Fatigue life prediction method for nickel-based single crystal superalloys based on three-dimensional micropore morphology

Abstract

The application provides a nickel-based single crystal superalloy fatigue life prediction method based on three-dimensional micropore morphology, and relates to the technical field of nickel-based single crystal superalloy fatigue life evaluation. S1, three-dimensional morphology data of micropores is obtained by scanning and reconstruction; S2, the reference maximum stress of micropores is obtained; S3, three-dimensional feature correction parameters are constructed; S4, the influence of micropore nonlinear damage is accumulated to construct a dynamic damage evolution index; S5, the stress characteristics and stress influence of micropore hole materials are obtained to obtain a fatigue life prediction value. The application aims to provide a life prediction method that can fuse real three-dimensional micropore morphology characteristics, accurately analyze local mechanical fields and construct nonlinear fatigue damage relationships, to solve the obvious deficiencies of the prior art in micropore three-dimensional morphology characterization, micropore surrounding stress field coupling and model construction.

Description

Technical Field

[0001] This invention relates to the field of performance evaluation and life prediction technology of core materials for aero-engine turbine blades, specifically to a method for predicting the fatigue life of nickel-based single-crystal superalloys based on three-dimensional micropore morphology. Background Technology

[0002] Nickel-based single-crystal superalloys have become key materials for aero-engine turbine blades due to their excellent high-temperature strength and creep resistance. However, in actual service, casting micropores inevitably exist within the material. These micropores are highly susceptible to becoming fatigue crack initiation points under cyclic loading, leading to premature component failure. Therefore, accurately predicting the fatigue life of microporous materials is crucial for ensuring the safety of aero-engines. However, existing technologies have the following shortcomings in practical applications: 1. Limitations of Micropore Characterization: Traditional methods often rely on scanning electron microscopy (SEM) or optical microscopy for two-dimensional observation of the sample surface, or employ traditional destructive metallographic analysis. These methods cannot intuitively and non-destructively obtain the true three-dimensional spatial distribution, connectivity, and surface irregularity of micropores within the material. This leads to the simplification or neglect of key geometric features such as the aspect ratio, orientation angle, and sphericity of the micropores, resulting in subsequent mechanical analysis being based on distorted geometric models.

[0003] 2. Inaccurate stress field analysis around micropores: When establishing finite element models, existing techniques often simplify micropores into ideal spheres or ellipsoids. This approach not only ignores the complex free-form surface characteristics of actual micropores but also fails to accurately capture the local effects of stress concentration on the micropore surface, resulting in significant deviations between the calculated results and the actual stress field.

[0004] 3. Low model prediction accuracy: Existing fatigue damage models are mostly based on the assumption of a macroscopic continuous medium, and usually only consider the influence of nominal stress or mean stress. These models fail to effectively couple the quantitative analysis results of the local mechanical field around the micropores into the damage evolution equation, and ignore the amplification effect of the three-dimensional morphology of the micropores on stress concentration and its accelerating effect on nonlinear damage accumulation, resulting in life prediction results that are often too conservative or deviate from reality.

[0005] In summary, existing technologies have significant shortcomings in characterizing the three-dimensional morphology of micropores, coupling the stress field around micropores, and model construction, which severely restricts the accuracy of fatigue life prediction for nickel-based single-crystal superalloys. Therefore, it is urgent to develop a life prediction method that can integrate real three-dimensional micropore morphology features, accurately analyze local mechanical fields, and construct nonlinear fatigue damage relationships to solve the aforementioned technical challenges. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention aims to provide a life prediction method that can integrate real three-dimensional micropore morphology features, accurately analyze local mechanical fields, and construct nonlinear fatigue damage relationships, thereby solving the significant deficiencies of existing technologies in micropore three-dimensional morphology characterization, stress field coupling around micropores, and model construction.

[0007] Specifically, the present invention provides a method for predicting the fatigue life of nickel-based single-crystal superalloys based on three-dimensional micropore morphology, which includes the following steps: S1. The micropores in the gauge length section of the nickel-based single-crystal superalloy sample are scanned and reconstructed to obtain the three-dimensional morphology data of the micropores in the sample. S2. Based on the three-dimensional morphology data obtained in S1, a finite element model containing all actual three-dimensional micropore morphologies in the sample is established to obtain the maximum stress of the micropore reference. S3. Based on the three-dimensional morphology data obtained in S1, construct three-dimensional feature correction parameters to quantitatively characterize the influence of the three-dimensional micropore morphology on the stress field around the micropores. This includes the following sub-steps: S31. Based on the three-dimensional morphology data obtained in S1, the micropore morphology parameters that can quantitatively characterize the angle, aspect ratio and roughness of the micropores are extracted through numerical calculation. S32. Quantitatively analyze the local mechanical field around the micropore, and obtain the first local stress, second local stress and third local stress that can characterize the influence of the angle, aspect ratio and roughness of the micropore on the stress field around the micropore through mathematical statistics and data fitting. S33. The first local stress, the second local stress and the third local stress obtained from S32 are coupled in a dimensionless manner and incrementally superimposed using the maximum stress of the micropore reference to obtain the three-dimensional feature correction parameter K. ; in, For the first local stress, , The maximum stress is the reference value for the micropore. For surface irregularity parameters; S4. Based on the maximum micropore reference stress obtained in S2 and the three-dimensional feature correction parameters obtained in S3, the critical maximum stress is derived by combining the Goodman equation, and the influence of the nonlinear damage of the micropore is accumulated to construct a dynamic damage evolution index. S5. Based on the nonlinear continuous fatigue damage model, and combined with the stress characteristics and stress effects of microporous materials, the fatigue life prediction value is obtained. for: ; in, For tensile strength, For the equivalent maximum stress, The fatigue limit under symmetrical cyclic conditions. The mean stress is given by α, and α is a parameter representing the degree of material damage. This is a parameter sensitive to material fatigue damage.

