Lattice structure and method for producing lattice structure

Abstract

To provide a lattice structure that enables weight reduction while having sufficient curved surface formability.SOLUTION: A lattice structure made of a material containing reinforcing fibers has a rectangular shape when viewed from a side face, and has a plurality of notches extending substantially parallel to a short side thereof in a comb-tooth manner, and has a plurality of comb-tooth-shaped plate-like members opened at one side or both sides of a long side by the notches, wherein the plurality of plate-like members are fitted to each other at the notches to cross each other to form fitting portions, and the plurality of plate-like members have, among all adjacent fitting portions, at least between some of the fitting portions, a region curved with the same or substantially the same curvature across a short side direction, or a region bent at the same or substantially the same angle across the short side direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a lattice structure having curved surface formability and a method for producing the same. [Background technology]

[0002] A honeycomb core is a planar assembly of numerous hollow, cylindrical cells separated by cell walls. The term "honeycomb core" refers not only to those with a hexagonal, close-packed structure, such as a beehive, but also to any assembly of regularly arranged, adjacent hollow cylindrical cells, with open surfaces at both the top and bottom (hereinafter referred to as "open end surfaces"). Honeycomb cores have excellent strength-to-weight ratios and planar accuracy (especially when used as honeycomb sandwich panels). Honeycomb cores made of materials containing reinforcing fibers are particularly lightweight. Similar to honeycomb cores made of other materials, these cores are manufactured using the so-called "corrugated" or "expanded" method. In the corrugated method, sheet-shaped base materials are corrugated, stacked, and the crests of the waves in the multiple base materials are glued together to form the honeycomb shape. In the stretching method, adhesive is applied in stripes at a fixed pitch to a sheet-like base material, and multiple base materials are overlapped so that the intervals between the applied adhesive are offset by half a pitch. After bonding and hardening, the honeycomb core is stretched in the overlapping direction to form a honeycomb shape. Honeycomb cores manufactured by these methods are often made into honeycomb sandwich panels, with flat plates bonded to both open end faces, and are used, for example, in aircraft engine covers, taking advantage of their high strength and high rigidity.

[0003] However, honeycomb cores manufactured by the above-mentioned manufacturing method have a problem of poor curved surface formability. When attempting to curve the above-mentioned honeycomb core from a flat plate shape into a quadratic curved surface such as a cylindrical shape, the planar cell walls generate forces that deform the cell walls themselves in the in-plane direction. However, the cell walls also suppress the deformation, making it difficult to bend along the curved surface. In other words, the planar shape of the cell walls generates forces that suppress the deformation of the honeycomb core, reducing the curved surface formability. Therefore, in order to improve the curved surface formability of the honeycomb core, it is effective to configure the cell walls in a bent or curved shape to allow the cell walls to deform. Furthermore, if the cell walls are bent or curved, the cell walls themselves are less likely to tilt when a compressive force is applied to the honeycomb core, which is thought to result in an increased compressive strength of the honeycomb core.

[0004] An example of this is disclosed in Patent Document 1. The honeycomb core described in Patent Document 1 is made up of an assembly of cells partitioned by bonded cell walls, and the cell walls between the bonded portions do not have a straight cross section, but have a shape that curves inward and outward from a straight line. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-329250 Summary of the Invention [Problem to be solved by the invention]

[0006] While Patent Document 1 provides technology related to honeycomb cores with high curved surface formability, there are significant challenges in actually manufacturing honeycomb cores using this technology. Patent Document 1 describes a process for forming a honeycomb core by stacking and bonding corrugated sheets with curved sections, followed by stretching. During this stretching process, the stacked corrugated sheets are pulled in the stacking direction, widening the gaps between the unbonded sections, creating the cellular structure of the honeycomb core, and the corrugated sheets form the cell walls. However, during this stretching process, the corrugated sheets are pulled in the stacking direction while also experiencing strong tensile forces in the longitudinal direction. As a result, the pre-established curved shape of the corrugated sheets collapses, resulting in a shape that is stretched longitudinally and nearly flat, making it difficult to fully achieve the desired curved surface formability. Another issue is that, because adjacent corrugated sheets are fixed together with adhesive, when compressive force is applied to the honeycomb core, the adhesive joints may peel off, potentially becoming the starting point for damage to the honeycomb core.

