Method for acquiring ultrahigh-cycle fatigue strength of special-shaped film hole of turbine blade

Abstract

The invention relates to the technical field of aero-engines, and discloses a turbine blade special-shaped air film hole ultra-high cycle fatigue strength obtaining method, which comprises the following steps: cutting to obtain a small sample containing a special-shaped air film hole, and fixing the small sample by using a round bar test fixture with a circumferential notch, so that the special-shaped air film hole is positioned in the notch; converting the amplitude-strain equation of the maximum vibration stress position of the small sample at the room temperature into the amplitude-strain equation of the small sample at the working temperature by carrying out a room temperature vibration stress distribution test so as to obtain the fatigue strength of the small sample at the maximum vibration stress position; the amplitude or exciting force meeting the fatigue strength value at the working temperature is analyzed and determined as the simulation condition, the stress distribution of the small sample is simulated according to the obtained simulation condition, and the fatigue strength of the special-shaped film hole is obtained through conversion based on the critical distance method, so that the problem that the small sample cannot be tested due to the irregular structure size and shape is solved, and the test efficiency is improved. And the test stress accuracy can be ensured, and an ultrahigh-cycle fatigue strength value with high reliability is provided.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology and discloses a method for obtaining the ultra-high cycle fatigue strength of irregularly shaped film vents in turbine blades. Background Technology

[0002] Increasing the turbine inlet temperature of aero-engines can effectively improve engine performance, thereby increasing engine output power. Excessively high exhaust gas temperatures, exceeding the material's operating temperature, significantly reduce its reliability and efficiency. Therefore, ultracooled blades with irregularly shaped film-forming holes and complex heat exchange structures at small scales have become the preferred structural form for high-performance engine turbine blades. According to engine blade failure modes, high-order blade resonance under long-term operation can cause film-forming hole location 10... 9 High-cycle fatigue failure under multiple cycles necessitates obtaining the ultra-high-cycle fatigue strength of turbine blades with irregularly shaped film-coated holes. However, existing research on the strength-life design of turbine blades with irregularly shaped film-coated holes is limited, and the design methods for strength-life need further improvement. Summary of the Invention

[0003] The purpose of this invention is to provide a method for obtaining the ultra-high cycle fatigue strength of irregularly shaped film vents in turbine blades. This method ensures the accuracy of the test stress and provides highly reliable ultra-high cycle fatigue strength values, thus providing technical support for the structural strength design of irregularly shaped film vents in turbine blades.

[0004] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows: A method for obtaining the ultra-high cycle fatigue strength of irregularly shaped film cooling holes in turbine blades includes: Small samples containing irregularly shaped film gas holes to be tested were obtained by wire cutting on a real turbine blade. The length direction of the small sample was consistent with the radial direction of the blade. The small sample is fixed at both ends along its length using a test fixture, which is a round bar structure with a circumferential notch in the middle, and the irregularly shaped air film hole is located inside the notch; A high-frequency induction vibration table is used to fix one end of the test fixture holding the small sample, while the other end is left as a free end. A vibration stress distribution test is carried out at room temperature under preset test conditions to determine the location of the maximum vibration stress in the irregular air film pore region and the amplitude-strain equation of the location of the maximum vibration stress at room temperature. The preset test conditions include test temperature and number of cycles. Based on the ratio of the elastic modulus of the turbine blade at different temperatures, the amplitude-strain equation at the location of maximum vibration stress at room temperature is transformed into the amplitude-strain equation of a small sample at the operating temperature. Based on the amplitude-strain equation of the small sample, the fatigue strength of the small sample at the position of maximum vibration stress is obtained by using the rise and fall method. Using different vibration amplitudes or excitation forces as inputs, the vibration amplitude and vibration frequency that satisfy the fatigue strength value at the maximum vibration stress location under the working temperature condition are obtained by finite element analysis at a preset fixed frequency. The stress distribution of the small sample under the simulation conditions was obtained using the finite element method, and the fatigue strength of the irregular air film pore was obtained by critical distance analysis based on the stress distribution.

[0005] Furthermore, the selection method for the irregular film air holes to be tested includes: conducting response analysis of turbine blades containing irregular film air holes under test conditions, and determining irregular film air holes in areas where the stress is greater than the preset stress threshold and the high-cycle fatigue life is less than the preset fatigue life threshold as irregular film air holes to be tested.

[0006] Furthermore, the test fixture has positioning grooves on both sides of the notch for the small sample end to be inserted and fixed.