[0008] Preferably, the micropore morphology parameters include angular parameters, aspect ratio parameters, and surface irregularity parameters, calculated using the following formula: ; ; ; in, Here, θ is the angle parameter, and θ is the spatial angle. For aspect ratio related parameters, It is the aspect ratio.

[0009] Preferably, the expressions for the first local stress, the second local stress, and the third local stress are as follows: ; ; ; Where A is the first far-field stress function, B is the first stress fitting coefficient, C is the first surface stress function, b is the second far-field stress function, and c is the second surface stress function. for .

[0010] Preferably, S4 specifically includes: S41. Three-dimensional feature correction parameters obtained using S3 The equivalent maximum stress of the micropore is obtained by combining the maximum stress of the micropore reference. S42. Perform stress analysis on the maximum stress under uniaxial cyclic loading to obtain the critical maximum stress corresponding to the fatigue limit boundary. ; S43, Using equivalent maximum stress With the critical maximum stress The dynamic damage evolution index is obtained by accumulating the nonlinear continuous damage process of micropores. : ; in, This is the critical maximum stress.

[0011] Preferably, the equivalent maximum stress of the micropore is: ; in, This represents the initial porosity.

[0012] Preferably, the critical maximum stress is: ; in, This is a correction term for fatigue load capacity.

[0013] Preferably, S5 specifically includes: S51. Based on the nonlinear continuous fatigue damage model, establish the rate of change of fatigue damage variables for microporous materials. S52. Under constant amplitude cyclic loading conditions, the rate of change of the fatigue damage variable obtained in S51 is integrated, and the fatigue life prediction value is obtained by combining the dynamic damage evolution index, fatigue limit value and critical maximum stress.

[0014] Preferably, the rate of change of fatigue damage variables for: ; in, For fatigue damage variables, The number of loops. It is a dynamic damage evolution index. It is a parameter sensitive to material fatigue damage. This is a correction term for fatigue load capacity.

[0015] Preferably, S1 specifically includes: S11. The gauge length of the nickel-based single-crystal superalloy sample was scanned using an X-ray computed tomography system to obtain a two-dimensional slice image of the micropores inside the sample. S12. Perform image segmentation, hole identification and three-dimensional reconstruction on the two-dimensional slice image to obtain a three-dimensional micropore model that reflects the real spatial morphology of the micropores, and then extract the three-dimensional morphology data of the micropores in the sample.

[0016] Preferably, S2 specifically includes: S21. Based on the three-dimensional morphology data obtained in S1, a finite element model containing all actual three-dimensional micropore morphologies in the sample is established. The finite element model is geometrically extracted and meshed to obtain a meshed micropore finite element model containing only a single micropore. S22. Apply an equivalent load to the micropore finite element model obtained in S21, perform crystal plastic finite element analysis, and obtain the maximum stress of the micropore reference.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By introducing X-ray computed tomography (XCT) technology combined with threshold segmentation and watershed algorithms, this invention overcomes the limitations of traditional 2D characterization methods. It can non-destructively and intuitively obtain the three-dimensional spatial distribution of micropores inside the sample, and accurately extract three-dimensional morphological data such as the aspect ratio, orientation angle, and surface irregularity of the micropores, providing a real data foundation for the subsequent establishment of high-fidelity physical models.

[0018] 2. This invention introduces crystal plasticity theory into finite element modeling and performs local mesh refinement on the micropore surface. By using C3D4 tetrahedral elements to discretize complex freeform surfaces with high quality, the problem of stress calculation distortion caused by mesh coarseness in existing technologies is effectively solved. This makes quantitative analysis of the local mechanical field around the micropore possible, thereby accurately capturing the maximum stress concentration phenomenon at the micropore tip.

[0019] 3. By introducing three-dimensional feature correction parameters, this invention quantitatively correlates the geometric features of the micropores with the stress field around the micropores to obtain the equivalent maximum stress. Using the equivalent maximum stress as the core driving variable of the nonlinear continuous fatigue damage model, the microscale stress concentration effect is successfully coupled to the macroscale life prediction. This not only corrects the bias of traditional models that only consider nominal stress, but also significantly improves the predictive model's ability to describe the actual damage accumulation process, making the prediction results closer to real service conditions. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to the present invention. Figure 2 This is a flowchart of the XCT scanning process of the present invention; Figure 3 This is the meshed model of the finite element model of the present invention; Figure 4 This is a simulation result diagram of the idealized micropore major axis with different angles to the loading direction according to the present invention; Figure 5 This is a schematic diagram illustrating the effect of the angle parameters of the present invention on the stress field around the micropores; Figure 6 The present invention shows the fitting relationship between the first far-field stress function parameter A and the first surface stress function parameter C in the model under different sample surface stress finite element simulation values; Figure 7 This is a schematic diagram illustrating the influence of the aspect ratio correlation parameter of the present invention on the stress field around the micropore; Figure 8 The figure shows the fitting relationship between the second far-field stress function parameter b and the second surface stress function parameter c in the model under different sample surface stress finite element simulation values. Figure 9 This is a comparison of the idealized and the equivalent maximum stress of irregular micropores in this invention; Figure 10 This is a curve showing the fitting of fatigue test data to material-related parameters according to the present invention. Detailed Implementation

[0021] The following is for reference Figure 1 The embodiments of the present invention will be described.

