Steel plate-fiber-reinforced plastic composites, and automotive components

Abstract

To provide a steel fiber reinforced plastic composite that improves mechanical properties and reduces the volume of carbon fiber reinforced plastic (CFRP). [Solution] A steel plate fiber-reinforced plastic composite comprising a steel plate and a rib-shaped fiber-reinforced plastic laminate having a smaller area than the steel plate, wherein the fiber-reinforced plastic laminate is made up of alternating layers of fiber-reinforced plastic containing CFRP and fibers other than carbon fiber, and the volume of CFRP is 70% or less and the maximum bending stiffness is 80% or more compared to the target composite. The target composite comprises a target steel plate and a target fiber-reinforced plastic laminate having the same area as the target steel plate and consisting only of CFRP, wherein the target steel plate is made of the same material, has the same area and the same thickness as the steel plate, and the CFRP in the target fiber-reinforced plastic laminate is made of the same material as the CFRP in the steel plate fiber-reinforced plastic composite and has a thickness of 1.0 mm.

Description

[Technical Field]

[0001] This disclosure relates to steel plate-fiber-reinforced plastic composites and automotive components. [Background technology]

[0002] In the automotive sector, there is a demand for both lightweight components and safe crash performance. For example, high-strength steel plates, high-strength aluminum alloys, and composites of steel plates and fiber-reinforced plastics are being developed. In steel plate-fiber-reinforced plastic composites, technologies have been developed to bond lightweight materials such as carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) to steel plates.

[0003] For example, Patent Document 1 discloses a steel plate-fiber-reinforced resin composite comprising: a steel plate member made of a steel plate or a molded body of the steel plate; a first resin layer located on at least a part of the surface of the steel plate member and mainly composed of resin compositions of two different materials; and a second resin layer located on at least a part of the surface of the first resin layer and composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, wherein the resin composition of the first resin layer contains phenoxy resin and polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:20; and in elastic modulus phase image images obtained by observing the resin composition with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of locations forming a phase separation structure due to the phenoxy resin and polyester elastomer is 1 area % or less of the total observed area.

[0004] Furthermore, Patent Document 2 discloses an isogrid panel structure comprising cutting a pipe into multiple pipes (step S1), and joining the multiple pipes to an outer plate (step S2) such that ribs reinforcing the outer plate are formed from the multiple pipes.

[0005] Patent Document 3 also discloses a three-dimensional fiber-reinforced resin molded body comprising a matrix resin which is a thermoplastic resin and reinforcing fibers impregnated with the matrix resin, wherein a prepreg made of a sheet-like fiber-reinforced resin is compression-molded, and the molded body has at least a flat plate-like portion and a plurality of cylindrical portions provided substantially perpendicular to the plate-like portion, wherein the plurality of cylindrical portions have portions to which the cylindrical portions are connected, and the reinforcing fibers are filled from the bottom to the tip of the plate-like portion. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2022 / 014587 [Patent Document 2] Japanese Patent Publication No. 2015-127121 [Patent Document 3] Japanese Patent Publication No. 2023-143202 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Traditionally, laminates consisting of steel plates and carbon fiber reinforced plastic (CFRP) have been used. However, there is a need for further improvement in the bending rigidity of these laminates, as well as further cost reduction, specifically a reduction in the amount of CFRP used.

[0008] In contrast, the present disclosure aims to provide a steel plate-fiber-reinforced plastic composite that can improve the mechanical properties of the composite and reduce the volume of carbon fiber-reinforced plastic (CFRP), and an automotive component comprising the steel plate-fiber-reinforced plastic composite. [Means for solving the problem]

[0009] The means for solving the problem include the following aspects: <1> Steel plate and, The steel plate comprises one or more rib-shaped fiber-reinforced plastic laminates that protrude from the steel plate in the thickness direction, have an area smaller than that of the steel plate in a direction perpendicular to the thickness direction, and are bonded to the steel plate. The fiber-reinforced plastic laminate is formed by alternately laminating one or more layers of carbon fiber-reinforced plastic and one or more layers of fiber-reinforced plastic containing fibers other than carbon fibers in the thickness direction. Steel plate-fiber-reinforced plastic composite. <2> The fiber-reinforced plastic laminate is a fiber-reinforced plastic in which the fiber-reinforced plastic containing fibers other than carbon fibers is glass fiber-reinforced plastic. <1> The steel plate-fiber-reinforced plastic composite described above. <3> The fiber-reinforced plastic laminate has a layer located closest to the steel plate that is the glass fiber-reinforced plastic layer. <2> The steel plate-fiber-reinforced plastic composite described above. <4> Between the steel plate and the fiber-reinforced plastic laminate, there is a layer of glass fiber-reinforced plastic with an area larger than that of the fiber-reinforced plastic laminate, and the fiber-reinforced plastic laminate is bonded to the steel plate via the glass fiber-reinforced plastic layer. <2> or <3> The steel plate-fiber-reinforced plastic composite described above. <5> The fiber-reinforced plastic laminate has a four-layer structure in which layers of glass fiber-reinforced plastic and layers of carbon fiber-reinforced plastic are alternately laminated. <2> ~ <4> A steel plate-fiber-reinforced plastic composite as described in any one of the items. <6> The fiber-reinforced plastic laminate has a five-layer structure in which layers of glass fiber-reinforced plastic and layers of carbon fiber-reinforced plastic are alternately laminated. <2> ~ <4> A steel plate-fiber-reinforced plastic composite as described in any one of the items. <7> The fiber reinforced plastic laminate is the steel plate-fiber reinforced plastic composite according to <6>, wherein the central position in the lamination direction of the fiber reinforced plastic laminate exists in the middle layer of the five-layer structure. <8> The fiber reinforced plastic laminate is the steel plate-fiber reinforced plastic composite according to any one of <2> to <4>, having a structure of six or more layers in which the layers of the glass fiber reinforced plastic and the layers of the carbon fiber reinforced plastic are alternately laminated. <9> The fiber reinforced plastic laminate is the steel plate-fiber reinforced plastic composite according to any one of <2> to <4>, having a two-layer structure in which the layers of the glass fiber reinforced plastic and the layers of the carbon fiber reinforced plastic are alternately laminated. <10> The fiber reinforced plastic laminate is the steel plate-fiber reinforced plastic composite according to any one of <2> to <4>, having a three-layer structure in which the layers of the glass fiber reinforced plastic and the layers of the carbon fiber reinforced plastic are alternately laminated. <11> Having a plurality of rib-shaped fiber reinforced plastic laminates Having a support between the plurality of fiber reinforced plastic laminates The steel plate-fiber reinforced plastic composite according to any one of <1> to <10>. <12> The steel plate-fiber reinforced plastic composite according to any one of <1> to <11>, having another steel plate on the side of the fiber reinforced plastic laminate opposite to the steel plate. <13> For the following target composite, the volume of the carbon fiber reinforced plastic is 70% or less For the following target composite, the maximum bending rigidity is 80% or more The steel plate-fiber reinforced plastic composite according to any one of <1> to <12>. -Target composite- The target composite comprises a target steel plate and a single target fiber-reinforced plastic laminate bonded to the target steel plate, having the same area in a direction perpendicular to the thickness direction of the target steel plate as the target steel plate, and consisting solely of carbon fiber-reinforced plastic. The aforementioned steel plate is a steel plate of the same material, same area, and same thickness as the steel plate in the steel plate-fiber-reinforced plastic composite. The above-mentioned fiber-reinforced plastic laminate represents a laminate in which the carbon fiber-reinforced plastic is made of the same material as the carbon fiber-reinforced plastic in the steel plate-fiber-reinforced plastic composite, and has a thickness of 1.0 mm. <14> For the target composite described below, the volume of the carbon fiber reinforced plastic is less than 100%, For the composite materials listed below, the maximum bending stiffness is 100% or more. <1> ~ <12> A steel plate-fiber-reinforced plastic composite as described in any one of the items. -Target Complex- The target composite comprises a target steel plate and a single target fiber-reinforced plastic laminate bonded to the target steel plate, having the same area in a direction perpendicular to the thickness direction of the target steel plate as the target steel plate, and consisting solely of carbon fiber-reinforced plastic. The aforementioned steel plate is a steel plate of the same material, same area, and same thickness as the steel plate in the steel plate-fiber-reinforced plastic composite. The above-mentioned fiber-reinforced plastic laminate represents a laminate in which the carbon fiber-reinforced plastic is made of the same material as the carbon fiber-reinforced plastic in the steel plate-fiber-reinforced plastic composite, and has a thickness of 1.0 mm. <15> The aforementioned fiber-reinforced plastic laminate is The ratio of the thickness of the target composite to the target fiber-reinforced plastic laminate is 1.4 or more and 1.8 or less. Furthermore, the ratio of the volume of the carbon fiber reinforced plastic to the volume of the fiber reinforced plastic laminate is 0.5 or more and 0.6 or less. <13> The steel plate-fiber-reinforced plastic composite described above. <16> The fiber-reinforced plastic laminate has a thickness ratio of 1.4 or more and 1.9 or less with respect to the target fiber-reinforced plastic laminate in the target composite. Furthermore, the ratio of the volume of the carbon fiber reinforced plastic to the volume of the fiber reinforced plastic laminate is 0.3 or more and 0.9 or less. <14> The steel plate-fiber-reinforced plastic composite described above. <17> <1> ~ <16> An automotive component comprising a steel plate-fiber-reinforced plastic composite as described in any one of the items. [Effects of the Invention]

[0010] According to this disclosure, a steel plate-fiber-reinforced plastic composite that can improve the mechanical properties of the composite and reduce the volume of carbon fiber-reinforced plastic (CFRP), and an automotive component comprising the steel plate-fiber-reinforced plastic composite can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the first embodiment. [Figure 2] This is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to the first embodiment. [Figure 3] This is a schematic side view showing a conventional steel-fiber-reinforced plastic composite. [Figure 4] This is a schematic perspective view showing a steel sheet fiber-reinforced plastic composite according to a second embodiment. [Figure 5] This is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to a third embodiment. [Figure 6] This is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to the fourth embodiment. [Figure 7] This is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to the fifth embodiment. [Figure 8] This is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to the sixth embodiment. [Figure 9]This is a schematic perspective view showing a steel sheet fiber-reinforced plastic composite according to the seventh embodiment. [Figure 10] This is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to the eighth embodiment. [Figure 11] This is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to the ninth embodiment. [Figure 12] This is a schematic side view showing a steel sheet fiber-reinforced plastic composite according to an embodiment of the present disclosure, comprising a support. [Figure 13] This graph shows the relationship between the plastic equivalent strain and stress of the steel plate in Example 1. [Figure 14] This is a schematic perspective view illustrating the method of a three-point bending test. [Figure 15] This graph compares the calculation results showing the relationship between load and stroke obtained by simulation in Example 1 with the test results showing the relationship between load and stroke obtained by a three-point bending test. [Modes for carrying out the invention]

[0012] An example of an embodiment of this disclosure will be described. In this specification, a numerical range represented by "~" means a range that includes the numbers before and after "~" as lower and upper limits, unless those numbers are preceded by "greater than" or "less than". If the numbers before and after "~" are preceded by "greater than" or "less than", the numerical range means a range that does not include those numbers as lower or upper limits. In the numerical ranges described stepwise in this specification, the upper limit of one stepwise numerical range may be replaced with the upper limit of another stepwise numerical range, or with the values ​​shown in the examples. Similarly, the lower limit of one stepwise numerical range may be replaced with the lower limit of another stepwise numerical range, or with the values ​​shown in the examples. Furthermore, unless otherwise specified, the percentage (%) used for content refers to "mass%". A percentage of "0" indicates that the component is optional and does not need to be included.

[0013] <Steel plate-fiber-reinforced plastic composite> A steel plate-fiber-reinforced plastic composite according to an embodiment of this disclosure (also referred to herein as "steel plate fiber-reinforced plastic composite," and hereinafter simply as "composite") comprises a steel plate and a fiber-reinforced plastic laminate (hereinafter simply as "laminated"). The laminate protrudes from the steel plate in the thickness direction of the steel plate, has a smaller area in the direction perpendicular to the thickness direction than the steel plate, and is bonded to the steel plate. The laminate has a rib shape and one or more are provided. A fiber-reinforced plastic laminate is formed by alternately laminating one or more layers of carbon fiber reinforced plastic (CFRP) and one or more layers of fiber-reinforced plastic (FRP) containing fibers other than carbon fibers in the thickness direction. In the steel fiber-reinforced plastic composite according to the embodiments of this disclosure, the above configuration is essential (hereinafter referred to as the "essential configuration of this disclosure"). The following description will focus on preferred embodiments.