[0007] Furthermore, mounting holes are provided at both ends of the small sample along its length, and the irregularly shaped air film hole is located between the two mounting holes; a positioning pin that mates with the mounting hole is provided in the positioning groove to fix the small sample at the notch position of the round bar structure, and to make the irregularly shaped air film hole located within the notch.

[0008] Furthermore, the length of the small sample is more than three times the equivalent diameter of the irregular air film hole, and the axial length of the test fixture is 3 to 4 times the length of the small sample.

[0009] Furthermore, the amplitude-strain equation for the location of maximum vibrational stress at room temperature is: ,in The amplitude is the location of the maximum vibrational stress at room temperature. The strain at the location of maximum vibration stress at room temperature. To and The relevant functional expressions; the amplitude-strain equation for the small sample at the working temperature after conversion is: ,in Operating temperature The amplitude of the small sample containing irregularly shaped air film pores To adapt the calculation coefficients, , This represents the elastic modulus of the turbine blade material at room temperature. Operating temperature The elastic modulus of the turbine blade material.

[0010] Furthermore, the method for obtaining the fatigue strength of the irregularly shaped air film pores using the critical distance method includes: Based on the stress distribution, the stress at the circumferential position with the maximum principal stress as the center and the critical distance on the path of minimum stress gradient as the radius is the fatigue strength of the irregular film pore.

[0011] Furthermore, the critical distance of the small sample ,in, This represents the fatigue limit of a standard smooth specimen for turbine blade material. It is the critical stress intensity factor. .

[0012] Compared with the prior art, the beneficial effects of this invention are as follows: This invention solves the problem of being unable to conduct tests due to the irregular size and shape of small samples by cutting small samples with irregular film cooling holes from real turbine blades and using a test fixture with a circumferential notch for clamping and fixing; it obtains the nominal stress at the patch position based on the method of room temperature calibration and high temperature conversion, and calculates the fatigue strength of the irregular film cooling holes by combining the critical distance method, ensuring the accuracy of the test stress, providing a highly reliable ultra-high circumferential fatigue strength value, and providing technical support for the structural strength design of irregular film cooling holes in turbine blades. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating the method for obtaining the ultra-high cycle fatigue strength of the turbine blade with irregular film cooling holes in the embodiment. Figure 2 This is a schematic diagram of the structure of the test fixture in the embodiment; Among them, 1. test fixture; 2. notch; 3. positioning groove; 4. positioning pin. Detailed Implementation

[0014] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0015] Example 1 See Figure 1 A method for obtaining the ultra-high cycle fatigue strength of irregularly shaped film cooling holes in turbine blades includes: Small samples containing irregularly shaped film gas holes to be tested were obtained by wire cutting on a real turbine blade. The length direction of the small sample was consistent with the radial direction of the blade. The small sample is fixed at both ends along its length using a test fixture 1. The test fixture 1 is a round bar structure with a circumferential notch 2 in the middle, and the irregular air film hole is located inside the notch 2. A high-frequency induction vibration table is used to fix one end of the test fixture 1 holding the small sample, while the other end is left as a free end. A vibration stress distribution test is carried out at room temperature under preset test conditions to determine the location of the maximum vibration stress in the irregular air film hole region and the amplitude-strain equation of the location of the maximum vibration stress at room temperature. The preset test conditions include test temperature and number of cycles. Based on the ratio of the elastic modulus of the turbine blade at different temperatures, the amplitude-strain equation at the location of maximum vibration stress at room temperature is transformed into the amplitude-strain equation of a small sample at the operating temperature. Based on the amplitude-strain equation of the small sample, the fatigue strength of the small sample at the position of maximum vibration stress is obtained by using the rise and fall method. Using different vibration amplitudes or excitation forces as inputs, the vibration amplitude and vibration frequency that satisfy the fatigue strength value at the maximum vibration stress location under the working temperature condition are obtained by finite element analysis at a preset fixed frequency. The stress distribution of the small sample under the simulation conditions was obtained using the finite element method, and the fatigue strength of the irregular air film pore was obtained by critical distance analysis based on the stress distribution.

[0016] In this embodiment, a method for cutting small samples with irregular film cooling holes from actual turbine blades is used. The test fixture 1 with a circumferential notch 2 is used for clamping and fixing, which solves the problem that the test cannot be carried out due to the irregular size and shape of the small sample. The fatigue strength of the irregular film cooling hole is obtained by converting it with the critical distance method, which ensures the accuracy of the test stress and provides a highly reliable ultra-high cycle fatigue strength value, providing technical support for the structural strength design of irregular film cooling holes in turbine blades.

