Fatigue test fixture and high-frequency high-cycle fatigue test experimental method

Abstract

The fatigue test clamp comprises a blade clamping block, a base, an adjusting beam, a balancing weight and a plurality of fixing pieces, and the blade clamping block is used for clamping a blade; the base comprises a chassis and a vertical beam extending in the first direction, the chassis is arranged on the shock excitation table, and a cavity is formed in the end of the vertical beam and used for containing the blade clamping block; the adjusting beam is arranged on the vertical beam and can move in the first direction, and the balance weight adjusting groove extends in the second direction; the balancing weight is located above the balancing weight adjusting groove and can move in the second direction. The multiple fixing pieces are used for fixing the relative position of the blade clamping block and the base, the relative position of the balancing weight and the adjusting beam and the relative position of the adjusting beam and the vertical beam correspondingly. The clamp has good clamp frequency adjusting performance. The invention further provides a high-frequency high-cycle fatigue test experiment method.

Description

Technical Field

[0001] The invention relates to the field of testing, and in particular to the field of blade vibration testing. Background Art

[0002] The working environment of high-pressure turbine blades of aircraft engines is harsh. High speed, high temperature and high pressure put great pressure on the static strength of the blades, and also greatly reduce the allowable vibration stress of the blades. Due to the complex airflow conditions in the high-vortex flow channel, the blades will not only be subject to the common low-frequency excitation of the source rotor, but also to the high-frequency excitation caused by the instability of the upstream and downstream airflow. Especially at high temperature and high speed, the excitation energy is greater and the frequency is higher, which is more likely to cause high-frequency and high-cycle fatigue failure of the blades. Therefore, it is necessary to carry out high-frequency and high-cycle fatigue tests on high-vortex blades to determine the high-cycle fatigue limits of the high-order modes of the blades, so as to reproduce the high-frequency and high-cycle fatigue failure problems that occur in the core engine test or the core engine test.

[0003] At present, most vibration tables used for high-cycle fatigue tests are driven by electromagnetics, and the energy and frequency range of the excitation that can be provided are limited. The upper limit of the frequency of the existing electromagnetic excitation table is generally 10,000 Hz, and very few excitation tables can reach 20,000 Hz. However, due to the limitations of the operating principle of the excitation table itself, under the premise of inputting a certain amount of energy, the higher the frequency, the smaller the table acceleration that can be achieved. In particular, in order to ensure that the blade and the table can be assembled firmly, the blade fixture is often of large mass, which divides most of the excitation energy. Ultimately, the energy that the excitation table can provide to the blade in the high-frequency state is very small, so that the blade cannot achieve a large enough vibration, so that it cannot initiate cracks within a limited time.

[0004] On the basis of the existing vibration table excitation capability level, by designing the natural frequency of the fixture to be close to that of the blade, the excitation provided by the vibration table can be amplified, so that the blade can produce greater vibration at the same excitation level. However, the natural frequencies of blades with different configurations are different, and the natural frequencies of different orders of the same blade are also different. If a resonant fixture is designed for different configurations and different orders, it will consume too much manpower and material resources. At the same time, due to the existence of processing tolerances, the frequencies of different blades of the same configuration and the same order are also different, which will cause the same resonant fixture to have a poor vibration amplification effect on some blades with larger tolerances. Therefore, it is necessary to design a fixture with an adjustable natural frequency within a certain range. Summary of the invention

[0005] An object of the present invention is to provide a fatigue test fixture having better fixture frequency adjustment performance.

[0006] To achieve the above-mentioned purpose, a fatigue test fixture is arranged on an excitation table for clamping a blade, and the fixture includes a blade clamp, a base, an adjustment beam, a counterweight block and a plurality of fixing parts, wherein the blade clamp is used to clamp the blade; the base includes a chassis and a vertical beam extending in a first direction, the chassis is arranged on the excitation table, and a cavity is provided at the end of the vertical beam for accommodating the blade clamp; the adjustment beam is arranged on the vertical beam and can move in the first direction, and also includes a counterweight adjustment slot extending in a second direction; the counterweight block is located above the counterweight adjustment slot and is arranged to be able to move in the second direction; a plurality of fixing parts are respectively used to fix the blade clamp and the base, the counterweight block and the adjustment beam, and the adjustment beam and the vertical beam.

