High temperature vibration fatigue test method for turbine blades

Abstract

A method for high-temperature vibration fatigue testing of turbine blades includes S1: preparation of a fixture; S2: installing the turbine blades into the mortise and tenon of a clamp; S3: installing the fixture with the turbine blades clamped onto a vibration table of an excitation device, pasting strain gauges at room temperature, and conducting amplitude and strain calibration tests to obtain a functional relationship between stress and amplitude at the maximum stress point, and converting the amplitude value corresponding to the target stress value; S4: placing the fixture together with the turbine blades into a heating device for heating, heating to a set value, and then keeping the temperature, and starting a high-temperature vibration fatigue test; and using a displacement sensor for real-time amplitude monitoring and forming a closed-loop control with the control system of the vibration device, so that the turbine blades are in a resonant state in real time and the amplitude remains stable until the end of the test. The present invention adopts room-temperature "amplitude-strain" calibration, high-temperature strain measurement, and elastic modulus correction for data post-processing, thereby achieving the correctness, accuracy, and precision of the high-temperature vibration fatigue test.

Description

Technical Field

[0001] The present invention relates to the technical field of turbine blade testing, and in particular to a high-temperature vibration fatigue testing method for turbine blades. Background Art

[0002] In aerospace engineering, turbine blades are critical components of the engine. Their sustained fatigue strength in high-temperature environments (around 1000°C) will directly affect the overall safety and reliability of the engine. Therefore, it is very necessary to conduct vibration fatigue strength test assessment, verification and research on turbine blades under high-temperature conditions.

[0003] Several related documents disclose technologies related to turbine blade vibration fatigue testing. For example, patent publication number CN209069545U discloses a high-temperature blade vibration fatigue testing system, comprising a temperature-controlled box, a vibration table, and a fixture for securing the blade, the fixture being secured to the vibration table. The temperature-controlled box can house the vibration table and the fixture, and is equipped with several electric heating elements to increase the test temperature of the blade placed therein. The temperature-controlled box is equipped with a displacement sensor and an incident aperture that cooperates with the displacement sensor to detect blade tip displacement. High-temperature strain gauges are also provided on the blade to detect blade stress and strain. The electric heating elements within the temperature-controlled box heat the interior of the temperature controller, thereby controlling the blade temperature during the vibration fatigue test. Furthermore, the displacement sensor and high-temperature strain gauge are used to measure blade tip displacement, stress, and strain in a high-temperature environment. The patent states that a high-temperature strain gauge is fixedly installed on the blade, and the high-temperature strain gauge can be used to detect the stress and strain of the blade during a vibration fatigue test under high temperature conditions.

[0004] However, when detecting the stress and strain of the blade under high temperature conditions, the changes in the material properties of the blade compared to the normal temperature state cannot be ignored. Only strain can be measured under high temperature conditions, and the stress under high temperature conditions calculated by strain transformation is an estimated value, which cannot accurately and directly measure the stress. In addition, the preliminary preparation work for the arrangement of high-temperature strain gauges is cumbersome and time-consuming.

[0005] In addition, the traditional "fixed frequency method" is used to excite the turbine blades. However, due to the high temperature creep, the rigidity of the blades decreases, resulting in a decrease in the resonance frequency. The traditional excitation method cannot effectively excite the blades, and the blade vibration will become unstable, making it impossible for the test to be carried out normally and effectively.

[0006] Furthermore, the bottom of the traditional fixture is designed as a flat surface that makes seamless contact with the platform of the excitation equipment (vibration table, etc.). Since the test lasts for a long time (usually tens of hours), the heat conduction effect of high temperature will cause the temperature of the fixture and the vibration table surface to be very high, thereby damaging the vibration table (or the vibration table will alarm due to excessive temperature), making it impossible to continue the test for a long time. Summary of the Invention

[0007] The main purpose of the present invention is to propose a high-temperature vibration fatigue test method for turbine blades, aiming to solve the above technical problems.

[0008] To achieve the above object, the present invention proposes a method for high-temperature vibration fatigue testing of turbine blades, comprising the following steps:

[0009] S1: Preparation of a fixture. The fixture includes a base and a clamping block disposed on top of the base. The clamping block is provided with a tongue and groove. The base is used to be mounted on a vibration table of an excitation device. The lower end surface of the base that contacts the vibration table of the excitation device is provided with multiple cooling channels.

