Anti-ballistic structural panel

Abstract

An anti-ballistic structural panel. The anti-ballistic structural panel comprising: a structural layer arranged between an outer enclosing layer and an inner enclosing layer, the outer enclosing layer disposed on an outwardly facing side of the structural layer and the inner enclosing layer disposed on an inwardly facing side of the structural layer; a capture layer adjoining the inner enclosing layer and disposed inboard of the inner enclosing layer, the capture layer defining an inwardly facing surface; wherein the structural layer comprises a plurality of hollow cells extending through the structural layer, wherein a plurality of the cells comprise a ceramic unit disposed within the cell.

Description

[0001] ANTI-BALLISTIC STRUCTURAL PANEL

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to a structure or panel with anti-ballistic properties particularly, although not exclusively, for use in aerospace applications; and a method of forming the same.

[0004] BACKGROUND

[0005] Many applications involve structures, machinery or vehicles that need to withstand high shear loads. In particular, aircraft must be made to withstand numerous forces and meet numerous operational requirements. For example, the floors of aircraft must integrate with the fuselage and provide the necessary stiffness. They must also be strong enough to support internal loads, for example from passengers and / or cargo and must not unduly wear. Any lateral walls of the aircraft must also be strong enough to protect passengers and / or cargo from the environmental conditions and the elements, in particular as the aircraft is in flight.

[0006] Weight is also an important feature in structural or vehicle design, where the minimum weight possible while still providing the required functionality, is usually desirable so as to maximise efficiency. For aircraft design and aircraft components, weight is an essential feature for flight, in particular aircraft structures, such as flooring and wall design, must be as light as possible.

[0007] To help structures, machinery or vehicles withstand high loads and keep their shape, their housing, e.g. wall and flooring, are often made stiffer and stronger. This is usually done by increasing the thickness of the layers making up the wall and floor panels or adding further panels or layers to the wall / flooring so as to increase their structural capabilities. However, this results in heavier structures making this unsuitable for applications where lightweight structures can be required or where overall weight must be kept to a minimum. These solutions are particularly disadvantageous in aircraft design as the added volume and weight can have significant impact on the payload volume or size capacity of the aircraft.

[0008] The difficulties of aircraft design are further compounded when ballistic requirements are introduced. For example, aircraft being used in areas of conflict are often the target of ballistics from rifle or hand gun projectiles. In circumstances where an aircraft is the target of ballistics, the flooring and / or the side walls of the aircraft can be modified to absorb ballistics impacting the aircraft. In particular, this is achieved by adding a supplemental layer to the inside of the aircraft (sometimes referred to as ‘add-on’ armour). Such a layer (depending on the threat level) can comprise very hard and brittle materials (such as ceramics) or strong and ductile materials (such as metallic), combined with spall liners, that absorb the impact and prevent the projectile from penetrating into the aircraft cabin or cargo area.

[0009] Such wall and flooring modifications allow the aircraft to operate in dangerous regions and allow for the protection of the occupants, pilots and also cargo. However, these modifications can add significant weight to the aircraft, which is detrimental, for example to payload volume and size capacity. The additional weight can also affect aircraft control due to the shift in the centre of gravity. A balance must therefore be struck between the ballistic properties of the wall and floor structure and the other functional requirements of the aircraft.

[0010] In circumstances where an aircraft is the target of high threat level ballistics such as armour- piercing projectiles, the add-on armour can include ceramic layers or panels, the ceramic material being effective at defeating the hardened cores from armour-piercing projectiles. These add-on ceramic layers or panels add significant parasitic weight to the aircraft, reduce payload volume and size capacity and take up considerable additional space and volume. Furthermore, the brittle ceramic layers or panels need to be protected from possible blunt impact damage during handling as any damage to the ceramic layers or panels prior to use affects the anti-ballistic function of the ceramics. The required added protection for the ceramic layers or panels adds even further weight and volume to the aircraft.

[0011] The present disclosure has been devised in the light of the above considerations. In particular, an invention described herein is concerned with an anti-ballistic structural panel that introduces a high level of ballistic protection and minimises the additional volume and weight provided by the anti-ballistic protection.

[0012] SUMMARY

[0013] Aspects of the invention are set out in the accompanying claims.

[0014] In a first aspect, there is provided an anti-ballistic structural panel, said panel comprising: a structural layer arranged between an outer enclosing layer and an inner enclosing layer, the outer enclosing layer disposed on an outwardly facing side of the structural layer and the inner enclosing layer disposed on an inwardly facing side of the structural layer; a capture layer adjoining the inner enclosing layer and disposed inboard of the inner enclosing layer, the capture layer defining an inwardly facing surface; wherein the structural layer comprises a plurality of hollow cells extending through the structural layer, wherein a plurality of the cells comprise a ceramic unit disposed within the cell. In effect, a structural panel with anti-ballistic properties is provided, said panel comprising a structural layer arranged between two enclosing layers where the structural layer comprises a plurality of hollow cells extending through the structural layer. A plurality of the cells comprise a ceramic unit disposed within the cell.

[0015] Such an arrangement provides a structural panel with added anti-ballistic properties, where the anti-ballistic capabilities are integrated into the panel itself. The panel may be a structural component of a larger construction, assembly or vehicle, for example a wall or floor of a building or of an aerospace structure such as an aircraft. As an oncoming projectile meets the panel, the panel is capable of affecting the shape of the projectile and thereby slowing or arresting the movement of the projectile, including high threat ballistics such as an armour- piercing projectile, while also minimising any additional weight or volume required to provide the anti-ballistic properties. By integrating the anti-ballistic capabilities into the structural panel itself, the need for additional ‘add-on’ armour to provide ballistic protection can advantageously be dispensed with.

[0016] The term ‘anti-ballistic’ is intended to refer to the prevention of movement of a ballistic projectile, such as a bullet, or other oncoming object.

[0017] Advantageously, providing a panel with a structural layer comprising a plurality of hollow cells allows the structural layer to reinforce and strengthen the overall panel while minimising additional weight to the panel. In effect, the structural layer improves the structural performance of the panel without adding significant weight to the structure. The plurality of cells reduce the amount of material used in the structural layer, thereby reducing the weight of the structural layer, however without compromising the structural capability of the layer to the panel. The structural layer provides structural strength to the overall panel, while keeping the weight of the structural layer (and therefore the overall weight of the panel) to a minimum.

[0018] The units disposed within the cells being of ceramic material allows the panel to withstand particularly high ballistic threat levels, including for example armour-piercing projectiles.