[0017] Example 2 A method for obtaining the ultra-high cycle fatigue strength of irregularly shaped film cooling holes in turbine blades includes: S1. Conduct response analysis of turbine blades containing irregularly shaped film cooling holes under test conditions, and identify irregularly shaped film cooling holes in areas where the stress is greater than the preset stress threshold and the high-cycle fatigue life is less than the preset fatigue life threshold as irregularly shaped film cooling holes to be tested.

[0018] S2. A small sample containing the irregularly shaped film gas holes to be tested is obtained by wire cutting on a real turbine blade. The length direction of the small sample is consistent with the radial direction of the blade. In this embodiment, the length of the small sample is more than three times the equivalent diameter of the irregular air film hole, and the axial length of the test fixture 1 is 3 to 4 times the length of the small sample.

[0019] S3. Fix the small sample at both ends of the length direction of the small sample using the test fixture 1. The test fixture 1 is a round bar structure with a circumferential notch 2 in the middle. The irregular air film hole is located in the notch 2. In this embodiment, the circumferential notch 2 of the test fixture 1 facilitates a larger response from the small sample due to stress concentration during the test. The turbine blade's irregular film cooling structure is subjected to high temperatures, requiring corresponding high temperatures during the test. To ensure consistent displacement during the high-temperature test, the material of the test fixture 1 should be the same as the blade or have a similar coefficient of linear expansion. Positioning grooves 3 are provided on both sides of the notch 2 of the test fixture 1 for the small sample end to be inserted and fixed. During the test, the positioning grooves 3 are connected to the small sample by screws, with the contact surface shape consistent with the clamping end profile of the small sample. Furthermore, the radial distance from the center of the screw hole to the stress concentration notch 2 is greater than 2 mm to prevent the screw hole from failing due to stress concentration during the test.

[0020] In some other embodiments, mounting holes are provided at both ends of the small sample along its length, and the irregular air film hole is located between the two mounting holes; a positioning pin 4 (equivalent to a screw) is provided in the positioning groove 3 to cooperate with the mounting hole, so as to fix the small sample at the notch 2 position of the round bar structure and to make the irregular air film hole located in the notch 2.

[0021] S4. Using a high-frequency induction vibration table, fix one end of the test fixture 1 holding the small sample, and leave the other end as a free end. Conduct a vibration stress distribution test at room temperature under preset test conditions to determine the location of the maximum vibration stress in the irregular air film hole region and the amplitude-strain equation of the location of the maximum vibration stress at room temperature. In this embodiment, the preset test conditions include test temperature and number of cycles.

[0022] S5. Based on the ratio of the elastic modulus of the turbine blade at different temperatures, the amplitude-strain equation at the location of maximum vibration stress at room temperature is transformed into the amplitude-strain equation of the small sample at the working temperature. In this embodiment, the amplitude-strain equation for the location of maximum vibration stress at room temperature is: ,in The amplitude is the location of the maximum vibrational stress at room temperature. The strain at the location of maximum vibration stress at room temperature. To and The relevant function expressions; In the amplitude-strain equation of a small sample with irregularly shaped gas film pores at room temperature, the strain value is divided by a coefficient. The amplitude-strain equation for a small sample at high temperature can be obtained. After conversion, the amplitude-strain equation for the small sample at the working temperature is: ,in Operating temperature The amplitude of the small sample containing irregularly shaped air film pores To adapt the calculation coefficients, , This represents the elastic modulus of the turbine blade material at room temperature. Operating temperature The elastic modulus of the turbine blade material.

[0023] S6. Based on the amplitude-strain equation of the small sample, the fatigue strength of the small sample at the position of maximum vibration stress is obtained by using the rise and fall method.

[0024] S7. Using different vibration amplitudes or excitation forces as inputs, the vibration amplitude and vibration frequency that satisfy the fatigue strength value at the maximum vibration stress location under the working temperature condition are obtained by finite element analysis under a preset fixed frequency.

[0025] S8. The stress distribution of the small sample under the simulation conditions is obtained using the finite element analysis method, and the fatigue strength of the irregular air film pore is obtained by analyzing the stress distribution using the critical distance method, specifically including: Based on the stress distribution, the stress at the circumferential position with the maximum principal stress as the center and the critical distance on the path of minimum stress gradient as the radius is the fatigue strength of the irregularly shaped air film hole, wherein the critical distance of the small sample... ,in, This represents the fatigue limit of a standard smooth specimen for turbine blade material. Critical stress intensity factor, in units of , .

