Fatigue life prediction method of two-dimensional stress gradient line with circular hole mounting base structure

Abstract

The application provides a fatigue life prediction method for a mounting seat structure with a circular hole considering a two-dimensional stress gradient line. The basic idea is that the traditional Theory of Critical Distance (TCD) model is improved. Since the thickness of the hole edge structure of the mounting seat is large, the stress gradient line of the hole edge is not simply one-dimensional along the hole edge extension line direction, but gradually deflects to the thickness direction. Therefore, the actual two-dimensional stress gradient line on the dangerous cross section of the mounting seat hole edge is taken as the basis, and the SWT parameter on the curve is combined to determine the critical distance, so as to establish a TCD-SWT fatigue life prediction model considering the multi-dimensional stress gradient line. The life prediction model is suitable for the fatigue life prediction of the notch structure of the mounting seat with a large two-dimensional stress gradient, the prediction results are all within the 2 times dispersion band, the prediction accuracy is high, and the life prediction model has good engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of fatigue life prediction technology for mounting base structures with circular holes, and specifically relates to a method for predicting the fatigue life of mounting base structures with circular holes that considers two-dimensional stress gradient lines. Background Technology

[0002] The aircraft engine is the "heart" of an aircraft and a crucial power output component. The casing is an important part of the aircraft engine, serving to support the rotor, fix the stator blades and accessories, and together with other components, form the airflow channel of the engine, transmitting the thrust generated by the engine to the aircraft.

[0003] In typical combustion chamber casing structures, various types of mounting bases with circular holes are typically included due to structural design requirements. The combustion chamber casing is subjected to a variety of complex loads, such as pressure differences between the inside and outside of the casing, axial gas forces, torque from the front and rear mounting edges, and loads on various mounting joints on the outer wall of the casing. Under multiaxial loads, these mounting base structures experience stress concentration at the hole edges. The stress level and stress gradient at the mounting base hole edges are high, making them highly susceptible to crack initiation and eventual failure; therefore, they are critical areas of the combustion chamber casing. Thus, when assessing the fatigue life of the combustion chamber casing, low-cycle fatigue damage at the mounting base hole edges must be a primary focus. Furthermore, modern high-performance engine combustion chamber casings operate at temperatures as high as 450–650°C, and the entire casing is subjected to high-temperature combustion gas pressure. Therefore, the influence of temperature must also be considered when assessing the life of the combustion chamber casing. Against this backdrop, this invention proposes a novel method for predicting the fatigue life of structures with circular hole mounting bases. Summary of the Invention

[0004] The purpose of this invention is to establish a TCD-SWT fatigue life prediction model that considers multidimensional stress gradient lines based on the actual two-dimensional stress gradient line on the critical section of the mounting hole, and to combine the SWT parameter on the curve to determine the critical distance, thereby providing a fatigue life prediction method for mounting structures with circular holes that consider two-dimensional stress gradient lines.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for predicting the fatigue life of a mounting base structure with a circular hole considering two-dimensional stress gradient lines, comprising:

[0006] Step 1: Using numerical simulation, perform finite element simulation calculations on the critical section of the mounting hole edge structure to obtain the stress distribution of the critical section of the mounting hole edge structure. Then, use the gradient descent method to calculate the two-dimensional stress gradient of the stress distribution of the critical section of the mounting hole edge structure to obtain the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure.

[0007] Step 2: Based on the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure, determine the SWT parameter distribution line on the two-dimensional stress gradient curve;

[0008] Step 3: Determine the SWT model and its related parameters through material smoothing tests, and then combine this with fatigue tests on the mounting hole edge structure specimen to obtain the effective SWT parameter (σ) of the mounting hole edge structure specimen. max ε a ) eff ;

[0009] Step 4: Fit the SWT parameter distribution line on the two-dimensional stress gradient curve and integrate to obtain the average value within the critical distance segment, so that the average value within the critical distance segment is consistent with the effective SWT parameter (σ) of the mounting hole edge structure specimen. max ε a ) eff If they are equal, establish an equation, solve the equation, and obtain the critical distance;

[0010] Step 5: Fit the SWT parameter distribution line on the two-dimensional stress gradient line l, and integrate to obtain the average value within the critical distance segment on the SWT parameter distribution line. Make the average value within the critical distance segment on the SWT parameter distribution line equal to the SWT model of the material smooth part, and obtain the fatigue life prediction model of the mounting seat hole edge structure.