[0019] Optional features will now be set out. These are applicable singly or in any combination with any aspect.

[0020] The structural layer is arranged between an outer enclosing layer disposed on an outwardly facing side of the structural layer and an inner enclosing layer disposed on an inwardly facing side of the structural layer, the outer and inner enclosing layers being disposed on opposite faces (i.e. opposite main surfaces) of the structural layer. The panel comprises a capture layer adjoining (for example directly adjoining) the inner enclosing layer and disposed inboard of the inner enclosing layer.

[0021] The outer enclosing layer may define a strike layer, that is the first layer against which a projectile or approaching object would strike and that is required to perform an anti-ballistic functionality or task. The strike layer may itself (partially) stop or slow down the projectile or it may be penetrated by the projectile. The projectile may then penetrate the structural layer by striking and breaking one of the ceramic units within the structural layer. As the ceramic unit is struck by the oncoming projectile the unit inevitably breaks. This intended failure mode of the ceramic unit as it is struck disrupts the shape, trajectory and / or path of flight of the projectile or oncoming object and slows down the projectile. The projectile may therefore pass through the structural layer and meet the capture layer. Here, the projectile comes into contact with e.g. the fibres of the ultra-high molecular weight polyethylene of the capture layer which are able to arrest the movement of the projectile and prevent the projectile leaving the anti-ballistic panel. As described above, the ceramic units within the cells of the structural layer inevitably break as they are struck by the projectile, thereby absorbing the energy of the projectile by deforming or breaking up the projectile and significantly slowing down the projectile (and / or projectile remnants) before it meets the capture layer. This increases the likelihood of the capture layer arresting movement of the projectile.

[0022] This intended failure mode of the ceramic units as they are struck by the projectile allows the panel to be particularly effective at capturing projectiles. In particular, the ceramic units provide the panel with a particularly high level of ballistic protection including against armour piercing projectiles.

[0023] As described above, the structural layer is arranged between two enclosing layers disposed on opposite faces of the structural layer, such that the structural layer and the enclosing layers may form a laminate within the panel with the structural layer defining a core between the enclosing layers. In effect, the enclosing layers and the structural layer form a sandwich- structured composite within the panel.

[0024] The enclosing layers may enclose the ceramic units within the cells. In particular, the enclosing layers may be flush against each opposite face of the structural layer and may be bonded to the opposite faces of the structural layer such that the units are fully enclosed within their respective cells by the enclosing layers. The enclosing layers may define outer skins to the core of the laminate. In particular, the enclosing layers and the structural layer may form a single unitary and integrally formed structure. By enclosing the units within the structural layer, the enclosing layers can aid in keeping the ceramic units intact during projectile penetration such that they may better erode the projectiles as they pass through the ceramic units.

[0025] This anti-ballistic sandwich-structured composite or laminate increases the structural integrity of the overall panel and significantly improves the structural performance of the panel. This allows the panel to be used as a structural component, in particular an integrated load bearing component in a larger structure (e.g. an aircraft or a building). The increased structural performance of the panel provided by the anti-ballistic laminate advantageously allows the panel to be used in particularly high load-bearing structures, such as the floor or walls of an aerospace structure (e.g. an aircraft or rotorcraft) as these are subject to particularly high (e.g. aerodynamic) forces. The panel may also be used as the floor or a ramp for driving on or as a wall for buildings subject to high loads and requiring anti-ballistic capability.

[0026] The inclusion of the ceramic units within the cells of the structural layer provides anti-ballistic properties to the panel such that, in effect, the anti-ballistic properties can be combined with the structural properties in the design of the overall structure. The anti-ballistic capability advantageously allows the panel to be used as an armour as well as a load bearing part as opposed to, with conventional arrangements, merely a structural panel in need of add-on armour. In effect, the combination of the structural layer comprising a plurality of hollow cells and a plurality of the cells comprising a ceramic unit disposed within the cell provides a synergy in that the structural layer / laminate provides a structural functionality to the panel, while the ceramic units provide an anti-ballistic capability to the panel.

[0027] Advantageously, by including the units within the cells of the structural layer, the panel is provided with superior ballistic protection without increasing the overall volume of the panel. The anti-ballistic properties of the panel are provided by the ceramic units installed within the cells of the structural layer. The ceramic units occupy unused spaces or areas within the panel, in particular the hollow cells already present in the structural layer that may otherwise remain un-occupied. In effect, the anti-ballistic capabilities are integrated into the design of the panel itself. This can result in a significantly slimmer and leaner anti-ballistic panel compared to add-on armour that may include a supplemental ceramic panel positioned, e.g. on top of / below or either side of structural layers or panels and taking up additional space and volume.

[0028] The combination of the structural layer with the plurality of hollow cells and a plurality of the cells comprising a ceramic unit disposed within the cell may seem counterintuitive. In particular, the structural layer being designed to provide strength to the panel while keeping additional weight to a minimum by including the hollow cells contrasts with the addition of the ceramic units within the cells which will inevitably add weight to the panel. This may seem like a combination of two incompatible solutions. However, the inventor has found that by including the ceramic units within the cells of the structural layer, an anti-ballistic structural panel with the following advantages can be provided: particularly high level of ballistic protection a structure which does not add to the overall volume of the panel a structure that minimises the additional weight of the panel and therefore the overall weight of applying the anti-ballistic panel to e.g. an aircraft or other protective article a structure which, if applied to an aircraft, does not compromise the payload volume or size capacity of the aircraft a panel with improved structural performance which can be used as an integrated load bearing component in high load-bearing structures a structure that can be optimized for ballistic threats and structural requirements

[0029] The anti-ballistic panel described herein strikes an optimal balance between the ballistic properties of the structure and the load-bearing capabilities of the structure, while not impacting the overall size and volume of the design. This is particularly advantageous in aerospace applications, where maximising strength and stiffness, while keeping weight to a minimum is often required, for example when seeking to maximise payload volume and size capacity during aircraft design.

[0030] The unit comprises ceramic material, including for example natural ceramics including oxide ceramics (e.g. aluminum oxide), synthetic ceramics including silicon carbide (SiC) or boron carbide (B4C) or a hybrid of different ceramic forms. The hard, brittle, erosion-resistant material properties of ceramic make it an optimal material for the units.

[0031] The skilled person will appreciate that embodiments may be envisioned where the unit may be formed of any hard brittle material (e.g. ceramic, glass, graphite, low plasticity composites and alloys etc.) displaying the above characteristics, in particular a unit that by its hardness and / or toughness deforms and / or breaks up and erodes the oncoming projectile and effectively dissipates the projectile’s kinetic energy.

