Method for reinforcing base material and composite obtained thereby

Abstract

To provide a reinforcement method of a base material that combines peeling resistance and rigidity by adhering a reinforcement materials on both sides of a base material with adhesive, advantageous in a point of cost and workability, and capable of realizing light weight and a composite.SOLUTION: A method of reinforcing a base material in which reinforcing materials are adhered to both sides of the base material across a thickness center line of the composite, and which satisfies the following formulas (1) and (2). E1 and t1 represent the elastic modulus and thickness of the reinforcing material, E2 and 2 t2 represent the elastic modulus and thickness of the base material, G and h represent the shear elastic modulus and thickness of the adhesive layer made of an adhesive, and l represents a bonding half length between the base material and the reinforcing material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for reinforcing a base material and a composite obtained thereby, and more specifically, although not particularly limited to, a method for reinforcing a base material that can be used in cases such as repairing and reinforcing (in this specification simply referred to as "reinforcement") structures such as bridges, buildings, and other construction structures, and structures such as automobiles, ships, and other transportation vehicles, and for example, by bonding a reinforcing material to a steel material to obtain a composite that can be used in vehicle manufacturing and the like, while ensuring rigidity and reducing weight, and a composite in which a reinforcing material is bonded to the base material obtained thereby. [Background technology]

[0002] Not only structures made of wooden building materials, but also those made of steel or concrete, lose their strength over time due to various factors such as corrosion, salt damage, and load, leading to cracks and distortions. In some cases, this can lead to destruction or collapse.

[0003] To prevent these problems, methods such as using high-strength bolts or splice plates to restrain construction materials or repairing them by welding can be adopted, but in recent years, attention has been focused on a method of reinforcing by bonding reinforcing materials made of fiber-reinforced composite materials with adhesives (see, for example, Patent Documents 1 and 2).

[0004] This reinforcement method, in which a reinforcing material is bonded to the surface of the base material that constitutes the structure with an adhesive, does not require the use of heavy reinforcing steel plates as splices, and does not require special processing such as drilling bolt holes, so the work can be completed in a relatively short time.Furthermore, unlike welding, it is not limited to structures made of steel.

[0005] In this type of reinforcing method, epoxy resins are primarily used as adhesives because they are heat-resistant and water-resistant. Moreover, epoxy resin adhesives generally have high strength and rigidity, allowing the reinforcing material to fully exert its stiffening effect.

[0006] However, with so-called "rigid" bonding, such as using epoxy resin or thinning the adhesive layer, peeling is likely to occur at the area where the rigidity changes. To prevent this, it is possible to use an adhesive softer than epoxy resin or increase the thickness of the adhesive layer to achieve so-called "soft" bonding, thereby improving peel resistance, but this would mean that the stiffening efficiency of the reinforcing material would not be fully achieved. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Republished Publication No. 2006-088184 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-119607 Summary of the Invention [Problem to be solved by the invention]

[0008] A reinforcement method in which a reinforcing material such as a fiber-reinforced composite material is bonded to the surface of a base material with an adhesive can reinforce a structure without using bolts, splices, etc. Therefore, if the stiffening efficiency of the reinforcing material is high, the amount of material used for reinforcement can be minimized, which is advantageous in terms of cost and workability. Furthermore, the stiffening efficiency of the reinforcing material is extremely important in terms of reducing the weight of a reinforced structure.

[0009] However, as mentioned above, if a so-called "rigid" adhesive is used to increase the stiffening efficiency of the reinforcing material, separation becomes more likely due to stress concentration at the bonded edge between the reinforcing material and the base material. If a so-called "soft" adhesive is used to solve this problem, the stiffening efficiency will decrease, so there is a trade-off between the two.

[0010] Therefore, the present inventors conducted a detailed study on factors that contribute to the peel resistance and rigidity of the base material and reinforcement material in a method of reinforcing a base material by adhering a reinforcement material to the surface of the base material with an adhesive. As a result, they found that when adhering a reinforcement material to the surface of a base material to obtain a composite, a reinforced structure that achieves both peel resistance and rigidity can be achieved by using parameters expressed by a predetermined formula, and completed the present invention.

[0011] Therefore, an object of the present invention is to provide a method for reinforcing a base material by bonding a reinforcing material to the surface of the base material with an adhesive to form a composite, which method achieves both peel resistance and rigidity, is advantageous in terms of cost and workability, and can also achieve weight reduction.

