Experimental Verification Method for the Repair-Free Limit of Crack-Type Damage at the Leading and Trailing Edges of Blades

Abstract

The present disclosure provides a test verification method for the repair-free limit of crack-type damage at the leading and trailing edges of blades, including: determining the theoretical repair-free limit; providing a plurality of blade simulation parts, respectively introducing initial cracks with different lengths at different blade heights at the leading and trailing edges of the plurality of blade simulation parts to simulate crack-type damage; performing vibration fatigue tests on the first three natural frequencies of the plurality of blade simulation parts, and monitoring the stress levels of preset reference points on the blade simulation parts; if cracks appear on the blade simulation parts or there is an amplitude drop greater than the set range, and the fatigue cycle is less than the preset number of times, then record the fatigue cycle; if no cracks appear on the blade simulation parts or no amplitude drop greater than the set range appears, and the fatigue cycle is greater than the preset number of times, then it is considered that the damage is repair-free; comparing the determined test repair-free limit with the theoretical repair-free limit, if the absolute value of the difference between the test repair-free limit and the theoretical repair-free limit is within the preset range of the theoretical repair-free limit, then it is determined that the determined theoretical repair-free limit is reasonable.

Description

Technical Field

[0001] The present disclosure relates to the technical field of engine blades, and in particular, to a test verification method for the repair-free limit of crack-type damage at the leading and trailing edges of blades. Background Technique

[0002] When an aircraft takes off, lands, or flies at low altitude, its engine may inhale hard objects such as gravel, grit, and metal (such as small nuts, bolts, etc.), causing high-speed hard object impacts. High-speed hard object impacts can cause various damages to the blades, such as dents, pits, notches, tears, and local curling, etc. These damages will reduce the working life of the blades, affect flight safety, increase the maintenance cost, and even cause huge economic losses.

[0003] Regarding the problem of hard object damage to the blades, although the engine is designed to enable the blades to have a certain hard object damage tolerance ability, it is also necessary to provide a maintenance manual for the blades with hard object damage to the user in the later stage of engine development to provide necessary reference for the user when maintaining the engine blades. For example, after the blades are damaged by hard objects, how to determine whether the blades can be used without repair.

[0004] It should be noted that the information disclosed in the above background technique section is only used to enhance the understanding of the background of the present disclosure, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0005] The purpose of the embodiments of the present disclosure is to provide a test verification method for the repair-free limit of crack-type damage at the leading and trailing edges of blades, which is used to verify the theoretical repair-free limit of hard object damage to the blades.

[0006] Other characteristics and advantages of the present disclosure will become apparent through the following detailed description, or will be learned in part through the practice of the present disclosure.

[0007] According to one aspect of the embodiments of the present disclosure, a test verification method for the repair-free limit of crack-type damage at the leading and trailing edges of blades is provided, including:

[0008] Determine the theoretical repair-free limit;

[0009] Provide a plurality of blade simulation parts, and introduce initial cracks with different lengths at different blade heights at the leading and trailing edges of the plurality of blade simulation parts respectively to simulate crack-type damage. The length value range of different initial cracks is determined according to the theoretical repair-free limit at the corresponding height of the blade;

[0010] Determine the first three natural frequencies of the blade simulation parts;

[0011] Vibrate and fatigue test multiple of the blade simulation components at their first three natural frequencies, monitor the stress level of a preset reference point on the blade simulation component, and control the excitation acceleration to make the stress at the preset reference point reach a preset stress level; meanwhile, monitor whether cracks appear at the tip of the blade simulation component or whether the amplitude drops by more than a set range.

[0012] If cracks appear on the blade simulation component or the amplitude drops by more than a set range, and the fatigue cycle count is less than a preset number, record the fatigue cycle count; if no cracks appear on the blade simulation component or the amplitude does not drop by more than a set range, and the fatigue cycle count is greater than a preset number, consider the damage of the blade simulation component to be repairable.

[0013] Compare the determined test repairable limit with the theoretical repairable limit. If the absolute value of the difference between the test repairable limit and the theoretical repairable limit is within the preset range of the theoretical repairable limit, determine that the determined theoretical repairable limit is reasonable.