[0007] Therefore, an object of the present invention is to overcome the above-mentioned problems and to provide a lattice structure having high curved surface formability. [Means for solving the problem]

[0008] The technical means of the present invention to solve such problems are as follows. 1. A lattice structure comprising a plurality of comb-tooth plate-like members made of a material containing reinforcing fibers, rectangular in shape when viewed from the side, with a plurality of comb-tooth cutouts extending approximately parallel to the short sides of the member, and with one or both long sides opened by the cutouts, and in which the plurality of plate-like members intersect and fit together at the cutouts to form fitting portions, and in which the plurality of plate-like members have regions curved with the same or approximately the same curvature along the short side, or regions bent at the same or approximately the same angle along the short side, between at least some of the fitting portions among all adjacent fitting portions. 2. Furthermore, the second invention is characterized in that, in the lattice structure according to the first invention, the plate-like member has the curved or bent region between more than half of all adjacent fitting portions. 3. Furthermore, a third invention is characterized in that in the grid structure according to the first invention, the plate-like member has the curved or bent region between all adjacent fitting portions. 4. Furthermore, the fourth invention is characterized in that, in the lattice structure according to the second or third invention, when there is a curved or bent region between adjacent mating portions, the length along the surface of the long side of at least a portion of the mating portions is 120% or more and less than 200% of the shortest distance between the adjacent mating portions. 5. Furthermore, a fifth invention relates to a method for manufacturing a grid structure, and includes the steps of: preparing a plurality of comb-shaped plate-like members made of a material containing reinforcing fibers, having a rectangular shape when viewed from the side, having a plurality of comb-tooth-shaped cutouts extending approximately parallel to the short sides of the plate-like members, and having openings on one or both long sides via the cutouts; and wherein, between all adjacent cutouts, at least some of the cutouts have regions curved with the same or approximately the same curvature across the short side, or regions bent at the same or approximately the same angle in the short side direction; and fitting the plurality of plate-like members together so that they intersect with each other at the cutouts to form a grid structure. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain a lattice structure that is lightweight and has sufficient curved surface formability. [Brief explanation of the drawings]

[0010] [Figure 1] Top view (top) and side view (bottom) of comb-tooth-shaped plate-shaped member 1 [Figure 2] Top view of the grid structure 100 [Figure 3]FIG. 1 is a diagram showing a part of the plate-like member 1, illustrating a deformed state of a bent portion 2. [Figure 4] Several patterns of cell shapes of the grid structure 100 [Figure 5] Top view of grid structure 200 [Figure 6] Top view of grid structure 300 [Figure 7] Top view (top) and side view (bottom) of a plate-shaped member 1A made of CFRP [Figure 8] 1 is a perspective view showing a state in which a plurality of plate-like members 1A are arranged parallel to one another in a first step for manufacturing a grid structure 300. [Figure 9] 1 is a perspective view showing a state in which plate-like member 1B is fitted onto plate-like member 1A in a second step for manufacturing the grid structure 300, and the grid structure 300 is obtained. [Figure 10] 10 is a perspective view showing a state in which the plate-like members 2A and 2B are compressed against each other in a third step for manufacturing the grid structure 400. [Figure 11] Top view (top) and side view (bottom) of plate-shaped member 3A [Figure 12] 5 is a perspective view showing a state in which a plurality of plate-like members 3A are arranged parallel to one another in a first step for manufacturing the grid structure 500. [Figure 13] 10 is a perspective view showing a state in which plate-like member 3B is fitted to plate-like member 3A in a second step for manufacturing the grid structure 500, and the grid structure 500 is obtained. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a grid structure according to an embodiment will be described with reference to the drawings. Note that the following description exemplifies an embodiment of the invention, and the present invention should not be construed as being limited thereto. Various modifications are possible within the scope of the objects and effects of the present invention, and the description of these specific embodiments can also be understood as a description of the present invention as a general concept.