[0012] Another object of the present invention is to provide a composite in which a reinforcing material is bonded to a base material, which has both peel resistance and rigidity and is also lightweight. [Means for solving the problem]

[0013] That is, the gist of the present invention is as follows. [1] A method for reinforcing a base material by bonding a reinforcing material to the surface of the base material with an adhesive to form a composite, A method for reinforcing a base material, characterized in that, when viewed in a longitudinal cross section of the resulting composite, reinforcing materials are bonded to both sides of the thickness centerline of the composite, and the following formulas (1) and (2) are satisfied:

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[10] A composite body comprising a reinforcing material bonded to the base material according to any one of [6] to [9], wherein the base material is made of steel. [Effects of the Invention]

[0014] By reinforcing a base material using the reinforcing method of the present invention, a reinforced structure that combines peel resistance and rigidity can be realized. As a result, the amount of material used for reinforcement can be minimized while increasing stiffening efficiency, which is advantageous in terms of cost and workability, and furthermore, the resulting composite can be made lighter. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 shows an example of a composite in which a reinforcing material is bonded to a plate-shaped base material using the reinforcing method of the present invention, where (a) is an explanatory cross-sectional view (longitudinal cross-section) showing the longitudinal direction of the composite, and (b) is an explanatory cross-sectional view (transverse cross-section) taken along the cutting line AA. [Figure 2] FIG. 2 shows the shear stress τ when the composite of FIG. 1 is subjected to a tensile load 2P in the longitudinal direction, as a function of the position x at the bond length 2l. [Figure 3] FIG. 3 is a schematic explanatory diagram showing the concept of determining the stiffness development rate ξ. [Figure 4] FIG. 4 is a graph showing the relationship between cl and the stress concentration factor α, and the relationship between cl and the stiffness development rate ξ. [Figure 5] FIG. 5 shows an example of a composite in which a reinforcing material is bonded to a hollow columnar base material having a square pipe shape by the reinforcing method of the present invention, where (a) is an explanatory oblique view of the hollow columnar base material, and (b) is an explanatory cross-section of the obtained composite (a cross-section along the cutting line BB of the hollow columnar base material). [Figure 6] FIG. 6 shows an example of a composite in which a reinforcing material is bonded to a hollow columnar base material, which is formed by bonding a plate-shaped base material to a hat-shaped base material, using the reinforcing method of the present invention. (a) is an oblique explanatory view of the hollow columnar base material, and (b) is an explanatory view of a cross section of the obtained composite (a cross section along the cutting line CC of the hollow columnar base material). [Figure 7] FIG. 7 is an explanatory diagram showing the relationship between the thickness centerline H of the composite and the rigidity centerline H' of the composite. [Figure 8] FIG. 8 is a schematic diagram for explaining a test complex prepared in an example of the present invention, where (a) is a perspective explanatory view and (b) is a longitudinal cross-sectional explanatory view. [Figure 9] FIG. 9 is a graph plotting the region defined by the relationship equations (1) and (2) for realizing an ideal reinforcement method according to the present invention, and the results of each test composite in the experimental examples. [Figure 10] FIG. 10 is a conventional example for explaining the shear lag theory, and is an explanatory cross-sectional (longitudinal) view showing a joint having an adhesive layer formed by bonding two adherends with an adhesive. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below. The present invention is a method for reinforcing a base material by bonding a reinforcing material to the surface of the base material with an adhesive to form a composite, characterized in that, when viewed in a longitudinal cross section of the resulting composite, reinforcing materials are bonded to both sides of the thickness centerline of the composite, and the following formulas (1) and (2) are satisfied:

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[0017] The reinforcement method of the present invention makes it possible to realize a reinforced structure that combines peel resistance and rigidity based on the above equations (1) and (2). Of these, c in equation (2) is also used in differential equations that appear in shear lag theory, and is represented by ω in the following equation, for example.

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[0018] That is, the shear lag theory states that when two adherends 31, which are assumed to undergo only elongation deformation, are bonded with an adhesive to form a joint having an adhesive layer 12, as in the lap joint shown in Figure 10, and the upper and lower adherends 31 and adhesive layer 12 are both considered to be elastic, and a tensile load P is applied in the x-axis direction of these adherends 31 to pull them against each other, a so-called "shear lag" occurs, whereby uniform shear stress does not occur in the adhesive layer 12. When this "shear lag" occurs, it is thought that shear stress will concentrate at the edge of the adhesive layer 12, causing peeling.

