Additive manufacturing lattice structure fatigue damage analysis method considering roughness influence

Abstract

The invention provides an additive manufacturing lattice structure fatigue damage analysis method considering roughness influence, which comprises the following steps: carrying out a fatigue test on a lattice structure test piece to obtain fatigue life test data of the lattice structure test piece; constructing a damage evolution equation based on fatigue life test data; based on the fluctuating form of the surface of the lattice structure test piece, obtaining a surface roughness degree influence factor of the lattice structure test piece; introducing the surface roughness influence factor into a damage evolution equation to obtain a damage evolution equation considering the surface roughness; and constructing a finite element model of the lattice structure test piece based on finite element software, and performing fatigue life prediction on the lattice structure test piece in combination with the damage evolution equation considering the surface roughness to complete additive manufacturing lattice structure fatigue damage analysis considering the roughness influence. According to the technical scheme, repeated tests can be reduced, the measurement and calculation cost is reduced, and meanwhile reference can be provided for design and formulation of the lattice structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of fatigue damage analysis of additively manufactured lattice structures, and in particular relates to a fatigue damage analysis method of additively manufactured lattice structures taking into account the influence of roughness. Background Art

[0002] In recent years, with the rapid development of aerospace technology, the requirements for lightweight aircraft and its components have been continuously improved. Due to the constraints of the accessibility of traditional manufacturing methods, it is becoming increasingly difficult to reduce the weight of the product structure of key aircraft components. In order to pursue the goal of lighter weight reduction, its structure is becoming more and more complex. The traditional manufacturing cost is extremely high, or even impossible to manufacture, which has seriously restricted the development of high-performance aircraft components. Lattice structures have attracted much attention due to their lightweight, high specific strength and design flexibility. They are usually composed of periodic or non-periodic units. Due to their complex structural state, traditional manufacturing methods are difficult to achieve. In recent years, due to the development of additive manufacturing technology, lattice structures have been made easier to manufacture through reasonable design. This makes lattice structures have broad application prospects in aerospace, automotive engineering and biomedical fields. However, the complex geometric characteristics of lattice structures and the microscopic defects (such as pores, unfused areas, etc.) that may be generated during additive manufacturing have brought major challenges to the prediction of their fatigue life. These defects and geometric complexity increase the uncertainty of fatigue performance, making it difficult for traditional fatigue life prediction methods to effectively evaluate their fatigue life in practical applications. Existing studies have shown that the fatigue properties of lattice structures under different conditions have not been fully explored, and relevant literature is relatively scarce. Therefore, it is particularly important to conduct a systematic study on the fatigue properties of lattice structures.

[0003] In this context, it is urgent to develop a fatigue life prediction method specifically for lattice structures, taking into account their geometric complexity and the defects that may occur during additive manufacturing. This method should not only focus on the impact of a single defect, but also consider the interaction between defects and their impact on the overall fatigue performance. In addition, the fatigue performance of lattice structures is affected by many factors, including load mode, material properties, and manufacturing parameters. These factors work together to further increase the difficulty of fatigue life prediction. Therefore, for the fatigue life prediction of lattice structures, innovative theoretical and technical solutions are urgently needed to improve the accuracy and reliability of the prediction. This is not only crucial to enhancing the application performance of lattice structures, but will also provide strong support for engineering design and optimization in related fields. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a fatigue damage analysis method for additively manufactured lattice structures taking into account the influence of roughness, and improves the accuracy of fatigue life prediction through computer simulation, so that the prediction results are closer to engineering practice.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A fatigue damage analysis method for additively manufactured lattice structures considering the influence of roughness, comprising:

[0007] Performing fatigue tests on the lattice structure specimens to obtain fatigue life test data of the lattice structure specimens; and constructing a damage evolution equation based on the fatigue life test data;

[0008] Based on the undulating morphology of the surface of the lattice structure specimen, the influencing factor of the surface roughness of the lattice structure specimen is obtained;

[0009] Introducing the surface roughness influencing factor into the damage evolution equation to obtain the damage evolution equation taking the surface roughness into consideration;

[0010] The finite element model of the lattice structure specimen is constructed based on the finite element software. Combined with the damage evolution equation considering the surface roughness, the fatigue life of the lattice structure specimen is predicted, and the fatigue damage analysis of the additively manufactured lattice structure considering the influence of roughness is completed.

