Thermoplastic aircraft structures with localized ply insulation and methods for forming aircraft structures - Patents.com

Abstract

To provide a laminate structure configured to localize heat that is generated in an induction-welding step.SOLUTION: A complex wing box structure formed of reinforced thermoplastic materials includes a carbon fiber reinforcement material and a plurality of insulation elements that localize heat that is generated in a step of manufacturing the structure. The step of manufacturing the wing box structure includes a step of arranging a series of insulation elements alternately in a plurality of thin films and a step of integrating the insulation elements with the thin films to form a laminate body. Then, the laminate body is aligned with a support structure so that the insulation elements overlap on the support structure. Subsequently, the laminate body is fused to the support structure using induction welding for instance, in a non-contact type heating step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This application claims priority to U.S. Provisional Patent Application No. 62 / 666,193, filed May 3, 2018, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to the field of composite materials. In particular, the present application relates to a structure made of a number of components made of composite materials. The invention is particularly intended for application in the field of aircraft structures made of a number of composite elements. [Background technology]

[0003] Composite materials have been used in a wide variety of applications where the advantages of lightweight, high-strength materials outweigh the cost of materials. For example, historically, aircraft structures have been made of lightweight metals, such as aluminum and, more recently, titanium. However, modern airplanes are made of composite materials for the majority of their structure. A commonly used material in the aerospace industry is carbon fiber reinforced thermosetting plastics. Such materials allow the creation of complex structures that, once hardened, will retain their shape permanently. However, this advantage limits the ability to fuse the created structure with separate structures. Instead, the separate elements are connected using separate connectors, such as fasteners. Structural elements made of reinforced thermoplastic materials can be connected without separate fasteners, but the process of melting the elements requires heating the components above a temperature that could cause damage to the structure. Thus, there is a need for an efficient process for connecting composite components of a structure without causing damage to the components of the structure. Summary of the Invention [Means for solving the problem]

[0004] In view of the above, according to one aspect, the present invention provides a laminate structure configured to localize heat generated during an induction welding process. In particular, the laminate is configured to localize heat to specific regions of one or more specific plies of a multi-layer carbon fiber reinforced thermoplastic composite laminate. According to one aspect, the heat is localized to specific regions of specific plies by implementing multiple layers of insulating elements configured and embedded in a pattern within the layers of the laminate. Optionally, the laminate can be implemented in an aircraft structure, for example a wing box.

[0005] According to another aspect, the present invention provides a composite aircraft structure having a plurality of longitudinally elongated spars and ribs interconnected with the plurality of spars to form a grid, each of the spars and ribs having an upper element with a layer of unidirectional or woven carbon fiber reinforced thermoplastic material forming a weld zone. A composite skin is connected with the grid of spars and ribs. The laminate includes at least five plies of carbon fiber reinforced thermoplastic material. In a first ply, the carbon fibers are oriented in a first direction. In a second ply, the carbon fibers are oriented in the first direction, the first ply overlaying and directly connected to the second ply. A third ply has carbon fibers oriented in a second direction transverse to the first direction, and a fourth ply has carbon fibers oriented in the second direction, the third ply overlaying and directly connected to the fourth ply. A fifth ply has carbon fibers oriented in a direction transverse to the carbon fibers of the upper elements of the spars and ribs. The laminate also includes a plurality of elongated insulating elements formed of an electrically insulating material. Each of the insulating elements has a length and a width, with at least some of the insulating elements having a length that substantially exceeds the width. The insulating elements form a grid configured substantially similarly to the grid formed by the ribs and spars such that the insulating elements overlie the upper elements of the ribs and spars. The grid of insulating elements is disposed between the second layer and the third layer. Optionally, each insulating element comprises glass fibers embedded in a matrix of thermoplastic material. The insulating elements may also comprise a plurality of elongated spar insulators overlying the spars, and a plurality of elongated rib insulators overlying the ribs, the rib insulators being shorter than the spar insulators. The rib insulators may extend between the spar insulators without substantially overlying the spar insulators. Additionally, the spar insulators may be optionally spaced apart from one another.

[0006] Optionally, the composite skin may include an additional layer of carbon fiber reinforced thermoplastic material, and the grid of insulating elements may form a first grid and the plurality of insulating elements may form a second grid configured substantially similarly to the first grid of insulating elements, and the second grid may be disposed between the additional layer of carbon reinforced thermoplastic material such that the second grid is aligned with the first grid.

[0007] The aircraft structure may have a second composite skin connected to a grid of ribs and spars. Each spar and rib may include a lower element having a layer of unidirectional or woven carbon fiber reinforced thermoplastic material forming a lower weld zone, and the second skin may be connected to the lower elements of the ribs and spars.

[0008] According to yet another aspect, the present invention provides an aircraft structure in which a plurality of isolation elements form a grid, the isolation elements being configurable to define a plurality of openings.

[0009] According to another aspect, the present invention provides an aircraft structure formed of a thermoplastic material comprising a polyaryletherketone class semi-crystalline thermoplastic material.

[0010] According to another aspect, the present invention provides an aircraft structure formed from a thermoplastic material having a melting point above 500 degrees Fahrenheit.