[0019] Shear lag theory deals with the shear stress distribution when dissimilar materials are bonded together with an adhesive. Therefore, in this invention, the thickness and elastic modulus of the adhesive layer consisting of the base material, reinforcing material, and adhesive are used as material parameters, as shown in equation (2) above. However, unlike the joint of adherends shown in Figure 10, the reinforcement method of this invention relates to a continuous structure of the base material and reinforcing material, in which the reinforcing material is bonded to the surface of the base material to form a composite.

[0020] FIG. 1 shows an example of a composite obtained by the method for reinforcing a base material according to the present invention. This composite has a plate-shaped base material 1, which is a plate-shaped base material, and a reinforcing material 3 bonded to both the front and back surfaces of the base material 1 with adhesive layers 2 made of adhesive. FIG. 2 shows the shear stress τ when the composite of FIG. 1 is subjected to a tensile load 2P in its longitudinal direction (x-axis direction), as a function of the position x at the bond length 2l between the base material and the reinforcing material. This FIG. 2 is based on the shear stress distribution of the shear lag theory mentioned above, but the shear stress τ reaches its minimum value at the center of the bond in the longitudinal direction of the composite (x=0), and the shear stress distribution is symmetrical around this center of the bond, with the shear stress τ at both ends of the bond (bond end stress τx=±l ) is considered to be the highest. The average shear stress shown in Figure 2 represents the average value of stress at positions x = -l to l. As shown in Figure 1(a), in this composite, the reinforcing materials are bonded symmetrically on both sides of the thickness centerline M of the base material, so the tensile load is set to 2P.

[0021] Therefore, in the present invention, the rigidity ratio r between the base material and the reinforcement is expressed by the above formula (4), and it is assumed that the material parameter c expressed by the above formula (3) multiplied by the half-length l of the bond between the base material and the reinforcement is sufficiently large, and the bond end stress τ in the composite of the continuous structure shown in Figure 1 is x=±l (MPa), the edge stress concentration coefficient α of the adhesive layer, and the stiffness development rate ξ can be derived based on the shear lag theory and expressed by the formulas shown in Table 1 below. Table 1 also shows the material parameter c and stiffness ratio r mentioned above. [Table 1]

[0022] In determining these equations, it is known that in a double-sided adhesive structure such as that shown in Figure 1, the distribution of shear stress acting on the adhesive layer in the range of 0≦x≦l under tension can be expressed as follows (8).

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[0023] Therefore, since the formula for the bonded edge stress shown in Table 1 is x = l, if we insert this into the above formula (8) and if cl is sufficiently large, the bonded edge stress τ x=l can be expressed as follows. As shown in Figure 2, the adhesive edge stress is equal at both ends (τ x=-l =τ x=+l ).

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[0024] The stress concentration factor α at the end of the adhesive layer (hereinafter simply referred to as the stress concentration factor α) is the ratio of the adhesive end stress τ to the average shear stress in the adhesive length as shown in Figure 2. x=-l,+l This represents the ratio (adhesion end stress / average shear stress). In other words, the previous τ(l) is converted to the average shear stress τ ave The stress concentration factor α is the sum of the average shear stress τ ave Since the stress concentration factor α can be calculated by dividing the tensile force P by the adhesive area (P / l), the stress concentration factor α can be expressed as follows:

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[0025] Furthermore, as shown in the schematic diagram of Figure 3, the stiffness development ratio ξ is the displacement of the adhesive layer edge when a tensile load is applied to a composite in which a reinforcement material is bonded to a base material, compared to the displacement when a perfect composite cross-section of the base material and reinforcement material is assumed without the adhesive layer. In other words, a perfect composite cross-section is a state (conceptually ideal state) in which all cross-sections of a component made of multiple materials are effective against tensile and bending forces, there is no shear deformation between the base material and reinforcement material, and they are completely integrated. The stiffness development ratio ξ is then calculated by dividing the stiffness of the composite (i) by the stiffness of the composite assuming a perfect composite cross-section (ii).

[0026] Here, when expressing the stiffness development rate ξ% using formula (7) shown in Table 1, the tensile stress generated in the bonded length of the base material with respect to the above "stiffness (i) of the composite" is as follows:

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[0027] Figure 4 shows graphs of the relationship between cl and the stress concentration factor α, which is an index of peel resistance, and the relationship between cl and the stiffness expression factor ξ, which is an index of stiffness. In Figure 4, the graph shown as an approximate curve is the relationship between cl and the stiffness expression factor ξ. Also, the graph shown as an approximate straight line is the relationship between cl and the stress concentration factor α. In both graphs, the horizontal axis represents cl, the left vertical axis represents the value of the stiffness expression factor ξ, and the right vertical axis represents the stress concentration factor α. In addition, in these graphs, the stiffness ratio between the base material and the reinforcement material is r = 0.25, 0.5, 1, 2, and 4, respectively.

