A large-size double-end bolt fatigue test tool and a method of using the same

Abstract

The application provides a large-size double-end bolt fatigue test tool and a use method thereof. The tool is a symmetrical structure of two sets of upper and lower structures, comprising a connecting cylinder, a centering positioning structure and a switching bearing structure. The connecting cylinder is connected with a fatigue testing machine. The switching bearing structure is movably connected with the inner side of the connecting cylinder. The centering positioning structure comprises a convex composite body. The switching bearing structure comprises a concave composite body. The convex composite body is provided with a first through hole. The concave composite body is provided with a second through hole. The double-end bolt passes through the second through hole and the first through hole in sequence. Through the cooperation of the convex composite body and the concave composite body, automatic centering positioning between the axial center line of the double-end bolt and the load center line is realized. The application has the advantages of simple structure and convenient installation. The automatic centering positioning between the axial center line of the double-end bolt and the load center line can be realized, and manual centering positioning between the two can also be realized.

Description

Technical Field

[0001] This invention relates to a fatigue testing fixture for large-size double-ended bolts and its method of use. Background Technology

[0002] Large-size double-ended studs are widely used in mining machinery, bridges, wind power, rail transportation, shipbuilding, long-span steel structures, and large-scale buildings. In these fields, structures using double-ended studs often bear large or even extremely large loads, such as static loads due to the structure's own weight, dynamic loads from external factors like wind, train operation, earthquakes, and waves, and high-temperature creep loads caused by significant temperature differences. These loads lead to stress concentration in certain areas of the bolt, resulting in crack formation and propagation under alternating loads. Once the cracks reach a certain extent, the bolt breaks, causing major engineering accidents, significant economic losses, and negative social impacts. Therefore, fatigue performance testing of large-size double-ended studs is crucial.

[0003] During fatigue testing, if the load centerline deviates from the bolt axial centerline, it will lead to excessive stress concentration near the junction of the nut and the bolt rod. These stresses will seriously affect the accuracy of the test results. Summary of the Invention

[0004] In view of this, the present invention aims to propose a fatigue testing fixture for large-size double-ended bolts and its usage method to solve the above-mentioned problems in existing methods, and to design a matching fixture so that the load centerline is consistent with the bolt axial centerline, thereby avoiding or reducing the influence of stress caused by installation errors on the experiment.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A fatigue testing fixture for large-size double-ended bolts is disclosed. The fixture comprises two symmetrical structures, including a connecting cylinder, a centering and positioning structure, and a transition bearing structure. The connecting cylinder is connected to a fatigue testing machine, and the transition bearing structure is movably connected to the inner side of the connecting cylinder. The centering and positioning structure includes a convex composite body, and the transition bearing structure includes a concave composite body. The convex composite body has a first through hole, and the concave composite body has a second through hole. The double-ended bolt passes through the second through hole and the first through hole on both sides in sequence. Through the cooperation of the convex composite body and the concave composite body, automatic centering and positioning between the axial centerline of the double-ended bolt and the load centerline is achieved.

[0007] When using this fixture, if the axial centerline of the double-ended bolt is not on the same axis as the load centerline, automatic alignment between the two centerlines can be achieved by applying a certain load.

[0008] Furthermore, the convex composite includes a first protrusion, a second protrusion, and a third protrusion connected in sequence, and the concave composite includes a first concave protrusion, a second concave protrusion, and a third concave protrusion connected in sequence, wherein the first protrusion and the first concave protrusion are correspondingly arranged, the second protrusion and the second concave protrusion are correspondingly arranged, and the third protrusion and the third concave protrusion are correspondingly arranged.

[0009] This structure enables automatic centering and positioning of double-headed bolts, and also prevents bolts from shifting to the left or right.

[0010] Furthermore, the central axis of both the second protrusion and the second concave protrusion is L, the first protrusion and the third protrusion are symmetrically arranged about the central axis L, and the first concave protrusion and the third concave protrusion are symmetrically arranged about the central axis L.

[0011] Furthermore, the bottom end of the second protrusion is a spherical structure or a straight structure, and the bottom end of the second concave protrusion is a spherical structure or a straight structure.

