Fatigue test device and method for large-diameter high-strength bolts

Abstract

The application discloses a large-diameter high-strength bolt fatigue test device and method, and relates to the field of test equipment.The large-diameter high-strength bolt fatigue test device comprises a loading tool, a bolt connecting seat and a fatigue testing machine hydraulic cylinder which are respectively connected to the bottom and the top of the loading tool, a threaded hole for being threadedly connected with a bolt is arranged at the top of the bolt connecting seat, a connecting plate sleeved on the bolt is connected to the bottom of the fatigue testing machine hydraulic cylinder through an actuator head, the fatigue testing machine hydraulic cylinder is used for stretching the connecting plate upwards, a pressing plate is connected to the connecting plate, the bolt is fixed on the connecting plate by the pressing plate, and at least one strain gauge is arranged on the outer wall of the bolt.The large-diameter high-strength bolt fatigue test device and method can ensure that the load applied to the bolt is quickly and accurately controlled during bolt fatigue test, and the bolt fatigue test can be carried out under two different working conditions of pre-tightening force and no pre-tightening force, so that the bolt fatigue test is high in efficiency, low in cost and wide in adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of test equipment, in particular, to a large-diameter high-strength bolt fatigue test device and method. BACKGROUND

[0002] When using a bolt fatigue test device to perform fatigue test on a large-size high-strength bolt, the test load can reach several hundred kilo-newtons (several tens of tons), and meanwhile, the large size of the bolt will result in a very large tool size, which will inevitably cause a certain degree of load reduction when performing the fatigue test, regardless of how much rigidity the material used for the tool has, so that the axial load borne by the bolt is smaller than the loading force of the test machine, and the reduction coefficient can reach 10-20%. At this time, if the fatigue test is performed by taking the loading force of the test machine as a reference, a relatively large error will be caused. In the exploration of bolt fatigue strength, applying or not applying a pre-tightening force is currently two commonly used research methods, which are equally important. Meanwhile, different test requirements need to perform bolt fatigue test under the conditions of having and not having a pre-tightening force, and the present test device can adjust the tool combination according to the test requirements to realize fatigue test under the two working conditions.

[0003] Therefore, there is a need for a large-diameter high-strength bolt fatigue test device and method capable of accurately controlling the size of the applied loading force and applying a pre-tightening force to meet different test requirements. SUMMARY

[0004] The present application aims to provide a large-diameter high-strength bolt fatigue test device and method, which can quickly and accurately control the size of the loading force applied to the bolt during bolt fatigue test, and realize fatigue test under two different working conditions of having and not having a pre-tightening force, thereby realizing efficient, low-cost, and widely adaptable bolt fatigue test.

[0005] The present application is achieved in the following manner:

[0006] The present application provides a large-diameter high-strength bolt fatigue test device, which comprises a loading tool, a bolt connecting seat and a fatigue test machine hydraulic cylinder connected to the bottom and top of the loading tool respectively, a threaded hole for threadedly connecting with a bolt is arranged at the top of the bolt connecting seat, a connecting plate sleeved on the bolt is connected to the bottom of the fatigue test machine hydraulic cylinder through an actuator head, the fatigue test machine hydraulic cylinder is used to stretch the connecting plate upward, a pressing plate is connected to the connecting plate, the pressing plate presses and fixes the bolt on the connecting plate, and at least one strain gauge is arranged on the outer wall of the bolt.

[0007] In some alternative embodiments, the loading fixture comprises two fixed bases, two vertical beams and two horizontally arranged cross beams, the bottom of the two vertical beams is connected to the two fixed bases respectively, the two ends of the cross beams are connected to the two vertical beams respectively, the two cross beams are connected to the bolt connecting seat and the hydraulic cylinder of the fatigue testing machine through the fixing assembly, the fixing assembly comprises an upper hanging plate and a lower hanging plate arranged at the top and bottom of the cross beam respectively and a plurality of first connecting bolts connecting the upper hanging plate and the lower hanging plate, the upper hanging plate of one fixing assembly is connected to the bolt connecting seat, the lower hanging plate of the other fixing assembly is connected to a rotating end head rotatable along a vertical plane, and the rotating end head is connected to the hydraulic cylinder of the fatigue testing machine.