[0032] A plurality of the cells comprise a ceramic unit (e.g. a ceramic component or piece) disposed within the cell. Each unit is disposed or installed within a cell of the structural layer such that the walls of the cell surround the unit. The unit may be in the form of a tile (e.g. a ceramic tile). The units being in the form of tiles make them particularly suitable for conveniently disposing or installing them within the cells. The (usually) substantially thin, flat or slightly curved shape of the tiles advantageously allows the structural layer supporting the tiles to be substantially thin thereby minimising the volume taken up by the structural layer within the panel and minimising the additional weight of the structural layer or laminate. Furthermore, by providing the units in the form of tiles, the thickness of the individual tiles can be tailored based on the anticipated projectile threat and / or the size (i.e. width) of the tiles can be tailored based on the cell size (which may be customised based on the structural requirements of the panel), as described further below.

[0033] A plurality, e.g. at least half of the cells may comprise a ceramic unit. The un-filled cells may be left empty (i.e. with no ceramic unit or any other component) or they may be left unoccupied by a ceramic unit such that they may be occupied by another component configured to provide some other functionality to the panel, e.g. an interface point. In some embodiments, an un-occupied cell may be filled with the material forming the structural layer or, for example, any other (e.g. thermoplastic) material so as to increase the structural strength of the structural layer.

[0034] In some embodiments, every other cell within the structural layer may comprise a ceramic unit (for example the cells may alternate between a cell / cells occupied by a ceramic unit, followed by a cell / cells un-occupied by a ceramic unit, followed by a cell / cells occupied by a ceramic unit etc.). For example, the majority of the cells may comprise a ceramic unit. In some embodiments, each cell within the structural layer may comprise a ceramic unit disposed within the cell.

[0035] In effect, this provides an anti-ballistic structure with multiple instances of ceramic material or ceramic units that may individually and independently break (as a unit is struck by an oncoming projectile or object) without affecting a ceramic unit in another cell. This increases the number of instances the anti-ballistic sandwich-structured composite or laminate can be struck by projectiles and the panel continuing to provide anti-ballistic functionality. In effect, the panel described herein comprises a multi-hit capability. This results in a significantly more effective anti-ballistic panel compared to conventional add-on armour that may include a (e.g. single or relatively few) ceramic panel(s) which may only be struck once or a relatively few number of times before the ceramic panel in the armour becomes ineffective at providing ballistic protection.

[0036] The structural layer may comprise an array of cells such that, in effect, the structural layer provides a honeycomb core layer within the panel. The cells may be uniformly distributed across the structural layer and may extend across substantially most of or along the entire length and / or width of the structural layer. Each cell comprises cell walls defining the cells (i.e. the lateral walls of the cells) such that the cells extend transversely through the structural layer, i.e. through the thickness of the structural layer. For example, the cells may extend perpendicularly through the structural layer, i.e. the cell walls may be perpendicular to the enclosing layers (e.g. each of the enclosing layers). For example, the cells may comprise rectangular lateral walls or faces that extend perpendicularly to the faces of the enclosing layers. In some embodiments, the cell walls may be angled relative to the enclosing layers (e.g. each of the enclosing layers). In effect, the cells may be shaped as trapezoidal prisms.

[0037] The cell walls may be relatively thin such that the spacing between the ceramic units is minimal. In effect, the plurality of ceramic units within the structural layer may act substantially as a ceramic panel within the overall structural panel but with the added advantage that the units provide significantly more instances than a single ceramic panel to be stuck by projectiles and the laminate continuing to provide anti-ballistic functionality to the panel.

[0038] The cell walls being relatively thin may result in the walls being susceptible to collapsing, particularly when the panel is being subject to high load-bearing forces. By including the ceramic units within the cells, the units are able to support the cell walls, in effect stabilising the honeycomb core layer within the panel and prolonging the amount of time a load can be supported or absorbed by the panel before potential collapse of the cell walls.

[0039] The cells may be uniform, i.e. each cell may have substantially the same shape and / or size. The cells may be any suitable shape. For example, the base face or top and / or bottom face of each cell may be generally circular, oval, quadrilateral, square, rectangular, triangular etc. In some embodiments, the cells (e.g. each cell) may be generally hexagonal. For example, the top and bottom face of each cell may be hexagonal. In particular, the cells may be shaped as hexagonal prisms. In effect, the structural layer may comprise an array of generally hexagonal cells. The structural layer may provide a honeycomb core layer, the core layer comprising a hexagonal cell honeycomb framework.

[0040] The hexagonal cell honeycomb framework advantageously provides a core with minimal material density and relatively high out-of-plane compression strength and out-of-plane shear strength. In particular, the hexagonal cells allow the laminate to provide maximum structural strength to the structural panel while minimising material (and therefore additional volume and weight) to the panel.

[0041] In other embodiments, the structural layer may comprise hollow cells of different or varying shapes and sizes distributed across the structural layer and thus the structural panel. The shape may be different and / or the size of the cells may be larger or smaller (compared to the cells across the rest of the panel) across a given area of the panel depending on the level of anti-ballistic protection required in the given area. For example, the ceramic units in an area of the panel needing higher anti-ballistic protection (e.g. near and / or around a pilot seating area in an armoured aerospace structure) may need to be thicker compared to other areas of the panel. In other embodiments, the size (e.g. the width) of the ceramic units may be larger in a given area of the panel that is expected to be subject to lower load-bearing forces or shear loads compared to other areas of the panel. The cells may vary in size in a given area of the panel so as to accommodate the different size and / or shape of the ceramic units.

[0042] The cell size (i.e. diameter or width of each cell) may be selected based on the structural requirements of the panel, i.e. the amount of load or shear load that may be applied to the panel. In effect, the load-bearing strength and / or shear strength of the panel may be largely dictated by the strength, stiffness and structural capability of the laminate and the structural layer within the panel. In particular, the need for a relatively strong panel may dictate the number of cells and / or the cell walls requiring a predetermined (e.g. minimum) thickness, thereby dictating the cell size. Furthermore, the anticipated size (calibre) of the projectiles which may be directed at the structure (e.g. the aircraft) may also affect cell wall size (and thus the resulting cell size). In particular, the cell wall may need to be less than a predetermined maximum thickness to ensure the projectile strikes a ceramic unit rather than the cell wall. For example, the cell wall thickness may need to be substantially smaller than the smallest anticipated projectile calibre.

