An accelerated test method for ultra-high cycle fatigue of titanium alloy blades for a small number of samples

Abstract

The present application discloses a method for accelerating ultra-high cycle fatigue test of titanium alloy blades of a few-carrier sample compressor, comprising the steps of: S1, specifying the cycle base number N of the ultra-high cycle fatigue acceleration test, N < 10 9 , use the step-by-step loading method or the lifting method to conduct a high-cycle fatigue test on the blade test sample to obtain the test results under the specified cycle base N, and the test results include vibration fatigue strength; S2, calculate the mean S, standard deviation and coefficient of variation of the vibration fatigue strength of the blade test sample based on the test results; S3, if the number of blade test samples meets the minimum number of observations required when the confidence level is set, substitute the mean S of the vibration fatigue strength of the high-cycle fatigue accelerated test and the specified cycle base N into the S-N curve equation to calculate the fatigue limit, and obtain the cycle base N of 10 9 This application shortens the test time, significantly improves the test efficiency, reduces the test cost, and ensures the comparability and reproducibility of the test results.

Description

Technical Field

[0001] The present application relates to the field of aero-engine technology, and in particular, to a method for accelerating ultra-high cycle fatigue testing of titanium alloy blades of a minority-sample compressor. Background Art

[0002] Aircraft engine blades are one of the most critical components of aircraft engines. They operate in harsh environments, require complex design and testing techniques, and require high-tech processing and inspection capabilities. They are knowledge-intensive and technology-intensive products. During operation, aircraft engine blades are susceptible to vibration due to gas and mechanical excitation forces. Vibration is a major factor in mechanical failure in rotating machinery blades. Therefore, high-cycle fatigue testing of blades is essential to determine their fatigue limits and provide reliable data support for blade strength optimization design. Existing testing methods include step-by-step loading and the lift method.

[0003] When conducting vibration fatigue tests on aircraft engine blades, the above two test methods are to obtain the vibration fatigue strength at a specified cycle base. The fewer the cycle base, the shorter the test period. For titanium alloy blades, 10 9 Vibration fatigue strength under multiple cycles will result in excessively long test cycles, occupying test resources and incurring high test costs. For a certain stage of aircraft engine blades, the cycle time statistics for each stress level are shown in Table 1. The cycle base results in a 100-fold difference in test duration. If the lifting method specified in the "Statistical Analysis Method for Material Fatigue Testing HB-Z112-86" is used, a minimum of 12 blades are required for each stage, and the entire test process requires 1521.6 hours. If each blade is driven to fracture using the step-by-step loading method, the test stress level for each blade is uncertain, and the number of blades is uncertain, given the dispersion of the blades. The estimated test time will be longer than the lifting method. Both methods will lead to a severe shortage of human and equipment resources, slow test progress, and hinder aircraft engine development. Summary of the Invention

[0004] The present application provides a method for accelerating ultra-high cycle fatigue testing of titanium alloy blades of a small number of sample compressors, in order to solve the technical problems that the existing high-cycle fatigue testing of blades has a long cycle and high cost, resulting in a high shortage of human and equipment resources, slow progress and affecting the development of aircraft engines.

[0005] The technical solutions adopted in this application are as follows:

[0006] A method for accelerating ultra-high cycle fatigue testing of a titanium alloy blade of a small number of carrier samples for a compressor comprises the following steps:

[0007] S1. Specify the cycle number N of the ultra-high cycle fatigue accelerated test, N<10 9, using a step-by-step loading method or a lifting method to conduct a high-cycle fatigue test on the blade test sample to obtain test results under a specified cycle base number N, the test results including vibration fatigue strength;

[0008] S2. Calculate the mean S, standard deviation and coefficient of variation of the vibration fatigue strength of the blade test sample based on the test results;

[0009] S3. If the number of blade test samples meets the minimum number of observations required when setting the confidence level, the mean value S of the vibration fatigue strength of the high-cycle fatigue accelerated test and the specified cycle base N are substituted into the SN curve equation to calculate the fatigue limit. The cycle base is 10 9 The fatigue strength under the condition of SN curve is as follows:

[0010]

[0011] Where: S is the alternating stress / load amplitude; S ∞ is the fatigue limit; N is the number of failure cycles corresponding to alternating stress / load, which is 10 6 times; A and γ are the shape parameters of the fatigue curve.

