A micro-tribological test scheme for a tenon connection structure under blade vibration

Abstract

The application discloses a kind of mortise connection structure fretting wear test scheme under blade vibration carried out in laboratory environment, belong to vibration fatigue test design technical field.The application scheme is based on the most basic blade vibration test, introduce the assembly of mortise connection structure, mortise groove is fixed on the vibration table, blade is fixed in mortise groove by mortise connection structure, vibration table is excited as a whole, so that blade and mortise groove produce vibration, realize the test research to high cycle fatigue.Meanwhile, using the method of theoretical calculation and numerical simulation, the natural frequency of blade and each order modal and the average contact stress of mortise head mortise groove contact surface are calculated, so as to determine the test load.Through the application scheme, fretting wear change under different excitation frequencies and mortise connection clamping degree can be studied, which has good application significance and test value.

Description

Technical Field

[0001] This invention belongs to the field of vibration fatigue test design technology, and relates to a fretting wear test method for tenon connection structure under blade vibration state. With this test device, fretting wear and crack propagation tests of tenon surface under high cyclic vibration load excitation can be carried out. Background Technology

[0002] The tenon joint is the most common connection method between aero-engine blades and rotors. Its main sources of wear are twofold: low-cyclic load and high-cyclic load. Low-cyclic load is primarily related to the influence of centrifugal force. When the rotor rotates, the blade slides relative to the tenon under the action of centrifugal force, significantly increasing the contact stress between them and leading to low-cyclic fatigue. High-cyclic load is mainly caused by blade vibration due to gas flow across the blade surface, resulting in fretting between the tenon and tenon, thus leading to high-cyclic fatigue. Fretting refers to a relatively small sliding amplitude relative motion occurring between the surfaces of two approximately tightly fitted contacting objects. The presence of fretting effect results in a large stress gradient and stress concentration at the edge of the contact area between the two components. When the contact stress is low, the wear caused by fretting has a significant impact on the fatigue life of the component.

[0003] In existing fatigue testing protocols, low-cycle fatigue tests and high-cycle fatigue tests are often conducted separately to simplify the load application device and to investigate the effects of both. While low-cycle fatigue tests have been extensively studied due to their simpler loading methods, high-cycle fatigue tests have received less attention. The fretting wear testing device described in this invention is designed for fatigue testing of tenon joint structures under high-cycle loads. It utilizes real blades and tenon structures, applying an excitation force to induce blade vibration, and observing the fretting characteristics of the tenon joint structure and the fretting wear on the tenon surface. Furthermore, the magnitude of the excitation force and the clamping degree of the tenon joint structure can be adjusted, allowing for fretting wear tests under various load conditions to simulate the real operating conditions of an engine. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a fretting wear test method considering the tenon connection structure under blade vibration conditions. A novel vibration testing device is used, where the tenon groove is fixed to a vibration table, and the blade is fixed within the tenon groove via the tenon connection structure. The entire vibration table is excited, causing the blade and tenon groove to vibrate, thus enabling experimental research on high-cyclic fatigue.

[0005] The specific steps of the fretting wear test scheme for the tenon connection structure under blade vibration according to the present invention are as follows:

[0006] Step 1: Establish a three-dimensional geometric model of the test blade.

[0007] Step 2: Use commercial finite element software to perform modal analysis on the test blade structure and obtain the natural frequencies of each order of the test blade.

[0008] Step 3: Use commercial finite element software to perform an overall static analysis of the test device to determine the magnitude of the surface contact stress corresponding to different rotational speeds of the test blade.

[0009] Step 4: Apply preload to the mortise and tenon, and change the clamping state between the tenon and the mortise by adjusting the magnitude of the preload. The stress distribution on the tenon surface under different bolt preloads can be numerically calculated using the finite element method, and the average normal stress on the tenon surface, i.e., the average surface contact stress between the tenon and the mortise and tenon, can also be obtained.

[0010] Step 5: Determine the frequency of the test excitation force and the magnitude of the tenon clamping load.