[0011] According to yet another aspect, an aircraft structure is provided in which a laminate includes an insulating layer and a structural layer, the insulating layer configured such that when the bottom layer is heated above its melting point by an induction welding head, a thermoplastic material of the structural layer remains below its melting point.

[0012] According to yet another aspect, an aircraft structure is provided, in which a laminate includes insulating layers and structural layers, the insulating element configured such that a bottom layer of the structural layers has a melting point, and the insulating element configured to prevent the structural layers other than the bottom layer from heating above the melting point when the bottom layer is exposed to an electromagnetic field sufficient to heat a bottom portion of the laminate above the melting point.

[0013] Similarly, the present invention also provides an aircraft structure having a laminate formed of a plurality of structural layers and a plurality of insulating elements embedded within a bottom layer, the thermoplastic material of the bottom layer having a melting point, the insulating elements being configured to prevent melting of the thermoplastic material of the structural layers when the bottom layer is welded to the separate aircraft structure by induction welding.

[0014] According to yet another aspect, the present invention provides a composite aircraft structure formed of a plurality of longitudinally elongated spars, a plurality of elongated ribs connected to the plurality of spars to form a grid, and a composite skin. The composite skin includes a plurality of structural layers, a plurality of insulating elements, and a welded layer. The structural layers are each formed of a unidirectional or woven carbon fiber reinforced thermoplastic material. The insulating elements are formed of an electrically insulating material and form a plurality of insulating grids, the insulating grids being aligned with one another and disposed between the structural layers. The welded layer is also formed of a unidirectional or woven carbon fiber reinforced thermoplastic material. The aircraft structure also includes a plurality of connecting elements having a layer of unidirectional or woven carbon fiber reinforced thermoplastic material. Each connecting element is connected to one of the spars or one of the ribs. Also, the carbon fibers of the welded layers are oriented in a first direction and the carbon fibers of the connecting elements are oriented in a second direction transverse to the first direction. The welded layer overlies and is connected to the connecting elements.

[0015] The present invention further provides a composite laminate for use in aircraft structures, the laminate comprising a plurality of structural layers, a plurality of insulating elements, and a welded layer, each of the structural layers being formed of a unidirectional or woven carbon fiber reinforced thermoplastic thin film, the fiber orientation of at least some of the structural layers being transverse to the fiber orientation of adjacent structural layers, the insulating elements being formed of an electrically insulating material forming a plurality of insulating grids, the insulating grids being aligned with one another, the insulating grids being embedded between adjacent structural layers whose fiber orientations of the carbon fibers are transverse to one another, the welded layer also being formed of a unidirectional or woven carbon fiber reinforced thermoplastic thin film.

[0016] The present invention further provides a method of forming a composite wing box. The method includes providing a plurality of spars, connecting a plurality of ribs to the plurality of spars, and forming a composite skin. The composite skin includes a plurality of structural layers, a plurality of insulating layers, and a weld layer. Each structural layer is formed of a unidirectional or woven carbon fiber reinforced thermoplastic material. Each insulating layer is formed of a plurality of spaced apart electrical insulating elements. Each insulating element has a length and a width, the length being substantially greater than the width. The insulating layers are aligned with each other and disposed between the structural layers. The insulating layers are configured such that when the composite skin overlies the spar and ribs, the insulating elements overlie the spar and ribs. The weld layer is formed of a unidirectional or woven carbon fiber reinforced thermoplastic material. The method includes disposing the composite skin over the ribs and spars such that the layers of the composite skin overlie the ribs and spars. The composite skin is then welded to the ribs and spars. The welding process includes bringing an induction welding head over the composite laminate adjacent the rib and spar, where the induction welding head applies an electromagnetic field through the composite laminate to heat the weld layer above the melting point of the thermoplastic material of the weld layer and where the insulating layer prevents the structural layer from heating above the melting point of the thermoplastic material.

[0017] Optionally, the method can include connecting a plurality of connecting elements to the ribs and the spars. Each connecting element can include a layer of unidirectional or woven carbon fiber reinforced thermoplastic material, and the welding step can include welding the welded layers to the connecting elements. Also, the carbon fibers of the welded layers can be oriented in a first direction and the carbon fibers of the connecting elements can be oriented in a second direction. Connecting the plurality of connectors can include connecting the connectors such that the second direction is transverse to the first direction.

[0018] According to yet another aspect, the present invention provides a method including providing a composite laminate having a plurality of insulating layers, the providing a composite laminate comprising arranging the plurality of insulating elements into a grid.

[0019] According to yet another aspect, the present invention provides a method including providing a composite laminate having a plurality of insulating layers, the method including configuring the plurality of insulating elements such that a plurality of openings are formed between the insulating elements.

[0020] According to yet another aspect, the present invention provides a method comprising forming the composite skin, the method comprising providing pairs of the structural layers, each layer of the structural layer pair being adjacent to and directly connected to the other structural layer of the pair, the two layers of the pair being oriented such that the fibers of both layers are substantially parallel. Adjacent pairs of structural layers are oriented such that the fibers of one pair are oriented transverse to the fibers of the adjacent pair. Optionally, the method comprises providing the insulating layer by interposing an insulating layer between the one pair and the adjacent pair. An insulating layer can also be interposed between each adjacent pair of structural layers.