[0012] FIG. 1 shows a top view (upper view of FIG. 1) and a side view (lower view of FIG. 1) of a comb-shaped plate-like member that constitutes the grid structure of this embodiment. The plate-like member 1 is made of a material containing reinforcing fibers, has a rectangular shape in side view, and has multiple cutouts 1a extending in a direction approximately parallel to its short sides. These cutouts 1a open on one of its long sides (the upper edge side in the side view of FIG. 1), forming a comb-like shape (a single comb-like shape). The multiple cutouts 1a may also open on the lower edge side, forming a double comb-like shape. "Approximately parallel" here means that the angle between two sides, or two planes when viewed as a surface, is between 0° and 5°. Furthermore, the plate-like member 1 has, between at least some of the adjacent mating portions, a region (curved portion) that is curved with the same or approximately the same curvature along its short side, or a region (bent portion) that is bent at the same or approximately the same angle along its short side (shown in FIG. 1 as having a bent portion). Here, "approximately the same" means that even if the curvature or angle is not the same along the short side, the difference in curvature is within ±0.1 (1 / r) and the difference in angle is within 10°. A curved state refers to a state in which a surface is bent in an arc, while a bent state refers to a state in which a plane is bent without drawing an arc, which may also be called a refracted state. The curve or bend may be located anywhere between the mating portions of the plate-like member 1. It may also have a shape that combines both curvature and bend, such as a bent portion at one position and another bent portion between the adjacent bent portion. Furthermore, an object having a bent portion as part of a curved shape may be called a curved region, and an object having a bent portion as part of a curved shape may be called a bent region.

[0013] In this embodiment, the plate-shaped member 1 has a bent portion 2 between adjacent cutout portions 1a. In the top view of FIG. 1, the distance p between adjacent cutout portions 1a is constant, and the distance 2p between adjacent bent portions 2 is also constant. The distance 1 / 2p between a bent portion 2 and a cutout portion 1a adjacent to the bent portion 2 is also constant. The above distances, for both the cutout portion and the bent portion, are based on the center position in the long side direction of the plate-shaped member (starting point or ending point). This also applies to other embodiments described below. Furthermore, the plate-shaped member 1 is preferably made of a fiber-reinforced composite material with a resin matrix. This structure allows for a lightweight lattice structure with high compressive strength. The resin used as the matrix may be a thermoplastic resin or a thermosetting resin.

[0014] Examples of reinforcing fibers that can be used in the plate-like member 1 of the present invention include carbon fibers, glass fibers, aramid fibers, alumina fibers, silicon carbide fibers, boron fibers, metal fibers, natural fibers, and mineral fibers, and these may be used alone or in combination of two or more. Among these, PAN-based, pitch-based, and rayon-based carbon fibers are preferred from the viewpoint of their high specific strength and specific rigidity and lightweight effect, and carbon fiber reinforced composite materials with a resin matrix are suitable for use in aircraft, etc.

[0015] Examples of the thermoplastic resin include polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyolefins such as polyethylene, polypropylene, polybutylene, and modified polypropylene, polyamides such as polyoxymethylene, polyamide 6 and polyamide 66, polycarbonate, polymethyl methacrylate, polyvinyl chloride, polyarylene sulfides such as polyphenylene sulfide, polyphenylene ether, modified polyphenylene ether, polyimide, polyamideimide, polyetherimide, polysulfone, modified polysulfone, polyethersulfone, polyarylene ether ketones such as polyketone, polyether ketone, polyether ether ketone, and polyether ketone ketone, polyarylate, polyether nitrile, and phenoxy resin. These thermoplastic resins may also be copolymers, modified products, and / or blends of two or more types. Among these, a thermoplastic resin containing any one of polyarylene sulfide, polyetherimide, polyethersulfone, polysulfone, and polyarylene ether ketone is more preferable in terms of heat resistance and mechanical properties.

