GB2258389A

GB2258389A - Ballistic resistant shield

Info

Publication number: GB2258389A
Application number: GB9115932A
Authority: GB
Inventors: Michael Sacks; Glynn Jones
Original assignee: Dowty Armourshield Ltd
Current assignee: Dowty Armourshield Ltd
Priority date: 1991-07-24
Filing date: 1991-07-24
Publication date: 1993-02-10
Anticipated expiration: 2011-07-24
Also published as: GB9115932D0; GB2258389B; WO1993002332A1

Abstract

A ballistic-resistant shield incorporating a plurality of layers of high tensile strength fibres comprising first layers (6) with fibres that are embedded in a plastic matrix, and second layers (7) with fibres that are interlocking and not embedded in an elastomer matrix, and a third layer (8) of an impact absorbing and impact mouldable material, the majority of the first layers (6) being incorporated face-to-face in a first set of layers adjacent to the front face of the shield which is directed towards a region of ballistic threat, the third layer (8) being located adjacent to the rear face of the shield, and the majority of the second layers (7) being incorporated face-to-face in a second set of layers between the first set of layers (6) and the third layer (8) with one of said second layers (7) in face-to-face contact with the third layer (8).

Description

PROTECTIVE SHIELD Technical Field This invention relates to ballistic-resistant shields, especially shields for use as body armour.

Most body armour today makes use of ballistic cloth woven from aramid fibre such as that sold by Du Pont under their trade mark "Kevlar" and by Akzo under their trade mark "Twaron". However, another form of ballistic cloth is now available woven from high density polyethylene fibre and sold by Allied Signal under their trade mark "Spectra" and by Dutch State Mines under their trade mark "Dyneema". The fibres of both of these cloths have a sufficiently high tensile strength to make them resistant to penetration by a bullet, the level of protection being dependent on the density of the fibres in the cloth and the number of layers of cloth employed in a shield.However, the weight and flexibility of the shield are also relevant factors if it is to be incorporated in protective clothing, and thus a balance is required between the level of protection required and the comfort of the user in selecting the materials to be used.

High density polyethylene fibre is also available in a non-woven film or sheet form in which the fibres are laid-up as two orthogonal sets of plies in an elastomeric matrix of low density polyethylene. This non-woven ballistic-resistant material is sold by Allied Signal under their trade mark "Spectra Shield" and by Dutch State Mines under their trade mark "UD66". An advantage of this material is that the lack of a woven structure and the provision of a plastic matrix helps resist ply separation when struck by a bullet and thus it is more resistant to penetration. This in turn helps to improve the capability of "Spectra Shield" to withstand penetration by bullets fired in a multi-shot sequence.

It is known (US Patent No. 4989266) to produce body armour which uses layers of both woven aramid fibres and non-woven polyethylene fibres, the layers of non-woven polyethylene fibres being sandwiched between two multiple layers of woven aramid fibres. The same number of layers of aramid fibres are used both sides of the layers of non-woven polyethylene, typically, there being eight layers of woven aramid fibres each side of ten layers of non-woven polyethylene fibres.

These outer layers of woven aramid fibres are said to enhance comfort, to hold the inner layers of non-woven polyethylene together, and to enhance safety by virtue of the fact that the aramid is particularly fire-resistant.

It is also known (GB Patent No. 1556245) to produce body armour with one or more sheets of an impact absorbing plastics material between the ballistic woven cloth in the form of "Kevlar", and the body of the person being protected so as to absorb and limit transmission of the impact shock of a bullet striking the armour. The preferred impact absorbing plastics material used comprises one or more thin flexible polycarbonate sheets backed up by one or more resiliently compressible sheets of a foamed plastics material. This impact absorbing material has become known as a trauma pack or trauma shield.

Disclosure of.the Invention An object of the present invention is to provide an improved ballistic-resistant shield, especially a shield with improved capability to withstand penetration by bullets fired in a multi-shot sequence.

This is achieved according to the invention by providing a shield incorporating a plurality of layers of high tensile strength fibres comprising first layers with fibres that are embedded in a plastic matrix, and second layers with fibres that are interlocking and not embedded in an elastomer matrix, and a third layer of an impact absorbing and impact mouldable material, the majority of the first layers being incorporated face-to-face in a first set of layers adjacent to the front face of the shield which is directed towards a region of ballistic threat, the third layer being located adjacent to the rear face of the shield, and the majority of the second layers being incorporated face-to-face in a second set of layers between the first set of layers and the third layer with one of said second layers in face-to-face contact with the third layer.

The invention is based on the appreciation of the fact that the ballistic-resistance of a shield is improved if the layers of high tensile strength fibres are arranged so that a bullet first impacts on layers of fibres embedded in a plastic matrix and thereafter impacts on layers of interlocking (e.g. woven or knitted) fibres. It seems that the embedded fibres of the first layers are better at "catching" the bullet and transferring the impact to the second layers of interlocking fibres with the minimum disturbance to the stacked layers so that they can better resist multiple shots.

Further, the interlocking nature of the fibres of the second layers, especially that one in face-to-face contact with the third impact absorbing and impact mouldable material, produces higher slip resistant surfaces to resist lateral slipping of the second and third layers on one another and thus further reduces disturbance of the layers when impacted upon by a bullet.

In a particular example of the invention, all of the layers of the first set of layers are composed of "Spectra Shield", and all of the layers of the second set of layers are composed of woven "Kevlar", and the third layer comprises one or more sheets of polycarbonate.