[0028] In the present invention, in order to maximize the rigidity of the composite while preventing peeling at the adhesive layer edges, the following conditions were set for the stress concentration factor α, which is an index of peel resistance, and the rigidity expression rate ξ, which is an index of rigidity. In other words, with regard to the rigidity expression rate ξ, in adhesive structures, the rigidity of the adhesive is generally lower than that of the base material, so the rigidity of the reinforcing material is not fully expressed. Therefore, a rigidity expression rate ξ of 50% or more can be said to ensure sufficient rigidity. Furthermore, a stress concentration factor α of 10 or less can be said to satisfy peel resistance. Incidentally, when using epoxy resin as an adhesive to achieve a so-called "rigid" bond, it is generally difficult to achieve a stress concentration factor α of 10 or less.

[0029] Therefore, assuming that the ideal state in the base material reinforcing method of the present invention is one in which the stiffness development rate ξ is 50% or more and the stress concentration coefficient α is 10 or less, solving the equations in the graphs shown in Figure 4 (both r and cl are 0 or more) results in the following i) and ii). In other words, to obtain the above ideal state, it is necessary to satisfy condition iii).

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[0030] Considering the types and thicknesses of the base material and reinforcing material used in the base material reinforcement method of the present invention, it is realistic for the rigidity ratio r to be 9 or less. Therefore, to realize an ideal reinforcement method that can maximize the rigidity of the composite while preventing peeling at the adhesive layer edges, it is necessary to satisfy r≦9 and r≦cl≦(10 / r)+10, i.e., satisfy formulas (1) and (2) of the present invention. In the examples described below, the region defined by formulas (1) and (2) is shown in a graph ( FIG. 8 ).

[0031] In the present invention, there are no particular limitations on the base material to be reinforced, and it can be used for any structure that requires reinforcement, such as steel, aluminum (including aluminum alloys, the same applies below), titanium (titanium alloys), magnesium (magnesium alloys), etc., with steel being particularly preferred.

[0032] Examples of steel materials include iron and iron-based alloys, including stainless steel. Iron and iron-based alloys are preferred, and steel materials with a higher elastic modulus than other metals are even more preferred. Examples of such steel materials include cold-rolled steel sheets for general use, drawing, or ultra-deep drawing, as specified by the Japanese Industrial Standards (JIS) and other standards, as thin steel sheets used in automobiles, cold-rolled high-tensile steel sheets with workability for automobiles, hot-rolled steel sheets for general use or processing, hot-rolled steel sheets for automobile structures, and hot-rolled high-tensile steel sheets with workability for automobiles. Carbon steels, alloy steels, and high-tensile steels used for general structural and mechanical structures are also included. The components of such steel materials are not particularly limited, but may contain, in addition to Fe and C, one or more of Si, Mn, S, P, Al, N, Cr, Mo, Ni, Cu, Ca, Mg, Ce, Hf, La, Zr, and Sb. One or more of these additive elements can be appropriately selected to obtain the desired material strength and formability, and the content can also be adjusted appropriately.

[0033] The various steel materials described above preferably have a tensile strength of 590 MPa or more, and more preferably have a tensile strength of 980 MPa or more.

[0034] The steel material may also be subjected to any surface treatment. Examples of surface treatment 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 surface roughening treatments such as sandblasting or chemical surface roughening treatments such as chemical etching. Furthermore, the steel material may be subjected to alloying of plating or multiple types of surface treatments. It is preferable that the surface treatment be at least a treatment aimed at imparting rust prevention properties.

[0035] The type of plating applied to the steel material is not particularly limited, and various known platings such as zinc-based plating can be used. For example, as the plated steel sheet (steel material), hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, Zn-Al-Mg alloy-plated steel sheet, aluminum-plated steel sheet, electrogalvanized steel sheet, electro-Zn-Ni alloy-plated steel sheet, etc. can be used.

[0036] Furthermore, there are no particular limitations on the structures that require reinforcement, and examples include transportation and transport equipment such as automobiles, trains, ships, and airplanes, as well as general industrial structures such as unmanned aerial vehicles such as drones, industrial robot components in manufacturing factories for liquid crystal displays, etc., bridges for rivers, roads, railways, etc., as well as buildings, houses, livestock barns, and other architectural structures such as signs, and various other structures and constructions. The thickness of the base material is not particularly limited, but for example, in the case of steel materials that make up these structures, it is generally within the range of 0.8 to 9 mm.