[0022] S1. The micropores in the gauge length of the nickel-based single-crystal superalloy sample are scanned and reconstructed to obtain the three-dimensional morphology data of the micropores in the sample.

[0023] S11. The gauge length of the nickel-based single-crystal superalloy sample was scanned using an X-ray computed tomography system to obtain a two-dimensional slice image of the micropores inside the sample. The nickel-based single-crystal superalloy sample was scanned using an X-ray computed tomography system along the gauge length. An appropriate voxel size was selected: actual size = voxel size × number of voxels, to ensure that the three-dimensional characteristic parameters obtained from subsequent quantitative analysis are consistent with the actual size of the scanned sample.

[0024] S12. Perform image segmentation, hole identification and three-dimensional reconstruction on the two-dimensional slice image to obtain a three-dimensional micropore model that reflects the real spatial morphology of the micropores, and then extract the three-dimensional morphology data of the micropores in the sample. Specifically, threshold segmentation combined with the watershed algorithm is used to efficiently and accurately separate micropores from the material matrix in a two-dimensional image, obtaining clear boundaries; then the two-dimensional XCT image is reconstructed into a three-dimensional model to achieve quantitative characterization of the micropore morphology.

[0025] Specifically, the three-dimensional morphology data includes the maximum extreme length of the micropore, the minimum extreme width, the aspect ratio, the spatial angle, the total volume of the micropore, the total volume of the sample section, and the spatial position and relative volume of the micropore.

[0026] The aspect ratio of the micropores ,satisfy: ; initial porosity satisfy: ; Where L is the maximum extremum length of the micropore, and W is the minimum extremum width. The total volume of the micropores This represents the total volume of the sample section.

[0027] S2. Based on the three-dimensional morphology data obtained from S1, a finite element model containing all actual three-dimensional micropore morphologies within the sample is established to obtain the maximum stress at the micropore reference.

[0028] S21. Based on the three-dimensional morphology data obtained in S1, a finite element model containing all actual three-dimensional micropore morphologies within the sample is established. The finite element model is then subjected to geometric extraction and mesh processing to obtain a meshed micropore finite element model containing only a single micropore.

[0029] Within the framework of crystal plasticity theory, a finite element model incorporating the actual three-dimensional micropore morphology of nickel-based single-crystal superalloys is established to accurately simulate the deformation and failure behavior of the samples. Through reasonable parameter calibration, the model can predict the elastoplastic mechanical response of the material and provide a detailed evolution process of physical fields such as stress and strain related to local deformation and damage within and around the micropores, thus exploring the evolution mechanism while considering the three-dimensional morphology of the micropores. The model establishment method mainly includes the following steps: Geometric extraction: Extract a three-dimensional geometric model of the gauge length of the sample containing multiple actual micropores, preserving the spatial position and relative volume of all micropores in the original sample; export the geometric model as an INP file for subsequent processing.

[0030] Mesh processing: The irregular microporous geometry was meshed, smoothed, and optimized. Mesh refinement was performed based on the geometric topology defined in the INP file, including generating high-quality elements such as tetrahedral, hexahedral, or hybrid types, repairing mesh defects, and adjusting mesh density to meet computational and simulation accuracy requirements. By checking the quality indicators of key elements, the mesh was ensured to be suitable for subsequent analysis, significantly improving the overall mesh quality. In this study, the finite element model used four-node linear tetrahedral elements.

[0031] S22. Apply an equivalent load to the micropore finite element model obtained in S21, perform crystal plastic finite element analysis, and obtain the maximum stress of the micropore reference.

[0032] Specifically, the equivalent load is a uniaxial cyclic load or an equivalent uniaxial load boundary condition.

[0033] S3. Based on the three-dimensional morphology data obtained in S1, construct three-dimensional feature correction parameters to quantitatively characterize the influence of the three-dimensional micropore morphology on the stress field around the micropore.

[0034] S31. Based on the three-dimensional morphology data obtained in S1, micropore morphology parameters that can quantitatively characterize the angle, aspect ratio, and roughness of the micropores are extracted through numerical calculation: Specifically, the micropore morphology parameters include angular parameters, aspect ratio parameters, and surface irregularity parameters.

[0035] ; ; ; in, Here, θ is the angle parameter, and θ is the spatial angle. For aspect ratio related parameters, The aspect ratio is... is the surface irregularity parameter.

[0036] Specifically, the surface irregularity parameter needs to be manually determined according to the actual roughness of the hole. For ideal smooth holes, the value is 0; for normal working conditions, the default value is 0.05; and for extremely irregular or conservative safety designs, the value is 0.1. The spatial angle is characterized as the angle between the long axis direction of the micro-hole space and the direction of the applied load.

