High-strength bolt friction joint structure

Abstract

To improve a slip factor of a joint part efficiently in high power bolt friction joint including a steel material having a joint surface which has been subjected to surface treatment that makes the slip factor larger as a contact pressure reduces.SOLUTION: A high power bolt friction joint structure 10 includes: a first steel material 11 having a first joint surface 11A in which a periphery of a first bolt hole 11B has been subjected to surface treatment that makes a slip factor larger as a contact pressure reduces; a second steel material 12 having a second joint surface 12A overlapped with the first joint surface 11A of the first steel material 11, and a second bolt hole 12B; a high power bolt 14 and a nut 16 which allow friction joint of the first steel material 11 and the second steel material 12; and a washer member 18 configured to contact with the first steel material 11 and having a bolt hole 20 in which a diameter expanding part EP having a hole diameter d' larger than or equal to a hole diameter d of the first bolt hole 11B of the first steel material 11 is formed at the side of the first joint surface 11A of the first steel material 11 of the first bolt hole 11B.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This disclosure relates to a high-strength bolt friction joint structure.

Background Art

[0002] Conventionally, as in Patent Documents 1 and 2, a high-strength bolt friction joint structure in which steel materials are frictionally joined with high-strength bolts is known. In a high-strength bolt friction joint structure, the slip resistance is determined by the product of the contact pressure applied from the high-strength bolt to the steel material and the coefficient of friction.

[0003] Patent Document 1 discloses a technique for improving the coefficient of friction of a joint by subjecting the joint surface of a galvanized steel sheet to a phosphate treatment.

[0004] Patent Document 2 discloses a technique for improving the coefficient of friction of a joint by subjecting the joint surface to an aluminum spraying treatment. The aluminum spraying treatment is a friction surface treatment in which the coefficient of friction increases as the contact pressure decreases. Also, in Patent Document 2, a plate-shaped plate thickness increasing member is provided between the high-strength bolt and the steel material. By the plate thickness increasing member, the length along the plate thickness direction between the high-strength bolt and the steel material is extended, thereby controlling the contact pressure.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, the disclosers considered that the slip coefficient of a joint portion with a phosphate treatment on the joint surface of a plated steel sheet disclosed in Patent Document 1 would behave similarly to a joint surface with a surface treatment such as Patent Document 2, where the slip coefficient increases as the contact pressure decreases. Therefore, they investigated the relationship between the position of the inner edge of the washer and the value of the slip coefficient, focusing on a high-strength bolt friction joint structure.

[0007] Furthermore, the inner diameter of the washer is generally smaller than the diameter of the bolt hole in the steel material to facilitate alignment during installation. Therefore, when steel materials are friction-joined with high-strength bolts, the inner edge of the washer protrudes beyond the inner wall of the bolt hole in the steel material towards the high-strength bolt.

[0008] The investigation revealed that when the inner edge of the washer protrudes beyond the inner wall of the bolt hole in the steel material towards the shaft of the high-strength bolt, the slip coefficient obtained by the surface treatment of the joint surface is limited due to the distribution of contact pressure. In other words, the slip coefficient cannot be obtained efficiently, and as a result, it is difficult to improve the sliding resistance.

[0009] In this regard, Patent Document 2 does not examine the relationship between the peak position of contact pressure and the effect of surface treatment on the joint surface on improving the coefficient of slip.

[0010] This disclosure provides a technology that can efficiently improve the slip coefficient of a joint in a high-strength bolt friction joint, which includes steel materials having a joint surface treated to increase the slip coefficient as the contact pressure decreases. [Means for solving the problem]

[0011] The high-strength bolt friction joint structure according to this disclosure comprises: a first steel material having a first joint surface that is surface-treated around a first bolt hole such that the coefficient of slip increases as the contact pressure decreases; a second steel material having a second bolt hole, with the second joint surface superimposed on the first joint surface of the first steel material; a high-strength bolt and nut for frictionally joining the first steel material and the second steel material; and a washer member having a bolt hole that is in contact with the first steel material and has an enlarged diameter portion formed on the side of the first joint surface having a hole diameter greater than or equal to the hole diameter of the first bolt hole.

[0012] In this disclosure, the first steel material has a first joint surface around the first bolt hole that is surface-treated such that the coefficient of slip increases as the contact pressure decreases. In addition, in the bolt hole of the washer member in contact with the first steel material, an enlarged diameter portion is formed on the side of the first joint surface, having a hole diameter greater than or equal to the hole diameter of the first bolt hole.

[0013] The washer member with the enlarged diameter shifts the position of the contact pressure peak outward from the edge of the first bolt hole in the first steel material. Therefore, in the contact pressure distribution of this embodiment, the region where the contact pressure gradually decreases as you move outward from the peak position is shifted outward compared to when the diameter of the bolt hole in the washer member is less than the diameter of the first bolt hole in the first steel material. In addition, a pattern where the contact pressure gradually decreases from the outside to the inside is formed between the position of the contact pressure peak and the edge of the first bolt hole in the first steel material. As a result, the area of ​​the region where contact pressure is distributed within the surface-treated joint surface increases.

[0014] Therefore, the effect of improving the coefficient of slip obtained by surface treatment can be utilized more effectively compared to the case where the diameter of the bolt hole in the washer member is less than the diameter of the first bolt hole in the first steel material. Thus, the coefficient of slip of the joint can be improved efficiently. [Effects of the Invention]

[0015] According to this disclosure, in a high-strength bolt friction joint including a steel material having a joint surface that is treated in such a way that the coefficient of slip increases as the contact pressure decreases, the coefficient of slip of the joint can be efficiently improved. [Brief explanation of the drawing]