[0037] Furthermore, the reinforcing material is not particularly limited, but is preferably a woven, knitted or nonwoven fabric using reinforcing fibers such as glass fiber or carbon fiber, a unidirectional material (UD material) in which fibers are aligned in one direction, impregnated with resin and cured, or a fiber reinforced composite material (Fiber Reinforced Plastics: FRP) obtained by dispersing short fibers of the reinforcing fibers in resin.

[0038] Examples of fiber materials (reinforcing fiber materials) used in FRP include glass fiber, carbon fiber, aramid fiber, basalt fiber, and ceramic fiber, but in the present invention, glass fiber and carbon fiber are preferred, and carbon fiber is particularly preferred.

[0039] Furthermore, the FRP reinforcing material is preferably in the form of a plate. Its production can be achieved by any of the following commonly known methods: heat-pressure molding of laminated FRP molding prepregs (autoclave method, hot press method); RTM (reinforced to mold) method, in which a liquid resin is injected into a reinforcing fiber substrate placed in a mold and then impregnated; pultrusion molding (pultrusion method), in which continuous fibers are impregnated with resin and then drawn into a mold for heat curing; and injection molding (injection molding). The width of the reinforcing material is difficult to specify because it varies depending on the type of reinforcing material, the intended use of the resulting composite, and the purpose of the reinforcement. However, the width of the reinforcing material as viewed in a cross section perpendicular to the longitudinal direction of the composite is generally approximately 10 to 300 mm. The thickness of the reinforcing material also varies depending on the type and purpose of the reinforcement. For example, when the reinforcing material is made of the fiber-reinforced composite material described above, it is generally within the range of 1 to 20 mm.

[0040] Furthermore, the resin (matrix resin) that forms the reinforcing material is not particularly limited, and may be any of thermosetting resins such as epoxy resin and vinyl ester resin, and thermoplastic resins such as nylon, polyphenylene sulfide (PPS) resin, and phenoxy resin.

[0041] Furthermore, the adhesive used in the present invention is not particularly limited, and commonly used thermosetting or thermoplastic resins can be used. For example, suitable thermosetting resins include room-temperature curing or thermosetting epoxy resins, vinyl ester resins, MMA resins, acrylic resins, unsaturated polyester resins, and phenolic resins. Suitable thermoplastic resins include thermoplastic polyesters, polyolefins, polyamides, and ethylene vinyl acetate. The resin used as the adhesive may be the same as or different from the resin used in the fiber-reinforced composite material used as the reinforcing material. The thickness of the adhesive layer formed by these adhesives is generally within the range of 0.1 to 5 mm.

[0042] In the method for reinforcing a base material according to the present invention, when viewed in a longitudinal cross section of the resulting composite, reinforcing materials are bonded to both sides of the thickness centerline of the composite. This is because if a reinforcing material is bonded only to one side, the effect of bending on the composite when a tensile load is applied cannot be ignored. If the base material and reinforcing material have similar elastic moduli and similar thicknesses, the concept of the present invention can be applied to a composite in which a reinforcing material is bonded to one side of the base material. However, this is not realistic in terms of the idea of ​​reinforcing a base material while reducing its weight by using a reinforcing material made of a different material from the base material. Therefore, in this invention, taking into account the effect of eccentric bending that occurs when tension is applied to the base material, the method specifies a case in which a base material is reinforced by reinforcing materials bonded to both sides of the thickness centerline of the composite when viewed in a cross section (transverse cross section) perpendicular to the longitudinal direction of the composite.

[0043] As a form of such reinforcement, first, there is a case where reinforcing materials are bonded to both the front and back surfaces of a plate-shaped base material, as shown in Fig. 1. That is, in this example, as shown in Fig. 1(b), reinforcing materials 3 are bonded via adhesive layers 2 to both sides of a thickness centerline M in a longitudinal cross section of the plate-shaped base material 1.

[0044] Another example is a hollow columnar base material having a box-shaped cross section and a hollow portion, to which a reinforcing material is bonded via an adhesive layer 2 to the inner or outer wall surface thereof. For example, in FIG. 5(a), a hollow columnar base material 11 having a box-shaped cross section and a hollow portion 4 in the shape of a square pipe is bonded via an adhesive layer 2 to the opposing inner wall surfaces thereof, as shown in the cross section (transverse cross section) of FIG. 5(b). In other words, the reinforcing material 3 is bonded to both sides of the thickness centerline M of the square pipe-shaped hollow columnar base material 11 in the transverse cross section. In this case, the reinforcing material 3 may be bonded via an adhesive layer 2 to the outer wall surface of the hollow columnar base material 11, rather than to the inner wall surface thereof.

