A fatigue performance evaluation method for aircraft additively manufactured structures

Abstract

This invention discloses a method for evaluating the fatigue performance of aircraft additive manufacturing structures: A typical part is fabricated using additive manufacturing, and samples are taken from this part. The sampling includes two types of samples: low-cycle fatigue samples and high-cycle fatigue samples in the forming direction. The low-cycle fatigue samples are divided into three groups, and the high-cycle fatigue samples are divided into four groups. Samples from the three groups are subjected to constant-amplitude low-cycle fatigue tests, and the corresponding strain fatigue analysis material performance parameters are obtained by fitting the data. Samples from the four groups are subjected to constant-amplitude high-cycle fatigue tests, and the corresponding stress fatigue analysis material performance parameters are obtained by fitting the data. Based on the constant-amplitude high-cycle fatigue tests of the high-cycle fatigue samples, surface roughness correction coefficients, heat treatment dimension correction coefficients, residual stress correction coefficients, and defect life influence correction coefficients are calculated. A simulated part with structural details is fabricated using additive manufacturing. The above parameters are then substituted into the life analysis method to predict the fatigue life of the simulated part. This invention improves the accuracy of life prediction.

Description

Technical Field

[0001] This invention belongs to the field of aircraft additive manufacturing technology, and specifically relates to a method for evaluating the fatigue performance of aircraft additive manufacturing structures. Background Technology

[0002] Additive manufacturing technology, hailed as a hallmark of the Third Industrial Revolution, represents a revolutionary breakthrough in manufacturing technology. It boasts numerous advantages, including high material utilization, minimal geometric constraints, rapid iterative improvement, and a high degree of digitalization, aligning with the aerospace industry's pursuit of lightweight and low-cost structures, and has been gradually adopted. Represented by selective laser melting and laser melting deposition technologies, additive manufacturing has already been applied to secondary load-bearing structures and a small number of primary load-bearing structures in military aircraft. However, due to the significant anisotropy and greater lifespan dispersion of additively manufactured structures, a comprehensive fatigue performance evaluation method for additively manufactured structures, tailored to their process and material properties, has yet to be established, limiting its widespread application in primary load-bearing structures. Summary of the Invention

[0003] The purpose of this invention is to provide a method for evaluating the fatigue performance of additively manufactured aircraft structures. This invention improves the accuracy of lifespan prediction.

[0004] The technical solution is as follows: A method for evaluating the fatigue performance of additively manufactured aircraft structures, comprising the following steps:

[0005] Step S1: Fabricate typical parts based on additive manufacturing and sample from the typical parts; sampling includes two types of samples: low-cycle fatigue samples and high-cycle fatigue samples in the forming direction; low-cycle fatigue samples are divided into three groups: Group 1.1: samples in the forming direction, Group 1.2: samples perpendicular to the forming direction, and Group 1.3: samples at an angle α to the forming direction, 0 < α < 90°; high-cycle fatigue samples are divided into four groups: Group 2.1: samples with Ra 0.32, heat-treated thickness less than 20 mm, and no stress-relief annealing after polishing; Group 2.2: samples with Ra 0.32, heat-treated thickness less than 20 mm, and stress-relief annealing after polishing; Group 2.3: samples with Ra as the original additive manufacturing surface, heat-treated thickness less than 20 mm, and no stress-relief annealing after sampling; Group 2.4: samples with Ra 0.32, heat-treated thickness of 200 mm, and no stress-relief annealing after polishing.

[0006] Step S2: Extract samples from groups 1.1 to 1.3 and conduct constant amplitude low-cycle fatigue tests to obtain the material strain-life relationship in three directions, and fit the corresponding strain fatigue analysis material performance parameters; extract samples from groups 2.1 to 2.4 and conduct constant amplitude high-cycle fatigue tests to obtain the stress-life relationship of four groups of samples, and fit the corresponding stress fatigue analysis material performance parameters.

[0007] Step S3: Based on the constant amplitude high cycle fatigue tests of groups 2.1 to 2.4, calculate the surface roughness correction factor, heat treatment size correction factor, residual stress correction factor, and defect life influence correction factor.

