Method for predicting fatigue life scatter based on printing defects of additive manufacturing material

Abstract

The present application relates to the technical field of additive manufacturing, in particular to a fatigue life dispersion prediction method based on printing defects of additive manufacturing materials, and the specific steps are as follows: step S1; fracture analysis; step S2; fatigue test; step S3; crack propagation rate determination test; step S4; model construction; step S5; model integration; step S6; function model; step S7; extended life; step S8; final fatigue life; the present application extends the small crack propagation threshold value model into a model that can predict the limited fatigue life, links the crack propagation threshold values of the small crack stage and the long crack stage, establishes the functional relationship between the crack length and the crack propagation threshold value, comprehensively considers the influences of the notch stress concentration and the average stress of the fatigue sample, and compared with the test results, the error of the fatigue life prediction result is small.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically a method for predicting the dispersion of fatigue life based on printing defects in additive manufacturing materials. Background Technology

[0002] Additive manufacturing is a manufacturing technology that directly shapes materials by accumulating them layer by layer. It offers flexibility and design freedom, enabling the construction of complex and precise structures. However, although its static mechanical properties can rival those of traditional manufacturing technologies after post-processing, additively manufactured parts still fall short in terms of fatigue performance. This is mainly due to microscopic defects and complex structures in the material, which can lead to the early initiation and propagation of fatigue cracks, thus affecting the service life and reliability of the parts.

[0003] Furthermore, residual stress and inhomogeneous grain structure that may arise during additive manufacturing exacerbate the fatigue susceptibility of materials. In addition, although additive manufacturing materials from different suppliers may share the same name, their fatigue performance varies significantly due to factors such as manufacturing processes and raw material batches, posing a challenge to fatigue performance assessment. Therefore, a deep understanding of the fatigue initiation and fracture mechanisms of additive manufacturing materials, and the correlation between material defects and microstructural characteristics and fatigue life, are crucial means to improve prediction accuracy.

[0004] Metallographic analysis revealed that microscopic defects during additive manufacturing, such as incomplete fusion between layers, inclusions, and porosity, are the main causes of fatigue cracks, and the location and size of these pores significantly influence crack propagation. After hot isostatic pressing and other treatments, the fatigue properties of additively manufactured titanium alloys were significantly improved. Summary of the Invention

[0005] The small crack propagation theory provides a theoretical basis for predicting the fatigue life of materials containing printing defects. This theory divides small crack propagation into three stages. By defining the crack propagation threshold for different stages, it explores the influence of microstructure characteristics, load application, and crack size on fatigue crack propagation, thus providing strong support for optimizing the fatigue performance of additive manufacturing materials. This invention proposes a method for predicting the dispersion of fatigue life based on printing defects in additive manufacturing materials.

[0006] The specific steps of the fatigue life dispersion prediction method based on additive manufacturing material printing defects are as follows: Step S1: Fracture analysis: Through fracture analysis, determine the critical crack size d for small cracks in the microstructure of ideal additive manufacturing titanium alloy materials, and determine the crack shape factor Y for crack propagation; Step S2: Fatigue test: Determine the fatigue limit of the ideal material under a given stress ratio R through fatigue testing. ; Step S3: Crack propagation rate determination experiment: Through the crack propagation rate determination experiment, obtain the material constants C and m, which express the long crack propagation rate, and the long crack propagation threshold. Construct the Paris formula for long crack propagation; Step S4: Model Construction: Construct the effective stress intensity factor range for small crack propagation in the PSC stage. A functional model for the small crack length 'a'; Step S5: For the steps in S4 Integrating the function model yields the propagation lifetime of the small crack during the PSC stage. ; Step S6: Using the corresponding model in the stress intensity factor handbook, construct the effective stress intensity factor range for long crack propagation. A functional model for the length 'a' of a long crack; Step S7: For the steps in S6 Integrating the function model yields the propagation lifetime of the long crack in the LC stage. ; Step S8: Based on steps S5 and S7, the final fatigue life is obtained by summing the number of cycles in the small crack and long crack stages.