[0021] According to another aspect, a method is provided that includes a method of forming a composite laminate for an aircraft structure. The method includes providing a plurality of structural layers, each formed of a unidirectional or woven carbon fiber reinforced thermoplastic film, and providing a plurality of insulating elements formed of an electrically insulating material, each insulating element having a length and a width, the length being substantially greater than the width. The method further includes fabricating a plurality of insulating layers, each layer formed in a pattern in which the insulating elements are spaced apart from one another by configuring the insulating elements. The insulating layers are positioned between the structural layers by aligning the pattern with each insulating layer. The structural layers are configured such that the bottom layer forms a weld layer. The method includes integrating the structural layers and the insulating layers by applying heat and pressure to the structural layers and the insulating layers to form a composite laminate in which the insulating layers are embedded within the structural layers. Optionally, the configuring step includes configuring the insulating elements such that the insulating elements extend between the spaced apart insulating elements. The configuring step can also include configuring the insulating elements such that there are gaps between each individual insulating element.

[0022] According to yet another aspect, a method is provided that includes placing the consolidated laminate over a tie layer of unidirectional carbon fiber reinforced thermoplastic material such that the fibers of the welded layer are oriented transverse to the fibers of the tie layer, and inducing an electromagnetic field that penetrates a thickness of the laminate and the tie layer to heat the welded layer and the tie layer sufficiently to weld the welded layer and the tie layer together.

[0023] According to another aspect, a method is provided that includes inducing the electromagnetic field by moving an induction coil over the stack along a pattern of the insulating layers in the stack.

[0024] The invention further provides a method comprising inducing the electromagnetic field by concentrating the electromagnetic field within a width of a plurality of insulating elements, Optionally, the interconnect layer is rigidly coupled to the aircraft structure such that the inducing comprises welding the laminate to the interconnect layer, thereby fixedly coupling the laminate to the aircraft structure.

[0025] According to yet another aspect, a method is provided in which the aircraft structure has a plurality of structural elements forming a pattern, the method comprising aligning the pattern of the structural elements in the laminate with the pattern of the insulating layer. The insulating layer can be formed with insulating elements arranged into a grid. Optionally, arranging the insulating elements in a pattern can include configuring the insulating elements such that a plurality of openings are formed between the insulating elements.

[0026] Although the method and apparatus are described herein with reference to several embodiments and exemplary drawings, those skilled in the art will appreciate that the inventive method and apparatus for sorting articles using a dynamically reconfigurable sorting array are not limited to the described embodiments or drawings. It should be understood that the drawings and their detailed description are not intended to limit the embodiments to the particular forms disclosed. Rather, they are intended to cover all modifications, equivalents, and alternatives within the scope of the method and apparatus for sorting articles using one or more dynamically reconfigurable sorting arrays as defined in the appended claims. Any headings used herein are merely organizational and are not intended to limit the scope of the description or the claims. The words "may" and "may" are used herein in a permissive sense (i.e., in the sense of possible) rather than a mandatory sense (i.e., in the sense of must). The words "include", "including", and "includes" are used herein to mean "including and not limited to". [Brief description of the drawings]

[0027] The foregoing summary, as well as the following detailed description of preferred embodiments of the present invention, are best understood when read in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is an exploded perspective view of a wing box implementing an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a system for forming the wingbox of FIG. [Diagram 3] FIG. 3 is an enlarged perspective view of a portion of the wing box of FIG. [Figure 4] FIG. 4 is a schematic side view of the wing-box portion illustrated in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Referring now generally to the drawings and in particular to FIG. 1, a composite aircraft structure is generally designated 10. In the present example, the aircraft structure 10 is a wing box having an upper skin 40 and a lower skin, both of which are supported by a support structure 15. The upper and / or lower skins are formed of carbon fiber reinforced thermoplastic materials. The composite skin includes insulating elements that allow the skin to be efficiently welded to the support structure without heating a significant portion of the skin, which may be damaged if heated. In particular, the skin 40 is formed of a laminate configured to localize the heating action produced by an induction welding head to limit heating of the skin, such that only the portion of the skin that is within the weld zone is heated to the welding temperature.

[0029] Details of the aircraft structure will now be described in greater detail with reference to Figure 1, where the aircraft structure implements the laminate within a wing box structure, although it should be understood that this is merely an exemplary structure. The laminate may be implemented within a variety of composite structures, and the laminate has particular application in aircraft structures, but is not limited to use in aircraft structures.

[0030] The aircraft structure 10 in FIG. 1 is a wing box and includes a support structure 15 on the inside of the wing box and a cover overlaying the support structure. In the present example, the cover 40 is called a skin and is shown in FIG. 3. For clarity, the skin is shown in FIG. 1 with the structural layers separated from the insulating layers, and only one structural layer is shown (designated 50). Also in FIG. 1, the assembly is illustrated with one skin overlaying the top of the support structure. However, it should be understood that the assembly 10 can also include a lower skin covering the bottom of the support structure. The lower skin can be formed of a laminate similar to the laminate of the upper skin 40. The top and / or bottom skins can also wrap around the leading and / or trailing edges of the support structure to form a closed assembly.