Description of the Drawings The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows the front piece of a two piece shield designed to be worn as body armour, Figure 2 shows the rear piece for use with the front piece of body armour shown in Figure 1, Figure 3 shows the two pieces of body armour of Figures 1 and 2 when in use, and Figure 4 shows the internal laminated construction of the front and rear pieces of body armour in Figures 1 and 2.

Mode of Carrying Out the Invention The illustrated shield is a two-piece shield 1, 2 adapted to be worn as body armour by a user. Each piece of the shield comprises multiple layers of ballistic resistant material and impact absorbing material laminated together within an outer fabric casing 3, as described in more detail hereinafter with reference to Figure 3. One piece 1 of the shield is shaped to fit the chest of the user, and the other piece 2 is shaped to fit the back of the user, and the two pieces are connected together by fastening straps 4 over the shoulders and around the sides of the body of the user, as shown in Figure 4. The straps 4 may conveniently incorporate hook-and-felt type fasteners 5 such as sold under the trade mark "Velcro".

The multiple layers of ballistic resistant material comprise a first set of layers 6 of a non-woven fibre material comprising high density polyethylene fibres laid up as two orthogonal sets of plies in a plastic matrix of low density polyethylene, and a second set of layers 7 of woven aramid fibres. The first set of layers 6 may be material such as that sold under the trade mark "Spectra Shield", and the second set of layers 7 may be material such as that sold under the trade mark "Kevlar". The "Spectra Shield" typically has an areal mass of 145 grams/square metre, and between 5 and 15 layers form the first set. The "Kevlar" fabric typically has an areal mass of 280 grams/square metre, and between 5 and 30 layers form the second set. Preferably, the "Kevlar" layers are held together by light stitching which passes through all the layers of the second set.

According to the invention, the first set of layers of "Spectra Shield" are located adjacent to the front face of the shield which in use is directed away from the body of the user towards the region of ballistic threat i.e. towards the left in Figure 3. Furthermore, a third layer of impact absorbing and impact mouldable material is located adjacent to the rear face of the second set of "Kevlar" layers 7, and comprises one or more sheets of polycarbonate 8 typically lmm thick, and one or more sheets 9 of resiliently compressible closed cell foamed plastics. The polycarbonate may be that sold under the trade mark "Lexan" and the foamed plastics may be cross-linked polyethylene such as that sold under the trade mark "Plastazote" or "Evazote". The total thickness of this third impact absorbing layer may be between 0.5mm and 12mm thick.

All of these layers 6, 7, 8 are assembled as a pack in face-to-face contact within the outer casing 3 as shown in Figure 3.

It has been found that a shield constructed as described and illustrated herein is especially effective in the improved level of protection it provides against bullets fired in a multi-shot sequence. Bullets may penetrate one or more of the first layers of "Spectra Shield" but they are stopped and the impact absorbed, moulding an indentation in the polycarbonate in the process.

On multi-shot tests, typically involving a sequence of six bullets, all bullets were stopped.

inspection of the layers of "Spectra Shield" 6 and "Kevlar" 7 after the test, reveal that these layers tend to resist disruption and maintain their laminated formation in which they are most effective in resisting ballistic penetration.

The layers of "Spectra Shield" and "Kevlar" can be stitched together by lines of light stitching running as two sets of parallel lines intersecting one another. This enhances the multi-shot performance of the shield still further, although too much stitching may reduce its flexibility and impair performance.

The shield according to the invention may be used in combination with an additional plate such as a ceramic faced plate in front of it to protect against higher levels of ballistic threat.

Claims

1. A ballistic-resistant shield having a front face and a rear face and adapted for use with the front face directed towards a region of ballistic threat to protect the region adjacent to the rear face, the shield incorporating a plurality of layers of high tensile strength fibres comprising first layers with fibres that are embedded in a plastic matrix and second layers with fibres that are interlocking and not embedded in a plastic matrix, the majority of the first layers being incorporated face-to-face in a first set of layers adjacent to the front face of the shield and the majority of the second layers being incorporated face-to-face in a second set of layers between the first set of layers, and a third layer of an impact absorbing and impact mouldable material located adjacent to the rear face of the shield, one of said second layers being in face-to-face contact with the third layer.

2. A shield as claimed in claim 1 in which all.of the layers of the first set of layers have fibres embedded in a plastic matrix.

3. A shield as claimed in claim 1 or 2 in which all of the layers of the second set of layers have interlocking fibres not embedded in a plastic matrix.

4. A shield as claimed in any one of the preceding claims in which the fibres are aramid fibres or polyethylene fibres.

5. A shield as claimed in claim 4 in which the first layers have polyethylene fibres.

6. A shield as claimed in claim 5 in which the fibres of the first layers are embedded in polyethylene.

7. A shield as claimed in any one of the preceding claims in which the fibres of the first layers are laid up to form each layer.

8. A shield as claimed in claim 7 in which the fibres of the first layers are laid in uni-directional sets angled relative to one another.

9. A shield as claimed in any one of the preceding claims in which the first and second layers are stitched together.

10. A shield as claimed in any one of the preceding claims in which the third layer comprises one or more sheet of polycarbonate.

11. A shield as claimed in any one of the preceding claims in which the third layer comprises one or more sheet of foamed plastics.

12. A shield as claimed in claim 10 in which the third layer comprises a sheet of polycarbonate in face-to-face contact with the second set of layers and a sheet of foamed plastics in face-to-face contact with the polycarbonate.

13. A ballistic-resistant shield substantially as herein described with reference to the accompanying drawings.