[0012] Furthermore, when the bottom ends of the second protrusion and the second concave are both straight structures, the intersection point formed by the extended lines of the arc segments on both sides of the second protrusion is the third point, and the radius of curvature of the third point is R1; the intersection point formed by the extended lines of the arc segments on both sides of the second concave is the sixth point, and the radius of curvature of the sixth point is R2; the connection point between the first protrusion and the second protrusion is the second point, and the radius of curvature of the second point is R3; the connection point between the first concave and the second concave is the fifth point, and the radius of curvature of the fifth point is R4; the first protrusion includes a first point, and the radius of curvature of the first point is R5; the first concave includes a fourth point, and the radius of curvature of the fourth point is R6, wherein R1>R5>R3, R2>R6>R4.

[0013] This design prevents misalignment between the transfer bearing structure and the centering positioning structure.

[0014] Furthermore, the second protrusion includes a first segment, a second segment, and a third segment, the first segment and the third segment being symmetrical about the central axis L; the second concave protrusion includes a fourth segment, a fifth segment, and a sixth segment, the fourth segment and the sixth segment being symmetrical about the central axis L.

[0015] Furthermore, the distance between the second segment and the fifth segment is H1, the distance between the horizontal line where the second point is located and the horizontal line where the fifth point is located is H2, and the distance between the horizontal line where the first point is located and the horizontal line where the fourth point is located is H3, where H1>H3>H2.

[0016] During the experiment, when the transfer bearing structure and the centering positioning structure are in conjunction, this setting will first ensure that R3 and R4 are in contact, so that this area is the main stress zone. When adjusting the bolts during the experiment, they can be moved within a certain range to avoid excessive offset.

[0017] Furthermore, the connecting cylinder is provided with multiple positioning blocks and multiple adjustment holes. The positioning blocks are located on the outside of the connecting cylinder, and the adjustment holes penetrate through the outer wall and inner wall of the connecting cylinder. The positioning blocks and the adjustment holes are at the same height.

[0018] The positioning block and adjustment hole are mainly used to realize the manual centering and positioning function.

[0019] Furthermore, the centering and positioning structure includes an adjusting block, which is a toothed structure distributed along the outer ring. The adjusting block is located at both ends of the convex composite body, and the adjusting block and the adjusting hole are located on the same horizontal line.

[0020] This setting enables manual centering and positioning.

[0021] A method for using a fatigue testing fixture for large-size double-ended bolts, comprising the following steps when conducting experiments using the aforementioned testing fixture:

[0022] S1. Install and clamp the connecting cylinder to the testing machine clamps respectively;

[0023] S2. Pass the double-ended bolts through the transition bearing structure and the centering positioning structure on both sides in sequence, and place them between the two connecting cylinders after tightening the nuts to a certain position.

[0024] S3. Use a wrench to fix the transition bearing structure to the corresponding connecting cylinder;

[0025] S4. Adjust the distance between the upper and lower clamps of the testing machine to create a certain tension between the double-ended bolt and the tooling. Under the action of tension, the axial center line of the bolt coincides with the load center line between the upper and lower clamps of the testing machine. At the same time, use a manual adjustment tool to manually adjust the center line to further ensure that the axial center line of the bolt is completely coincident with the load center line between the upper and lower clamps of the testing machine.

[0026] S5. Set experimental parameters and start fatigue test.

[0027] Compared with existing technologies, the fatigue testing fixture for large-size double-ended bolts and its usage method described in this invention have the following advantages:

[0028] (1) The test fixture provided by the present invention has two sides of the double-ended bolt passing through the through holes between the concave composite and the convex composite respectively. Through the cooperation of the convex composite and the concave composite, the self-alignment and positioning function between the axial center line of the double-ended bolt and the load center line can be realized.

[0029] (2) The present invention adopts the first protrusion and the first concave protrusion, the second protrusion and the second concave protrusion, and the third protrusion and the third concave protrusion, which can realize the automatic centering and positioning function between the axial center line of the bolt and the load center line, and also prevent the double-headed bolt from shifting too much to the left and right.

[0030] (3) The present invention can realize the manual positioning and centering function by setting an adjustment block on the centering and positioning structure and setting a positioning block and adjustment hole on the connecting cylinder. The present invention adds a manual positioning and centering function on the basis of the automatic positioning and centering function, further ensuring the accuracy of the experiment. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of a large-size double-ended bolt fatigue testing fixture according to the present invention;

[0032] Figure 2 This is a schematic diagram of the overall structure of the connecting cylinder of the present invention;

[0033] Figure 3 for Figure 2 A cross-sectional view along the AA direction;

[0034] Figure 4 for Figure 2 A cross-sectional view along the BB direction;

[0035] Figure 5 This is a schematic diagram of the positioning block structure of the present invention;

[0036] Figure 6 This is a top view of the centering and positioning structure of the present invention;

[0037] Figure 7 for Figure 6 A cross-sectional view along the CC direction;

[0038] Figure 8 This is a front view of the transfer bearing structure of the present invention;

[0039] Figure 9 This is a top view of the transfer bearing structure of the present invention;

[0040] Figure 10 This is a partial structural diagram of the cooperation between the convex composite and the concave composite of the present invention.

