Sandwich structure, method of producing sandwich structure, and aircraft

Abstract

To further reduce a weight of a sandwich structure used as a structural component for a small aircraft such as air mobility.SOLUTION: There is provided a sandwich structure that is a structure in which a honeycomb core or a foam core is sandwiched on both sides with at least one layer of carbon fiber reinforced plastic. The sandwich structure has a thickness of the one layer of carbon fiber reinforced plastic of 0.05 mm or more and 0.15 mm or less, and a thermosetting resin is directly bonded to the honeycomb core or foam core without interposing any other layer between the thermosetting resin as a matrix reinforced with carbon fibers contained in the carbon fiber reinforced plastic and the honeycomb core or foam core.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate to a sandwich structure, a method for manufacturing a sandwich structure, and an aircraft. [Background technology]

[0002] Conventionally, sandwich structures have been known in which a honeycomb core is sandwiched between fiber reinforced plastics (FRP), also known as composite materials such as glass fiber reinforced plastics (GFRP), carbon fiber reinforced plastics (CFRP), and aramid fiber reinforced plastics (AFRP) (see, for example, Patent Documents 1 to 4).

[0003] Like FRP, sandwich structures are mainly used as structural materials for aircraft. In recent years, they have been attracting attention as a possible structural material for air mobility, also known as drones and flying cars, as well as fixed-wing aircraft and rotorcraft such as helicopters. Small aircraft such as air mobility require less strength from structural materials than large aircraft such as fixed-wing aircraft. For this reason, when using sandwich structures as structural materials for air mobility, it becomes possible to use sandwich structures with honeycomb cores sandwiched between FRP plates with thinner plate thicknesses than conventional sandwich structures used as structural members for large aircraft. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 174217 [Patent Document 2] JP 2013-001006 A [Patent Document 3] Japanese Patent Application Publication No. 58-082755 [Patent Document 4] Japanese Utility Model Publication No. 61-023385 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to further reduce the weight of sandwich structures used as structural members of small aircraft such as air mobility aircraft. [Means for solving the problem]

[0006] A sandwich structure according to an embodiment of the present invention has at least one layer of carbon fiber reinforced plastic sandwiched between both sides of a honeycomb core or a foam core. In this 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 the thermosetting resin is directly bonded to the honeycomb core or foam core without any other layer being interposed between the honeycomb core or foam core and a thermosetting resin serving as a matrix reinforced with carbon fibers contained in the carbon fiber reinforced plastic.

[0007] Moreover, an aircraft according to an embodiment of the present invention includes the above-mentioned sandwich structure as a structural material.

[0008] Furthermore, a manufacturing method for a sandwich structure according to an embodiment of the present invention is a manufacturing method for a sandwich structure in which a honeycomb core or a foam core is sandwiched on both sides with at least one layer of carbon fiber reinforced plastic, in which a prepreg having a thickness of 0.05 mm or more and 0.15 mm or less is used as the material for the carbon fiber reinforced plastic, and no other layer is interposed between the uncured thermosetting resin as a matrix reinforced with carbon fibers contained in the prepreg and the honeycomb core or foam core, and the uncured thermosetting resin is brought into direct contact with both sides of the honeycomb core or foam core, respectively, and the thermosetting resin is heated and cured to produce a sandwich structure in which the thermosetting resin after curing is directly bonded to both sides of the honeycomb core or foam core, respectively. [Brief description of the drawings]

[0009] [Figure 1] 1A to 1C are views for explaining a method for manufacturing a sandwich structure according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view showing a structural example of the honeycomb core shown in FIG. [Diagram 3] 5A to 5C are views for explaining a modified example of the manufacturing method of the sandwich structure according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a perspective view showing an example of an aircraft including, as a structural material, a sandwich structure manufactured by the manufacturing method shown in FIG. 1 or FIG. 3. [Diagram 5] FIG. 5 is a cross-sectional view of the aircraft arm shown in FIG. [Figure 6] FIG. 1 is a cross-sectional view of a conventional honeycomb sandwich structure. [Figure 7] 1 is a graph illustrating problems with a conventional honeycomb sandwich structure. [Figure 8] 5A to 5C are views for explaining a method for manufacturing a sandwich structure according to a second embodiment of the present invention. [Figure 9] 7A to 7C are views for explaining a modified example of the manufacturing method of a sandwich structure according to the second embodiment of the present invention. [Figure 10] 8A to 8C are views for explaining a method for manufacturing a sandwich structure according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A sandwich structure, a method for manufacturing a sandwich structure, and an aircraft according to embodiments of the present invention will be described with reference to the accompanying drawings.

[0011] (First embodiment) (Method of manufacturing sandwich structure) FIG. 1 is a diagram illustrating a method for manufacturing a sandwich structure 1 according to a first embodiment of the present invention.

[0012] 1 shows a manufacturing method for a sandwich structure 1 in which both sides of a honeycomb core 2 are sandwiched between skins 3 made of a single layer of CFRP 3A. The CFRP 3A is produced by heat curing a prepreg 4A, which is the material for the CFRP 3A.

[0013] Therefore, first, in step P1, the honeycomb core 2 sandwiched between two prepregs 4A is placed on a rigid lower mold M. The prepregs 4A are made of carbon fibers 5 impregnated with uncured thermosetting resin 6. In the example shown in Fig. 1, the prepregs 4A are made by crossing carbon fibers 5 whose length direction is parallel to the page and carbon fibers 5 whose length direction is perpendicular to the page, but the orientation of the carbon fibers 5 is arbitrary.

[0014] Also, the prepreg 4A used has a fiber volume fraction (VF) of 20% by volume or more and 40% by volume or less, which gives it self-adhesiveness. VF is the ratio of the volume of the fibers contained in the prepreg or FRP. Therefore, if the VF is reduced, the volume of the resin contained in the prepreg or FRP increases, and the increased volume of the resin can improve the self-adhesiveness of the prepreg.

[0015] When the fiber contained in the prepreg is carbon fiber and the VF is between 20% and 40% by volume, the resin content (RC) of the prepreg is between 50% and 70% by mass, ignoring the difference in resin density according to the resin composition. RC is the weight ratio of the resin contained in the prepreg. Therefore, it can be said that prepreg 4A is a prepreg for CFRP3A that has been given self-adhesiveness by increasing the RC to the range between 50% and 70% by mass.

[0016] The VF of prepreg for CFRP, which is made by impregnating carbon fiber with resin, is usually about 40% to 60% by volume, and the RC is usually about 30% to 50% by mass. This is because if the VF is too small (RC is too high), the reinforcing fiber content decreases, and the mechanical properties such as specific strength and specific rigidity of CFRP, which are superior to metal materials, decrease.

