Joint structure

Abstract

To provide a joint structure that can suppress the creep at the part where a bolt and a nut are fastened.SOLUTION: The joint structure is formed by joining an FRP mold body 4 and a metallic component 5 together with a bolt 1 and a nut 7. A metal pipe 6 is inserted into a bolt hole provided in the FRP mold body 4, and the metal pipe 6 is compressed in the longitudinal direction without buckling when the bolt is tightened.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a joint structure in which a FRP molded body and a FRP molded body or a metal member are joined with bolts and nuts.

Background Art

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

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

[0004] Recently, there have been changes in social infrastructure facilities, and needs such as enlargement of facilities due to changes in power generation methods such as wind power generation, and enlargement, thin-walling, and weight reduction for improving fuel efficiency of transportation facilities such as trains, automobiles, and airplanes have been increasing. Along with the enlargement, improvement of reliability of bolt and nut joint rivet joint etc. is desired. While the demand for lightweight and thin-walled FRP molded bodies is increasing, a technology for suppressing the occurrence and progression of cracks in bolt tightening parts and rivet joint parts is desired, and a countermeasure has been proposed (Patent Document 1).

[0005] On the other hand, suppression of loosening of bolt and nut tightening parts during bonding of FRP and metal or bonding of FRP and FRP by bolt tightening has been an old problem. In connections using bolts and nuts made of stainless steel and FRP molded bodies, which are often used in corrosion-resistant environments, loosening of the fastening part has been said to be due to the creep phenomenon of the stainless steel bolt and FRP.

[0006] Regarding the concept of creep fracture in metallic materials, when metallic materials are used at room temperature, it is generally considered that there is little need to worry if the yield strength is used as the design standard and multiplied by an appropriate safety factor (Non-Patent Literature 1). Furthermore, the high-temperature creep behavior of various stainless steels has already been elucidated (Non-Patent Literature 2), and creep phenomena are minimal at room temperature. In contrast, the effect of creep phenomena cannot be ignored in resins and FRPs.

[0007] FRP is prone to cracking and lacks strength when thin, so preventing this and developing creep suppression technologies for FRP molded joints are current challenges. Disc-shaped reinforcing patches (Patent Document 1) have already been proposed as simple reinforcing materials to reinforce areas where excessive stress may be applied, such as around bolt holes or holes drilled for other purposes, but the need for creep countermeasures for joints where creep is a problem is increasing.

[0008] A review of literature published in Japan since 1980 reveals that a vibration-damping mount structure for motors is known to use metal bolts and irregularly shaped metal nuts, with the irregular shape supporting a resin plate, thereby suppressing creep through metal-to-metal tightening (Patent Document 2). Furthermore, a similar structure for vehicle door handle devices is known to use irregularly shaped metal nuts to hold and support a resin plate, suppressing creep through metal-to-metal tightening (Patent Document 3). In addition, from an industrial practical standpoint, a specified torque for tightening bolts and nuts is recommended for both metal and resin (Non-Patent Document 3). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 7190087 [Patent Document 2] Japanese Patent Publication No. 2010-54036 [Patent Document 3] Unexamined Japanese Patent Publication No. 2015-196985 [Non-patent literature]

[0010] [Non-Patent Document 1] Etsujiro Yajima, Rie Ichikawa, and Koichi Furusawa: Mechanical and Metal Materials for Young Engineers, Maruzen Co., Ltd., April 10, 1975, p. 61. [Non-Patent Document 2] Yoshihiro Uematsu, Shozo Iizumi, Kazuo Hoshino: Nisshin Steel Technical Report No. 41, pp. 65-81 [Non-Patent Document 3] Nitto Manufacturing Co., Ltd. Nitto Torque Handbook (https: / / www.tohnichi.co.jp / download_services_sharp_type_5) [Overview of the project] [Problems that the invention aims to solve]

[0011] When connecting FRP molded parts to other FRP molded parts or metal components, bolts and nuts are typically used for fastening. However, in large structures such as large medical equipment, bridges, aircraft, drones, and wind power generation facilities, the joints are subjected to significant forces, making technologies to suppress creep in bolt and nut fastening areas desirable.

[0012] The present invention has been made in view of the above-mentioned prior art, and its object is to provide a joint structure that can suppress creep in the bolt and nut tightening portion, in a joint structure having at least an FRP structure and other structures and joining them with bolts and nuts. [Means for solving the problem]

[0013] The present invention relates to a joined structure having at least an FRP structure and another structure, which are joined by bolts and nuts. A metal tube is inserted into a bolt hole provided in the FRP structure, and the metal tube is compressed and deformed in the longitudinal direction without buckling by bolt tightening. (Claim 1)

[0014] It is preferable that the metal tube is inserted across the bolt hole of the FRP structure and the bolt hole of the other structure. (Claim 2)

[0015] Also, it is preferable that the other structure is made of plastic, FRP or metal. (Claim 3)

[0016] Also, it is preferable that the bolts and nuts are provided with a pair of metal washers. (Claim 4)

[0017] Also, it is preferable that a disk-shaped reinforcing material provided with bolt holes is attached to the surface of the FRP structure. (Claim 5)