[0007] In one or more embodiments, the first direction and the second direction are arranged orthogonally.

[0008] In one or more embodiments, the blade includes a tenon, and the blade clamp includes a tenon groove that cooperates with the tenon.

[0009] In one or more embodiments, the adjusting beam comprises a mounting groove, and is sleeved on the outer periphery of the vertical beam by means of the mounting groove.

[0010] In one or more embodiments, the fixing member includes a clamping bolt for clamping the adjusting beam and the vertical beam.

[0011] In one or more embodiments, the counterweight block includes a central through hole for the fixing member to pass through.

[0012] In one or more embodiments, the counterweight includes a variety of weight specifications.

[0013] In one or more embodiments, the height of the vertical beam is configured to be self-adjustable.

[0014] A high-frequency and high-cycle fatigue test experimental method for achieving the above-mentioned purpose is carried out using the above-mentioned fatigue test fixture, and the method includes the following steps: S1. Obtaining the natural frequency information of a batch of test pieces, and calculating the median and dispersion of the natural frequencies of the batch of test pieces; S2. Adjusting the relative position of the adjusting beam and the vertical beam of the fixture according to the median so that the natural frequency of the fixture is close to the median; S3. Selecting the number and weight of the counterweight blocks according to the dispersion and adjustment accuracy; S4. Installing the test pieces to be tested onto the fixture one by one, adjusting the relative position and weight of the counterweight blocks on the adjusting beam, and conducting the test when the fixture frequency is consistent with the natural frequency of the currently measured blade.

[0015] The above fatigue test fixture can adjust the frequency of the fixture within a wide range by adjusting the relative height of the vertical beam and the adjustment beam, the counterweight block and the relative position of the counterweight block on the adjustment beam without replacing the excitation table, and can amplify vibrations of different orders of blades with different configurations, thus having a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which:

[0017] Figure 1 is a schematic diagram of the fatigue test fixture;

[0018] Figure 2 It is a schematic diagram of the assembly structure of the base, the adjustment beam and the counterweight block;

[0019] Figure 3 It is a schematic diagram of the assembly of the blade and the fixture;

[0020] Figure 4 It is a graph showing the change of the natural frequency of the fixture with the relative position of the adjustment beam and the vertical beam;

[0021] Figure 5 It is a graph showing the change of the fixture's natural frequency with the counterweight, and the relative position of the counterweight and the adjustment beam;

[0022] Figure 6 It is a flow chart of the high frequency and high cycle fatigue test experimental method;

[0023] Figure 7 It is a flow chart of a specific embodiment of a high-frequency high-cycle fatigue test experimental method. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with specific embodiments and drawings. More details are elaborated in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description herein. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0025] It should be noted that these and other subsequent drawings are only examples and are not drawn to scale, and should not be used to limit the actual scope of protection required by the present invention.

[0026] High cycle fatigue refers to the number of cycles exceeding 10 4 or 10 5The alternating stress is often lower than the material yield limit, and the material is in an elastic state. The high-frequency and high-cycle fatigue test of the high-pressure turbine blades of aircraft engines requires high excitation capabilities of the test bench. At present, conventional electromagnetic excitation benches are difficult to provide sufficiently large high-frequency excitation forces. The excitation force of the excitation bench can be amplified by fixture resonance, but the cost of designing fixtures of different frequencies for different blades and different orders is high, and the fixed structure fixtures are not very adaptable to the frequencies of different individuals in the same batch of blades.

[0027] Therefore, the present invention proposes a frequency-adjustable high-cycle fatigue test fixture, which can perform coarse adjustment of frequency within a wide range and fine adjustment of frequency within a certain range. At the same time, the structure is simple and reliable, the force transmission path has no connectors, and the force transmission efficiency is high. The stability of the natural frequency of the structure at high frequencies can be ensured, thereby making the resonance fixture universal.