[0011] Preferably, the method for constructing the damage evolution equation includes:

[0012] The damage variable is introduced into the constitutive model to obtain the stress-strain relationship of the lattice structure specimen after being subjected to force; the value of the damage variable is used to determine the damage degree of the material at the representative volume unit of the lattice structure specimen;

[0013] Based on the fatigue life test data, combined with the damage variables and the stress-strain relationship, the damage evolution equation is constructed.

[0014] Preferably, the constitutive model includes an elastic constitutive model and a plastic constitutive model; wherein the elastic constitutive model adopts Hooke's law, and the plastic constitutive model adopts Chaboche model.

[0015] Preferably, the method for obtaining the surface roughness influencing factor of the lattice structure specimen includes:

[0016] Based on the length and height of the measuring section of the lattice structure specimen, the average surface roughness of the lattice structure specimen is obtained;

[0017] The surface of the lattice structure specimen is polished smooth to obtain the reference surface roughness;

[0018] Based on the average surface roughness and the reference surface roughness and in combination with the additive manufacturing direction of the lattice structure specimen, the surface roughness influencing factor of the lattice structure specimen is obtained.

[0019] Preferably, the expression of the surface roughness influencing factor is as follows:

[0020]

[0021] In the formula, γ is the angle parameter, R a is the average surface roughness, R a0 is the reference surface roughness.

[0022] Preferably, the method for obtaining the damage evolution equation taking into account the surface roughness comprises:

[0023] Integrating the damage variable in the damage evolution equation from 0 to 1 to obtain a fatigue life calculation formula for the lattice structure specimen;

[0024] Based on the fatigue life test data of the lattice structure specimen, the SN curve of the lattice structure specimen with smooth surface under the preset stress ratio is fitted;

[0025] Based on the SN curve and the fatigue life calculation formula, the fatigue life of the lattice structure specimen with a smooth surface under uniaxial loading with a preset stress ratio is obtained through the continuous damage mechanics theory;

[0026] Based on the fatigue life under uniaxial loading and the fatigue life test data, the parameters of the damage evolution equation are calibrated using MATLAB curve fitting tools, least squares method and finite element numerical simulation;

[0027] The parameters of the calibrated damage evolution equation and the influencing factor of the surface roughness are introduced into the damage evolution equation to obtain the damage evolution equation taking the surface roughness into consideration.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: the lattice structure fatigue damage analysis method considering the influence of roughness proposed in the present invention can predict the fatigue life of various lattice configuration specimens under different roughness with a small number of tests or no tests, thereby reducing repeated tests and reducing measurement costs, and can also provide a reference for the design and formulation of the lattice structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 A flow chart of a fatigue damage analysis method for additively manufactured lattice structures taking into account the influence of roughness according to an embodiment of the present invention;

[0031] Figure 2 This is a flow chart of calculating the fatigue life of a lattice structure based on the continuum damage mechanics theory according to an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the shape and loading of a lattice structure test piece of additive manufacturing material according to an embodiment of the present invention;

[0033] Figure 4 Schematic diagram of load peak-life curve under different roughness in an embodiment of the present invention;

[0034] Figure 5 It is a schematic diagram of the displacement-lifetime curve of the lattice structure of an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The nouns appearing in this embodiment are explained as follows:

[0038] The SN curve characterizes the number of load cycles that a material can withstand at different stress levels. In the SN curve, S represents the stress level, usually expressed as stress amplitude or maximum stress; N represents the number of load cycles that the material can withstand at this stress level, that is, the fatigue life. This curve is an empirical formula obtained through a large number of fatigue tests on materials and is the basis for studying material fatigue properties.

[0039] The Chaboche model is a constitutive model used to describe the inelastic deformation behavior of materials under cyclic loads. It is particularly suitable for material analysis under high temperature and complex stress states. The model was proposed by French engineer Chaboche and is mainly used to solve the inelastic analysis problem of structures under cyclic loads.