[0017] In contrast, in the case of prepreg 4A for CFRP 3A in which VF is reduced to a range of 20% by volume or more and 40% by volume or less, in other words, in the case of prepreg 4A for CFRP 3A in which RC is increased to a range of 50% by volume or more and 70% by mass or less, it has been confirmed by tests that a part of the uncured thermosetting resin 6 can be used as an adhesive for bonding prepreg 4A to honeycomb core 2. In other words, it has been confirmed by tests that when VF is reduced to a range of 20% by volume or more and 40% by volume or less, prepreg 4A can be bonded to honeycomb core 2 using the uncured thermosetting resin 6 itself as an adhesive, which is a matrix (base material) reinforced with carbon fibers 5 contained in prepreg 4A, as the adhesive, without laminating a layer for imparting self-adhesiveness to prepreg 4A or using an adhesive film.

[0018] As a result of tests on prepreg 4A for CFRP3A, it was confirmed that the smaller the VF is within the range of 20 volume % or more and 40 volume % or less, the better the self-adhesion of prepreg 4A is, and that a VF of 20 volume % or more and 35 volume % or less is preferable from the standpoint of improving the self-adhesion of prepreg 4A for bonding prepreg 4A to honeycomb core 2, and that a VF of 20 volume % or more and 30 volume % or less is most preferable from the standpoint of improving the self-adhesion of prepreg 4A for bonding prepreg 4A to honeycomb core 2.

[0019] Expressed in terms of RC, the higher the RC in the range of 50 mass% to 70 mass%, the better the self-adhesiveness of the prepreg 4A becomes, and setting the RC at 55 mass% or more and 70 mass% or less is preferable from the viewpoint of improving the self-adhesiveness of the prepreg 4A for bonding the prepreg 4A to the honeycomb core 2, and setting the RC at 60 mass% or more and 70 mass% or less is most preferable from the viewpoint of improving the self-adhesiveness of the prepreg 4A for bonding the prepreg 4A to the honeycomb core 2. This is thought to be because, while the VF is reduced, the volume and mass of the uncured thermosetting resin 6 required for bonding to the honeycomb core 2 increases as the RC is increased.

[0020] As the composition of the thermosetting resin 6 that imparts self-adhesiveness, an epoxy resin having excellent heat resistance, elastic modulus, and chemical resistance can be used as in a typical prepreg, but various additives may be added to adjust the physical properties of the thermosetting resin 6. As a specific example, a prepreg having a 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 composition containing dicyandiamide (DICY) and aromatic amine, which are typical epoxy resin curing agents, is impregnated into carbon fibers as described in JP 2019-156982 A, or a base prepreg having a VF reduced to 20% by volume or more and 40% by volume or less (RC increased from 50% by mass to 70% by mass) as described in WO 2018 / 174217 A can be used as a prepreg 4A having self-adhesiveness for bonding to a honeycomb core 2.

[0021] Examples of the epoxy resin include bifunctional epoxy resins such as bisphenol type epoxy resins, alcohol type epoxy resins, biphenyl type epoxy resins, hydrophthalic acid type epoxy resins, dimer acid type epoxy resins, and alicyclic type epoxy resins; glycidyl ether type epoxy resins such as tetrakis(glycidyloxyphenyl)ethane and tris(glycidyloxyphenyl)methane; glycidyl amine type epoxy resins such as tetraglycidyldiaminodiphenylmethane; naphthalene type epoxy resins; and novolac type epoxy resins such as phenol novolac type epoxy resins and cresol novolac type epoxy resins.

[0022] 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 ester resins, resins obtained by prepolymerizing maleimide resins and cyanate ester resins, etc. Also, mixtures of these resins can be used.

[0023] In addition, as additives, as described in JP 2019-156982 A, urea-based curing accelerators such as phenyldimethylurea (PDMU) and toluenebisdimethylurea (TBDMU); thermoplastic resins such as polyimide, polyetherimide, polysulfone, polyethersulfone, and polyvinyl formal; and / or thickening particles made of a polymer consisting of one or more polymerization units of a methacrylic acid ester compound, an acrylic acid ester compound, and a vinyl compound may be added to the epoxy resin.

[0024] As described above, when manufacturing the sandwich structure 1 using as a material the prepreg 4A containing the uncured thermosetting resin 6 having adhesive properties with the honeycomb core 2, as shown in step P1, the honeycomb core 2 sandwiched between two prepregs 4A can be placed on a lower mold M with the uncured thermosetting resin 6 in direct contact with both sides of the honeycomb core 2 without interposing another layer such as an adhesive film between the prepreg 4A and the honeycomb core 2. After the lower prepreg 4A is laminated on the lower mold M, the honeycomb core 2 can be placed directly on the lower prepreg 4A, and the upper prepreg 4A can be laminated directly on the honeycomb core 2.

[0025] Therefore, while reducing the VF reduces the specific strength and specific rigidity of the prepreg 4A, the weight of the sandwich structure 1 can be reduced by the weight of the adhesive film that was previously required and the adhesive layer superimposed on the conventional self-adhesive prepreg.

[0026] In addition, from the viewpoint of reducing the weight of the sandwich structure 1, it is appropriate to set the thickness of the self-adhesive prepreg 4A 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 of the prepregs 4A arranged on both sides of the honeycomb core 2 to 0.05 mm to 0.15 mm. One of the reasons for this is that if the thickness of the prepreg 4A is too thick, the increase in the weight of the thermosetting resin 6 caused by reducing the VF becomes non-negligible.

[0027] In particular, unlike prepregs for AFRP and GFRP, in the case of prepreg 4A for CFRP3A, the development of fiber spreading technology for carbon fibers 5 has established a technology for making a thin layer material having a thickness of 0.05 mm to 0.15 mm, and the thin layer material is easy to manufacture and obtain. When prepreg 4A is made into a thin layer material having a thickness of 0.05 mm to 0.15 mm, the basis weight of carbon fibers 5 constituting prepreg 4A is typically 50 g / m 2 From 100g / m 2 It becomes.

[0028] FIG. 2 is a perspective view showing an example of the structure of the honeycomb core 2 shown in FIG.

[0029] The honeycomb core 2 has a structure in which cells made of square tubes with a cross section of a regular hexagon are arranged without gaps as shown in Fig. 2, and bending molding is also possible. Therefore, the surface of the lower mold M is not limited to a flat surface, and may be a curved surface. The honeycomb core 2 is made of aluminum, Nomex (registered trademark) made of aramid paper impregnated with resin, or FRP such as CFRP or GFRP.

[0030] After lamination of the two prepregs 4A and the honeycomb core 2 in step P1 is completed, next, in step P2, the thermosetting resin 6 contained in the prepreg 4A is heated and cured, and the prepreg 4A is bonded to the honeycomb core 2 by the curing of the thermosetting resin 6. The heat curing and bonding of the prepreg 4A are performed by heating in a low-pressure environment of 1 to 2 atmospheres so as not to crush the hollow honeycomb core 2.

[0031] The pressure can be applied by bagging the honeycomb core 2 sandwiched between the prepregs 4A. Specifically, the honeycomb core 2 sandwiched between the prepregs 4A is covered with a bagging film B, and the space sealed by the lower mold M and the bagging film B is evacuated with a vacuum device V, so that the differential pressure between the vacuum pressure and atmospheric pressure can be applied to the honeycomb core 2 sandwiched between the prepregs 4A.