[0026] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for obtaining the ultra-high cycle fatigue strength of irregularly shaped film cooling holes in turbine blades, characterized in that, include: Small samples containing irregularly shaped film gas holes to be tested were obtained by wire cutting on a real turbine blade. The length direction of the small sample was consistent with the radial direction of the blade. The small sample is fixed at both ends along its length using a test fixture, which is a round bar structure with a circumferential notch in the middle, and the irregularly shaped air film hole is located inside the notch; A high-frequency induction vibration table is used to fix one end of the test fixture holding the small sample, while the other end is left as a free end. A vibration stress distribution test is carried out at room temperature under preset test conditions to determine the location of the maximum vibration stress in the irregular air film pore region and the amplitude-strain equation of the location of the maximum vibration stress at room temperature. The preset test conditions include test temperature and number of cycles. Based on the ratio of the elastic modulus of the turbine blade at different temperatures, the amplitude-strain equation at the location of maximum vibration stress at room temperature is transformed into the amplitude-strain equation of a small sample at the operating temperature. Based on the amplitude-strain equation of the small sample, the fatigue strength of the small sample at the position of maximum vibration stress is obtained by using the rise and fall method. Using different vibration amplitudes or excitation forces as inputs, the vibration amplitude and vibration frequency that satisfy the fatigue strength value at the maximum vibration stress location under the working temperature condition are obtained by finite element analysis at a preset fixed frequency. The stress distribution of the small sample under the simulation conditions was obtained using the finite element method, and the fatigue strength of the irregular air film pore was obtained by critical distance analysis based on the stress distribution.

2. The method for obtaining ultra-high cycle fatigue strength of turbine blades with irregularly shaped film cooling holes according to claim 1, characterized in that, The selection method for the irregular film cooling holes to be tested includes: conducting response analysis of turbine blades containing irregular film cooling holes under test conditions, and identifying irregular film cooling holes in areas where the stress is greater than the preset stress threshold and the high-cycle fatigue life is less than the preset fatigue life threshold as irregular film cooling holes to be tested.

3. The method for obtaining ultra-high cycle fatigue strength of turbine blades with irregularly shaped film cooling holes according to claim 1, characterized in that, The test fixture has positioning grooves on both sides of the notch for the small sample end to be inserted and fixed.

4. The method for obtaining ultra-high cycle fatigue strength of turbine blades with irregularly shaped film cooling holes according to claim 3, characterized in that, The small sample has mounting holes at both ends along its length, and the irregularly shaped air film hole is located between the two mounting holes. The positioning groove is provided with a positioning pin that mates with the mounting hole to fix the small sample at the notch of the round bar structure and to make the irregularly shaped air film hole located within the notch.

5. The method for obtaining ultra-high cycle fatigue strength of turbine blades with irregularly shaped film cooling holes according to claim 1, characterized in that, The length of the small sample is more than three times the equivalent diameter of the irregular air film hole, and the axial length of the test fixture is 3 to 4 times the length of the small sample.

6. The method for obtaining ultra-high cycle fatigue strength of turbine blades with irregularly shaped film cooling holes according to claim 1, characterized in that, The amplitude-strain equation for the location of maximum vibration stress at room temperature is: ,in The amplitude is the location of the maximum vibrational stress at room temperature. The strain at the location of maximum vibration stress at room temperature. To and The relevant functional expressions; the amplitude-strain equation for the small sample at the working temperature after conversion is: ,in Operating temperature The amplitude of the small sample containing irregularly shaped air film pores To adapt the calculation coefficients, , This represents the elastic modulus of the turbine blade material at room temperature. Operating temperature The elastic modulus of the turbine blade material.

7. The method for obtaining ultra-high cycle fatigue strength of turbine blades with irregularly shaped film cooling holes according to claim 1, characterized in that, The method for obtaining the fatigue strength of the irregularly shaped air film pores using the critical distance method includes: Based on the stress distribution, the stress at the circumferential position with the maximum principal stress as the center and the critical distance on the path of minimum stress gradient as the radius is the fatigue strength of the irregular film pore.

8. The method for obtaining ultra-high cycle fatigue strength of turbine blades with irregularly shaped film cooling holes according to claim 1, characterized in that, The critical distance of the small sample ,in, This represents the fatigue limit of a standard smooth specimen for turbine blade material. It is the critical stress intensity factor. .

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