[0014] In the steel fiber reinforced plastic composite according to the first embodiment of this disclosure, it is preferable that the following conditions (1A) and (1B) are met, from the viewpoint of balancing two fundamentally conflicting issues: improving the mechanical properties of the composite while reducing the amount (i.e., volume) of carbon fiber reinforced plastic used. (1A) The volume of carbon fiber reinforced plastic is 70% or less of the target composite. (1B) For the target composite, the maximum bending stiffness is 80% or more.

[0015] In the steel fiber reinforced plastic composite according to the second embodiment of this disclosure, it is preferable that the following conditions (2A) and (2B) are met, from the viewpoint of further improving the mechanical properties of the composite while minimizing the reduction in the amount (i.e., volume) of carbon fiber reinforced plastic used. (2A) The volume of carbon fiber reinforced plastic is less than 100% of the target composite. (2B) For the target composite, the maximum bending stiffness is 100% or more.

[0016] In this disclosure, "rib shape" refers to a shape that extends perpendicular to a plane perpendicular to the thickness direction of the steel plate. In this disclosure, "area of ​​steel plate and fiber-reinforced plastic laminate" refers to the area in the direction perpendicular to the thickness direction of the steel plate. That is, the area of ​​the laminate in the direction perpendicular to the thickness direction is the projected area of ​​the laminate in the direction perpendicular to the thickness direction when the rib-shaped laminate is viewed from the thickness direction (from the side where the laminate protrudes in the thickness direction of the steel plate). Furthermore, the area of ​​the steel plate in the direction perpendicular to the thickness direction is the projected area of ​​the steel plate that includes both the areas where the laminate is present and the areas where it is not present when the steel plate is viewed from the thickness direction (from the side where the laminate protrudes in the thickness direction of the steel plate).

[0017] Traditionally, laminates consisting of steel plates and carbon fiber reinforced plastic (CFRP) have been used. For example, in the automotive sector, the demand for weight reduction has been rapidly increasing in recent years, and the development of materials that can balance weight reduction with automotive safety is progressing. Bending stiffness is a representative material property related to automotive safety. Therefore, by reducing the proportion of steel plates, which have a large mass, and combining them with lightweight CFRP, it is being considered that both weight reduction and high bending stiffness can be achieved. The bending stiffness of a material is greatly affected by the thickness of the material, and the thicker the material, the greater the improvement in the second moment of area, which can lead to improved bending stiffness. Therefore, in laminates of steel plates and CFRP, increasing the thickness of the lightweight CFRP is effective in further improving bending stiffness.

[0018] Here, Figure 3 shows the lamination structure of a conventional laminate. The conventional laminate shown in Figure 3 has a steel plate 102 and a CFRP layer C101. In other words, the conventional laminate shown in Figure 3 has the same lamination structure as the target composite. However, further improvement in bending rigidity is required for the laminate. Furthermore, further cost reduction is also required for the laminate, and from this perspective, a reduction in the amount of CFRP used is also required. However, achieving a reduction in material usage while maintaining mechanical properties is not easy with the lamination structure of conventional laminates.

[0019] In contrast, the composites according to the first and second embodiments of the present disclosure, which are preferred embodiments of the present disclosure (hereinafter, when referring to both the composites according to the first and second embodiments of the present disclosure, they will simply be referred to as "the composites of the present disclosure") use, in addition to steel plates and carbon fiber reinforced plastics (CFRP) of the same material as the target composite, which is an example of a conventional composite, fiber reinforced plastics (other FRPs) containing fibers other than carbon fibers. Furthermore, the composites of the present disclosure have a fiber reinforced plastic laminate with a smaller area than the steel plate, a rib shape (a shape extending perpendicular to the plane perpendicular to the thickness direction of the steel plate), and are provided so as to protrude in the thickness direction from the steel plate. In addition, the fiber reinforced plastic laminate has a configuration in which one or more layers of CFRP and one or more layers of other FRP are alternately laminated.

[0020] The inventors have found that in a composite in which this rib-shaped laminate is provided on a steel plate, by further controlling the thickness of the laminate, it is possible to improve the mechanical properties of the composite while reducing the amount (i.e., volume) of carbon fiber reinforced plastic used compared to the target composite. Furthermore, they have found that by controlling the thickness of the laminate, the mass of the composite can be made lighter compared to the target composite.

[0021] In other words, the composite of this disclosure improves the mechanical properties of the composite (specifically, its bending stiffness) and reduces the volume of carbon fiber reinforced plastic (CFRP) compared to the composite of the subject.

[0022] -Target Complex- The target composite comprises a target steel plate and a single target fiber-reinforced plastic laminate whose area in a direction perpendicular to the thickness direction of the target steel plate is the same as that of the target steel plate, and which is made only of carbon fiber-reinforced plastic. The aforementioned steel plate is a steel plate of the same material, same area, and same thickness as the steel plate in the steel plate-fiber-reinforced plastic composite. The above-mentioned fiber-reinforced plastic laminate represents a laminate in which the carbon fiber-reinforced plastic is made of the same material as the carbon fiber-reinforced plastic in the steel plate-fiber-reinforced plastic composite, and has a thickness of 1.0 mm.

[0023] -Definition of the target complex- Here, we will explain the target complex. The target composite comprises a target steel plate and a single target fiber-reinforced plastic laminate, the area of ​​which in a direction perpendicular to the thickness direction of the target steel plate is the same as that of the target steel plate, and which consists only of carbon fiber-reinforced plastic. The target steel plate is a steel plate of the same material, same area, and same thickness as the steel plate in the steel plate-fiber-reinforced plastic composite, and the carbon fiber-reinforced plastic in the target fiber-reinforced plastic laminate is of the same material as the carbon fiber-reinforced plastic in the steel plate-fiber-reinforced plastic composite, and has a thickness of 1.0 mm.

[0024] The statement that the target steel plate and the steel plate in the composite have the same thickness means that, with respect to the thickness determined by the method described later, the thickness of the target steel plate and the thickness of the steel plate in the composite are equal. The statement that the target steel plate and the steel plate in the composite have the same area means that the area viewed from the thickness direction is equal, and specifically, the target steel plate used is one whose shape (contour) viewed from the thickness direction is the same as that of the steel plate in the composite.

[0025] The carbon fiber reinforced plastic used in the target fiber-reinforced plastic laminate is the same material as the carbon fiber reinforced plastic used in the steel plate-fiber-reinforced plastic composite. If the steel plate-fiber-reinforced plastic composite consists of multiple steel plate-fiber-reinforced plastic composites (CFRPs), and different materials of CFRP are used in those multiple CFRPs, then each CFRP will be designated as a target composite, each comprising its own target fiber-reinforced plastic laminate. In other words, there are as many target composites as there are CFRPs of different materials.

[0026] Furthermore, if the composite of the present disclosure has another steel plate on the opposite side of the steel plate of the fiber-reinforced plastic laminate, the target composite will also be defined as having another target steel plate on the opposite side of the target steel plate of the target fiber-reinforced plastic laminate. The other target steel plate will be a steel plate of the same material, the same area, and the same thickness as the other steel plate in the steel plate-fiber-reinforced plastic composite. In comparison with the target composite, the first embodiment satisfying the conditions (1A) and (1B) above, and the second embodiment satisfying the conditions (2A) and (2B) above, are preferred forms. However, any configuration that satisfies the essential configuration of this disclosure described above is acceptable, without comparison to the target composite. Since the type, area, and thickness of the steel material required, as well as the area, thickness, and number of rib-like laminates that can be allowed, will vary depending on the application of the steel fiber reinforced plastic composite to which this disclosure applies, it is sufficient to design appropriately within the scope of the essential configuration of this disclosure described above so as to solve the problems of this disclosure. Whether problems such as reducing the volume of CFRP in the composite or improving the mechanical properties of the composite (e.g., improving bending load) can be solved can be confirmed not only by creating a sample and verifying it experimentally, but also by numerical simulation. Therefore, there is no need for excessive trial and error when designing an appropriate solution to these problems.

[0027] - How to determine the thickness - The thickness of each layer is measured by cross-sectional observation using a microscope. First, the composite is cut so that a cross-section parallel to both the thickness direction and the longitudinal direction of the laminate is formed, and the resulting first cross-section is observed with an optical microscope. When measuring the thickness of each layer, two points A and B are taken in the longitudinal direction of the first cross-section such that the straight-line distance AB is longest, and this straight line AB is divided into six equal parts. At five of these points, excluding the ends A and B, the thickness of the steel plate is measured, that is, the perpendicular distance from the interface between the adhesive layer and the steel plate (if there is an adhesive layer) or the interface between the steel plate and the layer in contact with the steel plate (i.e., the CFRP layer or other FRP layer) to the other end of the steel plate. The perpendicular distance is also measured for the thickness of the other layers in the same way as the steel plate. Furthermore, the composite is cut at a point shifted perpendicular to the first cross-section by an arbitrary distance from the first cross-section to form a second cross-section, and the thickness of each layer is measured at five locations in the same way as the first cross-section. The average value of the thickness of each layer at a total of 10 points obtained from the two cross-sections is calculated and used as the thickness of each layer. The measured value should be rounded to two or three decimal places (mm).

[0028] Furthermore, it is preferable that the fiber-reinforced plastic laminate has a multilayer structure of three or more layers, in which two or more fiber-reinforced plastic (FRP) layers containing fibers other than carbon fiber and one or more carbon fiber reinforced plastic (CFRP) layers are alternately laminated. By having a multilayer structure of three or more layers, it becomes easier to achieve cost reduction and higher strength.

[0029] In the composite of this disclosure, an independent adhesive layer (a separate adhesive layer different from the resin contained in the FRP layer, for example, an adhesive resin) may be interposed between the steel plate and the laminate, or there may be no separate adhesive layer. If there is no separate adhesive layer, the steel plate and the laminate may be bonded by a resin contained in, for example, the CFRP layer or other FRP layers. In this case, the base resin seeping out from the fiber-reinforced plastic will act as the adhesive. From the viewpoint of efficiently exhibiting the effects of this disclosure, the thickness of the separate adhesive layer (average thickness at any 10 points) is preferably 1.0 mm or less, and more preferably 0.5 mm or less. Furthermore, when the steel plate and the laminate are bonded by a resin contained in the FRP layer, the thickness of the base resin between the steel plate and the reinforcing fibers is not particularly limited as long as they are bonded by the method of bonding the steel plate and the laminate described later, but it is preferably 1.0 mm or less, and more preferably 0.5 mm or less.

[0030] In the composite of this disclosure, a layer of other resin (i.e., a resin layer that does not fall under the category of other FRP layers or CFRP, such as an adhesive layer containing an adhesive resin) may be interposed between the fiber-reinforced plastic (other FRP) layer containing fibers other than carbon fiber and the carbon fiber reinforced plastic (CFRP) layer. However, from the viewpoint of efficiently exhibiting the effects of this disclosure, the thickness of the other resin layer (average thickness at any 10 points) is preferably 1.0 mm or less. Therefore, in this disclosure, the alternating lamination of other FRP layers and CFRP layers includes not only the case where the other FRP layers and CFRP layers are laminated in direct contact without an intervening layer, but also the case where another resin layer is interposed between the other FRP layers and CFRP layers. Note that one layer of other FRP and one layer of CFRP are based on the definition of "one layer" described later.

