Repair blade polishing geometric dimension design method based on fatigue evaluation

Abstract

The invention discloses a repairing blade polishing geometric dimension design method based on fatigue evaluation. In the method, the polishing size is preliminarily determined according to the position of a damaged notch; performing a high-cycle fatigue test on the simulation blade with the damage notch by using a stepping method to obtain the high-cycle fatigue strength of the blade with the damage notch; the influence rule of the blade gap critical distance RC and the gap size on the fatigue strength is obtained based on a critical distance method by combining test data; and performing vibration mode simulation on the real blade, predicting the fatigue limit of the real blade with the gap by using Peterson formulas in the critical distance model and the average stress model, comparing the dynamic stress obtained by the vibration experiment of the real blade, and if the design index is met, indicating that the polishing size is feasible. The method is a repairing blade grinding geometric dimension design method based on fatigue evaluation, is more scientific and is suitable for various grinding positions and scenes.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft engine fan and compressor blades, and specifically relates to a method for designing geometric dimensions of blade grinding for repair based on fatigue assessment. Background Art

[0002] During the service life of aircraft engines, it is inevitable that sand, metal fragments, birds and other foreign objects will be inhaled, causing foreign object damage (FOD) to fan and compressor blades [1, 2]. Foreign object damage has become the most important factor affecting the service safety of fan and compressor blades. For small-sized foreign object damage notches, mechanical processing (hereinafter referred to as "machining") or manual grinding is usually used for repair [3]. However, the current grinding size is mainly based on research based on engineering experience, and for new models of blades, it is also based on the experience of existing mature models, and there is still a lack of independent scientific experience. In many cases, it is copied from other models, but the sizes of the blades of the two are different. Therefore, for the determination of the grinding repair size of the damaged notch, there is an urgent need for a method that can be applied to the formulation of grinding repair standards for damaged blades of different models.

[0003] However, the current maintenance standards for blades damaged by foreign objects still follow the maintenance standards for foreign engine blades, and there is a lack of scientific research on the formulation of maintenance standards. However, blades of different models have different configurations and sizes, and unified maintenance standards cannot guarantee that their mechanical properties such as fatigue performance after repair meet the requirements, or the standards are too strict, resulting in waste. Summary of the invention

[0004] The purpose of the present invention is to provide a method for designing geometric dimensions of blade grinding for repair based on fatigue assessment in order to solve the above-mentioned problems.

[0005] The technical solution adopted by the present invention is as follows: a method for designing geometric dimensions of blade grinding for repair based on fatigue assessment, the method comprising the following steps: S1: Design the shape and size of the notch for grinding. According to research and simulation calculations, the elliptical shape is the optimal solution for the grinding shape of the notched blade. Therefore, this method designs the notch for the elliptical shape and the current standard grinding solution with a width-to-depth ratio; S2: Design and process the simulated blade so that its leading edge position is consistent with that of the real blade. Grind it according to step 1 and ensure that the width-to-depth ratio is consistent with that of the real blade to form a notched simulated blade; S3: Evaluate the fatigue performance of the notched simulated blade, conduct a vibration fatigue test, and measure the fatigue strength at point A; S4: Obtain the relationship between grinding size and fatigue performance and the quantitative theoretical model; S5: Design and process real blades; S6: Evaluate the fatigue performance of real blades with notches, calculate fatigue strength based on critical distance theory, and conduct vibration modal experimental research; S7: Compare with the blade dynamic stress and finally determine the grinding and repair size.

[0006] In a preferred embodiment, in step S3, the empirical formula model for evaluating the fatigue performance of the notched simulated blade includes performing vibration modal analysis on the complete blade using a finite element method and predicting the fatigue strength of the blade based on a Peterson model.

[0007] In a preferred embodiment, the process of performing vibration modal analysis on a complete blade using the finite element method specifically includes: The notched blade is modeled using isotropic elastic material to constrain the displacement of the six faces of the fixed end in three directions. The entire structure is meshed using C3D4 (4-node linear tetrahedron) units, and the convergence of the mesh scale is verified to calculate the Mises stress distribution.