[0041] Figure 11 This is a schematic diagram showing the relevant dimensions of the convex composite and concave composite of the present invention.

[0042] Figure 12 These are the front view and top view of the convex composite of the present invention;

[0043] Figure 13These are the front view and top view of the concave composite of the present invention.

[0044] Explanation of reference numerals in the attached figures:

[0045] 1-Connecting cylinder, 11-Positioning block, 12-Adjusting hole, 2-Centering and positioning structure, 21-Convex composite body, 211-First protrusion, 2111-First point, 2112-Second point, 2113-First singularity, 212-Second protrusion, 2121-First segment, 2122-Second segment, 2123-Third segment, 2124-Third point, 2125-Second singularity, 213-Third protrusion, 214-First through hole, 215-Bearing boss, 22-Adjusting block, 3-Transfer bearing structure, 3 1-Concave composite, 311-First recess, 3111-Fourth point, 3112-Fifth point, 312-Second recess, 3121-Fourth segment, 3122-Fifth segment, 3213-Sixth segment, 3124-Sixth point, 313-Third recess, 314-Second through hole, 32-Rotating part, 4-First fastener, 5-Double-ended bolt, L-Central shaft, E-Front view of convex composite, F-Top view of convex composite, H-Front view of concave composite, I-Top view of concave composite. Detailed Implementation

[0046] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Furthermore, a brief explanation of the orientations involved in the following specific embodiments is provided: the directions or positional relationships indicated by "up," "down," "left," "right," etc., mentioned in the embodiments refer to the orientations or positional relationships shown in the accompanying drawings.

[0047] This invention relates to a fatigue testing fixture for large-size double-ended bolts, such as... Figure 1-13 As shown, the tooling consists of two symmetrical structures, including a connecting cylinder 1, a centering and positioning structure 2, and a transition bearing structure 3. When used with a fatigue testing machine, it can perform fatigue performance tests on double-ended bolts under tensile stress conditions.

[0048] Specifically, the connecting cylinder 1 is connected to the fatigue testing machine, the transition bearing structure 3 is movably connected to the inner side of the connecting cylinder 1, the centering and positioning structure 2 is provided with a convex composite 21, the transition bearing structure 3 includes a concave composite 31, the convex composite 21 is disposed in the concave composite 31, the convex composite 21 is provided with a first through hole 214, the concave composite 31 is provided with a second through hole 314, the first through hole 214 and the second through hole 314 are connected, the double-ended bolt 5 passes through the second through hole 314 and the first through hole 214 in sequence, and the bolt is fixed by the first fastener 4. Through the cooperation of the convex composite 21 and the concave composite 31, under a certain load, the automatic centering and positioning between the axial center line of the double-ended bolt and the load center line is achieved.

[0049] In this setup, when the axial centerline of the double-ended bolt and the load centerline are not on the same axis, the two centerlines are automatically aligned by applying a certain load.

[0050] Preferably, the first fastener 4 is a nut.

[0051] Specifically, the upper end of the convex composite 21 is a bearing boss 215, which cooperates with the nut, and the transition of the bearing boss is provided with corresponding chamfers.

[0052] Specifically, the connecting cylinder 1 has an internal thread on its inner side, the thread height and form of which depend on the specific circumstances. The transition bearing structure 3 has an external thread on its outer side, and the connecting cylinder 1 and the transition bearing structure 3 are connected by the thread. Preferably, the external thread is located on the outer side of the concave composite.

[0053] Specifically, the centering and positioning structure is used for automatic centering and positioning, and manual adjustment can be performed using special tools to further ensure accurate centering and positioning.

[0054] Specifically, the connecting cylinder 1 is provided with a plurality of positioning blocks 11 and a plurality of adjusting holes 12. The positioning blocks 11 are located on the outside of the connecting cylinder 1, and the adjusting holes 12 penetrate through the outer wall and the inner wall of the connecting cylinder 1. The positioning blocks 11 and the adjusting holes 12 are at the same height.