[0011] Based on the blade vibration characteristics, the frequency of the test excitation force is determined. Simultaneously, combining the theoretical calculation results of the average surface contact stress between the tenon and mortise obtained in step 4, the average surface contact stress between the tenon and mortise is determined by adjusting the preload and using finite element numerical calculations. This ensures that the average surface contact stress between the tenon and mortise in the test is equal to the average surface contact stress at the required blade speed obtained in step 3. At this point, the bolt preload is the preload applied in the test.

[0012] Step 6: Conduct blade vibration tests;

[0013] By keeping the frequency and magnitude of the excitation force constant, the fretting wear of the tenon connection structure under different clamping states was studied; by keeping the clamping degree of the tenon connection structure constant, the fretting wear under different excitation force frequencies was studied.

[0014] The advantages of this invention are:

[0015] 1. This invention proposes a test scheme for high-cyclic fatigue of blades in a laboratory environment. By building a vibration test bench, the blade is made to vibrate at its natural frequency to explore the effects of different clamping degrees of tenon connection structures and blade excitation frequency on high-cyclic wear and fatigue of the tenon.

[0016] 2. In the blade vibration test proposed in this invention, the clamping degree of the tenon connection structure is adjusted by controlling the preload of the bolts, and bolt safety, thread sealant and double-layer self-locking washers are used to ensure that the bolts do not loosen during the vibration test;

[0017] 3. In the blade vibration test proposed in this invention, a unique bolt loosening monitoring device is designed to monitor in real time whether the bolts have become loose during the vibration test. The methods include: blade tip displacement laser sensor method, adhesive strain gauge method and washer scribing method. Attached Figure Description

[0018] Figure 1 The figure shows the numerical calculation results of the first mode of a certain blade test specimen.

[0019] Figure 2 The figure shows the numerical calculation results of the second mode of a certain blade test specimen.

[0020] Figure 3 The figure shows the numerical calculation results of the third mode of a certain blade test specimen.

[0021] Figure 4 This is a three-dimensional model of the blade vibration test platform.

[0022] Figure 5 This is a schematic diagram of the working principle of the blade vibration test platform.

[0023] Figure 6 Schematic diagram of the contact edge of the tenon and mortise.

[0024] Figure 7 Schematic diagram of the slight movement phenomenon at the contact edge of the tenon and mortise.

[0025] In the picture:

[0026] 1-Fan blade test piece; 2-Tongue and tenon clamp; 3-Clamping frame

[0027] 4-Place block 5-Preload bolt 6-Locking washer

[0028] 7-Laser displacement sensor 101-Tenon 201-Clamp body

[0029] 202-Tongue and Groove Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings.

[0031] The present invention provides a test scheme for fretting wear of tenon joint structure under blade vibration. First, the test excitation force frequency and the magnitude of the tenon clamping load are determined by the test load application scheme. Then, a test platform is built based on the scheme to realize the fretting wear test of tenon joint structure under blade vibration.

[0032] The method for determining the test load is as follows:

[0033] Step 1: Establish a three-dimensional geometric model of the test blade.

[0034] If you already have a blade prototype and 3D geometric model file used in actual engineering, you can directly use them for subsequent steps to conduct blade vibration tests and study the vibration characteristics of the structure. Otherwise, when designing and modeling the test blade structure, the aspect ratio of the blade should be appropriately increased. Increasing the aspect ratio will increase the amplitude of the blade in the vibration test, making it easier to generate fretting and wear at the tenon joint, which helps to obtain better test results.

[0035] Step 2: Perform modal analysis on the blade structure using commercial finite element software.

[0036] If the frequency of the excitation force equals the frequency of a certain mode shape of the blade, the blade will resonate. The wear and damage to the tenon joint structure are greatest under resonant conditions. Therefore, in vibration tests, to obtain better test results, the frequency of the applied blade excitation force should be selected near its natural frequency. Numerical simulation can be used to conveniently and accurately obtain each natural frequency of the blade (generally, obtaining the first five frequencies is sufficient). The specific method is as follows:

[0037] The three-dimensional geometric model of the blade established in step 1 was imported into commercial finite element analysis software. Boundary conditions identical to those in the actual experiment were set at the tenon of the blade prototype. A frequency analysis step was then inserted to perform numerical calculations on the first five modes of the blade. Taking a specific blade prototype as an example, the calculated results are as follows: Figures 1-3 These are displacement deformation contour maps at the first three natural frequencies. Based on the calculation results, the first five natural frequencies and their corresponding mode shapes can be obtained.