[0031] Herein, we will explain the fiber-reinforced plastic layer (other FRP layer) containing fibers other than carbon fiber in the "one layer" and the carbon fiber-reinforced plastic layer (CFRP layer) in this disclosure. A single CFRP layer refers to the area in the lamination direction of a laminate from one boundary to the other of the region where carbon fibers are contained in the matrix resin. For example, consider a laminate where other FRPs are laminated from top to bottom in the lamination direction. Observing the CFRP in the middle, one boundary (one boundary) is observed between the region where glass fibers are contained in the matrix resin and the region where carbon fibers are contained in the matrix resin. Below that, the other boundary (the other boundary) is observed between the region where carbon fibers are contained in the matrix resin and the region where glass fibers are contained in the matrix resin. This area from one boundary to the other is considered a single CFRP layer. Alternatively, considering a laminate where other FRPs are laminated from top to bottom in the lamination direction (i.e., two CFRPs are laminated between other FRPs), the two CFRPs in the middle are considered a single CFRP layer. Observing the two CFRPs in the middle, one boundary (one boundary) is observed between the region containing glass fibers in the matrix resin and the region containing carbon fibers in the matrix resin. Below that, another region containing carbon fibers in the matrix resin (two CFRPs, i.e., one CFRP layer) is observed. Further below that, the boundary (the other boundary) is observed between the region containing carbon fibers in the matrix resin and the region containing glass fibers in the matrix resin. The area from one boundary to the other (i.e., the area of ​​two CFRPs) is considered a single CFRP layer. Similarly, for a single layer of other FRP, it refers to the area from one boundary to the other boundary of the region containing glass fibers in the matrix resin, in the lamination direction of the laminate. Therefore, even if two (or more) other FRP layers are laminated in contact with each other in the lamination direction of the laminate, the area from one boundary to the other boundary of the region containing glass fibers in the matrix resin is considered as a single layer of other FRP.

[0032] Furthermore, the boundaries of CFRP layers (regions containing carbon fibers in the matrix resin) and other FRP layers (regions containing glass fibers in the matrix resin) can be distinguished by color differences using an optical microscope. If it is not easy to distinguish them by color differences using an optical microscope, the boundaries can also be identified by component analysis.

[0033] Preferred examples of fiber-reinforced plastics (other FRPs) containing fibers other than carbon fibers in fiber-reinforced plastic laminates include glass fiber reinforced plastics (GFRP), aramid fiber reinforced plastics (AFRP), basalt fiber reinforced plastics, and cellulose fiber reinforced plastics. Among these, glass fiber reinforced plastics (GFRP) are more preferred as other FRPs.

[0034] To determine whether a material is a CFRP layer or a GFRP layer, nuclear magnetic resonance (NMR), infrared (IR), and energy-dispersive X-ray (EDS) analysis are performed by selecting these methods appropriately and, if necessary, combining two or more of them to analyze the types and concentrations of the components present.

[0035] When glass fiber reinforced plastic (GFRP) is used as another type of FRP, it is preferable that the layer closest to the steel plate in the fiber-reinforced plastic laminate is the GFRP layer. The GFRP layer, acting as an insulator, can prevent galvanic corrosion that occurs at the contact point between the steel plate and the CFRP layer.

[0036] Furthermore, a layer of glass fiber reinforced plastic (GFRP) with a larger area than the fiber reinforced plastic laminate may be present between the steel plate and the fiber reinforced plastic laminate, and the fiber reinforced plastic laminate may be bonded to the steel plate via the GFRP layer. By making the area of ​​this GFRP layer larger than the area of ​​the end face on the steel plate side of the fiber reinforced plastic laminate (the area of ​​the end face of the FRP layer located closest to the steel plate), galvanic corrosion that may occur at the contact portion between the steel plate and the CFRP layer can be more reliably prevented by the insulating GFRP layer. When there are multiple fiber reinforced plastic laminates, it is preferable to have only one GFRP layer, which spans the multiple fiber reinforced plastic laminates and is located between the steel plate and the fiber reinforced plastic laminate, as this facilitates manufacturing and allows for stable galvanic corrosion prevention.

[0037] -Preferred embodiment- Next, preferred embodiments of the composite of the present disclosure will be described with reference to the drawings.

[0038] • First aspect Figure 1 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the first embodiment, and Figure 2 is a schematic perspective view showing a steel sheet fiber reinforced plastic composite according to the first embodiment. The steel plate fiber-reinforced plastic composite 110 according to the first embodiment includes a steel plate 2 and three rib-shaped fiber-reinforced plastic laminates 10 on the steel plate 2, as shown in Figures 1 and 2. Although not shown in Figures 1 and 2, there may be an adhesive layer between the steel plate 2 and the fiber-reinforced plastic laminates 10. The fiber-reinforced plastic laminates 10 have a four-layer structure in which two glass fiber reinforced plastic (GFRP) layers G11 and G12 and two carbon fiber reinforced plastic (CFRP) layers C11 and C12 are alternately laminated. In the fiber-reinforced plastic laminates 10, the glass fiber reinforced plastic (GFRP) layer G11 constitutes the layer closest to the steel plate 2.

[0039] By using a four-layer structure, the number of stacked layers is not excessive, making it easier to increase bending rigidity. Also, compared to a three-layer structure, there are more interfaces, making it less likely for the laminate to peel off from the steel plate.

[0040] Each of the three rib-shaped fiber-reinforced plastic laminates 10 has a width (length in the short direction) of 2.5 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 3.75 mm is provided between each of the fiber-reinforced plastic laminates 10.

[0041] In the configuration of the steel fiber reinforced plastic composite according to this first embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0042] Note that while the number of rib-shaped fiber-reinforced plastic laminates 10 is shown as three in Figures 1 and 2, it is not limited to this number. Preferably, the rib-shaped fiber-reinforced plastic laminate provided on the steel plate has a width (length in the shorter direction) shorter than the width of the steel plate, and a length in the longer direction equal to the length of the steel plate in the longer direction.

[0043] • Second aspect Figure 4 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the second embodiment. The steel sheet fiber-reinforced plastic composite 120 according to the second embodiment has a steel sheet 2 and three rib-shaped fiber-reinforced plastic laminates 20 on the steel sheet 2, as shown in Figure 4. Although not shown in Figure 4, there may be an adhesive layer between the steel sheet 2 and the fiber-reinforced plastic laminates 20. The fiber-reinforced plastic laminates 20 have a five-layer structure in which three glass fiber reinforced plastic (GFRP) layers G21, G22, and G23 and two carbon fiber reinforced plastic (CFRP) layers C21, C22 are alternately laminated. In the fiber-reinforced plastic laminates 20, the glass fiber reinforced plastic (GFRP) layer G21 constitutes the layer closest to the steel sheet 2.

[0044] By using a five-layer structure, although strain tends to accumulate at material interfaces, the numerous interfaces due to the fine multi-layer configuration reduce the possibility of strain concentration in one area, thereby suppressing fracture. In addition, the abundance of interfaces makes it less likely for the laminate to peel off the steel plate.

[0045] Each of the three rib-shaped fiber-reinforced plastic laminates 20 has a width (length in the short direction) of 2.5 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 3.75 mm is provided between each of the fiber-reinforced plastic laminates 20.

[0046] In the configuration of the steel fiber reinforced plastic composite according to this second embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0047] Note that while Figure 4 shows three rib-shaped fiber-reinforced plastic laminates 20, the number is not limited to this.

[0048] The steel sheet fiber-reinforced plastic composite 120 according to the second embodiment has a five-layer structure, in which three glass fiber-reinforced plastic layers G21, G22, and G23 and two carbon fiber-reinforced plastic layers C21, C22 are alternately laminated. In this five-layer structure, it is preferable that the central position in the lamination direction of the fiber-reinforced plastic laminate is located in the middle layer (i.e., G22) of the five-layer structure. As a result, the fiber-reinforced plastic laminate has a structure that is close to symmetrical, so that thermal strain due to temperature changes during molding and use can be dispersed, thereby preventing fracture due to localized stress concentration.

[0049] Preferably, the rib-shaped fiber-reinforced plastic laminate provided on the steel plate has a width (length in the shorter direction) shorter than the width of the steel plate, and a length in the longer direction equal to the length of the steel plate in the longer direction.

[0050] • Third aspect Figure 5 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to a third embodiment. The third embodiment of the steel plate fiber-reinforced plastic composite 130, as shown in Figure 5, comprises a steel plate 2 and three rib-shaped fiber-reinforced plastic laminates 30 on the steel plate 2. Although not shown in Figure 5, an adhesive layer may be provided between the steel plate 2 and the fiber-reinforced plastic laminates 30. The fiber-reinforced plastic laminates 30 have a six-layer structure in which three glass fiber reinforced plastic (GFRP) layers G31, G32, and G33 and three carbon fiber reinforced plastic (CFRP) layers C31, C32, and C33 are alternately laminated. In the fiber-reinforced plastic laminates 30, the glass fiber reinforced plastic (GFRP) layer G31 constitutes the layer closest to the steel plate 2.

[0051] By using a six-layer structure, although strain tends to accumulate at material interfaces, the numerous interfaces due to the fine multi-layer configuration reduce the possibility of strain concentration in one area, thereby suppressing fracture. In addition, the abundance of interfaces makes it less likely for the laminate to peel off the steel plate.

[0052] Each of the three rib-shaped fiber-reinforced plastic laminates 30 has a width (length in the short direction) of 2.5 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 3.75 mm is provided between each of the fiber-reinforced plastic laminates 30.

[0053] In the configuration of the steel fiber reinforced plastic composite according to this third embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0054] Note that while Figure 5 shows three rib-shaped fiber-reinforced plastic laminates 30, the number is not limited to this. Preferably, the rib-shaped fiber-reinforced plastic laminate provided on the steel plate has a width (length in the shorter direction) shorter than the width of the steel plate, and a length in the longer direction equal to the length of the steel plate in the longer direction.

[0055] • Fourth aspect Figure 6 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the fourth embodiment. The fourth embodiment of the steel sheet fiber-reinforced plastic composite 140, as shown in Figure 6, comprises a steel sheet 2 and three rib-shaped fiber-reinforced plastic laminates 40 on the steel sheet 2. Although not shown in Figure 6, an adhesive layer may be provided between the steel sheet 2 and the fiber-reinforced plastic laminates 40. The fiber-reinforced plastic laminates 40 have a two-layer structure in which one glass fiber reinforced plastic (GFRP) layer G41 and one carbon fiber reinforced plastic (CFRP) layer C41 are alternately laminated. In the fiber-reinforced plastic laminates 40, the glass fiber reinforced plastic (GFRP) layer G41 constitutes the layer closest to the steel sheet 2.

[0056] The two-layer structure results in a simpler design, making it easier to increase bending rigidity. Furthermore, the simple design also makes manufacturing easier.

[0057] Each of the three rib-shaped fiber-reinforced plastic laminates 40 has a width (length in the short direction) of 2.5 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 3.75 mm is provided between each of the fiber-reinforced plastic laminates 40.

[0058] In the configuration of the steel fiber reinforced plastic composite according to this fourth embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0059] Note that while Figure 6 shows three rib-shaped fiber-reinforced plastic laminates 40, the number is not limited to this. Preferably, the rib-shaped fiber-reinforced plastic laminate provided on the steel plate has a width (length in the shorter direction) shorter than the width of the steel plate, and a length in the longer direction equal to the length of the steel plate in the longer direction.

[0060] • Fifth aspect Figure 7 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the fifth embodiment. The fifth embodiment of the steel sheet fiber-reinforced plastic composite 150, as shown in Figure 7, comprises a steel sheet 2 and three rib-shaped fiber-reinforced plastic laminates 50 on the steel sheet 2. Although not shown in Figure 7, an adhesive layer may be provided between the steel sheet 2 and the fiber-reinforced plastic laminates 50. The fiber-reinforced plastic laminates 50 have a three-layer structure in which two glass fiber reinforced plastic (GFRP) layers G51 and G52 and one carbon fiber reinforced plastic (CFRP) layer C51 are alternately laminated. In the fiber-reinforced plastic laminates 50, the glass fiber reinforced plastic (GFRP) layer G51 constitutes the layer closest to the steel sheet 2.

[0061] The three-layer structure results in a simpler configuration, making it easier to increase bending rigidity and simplifying manufacturing. Furthermore, compared to a two-layer structure, the increased number of interfaces makes it less likely for the laminate to peel off the steel sheet.

[0062] Each of the three rib-shaped fiber-reinforced plastic laminates 50 has a width (length in the short direction) of 2.5 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 3.75 mm is provided between each of the fiber-reinforced plastic laminates 50.

[0063] In the configuration of the steel fiber reinforced plastic composite according to this fifth embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0064] Note that while Figure 7 shows three rib-shaped fiber-reinforced plastic laminates 50, the number is not limited to this.

[0065] Preferably, the rib-shaped fiber-reinforced plastic laminate provided on the steel plate has a width (length in the shorter direction) shorter than the width of the steel plate, and a length in the longer direction equal to the length of the steel plate in the longer direction.

