GB1604010A

GB1604010A - Armour piercing projectiles

Info

Publication number: GB1604010A
Application number: GB1496973A
Authority: GB
Original assignee: Forces Armees Francaises
Current assignee: Forces Armees Francaises
Priority date: 1972-04-28
Filing date: 1973-03-28
Publication date: 1981-12-02
Also published as: IT1050367B

Description

(54) IMPROVEMENTS IN OR RELATING TO ARMOUR PIERCING PROJECTILES (71) We, ETAT FRANCAIS represented by the Ministry of the Armed Forces, the Ministerial Delegation for Armaments of 10 Rue Saint-Dominique, Paris 7e, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, ta be particularly described in and by the following statement: This invention relates to an armour-piercing projectile having a shaped explosive charge therein, the shaped charge being formed, more particularly with a recess in its forward face.

Armour-piercing projectiles, such as aeror dynamically stabilised rockets, which house shaped bodies of explosive material and which have a high armour-piercing capacity are known. Such projectiles, of necessity, have a very low speed of rotation about their axis and hence poor stabilisation of their trajectory.

This latter matter has been necessitated by the observation that, as soon as the speed of rota tion of such a projectile about its axis exceeds a value of the order of several tens of revolutions per second, its armour-piercing capacity decreases considerably. This armour-piercing capacity becomes substantially zero at speeds of rotation of several hundred revolutions per second, such as those of artillery projectiles fired from guns having a rifled barrel.

In order to relieve the shaped charge from the effects of the cenrifugal force produced by the rotation of the projectiles and desirable for the stable trajectory of the projectile, it has been proposed to mount this charge in a housing which is free to rotate in relation to the body of the projectile, for example by means of ball bearings. However, such an arrangement is complicated and costly and is weighty and takes up space, thus reducing the amount of useful charge wihch can be carried.

According to the present invention, there is provided an armour-piercing projectile comprising a substantially cylindrical casing ho,us- ing a shaped explosive charge body having a forward end face in the intended direction of flight of the projectile, which body is formed with an axially symmetrical recess and the rear end of which has associated means for the production of a substantially planar detonation wave therein, which axially symmetrical recess contains a liner in intimate contact with explosive charge material in which the recess is formed, the liner comprising a surface of revolution coaxial with the projectile and enclosing a volume of revolution whose cross-section at right angles to the axis of the projectile commences at a maximum value at its forward end and decreases rearwardly of the projectile to a minimum value which may be zero, which volume of revolution is a cone having a cone angle of at least 1200 or is such that a pair of tangents thereto at the maximum crosssection thereof and coplanar with the axis of the projectile are at an angle of at least 1200 with respect to each other, and the liner being constrained to remain axially symmetrically disposed in the recess.

In preferred practice, the liner is constrained to remain axially disposed in the recess in the forward end of the shaped explosive charge by means of a fixedly disposed confinement ring acting on the outer margin of the liner.

By constructing an armour-piercing projectile of simple construction according to the present invention, it is possible to achieve considerable armour-piercing capacity even at high speeds of rotation.

For a better understanding of this invention and to show how the same can be carried into effect, reference will now be made, by way of example only, to the accompanying drawing which is a diagrammatic longitudinal section through a projectile according to the present invention.

Referring to the drawing, the projectile, shown generally at 1 comprises a cylindrical steel body 2 having an axis of revolution X-Y, and a base 21 part of which houses an inertia fuse 31 fixed in place by means of a removable plug 22 and in surface contact with a detonating charge 32. Two explosive charges 33, 34 are disposed in conventional manner in the rear part of the body 2 of the projectile, serving to create therein a substantially plane detonation wave.

Beyond the second explosive charge 34 and occupying a major part of the body of the projectile 2, is situated a shaped charge body 35, the forwardly directed face of which is formed with a conical recess, having the same axis X-Y as the projectile 1. The angle A at the apex of this conical recess is 140".

