Sandwich structure, method for manufacturing sandwich structure, and aircraft

Abstract

The invention relates to a sandwich structure. The purpose of the present invention is to further reduce a sandwich structure used as a structural member of a small aircraft such as an air moving tool. The sandwich structure body is a structure body obtained by clamping the two sides of a honeycomb core or a foam core with at least one layer of carbon fiber reinforced plastic respectively. In the sandwich structure, the thickness of one layer of the carbon fiber reinforced plastic is 0.05 mm or more and 0.15 mm or less, and no other layer is sandwiched between the honeycomb core or the foam core and a thermosetting resin as a matrix reinforced by carbon fibers contained in the carbon fiber reinforced plastic, and the thermosetting resin is directly bonded to the honeycomb core or the foam core.

Description

Technical Field

[0001] Embodiments of the present invention relate to a sandwich structure, a method for manufacturing a sandwich structure, and an aircraft. Background Art

[0002] At present, sandwich structures in which a honeycomb core is sandwiched by fiber reinforced plastics (FRP: Fiber Reinforced Plastics) are known (for example, refer to Patent Documents 1 to Patent Documents 4). Fiber reinforced plastics are also called composite materials such as glass fiber reinforced plastics (GFRP: Glass Fiber Reinforced Plastics), carbon fiber reinforced plastics (CFRP: Carbon Fiber Reinforced Plastics) and aramid fiber reinforced plastics (AFRP: Aramid Fiber Reinforced Plastics).

[0003] Sandwich structures, like FRP, are mainly used as structural materials for aircraft. In recent years, it has attracted much attention as a candidate structural material for aerial vehicles, also known as drones or flying cars, in addition to fixed-wing aircraft and rotorcraft such as helicopters. In the case of small aircraft such as aerial vehicles, the strength required for structural materials is smaller than that of large aircraft such as fixed-wing aircraft. Therefore, when a sandwich structure is used as a structural material for an aerial vehicle, a sandwich structure in which a honeycomb core is sandwiched by FRP whose plate thickness is thinner than that of an existing sandwich structure used as a structural component of a large aircraft can be used as a structural material.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2018 / 174217

[0007] Patent Document 2: Japanese Patent Application Publication No. 2013-001006

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 58-082755

[0009] Patent Document 4: Japanese Utility Model Publication No. 61-023385 Summary of the invention

[0010] Problems to be solved by the invention

[0011] An object of the present invention is to further lighten a sandwich structure used as a structural member of a small aircraft such as an air vehicle.

[0012] Technical solutions for solving technical problems

[0013] The sandwich structure of the embodiment of the present invention is a structure obtained by sandwiching both sides of a honeycomb core or a foam core with at least one layer of carbon fiber reinforced plastic. In the sandwich structure, the thickness of one layer of the carbon fiber reinforced plastic is 0.05 mm or more and 0.15 mm or less, and no other layer is sandwiched between the thermosetting resin as a matrix reinforced by carbon fibers contained in the carbon fiber reinforced plastic and the honeycomb core or the foam core, and the thermosetting resin is directly bonded to the honeycomb core or the foam core.

[0014] Furthermore, an aircraft according to an embodiment of the present invention includes the above-described sandwich structure as a structural material.

[0015] In addition, a method for manufacturing a sandwich structure according to an embodiment of the present invention is a method for manufacturing a sandwich structure obtained by sandwiching both sides of a honeycomb core or a foam core with at least one layer of carbon fiber reinforced plastic, wherein a semi-cured sheet with a thickness of 0.05 mm or more and 0.15 mm or less is used as a raw material for the carbon fiber reinforced plastic, and the uncured thermosetting resin as a matrix reinforced with carbon fibers contained in the semi-cured sheet is heated and cured without interposing other layers between the uncured thermosetting resin and the honeycomb core or the foam core so that the uncured thermosetting resin is in direct contact with both sides of the honeycomb core or the foam core, thereby manufacturing a sandwich structure in which the cured thermosetting resin is directly bonded to both sides of the honeycomb core or the foam core, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1 is a diagram illustrating a method for manufacturing a sandwich structure according to a first embodiment of the present invention;

[0017] Figure 2 Yes means Figure 1 A perspective view of a structural example of a honeycomb core shown;

[0018] Figure 3 1 is a diagram for explaining a modified example of the method for manufacturing the sandwich structure according to the first embodiment of the present invention;

[0019] Figure 4 It means including Figure 1 or Figure 3 A perspective view of an example of an aircraft in which a sandwich structure manufactured by the manufacturing method shown is used as a structural material;

[0020] Figure 5 yes Figure 4 A cross-sectional view of the arm of the aircraft shown;

[0021] Figure 6 is a cross-sectional view of an existing honeycomb sandwich structure;

[0022] Figure 7It is a diagram illustrating the problems existing in the conventional honeycomb sandwich structure;

[0023] Figure 8 2 is a diagram illustrating a method for manufacturing a sandwich structure according to a second embodiment of the present invention;

[0024] Fig. 9 1 is a diagram for explaining a modified example of the method for manufacturing a sandwich structure according to the second embodiment of the present invention;

[0025] Fig.10 It is a diagram for explaining a method for producing a sandwich structure according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0026] The sandwich structure, the method for manufacturing the sandwich structure and the aircraft according to the embodiments of the present invention will be described below with reference to the accompanying drawings.

[0027] (First Embodiment)

[0028] (Method for producing sandwich structure)

[0029] Figure 1 It is a diagram for explaining the method for producing the sandwich structure 1 according to the first embodiment of the present invention.

[0030] Figure 1 The present invention shows a method for manufacturing a sandwich structure 1 in which both sides of a honeycomb core 2 are sandwiched by an outer skin 3 composed of a layer of CFRP 3A. The CFRP 3A is manufactured by heat-curing a prepreg 4A which is a raw material of the CFRP 3A.

[0031] Therefore, first, in step P1, the honeycomb core 2 sandwiched between two prepregs 4A is placed on a rigid lower mold M. As the prepreg 4A, a prepreg in which carbon fibers 5 are impregnated with an uncured thermosetting resin 6 is used. Figure 1 In the example shown, the prepreg 4A is used in which the carbon fibers 5 whose longitudinal directions are parallel to the paper surface and the carbon fibers 5 whose longitudinal directions are perpendicular to the paper surface are crossed, but the orientation of the carbon fibers 5 is arbitrary.

[0032] In addition, as the prepreg 4A, a prepreg that is given self-adhesiveness by reducing the fiber volume content (VF: fiber volume) to 20 volume % or more and 40 volume % or less is used. VF is the volume ratio of the fiber contained in the prepreg or FRP. Therefore, if VF is reduced, the volume of the resin contained in the prepreg or FRP will increase, and the self-adhesiveness of the prepreg can be improved by increasing the resin volume.

[0033] When the fiber contained in the prepreg is a carbon fiber, if VF is set to be greater than 20% by volume and less than 40% by volume, ignoring the difference in resin density corresponding to the resin component, the resin content (RC: Resin Content) of the prepreg reaches greater than 50% by mass and less than 70% by mass. RC is the weight ratio of the resin contained in the prepreg. Therefore, the prepreg 4A can also be called a prepreg for CFRP3A that is given self-adhesiveness by increasing RC to a range of greater than 50% by mass and less than 70% by mass.

[0034] The VF of the prepreg for CFRP, which is a resin impregnated carbon fiber, is usually about 40% to 60% by volume, and the RC is usually about 30% to 50% by mass. This is because when the VF is too small (RC is too high), the content of reinforcing fibers will decrease, and the mechanical properties of CFRP, which are more advantageous than metal materials, such as specific strength and specific stiffness, will decrease.