[0038] Step 3: Perform an overall static analysis of the test setup using commercial finite element software.

[0039] The idle speed of aero-engine fan blades is typically about 20%-30% of their maximum speed. The clamping tightness of the tenon joint decreases as the speed decreases, especially at idle. The reduced centrifugal force of the blades makes it easier for relative micro-slippage to occur between the tenon and the mortise, resulting in wear caused by micro-movement.

[0040] Currently, there is no good method to apply rotational speed to experiments in a laboratory setting. Instead, a certain clamping force is applied to simulate the clamping degree of the mortise and tenon joint. The clamping degree of the mortise and tenon joint can be characterized by the average surface contact stress between the tenon and the mortise; that is, the greater the contact stress, the greater the clamping degree. An approximate value of the average surface contact stress between the tenon and the mortise is obtained through theoretical calculations:

[0041]

[0042] in, Let ρ be the average surface contact stress between the tenon and the mortise, ρ be the material density, and V be the blade volume. Let ω be the volume ratio of the tenon, R be the blade rotational speed, S be the distance from the blade's center of mass to the engine shaft, μ be the contact area between the tenon and mortise, μ be the coefficient of friction, and θ be the tenon angle. Based on this, the magnitude of the surface contact stress corresponding to different blade rotational speeds can be obtained.

[0043] Step 4: Using five M14 bolts, apply preload to the mortise through the bolts and the outer frame components. Adjust the bolt preload to change the clamping state of the tenon and mortise. Based on this, the stress distribution on the tenon surface under different bolt preloads can be numerically calculated using the finite element method. Simultaneously, the average normal stress on the tenon surface, i.e., the average surface contact stress between the tenon and the mortise, can be obtained.

[0044] Step 5: Determine the frequency of the test excitation force and the magnitude of the tenon clamping load.

[0045] Based on the blade vibration characteristics, the test excitation force frequencies were selected to correspond to the blade natural frequencies of the first bend and the second bend, respectively. If more vibration tests are required at different frequencies, the third bend and the first torsion can be further selected.

[0046] Combining the theoretical calculation results of the average surface contact stress between the tenon and the mortise obtained in step 4, the average surface contact stress between the tenon and the mortise is determined by adjusting the bolt preload and using finite element numerical calculation. This ensures that the average surface contact stress between the tenon and the mortise in the experiment is equal to the average surface contact stress between the tenon and the mortise at the required blade speeds obtained through theoretical calculation in step 3. At this point, the bolt preload is the preload applied in the experiment.

[0047] Step 6: Conduct blade vibration tests;

[0048] By keeping the frequency and magnitude of the excitation force constant, the fretting wear of the tenon connection structure under different clamping states was studied; by keeping the clamping degree of the tenon connection structure constant, the fretting wear under different excitation force frequencies was studied.

[0049] In step 4 above, the method for applying the tenon clamping load during the blade vibration test is achieved using a vibration testing device, such as... Figure 4 , Figure 5 As shown, specifically:

[0050] The vibration testing equipment includes a fan blade test piece 1, a tenon and groove fixture 2, a clamping frame 3, a pad 4, a preload bolt 5, a locking washer 6, and a laser displacement sensor 7.

[0051] The tenon and groove clamp 2 includes a clamp body 201 with a rectangular cross-section. The bottom of the clamp body 201 is a disc structure with screw holes around its circumference. It is fixedly installed on the vibration test bench by bolts engaging with the screw holes. A tenon 202 is formed along the longitudinal direction in the middle of the top surface of the clamp body 201. The tenon 101 of the fan blade test piece 1 is placed in the tenon 202 from one side, and the bottom of the tenon 101 contacts the bottom of the tenon 102 through the pad 4. The contact surfaces of the tenon 101 on both sides of the tenon 202 are respectively fitted with the inner wall surfaces on both sides of the opening of the tenon 202, realizing the tenon joint positioning between the tenon 201 and the tenon 202, and is fixed by clamping the outer frame 3.