[0008] In a preferred embodiment, the process of predicting blade fatigue strength based on the Peterson model specifically includes: Import the complete blade 3D model into the Abaqus software, combine the complete blade modal analysis results, and find the point with the largest Mises stress at the leading edge position of each partition obtained in step 1 as the leading edge danger point of the corresponding area. Establish a reference point at the danger point position in accordance with the current repair standards, and use this reference point to make an elliptical notch (the repair width and depth are proportional). Enter the material parameters in the Abaqus software, constrain the displacement of the three directions of the clamping end at the bottom of the blade, perform meshing, perform convergence verification, and carry out vibration modal simulation to obtain the Mises stress distribution of the blade.

[0009] The calculation formula of stress concentration factor at blade notch is: ; In the formula, s A'_Simu_Mises and s B'_Simu_Mises They are the modal Mises stress at point A of the notched blade modal simulation (point A is far away from the notch. The specific location is determined as follows: in the blade thickness direction, it is located on the back of the blade; in the blade width direction, it is located near the center; in the blade length direction, it is located near the center) s A_Simu_Mises and the modal Mises stress at the corresponding position at point B (where the Mises stress around the notch is maximum), s A_仿真 and sB_仿真 They are the modal stresses at points A and B of the complete blade modal simulation.

[0010] In engineering, the classic Peterson model is widely used in fatigue strength assessment of various notches. The specific expression is as follows: ; In the formula, K f is the fatigue notch factor, K t is the stress concentration factor, r is the curvature radius of the notch root. The fatigue limit evaluation method based on the Peterson model is as follows: The fatigue notch coefficient is calculated using formula (2): K f After that, the fatigue limit of the smooth specimen is s -1 , the fatigue limit of the notched specimen is calculated s -1 / K f .

[0011] For the semi-elliptical notch in this method, ; a p is a material constant related to the strength limit

[20] : ; In the formula, s u For the strength limit.

[0012] A strain gauge was attached at a position far from the notch (denoted as point A) to monitor the normal stress at point A along the length of the blade. The “step method” was used to measure the normal stress at this point 3×10 7 Fatigue limit under cycle s A' , carried out vibration fatigue test and measured the fatigue strength at point A.

[0013] In a preferred embodiment, after the fatigue strength at point A is measured, the fatigue strength is calculated based on the critical distance theory. The critical distance theory model flow chart is as follows: Figure 2 As shown, R C The calculation process is as follows Figure 3 As shown, specifically including: Step 1: Carry out the first-order modal simulation of the complete blade.

[0014] The complete blade is modeled using isotropic elastic material (material parameters include density, elastic modulus, Poisson's ratio), and the displacements of the six faces of the fixed end are constrained in three directions. The entire structure is meshed using C3D4 (4-node linear tetrahedron) units, and the convergence of the mesh scales at A and B is verified. The first-order mode is analyzed, and the modal Mises stress at point A is output. s A_Simu_Mises and the modal Mises stress at point B s B_Simu_Mises (Obtained by interpolating the position of the dangerous point on the notched blade).

[0015] Step 2: Carry out the first-order modal simulation of the notched blade.

[0016] The complete blade is modeled using isotropic elastic material (material parameters include density, elastic modulus, and Poisson's ratio) to constrain the displacement of the six faces of the fixed end in three directions. The entire structure is meshed using C3D4 (4-node linear tetrahedron) units, and the convergence of the mesh scales at A and B is verified. The first-order mode is analyzed to calculate the normal stress at point A along the length of the blade. s A'_Simu As well as the node position coordinates, unit volume and principal stress of each unit around point B.

[0017] Step 3: Use the critical distance method to evaluate the vibration fatigue strength of the notched blade and the critical distance R C Calculation.

[0018] In a preferred embodiment, the step 3 specifically includes: (a) Modal Mises stress at point A obtained from simulation s A_Simu_Mises Modal Mises stress at the corresponding position of the critical point (point B) at the root of the notch s B_Simu_Mises , the fatigue limit along the length direction of the blade at the dangerous point (point B) of the notched blade is calculated using formula (1): s B_Test (1) (b) According to s B_Test , the value of each specimen can be calculated using formula (3) r c , and take the average value.