[0035] In contrast, it was confirmed through testing that, in the case of the CFRP3A prepreg 4A in which the VF was reduced to a range of 20% by volume or more and 40% by volume or less, in other words, in the case of the CFRP3A prepreg 4A in which the RC was increased to a range of 50% by mass or more and 70% by mass or less, a part of the uncured thermosetting resin 6 could be used as an adhesive for bonding the prepreg 4A to the honeycomb core 2. That is, it was confirmed through testing that, when the VF was reduced to 20% by volume or more and 40% by volume or less, the uncured thermosetting resin 6 as a matrix reinforced by the carbon fibers 5 contained in the prepreg 4A could itself be used as an adhesive for bonding the prepreg 4A to the honeycomb core 2 without laminating a layer for imparting self-adhesiveness to the prepreg 4A or using an adhesive film.

[0036] The test results of the prepreg 4A for CFRP3A confirmed the following: the smaller the VF is within the range of 20 volume % to 40 volume %, the better the self-adhesion of the prepreg 4A is. From the perspective of improving the self-adhesion of the prepreg 4A used to bond the prepreg 4A to the honeycomb core 2, it is preferred to set the VF to 20 volume % to 35 volume %; from the perspective of improving the self-adhesion of the prepreg 4A used to bond the prepreg 4A to the honeycomb core 2, it is most preferred to set the VF to 20 volume % to 30 volume %.

[0037] If expressed by RC, the higher the RC is within the range of 50 mass % to 70 mass %, the better the self-adhesion of the prepreg 4A is. From the viewpoint of improving the self-adhesion of the prepreg 4A used to bond the prepreg 4A to the honeycomb core 2, it is preferred to set the RC to 55 mass % or more and 70 mass % or less. From the viewpoint of improving the self-adhesion of the prepreg 4A used to bond the prepreg 4A to the honeycomb core 2, it is most preferred to set the RC to 60 mass % or more and 70 mass % or less. This can be considered that, while VF decreases, the higher the RC is, the more the volume and mass of the uncured thermosetting resin 6 required for bonding to the honeycomb core 2 increases.

[0038] As a component of the thermosetting resin 6 that imparts self-adhesiveness, an epoxy resin having excellent heat resistance, elastic modulus, and chemical resistance as typical prepregs can be used, but various additives can also be added to adjust the physical properties of the thermosetting resin 6. As a specific example, the following prepregs can be used as the prepreg 4A having self-adhesiveness for bonding to the honeycomb core 2: a prepreg having VF reduced to 20% by volume or more and 40% by volume or less (RC increased from 50% by mass to 70% by mass) in which an epoxy resin, an epoxy resin composition containing dicyandiamide (DICY) as a representative curing agent for epoxy resin, and aromatic amines are impregnated in carbon fibers as described in Japanese Patent Application Laid-Open No. 2019-156982; a prepreg having VF reduced to 20% by volume or more and 40% by volume or less (RC increased from 50% by mass to 70% by mass) in which the base prepreg described in International Publication No. 2018 / 174217 Specification has VF reduced to 20% by volume or more and 40% by volume or less (RC increased from 50% by mass to 70% by mass).

[0039] Examples of epoxy resins include: bifunctional epoxy resins such as bisphenol epoxy resins, alcohol epoxy resins, biphenyl epoxy resins, hydrogenphthalic acid epoxy resins, dimer acid epoxy resins, alicyclic epoxy resins, etc.; glycidyl ether epoxy resins such as tetrakis(glycidyl oxyphenyl)ethane and tris(glycidyl oxyphenyl)methane; glycidyl amine epoxy resins such as tetraglycidyl diaminodiphenylmethane; naphthalene epoxy resins; phenol novolac epoxy resins such as o-cresol novolac epoxy resins and cresol novolac epoxy resins, etc.

[0040] On the other hand, examples of resins other than epoxy resins include unsaturated polyester resins, vinyl ester resins, phenolic resins, melamine resins, polyurethane resins, silicone resins, maleimide resins, cyanate resins, and resins obtained by prepolymerization of maleimide resins and cyanate resins. In addition, mixtures of these resins may also be used.

[0041] In addition, as additives, as described in Japanese Patent Gazette No. 2019-156982, the following substances can also be added to the epoxy resin: urea curing accelerators such as phenyl dimethyl urea (PDMU) and toluene bis dimethyl urea (TBDMU); thermoplastic resins such as polyimide, polyether imide, polysulfone, polyether sulfone and polyvinyl formaldehyde; and / or thickening particles composed of polymers composed of one or more polymerization units of methacrylate compounds, acrylate compounds and vinyl compounds.

[0042] When the sandwich structure 1 is manufactured using the prepreg 4A including the uncured thermosetting resin 6 having adhesion to the honeycomb core 2 as a raw material, as shown in step P1, the honeycomb core 2 sandwiched between two prepregs 4A can be placed on the lower mold M in a state where the uncured thermosetting resin 6 is in direct contact with both sides of the honeycomb core 2 without interposing other layers such as adhesive films between the prepreg 4A and the honeycomb core 2. After the prepreg 4A on the lower surface side is stacked on the lower mold M, the honeycomb core 2 can be directly placed on the prepreg 4A on the lower surface side, and the prepreg 4A on the upper surface side can be directly stacked on the honeycomb core 2.

[0043] Therefore, although lowering VF reduces the specific strength and specific rigidity of the prepreg 4A, on the other hand, the weight of the sandwich structure 1 can be reduced by the weight of the currently required adhesive film or the currently required adhesive layer overlapping the self-adhesive prepreg.

[0044] In addition, from the viewpoint of reducing the weight of the sandwich structure 1, it is appropriate to set the thickness of the prepreg 4A having self-adhesiveness to 0.05 mm to 0.15 mm. That is, in order to reduce the weight of the sandwich structure 1, it is appropriate to set the thickness of each prepreg 4A disposed on both sides of the honeycomb core 2 to 0.05 mm to 0.15 mm. One of the reasons is that if the thickness of the prepreg 4A is too thick, the weight increased by the thermosetting resin 6 due to the reduction of VF will become a non-negligible degree.

[0045] In particular, unlike the prepreg for AFRP and the prepreg for GFRP, due to the development of the fiber opening technology of the carbon fiber 5, the prepreg 4A for CFRP3A has been developed into a thin layer material with a thickness of 0.05 mm to 0.15 mm, and the thin layer material is easy to manufacture and obtain. In addition, when the prepreg 4A is made into a thin layer material with a thickness of 0.05 mm to 0.15 mm, the unit area weight of the carbon fiber 5 constituting the prepreg 4A is typically 50 g / m 2 Up to 100g / m 2 .

[0046] Figure 2 Yes means Figure 1 A perspective view of a structural example of the honeycomb core 2 is shown.

[0047] like Figure 2 As shown, the honeycomb core 2 has a structure in which cells are seamlessly arranged, which is composed of angular tubes with regular hexagonal cross sections, and can also be bent. Therefore, the surface of the lower mold M is not limited to a flat surface, but can also be a curved surface. The honeycomb core 2 is composed of aluminum, NOMEX (registered trademark) made of aramid paper impregnated with resin, or FRP such as CFRP and GFRP.

[0048] After the lamination of the two prepregs 4A and the honeycomb core 2 is completed in step P1, the thermosetting resin 6 contained in the prepreg 4A is heated and cured in step P2, so that the thermosetting resin 6 is cured, thereby adhering the prepreg 4A to the honeycomb core 2. In order to prevent the hollow honeycomb core 2 from breaking, the prepreg 4A is heated, cured and bonded by heating in a low pressure environment of 1 to 2 atmospheres.