[0007] The method further includes: Step S9: Analyze the printing defect characteristics of the fracture surface of the additive manufacturing sample, obtain the maximum equivalent printing defect size of different samples, analyze the obtained printing defect characteristics, set its initial crack, calculate its fatigue life under the corresponding fatigue load, and obtain the comparison data of predicted life and fatigue test life. Step S10: Based on the printing defect characteristics obtained from step S9, set different initial crack sizes for small crack propagation, and simultaneously set a series of monotonically changing cyclic loads. Using steps S4 to S8, fatigue life dispersion bands under different defect sizes are calculated, and the influence of printing defects on fatigue life dispersion in additive manufacturing of titanium alloy materials is quantified by graphical method. Step S11: If the stress level of the material application environment is low, perform the reverse operation by selecting different... Size analysis reveals the maximum allowable critical defect size d, enabling relaxed defect control in additive manufacturing processes and improving the processability of additive manufacturing materials.

[0008] In step S1, the Paris formula for stable crack propagation is established: (1); in, Indicates crack length The rate of change of fatigue cycle number N, where C is a material constant, is called the Paris constant. It is the effective stress intensity factor range, also known as the stress intensity factor range of a crack.

[0009] In step S4, the effective stress intensity factor range of the equivalent crack corresponding to the printing defect in the PSC stage is established. Computational model: (2); In formula (2), It is the stress concentration factor of the specimen; This is the crack length, which is the independent variable. It is the radius of curvature at the root of the notch in the sample; Y is the range of cyclic loads applied to the specimen; Y is the crack shape factor. The long crack propagation threshold is obtained by regression using formula (1); ; n is a material constant representing the effect of stress ratio R on crack propagation rate, where n = 0.5.

[0010] In step S5, a calculation model for the small crack propagation life of printing defects in the PSC stage is established using formula (3). (3); In formula (3), The initial crack size can be obtained from the effective size of the printed defect based on the metallographic analysis of the material; l is the critical crack length value for the transition between the PSC stage and the LC stage. Step S6 specifically includes: Using knowledge from the stress intensity factor handbook, the effective stress intensity factor range for crack propagation to the LC stage corresponding to printing defects is established. Computational model: (4); In formula (4), f(a) is the crack length correlation coefficient, which is obtained by consulting the stress intensity factor handbook.

[0011] In step S7, a calculation model for the number of cycles required to determine the critical final crack size when the crack corresponding to the printing defect expands to the final abrupt structural failure state is established using formula (5): (5); In formula (5), The critical final crack size, without loss of generality. =5mm.

[0012] In step S8, the final fatigue life is obtained by summing the number of cycles in the small crack and long crack stages. (6).

[0013] Step S11 specifically includes: Using the MSC stage microstructure small crack propagation threshold calculation model shown in formula (7), maintain No change, adjustment The size of the critical defect size d under different cyclic loads is obtained. Functional relationship; when the maximum equivalent defect size of the surface layer is less than the critical defect size d, it is confirmed that the defect has no direct impact on the fatigue life of the material, and the life of the specimen tends to be the fatigue life of the ideal material. Then, based on the applied cyclic load level... Determine the maximum acceptable equivalent defect size for a printing defect; (7); In formula (7), d is the fatigue limit of a smooth sample of additive manufacturing printed material; d is the critical crack size of microcracks, d=0.02mm.

[0014] The beneficial effects of this invention are: This invention extends the small crack propagation threshold value model into a model that can predict finite fatigue life, links the crack propagation threshold values ​​of the small crack stage and the long crack stage, establishes a functional relationship between crack length and crack propagation threshold value, comprehensively considers the influence of notch stress concentration and mean stress of fatigue specimen, and the fatigue life prediction results have small errors compared with experimental results. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] Figure 1 A geometric diagram of the fatigue standard specimen used in the fatigue tests conducted for this invention; Figure 2 The crack propagation mode discovered during fatigue test fracture analysis for this invention; Figure 3 The surface crack propagation mode discovered during surface crack fracture analysis for this invention; Figure 4 The corner crack propagation mode discovered during corner crack fracture analysis for this invention; Figure 5 The relationship between crack propagation threshold and crack length established for the small crack propagation theory; Figure 6The curve showing the variation of the stress intensity factor range with crack length obtained by the prediction method proposed in this invention includes the PSC stage and the LC stage. Figure 7 This invention addresses the defects in fracture porosity caused by additive manufacturing. Figure 8 This invention addresses the lack of fusion at the fracture surface in additive manufacturing. Figure 9 The fatigue origin region characteristics of the printing defects of this invention; Figure 10 The present invention provides three defect fatigue fracture modes and Statistical methods: (a) Stomata =22μm; (b) Incomplete fusion defects =60μm; (c) Surface defects =43μm; Figure 11 This is a comparison chart of the predicted life obtained by the prediction method proposed in this invention and the corresponding fatigue test life. Figure 12 The fatigue life dispersion bands under different defect sizes are obtained using the prediction method proposed in this invention. Figure 13 This describes the relationship between load and maximum allowable defect size obtained using the prediction method proposed in this invention. Detailed Implementation

[0017] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below.

