Joint structure of FRP molded body and method for producing the same

Abstract

To provide an adhesive joint structure and a method for producing the same, in consideration of the need for higher shear stress strength in high-reliability FRP joining, FRP-to-FRP joining, and FRP-to-metal joining.SOLUTION: The present invention provides a joint structure in which an FRP molded body and another molded body made of FRP or metal are bonded and joined by an adhesive, and in which metal needle-like pins are disposed perpendicular to a joint surface of the adhesive joint portion so as to span the FRP molded body and the other molded body at the adhesive joint portion.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a joining structure of a fiber-reinforced plastic (FRP) molded body and another FRP molded body or a metal molded product, and a manufacturing method thereof.

Background Art

[0002] FRP is a material that is lighter and stronger than metal materials, that is, a material with high specific strength. Glass fiber reinforcement materials, carbon fiber materials, and aramid fibers are also used depending on the application. As manufacturing methods of FRP, there are methods such as uniformly coating finely cut glass fibers, and methods such as infiltrating resin into glass fibers or carbon fibers. Thermosetting resins such as unsaturated polyester are often used as the matrix of fiber-reinforced plastics.

[0003] As manufacturing methods of FRP, there are a hand lay-up method, a spray-up method, an SMC (Sheet Molding Compound) press method, an RTM (Resin Transfer Molding) method using resin high-pressure injection technology by injection, an autoclave method, etc., and it is at a stage where high-quality products can be produced.

[0004] Recently, there have been changes in social infrastructure facilities, and needs such as enlargement of facilities due to changes in power generation methods adopted such as wind power generation, and enlargement, thinning, and weight reduction for improving fuel efficiency of transportation facilities such as trains, automobiles, and airplanes have been increasing. FRP that can cope with enlargement can be considered to increase its thickness and strength, but weight reduction is also desired. Therefore, it is desirable to improve the fracture strength of the FRP body and the connection part while suppressing an increase in the FRP thickness as much as possible. FRP often has a size of 3 to 5 mm, but when the load increases, improvement of shear strength is desired.

[0005] The fibers that make up FRP are strong, but the resin is weak and prone to cracking. Stress is particularly strong around bolt fastening holes, or around holes in FRP products. Even if there are no holes, there are cases where structural stress is unavoidable, such as when the bending radius of the FRP molded body is small, and cracks can occur.

[0006] A search of patents from 1974 to 2019 reveals that in Japan, technologies have been proposed to improve the strength around bolt holes by changing the fiber structure of the FRP structure itself (Patent Document 1, Patent Document 2). Recently, to address this issue, a disk-shaped reinforcing member that is applied for reinforcement has been proposed (Patent Document 3). However, because this is simply applied using an adhesive, there is a need for an application technology with higher shear strength. Meanwhile, a technology has also been proposed in which a resin reinforcing sheet is applied to the bolt holes (Patent Document 4), but this does not result in a significant improvement in shear strength. Furthermore, a composite technology has been disclosed that adds carbon nanotubes to the unevenness of the connecting surface and then fastens with a bolt to improve the reliability of the connection (Patent Document 5). However, the shear strength improvement technology aimed at dealing with bending and twisting on an industrial scale is not sufficient.

[0007] Non-Patent Document 1 introduces a method for connecting FRP to itself with adhesive, and a bolt connection technology for connecting FRP to metal. Some stress analysis has also been conducted around bolts, and Non-Patent Document 2 reports that compressive stress increases around bolt holes. Among the technologies for preventing crack progression by attaching reinforcing members with a thickness of at least several millimeters, similar to the FRP, to bolt holes or areas where cracking is likely, there is also a demand for technologies that can further improve shear strength.