[0014] In an embodiment of the present disclosure, introducing initial cracks of different lengths at different blade heights on the front and rear edges of multiple blade simulation components to simulate crack-type damage includes:

[0015] Process crack-type damage with a depth of a at heights h = 2%H, 5%H, 10%H, 20%H, 50%H, and 90%H on the front edge and the rear edge of the blade body of the blade simulation component respectively. The range of values of a is determined according to the theoretical repairable limit at the corresponding height of the blade and takes multiple values.

[0016] In an embodiment of the present disclosure, the theoretical repairable limit at the corresponding height of the blade is within the range of values of the processing depth a.

[0017] In an embodiment of the present disclosure, when at 90%H of the front edge, the calculated theoretical repairable limit is 4.6 mm, the crack depth a in the blade simulation component can take values of 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, and 5.0 mm.

[0018] In an embodiment of the present disclosure, process multiple test pieces for each crack depth.

[0019] In an embodiment of the present disclosure, determining the first three natural frequencies of the blade simulation component includes:

[0020] Start the vibration table to sweep the frequency within the range of the first three simulation modal frequencies of the blade simulation component, observe the data collected by the strain gauges and displacement sensors until the data reflects that the first three modal frequencies of the blade simulation component are stable, stop further tightening the axial fastening bolts and circumferential fastening bolts, and record the torque wrench value and the first three modal frequency values of the blade at this time.

[0021] In one embodiment of the present disclosure, vibration fatigue tests are performed on the blade simulation components in their first three natural modes, and when applying boundary loading, it is ensured that the axial fastening bolts have the same torque.

[0022] In one embodiment of the present disclosure, the preset number of cycles is 8 million - 12 million cycles.

[0023] In one embodiment of the present disclosure, the preset range is 5% - 20%.

[0024] In one embodiment of the present disclosure, if the absolute value of the difference between the experimental repair exemption limit and the theoretical repair exemption limit is not within the preset range of the theoretical repair exemption limit, it is determined that the determined theoretical repair exemption limit is unreasonable.

[0025] The experimental verification method for the repair exemption limit of the leading and trailing edge crack - type damage of the blades provided by the present disclosure is as follows: First, determine the theoretical repair exemption limit of the leading and trailing edge crack - type damage of the blade model; then provide multiple blade simulation components, and introduce initial cracks with different lengths at different blade heights on the leading and trailing edges of the multiple blade simulation components to simulate crack - type damage. The value range of the lengths of different initial cracks is determined according to the theoretical repair exemption limit at the corresponding blade height; then determine the first three natural frequencies of the blade simulation components; then perform vibration fatigue tests on the multiple blade simulation components at their first three natural frequencies, monitor the stress level at a preset reference point on the blade simulation components, and control the excitation acceleration to make the stress at the preset reference point reach the preset stress level; at the same time, monitor whether cracks appear at the blade tip of the blade simulation components or whether there is an obvious amplitude drop; if cracks appear at the blade simulation components or there is an obvious amplitude drop, and the fatigue cycle count is less than the preset number of cycles, record the fatigue cycle count; if no cracks appear at the blade simulation components or there is no obvious amplitude drop, and the fatigue cycle count is greater than the preset number of cycles, it is considered that the damage of the blade simulation components is repair - exempt; finally, compare the determined experimental repair exemption limit with the theoretical repair exemption limit. If the absolute value of the difference between the experimental repair exemption limit and the theoretical repair exemption limit is within the preset range of the theoretical repair exemption limit, it is determined that the determined theoretical repair exemption limit is reasonable.

[0026] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present disclosure, and are used together with the specification to explain the principles of the present disclosure. Obviously, the following - described drawings are only some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. In the drawings:

[0028] Figure 1Flowchart of a test verification method for the repair-free limit of crack-type damage at the leading and trailing edges of a blade provided by an embodiment of the present disclosure;

[0029] Figure 2 Schematic diagram of a blade provided by an embodiment of the present disclosure;

[0030] Figure 3 Schematic diagram of the result of calculating the repair-free limit of the leading and trailing edges of a blade model by using finite element provided by an embodiment of the present disclosure;

[0031] Figure 4 Schematic diagram of a blade simulation provided by an embodiment of the present disclosure;

[0032] Figure 5 Schematic diagram of a blade simulation installed on a test bench provided by an embodiment of the present disclosure. Detailed implementation manners

[0033] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art.