[0031] The support structure 15 can have any type of configuration depending on the application of the structure. In the present example, the support structure 15 is formed of a number of elongated spars and ribs. A forward spar 20 extends the entire length of the wing box. A first end of the forward spar is connected to a first end rib 30 and a second end of the forward spar is connected to a second end rib 30 such that the forward spar spans the entire distance between the two end ribs. The end rib 30 extends the entire width of the wing box and is oriented transversely to the forward spar 20. The forward spar 20 is an elongated beam having a central web of height and thickness, the height being substantially greater than the thickness. The web of the forward spar can be implemented in any type of beam configuration, such as a box beam, a channel beam, or an I-beam. In the present example, the spar can be a channel beam with the web extending between an upper surface 22 and a lower surface 24. As will be described below, the upper and lower surfaces 22, 24 may form connecting surfaces that connect the skin 40 to the spar.

[0032] A rear spar 25, spaced apart from the forward spar 20, is also connected to the two end ribs 30 such that the forward spar spans the entire length between the two end ribs. The rear spar 25 may be constructed substantially similarly to the forward spar. In the present example, the rear spar 25 is substantially similar to the forward spar, except that the rear spar is shorter than the forward spar. The interconnected spars 20, 25 and end ribs 30 thus form the sides of a generally box-shaped support structure 15. The support structure 15 may also include a number of additional elements that stiffen and / or strengthen the structure. For example, the support structure 15 may include additional spars that extend the entire length of the structure. In the present example, the support structure 15 includes a number of intermediate ribs 35.

[0033] In this embodiment, the height of the ribs 30, 35 tapers to form a tapered wing box. In particular, the height of the ribs 30, 35 adjacent the forward spar 20 is greater than the height of the ribs 30, 35 adjacent the aft spar 25. The intermediate ribs 35 are spaced apart from the end ribs 30 and from each other. The ribs 30, 35 may be configured as elongated beams similar to the spars 20, 25 described above. In the present example, the ribs 30, 35 are configured similar to channel beams, with a central web extending between transverse upper and lower legs. Also, similar to the spars, the upper and lower legs of the ribs 30, 35 may form surfaces that contact the skin 40 to provide a connection point between the skin and the support structure 15. Specifically, the end ribs 30 may include upper and lower flanges 32, 34 which form contact surfaces, and the intermediate ribs 35 may include upper and lower flanges 37, 38 which form contact surfaces.

[0034] 1 and 3-4, the details of the laminate forming the skin 40 will now be described. The laminate includes a plurality of structural layers 50, 52, 54, 56, 58 with a plurality of insulating elements 60 embedded between one or more of the structural layers. Each structural layer has reinforcing elements embedded in a matrix material. Depending on the application, the reinforcing elements may be any type of reinforcing material. By way of example, the reinforcing elements may be elongated strands or fibers of glass or carbon. For example, an exemplary carbon fiber is a continuous high strength, high strain rate PAN-based fiber with a tow of 3,000 to 12,000 fibers. These reinforcing fibers may be surface treated and sized to improve interlaminar shear properties with the matrix material. However, it should be understood that these materials are intended as exemplary materials. Other materials may be utilized depending on the environment in which the laminate will be used.

[0035] The reinforcing elements are embedded in a matrix material, for example a polymer. Depending on the application, any type of polymer can be used for the matrix material, including amorphous, crystalline and semi-crystalline polymers. In the present example, the matrix material is a thermoplastic material, for example a thermoplastic elastomer. More specifically, the thermoplastic material is a semi-crystalline thermoplastic material. In particular, the thermoplastic material may be a thermoplastic polymer of the polyaryletherketone (PAEK) family, including but not limited to polyetheretherketone (PEEK) and polyetherketoneketone (PEKK).

[0036] As mentioned above, the structural layers 50, 52, 54, 56, 58 may be composite materials, which may be carbon fiber reinforced thermoplastic materials. In particular, the thin film may be a thermoplastic prepreg, which is a thin film in which reinforcement material is previously impregnated with resin. For example, the prepreg may be a thermoplastic prepreg manufactured by coating reinforcement fibers with a thermoplastic matrix. Such a prepreg thin film may be reheated and reformed by heating the thin film above the melting point of the thermoplastic matrix. Some exemplary prepreg materials that may be used to form the structural elements 25, 26 include, but are not limited to, CETEX, such as materials sold under the product names TC1200, TC1225, and TC1320, manufactured by TenCate Advanced Composites USA (Morgan Hill, California, USA). TC1200 is a carbon fiber reinforced semi-crystalline PEEK composite material with a glass transition temperature (T g )143°C / 289°F, melting point (T m ) 343°C / 649°F. TC1225 is a carbon fiber reinforced semi-crystalline PAEK composite with a T g 147℃ / 297℃, T m TC1320 is a carbon fiber reinforced semi-crystalline PEKK composite with a T g150℃ / 318℃, T m is 337°C / 639°F.

[0037] Referring again to FIG. 1, the stack 40 has a number of structural layers configured to carry structural loads. A number of insulating layers 60 are embedded within the structural layers. While the insulating layers can be configured to carry structural loads, the insulating layers in the present example are configured to insulate the stack from heating without carrying significant structural loads (if any). To illustrate the details of the insulating layers 60, the insulating layers 60 are shown in FIG. 1 separately from the structural layers of the stack, as well as the single structural layer 50 of the stack. In the illustrated embodiment, FIG. 1 illustrates a number of aligned overlapping insulating layers 60, but it should be understood that the number and location of these insulating layers will vary depending on the application.