[0052] The outer frame clamp 3 is a rectangular frame structure, with a length equal to that of the clamp body 201, and is fitted onto the outside of the clamp body 201. Five screw holes are evenly spaced along the length of the left side of the outer frame clamp 3, with the axis of the screw holes running left-right. Pre-tightening bolts 5 are connected to the internal threads of the screw holes. By tightening the pre-tightening bolts 5, the clamp body 201 is tightened, and the clamp body 201 clamps the blade test piece 1. The clamping force can be adjusted by adjusting the tightness of the pre-tightening bolts 5. A locking washer 6 is fitted onto the pre-tightening bolt 5, located between the nut of the pre-tightening bolt 5 and the outer frame clamp 3; after the pre-tightening bolt 5 is tightened, the locking washer 6 prevents the pre-tightening bolt 5 from loosening during the test.

[0053] The process of building the test platform for the fretting wear test of the tenon connection structure under blade vibration using the above scheme is as follows:

[0054] Step A: Assemble the tenon and groove fixture 2, pad 4, clamping frame 3, fan blade test piece 1, pre-tightening bolt 5 and locking washer 6 on the vibration test bench according to the above structure.

[0055] First, the fixture body 201 is fixed to the vibration test bench using screws connected through the circumferential connecting holes on the bottom disc of the fixture body 201. Next, the tenon 101 of the fan blade test piece 1 and the pad 4 below the tenon 101 are inserted into the tenon 202 from the side of the fixture body 201 along the tenon 202 direction. After assembly, bolts are used to apply preload to the side of the tenon 202 through the clamping frame 3, clamping the tenon fixture 2. The magnitude of the preload is adjusted using a torque wrench to control the contact stress on the contact surface of the tenon connection structure, thereby simulating the clamping state of the tenon connection structure at different speeds. To reduce stress and wear on the contact surface between the pad 4 and the fixture body 201, lubricant is applied appropriately to the contact surfaces of the pad 4, the tenon 202, and the tenon 201. The edges of the contact surfaces are rounded, and rounding is also applied to other key parts of the fixture body 201, such as the bottom of the tenon 202.

[0056] Step B: Install the fastening device to prevent the pre-tightening bolt 5 from loosening during the prevention test.

[0057] During vibration testing, if the preload bolt 5 loosens, causing a decrease in preload, the fan blade test piece 1 will not achieve the required clamping state of the tenon 202, resulting in inaccurate test results. Therefore, a fastening device should be installed to ensure that the preload bolt 5 does not loosen. The aforementioned fastening devices mainly come in three forms: bolt safety, threadlocker, and double-layer self-locking washers.

[0058] The installation method for the bolt safety device is as follows:

[0059] Small holes are drilled in the nuts of the five pre-tightening bolts 5. A thin fuse wire, twisted in double strands into a braid, is used to connect the five pre-tightening bolts together in a 3+2 group. The fuse wire is generally made of low-carbon steel wire. When any of the pre-tightening bolts 5 shows signs of loosening, it will be restrained by the fuse wire and stop from loosening further. When using a fuse wire as an anti-loosening measure, the following basic rules should be followed:

[0060] (1) A new fuse must be used for each test group;

[0061] (2) The fuse should be wound in the same direction as the tightening of the preload bolt 5;

[0062] (3) When installing a fuse, always pay attention to maintaining a moderate tension to prevent it from breaking during vibration, but do not overtighten it;

[0063] (4) The braids should be tight and even, and the braids between the safety sections should be moderately taut, without leaving any excess braids;

[0064] (5) When securing the 5 heads of the pre-tightening bolt, ensure that the braid is wrapped around the bolt head to prevent the fuse from loosening;

[0065] (6) After securing the braid, leave about 3 to 6 braids at the end of the braid and bend or press the end of the braid underneath to prevent it from coming loose on its own.