[0037] S32. Quantitatively analyze the local mechanical field around the micropores. Through mathematical statistics and data fitting, obtain the first local stress, second local stress, and third local stress, which can characterize the influence of the angle, aspect ratio, and roughness of the micropores on the stress field around the micropores: ; ; ; in, Let A be the first local stress, B be the first far-field stress function, C be the first stress fitting coefficient, and D be the first surface stress function. b is the second far-field stress function, and c is the second surface stress function. for , This represents the maximum stress at the micropore reference.

[0038] S33. The first local stress, second local stress, and third local stress obtained from S32 are coupled in a dimensionless manner and incrementally superimposed using the maximum stress of the micro-pore reference to obtain the three-dimensional feature correction parameters.

[0039] Since real micropores are not ideally spherical, their local stress is closely related to the spatial orientation, aspect ratio, and surface irregularity of the pores. Therefore, it is necessary to transform these three-dimensional morphological features into a dimensionless stress amplification parameter that can be used in fatigue life models.

[0040] Based on the concept of dimensionless and incremental superposition of local stress amplification effect, a three-dimensional feature correction parameter K is introduced to quantitatively analyze the influence of micropore morphology on the micropore stress field: +Orientation increment +Shape increment +Irregularity increment; Wherein, 1 represents the reference stress state, and the change in local stress relative to the maximum stress of the micropore reference is characterized by superimposing three increments: The orientation increment represents the change in local stress relative to the maximum stress of the micropore reference caused by the spatial angle between the long axis of the hole and the loading direction; the shape increment represents the change in local stress relative to the maximum stress of the micropore reference caused by changes in aspect ratio, flatness, and local curvature; and the irregularity increment represents the additional change in local stress relative to the maximum stress of the micropore reference caused by non-ideal morphologies such as unevenness, sharp corners, and abrupt changes in local curvature on the hole surface. Therefore, the three-dimensional feature correction parameter K is: ; Summarized as follows: ; in, The stress amplification ratio for the orientation of the hole, The stress amplification ratio is the shape of the hole.

[0041] S4. Based on the maximum micropore reference stress obtained in S2 and the three-dimensional feature correction parameters obtained in S3, the critical maximum stress is derived by combining the Goodman equation, and the influence of the nonlinear damage of the micropore is accumulated to construct a dynamic damage evolution index.

[0042] S41. Three-dimensional feature correction parameters obtained based on S3 The maximum stress of the micropore reference obtained by S2 is corrected to obtain the equivalent maximum stress of the micropore. : ; in, The initial porosity, Maximum stress of the micropore reference.

[0043] This invention, based on the concept of equivalent homogenization of defective materials, equivalently divides the fatigue-prone region of microporous materials into a continuous matrix control region and a pore defect control region. The equivalent maximum stress considering defects is obtained by weighted superposition of the stress contributions of both regions. The continuous matrix control region is not significantly affected by defects; its stress contribution is characterized by multiplying the weighted values ​​by the maximum stress at the micropore reference level. The void defect control zone is affected by void orientation, aspect ratio, and surface irregularities. A three-dimensional feature correction parameter is introduced, and its stress contribution is... .

[0044] Specifically, fatigue cracks tend to initiate preferentially at the edges of pores, sharp corners, or areas of abrupt changes in curvature. Therefore, in fatigue life prediction models, directly using the maximum stress based on micropores is insufficient. As a damage driving force, it is difficult to reflect the amplifying effect of pore volume fraction and pore three-dimensional morphology on local fatigue risk.

[0045] This invention equivalently divides the fatigue-prone region of microporous materials into a continuous matrix control region and a porosity defect control region. The continuous matrix control region is not significantly controlled by porosity defects, and its stress contribution can still be determined by the maximum stress at the micropore reference. Characterization. The weight of the continuous matrix control region can be approximated as: Then its contribution to the corresponding force is The void defect control zone is affected by void defects. Since the local stress near the void is affected by the void orientation, aspect ratio, and surface irregularity, a three-dimensional feature correction parameter is introduced. Its contribution to the corresponding force is By weighted superposition of the stress contributions from the continuous matrix control region and the porosity defect control region, the equivalent maximum stress considering micropore defects can be obtained. .

[0046] It should be noted that the initial porosity here... It does not refer to the load borne by the hole itself, but rather to the volume distribution of micropore defects in the material and their weighted influence on fatigue-prone areas.

[0047] This formula illustrates that as porosity increases or the morphology of the pores becomes more dangerous, the equivalent maximum stress increases, the fatigue damage driving force increases, and the life prediction result decreases accordingly. This is consistent with the physical phenomenon that fatigue cracks preferentially initiate and accelerate near pores in microporous superalloys.

[0048] S42. Perform stress analysis on the maximum stress under uniaxial cyclic loading to obtain the critical maximum stress corresponding to the fatigue limit boundary. for: ; in, This is a correction term for fatigue load capacity. The fatigue limit under symmetrical cyclic conditions. For tensile strength, The average stress is given.

[0049] Specifically, this formula is derived from the Goodman mean stress correction relation and is used to transform the weakening effect of mean stress on the fatigue limit into the critical maximum stress corresponding to the mean stress state. Among these, the fatigue limit under symmetrical cyclic conditions... Characterized by the fatigue stress amplitude that a material can withstand over a long period of time, the critical maximum stress It is characterized as the maximum fatigue threshold stress after the mean stress correction.

[0050] S43, Using equivalent maximum stress With the critical maximum stress The dynamic damage evolution index is obtained by accumulating the nonlinear continuous damage process of micropores. for: ; Where 'a' is a parameter representing the degree of material damage.