[0012] Furthermore, in step S1, if the number of blade test samples is less than 12, a high cycle fatigue test is performed using a stepwise loading method to obtain test results under a specified cycle base number N.

[0013] Furthermore, in step S1, if the number of blade test samples is ≥12, a high cycle fatigue test is performed using a stepwise loading method or a lifting method to obtain test results under a specified cycle base number N.

[0014] Furthermore, in step S1, a closed-loop control method is adopted when performing high-cycle fatigue tests using the step-by-step loading method or the lifting method. The amplitude of the blade test sample is measured in real time and fed back to the vibration controller. The controller automatically adjusts the control signal output to the vibration table based on the feedback signal to ensure that the blade test sample is always tested in a resonant state and at the specified amplitude.

[0015] Furthermore, before performing the high cycle fatigue test on the blade test sample using the stepwise loading method or the lifting method in step S1, the method further includes the following steps:

[0016] Calculate the vibration characteristics of the blade and transition section to obtain the blade's natural frequency, modal vibration shape, and stress distribution. Determine the test frequency and patch position. Select an electromagnetic vibration table with appropriate specifications. The first-order natural frequency of the transition section deviates from the blade's natural frequency to prevent vibration coupling.

[0017] The strain gauge measurement method is used to obtain the stress distribution at the strain gauge attachment location. That is, based on theoretical calculations or modal measurements, multiple strain gauges are attached to the maximum stress area. The vibration table frequency is adjusted to maintain constant excitation at a certain natural frequency of the blade. Repeat the measurement multiple times or adjust the magnitude of the excitation force to measure multiple sets of data. Based on the strain value of each point in each set of data, the stress distribution results at the attachment location can be obtained and compared with the finite element calculation results. The actual measurement shall prevail.

[0018] Stress calibration: stick strain gauges at the maximum stress point or the area with small stress gradient, vibrate at the natural frequency of the blade, measure the strain and blade tip amplitude, adjust the magnitude of the exciting force, measure the strain value and amplitude at the same time, measure at least 5 sets of data, and fit the linear relationship based on the measured data to obtain the strain-amplitude curve. The stress is calculated by strain and elastic modulus to obtain the stress-amplitude curve. For patches at non-maximum stress points, the maximum stress-amplitude curve is converted based on the proportional relationship between the patch point and the maximum stress point.

[0019] Furthermore, in step S3, when the material and process of the titanium alloy are consistent with the preset values, A and γ are the shape parameters of the fatigue curve and adopt the recommended values, where, in the absence of corrosion, the recommended value of A is 0.205, and the recommended value of γ is 0.49; in the case of corrosion, the recommended value of A is 0.811, and the recommended value of γ is 0.63.

[0020] Furthermore, in step S3, when the material and process of the titanium alloy are inconsistent with the preset ones, first select 2 to 3 stress levels in the middle life region of the SN curve, and use the grouping method to determine the median fatigue life of the blade test sample. In the long life region of the SN curve, specify several groups of cycle bases, and use the lifting and lowering method to determine the fatigue limit of the blade test sample. Then, fit the SN curve formula to solve the shape parameters A and γ of the fatigue curve.

[0021] Furthermore, in step S3, if the number of blade test samples does not meet the minimum number of observations required when the confidence level is set, the number of blade test samples is continued to be increased and the above steps are repeated until the number of blade test samples meets the minimum number of observations required when the confidence level is set.

[0022] Furthermore, in step S3, the confidence level is set to 90% or 95%.

[0023] Furthermore, in step S1, the cycle base N of the specified ultra-high cycle fatigue accelerated test is 10 7 or 3*10 7 .

[0024] Compared with the existing technology, this application has the following beneficial effects:

[0025] The present application provides a method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for compressors with a small number of samples. The method integrates the characteristics of SN curve formula fitting and step-by-step loading method or lifting method to perform high cycle fatigue testing on blade test samples. The method can be used in a small number of samples and only in a smaller cycle base number N < 10 9 Under the condition of ultra-high cycle acceleration test, the titanium alloy blade can be obtained at a cycle base of 10 9 The high cycle fatigue limit under the test condition is greatly shortened, the test time is significantly improved, the test efficiency is significantly improved, the test cost is reduced, and relatively accurate and reliable data is provided to ensure the comparability and reproducibility of the test results.

