Joining structure for FRP molded body and method for manufacturing 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 a method of uniformly coating finely cut glass fibers, a method of infiltrating resin into glass fibers or carbon fibers, and the like. 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 utilizing injection, an autoclave method, etc., and they are at a stage where high-quality products can be produced.

[0004] Recently, there have been changes in social infrastructure facilities, and needs such as an increase in the size of facilities due to changes in power generation methods such as wind power generation, and an increase in the fuel efficiency of transportation facilities such as trains, automobiles, and airplanes, resulting in a trend towards larger and thinner and lighter designs. FRP, which can handle larger sizes, can be considered to increase its thickness and strength, but further weight reduction is also desired. Therefore, it is desirable to improve the fracture strength of the FRP main 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, an improvement in shear strength is desired.

[0005] While the fiber that makes up FRP is strong, the resin is weak and prone to cracking. Stress is particularly concentrated around bolt holes or around holes in FRP products. Even without holes, cracking can occur in FRP molded substrates where structural stress is unavoidable, such as when the bending radius is small, due to the nature of the material.

[0006] A review of patents from 1974 to 2019 reveals that in Japan, technologies have been proposed to strengthen FRP structures by altering their fiber structure to improve the strength around bolt holes (Patent Documents 1 and 2). More recently, disc-shaped reinforcing members that are attached to reinforce the structure have been proposed to address this issue (Patent Document 3), but since this is merely done using adhesive, a bonding technology with higher shear strength is desired. On the other hand, a technology has also been proposed to attach resin reinforcing sheets to bolt holes (Patent Document 4), but this does not offer a significant improvement in shear strength. Furthermore, composite technologies have been published to improve the reliability of connection points, such as adding carbon nanotubes to the surface irregularities of the connection point and then bolting them together (Patent Document 5). However, there are not enough shear strength improvement technologies aimed at industrially dealing with bending and twisting.

[0007] Non-patent document 1 introduces methods for bonding FRPs together and bolting FRPs to metals. Stress analysis around bolts has also been partially performed, and non-patent document 2 reports that compressive stress can be high around bolt holes. While there is a need for techniques to suppress crack propagation by attaching reinforcing members with a thickness of several millimeters or more, similar to that of the FRP, to bolt holes or areas prone to cracking, there is also a need for techniques to further improve shear strength.

[0008] Furthermore, Non-Patent Document 2 introduces bonding technology for FRP and steel materials, and presents analysis results regarding shear stress and normal stress generated in the adhesive. The analysis results include examples of analyzing failure modes classified into interfacial failure between the steel member and the adhesive, interfacial delamination between the adhesive and FRP, internal failure of the adhesive, interlaminar failure of the FRP, yielding of the steel member, and rupture of the FRP. In particular, it describes evaluation methods for the high stress generated in the adhesive and interlaminar delamination of the FRP, which is close to the adhesive. It is known that the peel strength of the FRP, which is important here, is greatly influenced by the surface treatment of the steel material, and surface roughness of the steel material by blast treatment or power tools is considered important. Surface fine pattern manufacturing techniques such as sandblasting, acid etching, and photolithography are used to create roughness. In addition, methods for treating the edges of the FRP are proposed, such as edge taper, reverse taper, edge step, and the use of low-elasticity adhesive at the edges. Therefore, the inventors fabricated and experimented with samples with altered surface irregularities, and while some effect was observed, it did not lead to a significant improvement in shear strength.

[0009] Non-patent document 3 describes methods for improving the low interlaminar strength of fiber-reinforced polymers (CFRP), including stitching using a sewing machine, Z-anchor (where the fibers of the upper and lower layers are intertwined by poking the preform with a needle), and Z-pin (where thin pins are inserted into the prepreg). Z-anchor is applied to the preform before resin impregnation, while Z-pin is described as a reinforcement method in which stainless steel pins are directly inserted into the laminated prepreg before molding. Non-patent document 3 includes a specific experimental example of bolt fastening, introducing an example of joining using a dense arrangement of thin bolts. There is also an example of 10x10 densely arranged M1 bolts, and since the holes for the thin-diameter bolts are small, a technique is introduced in which a sharp needle is inserted into the prepreg before molding to create a hole, then removed, and a release tube is inserted to form the bolt hole, and the metal material and the thin-diameter bolt are tightly inserted and joined. However, this only shows an example of fastening densely arranged bolts and does not touch on adhesive bonding. In conclusion, higher shear stress is required for highly reliable FRP connections, FRP-to-FRP connections, and FRP-to-metal connections, which remains an unresolved challenge. Rather than high-level micro-bolt and nut technology for space applications, there is a need for a connection technology that is easy to use in general society. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2002-307585 [Patent Document 2] Japanese Patent Publication No. 2003-225914 [Patent Document 3] Patent No. 7190087 [Patent Document 4] Japanese Patent Publication No. 2017-19311 [Patent Document 5] Japanese Patent Publication No. 2011-42930 [Non-patent literature]