[0043] In order to accommodate the ceramic units, the cells may need to be larger (i.e. wider) than in conventional structural panels comprising honeycomb cores. For example, conventional structural panels may comprise honeycomb structures or cores with cells that are approximately up to 4-8mm in size (e.g. width or diameter). In order to accommodate the ceramic units, the size (i.e. diameter or width) of the cells may, in some embodiments, be approximately 20-40 mm or larger. The larger cells can result in the enclosing layers being less supported by the cell walls, thereby reducing the stability of the enclosing layers. In particular, the enclosing layers may flex or buckle into the cells, particularly when high compression loads are applied to the panel. By disposing the ceramic units within the cells, the ceramic units advantageously provide an element of support to the enclosing layers. In particular, by including the ceramic units within the cells, the ceramic units prevent the enclosing layers from flexing / buckling or collapsing into the cells.

[0044] The ceramic units may be uniform, i.e. each unit may have substantially the same shape and size. The units may be any suitable shape, e.g. generally circular, oval, quadrilateral, square, rectangular, triangular etc. For example, the units may be generally hexagonal. In particular, the units may be shaped as hexagonal prisms. The thickness of the ceramic units may be selected based on the anticipated type of projectile, i.e. such that the ceramic units provide effective anti-ballistic protection (i.e. the units behave as described above when struck by a projectile and deform, break up and / or erode the oncoming projectile). In particular, the thickness of the ceramic units may be selected based on the anticipated threat level the panel is intended to stop while also remaining relatively thin so as to minimise the additional volume and weight to the panel.

[0045] The size of the ceramic units (i.e. diameter or width of each unit) may be selected based on the structural requirements of the panel (i.e. the amount of load / shear load that may be applied to the panel) and / or the size of the cells configured to receive the ceramic units.

[0046] In embodiments where the cells may be hexagonal, the ceramic units may similarly be hexagonal such that the units may advantageously fit conveniently and accurately within the cells.

[0047] The ceramic units may be sized (e.g. in diameter / width and depth) to substantially fit within the cells such that the ceramic units fit securely within the cells, i.e. the ceramic units may be made, formed, or chosen (if pre-formed or off-the-shelf tiles) to substantially fit the size of the cells (e.g. determined based on the desired structural requirements of the panel). In particular, the ceramic units may have substantially the same diameter or width as the cells such that the ceramic units may provide support to the cell walls. This can also ensure that the cell walls may prevent movement of the units within the cells. The ceramic units may have substantially the same thickness as the depth or height of the cells. In effect, the units may substantially fill (e.g. substantially completely) the cells. In this way, the ceramic units may optimally support the cell walls and the enclosing layers so as to prevent the cell walls and the enclosing layers from collapsing. Thus the ceramic units may optimally support and stabilise the honeycomb core (i.e. the anti-ballistic laminate).

[0048] The skilled person will appreciate that in embodiments where the size of the ceramic units is the primary deciding factor, the cells may be sized (e.g. in diameter / width and depth) to substantially fit the units such that the units may fit securely within the cells.

[0049] In embodiments where the ceramic units substantially fill the cells, the distance between the enclosing layers (i.e. the depth of the cells) may be substantially the same as the thickness of the units such that each opposing face of the ceramic units may contact (e.g. directly contact) the enclosing layers. Advantageously, this aids the ceramic units in preventing the enclosing layers from collapsing in on themselves (particularly when the panel is subject to high bending moments resulting in shear stresses) such that the ceramic units may support the enclosing layers and thus further stabilise the honeycomb core. This also allows the cells to protect the ceramic units within the cells. The opposing faces of each ceramic unit may be smooth and / or may comprise a smooth surface finish. This may be achieved by omitting the sandblasting step often applied to ceramic units after the ceramic sintering process. By omitting the sandblasting step, the ceramic units may comprise smooth faces. The opposing faces of the ceramic units being smooth and / or comprising a smooth surface finish can help in eliminating or reducing the mechanical adhesion of the ceramic units to the enclosing layers encasing the units. In some embodiments, the ceramic units may comprise a surface treatment (for example a release coating) on the opposing faces of the units to help in eliminating or reducing the adhesion (mechanical and / or chemical adhesion) of the ceramic units to the enclosing layers. By eliminating or reducing the adhesion (mechanical and / or chemical) of the ceramic units to the enclosing layers as described above, any shear loads applied to the panel are prevented from being transferred onto the enclosing layers by the ceramic units.

[0050] The structural layer may comprise a thermoplastic material or a thermo-set material. In some embodiments, the structural layer may comprise a thermoplastic and thermo-set hybrid material. In particular, the structural layer may advantageously be formed of a fibre reinforced plastic material, for example a carbon fibre reinforced plastic material. This not only allows for a reduction in weight but also allows for convenient manufacture into a required shape. The structural layer may be an additive manufactured layer. In other embodiments, the structural layer may be an injection moulded or compression moulded layer. In some embodiments, the structural layer may be a machined layer.

[0051] The enclosing layers may comprise a thermoplastic material or a thermo-set material or, in some embodiments, a thermoplastic and thermo-set hybrid material. In particular, the enclosing layers may be formed of continuous fibre reinforced plastic (FPRs). The enclosing layers may be made in advance before being co-consolidated with the structural layer. In other embodiments, the enclosing layers may be co-cured with the structural layer. In some embodiments, the enclosing layers may be bonded (for example adhesively bonded or welded or fused) with the structural layer.

[0052] In particular, the structural layer and the enclosing layers may be formed as a single unitary structure or laminate (thereby forming the sandwich-structured composite) securely enclosing the ceramic units within the cells.

[0053] The panel may comprise one or more reinforcement elements. For example, the outer enclosing layer may comprise one or more reinforcement elements, e.g. disposed on or extending from an outer face of the outer enclosing layer. The reinforcement elements may be bonded to the outer enclosing layer (e.g. the outer face of the outer enclosing layer). The reinforcement elements can further increase the structural performance of the panel and improve the rigidity and strength of the panel. In particular, the reinforcement elements can help stiffen the outer enclosing layer and the structural layer. The reinforcement elements can be particularly effective at strengthening the panel, in particular the structural layer, when subject to compression forces. The reinforcement elements may comprise discreet reinforcement elements, for example ribs or beam stiffeners that extend longitudinally across the panel (for example across the length and / or width of the panel). The ribs may be, for example, beams of any suitable cross-section (e.g. I beams, Y beams, omega profile beams etc.), blade stiffeners or hat stiffeners. In effect, the panel may comprise a composite sandwich discretely stiffened by ribs. The discreet reinforcement elements may be formed using fibre reinforced plastic.