[0066] In addition to the aforementioned fuse tightening, using threadlocker and double-layer self-locking washers are also effective methods to prevent the pre-tightened bolt 5 from loosening, and these two methods are also simpler to operate. The threadlocker method involves applying the threadlocker to the bolt hole, then screwing in the bolt. After reaching the preset pre-tightening force, let it stand for about two hours until the threadlocker hardens before conducting the test. The double-layer self-locking washer method involves replacing the original washer with a double-layer self-locking washer. The two self-locking washers have teeth or ridges on their surfaces. When tightened, the two washers begin to compress under pressure, causing friction between them and resisting any rotational force acting on them.

[0067] Step C: Install the loosening monitoring device for pre-tightening bolt 5.

[0068] After installing the pre-tightening bolt 5 fastening device before the start of the test, it is also necessary to install a pre-tightening bolt 5 loosening monitoring device. Its main purpose is to monitor in real time whether the pre-tightening bolt 5 will loosen during the vibration test. The following three methods are mainly adopted: laser sensor method, washer scribing method, and strain gauge bonding method.

[0069] The laser displacement sensor 7 features non-contact measurement, high precision, high resolution, and fast response, enabling accurate measurement of an object's position or displacement. The laser displacement sensor 7 is mounted next to the vibration test bench, at the same height as the blade tip, to measure the displacement changes of the blade tip in real time during the vibration test. With the pre-tightening bolt 5 in place, the peak and trough values ​​of displacement within each cycle should vary within a small range without significant abrupt changes. Therefore, if a significant change in the peak and trough values ​​of displacement is detected during the test, it indicates that the experimental setup has become loose, and the test should be stopped immediately for equipment inspection.

[0070] In addition, the washer marking method and strain gauge method are relatively convenient methods. The main principle of the washer marking method is to use a marker to draw a straight line along the axis of the preload bolt 5 on each set of washers, the nut of the preload bolt 5, and the fixture after tightening the preload bolt 5. If the preload bolt 5 loosens during the vibration test, the marked line will be misaligned, such as... Figure 4 As shown.

[0071] The strain gauge method involves pre-attaching strain gauges to the tenon clamp 2 or tenon 101, then tightening the preload bolt 5 to induce strain in the structure, and recording the strain gauge values ​​at this point. During the test, if the preload bolt 5 loosens and fails to provide the preset preload force, the strain of the tenon clamp 2 or tenon 101 will decrease, resulting in a lower strain gauge value. This allows for direct monitoring of the loosening of the test setup.

[0072] Step D: Conduct vibration tests according to the existing test load scheme, and use video equipment to record the contact surface between the tenon 101 and the mortise 202 during the test.

[0073] After the aforementioned test platform was constructed, blade vibration tests were conducted. Vibration excitation could be achieved using either tip excitation or vibration table vibration, both of which can induce blade vibration. The purpose of this experiment was to investigate the effect of high cyclic loads on fretting wear in tenon joint structures. During the experiment, the fretting phenomenon between the contact surfaces of the tenon 101 and the mortise 202 was observed and recorded. Figure 6The diagram shows the edge of the contact area between the tenon 101 and the mortise 202. To more intuitively illustrate the micro-motion phenomenon, a mesh was created, with each element being an 8μm × 8μm square. When the blade vibration displacement is zero, nodes 1 and 2 in the diagram are perfectly aligned at the edge of the contact area. When the blade vibration displacement is at its maximum, the relative displacement between nodes 1 and 2 also reaches its maximum value, indicating micro-slippage. Figure 7 As shown. During the experiment, professional video equipment was used to record the micro-movement state and crack initiation process between the contact surfaces of the tenon 101 and the mortise 202, which helps to further understand and analyze the micro-movement phenomenon.

[0074] Example

[0075] The existing fan blade test specimen and tenon-groove fixture components for blade vibration testing have been determined in terms of model dimensions and test scheme. The model material is TC4. Under the action of bolt preload, the blade tenon and the tenon-groove fixture come into contact, and fretting wear occurs in the contact edge area of ​​the tenon and tenon.

[0076] Based on the test load design method, modal and static analyses were performed on the fan blades. The excitation frequency and bolt preload magnitude were determined based on the numerical calculation results. All test equipment was installed according to the test platform construction method.