[0010] S2: Install the turbine blade into the tenon groove of the clamp;

[0011] S3: Install the fixture with the turbine blades on the vibration table of the excitation equipment, attach the strain gauges at room temperature, and perform amplitude and strain calibration tests to obtain the functional relationship between the stress and amplitude at the maximum stress point, and convert the amplitude value corresponding to the target stress value;

[0012] S4: Place the fixture together with the turbine blade into the heating device for heating. After heating to the set value, keep warm and start the high-temperature vibration fatigue test. Use a displacement sensor to monitor the amplitude in real time, and form a closed-loop control with the control system of the vibration equipment based on the amplitude value corresponding to the target stress value converted in step S3, so that the turbine blade is in a resonant state in real time and the amplitude remains stable until the end of the test.

[0013] In step S4, when closed-loop control is performed, the following formula is used:

[0014]

[0015] Dynamically correct the strain value corresponding to the target stress value, perform real-time automatic tracking and complete the test;

[0016] in:

[0017] E t : Elastic modulus at different temperatures, unit: GPa;

[0018] σ: stress, unit: MPa;

[0019] : mechanical strain;

[0020] R L : The resistance of a wire, unit: Ω;

[0021] : Strain gauge resistance value, unit: Ω.

[0022] Preferably, the clamp also includes a bolt; a mounting groove is provided on the top of the base; the clamping block is movably installed in the mounting groove, and the clamping block includes clamping parts located on both sides of the mortise and tenon, and an elastic part connecting the two clamping parts; the bolt is screwed onto the base and tightens the clamping part on one side of the clamping block.

[0023] Preferably, the material of the base, the clamping block and the bolts are the same as the material of the turbine blades.

[0024] Specifically, the base, clamping block and bolts are all made of high-temperature alloy, and the material grade is GH39.

[0025] Preferably, the cooling channels on the lower end surface of the base are grooves that are evenly spaced.

[0026] Preferably, in step S4, the heating device heats to ≥1000°C and then keeps the temperature.

[0027] Preferably, in step S4, a high temperature vibration fatigue test is performed with a cycle number of not less than 2×10 7 Second-rate.

[0028] Preferably, the heating device is installed on a lifting frame, and the lifting frame is used to adjust the height of the heating device.

[0029] Preferably, in step S4, the displacement sensor is a laser displacement sensor.

[0030] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0031] (1) In the present invention, by attaching strain gauges at room temperature and conducting amplitude and strain calibration tests, the functional relationship between stress and amplitude at the maximum stress point is obtained, and the amplitude value corresponding to the target stress value is converted. At the same time, a displacement sensor is used to monitor the amplitude in real time under high temperature conditions, forming a closed-loop control with the control system of the vibration equipment, so that the turbine blades are in a resonant state in real time and the amplitude is stable. In other words, the "resonance dwell" technology of the present invention keeps the turbine blades at the resonance point for real-time excitation, thereby achieving accurate, efficient and precise test execution. The "amplitude-strain" calibration at room temperature, strain measurement at high temperature, and elastic modulus correction technology are used in data post-processing to achieve the correctness, accuracy and precision of the high-temperature vibration fatigue test.

[0032] (2) In the present invention, by providing a plurality of cooling channels on the lower end surface of the base in contact with the vibration table of the excitation device, the heat conduction area can be reduced, the influence of temperature transfer on the excitation device can be weakened, and the high temperature of the excitation device causing equipment failure or alarm can be avoided; at the same time, it is convenient to use cooling air to blow cooling to the bottom, forming a plurality of effective cooling air channels.

[0033] (3) In the present invention, the entire test process is monitored by real-time amplitude monitoring using a laser displacement sensor. The laser displacement sensor and the control system of the vibration equipment form a closed-loop control to ensure dynamic automatic control of the test. The use of the laser displacement sensor for non-contact measurement, on the one hand, avoids the interference and influence of the attached objects on the test piece (turbine blade); on the other hand, the laser displacement sensor has extremely high measurement accuracy, which ensures the accuracy of the test data. Furthermore, the closed-loop control system composed of the laser displacement sensor and the control system of the vibration equipment facilitates the effective and continuous implementation of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0035] Figure 1 This is a block diagram of the experimental test system in the present invention;

[0036] Figure 2 Schematic diagram of the turbine blade in the present invention;

[0037] Figure 3 Schematic diagram of the clamping block in the present invention;

[0038] Figure 4 is a schematic diagram of the base in the present invention;

[0039] Figure 5 This is a schematic diagram of a turbine blade in the present invention being clamped on a fixture and extending into the interior of a heating device;

[0040] Figure 6 Schematic diagram of the heating device distributed on the lifting frame in the present invention