[0008] In some alternative embodiments, the upper hanging plate and the lower hanging plate are respectively protruded to form a plurality of reinforcing ribs.

[0009] In some alternative embodiments, it further comprises a top and a bottom spacer respectively abutting against the actuator head and the connecting plate.

[0010] In some alternative embodiments, the actuator head is connected to the connecting plate through a plurality of second connecting bolts, and the second connecting bolts pass through the spacer.

[0011] In some alternative embodiments, the outer wall of the connecting plate is provided with at least one threading hole, and the lead wire of the strain gauge extends out through the threading hole.

[0012] In some alternative embodiments, it further comprises a force sensor and a wrench which can be sleeved on the bolt, a dynamometer connected to the wrench and a stretching mechanism connected to the dynamometer.

[0013] In some alternative embodiments, the bolt connecting seat comprises a connecting seat body connected to the bottom of the loading fixture and a nut provided with a threaded hole, the connecting seat body is provided with a connecting hole with a diameter gradually increasing from bottom to top, and the outer diameter of the nut gradually increases from bottom to top to be inserted into and clamped in the connecting hole.

[0014] In some alternative embodiments, it further comprises a camera rotatable along a vertical plane and a horizontal plane, and the camera is used to shoot images of the hydraulic cylinder of the fatigue testing machine and the bolt connecting seat.

[0015] The application also provides a large-diameter high-strength bolt fatigue testing method, which is performed by using the large-diameter high-strength bolt fatigue testing device described above, and comprises the following steps:

[0016] At least one strain gauge is arranged on the outer wall of the bolt;

[0017] The bottom of the bolt is connected to the threaded hole at the top of the bolt connecting seat after passing through the connecting plate;

[0018] The pressing plate is connected to the connecting plate to abut and fix the bolt to the connecting plate;

[0019] The fatigue testing machine hydraulic cylinder connected with the top of the loading tool is used to stretch the connecting plate upward;

[0020] The strain value detected by the strain gauge is received, and the tension of the fatigue testing machine hydraulic cylinder stretching the connecting plate upward is adjusted.

[0021] The beneficial effects of the present application are that the large-diameter high-strength bolt fatigue testing device provided by the present application comprises a loading tool, a bolt connecting seat connected to the bottom of the loading tool, and a fatigue testing machine hydraulic cylinder connected to the top of the loading tool, a threaded hole for threaded connection with a bolt is arranged at the top of the bolt connecting seat, the bottom of the fatigue testing machine hydraulic cylinder is connected with a connecting plate sleeved on the bolt through an actuator head, the fatigue testing machine hydraulic cylinder is used to stretch the connecting plate upward, a pressing plate is connected to the connecting plate, the bolt is pressed and fixed on the connecting plate by the pressing plate, and at least one strain gauge is arranged on the outer wall of the bolt. The large-diameter high-strength bolt fatigue testing device and method provided by the present application can quickly and accurately control the load applied to the bolt during bolt fatigue testing, and can realize fatigue testing under two different working conditions of pre-tightening force and no pre-tightening force, thereby realizing efficient, low-cost, and wide-adaptability bolt fatigue testing. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0023] Figure 1 The structure schematic diagram of the large-diameter high-strength bolt fatigue testing device provided by the present application;

[0024] Figure 2 The structure schematic diagram of the large-diameter high-strength bolt fatigue testing device provided by the present application; Figure 1 The cross-sectional structure schematic diagram along the A-A cross-sectional line;

[0025] Figure 3 The cross-sectional structure schematic diagram along the B-B cross-sectional line; Figure 1 The cross-sectional structure schematic diagram along the C-C cross-sectional line;

[0026] Figure 4 The cross-sectional structure schematic diagram along the C-C cross-sectional line; Figure 1 The cross-sectional structure schematic diagram along the C-C cross-sectional line;

[0027] Figure 5 The partial cross-sectional structure schematic diagram of the large-diameter high-strength bolt fatigue testing device provided by the present application when no pre-tightening force is tested, and the actuator head, the connecting plate, the pressing plate, and the bolt connecting seat are connected;

[0028] Figure 6The partial cross-sectional structure schematic diagram of the connection of the actuator head, the connecting plate, the pressing plate and the bolt connecting seat in the pre-tightening force test of the large-diameter high-strength bolt fatigue test device provided by the embodiment of the present application;

[0029] Figure 7 The cross-sectional structure schematic diagram of the connection of the connecting seat body and the nut in the large-diameter high-strength bolt fatigue test device provided by the embodiment of the present application;

[0030] Figure 8 The perspective structure schematic diagram of the connection of the connecting seat body and the nut in the large-diameter high-strength bolt fatigue test device provided by the embodiment of the present application;

[0031] Figure 9 The structure schematic diagram of the connection of the wrench, the force meter, the pull rope, the fixed pulley and the hand-operated hoist of the bolt in the prestress loading device in the large-diameter high-strength bolt fatigue test device provided by the embodiment of the present application.

