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 joined structure in which an FRP molded body is joined to an FRP molded body or a metal member 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. 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 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 manufactured.

[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 large-scale thin-walled weight reduction for improving the fuel efficiency of transportation facilities such as trains, automobiles, and airplanes have been increasing. Along with the increase in size, improvement in reliability of bolt and nut joining, rivet joining, etc. is desired. In the midst of the increasing demand for lightweight and thin-walled FRP molded bodies, a technology for suppressing the occurrence and progression of cracks in bolt tightening parts and rivet joining parts is desired, and a countermeasure method has been proposed (Patent Document 1).

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

[0006] Regarding the concept of creep rupture of metal materials, when using metal materials at room temperature, it is said that there is generally no need to worry as long as the proof stress is used as the design criterion and multiplied by an appropriate safety factor (Non-Patent Document 1). In addition, the high-temperature creep behavior of various stainless steels has already been clarified (Non-Patent Document 2), and at around room temperature, the creep phenomenon is less. In contrast, the influence of the creep phenomenon cannot be ignored in resins and FRP.

[0007] Since FRP is weak in strength and prone to cracking when thin, preventing this and the creep suppression technology at the joint of the FRP molded body are current issues. A disk-shaped reinforcing material, a disc washer (Patent Document 1), has already been proposed as a simple reinforcing material for reinforcing parts where excessive stress may be applied around bolt tightening holes or holes drilled for other purposes. However, the need for creep countermeasures at joints where creep becomes a problem is increasing.

[0008] When examining the documents published in Japan after 1980, there is a known structure that uses a metal bolt and a non-standard-shaped metal nut as a vibration-proof mount structure for a motor. By making it non-standard-shaped, it supports a resin plate, and creep is suppressed by tightening between metals (Patent Document 2). Furthermore, regarding the structure of a vehicle door handle device, there is also a known special-shaped structure that uses a non-standard-shaped metal nut to hold and support a resin plate, and creep is suppressed by tightening between metals (Patent Document 3). Also, in industrial practical applications, a predetermined torque for bolt and nut tightening is recommended for metals and resins (Non-Patent Document 3).

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

[0010] [Non-Patent Document 1] Etsujiro Yajima, Michie Ichikawa, Hiroshi Kosawa: Machinery and Metal Materials for Young Engineers, Maruzen Co., Ltd., April 10, 1975, P61 [Non-Patent Document 2] Yasuhiro Uematsu, Shozo Izumi, Kazuo Hoshino: Nisshin Steel Technical Report No. 41, p65-81 [Non-Patent Document 3] Tohnichi Manufacturing Co., Ltd. Tohnichi Torque Handbook (https: / / www.tohnichi.co.jp / download_services Sharp type_5) [Summary of the Invention] [Problems to be Solved by the Invention]

[0011] When connecting an FRP molded body to an FRP molded body or a metal member, it is often joined by tightening with bolts and nuts. However, for large structures such as large medical equipment, bridges, aircraft, drones, and wind power generation facilities, since the joints are subjected to large forces, a technique for suppressing creep at the bolt and nut tightening portions is desired.

[0012] The present invention has been made in view of the above prior art, and an object thereof is to provide a joint structure capable of suppressing creep at a bolt and nut tightening portion in a joint structure having at least an FRP structure and another structure and joining them with bolts and nuts. [Means for Solving the Problems]

[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 bolt and nut are provided with a pair of metal washers. (Claim 4)

[0017] Also, it is preferable that a disk-shaped reinforcing material provided with a bolt hole 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 and nut tightening portion can be suppressed

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

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 (for example, plastics or metals). Also, many of them have complex shapes depending on their uses. For example, there are those that are used under stress due to their complex structures such as fastening parts using bolts and 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 with reference to the drawings. FIG. 1 is a partial cross-sectional view showing three embodiments of the present invention. FIG. 1(a) shows the first embodiment, and 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, it shows 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. Note that a reinforcing material washer 3 having bolt holes is attached to the surface of the FRP molded body 4 with an adhesive.

[0026] In this embodiment, one end (the upper end in the figure) of the metal pipe 6 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 inserted in contact with the metal member 5. Before being bolted, one end (the upper end in the figure) of the metal pipe 6 has a length protruding from the surface of the FRP molded body 4, and it is compressed and deformed in the tightening direction by bolt tightening to exhibit a creep suppression effect. Here, it is important that since the creep suppression effect cannot be exerted when the metal pipe buckles, it must be in a compressed and deformed state at all times. When the metal pipe is compressed and deformed, looseness between the bolt and nut, that is, loosening due to the creep phenomenon of the FRP molded body 4 at the joint part can be suppressed.

[0027] Note that the metal pipe 6 inserted into the bolt hole before bolt tightening protrudes from the surface of the FRP molded body 4, and its length is desirably about 1% to 3% of the total length of the metal pipe 6 considering the elastic deformation of the metal pipe. If it is less than 1%, there is a possibility that the creep suppression effect cannot be exerted, and if it exceeds 3%, the metal pipe 6 may buckle. As the material of the metal pipe 6, for example, AISI304 stainless steel or AISI316 stainless steel of the AISI standard can be used.

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

[0029] Figure 1(b) shows the second embodiment, which is different from the first embodiment in Figure 1(a) in that the metal member is a shaped metal member 50. Also in this embodiment, the metal pipe 6 is compressed and deformed in the tightening direction by bolt tightening to exhibit a creep suppression effect.