[0041] Explanation of the accompanying drawings: 1. Blade; 2. Base; 201. Cooling channel; 202. Mounting groove; 3. Clamp; 301. Mortise and tenon; 302. Elastic part; 4. Heating device; 5. Bolt; 6. Lifting frame. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0044] Combine Figures 1 to 5 As shown, a high temperature vibration fatigue test method for turbine blades includes the following steps:

[0045] S1: Preparation of a fixture. The fixture includes a base 2 and a clamping block 3 disposed on top of the base 2. The clamping block 3 is provided with a tongue and groove 301. The base 2 is used to be mounted on a vibration table of an excitation device. The lower end surface of the base 2 that contacts the vibration table of the excitation device is provided with multiple cooling channels 201.

[0046] S2: Install the turbine blade 1 into the tenon groove 301 of the clamping block 3;

[0047] S3: Mount the fixture holding the turbine blade 1 on the vibration table of the excitation equipment, attach the strain gauge at room temperature, and perform amplitude and strain calibration tests to obtain the functional relationship between the stress and amplitude at the maximum stress point, and convert the amplitude value corresponding to the target stress value;

[0048] S4: Place the fixture together with the turbine blade 1 into the heating device 4 for heating. After heating to the set value, keep the temperature and start the high-temperature vibration fatigue test. Use a displacement sensor to monitor the amplitude in real time, and form a closed-loop control with the control system of the vibration equipment according to the amplitude value corresponding to the target stress value converted in step S3, so that the turbine blade 1 is in a real-time resonant state and the amplitude remains stable until the end of the test. Specifically, the control system of the vibration equipment includes a vibration table controller, a power amplifier, and an acceleration sensor, etc., combined with Figure 1 In the test system block diagram shown, the displacement sensor, vibration table controller, power amplifier, acceleration sensor, and vibration table together form a closed-loop control. The "resonance dwell" technology is used to perform real-time resonance excitation and measurement of the blades. The dual automatic control of amplitude monitoring and resonance dwell ensures the accurate and efficient implementation of the test until its completion.

[0049] Specifically, in this embodiment, in step S4, when closed-loop control is performed, the following formula is used:

[0050]

[0051] Dynamically correct the strain value corresponding to the target stress value, perform real-time automatic tracking and complete the test;

[0052] in:

[0053] E t : Elastic modulus at different temperatures, unit: GPa;

[0054] σ: stress, unit: MPa;

[0055] : mechanical strain;

[0056] R L : The resistance of a wire, unit: Ω;

[0057] : Strain gauge resistance value, unit: Ω.

[0058] In this embodiment, the clamp further includes a bolt 5; a mounting slot 202 is provided at the top of the base 2; the clamping block 3 is movably mounted within the mounting slot 202, and the clamping block 3 includes clamping portions located on either side of the tenon groove 301, and an elastic portion 302 connecting the two clamping portions; the bolt 5 is screwed onto the base 2 and tightens against the clamping portion on one side of the clamping block 3. In the present invention, the base 2 and clamping block 3 are movably mounted. When testing different blades, only the corresponding clamping block 3 needs to be replaced, without replacing the base 2. When clamping the turbine blade 1, the turbine blade 1 can be clamped and fixed by limiting the force with a torque wrench and tightening the bolt 5, which is simple and convenient to operate.

[0059] In this embodiment, the base 2, clamping block 3, and bolts 5 are all made of the same material as the turbine blade 1. Using the same material ensures that the linear expansion coefficients of the fixture and turbine blade 1 are consistent during heating, preventing the problem of loosening the clamping force at high temperatures. Furthermore, since turbine blades 1 are commonly made of high-temperature alloys, specifically GH39, the base 2, clamping block 3, and bolts 5 are also made of a high-temperature alloy, also designated GH39. GH39 can withstand the test temperatures without significant deformation.

[0060] Combine Figure 4The cooling channels 201 on the lower surface of the base 2 are uniformly spaced grooves. By providing these uniformly spaced grooves to form the cooling channels 201, uniform heat dissipation from the base 2 is ensured, significantly reducing the heat conduction effect between the base 2 and the vibration table. The cooling channels 201 reduce the heat conduction area, weakening the impact of temperature transfer on the excitation equipment, thus preventing equipment failure or alarms caused by high temperatures in the excitation equipment. Furthermore, they facilitate cooling with cooling air blowing to the bottom, forming multiple effective cooling channels.

[0061] In this embodiment, in order to simulate the actual use scenario of the turbine blade 1, in step S4, the heating device 4 is heated to ≥1000°C and then kept warm. When performing the high temperature vibration fatigue test, the number of cycles is not less than 2×10 7 Second-rate.