[0008] Step S4: Additively manufacture a simulated part with structural details; substitute the surface roughness correction coefficient, heat treatment dimension correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S3 into the life analysis method to predict the fatigue life of the simulated part.

[0009] Step S5: Conduct fatigue tests on the simulated part under random spectrum, and obtain the crack initiation life by back-calculating the fracture surface of the fatigue test.

[0010] Step S6. Compare the predicted lifetime obtained in steps S4 and S5 with the crack initiation lifetime. When 0.5 < predicted lifetime / crack initiation lifetime < 2, each correction coefficient is reasonable and usable.

[0011] Step S7: Identify the key components of any additive manufacturing structure;

[0012] Step S8: Based on the aircraft design load spectrum, use the multiple linear regression method or machine learning method to obtain the stress spectrum of key parts of the additive manufacturing structure;

[0013] Step S9: Based on the placement method and forming direction during the additive manufacturing structure forming process, as well as the direction of the maximum principal stress in the key parts, calculate the angle β between the forming direction of the key parts and the forming direction of the structure; if 0≤β<30°, select the material performance parameters of group 1.1 in step S2; if 60≤β≤90°, select the material performance parameters of group 1.2 in step S2; if 30°≤β<60°, select the material performance parameters of group 1.3 in step S2.

[0014] Step S10: Using the stress spectrum from step S8 and the material property parameters from step S9 as input, the life assessment of key parts of the additive manufacturing structure is performed using the life analysis method verified in step S6 and the surface roughness correction coefficient, heat treatment size correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S3.

[0015] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, step S1 involves the fabrication of a typical component as follows: based on the life analysis method and combined with the geometric features of the additive manufacturing structure, a typical component for material performance testing and sampling is designed.

[0016] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, in step S1, during the fabrication of a typical component, a stress fatigue analysis method or a strain fatigue analysis method is selected as the life analysis method based on the load characteristics, stress level, and life requirements of the additive manufacturing structure; when the local linear elastic stress of the structure exceeds the yield strength, the strain fatigue analysis method is used; otherwise, the stress fatigue analysis method is used.

[0017] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, in step S1, there are no fewer than 120 samples in group 2.1.

[0018] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, the test conditions for the constant amplitude low-cycle fatigue test in step S2 are: room temperature, strain ratio Rε = -1, and strain level of not less than 5.

[0019] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, the test conditions for the constant amplitude high-cycle fatigue test in step S2 are: room temperature, stress ratio R = 0.06, and stress level of not less than 5.

[0020] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, in step S2, during the constant amplitude high-cycle fatigue test, the effective data for each stress level in group 2.1 shall be no less than 20 pieces.

[0021] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, step S3 is as follows: Based on the stress-life relationship and stress fatigue analysis material performance parameters, the fatigue performance of samples in groups 2.1 to 2.4 at 10°C is calculated. 5 The corresponding stresses σ1, σ2, σ3, and σ4 during the cycle are: σ3 / σ1 is the surface roughness correction factor, σ4 / σ1 is the heat treatment dimension correction factor, and σ2 / σ1 is the residual stress correction factor; all fatigue test fracture surfaces of the samples in group 2.1 of step S2 are analyzed to determine their fatigue sources, and it is observed whether the fatigue sources are manufacturing defects. The stress-life data are divided into two categories: fatigue sources without defects and fatigue sources with defects. The stress-life relationship equations are fitted to them respectively, and the stress-life relationship equations for fatigue sources without defects and fatigue sources with defects are calculated respectively. 5 Stress σ corresponding to the cycle 11 σ 12 , σ 12 / σ 11 This is the defect lifetime impact correction factor.

[0022] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, step S4 includes structural detail features such as rounded corners, holes, and slots.

[0023] In the aforementioned method for evaluating the fatigue performance of aircraft additive manufacturing structures, in step S5, when conducting fatigue tests under a random spectrum, a marker load is added at the end of the random spectrum.

[0024] Beneficial effects: 1) The fatigue performance evaluation method for aircraft additive manufacturing structures established in this invention fully considers the geometric and process characteristics of additive manufacturing structures, designs typical material performance test sampling parts, and obtains samples that can reflect the forming process of additive manufacturing structures and the anisotropic characteristics of additive manufacturing, so as to obtain material performance data that are closer to the performance of additive manufacturing structures in a more realistic way.