[0019] When the notched blade reaches the fatigue limit, the stress at point A is its fatigue limit. s A'According to the critical distance theory (volume method), the area near point B (with point B as the center and the critical distance r c is the radius, and the average stress within the hemispherical surface along the notch depth direction) s aver_0 , which is exactly equal to the fatigue limit of the smooth specimen s -1 ,Right now s aver_0 = s -1 In the numerical simulation results of the vibration mode of the notched blade, although there is a deviation between its modal stress and the true stress, the proportional relationship of the stress at each point still holds, that is, (2) Multiply both sides of the equal sign by s B_Simu_Mises / s A_Simu_Mises , and transform (1) and s aver_0 = s -1 Substituting in, we get: (3) in, s B_Test is the fatigue limit along the length direction of the blade at the dangerous point of the notch root measured in the test; s -1 is the fatigue limit of the smooth specimen, and is the material constant; s A'_Simu is the modal stress along the length direction of the blade at the strain gauge (A) in the first-order modal simulation of the notched blade, s aver_Simu is the area near point B in the first-order mode simulation of the notched blade (with point B as the center of the sphere and the critical distance r c is the radius, the average stress within the hemispherical surface along the notch depth direction; s A_Simu_Mises and s B_Simu_Mises is the modal Mises stress at points A and B in the first-order modal simulation of the complete blade.

[0020] When using the critical distance method to evaluate the vibration fatigue strength of blades with different grinding size notches, the theoretical critical distance R C Substitute into formula (3) to calculate the sample s B_Test , summarize the influence of grinding size on fatigue performance.

[0021] (c) Use formula (3) to predict the vibration fatigue limit of the notched blade. s aver_Simu is the area near point B in the numerical simulation of the notched blade (with point B as the center of the sphere and the critical distance obtained in the third step r c The stress average value within the hemispherical surface along the notch depth direction (where ) is the radius, is calculated using formula (4).

[0022] (4) In the formula, N is the number of tetrahedral units whose center of gravity is within the hemisphere, s i is the maximum absolute value of the three principal stresses of the element, V i Since the TCD theory is based on a two-dimensional plate model, this method uses the TCD model to evaluate the bending performance of a three-dimensional complex structure. Considering the uneven stress distribution along the thickness direction of the structure, it is necessary to introduce a correction factor that considers the bending effect. or According to the measured s B_Test , the value of each specimen can be obtained by iterative calculation using formula (3) R C .

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. In the present invention, the fatigue performance of the blade is evaluated instead of relying solely on experience or analogy. Through finite element simulation, vibration fatigue test and critical distance theory, this method can more accurately predict the impact of notches of different sizes on the fatigue performance of the blade, thereby formulating a more reasonable grinding size standard. A variety of evaluation methods are combined, including finite element simulation, vibration fatigue test and critical distance theory, to ensure the accuracy and reliability of the evaluation results. A variety of influencing factors are taken into account, including notch shape, size, position, material properties, etc., so as to more comprehensively evaluate the fatigue performance of the blade.

[0024] 2. The present invention breaks through the limitation that traditional maintenance standards cannot cover all types of blades. By establishing a regular model for the influence of notch size on fatigue performance, this method can formulate personalized grinding size standards based on the damage conditions of blades of different models to ensure that the fatigue performance of the repaired blades meets the design requirements. According to the damage conditions of different blades, personalized grinding size standards can be formulated to avoid a "one-size-fits-all" maintenance method, thereby improving maintenance efficiency and blade service life. Excessive grinding can be avoided, thereby reducing maintenance costs. At the same time, this method can also increase the service life of the blades, thereby reducing the frequency of blade replacement and further reducing maintenance costs. The geometric size design method for repairing blades based on fatigue assessment is a more scientific, more applicable, and more economical blade maintenance method, which can effectively increase the service life of blades, reduce maintenance costs, and ensure the safe operation of aircraft engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of the overall technical solution of the present invention; Figure 2 It is a structural block diagram of the critical distance theoretical model in the present invention; Figure 3 is a flow chart for calculating the critical distance RC in the present invention; Figure 4 This is a flow chart for studying the influence of notch size on fatigue performance in the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Reference Figure 1-4 , A method for designing geometric dimensions of blade grinding for repair based on fatigue assessment, the method comprising the following steps: S1: Design the shape and size of the notch for grinding. According to research and simulation calculations, the elliptical shape is the optimal solution for the grinding shape of the notched blade. Therefore, this method designs the notch for the elliptical shape and the current standard grinding solution with a width-to-depth ratio; S2: Design and process the simulated blade so that its leading edge position is consistent with that of the real blade. Grind it according to step 1 and ensure that the width-to-depth ratio is consistent with that of the real blade to form a notched simulated blade; S3: Evaluate the fatigue performance of the notched simulated blade, conduct a vibration fatigue test, and measure the fatigue strength at point A; S4: Obtain the relationship between grinding size and fatigue performance and the quantitative theoretical model; S5: Design and process real blades; S6: Evaluate the fatigue performance of real blades with notches, calculate fatigue strength based on critical distance theory, and conduct vibration modal experimental research; S7: Compare with the blade dynamic stress and finally determine the grinding and repair size.