[0062] Combine Figure 6 As shown, the heating device 4 is mounted on a lifting frame 6, which is used to adjust the height of the heating device 4. The lifting frame 6 dynamically adjusts the position and height of the turbine blade 1 and fixture assembly within the heating device 4, automatically controlling heating of the heating device 4 to the target test temperature. During the temperature adjustment process, thermocouples are placed at different cross-sections within the heating device 4 to precisely control and monitor the test temperature and uniformity.

[0063] In this embodiment, in step S4, the displacement sensor is a laser displacement sensor.

[0064] The working principle of the present invention is mainly as follows: at room temperature, a strain gauge is attached and an "amplitude-stress" calibration test is carried out to obtain the functional relationship between the maximum stress point and the amplitude (the monitoring position remains unchanged during the test), and the amplitude value under the target test stress level is converted from the functional relationship, and the amplitude value is used for monitoring until the end of the test.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformation made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A high temperature vibration fatigue test method for turbine blades, characterized in that: The following steps are involved: S1: Preparation of a fixture, the fixture comprising a base (2) and a clamping block (3) arranged on the top of the base (2), wherein a tongue and groove (301) is arranged on the clamping block (3); the base (2) is used to be mounted on a vibration table of an excitation device, and a lower end surface of the base (2) in contact with the vibration table of the excitation device is provided with a plurality of cooling channels (201); S2: Install the turbine blade (1) into the mortise and tenon groove (301) of the clamp (3); S3: The fixture with the turbine blade (1) mounted thereon is mounted on a vibration table of the excitation device, a strain gauge is attached at room temperature, and an amplitude and strain calibration test is performed to obtain a functional relationship between the stress and amplitude at the maximum stress point, and the amplitude value corresponding to the target stress value is converted; S4: The fixture and the turbine blade (1) are placed together in a heating device (4) for heating. After heating to a set value, the temperature is maintained and a high-temperature vibration fatigue test is started. A displacement sensor is used for real-time amplitude monitoring. Based on the amplitude value corresponding to the target stress value converted in step S3, a closed-loop control is formed with the control system of the vibration equipment, so that the turbine blade (1) is in a resonance state in real time and the amplitude is kept stable until the end of the test.

2. A turbine blade high temperature vibration fatigue test method according to claim 1, characterized in that: In step S4, when closed-loop control is performed, the following formula is used: Dynamically correct the strain value corresponding to the target stress value, perform real-time automatic tracking and complete the test; in: E t : Elastic modulus at different temperatures, unit: GPa; σ: stress, unit: MPa; : mechanical strain; R L : The resistance of a wire, unit: Ω; : Strain gauge resistance value, unit: Ω.

3. A turbine blade high temperature vibration fatigue test method according to claim 1, characterized in that: The clamp further comprises a bolt (5); a mounting groove (202) is provided on the top of the base (2); the clamping block (3) is movably mounted in the mounting groove (202), and the clamping block (3) comprises clamping portions located on both sides of the tenon groove (301), and an elastic portion (302) connecting the two clamping portions; the bolt (5) is screwed onto the base (2) and presses against the clamping portion on one side of the clamping block (3).

4. A turbine blade high temperature vibration fatigue test method according to claim 3, characterized in that: The materials of the base (2), the clamping block (3), and the bolt (5) are all the same as the material of the turbine blade (1).

5. A turbine blade high temperature vibration fatigue test method according to claim 3, characterized in that: The base (2), the clamping block (3), and the bolt (5) are all made of a high-temperature alloy, and the material grade is GH39.

6. A turbine blade high temperature vibration fatigue test method according to claim 1, characterized in that: The cooling channels (201) on the lower end surface of the base (2) are grooves evenly distributed at equal intervals.

7. A turbine blade high temperature vibration fatigue test method according to claim 1, characterized in that: In step S4, the heating device (4) heats to ≥1000°C and then keeps the temperature.

8. A turbine blade high temperature vibration fatigue test method according to claim 1, characterized in that: In step S4, a high temperature vibration fatigue test is performed with the number of cycles not less than 2×10 7 Second-rate.

9. A turbine blade high temperature vibration fatigue test method according to claim 1, characterized in that: The heating device (4) is mounted on a lifting frame (6), and the lifting frame (6) is used to adjust the height of the heating device (4).

10. A turbine blade high temperature vibration fatigue test method according to claim 1, characterized in that: In step S4, the displacement sensor is a laser displacement sensor.

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