[0040] Embodiment 1

[0041] like Figure 1 As shown, a fatigue damage analysis method for additively manufactured lattice structures considering the influence of roughness includes:

[0042] S1: Perform fatigue test on the lattice structure specimen to obtain fatigue life test data of the lattice structure specimen; and construct a damage evolution equation based on the fatigue life test data; a further implementation method is that the method for constructing the damage evolution equation includes:

[0043] S11: Introduce the damage variable into the constitutive model to obtain the stress-strain relationship of the lattice structure specimen after being subjected to force; wherein the value of the damage variable is used to determine the degree of damage of the material at the representative volume unit of the lattice structure specimen; the constitutive model includes an elastic constitutive model and a plastic constitutive model. In this embodiment, a user-defined material subroutine is written based on the continuous damage mechanics theory to define the constitutive equation and the damage evolution equation.

[0044] Specifically, damage mechanics describes the damage in materials by introducing damage variables. Considering the rationality of damage description and the convenience of engineering application, a one-dimensional damage variable D is introduced in the representative volume unit. When D=1, it means that the material at the representative volume unit is completely damaged. The damage variable is introduced into the constitutive model, the elastic constitutive model adopts Hooke's law, and the plastic constitutive model adopts the Chaboche model. The stress-strain relationship is as follows:

[0045]

[0046] C k =p k t k (2)

[0047] γ k =t k (3)

[0048] Q=p4 (4)

[0049] b=t4 (5)

[0050] In the formula, σ y represents the material yield stress, p k represents the hardening parameter, t k represents the time constant of hardening, C k represents the elastic modulus of the material, Q represents the saturation value of material hardening, b represents the rate of controlling hardening evolution, ε p represents the plastic strain, and M represents the number of nonlinear regression hardening terms, which is usually 3.

[0051] S12: Based on fatigue life test data, combined with damage variables and stress-strain relationship, a damage evolution equation is constructed.

[0052] In this embodiment, the continuous damage mechanics theory contains a variety of fatigue analysis models. The high-cycle fatigue damage model is suitable for the case where the loading stress level is low, and the damage evolution is mainly dominated by stress. Under multi-axial loading, the damage evolution equation is shown in formula (6):

[0053]

[0054] a, m, n, β represent material parameters obtained from fatigue tests.

[0055] Among them, σ * is the damage equivalent stress:

[0056]

[0057]

[0058]

[0059] σ a * is the equivalent stress amplitude, σ m * is the mean value of equivalent stress, σ H represents the hydrostatic pressure, σ eq represents the Mises equivalent stress, σ ij represents the stress tensor and v represents Poisson's ratio.

[0060]

[0061] S2: The surface of the rough test piece is observed by electron microscopy, and the surface roughness influencing factor of the lattice structure specimen is obtained based on the undulating morphology of the surface of the lattice structure specimen.

[0062] A further implementation method is that the method for obtaining the surface roughness influencing factor of the lattice structure specimen includes:

[0063] S21: Based on the length and height of the measuring section of the lattice structure specimen, the average surface roughness of the lattice structure specimen is obtained; specifically, due to the particularity of some structures of additive manufacturing process materials, there is currently no method to polish and grind their surfaces, and the roughness of their outer surface has a certain influence on fatigue life. The average surface roughness R of the specimen a It can be expressed as:

[0064]

[0065] Where L is the length of the measuring section of the specimen and Z(x) is the height of point x along the measuring line.

[0066] S22: The surface of the lattice structure specimen is polished to be smooth to obtain the reference surface roughness; specifically, the roughness of the polished specimen is defined as R a0 , as a reference for the surface roughness of the specimen during the analysis process, and for subsequent fatigue damage analysis and life prediction calculations.

[0067] S23: Based on the average surface roughness and the reference surface roughness, combined with the additive manufacturing direction of the lattice structure specimen, the surface roughness influencing factor of the lattice structure specimen is obtained.

[0068] S3: Introduce the surface roughness influence factor into the damage evolution equation to obtain the damage evolution equation considering the surface roughness. Specifically, based on the above definition of average surface roughness, the surface roughness influence factor can be further defined to describe the influence of different additive manufacturing technologies on the fatigue performance of the manufactured material, and further reflect the influence of different processes on the evolution of fatigue damage. Considering the convenience of application, the roughness influence factor R is defined as * :

[0069]

[0070] Among them, γ is the angle parameter, which is related to the additive manufacturing direction of the specimen.