[0030] Fig. 1(c) shows the third embodiment, which is different from the second embodiment in Fig. 1(b) in that the structure joined to the FRP molded body 4 is the irregular-shaped FRP molded body 40, and the other end (the 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 bolt tightening protrudes from the surface of the FRP molded body 4 or / and the irregular-shaped FRP molded body 40, and the total protruding length is preferably about 1% to 3% of the total length of the metal pipe 6, similar to the first and second embodiments. Also in this embodiment, the metal pipe 6 is compressed and deformed in the tightening direction by bolt tightening, exerting a creep suppression effect.

[0031] In the above embodiments, the cases of metal members and FRP molded bodies as "other structures" have been described, but it is also applicable to plastic molded bodies.

[0032] An example of the metal pipe is shown in Fig. 2. The metal pipe in Fig. 2(a) has no slit (hole) provided on its side surface, while the metal pipes in Fig. 2(b) to (h) have a plurality of slits provided on their side surfaces. The shapes of the slits can be circular (Fig. 2(b) to (e)), rhombic (Fig. 2(e) to (g)), rectangular (Fig. 2(h)), etc. The slits can be provided about 4 to 8 in the circumferential direction of the metal pipe as shown in Fig. 2(b) and (c), or arranged in a staggered pattern as shown in Fig. 2(d) to (g). Also, when the slit is rectangular, a plurality of slits can be arranged obliquely with respect to the circumferential direction as shown in Fig. 2(h). Since weight reduction is generally required for the FRP joint, the metal pipe 6 can also contribute to the overall weight reduction by reducing its weight.

[0033] Generally, the evaluation of creep characteristics requires a long-term constant strain experiment. Here, a relaxation test was conducted for short-term evaluation. FIG. 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 as to obtain a load 11 corresponding 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, the stress after holding for a predetermined time with respect to the initial stress applied with the load is measured, and the stress relaxation rate (%) is obtained.

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

[0035] Also, 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 is a metal tube corresponding to FIG. 2(a), Sample No. 2 is a metal tube corresponding to FIG. 2(b) (number of slits: 4), and Sample No. 3 is a metal tube corresponding to FIG. 2(c) (number of slits: 8). Further, Sample No. 4, which is a comparative example, is an FRP ring made of glass fiber / unsaturated polyester resin and has no slit on the side surface. The dimensions of Samples No. 1 to No. 4 before the test are 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 slit provided on the side surface of the tube has a diameter of 3 mm.

[0036] Figure 4 shows the results of the relaxation tests for Specimens No. 1 to 4. For all of Specimens No. 1 to 4, the height after the relaxation test remained at 5.95 mm, and no change from before the test was observed. Buckling due to plastic deformation did not occur. Next, stress relaxation was examined. As a result, the stress relaxation rate of the glass fiber / unsaturated polyester resin (FRP) of Specimen No. 4 was as high as 22%, but the stress relaxation rates of Specimens No. 1 to 3 were as low as 6 to 8%, which was about one-third of that of Specimen No. 4. Further, when evaluating the ratio occupied by the slits with respect to the entire tube, as per the results of this test, it was determined that up to about 85% of the weight (in other words, the ratio occupied by the slits with respect to the entire tube was up to about 15%) was acceptable compared to the metal tube without slits. As per the test results, although the metal tube with slits on the side had a slightly inferior stress relaxation rate compared to the metal tube without slits, spring properties could be expected. If the number of slits is increased, it is conceivable to increase the thickness of the metal tube to achieve balance.

Industrial Applicability

[0037] The joining structure of the present invention can suppress the loosening (creep) of bolts due to FRP, and thus can be applied to various products and product industrial parts that require joining such as bolts, nuts, rivets, etc., such as members for aircraft, lightweight small airplanes, air conditioning equipment, industrial and care robots, trucks, automobile parts, train parts, components for wind power generation equipment, etc., housings for medical devices, parts for drones, FRP housings, medical equipment, parts for wind power generation, etc.

Explanation of Signs

[0038] 1 Bolt 2 Washer 3 Wappen 4 FRP Formed Body 40 Irregularly Shaped FRP Formed Body 5 Metal Member 50 Irregularly Shaped Metal Member 6 Metal Tube 7 Nut 11 Displacement Corresponding to Load 12 Cemented Carbide Plate 13 Ring-Shaped Specimen

Claims

1. In a joined structure having at least an FRP structure and another structure, and joining them with 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. A joined structure characterized by that.

2. The joined structure according to claim 1, wherein the metal tube is inserted across the bolt hole of the FRP structure and the bolt hole of the other structure.

3. The joined structure according to claim 1 or claim 2, wherein the other structure is made of plastic, FRP or metal.

4. The joined structure according to claim 1, wherein the bolt and the nut are provided with a pair of metal washers.

5. The joined structure according to claim 1, wherein a disk-shaped reinforcing material provided with bolt holes is attached to the surface of the FRP structure.

6. The joined structure according to claim 1, wherein the metal tube is made of AISI 304 stainless steel or AISI 316 stainless steel of AISI standard.

7. The joined structure according to claim 1, wherein a plurality of slits are provided on the side surface of the metal tube.

8. The joined structure according to claim 7, wherein the shape of the slit is round or square and is arranged in a staggered pattern.

9. The joined structure according to claim 7, wherein the slit has an elongated shape and is arranged at an angle inclined with respect to the longitudinal direction of the metal tube.

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