[0045] 6(a), a hollow columnar base material 21 having a hollow portion 4 formed by bonding a plate-shaped base material 21b to a hat-shaped base material 21a has a cross section (transverse cross section) in which reinforcing materials 3 are bonded to opposing inner wall surfaces via adhesive layers 2, as shown in the cross section (horizontal cross section) of the hollow columnar base material 21. That is, the reinforcing materials 3 are bonded to both sides of the thickness centerline M in the transverse cross section of the hollow columnar base material 21 formed by bonding the plate-shaped base material 21b to the hat-shaped base material 21a. In this case, the reinforcing materials 3 may also be bonded to the outer wall surfaces of the hat-shaped base material 21a and the plate-shaped base material 21b.

[0046] The present invention also covers cases where the width of the reinforcing material does not match the width of the base material, as in the examples of Figures 5 and 6 above. In other words, it also covers reinforcing methods in cases where the width of the reinforcing material 3 shown in Figure 5(b) does not match the width of the base material 1, or where the width of the reinforcing material 3 shown in Figure 6(b) does not match the width of the base material 21a or 21b. In such cases, the present invention works in the adhesive region where the reinforcing material is adhered to the base material.

[0047] In the present invention, as described above, taking into consideration the effect of eccentric bending that occurs when tension is applied to the base material, the base material is reinforced by bonding reinforcing materials to both sides of the thickness centerline when viewed in a longitudinal cross section of the composite, but from the viewpoint of making the effect on stress distribution virtually negligible even when a bending moment is applied to the composite, it is preferable that the percentage of the ratio H' / H be within 2%. Here, H' is the eccentric distance that represents the distance between the height (position of the center of gravity) of the base material and the centerline of the rigidity of the composite, and H represents the thickness of the entire composite.

[0048] 1, if the thickness of the adhesive layer 2 on both sides of the plate-shaped base material 1 and the thickness of the reinforcing material 3 are the same, and if the materials are also the same and have the same shear modulus and elastic modulus, the height of the center of gravity of the plate-shaped base material 1 and the rigid centerline of the composite will coincide, and the percentage of the ratio H' / H will be 0%. On the other hand, for example, as shown in Fig. 7, in the example using the hollow columnar base material 21 shown in Fig. 6, if the reinforcing material 3 is attached to the outer wall surface side of the hat-shaped base material 21a via the adhesive layer 2, unlike Fig. 6(b), then if the percentage of the ratio H' / H [(H' / H) × 100] of the eccentricity distance H', which is the distance between the height of the center of gravity of the hollow columnar base material 21 in Fig. 6 and the rigid centerline of the composite, to the height H of the composite, is within 2%, the effect on the stress distribution even when a bending moment is applied to the composite can be substantially ignored, and the present invention can be reliably applied. Similarly, in the example of Figure 1, even if the material and thickness of the reinforcing material 3 on both the front and back sides of the plate-shaped base material 1 are different, the present invention can be reliably applied as long as the percentage of this ratio H' / H is within 2%.

[0049] As described above, the base material reinforcing method of the present invention can be applied to reinforcing base materials such as light metals such as steel and aluminum used in various structures, such as reinforcing transportation equipment such as automobiles, trains, and aircraft, reinforcing structural members in general industrial structures such as industrial robots and drones, and reinforcing construction structures such as bridges, buildings, and structures.It can also be applied to bonding a reinforcing material to a base material to obtain a composite that ensures rigidity while reducing weight.That is, for example, it can be suitably used when bonding a reinforcing material to a steel material to obtain a composite that can be used in the manufacture of vehicles such as trains and automobiles, or to obtain a composite that can be used as a structural member for the arm of an industrial robot or a drone. [Example]

[0050] The following experimental examples were carried out to demonstrate the effects of the base material reinforcing method according to the present invention, but the present invention is not limited to these examples.

[0051] Example 1 A test composite was prepared using a base material, a reinforcing material, and an adhesive. As shown in Figure 1, this test composite consisted of a plate-shaped base material 1 having a thickness 2t2 = 1.6 mm, a width w = 25 mm, and a length L = 250 mm. Reinforcing materials 3 each having a thickness t1 = 0.4 mm, a width w = 25 mm, and a length 2l = 160 mm were bonded to the front and back surfaces (top and bottom surfaces) of the base material 1 via adhesive layers 2 having a thickness h = 0.2 mm. Figure 8(a) shows a perspective view of the test composite according to Example 1, and Figure 8(b-2) shows its longitudinal cross section.