[0030] In step S3, the empirical formula model for evaluating the fatigue performance of the notched simulated blade includes performing vibration modal analysis on the complete blade using the finite element method and predicting the fatigue strength of the blade based on the Peterson model.

[0031] The process of performing vibration modal analysis on a complete blade using the finite element method specifically includes: The notched blade is modeled using isotropic elastic material to constrain the displacement of the six faces of the fixed end in three directions. The entire structure is meshed using C3D4 (4-node linear tetrahedron) units, and the convergence of the mesh scale is verified to calculate the Mises stress distribution.

[0032] The process of predicting blade fatigue strength based on the Peterson model specifically includes: Import the complete blade 3D model into the Abaqus software, combine the complete blade modal analysis results, and find the point with the largest Mises stress at the leading edge position of each partition obtained in step 1 as the leading edge danger point of the corresponding area. Establish a reference point at the danger point position in accordance with the current repair standards, and use this reference point to make an elliptical notch (the repair width and depth are proportional). Enter the material parameters in the Abaqus software, constrain the displacement of the three directions of the clamping end at the bottom of the blade, perform meshing, perform convergence verification, and carry out vibration modal simulation to obtain the Mises stress distribution of the blade.

[0033] The calculation formula of stress concentration factor at blade notch is: ; In the formula, s A'_Simu_Mises and s B'_Simu_Mises They are the modal Mises stress at point A of the notched blade modal simulation (point A is far away from the notch. The specific location is determined as follows: in the blade thickness direction, it is located on the back of the blade; in the blade width direction, it is located near the center; in the blade length direction, it is located near the center) s A_Simu_Mises and the modal Mises stress at the corresponding position at point B (where the Mises stress around the notch is maximum), s A_仿真and s B_仿真 They are the modal stresses at points A and B of the complete blade modal simulation.

[0034] In engineering, the classic Peterson model is widely used in fatigue strength assessment of various notches. The specific expression is as follows: ; In the formula, K f is the fatigue notch factor, K t is the stress concentration factor, r is the curvature radius of the notch root. The fatigue limit evaluation method based on the Peterson model is as follows: The fatigue notch coefficient is calculated using formula (2): K f After that, the fatigue limit of the smooth specimen is s -1 , the fatigue limit of the notched specimen is calculated s -1 / K f .

[0035] For the semi-elliptical notch in this method, ; a p is a material constant related to the strength limit

[20] : ; In the formula, s u For the strength limit.

[0036] A strain gauge was attached at a position far from the notch (denoted as point A) to monitor the normal stress at point A along the length of the blade. The “step method” was used to measure the normal stress at this point 3×10 7 Fatigue limit under cyclic conditions s A' , carried out vibration fatigue test and measured the fatigue strength at point A.

[0037] After measuring the fatigue strength at point A, the fatigue strength is calculated based on the critical distance theory. The critical distance theory model flow chart is as follows: Figure 2 As shown, R C The calculation process is as follows Figure 3 As shown, specifically including: Step 1: Carry out the first-order modal simulation of the complete blade.

[0038] The complete blade is modeled using isotropic elastic material (material parameters include density, elastic modulus, Poisson's ratio), and the displacements of the six faces of the fixed end are constrained in three directions. The entire structure is meshed using C3D4 (4-node linear tetrahedron) units, and the convergence of the mesh scales at A and B is verified. The first-order mode is analyzed, and the modal Mises stress at point A is output. s A_Simu_Mises and the modal Mises stress at point B s B_Simu_Mises (Obtained by interpolating the position of the dangerous point on the notched blade).

[0039] Step 2: Carry out the first-order modal simulation of the notched blade.