[0066] The number of rib-shaped fiber-reinforced plastic laminates is not particularly limited. The following describes embodiments with different numbers of rib-shaped fiber-reinforced plastic laminates.

[0067] • Sixth aspect Figure 8 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the sixth embodiment. The sixth embodiment of the steel sheet fiber-reinforced plastic composite 160, as shown in Figure 8, comprises a steel sheet 2 and a rib-shaped fiber-reinforced plastic laminate 60 on the steel sheet 2. Although not shown in Figure 8, an adhesive layer may be provided between the steel sheet 2 and the fiber-reinforced plastic laminate 60. The fiber-reinforced plastic laminate 60 has a four-layer structure in which two glass fiber reinforced plastic (GFRP) layers G61 and G62 and two carbon fiber reinforced plastic (CFRP) layers C61 and C62 are alternately laminated. In the fiber-reinforced plastic laminate 60, the glass fiber reinforced plastic (GFRP) layer G61 constitutes the layer closest to the steel sheet 2.

[0068] Each rib-shaped fiber-reinforced plastic laminate 60 has a width (length in the short direction) of 7.5 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 3.75 mm is provided on each side of the fiber-reinforced plastic laminate 60.

[0069] In the configuration of the steel fiber reinforced plastic composite according to this sixth embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0070] • Seventh aspect Figure 9 is a schematic side view showing a steel sheet fiber-reinforced plastic composite according to the seventh embodiment. The seventh embodiment of the steel sheet fiber-reinforced plastic composite 170 includes a steel sheet 2 and two rib-shaped fiber-reinforced plastic laminates 70 on the steel sheet 2, as shown in Figure 9. Although not shown in Figure 9, an adhesive layer may be provided between the steel sheet 2 and the fiber-reinforced plastic laminates 70. The fiber-reinforced plastic laminate 70 has a four-layer structure in which two glass fiber reinforced plastic (GFRP) layers G71 and G72 and two carbon fiber reinforced plastic (CFRP) layers C71 and C72 are alternately laminated. In the fiber-reinforced plastic laminate 70, the glass fiber reinforced plastic (GFRP) layer G71 constitutes the layer closest to the steel sheet 2.

[0071] Each of the two rib-shaped fiber-reinforced plastic laminates 70 has a width (length in the shorter direction) of 3.75 mm and a length in the longer direction of 100 mm (the same length as the steel plate 2). A 7.5 mm gap is provided between the two fiber-reinforced plastic laminates 70.

[0072] In the configuration of the steel fiber reinforced plastic composite according to this seventh embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0073] • Eighth aspect Figure 10 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the eighth embodiment. The eighth embodiment of the steel sheet fiber-reinforced plastic composite 180 includes a steel sheet 2 and five rib-shaped fiber-reinforced plastic laminates 80 on the steel sheet 2, as shown in Figure 10. Although not shown in Figure 10, an adhesive layer may be provided between the steel sheet 2 and the fiber-reinforced plastic laminates 80. The fiber-reinforced plastic laminates 80 have a four-layer structure in which two glass fiber reinforced plastic (GFRP) layers G81 and G82 and two carbon fiber reinforced plastic (CFRP) layers C81 and C82 are alternately laminated. In the fiber-reinforced plastic laminates 80, the glass fiber reinforced plastic (GFRP) layer G81 constitutes the layer closest to the steel sheet 2.

[0074] Each of the five rib-shaped fiber-reinforced plastic laminates 80 has a width (length in the short direction) of 1.5 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 1.875 mm is provided between each of the fiber-reinforced plastic laminates 80.

[0075] In the configuration of the steel fiber reinforced plastic composite according to this eighth embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0076] • The ninth aspect Figure 11 is a schematic side view showing a steel sheet fiber reinforced plastic composite according to the ninth embodiment. The ninth embodiment of the steel sheet fiber-reinforced plastic composite 190, as shown in Figure 11, comprises a steel sheet 2 and 10 rib-shaped fiber-reinforced plastic laminates 90 on the steel sheet 2. Although not shown in Figure 11, an adhesive layer may be present between the steel sheet 2 and the fiber-reinforced plastic laminates 90. The fiber-reinforced plastic laminates 90 have a four-layer structure in which two glass fiber reinforced plastic (GFRP) layers G91 and G92 and two carbon fiber reinforced plastic (CFRP) layers C91 and C92 are alternately laminated. In the fiber-reinforced plastic laminates 90, the glass fiber reinforced plastic (GFRP) layer G91 constitutes the layer closest to the steel sheet 2.

[0077] Each of the 10 rib-shaped fiber-reinforced plastic laminates 90 has a width (length in the short direction) of 0.75 mm and a length in the long direction of 100 mm (the same length as the steel plate 2). A gap of 0.834 mm is provided between each of the fiber-reinforced plastic laminates 90.

[0078] In the configuration of the steel fiber reinforced plastic composite according to this ninth embodiment, by controlling the thickness (length in the thickness direction) of the rib-shaped laminate, the width of the laminate, and the width of the gaps between the laminates, it is possible to reduce the amount (i.e., volume) of carbon fiber reinforced plastic used while improving the mechanical properties of the composite compared to the target composite. As a result, the conditions of (1A) and (1B) above can be satisfied, or the conditions of (2A) and (2B) above can be satisfied.

[0079] ·Support If the composite of the present disclosure has multiple rib-shaped fiber-reinforced plastic laminates, a support may be provided between the multiple fiber-reinforced plastic laminates. For example, as shown in the steel plate fiber-reinforced plastic composite 200 in Figure 12, a support 202 may fill the gaps between the three rib-shaped fiber-reinforced plastic laminates 10Y. The presence of a support between the fiber-reinforced plastic laminates can suppress the tilting of the rib-shaped fiber-reinforced plastic laminates and further increase the bending rigidity. The shape of the support is not limited to the shape shown in Figure 12. For example, the support does not have to be shaped to fill the gaps between the rib-shaped fiber-reinforced plastic laminates 1, but rather to bridge (cross-link) the rib-shaped fiber-reinforced plastic laminates 10Y (for example, a shape like a beam in a ceiling). Furthermore, the support may or may not be bonded to the rib-shaped fiber-reinforced plastic laminate, but it is preferably bonded. It is preferable that the support is bonded perpendicular to the direction in which the rib-shaped fiber-reinforced plastic laminate protrudes (i.e., the thickness direction). The material of the support is not particularly limited as long as it has the function of supporting the rib-shaped fiber-reinforced plastic laminate, and examples include resin, fiber-reinforced plastic (FRP), foaming agent, etc. Preferably, the support material is a material that is cheaper and has a lower specific gravity than CFRP.

[0080] • Another steel plate The composite of the present disclosure may have two steel plates, one above the other. That is, the fiber-reinforced plastic laminate may have another steel plate on the opposite side of the steel plate. Furthermore, if the composite of this disclosure has another steel plate on the opposite side of the steel plate of the fiber-reinforced plastic laminate, then the target composite will also have another target steel plate on the opposite side of the target steel plate of the target fiber-reinforced plastic laminate. The other target steel plate will be a steel plate of the same material, the same area, and the same thickness as the other steel plate in the steel plate-fiber-reinforced plastic composite.

[0081] From the viewpoint of balancing two fundamentally conflicting challenges—improving the mechanical properties of the composite while reducing the amount (i.e., volume) of carbon fiber reinforced plastic used—it is preferable that the fiber-reinforced plastic laminate has a thickness ratio of 1.4 to 1.8 relative to the target fiber-reinforced plastic laminate in the target composite, and that the ratio of the volume of carbon fiber reinforced plastic to the volume of the fiber-reinforced plastic laminate (or the ratio of the total volume if there are multiple layers of carbon fiber reinforced plastic) is 0.5 to 0.6. Furthermore, from the viewpoint of minimizing the reduction in the amount (i.e., volume) of carbon fiber reinforced plastic used and further improving the mechanical properties of the composite, it is preferable that the fiber-reinforced plastic laminate has a thickness ratio of 1.4 to 1.9 relative to the target fiber-reinforced plastic laminate in the target composite, and that the ratio of the volume of carbon fiber reinforced plastic to the volume of the fiber-reinforced plastic laminate (or the ratio of the total volume if there are multiple layers of carbon fiber reinforced plastic) is 0.3 to 0.9. The ratio of the volume of carbon fiber reinforced plastic to the volume of the fiber-reinforced plastic laminate is expressed rounded to two decimal places. For example, if the ratio of the volume of carbon fiber reinforced plastic to the volume of the fiber-reinforced plastic laminate is 1 / 3 (one-third, or 0.333...), it is expressed as "0.3" after rounding to two decimal places.

[0082] -Components of the composite- Next, each component constituting the steel sheet fiber-reinforced plastic composite according to the embodiment of this disclosure will be described.

[0083] • Carbon fiber reinforced plastic (CFRP) layer The carbon fiber reinforced plastic used in the CFRP layer is not particularly limited, but from the viewpoint of easily increasing rigidity (e.g., maximum bending load), it is preferable that its tensile modulus is in the range of 100 GPa to 160 GPa, and more preferably 125 GPa to 160 GPa.

[0084] CFRP, for example, comprises a matrix resin and carbon fibers contained within the matrix resin.

[0085] (Carbon fiber) As the carbon fibers, pitch-based carbon fibers and PAN-based carbon fibers can be used. The carbon fibers may consist of only one type of carbon fiber or two or more types of carbon fibers. The carbon fibers may be UD material in which the fiber bundles are aligned in one direction, cross material in which the fibers are woven in a mesh-like structure, or alternating laminate material in which UD material is laminated alternately. Here, the thickness of the carbon fiber bundles is not particularly specified, but it is possible to increase the impregnation of the resin by spreading them thinly, for example by using fiber-opening technology, and it is preferable that the thickness be 100 μm to 200 μm.

[0086] Carbon fiber content of CFRP (fiber volume content V) f From the viewpoint of ensuring strength and processability, the carbon fiber content is preferably 10% to 70% by volume. The carbon fiber content in CFRP is preferably 15% to 20% or 30% by volume, and also 65% or less by volume, 60% or less by volume, or 55% or less by volume. Carbon fiber content of CFRP f The measurement method (by volume %) can be performed as follows: The CFRP layer is peeled from the composite to obtain a test specimen for measuring the carbon fiber content. The oven-dry mass (W3) of the test specimen is measured. Next, the test specimen is immersed in 20% hydrochloric acid to dissolve the matrix resin, and the oven-dry mass (W4) of the carbon fibers obtained as residue is measured. After measurement, the carbon fiber content W based on mass is calculated. f Calculate (mass%) = (W4 / W3) × 100, and then determine the density of the test specimen ρ3 (g / cm³). 3 ) and the density of carbon fibers ρ4 (g / cm³) 3 ) The carbon fiber content V in CFRP f (Volume %) = W f Calculate ×(ρ3 / ρ4).

[0087] (Matrix resin) The matrix resin is the resin that constitutes the CFRP. The type of resin used for the matrix resin is not particularly limited, and either a thermoplastic resin or a thermosetting resin can be used. Preferably, a thermoplastic resin that has good flexural strength and excellent processability is used. The type of thermoplastic resin that can be used as the matrix resin is not particularly limited. For example, resins selected from phenoxy resin, polyolefin and its acid-modified products, polypropylene, polystyrene, polymethyl methacrylate, AS resin, ABS resin, thermoplastic aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, polycarbonate, polyimide, polyamide, polyamide-imide, polyetherimide, polyethersulfone, polyphenylene ether and its modified products, polyphenylene sulfide, polyoxymethylene, polyarylate, polyether ketone, polyether ether ketone, polyether ketone ketone, thermoplastic epoxy resin, unsaturated polyester resin, phenolic resin, urethane resin, and nylon can be used.

[0088] Preferred examples of fiber-reinforced plastics (other FRPs) containing fibers other than carbon fibers in fiber-reinforced plastic laminates include glass fiber reinforced plastics (GFRP), aramid fiber reinforced plastics (AFRP), basalt fiber reinforced plastics, and cellulose fiber reinforced plastics. Among these, glass fiber reinforced plastics (GFRP) are more preferred as other FRPs.

[0089] • Glass fiber reinforced plastic (GFRP) layer The glass fiber reinforced plastic used in the GFRP layer is not particularly limited, but from the viewpoint of easily increasing rigidity (e.g., maximum bending load), it is preferable that the tensile modulus is in the range of 25 GPa to 60 GPa, and more preferably 45 GPa to 60 GPa.