[0071] A further embodiment is that the method for obtaining the damage evolution equation considering the surface roughness comprises:

[0072] S31: Integrate the damage variable in the damage evolution equation from 0 to 1 to obtain the fatigue life calculation formula of the lattice structure specimen; in this embodiment, by integrating equation (6) from D=0 to D=1, the following fatigue life calculation formula is obtained:

[0073]

[0074] S32: Based on the fatigue life test data of the lattice structure specimen, the SN curve of the lattice structure specimen with smooth surface under the preset stress ratio is fitted;

[0075] S33: Based on the SN curve and fatigue life calculation formula, the fatigue life of the smooth surface lattice structure specimen under uniaxial loading with a preset stress ratio is obtained through the continuous damage mechanics theory.

[0076] Specifically, the data obtained from the test are processed to fit the SN curve of the smooth material under the stress ratio R = -1 and an SN curve under other stress ratios (fitted by the longest life point in the fatigue life of the material test). According to the theory of continuous damage mechanics, the fatigue life calculation formula under uniaxial loading with a stress ratio of R = -1 is:

[0077]

[0078] S34: Based on the fatigue life under uniaxial loading and fatigue life test data, the parameters of the damage evolution equation are calibrated using the MATLAB curve fitting tool, the least squares method and the finite element numerical simulation; specifically, the values ​​of the parameters m and a(1+β) are obtained by combining the MATLAB curve fitting toolbox. Then, the parameter n is fitted using the test data under other stress ratios and the least squares method. Based on the fatigue test data of a notched component and the finite element numerical calculation method, the specific value of β is determined. Finally, the R of the test piece is calculated using formula (12) based on the measured data. a , γ is obtained by comparing the finite element numerical calculation with the fatigue test data of rough parts.

[0079] S35: Introduce the parameters of the calibrated damage evolution equation and the surface roughness influencing factor into the damage evolution equation to obtain the damage evolution equation that takes into account the surface roughness. Specifically, based on the roughness influencing factor, the existing damage evolution law can be modified to reflect the influence of different roughness on damage evolution. Therefore, the damage evolution equation that takes into account the roughness is established:

[0080]

[0081] S4: Based on the finite element software, a finite element model of the lattice structure specimen is constructed, and the fatigue life of the lattice structure specimen is predicted by combining the damage evolution equation considering the surface roughness, and the fatigue damage analysis of the additive manufacturing lattice structure considering the influence of roughness is completed. Specifically, the material damage analysis and life prediction method based on the above content can be implemented with the help of the ABAQUS finite element calculation platform and its subroutine interface. Through the program customization of damage evolution and the numerical simulation of the fatigue process, combined with the destruction form of the lattice structure, the fatigue life prediction results of the lattice structure of a specific additive manufacturing material are obtained.

[0082] S41: According to the specific configuration of the lattice structure specimen, a finite element model for numerical simulation is established, and the support rods are meshed using beam elements, and the converged mesh density is determined. This can more accurately simulate the damage process of the support rods, while applying correct boundary conditions and loads that meet the test conditions.

[0083] S42: The fatigue life calculation method of lattice structure based on continuum damage mechanics theory is as follows Figure 2 As shown, the stress field and strain field of the whole model are calculated after each cycle, and then the damage increment ΔD is calculated. The damage increment at the integration point after each cycle is calculated according to the above method, and the damage increment is accumulated to obtain the damage size at the integration point under the current cycle number ΔN:

[0084] Di+1 =D i +ΔD i ·ΔN (17)

[0085] When using the finite element method for calculation, the entire model is discretized into a finite number of units. After each cycle, the stress and strain values ​​at the integration points in all units are calculated, and then the damage increment is calculated based on the modified damage evolution equation in the previous section (taking into account the damage evolution variance of the surface roughness). The damage increment at the integration point after each cycle is calculated according to the above method, and the damage increment is accumulated to obtain the damage magnitude at the integration point under the current number of cycles. After N i When the damage degree reaches 1, delete the strut element and determine whether the overall displacement U of the structure reaches the failure value U. c If the above process is not repeated until failure, the fatigue life of the structure is:

[0086]

[0087] N i It refers to the fatigue life when the i-th element is deleted.

[0088] Finite element software is used to carry out numerical simulation, complete the fatigue life calculation of multiple lattice structural parts, and obtain component fatigue life data under various stress level distributions.

