AIRCRAFT STRUCTURAL, ANTI-BALLISTIC FLOOR PANEL

Abstract

There is provided an anti-ballistic aerospace structure, said structure comprising a strike layer defining an outwardly facing surface and an opposing capture layer defining an inwardly facing surface and an intermediate structural layer arranged between the strike layer and capture layer, wherein the intermediate structural layer is spaced relative to the strike layer to define a space between the intermediate structural layer and the strike layer, said space comprising one or more reinforcement elements, and wherein the strike layer is formed of a fiber reinforced plastic laminate comprising at least one metallic layer.

Claims

1.-15. (canceled)

16. A fiber reinforced plastic structure comprising: a strike layer defining an outwardly facing surface; an opposing capture layer defining an inwardly facing surface; and an intermediate structural layer arranged between the strike layer and capture layer; wherein the intermediate structural layer is spaced relative to the strike layer to define a space between the intermediate structural layer and the strike layer, the space comprising one or more reinforcement elements, together forming a sandwich-structured composite; and wherein the strike layer is formed of a fiber reinforced plastic laminate comprising at least one metallic layer.

17. The fiber reinforced plastic structure of claim 16, wherein the metallic layer comprises a plurality of apertures passing all the way through the metallic layer.

18. The fiber reinforced plastic structure of claim 17, wherein the apertures are in the form of a plurality of distributed circular perforations extending across the metallic layer.

19. The fiber reinforced plastic structure of claim 16, wherein the metallic layer is embedded on at least one side of the strike layer adjacent to at least one fiber reinforced plastic layer.

20. The fiber reinforced plastic structure of claim 19, wherein the fiber reinforced plastic layer is a carbon fiber reinforced plastic layer.

21. The fiber reinforced plastic structure of claim 16, wherein the capture layer comprises an ultra-high molecular weight polyethylene material.

22. The fiber reinforced plastic structure of claim 16, wherein the intermediate structural layer is formed of a fiber reinforced plastic material.

23. The fiber reinforced plastic structure of claim 16, wherein the one or more reinforcement elements is in the form of a plurality of ribs extending between the strike layer and the intermediate structural layer.

24. The fiber reinforced plastic structure of claim 16, wherein the one or more reinforcement elements is in the form of a foam or honeycomb core material.

25. The fiber reinforced plastic structure of claim 16, wherein the strike layer, reinforcement elements, and intermediate structural layer are co-cured layers within the structure, together forming a sandwich-structured composite.

26. The fiber reinforced plastic structure of claim 16, wherein the layers are non-planar in shape and parallel to each other.

27. The fiber reinforced plastic structure of claim 16, wherein the fiber reinforced plastic structure is an anti-ballistic aerospace structure.

28. A method of forming an anti-ballistic aerospace structure, the structure comprising a strike layer defining an outwardly facing surface, an opposing capture layer defining an inwardly facing surface, and an intermediate structural layer arranged between the strike layer and capture layer, wherein the intermediate structural layer is spaced relative to the strike layer to define a space between the intermediate structural layer and the strike layer, the space comprising one or more reinforcement elements, and wherein the strike layer is formed of a fiber reinforced plastic laminate comprising at least one metallic layer, the method comprising: laying-up the strike layer to incorporate the metallic layer; and co-curing the strike layer, the reinforcement elements, and intermediate structural layer of the structure.

29. The method of claim 28, further comprising the step of bonding the capture layer to the structure intermediate layer of the co-cured structure.

30. The method of claim 29, further comprising the step of bonding a backing layer to the inwardly facing surface of the capture layer.

31. The method of claim 28, wherein the layers are non-planar in shape and parallel to each other.

Description

DRAWINGS

[0049] Aspects of the invention will now be described, by way of example only, with reference to the accompanying figures in which:

[0050] FIG. 1 shows a schematic of a structure;

[0051] FIG. 2 illustrates the distribution of apertures through the metallic layer in one arrangement of the structure; and

[0052] FIG. 3 illustrates movement and failure mechanism of various projectiles through the structure.