[0077] (1) Modal analysis of the fan blade. The geometric model of the fan blade was imported into ABAQUS for finite element analysis. According to the experimental conditions, normal displacement constraints on the two contact surfaces of the tenon and axial displacement constraints on the end face of the tenon were set. The first five natural frequencies of the blade were calculated, and the results are shown in Table 1.

[0078] Table 1. First five natural frequencies of fan blades

[0079]

[0080] (2) Static analysis of the test setup. A general finite element method (FEM) was used to perform a static analysis of the test setup. Different preloads were applied to the bolt holes, and the average contact compressive stress on the tenon surface under different preloads was calculated. Simultaneously, the actual operating speed of the fan blades was 8000 r / min. Combining the relevant parameters of blade volume, rotation radius, tenon volume, and surface area, the average contact compressive stress on the tenon surface at different speeds could be calculated. Comparing the experimental results with actual operating conditions, the relationship between preload and rotation speed under different average contact compressive stresses on the tenon surface can be obtained, as shown in Table 2.

[0081] Table 2. Relationship between preload and rotation speed

[0082]

[0083] (3) Determination of test load. Because the fan blade test pieces made of TC4 material are difficult to process and have high costs, a total of 6 sets of blade test pieces were processed and produced for this test. Based on the calculated blade frequency and the relationship between preload and rotational speed, the test plan is shown in Table 3. In the vibration test, the lower the frequency of the excitation force, the larger the amplitude. Therefore, the first two natural frequencies of the blade test piece were selected for the frequency. The selection of preload simulated the clamping degree of the tenon connection structure at 100%, 72%, and 36% of the maximum rotational speed.

[0084] Based on this test plan, a fretting wear test of blade vibration was carried out. By comparing the test results of test pieces FW-1, FW-2, and FW-3, the influence of different clamping degrees on the fretting wear of the tenon under the same excitation frequency can be analyzed. By comparing test pieces FW-1 and FW-4, the influence of different excitation frequencies on the fretting wear of the tenon under the same clamping degree can be analyzed.

[0085] Table 3 Experimental Scheme

[0086]

[0087]

[0088] (4) Test platform construction. The test platform was constructed according to the test platform construction scheme proposed in this invention, and the tests were carried out in sequence according to the test scheme in Table 3.

[0089] (5) Fretting wear test. Record the test phenomena and the number of cycles. After the test is completed, retain the test piece and conduct further analysis and research on the surface condition, crack initiation, etc.

[0090] In summary, this invention presents a laboratory-based test scheme for fretting wear of tenon joint structures under blade vibration. This scheme, based on fundamental blade vibration testing, introduces the assembly of tenon joint structures. According to the test load determination and test equipment setup methods described in this invention, it is possible to conduct research on fretting wear of the tenon and mortise contact surfaces under high cyclic vibration loads, demonstrating significant application and experimental value. In the application example, this invention provides a demonstration case of a fan blade test piece of a certain model. Based on the test load determination and test equipment setup methods provided by this invention, the test scheme was established.

Claims

1. A method for testing the fretting wear of a tenon connection structure under blade vibration, characterized in that: The specific steps are as follows: Step 1: Establish a three-dimensional geometric model of the test blade; Step 2: Use commercial finite element software to perform modal analysis on the test blade structure and obtain the natural frequencies of each order of the test blade; Step 3: Use commercial finite element software to perform an overall static analysis of the test device to determine the magnitude of the surface contact stress corresponding to different rotational speeds of the test blade; Step 4: Apply preload to the tenon and change the clamping state between the tenon and the tenon by adjusting the magnitude of the preload; the stress distribution on the tenon surface under different bolt preloads can be numerically calculated using the finite element method, and the average normal stress on the tenon surface, i.e. the average contact stress between the tenon and the tenon, can also be obtained. Step 5: Determine the frequency of the test excitation force and the magnitude of the tenon clamping load; Based on the blade vibration characteristics, the frequency of the test excitation force is determined. At the same time, combined with the theoretical calculation results of the average surface contact stress between the tenon and the mortise obtained in step 4, the average surface contact stress between the tenon and the mortise is determined by adjusting the preload and using finite element numerical calculation, so that the average surface contact stress between the tenon and the mortise in the test is equal to the average surface contact stress between the tenon and the mortise at the required blade speed obtained in step 3. At this time, the bolt preload is the preload applied in the test. Step 6: Conduct blade vibration tests; By keeping the frequency and magnitude of the excitation force constant, the fretting wear of the tenon connection structure under different clamping states was studied; by keeping the clamping degree of the tenon connection structure constant, the fretting wear under different excitation force frequencies was studied.