At the forward end of the projectile, a highstrength steel confinement band 4 is screwed between the body 2 and a shaped aluminiumalloy cap 23. In its central part, the confinement band 4 has an annular inward projection having a thickness which is substantially greater than the general thickness of the walls of the cylindrical body 2 which is designated by the reference letter e and which divides from one another an externally screw-threaded section 41 of the band 4 engaging a screw-threaded part of the body 2, and an internally screwthreaded part 42 of the band which engages an externally screw-threaded portion 24 of the cap 23.The inner margin of the annular pro- jection on the band 4 is constituted by a first conical surface 43 which is flared towards the rear of the projectile at an angle B to the axis X-Y of the order of S The surface 43 is joined to the outer part of the ring 4 by two surfaces, the rearward one being a second conical surface 44, which is also rearwardly flared, but at an angle C to the axis X-Y which is greater than that of the surface 43 and is of the order of 45".

A liner 5 formed of a metal which is plastically deformable so that it may absorb high dynamic tensile stresses, such as copper or steel having a very lo;w carbon content, for instance the substantially pure iron marketed under the Registered Trade Mark ARMCO and having a substantially constant thickness E between rear and forward faces 51 and 52, makes contact at its periphery with the conical surface 43 of the confinement band 4. The liner 5 has its rear face 51 applied to the recess in the forward face of the shaped charge body 35.

The faces 51 and 52 of the liner 5 are both conical in the illustrated embodiment, having the same axis X-Y as the projectile, the apex of the cone thus formed being rearwardly directed.

The parameters of a projectile according to the present invention can generally be varied within certain limits to be set out hereinafter.

The surface of the liner is a surface of revolution enclosing a volume of revolution whose cross-section at right angles to the axis of the projectile commences at a maximum value at its forward end decreases rearwardly of the projectile to a minimum value which may be zere, as in the illustrated embodiment.

The volume of revolution may be a cone, as illustrated having a cone angle of at least 1200 or is defined by a curved surace of revolution dimensioned so that a pair of tangents thereto, at the maximum cross-section thereof and coplanar with the axis of the projectile are at an angle of at least 1200 to each other. The liner 5 is relatively thick, the ratio E/D2 between the mean thickness of this liner (E) and its largest diameter (D2) is preferably frown 0.07:1 to 0.11:1. Experience shows that, under these conditions, in particular, the armour-piercing capacity of the projectile remains substantially constant for speeds of rotation ranging from zero to, several hundred revolutions per second.The ratio D2/D1 between the largest diameter (D2) of the liner 5 and the internal diameter (D1) of the body 2 of the projectile is preferably from 0.7:1 to, 1:1. The ratio D2/L between the largest diameter (D2) of the liner 5 of the shaped charge body 35 and the length (L) of the shaped charge body measured in a direction parallel to the axis of the projectile, is preferably from 0.35:1 to 0.6:1.

The confinement ring 4 and the liner 5 are preferably made from materials which have similar shock impedances.

The following example illustrates the invention: EXAMPLE.

A projectile (bazooka shell) was constructed as shown in the accompanying drawing with the following dimensions: calibre -- 105 mm; angle at the apex A of the conical surface of the liner -- 140"; the thickness E of liner 7 mm; maximum diameter D2 of the liner 5 - 75 mm; the internal diameter D1 of the body 2 - 94 mm; and the length L of the shaped charge 35 - 150 mm.

When a projectile thus constructed and dimensioned but with detonation means absent or inactivated, was fired at a steel armour plate of great thickness, at an angle of incidence of 90" and with a speed of rotation of the projectile about its axis of 300 revolutions per second, the following results were obtained: Depth of penetration 160 mm Diameter of the entry hole 30 mm Diameter of the exit hole 20 mm Volume of the metal removed 61 cm3 When no rotation took place at the instant of impact, it was found that the projectile penetrated a similar plate to a depth of 170 mm. It will therefore be seen that the piercing capacity of the projectile is not substantially acted by its rotation in the above-indicated rotational speed range.

These results are to be compared with the penetration of a projectile of the same calibre, but comprising a conventional hollow charge having a much deeper recess and which is not free to rotate in relation ta the body of the projectile and does not have a confinement ring.