[0026] In addition to the above-described purposes, features and advantages, the present application also has other purposes, features and advantages. The present application will be further described in detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0028] Figure 1 This is a schematic diagram of the step-by-step loading method for a single blade;

[0029] Figure 2 It is a schematic diagram of the lifting method;

[0030] Figure 3 Schematic diagram of the ultra-high cycle fatigue accelerated test method for minority-carrier compressor titanium alloy blades according to the preferred embodiment of the present application;

[0031] Figure 4 It is a schematic diagram of the principle of vibration fatigue test device;

[0032] Figure 5 It is a schematic diagram of the accelerated test fitting curve. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below with reference to the accompanying drawings, but the present application can be implemented in a variety of different ways defined and covered below.

[0034] Existing aero-engine blade vibration fatigue test methods include the step-by-step loading method and the lifting method, among which:

[0035] The technical solution of the step-by-step loading method is: conduct the test under a specified cycle base, obtain the blade failure stress level according to the SN curve of the blade material or take 1 to 2 pieces for exploratory testing, take 80% of the material fatigue limit or failure stress level as the initial stress level for testing, at this time the maximum stress level in the blade is also correspondingly low, the blade will have an infinite life, after the blade completes the specified test cycle base, increase the stress increment, and continue the test until cracks appear on the blade. The test process diagram is shown as follows Figure 1 The stress increment is generally 4% to 6% of the initial stress level. Each blade must undergo a set number of cycles, and the average of the last two stress levels of each blade is taken as the fatigue strength of the blade under the set number of cycles.

[0036] The technical solution of the lifting method is: conduct tests at a specified cycle base, obtain the blade failure stress level based on the SN curve of the blade material or take 1 to 2 pieces for exploratory tests, and take 90% of the material fatigue limit or failure stress level as the initial stress level. The first test piece is tested at the initial stress level. If no cracks appear after completing the specified cycle base, the second piece is tested by adding a stress gradient; if cracks appear before the first piece completes the specified number of cycles, the second piece is tested by reducing the stress gradient. The tests of all test pieces are completed in sequence, and the stress gradient is generally 4%-6% less than the initial stress level. The above two stress levels are regarded as a pair of data with opposite results (destruction and exceeding). Based on this, the paired stress values ​​(the average of the two stress levels) are statistically analyzed as random variables, such as Figure 2 As shown in the figure, × indicates that the blade has cracks, that is, "damage"; ● indicates that the blade has no cracks, that is, "overrun", and the number indicates the blade number.

[0037] According to the step-by-step loading method or lifting method, n * The fatigue strength σ * According to formula (1), the median fatigue strength of the blade under the set cycle base can be calculated:

[0038]

[0039] Conduct statistical analysis on the test data in accordance with the "Statistical Analysis Method for Material Fatigue Test" (HB / Z112-1986), calculate the coefficient of variation, and query Appendix 1 or Appendix 2 of the "Statistical Analysis Method for Material Fatigue Test". The number of blades must meet the minimum observation quantity requirement of 90% or 95% confidence level. If the number of blades is insufficient, it is necessary to continue to increase the number of blades until the minimum quantity requirement is met.

[0040] When conducting vibration fatigue tests on aircraft engine blades, the above two methods are to obtain the vibration fatigue strength at a specified cycle base. The smaller the cycle base, the shorter the test period. For titanium alloy blades, 10 9 Vibration fatigue strength under multiple cycles will result in excessively long test cycles, occupying test resources and incurring high test costs. For a certain stage of aircraft engine blades, for example, the cycle time statistics for each stress level are shown in Table 1. The cycle base results in a 100-fold difference in test duration. If the lifting method specified in the "Statistical Analysis Method for Material Fatigue Testing HB-Z112-86" is used, a minimum of 12 blades are required for each stage, and the entire test process requires 1521.6 hours. If each blade is driven to fracture using the step-by-step loading method, the test stress level for each blade is uncertain, and the number of blades is uncertain, given the dispersion of the blades. The estimated test time will be longer than the lifting method.