[0049] The pressure can be applied by bagging the honeycomb core 2 sandwiched by the prepreg 4A. Specifically, the honeycomb core 2 sandwiched by the prepreg 4A is covered with a bagging film B, and the space sealed by the lower mold M and the bagging film B is evacuated by a vacuum device V, thereby applying the differential pressure between the vacuum pressure and the atmospheric pressure to the honeycomb core 2 sandwiched by the prepreg 4A.

[0050] In addition, auxiliary materials such as anti-adhesion film and ventilator may be arranged between the bag film B and the prepreg 4A. The anti-adhesion film is a peeling (mold release) film used to prevent the bag film B from adhering to the prepreg 4A and the cured CFRP 3A. As a specific example, a FEP (tetrafluoroethylene-hexafluoropropylene copolymer) film composed of fluororesin is known. On the other hand, the ventilator is a sheet made of non-woven polyester or nylon fiber, etc., and the main purpose of inserting the sheet is to easily discharge the air in the area surrounded by the bag film B. Therefore, the ventilator is inserted between the anti-adhesion film and the bag film B, etc.

[0051] As the heating device H for heating in a low-pressure environment, an oven can be used in addition to an autoclave device. When an oven is used, it is necessary to give the semi-cured sheet 4A the properties of a semi-cured sheet for use outside the autoclave (OoA: Out of Autoclave). The semi-cured sheet for OoA is a semi-cured sheet having the property of impregnating the fiber with resin by applying a pressure of the difference between vacuum pressure and atmospheric pressure, and curing the resin by heating in an oven. Therefore, if the semi-cured sheet for OoA is used, FRP can be molded in a cheap oven without using a large-scale and expensive autoclave device.

[0052] When the prepreg 4A is heated to 80°C to 180°C, typically to about 120°C to 130°C, by the heating device H, fluidity can be imparted to the uncured thermosetting resin 6. As a result, the thermosetting resin 6 flows due to the surface tension between the plate materials forming each cell of the honeycomb core 2, thereby forming the fillet 7 shown in step P2. That is, the end of the plate materials forming each cell of the honeycomb core 2 is sandwiched by the fillet 7 whose surface is a smooth curved surface.

[0053] In addition, when the heating device H continues to heat the prepreg 4A, the thermosetting resin 6 including the fillet 7 is cured. That is, the thermosetting resin 6 is heated and cured in a state where the thermosetting resin 6, which is the matrix of the prepreg 4A, and the honeycomb core 2 are in direct contact with both sides of the honeycomb core 2 without any other layer being sandwiched between them.

[0054] In this way, the thermosetting resin 6 can be heated and cured in a state where the fillet 7 composed of the thermosetting resin 6 is formed on the honeycomb core 2 side of the prepreg 4A, so that the cured thermosetting resin 6 is directly bonded to the honeycomb core 2. In addition, the CFRP 3A can be molded by heating and curing the thermosetting resin 6 contained in the prepreg 4A. That is, by forming the fillet 7, the bonding force between the CFRP 3A and the honeycomb core 2 can be ensured.

[0055] Furthermore, after the prepreg 4A is heated by the heating device H, if the fluidity of the thermosetting resin 6 is too high, the thermosetting resin 6 may flow downward under the action of gravity, thereby forming an uneven fillet 7. Therefore, it is appropriate to adjust the type and content of the additive in the thermosetting resin 6 so that the viscosity of the thermosetting resin 6 when imparting fluidity reaches an appropriate viscosity.

[0056] Next, in step P3, the sandwich structure 1 formed by sandwiching the honeycomb core 2 with CFRP 3A is removed from the heating device H, and the clamps such as the bag film B and the lower mold M are removed. In this way, a honeycomb sandwich structure 1 in which the thermosetting resin 6 of the cured CFRP 3A is directly bonded to both sides of the honeycomb core 2 can be obtained.

[0057] Figure 3 These are diagrams for explaining a modified example of the method for producing the sandwich structure 1 according to the first embodiment of the present invention.

[0058] The two outer skins 3 sandwiching the honeycomb core 2 may be composed not only of a single layer of CFRP 3A but also of multiple layers of CFRP 3A. Figure 3 Although the method for manufacturing the sandwich structure 1 in which both sides of the honeycomb core 2 are sandwiched by multiple layers of CFRP 3A is shown, the sandwich structure 1 in which the honeycomb core 2 is sandwiched by the outer skin 3 composed of one layer of CFRP 3A and the outer skin 3 composed of multiple layers of CFRP 3A may also be manufactured.

[0059] In the case where at least one of the outer skins 3 sandwiching the honeycomb core 2 is composed of multiple layers of CFRP 3A, as Figure 3 As shown, Figure 1 The manufacturing method of the sandwich structure 1 shown in the figure, which is composed of two outer skins 3 sandwiching a honeycomb core 2 formed by a single layer of CFRP3A, can also be manufactured by the following steps: Step P11, stacking one or more semi-cured sheets 4 on the lower surface side, which are given self-adhesion by reducing VF (increasing RC), the honeycomb core 2, and one or more semi-cured sheets 4 on the upper surface side, which are given self-adhesion by reducing VF (increasing RC), on the lower mold M; Step P12, by heating in a low-pressure environment to a degree that does not cause the honeycomb core 2 to rupture, the thermosetting resin 6 contained in the semi-cured sheets 4A on the upper and lower surfaces is given fluidity and fillets 7 are formed, and then each fillet 7 is cured; Step P13, taking out the sandwich structure 1 with the honeycomb core 2 sandwiched by the cured CFRP3A.

[0060] In the case where at least one of the outer skins 3 sandwiching the honeycomb core 2 is composed of multiple layers of CFRP 3A, a portion of the thermosetting resin 6 that becomes the matrix of the prepreg 4A, whose VF is reduced to a range of 20% by volume or more and 40% by volume or less and RC is increased to a range of 50% by mass or more and 70% by mass or less, will function as an adhesive for bonding to the honeycomb core 2, and therefore no adhesive film is used. In addition, by setting the thickness of each of the one or more prepregs 4 disposed on both sides of the honeycomb core 2 to 0.05 mm to 0.15 mm, the VF of the prepreg 4 is reduced and the RC is increased, and thus the sandwich structure 1 can also be lightweight.

[0061] Even if the thickness of the prepreg 4 itself is relatively thin, the thickness and weight of the outer skin 3 will increase as long as the number of laminated sheets of the prepreg 4 is increased. Therefore, from the viewpoint of achieving the weight reduction effect of the sandwich structure 1, it is appropriate to set the plate thickness of the outer skin 3 obtained by heat-curing one or more prepregs 4 respectively arranged on both sides of the honeycomb core 2 to be less than 1 mm to achieve a significant weight reduction effect of the adhesive layer such as the adhesive film.

[0062] When at least one of the two outer skins 3 sandwiching the honeycomb core 2 is composed of the multilayer CFRP 3A, the formation of the fillet 7 and the bonding to the honeycomb core 2 are limited to the two prepregs 4A adjacent to the honeycomb core 2. Therefore, only the prepregs 4A containing the thermosetting resin 6 directly contacting both sides of the honeycomb core 2 are used as self-adhesive prepregs with a VF of 20% to 40% by volume and a RC of 50% to 70% by mass, while the other prepregs 4B containing the uncured thermosetting resin 6 not in direct contact with the honeycomb core 2 can be used as existing prepregs with a VF of 40% to 60% by volume and a RC of 30% to 50% by mass.

[0063] That is, the prepreg 4B including the uncured thermosetting resin 6 not in direct contact with the honeycomb core 2 can be a conventional non-self-adhesive prepreg having a VF greater than 40% by volume and less than 60% by volume (RC greater than 30% by mass and less than 50% by mass).