[0032] In addition, secondary materials such as anti-adhesion film and breather may be placed between the bagging film B and the prepreg 4A. The anti-adhesion film is a release film to prevent the bagging film B from adhering to the prepreg 4A and the CFRP 3A after curing. A specific example is FEP (tetrafluoroethylene-hexafluoropropylene copolymer) film made of fluororesin. On the other hand, the breather is a sheet made of non-woven polyester or nylon fiber, etc., that is inserted mainly for the purpose of making it easier to remove air from the area surrounded by the bagging film B. For this reason, the breather is inserted between the anti-adhesion film and the bagging film B.

[0033] As the heating device H for heating in a low pressure environment, an oven can be used in addition to an autoclave. When using an oven, it is necessary to give the prepreg 4A the properties of an out-of-autoclave (OoA) prepreg. An OoA prepreg has the property that the fibers are impregnated with resin by applying a pressure equivalent to the differential pressure between vacuum pressure and atmospheric pressure, and the resin can be heated and cured in an oven. For this reason, if an OoA prepreg is used, it is possible to mold FRP in an inexpensive oven without using a large-scale and expensive autoclave.

[0034] Heating the prepreg 4A to 80°C to 180°C, typically to about 120°C to 130°C, in the heating device H can impart fluidity to the uncured thermosetting resin 6. As a result, the thermosetting resin 6 flows due to the surface tension between the plate materials that form each cell of the honeycomb core 2, and fillets 7 are formed as shown in step P2. In other words, the ends of the plate materials that form each cell of the honeycomb core 2 are sandwiched by the fillets 7, which have smoothly curved surfaces.

[0035] Furthermore, when the prepreg 4A continues to be heated by the heating device H, the thermosetting resin 6 including the fillets 7 is cured. That is, the thermosetting resin 6 is heated and cured in a state where the thermosetting resin 6 is in direct contact with both sides of the honeycomb core 2, without any other layer being interposed between the thermosetting resin 6 as the matrix of the prepreg 4A and the honeycomb core 2.

[0036] In this way, the thermosetting resin 6 can be heated and cured with the fillet 7 made of the thermosetting resin 6 formed on the honeycomb core 2 side of the prepreg 4A, and the cured thermosetting resin 6 can be directly bonded to the honeycomb core 2. Also, the CFRP 3A can be molded by heating and curing the thermosetting resin 6 contained in the prepreg 4A. In other words, by forming the fillet 7, the bonding strength between the CFRP 3A and the honeycomb core 2 can be ensured.

[0037] Furthermore, if the fluidity of the thermosetting resin 6 is too high after the prepreg 4A is heated by the heating device H, the thermosetting resin 6 may flow downward due to gravity, resulting in the formation of non-uniform fillets 7. For this reason, it is appropriate to adjust the type and content of additives in the thermosetting resin 6 so that the viscosity of the thermosetting resin 6 when fluidized is appropriate.

[0038] Next, in step P3, the sandwich structure 1 in which the honeycomb core 2 is sandwiched between the CFRP 3A is removed from the heating device H, and the bagging film B and jigs such as the lower mold M are removed. Then, a honeycomb sandwich structure in which the thermosetting resin 6 of the hardened CFRP 3A is directly bonded to both sides of the honeycomb core 2 can be obtained as the sandwich structure 1.

[0039] FIG. 3 is a diagram illustrating a modified example of the manufacturing method of the sandwich structure 1 according to the first embodiment of the present invention.

[0040] The two skins 3 sandwiching the honeycomb core 2 are not limited to being made of a single layer of CFRP 3A, but can also be made of multiple layers of CFRP 3A. Fig. 3 shows a manufacturing method for a sandwich structure 1 in which both sides of a honeycomb core 2 are sandwiched between multiple layers of CFRP 3A, but it is also possible to manufacture a sandwich structure 1 in which a skin 3 made of a single layer of CFRP 3A and a skin 3 made of multiple layers of CFRP 3A sandwich the honeycomb core 2.

[0041] Even when at least one of the skins 3 sandwiching the honeycomb core 2 is made of multiple layers of CFRP 3A, the sandwich structure 1 can be manufactured in the same manner as in the manufacturing method of the sandwich structure 1 in which both skins 3 sandwiching the honeycomb core 2 shown in FIG. 1 are made of a single layer of CFRP 3A, as shown in FIG. 3, by stacking on a lower mold M, one or more bottom prepregs 4 that have been given self-adhesiveness by reducing the VF (increasing the RC), the honeycomb core 2, and one or more top prepregs 4 that have been given self-adhesiveness by reducing the VF (increasing the RC), as well as the honeycomb core 2, in a process P11; heating the honeycomb core 2 in a low-pressure environment so as not to crush it to give fluidity to the thermosetting resin 6 contained in the top and bottom prepregs 4A to form fillets 7, and then curing each prepreg 4 in a process P12; and removing the sandwich structure 1 in which the honeycomb core 2 is sandwiched between the cured CFRP 3A in a process P13.

[0042] Even when at least one of the skins 3 sandwiching the honeycomb core 2 is composed of multiple layers of CFRP 3A, an adhesive film is not used because part of the thermosetting resin 6 that forms the matrix of the prepregs 4A, in which the VF is reduced to between 20% and 40% by volume while the RC is increased to the range of between 50% and 70% by mass, functions as an adhesive for the honeycomb core 2. In addition, by setting the thickness of each of the one or more prepregs 4 arranged on both sides of the honeycomb core 2 to 0.05 mm to 0.15 mm, it is possible to reduce the VF of the prepregs 4 while reducing the weight of the sandwich structure 1 even if the RC is increased.

[0043] Even if the thickness of the prepreg 4 itself is thin, increasing the number of laminated prepregs 4 increases the thickness and weight of the skin 3. For this reason, from the viewpoint of obtaining the effect of reducing the weight of the sandwich structure 1, it is appropriate to set the thickness of the skin 3 obtained by heat-curing one or more prepregs 4 arranged on both sides of the honeycomb core 2 to less than 1 mm so that the weight reduction effect of the adhesive layer such as the adhesive film becomes significant.

[0044] When at least one of the two skins 3 sandwiching the honeycomb core 2 is made of multiple layers of CFRP 3A, only the two prepregs 4A adjacent to the honeycomb core 2 form fillets 7 and are bonded to the honeycomb core 2. For this reason, only the prepregs 4A containing thermosetting resin 6 that are in direct contact with both sides of the honeycomb core 2 may be a self-adhesive prepreg having 20% ​​by volume to 40% by volume of VF and 50% by mass to 70% by mass of RC, and the other prepregs 4B containing uncured thermosetting resin 6 that are not in direct contact with the honeycomb core 2 may be a conventional prepreg having 40% by volume to 60% by volume of VF and 30% by mass to 50% by mass of RC.

[0045] That is, the prepreg 4B containing uncured thermosetting resin 6 that is not in direct contact with the honeycomb core 2 may be a conventional non-self-adhesive prepreg having a VF greater than 40 volume % and less than 60 volume % (RC greater than 30 mass % and less than 50 mass %).