[0018] Example: like Figures 1 to 13 As shown, in order to effectively improve the fatigue life of additively manufactured titanium alloy materials, this invention proposes a method for predicting the dispersion of fatigue life of titanium alloy materials based on printing defects formed by different additive manufacturing processes, including the following steps: Step S1, as follows Figure 1 As shown, by observing the fracture surface of an ideal additively manufactured titanium alloy material and maximizing its fatigue performance through hot isostatic pressing, the following results are observed: Figure 2 As shown, the critical crack size d for small cracks in the microstructure of ideal additively manufactured titanium alloy materials was found. Typically, the value of d is given by the average grain size M of the additively manufactured material. For titanium alloys, d = M is taken, and by observing the fatigue fracture surface, the value of M for titanium alloys is 0.02 mm. Step S2: Observe the fracture surface of the ideal additively manufactured titanium alloy material. The fracture structure is as follows: Figure 3 and Figure 4As shown, the possible forms and locations of material printing defects were discovered. Generally, the observed defects are located on the sample surface or at a distance M from the surface, i.e., the surface layer within the average grain size range. Therefore, the crack propagation law can be calculated as a surface crack. According to the propagation law of type I crack, its tensile and compressive load crack shape factor Y = 0.65. Step S3: Conduct fatigue tests on the smooth specimens of the given additive manufacturing process to obtain the fatigue SN curves of the smooth specimens under a given stress ratio for ideal additively manufactured titanium alloy materials, and obtain the ideal material fatigue limit under a given stress ratio R. ; Obtaining the ideal material fatigue limit Detailed process: Core objective: To determine the fatigue limit of ideal additively manufactured titanium alloy materials by obtaining fatigue SN curves under a given stress ratio R through fatigue tests on smooth specimens without obvious printing defects. , that is, the symmetrical cyclic fatigue limit of crack-free materials; The following preparations are required: Sample preparation: Using parameters that are completely consistent with the target additive manufacturing process, such as laser power, scanning speed, and layer thickness, smooth samples are printed to avoid introducing additional defects due to process differences.

[0019] The specimens must meet the fatigue test standards, referring to GB / T3075 and ISO1143. The geometry should be a smooth part without notches, such as a round bar or plate-shaped smooth specimen. The surface should be polished to remove oxide scale, burrs, etc. after printing, and ensure that there are no obvious stress concentration sources on the surface.

[0020] Number of specimens: at least 3 specimens per stress level to ensure the statistical validity of the test data; Test equipment and environment: The equipment selected is an electromagnetic resonant fatigue testing machine or a hydraulic servo fatigue testing machine, which must have constant amplitude cyclic load control function and the accuracy must meet the requirement of load fluctuation ≤ ±1%; Environment: Room temperature 23±5℃, dry environment, avoid the influence of humidity and temperature changes on the test results; Parameter settings: Stress ratio R: Set according to the actual application scenario, such as R=0.06, R=-1 for symmetric / asymmetric cycles, and keep R constant throughout the test; Loading frequency: Select a sine wave with a frequency of 10-50Hz to avoid the sample heating up due to excessively high frequency or the test efficiency being affected by excessively low frequency. The test procedure is as follows: (1) Sample installation and calibration The smooth specimen is clamped in the testing machine chuck, ensuring coaxiality of the clamping and avoiding additional bending moment; the actual load and displacement relationship of the stress area of ​​the specimen is calibrated by an extensometer or displacement sensor to verify the loading accuracy.

[0021] (2) Multi-stress horizontal cyclic loading Select a series of decreasing alternating stress amplitudes Starting from a level higher than the estimated fatigue limit, the load was gradually reduced, and constant amplitude cyclic loads were applied to different specimens.