[0028] Figures 1 to 3 The schematic diagram of the structure of the frequency modulation clamp is shown, and the clamp includes a base 1, an adjustment beam 2, a counterweight 3, and a blade clamp 4. The blade clamp 4 is used to clamp the blade. The base 1 includes a chassis 11 and a vertical beam 13 extending in a first direction. The chassis 11 is arranged on an excitation table (not shown in the figure) through a base mounting hole 12 and a connecting piece. A cavity is provided at the end of the vertical beam 13 as a clamp mounting groove 14 for accommodating the blade clamp 4. The adjustment beam 2 is arranged on the vertical beam 13 and can move in the first direction, and also includes a counterweight adjustment groove 24 extending in the second direction. The counterweight 3 is located above the counterweight adjustment groove 24 and is arranged to be able to move in the second direction. A plurality of fixing members are respectively used to fix the blade clamp 4 and the base 1, the counterweight 3 and the adjustment beam 2, and the adjustment beam 2 and the vertical beam 13.

[0029] In the embodiment shown in the drawings, the first direction is the z direction, and the second direction is the y direction.

[0030] Specifically, the base 1 is as Figure 2 As shown, it includes a chassis 11, a base mounting hole 12, a vertical beam 13, and a clamp block mounting threaded hole 15. The adjusting beam 2 includes a mounting groove 21, an adjusting beam fastening threaded hole 22 and a counterweight adjustment groove 24. The adjusting beam 2 is sleeved on the outer periphery of the vertical beam 13 of the base 1 through the mounting groove 21. The mounting groove 21 and the vertical beam 13 are clearance-matched so that the adjusting beam 2 can slide up and down on the vertical beam. Preferably, the height of the vertical beam 13 can also be set to be self-adjustable to further adjust the coverage range of the natural frequency of the fixture.

[0031] After determining the relative position of the mounting slot 21 and the vertical beam 13, the adjusting beam 2 is fixed to the vertical beam 13 by using the first bolt 23 as a fixing member through the threaded hole 22 at the rear of the adjusting beam 2. By moving the adjusting beam 2 up and down, the natural frequency of the entire fixture is changed so that the natural frequency of the fixture is close to the natural frequency of the blade, and then the first bolt 23 is tightened to fix the adjusting beam 2 on the fixture base.

[0032] The middle of the counterweight block 3 is provided with a through hole 31 for the fixing member to pass through. Figure 2 In the illustrated embodiment, the fixing member is a second bolt 32 and a nut 33. The second bolt 32 passes through the middle through holes 31 of a plurality of stacked counterweights 3, and the counterweight adjustment slot 24 of the adjustment beam 2 cooperates with the nut 33 to fix the counterweight 3 on the adjustment beam 2. The second bolt 32 and the adjustment slot 24 are clearance fits, and before the nut 33 is tightened, the counterweight 3 can slide freely on the adjustment slot 23 along the y direction.

[0033] The counterweight 3 includes a variety of weight specifications, and multiple layers of counterweights can also be stacked to adjust the total counterweight weight. According to the measured natural frequency of a single blade, the number and position of the counterweights 3 on the adjustment beam 2 can be adjusted to make the fixture natural frequency consistent with the blade natural frequency. The counterweight 3 can be moved forward and backward along the counterweight adjustment slot 24 to fine-tune the fixture natural frequency based on the current position of the adjustment beam. If the number of counterweights 3 is small, the adjustment range is small, but the adjustment is more precise; if the number of counterweights 3 is large, the adjustment range is large, but the frequency change per unit distance of movement increases, and the adjustment sensitivity becomes higher.

[0034] Blade clamp 4 Figure 3 As shown, it includes a tenon groove 41 for fitting and fastening with the tenon 5 of the blade. During installation, the tenon 5 of the blade is first inserted into the tenon clamp block 4 along the axial direction of the tenon groove 41, that is, the x or -x direction, and then the combination of the tenon clamp block 4 and the blade 5 is pushed into the clamp block installation groove 14 of the vertical beam 13 along the -y direction. The third bolt 42 is screwed into the threaded hole 15 at the top of the vertical beam as a fixing member, and the upper part of the blade tenon clamp block 4 is pressed from above to fix the blade.

