A new type of gas turbine turbine blade vibration fatigue test method
By employing step stress loading and progressive stress loading methods, along with the stress concession principle, in gas turbine blade testing, the problems of high cost and data dispersion in traditional testing were solved, achieving efficient and accurate fatigue strength assessment.
Patent Information
- Application Number
- CN202610812001.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-06
- Publication Date
- 2026-07-10
AI Technical Summary
Traditional vibration fatigue tests of gas turbine blades require a large number of test specimens and the data is highly dispersed, resulting in high test costs and large errors in the results, which cannot meet the confidence requirements.
By employing step stress loading and progressive stress loading methods, combined with the stress concession principle, the median fatigue strength of turbine blades is obtained through finite test specimens. This method follows the standard of the step-up method, reducing test costs and improving the coverage and accuracy of test data.
Fatigue tests at multiple stress levels can be performed on a limited number of test specimens, shortening the test time and improving the confidence and accuracy of the test data. Only 2-3 stress levels are needed to achieve 95% confidence, reducing test costs and indicating manufacturing defects.
Smart Images
Figure CN122360853A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of gas turbine technology, specifically relating to a novel method for testing the vibration fatigue of moving blades in a gas turbine. Background Technology
[0002] Gas turbines, as the main propulsion devices of ships, have the characteristics of high power density and low pollution emissions. As the product range of gas turbines becomes more complete, the working environment of turbine blades becomes more complex. Therefore, it is necessary to carry out turbine blade vibration fatigue tests to check whether the turbine blade structure meets the strength design requirements and to evaluate the rationality of the manufacturing process.
[0003] Vibration fatigue tests of gas turbine blades generally use the traditional lifting method to obtain the fatigue limit value of the blades. However, the lifting method requires a large number of test blades to meet the confidence requirements of the results, and each blade is only tested at one stress level, which increases the consumption of test pieces. When the test data is highly dispersed, the obtained fatigue limit value will also have a large error. Summary of the Invention
[0004] The purpose of this invention is to provide a novel method for testing the vibration fatigue of moving blades in a gas turbine.
[0005] A novel method for vibration fatigue testing of moving blades in a gas turbine includes the following steps: S1. Conduct blade modal analysis to determine the blade resonant frequency and dynamic stress distribution, pinpoint the stress monitoring point location and maximum stress ratio, and estimate the initial stress value of the experiment. ; S2, combined with the analysis results of S1, the blade is excited to generate resonance on the electromagnetic vibration table through the test fixture. The relationship function between the peak-to-peak value of the blade tip amplitude and the peak-to-peak value of the stress is calibrated using the least squares method. The target stress and the corresponding blade vibration peak value are determined and fed back to the control system to start the test. S3, take 0.6 times. As the initial stress, the stress interval is taken Apply step stress and take stress intervals. Apply stress in stages. Values 4% to 6%, taking multiples of 5 or 10; S4. For the first few blades in the same batch, when the stress levels achieved by the preceding and subsequent blades differ significantly, apply a step-load stress to the same blades, based on the stress at which the previous blade fractured before completing the specified number of vibration cycles. and the applied stress interval The initial stress is Stress interval according to Furthermore, the values are rounded down to multiples of 5 or 10 to determine the range of fatigue limits for the blades and save testing time. S5, the stress level difference that the front and rear blades can achieve is approximately At that time, according to the stress level when the previous stage blade fractured. reduce The test begins at a certain level and stress is gradually applied until the blade breaks. When the test data are relatively consistent, the initial stress can be increased by one stress level to ensure that the test data has low dispersion and the test blade has high utilization rate.
[0006] Furthermore, when the limited number of test specimens cannot meet the pairing requirements of the lifting method, a concession method is adopted. For the same turbine blade, due to the influence of structural characteristics and fatigue strength, at the current stress level... If the specified target number of cycles is completed without fracture, then the yield can be made to the stress level [ , The specified target number of cycles was achieved within the interval without any break.