[0008] Furthermore, Non-Patent Document 2 introduces the adhesion technology between FRP and steel materials, and shows the analysis results regarding the shear stress and perpendicular stress generated in the adhesive. The analysis results include examples of classifying and analyzing the failure modes into interfacial failure between the steel member and the adhesive, interfacial peeling between the adhesive and the FRP, failure inside the adhesive, interlayer failure of the FRP, yielding of the steel member, and fracture of the FRP. In particular, the high stress generated in the adhesive and the evaluation method for the interlayer peeling of the FRP close to the adhesive are described. Here, it is known that the peeling strength of the FRP is greatly affected by the surface treatment on the steel side, and the blasting treatment on the steel surface and the unevenness of the steel surface by power tools are considered important. Surface fine pattern manufacturing technologies such as sandblasting, acid etching, and photolithography technology are used to form unevenness. Also, as methods for treating the FRP end, tapering of the end, reverse tapering, end step, and use of a low-elastic adhesive at the end have been proposed. Therefore, the inventors of the present invention prototyped and experimented with samples having different surface unevenness, and although a certain degree of effect was recognized, a significant improvement in the shear force was not achieved.

[0009] Non-Patent Document 3 describes a method for improving the low interlayer strength of fiber-reinforced composite materials (CFRP). Stitching using a sewing machine, Z-anchor in which a preform is pierced with a needle to entangle the upper and lower layer fibers with each other, and Z-pin in which a thin pin is pierced into a prepreg are put into practical use. Z-anchor is applied to the preform before resin impregnation, and Z-pin is a strengthening method in which a stainless steel pin is directly inserted into the prepreg before lamination and molding. Specific experimental examples in Non-Patent Document 3 show an example of bolt fastening, and a joining example by dense arrangement of thin bolts is introduced. There is also an example of 10×10 densely arranged M1 bolts. Since the bolts with a small diameter have small holes, the pointed needles at the tip of the prepreg before molding are inserted, the holes are drilled and removed, and then a release tube is inserted to form bolt holes. A technique of closely inserting and joining a metal material and a small-diameter bolt is introduced. Here, only the example of tightening densely arranged bolts is mentioned, and the adhesion is not touched upon. From the above, higher shear stress is required for highly reliable FRP connections, joining of FRP to each other, and joining of FRP and metal, which is an unsolved problem. A connection technique that is not for space use but is generally easy to use in society and consists of high-level fine bolt and nut technology is desired.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0011]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0012] As conventional technologies, connection methods between FRPs and connection technologies between FRP and metal have been introduced. However, for parts that are highly stressed at bolt-nut tightening parts or bending parts with extremely high angles, technologies for preventing crack generation and propagation are necessary. At this time, improvement of the shear force applied to the connection interface is desired.

[0013] An object of the present invention is to provide a method for connecting FRP reinforcing members that enhances the action of preventing the occurrence or progression of cracks that may occur at bolt-nut tightening parts as a countermeasure against the demand for weight reduction of FRP products, and to provide a connection method with higher shear force than conventional adhesive methods.

Means for Solving the Problems

[0014] The present invention has been made to achieve the above object, and an FRP molded body and another molded body made of FRP or metal are adhesively joined by an adhesive, and metal needle-shaped pins are vertically arranged on the joint surface of the adhesive joint portion so as to straddle the FRP molded body and the other molded body (Claim 1).

[0015] Further, in the present invention, an FRP reinforcing material is adhesively joined to the surface of an FRP molded body by an adhesive, and metal needle-shaped pins are vertically arranged on the joint surface of the adhesive joint portion so as to straddle the FRP molded body and the FRP reinforcing material (Claim 2).

[0016] Furthermore, in the present invention, an FRP molded body and another molded body made of FRP or metal are adhesively joined by an adhesive, and an FRP reinforcing material is adhesively joined to the surface of the FRP molded body or the other molded body at the adhesive joint portion by an adhesive, and metal needle-shaped pins are vertically arranged on the joint surface of the adhesive joint portion so as to straddle the FRP molded body, the other molded body, and the FRP reinforcing material (Claim 3).

[0017] In addition, the FRP reinforcing material is preferably an FRP reinforcing material having a spiral fiber layer formed by shaping reinforcing fibers into a spiral shape and a fiber layer including linear fibers laminated on the spiral fiber layer and extending in a direction intersecting the spiral fibers of the spiral fiber layer when viewed from the lamination direction (Claim 4).

[0018] Further, the FRP reinforcing material is preferably formed by wiring with a three-dimensional printer so that the spiral fibers have a pitch of 0.7 mm or more, and metal needle pins having a diameter larger than the pitch are inserted in advance so as not to break the spiral fibers and the linear fibers (Claim 5).