[0038] The insulating layer 60 is embedded in a matrix material, which is preferably a thermoplastic material that is heat fusible with the other layers of the laminate. By heating and melting the matrix material of the insulating layer, the insulating layer is integrally formed with the laminate. In particular, in the present example, the insulating layer is formed of a composite material having a matrix substantially similar to the matrix material of the structural layer. For example, the resistive element is carbon fiber and the matrix material is a thermoplastic material, such as a semi-crystalline thermoplastic material of the polyaryletherketone (PAEK) class.

[0039] The insulating layer 60 provides electrical insulation between portions of the structural layers when an electromagnetic field is applied to the stack adjacent to the insulating layer 50. The insulating layers 60 can comprise any type of electrically insulating material. These insulating layers 60 preferably comprise a thermoplastic material. In the present example, the insulating layer comprises one or more thin films of a glass-reinforced thermoplastic material.

[0040] The insulating layer 60 is configured to insulate certain zones or regions of the laminate from the heat process. It should be understood that while the insulating layer 60 limits the heating of the structural layers, the insulating layer does not limit the heating by providing significant thermal insulation. Instead, the insulating layer selectively isolates various regions from being heated by inductive heating by providing electrical insulation.

[0041] For example, during the process of welding the skin 40 to the support structure 15, the insulating layer limits the heat generated during the welding process so that only selected plies or plies of the stack are heated and only certain areas of the selected plies or plies are heated. To this end, the insulating layer 60 is configured to form a pattern corresponding to the stack portions intended to be heated. In particular, the insulating layer 60 is configured to form a pattern corresponding to the stack portions intended to be welded. In particular, the pattern can correspond to the areas of the stack that are in contact with the stack portions to be welded. For example, the insulating layer 60 is configured to correspond to the pattern formed by the top surfaces (e.g., top surfaces 22, 27, 32, and 37) of the spars 20, 25 and the ribs 30, 35.

[0042] Each insulating layer 60 may be formed of a single piece of insulating material arranged in a desired pattern. In some cases, the pattern may be a solid pattern, with the insulating material simply forming blocks, stripes, or the like. However, in the present example, the insulating layer 60 forms a pattern with a plurality of openings such that the area over which the insulating layer 60 overlies the stack is less than half the area of ​​the stack. In some cases, the insulator forms a pattern with sufficient open area such that the area over which the insulator overlies the stack is less than 40% of the total area of ​​the stack. Furthermore, in some applications, the insulating layer forms a pattern with sufficient open area such that the area over which the insulator overlies the stack is less than 30% of the total area of ​​the stack. In some applications, it may be desirable to configure an insulating layer with sufficient open area such that the area over which the insulator overlies the stack is less than 20% of the total area of ​​the stack. Furthermore, the insulating layer in the above example structure forms a pattern that covers at least about 5% of the total area of ​​the stack.

[0043] Referring again to FIG. 1, in the present example, the insulation layer 60 forms a grid pattern of intersecting stripes of insulating material. Specifically, the insulation layer 60 is formed of a plurality of elongated insulation elements having a length and a width, the length being substantially greater than the width. An exemplary material for forming the insulation elements is fiberglass tape embedded in a thermoplastic material. A first set of insulation elements forms a spar insulation element 70 that extends at least substantially the entire length of the spars 20, 25. As shown in FIG. 1, the spar insulation element 70 is laid such that a first spar insulation element overlies the upper surface 22 of the forward spar 20 and a second spar insulation element 70 overlies the upper surface 27 of the aft spar 25. A pair of end rib insulation elements 80 are laid adjacent the ends of the aft spar such that the end rib insulation elements overlie the upper surfaces 32 of the end ribs. Similarly, a plurality of insulating elements 82 extend between the spar insulation elements 72 and overlie the intermediate rib 35. It will be seen that the ribs 30, 35 extend aft beyond the aft spar 25. The intermediate rib insulating elements can therefore extend beyond the spar insulation elements 70 and overlie the aft spar 25. The rib insulating elements 82 and the spar insulation elements 70 overlap to form an insulating element having a double thickness. However, in the present example, the insulating elements of the insulating layer do not substantially overlap, so that the entire insulating layer is a single layer thick. Therefore, to prevent significant overlap of insulating elements, the intermediate rib insulating elements are formed in two segments. A first segment 82 extends beyond the intermediate spar and spans the entire area between the spar insulation elements 70, while a second segment 84 extends beyond the aft end of the intermediate rib 35 such that the second segment extends away from the spar insulation elements 70 overlying the aft spar.

[0044] From the above, it can be seen that the insulating layer 60 forms a pattern having a plurality of open areas. In particular, the insulating layer forms a pattern that forms a grid connecting the laminate 40 with the tops of the ribs and spars.

[0045] In some applications, it may be desirable to vary the pattern or size of the various insulating layers so that they insulate various plies of the stack. However, in the present example, each of the insulating layers 60 is substantially similar. Specifically, each insulating layer 60 has a similar size and pattern. Also, as shown in FIG. 1, each of the insulating layers 60 of the stack is aligned such that the insulating elements that form the pattern of each layer overlie corresponding elements in the other insulating layers.