[0016] [Figure 1] This is a cross-sectional view taken along line 1-1 in Figure 3(A), illustrating a high-strength bolt friction joint structure according to an embodiment of the present disclosure. [Figure 2] This is a perspective view illustrating the high-strength bolt friction joint structure according to this embodiment. [Figure 3]FIG. 3(A) is a plan view for explaining the high-strength bolt friction joint structure according to the present embodiment, and FIG. 3(B) is a side view for explaining the high-strength bolt friction joint structure according to the present embodiment. [Figure 4] It is a cross-sectional view for explaining the high-strength bolt friction joint structure according to the comparative example. [Figure 5] It is a cross-sectional view for explaining the high-strength bolt friction joint structure according to the first modification example of the present embodiment. [Figure 6] It is a cross-sectional view for explaining the high-strength bolt friction joint structure according to the second modification example of the present embodiment. [Figure 7] It is a cross-sectional view for explaining the high-strength bolt friction joint structure according to the third modification example of the present embodiment. [Figure 8] It is a cross-sectional view for explaining the high-strength bolt friction joint structure according to the fourth modification example of the present embodiment. [Figure 9] It is a perspective view for explaining the high-strength bolt friction joint structure according to the fourth modification example. [Figure 10] It is a perspective view for explaining the auxiliary washer member of the high-strength bolt friction joint structure according to the fourth modification example. [Figure 11] It is a cross-sectional view for explaining the high-strength bolt friction joint structure according to the fifth modification example of the present embodiment. [Figure 12] FIG. 12(A) is a plan view for explaining the high-strength bolt friction joint structure according to the sixth modification example of the present embodiment, and FIG. 12(B) is a cross-sectional view taken along line 12B-12B in FIG. 12(A). [Figure 13] It is a cross-sectional view for explaining the high-strength bolt friction joint structure according to the seventh modification example of the present embodiment. [Figure 14] It is a graph for explaining the relationship between the contact pressure and the slip coefficient obtained in the experiment. [Figure 15] It is a photograph of the cross-section of the steel material obtained in the experiment. [Figure 16] It is a side view for explaining the high-strength bolt friction joint structure according to the analysis model in the example. [Figure 17] It is a graph for explaining the results obtained from the analysis model of CASE1 in the first analysis example. [Figure 18]This graph explains the results obtained from the CASE2 analysis model in the first analysis example. [Figure 19] This graph explains the results obtained from the CASE 3 analysis model in the first analysis example. [Figure 20] This graph illustrates the effect of the plate thickness of the auxiliary washer section using the analysis model from CASE 1 in the second analysis example. [Figure 21] This graph illustrates the effect of the plate thickness of the auxiliary washer section using the analysis model from CASE 3 in the second analysis example. [Figure 22] This graph illustrates the effect of the hole diameter in the auxiliary washer section, using the analysis model from CASE 1 in the second analysis example. [Figure 23] This graph illustrates the effect of the hole diameter in the auxiliary washer section, using the analysis model from CASE 3 in the second analysis example. [Figure 24] This graph illustrates the effect of the outer diameter of the auxiliary washer portion using the analysis model from CASE 1 in the second analysis example. [Figure 25] This graph illustrates the correspondence between the converted slip coefficient set in this embodiment and the experimental value. [Figure 26] This graph illustrates the relationship between the hole diameter ratio and the converted slip coefficient in the third analysis example. [Figure 27] This graph illustrates the relationship between the hole diameter ratio and the converted slip coefficient in the fourth analysis example. [Figure 28] This graph illustrates the relationship between plate thickness ratio and converted slip coefficient in the fourth analysis example. [Figure 29] This graph illustrates the relationship between the outer diameter ratio and the converted slip coefficient in the fourth analysis example. [Figure 30] This graph illustrates the relationship between the difference in hole diameter between plates and the converted slip coefficient in the fifth analysis example. [Figure 31] This graph in the sixth analysis example illustrates the relationship between the methods of increasing plate thickness—specifically, increasing the plate thickness using auxiliary washers and increasing the plate thickness of the steel material—and the converted coefficient of slip. [Figure 32]This graph illustrates the relationship between the enlarged diameter section and the converted slip coefficient when a stepped section or tapered section is provided as the enlarged diameter section in the seventh analysis example. [Figure 33] In the eighth analysis example, using the analysis models A-2 and A-2' of CASE 1, this graph explains the effect of differences in the contact area between the washer member and the steel material on the contact pressure distribution. [Figure 34] In the eighth analysis example, using the analysis models A-3 and A-3' of CASE 1, this graph explains the effect of differences in the contact area between the washer member and the steel material on the contact pressure distribution. [Figure 35] In the eighth analysis example, using the analysis models A-4 and A-4' of CASE 1, this graph explains the effect of differences in the contact area between the washer member and the steel material on the contact pressure distribution. [Figure 36] In the eighth analysis example, using the analysis models A-5 and A-5' of CASE 1, this graph explains the effect of differences in the contact area between the washer member and the steel material on the contact pressure distribution. [Figure 37] In the eighth analysis example, using the analysis models A-6 and A-6' of CASE 1, this graph explains the effect of differences in the contact area between the washer member and the steel material on the contact pressure distribution. [Figure 38] In the eighth analysis example, this graph explains the effect of the difference in contact area between the washer member and the joined member on the converted slip coefficient, using the analysis model from CASE 1. [Modes for carrying out the invention]

[0017] Embodiments of the present disclosure are described below. In the following drawings, identical and similar parts are denoted by the same or similar reference numerals. However, the relationship between thickness and planar dimensions, the ratio of thickness of each device and component, etc., in the drawings differ from those in reality. Therefore, specific thicknesses and dimensions should be determined by referring to the following explanation. Furthermore, there are parts where the relationships and ratios of dimensions differ between drawings.

[0018] <High-strength bolt friction joint structure> The high-strength bolt friction joint structure according to this embodiment will be described with reference to Figures 1 to 3. As shown in Figures 1 and 2, the high-strength bolt friction joint structure 10 according to this embodiment comprises a first steel member 11, a second steel member 12, a high-strength bolt 14, a nut 16, and a washer member 18.

[0019] As shown in Figure 3(A), in this embodiment, four high-strength bolt friction joint structures 10 are configured at the joint between the first steel material 11 and the second steel material 12. As shown in Figure 3(B), the number of friction surfaces of the high-strength bolt friction joint structure 10 in this embodiment is one. In this disclosure, the number of high-strength bolt friction joint structures 10 configured at the joint between steel materials can be one or more, or any number.

[0020] (Daiichi Steel) As shown in Figure 1, the first steel material 11 is one of the two joined members in the high-strength bolt friction joint structure 10. The first steel material 11 is a plated steel sheet having a substantially constant thickness t1 along the thickness direction (i.e., the vertical direction in Figure 1). In this disclosure, the steel sheet as the first steel material is not limited to a plated steel sheet.

[0021] The first steel member 11 has a first bolt hole 11B and a first joint surface 11A around the first bolt hole 11B that is surface-treated so that the coefficient of slip increases as the contact pressure decreases. The first joint surface 11A of the first steel member 11 is in contact with the second joint surface 12A of the second steel member 12. The opening of the first bolt hole 11B is circular in shape. The first bolt hole 11B has a hole diameter d that is approximately constant along the plate thickness direction.

[0022] (Second steel material) The second steel material 12 is the other of the two joined members in the high-strength bolt friction joint structure 10. The second steel material 12 is a plated steel sheet having a substantially constant thickness t2 along the thickness direction. In this disclosure, the steel sheet as the second steel material is not limited to a plated steel sheet. In this embodiment, the thickness t2 of the second steel material 12 is the same as the thickness t1 of the first steel material 11, but in this disclosure, the thickness of the second steel material 12 may be different from the thickness of the first steel material 11.

[0023] The second steel member 12 has a second bolt hole 12B and a second joint surface 12A around the second bolt hole 12B that is treated to increase the coefficient of slip as the contact pressure decreases. The second joint surface 12A of the second steel member 12 is superimposed on the first joint surface 11A of the first steel member 11.

[0024] The opening of the second bolt hole 12B is circular in shape. The second bolt hole 12B has a substantially constant diameter d along the plate thickness direction. In this embodiment, the diameter d of the second bolt hole 12B of the second steel material 12 is the same as the diameter d of the first bolt hole 11B of the first steel material 11. However, in this disclosure, the diameter of the second bolt hole 12B of the second steel material 12 may be different from the diameter of the first bolt hole 11B of the first steel material 11.

[0025] (Surface treatment) In this embodiment, the surface treatment applied to the first joint surface 11A of the first steel material 11 and the second joint surface 12A of the second steel material 12 is a phosphate treatment. The phosphate treatment may be applied by coating or by immersion. Note that surface treatment on the upper surface of the first steel material 11 opposite to the first joint surface 11A and the lower surface of the second steel material 12 opposite to the second joint surface 12A in Figure 1 is not essential.

[0026] Furthermore, in this disclosure, the surface treatment applied to the joint surface of the joint is not limited to phosphate treatment, but may be other surface treatments such as aluminum thermal spraying.

[0027] (Parts to be joined) In this embodiment, the first steel material 11 and the second steel material 12 are, for example, thin steel plates. In this disclosure, the members to be joined are not limited to thin steel plates, but may also be thick steel plates. In this disclosure, the plate thickness of the steel material is arbitrary. Also, in this embodiment, the first steel material 11 and the second steel material 12 are not limited to steel plates. In this disclosure, the members to be joined may be so-called metal fittings or structural steel. In this disclosure, the part to which the high-strength bolt friction joint structure 10 is applied only needs to be plate-shaped.

[0028] Furthermore, in this disclosure, the number of members to be joined is not limited to two, but may be three or more. In other words, the number of members to be joined is arbitrary. For example, in this disclosure, one or more other steel materials may be superimposed between the first steel material 11 and the second steel material 12 as members to be joined.