[0032] In the figure: 100, loading tool; 110, base; 120, vertical beam; 130, cross beam; 140, upper hanging plate; 150, lower hanging plate; 160, first connecting bolt; 170, rotating end; 180, reinforcing rib; 190, ear plate; 191, rotating shaft; 200, bolt connecting seat; 210, threaded hole; 220, connecting seat body; 230, nut; 240, connecting hole; 300, fatigue test machine hydraulic cylinder; 310, actuator head; 320, second connecting bolt; 330, connecting plate; 331, threading hole; 332, through hole; 340, third connecting bolt; 350, pressing plate; 360, strain gauge; 370, spacer; 380, limiting hole; 400, bolt; 410, force sensor; 420, wrench; 430, force meter; 440, pull rope; 450, fixed pulley; 460, hand-operated hoist. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts are within the scope of protection of the present application.

[0035] It should be noted that similar reference numerals and letters refer to similar items throughout the accompanying drawings, and once an item is defined in one drawing, it is not necessary for it to be further defined and explained in the subsequent drawings.

[0036] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like, indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the application is usually placed during use, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0037] In addition, the terms "horizontal", "vertical", "overhanging", and the like do not mean that the components must be absolutely horizontal or overhanging, but can be slightly inclined. For example, "horizontal" only means that it is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0038] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "provided", "mounted", "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0039] In the present application, unless otherwise explicitly specified and limited, "on" or "under" the first feature of the second feature can include the first and second features in direct contact, or the first and second features not in direct contact but in contact through another feature between them. Moreover, the first feature "on", "above" and "above" the second feature includes the first feature directly above and obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature includes the first feature directly below and obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

[0040] The features and performance of the large-diameter high-strength bolt fatigue test device and method of the present application are further described in detail below in conjunction with the embodiments.

[0041] As Figure 1 ,Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 、 Figure 8 and Figure 9 As shown in the drawings, the embodiment of the application provides a large-diameter high-strength bolt fatigue test device, which comprises a loading tool 100, a bolt connecting seat 200 and a fatigue testing machine hydraulic cylinder 300 connected to the bottom and top of the loading tool 100 respectively, a prestress loading device, and a camera rotatable along a vertical plane and a horizontal plane.

[0042] The loading tool 100 comprises two base seats 110 fixed to the ground, two vertical beams 120, and two horizontally arranged cross beams 130. The bottom of the two vertical beams 120 is connected to the two base seats 110 respectively, and the two ends of the cross beam 130 are connected to the two vertical beams 120 respectively. The two cross beams 130 are connected to the bolt connecting seat 200 and the fatigue testing machine hydraulic cylinder 300 through fixing assemblies respectively. The fixing assembly comprises an upper hanging plate 140 and a lower hanging plate 150 arranged at the top and bottom of the cross beam 130 respectively, and six first connecting bolts 160 connecting the upper hanging plate 140 and the lower hanging plate 150. The upper hanging plate 140 of one fixing assembly is connected to the bolt connecting seat 200 through a bolt, and the lower hanging plate 150 of the other fixing assembly is connected to two ear plates 190 and a rotating shaft 191 penetrating through the two ear plates 190. A rotating end head 170 rotatable along a vertical plane is sleeved on the rotating shaft 191, and the rotating end head 170 is connected to the top of the fatigue testing machine hydraulic cylinder 300. The upper hanging plate 140 and the lower hanging plate 150 are respectively provided with two longitudinal reinforcing ribs 180 and two transverse reinforcing ribs 180.