[0090] GFRP, for example, comprises a matrix resin and glass fibers contained within the matrix resin.

[0091] The reinforcing fibers included in glass fiber reinforced plastic (GFRP) are not particularly limited, but for example, E-glass, S-glass, T-glass, etc., can be used.

[0092] The type of resin used for the matrix resin is not particularly limited, but it is preferably one that exhibits insulating properties, and either a thermoplastic resin or a thermosetting resin can be used. A thermoplastic resin that has good flexural strength and excellent processability is preferred. The type of thermoplastic resin that can be used for the matrix resin is not particularly limited. For example, resins selected from phenoxy, polyolefins and their acid-modified products, polypropylene, polystyrene, polymethyl methacrylate, AS resin, ABS resin, thermoplastic aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, polycarbonate, polyimide, polyamide, polyamide-imide, polyetherimide, polyethersulfone, polyphenylene ether and its modified products, polyphenylene sulfide (PPS), polyoxymethylene, polyarylate, polyether ketone, polyetherether ketone (PEEK), polyether ketone ketone, thermoplastic epoxy resin, unsaturated polyester resin, phenolic resin, urethane resin, and nylon can be used.

[0093] ·Steel plate The steel plate is not particularly limited in terms of material, shape, and thickness, but it is preferably one that can be formed by pressing or other processing, and a thin plate shape is preferred.

[0094] The steel plate is preferably one with a tensile strength in the range of 270 MPa to 2000 MPa, and more preferably 590 MPa or higher, from the viewpoint of easily increasing rigidity (e.g., maximum bending load).

[0095] The steel sheet may be surface-treated. Examples include, but are not limited to, various plating treatments such as zinc plating and aluminum plating, chemical conversion treatments such as chromate treatment and non-chromate treatment, and physical etching such as sandblasting or chemical surface roughening treatments such as chemical etching. Furthermore, the plating may be alloyed or multiple types of surface treatments may be applied. Preferably, the surface treatment is performed to provide at least rust prevention.

[0096] ·Adhesive layer When a separate adhesive layer (a single adhesive layer) is provided, the type of adhesive layer is not particularly limited, and organic adhesives such as thermoplastic resins and thermosetting resins, or inorganic adhesives such as water glass, silicate, cement, and gypsum can be used. Alternatively, even without an adhesive layer, the base resin seeping from the glass fiber reinforced plastic may act as the adhesive. More preferably, bonding is done with an organic adhesive or the base resin.

[0097] • Method of bonding steel plates to laminates The method for bonding the steel plate and the fiber-reinforced plastic laminate in this disclosure is described below. There are no particular limitations on the bonding method of this composite, and any suitable method may be used. For example, this composite can be manufactured by the following method. When bonding steel plates and laminates with an adhesive, for example, the adhesive is applied to a pre-formed rib-shaped laminate, and then bonded to the steel plate to create a composite. In the case of room-temperature curing adhesives, the bond is held for a predetermined curing time. In the case of heat-curing adhesives, the composite is obtained by heating and pressing with a hot press. When bonding a steel plate and a laminate by the seepage of the base resin, for example, a rib-shaped laminate is placed on a steel plate that has been treated with a release agent, a heat-resistant sheet of the same thickness as the ribs is placed to fill the areas other than the ribs, and the composite is obtained by heating and pressing with a hot press. In the above bonding method, whether the steel plate and the fiber-reinforced plastic laminate are bonded can be confirmed by checking whether there is adhesive or resin present between the steel plate and the FRP closest to the steel plate.

[0098] -Applications- The steel fiber-reinforced plastic composite according to the embodiments of this disclosure can be publicly used, in particular, for automotive components. [Examples]

[0099] The effects of this disclosure will be specifically described below with reference to examples.

[0100] <Example 1> • Evaluation of the consistency between calculation results and experimental results First, we confirmed the consistency of the experimental results obtained from simulations in Examples 2 to 10, which will be described later.

[0101] 1. Creation of a three-point bending calculation model 1-1. Creation of a computational model for steel plate fiber-reinforced plastic composites A computational model was created for a steel plate fiber-reinforced plastic composite with a width of 15 mm and a length of 130 mm, consisting of a steel plate with a tensile strength of 590 MPa and a thickness of 0.4 mm, and a fiber-reinforced plastic laminate with a thickness of 1.0 mm. At this time, the fiber-reinforced plastic laminate was constructed with a four-layer structure as shown in Figure 1, with the layers being a 0.167 mm glass fiber reinforced plastic (GFRP) layer, a 0.167 mm carbon fiber reinforced plastic (CFRP) layer, a 0.5 mm glass fiber reinforced plastic (GFRP) layer, and a 0.167 mm carbon fiber reinforced plastic (CFRP) layer from the steel plate side.

[0102] 1-2. Physical properties of each material The physical property values (density, elastic modulus, Poisson's ratio, shear coefficient, coefficient of linear expansion) of the steel plate, CFRP layer, GFRP layer, and adhesive resin (not used in Example 1 but used in Example 9) that make up the steel plate fiber-reinforced plastic composite are shown in Table 1, and a curve showing the relationship between the plastic equivalent strain and stress of the steel plate is shown in Fig. 13. At this time, for CFRP and GFRP, physical property values corresponding to a fiber volume ratio (V f ) = 60% were set.

[0103]

Table 1

[0104] 2. Preparation of three-point bending test specimens [Fiber Reinforced Plastic Laminate] A fiber-reinforced plastic laminate was prepared using a polyacrylonitrile (PAN)-based carbon fiber unidirectional prepreg (V f = 60%) (manufactured by Toray, product name: TORAYCA PREPREG, P3252S-20) with a width of 100 mm and a length of 130 mm, and a glass fiber unidirectional prepreg (V f = 58%) (manufactured by Nissei Co., Ltd., product name: E13-35). The first layer was laminated with 2 sheets (0.167 mm) of glass fiber unidirectional prepreg so that the volume ratio of the GFRP layer was 30%, the second layer was 1 sheet (0.167 mm) of PAN-based carbon fiber unidirectional prepreg, the third layer was 6 sheets (0.5 mm) of glass fiber unidirectional prepreg, and the fourth layer was 1 sheet (0.167 mm) of PAN-based carbon fiber unidirectional prepreg, for a total of 10 sheets. Three pieces of this fiber-reinforced plastic laminated sheet cut to a width of 2.5 mm and a length of 130 mm were prepared.

[0105] [Steel Plate - Fiber Reinforced Plastic Composite] Three fiber-reinforced plastic laminate sheets were laminated onto a GA steel plate measuring 15 mm wide x 130 mm long with a tensile strength of 590 MPa, with a 3.75 mm gap between them, so that the GFRP layers were adjacent to the steel plate. A shim (1 mm thick) of Nafuron sheet, with holes the same area as the bonding area of ​​the fiber-reinforced plastic laminate sheets, was placed on top to secure the steel plate and fiber-reinforced plastic laminate sheets without any gaps. This was then hot-pressed at 1.0 MPa, 130°C, and 1 hour to obtain a steel plate-fiber-reinforced plastic composite.

[0106] [Conditions for bending tests and bending calculations] Figure 14 is a perspective view showing the method of the three-point bending test. The dimensions of the three-point bending test machine were as follows: the radius r of the indenter 82 was 5 mm, the radius of the support point 84 was 15 mm, and the distance between the support points 84 was 100 mm. The test specimen was set up so that the indenter 82 struck the steel plate 2 side of the steel plate-fiber-reinforced plastic composite 110. The same dimensions and measurement conditions were used for the three-point bending calculation.

[0107] 3. Validation of calculation and experimental results Figure 15 shows a comparison of the obtained test results and calculation results. The calculation results and experimental results were in general agreement, confirming the validity of the calculation results.

[0108] <Example 2> • Evaluation of corrosion prevention properties 1-1. Insulation Evaluation 1-1-1. Preparation of test specimens To evaluate its insulating properties, a steel plate-fiber-reinforced plastic composite with GFRP as an insulating layer was fabricated. PAN-based carbon fiber unidirectional prepreg (V f =60%) and glass fiber unidirectional prepreg (V fUsing (=58%), the CFRP layer thickness was set to 800 μm, and the GFRP layer thickness was varied from 15 μm to 700 μm as shown in Table 2. These were then bonded to a steel plate (tin-free steel plate manufactured by Nippon Steel Corporation) measuring 100 mm in length, 100 mm in width, and 0.2 mm in thickness. This was then hot-pressed at 1.0 MPa, 130°C, and 1 hour to obtain a steel plate-fiber-reinforced plastic composite sample.

[0109] 1-1-2. Method for Evaluating Insulation Properties The through-resistance (resistance value) of each sample was measured using an insulating layer resistance measuring device. First, the sample was measured by 1 cm 2 The material was sandwiched between Toray Industries, Inc.'s carbon paper (TGP-H-12), and a 20mmφ gold-plated terminal was placed on the outside of the carbon paper. A load of 100kgf (approximately 980N) per square centimeter was then applied, and a 0.1mA DC current was passed between the gold-plated terminals using a constant current power supply (Kikusui Electronics PAN16-10A). The through-resistance was evaluated by reading the resistance value from the voltage between the terminals. A voltmeter (HEWLETTPACKARD MULTIMETER34401A) was used. Regarding the obtained through-resistance values, those showing a resistance value of 100 mΩ or higher were judged to have sufficient conductivity blocked and galvanic corrosion significantly suppressed, and were given an "A" rating. Furthermore, if the obtained through-resistance value was between 50 mΩ and 100 mΩ, it was judged that conductivity was blocked and galvanic corrosion was suppressed, and was given a "B" rating. On the other hand, if the through-resistance value was low, such as less than 50 mΩ, it was judged that conductivity was not blocked, and was given a "C" rating.

[0110] [Table 2]

[0111] <Example 3> 1. Performance evaluation method using three-point bending calculation Similar to Example 1, a three-point bending test was performed using the three-point bending test method shown in Figure 14. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, curves for the horizontal axis stroke and vertical axis load were calculated. In addition, the configuration disclosed in prior art publications JP 2019-119213 and JP 2021-98374 was set to proportionality 1 (object, i.e., object composite). The maximum bending load was evaluated as follows: A (〇) if it was 304.95N or more (i.e., the maximum bending load with proportionality 1), B (△) if it was 80% or more of 304.95N (i.e., 243.96N), and C (×) if it was less than 243.96N. For mass, items with a mass of 9.2g or less (i.e., a proportional mass of 1) were evaluated as A (○), and those with a mass greater than that were evaluated as B (×). The amount of CFRP used (by volume) is 1.95 cm³. 3 We evaluated samples with a CFRP usage amount less than (i.e., a proportional ratio of 1) as A (○), and those with a usage amount equal to or greater than that as B (×). CFRP reduction rates were evaluated as follows: A (〇) for 30% or more, B (△) for over 0% but less than 30%, and C (×) for 0% or less.

[0112] 2. Calculation level Assuming the same material used for the three-point bending test specimen in Example 1, three-point bending calculations were performed at the following levels. The proportionality 1 (object) was constructed with a fiber-reinforced plastic (FRP) laminate portion that was not ribbed but had a flat plate shape (a flat plate shape with the same area as the steel plate). The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer). Comparative Example 3-1 was constructed by changing the volume ratio of the GFRP layer in the FRP laminate to 0.05 in the proportionality 1 (target object). The FRP laminate had a two-layer structure, consisting of a 0.05 mm GFRP layer and a 0.95 mm CFRP layer from the steel plate side.

[0113] Comparative Example 3-2 uses a rib-shaped FRP laminate, with the FRP laminate consisting of three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness is 0.4 mm, the FRP laminate thickness is 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate is 0.7 (more specifically, 0.666...). The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 0.167mm GFRP layer, 0.167mm CFRP layer 0.5mm GFRP layer 0.167mm CFRP layer

[0114] Example 3-1 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 1.5 mm in Comparative Example 3-2. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 0.25mm GFRP layer 0.25mm CFRP layer 0.75mm GFRP layer 0.25mm CFRP layer

[0115] Example 3-2 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 1.7 mm in Comparative Example 3-2. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 0.284 mm GFRP layer 0.284mm CFRP layer 0.85mm GFRP layer 0.284mm CFRP layer

[0116] Example 3-3 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 2.0 mm in Comparative Example 3-2. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 0.334 mm GFRP layer 0.334mm CFRP layer 1.0 mm GFRP layer 0.334mm CFRP layer

[0117] 3. Calculation results In Examples 3-1, 3-2, and 3-3 of the present invention, the amount of CFRP used can be reduced by more than 30% compared to the proportionality 1 (target object) configuration, and it was also confirmed that the maximum bending load is higher than that of proportionality 1 (target object). Furthermore, in Examples 3-1 and 3-2 of the present invention, it was confirmed that the mass can be made equivalent to or lighter than that of proportionality 1 (target object) by using a rib shape compared to the proportionality 1 (target object) configuration.