[0046] As described above, the structural layers 50, 52, 54, 56, 58 and the insulating layer 60 can each comprise a layer of reinforced thermoplastic composite material. As such, the structural layers and the insulating layers can be joined together by fusing the layers together. Specifically, the layers can be consolidated by applying sufficient heat to exceed the melting point of the thermoplastic matrix and sufficient pressure to fuse the layers together. In this manner, the insulating layer 60 is embedded within the laminate between the structural layers.

[0047] The number of structural plies and the orientation of the plies within the stack will vary depending on the application. Additionally, the orientation of the plies and the placement of the insulation layers can be altered depending on the thermal insulation desired. Figures 3 and 4 show an exemplary layup of the stack 40. However, it should be understood that the number of plies, the orientation of the plies, as well as the number and location of the insulation layers 60 are merely exemplary. The invention is not limited to the layup shown in this exemplary stack.

[0048] The laminate includes ten structural layers, designated 50a,b, 52a,b, 54a,b, 56a,b, and 58a,b. As mentioned above, each structural layer may be a thin film or layer of composite material, such as unidirectional or woven carbon fiber reinforced thermoplastic tape. The fiber orientation of each structural layer may vary to provide strength in multiple directions. However, in the present example, the layers may be laid in pairs, with the fiber orientations of both layers in the pair being parallel. For example, the first layer of the laminate, designated 50a, has a fiber orientation of 90°, and the second layer of the laminate, designated 50b, also has a fiber orientation of 90°. These first two layers 50a, 50b are adjacent to each other in a pair and are bonded together. The third and fourth structural layers include a second pair of layers 52a, 52b. Each layer of this second pair has a fiber orientation of 0°. The fifth and sixth structural layers comprise a third pair of plies 54a, 54b, each of which has a fiber orientation of 45°. The seventh and eighth structural layers comprise a fourth pair of plies 56a, 56b. The laminate is formed symmetrically about its midline, which in the present example is the third pair of plies. Thus, the fourth pair of structural plies 56a, 56b may have a fiber orientation similar to that of the second pair of structural plies (e.g., 0°). Similarly, the ninth and tenth plies form a fifth pair, each of which may have a fiber orientation of 90°. It should be noted that the plies do not have to be laid in pairs. For example, the plies are laid in pairs as shown in FIG. 4. However, in FIG. 3 the top and bottom layers 52, 58 are laid as a single layer, while the six plies between them are laid in pairs.

[0049] The insulating layer 60 is selectively inserted between the structural layers of the laminate. An insulating layer can be inserted between each layer of the laminate, but in the present example, the insulating layer is inserted between fewer than all structural layers. In particular, the insulating layer is inserted between layers having a selected characteristic. For example, in the present example, the selected characteristic is a change in fiber direction. The insulating layer 60 is inserted between adjacent layers having different fiber angles. Thus, in the above layup, the insulating layer is interposed between pairs of structural layers and not between pairs of layers. More specifically, with reference to Figures 3-4, a first insulating layer 60a is disposed between layer 50 (Figure 3) or 50b (Figure 4) and layer 52a, because the interface between layer 50 / 50b and layer 52a is an interface where the fibers of adjacent layers are transverse to each other (i.e., the fiber angle changes from 90° to 0°). Similarly, a second insulating layer 60b is disposed between layers 52b and 54a where the fiber angle changes from 0° to 45°. A third insulating layer 60c is disposed between the third and fourth pairs where the fiber angle changes from 45° to 0° (i.e., at the interface of layers 54b and 56a). A fourth insulating layer 60d is disposed between the fourth and fifth pairs where the fiber angle changes from 0° to 90° (i.e., at the interface of layers 56b and 58a or layer 58 in FIG. 3).

[0050] It should be noted that the thicknesses of the layers in the figures are not to scale and in some cases have been exaggerated for illustrative purposes only. For example, in FIG. 2, the structural layers 50, 52, 54, 56, 58 and the insulating layer 60 are shown as having gaps between adjacent layers. However, it should be understood that the layers of the stack are integral layers in which different layers have been fused together. Furthermore, as described above, each insulating layer 60 has been described as a single layer of insulating material formed of one or more insulating elements. However, in certain applications, it may be desirable to add one or more of the insulating layers so that the insulating layer is formed of multiple layers of insulating material. Also, as shown in FIG. 2, the insulating layer 60 does not have to be a continuous layer extending the entire length and width of the stack as shown in FIG. 1. Instead, the insulating layer 60 may cover only a small portion of the area of ​​the structural layer.

[0051] The laminate 40 can be formed using a variety of processes. Methods for forming the laminate 40 from multiple reinforced thermoplastic layers are described in detail below. Methods for using the laminate to form an aircraft structure are also described.