[0022] At each stress level, the load is continuously applied until the specimen fractures, and the number of cycles N at fracture is recorded. If the number of cycles reaches 10... 7 If the stress level does not fracture after the second test, the loading is stopped, and the stress level is determined to be "no fracture". (3) Data Recording Record the stress amplitude of each specimen. Number of cycles N, break or 10 7 The values ​​at the time of the stop were recorded, and the fracture location and macroscopic characteristics of the fracture surface were also recorded, such as whether it was surface cracking. Data processing and The process is as follows: (1) Plot the SN curve With stress amplitude The vertical axis is a logarithmic or linear coordinate; the number of cycles N is the horizontal axis, a logarithmic coordinate; plot all experimental data points on the coordinate system.

[0023] The least squares method was used to fit the data points to obtain the fatigue SN curve, which was divided into the high-cycle fatigue region and the transition region. (2) Extracting the fatigue limit

[0024] For materials with a defined fatigue limit, such as steel and titanium alloys, the stress amplitude corresponding to the horizontal segment of the SN curve is taken as the fatigue limit. That is, the number of cycles reaches 10. 7 The maximum stress amplitude that prevents fracture at this time.

[0025] If the experimental data do not show a clear level, the 10 can be determined by linear extrapolation. 7 The stress amplitude corresponding to the next cycle, as ; Step S4: Print a standard compact tensile specimen for determining the type I crack propagation rate using the same additive manufacturing process. Through crack propagation rate measurement experiments, obtain the material constants C and m, and the long crack propagation threshold, which express the stable crack propagation rate characteristics under a given stress ratio R. Establish the Paris formula for stable crack propagation: (1); Obtain crack propagation parameters C, m, The detailed process is as follows: Core objective: To obtain the material constants C and m, as well as the long crack propagation threshold, from the Paris formula through crack propagation rate tests on standard compact tensile specimens. This provides basic parameters for subsequent crack propagation life calculations.

[0026] The following preparations are required: (1) Sample preparation Standard compact tensile specimens, CT specimens, are printed using an additive manufacturing process identical to that in step S3, conforming to ASTM E647 or GB / T6398 standards. The specimen size is determined based on the material thickness, such as CT25 or CT50. Pre-cracked specimen: An initial crack is machined at the notch of the specimen using wire cutting, and the crack length is... Standard requirements must be met, typically =2~5mm; the crack surface is perpendicular to the loading direction to ensure it is a type I crack, an open crack; Sample quantity: at least 3 samples, used to verify data repeatability; (2) Test equipment and measuring tools Equipment: The same fatigue testing machine as in step S3, equipped with a crack length measurement system, such as extensometer method, potentiometer method or optical microscope method; Measuring tools: Crack length measuring instruments with an accuracy of ≥0.001mm, used for real-time monitoring of crack propagation; (3) Parameter setting Stress ratio R: Keep consistent with step S3 to ensure parameter matching; loading frequency 10-30Hz, sinusoidal loading; Load level: Select 3 to 5 different stress intensity factor ranges. From higher than expected The range is significantly higher than this threshold; covering the stable crack propagation stage; The test procedure is as follows: (1) Sample installation and initial calibration Clamp the CT specimen on the testing machine and install a crack length measuring device, such as fixing an extensor on both sides of the specimen notch; calibrate the relationship between load and crack opening displacement. Measure the initial crack length Record the geometric parameters of the specimen, such as specimen width W, thickness B, and initial crack length. Used to calculate the stress intensity factor K; (2) Constant amplitude loading and crack propagation monitoring A constant amplitude cyclic load is applied to the specimen, and the change in crack length 'a' with the number of cycles N is monitored in real time. For each certain length extension, such as Δa... =0.1~0.2mm; record the number of cycles N until the crack extends to the point of specimen fracture or reaches the preset crack length, such as a=0.8W; At each load level, at least 10 sets of a and N data points are obtained to ensure that the crack propagation rate da / dN can be accurately fitted. 3) Threshold test ( (Measurement); Using "decreasing" "Law": from a higher Starting horizontally, once the crack propagation rate stabilizes, the load is gradually reduced to decrease... Until the crack propagation rate da / dN ≤ 10 -10 m / time, industry-standard threshold for judgment; At this time, the corresponding The value is the long crack propagation threshold. ; Data processing and parameter calculation are as follows: (1) Stress intensity factor calculate The stress intensity factor formula for each measurement is used to calculate the corresponding stress intensity factor for the CT specimen. : = ×f (a / W)×√(πa), where The stress amplitude corresponding to the load. = / B√W, The load range is given by f (a / W), which is the geometric correction factor for the CT specimen. It can be found or calculated using the ASTM E647 standard. (2) Calculation of crack propagation rate da / dN For each set of (a,N) data, the crack propagation rate is calculated using the adjacent two-point difference method: , where i is the data point number; (3) Fitting the Paris formula and extracting parameters Plot da / dN on a logarithmic scale; Use x-axis and logarithmic coordinates to plot da / dN- Double logarithmic curve; The Paris formula is: In this invention The double logarithmic curve is linearly fitted, the slope is m, the intercept is lnC, and the material constant C is then calculated. (4) Determine