[0064] In this case, although two kinds of prepregs 4A and 4B having different VF and RC need to be prepared, the amount of thermosetting resin 6 is reduced, thereby having the effect of reducing the weight of the sandwich structure 1. On the contrary, if the VF and RC of the prepregs 4A and 4B are the same, the sandwich structure 1 in which the honeycomb core 2 is sandwiched by the skin 3 having a desired thickness can be manufactured by laminating one kind of prepreg. Therefore, when the prepreg tape is laminated using an automated fiber placement (AFP) device, the structure of the lamination head of the AFP device can be simplified.

[0065] Between the prepreg 4A directly contacting the two sides of the honeycomb core 2 and the prepreg 4B not in direct contact with the honeycomb core 2, the thickness can be changed without being limited to VF and RC. For example, the prepreg 4A directly contacting the two sides of the honeycomb core 2 can be made into a thin layer material with a thickness of 0.05mm to 0.15mm, and all or part of the prepreg 4B not in direct contact with the honeycomb core 2 can be made into a thick layer material with a thickness of 0.15mm to 0.25mm. As mentioned above, the unit area weight of a typical fiber of the thin layer material with a thickness of 0.05mm to 0.15mm is 50g / m 2 Up to 100g / m 2 , the typical fiber weight per unit area of ​​thick layers with a thickness of 0.15 mm to 0.25 mm is 150 g / m 2 Up to 250g / m 2 .

[0066] In addition, the thickness of the standard commercially available semi-cured sheet tape is 0.2mm to 0.8mm. Although there are semi-cured sheets with a thickness exceeding 0.25mm, as a semi-cured sheet used in combination with a thin layer material with a thickness of 0.05mm to 0.15mm to make a small sandwich structure 1, a thick layer material with a thickness of 0.15mm to 0.25mm is almost always used.

[0067] As a specific example, sometimes a C-chamfer is implemented at the end of the honeycomb core 2. In this case, the thickness of the outer skin 3 covering the portion where the C-chamfer is implemented needs to be set thicker than other portions. In this case, the thickness of the outer skin 3 can be ensured by increasing the number of laminated sheets or the thickness of the prepreg sheets 4B that are not in direct contact with the honeycomb core 2.

[0068] (Sandwich structure)

[0069] When using Figure 1 or Figure 3 When the manufacturing method shown in the figure manufactures a sandwich structure 1 in which at least one layer of CFRP3A sandwiches both sides of the honeycomb core 2, the sandwich structure 1 having the structure shown in step P3 or step P13 is obtained. Specifically, it is possible to obtain a sandwich structure 1 in which the thermosetting resin 6 is directly bonded to the honeycomb core 2 in a state where a fillet 7 composed of the thermosetting resin 6 is formed on the honeycomb core 2 side of the CFRP3A without inserting other layers between the thermosetting resin 6 as a matrix reinforced by the carbon fibers 5 contained in the CFRP3A and the honeycomb core 2.

[0070] In addition, the CFRP 3A including at least the thermosetting resin 6 directly contacting both sides of the honeycomb core 2 is obtained by heat-curing to reduce the VF to a range of 20% by volume or more and 40% by volume or less and to increase the RC to a range of 50% by mass or more and 70% by mass or less. That is, the content of the thermosetting resin 6 is higher than the typical content, and on the contrary, the content of the carbon fiber 5 is lower than the typical content. Therefore, if the influence of the resin flow and the generation of voids that may occur when the thermosetting resin 6 is heat-cured is ignored, the sandwich structure 1 having a VF of 20% by volume or more and 40% by volume or less of the CFRP 3A including the thermosetting resin 6 directly contacting both sides of the honeycomb core 2 can be obtained.

[0071] Similarly, when CFRP3A is molded by curing the semi-cured sheet 4A with a VF of 20% to 35% by volume (RC of 55% to 70% by mass) , the VF of CFRP3A is 20% to 35% by volume; when CFRP3A is molded by curing the semi-cured sheet 4A with a VF of 20% to 30% by volume (RC of 60% to 70% by mass) , the VF of CFRP3A is 20% to 30% by volume.

[0072] When the thickness of at least the CFRP3A layers adjacently arranged on both sides of the honeycomb core 2 is 0.05 mm to 0.15 mm, Figure 3 When the semi-cured sheet 4B shown as not in direct contact with the honeycomb core 2 is made into a thin layer material with a thickness of 0.05 mm to 0.15 mm in the same way as the semi-cured sheet 4A in direct contact with both sides of the honeycomb core 2, a sandwich structure 1 with one or more CFRP3A layers with a thickness of 0.05 mm to 0.15 mm respectively arranged on both sides of the honeycomb core 2 will be obtained.

[0073] The thickness of the outer skin 3 composed of at least one or more CFRP 3A layers disposed on both sides of the honeycomb core 2 is less than 1 mm. The overall thickness of the sandwich structure 1 including the honeycomb core 2 and the outer skin 3 is approximately 2 mm to 25.4 mm.

[0074] (Aircraft)

[0075] Figure 4 It means including Figure 1 or Figure 3 The perspective view of an example of an aircraft 10 using the sandwich structure 1 manufactured by the manufacturing method shown as a structural material.

[0076] Figure 4 An example is shown in which an aircraft 10 including a sandwich structure 1 as a structural material is an aerial vehicle having a fuselage 11 provided with a plurality of rotors 12. In the case of a small aircraft 10 represented by an aerial vehicle, since its weight is smaller than that of a large fixed-wing aircraft such as a passenger plane, a sandwich structure 1 having an outer skin 3 having a thickness of less than 1 mm can be used as a structural material.

[0077] Aerial mobility tools include electric aircraft such as electric vertical take-off and landing aircraft (eVTOL) and electric short take-off and landing aircraft (eSTOL), as well as rotorcraft such as helicopters and multi-rotors. Among aerial mobility tools, unmanned aerial vehicles (UAVs) such as helicopters and multi-rotors are called drones, and manned aircraft consisting of multi-rotors are sometimes called flying cars.

[0078] If Figure 4 As shown, a plurality of rotors 12 are connected to the fuselage 11 via arms 13, and the arms 13 may be formed by a sandwich structure 1. Of course, the sandwich structure 1 may also be used as a structural component of other parts.

[0079] Figure 5 yes Figure 4 A cross-sectional view of the arm 13 of the aircraft 10 is shown.

[0080] like Figure 5 As shown, the outer plate of the tubular arm 13 having a hollow structure can itself be composed of a sandwich structure 1. Figure 5As shown, a sandwich structure 1 can also be made by sandwiching multiple honeycomb cores 2 with a common outer skin 3. In this case, the surface of the lower mold M does not need to be set as a plane, and can be formed into a desired shape. Alternatively, multiple sandwich structures 1 can be joined to each other after being made.

[0081] The space inside the arm 13 can be used for laying wiring, etc. In addition, as described in the specification and drawings of Japanese Patent Application No. 2022-178242, a longitudinal beam may be fixed inside or outside the arm 13, or a part of the outer plate of the arm 13 may not be used as the sandwich structure 1 but as a simple panel or a panel reinforced with a longitudinal beam.

[0082] (Effect)

[0083] In the sandwich structure 1, the method for manufacturing the sandwich structure 1, and the aircraft 10, the honeycomb core 2 is sandwiched with CFRP 3A, which is easy to manufacture and obtain as a thin layer material, and the VF of the prepreg 4A for the CFRP 3A is reduced, while the RC is improved, so that the prepreg 4A can be directly bonded to the honeycomb core 2 by practical bonding force without sandwiching an adhesive film or adhesive layer. Therefore, according to the sandwich structure 1, the method for manufacturing the sandwich structure 1, and the aircraft 10, in particular, when a thin prepreg 4 with a thickness of 0.05 mm to 0.15 mm is used as a raw material for the outer skin 3, the weight can be further reduced.