[0034] In addition, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of the embodiments of the present disclosure. However, those skilled in the art will realize that the technical solutions of the present disclosure can be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. can be adopted. In other cases, well-known methods, devices, implementations, or operations are not shown or described in detail to avoid obscuring aspects of the present disclosure.

[0035] The block diagrams shown in the accompanying drawings are only functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0036] The flowcharts shown in the accompanying drawings are only illustrative and do not necessarily include all the contents and operations / steps, nor do they necessarily need to be executed in the described order. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to the actual situation.

[0037] Embodiments of the present disclosure provide a test verification method for the repair-free limit of crack-type damage at the leading and trailing edges of a blade, asFigure 1 As shown in the figure, the test verification method includes:

[0038] Step S100: Determine the theoretical repair-free limit;

[0039] Step S200: Provide multiple blade simulation parts, and introduce initial cracks with different lengths at different blade heights on the leading and trailing edges of the multiple blade simulation parts to simulate crack-type damage. The value range of the lengths of different initial cracks is determined according to the theoretical repair-free limit at the corresponding height of the blade;

[0040] Step S300: Determine the first three natural frequencies of the blade simulation parts;

[0041] Step S400: Conduct vibration fatigue tests on the first three natural frequencies of the multiple blade simulation parts, monitor the stress levels at preset reference points on the blade simulation parts, and control the excitation acceleration to make the stress at the preset reference points reach the preset stress level; at the same time, monitor whether cracks appear at the blade tips of the blade simulation parts or whether the amplitude decreases by more than the set range;

[0042] Step S500: If cracks appear in the blade simulation parts or the amplitude decreases by more than the set range, and the fatigue cycle is less than the preset number of times, record the fatigue cycle; if no cracks appear in the blade simulation parts or the amplitude does not decrease by more than the set range, and the fatigue cycle is greater than the preset number of times, it is considered that the damage to the blade simulation parts is repair-free;

[0043] Step S600: Compare the determined test repair-free limit with the theoretical repair-free limit. If the absolute value of the difference between the test repair-free limit and the theoretical repair-free limit is within the preset range of the theoretical repair-free limit, it is determined that the determined theoretical repair-free limit is reasonable.

[0044] The experimental verification method for the repair-free limit of crack-type damage at the leading and trailing edges of a blade provided by the present disclosure first determines the theoretical repair-free limit of crack-type damage at the leading and trailing edges of the blade model; then provides a plurality of blade simulation parts, and respectively introduces initial cracks with different lengths at different blade heights at the leading and trailing edges of the plurality of blade simulation parts to simulate crack-type damage. The value range of the lengths of different initial cracks is determined according to the theoretical repair-free limit at the corresponding blade height; then determines the first three natural frequencies of the blade simulation parts; then conducts vibration fatigue tests on the first three natural frequencies of the plurality of blade simulation parts, monitors the stress level of a preset reference point on the blade simulation parts, and controls the excitation acceleration to make the stress at the preset reference point reach the preset stress level; at the same time, monitors whether cracks appear at the blade tip of the blade simulation parts or there is an obvious decrease in the amplitude; if cracks appear in the blade simulation parts or there is an obvious decrease in the amplitude, and the fatigue cycle is less than the preset number of times, then records the fatigue cycle; if no cracks appear in the blade simulation parts or there is an obvious decrease in the amplitude, and the fatigue cycle is greater than the preset number of times, then it is considered that the damage of the blade simulation parts is repair-free; finally, compares the determined experimental repair-free limit with the theoretical repair-free limit. If the absolute value of the difference between the experimental repair-free limit and the theoretical repair-free limit is within the preset range of the theoretical repair-free limit, then it is judged that the determined theoretical repair-free limit is reasonable.

[0045] Next, each step in the experimental verification method for the repair-free limit of crack-type damage at the leading and trailing edges of the blade provided by the present disclosure will be described in detail.

[0046] In step S100, the theoretical repair-free limit is determined.