[0011] Further, step 1 includes:

[0012] Step 1.1: Using numerical simulation, perform finite element simulation calculations on the critical section of the mounting hole edge structure to obtain the stress of each node on the critical section of the mounting hole edge structure. Then, extract the stress of each node on the critical section of the mounting hole edge structure and form a matrix. Next, plot the matrix data into a two-dimensional planar diagram. Finally, obtain the stress distribution of the critical section of the mounting hole edge structure based on the two-dimensional planar diagram.

[0013] Step 1.2: Set the point with the maximum stress as the initial point (x1, y1), determine the position of the second point according to the formula of the gradient descent method, and so on, determine the positions of all remaining points, and draw these points into the two-dimensional planar diagram in step 1.1 to obtain the actual two-dimensional stress gradient curve on the dangerous section of the mounting hole edge structure.

[0014] Furthermore, the formula for the gradient descent method is as follows:

[0015]

[0016]

[0017] Where x and y are coordinates; λ is the step size; f is a function of x and y; and σ is the stress in the stress matrix.

[0018] Furthermore, step 2 specifically includes:

[0019] Taking the starting point of the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure as the center, draw several arcs with different radii. Let the intersection points of the arcs and the stress gradient lines be P1, P2, P3, etc., and extract the coordinates (x, y) of the intersection points P1, P2, P3, etc. i ,y i Then, the stress and strain at these intersection points are extracted and substituted into the formula for the SWT parameters to obtain the SWT parameters at these intersection points. Next, the SWT parameters are plotted with the SWT parameters as the vertical axis and l / r as the horizontal axis to obtain the SWT parameter distribution line on the two-dimensional stress gradient curve.

[0020] Furthermore, the formula for the SWT parameter is:

[0021]

[0022] Where, σ max ε is the maximum stress at the edge of the hole in the mounting structure. max and ε min These represent the maximum and minimum strains at the hole edge, ε a This represents the strain amplitude.

[0023] Further, step 3 includes:

[0024] Step 3.1: Obtain the nominal stress-life curve based on the fatigue test fitting of the specimen with the mounting hole edge structure. The nominal stress-life curve is as follows:

[0025] lgσ nor =A+BlgN f

[0026] Where A and B are material parameters, σ nor For nominal stress, N f This refers to the fatigue test life.

[0027] Step 3.2: The relationship between strain and life is described using the Manson-Coffin equation, and relevant material parameters are obtained through strain tests on smooth parts of the material. The relationship between strain and life is then obtained as follows:

[0028]

[0029] Furthermore, based on symmetrical cyclic parameters, and taking into account the strain amplitude ε, a and maximum stress σ max The effect of low-cycle fatigue, and based on the strain-life relationship, the strain amplitude ε a and maximum stress σ maxA SWT model of the material smoothing component is established through fitting. The SWT model of the material smoothing component is as follows:

[0030]

[0031] Where, σ′ f ε′ is the fatigue strength coefficient. f denoted as σf, b as σf, c as σf, and E as σelastic modulus.

[0032] Step 3.3: Calculate the nominal stress σ for each load level. nor By substituting the nominal stress-life curve, the theoretical life corresponding to each load level can be obtained. Theoretical lifespan Substituting the material into the SWT model of the smooth part, the effective SWT parameter (σ) of the mounting hole edge structure specimen is obtained by reverse calculation. max ε a ) eff .

[0033] Furthermore, the equation in step 4 is:

[0034]

[0035] Among them, D LM For the critical distance, σ max ε a Let σ be the SWT parameter on the stress gradient line. max ε a ) eff The effective SWT parameter for the mounting hole edge structure specimen is denoted by l, which is the distance from the bottom corner of the hole to the stress gradient line of the critical section.

[0036] Furthermore, the fatigue life prediction model for the mounting hole edge structure is as follows:

[0037]

[0038] Among them, D LM For the critical distance, σ max ε a Let σ′ be the SWT parameter on the stress gradient line l. f ε′ is the fatigue strength coefficient. f denoted as σ, b is the fatigue ductility coefficient, c is the fatigue strength index, and E is the elastic modulus.