[0052] A number of layers of carbon fiber reinforced thermoplastic tape are laid one on top of the other to form a number of structural plies. The fiber orientation of the plies can be varied and insulating plies can be placed at the interface of the plies with transverse fiber orientation to each other. For example, the layer can be formed of ten structural plies and four insulating layers oriented at 90°, 90°, Ins, 0°, 0°, Ins, 45°, 45°, Ins, 0°, 0°, Ins, 90°, 90° (where "Ins" refers to the insulating layers). The insulating layers are formed of one or more insulating elements forming a pattern. The insulating layers can be aligned through the thickness of the stack such that the pattern of each insulating layer overlaps the pattern of the other insulating layers of the stack. In this exemplary stack, the carbon fiber layers of the structural layers are formed of PEEK / AS4 carbon fiber reinforced unidirectional tape and the insulating layers are formed of PEEK / S2 glass fiber reinforced thermoplastic unidirectional tape.

[0053] The structural and insulating layers are consolidated to form a laminate by heating the assembled layers under pressure. For example, the assembly is heated to a temperature above its melting point. In the current example, the assembled layers are heated to about 725° under a pressure of about 30 psi. After the assembled layers reach 725°, the pressure is increased to about 100 psi and the assembly is held at the elevated temperature for an extended period of time, for example, about 30 minutes. Pressure is then removed and the consolidated laminate is allowed to cool to ambient temperature.

[0054] The laminate formed as described above can be joined with one or more separate components to form a structure. One exemplary structure is an aircraft structure. More specifically, the laminate is configured to allow the laminate to be welded to a separate structure. Additionally, the laminate is configured such that heat generated during the welding process is isolated from a selected ply or plies of the laminate. Additionally, the heat generated can be isolated from selected regions of the selected plies. The process of welding the laminate to a separate component is described in more detail below.

[0055] As mentioned above, the laminate is formed with one or more insulating layers. The insulating layers can be formed according to a pattern. In particular, the pattern can be similar to the contact areas of the separate elements or assemblies to be welded to the laminate. For example, with reference to FIG. 1, the insulating layer can form a grid formed similar to the grid formed by the ribs 30, 35 and spars 20, 25 of the support structure 15. The method therefore includes a step of aligning the pattern of the insulating layer to the grid formed by the ribs and spars. With reference to FIG. 2, the top surface of the support structure has one or more connecting elements for welding the support structure to the laminate. In particular, the ribs 30, 35 and spars 20, 25 can be formed such that the top surfaces 22, 27, 32, 37 form connecting elements. Alternatively, the connecting elements can be separate elements that can be fixedly connected to the ribs and spars.

[0056] In the illustrated embodiment, the connecting element is a ply of carbon fiber reinforced thermoplastic material similar to the material forming the structural plies of the laminate 40. In FIG. 2, the connecting element is shown at 39 and is illustrated as a laminate fixedly connected to the top of the flange 37 of the intermediate rib 35. However, it should be understood that the connecting element may be an integral part of the underlying structure. For example, the rib 35 may be formed such that the flange 37 is formed of a carbon fiber reinforced thermoplastic material that acts as the connecting element. Alternatively, the connecting element may be a separate element that is mechanically secured, for example by clips or fasteners.

[0057] The fiber direction of the carbon fibers of the connecting element 39 is oriented transverse to the fiber direction of the bottom ply 58b of the stack. The stack 40 is placed over the structure such that the bottom layer 58b contacts the connecting element 39, with the insulating layers 60a,b,c,d aligned with the connecting element. An induction welding head 100 is then operatively placed over the stack to induce an electromagnetic field that penetrates the thickness of the stack. In particular, the induction welding head 100 moves over the top surface of the stack. The welding head does not need to contact the top surface, but is close enough to the top surface of the stack to induce an electromagnetic field through the thickness of the stack that has sufficient strength to weld the bottom layer 58a and the connecting element 39.

[0058] The welding head 100 heats the bottom layer and the connecting elements through electromagnetic induction induced eddy current heat. The welding head includes an electronic oscillator that sends a high frequency alternating current through an electromagnet. A high velocity alternating magnetic field is then passed through the laminations and connecting elements to generate eddy currents that in turn heat the bottom layer and connecting elements.

[0059] In the present example, the welding head induces an electromagnetic field that penetrates the laminate and the joining element such that adjacent layers having transverse carbon fibers heat in response to the electromagnetic field, but layers separated by the insulating layer 60 do not heat above their melting point in response to the electromagnetic field. In particular, in the present example, the electromagnetic field generated by the welding head is sufficient to heat the bottom layer 58a and the joining element 39 above the melting point of the thermoplastic matrix material of the bottom layer and the joining element. When the bottom layer and the joining element are raised above the melting layer under pressure, the bottom layer fuses with the joining element and the two elements are welded together. Also, as discussed above, the insulating layer 60 insulates the adjacent layers from the induced heat generated by the welding head. In particular, it should be noted that a portion of the electromagnetic field extends beyond the edge of the insulating element of the insulating layer. Thus, the electromagnetic field may induce some heating in the structural plies. However, the induced heating is substantially less than the heating induced between non-insulating layers (i.e., 58b and 39) and is substantially below the melting point of the structural layer. The insulating layer thereby allows heating of the bottom layer and the connecting elements above the melting point while limiting heating of the structural layers below the melting point. Thus, while the insulating layer does not necessarily prevent all heating of a layer adjacent to it, for purposes of this method, the insulating layer prevents heating of the layer if it limits heating of the layer substantially below the melting point.