[0047] Specifically, according to the experimental verification method for the repair-free limit of crack-type hard object damage at the leading and trailing edges of the blade to be verified, for the crack-type damage at the leading and trailing edges of the engine compressor blade, it is simplified to a single-edge through crack in a semi-infinite large plate, and a calculation model of the stress intensity factor K is established based on the stress intensity manual. At the same time, a calculation model of the crack propagation threshold value ΔK th is established, and the relationship between the crack propagation threshold value and the stress ratio is obtained. The vibration stress and steady-state stress distribution nephograms are obtained by using the finite element calculation results, and the stress ratio distribution nephogram is obtained through result post-processing. According to the principle that the crack does not expand, the stress intensity factor K at the crack is made equal to the crack propagation threshold value ΔK th , and finally a model for the repair-free limit of crack-type damage at the leading and trailing edges of the compressor blade is established to determine the theoretical repair-free limit.

[0048] Of course, the theoretical repair-free limit can also be calculated by other methods, and the present disclosure does not limit this.

[0049] In step S200, a plurality of blade simulation parts are provided, and initial cracks with different lengths are respectively introduced at different blade heights at the leading and trailing edges of the plurality of blade simulation parts to simulate crack-type damage. The value range of the lengths of different initial cracks is determined according to the theoretical repair-free limit at the corresponding blade height.

[0050] Specifically, in the example of the present disclosure, a compressor blade of a TC4 material for an aeroengine is taken as the research object, and its model is as follows Figure 2 shown. The basic data are a chord length of 70 mm, a blade height of 50 mm, and a leading edge radius of 0.15 mm. When calculating the fatigue endurance limit of the material, in this example, the prestress distribution under the working condition of 13000 rad / min of the steady-state stress is taken; for the vibration stress, the maximum value points of each order of mode under the prestress working condition of 13000 rad / min are taken, and the maximum point is assigned as 40% of the fatigue endurance limit σ a of the material, and the vibration stress at each point in the model is calculated according to the proportionality coefficient.

[0051] The repair-free limits of the leading and trailing edges of the TC4 aeroengine compressor blade model are calculated by finite element, and the results are as follows Figure 3 shown. Some of the results are as follows

[0052] The repair-free limit of the leading edge at a height of 5 mm from the blade tip is 4.6 mm, and the repair-free limit of the trailing edge is 25.3 mm;

[0053] The repair-free limit of the leading edge at a height of 10 mm from the blade tip is 1.330 mm, and the repair-free limit of the trailing edge is 6.046 mm;

[0054] The repair-free limit of the leading edge at a height of 20 mm from the blade tip is 0.264 mm, and the repair-free limit of the trailing edge is 0.626 mm;

[0055] The repair-free limit of the leading edge at a height of 30 mm from the blade tip is 0.148 mm, and the repair-free limit of the trailing edge is 0.073 mm;

[0056] The repair-free limit of the leading edge at a height of 40 mm from the blade tip is 0.110 mm, and the repair-free limit of the trailing edge is 0.017 mm;

[0057] The repair-free limit of the leading edge at a height of 45 mm from the blade tip is 0.058 mm, and the repair-free limit of the trailing edge is 0.005 mm.

[0058] As shown in Figure 4 , a batch of blade simulation parts are designed and processed, and crack-type damages with a depth of a are processed at the leading edge of the blade body and at heights h = 2%H, 5%H, 10%H, 20%H, 50%H, 90%H at the trailing edge of the blade body. The range of a is near the repair-free limit at the corresponding position.

[0059] Among them, a can be evenly taken as multiple values. For example, at 90%H of the leading edge, the calculated repair-free limit is 4.6 mm, then the crack depth a in the processed test parts can be taken as 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, 5.0 mm.

[0060] Among them, multiple test parts are processed for each crack depth, for example, three.

[0061] Next, as Figure 5 shown, install the blade simulation components with different leading and trailing edge crack damages on the shaker, paste strain gauges and displacement sensors on the blade simulation components, and after confirming that the paste is firm, place the blade simulation components into the slot of the blade simulation component fixture, and gradually tighten the axial fastening bolts and circumferential fastening bolts using a torque wrench.

[0062] Specifically, the entire test is completed on the shaker 1. Fix the blade simulation component fixture 2 on the shaker 1 with 4 positioning bolts 5. Paste the strain gauge 7 and the displacement sensor 8 on the blade simulation component 3. After confirming that the paste is firm, place the blade simulation component 3 into the slot of the blade simulation component fixture 2, and gradually tighten the axial fastening bolt 4 and the circumferential fastening bolt 6 using a torque wrench.