[0016] The thermosetting resin may be, for example, an unsaturated polyester resin, a vinyl ester resin, an epoxy resin, a phenolic resin, a urea resin, a melamine resin, a thermosetting polyimide resin, a BT resin, a cyanate ester resin, a bismaleimide resin, a benzoxazine resin, or a copolymer, modified product, or blend of two or more of these. Among these, a thermosetting resin containing any of an epoxy resin, a phenolic resin, a benzoxazine resin, a BT resin, a cyanate ester resin, a bismaleimide resin, or a polyimide resin is more preferred in terms of heat resistance and mechanical properties.

[0017] FIG. 2 is a top view of a lattice structure 100 according to the present invention. When the angle Φ between the u axis and the v axis is 90°, one plate-like member 1 in the lattice structure 100 is arranged with its long side parallel to the u axis and multiple members arranged parallel to the v axis at intervals p. The other plate-like member 1 is arranged with its long side parallel to the v axis and multiple members arranged parallel to the u axis at intervals p. One plate-like member 1 and the other plate-like member 1 have fitting portions 3 that intersect and fit together at cutout portions 1a. A portion of the plate-like member 1 (hereinafter referred to as the cell wall) sandwiched between adjacent fitting portions 3 has a bent portion 2 that is bent at the same angle along the short side of the plate-like member. In FIG. 3, the left side shows a cell wall with a bent portion, which is a portion of the plate-like members 1 arranged parallel to the u axis. When no external force is applied to the plate-shaped member 1, when both end faces in the short side direction (the upper and lower faces in Figure 3, referred to as the upper and lower faces, respectively) are viewed from the top or bottom, the angle formed by the two sides constituting the bent portion that are not parallel to the long side direction of the plate-shaped member 1 is the same, from the angle θa at the upper end face to the angle θb at the lower end face. Hereinafter, the angle formed by the two sides (if the bent portion is composed of three or more sides, the angle formed by any two adjacent sides) is referred to as the angle of bending, and the point at which this angle exists when viewed from the top or bottom is referred to as the apex of bending. When a force is applied to bend the plate-shaped member 1 along the v axis in a direction that closes the lower end faces on both sides of the bent portion inward, the maximum tensile stress occurs in the bent portion at the upper end face in the short side direction, and the maximum compressive stress occurs in the bent portion at the lower end face in each cell wall of the plate-shaped member 1. At this time, as shown on the right side of Figure 3, the angle of the bent portion 2 of the cell wall having the bent portion is no longer uniform along the short side direction, and a difference occurs between the angles θa and θb (hereinafter referred to as the difference in the bending angle), so that each cell wall having the bent portion of the plate-like member 1 can be bent around the apex of the bend along the v axis. Note that hereinafter, bending around the apex of the bend along the v axis will be expressed as "bending around the v axis," and the same applies to the other axes.

[0018] Furthermore, without applying the above-mentioned bending, it is preferable that the curvature of the curve at the curved portion is 0.01 (1 / r) or more and 1 (1 / r) or less, and the bending angle at the bent portion is 10° or more and 150° or less. By setting it in this range, the amount of expansion and contraction of the cell wall (here, expansion and contraction refers to the change in the length of the upper and lower end faces of the cell wall in the long side direction of the plate-like member 1 by bending about the above-mentioned axis center) is increased, improving the curved surface formability. On the other hand, if the curvature of the curve exceeds 1 (1 / r) or the bending angle is less than 10°, the amount of contraction of the cell wall is reduced, while if the curvature of the curve is less than 0.01 (1 / r) or the bending angle is more than 150°, the amount of expansion of the cell is reduced, making it difficult to obtain a curved surface formability.

[0019] Furthermore, as shown in FIG. 3, when a cell wall including a bent portion is bent, the angle of bending at its lower end surface becomes smaller, the length of the bent portion of the cell wall in the long side direction of the plate-like member 1 becomes shorter, and the distance from one end of the cell wall to the other becomes shorter. The same is true when the cell wall includes a curved portion. This increases the risk of adjacent cell walls interfering with each other. Therefore, it is preferable that the positions, curved shapes, and bent shapes of the curved and bent portions of the cell walls that make up one cell are positioned and shaped so that they do not interfere with each other when the cells (the area surrounded on all sides by the cell walls) expand and contract.