[0055] More specifically, the plurality of positioning blocks 11 include two positioning blocks, and the plurality of adjusting holes 12 include two adjusting holes. The positioning blocks and adjusting holes are on the same cross section and are arranged equidistantly in sequence. The distance between the adjusting holes and the positioning blocks is set according to the adjusting tool. The adjusting holes are non-radial holes. This setting allows the adjusting tool to be inserted into the adjusting holes. The positioning blocks are used to fix the adjusting tool and realize the manual positioning of the double bolts on the convex body.

[0056] More specifically, the positioning block has an Ω-shaped cross-section, ensuring a tight fit between the adjusting tool and the connecting cylinder during manual positioning adjustment, preventing them from falling off and guaranteeing a stable and reliable positioning force. The adjusting hole is circular, but its opening direction is not radial; that is, the opening direction deviates slightly from the diameter passing through this point. The deviation distance depends on the specific situation. This hole opening method avoids adjustment failure caused by the coincidence of the adjusting force and the diameter.

[0057] Specifically, the centering and positioning structure 2 includes adjusting blocks 22, which are located at both ends of the convex composite body 21. The adjusting blocks 22 and the adjusting holes 12 are on the same horizontal line. The adjusting blocks 22 are used in conjunction with a manual adjustment tool. The surfaces of the convex composite body and the concave composite body have a high degree of smoothness. Lubricant is used when necessary to reduce the friction generated when the two move relative to each other, thereby making it easier for the load center line and the axial center line of the double-ended bolt to achieve automatic centering under external load.

[0058] Specifically, the adjusting block has a ring structure, and the outer side of the adjusting block is designed with a tooth shape. The tooth shape of the adjusting block is designed according to actual needs, and the number of teeth should not be too sparse or too dense.

[0059] Specifically, the convex composite 21 includes a first protrusion 211, a second protrusion 212, and a third protrusion 213 connected in sequence. The first protrusion 211 and the third protrusion 213 are symmetrically arranged about the central axis L of the second protrusion 212. The concave composite 31 includes a first concave protrusion 311, a second concave protrusion 312, and a third concave protrusion 313 connected in sequence. The first concave protrusion 311 and the third concave protrusion 313 are symmetrically arranged about the central axis L of the second concave protrusion 312. The first protrusion 211 and the first concave protrusion 311 are correspondingly arranged, the second protrusion 212 and the second concave protrusion 312 are correspondingly arranged, and the third protrusion 213 and the third concave protrusion 313 are correspondingly arranged.

[0060] Specifically, the second protrusion 212 includes a first segment 2121, a second segment 2122, and a third segment 2123, wherein the first segment 2121 and the third segment 2123 are symmetrical about the central axis L. The second concave protrusion includes a fourth segment, a fifth segment, and a sixth segment, wherein the fourth segment and the sixth segment are symmetrical about the central axis L. Preferably, the first segment 2121 and the third segment 2123 are curved surfaces, the second segment is a straight surface or an arc surface, the fourth segment and the sixth segment are curved surfaces, and the fifth segment is a straight surface or an arc surface.

[0061] Preferably, both the second and fifth segments are straight surfaces, and the second segment is parallel to the fifth segment.

[0062] Specifically, the distance between the second segment and the fifth segment is H1, the distance between the horizontal line where the second point is located and the horizontal line where the fifth point is located is H2, and the distance between the horizontal line where the first point is located and the horizontal line where the fourth point is located is H3, where H1>H3>H2.

[0063] Specifically, the intersection of the extended arcuate segments on both sides of the second protrusion 212 is the third point 2124, with a radius of curvature of R1. The intersection of the extended arcuate segments on both sides of the second concave protrusion 312 is the sixth point 3124, with a radius of curvature of R2. The connection between the first protrusion 211 and the second protrusion 212 is the second point 2112, with a radius of curvature of R3. The first concave protrusion 311... The fifth point 3112 is located at the connection point with the second concave protrusion 312, and the radius of curvature of the fifth point is R4. The first protrusion 211 includes a first point 2111, and the radius of curvature of the first point 2111 is R5. The first concave protrusion 311 includes a fourth point 3111, and the radius of curvature of the fourth point 3111 is R6. Where R1>R5>R3, R2>R6>R4; the centers of R5 and R6 are not on the same vertical line, and the centers of R3 and R4 are not on the same vertical line. Simultaneously, R2>R1, R6>R5, and R3>R4.