[0040] The complete blade is modeled using isotropic elastic material (material parameters include density, elastic modulus, and Poisson's ratio) to constrain the displacement of the six faces of the fixed end in three directions. The entire structure is meshed using C3D4 (4-node linear tetrahedron) units, and the convergence of the mesh scales at A and B is verified. The first-order mode is analyzed to calculate the normal stress at point A along the length of the blade. s A'_Simu As well as the node position coordinates, unit volume and principal stress of each unit around point B.

[0041] Step 3: Use the critical distance method to evaluate the vibration fatigue strength of the notched blade and the critical distance R C Calculation.

[0042] The step 3 specifically includes: (a) Modal Mises stress at point A obtained from simulation s A_Simu_Mises Modal Mises stress at the corresponding position of the critical point (point B) at the root of the notch s B_Simu_Mises , the fatigue limit along the length direction of the blade at the dangerous point (point B) of the notched blade is calculated using formula (1): s B_Test (1) (b) According to s B_Test , the value of each specimen can be calculated using formula (3) r c , and take the average value.

[0043] When the notched blade reaches the fatigue limit, the stress at point A is its fatigue limit. s A' According to the critical distance theory (volume method), the area near point B (with point B as the center and the critical distancer c is the radius, and the average stress within the hemispherical surface along the notch depth direction) s aver_0 , which is exactly equal to the fatigue limit of the smooth specimen s -1 ,Right now s aver_0 = s -1 In the numerical simulation results of the vibration mode of the notched blade, although there is a deviation between its modal stress and the true stress, the proportional relationship of the stress at each point still holds, that is, (2) Multiply both sides of the equal sign by s B_Simu_Mises / s A_Simu_Mises , and transform (1) and s aver_0 = s -1 Substituting in, we get: (3) in, s B_Test is the fatigue limit along the length direction of the blade at the dangerous point of the notch root measured in the test; s -1 is the fatigue limit of the smooth specimen, and is the material constant; s A'_Simu is the modal stress along the length direction of the blade at the strain gauge (A) in the first-order modal simulation of the notched blade, s aver_Simu is the area near point B in the first-order mode simulation of the notched blade (with point B as the center of the sphere and the critical distance r c is the radius, the average stress within the hemispherical surface along the notch depth direction; s A_Simu_Mises and s B_Simu_Mises is the modal Mises stress at points A and B in the first-order modal simulation of the complete blade.

[0044] When using the critical distance method to evaluate the vibration fatigue strength of blades with different grinding size notches, the theoretical critical distance R C Substitute into formula (3) to calculate the sample s B_Test , summarize the influence of grinding size on fatigue performance.

[0045] (c) Use formula (3) to predict the vibration fatigue limit of the notched blade. s aver_Simu is the area near point B in the numerical simulation of the notched blade (with point B as the center of the sphere and the critical distance obtained in the third step r c The stress average value within the hemispherical surface along the notch depth direction (where ) is the radius, is calculated using formula (4).

[0046] (4) In the formula, N is the number of tetrahedral units whose center of gravity is within the hemisphere, s i is the maximum absolute value of the three principal stresses of the element, V i Since the TCD theory is based on a two-dimensional plate model, this method uses the TCD model to evaluate the bending performance of a three-dimensional complex structure. Considering the uneven stress distribution along the thickness direction of the structure, it is necessary to introduce a correction factor that considers the bending effect. or According to the measured s B_Test , the value of each specimen can be obtained by iterative calculation using formula (3) R C .

[0047] In the present invention, the fatigue performance of the blade is evaluated instead of relying solely on experience or analogy. Through finite element simulation, vibration fatigue test and critical distance theory, this method can more accurately predict the impact of notches of different sizes on the fatigue performance of the blade, thereby formulating a more reasonable grinding size standard. A variety of evaluation methods are combined, including finite element simulation, vibration fatigue test and critical distance theory, to ensure the accuracy and reliability of the evaluation results. A variety of influencing factors are taken into account, including notch shape, size, position, material properties, etc., so as to more comprehensively evaluate the fatigue performance of the blade.

