GB2272272A

GB2272272A - Armour

Info

Publication number: GB2272272A
Application number: GB9223485A
Authority: GB
Inventors: Robert Alan Wordsworth
Original assignee: T&N Technology Ltd
Current assignee: Federal Mogul Technology Ltd
Priority date: 1992-11-10
Filing date: 1992-11-10
Publication date: 1994-05-11
Anticipated expiration: 2012-11-10
Also published as: GB9223485D0; GB2272272B

Abstract

Armour (10) comprises a sheet (12) of composite material and a layer of individual ceramic members (20) secured to a support surface (14) of the sheet. The members (20) abut one another and substantially cover an area of the surface (14). Each member (20) has the ratio of its maximum thickness normal to the surface (14) to its mean extent in any direction parallel to said surface (14) between 0.5 and 2.0. The sheet (12) is preferably multi-layer glass fibre reinforced plastics and the frame 16 may be the same material or aluminium. A second layer of ceramic members may be secured to the backing layer. The ceramic members may be covered by a thin metal sheet. The armour may be used for vehicle or bullet proof jackets. <IMAGE>

Description

ARMOUR This invention is concerned with armour for use in protection against ballistic threats. Typical applications for such armour are in bullet-proof jackets and vehicle armour.

Armour which comprises a sheet of composite material and a layer of ceramic material secured to a surface of the sheet is well-known. Such armour relies on the hardness of the ceramic which blunts an incoming projectile thereby reducing its penetrating ability. The ceramic fractures at the point of impact creating a cone of debris which increases the area over which the impact is distributed.

The composite sheet comprises a number of laminated fabric layers, e.g. of glass, aramid, polyethylene or carbon, and is intended to retain the blunted projectile and the fragments of ceramic. The composite material absorbs energy in delaminating and rupturing the fabric layers.

Aluminium oxide is the most common ceramic used in such armour but others are possible, e.g. silicon carbide and boron carbide.

Armour which incorporates large pieces of ceramic material suffers from the inherent brittleness of ceramic materials. Such armour may successfully protect against a first incoming projectile but be so cracked thereby that little protection is provided against subsequent incoming projectiles. Furthermore, such armour is prone to accidental damage causing the ceramic to crack and reducing the protection afforded. This problem has been previously reduced by providing the ceramic as a mosaic of relatively small ceramic tiles so that damage is confined to a relatively small area.Such tiles, although small, are considerably longer and wider than their thickness, typically they are 6 to 8mm thick and 50mm square, so that such tiles tend to bend under impact, as they have a relatively high surface area compared to the crosssectional area of the projectile, and become detached from said composite material.

It is an object of the present invention to provide improved armour which retains the advantages obtained from the use of tiles but avoids the disadvantages thereof.

The invention provides armour comprising a sheet of composite material and a layer of individual ceramic members secured to a support surface of the sheet so that the ceramic members abut one another or are adjacent to one another, and substantially cover an area of the support surface, wherein each ceramic member has the ratio of its maximum thickness normal to the support surface to its mean extent in any direction parallel to said surface between 0.5 and 2.0.

The armour of the invention has its ceramic material in "blocks" with similar dimensions in thickness, length and width as opposed to the previously-used tiles which are much thinner relative to their width and length. This provision makes better use of the inherent properties of ceramic materials than do tiles. Ceramics are brittle and have low tensile strength but they are very hard, very stiff and have a high compressive strength. The blocks are subjected mainly to compressive stress on impact instead of bending and tensile stress, as is the case with tiles.

Armour, according to the invention, preferably has said ratio between 0.8 and 1.2. In some cases, the ratio can be approximately 1.

Since the blocks of ceramic material are relatively thicker than tiles, it is feasible to engineer their shape to provide improved ballistic properties. For example, each ceramic member may have an inclined or curved surface arranged to deflect projectiles away from a direction normal to said support surface. This provision enables the penetration of projectiles to be further reduced.

In order to further enhance the protection afforded, at least one further layer of ceramic members may be secured to said layer.

In order to ensure that the ceramic members retain their positions and to retain fragments thereof after impact, the layer or layers of ceramic material may be encased in an elastomeric material, e.g. polyurethane, or in a metal, e.g. aluminium or an alloy thereof. The metal is preferably light and ductile. In addition or alternatively, a thin laminated or metal plate may be employed as a covering. This may also have a decorative effect and provide protection against accidental damage.

A thin layer of metal e.g. aluminium or steel, or of another suitable material may also be introduced between the composite sheet and the ceramic members.

The ceramic members may each be in the form of a cylinder, e.g. with its diameter equal to its length, with the longitudinal axis of the cylinder extending parallel to said support surface. In this case, the longitudinal axis of each ceramic member may extend in one of two orthogonal directions. Other possibilities for the shape of the ceramic members are hexagonal prisms and tetrahedra.

Randomly shaped grit fragments may also be used. Where a further layer of ceramic members is present, spheres may be used.