[0084] Figure 6 It is a cross-sectional view of a conventional honeycomb sandwich structure 20 .

[0085] In the conventional honeycomb sandwich structure 20, when the honeycomb core 21 and the outer skin 22 composed of CFRP 22A are to be bonded with a strong adhesive force, the honeycomb core 21 and the CFRP 22A are bonded with an adhesive 23. Specifically, the adhesive film is arranged between the conventional prepreg for CFRP 22A, which has insufficient adhesion to the honeycomb core 21, and the honeycomb core 21, and the prepreg is heated and cured. In this case, the fillet 24 is formed by the adhesive 23. Therefore, it is particularly important to use an adhesive film having excellent adhesion to the honeycomb core 21.

[0086] In addition, although there are existing prepregs for CFRP 22A that are marketed as having self-adhesive properties, in reality, none of the prepregs has sufficient adhesion to the honeycomb core 21, and the adhesive film or a layer replacing the adhesive film cannot be omitted. This is believed to be because the fillet 24 needs to be formed in order to adhere the CFRP 22A to the honeycomb core 21, and the existing prepregs for CFRP 22A do not contain enough resin to form the fillet 24.

[0087] In addition, even if the CFRP 22A can be directly bonded to the honeycomb core 21 using an existing prepreg, since the amount of resin contained in the existing prepreg is not enough to allow for bonding to the honeycomb core 21, a defect that induces resin defect will occur in the outer skin 22. That is, the resin that should be used to form the outer skin 22 is used to form the fillet 24, resulting in deterioration in the quality of the outer skin 22.

[0088] Figure 7 This is a diagram for explaining the problems existing in the conventional honeycomb sandwich structure 20 .

[0089] Figure 7 The vertical axis of the bar graph shows the weight ratio (%) of the materials constituting the conventional honeycomb sandwich structure 20. The standard weight per square meter of the adhesive film used for the conventional honeycomb sandwich structure 20 is 300 g / m2. 2 ~400g / m 2 In the case of a conventional thick honeycomb sandwich structure 20 as a structural member for large aircraft such as passenger aircraft, which is produced by laminating a plurality of prepregs made of thick layer materials, as shown in the bar graph on the left, the weight ratio of the adhesive film is small and there is no problem.

[0090] As a specific example, two sheets with a density of 1.6 g / cm 3 The outer skin 22 made of CFRP with a thickness of 2 mm and a density of 80 kg / m 3 , a honeycomb core 21 with a thickness of 20 mm, and a weight of 300 g / m 2 In the case of a thick honeycomb sandwich structure 20 in which the outer skin 22 is bonded to both sides of the honeycomb core 21 by an adhesive film, the weight Ws_thick of the outer skin 22 per square meter is as shown in formula (1-1), the weight Wh_thick of the honeycomb core 21 per square meter is as shown in formula (1-2), and the weight Wa_thick of the adhesive film per square meter is as shown in formula (1-3).

[0091] Ws_thick=100×100×0.2×1.6×2=6400g / m 2 …Formula (1-1)

[0092] Wh_thick=80×1000 / 100×2=1600g / m 2 …Formula (1-2)

[0093] Wa_thick=300×2=600g / m 2 …Formula (1-3)

[0094] In this case, the weight ratio Ra_thick of the adhesive film becomes a small value as shown in Formula (1-4), and the weight of the adhesive film does not account for a large weight.

[0095] Ra_thick=600 / (6400+1600+600)=7%…Formula (1-4)

[0096] On the other hand, in the case of a honeycomb sandwich structure 20 for a small aircraft such as an aerial vehicle, an outer skin 22 obtained by heat-curing 1 to 15 thin layers of material with a thickness of 0.05 mm to 0.15 mm can be used as a prepreg. When such an outer skin 22 is a thin honeycomb sandwich structure 20, as shown in the bar graph on the right, the weight ratio of the adhesive film increases and cannot be ignored.

[0097] As a specific example, two sheets with a density of 1.6 g / cm 3 The outer skin 22 made of CFRP with a thickness of 0.1 mm and a density of 80 kg / m 3 , a honeycomb core 21 with a thickness of 5 mm, and a weight of 300 g / m 2 In the case of a thin layer honeycomb sandwich structure 20 in which the outer skin 22 is bonded to both sides of the honeycomb core 21 by an adhesive film, the weight Ws_thin of the outer skin 22 per square meter is as shown in formula (2-1), the weight Wh_thin of the honeycomb core 21 per square meter is as shown in formula (2-2), and the weight Wa_thin of the adhesive film per square meter is as shown in formula (2-3).

[0098] Ws_thin=100×100×0.01×1.6×2=320g / m 2 …Formula (2-1)

[0099] Wh_thin=80×1000 / 100 / 2=400g / m 2 …Formula (2-2)

[0100] Wa_thin=300×2=600g / m 2 …Formula (2-3)

[0101] In this case, the weight ratio Ra_thin of the adhesive film becomes a large value as shown in formula (2-4), and the weight of the adhesive film has a large weight. Specifically, nearly half of the weight of the thin-layer honeycomb sandwich structure 20 is the adhesive.

[0102] Ra_thin=600 / (320+400+600)=45%…Formula (2-4)

[0103] The adhesive film is not a structural component that bears strength and rigidity like the CFRP and the honeycomb core 21. Therefore, if the weight of the adhesive film can be reduced, the weight of the thin-layer honeycomb sandwich structure 20 can be reduced.

[0104] Therefore, in the case of a thin layer honeycomb sandwich structure, if combined Figure 1 and Figure 3 As explained above, by reducing the VF of the prepreg 4A and increasing the RC, although the mechanical properties such as the specific strength and specific stiffness of the prepreg 4A are sacrificed to a certain extent, the prepreg 4A can be given sufficient self-adhesiveness to be bonded to the honeycomb core 2. As a result, the weight of the thin-layer honeycomb sandwich structure can be reduced without the need for an adhesive film. That is, according to the combination Figure 1 and Figure 3 The method for manufacturing the sandwich structure 1 described above does not require an adhesive film, and therefore can obtain the lightest sandwich structure 1 that can be imagined when a thin layer material with a thickness of 0.05 mm to 0.15 mm is used as the prepreg 4 .

[0105] Therefore, by combining Figure 1 and Figure 3 The method for manufacturing the sandwich structure 1 described above achieves a weight reduction effect on the sandwich structure 1 when the sandwich structure 1 is a thin-layer honeycomb sandwich structure having an outer skin 3 with a thickness of less than 1 mm, as described above.

[0106] This thin-layer honeycomb sandwich structure can be used as a structural component of a small aircraft 10 represented by aerial mobile tools such as drones and flying cars. In particular, in the case of secondary structures such as fairings that are subjected to a relatively small load, even if only the semi-cured sheet 4A composed of a thin layer of material is heated and cured, it is sometimes possible to produce an outer skin 3 of the sandwich structure 1 having the required strength. In addition, in the case of an aircraft 10 of the size of a drone, the sandwich structure 1 can also be used as a main structural component. Therefore, if the sandwich structure 1 is used as a structural component, the weight of the small aircraft 10 is expected to be significantly reduced.