[0029] Furthermore, one or more other steel materials to be joined may be superimposed on the side of the first steel material 11 opposite to the second steel material 12, and one or more other steel materials to be joined may be superimposed on the side of the second steel material 12 opposite to the first steel material 11. In other words, in this disclosure, the expressions "first steel material" and "second steel material" refer to two steel materials that form a joint, and do not refer to steel materials placed at a specific position.

[0030] (High-strength bolts and nuts) The high-strength bolt 14 and nut 16 are connecting members that frictionally join the first steel material 11 and the second steel material 12. The shaft portion of the high-strength bolt 14 has a constant shaft diameter D. The shaft portion of the high-strength bolt 14 is inserted into the first bolt hole 11B and the second bolt hole 12B.

[0031] In this embodiment, the high-strength bolt 14 is a high-strength hexagonal bolt, but the high-strength bolt 14 in this disclosure is not limited to a hexagonal bolt and may be, for example, a torque-shear type. Also, in this disclosure, the shape of the nut 16 can be changed as appropriate.

[0032] (Washer component) In this embodiment, the high-strength bolt friction joint structure 10 includes a pair of washer members 18. One of the pair of washer members 18 is positioned between the head of the high-strength bolt 14 and the first steel member 11, while the other washer member 18 is positioned between the nut 16 and the second steel member 12. That is, the washer member 18 located on the upper side in Figure 1 is in contact with the first steel member 11, and the other washer member 18 located on the lower side in Figure 1 is in contact with the second steel member 12.

[0033] The washer member 18 is ring-shaped and, in plan view, has a bolt hole 20 in the center. The outer and inner edges of the washer member 18 are circular in shape. The washer member 18 in this embodiment is composed of only one flat washer section. The washer member 18 has an outer diameter Dw that is approximately constant and a plate thickness tw that is approximately constant, corresponding to the bolt shaft diameter D. The washer member 18 can be made from, for example, a steel plate.

[0034] (Expanded diameter part) In this embodiment, in the case of the upper washer member 18 in Figure 1, an enlarged diameter portion EP is formed on the side of the bolt hole 20 facing the first steel member 11, having a hole diameter d' that is greater than or equal to the hole diameter d of the first bolt hole 11B of the first steel member 11. That is, d ≤ d'.

[0035] In this embodiment, for the sake of explanation, when the washer member 18 and the steel material are in contact, the "bottom surface" of the washer member 18 is defined as the surface on the side facing the steel material, and the "top surface" of the washer member 18 is defined as the surface on the opposite side from the steel material. That is, the area on the bottom surface side is the area on the side facing the first joint surface, or the area on the side facing the second joint surface. The area on the top surface side is the area on the side facing the head of the high-strength bolt 14, or the area facing the nut 16.

[0036] In this embodiment, the hole diameter d' on the bottom side of the flat washer portion of the washer member 18 and the hole diameter dw on the top side are approximately the same. That is, the entire diameter of the enlarged portion EP in the plate thickness direction is enlarged almost uniformly to a size greater than or equal to the hole diameter d of the first bolt hole 11B. The enlarged portion EP can improve the slip coefficient of the joint.

[0037] In this embodiment, the center of the first bolt hole 11B, the center of the second bolt hole 12B, and the center of the bolt hole 20 of the washer member 18 are shown aligned on the same axis C. However, this disclosure is not limited to this, and states where their centers are offset are not excluded.

[0038] (Comparative example) On the other hand, as shown in Figure 4, in the comparative example high-strength bolt friction joint structure 10Z, the enlarged diameter portion EP is not formed in the washer member 18Z in the region on the bottom side of the bolt hole 20. That is, in the comparative example, the hole diameter d' on the bottom side of the bolt hole 20 is smaller than the hole diameter d of the first bolt hole 11B of the first steel material 11. For this reason, the slip coefficient of the joint cannot be improved by the enlarged diameter portion EP as in this embodiment.

[0039] <Variation> Next, the high-strength bolt friction joint structures according to the first to seventh modified examples of this embodiment will be described with reference to Figures 5 to 13. In the first to seventh modified examples as well, the sliding coefficient of the joint can be improved by the enlarged diameter portion EP. In the following descriptions of the first to seventh modified examples, we will mainly describe the differences from the high-strength bolt friction joint structure 10 according to this embodiment illustrated in Figure 1, and will omit redundant explanations of structures similar to this embodiment.

[0040] (First variation) As shown in Figure 5, in the high-strength bolt friction joint structure 10A according to the first modified example, the washer member 18 is provided only on the head side of the high-strength bolt 14 at the joint. That is, there is only one washer member 18 having an enlarged diameter portion EP. In this disclosure, the washer member 18 may be provided only on the nut 16 side at the joint. As in the first modified example, in this disclosure, the washer member 18 having an enlarged diameter portion EP only needs to be placed on at least one of the head side of the high-strength bolt 14 and the nut 16 side.

[0041] (Second variation) As shown in Figure 6, in the high-strength bolt friction joint structure 10B according to the second modified example, the area on the bottom side of the inner wall surface forming the bolt hole 20 of the washer member 18B is partially enlarged in diameter compared to the area on the top side. Specifically, in the second modified example, a step is formed between the top and bottom surfaces of the washer member 18B such that the bolt hole 20 has two different hole diameters, dw on the top side and d' on the bottom side. In this disclosure, the number of such steps is not limited to one, but can be two or more.

[0042] In the second modified example, the hole diameter d' on the bottom side is larger than the hole diameter dw on the top side. The region having the hole diameter d' on the bottom side is the enlarged diameter portion EP of the washer member 18B. Furthermore, as in the second modified example, when the hole diameter dw on the top side is smaller than the hole diameter d of the first bolt hole 11B of the first steel material 11, it is easier to align the high-strength bolt 14 with the first bolt hole 11B during bolt tightening.

[0043] (Third variation) As shown in Figure 7, in the high-strength bolt friction joint structure 10C according to the third modified example, the area on the bottom side of the inner wall surface forming the bolt hole 20 of the washer member 18C is partially enlarged in diameter compared to the area on the top side. Specifically, in the third modified example, the bolt hole 20 has a hole diameter dw on the top side and a hole diameter d' on the bottom side, and a tapered portion (i.e., an inclined surface) is formed between the top and bottom surfaces of the washer member 18C. In this disclosure, the number of tapered portions is not limited to one, and two or more tapered portions with different inclination angles may be formed.

[0044] In the third modification, the hole diameter d' on the bottom side is larger than the hole diameter dw on the top side. In the third modification, the tapered portion is the enlarged diameter portion EP of the washer member 18C. That is, in the enlarged diameter portion EP, the hole diameter of the bolt hole 20 gradually increases along the plate thickness direction from the top surface to the bottom surface. In this disclosure, the enlarged diameter portion may be formed by a combination of the tapered portion of the second modification and the stepped portion of the third modification.

[0045] (Fourth variation) As shown in Figure 8, in the high-strength bolt friction joint structure 10D according to the fourth modified example, the washer member 18D has a flat washer portion 18D1 and an auxiliary washer portion 18D2.

[0046] (Flat washer section) As shown in Figure 9, the flat washer portion 18D1 is a ring-shaped member in which one surface, i.e., the top surface, is in contact with the high-strength bolt 14 or nut 16.

[0047] (Auxiliary washer section) As shown in Figure 10, the auxiliary washer portion 18D2 is a ring-shaped member positioned between the flat washer portion 18D1 and the first steel member 11. The auxiliary washer portion 18D2 has a bottom portion 19A as an enlarged diameter portion EP, and a side wall portion 19B extending from the outside of the bottom portion 19A to the side of the high-strength bolt 14 or the side of the nut 16, i.e., the side of the flat washer portion 18D1. The auxiliary washer portion 18D2 has a recess 19C formed by the bottom portion 19A and the side wall portion 19B that corresponds to the flat washer portion 18D1.