[0053] While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood however that drawings and detailed description attached hereto are not intended to limit the invention to the particular form disclosed but rather the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claimed invention.

[0054] It will be recognized 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 recognized that the invention covers not only individual embodiments but also combinations of the embodiments that have been discussed herein.

DETAILED DESCRIPTION

[0055] The structure described herein has particularly advantageously applications in aircraft design.

[0056] The example below focusses on such an application. However, the structure may equally be used in other application where the novel combination of structure performance and ballistic protection is needed. For example, other parts of an aircraft (e.g., the cockpit) may equally benefit. Other applications include general structures such as buildings or even automobiles. The arrangement described herein may also be applied to non-planar panels; even double curved panelling provided the strike face layer and capture layer/spall liner remain parallel and equidistant.

[0057] Focussing on the example application of the aerospace industry, floors for fixed wing and rotorcraft aircraft are designed for usage loads (airframe loads, and/or loads resulting from cargo and/or loads resulting from troops). The floor panels are designed for these loads (including impact and wear and tear) only and have no/negligible anti-ballistic function.

[0058] To protect occupants and/or cargo, an anti-ballistic protection system has to be added. Conventional arrangements involve an anti-ballistic protection system being added separately, on top of or below the structural floor, and at the (lower) side panels of the fuselage, often consisting of special grades of ceramic, steel, or other metal materials and also sometimes other material compositions whose only function is to stop the projectile. Such conventional arrangements add significant weight and cost. They also occupy additional space. In many cases it also poses a logistical disadvantage due to the inherent fact that the armor is separable. However, the main advantage of a separate anti-ballistic protection system is that some of these systems can be easily removed when the anti-ballistic protection is not necessary.

[0059] The arrangement shown in FIG. 1 is a composition of a (monolithic) ‘spaced armor’ solution comprising a strike face 2 and spall liner (catching or capture layer) 3 with some space in between 4, 5. The term ‘spaced armor’ refers to an arrangement in which the strike face and spall liner, or other secondary (and or tertiary) face are not directly connected but have a certain stand-off.

[0060] The arrangement described herein uses a titanium alloy for the strike face and a specific hard-armor Dyneema solution for the spall liner. These functions can be fulfilled by strike face materials such as ceramics, other metallic alloys like aluminum or armor steel. The spall liner material may be, e.g., an aramid fiber based hard armor plates (Kevlar) or even soft metal alloys).

[0061] By utilizing/adopting a ‘perforated armor’, some of these problems associated with existing structures can be made to disappear. As aforementioned, a perforated armor strike face comprises a repeating pattern of numerous holes/perforations (can be, e.g., circular holes, slits, cross-shapes, triangles; completely chosen/tailored for a certain set of threats) which effectively reduces the amount of material in the strike face.

[0062] The reduction in (isotropic) material also means that a proportional reduction in stiffness (and structural ‘layer’ strength; but is less important; especially for sandwich balance) is created. The combination of the correct material (w.r.t. small CTE difference compared to fiber reinforced composite material) for the strike face, correct thickness for structural performance and anti-ballistic effect and correct hole pattern (to effectively affect the set of threats) and reducing the amount of stiffness to be equal to the stiffness of a same-thickness fiber reinforced composite, provides a partially metallic strike face (the bottom sandwich face) with similar structural performance, but with the added function of strike face for incoming projectiles.

[0063] For example, approximately 40% of the titanium strike face material (by the hole pattern) may be removed which reduces the original in-plane stiffness of the titanium by 40% (using a repetitive set of perforations that enable the strike face to keep exhibiting quasi-isotropic behavior). The in-plane stiffness of the quasi-isotropic carbon fiber reinforced plastic in the top skin of the sandwich is equal to the new stiffness of the perforated titanium, which provides for a balanced overall laminate. Orthotropic designs can also be formed provided that the amount of orthotropy is similar for top and bottom face for a laminate to be balanced. If desired, also non-balanced laminates can be created. The metal strike face layer having sufficient material removed to lower the in-plane stiffness to the same level as the other fiber reinforced laminate, can be considered an equivalent, same stiffness (quasi-isotropic) layer to be combined in any fiber reinforced plastic laminate composition.