The ceramic members may have a maximum thickness between 25mm and 2mm with their dimensions falling also into this range.

Where appropriate, the ceramic members in a layer, may be of two or more different sizes and/or shapes. This may improve packing of the ceramic members.

The ceramic members may be made, for example, of a material selected from aluminium oxide, silicon carbide and boron carbide.

There now follows a detailed description, to be read with reference to the accompanying drawings of armour which is illustrative of the invention.

In the drawings: Figure 1 shows a portion of the illustrative armour in perspective; and Figure 2 is a cross-section taken through the illustrative armour.

The illustrative armour 10 comprises a sheet 12 of composite material. Specifically, the composite material is a laminate of layers of glass fabric (aramid or polyethylene fabric could also be used) impregnated with polyester. The sheet 12 is 15mm thick and of a generally rectangular shape. The sheet 12 has a rectangular upper surface 14 which provides a support surface of the armour 10.

The armour 10 also comprises edging strips 16 which are made of the same composite material as the sheet 12 but could be thin metal strips, possibly upstanding portions of strips of angle or T-section secured to the underside of the sheet 12. The strips 16 are secured by adhesive to the surface 14 adjacent to the four edges of the sheet 12. The strips 16 and the sheet 12, thus, define a rectangular open-topped recess 18.

The recess 18 contains individual ceramic members 20 of the armour 10 which are made of aluminium oxide. The ceramic members 20 are secured to the surface 14, by polyurethane adhesive, so that they abut one another and entirely cover the area of the surface 14 which is bounded by the strips 16.

Each ceramic member 20 is in the shape of a solid cylinder having its diameter equal to its longitudinal extent. The diameter and the longitudinal extent are both 12.5mm, this dimension being selected as being similar to projectile cross-sections. Each member 20 engages the surface 14 with its curved surface and occupies a square of the surface 14. A member 20 can be placed on the square which it occupies with its longitudinal axis extending in either of two orthogonal directions both of which extend parallel to the surface 14. The members 20 are positioned on the surface 14 in a rectilinear array with the members 20 which lie along a straight line in the array alternating in the direction of their longitudinal axes. Thus, taking a straight line of members 20 extending north-south in the array, a first member 20 on said line may have its axis pointing north-south, the second member's axis then points east-west, the third member's axis points north-south, and so on. Proceeding east or west from said first member 20 on said line the first other member 20 encountered has its axis pointing east-west. As the diameter equals the longitudinal axis, each member 20 has the ratio of its maximum thickness normal to the surface 14 to its mean extent in any direction parallel to the surface 14 equal to unity. In this case, said maximum thickness equals the diameter of the cylinder while the mean extent in any direction parallel to the surface 14 is equal. It is, however, possible to align the axes of all the members 20 to point in the same or parallel directions so that a ribbed surface is achieved.

As the members 20 are cylindrical, each presents a curved (half cylindrical) surface to a projectile arriving at the armour 10. This surface is, therefore, arranged to deflect such a projectile away from a direction normal to the surface 14.

A thin metal covering sheet 22 (not shown in Figure 1) is adhered to the members 20 on their opposite side to the sheet 12 This covering sheet 12 acts to retain the members 20 and as a decorative facing.

The armour 10 was subjected to tests in which a 100mm square sample was subjected to NATO standard projectiles, 7.62mm in diameter, and armour piercing projectiles of the same diameter, both fired at 840m/sec. In both cases, the armour stopped the projectile; in the first case, 25% of the members 20 being damaged and in the second case 33%.

Claims

1 Armour comprising a sheet of composite material and a layer of individual ceramic members secured to a support surface of the sheet so that the ceramic members abut one another or are adjacent to one another and substantially entirely cover an area of the support surface, wherein each ceramic member has the ratio of its maximum thickness normal to the support surface to its mean extent in any direction parallel to said surface between 0.5 and 2.0.

2 Armour according to Claim 1, wherein said ratio is between 0.8 and 1.2.

3 Armour according to either one of Claims 1 and 2, wherein each ceramic member has an inclined or curved surface arranged to deflect projectiles away from a direction normal to said support surface.

4 Armour according to any one of Claims 1 to 3, wherein at least one further layer of ceramic members is secured to said layer.

5 Armour according to any one of Claims 1 to 4, wherein said layer or layers of ceramic material are encased in a metal or an elastomeric material.

6 Armour according to any one of Claims 1 to 5, wherein the ceramic members are each in the form of a cylinder with its longitudinal axis extending parallel to said support surface.

7 Armour according to Claim 6, wherein the longitudinal axis of each ceramic member extends in one of two orthogonal directions.

8 Armour according to any one of Claims 1 to 7, wherein the ceramic members have a maximum thickness between 25mm and 2mm.

9 Armour according to any one of Claims 1 to 8, wherein the ceramic members in a layer are of two or more different sizes and/or shapes.

10 Armour according to any one of Claims 1 to 9, wherein the ceramic members are made of a material selected from aluminium oxide, silicon carbide and boron carbide.

11 Armour substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.