomb at lower altitude, which is a factor of safety for the carrier plane facing a defense anti-aircraft.

Claims (10)

1. A penetration bomb comprising a body and an explosive charge, said body having a front part (11-11 c) having a thick wall and a rear part having a diameter higher than that of the front part and a high explosive coefficient, characterized in that the front part (11-iic) comprises explosive, has a filling coefficient much lower than that of the rear part and is connected to the rear part (12-12c) by an intermediate portion (13-13c) capable to transmit the kinetic energy of the rear part to the front part upon impact.

2. A bomb according to claim 1, characterized in that said front part has a diameter of from 0.2 and 0.8 that of the rear part and preferably of about one half.

3. A bomb according to claim 1 or 2, characterized in that the filling coefficient is comprised between 0.1 and 0.25 for the front part and is of more than 0.75 for the rear part.

4. A bomb according to claim 1, 2 or 3, characterized in that the intermediate portion (13) arranged for transmitting the forces for driving the front part, has a shape which is flared rearwardly with an angle of from 60 to 120°.

5. A bomb according to claim 4, characterized in that the wall has reinforcing belts (26, 27) at the junctions between the intermediate zone (13,13a) and the front and rear parts.

6. A bomb according to any one of the preceding claims, characterized in that the wall of the front part is of steel or light alloy and the wall of the rear part is of steel, light alloy or composite material.

7. A bomb according to any one of the preceding claims, characterized in that the front part is provided with a part which constitutes a penetration tool, possibly of ablative material which is removed during the penetration.

8. A bomb according to any one of the preceding claims, characterized in that the front part carries a front hollow or flat charge for forming a fore-hole.

9. A bomb according to any one of the preceding claims, characterized in that it is provided with a firing fuse operating with a time delay after impact.

10. A bomb according to any one of the preceding claims, characterized in that it is of the glider type and is provided with guiding devices for attack of objectives having a vertical extension.

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