[0025] 2) Existing surface roughness correction coefficients for life analysis methods are designed for subtractive manufacturing structures and only have three values: Ra1.6, Ra3.2, and Ra6.3. However, additive manufacturing structures, especially laser selective melting structures, control surface quality through grinding. For complex structures, the surface often has multiple roughnesses, and the surface roughness of inaccessible internal parts may even exceed Ra6.3. Therefore, it is unreasonable to continue using existing coefficients. This invention obtains surface roughness correction coefficients suitable for fatigue life prediction of additive manufacturing structures by comparing fatigue tests of original surface samples and standard samples, which can improve the accuracy of life prediction.

[0026] 3) Existing heat treatment dimension correction factors are proposed for sheet metal and forgings. The reason for the correction is that after subtractive processing, the geometric dimensions of the structure differ significantly from those at the time of heat treatment. Critical parts may be located in the worst-performing areas, requiring correction to ensure that the life prediction is conservative and to guarantee the structural safety. However, the difference between the heat treatment dimensions and the final geometric dimensions of additive manufacturing structures is smaller. The traditional heat treatment dimension correction factors for subtractive manufacturing are clearly unreasonable for additive manufacturing. Therefore, this invention addresses the maximum heat treatment thickness that may exist in additive manufacturing structures and determines the applicable heat treatment dimension correction factor for additive manufacturing structures through high-cycle fatigue comparative tests, which helps to further ensure the rationality of the life prediction results.

[0027] 4) Due to the complexity of additive manufacturing processes, currently, after the formation and surface treatment or conformal machining of some areas of the aircraft structure are completed, stress-relief annealing is no longer performed. Residual tensile stress may exist on or near the surface. However, current non-destructive residual stress testing techniques cannot accurately determine the residual stress of the structure. This invention determines the influence of residual stress through high-cycle fatigue comparative tests and also improves the accuracy of life prediction methods.

[0028] 5) Even after hot isostatic pressing, additive manufacturing structures still have widespread internal micro-defects. These defects have a significant impact on the fatigue life of the structure. A correction factor needs to be introduced to account for this impact and ensure that the structure can meet the life requirements even in the presence of defects. This invention uses a sufficient number of high-cycle fatigue tests on samples and classifies the test results according to whether there are defects on the fracture surface to determine the impact of defects on the structural life, thereby further improving the accuracy of life prediction.

[0029] 6) This invention innovatively designed a simulated part with structural details. Through fatigue tests on simulated parts with different surface conditions, the method for predicting the life of additive manufacturing structures was verified. A method for predicting the fatigue life of additive manufacturing structures through the material performance data of additive manufacturing samples was established, providing support for the durability design of such structures.

[0030] This invention can be further applied to the construction of life prediction methods for new materials and new manufacturing processes. Attached Figure Description

[0031] Figure 1 Technical process for evaluating the fatigue performance of additive manufacturing structures for aircraft;

[0032] Figure 2 Sample a typical specimen for a possible material property test;

[0033] Figure 3 To obtain a graph of various correction factors;

[0034] Figure 4 It is a typical simulation component with structural details. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1. A method for evaluating the fatigue performance of additively manufactured aircraft structures, see [link to example]. Figures 1-4 The possible implementation methods are as follows:

[0037] Step S1: Based on the load characteristics, stress level, and life requirements of the additive manufacturing structure, select an appropriate life analysis method, including stress fatigue analysis (high-cycle fatigue) and strain fatigue analysis (low-cycle fatigue); when the local linear elastic stress of the structure exceeds the yield strength, the strain fatigue analysis method is used; otherwise, the stress fatigue analysis method is used.