[0118] [Table 3]

[0119] Note that the volume ratio of the GFRP layer (GFRP ratio listed in the table) is rounded to two decimal places. For example, in Comparative Example 3-2, the volume ratio of the GFRP layer is 0.666..., but it is rounded to two decimal places and expressed as "0.7". Furthermore, the volume ratio of the CFRP layer is the value obtained by subtracting the volume ratio of the GFRP layer from 1, that is, "CFRP volume ratio = 1 - GFRP volume ratio". Therefore, the volume ratio of the CFRP layer in Comparative Example 3-2 is 1 - GFRP volume ratio (0.7) = "0.3". The volume ratios of the GFRP layer and the CFRP layer are the same in other examples (except for Example 5, in which the fiber-reinforced plastic laminate (FRP laminate) is formed by an AFRP layer and a CFRP layer).

[0120] <Example 4> • Number of layers in the FRP laminate 1. Performance evaluation method using three-point bending calculation A three-point bending test was performed in the same manner as in Example 1. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, curves for the horizontal axis stroke and vertical axis load were calculated. The proportionality 1 (object, i.e., the target composite) is the same as in Example 3. The calculation conditions and evaluation methods were the same as in Example 3.

[0121] 2. Calculation level Assuming the same material used for the three-point bending test specimen in Example 1, three-point bending calculations were performed at the following levels. The proportionality 1 (object) was constructed with a fiber-reinforced plastic (FRP) laminate portion that was not ribbed but had a flat plate shape (a flat plate shape with the same area as the steel plate). The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer).

[0122] Example 4-1 of the present invention features a rib-shaped FRP laminate, with the FRP laminate consisting of three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness is 0.4 mm, the FRP laminate thickness is 1.5 mm, and the volume ratio of the GFRP layer in the FRP laminate is 0.7. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.167 mm GFRP layer 2) 0.167 mm CFRP layer 3) 0.5 mm GFRP layer 4) 0.167 mm CFRP layer

[0123] Example 4-2 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from that of Example 4-1 of the present invention. The FRP laminate has a five-layer configuration, with the following layers laminated from the steel plate side. 1) 0.25 mm GFRP layer 2) 0.25 mm CFRP layer 3) 0.5 mm GFRP layer 4) 0.25 mm CFRP layer 5) 0.25 mm GFRP layer

[0124] Example 4-3 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from that of Example 4-1 of the present invention. The FRP laminate has a 13-layer structure, with the following layers laminated from the steel plate side. 1) 0.083 mm GFRP layer 2) 0.083 mm CFRP layer 3) 0.167 mm GFRP layer 4) 0.083 mm CFRP layer 5) 0.167 mm GFRP layer 6) 0.083 mm CFRP layer 7) 0.167 mm GFRP layer 8) 0.083 mm CFRP layer 9) 0.167 mm GFRP layer 10) 0.083 mm CFRP layer 11) 0.167 mm GFRP layer 12) 0.083 mm CFRP layer 13) 0.083 mm GFRP layer

[0125] Example 4-4 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from that of Example 4-1 of the present invention. The FRP laminate has a two-layer configuration, with the following layers laminated from the steel plate side. 1) 1.0 mm GFRP layer 2) 0.5mm CFRP layer

[0126] Example 4-5 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Example 4-1 of the present invention. The FRP laminate has a three-layer configuration, with the following layers laminated from the steel plate side. 1) 0.5 mm GFRP layer 2) 0.5mm CFRP layer 3) 0.5 mm GFRP layer

[0127] 3. Calculation results In Examples 4-1 to 4-5 of the present invention, the amount of CFRP used can be reduced by more than 30% compared to the proportionality 1 (object) configuration, the mass can be made lighter than proportionality 1 (object) by using a rib shape, and it was confirmed that the maximum bending load is 80% or more of that of proportionality 1 (object) (Examples 4-2, 4-3, 4-5), or greater than that of proportionality 1 (object) (Examples 4-1, 4-4).

[0128] [Table 4]

[0129] <Example 5> • Laminate of AFRP and CFRP 1. Performance evaluation method using three-point bending calculation A three-point bending test was performed in the same manner as in Example 1. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, curves for the horizontal axis stroke and vertical axis load were calculated. The proportionality 1 (object, i.e., the target composite) is the same as in Example 3. The calculation conditions and evaluation methods were the same as in Example 3.

[0130] 2. Calculation level Assuming the same material used for the three-point bending test specimen in Example 1, three-point bending calculations were performed at the following levels. The proportionality 1 (object) was constructed with a fiber-reinforced plastic (FRP) laminate portion that was not ribbed but had a flat plate shape (a flat plate shape with the same area as the steel plate). The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer).

[0131] Example 5-1 of the present invention features a rib-shaped FRP laminate, with three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate has a thickness of 0.4 mm, the FRP laminate has a thickness of 1.5 mm, and the FRP laminate is a laminate of AFRP (aramid fiber reinforced plastic) and CFRP, with a volume ratio of AFRP layer to FRP layer of 0.3. The FRP laminate has a three-layer structure, with the following layers laminated from the steel plate side, and the AFRP layer positioned in the middle of the FRP laminate. 1) 0.5mm CFRP layer 2) 0.5 mm AFRP layer 3) 0.5mm CFRP layer

[0132] Example 5-2 of the present invention is a configuration in which the layer structure of the FRP laminate is changed from that of Example 5-1 of the present invention. The FRP laminate has a two-layer structure, with the following layers laminated from the steel plate side, and the AFRP layer is located on the steel plate side of the FRP laminate. 1) 0.5 mm AFRP layer 2) 1.0 mm CFRP layer

[0133] Example 5-3 of the present invention is a configuration in which the layer structure of the FRP laminate is changed from that of Example 5-1 of the present invention. The FRP laminate has a two-layer structure, with the following layers laminated from the steel plate side, and the AFRP layer is located on the opposite side of the FRP laminate from the steel plate. 1) 1.0 mm CFRP layer 2) 0.5 mm AFRP layer

[0134] 3. Calculation results In Examples 5-1 to 5-3 of the present invention, the amount of CFRP used can be reduced by more than 30% compared to the proportionality 1 (object) configuration, the mass can be made lighter than proportionality 1 (object) by using a rib shape, and it was confirmed that the maximum bending load is also greater than or equal to proportionality 1 (object).

[0135] [Table 5]

[0136] In Example 5, the volume ratio of the AFRP layer (AFRP ratio listed in Table 5) is rounded to two decimal places. Also, in Example 5, the volume ratio of the CFRP layer is the value obtained by subtracting the volume ratio of the AFRP layer from 1, i.e., "CFRP volume ratio = 1 - AFRP volume ratio".

[0137] <Example 6> • Number of layers in the FRP laminate 1. Performance evaluation method using three-point bending calculation A three-point bending test was performed in the same manner as in Example 1. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, curves for the horizontal axis stroke and vertical axis load were calculated. The proportionality 1 (object, i.e., the target composite) is the same as in Example 3. The calculation conditions and evaluation methods were the same as in Example 3.

[0138] 2. Calculation level Assuming the same material used for the three-point bending test specimen in Example 1, three-point bending calculations were performed at the following levels. The proportionality 1 (object) was constructed with a fiber-reinforced plastic (FRP) laminate portion that was not ribbed but had a flat plate shape (a flat plate shape with the same area as the steel plate). The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer).

[0139] Comparative Example 6-1 had a rib-shaped FRP laminate, with the FRP laminate consisting of three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0.7. The FRP laminate had a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.167 mm GFRP layer 2) 0.167 mm CFRP layer 3) 0.5 mm GFRP layer 4) 0.167 mm CFRP layer

[0140] Example 6-1 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 1.3 mm in Comparative Example 6-1. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.217 mm GFRP layer 2) 0.217 mm CFRP layer 3) 0.651 mm GFRP layer 4) 0.217 mm CFRP layer

[0141] Example 6-2 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 1.4 mm in Comparative Example 6-1. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.234 mm GFRP layer 2) 0.234 mm CFRP layer 3) 0.701 mm GFRP layer 4) 0.234 mm CFRP layer

[0142] Example 6-3 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 1.5 mm in Comparative Example 6-1. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.251 mm GFRP layer 2) 0.251 mm CFRP layer 3) 0.752 mm GFRP layer 4) 0.251 mm CFRP layer

[0143] Example 6-4 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 1.7 mm in Comparative Example 6-1. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.284 mm GFRP layer 2) 0.284 mm CFRP layer 3) 0.852 mm GFRP layer 4) 0.284 mm CFRP layer

[0144] Example 6-5 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 2.0 mm in Comparative Example 6-1. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.334 mm GFRP layer 2) 0.334 mm CFRP layer 3) 1.0 mm GFRP layer 4) 0.334 mm CFRP layer

[0145] Example 6-6 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.5 mm. The FRP laminate has a 5-layer structure, with the following layers laminated from the steel plate side. 1) 0.25 mm GFRP layer 2) 0.25 mm CFRP layer 3) 0.5 mm GFRP layer 4) 0.25mm CFRP layer 5) 0.25 mm GFRP layer

[0146] Example 6-7 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.6 mm. The FRP laminate has a 5-layer structure, with the following layers laminated from the steel plate side. 1) 0.267 mm GFRP layer 2) 0.267 mm CFRP layer 3) 0.533 mm GFRP layer 4) 0.267 mm CFRP layer 5) 0.267 mm GFRP layer

[0147] Example 6-8 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.5 mm. The FRP laminate has a 13-layer structure, with the following layers laminated from the steel plate side. 1) 0.083 mm GFRP layer 2) 0.083 mm CFRP layer 3) 0.167 mm GFRP layer 4) 0.083 mm CFRP layer 5) 0.167 mm GFRP layer 6) 0.083 mm CFRP layer 7) 0.167 mm GFRP layer 8) 0.083 mm CFRP layer 9) 0.167 mm GFRP layer 10) 0.083 mm CFRP layer 11) 0.167 mm GFRP layer 12) 0.083 mm CFRP layer 13) 0.083 mm GFRP layer

[0148] Example 6-9 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.6 mm. The FRP laminate has a 13-layer structure, with the following layers laminated from the steel plate side. 1) 0.089 mm GFRP layer 2) 0.089 mm CFRP layer 3) 0.178 mm GFRP layer 4) 0.089 mm CFRP layer 5) 0.178 mm GFRP layer 6) 0.089 mm CFRP layer 7) 0.178 mm GFRP layer 8) 0.089 mm CFRP layer 9) 0.178 mm GFRP layer 10) 0.089 mm CFRP layer 11) 0.178 mm GFRP layer 12) 0.089 mm CFRP layer 13) 0.089 mm GFRP layer

[0149] Example 6-10 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.6 mm. The FRP laminate has a two-layer structure, with the following layers laminated from the steel plate side. 1) 1.066 mm GFRP layer 2) 0.533 mm CFRP layer

[0150] Example 6-11 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.7 mm. The FRP laminate has a two-layer structure, with the following layers laminated from the steel plate side. 1) 1.133 mm GFRP layer 2) 0.566 mm CFRP layer

[0151] Example 6-12 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.4 mm. The FRP laminate has a three-layer structure, with the following layers laminated from the steel plate side. 1) 0.467 mm GFRP layer 2) 0.467 mm CFRP layer 3) 0.467 mm GFRP layer

[0152] Example 6-13 of the present invention is a configuration in which the number of layers in the FRP laminate is changed from Comparative Example 6-1, and the thickness of the FRP laminate is changed to 1.5 mm. The FRP laminate has a three-layer structure, with the following layers laminated from the steel plate side. 1) 0.5 mm GFRP layer 2) 0.5mm CFRP layer 3) 0.5 mm GFRP layer

[0153] 3. Calculation results In Examples 6-1 to 6-13 of the present invention, the amount of CFRP used can be reduced by more than 30% compared to the proportionality 1 (object) configuration, and it was confirmed that the maximum bending load is more than 80% of that of proportionality 1 (object) (Examples 6-1, 6-2, 6-6, 6-8, 6-10, 6-12), or greater than that of proportionality 1 (object) (Examples 6-3, 6-4, 6-5, 6-7, 6-9, 6-11, 6-13). Furthermore, in Examples 6-1 to 6-4 and 6-6 to 6-13 of the present invention, it was confirmed that the mass can be made equivalent to or lighter than that of proportionality 1 (object) by using a rib shape.