[0063] In step S300, determine the first three natural frequencies of the blade simulation component.

[0064] Specifically, start the shaker 1 to sweep the frequency within the range of the first three simulation modal frequencies of the blade simulation component 3, observe the data collected by the strain gauges and the displacement sensors, until the data reflects that the first three modal frequencies of the blade simulation component 3 are stable, stop further tightening the axial fastening bolt 4 and the circumferential fastening bolt 6, record the value of the torque wrench at this time, and then load according to this value in the subsequent vibration fatigue test.

[0065] In step S400, conduct vibration fatigue tests on multiple blade simulation components at their first three natural frequencies, monitor the stress level at a preset reference point on the blade simulation component, control the excitation acceleration to make the stress at the preset reference point reach the preset stress level; at the same time, monitor whether cracks appear at the tip of the blade simulation component or whether the amplitude drops by more than the set range.

[0066] Specifically, conduct vibration fatigue tests on the machined blade simulation components at their first three modes respectively, and ensure that the torques of the axial fastening bolts and the axial fastening bolts are consistent with the recorded value of the torque wrench during boundary loading.

[0067] Monitor the stress level at a preset reference point on the blade simulation component, control the excitation acceleration to make the stress at the preset reference point reach the preset stress level; at the same time, monitor whether cracks appear at the tip of the blade simulation component or whether the amplitude drops by more than the set range.

[0068] In step S500, if cracks appear on the blade simulation component or the amplitude drops by more than the set range, and the fatigue cycle number is less than the preset number, record the fatigue cycle number; if no cracks appear on the blade simulation component or the amplitude does not drop by more than the set range, and the fatigue cycle number is greater than the preset number, it is considered that the damage of the blade simulation component is free of repair.

[0069] Specifically, if cracks appear in the blade simulation part or there is an obvious decrease in amplitude, and the fatigue cycle is less than the preset number of times, the fatigue cycle is recorded.

[0070] Among them, if the amplitude decrease of the blade simulation part is greater than the set range, it is considered that there is an obvious amplitude decrease. The set range can be, for example, 5%-20% of the original amplitude (normal amplitude), such as 5%, 10%, 15%, 20%; of course, the set range can also be less than 5% of the original amplitude or greater than 20% of the original amplitude, and the present disclosure does not limit this.

[0071] If no cracks appear in the blade simulation part or there is an obvious amplitude decrease, and the fatigue cycle is greater than the preset number of times, it is considered that the damage to the blade simulation part is exempt from repair.

[0072] Among them, the preset number of times is 8 million - 12 million times, such as 10 million times, that is, it is judged whether the fatigue cycle is greater than 10 million times. If it is greater, it is considered that this kind of damage is exempt from repair; otherwise, it is considered that this kind of damage is greater than the repair exemption limit, and then this fatigue cycle is the crack initiation life of the blade.

[0073] In step S600, the determined test repair exemption limit is compared with the theoretical repair exemption limit. If the absolute value of the difference between the test repair exemption limit and the theoretical repair exemption limit is within the preset range of the theoretical repair exemption limit, it is judged that the determined theoretical repair exemption limit is reasonable.

[0074] Specifically, the determined test repair exemption limit is compared with the theoretical repair exemption limit. If the absolute value of the difference between the test repair exemption limit and the theoretical repair exemption limit is within the preset range of the theoretical repair exemption limit, it is judged that the determined theoretical repair exemption limit is reasonable.

[0075] For example, if the absolute value of the difference between the test repair exemption limit and the theoretical repair exemption limit is within 5%-20% of the preset range of the theoretical repair exemption limit, such as 5%, 10%, 15%, 20%, it is judged that the determined theoretical repair exemption limit is reasonable, and then the blade can be directly calculated according to the model of this theoretical repair exemption limit. Of course, the preset range can also be less than 5% or greater than 20%, and the present disclosure does not limit this.

[0076] If the absolute value of the difference between the test repair exemption limit and the theoretical repair exemption limit is outside the preset range of the theoretical repair exemption limit, it is judged that the determined theoretical repair exemption limit is unreasonable.

