Fretting fatigue test device and method for bolt connection

Abstract

The invention discloses a fretting fatigue test device and method for bolt connection, and belongs to the field of fatigue testing of parts in mechanical engineering, the fretting fatigue test device comprises a base, a lower clamp and an upper clamp, the lower clamp and the upper clamp are used for clamping an experimental bolt, the top of the upper clamp is provided with an axial load applying rod, and the base is rotatably provided with a turbine driven by power to rotate. The lower clamp and the turbine are fixed and rotate synchronously, one end of the experiment bolt is fixedly connected with the lower clamp, the other end of the experiment bolt penetrates through a penetrating groove in the upper clamp, extends into the rectangular cavity and is screwed and fixed through a nut and an upper locking washer, upper locking strips are symmetrically arranged on the side wall of the upper locking washer, and the ends of the upper locking strips abut against the inner wall of the rectangular cavity. According to the method, the fretting fatigue condition of the bolt in actual use can be simulated by accurately controlling the fretting displacement and the load of the bolt, and quantitative analysis of the fatigue performance of the bolt is realized, so that the fatigue life of the bolt is predicted more accurately, and the reliability and the safety of bolt design are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fatigue testing of components in mechanical engineering, in particular to a micro-motion fatigue test device and method for bolted connections. BACKGROUND

[0002] Bolts, as a common fastener, play a crucial role in various mechanical, architectural and engineering structures. They are used to connect two or more components and maintain their stability and safety under stress. The reliability of bolted connections directly affects the stability and durability of the entire structure.

[0003] In practical applications, bolts are often subjected to cyclic loads, which can come from mechanical vibrations, thermal expansion, impacts or external forces. Long-term cyclic loads can cause small relative movements between the bolt and its connected parts, a phenomenon known as micro-motion. Micro-motion can lead to wear and tear of the contact surfaces, corrosion and the formation of fatigue cracks, ultimately leading to the failure of bolted connections.

[0004] Micro-motion fatigue refers to the fatigue damage caused by micro-motion, which is one of the main reasons for the failure of bolted connections. Therefore, studying the micro-motion fatigue characteristics of bolts is of great significance for predicting their service life and improving their reliability and safety.

[0005] Traditional fatigue test methods, such as rotating bending fatigue test and tensile-compressive fatigue test, focus mostly on axial load fatigue tests and rarely consider micro-motion fatigue. Although these methods can evaluate the fatigue performance of materials, they cannot simulate the micro-motion conditions of bolts under actual working conditions.

[0006] There have been some studies on micro-motion fatigue in the prior art. For example, the invention patent with application number 201910333433.1 discloses a single chuck type micro-motion fatigue test device suitable for high temperature, and the invention patent with application number 202410809101.7 discloses a micro-motion test device and test method suitable for high temperature environment. Although both patents disclose micro-motion fatigue test devices, they are both aimed at high-temperature mortise joints. However, as known by those skilled in the art, although mortise joints and bolted connections are both common mechanical connection structures, there is no common logical chain in terms of failure mechanism, load transmission path and sensitive parameters between high-temperature mortise joints and normal-temperature bolted connections. Mortise joints are highly dependent on rigid fit, while bolted connections require dynamic balance of friction and pretightening force, etc. Therefore, the existing micro-motion fatigue test devices for high-temperature mortise joints cannot be used for micro-motion fatigue tests of bolted connections.

[0007] In addition, the application patent with the application number of 201810551614.7 discloses a fretting fatigue test device and a fretting fatigue test method, the core of which is to use the cooperation of the clamping piece 31 and the clamping pad 32 in the fretting fatigue clamp to solve the following problem: the following problem between the test pad 6 and the test piece 5 that abut against each other. However, this patent technology is also not suitable for the fretting fatigue test of the bolt, and the core reason is as follows: 1) The position of the fretting is different The bolt connection relies on the friction force generated by the pre-tightening force to resist external load, so the position of the fretting is at the thread root and the contact surface of the nut; and when abutting, the fretting position occurs at the contact surface of the two components; 2) The extension path of the damage is different The crack of the bolt connection mainly originates from the thread root, extends along the 45° direction of the thread, is mainly dominated by tangential fretting shear force, and the typical fracture morphology is cleavage fracture and fatigue streak; and when abutting, the damage mainly occurs at the edge of the contact surface, the crack extends vertically along the axial direction of the two contact components, is mainly dominated by the normal contact pressure, and the fracture morphology is mainly oxidation layer peeling and intergranular fracture; In the actual working condition of the bolt connection, the pre-tightening force, the friction coefficient and the surface roughness among the thread of the bolt root, the nut and the workpiece surface in contact with the nut are the key factors affecting the fretting fatigue, and how to accurately simulate the working condition among the three is the key of the bolt fretting fatigue test. SUMMARY