[0046] In that case, although it is necessary to prepare two types of prepregs 4A, 4B with different VF and RC, this has the effect of reducing the weight of the sandwich structure 1 because it reduces the amount of thermosetting resin 6. Conversely, if the VF and RC of the prepregs 4A, 4B are the same, it is possible to manufacture the sandwich structure 1 in which the honeycomb core 2 is sandwiched between skins 3 having a desired thickness by laminating one type of prepreg. Therefore, when laminating the prepreg tape using an automated fiber placement (AFP) device, the configuration of the lamination head of the AFP device can be simplified.

[0047] The thickness of the prepregs 4A that are in direct contact with both sides of the honeycomb core 2 and the prepregs 4B that are not in direct contact with the honeycomb core 2 can be different, not limited to VF and RC. For example, the prepregs 4A that are in direct contact with both sides of the honeycomb core 2 can be thin layer materials with a thickness of 0.05 mm to 0.15 mm, while all or part of the prepregs 4B that are not in direct contact with the honeycomb core 2 can be thick layer materials with a thickness of 0.15 mm to 0.25 mm. The typical fiber basis weight of a thin layer material with a thickness of 0.05 mm to 0.15 mm is 50 g / m, as mentioned above. 2 From 100g / m 2 and a typical fibre weight for a thick layer material having a thickness of 0.15 to 0.25 mm is 150 to 250 g / m2.

[0048] Incidentally, the thickness of standard commercially available prepreg tapes is 0.2 mm to 0.8 mm, and although there are prepregs with thicknesses exceeding 0.25 mm, it is believed that in most cases, thick layer materials with thicknesses of 0.15 mm to 0.25 mm are used as prepregs to be used in combination with thin layer materials with thicknesses of 0.05 mm to 0.15 mm to produce small sandwich structures 1.

[0049] As a specific example, there are cases where the end of the honeycomb core 2 is chamfered, and in such cases, it is often necessary to make the thickness of the skin 3 covering the C-chamfered portion thicker than the other portions. In such cases, the thickness of the skin 3 can be ensured by increasing the number or thickness of the prepregs 4B that are not in direct contact with the honeycomb core 2.

[0050] (Sandwich structure) 1 or 3, a sandwich structure 1 having a structure shown in step P3 or step P13 is produced in which at least one layer of CFRP 3A is sandwiched on each side of a honeycomb core 2. Specifically, a sandwich structure 1 is obtained in which the thermosetting resin 6 is directly bonded to the honeycomb core 2 with a fillet 7 made of the thermosetting resin 6 formed on the honeycomb core 2 side of the CFRP 3A, without any other layer being interposed between the honeycomb core 2 and the thermosetting resin 6 serving as a matrix reinforced with carbon fibers 5 contained in the CFRP 3A.

[0051] Moreover, the CFRP 3A containing the thermosetting resin 6 in direct contact with at least both sides of the honeycomb core 2 is obtained by heat-curing the prepreg 4A in which the VF is reduced to a range of 20% by volume or more and 40% by volume or less, while the RC is increased 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 conversely, 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 can be obtained in which the VF of the CFRP 3A containing the thermosetting resin 6 in direct contact with both sides of the honeycomb core 2 is 20% by volume or more and 40% by volume or less.

[0052] Similarly, when prepreg 4A with a VF of 20 volume % or more and 35 volume % or less (RC of 55 mass % or more and 70 mass % or less) is cured to form CFRP3A, the VF of CFRP3A will be 20 volume % or more and 35 volume % or less, and when prepreg 4A with a VF of 20 volume % or more and 30 volume % or less (RC of 60 mass % or more and 70 mass % or less) is cured to form CFRP3A, the VF of CFRP3A will be 20 volume % or more and 30 volume % or less.

[0053] At least the thickness of each of the CFRP 3A layers arranged adjacent to each other on both sides of the honeycomb core 2 is 0.05 mm to 0.15 mm, and if the prepreg 4B that is not in direct contact with the honeycomb core 2 shown in Figure 3 is also made into a thin layer material having a thickness of 0.05 mm to 0.15 mm, like the prepregs 4A that are in direct contact with each side of the honeycomb core 2, a sandwich structure 1 is obtained in which the thickness of each of the single or multiple CFRP 3A layers arranged on each side of the honeycomb core 2 is 0.05 mm to 0.15 mm.

[0054] The thickness of the skins 3, each consisting of at least one or more CFRP 3A layers arranged on both sides of the honeycomb core 2, is less than 1 mm. The thickness of the entire sandwich structure 1 including the honeycomb core 2 and the skins 3 is approximately 2 mm to 25.4 mm.

[0055] (aircraft) FIG. 4 is a perspective view showing an example of an aircraft 10 including, as a structural material, the sandwich structure 1 manufactured by the manufacturing method shown in FIG. 1 or FIG.

[0056] 4 shows an example of an aircraft 10 including the sandwich structure 1 as a structural material, which is air mobility having a fuselage 11 equipped with multiple rotors 12. Small aircraft 10, which is representative of air mobility, are lighter in weight than large fixed-wing aircraft such as passenger planes, and therefore a sandwich structure 1 with a skin 3 having a thickness of less than 1 mm can be used as the structural material.

[0057] There are various types of air mobility, including electric aircraft such as electric vertical take-off and landing aircraft (eVTOL) and electric short take-off and landing aircraft (eSTOL), and rotorcraft such as helicopters and multicopters. Among air mobility, unmanned aerial vehicles (UAVs) such as helicopters and multicopters are called drones, while manned aircraft such as multicopters are sometimes called flying cars.

[0058] 4, in the case where a plurality of rotors 12 are connected to the fuselage 11 by arms 13, the arms 13 can be formed of the sandwich structure 1. Of course, the sandwich structure 1 can also be used as a structural member for other parts.

[0059] FIG. 5 is a cross-sectional view of the arm 13 of the aircraft 10 shown in FIG.

[0060] As shown in Fig. 5, the outer plate of a hollow pipe-shaped arm 13 can itself be made of a sandwich structure 1. As shown in Fig. 5, a sandwich structure 1 can also be manufactured in which a plurality of honeycomb cores 2 are sandwiched between a common skin 3. In this case, it is not necessary to make the surface of the lower mold M flat, and it can be made into the desired shape. Alternatively, a plurality of sandwich structures 1 can be manufactured and then joined together.

[0061] The space inside the arm 13 can be used for laying wiring, etc. Also, as described in the specification and drawings of Japanese Patent Application No. 2022-178242, a stringer may be fixed to the inside or outside of the arm 13, or a part of the outer plate of the arm 13 may be a simple panel or a panel reinforced with a stringer instead of being a sandwich structure 1.

[0062] (effect) The sandwich structure 1, manufacturing method for the sandwich structure 1, and aircraft 10 described above sandwich a honeycomb core 2 with CFRP 3A, which is easy to manufacture and obtain as a thin layer material, and reduce the VF of prepreg 4A for CFRP 3A while increasing the RC, so that the prepreg 4A can be directly bonded to the honeycomb core 2 with a practical adhesive strength without the need for an adhesive film or adhesive layer. Therefore, according to the sandwich structure 1, manufacturing method for the sandwich structure 1, and aircraft 10, it is possible to achieve further weight reduction, especially when a thin prepreg 4 with a thickness of 0.05 mm to 0.15 mm is used as the material for the skin 3.