[0039] Beneficial Effects: The fatigue performance prediction method for mounting structures with circular holes provided by this invention has the following advantages compared with the prior art: The traditional critical distance method uses the extension line of the hole edge perpendicular to the loading direction as the stress gradient line when solving for the critical distance. This method is well adapted to thin plates with notches, but the thickness of the hole edge of the mounting seat with circular holes is large, and its stress gradient line is not along the extension line of the hole edge, but gradually deflects towards the thickness direction. Therefore, this invention uses the two-dimensional stress gradient line on the critical section of the hole edge of the mounting seat with circular holes as the basis, and combines the SWT parameter on the curve to determine the critical distance. The prediction results are all within the 2x dispersion zone, with higher prediction accuracy and better engineering application value. Attached Figure Description

[0040] Figure 1 This is a flowchart of the fatigue life prediction method of the present invention.

[0041] Figure 2 This is the process for calculating stress gradients.

[0042] Figure 3 This is a schematic diagram of the geometric dimensions of the mounting hole edge structure specimen in this invention, using the traditional TCD method.

[0043] Figure 4 This is a geometric dimension diagram of the mounting hole edge structure specimen in this invention.

[0044] Figure 5 A schematic diagram of the improved critical distance determination method.

[0045] Figure 6 A schematic diagram of the stress gradient line at the critical section of the GH4169 mounting hole edge structure specimen.

[0046] Figure 7 The fatigue life prediction results of GH4169 using the TCD-SWT model considering two-dimensional stress gradient are presented in this invention. Detailed Implementation

[0047] The invention will now be further explained with reference to the accompanying drawings.

[0048] like Figure 1 As shown, the present invention provides a method for predicting the fatigue life of a mounting base structure with a circular hole that considers a two-dimensional stress gradient line, comprising:

[0049] Step 1: Using numerical simulation, perform finite element simulation calculations on the critical section of the mounting hole edge structure to obtain the stress distribution of the critical section of the mounting hole edge structure. Then, use the gradient descent method to calculate the two-dimensional stress gradient of the stress distribution of the critical section of the mounting hole edge structure to obtain the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure.

[0050] In step 1, based on the finite element simulation calculation of the casing, the stress of the selected nodes is exported by ANSYS software. Then, the stress of each node on the critical section is extracted and formed into a matrix. Next, the matrix data is plotted into a two-dimensional planar diagram. Then, the stress distribution of the critical section of the mounting hole edge structure is obtained according to the two-dimensional planar diagram.

[0051] After obtaining the stress distribution at the critical section of the mounting hole edge structure, the point with the maximum stress is set as the initial point (x1, y1), and the gradient at this point is (dx1, dy1) = (dx 11 ,dy 11 The position of the second point is determined using the gradient descent formula, and so on, to determine the positions of all remaining points. The specific process is as follows: Figure 2 The stress gradient calculation process is shown below. These points are then plotted in the two-dimensional planar diagram in step 1.1 to obtain the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure. This process can be implemented using a custom calculation program developed in Matlab using the gradient descent method. The formula for the gradient descent method is as follows:

[0052]

[0053]

[0054] Where x and y are coordinates; λ is the step size; f is a function of x and y; and σ is the stress in the stress matrix.

[0055] Step 2: Determine the SWT parameter distribution line on the two-dimensional stress gradient curve based on the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure.

[0056] like Figure 3 As shown, the traditional TCD method uses the average stress of the element at a certain distance along the bottom edge of the hole when θ = 0° as the effective stress for fatigue strength prediction. The formula is:

[0057]

[0058] Where, Δσ eff For effective stress, Δσ y Let θ be the stress at a point a certain distance from the root of the notch, θ be the angle between the line connecting this point to the point of maximum stress at the edge of the hole and the bottom edge of the hole, r be the radius of the notch, and L be the stress at a point a certain distance from the root of the notch. M (N f () represents the critical distance.