[0043] The bolt connecting seat 200 comprises a connecting seat body 220 connected to the bottom of the loading tool 100 by a bolt and a nut 230. The connecting seat body 220 is provided with a hexagonal connecting hole 240 with a diameter gradually increasing from top to bottom. The nut 230 is hexagonal and has an outer diameter gradually increasing from top to bottom to be inserted into and clamped in the connecting hole 240 from bottom to top. The nut 230 is provided with a threaded hole 210 for threaded connection with the bolt 400. The bottom of the fatigue testing machine hydraulic cylinder 300 is connected with an actuator head 310. The actuator head 310 is connected with a connecting plate 330 sleeved on the threaded hole 210 of the bolt 400 through six second connecting bolts 320. A partition ring 370 is further arranged between the actuator head 310 and the connecting plate 330. The top and bottom of the partition ring 370 abut against the actuator head 310 and the connecting plate 330, respectively. The six second connecting bolts 320 pass through the partition ring 370, respectively. The connecting plate 330 is provided with through holes 332 for the bolt 400 to pass through. The fatigue testing machine hydraulic cylinder 300 is used to stretch the connecting plate 330 upward. The top of the connecting plate 330 is connected with a pressing plate 350 through four third connecting bolts 340. The bottom of the pressing plate 350 is provided with a limiting hole 380 for clamping the head of the bolt 400. The limiting hole 380 is a stepped hole corresponding to the head of the bolt 400, with a diameter gradually increasing from top to bottom. The pressing plate 350 is used to abut and fix the top of the bolt 400 to the top of the connecting plate 330. The outer wall of the bolt 400 is provided with four strain gauges 360 arranged at intervals in the circumferential direction. The outer side wall of the connecting plate 330 is provided with four wire passing holes 331 arranged at intervals in the circumferential direction. Each wire passing hole 331 is in communication with the through hole 332. The wires of the four strain gauges 360 respectively pass through the four wire passing holes 331 and extend out.

[0044] The prestress loading device comprises a force sensor 410 and a wrench 420 which can be sleeved on the bolt 400, a force gauge 430 connected with the wrench 420, and a stretching mechanism connected with the force gauge 430. The stretching mechanism comprises a pulling rope 440 connected with the force gauge 430, a fixed pulley 450, and a hand-operated hoist 460 for pulling and moving the pulling rope 440. The pulling rope 440 is wound on the fixed pulley 450. A camera is mounted on a rotating device for shooting images of the fatigue testing machine hydraulic cylinder 300 and the bolt connecting seat 200. The rotating device is used to drive the camera to rotate in the vertical plane and the horizontal plane to adjust the image shooting angle. The rotating device in the embodiment is a prior art, and thus the specific structure is not described in detail.

[0045] The embodiment of the application also provides a large-diameter high-strength bolt fatigue test method, which is performed by using the large-diameter high-strength bolt fatigue test device.

[0046] Step one, arranging four strain gauges 360 at intervals in the circumferential direction on the outer wall of the bolt 400 to be subjected to fatigue test.

[0047] Step two, control the hydraulic cylinder 300 of fatigue testing machine to retract and raise, insert the nut 230 from bottom to top into the connecting hole 240 on the connecting seat body 220, and then place it on the connecting and fixing assembly under the cross beam 130 of the loading tool 100 to fix, so that the upper hanging plate 140 in the connecting and fixing assembly connected by the lower cross beam 130 is connected to the connecting seat body 220 through bolt connection, the connecting plate 330 is placed on the connecting seat body 220, the bottom of the bolt 400 to be tested for fatigue is connected to the threaded hole 210 of the nut 230 on the top of the bolt connecting seat 200 through the through hole 332 on the connecting plate 330, and the wires of the four strain gauges 360 are connected to the strain gauge after being stretched out through the through hole 332 and the four wire holes 331 outside the connecting plate 330;

[0048] Step three, place the pressing plate 350 on the top of the connecting plate 330, so that the limiting hole 380 at the bottom of the pressing plate 350 is connected to the top of the bolt 400, and then the pressing plate 350 is connected to the connecting plate 330 through the third connecting bolt 340 to press and fix the bolt 400 to the connecting plate 330;