[0019] Moreover, the manufacturing method of the joining structure of the invention includes a step of mechanically forming a metal needle pin insertion hole in the FRP molded body with a drill, a step of applying an adhesive to the contact surface between the FRP molded body and the FRP reinforcing material, and a step of inserting the metal needle pin of the FRP reinforcing material according to Claim 5 into the metal needle pin insertion hole, which is a manufacturing method of a joining structure characterized by this (Claim 6).

[0020] Moreover, the manufacturing method of the joining structure of the invention includes a step of mechanically forming a metal needle pin insertion hole in the first FRP molded body and the other molded body with a drill, a step of applying an adhesive to the contact surfaces of the FRP molded body, the other molded body, and the FRP reinforcing material, and a step of inserting the metal needle pin of the FRP reinforcing material according to Claim 5 into the metal needle pin insertion holes of the FRP molded body and the other molded body, which is a manufacturing method of a joining structure characterized by this (Claim 7).

[0021] For adhering members to FRP products, instant adhesives, epoxy-based or acrylic-based adhesives, double-sided adhesive tapes, etc. can be used. The FRP molded body to which the FR reinforcing material (crest) invented by the present inventors was previously applied is effective for applications such as lightweight and small airplanes with improved joining reliability, air conditioning equipment, industrial and care robots, trucks, passenger cars, train parts, components for wind power generation equipment, etc., medical device casings, and large drones.

Advantages of the Invention

[0022] In the present invention that combines a stainless steel pin and an adhesive, as part of a method for addressing the demand for weight reduction, it is possible to provide a method for connecting an FRP reinforcing member with high shear strength that enhances the prevention of the occurrence or progression of cracks that may occur in the bolt-nut tightening part. Furthermore, with this method, a high shear strength at a level without bolt reinforcement can be obtained.

Brief Description of the Drawings

[0023]

Figure 1

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Figure 10

Modes for Carrying Out the Invention

[0024] In society, the industrial reliability of FRP products is important. Regarding parts that are used under high stress, such as bolt-nut tightening parts and parts with extremely high bending angles, a technology for preventing crack generation is desired, and a reinforcing material (hereinafter referred to as a crest) containing spiral fibers and fibers arranged perpendicular to the spiral fibers has been invented (Patent Document 3). The shape of this crest can be flexibly designed and manufactured as needed, such as in rectangular, square, or irregular shapes. FRP molded body substrates are often used by connecting and joining them to a single product or other materials. Also, many of their shapes are complex depending on the application. For example, there are those that are used under stress due to their complex structures such as bolt-nut tightening parts. The reinforcing material reinforces the FRP molded body by being attached to it. The reinforcing material has a configuration that includes spiral fibers and fibers arranged perpendicular to the spiral fibers, and it is desired to strengthen the adhesive surface for attachment considering this fiber arrangement structure.

[0025] FIG. 1 is a diagram showing an example of reinforcing a reinforcing material (crest) and FRP. In the figure, (a) shows an example of connecting two FRP substrates 1 using bolts 2, and (b) shows an example of connecting two FRP substrates 1 and a metal molded body 5. The arrows in the figure indicate the direction of crack generation. In contrast, structures composed of an FRP molded body and a reinforcing material with a reinforcing material 7 having a configuration including spiral fibers and fibers arranged perpendicular to the spiral fibers attached are shown in (c) and (d).

[0026] Next, in these structures, in the configuration of the FRP molded body and the reinforcing material, a comparative study of the adhesive strength of the following three structures for increasing the adhesive strength was conducted. The reinforcing material is basically a thermoplastic resin, and the FRP molded body is a thermoplastic resin or a thermosetting resin, which can be used separately as needed.