[0035] During the test, the exciting force will be directly applied to the blade by the chassis 11 through the vertical beam 13 and the clamp block 4. In addition, there is no other structure between the blade and the exciting table except the tenon clamp block and the base. The exciting force is transmitted from the base chassis to the blade through the base vertical beam. There is no connector on the force transmission path. The exciting force transmission is direct and effective, which can avoid the instability of the resonance frequency caused by the loosening of the connector under high-frequency excitation, and reduce the difficulty of resonance retention in the test.

[0036] The relative position of the adjusting beam 2 on the vertical beam 13 along the z direction and the relative position of the counterweight 3 on the adjusting beam 2 along the y direction can jointly control the natural frequency of the fixture.

[0037] The relationship between the natural frequency of the fixture and the relative position of the adjustment beam 2 on the vertical beam 13 is shown in the attached Figure 4 , the horizontal axis adjusts the relative position of the beam 0% represents the bottom of the vertical beam 13, Figure 4 The variation law shown in the figure shows that the higher the relative position of the adjusting beam 2 is, the weaker the dynamic stiffness of the fixture structure is, and the lower the natural frequency of the fixture is. In addition, the relative position change along the z direction has a greater impact on the natural frequency of the fixture.

[0038] The relationship between the natural frequency of the fixture and the relative position of the counterweight 3 on the adjustment beam 2 is shown in the attached Figure 5 , the relative position of the counterweight block 0% represents one end close to the vertical beam 13, and the relative position 100% represents one end away from the vertical beam 13 along the -y direction. Under the premise that the adjustment beam 2 is fixed, it can be seen from the figure that when the number of counterweight blocks 3 is constant, the larger the relative position, the lower the natural frequency of the fixture, that is, the farther the counterweight block 3 is from the side of the vertical beam 13, the lower the natural frequency of the fixture. In addition, when the number of counterweight blocks 3 increases, the natural frequency of the fixture at the same position decreases, and the larger the relative position, the greater the difference in natural frequencies caused by different numbers of counterweight blocks.

[0039] Therefore, the vibration characteristic curve of the fixture adjustment obtained based on the vibration characteristic analysis can also be adjusted by designing the width and height of the vertical beam on the fixture base and adjusting the length and width of the beam to adjust the upper and lower limits of the current fixture adjustment vibration characteristic curve, so that the vibration characteristic curve can cover the blade frequency designed for the current model / unit, that is, the fixture covers a sufficiently wide blade frequency range, and then according to the tenon processing corresponding to a number of tenon clamps of the blade, a set of fixture can be achieved to meet the high-frequency and high-cycle fatigue test requirements of a model / unit of blades.

[0040] The above-mentioned adjustable frequency fixture based on the principle of resonance amplification can adjust the fixture frequency to keep it consistent with the frequency of different types of blades, amplify the excitation of the blades on the basis of the original excitation table, and produce a larger amplitude under the same table acceleration, thereby increasing the vibration stress level of the test and reducing the difficulty of high-frequency and high-cycle tests.

[0041] In addition, a set of the above-mentioned fixtures can be used to amplify vibrations of different orders of blades of different configurations. The frequency adjustment range of the fixture effectively covers the high-order frequencies of high-pressure turbine blades, greatly reducing the design and processing costs of the test fixture. At the same time, the fixture has a simple structure, strong reliability, efficient excitation force transmission, and stable structural frequency under high-frequency excitation, and can adapt to frequency differences caused by blade tolerances.