[0154] [Table 6]

[0155] <Example 7> • Number of ribs in the FRP laminate 1. Performance evaluation method using three-point bending calculation A three-point bending test was performed in the same manner as in Example 1. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, curves for the horizontal axis stroke and vertical axis load were calculated. The proportionality 1 (object, i.e., the target composite) is the same as in Example 3. The calculation conditions and evaluation methods were the same as in Example 3.

[0156] 2. Calculation level Assuming the same material used for the three-point bending test specimen in Example 1, three-point bending calculations were performed at the following levels. The proportionality 1 (object) was constructed with a fiber-reinforced plastic (FRP) laminate portion that was not ribbed but had a flat plate shape (a flat plate shape with the same area as the steel plate). The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer).

[0157] Example 7-1 of the present invention features a rib-shaped FRP laminate, with three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness is 0.4 mm, the FRP laminate thickness is 1.5 mm, and the volume ratio of the GFRP layer in the FRP laminate is 0.7. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.251 mm GFRP layer 2) 0.251 mm CFRP layer 3) 0.752 mm GFRP layer 4) 0.251 mm CFRP layer

[0158] Example 7-2 of the present invention is a configuration in which the number of ribs in the FRP laminate is changed from that of Example 7-1 of the present invention. The FRP laminate is configured with five ribs, each 1.5 mm wide, spaced 1.875 mm apart (distance from end to end of rib is 15 mm).

[0159] Example 7-3 of the present invention is a configuration in which the number of ribs in the FRP laminate is changed from Example 7-1 of the present invention. The FRP laminate is configured with 10 ribs, each 0.75 mm wide, arranged at intervals of 0.833 mm (distance from end to end of rib is 15 mm).

[0160] Example 7-4 of the present invention is a configuration in which the number of ribs in the FRP laminate is changed from Example 7-1 of the present invention. The FRP laminate is configured with two ribs, each 3.75 mm wide, spaced 7.5 mm apart (distance from end to end of rib: 15 mm).

[0161] In Invention Example 7-5, the configuration was changed by varying the number of ribs in the FRP laminate in Invention Example 7-1. The FRP laminate was configured to have one rib with a width of 7.5 mm at the center position, and gaps of 3.75 mm (regions where no ribs are provided) on both sides of the rib.

[0162] In Invention Example 7-6, the configuration was changed by varying the thickness of the FRP laminate to 2.5 mm in Invention Example 7-1. The FRP laminate had a four-layer structure, with the following layers laminated from the steel plate side. 1) A GFRP layer of 0.418 mm 2) A CFRP layer of 0.418 mm 3) A GFRP layer of 1.253 mm 4) A CFRP layer of 0.418 mm

[0163] 3. Calculation Results In Invention Examples 7-1 to 7-6, it was confirmed that the amount of CFRP used could be reduced by 30% or more compared to the configuration of Comparative Ratio 1 (object), the mass could be made lighter than that of Comparative Ratio 1 (object) by adopting the rib shape, and the maximum bending load could also be made greater than that of Comparative Ratio 1 (object).

[0164]

Table 7

[0165] <Example 8> · Short fiber FRP and 90° oriented FRP 1. Performance Evaluation Method by Three-Point Bending Calculation Similar to Example 1, a three-point bending test was conducted using the three-point bending test method shown in FIG. 14. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, a curve with the horizontal axis stroke and the vertical axis load was calculated. Also, the configurations disclosed in the prior art documents JP-A-2019-119213 and JP-A-2021-98374 were used as Comparative Ratio 2 and Comparative Ratio 3 (objects, i.e., target composites).

[0166] In the example using short-fiber FRP, the maximum bending load was evaluated as follows: 157.25 N (i.e., the maximum bending load of proportionality 2) or higher was rated A (○), 80% of 157.25 N (i.e., 125.80 N) or higher was rated B (△), and less than 125.80 N was rated C (×). On the other hand, in the example using 90° oriented FRP, the maximum bending load was evaluated as follows: 122.10 N (i.e., the maximum bending load of proportionality 3) or higher was rated A (○), 80% of 122.10 N (i.e., 97.68 N) or higher was rated B (△), and less than 97.68 N was rated C (×). Masses of 9.2g or less (i.e., a mass of proportionality 2 or 3) were evaluated as A (○), and those exceeding that were evaluated as B (×). The amount of CFRP used (by volume) is 1.95 cm³. 3 We evaluated samples with CFRP usage less than (i.e., proportional to 2 or 3) as A (○), and those with usage equal to or greater than that as B (×). CFRP reduction rates were evaluated as follows: A (〇) for 30% or more, B (△) for over 0% but less than 30%, and C (×) for 0% or less.

[0167] 2. Calculation level The carbon fiber prepreg and glass fiber prepreg were modified from the materials used in the three-point bending test specimens in Example 1, as follows, and three-point bending calculations were performed at the following levels. (Proportional ratio 2, Example 8-1 of the present invention: Example using short fiber FRP) • Polyacrylonitrile (PAN) carbon short fiber prepreg (manufactured by Mitsubishi Chemical Corporation, product name: STR120N131) • Glass short fiber prepreg (manufactured by OJI F-TEX, product name: GFC-30C) (Proportional ratio 3, Examples 8-2 and 8-3 of the present invention: Examples using 90° oriented FRP) • Polyacrylonitrile (PAN) carbon fiber prepreg (V) with fiber direction oriented at 90° to the longitudinal direction of the composite. f =60%) (Manufactured by Toray, product name: Toraycap prepreg, P3252S-20) • Glass fiber prepreg (V) in which the fiber direction is oriented at a 90° angle to the longitudinal direction of the composite. f =58%) (Manufactured by Nissei Co., Ltd., Product name: E13-35)

[0168] In the proportionality test 2 (object), the fiber-reinforced plastic (FRP) laminate portion was configured as a flat plate shape (a flat plate shape with the same area as the steel plate) rather than a rib shape. The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer). In proportionality 3 (object), the carbon fiber prepreg and glass fiber prepreg were changed as described above in proportionality 2 (object).

[0169] Example 8-1 of the present invention features a rib-shaped FRP laminate, with three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness is 0.4 mm, the FRP laminate thickness is 1.5 mm, and the volume ratio of the GFRP layer in the FRP laminate is 0.7. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.251 mm GFRP layer 2) 0.251 mm CFRP layer 3) 0.752 mm GFRP layer 4) 0.251 mm CFRP layer

[0170] Example 8-2 of the present invention is obtained by changing the carbon fiber prepreg and glass fiber prepreg in Example 8-1 as described above.

[0171] Example 8-3 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 1.6 mm in Example 8-2 of the present invention. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.268 mm GFRP layer 2) 0.268 mm CFRP layer 3) 0.803 mm GFRP layer 4) 0.268 mm CFRP layer

[0172] 3. Calculation results In Invention Example 8-1, the amount of CFRP used can be reduced by 30% or more compared to the configuration of Comparative Ratio 2 (object), and by making it into a rib shape, the mass can be made lighter than that of Comparative Ratio 2 (object), and it was confirmed that the maximum bending load is also equal to or greater than that of Comparative Ratio 2 (object). In Invention Examples 8-2 to 8-3, the amount of CFRP used can be reduced by 30% or more compared to the configuration of Comparative Ratio 3 (object), and by making it into a rib shape, the mass can be made lighter than that of Comparative Ratio 3 (object), and furthermore, it was confirmed that the maximum load is 80% or more (Invention Example 8-2) or equal to or greater than that of Comparative Ratio 3 (object) (Invention Example 8-3) with respect to Comparative Ratio 3 (object).

[0173]

Table 8

[0174] <Example 9> · Influence of the thickness of the adhesive layer 1. Performance evaluation method by three-point bending calculation A three-point bending test was carried out in the same manner as in Example 1. The evaluation criterion for three-point bending was evaluated by the value of the maximum bending load. From the calculation results, a curve with the horizontal axis stroke and the vertical axis load was calculated. Comparative Ratio 1 (object, that is, the target composite) is the same as Comparative Ratio 1 in Example 3. The calculation conditions and evaluation methods were the same as in Example 3.

[0175] 2. Calculation level Assuming the same materials as those used for the three-point bending test piece in Example 1, three-point bending calculations were performed for the following levels. Comparative Ratio 1 (object) had a flat plate shape (flat plate shape with the same area as the steel plate) in which the fiber reinforced plastic laminate (FRP laminate) part was not in a rib shape. The thickness of the steel plate was 0.4 mm, the thickness of the FRP laminate was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (that is, it consisted of only one layer of CFRP layer).

[0176] Example 9-1 of the present invention features a rib-shaped FRP laminate, with the FRP laminate consisting of three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness is 0.4 mm, the FRP laminate thickness is 1.5 mm, and the volume ratio of the GFRP layer in the FRP laminate is 0.7. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 1) 0.251 mm GFRP layer 2) 0.251 mm CFRP layer 3) 0.752 mm GFRP layer 4) 0.251 mm CFRP layer

[0177] Example 9-2 of the present invention is a configuration in which a 0.05 mm thick adhesive layer (adhesive: manufactured by Illinois Tool Works, product name: Plexus (product number: MA1020)) is placed between the steel plate and the GFRP layer, as in Example 9-1 of the present invention.

[0178] Example 9-3 of the present invention is a configuration in which the thickness of the adhesive layer is changed to 0.2 mm in Example 9-2 of the present invention.

[0179] Example 9-4 of the present invention is a configuration in which the FRP thickness is changed to 1.3 mm in Example 9-3 (i.e., the combined thickness of the adhesive layer and the FRP laminate is changed to 1.5 mm).

[0180] 3. Calculation results In Examples 9-1 to 9-4 of the present invention, the amount of CFRP used can be reduced by more than 30% compared to the proportionality 1 (object) configuration, the mass can be made lighter than proportionality 1 (object) by using a rib shape, and it was confirmed that the maximum load is 80% or more of that of proportionality 1 (object) (Example 9-4), or greater than or equal to proportionality 1 (object) (Examples 9-1 to 9-3).

[0181] [Table 9]

[0182] <Example 10> • Laminate thickness and GFRP volume ratio 1. Performance evaluation method using three-point bending calculation A three-point bending test was performed in the same manner as in Example 1. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, curves for the horizontal axis stroke and vertical axis load were calculated. The proportionality 1 (object, i.e., the target composite) is the same as in Example 3. The calculation conditions and evaluation methods were the same as in Example 3.

[0183] 2. Calculation level Assuming the same material used for the three-point bending test specimen in Example 1, three-point bending calculations were performed at the following levels. The proportionality 1 (object) was constructed with a fiber-reinforced plastic (FRP) laminate portion that was not ribbed but had a flat plate shape (a flat plate shape with the same area as the steel plate). The steel plate thickness was 0.4 mm, the FRP laminate thickness was 1.0 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer).