[0041] Table 1: Statistics of stress level cycle time of a certain blade

[0042]

[0043] It can be seen that the number of test cycles for ultra-high cycle fatigue test of titanium alloy blades of existing aircraft engine compressors is 10 9 The long test cycle and high cost have led to a severe shortage of human and equipment resources, slow test progress, and affected the development of aircraft engines.

[0044] In response to technical problems such as small number of samples, long test cycle, inaccurate test results and low confidence, such as Figure 3 As shown, the preferred embodiment of the present application provides a method for accelerating ultra-high cycle fatigue testing of a small number of sample compressor titanium alloy blades, comprising the steps of:

[0045] S1. Specify the cycle number N of the ultra-high cycle fatigue accelerated test, N<10 9 , using a step-by-step loading method or a lifting method to conduct a high-cycle fatigue test on the blade test sample to obtain test results under a specified cycle base number N, the test results including vibration fatigue strength;

[0046] S2. Calculate the mean S, standard deviation and coefficient of variation of the vibration fatigue strength of the blade test sample based on the test results;

[0047] S3. If the number of blade test samples meets the minimum number of observations required when the confidence level is 90% or 95%, the mean value S of the vibration fatigue strength of the high-cycle fatigue accelerated test and the specified cycle base N are substituted into the SN curve equation to calculate the fatigue limit. The cycle base is 10 9 The fatigue strength under the condition of SN curve is as follows:

[0048]

[0049] Where: S is the alternating stress / load amplitude; S ∞ is the fatigue limit; N is the number of failure cycles corresponding to alternating stress / load, which is 10 6 times; A and γ are the shape parameters of the fatigue curve.

[0050] The existing lifting method has a long test cycle and requires at least 12 samples. Due to the structural reasons of some aircraft engine compressor blade disks, the number of blades after cutting is less than 12. Therefore, more than two compressor blade disks need to be cut to obtain blades that meet the number requirements, which will greatly increase the test cost. However, this embodiment provides a small sample compressor titanium alloy blade ultra-high cycle fatigue accelerated test method, which combines the characteristics of SN curve formula fitting and step-by-step loading method or lifting method to perform high cycle fatigue testing on blade test samples. It can be used with a small number of samples and only a smaller cycle base number N < 10 9 In the case of ultra-high cycle acceleration test, such as N=10 7 Or N = 3 * 10 7 You can get titanium alloy blades in a cycle base of 10 9 The high cycle fatigue limit under the test condition is greatly shortened, the test time is significantly improved, the test efficiency is significantly improved, the test cost is reduced, and relatively accurate and reliable data is provided to ensure the comparability and reproducibility of the test results.

[0051] In a preferred embodiment of the application, in step S1, if the number of blade test samples is less than 12, a high cycle fatigue test is performed using a step-by-step loading method to obtain test results under a specified cycle base number N.

[0052] In this embodiment, when the number of blade test samples is less than 12, a step-by-step loading method is used to perform a high-cycle fatigue test to obtain test results under a specified cycle base N, thereby reducing the requirement on the number of blade test samples and the test cycle base. From the perspectives of sample cost and test cycle, the cost is reduced and the test efficiency is improved.

[0053] In a preferred embodiment of the application, in step S1, if the number of blade test samples is ≥12, a high-cycle fatigue test is performed using a step-by-step loading method or a lifting method to obtain test results under a specified cycle base number N.

[0054] In this embodiment, when the number of blade test samples is ≥12, that is, when the number of blade test samples is large enough, either the step-by-step loading method or the lifting method can be used to perform high-cycle fatigue testing to obtain test results under a specified cycle base N, thereby reducing the test cycle base. From the perspective of the test cycle, this reduces costs and improves test efficiency.

[0055] In a preferred embodiment of the application, in step S1, a closed-loop control method is adopted when performing high-cycle fatigue testing using a step-by-step loading method or a lifting method, and the amplitude of the blade test sample is measured in real time and fed back to the vibration controller. The controller automatically adjusts the control signal output to the vibration table based on the feedback signal to ensure that the blade test sample is always tested in a resonant state and at the specified amplitude.

[0056] In a preferred embodiment of the application, before performing a high cycle fatigue test on the blade test sample using a stepwise loading method or a lifting method in step S1, the following steps are further included:

[0057] Calculate the vibration characteristics of the blade and transition section to obtain the blade's natural frequency, modal vibration shape, and stress distribution. Determine the test frequency and patch position. Select an electromagnetic vibration table with appropriate specifications. The first-order natural frequency of the transition section deviates from the blade's natural frequency to prevent vibration coupling.