[0027] Fig. 2(a) is a sample for evaluating the adhesive strength between a reinforcing material 7 containing an adhesive 6 and an FRP substrate 1 made of a thermoplastic resin or a thermosetting resin in a configuration without bolts in order to separate the influence of the strength of the connection part and the shear strength of the bolts when assuming bolt connection of the FRP reinforcing material made of a thermoplastic resin. Fig. 2(b) is a sample for evaluating the adhesive strength between a reinforcing material 7 containing a stainless steel pin 8 and an FRP substrate 1 in a configuration without bolts in order to separate the influence of the shear strength of the bolts when assuming bolt connection of the FRP reinforcing material. The FRP substrate 1 is drilled before connection. Fig. 2(c) is a sample for evaluating the adhesive strength between a reinforcing material 7 containing a stainless steel pin 8 and an adhesive 6 and an FRP substrate 1 in a configuration without bolts in order to separate the influence of the shear strength of the bolts when assuming bolt connection of the FRP reinforcing material made of a thermoplastic resin. Here, similar to (b), the FRP substrate 1 is drilled before connection.

[0028] Fig. 3 is an insertion model diagram of thermally inserting a stainless steel pin 8 into an FRP substrate 1 made of a thermoplastic resin in the procedure as shown in Fig. 3 when making the sample shown in Fig. 2. Fig. 3(a) shows the process of inserting a pointed needle-shaped plug-in tool 9 heated to 320 degrees into the FRP substrate 1 made of the thermoplastic resin constituting the reinforcing material, (b) inserting, (c) pulling out, and then (d) heating the stainless steel pin 9 to 280 °C and (e) thermally pressing it in.

[0029] Fig. 4(a) is a simulation diagram of an FRP molded body 10 made of a thermoplastic resin before inserting a stainless steel pin. Fig. 4(b) is a diagram after inserting the stainless steel pin. In (a), the FRP molded body 10 or the fiber configuration consists of glass fibers 11 linearly arranged in the FRP molded body 10. In (b), as shown in the figure, the stainless steel pin 8 is configured to spread the fibers so as not to break the glass fibers 11.

[0030] Figure 5 is a model diagram of a sample for a shear test. In this figure, (a) is a front view and (b) is a side view. It is configured to connect an FRP molded body 10 made of a thermoplastic resin and a reinforcing material wappen mock-up sample 13 made of a nylon plate with long fibers. The sample was tested by uniaxially pulling it in the upward and downward directions. To suppress the deviation of the tensile axis, as shown in (b), two stainless steel plates 12 were attached for use in a tensile test. The detailed configuration of this test sample is shown below.

[0031] Figure 6 is a detailed model diagram of the sample structure for a shear test. On the reinforcing material wappen 7 made of a thermoplastic resin shown on the right side of the figure, a stainless steel pin insertion position 14 for shear strengthening is marked. The details of the shear test sample before pasting, which simulates this wappen sample, are shown in the two figures on the left side. On the nylon FRP molded body 13 with long fibers made of a thermoplastic resin nylon, a stainless steel pin insertion position 14 for shear strengthening is shown. The FRP molded body 10 to be pasted in accordance with this member has been mechanically drilled with holes before connection. These holes were drilled with a drill for inserting stainless steel needles.

[0032] This is a diagram showing the other sample before connection. On the reinforcing material wappen mock-up sample 13 made of a long fiber nylon plate, a stainless steel pin insertion position 14 for shear strengthening before insertion is also shown. A sample is to be fabricated by pasting the reinforcing material wappen mock-up sample 13 made of a long fiber nylon plate and the FRP molded body 10 with an adhesive for a shear test.

[0033] Figure 7 is an explanatory diagram of the content of a shear test sample. The samples are of the following three types: only adhesion, stainless steel pin inserted products, and products with a combination of stainless steel pin insertion and adhesion.

[0034] Figure 8 is a distance-load test diagram showing the shear test results. In the figure, (a) is only adhesion, (b) is a stainless steel pin inserted product, and (c) is a combined product of stainless steel pin insertion and adhesion. Compared with the adhered product, the shear strength in the case of the combination of stainless steel pin insertion and adhesion is about twice as high, and looking at the fracture part, it was a fracture of the FRP base material. From this, an improvement in shear strength was seen due to the combined effect of pin insertion and adhesion.

[0035] Figure 9 is a diagram showing the connection structures between FRP base materials (molded bodies) with or without bolts and between an FRP base material and a reinforcing material, etc. In the figure, (a) shows the structure of FRP base material 1 / FRP base material 1 / bolt 2, (b) shows the structure of FRP base material 1 / FRP base material 1 / bolt 2 / reinforcing material 7, and (c) is a diagram showing a connection structure consisting of the structure of FRP base material 1 / adhesive 6 / reinforcing material 7 / stainless steel pin 9.