[0089] In this embodiment, step S5 is also included: data processing and life comparison, marking the fatigue life data points obtained by numerical simulation in the SN curve, and observing the consistency between the fatigue life simulation results and the test results at the same stress level.

[0090] Embodiment 2

[0091] This example adopts the method described in Example 1 to provide a specific test analysis process:

[0092] Assuming that there is Figure 3 The lattice structure test piece shown in the figure is subjected to fatigue test under fatigue load at stress ratio R=-1, and the roughness influence factor composed of surface roughness is quantitatively calculated. Based on the method described in Example 1, fatigue damage and life prediction of additively manufactured lattice structure are analyzed and calculated.

[0093] Program implementation process:

[0094] (1) Search for literature or conduct multiple fatigue tests under different stress ratios, stress peaks, and various surface roughnesses, and organize the data based on fatigue test conditions and test results;

[0095] (2) Take a group of specimens with smooth surfaces after grinding and record them as the reference group, and count them as Ra0 , calculate the R corresponding to each set of roughness * ;

[0096] (3) Based on the uniaxial tensile test result curve of homogeneous materials, the constitutive model parameters and damage evolution equation parameters of the material are fitted according to the least squares method or particle swarm calibration algorithm;

[0097] (4) Establish a lattice structure simulation model and use the above parameters calibrated by the standard test piece in the following lattice structure fatigue life prediction process;

[0098] (5) In ABAQUS software, a finite element calculation model of the specimen was established to carry out numerical simulation of the fatigue loading process, and the damage variables at the unit integration points were continuously updated with the help of the VUMAT subroutine;

[0099] (6) When the damage variable of a certain unit integration point reaches 1, the unit is deleted and the above cycle is repeated until the displacement of the overall structure is greater than the tensile failure displacement. At this time, the calculation stops and the fatigue life prediction results of the lattice structure with different roughness caused by different process conditions are obtained.

[0100] Result analysis:

[0101] According to the test results, the fatigue test data is analyzed, and the material constitutive and fatigue parameters are calibrated to obtain the expressions of load and fatigue life. The fatigue load stress peak value and calculated life value under different processing methods of the same manufacturing process are taken from the results, and the Figure 4 .

[0102] according to Figure 2 The process performs numerical calculations on the lattice structure and draws the following Figure 5 Displacement life curve shown.

[0103] Embodiment 3

[0104] The present invention also provides an additive manufacturing lattice structure fatigue damage analysis system taking into account the influence of roughness, which is used to implement the method, including:

[0105] A damage evolution equation construction module is used to perform fatigue tests on lattice structure specimens to obtain fatigue life test data of the lattice structure specimens; and to construct a damage evolution equation based on the fatigue life test data;

[0106] An influence factor acquisition module is used to obtain the influence factor of the surface roughness of the lattice structure specimen based on the undulating morphology of the surface of the lattice structure specimen;

[0107] The modified damage evolution equation building module is used to introduce the surface roughness influencing factor into the damage evolution equation to obtain the damage evolution equation considering the surface roughness;

[0108] The life prediction module is used to construct a finite element model of the lattice structure specimen based on the finite element software, and to predict the fatigue life of the lattice structure specimen in combination with the damage evolution equation considering the surface roughness, so as to complete the fatigue damage analysis of the additively manufactured lattice structure considering the influence of roughness.

[0109] In a further embodiment, the damage evolution equation building block includes:

[0110] A stress-strain relationship acquisition unit is used to introduce damage variables into the constitutive model to obtain the stress-strain relationship of the lattice structure specimen after being subjected to force; wherein the value of the damage variable is used to determine the degree of damage of the material at the representative volume unit of the lattice structure specimen; the constitutive model includes an elastic constitutive model and a plastic constitutive model;

[0111] The equation building unit is used to build the damage evolution equation based on fatigue life test data, combined with damage variables and stress-strain relationship.

[0112] A further implementation method is that the impact factor acquisition module includes:

[0113] An average roughness acquisition unit, used to obtain an average surface roughness of the lattice structure specimen based on the length and height of the measuring section of the lattice structure specimen;

[0114] A reference roughness acquisition unit is used to polish the surface of the lattice structure specimen to smoothness and obtain a reference surface roughness;

[0115] The influencing factor acquisition unit is used to obtain the surface roughness influencing factor of the lattice structure specimen based on the average surface roughness and the reference surface roughness in combination with the additive manufacturing direction of the lattice structure specimen.