[0058] The strain gauge measurement method is used to obtain the stress distribution at the strain gauge attachment location. That is, based on theoretical calculations or modal measurements, multiple strain gauges are attached to the maximum stress area. The vibration table frequency is adjusted to maintain constant excitation at a certain natural frequency of the blade. Repeat the measurement multiple times or adjust the magnitude of the excitation force to measure multiple sets of data. Based on the strain value of each point in each set of data, the stress distribution results at the attachment location can be obtained and compared with the finite element calculation results. The actual measurement shall prevail.

[0059] Stress calibration: stick strain gauges at the maximum stress point or the area with small stress gradient, vibrate at the natural frequency of the blade, measure the strain and blade tip amplitude, adjust the magnitude of the exciting force, measure the strain value and amplitude at the same time, measure at least 5 sets of data, and fit the linear relationship based on the measured data to obtain the strain-amplitude curve. The stress is calculated by strain and elastic modulus to obtain the stress-amplitude curve. For patches at non-maximum stress points, the maximum stress-amplitude curve is converted based on the proportional relationship between the patch point and the maximum stress point.

[0060] The above steps in this embodiment provide necessary preliminary preparations for the subsequent high-cycle fatigue test of the blade test sample using the step-by-step loading method or the lifting method, ensuring the smooth progress of the subsequent high-cycle fatigue test of the blade test sample using the step-by-step loading method or the lifting method and the accuracy, reliability and stability of the test data.

[0061] In a preferred embodiment of the application, in step S3, when the material and process of the titanium alloy are consistent with the preset values, A and γ are the shape parameters of the fatigue curve and adopt the recommended values. Among them, in the case of no corrosion, the recommended value of A is 0.205 and the recommended value of γ is 0.49; in the case of corrosion, the recommended value of A is 0.811 and the recommended value of γ is 0.63, as shown in Table 2:

[0062] Table 2: A and γ values ​​of different materials

[0063]

[0064] In this embodiment, when the materials and processes of titanium alloy are consistent with the preset ones, the recommended values ​​shown in the table can be directly adopted. The above recommended values ​​are empirical values ​​obtained from the test, and the data are reliable and representative. It is convenient to use the SN curve equation described in formula (2) to quickly calculate the cycle base of 10 9 Fatigue strength under .

[0065] In a preferred embodiment of the application, in step S3, when the material and process of the titanium alloy are inconsistent with the preset ones, first, in the middle life region of the SN curve, 2 to 3 stress levels are selected, and the median fatigue life of the blade test sample is determined by the grouping method. In the long life region of the SN curve, several groups of cycle bases are specified, and the fatigue limit of the blade test sample is determined by the lifting method. Then, the SN curve formula is fitted to obtain the shape parameters A and γ of the fatigue curve.

[0066] In this embodiment, when the material and process of the titanium alloy are inconsistent with the preset ones, 2 to 3 stress levels are selected in the middle life region of the SN curve, and the median fatigue life of the blade test sample is determined by the group method. In the long life region of the SN curve, several groups of cycle bases are specified, and the fatigue limit of the blade test sample is determined by the lifting method. Then, the SN curve formula is fitted to solve the shape parameters A and γ of the fatigue curve. Finally, the parameters A and γ obtained after fitting are substituted into the SN curve equation described in formula (2) to quickly calculate the cycle base of 10 9 Fatigue strength under conditions such as high fatigue life, thereby improving the scope of application and accuracy of this application.

[0067] In a preferred embodiment of the application, in step S3, if the number of blade test samples does not meet the minimum number of observations required when the confidence level is set to 90% or 95%, the number of blade test samples is continued to be increased and the aforementioned steps S1 to S2 are repeated until the number of blade test samples meets the minimum number of observations required when the confidence level is set.

[0068] In a preferred embodiment of the application, in step S1, the cycle base N of the specified ultra-high cycle fatigue accelerated test is 10 7 or 3*10 7 In addition, other methods greater than 10 can also be used. 6 The cycle base.