[0042] Combined with the above introduction to the fatigue test fixture, we can also understand a high-frequency and high-cycle fatigue test experimental method, which includes the following steps: S1. Obtain the natural frequency information of a batch of test pieces, and calculate the median and dispersion of the natural frequencies of the batch of test pieces; S2. Adjust the relative position of the adjusting beam and the vertical beam of the fixture according to the median of the natural frequency, so that the natural frequency of the fixture is close to the median; S3. Select the number and weight of the counterweights according to the dispersion of the natural frequency and the adjustment accuracy required for the test; S4. Install the test pieces to be tested on the fixture one by one, adjust the relative position and weight of the counterweights on the adjusting beam, and perform the test when the fixture frequency is consistent with the natural frequency of the currently measured blade, and finally complete the testing of all blades in the batch one by one.

[0043] Specifically, refer to Figure 7 A specific embodiment shown is understood. First, step S001 is performed to measure the natural frequencies of all test pieces through a vibration characteristic test, and the natural frequency information of all the test pieces of interest is obtained. Then step S002 is performed to process the data obtained in step S001 to obtain the median and dispersion of the natural frequencies of this batch of test pieces. Then step S003 is performed to adjust the position of the adjustment beam according to the median of the natural frequencies of this batch of test pieces so that the natural frequency of the fixture is close to the median of the natural frequency of the blade. Then step S004 is performed to select a suitable number of counterweights according to the dispersion of the natural frequencies of this batch of test pieces and the requirements for adjustment accuracy, and install the counterweights on the adjustment beam, but do not tighten the nuts. Then step S005 is performed to install a blade to be tested that has not yet been subjected to a high-cycle fatigue test on the fixture. Then step S006 is performed to adjust the relative position of the counterweight on the adjustment beam so that the fixture frequency is basically consistent with the natural frequency of the currently measured blade. Then step S007 is performed to carry out a high-frequency high-cycle fatigue test on this blade. Finally, steps S005 to S007 are repeated to complete the high-frequency and high-cycle fatigue test of this batch of blades.

[0044] The present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or multiple times in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0045] Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A fatigue test fixture, which is set on a vibration table and used to clamp the blade, is characterized in that: The fixture includes: A blade clamp, used for clamping the blade; A base, comprising a chassis and a vertical beam extending along a first direction, wherein the chassis is arranged on the excitation platform, and a cavity is arranged at an end of the vertical beam for accommodating the blade clamp; an adjusting beam, disposed on the vertical beam and movable along the first direction, and further comprising a counterweight adjusting slot extending along the second direction; a counterweight block, located above the counterweight adjustment slot and configured to be movable along the second direction; and A plurality of fixing members are used to fix the blade clamp and the base, the counterweight and the adjusting beam, and the adjusting beam and the vertical beam respectively.

2. The fatigue test fixture according to claim 1, characterized in that: The first direction and the second direction are arranged orthogonally.

3. The fatigue test fixture according to claim 1, characterized in that: The blade comprises a tenon, and the blade clamp comprises a tenon groove matched with the tenon.

4. The fatigue test fixture according to claim 1, characterized in that: The adjusting beam comprises a mounting groove, and is sleeved on the outer periphery of the vertical beam by means of the mounting groove.

5. The fatigue test fixture according to claim 4, characterized in that: The fixing member includes a clamping bolt for clamping the adjusting beam and the vertical beam.

6. The fatigue test fixture according to claim 1, characterized in that: The counterweight block comprises a middle through hole for the fixing member to pass through.

7. The fatigue test fixture according to claim 1, characterized in that: The counterweight block includes various weight specifications.

8. The fatigue test fixture according to claim 1, characterized in that: The height of the vertical beam is arranged to be self-adjustable.

9. High frequency high cycle fatigue test experimental method, characterized in that: Using the fatigue test fixture as described in any one of claims 1 to 8, the method comprises the following steps: S1. Obtain the natural frequency information of a batch of test pieces, and calculate the median and dispersion of the natural frequency of the batch of test pieces; S2. adjusting the relative position of the adjusting beam and the vertical beam of the fixture according to the median value so that the natural frequency of the fixture is close to the median value; S3. Select the number and weight of the counterweights according to the dispersion and adjustment accuracy; S4. Install the test pieces one by one on the fixture, adjust the relative position and weight of the counterweight on the adjustment beam, and conduct the test when the fixture frequency is consistent with the natural frequency of the blade being tested.

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