[0048] The present invention breaks through the limitation that traditional maintenance standards cannot cover all types of blades. By establishing a regular model of the influence of notch size on fatigue performance, this method can formulate personalized grinding size standards based on the damage conditions of blades of different models to ensure that the fatigue performance of the repaired blades meets the design requirements. According to the damage conditions of different blades, personalized grinding size standards can be formulated to avoid a "one-size-fits-all" maintenance method, thereby improving maintenance efficiency and blade service life. Excessive grinding can be avoided, thereby reducing maintenance costs. At the same time, this method can also increase the service life of the blades, thereby reducing the frequency of blade replacement and further reducing maintenance costs. The geometric size design method for repairing blades based on fatigue assessment is a more scientific, more applicable, and more economical blade maintenance method, which can effectively increase the service life of the blades, reduce maintenance costs, and ensure the safe operation of aircraft engines.

[0049] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for designing geometric dimensions of blade grinding for repair based on fatigue assessment, characterized in that: The method comprises the following steps: S1: Design the shape and size of the notch to be polished; after investigation and simulation calculation, it is known that the elliptical shape is the optimal solution for the notch blade polishing shape, so this method designs the notch for the elliptical shape and the current standard grinding solution with a width-to-depth ratio; S2: Design and process the simulated blade so that its leading edge position is consistent with that of the real blade; grind it according to step 1 and ensure that the width-to-depth ratio is consistent with that of the real blade to form a notched simulated blade; S3: Evaluate the fatigue performance of the notched simulated blade, conduct a vibration fatigue test, and measure the fatigue strength at point A; S4: Obtain the relationship between grinding size and fatigue performance and the quantitative theoretical model; S5: Design and process real blades; S6: Evaluate the fatigue performance of real blades with notches, calculate fatigue strength based on critical distance theory, and conduct vibration modal experimental research; S7: Compare with the blade dynamic stress and finally determine the grinding and repair size.

2. A method for designing geometric dimensions of blade grinding for repair based on fatigue assessment as claimed in claim 1, characterized in that: In step S3, the empirical formula model for evaluating the fatigue performance of the notched simulated blade includes performing vibration modal analysis on the complete blade using the finite element method and predicting the fatigue strength of the blade based on the Peterson model.

3. A method for designing geometric dimensions of blade grinding for repair based on fatigue assessment as claimed in claim 2, characterized in that: The process of performing vibration modal analysis on a complete blade using the finite element method specifically includes: The notched blade is modeled using isotropic elastic material to constrain the displacements of the six faces of the fixed end in three directions. The entire structure is meshed using four-node linear tetrahedron elements, and the convergence of the mesh scale is verified to calculate the Mises stress distribution.

4. The method for designing geometric dimensions of blade grinding for repair based on fatigue assessment according to claim 2, characterized in that: The process of predicting blade fatigue strength based on the Peterson model specifically includes: Import the complete blade 3D model into the Abaqus software, combine the complete blade modal analysis results, and find the point with the largest Mises stress at the leading edge position of each partition obtained in step 1 as the leading edge danger point of the corresponding area; establish a reference point at the danger point position in accordance with the current repair standard, and use this reference point to make an elliptical notch; input material parameters into the Abaqus software, constrain the displacement of the clamping end at the bottom of the blade in three directions, perform meshing, perform convergence verification, and carry out vibration modal simulation to obtain the Mises stress distribution of the blade; The calculation formula of stress concentration factor at blade notch is: ； In the formula, σ A'_Simu_Mises and σ B'_Simu_Mises They are the modal Mises stress at point A of the notched blade modal simulation σ A_Simu_Mises and the modal Mises stress at the corresponding position at point B, σ A_仿真 and σ B_仿真 They are the modal stresses at points A and B of the complete blade modal simulation; In engineering, the classic Peterson model is widely used in fatigue strength evaluation of various notches; the specific expression is as follows: ； In the formula, K f is the fatigue notch factor, K t is the stress concentration factor, ρ is the curvature radius of the notch root; the fatigue limit evaluation method based on the Peterson model is as follows: The fatigue notch coefficient is calculated using formula (2) K f After that, the fatigue limit of the smooth specimen is σ -1 , the fatigue limit of the notched specimen is calculated σ -1 / K f ; For the semi-elliptical notch in this method, ； a p is a material constant related to the strength limit [20] : ； In the formula, σ u is the strength limit; The position far away from the notch is marked as point A, and a strain gauge is attached to monitor the normal stress at point A along the length direction of the blade. The "step method" is used to measure the 3×10 7 Fatigue limit under cyclic conditions σ A' , carried out vibration fatigue test and measured the fatigue strength at point A.