[0018] Also, it is preferable that the metal tube is made of AISI304 stainless steel or AISI316 stainless steel of the AISI standard. (Claim 6)

[0019] Also, it is preferable that a plurality of slits are provided on the side surface of the metal tube. (Claim 7)

[0020] It should be noted that the shape of the slit is preferably round or square and is arranged in a staggered pattern. (Claim 8)

[0021] Also, it is preferable that the slit has an elongated shape and is arranged at an angle inclined with respect to the longitudinal direction of the metal tube. (Claim 9)

Advantages of the Invention

[0022] According to the joined structure of the present invention, creep at the bolt-nut tightening portion can be suppressed

Brief Description of the Drawings

[0023] [Figure 1] This is a partial cross-sectional view showing an embodiment of the present invention. [Figure 2] This is a perspective view showing an embodiment of a metal tube. [Figure 3] This is an explanatory diagram showing a stress relaxation experiment method. [Figure 4] This is an explanatory diagram showing the results of weight reduction and stress relaxation rate.

Modes for Carrying Out the Invention

[0024] FRP molded bodies (FRP structures) are often used by connecting them to each other or to molded bodies (other structures) made of other materials (such as plastics or metals). Also, the shapes are often complex depending on the application. For example, there are those that are used under stress due to their complex structures such as fastening parts by bolts, nuts or rivets. At that time, there are parts with high stress and parts with low stress, and it is necessary to strengthen the parts with high stress.

[0025] Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is a partial cross-sectional view showing three embodiments of the present invention. FIG. 1(a) shows the first embodiment, in which when fastening an FRP molded body 4 and a metal member 5 made of metal such as steel using, for example, steel bolts 1, washers 2, and nuts 7, the structure of a joined structure in which a metal tube 6 is incorporated into the bolt holes of the FRP molded body 4 and the metal member 5 is shown. Note that a reinforcing material emblem 3 having bolt holes is attached to the surface of the FRP molded body 4 with an adhesive.

[0026] In this embodiment, the metal tube 6 is inserted such that one end (the upper end in the figure) is in contact with the washer 2 on the FRP molded body 4 side, and the other end (the lower end in the figure) is in contact with the metal member 5. Before bolting, the metal tube 6 has a length that one end (the upper end in the figure) protrudes from the surface of the FRP molded body 4, and when bolted, it is compressed and deformed in the tightening direction, exhibiting a creep suppression effect. It is important here that the creep suppression effect cannot be exhibited if the metal tube buckles, so it must be in a compressed and deformed state. By compressing and deforming the metal tube, loosening between the bolts and nuts, that is, loosening due to the creep phenomenon of the FRP molded body 4 at the joint, can be suppressed.

[0027] The metal pipe 6 inserted into the bolt hole before tightening the bolts protrudes from the surface of the FRP molded body 4, and its length should preferably be about 1% to 3% of the total length of the metal pipe 6, taking into account the elastic deformation of the metal pipe. If it is less than 1%, the creep suppression effect may not be achieved, and if it exceeds 3%, the metal pipe 6 may buckle. As for the material of the metal pipe 6, for example, AISI standard AISI304 stainless steel or AISI316 stainless steel can be used.

[0028] Furthermore, in this embodiment, if the metal member 5 is replaced with another FRP molded body, it is necessary to modify the other end of the metal pipe 6 (the lower end in the figure) so that it contacts the washer 2 on the other FRP molded body side.

[0029] Figure 1(b) shows a second embodiment, which differs from the first embodiment in Figure 1(a) in that the metal member is an irregularly shaped metal member 50. In this embodiment as well, the metal pipe 6 is compressed and deformed in the tightening direction by bolting, thereby exhibiting a creep suppression effect.

[0030] Figure 1(c) shows a third embodiment, which differs from the second embodiment in Figure 1(b) in that the structure joined to the FRP molded body 4 is an irregularly shaped FRP molded body 40, and the other end (lower end in the figure) of the metal pipe 6 is in contact with the washer 2 on the FRP molded body 8 side. The metal pipe 6 inserted into the bolt hole before bolting protrudes from the surface of the FRP molded body 4 and / or the irregularly shaped FRP molded body 40, and the total length of the protruding metal pipe is preferably about 1% to 3% of the total length of the metal pipe 6, as in the first and second embodiments. In this embodiment as well, the metal pipe 6 is compressed and deformed in the tightening direction by bolting, exhibiting a creep suppression effect.

[0031] In the above embodiment, "other structures" were described in the case of metal members and FRP molded bodies, but the method can also be applied to plastic molded bodies.

[0032] Figure 2 shows examples of metal pipes. The metal pipe in Figure 2(a) does not have slits (holes) on its side, but the metal pipes in Figures 2(b) to (h) have multiple slits on their side. Possible slit shapes include circular (Figures 2(b) to (e)), diamond (Figures 2(e) to (g)), and rectangular (Figure 2(h)). The slits can be arranged in a circumferential direction around the metal pipe, with 4 to 8 slits as shown in Figures 2(b) and (c), or in a staggered pattern as shown in Figures 2(d) to (g). If the slits are rectangular, multiple slits can be arranged at an angle to the circumferential direction, as shown in Figure 2(h). Since there is a trend towards weight reduction in FRP joints, reducing the weight of the metal pipe 6 can contribute to overall weight reduction.