[0049] Step four, place the spacer 370 on the top of the connecting plate 330 and make the spacer 370 fit outside the pressing plate 350, then control the hydraulic cylinder 300 of the fatigue testing machine to extend and lower the connected actuator head 310 to press the top of the spacer 370, use the second connecting bolt 320 to pass through the connecting actuator head 310, the spacer 370 and the connecting plate 330, and control the hydraulic cylinder 300 of the fatigue testing machine to stretch the connecting plate 330 and the pressing plate 350 upwards, so as to stretch the bolt 400 fixed between the connecting plate 330 and the pressing plate 350 upwards to apply load to the bolt 400;

[0050] Step five, use the strain gauge to receive the strain value detected by the strain gauge 360, adjust the tension of the connecting plate 330 stretched upwards by the hydraulic cylinder 300 of the fatigue testing machine, accurately control the axial load of the bolt 400 according to the data detected by the strain gauge, and monitor the strain change of the bolt 400 in real time throughout the process, which solves the problem of load reduction of the tool during large load fatigue test, provides a feasible high-strength bolt fatigue test method for fatigue test devices with limited test conditions, and uses a camera to shoot images of the hydraulic cylinder 300 of the fatigue testing machine and the bolt connecting seat 200 during the test process.

[0051] The bolt fatigue test under pre-tightening force is performed by using the large-diameter high-strength bolt fatigue test device, and the steps are basically the same as the bolt fatigue test without pre-tightening force, and the difference is that the following steps are further included between the step two and the step three: the force sensor 410 and the wrench 420 are sleeved on the bolt 400, the wrench 420 is connected with the force gauge 430, the stretching mechanism is used to stretch the force gauge 430 and drive the wrench 420 to rotate and drive the bolt 400 to rotate to apply pre-tightening force until the force gauge 430 displays that the pre-tightening force reaches the preset size, and the force sensor 410, the wrench 420, the force gauge 430 and the stretching mechanism are removed; wherein when the stretching mechanism is used to stretch the force gauge 430, the hand-operated hoist 460 is used to drive the pull rope 440 to move stably around the fixed pulley 450 and drive the connected force gauge 430 and wrench 420 to move to rotate the bolt 400.

[0052] The large-diameter high-strength bolt fatigue test device and method provided by the embodiment can effectively improve the structural strength and support stability of the loading tool 100 by using two fixed bases 110 on the ground, two vertical beams 120 and two horizontally arranged cross beams 130 to form a stable loading tool 100 to support the bolt connection seat 200 and the fatigue test machine hydraulic cylinder 300, and using the upper hanging plate 140 and the lower hanging plate 150 and the first connecting bolt 160 to form a fixed assembly to fix the bolt connection seat 200 and the fatigue test machine hydraulic cylinder 300. At the same time, the bolt 400 is connected and fixed by the bolt connection seat 200, the connecting plate 330 and the pressing plate 350 connected by the fatigue test machine hydraulic cylinder 300 are used to pull the bolt 400, so as to ensure that the bolt 400 is stably stretched upward to apply load, and the strain of the bolt 400 is monitored by the strain gauge 360 arranged on the surface of the bolt 400 to accurately control the axial load of the bolt 400, and the load reduction coefficient of the bolt 400 is controlled within 5-10%.

[0053] The upper hanging plate 140 and the lower hanging plate 150 of the fixing assembly are respectively provided with reinforcing ribs 180 arranged along the longitudinal direction and the transverse direction, so that the structural strength and support stability of the fixing assembly can be effectively improved. Meanwhile, considering that the bolt 400 may be broken due to construction load, when the bolt 400 is broken, a large instantaneous stress is caused to the bolt connecting seat 200, and the bolt connecting seat 200 is easily damaged, therefore, the bolt connecting seat 200 is designed to be separated and is composed of a connecting seat body 220 and a nut 230 provided with a threaded hole 210, the bottom of the connecting seat body 220 is provided with a connecting hole 240 in a hexagonal shape and with a diameter gradually decreasing from top to bottom, the nut 230 is inserted into the connecting hole 240 from bottom to top and is clamped and nested in the connecting seat body 220, when the threaded hole of the nut 230 is damaged due to excessive construction load of the bolt 400, only the nut 230 needs to be replaced, and the whole bolt connecting seat 200 does not need to be replaced, so that the bolt connecting seat 200 is more convenient and economical, meanwhile, by using a pre-tightening force applying tool and applying method, different fatigue test requirements of the bolt 400 under pre-tightening force can be met, and different diameter bolts can be tested by simply adjusting the size of part tool components, so that the bolt connecting seat 200 has high popularization.