[0020] Furthermore, when a curved or bent region exists between adjacent mating portions, it is preferable that the length along the surface of the long side of at least a portion, more preferably all, of the mating portions has a ratio of 120% or more to less than 200% of the shortest distance between the adjacent mating portions. A plate-shaped member having the above-described length ratio can be obtained by providing the above-described curve or bend. The distance between the mating portions is measured based (starting or ending) on the center position of the mating portion in the long side direction of the plate-shaped member. When the above ratio is 120% or more, when the lattice structure is bent out of the plane of the uv plane formed by the u axis and v axis, the difference in the bending angle or curvature of the individual cell walls increases, as shown in FIG. 3, thereby increasing the maximum curvature of the lattice structure as a whole. On the other hand, when the above ratio is 200% or more, the maximum curvature of the plate-shaped member 1 can be increased, but the volume of the plate-shaped member 1 increases, which tends to increase the weight of the lattice structure. Furthermore, the ratio is more preferably 150% or more, and the upper limit is more preferably less than 170%.

[0021] In the grid structure of the present invention, at least one cell wall has the curved or bent region, and it is preferable that more than half of the cell walls have the curved or bent region, as in grid structure 100. With such a structure, more than half of the cell walls contribute to bending in the out-of-plane direction of the uv plane, so the maximum curvature when the grid structure is bent can be large. Furthermore, as will be described later as an example, it is also a preferred embodiment that all cell walls have the curved or bent region.

[0022] Furthermore, when viewed from the w direction shown in the figure, the lattice structure 100 is composed of cells 4a, 4b, 4c, and 4d, which are regions surrounded on all sides by cell walls (A, B, C, and D in Figure 4). Cell 4a cannot be bent around the v-axis or u-axis because none of the cell walls have a bent portion 2. On the other hand, cell 4b can be bent because the cell wall parallel to the u-axis has a bent portion. When a force is applied to bend cell 4b around the v-axis, the angle of bending is not uniform across the short side, so cell 4c can be bent around the u-axis. Similarly, cell 4d can be bent around either the u-axis or v-axis because all of the cell walls that make up the cell have bent portions. For this reason, when the lattice structure 100 is bent out of the plane of the uv plane, cell 4a does not contribute to the bending deformation, cell 4b and cell 4c contribute to the bending deformation centered on the v axis and the u axis, respectively, and cell 4d contributes to the bending deformation centered on both the u axis and the v axis.

[0023] 5 is a preferred embodiment of the lattice structure 200, in which all of the cells constituting the lattice structure 200 have regions in which all of the cell walls aligned parallel to the u axis are curved or bent, as in cell 4b. With this structure, when the lattice structure 200 is bent about the v axis, all of the cells contribute to the bending deformation, so that the maximum curvature when the lattice structure is bent about the v axis increases, improving the ability to form a curved surface.

[0024] 6 is also a preferred embodiment, in which all cells constituting the lattice structure are cells 4d, and all cell walls are curved. With this structure, all cells constituting the lattice structure can be deformed around both the u-axis and the v-axis, and all cells contribute to bending, improving the curved surface formability when bent around either the u-axis or the v-axis.

[0025] In the lattice structure of the present invention, it is preferable that at least one of the engaging portions 3 has a structure in which at least one plate-like member is compressed by the other plate-like member that intersects it, and the two plate-like members are gripped by each other.

[0026] Another suitable configuration is one in which the other plate-like member is compressed by the first plate-like member, thereby applying a mutual compressive force to increase the gripping force. Specifically, a cutout 1a in one plate-like member 1 compresses the other plate-like member 1 fitted into the cutout 1a from the out-of-plane direction of the other plate-like member 1. This fixes the plate-like members 1 together, maintaining the fixed cell walls in the vertical direction of the columnar cell structure. As shown in FIG. 2, the cell walls can be kept parallel to each other. Therefore, when a compressive force is applied in the vertical direction of the cell structure, the plate-like member 1 is less likely to buckle in the out-of-plane direction of the plate-like member 1. As a result, the compressive strength of the lattice structure is high. The compressive strength here refers to the compressive strength measured in accordance with ASTM C365 / C365M-22.