[0064] Specifically, the first point 2111 is located at the lowest end of the first protrusion 211, the fourth point 3111 is located at the lowest end of the first concave 311, the second point 2112 is located at the highest point of the first protrusion, and the fifth point 3112 is located at the highest point of the first concave 311.

[0065] Specifically, the distance of the first point 2111 from the central axis L is less than the distance of the fourth point 3111 from the central axis L, and the distance of the second point 2112 from the central axis L is greater than the distance of the fifth point 3112 from the central axis L.

[0066] During the experiment, this setup ensures that the transition bearing structure and the centering positioning structure first come into contact in the area between the first point 2111 and the second point 2112 and the fourth point 3111 and the fifth point 3112, indirectly ensuring that the bolts can move within a certain range and avoiding excessive offset.

[0067] Specifically, the convex composite 21 has multiple singularities, including a first singularity 2113 and a second singularity 2125. The first singularity 2113 is located between a first point and a second point, and the second singularity 2125 is located on the first segment. The requirement is that L1 > L2 and V2 > V1. In practical applications… Figure 10 The first singularity and the second singularity are not necessarily on the same horizontal or vertical line.

[0068] Wherein, L1 refers to the length of the intersection of the horizontal line from the first singularity to the first singularity and the curve of the first convex cross section; L2 refers to the length of the intersection of the horizontal line from the first singularity to the first singularity and the curve of the first concave cross section; V1 refers to the distance between the vertical line passing through the first singularity and the intersection of the first concave point and the horizontal line from the second point; V2 refers to the distance between the vertical line passing through the second singularity and the intersection of the second concave point and the horizontal line from the fourth point.

[0069] Specifically, the transition bearing structure 3 includes a rotating part 32, which is connected to the concave composite body 31 and is located at the lower end of the concave composite body 31. The rotating part 32 is hexagonal in shape. During installation, the transition bearing structure is aligned with the connecting cylinder, and a wrench is used in conjunction with the rotating part block to screw the upper part of the transition bearing structure into the connecting cylinder as a whole. During disassembly, the process is reversed.

[0070] A method for using a fatigue testing fixture for large-size double-ended bolts, comprising the following steps:

[0071] a. Install and clamp the upper and lower connecting cylinders to the upper and lower clamps of the testing machine respectively;

[0072] b. Pass the double-ended bolt through the transition bearing structure and the centering positioning structure on both sides in turn, and use them with nuts, with an appropriate length exposed;

[0073] c. Align the transition bearing structures and connecting cylinders on both sides, and use a wrench to tighten the transition bearing structures to the predetermined positions;

[0074] d. The bottom of the double-ended bolt is completed in steps b and c;

[0075] e. Adjust the distance between the upper and lower clamps of the testing machine so that there is just enough tension between the double-ended bolt and the tooling;

[0076] f. Theoretically, when the bolt is under pressure, the axial centerline of the bolt will coincide with the load centerline between the upper and lower clamps of the testing machine due to the curvature of the surface. If they do not coincide or there is still a certain degree of deviation, the bolt position will be adjusted by manually adjusting the tooling to make the two centerlines coincide.

[0077] g. Set the test parameters and begin the fatigue test;

[0078] h. After the test is completed, unload the test load, use a wrench to remove the connecting load-bearing structure on both sides in sequence, unscrew the nuts at both ends, replace with a new bolt, repeat the above steps to complete the fatigue test.

[0079] This invention utilizes the cooperation of a convex composite and a concave composite to enable the double-ended bolt to achieve automatic centering when a certain load is applied. If there is still a certain deviation in automatic centering, a manual adjustment function can be used. In addition, the first protrusion and the first concave protrusion, as well as the third protrusion and the third concave protrusion, also prevent misalignment between the structural modules.

[0080] The invention can be used for fatigue performance testing of different types of double-ended bolts. The precise centering and positioning technology used is innovative, reducing installation errors caused by the test and making it more consistent with the actual service condition of the bolt.