[0184] Example 10-1 of the present invention features a rib-shaped FRP laminate, with three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness is 0.4 mm, the FRP laminate thickness is 1.3 mm, and the volume ratio of the GFRP layer in the FRP laminate is 0.1. The FRP laminate has a three-layer structure, with the following layers laminated from the steel plate side. 1) 0.065 mm GFRP layer 2) 1,170 mm CFRP layer 3) 0.065 mm GFRP layer

[0185] Example 10-2 of the present invention is a modified version of Example 10-1 in which the thickness of the FRP laminate is changed to 1.4 mm, and the following layers are laminated from the steel plate side. 1) 0.070 mm GFRP layer 2) 1,260 mm CFRP layer 3) 0.070 mm GFRP layer

[0186] Example 10-3 of the present invention is a modified version of Example 10-2 in which the GFRP ratio is changed to 0.2, and the following layers are laminated from the steel plate side. 1) 0.140 mm GFRP layer 2) 1,120 mm CFRP layer 3) 0.140 mm GFRP layer

[0187] Example 10-4 of the present invention is a modified version of Example 10-1 in which the thickness of the FRP laminate is changed to 1.5 mm, the GFRP ratio is changed to 0.3, and the following layers are laminated from the steel plate side. 1) 0.225 mm GFRP layer 2) 1.050 mm CFRP layer 3) 0.225 mm GFRP layer

[0188] Example 10-5 of the present invention is a modified version of Example 10-4 in which the GFRP ratio is changed to 0.4, and the following layers are laminated from the steel plate side. 1) 0.300 mm GFRP layer 2) 0.900 mm CFRP layer 3) 0.300 mm GFRP layer

[0189] Example 10-6 of the present invention is a modified version of Example 10-1 in which the thickness of the FRP laminate is changed to 1.6 mm, the GFRP ratio is changed to 0.5, and the following layers are laminated from the steel plate side. 1) 0.400 mm GFRP layer 2) 0.800 mm CFRP layer 3) 0.400 mm GFRP layer

[0190] Example 10-7 of the present invention is a modified version of Example 10-6 in which the GFRP ratio is changed to 0.6, and the following layers are laminated from the steel plate side. 1) 0.480 mm GFRP layer 2) 0.640 mm CFRP layer 3) 0.480 mm GFRP layer

[0191] Example 10-8 of the present invention is a modified version of Example 10-1 in which the thickness of the FRP laminate is changed to 1.7 mm, the GFRP ratio is changed to 0.8, and the following layers are laminated from the steel plate side. 1) 0.680 mm GFRP layer 2) 0.340 mm CFRP layer 3) 0.680 mm GFRP layer

[0192] 3. Calculation results In Examples 10-1 to 10-8 of the present invention, the amount of CFRP used can be reduced by more than 30% compared to the proportionality 1 (object) configuration, and it was confirmed that the maximum load is more than 80% of that of proportionality 1 (object) (Examples 10-1, 10-3, 10-5), or greater than that of proportionality 1 (object) (Examples 10-2, 10-4, 10-6, 10-7, 10-8). In addition, in Examples 10-1 to 10-7 of the present invention, the mass can be made lighter than that of proportionality 1 (object) by using a rib shape.

[0193] [Table 10]

[0194] <Example 11> 1. Performance evaluation method using three-point bending calculation Similar to Example 1, a three-point bending test was performed using the three-point bending test method shown in Figure 14. The evaluation criterion for three-point bending was the value of the maximum bending load. From the calculation results, curves for the horizontal axis stroke and vertical axis load were calculated. Furthermore, the configurations disclosed in prior art, JP 2019-119213 and JP 2021-98374, were used as the proportional relationship (object, i.e., object composite). The maximum bending load was evaluated as follows: A (〇) if it was 3389.01N (i.e., the proportional maximum bending load) or higher, B (△) if it was 80% of 3389.01N (i.e., 2711.21N) or higher, and C (×) if it was less than 2711.21N. Masses of 23.01g or less (i.e., proportional mass) were rated A (○), and those exceeding that were rated B (×). The amount of CFRP used (by volume) is 4.875 cm³. 3 We evaluated samples with a usage amount less than (i.e., proportional to) the amount of CFRP used as A (○), and those with a usage amount equal to or greater than that as B (×). CFRP reduction rates were evaluated as follows: A (〇) for 30% or more, B (△) for over 0% but less than 30%, and C (×) for 0% or less.

[0195] 2. Calculation level Assuming the same material used for the three-point bending test specimen in Example 1, three-point bending calculations were performed at the following levels. The proportional (object) was configured with a fiber-reinforced plastic (FRP) laminate that was not ribbed but had a flat plate shape (a flat plate with the same area as the steel plate). The steel plate thickness was 1.0 mm, the FRP laminate thickness was 2.5 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0 (i.e., it consisted of only one CFRP layer). Comparative Example 11-1 was a configuration in which the volume ratio of the GFRP layer in the FRP laminate was changed to 0.05 in the proportional (target object) configuration. The FRP laminate had a two-layer structure, consisting of a 0.125 mm GFRP layer and a 2.375 mm CFRP layer from the steel plate side.

[0196] Comparative Example 11-2 had a rib-shaped FRP laminate, with the FRP laminate consisting of three 2.5 mm wide ribs spaced 3.75 mm apart. The steel plate thickness was 1.0 mm, the FRP laminate thickness was 2.5 mm, and the volume ratio of the GFRP layer in the FRP laminate was 0.7 (more specifically 0.666...). The FRP laminate had a four-layer structure, with the following layers laminated from the steel plate side. 0.417mm GFRP layer, 0.417mm CFRP layer 1.25mm GFRP layer 0.417mm CFRP layer

[0197] Example 11-1 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 3.75 mm (1.5 times that of Comparative Example 11-2) compared to Comparative Example 11-2. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 0.625mm GFRP layer 0.625mm CFRP layer 1.875 mm GFRP layer 0.625mm CFRP layer

[0198] Example 11-2 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 4.25 mm (1.7 times that of Comparative Example 11-2) compared to Comparative Example 11-2. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 0.71mm GFRP layer 0.71mm CFRP layer 2.12mm GFRP layer 0.71mm CFRP layer

[0199] Example 11-3 of the present invention is a configuration in which the thickness of the FRP laminate is changed to 5.0 mm (2.0 times that of Comparative Example 11-2) compared to Comparative Example 11-2. The FRP laminate has a four-layer structure, with the following layers laminated from the steel plate side. 0.834 mm GFRP layer 0.834mm CFRP layer 2.5mm GFRP layer 0.834mm CFRP layer

[0200] 3. Calculation results In Examples 11-1, 11-2, and 11-3 of the present invention, the amount of CFRP used could be reduced by more than 30% compared to the proportional (object) configuration, and it was also confirmed that the maximum bending load was higher than that of the proportional (object) configuration. Furthermore, in Examples 11-1 and 11-2 of the present invention, it was confirmed that by using a rib shape, the mass could be made equivalent to or lighter than that of the proportional (object) configuration.

[0201] [Table 11] [Explanation of Symbols]

[0202] 2, 102 steel plate 10, 10Y, 20, 30, 40, 50, 60, 70, 80, 90 Fiber-reinforced plastic laminates 82 Indenter 84 Support points 100X, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 Steel plate fiber reinforced plastic composite 202 Support C11, C12, C21, C22, C31, C32, C33, C41, C51, C61, C62, C71, C72, C81, C82, C91, C92, C101 Carbon Fiber Reinforced Plastic (CFRP) Layers G11, G12, G21, G22, G23, G31, G32, G33, G41, G51, G52, G61, G62, G71, G72, G81, G82, G91, G92 Glass Fiber Reinforced Plastic (GFRP) Layer

Claims

1. Steel plate and, The steel plate comprises one or more rib-shaped fiber-reinforced plastic laminates that protrude from the steel plate in the thickness direction, have an area smaller than that of the steel plate in a direction perpendicular to the thickness direction, and are bonded to the steel plate. The fiber-reinforced plastic laminate is formed by alternately laminating one or more layers of carbon fiber-reinforced plastic and one or more layers of fiber-reinforced plastic containing fibers other than carbon fibers in the thickness direction. Steel plate-fiber-reinforced plastic composite.

2. The steel plate-fiber-reinforced plastic composite according to claim 1, wherein the fiber-reinforced plastic laminate contains fiber-reinforced plastic other than carbon fiber, and the fiber-reinforced plastic is glass fiber-reinforced plastic.

3. The steel plate-fiber-reinforced plastic composite according to claim 2, wherein the layer of the fiber-reinforced plastic laminate that is positioned closest to the steel plate is the glass fiber-reinforced plastic layer.

4. The steel plate-fiber-reinforced plastic composite according to claim 2, wherein a layer of glass fiber-reinforced plastic having an area larger than that of the fiber-reinforced plastic laminate is provided between the steel plate and the fiber-reinforced plastic laminate, and the fiber-reinforced plastic laminate is bonded to the steel plate via the layer of glass fiber-reinforced plastic.

5. The steel plate-fiber-reinforced plastic composite according to claim 2, wherein the fiber-reinforced plastic laminate has a four-layer structure in which layers of glass fiber-reinforced plastic and layers of carbon fiber-reinforced plastic are alternately laminated.

6. The steel plate-fiber-reinforced plastic composite according to claim 2, wherein the fiber-reinforced plastic laminate has a five-layer structure in which layers of glass fiber-reinforced plastic and layers of carbon fiber-reinforced plastic are alternately laminated.

7. The steel plate-fiber-reinforced plastic composite according to claim 6, wherein the central position of the fiber-reinforced plastic laminate in the lamination direction is located in the middle layer of the five-layer structure.

8. The steel plate-fiber-reinforced plastic composite according to claim 2, wherein the fiber-reinforced plastic laminate has a structure of six or more layers in which layers of glass fiber-reinforced plastic and layers of carbon fiber-reinforced plastic are alternately laminated.

9. The steel plate-fiber-reinforced plastic composite according to claim 2, wherein the fiber-reinforced plastic laminate has a two-layer structure in which layers of glass fiber-reinforced plastic and layers of carbon fiber-reinforced plastic are alternately laminated.

10. The steel plate-fiber-reinforced plastic composite according to claim 2, wherein the fiber-reinforced plastic laminate has a three-layer structure in which layers of glass fiber-reinforced plastic and layers of carbon fiber-reinforced plastic are alternately laminated.

11. The system has multiple rib-shaped fiber-reinforced plastic laminates, Multiple fiber-reinforced plastic laminates are provided with a support between them. The steel plate-fiber-reinforced plastic composite according to claim 1.

12. The steel plate-fiber-reinforced plastic composite according to claim 1, wherein the fiber-reinforced plastic laminate has another steel plate on the side opposite to the steel plate.

13. For the target composite described below, the volume of the carbon fiber reinforced plastic is 70% or less. For the composites listed below, the maximum bending stiffness is 80% or more. The steel plate-fiber-reinforced plastic composite according to any one of claims 1 to 12. -Target Complex- The target composite comprises a target steel plate and a single target fiber-reinforced plastic laminate bonded to the target steel plate, having the same area in a direction perpendicular to the thickness direction of the target steel plate as the target steel plate, and consisting solely of carbon fiber-reinforced plastic. The aforementioned steel plate is a steel plate of the same material, same area, and same thickness as the steel plate in the steel plate-fiber-reinforced plastic composite. The above-mentioned fiber-reinforced plastic laminate represents a laminate in which the carbon fiber-reinforced plastic is made of the same material as the carbon fiber-reinforced plastic in the steel plate-fiber-reinforced plastic composite, and has a thickness of 1.0 mm.

14. For the target composite described below, the volume of the carbon fiber reinforced plastic is less than 100%, For the following target composites, the maximum bending stiffness is 100% or more. The steel plate-fiber-reinforced plastic composite according to any one of claims 1 to 12. -Target Complex- The target composite comprises a target steel plate and a single target fiber-reinforced plastic laminate bonded to the target steel plate, having the same area in a direction perpendicular to the thickness direction of the target steel plate as the target steel plate, and consisting solely of carbon fiber-reinforced plastic. The aforementioned steel plate is a steel plate of the same material, same area, and same thickness as the steel plate in the steel plate-fiber-reinforced plastic composite. The above-mentioned fiber-reinforced plastic laminate represents a laminate in which the carbon fiber-reinforced plastic is made of the same material as the carbon fiber-reinforced plastic in the steel plate-fiber-reinforced plastic composite, and has a thickness of 1.0 mm.

15. The aforementioned fiber-reinforced plastic laminate is The ratio of the thickness of the target composite to the target fiber-reinforced plastic laminate is 1.4 or more and 1.8 or less. Furthermore, the ratio of the volume of the carbon fiber reinforced plastic to the volume of the fiber reinforced plastic laminate is 0.5 or more and 0.6 or less. The steel plate-fiber-reinforced plastic composite according to claim 13.

16. The aforementioned fiber-reinforced plastic laminate is The ratio of the thickness of the target composite to the target fiber-reinforced plastic laminate is 1.4 or more and 1.9 or less. Furthermore, the steel plate-fiber-reinforced plastic composite according to claim 14, wherein the ratio of the volume of the carbon fiber-reinforced plastic to the volume of the fiber-reinforced plastic laminate is 0.3 or more and 0.9 or less.

17. An automotive component comprising the steel plate-fiber-reinforced plastic composite described in claim 1.

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