2. The method for testing the fretting wear of a tenon connection structure under blade vibration as described in claim 1, characterized in that: The application of the tenon clamping load in step 4 is achieved using the following structural vibration testing equipment; Vibration testing equipment includes fan blade test pieces, tenon and groove fixtures, clamping frames, and pre-tightening bolts; The tenon and groove clamp has an opening for connecting to the vibration test bench; the tenon and groove clamp is designed to mortise and tenon with the tenon of the fan blade test piece. The clamping frame is fitted onto the outside of the tenon groove. Screw holes are designed at equal intervals along the tenon groove direction on one side of the outer frame clamp. Pre-tightening bolts are connected to the threads inside the screw holes. By tightening the pre-tightening bolts, the pre-tightening bolts press against the main body of the clamp to clamp the blade test piece. The clamping force can be adjusted by adjusting the tightness of the pre-tightening bolts.

3. The method for testing the fretting wear of a tenon connection structure under blade vibration as described in claim 2, characterized in that: The tenon of the fan blade test piece is placed in the mortise from one side. The bottom of the tenon contacts the bottom of the mortise through a pad. The contact surfaces of the mortise on both sides of the tenon are respectively fitted with the inner wall surfaces on both sides of the mortise opening, so as to achieve the tenon joint positioning between the tenon and the mortise.

4. The method for testing the fretting wear of a tenon connection structure under blade vibration as described in claim 2, characterized in that: A locking washer is fitted on the pre-tightening bolt, located between the nut of the pre-tightening bolt and the outer frame clamp.

5. The method for testing the fretting wear of a tenon connection structure under blade vibration as described in claim 2, characterized in that: Design methods to prevent loosening of pre-tightened bolts, such as designing bolt safety features or using thread-locking adhesive or double-layered self-locking washers; The bolt safety and anti-loosening method is as follows: a small hole is made in the nut of the pre-tightening bolt, and a thin safety wire is used to connect the pre-tightening bolts in groups by twisting the two strands into a braid. The method for using threadlocker to prevent loosening is as follows: Apply threadlocker to the inside of the bolt hole, then screw in the bolt. After reaching the preset preload, let it stand for about two hours. The method for preventing loosening with double-layer self-locking washers is as follows: install double-layer self-locking washers on the pre-tightening bolt, located between the nut and the bolt; the double-layer self-locking washers consist of two self-locking washers stacked together.

6. The method for testing the fretting wear of a tenon connection structure under blade vibration as described in claim 2, characterized in that: Design a method for monitoring the loosening of pre-tightened bolts, and adopt the laser sensor method, the washer scribing method, or the adhesive strain gauge method; Among them, the laser sensor method involves setting up a laser displacement sensor on one side of the vibration test equipment at the same height as the blade tip. During the vibration test, the displacement change of the blade tip is measured in real time. If a significant change in the peak and valley values ​​of the displacement is detected, it indicates that the pre-tightening bolt has loosened. The washer marking method is as follows: After the pre-tightening bolt is tightened, draw a straight line along the radial direction of the pre-tightening bolt on each set of washers, the nut of the pre-tightening bolt, and the clamp; if the three lines deviate, it indicates that the pre-tightening bolt has become loose. The strain gauge method involves attaching strain gauges to the tenon or tenon beforehand, then tightening the preload bolts to induce strain in the structure, and recording the strain gauge values ​​at this point. If the strain of the tenon or tenon decreases, it indicates that the preload bolts have loosened.

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