[0051] The nonlinear accumulation of fatigue damage is not constant but varies with the stress state. When the equivalent maximum stress... Approaching the critical maximum stress At this time, the material is near the fatigue damage initiation interface, the damage evolution is slow, and the life tends to be very large; when the equivalent maximum stress... Significantly higher than the critical maximum stress As the material exceeds its fatigue threshold, damage accumulation accelerates significantly. Therefore, this invention employs... Characterizing effective overthreshold stress, and using tensile strength Dimensionless processing is performed; simultaneously, a material damage degree parameter 'a' is introduced to adjust the sensitivity of different materials to exceeding the threshold stress. This formula can guarantee that when... At that time, material damage degree parameter The value is 1, thus naturally reflecting the boundary characteristic that the lifespan tends to be very large or even infinite near the fatigue limit. This formula makes the material damage degree parameter no longer a constant, but determined by how much the current stress is higher than the fatigue threshold, and it can also satisfy the key physical requirement that the lifespan tends to be infinite when approaching the fatigue limit.

[0052] S5. Based on the nonlinear continuous fatigue damage model, and combined with the stress characteristics and stress effects of microporous materials, the fatigue life prediction value is obtained.

[0053] S51. Based on the nonlinear continuous fatigue damage model, establish the rate of change of fatigue damage variables for microporous materials. for: ; in, For fatigue damage variables, The number of loops. For the equivalent maximum stress, For average stress, It is a dynamic damage evolution index. This is a parameter sensitive to material fatigue damage.

[0054] S52. Under constant amplitude cyclic loading conditions, the rate of change of the fatigue damage variable obtained in S51 is integrated. Combined with the dynamic damage evolution index, fatigue limit value, and critical maximum stress, the predicted fatigue life value is obtained as follows: ; After sorting, we can obtain: .

[0055] The present invention will now provide a specific embodiment.

[0056] This embodiment uses a nickel-based single-crystal superalloy sample as the object, and follows... Figure 1 The process shown sequentially completes the acquisition of the three-dimensional morphology of micropores, the establishment of a finite element model containing actual micropores, and the correction of three-dimensional feature parameters. Construction, equivalent maximum stress Calculation and dynamic damage evolution index Determining fatigue life predict: S1. The micropores in the gauge length of the nickel-based single-crystal superalloy sample are scanned and reconstructed in three dimensions to obtain the three-dimensional morphology data of the micropores in the sample.

[0057] S11. The gauge length of the nickel-based single-crystal high-temperature alloy sample was scanned using an X-ray computed tomography system to obtain two-dimensional slice images of the micropores inside the sample.

[0058] Specifically, the gauge length of small samples was characterized using a GEPhoenix V|tome|XS240 X-ray computed tomography (XCT) system. Scanning parameters were set as follows: voltage 80 kV, current 100 μA, resolution 1.1 μm. Images were acquired as follows: Figure 2 The image shows a series of two-dimensional slices in the horizontal and vertical directions, with a slice spacing of 1.1 μm.

[0059] It is important to note that during the scanning process, an appropriate voxel size must be selected based on the sample size, micropore scale, and subsequent 3D reconstruction accuracy requirements. The voxel size and the actual size should satisfy the relationship of "actual size = voxel size × number of voxels" to ensure that the 3D feature parameters obtained from subsequent quantitative analysis are consistent with the true size of the scanned sample. In this embodiment, when the voxel size is set to 1.187 μm, the dimensions measured in the software closely match the corresponding scale bar size, meeting the accuracy requirements for quantitative characterization of the 3D morphology of micropores.

[0060] S12. Perform image segmentation, hole identification and three-dimensional reconstruction on the two-dimensional slice image to obtain a three-dimensional micropore model that reflects the real spatial morphology of the micropores, and then extract the three-dimensional morphology data of the micropores in the sample.

[0061] Specifically, the obtained two-dimensional image set is imported into AVIZO software for further processing. Threshold segmentation combined with the watershed algorithm is used to separate the micropores from the material matrix in the two-dimensional slice images, obtaining clear micropore boundaries. Subsequently, the two-dimensional XCT images are reconstructed into a three-dimensional model to achieve quantitative characterization of the true spatial morphology of the micropores.

[0062] In the three-dimensional reconstruction model, the maximum extreme length, minimum extreme width, aspect ratio, spatial angle, total volume of micropores, total volume of sample section, spatial position and relative volume of micropores are extracted.

[0063] The aspect ratio and initial porosity of the micropores can then be calculated based on the above fundamental variables, using the following formula: ; .

[0064] It should be noted that the above parameters are the basic inputs for subsequent modeling.

[0065] S2. Based on the three-dimensional morphology data obtained in S1, a finite element model containing all actual three-dimensional micropore morphologies within the sample is established to obtain the maximum stress at the micropore reference.

[0066] S21. Based on the three-dimensional morphology data obtained in S1, a finite element model containing all actual three-dimensional micropore morphologies within the sample is established. The finite element model is then subjected to geometric extraction and mesh processing to obtain a meshed micropore finite element model containing only a single micropore.

[0067] Specifically, based on the 3D reconstruction results obtained in S1, a 3D geometric model of the gauge length segment of the sample containing multiple actual micropores is extracted, preserving the spatial location, relative volume, and actual freeform surface features of the micropores in the original sample. This geometric model is exported as an INP file for subsequent mesh processing and model calculation in the finite element analysis software.