[0011] [Non-Patent Document 1] FRP Molding Skills Textbook (New Edition), Reinforced Plastics Association, published October 31, 1997. [Non-Patent Document 2] Advanced Technologies for Joining FRP Components and Adhesive Bonding of Steel and FRP Published November 12, 2013 [Non-Patent Document 3] Kazumasa Moriya, Katsuyoshi Kato, Hiroyuki Inoue: Joining of carbon fiber reinforced laminated composite materials by drilling with small-diameter pins and dense arrangement of small-diameter bolts, Journal of the Japan Society for Composite Materials, 37, 11-20, 2011. [Overview of the project] [Problems that the invention aims to solve]

[0012] Conventional technologies include methods for connecting FRPs to each other and connecting FRPs to metals. However, for parts subjected to high stress, such as bolt and nut tightening sections and extremely sharp bends, technologies are needed to prevent cracking and its propagation. In this regard, improving the shear force applied to the connection interface is desirable.

[0013] The objective of the present invention is to provide a connection method for FRP reinforcing members that enhances the prevention of crack occurrence or crack propagation that may occur in bolt and nut fastening areas, as a way to address the demand for weight reduction in FRP products, and to provide a connection method that has higher shear strength compared to conventional bonding methods. [Means for solving the problem]

[0014] The present invention has been made to achieve the above objective, and is a joining structure characterized in that an FRP molded body and another molded body made of FRP or metal are bonded together with an adhesive, and a metal needle-shaped pin is arranged perpendicular to the joining surface of the bonded joint so as to span the FRP molded body and the other molded body at the bonded joint (Claim 1).

[0015] Furthermore, the present invention relates to a joining structure characterized in that an FRP reinforcing material is bonded to the surface of an FRP molded body with an adhesive, and a metal needle-shaped pin is positioned perpendicular to the joining surface of the adhesive joint so as to straddle the FRP molded body and the FRP reinforcing material at the adhesive joint (Claim 2).

[0016] Furthermore, the present invention provides a joining structure characterized in that an FRP molded body and another molded body made of FRP or metal are bonded together with an adhesive, and an FRP reinforcing material is bonded together with an adhesive to the surface of the FRP molded body or the other molded body at the bonded joint, and a metal needle-shaped pin is arranged perpendicular to the joining surface of the bonded joint so as to span the FRP molded body, the other molded body and the FRP reinforcing material at the bonded joint (Claim 3).

[0017] In addition, the FRP reinforcing material is preferably an FRP reinforcing material having a spiral fiber layer formed by molding reinforcing fibers in 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] Also, the FRP reinforcing material is preferably formed by wiring with a three-dimensional printer such 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] The manufacturing method of the joining structure of the invention further 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 pins of the FRP reinforcing material according to Claim 5 into the metal needle pin insertion holes, and is a manufacturing method of a joining structure characterized by this (Claim 6).

[0020] The manufacturing method of the joining structure of the invention further 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 pins 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, and 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 enhanced joining reliability, air conditioning equipment, industrial and nursing robots, trucks, passenger cars, train parts, components for wind power generation equipment, etc., medical device housings, 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, a method for connecting an FRP reinforcing member with high shear force that enhances the prevention of the occurrence or progression of cracks that may occur in the bolt-nut tightening part can be provided. 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] It is an explanatory drawing showing an example of the joining structure of an FRP molded body. [Figure 2] It is an explanatory drawing showing an example of the adhesive joint part of the joining structure of an FRP molded body. [Figure 3] It is an insertion model diagram of a stainless steel pin into FRP. [Figure 4] It is an explanatory drawing showing the positional relationship between the glass fiber of the FRP molded body and the inserted stainless steel pin. [Figure 5] It is a model diagram of a sample for a shear test. [Figure 6] It is a detailed model diagram of the sample structure for a shear test. [Figure 7] It is an explanatory drawing of the content of a shear test sample. [Figure 8] It is a distance-load test diagram showing the results of a shear test. [Figure 9] It is an explanatory drawing showing the joining structure between FRP molded bodies and the connection structure between an FRP molded body and a reinforcing material, etc. [Figure 10] It is a distance-load test diagram of the sample of the joining structure shown in FIG. 9