[0027] The manufacturing process of the grid structure in one embodiment will be described in detail below.

[0028] Here, we will explain the case of manufacturing a lattice structure 300 made of carbon fiber reinforced plastic (referred to as CFRP in this specification) using continuous carbon fibers, and formed by fitting together multiple plate-like members 1A in which all cell walls have bent portions, i.e., all cutout portions have bent portions. (First step) As shown in FIG. 7, a plurality of comb-tooth-shaped plate members 1A made of CFRP and having a plurality of bent portions 2 are prepared and arranged in parallel.

[0029] In the plate-like member 1A, the distance p between adjacent cutout portions 1a is constant, and the distance p between adjacent bent portions 2 is also constant. In addition, the distance 1 / 2p between a bent portion 2 and a cutout portion 1a adjacent to the bent portion 2 is also constant. In this case, the bent or curved portion is formed by corrugating or pressing. However, the processing method may be other than those described above.

[0030] Furthermore, the relationship between the width c of the cutout portion 1a and the plate thickness t of the plate-like member 1A may be either c>t or t≧c. If c>t, when multiple plate-like members 1 are used and the cutout portions 1a are fitted together, a so-called "loose fit" is achieved, making the fitting process easier. On the other hand, if t>c, one plate-like member is compressed by the other intersecting plate-like member at the fitting portion, resulting in a structure in which the two plate-like members are gripped by each other, improving the compressive strength of the lattice structure 300.

[0031] As shown in Figure 8, multiple plate-like members 1A are arranged in parallel with each other at intervals p in the v-axis direction perpendicular to the u-axis, with the openings of the cutout portions 1a facing upward and their long sides oriented parallel to the u-axis. (Second step) 9, a comb-shaped plate member 1 (hereinafter referred to as plate member 1B) made of the same material and having the same shape as plate member 1A is fitted into plate member 1A arranged in the first step with the openings of the cutouts 1a facing downward. Specifically, the cutouts 1a opening on the upper side of plate member 1A are aligned with the cutouts 1a opening on the lower side of plate member 1B and inserted into the cutouts 1a opening on the upper side of plate member 1A.

[0032] In this example, the intersection angle between the multiple plate-shaped members 1A and the multiple plate-shaped members 1B is a constant 90°, and as shown in Figure 9, the plate-shaped members 1B are arranged in parallel with their long sides oriented parallel to the v-axis and at intervals p in the u-axis direction.

[0033] In this way, the grid structure 300 shown in FIG. 9 is manufactured.

[0034] The CFRP constituting the plate-like member 1A can be molded by stacking the required number of layers (e.g., 8 to 24 layers) of prepregs containing continuous fibers in a mold so that the fiber direction differs between adjacent layers, heating them to approximately 120°C to 130°C under reduced pressure, and applying pressure (bonding) to harden them. For example, UD (uni-directional) material can be used as the prepreg. UD material refers to a material in which the fibers extend in only one direction.

[0035] Furthermore, a portion of the CFRP plate-shaped component 1A can be made into a cross-ply laminate, in which prepregs are laminated so that the fiber orientation is at an angle of 0° / 90°. More specifically, the CFRP can be made into a symmetrical cross-ply laminate, in which the laminate configuration is vertically symmetrical about the center plane or center line. For example, in the side view (bottom) of the plate-shaped component 1A shown in Figure 7, a laminate can be made in which layers with fibers oriented in the vertical direction (w-axis direction) and layers with fibers oriented in the horizontal direction (u-axis direction) are laminated in the thickness direction (v-axis direction). CFRP manufactured in this way is a material that is lower in density (i.e., lighter) than metal materials such as iron and aluminum, yet has high strength. It also has pseudo-isotropic properties.

[0036] Furthermore, the plate-like member constituting the grid structure may be a plate-like member 2A made of a sheet substrate of a reinforcing fiber mat made of discontinuous fibers impregnated with resin. The reinforcing fiber mat is impregnated with resin and in a compressed state, and springback occurs when the resin melts or softens, releasing the compressed state. This springback causes the thickness of the sheet substrate to expand several times, forming a porous structure made of resin-coated fibers.