[0054] The panel may comprise a second sandwich-structured composite disposed outboard of the structural layer and wherein the outer enclosing layer defines a shared intermediate layer arranged between the structural layer and the second sandwich structured composite. In particular, the first sandwich structured composite (defined by the structural layer and the outer and inner enclosing layers) and the second sandwich structured composite may share the outer enclosing layer (of the first sandwich structured composite) as an intermediate layer between the two sandwich structured composites. In effect, the panel may comprise a double sandwich-structured composite.

[0055] The second sandwich-structured composite can further increase the structural performance of the panel and improves the rigidity and strength of the panel. In particular, the double sandwich-structured composite provides the panel with the dual functionality of high structural performance and high anti-ballistic functionality.

[0056] The second sandwich-structured composite may comprise an outer (lower) layer, e.g. a thermoplastic or thermo-set layer, the outer layer being spaced relative to the outer enclosing layer (of the anti-ballistic laminate) to define a space. In effect, the second sandwich-structured composite may be defined by the outer enclosing layer (shared with the first sandwich-structured composite), the outer (lower) layer and the space between the outer enclosing layer and the outer (lower) layer. The space may comprise one or more reinforcement elements. The space from the second sandwich-structured composite may increase the structural performance of the panel and improve the rigidity of the panel.

[0057] Additionally, the second sandwich-structured composite may further protect the ceramic units from possible damage during handling of the panel. The ceramic units can be particularly susceptible to blunt impact damage during handling of the panel. The second sandwich-structured composite provides added protection to the outer (lower) side of the first sandwich-structured composite (i.e. the anti-ballistic laminate), thereby protecting the units from possible damage during handling to ensure the units remain intact for when they are required during use.

[0058] The reinforcement elements extending within the second sandwich-structured composite may be any suitable arrangement based on the structural requirements of the panel. The reinforcement elements can be particularly effective at strengthening the panel, in particular the structural layer, when subject to compression forces. In one arrangement, the one or more reinforcement elements may be in the form of discreet reinforcement elements or other structure components extending within the sandwich core. For example, the reinforcement elements may be in the form of a plurality of ribs or beam stiffeners extending between the outer enclosing layer and the outer layer and longitudinally extending across the length and / or width of the panel. The ribs may be, for example, I beams, blade stiffeners or hat stiffeners extending between the outer enclosing layer and the outer layer. The reinforcement elements may be formed using fibre reinforced plastic. In effect a composite sandwich, or ‘box structure’ discretely stiffened by ribs, is formed having low weight and high strength.

[0059] In an alternative arrangement the one or more reinforcement elements may be in the form of a foam, honeycomb or similar ‘core’ material. Such materials are extremely light (low density) but can aid in providing the rigidity and shear strength needed within the sandwich- structured composite required for structural loading. In such an arrangement the core material may fill the entire space between the two layers. This arrangement of reinforcement elements may be particularly suitable in embodiments where the panel comprises a second sandwich-structured composite

[0060] As described above, the capture layer may be arranged to arrest the movement of a projectile that passes through the second sandwich-structured composite, the outer enclosing layer from the anti-ballistic laminate, the ceramic units and the inner enclosing layer. Advantageously the capture layer may be formed of an ultra-high molecular weight polyethylene material. Such materials exhibit extreme tensile strength and - being usually composed of multiple fibrous layers with (deliberate) poor inter-laminar shear strength - are able to deform excessively upon impact which allows for an optimal use of said tensile strength to arrest the projectile. The arrangement described herein advantageously increases the probability, by virtue of the structural layer together with the ceramic units disposed within the cells, that a projectile may contact the capture layer with a significantly reduced speed, changed or deformed shape (e.g. blunted), fractured and / or fragmented and significantly reduced force than when the projectile strikes (and penetrates) the strike layer (i.e. the outer enclosing layer). This improves the probability that the movement of the projectile can be arrested by the capture layer.

[0061] Various materials may be used for the capture layer. For example, the capture layer may comprise a (non-structural) ultra-high molecular weight polyethylene (UHMwPE) or equivalent spall liner material. Advantageously, the ultra-high molecular weight polyethylene material may be Dyneema® manufactured by DSM (e.g. HB26, HB210, etc.), Kevlar or another aramid fibre material or typical spall liner material could also be used.

[0062] The capture layer may contact (e.g. directly contact) the anti-ballistic laminate, in particular the inner enclosing layer. In effect, the capture layer may provide an element of rigid support to the structural layer / anti-ballistic laminate and may aid in protecting the ceramic units from blunt impact damage during handling of the panel. The support from the capture layer may also aid in keeping the units together for as long as possible as they are being struck by the projectile, thereby increasing the eroding effect of the ceramic unit on the projectile.

[0063] A (e.g. top) cover layer may be provided which may act as the upper or outer casing of the panel and may become the floor of the aircraft cabin for example. This layer may protect the panel and capture layer from wear and tear, damage and, for example, water / fluid ingress. This cover layer may be a metallic (e.g. aluminium) layer.

[0064] It will be appreciated that the above described anti-ballistic panel may be integrated into the floor of a vehicle or aircraft, in effect the anti-ballistic panel forming a structural panel of the aircraft flooring. For example, the outer layer of the second sandwich-structured composite may define a bottom outwardly facing surface of the aircraft. The capture layer or the top layer may define an upper inwardly facing surface of the aircraft.

[0065] The panel may be integrated into the fuselage design of an aircraft whilst simultaneously providing a level of ballistic protection. Using such an arrangement thereby negates the need for bespoke anti-ballistic add-on layers within the aircraft compartment or cargo area. This advantageously reduces the overall weight of applying an anti-ballistic system to an aircraft and increases the payload volume or size capacity of an aircraft with an anti-ballistic system.

[0066] The above described anti-ballistic panel may be integrated into a wall of a vehicle or aircraft, in effect the anti-ballistic panel forming a side panel or laminate within the walls of the vehicle or aircraft.

[0067] In some embodiments, the above described anti-ballistic structure may be integrated into body armour (e.g. in a bulletproof vest). It will be appreciated that the relatively light and thin panel described above may make the structure usable for anti-ballistic clothing. As discussed above, advantageously, the outer and / or inner enclosing layers may be coconsolidated , co-cured, bonded, welded or fused with the structural layer, so as to form a unitary laminate with the ceramic units disposed within the internal cells.