[0048] As shown in Figure 8, the inner diameter D'i of the auxiliary washer portion 18D2 is approximately the same as the outer diameter of the flat washer portion 18D1. Therefore, the flat washer portion 18D1 fits inside the recess 19C of the auxiliary washer portion 18D2. Also, the height of the side wall portion 19B of the auxiliary washer portion 18D2 is approximately the same as the plate thickness tw of the flat washer portion 18D1. In the fourth modified example, the total plate thickness of the washer member 18D is the sum of the plate thickness tw of the flat washer portion 18D1 and the plate thickness t' of the bottom portion 19A of the auxiliary washer portion 18D2.

[0049] In the fourth modification, a stepped portion is formed on the inner wall surface forming the bolt hole 20 of the auxiliary washer portion 18D2 such that the region on the bottom portion 19A side is larger in diameter than the region on the flat washer portion 18D1 side. The bottom portion 19A on which the stepped portion is formed is the enlarged portion EP of the washer member 18D. The enlarged portion EP of the auxiliary washer portion 18D2 has a substantially constant hole diameter over the entire thickness direction. Figure 8 illustrates the hole diameter d's on the bottom surface side of the auxiliary washer portion 18D2. In this disclosure, both the region on the flat washer portion 18D1 side and the region on the auxiliary washer portion 18D2 side of the inner wall surface forming the bolt hole 20 of the washer member 18D may be larger in diameter than the hole diameter of the first bolt hole 11B.

[0050] (Fifth variation) As shown in Figure 11, in the high-strength bolt friction joint structure 10E according to the fifth modified example, the washer member 18E has a flat washer portion 18E1 and an auxiliary washer portion 18E2, similar to the fourth modified example. Furthermore, on the inner wall surface forming the bolt hole 20 of the auxiliary washer portion 18E2, the region on the bottom portion 19A side is larger in diameter than the region on the flat washer portion 18E1 side. Specifically, the hole diameter of the bolt hole 20 is formed in a tapered portion that gradually increases in diameter along the plate thickness direction from the flat washer portion 18E1 side to the bottom surface side, which is different from the fourth modified example. In the fifth modified example, the bottom portion 19A where the tapered portion is formed is the enlarged diameter portion EP of the washer member 18E.

[0051] Since the other structures of the high-strength bolt friction joint structure 10E according to the fifth modified example are the same as those of the high-strength bolt friction joint structure 10D according to the fourth modified example, a redundant explanation will be omitted.

[0052] (Sixth variation) As shown in Figure 12(A), in the high-strength bolt friction joint structure 10F according to the sixth modified example, the end faces of the two second steel members 12 in their respective longitudinal directions (i.e., left-right directions in Figure 12) face each other with a gap between them. Also, as shown in Figure 12(B), an example is given in which the two second steel members 12 are friction-joined by four high-strength bolts 14 while sandwiched between the first steel member 11 and the third steel member 13. As shown in Figure 12(B), the number of friction surfaces in the high-strength bolt friction joint structure 10F according to the sixth modified example is two.

[0053] In the sixth modified example, the first steel member 11 and the third steel member 13 function as so-called splice plates. As exemplified by the first steel member 11, the second steel member 12, and the third steel member 13 in the sixth modified example, in this disclosure, the number of members to be joined used in the high-strength bolt friction joint structure can be set as appropriate.

[0054] (Seventh variation) As shown in Figure 13, in the high-strength bolt friction joint structure 10G according to the seventh modified example, the plate thickness t1 of the first steel material 11 is thinner than the plate thickness t2 of the second steel material 12. That is, in this disclosure, as in the seventh modified example, the plate thicknesses of the first steel material 11 and the second steel material 12 may be different from each other. Figure 13 illustrates a state in which two washer members 18 are placed in contact with both the first steel material 11 and the second steel material 12, but in this disclosure, the washer members 18 only need to be placed in contact with the steel material with the thinner plate thickness. [Examples]

[0055] <Experiment> Next, we will describe an experiment to confirm the effect of contact pressure on the coefficient of slip at a joint surface treated with phosphate as a surface treatment, referring to Figures 14 and 15.

[0056] Here, the contact pressure of the joint surface in a high-strength bolted joint varies depending on the distance from the bolt. Specifically, the closer to the bolt, the greater the contact pressure. This experiment was conducted to evaluate the coefficient of slip on a friction surface with nearly constant contact pressure and to understand the effect of differences in contact pressure on the coefficient of slip.

[0057] In this test, first, with three steel plate members stacked on top of each other, contact pressure was applied to the joint surface so that the distribution of contact pressure at the joint was nearly uniform. Then, while maintaining a nearly constant contact pressure, the coefficient of slip was measured by applying a load in the in-plane direction to the central steel plate member of the three steel plate members so that the joint surface would slide in the in-plane direction. In addition, measurements were taken for both coating type and immersion type phosphate treatments.

[0058] Figure 14 illustrates the approximate straight lines calculated from multiple data points obtained in the case of coating-type phosphate treatment (solid line) and the approximate straight lines calculated from multiple data points obtained in the case of immersion-type phosphate treatment (dashed line). As shown in Figure 14, it was found that in both coating-type and immersion-type phosphate treatments, the coefficient of slip decreases as the contact pressure increases. In particular, it was found that the coating-type treatment is more significantly affected by contact pressure, as indicated by the larger negative slope of the approximate straight line in Figure 14.

[0059] Furthermore, as shown in Figure 15, the micro-cross-sections of the steel after testing were compared for each of the two types of phosphate treatment: coating type and immersion type. The upper part of Figure 15 shows examples of micro-cross-sections obtained for the coating type phosphate treatment at contact pressures of 25 MPa, 130 MPa, and 300 MPa. The lower part of Figure 15 shows examples of micro-cross-sections obtained for the immersion type phosphate treatment at contact pressures of 25 MPa, 130 MPa, and 300 MPa.

[0060] As shown in Figure 15, in the case of the coating type, voids were observed in the phosphate-treated surface layer. These voids are layers where the coating agent remained and polymerized. In the case of the coating type, it was found that as the contact pressure increased, the voids in the surface layer were compressed. That is, similar to the results in the graph in Figure 14, it was found that in the case of the coating type, the state of the surface layer differs depending on the contact pressure, and this affects the difference in the coefficient of slip.

[0061] On the other hand, in the immersion type, the surface layer was composed solely of pure zinc phosphate, and almost no voids were observed. In the immersion type, it was found that the change in state due to differences in contact pressure was small; that is, the effect of contact pressure on the coefficient of slip was smaller than in the coating type.

[0062] <Analysis example> Next, an example of analysis of the high-strength bolt friction joint structure according to this embodiment will be described with reference to Figures 16 to 38. In the analysis, FEM analysis was performed to model the high-strength bolt friction joint structure and to confirm the effect of the washer shape on the contact pressure distribution. As shown in Figure 16, in the analysis, the displacement of the steel material in the XZ plane, which is the joint surface, was constrained, while the displacement in the Y direction, which is the plate thickness direction, was freely set.

[0063] In the analysis model, the length of the shaft of the high-strength bolt is the length from the base of the bolt head to the portion included in the nut, depending on the requirements of the analysis. Furthermore, the tensile strength of the steel material in the example analysis was set to 40k steel. However, the tensile strength of the steel material is not limited to this and can be changed as appropriate. The parameters of the CASE (case) of the analysis model for each high-strength bolt friction joint structure are shown in Table 1 below.

[0064] [Table 1]

[0065] Note that the D-5 patterns in CASE 1 and CASE 3 are comparative examples in which no enlarged diameter section is formed, similar to the 0 pattern in each case. Next, each of the analysis examples performed using the analysis model in Table 1 will be described below.