[0063] FIG. 6 is a cross-sectional view of a conventional honeycomb sandwich structure 20.

[0064] In a conventional honeycomb sandwich structure 20, when it is desired to bond a skin 22 made of a honeycomb core 21 and a CFRP 22A with strong adhesive strength, the honeycomb core 21 and the CFRP 22A are bonded using an adhesive 23. Specifically, an adhesive film is placed between a prepreg for the conventional CFRP 22A, which has insufficient adhesiveness to the honeycomb core 21, and the honeycomb core 21, and the prepreg is then heat cured. In this case, a fillet 24 is formed by the adhesive 23. Therefore, it is essential to use an adhesive film that has excellent adhesiveness to the honeycomb core 21.

[0065] Incidentally, there are conventional prepregs for CFRP 22A that are sold with the claim that they have self-adhesive properties, but none actually have sufficient adhesive properties for the honeycomb core 21, and it has not yet become possible to omit the adhesive film or a layer that replaces the adhesive film. This is thought to be because, in order to adhere CFRP 22A to honeycomb core 21, it is necessary to form fillets 24, but conventional prepregs for CFRP 22A do not contain sufficient resin to form fillets 24.

[0066] Even if the CFRP 22A could be directly bonded to the honeycomb core 21 using a conventional prepreg, the amount of resin contained in the conventional prepreg is not determined based on the adhesion to the honeycomb core 21, which causes a problem of resin loss being induced in the skin 22. In other words, the resin that should be used to form the skin 22 is used to form the fillet 24, which leads to deterioration in the quality of the skin 22.

[0067] FIG. 7 is a graph illustrating the problems with the conventional honeycomb sandwich structure 20.

[0068] The vertical axis of the bar graph shown in Fig. 7 indicates the weight ratio (%) of the material constituting the conventional honeycomb sandwich structure 20. The standard weight per square meter of the adhesive film used in the conventional honeycomb sandwich structure 20 is 300 g / m 2 ~400g / m 2 In the case of a conventional thick-layer honeycomb sandwich structure 20 that is manufactured by laminating a large number of prepregs made of thick-layer materials as structural members for large aircraft such as passenger planes, as shown in the bar graph on the left, the weight ratio of the adhesive film is small and does not pose a problem.

[0069] As a concrete example, a material with a density of 1.6 g / cm 3 The two skins 22 are made of CFRP with a thickness of 2 mm and a density of 80 kg / m 3 The honeycomb core 21 with a thickness of 20 mm is sandwiched between the two, and the weight per square meter is 300 g / m 2 In the case of a thick honeycomb sandwich structure 20 in which skins 22 are bonded to both sides of a honeycomb core 21 with an adhesive film, the weight of the skin 22 per square meter Ws_thick is given by equation (1-1), the weight of the honeycomb core 21 per square meter Wh_thick is given by equation (1-2), and the weight of the adhesive film per square meter Wa_thick is given by equation (1-3). Ws_thick=100×100×0.2×1.6×2=6400g / m 2 ...Formula (1-1) Wh_thick=80×1000 / 100×2=1600g / m 2 ...Formula (1-2) Wa_thick=300×2=600g / m 2 ...Formula (1-3)

[0070] In this case, the weight ratio Ra_thick of the adhesive film is a small value as shown in formula (1-4), and the weight of the adhesive film does not account for a large proportion. Ra_thick=600 / (6400+1600+600)=7%...Formula (1-4)

[0071] On the other hand, in the case of a honeycomb sandwich structure 20 for a small aircraft such as air mobility, it is possible to use a skin 22 obtained by heat-curing 1 to 15 plies of thin-layer material with a thickness of 0.05 mm to 0.15 mm as a prepreg. In the case of such a thin-layer honeycomb sandwich structure 20 in which the skin 22 is light and thin, as shown in the bar graph on the right, the weight ratio of the adhesive film becomes large and cannot be ignored.

[0072] As a concrete example, a material with a density of 1.6 g / cm 3 The two skins 22 are made of CFRP with a thickness of 0.1 mm and a density of 80 kg / m 3 The honeycomb core 21 with a thickness of 5 mm is sandwiched between the two, and the weight per square meter is 300 g / m 2 In the case of a thin honeycomb sandwich structure 20 in which skins 22 are bonded to both sides of a honeycomb core 21 with an adhesive film, the weight of the skin 22 per square meter, Ws_thin, is given by equation (2-1), the weight of the honeycomb core 21 per square meter, Wh_thin, is given by equation (2-2), and the weight of the adhesive film per square meter, Wa_thin, is given by equation (2-3). Ws_thin=100×100×0.01×1.6×2=320g / m 2 ...Formula (2-1) Wh_thin=80×1000 / 100 / 2=400g / m 2 ...Formula (2-2) Wa_thin=300×2=600g / m 2 ...Formula (2-3)

[0073] In this case, the weight ratio Ra_thin of the adhesive film becomes large as shown in the formula (2-4), and the weight of the adhesive film occupies a large portion. Specifically, nearly half of the weight of the thin honeycomb sandwich structure 20 becomes adhesive. Ra_thin=600 / (320+400+600)=45%...Equation (2-4)

[0074] The adhesive film is not a structural member responsible for strength and rigidity, like the CFRP or honeycomb core 21. Therefore, if the weight of the adhesive film can be reduced, the weight of the thin honeycomb sandwich structure 20 can be reduced.

[0075] Therefore, in the case of a thin-layer honeycomb sandwich structure, as explained with reference to Fig. 1 and Fig. 3, the VF of the prepreg 4A is reduced, while the RC is increased, sacrificing some of the mechanical properties of the prepreg 4A, such as the specific strength and specific rigidity, but the prepreg 4A can be endowed with sufficient self-adhesiveness for bonding to the honeycomb core 2. As a result, the adhesive film is no longer necessary, and the weight of the thin-layer honeycomb sandwich structure can be reduced. That is, according to the manufacturing method of the sandwich structure 1 explained with reference to Fig. 1 and Fig. 3, by eliminating the need for an adhesive film, it is possible to obtain the lightest possible sandwich structure 1 when a thin-layer material having a thickness of 0.05 mm to 0.15 mm is used as the prepreg 4.

[0076] Therefore, by adopting the manufacturing method of the sandwich structure 1 described with reference to Figures 1 and 3, the weight reduction effect can be obtained for the sandwich structure 1 only when the sandwich structure 1 is a thin-layer honeycomb sandwich structure in which the plate thickness of the skin 3 is less than 1 mm, as described above.

[0077] Such a thin honeycomb sandwich structure can be used as a structural member of a small aircraft 10, such as a drone or a flying car, which is a representative example of air mobility. In particular, in the case of a secondary structure such as a fairing that is subjected to a relatively small load, the skin 3 of the sandwich structure 1 having the required strength may be manufactured by simply heat-curing a prepreg 4A made of one thin layer of material. In addition, in the case of an aircraft 10 of a size such as a drone, the sandwich structure 1 can also be used as a main structural member. Therefore, if the sandwich structure 1 is used as a structural member, it is expected that the weight of the small aircraft 10 can be dramatically reduced.