[0064] By embedding the metal strike face layer (single layer) in a small number of fiber reinforced composite layers, ‘splicing’ techniques known to fiber reinforced composite structures can be utilized to advantageously redistribute loads around strike face edges and at e.g. panel interfaces.

[0065] A specific example will now be described in more detail with reference to FIGS. 1 to 3.

[0066] Referring again to FIG. 1, the structure 1 comprises a first, metallic strike face surface or layer 2 facing down towards the ground in flight. In one example the layer is a titanium layer and comprises a plurality of apertures or holes extending through the layer. In effect the layer is perforated with holes. The holes in the face layer are distributed across the surface and reduce the in-plane stiffness of the layer 2. The reduction in stiffness is selected to correspond with the stiffness of the upper parts of the sandwich structure (intermediate structural layer) 4, as described further below. Thus, advantageously, a balanced sandwich structure can be formed.

[0067] The metallic strike face 2 can itself either be embedded in a thin layer of fiber reinforced composite and or bonded to the rest of the structure using adhesive film materials. Embedding the layer in a composite or using adhesive film material in this way advantageously allows the entire structure, including the metallic layer, to be co-cured during manufacture. To ensure strength and reliability of the integrated metallic layer, proper surface treatment (like the application of adhesive primers) should be performed.

[0068] The structure comprises a capture layer/spall liner 3 which faces upwards and towards the inside of the aircraft (not shown). The capture or spall layer functions to arrest the movement of any projectile or part/remnant thereof that has passed through the lower layers of the structure. This prevents a projectile leaving the structure and entering into the aircraft to which the structure is connected.

[0069] An intermediate structural layer 4 is provided as shown in FIG. 1. This layer acts as the opposite/top layer/face of the sandwich structure which is formed by the combination of the strike face layer 2 and the layer 4. A separation d is provided between the two opposing surfaces 2, 4.

[0070] This separation delivers both the moment of inertia (necessary for the stiffness and structural performance of the structural panel) as well as the ‘time’ for the projectile to further divert from its initial trajectory, orientation and or shape, being affected by the metallic strike layer when passing through it, on its way to the capture layer.

[0071] A discrete reinforcement (described further below) structure (such as ribs or stiffeners) or core 5 is located within this space d. In the example in FIG. 1, the reinforcement arrangement is in the form of a plurality of ribs (dotted line) or a foam core (discrete dots) (discussed below). The structural sandwich with integrated strike face is denoted with s in FIG. 1.

[0072] In use, a projectile 6 may be directed towards the structure with the aim of penetrating through the structure and into the aircraft.

[0073] A top surface 7 may also be provided which may be an aluminum layer. This layer acts at the upper and outer casing of the structure and may become the floor of the aircraft cabin for example. This layer protects the structure and capture layer from wear and tear, damage and, for example, water/fluid ingress.

[0074] In one example the capture layer/spall liner is formed from an ultra-high molecular weight polyethylene material such as Dyneema® manufactured by DSM. Dyneema is a synthetic fiber (UHMWPE) with extremely high tensile strength.

[0075] The capture layer/spall liner does not have any structural characteristics within the panel; it is purely in position to capture the projectile 6 (or part thereof) which penetrates the structure. By combining functionalities of ballistic protection and structural capabilities instead of separating them, the total solution will be lighter and occupy less space.

[0076] FIG. 2 shows the strike face layer 2 in isolation with an array 8 of circular holes penetrating through the strike face (as also shown in FIG. 1). Any suitable distribution of holes or apertures (depending on the threat (projectile type and calibre) for which the structural armor is designed) may be used depending on the in plane stiffness required for the strike face surface (this being part of the structural sandwich).