[0052] Of the components that make up this test composite, a high-tensile steel plate with an elastic modulus E2 of 206,000 MPa was used as the plate-shaped base material 1. Furthermore, a pitch-based unidirectional reinforced CFRP (pitch-based CFRP-1) with an elastic modulus E1 of 411,000 MPa and an epoxy resin matrix was used as the reinforcement material 3. The carbon fiber in this CFRP was pitch-based carbon fiber (XN-80 manufactured by Nippon Graphite Fiber Co., Ltd.). Furthermore, a polyurea-based adhesive with a shear modulus G of 20 MPa (polyurea-based adhesive FU-Z manufactured by Nippon Steel Chemical & Material Co., Ltd.) was used as the adhesive (simply referred to as polyurea-based in Table 2).

[0053] To obtain the test composite, the adhesive surfaces of the plate-shaped base material 1 and the reinforcing material 3 were polished with #120 sandpaper and degreased. Then, the reinforcing material 3 was attached to both the front and back sides of the plate-shaped base material 1 with adhesive, and the composite was left to cure for 7 days at a constant temperature of 20°C to ensure proper hardening. The dimensions, elastic modulus, and shear modulus of the test composite described above are all those after curing. These values ​​are summarized in Table 2.

[0054] [Table 2]

[0055] For the test composite obtained as described above, the stiffness ratio r between the base material and the reinforcement material was calculated based on the previously described formula (4), and cl was calculated using the material parameter c in formula (3). The test composite was also evaluated using the method described below. These results are summarized in Table 3. In addition, Figure 9 shows the region consisting of the relational expressions (formulas (1) and (2)) for realizing the above-mentioned ideal reinforcement method, surrounded by a dashed line, and the area corresponding to the test composite of this example is indicated by a plot (● in Figure 1).

[0056] [Evaluation of peeling in the elastic range of steel] A tensile test on the test composite obtained above was performed using a universal testing machine (Instron Model 5985 Universal Testing Machine) under displacement control at a test speed of 2 mm / min, and the results were evaluated by comparing them with the yield strength (299 MPa) of the steel used as the plate-shaped base material 1 in a tensile test performed in the same manner. That is, the peel strength of the adhesive layer 2 of the test composite is calculated based on the yield strength of the steel material alone. If it's low It is judged that "peeling has occurred" and the peel strength of the adhesive layer 2 is If it's expensive It was judged as "no peeling".

[0057] [Rigidity development rate ξ] As mentioned above, the stiffness expression rate ξ (%) can be calculated from "stiffness of the composite (i) / stiffness of the composite assuming a completely composite cross section (ii)", and in this example, it was evaluated by FEM analysis (simulation). That is, analysis software was used, using MSC Software's Marc, to model a test composite having the same shape and made of the same materials as the base material, reinforcing material, and adhesive of this example. A tensile load was applied in the x-axis direction (longitudinal direction), and (ii) the composite rigidity when the base material and reinforcing material are integrated without an adhesive layer (fully composite), and (i) the composite rigidity of the test composite of this example were determined. The value of (i) was divided by the value of (ii) to calculate the stiffness expression rate ξ (%).

[0058] [Table 3]

[0059] (Examples 2 to 4, Comparative Examples 1 to 3) Test composites according to Examples 2 to 4 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the reinforcing materials and adhesives used were changed to those shown in Table 2, and the dimensions and thicknesses of each component were also changed as shown in Table 2. The PAN-based CFRP in the reinforcing materials shown in Table 2 was a PAN-based unidirectionally reinforced CFRP with an elastic modulus E1 of 135,000 MPa and an epoxy resin matrix, and the carbon fiber in this CFRP was a PAN-based carbon fiber (TR50S, manufactured by Mitsubishi Chemical Corporation). Furthermore, pitch-based CFRP-2 was a pitch-based quasi-isotropically reinforced CFRP ([(0 / 45 / 90 / -45)s]3) with an elastic modulus E1 of 137,000 MPa and an epoxy resin matrix, and the carbon fiber in this CFRP was a pitch-based carbon fiber (XN-80, manufactured by Nippon Graphite Fiber Co., Ltd.). Meanwhile, as for the adhesive, in addition to the polyurea-based adhesive used in Example 1, a bisphenol A-based epoxy resin adhesive (AW136N / HY994 manufactured by Nagase ChemteX Corporation) with a shear modulus G of 1154 MPa was used (simply referred to as "epoxy-based" in Table 2). FIG. 8(a) is a perspective view of the test composites of Examples 2 to 4 and Comparative Examples 1 to 3. FIG. 8(b-1) is a longitudinal cross-sectional view of the test composite of Example 2, and FIG. 8(b-2) corresponds to a longitudinal cross-sectional view of the test composites of the other Examples and Comparative Examples.