Modes for Carrying Out the Invention

[0024] In society, the industrial reliability of FRP products is important. For parts that are subjected to high stress, such as bolt and nut fastening areas and extremely sharp bends, crack prevention technology is desired. We have invented a reinforcing material (hereinafter referred to as "patch") containing spiral fibers and fibers arranged perpendicular to the spiral fibers (Patent Document 3). The shape of this patch can be flexibly designed and manufactured as needed, such as rectangular, square, or irregular shapes. FRP molded substrates are often used as standalone products or joined together with other materials. Their shapes are also often complex depending on the application. For example, some products are subjected to stress due to their complex structures, such as bolt and nut crimping sections. Reinforcement materials are attached to FRP molded bodies to strengthen them. These reinforcement materials consist of spiral fibers and fibers perpendicular to the spiral fibers, and strengthening the adhesive surface, taking this fiber arrangement structure into account, is desired.

[0025] Figure 1 shows an example of reinforcement using a reinforcing material (patch) and FRP. In the figure, (a) shows an example of connecting two FRP base materials 1 using bolts 2, and (b) shows an example of connecting two FRP base materials 1 to a metal molded body 5. The arrows in the figure indicate the direction of crack occurrence. (c)(d) shows a structure consisting of an FRP molded body and reinforcing material, to which a reinforcing material 7 having a configuration including spiral fibers and fibers arranged perpendicular to the spiral fibers is attached.

[0026] Next, in these structures, we compared the adhesive strength of the following three structures in the configuration of the FRP molded body and reinforcing material to increase the adhesive strength. The reinforcing material is basically a thermoplastic resin, and the FRP molded body is either a thermoplastic resin or a thermosetting resin, and can be used interchangeably as needed.

[0027] Figure 2(a) shows a sample used to evaluate the adhesive strength between a reinforcing material 7 containing adhesive 6 and an FRP base material 1 made of thermoplastic resin or thermosetting resin, in a boltless configuration, in order to isolate the effect of the bolt's shear strength on the strength of the connection point, assuming a bolted connection of an FRP reinforcing material made of thermoplastic resin. Figure 2(b) shows a sample used to evaluate the adhesive strength between a reinforcing material 7 containing stainless steel pins 8 and an FRP base material 1, in a boltless configuration, in order to isolate the effect of the bolt's shear strength, assuming a bolted connection of an FRP reinforcing material made of thermoplastic resin. The FRP base material 1 has been drilled before connection. Figure 2(c) shows a sample used to evaluate the adhesive strength between a reinforcing material 7 containing stainless steel pins 8 and adhesive 6 and an FRP base material 1, in a boltless configuration, in order to isolate the effect of the bolt's shear strength, assuming a bolted connection of an FRP reinforcing material made of thermoplastic resin. Here again, as in (b), the FRP base material 1 has been drilled before connection.

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

[0029] Figure 4(a) is a schematic diagram of the FRP molded body 10 made of thermoplastic resin before the stainless steel pins are inserted. Figure 4(b) is a diagram after the stainless steel pins have been inserted. Note that in (a), the structure consists of the FRP molded body 10 or glass fibers 11 arranged linearly within the FRP molded body 10. In (b), as shown in the diagram, the stainless steel pins 8 are configured to spread the fibers without damaging the glass fibers 11.

[0030] Figure 5 is a model diagram of a shear test specimen. In the figure, (a) is a front view and (b) is a side view. The specimen consists of an FRP molded body 10 made of thermoplastic resin and a reinforcement patch simulated specimen 13 made of long-fiber nylon plate connected together. The specimen was tested using a uniaxial pulling method in the upward and downward directions. To suppress misalignment of the tensile axis, two stainless steel plates 12 were attached as shown in (b) for use in the tensile test. The detailed configuration of this test specimen is shown below.