[0107] On the other hand, as the number of stacked sheets of the semi-cured sheets 4B with reduced VF (increased RC) increases, the weight of the thermosetting resin 6 increases, and thus the weight reduction effect of the sandwich structure 1 decreases, but the preparation and arrangement of the adhesive film required at present can be omitted. Therefore, there is an advantage that the manufacturing cost of the sandwich structure 1 can be reduced even when the thickness of the outer skin 3 exceeds 1 mm. The same is true when the semi-cured sheets 4, 4A and 4B with reduced VF (increased RC) are used as thick layer materials.

[0108] (Second Embodiment)

[0109] Figure 8 It is a diagram for explaining a method for producing a sandwich structure 1A according to a second embodiment of the present invention.

[0110] Figure 8The manufacturing method of the sandwich structure 1A in the second embodiment shown is different from the manufacturing method of the sandwich structure 1 in the first embodiment in that one prepreg 4C constituting the surface layer 30 of the outer skin 3 is first cured or semi-cured, and then the two prepregs 4A sandwiching the honeycomb core 2 are cured. The other contents of the manufacturing method of the sandwich structure 1A in the second embodiment are not substantially different from the manufacturing method of the sandwich structure 1 in the first embodiment, so the same objects or corresponding objects are denoted by the same reference numerals and their descriptions are omitted.

[0111] exist Figure 8 In the manufacturing method of the sandwich structure 1A shown, in step P21, a prepreg 4C which is a raw material of the CFRP 3A layer which forms one surface of the sandwich structure 1A without being in direct contact with the honeycomb core 2 is placed on the rigid lower mold M. When the sandwich structure 1A is used as a material for a panel (outer panel), it is appropriate to place the prepreg 4C which is a raw material of the CFRP 3A layer which forms the outer surface of the panel on the lower mold M.

[0112] Next, in step P22, a prepreg 4C placed on the lower mold M is heated under a high pressure environment of 3 to 8 atmospheres, thereby curing or semi-curing the prepreg 4C forming the surface layer 30. In addition, semi-curing of the prepreg 4C refers to a heating treatment that reduces the viscosity of the prepreg 4C to a degree that the shape of the prepreg 4C is not easily deformed, but does not cure the prepreg 4C to completely become a solid.

[0113] Pressurization and heating of the prepreg 4C can be performed by bagging the prepreg 4C and the autoclave device A. Bagging of the prepreg 4C is performed by covering the prepreg 4C with a bagging film B and evacuating the space sealed by the lower mold M and the bagging film B with a vacuum device V.

[0114] In addition, in order to prevent the prepreg 4C from adhering to the bag film B after heating the prepreg 4C under high pressure, a sheet S is arranged between the bag film B and the prepreg 4C to facilitate peeling of the bag film B after the prepreg 4C is cured or semi-cured.

[0115] In the next step P23, it is necessary to laminate another prepreg 4A for clamping the honeycomb core 2 on the prepreg 4C. Usually, after the prepreg is cured, if it is planned to laminate another uncured prepreg, a peeling layer is arranged between the prepreg that should be cured first and the bag film. The material of the peeling layer is mostly polyester, which has the property of absorbing resin. Therefore, after the prepreg is cured, if the peeling layer is peeled off, the effect of grinding the cured prepreg with sandpaper can be obtained. As a result, the surface of the cured prepreg is activated, which can improve the adhesion with another uncured prepreg.

[0116] However, when the prepreg 4C is a thin layer material with a thickness of 0.05 mm to 0.15 mm, it cannot withstand the pressure when the peeling layer is peeled off. That is, if the thin layer material with a thickness of 0.05 mm to 0.15 mm is covered with a peeling layer, and the peeling layer is peeled off after the thin layer material is cured, the thin layer material may be damaged.

[0117] Therefore, as the sheet S disposed between the bag film B and the prepreg 4C, an easily peelable release film is preferably used. As described above, the release film is an anti-adhesion film mainly composed of fluororesin. That is, as the sheet S to prevent the prepreg 4C from adhering to the bag film B, an anti-adhesion release film is preferably used.

[0118] When the prepreg 4C is loaded into the autoclave device A in a bagged state and pressurized by the autoclave device A, the differential pressure between the pressure in the autoclave device A and the vacuum pressure can be applied to the prepreg 4C. Then, the prepreg 4C is cured or semi-cured by heating it to a curing temperature or a semi-curing temperature by the autoclave device A. That is, by heating under a pressure of 3 atmospheres to 8 atmospheres using the autoclave device A, only the surface layer 30 of the outer skin 3 can be cured or semi-cured first.

[0119] Next, in step P23, on the cured or semi-cured surface layer 30, the semi-cured sheets 4A with VF reduced to a range of 20% by volume or more and 40% by volume or less and RC increased to a range of 50% by mass or more and 70% by mass or less are directly arranged to sandwich the honeycomb cores 2 on both sides. That is, no other layer is arranged between the surface layer 30 and the semi-cured sheet 4A below. In addition, as described in the first embodiment, the honeycomb core 2 sandwiched by the two semi-cured sheets 4A is directly arranged on the surface layer 30 in a state where the uncured thermosetting resin 6 contained in the two semi-cured sheets 4A sandwiching the honeycomb core 2 is in direct contact with the honeycomb core 2. For example, the lower semi-cured sheet 4A, the honeycomb core 2, and the upper semi-cured sheet 4A can be stacked in sequence.

[0120] After the surface layer 30 is cured or semi-cured in a state covered with a release film, the surface of the surface layer 30 after peeling off the release film is not activated as after peeling off the peeling layer, but the semi-cured sheet 4A, which is given self-adhesiveness by lowering VF and increasing RC, is in direct contact with the surface layer 30. Therefore, the semi-cured sheet 4A can be bonded to the surface layer 30 without sandwiching an adhesive film or other layer for improving adhesion.

[0121] Next, in step P24, in order to prevent the honeycomb core 2 from breaking, heating is performed in a low-pressure environment of 1 to 2 atmospheres, thereby bonding the semi-cured sheet 4A below the honeycomb core 2 and the surface layer 30, bonding is performed by forming a fillet 7 between the honeycomb core 2 and the semi-cured sheet 4A, and curing of the uncured semi-cured sheet 4A.

[0122] That is, the thermosetting resin 6 contained in the two prepregs 4A sandwiching the honeycomb core 2 is heat-cured in a state where no other layer is sandwiched between the uncured thermosetting resin 6 contained in the two prepregs 4A and the honeycomb core 2, and the uncured thermosetting resin 6 contained in the two prepregs 4A is in direct contact with the honeycomb core 2. In addition, the thermosetting resin 6 contained in the lower prepreg 4A sandwiching the honeycomb core 2 is heat-cured in a state where no other layer is sandwiched between the uncured thermosetting resin 6 contained in the lower prepreg 4A and the surface layer 30, and the uncured thermosetting resin 6 contained in the lower prepreg 4A is in direct contact with the surface layer 30.

[0123] In addition, when the surface layer 30 is not completely cured but semi-cured in step P22, not only the uncured thermosetting resin 6 disposed on the surface layer 30 becomes the object of heat curing, but also the surface layer 30 becomes the object of heat curing. That is, when the surface layer 30 contains the thermosetting resin 6 that is not completely cured, the thermosetting resin 6 contained in the surface layer 30 also becomes the object of heat curing.

[0124] As the heating device H for heating and curing the uncured thermosetting resin 6 under the pressure of 1 atmosphere to 2 atmospheres, an autoclave device or an oven can be used as in the first embodiment. In addition, as described in the first embodiment, if the prepreg 4A is used as a prepreg for OoA and an oven is used, the manufacturing cost of the sandwich structure 1A can be reduced.