[0066] Furthermore, in Table 1, the column for hole diameter in the "Flat Washer Section" item in the center of the top row contains two types of symbols: "dw" and "d'". Hole diameter dw represents the hole diameter on the top side of the bolt hole in the flat washer section of the washer member, viewed as a whole. On the other hand, hole diameter d' represents the hole diameter on the bottom side of the bolt hole in the flat washer section. In each CASE in Table 1, in pattern 0 where no enlarged diameter section is formed, and in patterns A, A', and D where an enlarged diameter section is formed, the washer member is composed of a single flat washer section with a hole diameter that is approximately constant throughout the entire thickness direction. Therefore, the values ​​of the hole diameter dw on the top side and the hole diameter d' on the bottom side are the same.

[0067] Furthermore, in Case 1 and Case 3 of Table 1, in patterns B and C where the hole diameter dw on the top side and the hole diameter d' on the bottom side of the enlarged diameter portion of the flat washer are different, the respective values ​​for the hole diameter dw on the top side and the hole diameter d' on the bottom side are shown separately.

[0068] Furthermore, in Case 1 and Case 3 in Table 1, in pattern D which has a flat washer portion and an auxiliary washer portion, the hole diameter d's on the bottom side of the auxiliary washer portion is shown. In pattern D, the hole diameter on the top side of the bolt hole of the washer member is the hole diameter dw on the top side of the flat washer portion. Also, the hole diameter on the bottom side of the bolt hole of the washer member is the hole diameter d's on the bottom side of the auxiliary washer portion.

[0069] (First analysis example: Regarding contact pressure distribution) In the first analysis example, the contact pressure distribution was evaluated. Figure 17 shows the contact pressure distribution for the CASE 1 analysis model, Figure 18 shows the CASE 2 analysis model, and Figure 19 shows the CASE 3 analysis model.

[0070] As shown in Figures 17 to 19, a similar trend was observed in all cases. Specifically, in each case, when no enlarged diameter section is formed, as shown by the thickest solid line in the "0" analysis model, the contact pressure is maximum at the 0 mm position on the horizontal axis of the graph, and decreases as the value on the horizontal axis increases.

[0071] On the other hand, in the analysis models A-1 to A-6 of CASE 1 in Figure 17, where an enlarged diameter section was formed, the peak position of the contact pressure moved further away from the bolt hole as the diameter d' of the bolt hole in the flat washer section increased. Furthermore, as the diameter d' of the bolt hole in the flat washer section increased, the area in contact between the steel material and the washer member moved further away from the edge of the bolt hole in the steel material, and the contact pressure at the position of 0 mm on the horizontal axis was suppressed. Similar trends were also confirmed in the analysis models A-1 to A-7 of CASE 2 in Figure 18, and in the analysis models A-1 to A-7 of CASE 3 in Figure 19.

[0072] (Second analysis example: Regarding the auxiliary washer section) In the second analysis example, the auxiliary washer section was evaluated. Figures 20 to 24 show graphs of the contact pressure distribution obtained from the analysis model of CASE 1. Figures 21 and 23 show graphs of the contact pressure distribution obtained from the analysis model of CASE 3.

[0073] (1) Influence of plate thickness of auxiliary washer Figure 20 illustrates the contact pressure distribution obtained in the analysis models 0, A-2, and D-1 to D-4 of CASE 1, along with the plate thickness t' of the auxiliary washer. Similarly, Figure 21 illustrates the contact pressure distribution obtained in the analysis models 0, A-2, and D-1 to D-4 of CASE 3, along with the plate thickness t' of the auxiliary washer. As shown in Figures 20 and 21, it was confirmed that as the plate thickness t' of the auxiliary washer increases, the range of contact pressure influence, i.e., the range of contact pressure influence, increases, and the peak value of the contact pressure can be suppressed.

[0074] (2) Influence of hole diameter in auxiliary washer section Figure 22 illustrates the contact pressure distributions obtained in the analysis models 0, A-2, D-5, D-2, and D-6 of CASE 1, along with the hole diameter d's on the bottom side of the bolt hole in the auxiliary washer. Similarly, Figure 23 illustrates the contact pressure distributions obtained in the analysis models 0, D-5, D-2, and D-6 of CASE 3, along with the hole diameter d's on the bottom side of the bolt hole in the auxiliary washer. As shown in Figures 22 and 23, it was found that by increasing the hole diameter d's on the bottom side of the auxiliary washer beyond the hole diameter d (16 mm) of the first bolt hole in the first steel material, the peak position of the contact pressure can be moved away from the bolt, the range of contact pressure influence can be increased, and the peak value of the contact pressure can be suppressed.

[0075] (3) Influence of the outer diameter of the auxiliary washer Figure 24 illustrates the contact pressure distributions obtained in the analysis models 0, D-7 to D-9, and D-2 of CASE 1, along with the outer diameter D' of the auxiliary washer. As shown in Figure 24, it was found that increasing the outer diameter D' of the auxiliary washer increases the contact area between the auxiliary washer and the steel material, thereby increasing the range of influence of contact pressure and suppressing the peak value of contact pressure.

[0076] (Converted slip coefficient) Next, the method for calculating the converted slip coefficient used in this embodiment, which was established using the findings from Figure 14 and the results of the first and second analysis examples, will be explained with reference to Figure 25.

[0077] Specifically, the sliding resistance in a small section can be calculated by multiplying the contact pressure in that small section by the corresponding sliding coefficient, as illustrated in Figure 14. The calculated sliding resistance can then be accumulated within the range where contact pressure occurs using the following conversion formula, and divided by the tension of the high-strength bolt to calculate the converted sliding coefficient μ' as the apparent sliding coefficient.

[0078] (conversion formula)

number

[0079] In Figure 25, three data points are illustrated with black circles, representing experimental values ​​obtained from the coating-type phosphate treatment test in Figure 14, and the corresponding converted slip coefficient μ' for each experimental value. In addition, two data points are illustrated with light gray data points in Figure 25, representing experimental values ​​obtained from the immersion-type phosphate treatment test in Figure 14, and the corresponding converted slip coefficient μ' for each experimental value.

[0080] As shown in Figure 25, there is a good, roughly one-to-one correspondence between the converted slip coefficient μ' and the experimental value, meaning that the actual slip coefficient can be evaluated fairly specifically using the conversion formula described above. In the following analysis examples, the converted slip coefficient μ' in each analysis result was compared to confirm the influence of various parameters on the converted slip coefficient μ'.

[0081] (Third analysis example: Relationship between hole diameter ratio and converted slip coefficient) In the third analysis example, the relationship between the hole diameter ratio and the converted slip coefficient was evaluated. The hole diameter ratio can be obtained by dividing the hole diameter d' on the bottom surface side of the flat washer portion or the hole diameter d's on the bottom surface side of the auxiliary washer portion in the washer member by the hole diameter d of the first bolt hole in the first steel material.

[0082] In Figure 26, data points representing the pore size ratio d' / d and the corresponding converted slip coefficient μ' obtained in the analysis models 0, A-1 to A-6 of CASE 1 are illustrated with black circles (●). Also in Figure 26, data points representing the pore size ratio d' / d and the corresponding converted slip coefficient μ' obtained in the analysis models 0, A-1 to A-7 of CASE 2 are illustrated with black triangles (▲). Also in Figure 26, data points representing the pore size ratio d' / d and the corresponding converted slip coefficient μ' obtained in the analysis models 0, A-1 to A-7 of CASE 3 are illustrated with white squares (◇).

[0083] As shown in Figure 26, it was confirmed that the converted slip coefficient μ' can be increased by enlarging the hole diameter of the washer member. On the other hand, in all cases, it was found that the converted slip coefficient μ' has a peak at a specific hole diameter.

[0084] (Fourth analysis example: Relationship between auxiliary washer and converted slip coefficient) In the fourth analysis example, the relationship between the auxiliary washer and the converted slip coefficient was evaluated.

