A low-pressure turbine blade vibration fatigue test acceleration test method

Abstract

The application belongs to the technical field of engine blade design, and particularly relates to a low-pressure turbine blade vibration fatigue test acceleration test method. The method comprises the following steps: determining a truncation height H; performing vibration stress analysis and vibration characteristic test on original blades and truncated blades, and comparing the stress gradient and the position of the section line; then performing vibration fatigue test and comparing the fatigue limit; and after ensuring that the key mechanical characteristics of the blades before and after truncation are consistent through multi-layer verification, solidifying the truncation scheme and using it for formal acceleration test. The application can effectively improve the vibration fatigue test efficiency of the low-pressure turbine blade.

Description

Technical Field

[0001] This application belongs to the field of engine blade design technology, specifically relating to an accelerated test method for vibration fatigue testing of low-pressure turbine blades. Background Technology

[0002] In recent years, with the increasing demands for long-life and high-reliability technologies in engines and the growing number of engines in production, how to test the fatigue performance of low-pressure turbine blades in mass production and quickly and accurately obtain the baseline fatigue performance of blades under specific confidence levels and survival rates has become an urgent problem to be solved. Generally, low-pressure turbine blades are crowned, high-aspect-ratio structures. Their inherent structural characteristics result in very weak modal stiffness; the first-order natural frequency under typical tenon clamping and crown-free conditions is only a few hundred or even tens of hertz. According to current general specifications, 10... 7 ~10 8 Vibration fatigue testing can take tens to hundreds of hours, and completing all fatigue tests requires a cycle of months, which severely restricts the efficiency of testing.

[0003] Existing technologies include truncated vibration fatigue tests on stator blades, accelerated testing based on linear damage accumulation, and tests that shorten the cycle number by increasing stress levels based on the functional relationship of the SN curve. Among these methods, the structural and stress distribution differences between stator and rotor blades make these methods unsuitable for accelerated rotor blade testing. Furthermore, current turbine stator blades are multi-unit cast structures with inherently high natural frequencies, making accelerated testing less necessary. The primary damage mode during blade vibration fatigue is high-cycle fatigue, which does not follow a linear accumulation principle. Therefore, increasing stress levels to increase damage is not suitable for accelerated vibration fatigue testing of low-pressure turbine blades. Vibration fatigue tests themselves exhibit significant divergence, and the SN curve is a stress-cycle relationship fitted by the Basquin equation. Using increased stress levels to shorten the cycle number for verification introduces errors and reduces test accuracy. Summary of the Invention

[0004] To address the aforementioned problems, this application provides an accelerated testing method for vibration fatigue testing of low-pressure turbine blades, applied to low-pressure turbine rotor blades, the method comprising:

[0005] Step S1: Shorten the low-pressure turbine blades and determine the height H of the shortened low-pressure turbine blades;

[0006] Step S2: Perform vibration stress analysis on the original blade and the truncated blade to obtain the relative vibration stress distribution and truncated line position of the blade before and after truncation.

[0007] Step S3: Determine whether the cut-off line position and stress gradient of the blade before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S4.

[0008] Step S4: Conduct vibration characteristic tests on the blades before and after truncation on a vibration table to obtain the measured vibration stress distribution of the blades before and after truncation.

[0009] Step S5: Determine whether the measured stress gradients of the blades before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S6.

[0010] Step S6: Under the same test conditions, conduct vibration fatigue tests on the blades before and after truncation to obtain the fatigue limits of the blades before and after truncation.

[0011] Step S7: Determine whether the fatigue limits of the blades before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S8.

[0012] Step S8: Determine the truncation height of the accelerated test blade and solidify the test method.

[0013] Preferably, in step S1, the principle for determining the height H is to reduce the height H to increase the natural frequency, provided that the stress gradient of the shortened blade is consistent with that of the original blade and the truncation line is located at the blade root.

[0014] Preferably, in step S2, the object of the vibration stress analysis includes at least the relative vibration stress distribution of the leading edge, trailing edge and middle of the back side of the blade.

[0015] Preferably, in step S4, the vibration characteristic test is used to obtain the measured vibration stress distribution at the leading edge, trailing edge, and middle of the back side of the blade.

[0016] Preferably, in step S6, the same test conditions include test equipment, test temperature, stress gradient, and clamp tightening torque.

[0017] Preferably, in steps S3, S5 and S7, the judgment of being the same means that the deviation between the corresponding parameters of the blades before and after truncation is within a preset allowable range.

[0018] Preferably, in step S6, the vibration fatigue test is conducted at the same confidence level and survival rate.

[0019] Preferably, the method further includes conducting vibration fatigue tests using truncated blades.