[0077] In effect the strike face or layer has two distinct purposes. First, the surface acts as one side of the multi-layer sandwich or laminate structure that provides the load bearing strength for the aircraft floor (in one example). Secondly the surface acts as the first component of a multi-component or multi-layer anti-ballistic panel.

[0078] FIG. 3 illustrates three projectiles 6a 6b 6c approaching the strike face apertures.

[0079] The projectiles can be comprised of different compositions (e.g., armor piercing, ball, and combinations thereof). Depending on the projectile type and calibre, different responses can be expected upon impact with the perforated strike face layer. AP (hard, brittle) projectiles 6a or jacketed projectiles with, e.g., hardened steel tips have the tendency to start tumbling 9 when loaded asymmetrically, effectively increasing the surface area of the projectile with respect to the rest of the structural panel and capture layer/spall liner.

[0080] This subsequently increases the effectiveness of the capture layer/spall liner to defeat/stop the projectile. Softer and ductile projectiles (ball) 6b, 6c have the tendency to either deform heavily upon impact with the strike face layer 10 or split into multiple deformed parts 11 depending on impact location with respect to aperture location. As with AP projectiles, this increases the projectile surface area with respect to the capture layer/spall liner and increases the effectiveness of the capture layer/spall liner to defeat/stop the projectile. The aperture size and array 8 design should be chosen specifically for anticipated projectile type (or range thereof) threats. Upon impact, the strike face layer is damaged and fragments may either be expelled from the panel 12 or enter the panel core and are caught by the capture layer/spall liner as well.

[0081] In effect a multi-stage process is achieved through the structure to arrest the projectile whilst maintaining structure strength of the structure around the penetration path of the projectile. The projectile can be stopped from penetrating all of the way through the panel and simultaneously the panel acts as a continuous structural part of the fuselage.

[0082] A combination of these reinforcement arrangements may equally be used.

[0083] Any suitable shape of perforation may be used, for example, circular holes, triangular holes, slots, squares, octagonal holes or the like. In each example, distributing these shapes in a repeating pattern has the same effect on the in-plane stiffness as long as the correct amount of the isotropic material is removed and the pattern is repeated enough for the face to be considered quasi-isotropic.

[0084] Circular holes or perforations provide particular advantages, including: [0085] 1. Ease of production. Aircraft grade titanium in one specific floor panel design (Ti-6Al-4V), is difficult to process/machine. Machining (drilling) of the holes provides a cost effective solution. [0086] 2. The distribution of stress. Since the metal strike face layer is used as both a strike face and also a fully structural face, the distribution of stress through this layer (as part of the composite) has to be taken into account. Using round holes instead of squares, triangles etc, removes the stress concentrations (Kts) around sharp hole edges. The circular hole version is therefore considered to be stronger.

[0087] It has further been established that the structure could be conveniently manufactured all, or in part, using additive manufacturing processes. This advantageously allows the reinforcement (metal strike face) layer to be fully optimized for both structural strength and additionally an ability to further disrupt the projectile's path.

[0088] For example, one of the following techniques could be used: [0089] Powder bed fusion methods [0090] Direct metal laser sintering (DMLS) [0091] Electron beam melting (EBM) [0092] Selective laser melting (SLM) [0093] Selective laser sintering (SLS) [0094] Direct metal wire deposition [0095] Direct metal powder deposition

[0096] Advantages of the present design include, but are not limited to: [0097] an armored, structural composite panel which is applicable for use as floor panels, as the fuselage, cockpit enclosure or any other structural part of a fixed wing aircraft or helicopter that needs ballistic protection [0098] it can be made lighter (areal weight) than the current gold standard for the intended range of threats with equivalent structural performance; and [0099] occupies less space than a structural panel with add-on armor.