[0068] During mesh processing, the irregular micropore geometry is meshed, smoothed, and optimized. Mesh refinement is performed based on the geometric topology defined in the INP file, including generating tetrahedral, hexahedral, or hybrid element types, repairing mesh defects, and adjusting mesh density to meet computational and simulation accuracy requirements. In this embodiment, the finite element model uses four-node linear tetrahedral elements. Since high stress gradients are easily generated at micropore edges, sharp corners, and regions with abrupt changes in curvature, local mesh refinement is performed in the vicinity of the micropores; a relatively coarser mesh is used in the continuous matrix region far from the micropores to balance computational accuracy and efficiency. The final meshed finite element model is shown below. Figure 3 As shown.

[0069] S22. Apply an equivalent load to the micropore finite element model obtained in S21, perform crystal plastic finite element analysis, and obtain the maximum stress of the micropore reference.

[0070] Specifically, within the framework of crystal plasticity theory, corresponding material parameters and crystal plasticity constitutive parameters are assigned to the nickel-based single-crystal superalloy, and uniaxial cyclic loading or equivalent uniaxial loading boundary conditions are applied to the micropore finite element model obtained in S21. After calculation, stress field data near the micropores and in the matrix region are extracted, and the maximum stress used to characterize the reference stress level in the current finite element analysis is recorded as the micropore reference maximum stress. .

[0071] It should be noted that the maximum stress of the micropore reference obtained in S2 It is the baseline mechanical response obtained under a given equivalent load and crystal plasticity finite element model, and its function is to provide the first local stress in subsequent S3. Second local stress Third local stress Dimensionless coupling and 3D feature correction parameters The construction provides a reference stress scale. Therefore, S2 is not a repetition of the quantitative analysis of the local mechanical field in S3, but rather provides a finite element reference stress for S3.

[0072] S3. Based on the three-dimensional morphology data obtained in S1, construct three-dimensional feature correction parameters to quantitatively characterize the influence of the three-dimensional micropore morphology on the stress field around the micropore.

[0073] S31. Based on the three-dimensional morphology data obtained in S1, micropore morphology parameters that can quantitatively characterize the angle, aspect ratio, and roughness of the micropores are extracted through numerical calculation.

[0074] Specifically, the micropore morphology parameters include angular parameters, aspect ratio parameters, and surface irregularity parameters.

[0075] Angle-related parameters satisfy: .

[0076] Aspect Ratio Related Parameters satisfy: .

[0077] Surface irregularity parameters satisfy: .

[0078] S32. Quantitatively analyze the local mechanical field around the micropore. Through mathematical statistics and data fitting, obtain the first local stress, the second local stress, and the third local stress that can characterize the influence of the angle, aspect ratio, and roughness of the micropore on the stress field around the micropore.

[0079] , , They respectively satisfy: ; ; .

[0080] Figure 4 Simulation results are presented for idealized micropores with their major axis forming different angles with the loading direction. Figure 4 It can be seen that, under the same micropore morphology and load level, the orientation change of the long axis of the micropore relative to the loading direction will cause the stress field distribution around the micropore to be different, indicating that the spatial angle is an important factor affecting the local stress state around the micropore.

[0081] Figure 5 The figure shows the finite element simulation and fitting results of the spatial angle and the first local stress of an ellipsoidal micropore with a porosity of 0.05% and an aspect ratio of 2:1. The scatter points in the figure represent the finite element results. The fitting process involves three parameters: the first stress fitting coefficient B changes very little under different stress conditions, so it is regarded as a constant in this invention, and the first stress fitting coefficient B is taken as 1.3375; in contrast, the first far-field stress function A and the first surface stress function C are stress-related functions, which can be determined by linear interpolation and nonlinear interpolation, respectively.

[0082] Figure 6 The effects of the angle parameter on the first far-field stress function A and the first surface stress function C in the model are shown under different finite element simulation values ​​of sample surface stress. Their expressions are as follows: ; .

[0083] A similar method was used to fit the local stress affected by the aspect ratio of micropores. For example... Figure 7 As shown, changes in the aspect ratio-related parameters alter the local stress field distribution around the micropores, indicating that the shape characteristics of the micropores affect the stress concentration near the pores.

[0084] Based on this, the local stress under the influence of aspect ratio-related parameters is fitted, such as... Figure 8 As shown, the second far-field stress function Second surface stress function With the application of surface stress The stress changes with the change in stress, and based on this, a second far-field stress function can be established. Second surface stress function Corresponding fitting relationship: ; .

[0085] Quantitative analysis of surface irregularities in micropores was performed, and the results are as follows: Figure 9 As shown. Combining mathematical statistics with the geometric mean stress concept introduced earlier, it is determined that the local geometric mean stress of irregular micropores is about 0-10% higher than that of ideal micropores. Therefore, the surface irregularity parameter... It can be used to characterize the additional local stress increment caused by actual irregular micropores relative to idealized micropores.

[0086] S33. The first local stress, second local stress, and third local stress obtained from S32 are coupled in a dimensionless manner and incrementally superimposed using the maximum stress of the micro-pore reference to obtain the three-dimensional feature correction parameters.

[0087] Since real micropores are not ideally spherical, their local stress is closely related to the spatial orientation, aspect ratio, and surface irregularity of the pores. Therefore, it is necessary to transform these three-dimensional morphological features into a dimensionless stress amplification parameter that can be used in fatigue life models.