[0020] This application can effectively improve the efficiency of vibration fatigue testing of low-pressure turbine blades. Attached Figure Description

[0021] Figure 1 This is a flowchart of the accelerated test design of a preferred embodiment of the accelerated test method for vibration fatigue testing of low-pressure turbine blades in this application.

[0022] Figure 2 This is a schematic diagram of a truncated low-pressure turbine blade.

[0023] Figure 3 This is a schematic diagram of vibration characteristic simulation analysis.

[0024] Figure 4 This is a schematic diagram of the simulated stress gradient.

[0025] Figure 5 This is a schematic diagram of the test stress calibration.

[0026] Figure 6 This is a schematic diagram of the stress distribution during the test vibration. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0028] This application provides an accelerated testing method for vibration fatigue testing of low-pressure turbine blades, such as... Figure 1 As shown, it mainly includes:

[0029] Step S1: Shorten the low-pressure turbine blades and determine the height H of the shortened low-pressure turbine blades;

[0030] Step S2: Perform vibration stress analysis on the original blade and the truncated blade to obtain the relative vibration stress distribution and truncated line position of the blade before and after truncation.

[0031] Step S3: Determine whether the cut-off line position and stress gradient of the blade before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S4.

[0032] Step S4: Conduct vibration characteristic tests on the blades before and after truncation on a vibration table to obtain the measured vibration stress distribution of the blades before and after truncation.

[0033] Step S5: Determine whether the measured stress gradients of the blades before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S6.

[0034] Step S6: Under the same test conditions, conduct vibration fatigue tests on the blades before and after truncation to obtain the fatigue limits of the blades before and after truncation.

[0035] Step S7: Determine whether the fatigue limits of the blades before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S8.

[0036] Step S8: Determine the truncation height of the accelerated test blade and solidify the test method.

[0037] This application shortens the vibration fatigue test time by truncating the blade to increase its natural frequency. However, truncating cannot be done arbitrarily; the truncated blade must maintain consistency with the original blade in key mechanical properties, such as stress gradient, truncation position, and fatigue limit. Otherwise, the test results are invalid. Therefore, this application establishes a three-layer verification process: simulation verification in steps S2-S3, vibration characteristic test verification in steps S4-S5, and vibration fatigue test verification in steps S6-S7. Only after all steps pass can the truncating scheme be finalized and solidified.

[0038] This application significantly improves testing efficiency. The truncated natural frequency increases, and the testing time is significantly shortened for the same number of cycles, reducing time and testing costs. Simultaneously, this application avoids damage conversion errors because it does not rely on SN curves or linear cumulative damage assumptions, but directly verifies through physical comparison, eliminating additional errors introduced by conversion. Finally, this application ensures the reliability and validity of accelerated testing results through multi-layer verification, solving the problem of neglecting stress gradient consistency in existing technologies.

[0039] In some alternative implementations, in step S1, the principle for determining the height H is to reduce the height H to increase the natural frequency, provided that the stress gradient of the shortened blade is consistent with that of the original blade and the truncation line is located at the blade root.

[0040] Understandably, a smaller height H results in a higher natural frequency and a better acceleration effect. However, excessive truncation can alter the stress gradient, and the truncation position may shift from the blade root to the extension root or tenon, distorting the experimental conditions. Therefore, it is essential to choose the smallest possible H while ensuring a consistent stress gradient and that the truncation position remains at the blade root.

[0041] This embodiment balances acceleration and experimental realism, avoiding the sacrifice of experimental representativeness in the blind pursuit of high frequency.

[0042] In some alternative implementations, in step S2, the object of the vibration stress analysis includes at least the relative vibration stress distribution of the leading edge, trailing edge, and middle of the back side of the blade.

[0043] In this embodiment, the leading edge, trailing edge, and middle of the dorsal side are critical areas for blade vibration fatigue, and the stress distribution at these locations determines the likelihood of fatigue crack initiation. By comparing the relative stress distribution at these locations before and after truncation, it can be determined whether the stress gradient is consistent.

[0044] This embodiment selected some representative hazardous sections mentioned above, which not only ensured the sufficiency of the verification but also avoided unnecessary detailed modeling of the entire blade, thus improving the analysis efficiency.

[0045] In some alternative implementations, in step S4, the vibration characteristic test is used to obtain the measured vibration stress distribution at the leading edge, trailing edge, and middle of the back side of the blade.

[0046] In some alternative implementations, the same test conditions in step S6 include test equipment, test temperature, stress gradient, and clamp tightening torque.

[0047] It is understandable that in vibration fatigue testing, the equipment model, ambient temperature, applied stress level, and clamping method all affect the test results. Only by unifying these factors can the comparison of the fatigue limits of the blade before and after truncation be meaningful. This embodiment eliminates the interference of external variables, attributing the difference in fatigue limits solely to the geometric changes of the blade, thereby accurately determining whether truncation has altered the intrinsic fatigue performance of the blade.