[0059] In step 2, this invention uses the starting point of the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure as the center, and draws several arcs with different radii. The intersection points of these arcs and the stress gradient lines are designated as P1, P2, P3, etc., and the coordinates (x, y, y) of these intersection points P1, P2, P3, etc., are extracted.i ,y i Then, the stress and strain at these intersection points are extracted and substituted into the formula for the SWT parameters to obtain the SWT parameters for these intersection points. Next, a graph is plotted with the SWT parameters as the ordinate and l / r as the abscissa to obtain the SWT parameter distribution line on the two-dimensional stress gradient curve. The distance between the intersection point and the center of the arc, i.e., the arc radius, is l1, l2, l3, etc. The radius r of the mounting hole is used as a reference to normalize l. The formula for the SWT parameters is:

[0060]

[0061] Where, σ max ε is the maximum stress at the edge of the hole in the mounting structure. max and ε min These represent the maximum and minimum strains at the hole edge, ε a This represents the strain amplitude.

[0062] Step 3: Determine the SWT model and its related parameters through material smoothing tests, and then combine this with fatigue tests on the mounting hole edge structure specimen to obtain the effective SWT parameter (σ) of the mounting hole edge structure specimen. max ε a ) eff .

[0063] In step 3, the nominal stress-life curve is first obtained by fitting the fatigue test results of the specimen with the mounting hole edge structure. The nominal stress-life curve is as follows:

[0064] lgσ nor =A+BlgN f

[0065] Where A and B are material parameters, obtained by fitting fatigue test data of the mounting hole edge structure specimen, σ nor For nominal stress, ...

[0066] Then, the Manson-Coffin equation is used to describe the relationship between strain and life, and relevant material parameters are obtained through strain tests on smooth parts of the material. The relationship between strain and life is then obtained as follows:

[0067]

[0068] Furthermore, based on symmetrical cyclic parameters, and taking into account the strain amplitude ε, a and maximum stress σ max The effect of low-cycle fatigue, and based on the strain-life relationship, the strain amplitude ε a and maximum stress σ max A SWT model of the material smoothing component is established through fitting. The SWT model of the material smoothing component is as follows:

[0069]

[0070] Where, σ′ f ε′ is the fatigue strength coefficient. f denoted as σ, b as σ, c as σ, and E as σ, are the fatigue ductility coefficients, respectively. σ is obtained by fitting strain test data of smooth material components.

[0071] Finally, the nominal stress σ of each load level is... nor By substituting the nominal stress-life curve, the theoretical life corresponding to each load level can be obtained. Theoretical lifespan Substituting the material into the SWT model of the smooth part, the effective SWT parameter (σ) of the mounting hole edge structure specimen is obtained by reverse calculation. max ε a ) eff .

[0072] Step 4: Fit the SWT parameter distribution line on the two-dimensional stress gradient curve and integrate to obtain the average value within the critical distance segment, so that the average value within the critical distance segment is consistent with the effective SWT parameter (σ) of the mounting hole edge structure specimen. max ε a ) eff If they are equal, establish an equation, solve the equation, and obtain the critical distance.

[0073] In step 4, the equation is:

[0074]

[0075] Among them, D LM For the critical distance, σ max ε a Let σ be the SWT parameter on the stress gradient line. max ε a ) eff The effective SWT parameter for the mounting hole edge structure specimen is denoted by l, which is the distance from the bottom corner of the hole to the stress gradient line of the critical section.

[0076] Step 5: Fit the SWT parameter distribution line on the two-dimensional stress gradient line l, and integrate to obtain the average value within the critical distance segment on the SWT parameter distribution line. Make the average value within the critical distance segment on the SWT parameter distribution line equal to the SWT model of the material smooth part, and obtain the fatigue life prediction model of the mounting seat hole edge structure.

[0077] In step 5, the fatigue life prediction model for the mounting hole edge structure is as follows:

[0078]

[0079] Among them, D LM For the critical distance, σ max ε a Let σ′ be the SWT parameter on the stress gradient line l. f ε is the fatigue strength coefficient. f ′ is the fatigue ductility coefficient, b is the fatigue strength index, c is the fatigue ductility index, and E is the elastic modulus.

[0080] The GH4169 mounting base hole edge structure specimen was measured using the method described above. The specific implementation is as follows:

[0081] The structure of the GH4169 mounting base hole edge structure specimen is as follows: Figure 4 As shown, a stress fatigue test (600℃) was performed on the GH4169 mounting hole edge structure specimen, and then the nominal stress-life curve was obtained by fitting. The specific nominal stress-life curve is as follows:

[0082] lgσ=3.616-0.142lgN f .