[0085] (1) Influence of hole diameter in auxiliary washer section Specifically, the effect of the hole diameter in the auxiliary washer section was analyzed using the hole diameter ratio. In Figure 27, data points representing the hole diameter ratio d's / d and the corresponding converted slip coefficient μ' obtained in the analysis models D-2, D-5, and D-6 of CASE 1 are illustrated with black triangles (▲). Also in Figure 27, data points representing the hole diameter ratio d' / d and the corresponding converted slip coefficient μ' obtained in the analysis model 0 of CASE 1 are illustrated with white triangles (△).

[0086] Furthermore, in Figure 27, data points representing the pore size ratio d's / d and the corresponding converted slip coefficient μ' obtained in the analysis models D-3, D-5, and D-6 of CASE 3 are illustrated with black circles (●). Also in Figure 27, data points representing the pore size ratio d' / d and the corresponding converted slip coefficient μ' obtained in the analysis model 0 of CASE 3 are illustrated with white circles (〇).

[0087] As shown in Figure 27, it was confirmed that the converted slip coefficient μ' increases as the hole diameter ratio increases. Furthermore, it was confirmed that a peak value is formed in CASE 1, where the plate thickness t1 of the first steel material is relatively small.

[0088] (2) Influence of plate thickness of auxiliary washer Specifically, the effect of the plate thickness of the auxiliary washer portion was analyzed using the plate thickness ratio. The plate thickness ratio can be obtained by dividing the plate thickness tw of the flat washer portion or the plate thickness t' of the bottom of the auxiliary washer portion in the washer member by the plate thickness t1 of the first steel material.

[0089] In Figure 28, data points representing the plate thickness ratio t' / t1 and the corresponding converted slip coefficient μ' obtained in the analysis models D-1 to D-4 of CASE 1 are illustrated with black triangles (▲). Also in Figure 28, data points representing the plate thickness ratio t' / t1 and the corresponding converted slip coefficient μ' obtained in the analysis models D-1 to D-4 of CASE 3 are illustrated with black circles (●).

[0090] As shown in Figure 28, it was confirmed that the converted slip coefficient μ' increases as the plate thickness ratio increases.

[0091] (3) Influence of the outer diameter of the auxiliary washer Specifically, the effect of the outer diameter of the auxiliary washer portion was analyzed using the ratio of the outer diameter to the hole diameter of the first bolt hole in the first steel material. The outer diameter ratio can be obtained by dividing the outer diameter Dw of the flat washer portion or the outer diameter D' of the auxiliary washer portion in the washer member by the hole diameter d of the first bolt hole in the first steel material.

[0092] In Figure 29, data points representing the outer diameter ratio D' / d and the converted slip coefficient μ' corresponding to the outer diameter ratio D' / d, obtained in the analysis models D-2, D-7 to D-9 of CASE 1, are illustrated with black triangles (▲). Also in Figure 29, data points representing the outer diameter ratio Dw / d and the converted slip coefficient μ' corresponding to the outer diameter ratio Dw / d, obtained in the analysis model 0 of CASE 1, are illustrated with white triangles (△).

[0093] As shown in Figure 29, it was confirmed that the converted slip coefficient increases as the outer diameter ratio D' / d increases. Furthermore, it was found that when the outer diameter ratio D' / d exceeds a certain value, the converted slip coefficient μ' hardly changes; in other words, it saturates. This is because the range of influence of contact pressure hardly changes.

[0094] (Fifth analysis example: Regarding the difference in hole diameter between plates) In the fifth analysis example, the relationship between the plate thickness-to-hole diameter difference dx / t1 and the converted slip coefficient μ' was evaluated for each analysis model. The hole diameter difference dx is the difference between the hole diameter on the first steel material side of the enlarged diameter section, i.e., the hole diameter d' on the bottom surface side of the flat washer section in the washer member or the hole diameter d's on the bottom surface side of the auxiliary washer section, and the hole diameter d of the bolt hole in the first steel material. The plate thickness-to-hole diameter difference dx / t1 can be obtained by dividing the hole diameter difference dx by the plate thickness t1 of the first steel material.

[0095] Furthermore, the vertical axis in Figure 30 shows the converted slip coefficient ratio. The converted slip coefficient ratio is calculated by dividing the converted slip coefficient μ' of each CASE by the converted slip coefficient μ' of the comparative example CASE within the same CASE.

[0096] In Figure 30, data points representing the plate thickness-to-hole diameter difference dx / t1 and the corresponding converted slip coefficient μ' obtained in the analysis models 0, A-1 to A-6 of CASE 1 are illustrated with black circles (●). Also in Figure 30, data points representing the plate thickness-to-hole diameter difference dx / t1 and the corresponding converted slip coefficient μ' obtained in the analysis models 0, A-1 to A-7 of CASE 2 are illustrated with black triangles (▲). Also in Figure 30, data points representing the plate thickness-to-hole diameter difference dx / t1 and the corresponding converted slip coefficient μ' obtained in the analysis models 0, A-1 to A-7 of CASE 3 are illustrated with white squares (◇).

[0097] Furthermore, in Figure 30, data points representing the plate thickness-to-hole diameter difference dx / t1 and the converted slip coefficient μ' corresponding to the plate thickness-to-hole diameter difference dx / t1 obtained in the analysis models D-2, D-5, and D-6 of CASE 1 are illustrated with light gray triangles. Also, in Figure 30, data points representing the plate thickness-to-hole diameter difference dx / t1 and the converted slip coefficient μ' corresponding to the plate thickness-to-hole diameter difference dx / t1 obtained in the analysis models D-3, D-5, and D-6 of CASE 3 are illustrated with light gray circles.

[0098] As shown in Figure 30, in all cases, it was confirmed that the converted slip coefficient μ' has a peak when the difference in hole diameter between the plate thickness and t1 is around 0.50 to 1.50.

[0099] Furthermore, the results shown in Figure 30 indicate that in this embodiment, when the difference in hole diameter relative to the plate thickness dx / t1 is greater than 0 and 1.5 or less, a slip coefficient of 1.0 times or more can be obtained compared to the comparative example in which no enlarged diameter portion is formed. When the difference in hole diameter relative to the plate thickness dx / t1 is less than or equal to the lower limit of 0, or exceeds the upper limit of 1.5, a slip coefficient of 1.0 or more may not be obtained. In this disclosure, the difference in hole diameter relative to the plate thickness dx / t1 may exceed 1.5.

[0100] (Sixth analysis example: Comparison of methods for increasing plate thickness) In the sixth analysis example, the relationship between the method of increasing the plate thickness of the joint and the converted slip coefficient μ' was evaluated. Specifically, as shown in Figure 31, the converted slip coefficient μ' for each plate thickness increase method was evaluated using the hole diameter ratio, in the case where the plate thickness was increased by the auxiliary washer and in the case where the plate thickness of the steel material was increased, while keeping the clamping thickness the same for both cases.

[0101] In Figure 31, data points representing the pore size ratio d's / d and the corresponding converted slip coefficient μ' obtained in the analysis models D-2, D-5, and D-6 of CASE 1 are illustrated with white squares (◇). Also in Figure 31, data points representing the pore size ratio d' / d and the corresponding converted slip coefficient μ' obtained in the analysis models 0, A-2, and A-4 of CASE 2 are illustrated with black circles (●).

[0102] As can be seen from the results in Figure 31 for the range where the hole diameter ratio is approximately 1.1 or higher, it was found that in the range where the hole diameter ratio is relatively large, the method of increasing the plate thickness using the auxiliary washer section results in a smaller converted slip coefficient μ' than the method of increasing the thickness of the steel plate. The reason why the converted slip coefficient μ' becomes smaller, as shown in Figure 31, is that the converted slip coefficient μ' exceeds the peak, as explained in the fifth analysis example.

[0103] Furthermore, in the sixth analysis example, when using the auxiliary washer section, the slip coefficient actually decreased when the hole diameter ratio exceeded approximately 1.1. Therefore, it was found that the specifications of the auxiliary washer section should preferably be set so that the difference in hole diameter relative to the plate thickness dx / t1 is greater than 0 and less than or equal to 1.5.