[0048] In some optional implementations, in steps S3, S5 and S7, the determination of being the same means that the deviation between the corresponding parameters of the blades before and after truncation is within a preset allowable range.

[0049] Since manufacturing tolerances and measurement errors are objectively present, setting a reasonable allowable deviation range is more in line with engineering practice. For example, stress gradients that differ by no more than 5% or 10% can be considered the same.

[0050] like Figure 3 As shown, simulation analysis of the truncation line position before and after leaf truncation shows that the distance deviation between the truncation line and the leaf root on the pot side and back side is within the allowable range. Figure 4 As shown, through simulation analysis, the corresponding vibration stress deviations of each key point (distance relative to the cut line) before and after the blade is cut are within the allowable range, which means that the simulated stress gradient is considered to be the same.

[0051] Similarly, refer to Figure 5 The test results were obtained by bonding strain gauges to determine whether the measured stress gradients of the blades before and after truncation were the same. Figure 6 As shown, if the corresponding vibration stress deviation at each key point (distance relative to the cut-off line) is within the allowable range, the test stress gradient is considered to be the same.

[0052] In some alternative implementations, in step S6, the vibration fatigue test is performed at the same confidence level and survival rate.

[0053] The results of fatigue tests exhibit statistical dispersion and typically require evaluation at a certain confidence level and survival rate. It is essential that tests before and after truncation be conducted under the same statistical indicators to ensure consistent benchmarks for comparison.

[0054] In some alternative embodiments, the method further includes conducting vibration fatigue tests using truncated blades.

[0055] After determining the truncation height and solidifying the method in the aforementioned steps, the final practical application involves conducting formal vibration fatigue tests on blades manufactured using this truncation scheme. This application not only outlines a process for determining truncation parameters but also includes steps for conducting accelerated testing using the truncated blade.

[0056] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An accelerated testing method for vibration fatigue testing of low-pressure turbine blades, characterized in that, include: Step S1: Shorten the low-pressure turbine blades and determine the height H of the shortened low-pressure turbine blades; Step S2: Perform vibration stress analysis on the original blade and the truncated blade to obtain the relative vibration stress distribution and truncated line position of the blade before and after truncation. Step S3: Determine whether the cut-off line position and stress gradient of the blade before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S4. Step S4: Conduct vibration characteristic tests on the blades before and after truncation on a vibration table to obtain the measured vibration stress distribution of the blades before and after truncation. Step S5: Determine whether the measured stress gradients of the blades before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S6. Step S6: Under the same test conditions, conduct vibration fatigue tests on the blades before and after truncation to obtain the fatigue limits of the blades before and after truncation. Step S7: Determine whether the fatigue limits of the blades before and after truncation are the same. If they are not the same, return to step S1 to redetermine the height H. If they are the same, proceed to step S8. Step S8: Determine the truncation height of the accelerated test blade and solidify the test method.

2. The accelerated test method for vibration fatigue testing of low-pressure turbine blades according to claim 1, characterized in that, In step S1, the principle for determining the height H is to reduce the height H to increase the natural frequency, provided that the stress gradient of the shortened blade is consistent with that of the original blade and the truncation line is located at the blade root.

3. The accelerated test method for vibration fatigue testing of low-pressure turbine blades according to claim 1, characterized in that, In step S2, the object of the vibration stress analysis includes at least the relative vibration stress distribution of the leading edge, trailing edge and middle of the back side of the blade.

4. The accelerated test method for vibration fatigue testing of low-pressure turbine blades according to claim 1, characterized in that, In step S4, the vibration characteristic test is used to obtain the measured vibration stress distribution at the leading edge, trailing edge, and middle of the back side of the blade.

5. The accelerated test method for vibration fatigue testing of low-pressure turbine blades according to claim 1, characterized in that, In step S6, the same test conditions include test equipment, test temperature, stress gradient, and clamp tightening torque.

6. The accelerated test method for vibration fatigue testing of low-pressure turbine blades according to claim 1, characterized in that, In steps S3, S5, and S7, the judgment of being the same means that the deviation between the corresponding parameters of the blades before and after truncation is within a preset allowable range.

7. The accelerated test method for vibration fatigue testing of low-pressure turbine blades according to claim 1, characterized in that, In step S6, the vibration fatigue test is conducted at the same confidence level and survival rate.

8. The accelerated test method for vibration fatigue testing of low-pressure turbine blades according to claim 1, characterized in that, The method also includes conducting vibration fatigue tests using truncated blades.

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