[0036] Figure 10 is a distance-load test diagram of the sample with the structure shown in Figure 9. In the figure, (a) shows the connection with only bolts, (b) shows the combined connection of bolts and a reinforcing material, and (c) shows the shear strength according to the distance-load test diagram when connecting with a stainless steel pin and an adhesive without bolts.

[0037] Even when there are no bolts, compared with the structure of FRP base material 1 / FRP base material 1 / bolt 2 with bolts, it showed twice the shear strength and fractured from the base material of the FRP base material. Although it is known to reinforce the adhesive part between the FRP member and the metal member by bolt tightening, when bending stress or torsion is applied to the FRP plate, there is a risk of deformation by shear. In the present invention, by installing a metal needle-shaped pin around the bolt hole, a significant improvement in shear force was achieved. From the above, a bolted joining technique that improves the shear force, which was an industrial problem, was established by the combined technique of stainless steel pin and adhesion. It can be said that the FRP connection technique was perfected by this combined technique.

Explanation of symbols

[0038] 1 FRP molded body (base material) 2 Bolt 3 Nut 4 Washers 5 Metal Formed Body 6 Adhesive 7 Reinforcement 8 Stainless Steel Pin 9 Plug-In Tool 10 FRP Formed Body 11 Glass Fiber 12 Stainless Steel Plate 13 Reinforcement Washer Simulation Specimen Made of Nylon Plate with Long Fibers 14 Shear Reinforcement Stainless Steel Pin Insertion Position

Claims

1. A joining structure, wherein an FRP molded body and another molded body made of FRP or metal are adhesively joined by an adhesive, and metal needle-like pins are vertically arranged on the joint surface of the adhesive joint portion so as to straddle the FRP molded body and the other molded body.

2. A joining structure, wherein an FRP reinforcing material is adhesively joined to the surface of an FRP molded body with an adhesive, and metal needle-like pins are vertically arranged on the joint surface of the adhesive joint portion so as to straddle the FRP molded body and the FRP reinforcing material.

3. An FRP molded body and another molded body made of FRP or metal are adhesively joined by an adhesive, and an FRP reinforcing material is adhesively joined to the surface of the FRP molded body or the other molded body at the adhesive joint portion with an adhesive. A joining structure, wherein metal needle-like pins are vertically arranged on the joint surface of the adhesive joint portion so as to straddle the FRP molded body, the other molded body, and the FRP reinforcing material.

4. The FRP reinforcing material according to claim 2 or 3, wherein the FRP reinforcing material has a fiber layer including a spiral fiber layer formed by molding reinforcing fibers in a spiral shape and linear fibers laminated on the spiral fiber layer and extending in a direction intersecting the spiral fibers of the spiral fiber layer when viewed from the lamination direction.

5. The joining structure according to claim 4, wherein the FRP reinforcing material is wire-produced by a three-dimensional printer such that the spiral fibers have a pitch of 0.7 mm or more, and metal needle-like pins having a diameter larger than the pitch are inserted in advance so as not to break the spiral fibers and the linear fibers.

6. In a method for manufacturing the joining structure according to claim 2, a step of mechanically forming metal needle-like pin insertion holes in the FRP molded body with a drill, a step of applying an adhesive to the contact surface between the FRP molded body and the FRP reinforcing material, and a step of inserting the metal needle-like pins of the FRP reinforcing material according to claim 5 into the metal needle-like pin insertion holes. A method for manufacturing a joining structure, characterized by comprising:

7. In the method for manufacturing the joining structure according to claim 3, a step of mechanically forming metal needle-shaped pin insertion holes in the FRP molded body and the other molded body with a drill, a step of applying an adhesive to the contact surfaces of the FRP molded body, the other molded body, and the FRP reinforcing material, and a step of inserting the metal needle-shaped pins of the FRP reinforcing material according to claim 5 into the metal needle-shaped pin insertion holes of the FRP molded body and the other molded body. A method for manufacturing a joining structure, characterized by comprising these steps.

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