[0078] On the other hand, as the number of layers of prepregs 4B with a smaller VF (higher RC) increases, the weight of the thermosetting resin 6 increases, and the effect of reducing the weight of the sandwich structure 1 decreases, but the preparation and arrangement of an adhesive film that was previously required can be omitted. Therefore, even if the plate thickness of the skin 3 exceeds 1 mm, there is an advantage in that the manufacturing cost of the sandwich structure 1 can be reduced. This is also true when the prepregs 4, 4A, and 4B with a smaller VF (higher RC) are used as thick layer materials.

[0079] Second Embodiment FIG. 8 is a diagram illustrating a method for manufacturing a sandwich structure 1A according to the second embodiment of the present invention.

[0080] The manufacturing method of sandwich structure 1A in the second embodiment shown in Fig. 8 differs from the manufacturing method of sandwich structure 1 in the first embodiment in that one prepreg 4C constituting surface layer 30 of skin 3 is first cured or semi-cured, and then two prepregs 4A sandwiching honeycomb core 2 are cured. Other details of the manufacturing method of sandwich structure 1A in the second embodiment are not substantially different from the manufacturing method of sandwich structure 1 in the first embodiment, so the same or corresponding objects are denoted by the same reference numerals and description thereof will be omitted.

[0081] 8, in step P21, a sheet of prepreg 4C that will be the material for the CFRP 3A layer that forms one surface of the sandwich structure 1A without direct contact with the honeycomb core 2 is placed on a 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 that will be the material for the CFRP 3A layer that forms the outer surface of the panel on the lower mold M.

[0082] Next, in step P22, one sheet of prepreg 4C placed on lower mold M is heated under a high pressure environment of 3 to 8 atm to harden or semi-harden the prepreg 4C that forms surface layer 30. Note that semi-hardening of prepreg 4C refers to a heat treatment in which the viscosity of prepreg 4C is reduced to a level where the shape of prepreg 4C is not easily deformed, but the prepreg 4C is not hardened until it becomes completely solid.

[0083] Pressurization and heating of the prepreg 4C can be performed by bagging the prepreg 4C and using an autoclave device A. The 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.

[0084] In addition, in order to prevent the prepreg 4C from adhering to the bagging film B when the prepreg 4C is heated under a high-pressure environment, a sheet S is placed between the bagging film B and the prepreg 4C to enable the bagging film B to be easily peeled off after the prepreg 4C is cured or semi-cured.

[0085] It is necessary to laminate another prepreg 4A on top of the prepreg 4C in order to sandwich the honeycomb core 2 in the next step P23. Usually, when it is planned to laminate another uncured prepreg after curing the prepreg, a peel ply is placed between the prepreg to be cured first and the bagging film. The material of the peel ply is often polyester, which has the property of absorbing resin. Therefore, when the peel ply is peeled off after the prepreg is cured, the effect of sanding the cured prepreg is obtained. As a result, the surface of the cured prepreg is activated, and the adhesion between the prepreg and another uncured prepreg can be improved.

[0086] However, if prepreg 4C is a thin layer material with a thickness of 0.05 mm to 0.15 mm, it cannot withstand the pressure when peeling off the peel ply. In other words, if a thin layer material with a thickness of 0.05 mm to 0.15 mm is covered with a peel ply and an attempt is made to peel off the peel ply after the thin layer material has hardened, the thin layer material may be damaged.

[0087] Therefore, it is appropriate to use a release film that can be easily peeled off as the sheet S to be placed between the bagging film B and the prepreg 4C. As described above, the release film is an anti-adhesion film mainly made of fluororesin. In other words, it is appropriate to use an anti-adhesion release film as the sheet S to prevent the prepreg 4C from adhering to the bagging film B.

[0088] When the prepreg 4C is carried into the autoclave apparatus A in a bagged state and pressure is applied by the autoclave apparatus A, the differential pressure between the pressure in the autoclave apparatus A and the vacuum pressure can be applied to the prepreg 4C. Then, the prepreg 4C can be cured or semi-cured by heating it to a curing temperature or semi-curing temperature in the autoclave apparatus A. That is, by heating it under a pressure of 3 to 8 atmospheres using the autoclave apparatus A, only the surface layer 30 of the skin 3 can be cured or semi-cured first.

[0089] Next, in step P23, the honeycomb core 2 sandwiched between prepregs 4A, each having a VF reduced to a range of 20% by volume or more and 40% by volume or less and an RC increased to a range of 50% by mass or more and 70% by mass or less, is placed directly on the cured or semi-cured surface layer 30. That is, no other layers are placed between the surface layer 30 and the lower prepreg 4A. As described in the first embodiment, the honeycomb core 2 sandwiched between the two prepregs 4A is placed directly on the surface layer 30 with the uncured thermosetting resin 6 contained in the two prepregs 4A sandwiching the honeycomb core 2 in direct contact with the honeycomb core 2. For example, the lower prepreg 4A, the honeycomb core 2, and the upper prepreg 4A can be laminated in this order.

[0090] After the surface layer 30 is cured or semi-cured while covered with a release film, the surface of the surface layer 30 from which the release film is removed is not activated as it is after the peel ply is removed, but the prepreg 4A, which has been given self-adhesiveness by reducing the VF and increasing the RC, comes into direct contact with the surface layer 30. This makes it possible to adhere the prepreg 4A to the surface layer 30 without the need for an adhesive film or other layers to improve adhesion.

[0091] Next, in process P23, the honeycomb core 2 is heated in a low-pressure environment of 1 to 2 atmospheres so as not to crush the honeycomb core 2, thereby bonding the lower prepreg 4A sandwiching the honeycomb core 2 and the surface layer 30, forming a fillet 7 between the honeycomb core 2 and the prepreg 4A, and curing the uncured prepreg 4A.

[0092] That is, the thermosetting resin 6 contained in the two prepregs 4A sandwiching the honeycomb core 2 is heated and cured in a state in which the uncured thermosetting resin 6 contained in the two prepregs 4A is in direct contact with the honeycomb core 2 without interposing any other layer between the uncured thermosetting resin 6 contained in the two prepregs 4A and the honeycomb core 2. In addition, the thermosetting resin 6 contained in the lower prepreg 4A sandwiching the honeycomb core 2 is heated and cured in a state in which the uncured thermosetting resin 6 contained in the lower prepreg 4A is in direct contact with the surface layer 30 without interposing any other layer between the uncured thermosetting resin 6 contained in the lower prepreg 4A and the surface layer 30.

[0093] Furthermore, in the case where the surface layer 30 is semi-cured rather than completely cured in step P22, not only the uncured thermosetting resin 6 arranged on the surface layer 30 but also the surface layer 30 is subject to heat curing. In other words, when the surface layer 30 contains thermosetting resin 6 that is not completely cured, the thermosetting resin 6 contained in the surface layer 30 is also subject to heat curing.