[0008] The purpose of the present application is to provide a bolt connection fretting fatigue test device and method, which can accurately control the fretting displacement and load of the bolt, simulate the fretting fatigue condition of the bolt in actual use, realize the quantitative analysis of the fatigue performance of the bolt, and thus more accurately predict the fatigue life of the bolt and improve the reliability and safety of the bolt design.

[0009] The technical scheme adopted by the present application to achieve the above technical purpose is as follows: a bolt connection fretting fatigue test device, comprising a base, a lower clamp and an upper clamp for clamping an experimental bolt, and an axial load applying rod is arranged on the top of the upper clamp, a turbine driven by a power source is rotatably arranged on the base, the lower clamp is fixed and synchronously rotated with the turbine, the upper clamp has a rectangular cavity, and the bottom wall of the rectangular cavity has a through groove extending to the center thereof, one end of the experimental bolt is fixedly connected with the lower clamp, the other end of the experimental bolt extends into the rectangular cavity through the through groove, and is fixedly screwed by a nut and an upper locking washer, the side wall of the upper locking washer is symmetrically provided with upper locking strips, and the end of the upper locking strip is tightly abutted against the inner wall of the rectangular cavity.

[0010] As an optimization scheme of the bolted fretting fatigue test device, the lower clamp has two side walls arranged oppositely and fixedly connected with the turbine, and the top of the two side walls has a horizontal connecting part, and the test bolt is fixed with the upper clamp after penetrating through the bolt hole on the connecting part.

[0011] As another optimization scheme of the bolted fretting fatigue test device, the test bolt has a lower locking washer between the connecting part, and the lower locking washer has lower locking strips symmetrically arranged on both sides, and the two ends of the lower locking strip are abutted against the two side walls.

[0012] As another optimization scheme of the bolted fretting fatigue test device, the test bolt has a lower locking washer between the connecting part, and the lower locking washer has lower locking strips symmetrically arranged on both sides, and the two side walls are provided with mirror-symmetric L-shaped clamping grooves, and the lower locking strips are clamped in the two L-shaped clamping grooves.

[0013] As another optimization scheme of the bolted fretting fatigue test device, the L-shaped clamping groove is formed by splicing a horizontal part and a vertical part, one end of the horizontal part extends to the end of the side wall, the other end communicates with the bottom end of the vertical part, the top end of the vertical part is flush with the bottom surface of the connecting part, and the end of the lower locking strip enters the L-shaped clamping groove along the horizontal part and is clamped at the top end of the vertical part by the end of the test bolt.

[0014] As another optimization scheme of the bolted fretting fatigue test device, the center of the turbine is provided with a mounting hole, and a thrust bearing is nested in the mounting hole, and a fixing bolt for fixing the turbine on the base is arranged in the bearing inner ring of the thrust bearing.

[0015] As another optimization scheme of the bolted fretting fatigue test device, the upper surface of the turbine has a recessed area, and the lower clamp is fixedly arranged in the recessed area.

[0016] As another optimization scheme of the bolted fretting fatigue test device, the turbine is engaged with a worm for transmission, and the worm is driven to rotate by a servo motor.

[0017] As another optimization scheme of the bolted fretting fatigue test device, the upper clamp is a rectangular frame structure, the axial load applying rod is arranged on the top wall opposite to the through groove, and the axial lines of the axial load applying rod and the test bolt are on the same vertical line with the center of the turbine.

[0018] A bolted fretting fatigue test method is provided, which is performed by using the above-mentioned fretting fatigue test device, and includes the following steps: 1) The lower end of the test bolt is fixedly connected with the lower clamp, the upper end penetrates through the through groove of the upper clamp and extends into the rectangular cavity, and is fixedly screwed by the nut and the upper locking washer; 2) Apply axial load to the experimental bolt through the axial load applying rod, so that the upper clamp and the lower clamp tighten the experimental bolt, simulating the normal working condition of the experimental bolt; 3) When the axial load reaches the set value, start the power-driven turbine to rotate, and then rely on the lower clamp to apply torque to the experimental bolt, simulating the fretting condition.