[0007] Furthermore, when the limited number of test specimens cannot meet the pairing requirements of the lifting method, a concession method is adopted. For the same turbine blade, due to the influence of structural characteristics and fatigue strength, at the current stress level... If fracture occurs before the specified number of cycles is completed, then a concession can be made to the stress level [ The loop breaks when the specified number of iterations is reached.
[0008] Furthermore, by adopting step stress loading and progressive stress loading methods, the required stress levels for the same blade are minimized. Only a limited number of stress levels of vibration fatigue tests are conducted on a limited number of blades. The concession method can supplement the missing test data based on the existing data, which follows the test standard of the step-up method and reduces the number of pairs.
[0009] Furthermore, according to the standard of the lifting method test, under the condition of a limited number of test pieces, the fewer the stress levels, the lower the coefficient of variation, and the higher the test accuracy. Moreover, the stress loading method invented can determine the fatigue strength level of individual blades and indicate the level of processing technology. When the stress level of individual blades is low, it proves that there are process defects.
[0010] Furthermore, the method of exciting blade resonance by using a novel step stress loading and step-by-step stress loading on the same turbine blade test piece, and using the stress concession principle to continue using the rise and fall method pairing standard to obtain the median fatigue strength of the turbine blade, shortens the number of test stress levels and has a high confidence level. The test results are highly accurate and have obvious application indication characteristics.
[0011] The beneficial effects of this invention are as follows: This invention uses a novel step stress loading and progressive stress loading method on the same blade test piece to conduct correlation tests and uses the stress concession principle to obtain the median fatigue strength of the blade. It can carry out fatigue limit tests at a limited number of stress levels on a limited number of blades while adhering to the traditional rise and fall method test standards, thereby reducing test costs and improving the coverage of test data. Only 2-3 stress levels are needed in the pairing process to achieve a confidence level of over 95% for the test fitting results, and the test results have small deviations. Attached Figure Description
[0012] Figure 1(a) shows the location of the turbine blade patch; Figure 1(b) is a calibration diagram of the stress-displacement relationship of the turbine blade; Figure 2 The logic block diagram for step-type stress loading and step-by-step stress loading is shown below. Figure 3 This is a flowchart of the novel turbine blade vibration fatigue test method of the present invention; Figure 4 This is a diagram illustrating the experimental process of implementing the present invention. Figure 5 This is a comparison chart of the results from the traditional elevation and lowering method. Detailed Implementation
[0013] The present invention will now be further described with reference to the accompanying drawings.
[0014] As shown in Figure 1- Figure 5 As shown, a novel method for vibration fatigue testing of gas turbine turbine blades includes the following steps: S1. Conduct blade modal analysis to determine the blade resonant frequency and dynamic stress distribution, pinpoint the stress monitoring points and maximum stress ratio, and estimate the initial stress value based on engineering experience and material mechanical properties. ; S2. Based on the analysis results of S1, the blade is excited to generate resonance on the electromagnetic vibration table using a special test fixture. The relationship function between the peak-to-peak value of the blade tip amplitude and the peak-to-peak value of the stress is calibrated using the least squares method. The target stress and the corresponding blade vibration peak value are determined and fed back to the control system to start the test. S3, take 0.6 times. As the initial stress, to avoid wasting test specimens due to incorrect estimation, the stress interval is taken. Apply step stress and take stress intervals. Apply stress in stages. The value is approximately 4% to 6%, generally taken as an integer multiple of 5 or 10; S4. For the first or first few blades in the same batch, if the stress levels achieved by the preceding and subsequent blades differ significantly, it is necessary to apply a step-load stress to the same blades, based on the stress at which the previous blade fractured before completing the specified number of vibration cycles. and the applied stress interval The initial stress is Stress interval according to Furthermore, the values are rounded down to multiples of 5 or 10 (i.e., 17.5 is rounded to 15, and 12.5 is rounded to 10) to determine the range of fatigue limit values for the blades and save testing time. S5, the stress level difference that the front and rear blades can achieve is approximately At that time, according to the stress level when the previous stage blade fractured. reduce The test begins at a certain level and stress is gradually applied until the blade breaks. When the test data are relatively consistent, the initial stress can be increased by one stress level to ensure that the test data has low dispersion and the test blade has high utilization rate.