5. A method for designing geometric dimensions of blade grinding for repair based on fatigue assessment as claimed in claim 4, characterized in that: After measuring the fatigue strength at point A, the fatigue strength is calculated based on the critical distance theory, including: Step 1: Carry out the first-order modal simulation of the complete blade; The complete blade is modeled using isotropic elastic material to constrain the displacement of the six surfaces at the fixed end in three directions; the entire structure is meshed using 4-node linear tetrahedron elements, and the convergence of the mesh scales at A and B is verified respectively; its first-order mode is analyzed, and the modal Mises stress at point A is output σ A_Simu_Mises and the modal Mises stress at point B σ B_Simu_Mises ; Step 2: Carry out the first-order modal simulation of the notched blade; The complete blade is modeled using isotropic elastic material to constrain the displacement of the six faces of the fixed end in three directions; the entire structure is meshed using 4-node linear tetrahedron elements, and the convergence of the mesh scales at A and B is verified respectively; its first-order mode is analyzed, and the normal stress at point A along the length direction of the blade is calculated. σ A'_Simu As well as the node position coordinates, unit volume and principal stress of each unit around point B; Step 3: Use the critical distance method to evaluate the vibration fatigue strength of the notched blade and the critical distance R C Calculation.

6. A method for designing geometric dimensions of blade grinding for repair based on fatigue assessment as claimed in claim 5, characterized in that: The step 3 specifically includes: (a) Modal Mises stress at point A obtained from simulation σ A_Simu_Mises The modal Mises stress at the corresponding position of the dangerous point B at the root of the notch σ B_Simu_Mises , the fatigue limit along the length direction of the blade at the dangerous point B of the notched blade is calculated using formula (1): σ B_Test （1） (b) According to σ B_Test , the value of each specimen can be calculated using formula (3) r c , and take the average value; When the notched blade reaches the fatigue limit, the stress at point A is its fatigue limit. σ A' According to the critical distance theory, the area near point B is centered at point B and has a critical distance r c is the radius, and the average stress within the hemispherical surface along the notch depth direction σ aver_0 , which is exactly equal to the fatigue limit of the smooth specimen σ -1 ,Right now σ aver_0 = σ -1 ; In the numerical simulation results of the vibration mode of the notched blade, although there is a deviation between its modal stress and the true stress, the proportional relationship of the stress at each point still holds, that is, （2） Multiply both sides of the equal sign by σ B_Simu_Mises / σ A_Simu_Mises , and transform (1) and σ aver_0 = σ -1 Substituting in, we get: （3） in, σ B_Test is the fatigue limit along the length direction of the blade at the dangerous point of the notch root measured in the test; σ -1 is the fatigue limit of the smooth specimen, and is the material constant; σ A'_Simu is the modal stress along the blade length direction at the strain gauge point A in the first-order modal simulation of the notched blade, σ aver_Simu The area near point B in the first-order modal simulation of the notched blade is centered at point B and the critical distance is r c is the radius, the average stress within the hemispherical surface along the notch depth direction; σ A_Simu_Mises and σ B_Simu_Mises is the modal Mises stress at points A and B in the first-order modal simulation of the complete blade; When using the critical distance method to evaluate the vibration fatigue strength of blades with different grinding size notches, the theoretical critical distance R C Substitute into formula (3) to calculate the sample σ B_Test , summarize the influence of grinding size on fatigue performance; (c) Use formula (3) to predict the vibration fatigue limit of the notched blade; where σ aver_Simu The critical distance obtained in the third step is the area around point B in the numerical simulation of the notched blade with point B as the center of the sphere r c is the radius, and the average stress value within the hemispherical surface along the notch depth direction is calculated using formula (4); （4） In the formula, N is the number of tetrahedral units whose center of gravity is within the hemisphere, σ i is the maximum absolute value of the three principal stresses of the element, V i is the unit volume; since the TCD theory is based on a two-dimensional plate model, this method uses the TCD model to evaluate the bending performance of a three-dimensional complex structure. Considering the uneven stress distribution along the thickness direction of the structure, it is necessary to introduce a correction factor that considers the bending effect. η According to the measured σ B_Test , the value of each specimen can be obtained by iterative calculation using formula (3) R C .

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