[0116] A further implementation method is that the modified damage evolution equation building module includes:

[0117] An integral calculation unit is used to integrate the damage variable in the damage evolution equation from 0 to 1 to obtain a fatigue life calculation formula for the lattice structure specimen;

[0118] A curve acquisition unit, used for fitting the SN curve of a lattice structure specimen with a smooth surface under a preset stress ratio based on the fatigue life test data of the lattice structure specimen;

[0119] The fatigue life calculation unit is used to obtain the fatigue life of a smooth-surface lattice structure specimen under uniaxial loading with a preset stress ratio based on the SN curve and fatigue life calculation formula through the continuous damage mechanics theory;

[0120] Parameter calibration unit, used to calibrate the parameters of the damage evolution equation based on fatigue life under uniaxial loading and fatigue life test data, using MATLAB curve fitting tools, least squares method and finite element numerical simulation;

[0121] The modified equation acquisition unit is used to introduce the parameters of the calibrated damage evolution equation and the surface roughness influencing factor into the damage evolution equation to obtain the damage evolution equation taking the surface roughness into consideration.

[0122] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A fatigue damage analysis method for additively manufactured lattice structures considering the influence of roughness, characterized in that: include: Perform fatigue tests on lattice structure specimens to obtain fatigue life test data of the lattice structure specimens; and constructing a damage evolution equation based on the fatigue life test data; Based on the undulating morphology of the surface of the lattice structure specimen, the influencing factor of the surface roughness of the lattice structure specimen is obtained; Introducing the surface roughness influencing factor into the damage evolution equation to obtain the damage evolution equation taking the surface roughness into consideration; The finite element model of the lattice structure specimen is constructed based on the finite element software. Combined with the damage evolution equation considering the surface roughness, the fatigue life of the lattice structure specimen is predicted, and the fatigue damage analysis of the additively manufactured lattice structure considering the influence of roughness is completed.

2. The method according to claim 1, characterized in that Methods for constructing the damage evolution equation include: The damage variable is introduced into the constitutive model to obtain the stress-strain relationship of the lattice structure specimen after being subjected to force; the value of the damage variable is used to determine the damage degree of the material at the representative volume unit of the lattice structure specimen; Based on the fatigue life test data, combined with the damage variables and the stress-strain relationship, the damage evolution equation is constructed.

3. The method according to claim 2, characterized in that The constitutive model includes an elastic constitutive model and a plastic constitutive model; wherein the elastic constitutive model adopts Hooke's law, and the plastic constitutive model adopts the Chaboche model.

4. The method according to claim 3, characterized in that The methods for obtaining the influencing factors of the surface roughness of the lattice structure specimen include: Based on the length and height of the measuring section of the lattice structure specimen, the average surface roughness of the lattice structure specimen is obtained; The surface of the lattice structure specimen is polished smooth to obtain the reference surface roughness; Based on the average surface roughness and the reference surface roughness and in combination with the additive manufacturing direction of the lattice structure specimen, the surface roughness influencing factor of the lattice structure specimen is obtained.

5. The method according to claim 4, characterized in that The expression of the surface roughness influencing factor is as follows: In the formula, γ is the angle parameter, R a is the average surface roughness, R a0 is the reference surface roughness.

6. The method according to claim 4, characterized in that Methods for obtaining the damage evolution equation considering surface roughness include: Integrating the damage variable in the damage evolution equation from 0 to 1 to obtain a fatigue life calculation formula for the lattice structure specimen; Based on the fatigue life test data of the lattice structure specimen, the SN curve of the lattice structure specimen with smooth surface under the preset stress ratio is fitted; Based on the SN curve and the fatigue life calculation formula, the fatigue life of the lattice structure specimen with a smooth surface under uniaxial loading with a preset stress ratio is obtained through the continuous damage mechanics theory; Based on the fatigue life under uniaxial loading and the fatigue life test data, the parameters of the damage evolution equation are calibrated using MATLAB curve fitting tools, least squares method and finite element numerical simulation; The parameters of the calibrated damage evolution equation and the influencing factor of the surface roughness are introduced into the damage evolution equation to obtain the damage evolution equation taking the surface roughness into consideration.

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