[0015] Example: To meet the needs of the unit's development, a vibration fatigue test was conducted on the newly developed low-pressure turbine blade. The blade material is a cast high-temperature alloy. Modal analysis was performed using finite element software, and the first natural frequency of the blade was determined to be approximately 750 Hz. The strain gauges were attached to a location on the back of the blade where the geometric gradient was small. The maximum stress ratio was 0.68. Based on engineering experience, the initial stress value of the monitoring location was set at 200 MPa.
[0016] The blade was subjected to fixed-frequency excitation by installing it on a blade vibration test bench with special tooling. The first-order frequency of the blade was determined to be 732.35Hz by frequency sweep test. The peak-to-peak amplitude and peak-to-peak stress were calibrated and fitted with formulas, as shown in Figure 1.
[0017] Based on the actual number of test specimens, we plan to conduct step-load and gradual stress loading to evaluate the fatigue strength of the blades. The specific implementation logic diagram is as follows: Figure 2 As shown, the stress starts at 120 MPa, and the stress interval is... =10MPa, vibration cycle number is 2×10 7 .
[0018] Vibration fatigue tests were conducted on the first blade (No. 1). After passing the specified number of cycles under a stress of 120 MPa, the test was continued using a new step stress loading method. The specified number of cycles was passed under stresses of 130 MPa and 160 MPa. The test was terminated after 3,536,238 vibration cycles under a stress of 220 MPa. Frequency sweeping showed that the blade frequency dropped by more than 1%, and dye penetrant testing revealed cracks at the blade root.
[0019] For blade #2, tests were conducted with an initial stress of 160 MPa, and 2 × 10⁻⁶ tests were completed under this stress. 7 The next vibration cycle, according to Figure 2 The next two stress levels were tested at 190MPa and 210MPa respectively. After 1,256,482 cycles at a stress of 210MPa, blade #2 developed cracks.
[0020] For blade #3, the test was conducted with an initial stress of 190 MPa. The blade under the stress of 190 MPa underwent a specified number of cycles. The subsequent two stress levels were tested at 200 MPa and 205 MPa, respectively. Blade #3 developed cracks after 7,135,535 cycles under the stress of 205 MPa.
[0021] The stress level difference between blades #2 and #3 is close to the stress interval. Therefore, the new blades will be tested using a step-by-step loading method. Figure 3 The test procedure is as follows: for blade #4, the test will start at 185 MPa and continue at stress intervals of 10 MPa until the blade breaks.
[0022] Following this pattern, blade #4 broke at 195 MPa and then at 205 MPa, blade #5 broke at 195 MPa, and so on, until the 9th blade was tested. The specific test process and results are as follows: Figure 4 As shown.
[0023] The test results were statistically analyzed. A total of 21 stress levels of step stress loading and progressive stress loading vibration fatigue tests were carried out on the 9 blades. The test results were analyzed according to the standard of measuring the median fatigue strength by the rise and fall method in HB / Z112-86 "Statistical Analysis Method for Fatigue Testing of Materials".
[0024] The yield method was used to reduce the stress level of blades #2 and #3. Blade #2 yielded at a stress level of 185 MPa, and blade #3 yielded at a stress level of 195 MPa.
[0025] Therefore, the test data from 8 out of 9 test blades were fully utilized, with a median fatigue strength of 197.5 MPa and a fatigue strength subsample standard deviation of [missing data]. S # The coefficient of variation is 5. C V The result is 0.0253, which meets the statistical standard of HB / Z112-86 "Statistical Analysis Method for Fatigue Testing of Materials" and satisfies the requirement that the confidence level of the result is 95% when the minimum number of observation samples is 4.
[0026] The stress concession method described in this invention enables the stress pairing process to be faster and more flexible, reduces the dispersion of experimental data, obtains the median fatigue strength of the blade using only 3 stress levels, has a low coefficient of variation, and can be inferred from this to have high accuracy of the experimental results.