[0081] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A fatigue testing fixture for large-size double-ended bolts, wherein the fixture has two symmetrical structures, characterized in that, The system includes a connecting cylinder (1), a centering and positioning structure (2), and a transition bearing structure (3). The connecting cylinder (1) is connected to a fatigue testing machine, and the transition bearing structure (3) is movably connected to the inner side of the connecting cylinder (1). The centering and positioning structure (2) includes a convex composite body (21), and the transition bearing structure (3) includes a concave composite body (31). The convex composite body (21) is provided with a first through hole (214), and the concave composite body (31) is provided with a second through hole (314). The double-ended bolt (5) passes through the second through hole (314) and the first through hole (214) on both sides in sequence, and passes through the convex composite body (21) and the concave composite body (31). The convex composite (21) includes a first protrusion (211), a second protrusion (212), and a third protrusion (213) connected in sequence, and the concave composite (31) includes a first concave protrusion (311), a second concave protrusion (312), and a third concave protrusion (313) connected in sequence. The first protrusion (211) and the first concave protrusion (311) are correspondingly arranged, the second protrusion (212) and the second concave protrusion (312) are correspondingly arranged, and the third protrusion (213) and the third concave protrusion (313) are correspondingly arranged. The second protrusion (212) and the first concave protrusion (313) are correspondingly arranged. The central axis of both concave protrusions (312) is L. The first protrusion (211) and the third protrusion (213) are symmetrically arranged about the central axis L. When the bottom ends of the second protrusion (212) and the second concave protrusion (312) are both straight structures, the intersection point formed by the extension lines of the arc segments on both sides of the second protrusion (212) is the third point (2124), and the radius of curvature of the third point (2124) is R1. The intersection point formed by the extension lines of the arc segments on both sides of the second concave protrusion (312) is the sixth point (3124), and the radius of curvature of the sixth point (3124) is R1. The radius is R2, the connection between the first protrusion (211) and the second protrusion (212) is the second point (2112), the radius of curvature of the second point (2112) is R3, the connection between the first concave protrusion (311) and the second concave protrusion (312) is the fifth point (3112), the radius of curvature of the fifth point (3112) is R4, the first protrusion (211) includes the first point (2111), the radius of curvature of the first point (2111) is R5, the first concave protrusion (311) includes the fourth point (3111), the radius of curvature of the fourth point (3111) is R6, wherein R1>R5>R3, R2>R6>R4;The second protrusion (212) includes a first segment (2121), a second segment (2122), and a third segment (2123). The second concave protrusion (312) includes a fourth segment (3121), a fifth segment (3122), and a sixth segment (3123). The first segment (2121) and the third segment (2123) are symmetrical about the central axis L. The fourth segment (3121) and the sixth segment (3123) are also symmetrical about the central axis L. The second segment (2122) and the fifth segment (3122) are both straight surfaces. The second segment (2122) and the fifth segment (3122) are parallel. The distance between the second segment (2122) and the fifth segment (3122) is H1. The horizontal line where the second point (2112) is located is parallel to the horizontal line. The distance between the horizontal lines where the fifth point (3112) is located is H2, and the distance between the horizontal line where the first point (2111) is located and the horizontal line where the fourth point (3111) is located is H3, where H1>H3>H2; the connecting cylinder (1) is provided with multiple positioning blocks (11) and multiple adjusting holes (12), the positioning blocks (11) and adjusting holes (12) are at the same height, the positioning blocks (11) are located on the outside of the connecting cylinder (1), and the adjusting holes (12) penetrate through the outer wall and inner wall of the connecting cylinder (1); the centering positioning structure (2) includes adjusting blocks (22), the adjusting blocks (22) are toothed structures distributed along the outer arc, and the adjusting blocks (22) and adjusting holes (12) are located on the same horizontal line.

2. A method for using a fatigue testing fixture for large-size double-ended bolts, wherein when conducting experiments using the testing fixture described in claim 1, the method is characterized in that... Includes the following steps: S1. Install and clamp the connecting cylinder to the testing machine clamps respectively; S2. Pass the double-ended bolts through the transition bearing structure and the centering positioning structure on both sides in sequence, and place them between the two connecting cylinders after tightening the nuts to a certain position. S3. Use a wrench to fix the transition bearing structure to the corresponding connecting cylinder; S4. Adjust the distance between the upper and lower clamps of the testing machine to create a certain tension between the double-ended bolt and the tooling. Under the action of tension, the axial center line of the bolt coincides with the load center line between the upper and lower clamps of the testing machine. At the same time, use a manual adjustment tool to manually adjust the center line to further ensure that the axial center line of the bolt is completely coincident with the load center line between the upper and lower clamps of the testing machine. S5. Set experimental parameters and start fatigue test.

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