[0038] Step S2: Based on the method selected in step S1, and combined with the geometric features of the additive manufacturing structure, design a typical sample for material performance testing and perform additive manufacturing. One possible example of this typical sample is shown below. Figure 1Sampling was conducted on typical additively manufactured parts. The sampling included two categories of samples. The first category consisted of low-cycle fatigue samples, all with a heat-treated thickness less than 20 mm. These samples were polished to a surface roughness of Ra 0.32 without stress-relief annealing. This category included three groups of samples: Group 1 (denoted as Group 1.1) samples along the forming direction, Group 2 (denoted as Group 1.2) samples perpendicular to the forming direction, and Group 3 (denoted as Group 1.3) samples at an angle α to the forming direction (0 < α < 90°). The second category consisted of high-cycle fatigue samples, all along the forming direction, including four groups: Group 1 (denoted as Group 2.1) samples with a surface roughness of Ra 0.32. 2. Samples with a heat-treated thickness of less than 20 mm and no stress-relief annealing after polishing are included in the following groups: Group 2 (2.2) consists of samples with a surface roughness of Ra0.32, a heat-treated thickness of less than 20 mm, and stress-relief annealing after polishing; Group 3 (2.3) consists of samples with the original additive manufacturing surface roughness (unpolished), a heat-treated thickness of less than 20 mm, and no stress-relief annealing after sampling; Group 4 (2.4) consists of samples with a surface roughness of Ra0.32, a heat-treated thickness of 200 mm, and no stress-relief annealing after polishing. Group 2.1 contains no fewer than 120 samples, and the sampling locations for Group 2.4 are as follows: Figure 2 A recommended sample size is shown in Table 1.

[0039] Table 1. One possible sample quantity

[0040]

[0041] Step S3: Using the low-cycle fatigue specimens obtained in Step S2, conduct constant-amplitude low-cycle fatigue tests at room temperature with a strain ratio of Rε = -1 and at least 5 strain levels. Obtain the material strain-life relationship in three directions and fit the corresponding material performance parameters of the strain fatigue analysis model. Using the four sets of high-cycle fatigue specimens obtained, conduct constant-amplitude high-cycle fatigue tests at room temperature with a stress ratio of R = 0.06 and at least 5 stress levels. Obtain the stress-life relationship of the four sets of specimens and fit the corresponding material performance parameters of the stress fatigue analysis model. Among them, 2.1 sets have at least 20 valid data points for each stress level.

[0042] Step S4: Using the stress-life relationship and stress fatigue analysis parameters of samples groups 2.1 to 2.4 obtained in step S3, calculate the stress-life relationship and stress fatigue analysis parameters of samples groups 2.1 to 2.4 at 10°C. 5The stresses σ1, σ2, σ3, and σ4 corresponding to the cycle are: σ3 / σ1, which is the surface roughness correction factor; σ4 / σ1, which is the heat treatment dimension correction factor; and σ2 / σ1, which is the residual stress correction factor. The fracture surfaces of all samples in group 2.1 of step S3 after fatigue testing are analyzed to determine their fatigue sources. It is observed whether the fatigue sources are manufacturing defects. The stress-life data are divided into two categories: fatigue sources without defects and fatigue sources with defects. The stress-life relationship equations are fitted for each category, and the stress-life relationship equations for fatigue sources without defects and fatigue sources with defects are calculated separately. 5 Stress σ corresponding to the cycle 11 σ 12 , σ 12 / σ 11 This refers to the correction factor for the impact of defects on lifespan; taking the defect impact correction factor as an example, the principle for obtaining each correction factor is explained in [link to documentation]. Figure 3 ;

[0043] Step S5: Design and manufacture a simulated part containing structural details using additive manufacturing processes (see...). Figure 4 The number of simulated parts is less than 10. Five parts are manufactured without surface polishing, while the other five parts are polished using the same polishing process as the actual additive manufacturing structure. The surface roughness correction coefficient, heat treatment size correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S4 are substituted into the life analysis method selected in step S1 to predict the fatigue life of the simulated parts with two different surface conditions.

[0044] Step S6: Conduct fatigue tests on the simulated parts under random spectrum, and obtain the crack initiation life (median test life) of the simulated parts under two surface conditions by back-calculation of the fracture surface of the fatigue test and statistical calculation; when conducting fatigue tests under random spectrum, add a label load at the end of the random spectrum.

[0045] Step S7: Compare the predicted lifetime obtained in step S5 with the median test lifetime obtained in step S6. When 0.5 < predicted lifetime / median test lifetime < 2, the correction coefficients in step S4 are reasonable and usable.