When the projectile does not undergo rotation it is possible to, obtain a depth of penetration of 400 to 500 mm on a steel armour plate, but the perforation diameter is very small. On the other hand, when such a 105 mm projectile having a conventional hollow charge rotates at 300 revolutions per second, the depth of penetration is negligible.

The following tentative explanation is given of this phenomenon.

In a conventional hollow-charge projectile, the liner is relatively thin and its wall is inclined to a relatively small extent with respect to the axis of the projectile. Under these conditions, when the detonation wave reaches the liner, the metal from which the liner is usually made, sonically melts or atomises, and the solid or liquid particles resulting therefrom are violently projected forwards towards the axis owing to their possessing a considerable velocity component in the direction of the axis (centripetal component). If the projectile rotates, these particles are, in addition, subjected to a centrifugal force produced by the rotation.

The principles of theoretical mechanics suggest that, since the centripetal velocity component will cause the particles to travel forwardly towards the axis, the particles will turn more and more rapidly about this axis and are consequently subjected to an ever increasing centrifugal force. The centrifugal force ultimately overcomes the centripetal force of inertia, so that the particles then diverge in relation to the axis and form a very widened centrifugal jet, the piercing capacity of which is very low. The existence of such centrifugal jets has been confirmed by flashlight radiographs taken of projectiles in the course of operation.

On the other hand, with a projectile according to the present invention, the initial centripetal components of velocity are limited because of the small angle of incidence of the plane detonation wave on the wall of the liner.

The speeds of rotation of the elements of the liner and the centrifugal forces to which they are subjected are therefore limited in the course of the compression of the liner. On the other hand, since the liner is relatively thick, it has sufficient strength to absorb high dynamic tensile stresses without melting or disintegrating. The more plastically deformable the liner material is the better, in this respect. The speed of rotation of the external parts of the liner is initially limited to that of the body of the projectile, and increases only slowly since their centripetal velocity component is low.

Hence, these parts of the liner can resist the divergence of the central parts of the liner.

Hence the liner is constrained to remain in position, the constraint being greatly assisted by the confinement ring of substantial thickness.

Under these conditions, the liner behaves in a manner characteristic of a solid projectile launched at high speed, the piercing capacity of which is only very slightly effected by the speed of rotation of the projectile.

WHAT WE CLAIM IS:- 1. An armour-piercing projectile comprising a substantially cylindrical casing housing a shaped explosive charge body having a forward end face in the intended direction of flight of the projectile, which body is formed with an axially symmetrical recess and the rear end of which has associated means for the production of a substantially planar detonation wave therein, which axially symmetrical recess contains a liner in intimate contact with explosive charge material in which the recess is formed, the liner comprising a surface of revolution coaxial with the projectile and enclosing a volume of revolution whose cross-section at right angles to the axis of the projectile commences at a maximum value at its forward end and decreases rearwardly of the projectile to a minimum value which may be zero, which volume of revolution is a cone having a cone angle of at least 1200 or is such that a pair of tangents thereto at the maximum cross-section thereof and coplanar with the axis of the projectile are at an angle of at least 1200 with respect to each other, and the liner being constrained to remain axially symmetrically disposed in the recess.

2. A projectile according to Claim 1, in which a fixedly disposed confinement ring acts on the outer margin of the liner to constrain it to remain axially disposed in the recess.

3. A projectile according to Claim 2, in which the radial thickness of the confinement ring is greater than the thickness of the wall of said casing.

4. A projectile according to Claim 2 or 3, in which the confinement ring abuts the periphery of the liner through a first substantially conical surface of the liner which is flared towards the rear of the projectile.

5. A projectile according to Claim 4, in which said first conical surface is connected to a surface which is cylindrical and continuous with the inner surface of said casing through a second substantially conical surface which is also flared towards the rear of the projectile, the second substantially conical surface having a cone angle substantially greater than the first substantially conical surface.

6. A projectile according to any one of Claims 2 to 5, in which the liner and the confinement ring are formed of materials having substantially the same shock impedences.