[0094] As the heating device H for heating and curing the uncured thermosetting resin 6 under a pressure of 1 to 2 atmospheres, an autoclave device or an oven can be used as in the first embodiment. Furthermore, as described in the first embodiment, using an oven to treat the prepreg 4A as a prepreg for OoA leads to a reduction in the manufacturing cost of the sandwich structure 1A.

[0095] When the bonding and curing in step 24 is complete, in step P25, the sandwich structure 1A including the cured surface layer 30 as part of the skin 3 can be removed from the equipment and jig. The skin 3 consisting of two layers of CFRP 3A including the surface layer 30 cured under high pressure can be the outer surface side of the panel consisting of the sandwich structure 1A, while the skin 3 consisting of one layer of CFRP 3A cured under low pressure can be the inner surface side of the panel consisting of the sandwich structure 1A.

[0096] FIG. 9 is a diagram illustrating a modified example of the manufacturing method of the sandwich structure 1A according to the second embodiment of the present invention.

[0097] In the example shown in Fig. 8, the surface layer 30, which is first cured or semi-cured under high pressure, is composed of one prepreg 4C and one layer of CFRP 3A, but the surface layer 30 may be composed of multiple prepregs 4C and multiple layers of CFRP 3A as shown in Fig. 9. For example, the surface layer 30 can be formed by curing two or three prepregs 4C.

[0098] 9, the prepregs 4 sandwiching the honeycomb core 2 to be cured under low pressure the second time may also be multiple sheets per side. That is, after the surface layer 30 is cured or semi-cured in the autoclave A, the prepreg 4A that comes into direct contact with the honeycomb core 2 and the prepreg 4B that does not come into direct contact with the honeycomb core 2 may be cured under low pressure in the heating device H.

[0099] When the surface layer 30 is made of multiple layers of CFRP 3A, in step P31, multiple prepregs 4C including one prepreg 4C forming the surface of the sandwich structure 1A are laminated on a lower mold M. Then, in step P32, the laminate of multiple prepregs 4C is heated under a pressure of 3 to 8 atmospheres using an autoclave apparatus A. This causes the surface layer 30 made of multiple layers to harden or semi-harden.

[0100] In the subsequent process P33, a plurality of prepregs 4 can be laminated between the honeycomb core 2 and the surface layer 30. That is, the honeycomb core 2 sandwiched between two prepregs 4A can be placed on the cured or semi-cured surface layer 30 with another prepreg 4B interposed therebetween.

[0101] Then, in the next step P34, the uncured thermosetting resin 6 contained in all of the prepregs 4 can be heat cured in a state in which the uncured thermosetting resin 6 contained in the prepregs 4B adjacent to the surface layer 30 in the thickness direction is in direct contact with the surface layer 30, without interposing any other layer between the surface layer 30 and the uncured thermosetting resin 6 contained in the prepregs 4B adjacent to the surface layer 30 in the thickness direction. This makes it possible to manufacture a sandwich structure 1A in which the honeycomb core 2 is sandwiched on both sides by skins 3 each made of a plurality of layers of CFRP 3A, as shown in step P35.

[0102] In addition, the strength of the surface layer 30 can be improved by increasing the number of prepregs 4C forming the surface layer 30. When the strength of the surface layer 30 can be sufficiently ensured, it is possible to use a peel ply instead of a release film as the sheet S arranged between the bagging film B and the prepreg 4C. After the surface layer 30 consisting of multiple layers is cured or semi-cured while covered with the peel ply, the surface of the surface layer 30 from which the peel ply has been peeled off is in an activated state. Therefore, if the peel ply is used as the sheet S, the adhesiveness of the surface layer 30 can be improved compared to the case of using a release film.

[0103] Therefore, when using a peel ply as the sheet S, it is not essential to reduce the VF (increase the RC) of the prepreg 4B that will be in contact with the surface layer 30 after the peel ply is peeled off to impart self-adhesion; however, from the standpoint of obtaining even better adhesion to the surface layer 30 after the peel ply is peeled off, it is preferable to reduce the VF (increase the RC) and impart self-adhesion to at least the prepreg 4B that is in direct contact with the surface layer 30, as with the prepreg 4A that is in direct contact with the honeycomb core 2.

[0104] On the other hand, when a release film is used as the sheet S, it is appropriate to impart self-adhesiveness by reducing the VF (increasing the RC) of the prepreg 4B that comes into direct contact with the surface layer 30. That is, like the prepreg 4A that comes into direct contact with the honeycomb core 2, it is appropriate to use, as the prepreg 4B that comes into direct contact with the surface layer 30, a prepreg that has been given self-adhesiveness by reducing the VF (increasing the RC).

[0105] (effect) In the second embodiment described above, only the surface layer 30 of the sandwich structure 1A is cured or semi-cured under high pressure in advance, which makes it possible to improve the appearance of the sandwich structure 1A.

[0106] In the conventional honeycomb sandwich structure 20 described with reference to Figure 6, when the prepreg for forming the skin 22 is made of a thin layer material, in addition to the problem that the weight of the adhesive film cannot be ignored, there is also an appearance problem in that the marks of the honeycomb core 21 are visible on the surface of the honeycomb sandwich structure 20.

[0107] This is because, when the prepreg is heated and cured under pressure, pressure is transmitted to the prepreg from the plate-like parts constituting the hexagonal cells of the honeycomb core 21, but pressure is not transmitted to the prepreg from the hollow parts of the cells. In other words, the prepreg to which pressure is transmitted from the honeycomb core 21 cannot be pressed uniformly against the lower mold, resulting in a problem that slight irregularities occur on the surface of the cured skin 22, impairing the appearance.

[0108] Furthermore, in terms of appearance, there is a problem in that when the prepreg is heated and cured, the resin flows toward the honeycomb core 21, and countless resin defects appear on the outer surface of the cured skin 22.

[0109] In contrast, according to the second embodiment, only the surface layer 30 of the skin 3 is cured or semi-cured under high pressure without contacting the honeycomb core 2, so that the above-mentioned problems in appearance can be avoided. As a result, even when the thickness of the skin 3 is thin, such as 1 mm or less, a good appearance can be maintained. In other words, a thin-layer sandwich structure with high cosmetic appeal can be manufactured.

[0110] The thermosetting resin 6 contained in the prepreg 4C forming the surface layer 30 does not function as an adhesive between the contacting and separating prepregs 4, and is not used to form the fillets 7 for bonding to the honeycomb core 2. For this reason, it is not essential to use a prepreg having self-adhesiveness by reducing the VF and increasing the RC as the prepreg 4C forming the surface layer 30. However, using a prepreg having reduced VF and increased RC has the effect of preventing resin defects, which often occur in the portions where the carbon fibers 5 cross, and leads to an improvement in the appearance of the sandwich structure 1A.

[0111] (Third embodiment) FIG. 10 is a diagram illustrating a manufacturing method of a sandwich structure 1B according to the third embodiment of the present invention.