[0037] As one embodiment, a first step and a third step for manufacturing a grid structure 400 made of plate-like members 2A will be described. The second step is the same as the second step for the grid structure 300, and therefore will not be described here.

[0038] The grid structure 400 shown in Figure 10 is formed by fitting together a plurality of plate-like members 2A in which all cell walls have bent portions, i.e., all cutout portions have bent portions, similar to the grid structure 300. (First step) A plurality of comb-shaped plate-like members 2A made of CFRP and having multiple bent portions are prepared and arranged in parallel. The positional relationship between the bent portions and cutout portions in the plate-like members 2A is the same as in the grid structure 300. In addition, to facilitate the fitting process (second step), the relationship between the width c of the cutout portions 1a and the plate thickness t1 of the plate-like members 2A is set to c>t1.

[0039] Similar to the lattice structure 300, the plate-like members 2A are arranged in parallel with each other at intervals p in the v-axis direction perpendicular to the u-axis, with the openings of the cutout portions 1a facing upward and their long sides oriented parallel to the u-axis. (Third step) As shown in Figure 10, in the second step, the mated structure is heated above its melting temperature for a certain period of time so that the resin impregnated in the sheet substrate melts or softens. The viscosity of the resin is controlled by the heating temperature, and the amount of springback of the reinforcing fibers is controlled by the heating time, so that the plate-like member has a desired thickness after expansion, t2 > c. In this heating step, the thickness of plate-like member 2A and plate-like member 2B (the plate-like members mated in the second step with the opening of cutout portion 1a of plate-like member 2A facing downward) becomes t2, and plate-like member 2A and plate-like member 2B, which are mated with each other at cutout portion 1a, are compressed by cutout portion 1a.

[0040] With this configuration, when a compressive force is applied to the lattice structure 400 from the short side direction of the plate-like members, the plate-like members are in a state of being gripped by each other, making the structure less likely to buckle.

[0041] Furthermore, the plate-like member may have curved portions instead of bent portions. As one embodiment, we will explain the case of manufacturing a grid structure 500 formed by fitting together a plurality of plate-like members 3A in which all cell walls have curved portions, i.e., plate-like members 3A having curved portions between all cutout portions. The manufacturing method for the grid structure 500 is similar to that for the grid structure 300, and Figures 7, 8, and 9 correspond to Figures 11, 12, and 13, respectively. The top view (upper) of the plate-like member 3A shown in Figure 11 is sinusoidal, and the spacing p of adjacent curved portions in the u-axis direction (the spacing p between the peaks and valleys of the sine wave) is constant. Furthermore, the spacing p between adjacent cutout portions 1a in the u-axis direction in the top view (upper) is also constant, and the distance 1 / 2p in the u-axis direction between a curved portion and a cutout portion 1a adjacent to the curved portion is also constant. Figures 12 and 13 are diagrams showing the (first step) and (second step) of the manufacturing method described above, respectively.

[0042] By constructing the lattice structure 500 in such a way that all cell walls are curved, the lattice structure generally exhibits improved curve-conforming ability compared to the lattice structure 300 when bent out of the plane of the u-axis-v plane defined by the u-axis and v-axis. High curve-conforming ability is defined as a state in which there is little gap between the lattice structure and the object when the lattice structure is fitted to the curved surface of the object. When a force is applied equally to the left and right sides to bend the lower end surfaces of the plate-like members 3A, which are arranged parallel to the u-axis direction and constitute the lattice structure 500, in a direction that closes inward (around the v-axis), maximum tensile stress is generated in the curved portion at the upper end surface in the short side direction of the plate-like member 3A, and maximum compressive stress is generated in the curved portion at the lower end surface. At this time, the lattice structure 500 bends globally at the curved portion, rather than locally at the bent portion as in the lattice structure 300, allowing for smoother bending compared to the lattice structure 300. To improve the curved surface conformability of a lattice structure with curved cell walls, such as the lattice structure 300, it is necessary to reduce the cell size and the spacing between the bent portions. However, this increases the weight of the lattice structure. On the other hand, when the cell walls have curved portions rather than curved portions, as in the lattice structure 500, it is easier to improve the curved surface conformability of the structure, thereby reducing the weight of the lattice structure. Furthermore, if the curved surface conformability of the lattice structure is low, when flat plates are bonded to both open end faces of the lattice structure to form a honeycomb sandwich, gaps may form between the flat plates and the lattice structure, which may become the starting point for delamination. Therefore, curved surface conformability is an important characteristic in the process of forming a honeycomb sandwich. On the other hand, when the lattice structure is bent locally with a large curvature, it is effective to have bent portions in the cell walls. 3, when a plate-like member having a bent portion is bent about the v-axis, the ratio of the angle of bending between the upper end face and the lower end face is generally larger than the ratio of the curvature between the upper end face and the lower end face when a plate-like member having a curved portion is bent. Therefore, the grid structure 300 having a bent portion in every cell has a larger maximum curvature when the grid structure is bent in the out-of-plane direction of the uv plane than the grid structure 500 having a curved portion in every cell.