7. A projectile according to any one of Claims 2 to 6, in which the confinement ring is made of high strength steel.

8. A projectile according to any one of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. projectile and does not have a confinement ring. When the projectile does not undergo rotation it is possible to, obtain a depth of penetration of 400 to 500 mm on a steel armour plate, but the perforation diameter is very small. On the other hand, when such a 105 mm projectile having a conventional hollow charge rotates at 300 revolutions per second, the depth of penetration is negligible. The following tentative explanation is given of this phenomenon. In a conventional hollow-charge projectile, the liner is relatively thin and its wall is inclined to a relatively small extent with respect to the axis of the projectile. Under these conditions, when the detonation wave reaches the liner, the metal from which the liner is usually made, sonically melts or atomises, and the solid or liquid particles resulting therefrom are violently projected forwards towards the axis owing to their possessing a considerable velocity component in the direction of the axis (centripetal component). If the projectile rotates, these particles are, in addition, subjected to a centrifugal force produced by the rotation. The principles of theoretical mechanics suggest that, since the centripetal velocity component will cause the particles to travel forwardly towards the axis, the particles will turn more and more rapidly about this axis and are consequently subjected to an ever increasing centrifugal force. The centrifugal force ultimately overcomes the centripetal force of inertia, so that the particles then diverge in relation to the axis and form a very widened centrifugal jet, the piercing capacity of which is very low. The existence of such centrifugal jets has been confirmed by flashlight radiographs taken of projectiles in the course of operation. On the other hand, with a projectile according to the present invention, the initial centripetal components of velocity are limited because of the small angle of incidence of the plane detonation wave on the wall of the liner. The speeds of rotation of the elements of the liner and the centrifugal forces to which they are subjected are therefore limited in the course of the compression of the liner. On the other hand, since the liner is relatively thick, it has sufficient strength to absorb high dynamic tensile stresses without melting or disintegrating. The more plastically deformable the liner material is the better, in this respect. The speed of rotation of the external parts of the liner is initially limited to that of the body of the projectile, and increases only slowly since their centripetal velocity component is low. Hence, these parts of the liner can resist the divergence of the central parts of the liner. Hence the liner is constrained to remain in position, the constraint being greatly assisted by the confinement ring of substantial thickness. Under these conditions, the liner behaves in a manner characteristic of a solid projectile launched at high speed, the piercing capacity of which is only very slightly effected by the speed of rotation of the projectile. WHAT WE CLAIM IS:-

1. An armour-piercing projectile comprising a substantially cylindrical casing housing a shaped explosive charge body having a forward end face in the intended direction of flight of the projectile, which body is formed with an axially symmetrical recess and the rear end of which has associated means for the production of a substantially planar detonation wave therein, which axially symmetrical recess contains a liner in intimate contact with explosive charge material in which the recess is formed, the liner comprising a surface of revolution coaxial with the projectile and enclosing a volume of revolution whose cross-section at right angles to the axis of the projectile commences at a maximum value at its forward end and decreases rearwardly of the projectile to a minimum value which may be zero, which volume of revolution is a cone having a cone angle of at least 1200 or is such that a pair of tangents thereto at the maximum cross-section thereof and coplanar with the axis of the projectile are at an angle of at least 1200 with respect to each other, and the liner being constrained to remain axially symmetrically disposed in the recess.

8. A projectile according to any one of

Claims 1 to 6, in which the liner is made of a metal which is plastically deformable.

9. A projectile according to Claim 8, in which the liner is made of substantially pure iron or of copper.

10. A projectile according to any one of the preceding claims, in which the ratio between the mean thickness of the liner and the maximum diameter of the liner is from 0.07:1 to 0.11:1.

11. A projectile according to any one of the preceding claims, in which the ratio between the maximum diameter of the liner and the internal diameter of the casing is from 0.7:1 to 1:1.

12. A projectile according to any one of the preceding claims, in which the ratio between the maximum diameter of the liner and the length of the shaped explosive charge is from 0.35:1 to 0.6:1.

13. An armour-piercing projectile substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.

14. An armour-piercing projectile as claimed in Claim 1, substantially as described in the foregoing Example.