[0019] Compared with the prior art, the present application has the following beneficial effects: 1) The present application can simulate the fretting fatigue condition of the bolt in actual use by precisely controlling the fretting displacement and load of the bolt, realize quantitative analysis of the fatigue performance of the bolt, and thus more accurately predict the fatigue life of the bolt and improve the reliability and safety of the bolt design; 2) In order to fully simulate the actual working condition of the bolt, the upper clamp of the present application is provided with a rectangular cavity, so that the upper locking strip of the upper locking washer clamps the inside of the rectangular cavity, thereby fixing the upper locking washer and the nut, preventing the synchronous rotation of the upper locking washer and the nut when the lower clamp drives the experimental bolt to fret, and as much as possible simulating the stress of the experimental bolt in the actual working condition; and the lower clamp is provided with an L-shaped clamping groove, and the lower locking strip of the lower locking washer is in full contact (whether abutting or clamped into the L-shaped clamping groove) with the lower clamp, thereby ensuring the integration of the experimental bolt and the lower clamp, ensuring that the lower clamp can accurately transmit the fretting to the experimental bolt, and improving the precision of the fretting experiment. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the overall structure of the present application; Figure 2 is a schematic diagram of the structure of the upper and lower clamps clamping the experimental bolt; Figure 3 is an exploded view of Figure 2 ; Figure 4 is a schematic diagram of the structure of the turbine; The drawing comprises: 1, base, 101, servo motor, 102, worm, 2, turbine, 201, mounting hole, 202, thrust bearing, 203, fixing bolt, 204, recessed area, 3, lower clamp, 301, horizontal part, 302, vertical part, 4, experimental bolt, 401, nut, 402, upper locking washer, 403, upper locking strip, 404, lower locking washer, 405, lower locking strip, 5, upper clamp, 501, axial load applying rod, 502, through slot, 503, rectangular cavity. DETAILED DESCRIPTION

[0021] The technical solutions of the present application are further described in detail below in combination with specific embodiments. The parts not described in the following embodiments of the present application, such as the control of the servo motor, the cooperation of the worm and the turbine, how to apply the axial load and the axial load applying device, are all regarded as the prior art known or should be known by the person skilled in the art.

[0022] Embodiment 1 A bolted micro-oscillation fatigue test device, as shown in Figure 1 , Figure 2 and Figure 3 , comprises a base 1, a lower clamp 3 and an upper clamp 5 for clamping an experimental bolt 4. The base 1 is generally rectangular and can be used as an operation platform in practice. The top of the upper clamp 5 is provided with an axial load applying rod 501. The axial load applying rod 501 is connected with an axial load applying device during the experiment, so as to apply a pulling force to the upper clamp 5, and then make the experimental bolt 4 bear axial force, so as to simulate the actual working condition. The axial load applying device can adopt a lead screw, that is, the linear movement of the lead screw slider mechanism driven by a motor is used to apply a pulling force to the axial load applying rod 501, or the linear movement of a slider driven by a hydraulic pressure is used to apply a pulling force to the axial load applying rod 501. The base 1 is rotatably provided with a turbine 2 driven by a power source to rotate. The turbine 2 is vertically arranged and perpendicular to the surface of the base 1. As shown in Figure 4 , the center of the turbine 2 is provided with a mounting hole 201. A thrust bearing 202 is nested in the mounting hole 201, that is, the outer ring of the thrust bearing 202 is fixed with the mounting hole 201. A fixing screw 203 is arranged in the bearing inner ring of the thrust bearing 202 to fix the turbine 2 on the base 1. The free end of the fixing screw 203 has a threaded section, which is screwed with a bolt hole on the base 1 to fix the turbine 2. The turbine 2 is in meshing transmission with a worm 102, and the worm 102 is driven to rotate by a servo motor 101 arranged on the base 1. The upper surface of the turbine 2 has a recessed area 204. The lower clamp 3 is fixedly arranged in the recessed area 204, generally welded with the surface of the recessed area 204, so as to connect the lower clamp 3 and the turbine 2 into an integrated structure, and then make the lower clamp 3 and the turbine 2 fixed and synchronously rotate. The upper clamp 5 is a rectangular frame structure, which is formed by four plates connected end to end, one of which is a top wall, the plate opposite to it is a bottom wall, and the other two plates are side walls. The axial load applying rod 501 is on the top wall opposite to the through groove 502, and the axial line of the axial load applying rod 501 and the experimental bolt 4 is the same as the center of the turbine 2. The upper clamp 5 has a rectangular cavity 503, and the opposite two side walls of the rectangular cavity 503 form an opening, which is convenient for the experimental personnel to manually screw on the nut 401. More importantly, a flat side wall is formed on the inner wall, and the bottom wall of the rectangular cavity 503 has a through groove 502 extending to the center, that is, the length of the through groove 502 is half of the width of the bottom wall. The lower end of the experimental bolt 4 is fixedly connected with the lower clamp 3, the bolt body of the experimental bolt 4 passes through the through groove 502, and the top end of the experimental bolt 4 extends into the rectangular cavity 503 and is fixedly screwed by the nut 401 and the upper locking washer 402. The side wall of the upper locking washer 402 is symmetrically provided with an upper locking strip 403, the cross section of the upper locking strip 403 is rectangular, and the end face is flat, so that the end of the upper locking strip 403 is in close contact with the inner wall of the rectangular cavity 503, and the lower surface is in contact with the bottom wall of the rectangular cavity 503, so that the upper locking strip 403 and the inner wall of the rectangular cavity 503 form a welding contact effect.