[0083] Strain fatigue tests were performed on smooth standard parts made of GH4169 material, and the nominal stress σ at each load level was measured. nor By substituting the nominal stress-life curve, the theoretical life corresponding to each load level can be obtained. Theoretical lifespan By substituting these parameters into the SWT model of the material smoothing component, the effective SWT parameters corresponding to each load level can be derived. The specific SWT model of the material smoothing component is as follows:

[0084] σ max ·Δε / 2=11.185(2N f ) -0.1518 +8174.1(2N f ) -1.1492

[0085] At this time, ε a =Δε / 2.

[0086] like Figure 5-6 As shown, based on the finite element analysis results of the specimen with the mounting hole edge structure, the stress gradient line on the critical section of the specimen was calculated using the gradient descent method in Matlab software. Several arcs with different radii were drawn with the starting point of the stress gradient line as the center. The intersection points of the arcs and the stress gradient line were designated as P1, P2, P3, etc., and the coordinates (x, y, y) of the intersection points P1, P2, P3, etc., were extracted. i ,y i Then, by extracting the stress and strain at these intersection points, the SWT parameters (σ) at these points can be obtained. max ε aThe distance between the intersection point and the center of the arc, i.e., the arc radius, is l1, l2, l3, etc. l is normalized with reference to the hole radius r. Next, a graph is plotted with the SWT parameter as the ordinate and l / r as the abscissa to obtain the SWT parameter distribution diagram on the stress gradient line, where r is the radius of the mounting hole. Finally, the SWT parameter distribution line on the two-dimensional stress gradient curve is fitted, and the average value within the critical distance segment is calculated by integration. This ensures that the average value within the critical distance segment is consistent with the effective SWT parameter (σ) of the mounting hole edge structure specimen. max ε a ) eff If they are equal, establish an equation, solve the equation, and obtain the critical distance. The equation is:

[0087]

[0088] Based on the calculated critical distance D LM =0.716r, and the SWT parameter distribution diagram on the stress gradient line obtained from the finite element calculation results of the mounting hole edge structure specimen, the predicted SWT parameter is calculated, and then substituted into the corresponding fatigue life prediction model of the mounting hole edge structure, to obtain the following formula:

[0089] Solving this equation yields the predicted lifespan of a smooth standard part made of GH4169 material. In this equation, σ... max ε a The SWT parameter on the stress gradient line can be considered as a function of l. The formula for calculating the SWT parameter is:

[0090]

[0091] Comparative analysis with fatigue test results under the same conditions, such as Figure 7 As shown in the figure, the error is within 2 times the tolerance zone, indicating that the prediction method is good.

[0092] This invention employs a numerical simulation method to perform finite element analysis on the critical section of the mounting seat hole edge structure. Using Matlab software and the gradient descent method, the actual two-dimensional stress gradient curve on the critical section is obtained. This is then combined with experimental results from a simulated mounting seat to determine the critical distance, thereby establishing a fatigue life prediction model for the mounting seat hole edge structure. This life prediction method is suitable for fatigue life prediction of notched structures like mounting seats with large two-dimensional stress gradients. The prediction results are all within a 2x dispersion band, demonstrating higher prediction accuracy than traditional methods and possessing greater engineering application value.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for predicting the fatigue life of a mounting base structure with a circular hole, considering two-dimensional stress gradient lines, characterized in that, include: Step 1: Using numerical simulation, perform finite element simulation calculations on the critical section of the mounting hole edge structure to obtain the stress distribution of the critical section of the mounting hole edge structure. Then, use the gradient descent method to calculate the two-dimensional stress gradient of the stress distribution of the critical section of the mounting hole edge structure to obtain the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure. Step 2: Based on the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure, determine the SWT parameter distribution line on the two-dimensional stress gradient curve; Step 3: Determine the SWT model and its related parameters through material smoothing part tests, and then combine this with fatigue tests on the mounting hole edge structure specimen to obtain the effective SWT parameters of the mounting hole edge structure specimen. ; Step 4: Fit the SWT parameter distribution line on the two-dimensional stress gradient curve and integrate to obtain the average value within the critical distance segment, so that the average value within the critical distance segment is consistent with the effective SWT parameter of the mounting hole edge structure specimen. If they are equal, establish an equation, solve the equation, and obtain the critical distance; Step 5: Fit the SWT parameter distribution line on the two-dimensional stress gradient line l, and integrate to obtain the average value within the critical distance segment on the SWT parameter distribution line. Make the average value within the critical distance segment on the SWT parameter distribution line equal to the SWT model of the material smooth part, and obtain the fatigue life prediction model of the mounting seat hole edge structure. Step 1 includes: Step 1.1: Using numerical simulation, perform finite element simulation calculations on the critical section of the mounting hole edge structure to obtain the stress of each node on the critical section of the mounting hole edge structure. Then, extract the stress of each node on the critical section of the mounting hole edge structure and form a matrix. Next, plot the matrix data into a two-dimensional planar diagram. Finally, obtain the stress distribution of the critical section of the mounting hole edge structure based on the two-dimensional planar diagram. Step 1.2: Set the point with the highest stress as the initial point. The position of the second point is determined according to the formula of the gradient descent method, and so on, to determine the position of all remaining points. These points are then plotted in the two-dimensional planar diagram in step 1.1 to obtain the actual two-dimensional stress gradient curve on the dangerous section of the mounting hole edge structure. The equation in step 4 is: ； in, This is the critical distance. The SWT parameter is located on the stress gradient line. The effective SWT parameter for the mounting hole edge structure specimen. This is the distance from the bottom corner of the hole to the stress gradient line of the critical section.