[0031] Figure 6 is a detailed model diagram of the sample structure for the shear test. The reinforcing patch 7 made of thermoplastic resin, shown on the right side of the figure, has markings indicating the insertion positions 14 for stainless steel pins for shear reinforcement. The two figures on the left show the details of the shear test sample before attachment, which simulates the sample with this patch. The long-fiber-reinforced nylon FRP molded body 13, made of thermoplastic nylon, also has markings 14 for inserting stainless steel pins for shear reinforcement. The FRP molded body 10 that is attached to this member has holes mechanically drilled in it before connection. These holes are drilled to insert stainless steel needles.

[0032] The figure shows the other sample before connection, and the insertion positions 14 for stainless steel pins for shear reinforcement before insertion are also shown on the reinforcement patch simulation sample 13 made of long-fiber nylon plate. The reinforcement patch simulation sample 13 made of long-fiber nylon plate and the FRP molded body 10 are attached with adhesive to create a sample, and a shear test will be performed.

[0033] Figure 7 is an explanatory diagram of the contents of the shear test specimens. There are three types of specimens: bonded only, stainless steel pin inserted, and a combination of stainless steel pin inserted and bonded.

[0034] Figure 8 is a distance-load test diagram showing the results of a shear test. In the figure, (a) is bonded only, (b) is a product with stainless steel pins inserted, and (c) is a product with a combination of stainless steel pins inserted and bonded. The shear strength of the product with stainless steel pins inserted and bonded was approximately twice that of the bonded product, and the failure point was found to be the FRP base material fracture. From this, an improvement in shear strength was observed due to the combined effect of pin insertion and bondedness.

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

[0036] Figure 10 is a distance-load test diagram of a sample of the structure shown in Figure 9. In the same figure, (a) shows the shear strength obtained from a distance-load test when connected with bolts only, (b) shows the shear strength when connected with bolts and reinforcing material, and (c) shows the shear strength when connected with stainless steel pins and adhesive without bolts.

[0037] Even without bolts, the shear strength was twice as high compared to the configuration with bolts (FRP base material 1 / FRP base material 1 / bolt 2), and the FRP base material fractured from the base material. While it is known that the bonding joint between FRP members and metal members can be reinforced with bolts, there is a risk of deformation due to shear when bending stress or torsion is applied to the FRP plate. In this invention, a significant improvement in shear strength is achieved by installing metal needle-shaped pins around the bolt holes. In summary, a bolted joining technology has been established that improves shear strength, which has been an industrial challenge, through the combination of stainless steel pins and bonding technology. This combination technology represents the pinnacle of FRP connection technology. [Explanation of symbols]

[0038] 1 FRP molded body (base material) 2 bolts 3 nuts 4 washers 5 Metal molded body 6. Adhesive 7. Reinforcement material 8 stainless steel pins 9 Plugin Tools 10 FRP molded parts 11 Glass Fiber 12 stainless steel plates 13. Reinforcement patch simulation sample made of long-fiber nylon plate 14. Insertion position of stainless steel pins for shear reinforcement

Claims

1. A joint structure comprising a joint between an FRP molded body and another molded body made of FRP or metal, which is joined by bolts and nuts and adhesive, An FRP reinforcing material is bonded to the surface of the FRP molded body or the other molded body at the joint with adhesive and fastened with bolts and nuts. The FRP reinforcing material has a spiral fiber layer formed by shaping reinforcing fibers into a spiral, and a fiber layer laminated on the spiral fiber layer, which includes linear fibers extending in a direction intersecting the spiral fibers of the spiral fiber layer when viewed from the lamination direction, and a plurality of metal needle-shaped pins are pre-inserted perpendicular to the joint surface so as not to break the spiral fibers and the linear fibers. The joining structure is characterized in that the metal needle-shaped pin is inserted into the FRP molded body and the other molded body so as to span across the FRP molded body and the other molded body at the joining portion.

2. The FRP reinforcing material is manufactured by wiring the spiral fibers with a pitch of 0.7 mm or more using a three-dimensional printer, and the metal needle-shaped pins have a diameter larger than the pitch and are pre-inserted so as not to break the spiral fibers and the straight fibers, as described in claim 1.

Images