[0068] The second sandwich-structured composite, including the reinforcement elements, the anti- ballistic laminate and the capture layer may be co-cured layers within the panel. This allows a single body panel to be formed using conventional FRP manufacturing techniques that will be well understood by a person skilled in the art of composite manufacturing.

[0069] Viewed from a second aspect there is provided a method of forming an anti-ballistic structural panel according to the first aspect, wherein the method comprises the step of forming the structural layer by additive manufacturing or injection moulding.

[0070] The method may comprise the step of forming the enclosing layers by co-consolidation cocuring, bonding, welding or fusing

[0071] The method may comprise the steps of laying-up and co-consolidating co-curing, bonding, welding or fusing the outer and / or inner enclosing layers with the structural layer, which may result in the outer / inner enclosing layers being bonded to the structural layer.

[0072] The second sandwich-structured composite, the anti-ballistic laminate, the capture layer and potentially the reinforcement elements may be co-cured during a single curing operation (for example in or out of autoclave).

[0073] Alternatively, second sandwich-structured composite, the anti-ballistic laminate and the reinforcement elements may be co-cured during a single curing operation and the capture layer may then be bonded to or brought into contact with (using a suitable housing) the inner / upper enclosing layer.

[0074] In an arrangement where the spall liner / capture layer material is composed of the Dyneema variant, it may be necessary to (cold) bond this layer separately to the cured double sandwich-structured composite due to the material and process used to make the Dyneema material. An autoclave or similar (hot) bonding process can alter the Dyneema performance. Since the spall liner is not considered a structural part of the panel design, it can be bonded separately.

[0075] The spall liner / capture layer may comprise a matrix material (e.g. epoxy resin) used in conjunction with an aramid fiber based spall liner / capture layer (e.g. the material combination epoxy / aramid). In these circumstances, the spall liner / capture layer may be cured with the structural double sandwich composite in a single cure step.

[0076] Viewed from another aspect there is provided a fibre reinforced plastic structure comprising: a structural layer arranged between an outer enclosing layer and an inner enclosing layer, the outer enclosing layer disposed on an outwardly facing side of the structural layer and the inner enclosing layer disposed on an inwardly facing side of the structural layer; a capture layer adjoining the inner enclosing layer and disposed inboard of the inner enclosing layer, the capture layer defining an inwardly facing surface; wherein the structural layer comprises a plurality of hollow cells extending through the structural layer, wherein a plurality of the cells comprise a ceramic unit disposed within the cell.

[0077] It will be recognised that such a structure, which is capable of providing both structural performance as well as anti-ballistic performance against high threat levels while minimising additional volume and weight of the structure, may be employed in many applications. In addition to the structure being suitable for integrating into the floor or the wall of an aircraft, including for example the fuselage design or a ramp of an aircraft, the structure may also be used in applications where protective structures around manufacturing are used or other areas where high velocity projectiles may be released. The structure may also be integrated or employed in blast walls or testing facility structures.

[0078] Aspects of inventions described herein extend to aircraft such as helicopters or aircraft structures incorporating structural laminates or panels.

[0079] Viewed from another aspect there is provided an anti-ballistic aerospace structure comprising: a structural layer arranged between an outer enclosing layer and an inner enclosing layer, the outer enclosing layer disposed on an outwardly facing side of the structural layer and the inner enclosing layer disposed on an inwardly facing side of the structural layer; a capture layer adjoining the inner enclosing layer and disposed inboard of the inner enclosing layer, the capture layer defining an inwardly facing surface; wherein the structural layer comprises a plurality of hollow cells extending through the structural layer, wherein a plurality of the cells comprise a ceramic unit disposed within the cell.

[0080] The invention includes the combination of the aspects and features described. The skilled person will appreciate that except where mutually exclusive, a feature or parameter described in relation to any one of the above aspects may be applied to any other aspect. Furthermore, except where mutually exclusive, any feature or parameter described herein may be applied to any aspect and / or combined with any other feature or parameter described herein. BRIEF DESCRIPTION OF THE FIGURES

[0081] Aspects of the invention will now be described, by way of example only, with reference to the accompanying figures, in which:

[0082] Figure 1 shows a schematic view of a first embodiment of an anti-ballistic structural panel;

[0083] Figure 2 shows a schematic of an exploded view of the anti-ballistic structural panel of Figure 1;

[0084] Figure 3 shows a schematic of another embodiment of anti-ballistic structural panel;

[0085] Figure 4 shows a schematic of an exploded view of the anti-ballistic structural panel of Figure 3.

[0086] It will be recognised that the features of the aspects of the invention(s) described herein can conveniently and interchangeably be used in any suitable combination. It will also be recognised that the invention covers not only individual embodiments but also combinations of the embodiments that have been discussed herein.

[0087] DETAILED DESCRIPTION

[0088] The present invention is concerned with an improved anti-ballistic structural panel particularly, but not exclusively, for use in aerospace applications such as in a fixed wing aircraft or a rotorcraft.

[0089] Figure 1 shows a schematic view of a structural panel 10 comprising a structural layer 16 arranged between an outer (lower) enclosing layer 24 disposed on an outwardly (lower) facing side of the structural layer 16 and an inner (upper) enclosing layer 26 disposed on an inwardly (upper) facing side of the structural layer 16. In effect, the outer and inner enclosing layers are disposed on opposite faces of the structural layer, the structural layer together with the enclosing layers 24, 26 forming an anti-ballistic laminate 11 within the panel 10.

[0090] The panel also comprises a capture layer 14 directly adjoining the inner enclosing layer and disposed inboard of the inner enclosing layer. The capture layer 14 defines an inwardly facing surface of an aerospace structure, for example a fixed or rotary wing aircraft. In this embodiment, the outer enclosing layer 24 defines a strike layer and is the first layer that is struck by a projectile or object approaching the panel. The structural layer 16 comprises a plurality of hollow cells 18, in particular hexagonally shaped hollow cells 18 (see Fig 2), that extend transversely (in this embodiment perpendicularly) through the structural layer 16 such that the structural layer 16 provides a hexagonal cell honeycomb core, integrally stiffening the anti-ballistic panel 10. In particular, the structural layer 16 provides structural integrity to the panel 10 and provides increased strength and stiffness to the overall panel 10. Each cell 18 comprises a ceramic tile 20 disposed within the cell 18. The hard, erosion resistant ceramic material makes the tiles 20 particularly suitable for anti-ballistic protection. An oncoming projectile or object approaching the panel will first strike the outer enclosing layer 24, penetrate the outer enclosing layer 24 and strike the ceramic tile 20. As the projectile strikes the ceramic tile 20, the tile absorbs the energy of the projectile by deforming and breaking up the projectile, significantly slowing down the projectile or the projectile remnants. The projectile / projectile remnants can then penetrate through the inner enclosing layer 26 and meet the capture layer 14. The ceramic tiles 20 are particularly effective at deforming and breaking up the projectiles, thereby increasing the likelihood of the capture layer arresting movement of the projectile / projectile remnants.