[0027] Vibration fatigue test data for blades of the same class in other units, such as Figure 5 As shown in the comparison, it can be seen that compared with the traditional lifting method, which requires 18 vibration fatigue tests to collect stress samples, this invention only uses 9 blades to determine the fatigue limit value of this stage of blades, and the coefficient of variation is low. It can be seen that the method of testing blade fatigue strength using this invention is efficient and fast. At the same time, the test data of 9 blades also show that the fatigue strength level of this batch of blades is relatively uniform, indicating that there are no problems with the processing technology.
Claims
1. A novel method for vibration fatigue testing of moving blades in a gas turbine, characterized in that, Includes the following steps: S1. Conduct blade modal analysis to determine the blade resonant frequency and dynamic stress distribution, pinpoint the stress monitoring point location and maximum stress ratio, and estimate the initial stress value of the experiment. ; S2, combined with the analysis results of S1, the blade is excited to generate resonance on the electromagnetic vibration table through the test fixture. The relationship function between the peak-to-peak value of the blade tip amplitude and the peak-to-peak value of the stress is calibrated using the least squares method. The target stress and the corresponding blade vibration peak value are determined and fed back to the control system to start the test. S3, take 0.6 times. As the initial stress, the stress interval is taken Apply step stress and take stress intervals. Apply stress in stages. Values 4% to 6%, taking multiples of 5 or 10; S4. For the first few blades in the same batch, when the stress levels achieved by the preceding and subsequent blades differ significantly, apply a step-load stress to the same blades, based on the stress at which the previous blade fractured before completing the specified number of vibration cycles. and the applied stress interval The initial stress is Stress interval according to Furthermore, the values are rounded down to multiples of 5 or 10 to determine the range of fatigue limits for the blades and save testing time. S5, the stress level difference that the front and rear blades can achieve is approximately At that time, according to the stress level when the previous stage blade fractured. reduce The test begins at a certain level and stress is gradually applied until the blade breaks. When the test data are relatively consistent, the initial stress can be increased by one stress level to ensure that the test data has low dispersion and the test blade has high utilization rate.
2. The novel vibration fatigue test method for gas turbine turbine blades according to claim 1, characterized in that, When the limited number of test specimens cannot meet the pairing requirements of the lifting method, the concession method is adopted. For the same turbine blade, due to the influence of structural characteristics and fatigue strength, at the current stress level... If the specified target number of cycles is completed without fracture, then the yield can be made to the stress level [ , The specified target number of cycles was achieved within the interval without any break.
3. The novel vibration fatigue test method for gas turbine turbine blades according to claim 1, characterized in that, When the limited number of test specimens cannot meet the pairing requirements of the lifting method, the concession method is adopted. For the same turbine blade, due to the influence of structural characteristics and fatigue strength, at the current stress level... If fracture occurs before the specified number of cycles is completed, then a concession can be made to the stress level [ The loop breaks when the specified number of iterations is reached.
4. The novel vibration fatigue test method for gas turbine turbine blades according to claim 1, characterized in that, By adopting step stress loading and progressive stress loading methods, the required stress levels for the same blade are minimized. Only a limited number of stress levels of vibration fatigue tests are conducted on a limited number of blades. The concession method can supplement the missing test data based on the existing data, which follows the test standard of the step-up method and reduces the number of pairs.
5. The novel vibration fatigue test method for gas turbine turbine blades according to claim 1, characterized in that, According to the standard of the lifting method test, under the condition of a limited number of test pieces, the fewer the stress levels, the lower the coefficient of variation, and the higher the test accuracy. Furthermore, the stress loading method invented can determine the fatigue strength level of individual blades and indicate the level of processing technology. When the stress level of individual blades is low, it proves that there are process defects.
6. The novel vibration fatigue test method for gas turbine turbine blades according to claim 1, characterized in that, The method described above uses a novel step stress loading and step-by-step stress loading method to excite blade resonance on the same turbine blade test specimen. The stress concession principle is adopted to continue using the rise and fall method to obtain the median fatigue strength of the turbine blade. This shortens the number of test stress levels and has a high confidence level. The test results are highly accurate and have obvious application indication characteristics.