[0125] When the bonding and curing in step P24 are completed, in step P25, the sandwich structure 1A including the cured surface layer 30 as a part of the outer skin 3 can be taken out from the device and the fixture. The outer skin 3 composed of 2 layers of CFRP3A including the surface layer 30 cured under high pressure can serve as the outer surface side of the panel composed of the sandwich structure 1A, and the outer skin 3 composed of 1 layer of CFRP3A cured under low pressure can serve as the inner surface side of the panel composed of the sandwich structure 1A.

[0126] Fig. 9 These are diagrams for explaining a modified example of the method for producing the sandwich structure 1A according to the second embodiment of the present invention.

[0127] exist Figure 8 In the example shown, the surface layer 30 which is first cured or semi-cured under high pressure is composed of a prepreg sheet 4C and a layer of CFRP 3A. Fig. 9 As shown, the surface layer 30 may also be composed of a plurality of prepreg sheets 4C and a plurality of CFRP 3A. For example, the surface layer 30 may be formed by curing 2 to 3 prepreg sheets 4C.

[0128] In addition, if Fig. 9 As shown, multiple prepregs 4 sandwiching the honeycomb core 2 that become the second object of low-pressure curing may be provided on each side. That is, after the surface layer 30 is cured or semi-cured by the autoclave device A, the prepreg 4A directly contacting the honeycomb core 2 and the prepreg 4B not directly contacting the honeycomb core 2 may be cured under low pressure by the heating device H.

[0129] When the surface layer 30 is a multilayer CFRP 3A, in step P31, a plurality of prepregs 4C including one prepreg 4C forming the surface of the sandwich structure 1A are stacked on the lower mold M. Then, in step P32, the stack of the plurality of prepregs 4C is heated under a pressure of 3 to 8 atmospheres using an autoclave device A. Thus, the surface layer 30 composed of the plurality of layers is cured or semi-cured.

[0130] In the subsequent step P33, a plurality of prepregs 4 may be stacked between the honeycomb core 2 and the surface layer 30. That is, the honeycomb core 2 sandwiched between two prepregs 4A may be arranged on the cured or semi-cured surface layer 30 with another prepreg 4B interposed therebetween.

[0131] Then, in the next step P34, the uncured thermosetting resin 6 contained in all the prepregs 4 can be heat-cured without interposing other layers between the surface layer 30 and the uncured thermosetting resin 6 contained in the prepreg 4B adjacent to the surface layer 30 in the thickness direction, so that the uncured thermosetting resin 6 contained in the prepreg 4B adjacent to the surface layer 30 in the thickness direction is in direct contact with the surface layer 30. Thus, as shown in step P35, a sandwich structure 1A in which both sides of the honeycomb core 2 are sandwiched by the outer skin 3 composed of multiple layers of CFRP 3A can be manufactured.

[0132] In addition, if the number of prepregs 4C forming the surface layer 30 is increased, the strength of the surface layer 30 can be improved. When the strength of the surface layer 30 can be sufficiently ensured, a peeling layer can be used instead of a release film as a sheet material S disposed between the bag film B and the prepreg 4C. After the surface layer 30 composed of multiple layers is cured or semi-cured in a state covered with the peeling layer, the surface of the surface layer 30 after the peeling layer is peeled off becomes an activated state. Therefore, if a peeling layer is used as the sheet material S, the adhesion of the surface layer 30 can be improved compared to the case of using a release film.

[0133] Therefore, when a peeling layer is used as the sheet S, it is not necessary to reduce the VF (increase the RC) of the semi-cured sheet 4B in contact with the surface layer 30 after the peeling layer is peeled off to impart self-adhesion. However, from the viewpoint of obtaining better adhesion with the surface layer 30 after the peeling layer is peeled off, for the semi-cured sheet 4B in direct contact with at least the surface layer 30, it is preferred to reduce the VF (increase the RC) in the same manner as the semi-cured sheet 4A in direct contact with the honeycomb core 2 to impart self-adhesion.

[0134] On the other hand, when a release film is used as the sheet material S, it is appropriate to reduce the VF (increase the RC) of the prepreg 4B in direct contact with the surface layer 30 to impart self-adhesion. That is, as the prepreg 4B in direct contact with the surface layer 30, it is appropriate to use a prepreg that imparts self-adhesion by reducing the VF (increasing the RC) like the prepreg 4A in direct contact with the honeycomb core 2.

[0135] (Effect)

[0136] In the above-described second embodiment, first, only the surface layer 30 of the sandwich structure 1A is cured or semi-cured under high pressure. Therefore, the appearance of the sandwich structure 1A can be improved.

[0137] In combination Figure 6 In the conventional honeycomb sandwich structure 20 described above, when the semi-cured sheet used to form the outer skin 22 is made into a thin layer material, in addition to the problem of the weight of the adhesive film which cannot be ignored, there is also the appearance problem that the traces of the honeycomb core 21 are prominent on the surface of the honeycomb sandwich structure 20.

[0138] This is because when the prepreg is cured by heating under pressure, pressure is transmitted to the prepreg from the plate-like portion of the hexagonal cells constituting the honeycomb core 21, but pressure is not transmitted to the prepreg from the cavity portion of the cells. In other words, the prepreg to which pressure is transmitted from the honeycomb core 21 cannot be uniformly pressed against the lower mold, resulting in slight unevenness on the surface of the cured outer skin 22, which deteriorates the appearance.

[0139] In addition, as a problem in terms of appearance, during the heat curing of the prepreg, the resin may flow to the honeycomb core 21 side, and countless resin defects may appear on the outer surface of the outer skin 22 after curing.

[0140] In contrast, according to the second embodiment, the surface layer 30 of the outer skin 3 is not merely brought into contact with the honeycomb core 2, but is first cured or semi-cured under high pressure, thereby being able to avoid the above-mentioned defects in appearance. As a result, even in the case where the thickness of the outer skin 3 is relatively thin, such as less than 1 mm, a good appearance can be maintained. That is, a thin-layer sandwich structure with high decorative properties can be manufactured.

[0141] Furthermore, the thermosetting resin 6 contained in the prepreg 4C forming the surface layer 30 does not function as an adhesive with the separated prepreg 4, nor is it used to form the fillet 7 for bonding with the honeycomb core 2. Therefore, as the prepreg 4C forming the surface layer 30, it is not necessary to use a prepreg that imparts self-adhesiveness by lowering VF and increasing RC, but if a prepreg that lowers VF and increases RC is used, it has an effect of making it less likely to cause resin loss that often occurs in the portion where the carbon fibers 5 intersect, thereby contributing to improving the appearance of the sandwich structure 1A.

[0142] (Third Embodiment)

[0143] Fig.10 It is a diagram for explaining a method for producing a sandwich structure 1B according to a third embodiment of the present invention.

[0144] Fig.10 The manufacturing method of the sandwich structure 1B in the third embodiment shown is different from the manufacturing method of the sandwich structure 1 in the first embodiment and the manufacturing method of the sandwich structure 1A in the second embodiment in that the core material sandwiched by the outer skin 3 composed of a single layer or multiple layers of CFRP 3A is set as a foam core 40 instead of a honeycomb core 2. The other contents of the manufacturing method of the sandwich structure 1B in the third embodiment are not substantially different from the manufacturing method of the sandwich structure 1 in the first embodiment and the manufacturing method of the sandwich structure 1A in the second embodiment, so the same objects or corresponding objects are marked with the same reference numerals and their descriptions are omitted.

[0145] like Fig.10 As shown, the core material sandwiched by the outer skin 3 composed of CFRP3A is not limited to the honeycomb core 2, but may also be a foam core 40. The foam core 40 is a foamed body used as the core material of the sandwich structure 1B. As a specific example of the material of the foam core 40, a foamed body based on PMI (polymethacrylimide) can be cited, and a foamed body of other materials can also be used.