[0112] The manufacturing method of sandwich structure 1B in the third embodiment shown in Figure 10 differs from the manufacturing method of sandwich structure 1 in the first embodiment and the manufacturing method 1A of sandwich structure 1 in the second embodiment in that the core material sandwiched between skins 3 consisting of a single layer or multiple layers of CFRP 3A is a foam core 40 rather than a honeycomb core 2. As other details of the manufacturing method of sandwich structure 1B in the third embodiment are not substantially different from the manufacturing method of sandwich structure 1 in the first embodiment and the manufacturing method 1A of sandwich structure 1 in the second embodiment, the same or corresponding objects will be denoted with the same reference numerals and description thereof will be omitted.

[0113] 10, the core material sandwiched between skins 3 made of CFRP 3A is not limited to a honeycomb core 2, but may be a foam core 40. The foam core 40 is a foam used as the core material of the sandwich structure 1B. A specific example of the material for the foam core 40 is a foam based on PMI (polymethacrylimide), but foams of other materials may also be used.

[0114] The method of manufacturing the sandwich structure 1B in which at least one layer of CFRP 3A is sandwiched on each side of the foam core 40 can be performed in the same manner as the steps shown in Fig. 1, Fig. 2, Fig. 8, or Fig. 9. In the case where the surface layer 30 consisting of a plurality of prepregs 4C is cured first, as shown in Fig. 10, the sandwich structure 1B can be manufactured by laminating the surface layer 30 in step P41, curing or semi-curing the surface layer 30 under high pressure in step P42, additionally laminating the foam core 40 and the prepregs 4A and 4B sandwiching the foam core 40 in step P43, bonding the foam core 40 and the prepreg 4A in step P44, curing the prepreg 4C constituting the surface layer 30 and the prepregs 4A and 4B sandwiching the foam core 40 when the surface layer 30 is semi-cured, and removing the sandwich structure 1B in which the foam core 40 is sandwiched between the CFRP 3A in step P45.

[0115] When the core material is foam core 40, the fillet 7 formed when the core material is honeycomb core 2 is not formed, but part of the uncured thermosetting resin 6 on the foam core 40 side of prepreg 4A, which has been given fluidity by heating, penetrates into the voids in foam core 40. Then, with part of the thermosetting resin 6 in the voids in foam core 40, the thermosetting resin 6 can be heated and cured, thereby directly bonding the thermosetting resin 6 to the foam core 40.

[0116] Therefore, a sandwich structure 1B is produced in which the thermosetting resin 6 is directly bonded to the foam core 40 with a portion of the thermosetting resin 6 on the foam core 40 side of the CFRP 3A penetrating into the voids of the foam core 40.

[0117] When bonding the prepreg 4A to the foam core 40, it is necessary to heat the foam core 40 in a low-pressure environment of 1 to 2 atmospheres so as not to crush it, as in the case of bonding the prepreg 4A to the honeycomb core 2. Therefore, it is appropriate to use an autoclave or an oven as the heating device H used in step P44.

[0118] On the other hand, as with the manufacturing method of the sandwich structure 1 shown in Figures 1 and 2, it is also possible to produce the sandwich structure 1B without first curing or semi-curing the surface layer 30 under high pressure. However, if the surface layer 30 is first cured or semi-cured under a high pressure of 3 to 8 atmospheres using an autoclave apparatus A as shown in step P42 of Figure 10, the appearance of the sandwich structure 1B can be improved.

[0119] As described above, even when the core material is a foam core 40, the adhesive film or adhesive layer can be omitted by reducing the VF of the prepreg 4A to a range of 20% by volume or more and 40% by volume or less, while increasing the RC to a range of 50% by mass or more and 70% by mass or less to improve the adhesion with the foam core 40. As a result, when the prepreg 4A made of a thin layer material having a thickness of 0.05 mm to 0.15 mm is heat-cured to form the skin 3 of the sandwich structure 1B, the weight of the sandwich structure 1B can be reduced compared to a conventional sandwich structure in which FRP is bonded to a foam core through an adhesive film or adhesive layer. In addition, if the surface layer 30 is cured or semi-cured first under high pressure, the appearance of the sandwich structure 1B can be improved.

[0120] (Other embodiments) Although specific embodiments have been described above, the described embodiments are merely examples and do not limit the scope of the invention. The novel methods and apparatus described herein may be embodied in various other forms. In addition, various omissions, substitutions, and modifications may be made in the forms of the methods and apparatus described herein without departing from the spirit of the invention. The appended claims and their equivalents include such various forms and modifications as falling within the scope and spirit of the invention.

[0121] For example, in the above-described embodiments, the prepreg 4 and the honeycomb core 2 are pressurized by utilizing atmospheric pressure, but the prepreg 4 and the honeycomb core 2 may be pressurized by pressing the upper mold. In other words, the prepreg 4 and the honeycomb core 2 may be pressurized by using a press machine. [Explanation of symbols]

[0122] 1, 1A, 1B Sandwich structure 2. Honeycomb core 3. Skin 3A Carbon Fiber Reinforced Plastics (CFRP) 4, 4A, 4B, 4C Prepreg 5 Carbon Fiber 6 Thermosetting resin 7. Fillet 10 aircraft 11. Torso 12 Rotor 13 Arm 20 Conventional honeycomb sandwich structure 21 Honeycomb core 22 Skin 22A Carbon Fiber Reinforced Plastic (CFRP) 23 Adhesive 24 Fillet 30 Surface layer 40 Foam Core A Autoclave Equipment B Bagging Film H heating device M lower mold S Seat V Vacuum device

Claims

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

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

3. A method for manufacturing a sandwich structure in which at least one layer of carbon fiber reinforced plastic is sandwiched between a honeycomb core or a foam core, the method comprising the steps of: A prepreg having a thickness of 0.05 mm or more and 0.15 mm or less is used as the material of the carbon fiber reinforced plastic, A method for manufacturing a sandwich structure, in which the uncured thermosetting resin as a matrix reinforced with carbon fibers contained in the prepreg and the honeycomb core or foam core are directly contacted with each other while the thermosetting resin is heated and cured, without any other layer being interposed between the uncured thermosetting resin and the honeycomb core or foam core, thereby manufacturing a sandwich structure in which the thermosetting resin after curing is directly bonded to each other on both sides of the honeycomb core or foam core.

4. 4. The method for manufacturing a sandwich structure according to claim 3, wherein the prepregs containing the uncured thermosetting resin, which are in direct contact with both sides of the honeycomb core or foam core, respectively, have a fiber volume content of 20 volume % or more and 40 volume % or less.

5. A single prepreg or a laminate of multiple prepregs including the single prepreg, which is a material for a carbon fiber reinforced plastic layer that forms one surface of the sandwich structure without directly contacting the honeycomb core or foam core, is heated under pressure to harden or semi-harden a surface layer consisting of one or multiple layers, and then On the cured or semi-cured surface layer, the honeycomb core or foam core is sandwiched on both sides by prepregs containing the uncured thermosetting resin that are in direct contact with the honeycomb core or foam core, and the honeycomb core or foam core is placed directly or via other prepregs; 5. The method for manufacturing a sandwich structure according to claim 3 or 4, wherein the sandwich structure including the surface layer after curing is manufactured by heating and curing the surface layer in a semi-cured state and the uncured thermosetting resin arranged on the surface layer.

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

Images