[0060] 2, the welding head 100 is shown as inducing an electromagnetic field that penetrates the laminate to weld the laminate to the rib 35. The method includes controlling the movement of the welding head such that the welding head is brought over the laminate to weld a plurality of points of the laminate to the support structure 15. In particular, the method can include controlling the position of the welding head to follow a pattern defined by the insulating layer such that the welding head welds the laminate to the support structure along areas that correspond to the pattern defined by the insulating layer 60.

[0061] In the above description, the laminate is described as a flat panel laminate. However, it should be understood that the present invention is not limited to flat panel structures. For example, the laminate can be used in a variety of applications in a variety of structures, and may have particular application in the aerospace field to provide a variety of components, including, but not limited to, fuselages, nacelles, and airfoils, such as wings, elevators, etc. The laminate 40 described above may be formed into curved structures and may be coupled with separate elements or structures.

[0062] It will be understood that those skilled in the art can change or modify the above-described embodiments without departing from the spirit and scope of the present invention. Therefore, it should be understood that the present invention is not limited to the specific embodiments described herein, but is intended to include all modifications that fall within the spirit and scope of the present invention as defined in the appended claims. [Explanation of symbols]

[0063] 1...Translation 2...Translation 10... Composite aircraft structures, aircraft structures, assemblies 15...Support structure 20...Front spar 22...Top surface 24...bottom surface 25...Rear spar 27...Top surface 30...First end rib, second end rib 32...Top, upper flange 34...Lower flange 35...Middle rib 37...Top, upper flange 38...Lower flange 39...Connected elements 40...Upper skin, cover, laminate 50...Structural layer 50a...Structural layer, first layer 50b...Structural layer, second layer 52...Structural Layer 52a...Structural layer, third structural layer 52b...Structural layer, fourth structural layer 54...Structural layer 54a...Structural layer, 5th structural layer 54b...Structural layer, 6th structural layer 56...Structural Layer 56a...Structural layer, 7th structural layer 56b...Structural layer, 8th structural layer 58...Structural layers 58a...Structural layer, bottom layer 58b...Structural layer, bottom layer 60...Multiple insulating elements 60a...First insulating layer 60b...Second insulating layer 60c...Third insulating layer 60d...fourth insulating layer 70...Spar insulation element 70...Second spar insulation element 80...End rib insulation element 82...insulating element, first segment 84...Second segment 100...induction welding head, welding head

Claims

1. 1. A composite laminate for use in an aircraft structure, comprising: a plurality of structural layers, each of which is formed of a carbon fiber reinforced thermoplastic thin film, the fiber orientation of at least a portion of the structural layers being transverse to the fiber orientation of an adjacent structural layer; a plurality of insulating elements formed of an electrically insulating material, the insulating elements forming a plurality of insulating grids, the insulating grids being aligned with one another, the insulating grids being embedded within the structural layer between adjacent structural layers whose fiber directions are transverse to one another; A welded layer formed of a carbon fiber reinforced thermoplastic thin film A composite laminate having:

2. 2. The composite laminate of claim 1, wherein the carbon fiber reinforced thermoplastic film comprises a unidirectional carbon fiber reinforced thermoplastic film.

3. 3. A composite laminate according to claim 1 or 2, wherein each insulating element comprises glass fibres embedded in a matrix of thermoplastic material.

4. 4. A composite laminate according to claim 1, wherein the insulating element comprises a plurality of elongated first insulating bodies having a width and a length, the length being substantially greater than the width.

5. 5. The composite laminate of claim 4, wherein said insulation element comprises a plurality of elongated second insulation bodies, said second insulation bodies having a length less than a length of said first insulation bodies.

6. 6. The composite laminate of claim 5, wherein said second insulation extends between said first insulation bodies without substantially overlapping said first insulation bodies.

7. 7. A composite laminate according to claim 5 or 6, wherein the first insulators are spaced apart from one another.

8. 8. The composite laminate of claim 1, wherein the insulating grids formed by the insulating elements have a plurality of openings.

9. 9. A composite laminate according to any one of the preceding claims, wherein the structural layer comprises a semi-crystalline thermoplastic material of the polyaryletherketone class.

10. 10. The composite laminate of any one of claims 1-9, wherein the structural layer comprises a thermoplastic material having a melting point above 500 degrees Fahrenheit.

11. 11. A composite laminate according to any one of claims 1 to 10, wherein the insulating element is configured such that when the weld layer is heated above its melting point by an induction welding head, the thermoplastic material of the structural layer is kept below its melting point.

12. 12. A composite laminate according to any one of claims 1 to 11, wherein the weld layer comprises a thermoplastic material having a melting point, and the insulating element is configured to prevent the thermoplastic material of the structural layer from melting when the weld layer is welded to a separate thermoplastic element.

13. 13. A composite laminate as claimed in any one of claims 1 to 12, wherein the structural layer comprises a plurality of pairs of unidirectional carbon fibre reinforced thermoplastic plies, each of said pairs comprising adjacent overlapping plies, the fibre orientation in each of said pairs being substantially parallel.

14. 14. The composite laminate of claim 13, wherein one of said insulating grids is disposed between an adjacent pair of structural plies.

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