[0023] The above is the basic embodiment of the present application, which can be further improved, optimized and limited on the basis of the above, so as to obtain the following embodiments: Embodiment 2 This embodiment is an improved scheme based on embodiment 1, and the main structure is the same as that of embodiment 1. The improvement lies in that: Figure 2 and Figure 3 As shown in the figure, the lower clamp 3 has two side walls arranged opposite to each other and fixedly connected with the upper surface of the turbine 2, and the top of the two side walls has a horizontal connecting part. The experimental bolt 4 passes through the bolt hole on the connecting part and is fixed with the upper clamp 5. In order to fully ensure that the micro motion can be transmitted from the turbine 2 to the experimental bolt 4, the experimental bolt 4 needs to be provided with a lower locking washer 404, and the lower locking washer 404 is relied on to realize the integral fixation with the connecting part under the action of the axial load. The setting mode of the lower locking washer 404 can be the following two kinds: The first kind is that the experimental bolt 4 has a lower locking washer 404 between the experimental bolt 4 and the connecting part, and the lower locking washer 404 is symmetrically provided with a lower locking strip 405 on both sides. The cross section of the lower locking strip 405 is rectangular, and the end face is flat. The two ends of the lower locking strip 405 are in close contact with the two side walls, and the lower surface is in contact with the lower surface of the connecting part, so that the lower locking strip 405 and the two side walls form a welding contact effect; The second is that the experimental bolt 4 is provided with a lower locking washer 404 between the connecting portion, and the lower locking washer 404 is symmetrically provided with a lower locking strip 405 on both sides, and the two sidewalls are provided with mirror-symmetrical L-shaped clamping grooves, and the lower locking strip 405 is clamped in the two L-shaped clamping grooves; The L-shaped clamping groove is formed by splicing a horizontal portion 301 and a vertical portion 302, one end of the horizontal portion 301 extends to the end of the sidewall, the other end communicates with the bottom end of the vertical portion 302, the top end of the vertical portion 302 is flush with the bottom surface of the connecting portion, and the end of the lower locking strip 405 enters the L-shaped clamping groove along the horizontal portion 301 and is clamped at the top end of the vertical portion 302 by the end of the experimental bolt 4.

[0024] Embodiment 3 A bolted micro-fatigue test method, which is carried out by using the micro-fatigue test device in Embodiment 1 or Embodiment 2, comprises the following steps: 1) The lower end of the experimental bolt 4 is fixedly connected with the lower clamp 3, the upper end is inserted into the rectangular cavity 503 through the through groove 502 of the upper clamp 5, and is fixedly screwed by the nut 401 and the upper locking washer 402; 2) The axial load applying rod 501 is used to apply axial load to the experimental bolt 4, so that the upper clamp 5 and the lower clamp 3 are tightened to simulate the normal working condition of the experimental bolt 4; 3) When the axial load reaches the set value, the power-driven turbine 2 is started to rotate, and then the lower clamp 3 is used to apply torque to the experimental bolt 4 to simulate the micro-motion condition.