[0077] In summary, the verification test process for the crack-type damage repair-free limit of the compressor blade leading and trailing edges proposed in the present disclosure can be used as a basis for verifying the accuracy of the crack-type damage repair-free limit of the compressor blade leading and trailing edges. The vibration fatigue test design method for the blade proposed in the present disclosure can meet the data requirements for verifying the existing blade repair-free limit method. Moreover, the instruments required for this test are common and highly feasible, having great engineering application value. The test piece installation method for the compressor blade vibration fatigue test proposed in the present disclosure can accurately measure the natural frequency of the blade simulation and the fatigue life of the test piece, meeting the strict boundary condition control requirements in the vibration fatigue test.

[0078] Those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include known common knowledge or conventional technical means in the technical field not disclosed in the present disclosure. The specification and examples are only to be considered as exemplary, and the true scope and spirit of the present disclosure are pointed out by the following claims.

[0079] It should be understood that the present disclosure is not limited to the exact structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is only limited by the appended claims.

Claims

1. An experimental verification method for the limit of crack-type damage at the leading and trailing edges of a blade without repair, characterized in that, Including: Determine the theoretical repair exemption limit; Provide multiple blade simulation parts, and introduce initial cracks with different lengths at different blade heights on the leading and trailing edges of the multiple blade simulation parts respectively to simulate crack-type damage. The length value ranges of the different initial cracks are determined according to the theoretical repair exemption limit at the corresponding height of the blade; Determine the first three natural frequencies of the blade simulation parts; Conduct vibration fatigue tests on the multiple blade simulation parts at the first three natural frequencies, monitor the stress levels of preset reference points on the blade simulation parts, and control the excitation acceleration to make the stress at the preset reference points reach the preset stress level; at the same time, monitor whether cracks appear at the tips of the blade simulation parts or whether the amplitude drops by more than the set range; If cracks appear on the blade simulation parts or the amplitude drops by more than the set range, and the fatigue cycle times are less than the preset number of times, record the fatigue cycle times; If no cracks appear on the blade simulation parts or no amplitude drop greater than the set range appears, and the fatigue cycle times are greater than the preset number of times, it is considered that the damage of the blade simulation parts is exempt from repair; Compare the determined test repair exemption limit with the theoretical repair exemption limit. If the absolute value of the difference between the test repair exemption limit and the theoretical repair exemption limit is within the preset range of the theoretical repair exemption limit, it is judged that the determined theoretical repair exemption limit is reasonable.

2. The test verification method according to claim 1, wherein The step of introducing initial cracks with different lengths at different blade heights on the leading and trailing edges of the multiple blade simulation parts respectively to simulate crack-type damage includes: At the heights of h = 2%H, 5%H, 10%H, 20%H, 50%H, and 90%H of the leading edge and trailing edge of the blade simulation part respectively, process cracks with a depth of type damage, The range of values is determined according to the theoretical limit of exemption at the corresponding height of the blade, and multiple values are taken.

3. The test verification method according to claim 2, wherein The theoretical maintenance-free limit at the corresponding height of the blade is located within the machining depth within the range of values 4. The test verification method according to claim 2, wherein When the calculated theoretical repair-free limit is 4.6 mm at 90%H of the leading edge, the crack depths in the blade simulation parts are taken as 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, and 5.0 mm.

5. The test verification method according to claim 4, characterized in that Machine multiple test pieces for each crack depth.

6. The test verification method according to claim 1, characterized in that Determine the first three natural frequencies of the blade simulation parts, including: Start the vibration table to sweep the frequency within the range of the first three simulation modal frequencies of the blade simulation parts, observe the data collected by the strain gauges and displacement sensors until the data reflects that the first three modal frequencies of the blade simulation parts are stable, stop tightening the axial fastening bolts and circumferential fastening bolts continuously, and record the torque wrench value and the first three modal frequency values of the blade at this time.

7. The test verification method according to claim 6, characterized in that Conduct vibration fatigue tests on the blade simulation parts respectively in their first three modes, and ensure that the torques of the axial fastening bolts are the same when applying boundary loading.

8. The test verification method according to claim 1, characterized in that, The preset number of times is 8 million - 12 million times.

9. The test verification method according to claim 1, characterized in that The preset range is 5% - 20%.

10. The test verification method according to claim 1, characterized in that, If the absolute value of the difference between the test repair exemption limit and the theoretical repair exemption limit is not within the preset range of the theoretical repair exemption limit, it is judged that the determined theoretical repair exemption limit is unreasonable.

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