[0091] In this embodiment, the tiles 20 are formed of silicon carbide material. However, any other ceramic material capable of providing anti-ballistic protection may be used. The ceramic tiles 20 are hexagonally shaped such that they match the hexagonal shape of the cells 18.

[0092] As shown by Figures 1 and 2, the enclosing layers 24, 26 are flush against each opposite face of the structural layer 16 and are bonded to the honeycomb core of the structural layer so as to fully enclose the ceramic tiles 20 within their respective cells 18. In effect, the structural layer and the enclosing layers form a sandwich-structured composite with anti- ballistic properties within the structural panel 10.

[0093] The structural layer 16 comprises an array of hexagonal cells 18, the hexagonal cells 18 extending through the structural layer 16 and across substantially the entire length and width of the structural layer 16.

[0094] The structural layer 16 (i.e. the honeycomb core) and the enclosing layers 24, 26, are formed of a fibre reinforced plastic material. The honeycomb core is formed by additive manufacturing techniques, but may also be formed by injection moulding or machining. The enclosing layers 24, 26 are formed of continuous fibre reinforced plastic (FPRs) and are made in advance before being co-consolidated with the structural layer or thermoset and cocured with the structural layer. In this way, the structural layer 16 and the enclosing layers 24, 26 form a single unitary structure or laminate, securely enclosing the tiles 20 within the cells 18. By enclosing the tiles 20 within the structural layer 16 in this way, the cells 18 aid in keeping the tiles 20 contained within their respective cells 18 and intact for as long as possible during projectile penetration, thereby increasing the eroding effect of the tiles 20 on the projectiles.

[0095] The tile size, in particular the tile thickness, is selected based on the anticipated size (calibre) of the projectiles, which may be directed at the aircraft. The tile width and length is defined by the structural requirements of the panel, in particular the amount of shear load that is expected to be applied to the panel. In one embodiment, the ceramic units have a width of approximately 20-40 mm and a length of approximately 20-40 mm.

[0096] Each cell 18 within the structural layer 16 comprises a ceramic tile 20 disposed within the cell 18. This allows the ceramic tiles 20 to effectively act as a ceramic panel within the anti- ballistic structure 10, however with the added significant benefit that the plurality of tiles 20 provide many more instances than a (single) ceramic panel to be struck by projectiles and the structural layer 16 continuing to provide anti-ballistic functionality; i.e. the panel provides multi-hit capability.

[0097] The cells 18 are hexagonal, similar to the tiles 20, and are sized to fit the tiles 20 accurately so as to secure the tiles 20 within their respective cells 18. The cell walls may be relatively thin, so as to ensure that an oncoming projectile is most likely to hit a ceramic tile rather than the cell walls. The thin wall cells may be particularly susceptible to collapsing, particularly when the panel is subjected to high shear loads. The cell width is substantially the same as the width of the tiles 20 such that the tiles can support the relatively thin cell walls and prevent them from collapsing.

[0098] As described above, the tile thickness is selected based on the calibre of the projectile. The cell depth is substantially the same as the thickness of the tiles 20 such that the tiles 20 completely fill the cells 18. The cells have substantially the same width and depth as the tiles 20 such that the ceramic tiles 20 can fit conveniently and accurately within the cells. The cell depth having substantially the same thickness as the tiles 20 ensures the opposing faces of the tiles 20 directly contact the enclosing layers 24, 26. This aids in keeping the tiles 20 intact during projectile penetration and increases the eroding effect of the tiles 20 on the penetrating projectiles, further deforming and / or breaking up the passing projectiles. The tiles 20 completely filling the cells 18 also allows the tiles 20 to support the enclosing layers and preventing them from buckling or collapsing. This also secures the tiles 20 within their respective cells 18 by preventing movement of the tiles within the cells.

[0099] The capture layer 14 comprises a spall liner formed of e.g. ultra-high molecular weight polyethylene material (e.g. Dyneema®). The capture layer 14 is in direct contact with the structural layer 16, in particular the inner (upper) enclosing layer 26 so as to provide cushioning and rigid support to the structural layer. This further aids in keeping the ceramic tiles 20 intact for as long as possible during projectile penetration, thereby increasing the erosive effect of the tiles 20 on the passing projectile. A top aluminium layer 28 covering the capture layer 14 is provided which protects the capture layer 14 from damage and wear. In embodiments where the anti-ballistic structure 10 is integrated into the floor of an aircraft, the top layer 28 acts as an upper casing and may be the floor of the aircraft cabin. The capture layer 14 and the top layer 28 are also helpful in protecting the ceramic tiles 20 from blunt impact damage during handling of the panel 10.

[0100] Figure 3 shows another embodiment of anti-ballistic panel 100 comprising a double sandwich-structured composite and Figure 4 shows an exploded view of the panel 100. The panel 100 comprises an anti-ballistic laminate 111 with a structural layer 116 and enclosing layers 124, 126 as described above in relation to Figures 1 and 2. As shown by Figure 3, the panel 100 includes a second sandwich-structured composite 117 disposed outboard of the anti-ballistic laminate 111 and directly adjacent the anti-ballistic laminate 111. The second sandwich-structured composite 117 is defined by the outer enclosing layer 124 and an outer (lower) layer 112 spaced relative to the outer enclosing layer 124. In particular, the outer enclosing layer 124 defines a shared intermediate layer arranged between the structural layer 116 and the second sandwich-structured composite 117. The outer (lower) layer 112 is a thermoplastic layer and is spaced relative to the outer enclosing layer 124 to define a space 122. The space 122 comprises a plurality of reinforcement elements 125 in the form of I beams extending between the outer layer 112 and the outer enclosing layer 124. In effect, the panel comprises a double sandwich-structured composite. The provision of the second sandwich structured composite 117 is particularly advantageous as it significantly improves the overall strength and rigidity of the structural panel 100. The second sandwich structured composite 117 also provides further protection to the anti-ballistic laminate 111 (which can be relatively thin) and protects the vulnerable ceramic tiles 120 from blunt impact damage during handling of the panel 100.