[0069] Specific experimental principle of the present invention:

[0070] (a) The alternating load is applied to the blade using the vibration displacement excitation and resonance principle. The test principle diagram is shown in the figure below. Figure 4As shown, a single blade is subjected to sinusoidal vibration excitation at a certain bending modal frequency and a certain excitation level, producing a corresponding level of bending resonance. When the vibration displacement / stress response is within the small deformation and linear elastic range, the ratio of the vibration strain response at each blade location should be constant. With the strain gauge center position and test direction clearly defined, the vibration strain response level obtained by a strain gauge at any location on the blade surface can be used to determine the actual value of the vibration strain response at each location on the blade, thus assessing the blade stress level.

[0071] (b) When the vibration excitation level (i.e., the test load level) is low, the maximum alternating stress level in the blade airfoil is also correspondingly low. When this maximum alternating stress level is below the blade stress fatigue limit, the blade will have an infinite life. When the vibration excitation level increases to a certain level, the maximum alternating stress level in the blade airfoil also increases accordingly, until it exceeds the blade stress fatigue limit, causing the blade to suffer high-cycle fatigue damage after a limited number of excitation cycles, and then fatigue cracks.

[0072] (c) In the medium life region of the SN curve, select 2 to 3 stress levels and use the group method to determine the median fatigue life of the material sample. In the long life region of the SN curve, specify several groups of cycle bases and use the rise and fall method to determine the fatigue limit of the material sample. Then fit the S-N curve formula and solve the parameters of formula 2, or directly use the recommended values ​​in Table 2. The fitting curve is as follows: Figure 5 As shown, it is only necessary to obtain a set of blade median fatigue strengths with a specified cycle base through the step-by-step loading method and substitute it into formula (2) to solve the blade median fatigue limit.

[0073] It can be seen that the accelerated test method of this application has the following characteristics:

[0074] 1. The fatigue limit cycle base number of titanium alloy blades is theoretically 10 9 The cycle base of this accelerated test method is 10 7 or 3*10 7 , or even just 10 6 The fatigue limit of the blade can be obtained by the above method. The test saves manpower and material resources and greatly reduces the test cost.

[0075] 2. When the fatigue limit of the blade follows the normal distribution, this method requires fewer sub-samples, and the minimum number of observations can be 3. Compared with the conventional lifting method (minimum 12 blades), the number of blade tests is reduced.

[0076] The ultra-high cycle fatigue accelerated test method of minority sample titanium alloy blades of the present invention has been successfully applied to the ultra-high cycle vibration fatigue test of a certain type of turboshaft engine compressor blade. The test cycle base number of the step-by-step loading is 10 7The number of blade tests was 7, the average vibration intensity was 310.7 MPa, and the coefficient of variation was 0.04776. According to the "Statistical Analysis Method for Material Fatigue Test" (HB / Z112-1986), the number of observations that meet the confidence level of 95% is at least 7, so the number of blade tests meets the statistical requirements. The fatigue limit calculated using the titanium alloy SN fitting curve is 291.7 MPa, which is not much different from the fatigue limit result obtained by the existing lifting method. This verifies that the results of the test of the present invention are accurate and reliable, provides technical support for blade strength assessment, and makes a positive contribution to model development. This test method can be promoted and applied to the development of other aviation gas turbine engine models and related research topics. This method will produce good economic and social benefits in terms of reducing test cycles and test operating costs, protecting equipment safety, etc.

[0077] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0078] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of sample compressors, characterized in that: Including steps: S1. Specify the cycle number N of the ultra-high cycle fatigue accelerated test, N<10 9 , using a step-by-step loading method or a lifting method to conduct a high-cycle fatigue test on the blade test sample to obtain test results under a specified cycle base number N, the test results including vibration fatigue strength; S2. Calculate the mean S, standard deviation and coefficient of variation of the vibration fatigue strength of the blade test sample based on the test results; S3. If the number of blade test samples meets the minimum number of observations required when setting the confidence level, the mean value S of the vibration fatigue strength of the high-cycle fatigue accelerated test and the specified cycle base N are substituted into the SN curve equation to calculate the fatigue limit. The cycle base is 10 9 The fatigue strength under the condition of SN curve is as follows: Where: S is the alternating stress / load amplitude; S ∞ is the fatigue limit; N is the number of failure cycles corresponding to alternating stress / load, which is 10 6 times; A and γ are the shape parameters of the fatigue curve.