[0043] That is, a lattice structure having both bent portions and curved portions, and in which the bent portions and curved portions are arranged in accordance with the final shape of the lattice structure, is also a preferred embodiment. [Explanation of symbols]

[0044] 1a: Notch portion of plate-like member 1: Plate-shaped member 2: Bend 3: Fitting part u, v, w: coordinate axes Φ: angle between u-axis and v-axis θa: Angle of bending at the top end surface in the short side direction of the plate-like member 1 θb: Angle of bending at the bottom end surface in the short side direction of the plate-like member 1 4a, 4b, 4c, 4d: Cell 1A: A plate-like member including CFRP and having a bent portion with the opening of the notch portion 1a facing upward 1B: A plate-like member including CFRP and having a bent portion with the opening of the cutout portion 1a facing downward 2A: A plate-like member having a bent portion, containing discontinuous fibers, with the opening of the notch portion 1a facing upward. 2B: A plate-like member having a bent portion, containing discontinuous fibers, with the opening of the notch portion 1a facing downward 3A: Plate-like member having a curved portion with the opening of the notch portion 1a facing upward c: Width of the notch 1a t, t1, t2: Plate thickness of plate-shaped member 100: Lattice structure 200: A lattice structure in which all cells are composed of cells 4b 300: A lattice structure in which all cells are composed of cell 4d 400: A lattice structure composed of plate-like members 2A and 2B 500: A lattice structure composed of plate-like members 3A and 3B

Claims

1. The plate-like member is made of a material containing reinforcing fibers, has a rectangular shape when viewed from the side, has a plurality of comb-tooth-shaped cutout portions extending approximately parallel to the short sides of the plate-like member, and is open on one or both long sides by the cutout portions. A lattice structure in which the plurality of plate-like members intersect with each other at the cutout portions and fit together to form fitting portions, A lattice-like structure in which the plurality of plate-like members have, between at least some of the adjacent fitting portions, regions curved with the same or approximately the same curvature along their short sides, or regions bent at the same or approximately the same angle along their short sides.

2. The grid structure according to claim 1 , wherein the plate-like member has the curved or bent region between at least half of all the adjacent fitting portions.

3. The grid structure according to claim 1 , wherein the plate-like member has the curved or bent region between all adjacent mating portions.

4. 4. The grid structure according to claim 2 or 3, wherein, when there is a curved or bent region between adjacent fitting portions, the length along the surface of the long side of at least a part of the space between the fitting portions is 120% or more and less than 200% of the shortest distance between the adjacent fitting portions.

5. a step of preparing a plurality of comb-shaped plate-like members made of a material containing reinforcing fibers, each having a rectangular shape when viewed from the side, a plurality of comb-shaped cutouts extending substantially parallel to its short sides, and one or both long sides being opened by the cutouts, wherein at least some of the cutouts between all adjacent cutouts have regions curved with the same or substantially the same curvature in the short side direction, or regions bent at the same or substantially the same angle in the short side direction; a step of fitting the plurality of plate-like members together so that they intersect with each other at the cutout portions to form a grid structure; A method for manufacturing a grid-like structure, comprising:

Images