[0104] (Seventh analysis example: Regarding stepped sections and tapered sections) In the seventh analysis example, the stepped portion and tapered portion that form the enlarged diameter portion were evaluated. Specifically, the analysis was performed using the height ratio of the stepped portion or tapered portion. The height ratio e / tw can be obtained by dividing the height e of the stepped portion or tapered portion of the flat washer portion in the washer member by the plate thickness tw of the flat washer portion.

[0105] In Figure 32, data points representing the height ratio e / tw and the corresponding converted slip coefficient μ' obtained in the analysis model for CASE 1, case 0, are illustrated with white circles (〇). Also in Figure 32, data points representing the height ratio e / tw and the corresponding converted slip coefficient μ' obtained in the analysis models B-1 to B-3 of CASE 1 are illustrated with light gray circles.

[0106] Furthermore, in Figure 32, data points representing the height ratio e / tw and the corresponding converted slip coefficient μ' obtained in the analysis models C-1 to C-4 of CASE 1 are illustrated with black circles (●). Also in Figure 32, data points representing the height ratio e / tw and the corresponding converted slip coefficient μ' obtained in the analysis model 0 of CASE 3 are illustrated with white triangles (△).

[0107] Furthermore, in Figure 32, data points representing the height ratio e / tw and the corresponding converted slip coefficient μ' obtained in the analysis models B-1 to B-3 of CASE 3 are illustrated with light gray triangles. Also in Figure 32, data points representing the height ratio e / tw and the corresponding converted slip coefficient μ' obtained in the analysis models C-1 to C-4 of CASE 3 are illustrated with black triangles (▲).

[0108] As shown in Figure 32, in all cases, even when the height ratio e / tw of the stepped or tapered section changed, a converted slip coefficient μ' that could be considered almost the same was obtained. In other words, it was confirmed that the influence of the height ratio e / tw of the stepped and tapered sections on the converted slip coefficient μ' was relatively small.

[0109] (8th analysis example: Regarding differences in contact area) In the eighth analysis example, the relationship between the difference in contact area and the converted slip coefficient μ' was evaluated.

[0110] Figure 33 shows the contact pressure distribution obtained in the analysis model A-2 of CASE 1 as a solid line, and the contact pressure distribution obtained in the analysis model A-2' of CASE 1 as a dashed line. Figure 34 also shows the contact pressure distribution obtained in the analysis model A-3 of CASE 1 as a solid line, and the contact pressure distribution obtained in the analysis model A-3' of CASE 1 as a dashed line.

[0111] Figure 35 illustrates the contact pressure distribution obtained in the analysis model A-4 of CASE 1 with a solid line, and the contact pressure distribution obtained in the analysis model A-4' of CASE 1 with a dashed line. Similarly, Figure 36 illustrates the contact pressure distribution obtained in the analysis model A-5 of CASE 1 with a solid line, and the contact pressure distribution obtained in the analysis model A-5' of CASE 1 with a dashed line. Furthermore, Figure 37 illustrates the contact pressure distribution obtained in the analysis model A-6 of CASE 1 with a solid line, and the contact pressure distribution obtained in the analysis model A-6' of CASE 1 with a dashed line.

[0112] The analytical models A'-2 to A'-6 in Table 1 have their outer diameters adjusted so that the contact area between the washer and the steel is the same as in CASE 0. On the other hand, the analytical models A'-2 to A'-6 have the same outer diameter (32 mm) as CASE 0. As shown in Figures 33 to 37, the contact area of ​​A'-2 to A'-6 is larger than that of the analytical models A'-2 to A'-6, so the range of influence of contact pressure is larger, and as a result, the absolute value of the peak value of contact pressure is smaller.

[0113] Furthermore, as shown in Figure 38, the converted slip coefficient μ' of the analysis models A'-2 to A'-6, exemplified by ○, is larger than the converted slip coefficient μ' of the analysis models A'-2 to A'-6, exemplified by ●. On the other hand, the peak position of the converted slip coefficient μ' is almost the same. In other words, the larger the pore size ratio, the greater the difference between the converted slip coefficient μ' of the analysis models A'-2 to A'-6 and the converted slip coefficient μ' of the analysis models A'-2 to A'-6. This is because, compared to the analysis models A'-2 to A'-6 where the contact area is constant, the contact area in each of the analysis models A'-2 to A'-6 becomes smaller as the pore size increases.

[0114] As shown in Figures 33 to 38, it was found that, for the same outer diameter, increasing the inner diameter can raise the peak contact pressure and decrease the coefficient of slip. However, increasing the outer diameter to increase the contact area can improve the coefficient of slip. Therefore, when enlarging the bolt hole of a washer member, it is preferable to increase the outer diameter as well to ensure sufficient contact area.

[0115] The analysis results shown in Table 1 were all obtained with a pair of washer members provided to a single high-strength bolt friction joint structure. However, although not disclosed here, analysis was also performed with only one washer member provided to a single high-strength bolt friction joint structure. The results of the analysis showed that even when only one washer member was provided to a single high-strength bolt friction joint structure, an improvement in the slip coefficient of the joint was confirmed, similar to the case when a pair of washers were provided.

[0116] (Effects and Benefits) In the high-strength bolt friction joint structure 10 according to this embodiment, the first steel member 11 has a first joint surface 11A around the first bolt hole 11B that is treated with a surface treatment such that the coefficient of slip increases as the contact pressure decreases. In addition, in the bolt hole 20 of the washer member 18 that contacts the first steel member 11, an enlarged diameter portion EP is formed on the bottom surface side, which is the side of the first joint surface 11A, having a hole diameter d' that is greater than or equal to the hole diameter d of the first bolt hole 11B.

[0117] The washer member 18, with its enlarged diameter portion EP, shifts the peak of the contact pressure outward from the edge of the first bolt hole 11B of the first steel member 11. Therefore, in the contact pressure distribution of this embodiment, the region where the contact pressure gradually decreases as you move outward from the peak is shifted outward compared to the case where the diameter of the bolt hole 20 in the washer member 18 is less than the diameter of the first bolt hole 11B of the first steel member 11. Furthermore, a pattern of gradually decreasing contact pressure from the outside to the inside is also formed between the peak of the contact pressure and the edge of the first bolt hole 11B of the first steel member 11. As a result, the area of ​​the region where contact pressure is distributed within the surface-treated joint surface increases.

[0118] Therefore, the effect of improving the coefficient of slip obtained by surface treatment can be utilized more effectively compared to the case where the diameter of the bolt hole 20 in the washer member 18 is less than the diameter of the first bolt hole 11B in the first steel material 11. Thus, the coefficient of slip of the joint can be improved efficiently.

[0119] Furthermore, in this embodiment, by increasing the area of ​​the region where contact pressure is distributed, when the contact area between the washer member 18 and the first steel material 11 is the same, the effect of reducing the absolute value of the peak can also be obtained. In addition, in this embodiment, as a means of improving the coefficient of slip, it is sufficient to simply form the enlarged diameter portion EP, so deformation or processing of the steel material is unnecessary.

[0120] Furthermore, as in the fourth and fifth modified examples, when the washer member 18 has a flat washer portion 18D1 and an auxiliary washer portion 18D2, the clamping thickness increases by the thickness t' of the bottom portion 19A of the auxiliary washer portion 18D2, which widens the contact distribution area between the steel materials and, as a result, improves the coefficient of slip. In particular, the effect of improving the coefficient of slip is greater when the thickness of the steel material is relatively thin.

[0121] Furthermore, the area of ​​the bottom surface of the washer member 18 that contacts the first steel material 11 can be increased by the width of the side wall portion 19B of the auxiliary washer portion 18D2 along the radial direction. As a result, the coefficient of slip is further improved.