2. The method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of carriers according to claim 1, characterized in that: In step S1, if the number of blade test samples is less than 12, a high cycle fatigue test is performed using a step-by-step loading method to obtain test results under a specified cycle base number N.

3. The method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of carriers according to claim 2, characterized in that: In step S1, if the number of blade test samples is ≥12, a high cycle fatigue test is performed using a stepwise loading method or a lifting method to obtain test results under a specified cycle base number N.

4. The method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of carriers according to claim 1, characterized in that: In step S1, a closed-loop control method is adopted when performing high-cycle fatigue tests using the step-by-step loading method or the lifting method. The amplitude of the blade test sample is measured in real time and fed back to the vibration controller. The controller automatically adjusts the control signal output to the vibration table based on the feedback signal to ensure that the blade test sample is always tested in a resonant state and at the specified amplitude.

5. The method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of carriers according to claim 1, characterized in that: Before the high cycle fatigue test of the blade test sample is performed using the stepwise loading method or the lifting method in step S1, the following steps are also included: Calculate the vibration characteristics of the blade and transition section to obtain the blade's natural frequency, modal vibration shape, and stress distribution. Determine the test frequency and patch position. Select an electromagnetic vibration table with appropriate specifications. The first-order natural frequency of the transition section deviates from the blade's natural frequency to prevent vibration coupling. The strain gauge measurement method is used to obtain the stress distribution at the strain gauge attachment location. That is, based on theoretical calculations or modal measurements, multiple strain gauges are attached to the maximum stress area. The vibration table frequency is adjusted to maintain constant excitation at a certain natural frequency of the blade. Repeat the measurement multiple times or adjust the magnitude of the excitation force to measure multiple sets of data. Based on the strain value of each point in each set of data, the stress distribution results at the attachment location can be obtained and compared with the finite element calculation results. The actual measurement shall prevail. Stress calibration: stick strain gauges at the maximum stress point or the area with small stress gradient, vibrate at the natural frequency of the blade, measure the strain and blade tip amplitude, adjust the magnitude of the exciting force, measure the strain value and amplitude at the same time, measure at least 5 sets of data, and fit the linear relationship based on the measured data to obtain the strain-amplitude curve. The stress is calculated by strain and elastic modulus to obtain the stress-amplitude curve. For patches at non-maximum stress points, the maximum stress-amplitude curve is converted based on the proportional relationship between the patch point and the maximum stress point.

6. The method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of carriers according to claim 1, characterized in that: In step S3, when the material and process of the titanium alloy are consistent with the preset values, A and γ are the shape parameters of the fatigue curve and adopt the recommended values. Among them, in the absence of corrosion, the recommended value of A is 0.205, and the recommended value of γ is 0.49; in the case of corrosion, the recommended value of A is 0.811, and the recommended value of γ is 0.

63.

7. The method for accelerating ultra-high cycle fatigue testing of titanium alloy compressor blades using a minority-carrier sample according to claim 1, characterized in that: In step S3, when the material and process of the titanium alloy are inconsistent with the preset ones, first select 2 to 3 stress levels in the middle life region of the SN curve, and use the grouping method to determine the median fatigue life of the blade test sample. In the long life region of the SN curve, specify several groups of cycle bases, and use the lifting and lowering method to determine the fatigue limit of the blade test sample. Then, fit the SN curve formula to solve the shape parameters A and γ of the fatigue curve.

8. The method for accelerating ultra-high cycle fatigue testing of titanium alloy compressor blades with a minority carrier sample according to claim 1, characterized in that: In step S3, if the number of blade test samples does not meet the minimum number of observations required when the confidence level is set, the number of blade test samples is increased and the above steps are repeated until the number of blade test samples meets the minimum number of observations required when the confidence level is set.

9. The method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of carriers according to claim 1, characterized in that: In step S3, the confidence level is set to 90% or 95%.

10. The method for accelerating ultra-high cycle fatigue testing of titanium alloy blades for a small number of carrier samples according to claim 1, characterized in that: In step S1, the cycle base N of the specified ultra-high cycle fatigue accelerated test is 10 7 or 3*10 7 .

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