[0060] The obtained test composites were evaluated in the same manner as in Example 1. The results are shown in Table 3 and Figure 9. In Figure 9, the position of the test composite corresponding to each Example and Comparative Example is plotted, and in this case, when the result of the peeling evaluation was no peeling, it is indicated by ●, and when peeling was present, it is indicated by ×.

[0061] As can be seen from the above results, the test composites according to Comparative Examples 1 to 3 either showed peeling in the previous peel evaluation or had a stiffness development rate ξ that did not reach 50%, and these test composites were outside the region defined by formulas (1) and (2) of the present invention, as shown in Figure 9. In contrast, the test composites according to Examples 1 to 4 did not show peeling in the peel evaluation and showed a stiffness development rate ξ of 50% or more (60% or more), and all of these were within the region defined by formulas (1) and (2) of the present invention.

[0062] Therefore, according to the present invention, a reinforced structure that combines peel resistance and rigidity can be realized. Moreover, the amount of material used for reinforcement can be minimized while increasing stiffening efficiency, which is advantageous in terms of cost and workability, and also allows for a reduction in the weight of the resulting composite. [Explanation of symbols]

[0063] 1: base material, 2: adhesive layer, 3: reinforcing material, 4: hollow part, 11: base material, 21a: hat-shaped base material, 21b: plate-shaped base material, 31: adherend.

Claims

1. A method for reinforcing a base material by bonding a reinforcing material to a surface of the base material with an adhesive to form a composite, comprising the steps of: A method for reinforcing a base material, characterized in that, when viewed in a longitudinal cross section of the resulting composite, one reinforcing material is adhered to each side of the thickness centerline of the composite, and the following formulas (1) and (2) are satisfied: [Equation 1] E １ and １ represents the elastic modulus and thickness of the reinforcement. E ２ and 2t ２ represents the elastic modulus and thickness of the base material. G and h represent the shear modulus and thickness of the adhesive layer made of adhesive. l represents the half-length of the bond between the base material and the reinforcing material.

2. The method for reinforcing a base material described in claim 1, wherein the composite is a plate-shaped base material having reinforcing materials adhered to both the front and back surfaces thereof, and the reinforcing materials are adhered to both sides of the thickness centerline in the longitudinal cross section of the plate-shaped base material.

3. 2. The method for reinforcing a base material according to claim 1, wherein the composite is a hollow columnar base material having a box-shaped cross section with a hollow portion, with a reinforcing material adhered to the inner wall surface or outer wall surface, and the reinforcing material is adhered to both sides of the thickness centerline in the longitudinal cross section of the hollow columnar base material.

4. 4. The method for reinforcing a base material according to claim 1, wherein the reinforcing material is made of a fiber-reinforced composite material.

5. 5. The method for reinforcing a base material according to claim 1, wherein the base material is made of steel.

6. A composite in which a reinforcing material is bonded to the surface of a base material with an adhesive, A composite in which a reinforcing material is bonded to a base material, characterized in that, when viewed in a longitudinal cross section of the composite, one reinforcing material is bonded to each side of the thickness centerline of the composite, and the following formulas (1) and (2) are satisfied: [Equation 2] E １ and １ represents the elastic modulus and thickness of the reinforcement. E ２ and 2t ２ represents the elastic modulus and thickness of the base material. G and h represent the shear modulus and thickness of the adhesive layer made of adhesive. l represents the half-length of the bond between the base material and the reinforcing material.

7. The composite is a plate-shaped base material having a reinforcing material bonded to both the front and back surfaces thereof, and the reinforcing material is bonded to both sides of the thickness centerline in the longitudinal cross section of the plate-shaped base material.

8. 7. The composite according to claim 6, wherein a reinforcing material is bonded to the inner wall surface or outer wall surface of a hollow columnar base material having a box-shaped cross section with a hollow portion, and the reinforcing material is bonded to both sides of the thickness centerline in the longitudinal cross section of the hollow columnar base material.

9. 9. A composite material comprising a base material and a reinforcing material bonded to the base material according to claim 6, wherein the reinforcing material is made of a fiber-reinforced composite material.

10. 10. A composite body comprising a base material and a reinforcing material bonded to the base material according to claim 6, wherein the base material is made of steel.

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