Claims

1. A bolted micro-oscillation fatigue test device, comprising a base (1), a lower clamp (3) and an upper clamp (5) for clamping an experimental bolt (4), and an axial load applying rod (501) is arranged at the top of the upper clamp (5), characterized in that: The base (1) is rotatably provided with a turbine (2) driven by power, the lower clamp (3) is fixed and synchronously rotated with the turbine (2), the upper clamp (5) has a rectangular cavity (503) therein, and the bottom wall of the rectangular cavity (503) has a through slot (502) extending to the center thereof, one end of the experimental bolt (4) is fixedly connected with the lower clamp (3), the other end extends into the rectangular cavity (503) through the through slot (502), and is fixedly screwed by a nut (401) and an upper locking washer (402), and the side wall of the upper locking washer (402) is symmetrically provided with an upper locking strip (403), and the end of the upper locking strip (403) is abutted against the inner wall of the rectangular cavity (503).

2. A bolted micro fatigue test apparatus according to claim 1, wherein: The lower clamp (3) has two side walls oppositely arranged and fixedly connected with the turbine (2), and the top of the two side walls has a horizontal connecting portion, and the experimental bolt (4) is fixed with the upper clamp (5) after penetrating through the bolt hole on the connecting portion.

3. A bolted micro fatigue test apparatus according to claim 2, wherein: The experimental bolt (4) and the connecting portion have a lower locking washer (404), and the two sides of the lower locking washer (404) are symmetrically provided with lower locking strips (405), and the two ends of the lower locking strips (405) are abutted against the two side walls.

4. A bolted micro fatigue test apparatus according to claim 2, wherein: The experimental bolt (4) and the connecting portion have a lower locking washer (404), and the two sides of the lower locking washer (404) are symmetrically provided with lower locking strips (405), and the two side walls are provided with mirror-symmetric L-shaped clamping grooves, and the lower locking strips (405) are clamped in the two L-shaped clamping grooves.

5. A bolted micro fatigue test apparatus according to claim 4, wherein: The L-shaped clamping groove is formed by splicing a horizontal portion (301) and a vertical portion (302), one end of the horizontal portion (301) extends to the end of the side wall, the other end communicates with the bottom end of the vertical portion (302), the top end of the vertical portion (302) is flush with the bottom surface of the connecting portion, and the end of the lower locking strip (405) enters the L-shaped clamping groove along the horizontal portion (301) and is clamped at the top end of the vertical portion (302) by the end of the experimental bolt (4).

6. A bolted micro fatigue test apparatus according to claim 1, wherein: The center of the turbine (2) is provided with a mounting hole (201), and the mounting hole (201) is nested with a thrust bearing (202), and the bearing inner ring of the thrust bearing (202) is provided with a fixing bolt (203) for fixing the turbine (2) on the base (1).

7. A bolted micro fatigue test apparatus according to claim 1, wherein: The upper surface of the turbine (2) has a recessed area (204), and the lower clamp (3) is fixedly arranged in the recessed area (204).

8. A bolted micro fatigue test apparatus according to claim 1, wherein: The turbine (2) is engaged with a worm (102) for transmission, and the worm (102) is driven to rotate by a servo motor (101).

9. A bolted micro fatigue test apparatus according to claim 1, wherein: The upper clamp (5) is a rectangular frame structure, the axial load applying rod (501) is on the top wall opposite to the through slot (502), and the axial lines of the axial load applying rod (501) and the experimental bolt (4) are on the same vertical line with the center of the turbine (2).

10. A bolted micro- fatigue test method, characterized by: The micromovement fatigue test method is carried out by using the micromovement fatigue test device of any one of claims 1-9, and comprises the following steps: 1) The lower end of the experimental bolt (4) is fixedly connected with the lower clamp (3), the upper end is inserted into the rectangular cavity (503) through the through slot (502) of the upper clamp (5), and is fixedly screwed by the nut (401) and the upper locking washer (402); 2) The axial load is applied to the experimental bolt (4) through the axial load applying rod (501), so that the upper clamp (5) and the lower clamp (3) pull the experimental bolt (4) tightly, and the normal working condition of the experimental bolt (4) is simulated; 3) When the axial load reaches the set value, the power-driven turbine (2) is started to rotate, and then the lower clamp (3) applies torque to the experimental bolt (4), simulating the micro-motion working condition.

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