[0046] Step S8: Using the finite element method, conduct detailed stress analysis of the additive manufacturing structure under typical load conditions, obtain its three-dimensional stress distribution, and determine the key parts; the typical load conditions should include at least the two conditions with the greatest compressive stress and tensile stress in the key parts.

[0047] Step S9: Based on the aircraft design load spectrum, and the stress of key parts and the corresponding component loads obtained in S8, establish the mapping relationship between the stress of key parts and the component loads using multiple linear regression or machine learning methods; use this mapping relationship and the component loads of other working conditions in the load spectrum to obtain the stress spectrum of key parts of the additive manufacturing structure.

[0048] Step S10: Based on the placement method and forming direction during the additive manufacturing structure forming process, as well as the direction of the maximum principal stress in the key parts, calculate the angle β between the direction of the maximum principal stress in the key parts and the forming direction of the structure; if 0≤β<30°, select the material performance parameters of group 1.1 in step S3; if 60≤β≤90°, select the material performance parameters of group 1.2 in step S3; if 30°≤β<60°, select the material performance parameters of group 1.3 in step S3.

[0049] Step S11: Using the stress spectrum from step S9 and the material property parameters from step S10 as inputs, the life analysis method selected in step S1 (verified in step S7) and the surface roughness correction coefficient, heat treatment size correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S4 are used to conduct a life assessment of key parts of the additive manufacturing structure.

[0050] Example 2. A method for evaluating the fatigue performance of additively manufactured aircraft structures, see [link to example]. Figures 1-4 This includes the following steps:

[0051] Step S1: Based on the load characteristics, stress level, and life requirements of the additive manufacturing structure, select an appropriate life analysis method, including stress fatigue analysis (high-cycle fatigue) and strain fatigue analysis (low-cycle fatigue); when the local linear elastic stress of the structure exceeds the yield strength, the strain fatigue analysis method is used; otherwise, the stress fatigue analysis method is used.

[0052] Step S2: Based on the method selected in Step S1 and combined with the geometric features of the additive manufacturing structure, design typical sample parts for material performance testing and perform additive manufacturing; sample from the typical additively manufactured parts; the sampling includes two types of samples. The first type is low-cycle fatigue samples, in which the heat-treated thickness is less than 20mm, and the surface roughness is polished to Ra0.32. No stress-relief annealing is performed after polishing. This type includes three groups of samples: the first group (denoted as group 1.1) consists of samples in the forming direction, the second group (denoted as group 1.2) consists of samples perpendicular to the forming direction, and the third group (denoted as group 1.3) consists of samples at an angle α to the forming direction, where 0 < α < 90°; the second type is high-cycle fatigue samples, all of which are samples in the forming direction, including... The sample set includes four groups: Group 1 (2.1) consists of samples with a surface roughness of Ra0.32, a heat-treated thickness of less than 20 mm, and which are not subjected to stress-relief annealing after polishing; Group 2 (2.2) consists of samples with a surface roughness of Ra0.32, a heat-treated thickness of less than 20 mm, and which are subjected to stress-relief annealing after polishing; Group 3 (2.3) consists of samples with a surface roughness equal to the original additive manufacturing surface (unpolished), a heat-treated thickness of less than 20 mm, and which are not subjected to stress-relief annealing after sampling; and Group 4 (2.4) consists of samples with a surface roughness of Ra0.32, a heat-treated thickness of 200 mm, and which are not subjected to stress-relief annealing after polishing. Group 2.1 contains no fewer than 120 samples.

[0053] Step S3: Using the low-cycle fatigue specimens obtained in Step S2, conduct constant-amplitude low-cycle fatigue tests at room temperature with a strain ratio of Rε = -1 and at least 5 strain levels. Obtain the material strain-life relationship in three directions and fit the corresponding strain fatigue analysis material performance parameters. Using the four sets of high-cycle fatigue specimens obtained, conduct constant-amplitude high-cycle fatigue tests at room temperature with a stress ratio of R = 0.06 and at least 5 stress levels. Obtain the stress-life relationship of the four sets of specimens and fit the corresponding stress fatigue analysis material performance parameters. Among them, 2.1 sets have at least 20 valid data points for each stress level.