[0088] Based on the concept of dimensionless and incremental superposition of local stress amplification effect, a three-dimensional feature correction parameter K is introduced to quantitatively analyze the influence of micropore morphology on the micropore stress field: +Orientation increment +Shape increment +Irregularity increment; Wherein, 1 represents the reference stress state, and the variation of local stress relative to the maximum stress of the micro-pore reference is characterized by superimposing three increments. Specifically, the orientation increment represents the change in local stress relative to the maximum stress of the micro-pore reference caused by the spatial angle between the long axis of the hole and the loading direction; the shape increment represents the change in local stress relative to the maximum stress of the micro-pore reference caused by changes in aspect ratio, flatness, and local curvature; and the irregularity increment represents the additional change in local stress relative to the maximum stress of the micro-pore reference caused by non-ideal morphologies such as unevenness, sharp corners, and abrupt changes in local curvature on the hole surface. Therefore, the three-dimensional feature correction parameters... for: .

[0089] Summarized as follows: .

[0090] in, The stress amplification ratio for the orientation of the hole, The stress amplification ratio is the shape of the hole.

[0091] Substitute the parameters obtained from the previous fitting into: .

[0092] It should be noted that, Instead of being directly given by geometric parameters, these are three-dimensional feature correction parameters obtained based on micropore morphology parameter extraction, local mechanical field analysis, mathematical statistical fitting, and dimensionless coupling. These parameters are used to transform the combined effects of micropore spatial orientation, aspect ratio, and surface irregularities on stress concentration into dimensionless correction parameters that can be incorporated into fatigue life prediction models.

[0093] S4. The critical maximum stress is derived by combining the Goodman equation, and the maximum stress of the micropore reference obtained in S2 is corrected. The influence of nonlinear damage of micropore is accumulated, and a dynamic damage evolution index is constructed.

[0094] S41. Three-dimensional feature correction parameters obtained based on S3 The maximum stress of the micropore reference obtained by S2 is corrected to obtain the equivalent maximum stress of the micropore. : .

[0095] S42. Perform stress analysis on the maximum stress under uniaxial cyclic loading to obtain the critical maximum stress corresponding to the fatigue limit boundary. : .

[0096] S43, Using maximum effective stress With the critical maximum stress The nonlinear continuous damage process of micropores is accumulated to obtain the dynamic damage evolution index. : .

[0097] S5. Based on the nonlinear continuous fatigue damage model, and combined with the stress characteristics and stress effects of microporous porous materials, the fatigue life prediction value is obtained.

[0098] S51. Based on the nonlinear continuous fatigue damage model, establish the rate of change of fatigue damage variables for microporous materials. : .

[0099] S52. Under constant amplitude cyclic loading conditions, the rate of change of the fatigue damage variable obtained in S51 is integrated, and the fatigue life prediction value is obtained by combining the dynamic damage evolution index, fatigue limit value and critical maximum stress.

[0100] .

[0101] S53. Combining fatigue test data with the material damage degree parameter 'a' and the material fatigue damage sensitivity parameter. Perform fitting.

[0102] Based on the previous derivation, when the angle parameter Aspect ratio related parameter is 0. 0.5 and surface irregularity parameter When the angle parameter is 0, the hole has the least impact on the equivalent maximum stress. 1. Aspect Ratio Related Parameter 1 and surface irregularity parameter When the value is 1, the hole has the greatest impact on the equivalent maximum stress. The two cases above correspond to the two boundaries of the degree of influence of the hole on the equivalent maximum stress.

[0103] This embodiment uses tensile strength. for MPa, fatigue limit under symmetrical cyclic conditions for Based on the calculation results of MPa and the key parameter K, tensile tests were conducted at room temperature and 980℃. The ratio of the maximum experimental stress to the minimum experimental stress in the tensile test was named the experimental stress ratio. The specific experimental parameters and life prediction results are shown in Table 1. Table 1. Fatigue test results at 980℃

[0104] right and Material damage parameters that do not consider the influence of pores Material fatigue damage sensitive parameters The fitting was performed, and the fitting result is as follows: Figure 10 As shown: The values ​​of each parameter and the predicted fatigue life are shown in Tables 2, 3, and 4: Table 2. Parameters and predicted fatigue life values ​​without considering the influence of voids.

[0105] Table 3. Parameters and predicted fatigue life when the effect of holes on the equivalent maximum stress is minimal.

[0106] Table 4. Parameters and predicted fatigue life values ​​when the effect of holes on the equivalent maximum stress is greatest.

[0107] Micropores constitute only a small portion of the material; therefore, under the three conditions described above, the fitting obtained... and The values ​​were not significantly different. To further describe the impact of micropores on lifetime, the above three groups were compared. and Take the average value and predict fatigue life under the same parameters. The value is -1.2259. The value is 8.551, here and Table 5 shows the fatigue life under the three conditions: Table 5 Comparison of fatigue life under the same parameters and the degree of influence of different pore sizes

[0108] The experimental results above clearly show that fatigue life differs significantly between considering and not considering micropores; the larger the impact of the micropores, the lower the fatigue life. Influencing factors include the aspect ratio of the micropores, the angle between the major axis of the micropores and the loading direction, and porosity. Fatigue life models that do not consider the influence of micropores overestimate material fatigue damage, causing unnecessary losses in engineering. In contrast, fatigue life prediction models that consider micropores are theoretically more reasonable, provide more conservative fatigue life predictions, and are more likely to react before fatigue failure, thus avoiding unnecessary losses.