[0122] Furthermore, the recess 19C in the auxiliary washer portion 18D2 makes it easier to align the bolt holes of the flat washer portion 18D1 with the bolt holes of the auxiliary washer portion 18D2 during installation. This helps to suppress misalignment between the bolt holes.

[0123] Furthermore, a flat washer included in a typical high-strength bolt set can be used as the flat washer portion 18D1 in this embodiment. Therefore, by only providing the auxiliary washer portion 18D2 that supports the flat washer, the washer member 18 of this embodiment can be easily constructed with minimal effort and burden.

[0124] Furthermore, in this embodiment, as explained with reference to Figure 30, the difference in hole diameter between plate thickness and hole diameter dx / t1 is greater than 0 and less than or equal to 1.5. Therefore, considering the hole diameter d' on the bottom surface side of the enlarged diameter portion EP, the hole diameter d of the first bolt hole 11B of the first steel material 11, and the plate thickness t1 of the first steel material 11, the slip coefficient of the joint can be efficiently improved.

[0125] Furthermore, in this embodiment, the first steel material 11 is a plated steel sheet that has been treated with phosphate. As shown in Figure 9, this embodiment is particularly advantageous in improving the slip coefficient of the joint in a high-strength bolt friction joint structure 10 that includes a plated steel sheet that has been treated with phosphate.

[0126] Furthermore, in this embodiment, as shown in Figure 5, the slip coefficient improvement effect can be obtained by arranging a washer member 18 having an enlarged diameter portion EP on at least one side of the high-strength bolt 14, either on the head side or the nut 16 side. However, as shown in Figure 1, by providing a pair of washer members 18 in the high-strength bolt friction joint structure 10, the slip coefficient can be further improved compared to a high-strength bolt friction joint structure 10 in which only one washer member 18 is arranged.

[0127] Furthermore, as shown in the seventh modified example, the plate thickness t1 of the first steel material 11 may be thinner than the plate thickness t2 of the second steel material 12. When the thicknesses of the two steel materials are different, the washer member 18 of this embodiment is positioned in contact with at least the steel material with the thinner plate thickness. For this reason, the high-strength bolt friction joint structure 10G according to the seventh modified example has a greater effect on improving the coefficient of slip compared to the case where the washer member 18 is positioned in contact only with the steel material with the thicker plate thickness.

[0128] <Other Embodiments> While the embodiments described above have illustrated the scope of this disclosure, this description is not intended to limit it. Those skilled in the art should be able to see from this disclosure a variety of alternative embodiments, examples, and operational techniques.

[0129] For example, the configurations shown in Figures 1 to 38 can be partially combined to constitute this disclosure. This disclosure includes various embodiments not described above, and the technical scope of this disclosure is determined solely by the inventive features of the claims that are reasonable from the above description.

[0130] ≪Note≫ The following embodiments are conceptualized herein.

[0131] Embodiment 1 is, A first steel material having a first joint surface around the first bolt hole that is treated with a surface treatment that increases the coefficient of slip as the contact pressure decreases, A second steel material having a second joining surface superimposed on the first joining surface of the first steel material, and a second bolt hole, A high-strength bolt and nut for friction-joining the first steel material and the second steel material, A washer member having a bolt hole that is in contact with the first steel material and has an enlarged diameter portion formed on the side of the first joining surface having a hole diameter greater than or equal to the diameter of the first bolt hole, A high-strength bolt friction joint structure.

[0132] Embodiment 2 is, The washer member is, One side of the flat washer portion is in contact with the high-strength bolt or the nut, An auxiliary washer portion is positioned between the flat washer portion and the first steel material, and has a bottom portion as the enlarged diameter portion and a side wall portion extending from the outside of the bottom portion towards the side of the high-strength bolt or the nut, wherein the bottom portion and the side wall portion form a recess corresponding to the flat washer portion. A high-strength bolt friction joint structure according to Embodiment 1.

[0133] Embodiment 3 is, When the difference in hole diameter between the hole diameter on the first steel material side of the enlarged portion and the hole diameter of the first bolt hole is dx, and the plate thickness of the first steel material is t1, the difference in hole diameter relative to plate thickness, dx / t1, obtained by dividing the hole diameter difference dx by the plate thickness t1, is greater than 0 and less than or equal to 1.5. A high-strength bolt friction joint structure according to embodiment 1 or 2.

[0134] Appearance 4 is, The first steel material is a plated steel sheet, The aforementioned surface treatment is a phosphate treatment. A high-strength bolt friction joint structure according to any of embodiments 1 to 3.

[0135] Embodiment 5 is, A pair of washer members are provided, One of the pair of washer members is positioned between the head of the high-strength bolt and the first steel member. The other washer member is positioned between the nut and the second steel material. A high-strength bolt friction joint structure according to any of embodiments 1 to 4.

[0136] Embodiment 6 is, The thickness of the first steel material is thinner than the thickness of the second steel material. A high-strength bolt friction joint structure according to any of embodiments 1 to 5. [Explanation of Symbols]

[0137] 10, 10A~10G, 10Z High-strength bolt friction joint structure 11 Daiichi Steel 11A First joint surface 11B First bolt hole 12 Second steel material 12A Second joint surface 12B Second bolt hole 13 Third steel material 14 High-strength bolts 16 nuts 18,18Z Washer component 18D1 Flat Washer Part 18D2 Auxiliary washer section 19A bottom 19B Side wall part 19C recess 20 bolt holes C axis D. Shaft diameter of the shaft portion of a high-strength bolt D' Outer diameter of the auxiliary washer section D'i Inner diameter of auxiliary washer Dw outer diameter of washer component EP enlarged diameter part d. Diameter of the first bolt hole dw Hole diameter on the top surface of the bolt hole of the washer member d' Diameter of the bolt hole on the bottom surface of the flat washer d's Bolt hole diameter on the bottom surface of the auxiliary washer t1 Plate thickness of Daiichi Steel t2 Plate thickness of the second steel material tw Flat washer plate thickness t' Plate thickness of the auxiliary washer section

Claims

1. A first steel material having a first joint surface around the first bolt hole that is treated with a surface treatment that increases the coefficient of slip as the contact pressure decreases, A second steel material having a second joining surface superimposed on the first joining surface of the first steel material, and a second bolt hole, A high-strength bolt and nut for friction-joining the first steel material and the second steel material, A washer member having a bolt hole that is in contact with the first steel material and has an enlarged diameter portion formed on the side of the first joining surface having a hole diameter greater than or equal to the diameter of the first bolt hole, Equipped with, When the difference in hole diameter between the hole diameter on the first steel material side of the enlarged diameter portion and the hole diameter of the first bolt hole is dx, and the plate thickness of the first steel material is t1, A high-strength bolt friction joint structure in which the difference in hole diameter between plate thickness and hole diameter, dx / t1, obtained by dividing the hole diameter difference dx by the plate thickness t1, is greater than 0 and less than or equal to 1.

5.

2. The washer member is, One side of the flat washer portion is in contact with the high-strength bolt or the nut, An auxiliary washer portion is positioned between the flat washer portion and the first steel material, and has a bottom portion as the enlarged diameter portion and a side wall portion extending from the outside of the bottom portion towards the side of the high-strength bolt or the nut, wherein the bottom portion and the side wall portion form a recess corresponding to the flat washer portion. The high-strength bolt friction joint structure according to claim 1.

3. The first steel material is a plated steel sheet, The aforementioned surface treatment is a phosphate treatment. The high-strength bolt friction joint structure according to claim 1 or 2.

4. A pair of washer members are provided, One of the pair of washer members is positioned between the head of the high-strength bolt and the first steel member. The other washer member is positioned between the nut and the second steel material. The high-strength bolt friction joint structure according to claim 1 or 2.

5. The thickness of the first steel material is thinner than the thickness of the second steel material. The high-strength bolt friction joint structure according to claim 1 or 2.

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