[0054] Step S4: Using the stress-life relationship and stress fatigue analysis parameters of samples groups 2.1 to 2.4 obtained in step S3, calculate the stress-life relationship and stress fatigue analysis parameters of samples groups 2.1 to 2.4 at 10°C. 5 The stresses σ1, σ2, σ3, and σ4 corresponding to the cycle are: σ3 / σ1, which is the surface roughness correction factor; σ4 / σ1, which is the heat treatment dimension correction factor; and σ2 / σ1, which is the residual stress correction factor. The fracture surfaces of all samples in group 2.1 of step S3 after fatigue testing are analyzed to determine their fatigue sources. It is observed whether the fatigue sources are manufacturing defects. The stress-life data are divided into two categories: fatigue sources without defects and fatigue sources with defects. The stress-life relationship equations are fitted for each category, and the stress-life relationship equations for fatigue sources without defects and fatigue sources with defects are calculated separately.5 Stress σ corresponding to the cycle 11 σ 12 , σ 12 / σ 11 This is the correction factor for the impact of defects on lifespan;

[0055] Step S5: Design and manufacture a simulated part with structural details using additive manufacturing process. The structural details include rounded corners, holes, slots, etc. Substitute the surface roughness correction coefficient, heat treatment size correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S4 into the life analysis method selected in step S1 to predict the fatigue life of the simulated part.

[0056] Step S6: Conduct fatigue tests on the simulated part under random spectrum, and obtain the crack initiation life (test life) by back-calculating the fracture surface of the fatigue test; when conducting fatigue tests under random spectrum, add a label load at the end of the random spectrum;

[0057] Step S7: Compare the predicted lifetime obtained in step S5 with the crack initiation lifetime obtained in step S6. When 0.5 < predicted lifetime / crack initiation lifetime < 2, each correction coefficient is reasonable and usable.

[0058] Step S8: Identify the key components of any additive manufacturing structure through analysis;

[0059] Step S9: Based on the aircraft design load spectrum, use multiple linear regression or machine learning methods to obtain the stress spectrum of key parts of the additive manufacturing structure.

[0060] Step S10: Based on the placement method and forming direction during the additive manufacturing structure forming process, as well as the direction of the maximum principal stress in the key parts, calculate the angle β between the forming direction of the key parts and the forming direction of the structure; if 0≤β<30°, select the material performance parameters of group 1.1 in step S3; if 60≤β≤90°, select the material performance parameters of group 1.2 in step S3; if 30°≤β<60°, select the material performance parameters of group 1.3 in step S3.

[0061] Step S11: Using the stress spectrum from step S9 and the material property parameters from step S10 as inputs, the life analysis method selected in step S1 (verified in step S7) and the surface roughness correction coefficient, heat treatment size correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S4 are used to conduct a life assessment of key parts of the additive manufacturing structure.