2. The fatigue life prediction method for a mounting base structure with a circular hole considering two-dimensional stress gradient lines according to claim 1, characterized in that, The formula for the gradient descent method is as follows: ； ； Where x and y are coordinates; is the step size; f is a function of x and y. It refers to the stress in the stress matrix.

3. The fatigue life prediction method for a mounting base structure with a circular hole considering two-dimensional stress gradient lines according to claim 1, characterized in that, Step 2 specifically involves: Taking the starting point of the actual two-dimensional stress gradient curve on the critical section of the mounting hole edge structure as the center, draw several arcs with different radii. Let the intersection of the arcs and the stress gradient line be... , , Extract the intersection point , , ...coordinates Then, the stress and strain at these intersection points are extracted and substituted into the formula for the SWT parameters to obtain the SWT parameters for these intersection points. Next, the SWT parameters are plotted as the ordinate and... Plotting the x-axis yields the SWT parameter distribution line on the two-dimensional stress gradient curve.

4. The fatigue life prediction method for a mounting base structure with a circular hole considering two-dimensional stress gradient lines according to claim 3, characterized in that, The formula for the SWT parameter is: ； in, The maximum stress at the edge of the mounting hole structure, and These represent the maximum and minimum strains at the edge of the hole, respectively. This represents the strain amplitude.

5. The fatigue life prediction method for a mounting base structure with a circular hole considering two-dimensional stress gradient lines according to claim 1, characterized in that, Step 3 includes: Step 3.1: Obtain the nominal stress-life curve based on the fatigue test fitting of the specimen with the mounting hole edge structure. The nominal stress-life curve is as follows: ； Where A and B are both material parameters, For nominal stress, For fatigue test life; Step 3.2: The relationship between strain and life is described using the Manson-Coffin equation, and relevant material parameters are obtained through strain tests on smooth parts of the material. The relationship between strain and life is then obtained as follows: ； Furthermore, based on symmetrical cyclic parameters, and taking strain amplitude into account... and maximum stress The effect on low-cycle fatigue, and based on the strain-life relationship, the strain amplitude... and maximum stress A SWT model of the material smoothing component is established through fitting. The SWT model of the material smoothing component is as follows: ； in, The fatigue strength coefficient, denoted as σf, b as σf, c as σf, and E as σelastic modulus. Step 3.3: Calculate the nominal stress for each load level. By substituting the nominal stress-life curve, the theoretical life corresponding to each load level can be obtained. The theoretical lifespan Substituting the material into the SWT model of the smooth part, the effective SWT parameters of the mounting hole edge structure specimen are obtained by reverse calculation. .

6. The fatigue life prediction method for a mounting base structure with a circular hole considering two-dimensional stress gradient lines according to claim 1, characterized in that, The fatigue life prediction model for the mounting hole edge structure is as follows: ； in, This is the critical distance. The SWT parameter is on the stress gradient line l. The fatigue strength coefficient, denoted as σ, b is the fatigue ductility coefficient, c is the fatigue strength index, and E is the elastic modulus.

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