[0033] Generally, evaluating creep characteristics requires long-term constant-strain experiments. Here, a relaxation test was conducted for a shorter-term evaluation. Figure 3 is an explanatory diagram showing a method for evaluating the creep characteristics of the component of the present invention. A ring-shaped sample 13 is placed between a pair of carbide plates 12 arranged vertically. In this state, the ring-shaped sample 13 is displaced so that the load 11 corresponds to the stress when the bolt is tightened. Then, a relaxation test is performed for a predetermined time while maintaining the distance between the carbide plates 12, and the stress after holding for the predetermined time is measured relative to the initial stress when the load is applied, and the stress relaxation rate (%) is determined.

[0034] In this relaxation test, based on Non-Patent Document 3 (Torque Handbook), a standard axial force of 33.0 kN was applied to metal samples No. 1 to No. 3, assuming an M16 bolt, and a standard axial force of 16.5 kN was applied to resin sample No. 4, assuming an M16 bolt. The feed rate was set to 0.1 mm / min, and after reaching the desired stress, the samples were held under constant strain for 1 hour to investigate the stress relaxation. The degree of buckling was determined from the change in height of each sample before and after relaxation.

[0035] Furthermore, in this relaxation test, in order to evaluate the relationship between the shape of the metal tube used in the present invention, the weight ratio for weight reduction, and the stress relaxation rate, sample No. 1 was a metal tube corresponding to Figure 2(a), sample No. 2 was a metal tube corresponding to Figure 2(b) (4 slits), and sample No. 3 was a metal tube corresponding to Figure 2(c) (8 slits). Sample No. 4, a comparative example, was an FRP ring made of glass fiber / unsaturated polyester resin, and did not have slits on the side. The dimensions of samples No. 1 to 4 before testing were a wall thickness of 2 mm, an inner diameter of 18 mm, an outer diameter of 22 mm, and a height of 5.95 mm, and the round slits provided on the side of the tubes had a diameter of 3 mm.

[0036] Figure 4 shows the results of the relaxation test for samples No. 1 to 4. The height of all samples No. 1 to 4 remained at 5.95 mm after the relaxation test, showing no change from before the test, indicating that buckling due to plastic deformation did not occur. Next, stress relaxation was examined. The results showed that the stress relaxation rate of sample No. 4 (glass fiber / unsaturated polyester resin (FRP)) was high at 22%, while the stress relaxation rates of samples No. 1 to 3 were low at 6-8%, about one-third of that of sample No. 4. Furthermore, an evaluation of the proportion of the slits to the total pipe size revealed that, as shown in the test results, up to approximately 85% of the weight of a metal pipe without slits (in other words, up to approximately 15% of the total pipe size of the slits) is acceptable. As the test results show, metal pipes with slits on the sides tend to have a slightly lower stress relaxation rate compared to metal pipes without slits, but springiness can be expected. If the number of slits is increased, it may be possible to balance this by increasing the thickness of the metal pipe. [Industrial applicability]

[0037] The joint structure of the present invention can suppress bolt loosening (creep) caused by FRP, and can therefore be applied to various products and industrial parts that require joining with bolts, nuts, rivets, etc., such as aircraft, light small airplanes, air conditioning equipment, industrial and nursing care robots, trucks, automobile parts, train parts, components for wind power generation equipment, medical equipment housings, drone parts, FRP housings, medical equipment, and wind power generation components. [Explanation of symbols]

[0038] 1 bolt 2 washers 3 patches 4 FRP molded body 40 irregularly shaped FRP molded body 5 Metal components 50 Irregularly Shaped Metal Components 6 metal tube 7 nuts 11 Displacement corresponding to the load 12 Carbide Plates 13. Ring-shaped sample

Claims

1. In a joint structure having at least an FRP structure and other structures, which are joined together with bolts and nuts, A metal pipe is inserted into a bolt hole provided in the FRP structure. The aforementioned metal tube has multiple slits on its side, The slits are round, square, or elongated in shape. When they are round or square, they are arranged in a staggered pattern. When they are elongated, they are arranged at an angle inclined with respect to the longitudinal direction of the metal tube. The aforementioned metal pipe is characterized by being compressed and deformed in the longitudinal direction without buckling by bolting.

2. The joining structure according to claim 1, characterized in that the metal pipe is inserted across the bolt holes of the FRP structure and the bolt holes of the other structure.

3. The joining structure according to claim 1 or 2, characterized in that the other structure is made of plastic, FRP, or metal.

4. The joining structure according to claim 1, characterized in that the bolt and nut are provided with a pair of metal washers.

5. The joint structure according to claim 1, characterized in that a disc-shaped reinforcing material having bolt holes is attached to the surface of the FRP structure.

6. The joint structure according to claim 1, characterized in that the metal pipe is made of AISI 304 stainless steel or AISI 316 stainless steel conforming to the AISI standard.

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