[0054] The embodiments described above are part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

Claims

1. A fatigue testing device for large-diameter high-strength bolts, characterized in that, It includes a loading tool and a bolt connecting seat and a fatigue testing machine hydraulic cylinder connected to the bottom and top of the loading tool respectively, the top of the bolt connecting seat is provided with a threaded hole for threaded connection with a bolt, the bottom of the fatigue testing machine hydraulic cylinder is connected with a connecting plate sleeved on the bolt through an actuator head, the fatigue testing machine hydraulic cylinder is used to stretch the connecting plate upward, the top of the connecting plate is connected with a pressing plate, the pressing plate presses and fixes the bolt on the connecting plate, the outer wall of the bolt is provided with at least one strain gauge; the loading tool includes two bases fixed on the ground, two vertical beams and two horizontally arranged cross beams, the bottoms of the two vertical beams are respectively connected with the two bases, the two ends of the cross beam are respectively connected with the two vertical beams, the two cross beams are respectively connected with the bolt connecting seat and the fatigue testing machine hydraulic cylinder through a fixing assembly, the fixing assembly includes an upper hanging plate and a lower hanging plate respectively arranged on the top and bottom of the cross beam and a plurality of first connecting bolts connecting the upper hanging plate and the lower hanging plate, the upper hanging plate of one fixing assembly is connected with the bolt connecting seat, the lower hanging plate of the other fixing assembly is connected with a rotating end head which can rotate along the vertical plane, and the rotating end head is connected with the fatigue testing machine hydraulic cylinder; the bolt connecting seat includes a connecting seat body connected to the bottom of the loading tool and a nut provided with the threaded hole, the connecting seat body is provided with a connecting hole with a diameter gradually increasing from bottom to top, and the outer diameter of the nut gradually increases from bottom to top to be inserted into and clamped in the connecting hole from bottom to top.

2. The large-diameter high-strength bolt fatigue test apparatus according to claim 1, characterized by The upper hanging plate and the lower hanging plate are respectively protruded to form a plurality of reinforcing ribs.

3. The large-diameter high-strength bolt fatigue test apparatus according to claim 1, characterized by It also includes a spacer ring which presses the actuator head and the connecting plate respectively at the top and bottom.

4. The large-diameter high-strength bolt fatigue testing device according to claim 3, characterized by The actuator head is connected with the connecting plate through a plurality of second connecting bolts which pass through the spacer ring.

5. The large-diameter high-strength bolt fatigue testing apparatus according to claim 1, wherein The outer side wall of the connecting plate is provided with at least one threading hole through which the lead wire of the strain gauge extends.

6. The large-diameter high-strength bolt fatigue testing apparatus according to claim 1, wherein It also includes a force sensor and a wrench which can be sleeved on the bolt, a dynamometer connected with the wrench and a stretching mechanism connected with the dynamometer.

7. The large-diameter high-strength bolt fatigue testing apparatus according to claim 1, wherein It also includes a camera which can rotate along the vertical plane and the horizontal plane, and the camera is used to shoot the images of the fatigue testing machine hydraulic cylinder and the bolt connecting seat.

8. A method of testing the fatigue of a large-diameter high-strength bolt, characterized by, It is performed by using the large-diameter high-strength bolt fatigue testing device according to any one of claims 1-7, including the following steps: At least one strain gauge is arranged on the outer wall of the bolt; The nut is inserted into the connecting hole on the connecting seat body from bottom to top and then placed on the cross beam fixing assembly below the loading tool to be fixed, the upper hanging plate in the fixing assembly connected with the lower cross beam is connected with the connecting seat body through the bolt, the connecting plate is placed on the connecting seat body, the bottom of the bolt to be subjected to fatigue test is passed through the through hole on the connecting plate and then threadedly connected with the threaded hole in the nut on the top of the bolt connecting seat through the threaded connection; The pressing plate is connected with the connecting plate to press and fix the bolt on the connecting plate; The fatigue testing machine hydraulic cylinder connected with the top of the loading tool is used to stretch the connecting plate upward; Receiving the strain value detected by the strain gauge and adjusting the pulling force of the hydraulic cylinder of the fatigue testing machine to stretch the connecting plate upward.

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