[0109] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for predicting the fatigue life of nickel-based single-crystal superalloys based on three-dimensional micropore morphology, characterized in that, It includes the following steps: S1. The micropores in the gauge length section of the nickel-based single-crystal superalloy sample are scanned and reconstructed to obtain the three-dimensional morphology data of the micropores in the sample. S2. Based on the three-dimensional morphology data obtained in S1, a finite element model containing all actual three-dimensional micropore morphologies in the sample is established to obtain the maximum stress of the micropore reference. S3. Based on the three-dimensional morphology data obtained in S1, construct three-dimensional feature correction parameters to quantitatively characterize the influence of the three-dimensional micropore morphology on the stress field around the micropores. This includes the following sub-steps: S31. Based on the three-dimensional morphology data obtained in S1, the micropore morphology parameters that can quantitatively characterize the angle, aspect ratio and roughness of the micropores are extracted through numerical calculation. S32. Quantitatively analyze the local mechanical field around the micropore, and obtain the first local stress, second local stress and third local stress that can characterize the influence of the angle, aspect ratio and roughness of the micropore on the stress field around the micropore through mathematical statistics and data fitting. S33. The first local stress, the second local stress and the third local stress obtained from S32 are coupled in a dimensionless manner and incrementally superimposed using the maximum stress of the micropore reference to obtain the three-dimensional feature correction parameter K. ； in, For the first local stress, , The maximum stress is the reference value for the micropore. For surface irregularity parameters; S4. Based on the maximum micropore reference stress obtained in S2 and the three-dimensional feature correction parameters obtained in S3, the critical maximum stress is derived by combining the Goodman equation, and the influence of the nonlinear damage of the micropore is accumulated to construct a dynamic damage evolution index. S5. Based on the nonlinear continuous fatigue damage model, and combined with the stress characteristics and stress effects of microporous materials, the fatigue life prediction value is obtained. for: ； in, For tensile strength, For the equivalent maximum stress, The fatigue limit under symmetrical cyclic conditions. The mean stress is given by α, and α is a parameter representing the degree of material damage. This is a parameter sensitive to material fatigue damage.

2. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 1, characterized in that, Micropore morphology parameters include angular parameters, aspect ratio-related parameters, and surface irregularity parameters, and the calculation formula is as follows: ； ； ； in, Here, θ is the angle parameter, and θ is the spatial angle. For aspect ratio related parameters, It is the aspect ratio.

3. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 2, characterized in that, The expressions for the first local stress, the second local stress, and the third local stress are: ； ； ； Where A is the first far-field stress function, B is the first stress fitting coefficient, C is the first surface stress function, b is the second far-field stress function, and c is the second surface stress function. for .

4. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 1, characterized in that, S4 specifically includes: S41. Three-dimensional feature correction parameters obtained using S3 The equivalent maximum stress of the micropore is obtained by combining the maximum stress of the micropore reference. S42. Perform stress analysis on the maximum stress under uniaxial cyclic loading to obtain the critical maximum stress corresponding to the fatigue limit boundary. ; S43, Using equivalent maximum stress With the critical maximum stress The dynamic damage evolution index is obtained by accumulating the nonlinear continuous damage process of micropores. : ； in, This is the critical maximum stress.

5. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 4, characterized in that, The equivalent maximum stress of the micropore is: ； in, This represents the initial porosity.

6. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 4, characterized in that, The critical maximum stress is: ； in, This is a correction term for fatigue load capacity.

7. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 1, characterized in that, S5 specifically includes: S51. Based on the nonlinear continuous fatigue damage model, establish the rate of change of fatigue damage variables for microporous materials. S52. Under constant amplitude cyclic loading conditions, the rate of change of the fatigue damage variable obtained in S51 is integrated, and the fatigue life prediction value is obtained by combining the dynamic damage evolution index, fatigue limit value and critical maximum stress.

8. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 7, characterized in that, Rate of change of fatigue damage variables for: ； in, For fatigue damage variables, The number of loops. It is a dynamic damage evolution index. It is a parameter sensitive to material fatigue damage. This is a correction term for fatigue load capacity.

9. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 1, characterized in that, S1 specifically includes: S11. The gauge length of the nickel-based single-crystal superalloy sample was scanned using an X-ray computed tomography system to obtain a two-dimensional slice image of the micropores inside the sample. S12. Perform image segmentation, hole identification and three-dimensional reconstruction on the two-dimensional slice image to obtain a three-dimensional micropore model that reflects the real spatial morphology of the micropores, and then extract the three-dimensional morphology data of the micropores in the sample.

10. The fatigue life prediction method for nickel-based single-crystal superalloys based on three-dimensional micropore morphology according to claim 1, characterized in that, S2 specifically includes: S21. Based on the three-dimensional morphology data obtained in S1, a finite element model containing all actual three-dimensional micropore morphologies in the sample is established. The finite element model is geometrically extracted and meshed to obtain a meshed micropore finite element model containing only a single micropore. S22. Apply an equivalent load to the micropore finite element model obtained in S21, perform crystal plastic finite element analysis, and obtain the maximum stress of the micropore reference.

Images