[0062] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for evaluating the fatigue performance of additively manufactured aircraft structures, characterized in that, Includes the following steps: Step S1: Fabricate typical parts based on additive manufacturing and sample from the typical parts; sampling includes two types of samples: low-cycle fatigue samples and high-cycle fatigue samples in the forming direction; low-cycle fatigue samples are divided into three groups: Group 1.1: samples in the forming direction, Group 1.2: samples perpendicular to the forming direction, and Group 1.3: samples at an angle α to the forming direction, 0 < α < 90°; high-cycle fatigue samples are divided into four groups: Group 2.1: samples with Ra 0.32, heat-treated thickness less than 20 mm, and no stress-relief annealing after polishing; Group 2.2: samples with Ra 0.32, heat-treated thickness less than 20 mm, and stress-relief annealing after polishing; Group 2.3: samples with Ra as the original additive manufacturing surface, heat-treated thickness less than 20 mm, and no stress-relief annealing after sampling; Group 2.4: samples with Ra 0.32, heat-treated thickness of 200 mm, and no stress-relief annealing after polishing. Step S2: Extract samples from groups 1.1 to 1.3 and conduct constant amplitude low-cycle fatigue tests to obtain the material strain-life relationship in three directions, and fit the corresponding strain fatigue analysis material performance parameters; extract samples from groups 2.1 to 2.4 and conduct constant amplitude high-cycle fatigue tests to obtain the stress-life relationship of four groups of samples, and fit the corresponding stress fatigue analysis material performance parameters. Step S3: Based on the constant amplitude high cycle fatigue tests of groups 2.1 to 2.4, calculate the surface roughness correction factor, heat treatment size correction factor, residual stress correction factor, and defect life influence correction factor. Step S3 is as follows: Based on the stress-life relationship and stress fatigue analysis of material performance parameters, the performance parameters of samples in groups 2.1 to 2.4 at 10°C are calculated respectively. 5 The corresponding stresses σ1, σ2, σ3, and σ4 during the cycle are: σ3 / σ1 is the surface roughness correction factor, σ4 / σ1 is the heat treatment dimension correction factor, and σ2 / σ1 is the residual stress correction factor; all fatigue test fracture surfaces of the samples in group 2.1 of step S2 are analyzed to determine their fatigue sources, and it is observed whether the fatigue sources are manufacturing defects. The stress-life data are divided into two categories: fatigue sources without defects and fatigue sources with defects. The stress-life relationship equations are fitted to them respectively, and the stress-life relationship equations for fatigue sources without defects and fatigue sources with defects are calculated respectively. 5 Stress σ corresponding to the cycle 11 σ 12 , σ 12 / σ 11 This is the defect lifetime impact correction factor; Step S4: Additively manufacture a simulated part containing structural details; Substitute the surface roughness correction coefficient, heat treatment size correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S3 into the life analysis method to predict the fatigue life of the simulated part. Step S5: Conduct fatigue tests on the simulated part under random spectrum, and obtain the crack initiation life by back-calculating the fracture surface of the fatigue test. Step S6. Compare the predicted lifetime obtained in steps S4 and S5 with the crack initiation lifetime. When 0.5 < predicted lifetime / crack initiation lifetime < 2, each correction coefficient is reasonable and usable. Step S7: Identify the key components of any additive manufacturing structure; Step S8: Based on the aircraft design load spectrum, use the multiple linear regression method or machine learning method to obtain the stress spectrum of key parts of the additive manufacturing structure; Step S9: Based on the placement method and forming direction during the additive manufacturing structure forming process, as well as the direction of the maximum principal stress in the key parts, calculate the angle β between the forming direction of the key parts and the forming direction of the structure; if 0≤β<30°, select the material performance parameters of group 1.1 in step S2; if 60≤β≤90°, select the material performance parameters of group 1.2 in step S2; if 30°≤β<60°, select the material performance parameters of group 1.3 in step S2. Step S10: Using the stress spectrum from step S8 and the material property parameters from step S9 as input, the life assessment of key parts of the additive manufacturing structure is performed using the life analysis method verified in step S6 and the surface roughness correction coefficient, heat treatment size correction coefficient, residual stress correction coefficient, and defect influence correction coefficient obtained in step S3.

2. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 1, characterized in that, In step S1, the typical part is fabricated as follows: Based on the life analysis method and combined with the geometric features of the additive manufacturing structure, a typical part for material performance testing and sampling is designed.

3. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 2, characterized in that, In step S1, during the fabrication of a typical component, the stress fatigue analysis method or the strain fatigue analysis method is selected as the life analysis method based on the load characteristics, stress level, and life requirements of the additive manufacturing structure; when the local linear elastic stress of the structure exceeds the yield strength, the strain fatigue analysis method is used. In addition, stress fatigue analysis methods are used.

4. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 1, characterized in that, In step S1, there shall be no fewer than 120 samples in group 2.

1.

5. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 1, characterized in that, In step S2, the test conditions for the constant amplitude low cycle fatigue test are: room temperature, strain ratio Rε = -1, and strain level of not less than 5.

6. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 1, characterized in that, In step S2, the test conditions for the constant amplitude high cycle fatigue test are: room temperature, stress ratio R = 0.06, and stress level of not less than 5.

7. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 1, characterized in that, In step S2, during the constant amplitude high cycle fatigue test, the effective data for each stress level in group 2.1 shall be no less than 20 pieces.

8. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 1, characterized in that, In step S4, structural details include rounded corners, holes, and grooves.

9. The method for evaluating the fatigue performance of aircraft additive manufacturing structures according to claim 1, characterized in that, In step S5, when conducting fatigue tests under random spectrum, a label load is added at the end of the random spectrum.

Images