[0101] The first 111 and second 117 sandwich-structured composite and the reinforcement elements 125 are co-cured and / or co-consolidated layers. In particular, the enclosing layers 24, 26 are co-cured and / or co-consolidated to the structural layer 16 so as to bond the enclosing layers 24, 26 to the structural layer 16. In some embodiments, the capture layer 114 is also co-cured and / or co-consolidated to the structural layer 16, for example, in embodiments where the enclosing layers 24, 26 comprise Kevlar or other aramid fibres. In embodiments where the capture layer comprises Dyneema® material, the capture layer / spall liner is cold bonded separately to the cured sandwich-structured composite to preserve the performance of the capture layer. The reinforcement elements 25 can be formed using fibre reinforced plastic allowing them to be co-consolidated I co-cured with the outer layer of the second sandwich-structured composite 117 and the outer enclosing layer 124.

[0102] While the disclosure is susceptible to various modifications and alternative forms, specific example approaches are shown by way of example in the drawings and are herein described in detail. It should be understood however that the drawings and detailed description attached hereto are not intended to limit the disclosure to the particular form disclosed but rather the disclosure is to cover all modifications, equivalents and alternatives falling within the scope of the invention.

[0103] As used in this specification, the words “have”, “comprise” and “include” and variations such as “having”, “comprises”, “comprising” and “including” and similar words are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”.

[0104] As used in the specification, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0105] The words “preferred” and “preferably” used herein refer to embodiments of the invention that may provide certain benefits under some circumstances. It is to be appreciated, however, that other embodiments may also be preferred under the same or different circumstances. The recitation of one or more preferred embodiments therefore does not mean or imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure, or from the scope of the claims.

[0106] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that various changes to the described embodiments may be made without departing from the scope of the invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Claims

CLAIMS1. An anti-ballistic structural panel, said panel comprising: a structural layer arranged between an outer enclosing layer and an inner enclosing layer, the outer enclosing layer disposed on an outwardly facing side of the structural layer and the inner enclosing layer disposed on an inwardly facing side of the structural layer; a capture layer adjoining the inner enclosing layer and disposed inboard of the inner enclosing layer, the capture layer defining an inwardly facing surface; wherein the structural layer comprises a plurality of hollow cells extending through the structural layer, wherein a plurality of the cells comprise a ceramic unit disposed within the cell.

2. An anti-ballistic panel according to claim 1, wherein each ceramic unit is in the form of a ceramic tile.

3. An anti-ballistic panel according to claim 1 or 2, wherein each of the cells comprises a ceramic unit disposed within the cell.

4. An anti-ballistic panel according to any one of the preceding claims, wherein the structural layer comprises an array of cells such that the structural layer provides a honeycomb core layer within the anti-ballistic panel.

5. An anti-ballistic panel according to any one of the preceding claims, wherein the cells are hexagonal.

6. An anti-ballistic panel according to any one of the preceding claims, wherein each ceramic unit is hexagonal.

7. An anti-ballistic panel according to any one of the preceding claims, wherein the cells are sized to substantially fit the ceramic units such that the ceramic units substantially fill the cells.

8. An anti-ballistic panel according to any one of the preceding claims, wherein the structural layer comprises a thermoplastic material, or a thermo-set material, or a hybrid thermoplastic and thermo-set material.

9. An anti-ballistic panel according to any one of the preceding claims, wherein the outer enclosing layer and the inner enclosing layer are bonded to opposite faces of thestructural layer such that the ceramic units are enclosed within the cells by the enclosing layers.

10. An anti-ballistic panel according to any one of the preceding claim, wherein a depth of the cells is substantially the same as the thickness of the ceramic units such that each opposing face of the ceramic units is in contact with the enclosing layers.

11. An anti-ballistic panel according to any one of the preceding claims, wherein the outer enclosing layer comprises one or more reinforcement elements.

12. An anti-ballistic panel according to any one of the preceding claims, wherein the enclosing layers comprise a thermoplastic material, or a thermo-set material, or a hybrid thermoplastic and thermo-set material.

13. An anti-ballistic panel according to any one of the preceding claims, wherein the enclosing layers are co-consolidated or co-cured layers within the panel.

14. An anti-ballistic panel according to any one of the preceding claims, wherein the structural layer is an additive manufactured layer or an injection moulded layer.

15. An anti-ballistic panel according to any one of the preceding claims, wherein the structural layer and the enclosing layers together form a first sandwich-structured composite.

16. An anti-ballistic panel according to claim 15, wherein the panel comprises a second sandwich-structured composite disposed outboard of the first sandwich-structured composite and wherein the outer enclosing layer defines a shared intermediate layer arranged between the first sandwich-structured composite and the second sandwich-structured composite.

17. An anti-ballistic panel according to claim 16, wherein the second-sandwich structured composite comprises an outer layer disposed outboard of the outer enclosing layer and spaced relative to the outer enclosing layer to define a space between the outer layer and the outer enclosing layer, said space comprising one or more reinforcement elements.

18. An anti-ballistic panel according to claims 11 or 17, wherein the one or more reinforcement elements is in the form of a plurality of ribs extending between the outer layer and the outer enclosing layer.

19. An anti-ballistic panel according to claims 11 or 17, wherein the one or more reinforcement elements is in the form of a foam material.

20. A method of forming an anti-ballistic panel according to any one of the preceding claims, wherein the method comprises the step of forming the structural layer by additive manufacturing or injection moulding.

21. A method of forming an anti-ballistic panel according to claim 20, wherein the method comprises the steps of: i. Laying up the structural layer on top of the outer enclosing layer; ii. Inserting the ceramic units into the cells defined by the cell walls; iii. Laying up the inner enclosing layer on top of the structural layer; iv. Co-consolidating or co-curing the outer enclosing layer, the structural layer and the inner enclosing layer so as to enclose the ceramic units within the cells.

22. A fibre reinforced plastic structure comprising: a structural layer arranged between an outer enclosing layer and an inner enclosing layer, the outer enclosing layer disposed on an outwardly facing side of the structural layer and the inner enclosing layer disposed on an inwardly facing side of the structural layer; a capture layer adjoining the inner enclosing layer and disposed inboard of the inner enclosing layer, the capture layer defining an inwardly facing surface; wherein the structural layer comprises a plurality of hollow cells extending through the structural layer, wherein a plurality of the cells comprise a ceramic unit disposed within the cell.

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