[0146] The method for manufacturing the sandwich structure 1B in which both sides of the foam core 40 are sandwiched by at least one layer of CFRP 3A can be adopted. Figure 1 , Figure 3 , Figure 8 or Fig. 9 If the surface layer 30 consisting of a plurality of prepreg sheets 4C is first cured, then Fig.10As shown, the sandwich structure 1B can be manufactured by the following steps: step P41, stacking the surface layer 30; step P42, curing or semi-curing the surface layer 30 under high pressure; step P43, additionally stacking the foam core 40 and the semi-cured sheets 4A, 4B that sandwich the foam core 40; step P44, bonding the foam core 40 and the semi-cured sheets 4A, and curing the semi-cured sheets 4C that constitute the surface layer 30 and the semi-cured sheets 4A, 4B that sandwich the foam core 40 when the surface layer 30 is semi-cured; step P45, taking out the sandwich structure 1B formed by sandwiching the foam core 40 with CFRP3A.

[0147] When the core material is the foam core 40, the fillet 7 formed when the core material is the honeycomb core 2 is not formed, but a portion of the uncured thermosetting resin 6 on the foam core 40 side of the prepreg 4A, which is given fluidity by heating, enters into the voids of the foam core 40. Then, the thermosetting resin 6 is cured by heating while a portion of the thermosetting resin 6 enters into the voids of the foam core 40, whereby the thermosetting resin 6 and the foam core 40 can be directly bonded.

[0148] Therefore, it is possible to produce a sandwich structure 1B in which the thermosetting resin 6 and the foam core 40 are directly bonded in a state in which a part of the thermosetting resin 6 on the foam core 40 side of the CFRP 3A enters into the voids of the foam core 40 .

[0149] Even in the case of bonding the prepreg 4A to the foam core 40, similarly to the case of bonding the prepreg 4A to the honeycomb core 2, heating is required in a low pressure environment of 1 atmosphere to 2 atmospheres to prevent the foam core 40 from being broken. Therefore, an autoclave device or an oven is preferably used as the heating device H used in step P44.

[0150] On the other hand, Figure 1 and Figure 2 The sandwich structure 1B can also be manufactured without first curing or semi-curing the surface layer 30 under high pressure. However, if the sandwich structure 1B is manufactured as shown in FIG. Fig.10 By first curing or semi-curing the surface layer 30 at a high pressure of 3 atmospheres to 8 atmospheres using an autoclave apparatus A as shown in step P42, the appearance of the sandwich structure 1B can be improved.

[0151] As described above, even in the case where the core material is a foam core 40, by reducing the VF of the prepreg 4A to a range of 20% by volume or more and 40% by volume or less and increasing the RC to a range of 50% by mass or more and 70% by mass or less to improve the adhesion to the foam core 40, the adhesive film and the adhesive layer can be omitted. As a result, when the prepreg 4A composed of a thin layer material with a thickness of 0.05 mm to 0.15 mm is heat-cured to form the outer skin 3 of the sandwich structure 1B, the weight of the sandwich structure 1B can be reduced compared to the existing sandwich structure in which the FRP is bonded to the foam core by sandwiching an adhesive film or an adhesive layer. In addition, if the surface layer 30 is first cured or semi-cured under high pressure, the appearance of the sandwich structure 1B can be improved.

[0152] (Other embodiments)

[0153] The above describes a specific embodiment, but the described embodiment is only an example and is not intended to limit the scope of the invention. The new method and device described herein can be implemented in various other ways. In addition, various omissions, substitutions and changes can be made in the methods and devices described herein without departing from the scope of the invention. The attached claims and their equivalents all include various modes and variations as elements included in the scope and spirit of the invention.

[0154] For example, in the above embodiments, the prepreg 4 and the honeycomb core 2 are pressurized by atmospheric pressure, but the prepreg 4 and the honeycomb core 2 may be pressurized by pressing the upper mold. That is, the prepreg 4 and the honeycomb core 2 may be pressurized by using a press machine.

[0155] Explanation of symbols

[0156] 1.1A, 1B sandwich structure

[0157] 2 Honeycomb core

[0158] 3. Skin

[0159] 3A Carbon Fiber Reinforced Plastic (CFRP)

[0160] 4, 4A, 4B, 4C prepreg

[0161] 5. Carbon Fiber

[0162] 6Thermosetting resin

[0163] 7 Round Corners

[0164] 10 Aircraft

[0165] 11 Body

[0166] 12 rotors

[0167] 13 arms

[0168] 20Existing honeycomb sandwich structures

[0169] 21 Honeycomb core

[0170] 22 skin

[0171] 22A Carbon Fiber Reinforced Plastic (CFRP)

[0172] 23 Adhesives

[0173] 24 Round Corners

[0174] 30 surface layer

[0175] 40 Foam Core

[0176] A Autoclave Device

[0177] B bag film

[0178] H Heating device

[0179] M lower die

[0180] S Sheet

[0181] V vacuum device.

Claims

1. A sandwich structure, which is obtained by sandwiching both sides of a honeycomb core or a foam core with at least one layer of carbon fiber reinforced plastic, wherein: The thickness of one layer of the carbon fiber reinforced plastic is 0.05 mm or more and 0.15 mm or less, and The thermosetting resin as a matrix reinforced by carbon fibers contained in the carbon fiber reinforced plastic is directly bonded to the honeycomb core or the foam core without any other layer interposed therebetween.

2. An aircraft comprising the sandwich structure according to claim 1 as a structural material.

3. A method for manufacturing a sandwich structure, wherein the sandwich structure is obtained by sandwiching both sides of a honeycomb core or a foam core with at least one layer of carbon fiber reinforced plastic, wherein: A prepreg having a thickness of 0.05 mm or more and 0.15 mm or less is used as a raw material of the carbon fiber reinforced plastic, and The thermosetting resin is heated and cured in a state where no other layer is sandwiched between the uncured thermosetting resin as a matrix reinforced with carbon fibers contained in the semi-cured sheet and the honeycomb core or the foam core and the uncured thermosetting resin is in direct contact with both sides of the honeycomb core or the foam core, thereby manufacturing a sandwich structure in which the cured thermosetting resin is directly bonded to both sides of the honeycomb core or the foam core.

4. The method for manufacturing a sandwich structure according to claim 3, wherein: The fiber volume content of the prepreg containing the uncured thermosetting resin directly contacting both sides of the honeycomb core or the foam core is set to 20 volume % or more and 40 volume % or less.

5. The method for manufacturing a sandwich structure according to claim 3 or 4, wherein: A prepreg sheet, which is a raw material of a carbon fiber reinforced plastic layer and forms one surface of the sandwich structure without being in direct contact with the honeycomb core or the foam core, or a laminate of a plurality of prepreg sheets including the prepreg sheet is heated under pressure, thereby curing or semi-curing a surface layer consisting of one or more layers, and then, The honeycomb core or foam core is directly arranged on the cured or semi-cured surface layer, or is arranged by sandwiching other semi-cured sheets, wherein both sides of the honeycomb core or foam core are respectively sandwiched by semi-cured sheets containing the uncured thermosetting resin in direct contact with the honeycomb core or foam core, The semi-cured surface layer and the uncured thermosetting resin disposed on the surface layer are heated and cured, thereby manufacturing the sandwich structure including the cured surface layer.

6. The method for manufacturing a sandwich structure according to claim 3 or 4, wherein: The fiber volume content of the prepreg containing the uncured thermosetting resin which is not in direct contact with the honeycomb core or the foam core is set to 40 volume % to 60 volume %.

Images