[0027] Take da / dN = 10 -10 m times corresponding to Value as the threshold for long crack propagation If the point does not appear directly in the experimental data, it is determined by linear extrapolation. Step S5: Establish the effective stress intensity factor range of the equivalent crack corresponding to the printing defect in the PSC stage. The computational model; (2); Step S6: As shown in Equation (3), establish a calculation model for the small crack propagation life of printing defects in the PSC stage; (3); Step S7: Using the knowledge in the stress intensity factor handbook, establish the effective stress intensity factor range for crack propagation to the LC stage corresponding to the printing defect. Computational model: (4); Step S8: According to Equation (5), establish a calculation model for the number of cycles required to determine the critical final crack size when the crack corresponding to the printing defect expands to the final abrupt structural failure state. (5) Step S9: Based on the curve showing the propagation of small cracks, such as... Figure 5 and Figure 6 As shown, the number of crack propagation cycles in the PSC stage is... and the number of crack propagation cycles in the LC stage Adding these together, we obtain the fatigue life predicted by this invention under given printing defect conditions: (6); Step S10: Analyze the printing defect characteristics of the fracture surface of the additive manufacturing sample, and the fracture surface microstructure is as follows. Figures 7-9 As shown, the maximum equivalent printing defect size of different specimens was obtained through analysis. (a) Specimen: =22μm, (b) Sample: =60μm; (c) Sample: =43μm, statistical results are as follows Figure 10 As shown. According to Figure 10 Analyze the characteristics of the printing defects obtained, set the initial crack, calculate the fatigue life under the corresponding fatigue load, and obtain the following results: Figure 11 The comparison chart shown is between the predicted life and the fatigue test life. This result indicates that the prediction method proposed in this invention has high prediction accuracy.

[0028] Step S11, according to Figure 10 The system feeds back different levels of printing defects, sets different initial crack sizes for small crack propagation, and simultaneously sets a series of monotonically varying cyclic loads. Following steps 5 through 9, the fatigue life dispersion bands under different defect sizes were calculated. The influence of printing defects on the fatigue life dispersion in additive manufacturing of titanium alloy materials was quantified using graphical methods. The results are as follows: Figure 12 As shown, this invention quantitatively analyzes the influence of different defect sizes on fatigue life. The results show that when the defect size is higher than a certain threshold, it will lead to a significant decrease in fatigue life, thereby causing a significant increase in the dispersion of fatigue life of the material. Therefore, reasonable defect size control is required in the additive manufacturing printing process. Step S12: Based on the MSC stage microstructure small crack propagation threshold calculation model shown in equation (7), maintain... No change, adjustment By determining the size of the critical defect size d under different cyclic loads, we can obtain the critical defect size d and d under different cyclic loads. Functional relationship: When the maximum equivalent defect size of the surface layer is less than the critical defect size d, it is considered that the defect has no direct impact on the fatigue life of the material, and the fatigue life of the specimen tends to be that of the ideal material. Based on this, the fatigue life can be determined according to the applied cyclic load level. The maximum permissible equivalent defect size for printing defects was determined, and the results are as follows: Figure 13 As shown, this invention provides the maximum permissible defect size under different stress levels and the reliable material fatigue life performance under different defect levels, thus better promoting the application of additive manufacturing materials in many high-performance industries. (7); In equation (2), k is the threshold value evolution rate constant parameter. This is the initial crack propagation threshold value. It is the stress concentration factor of the specimen; This is the crack length, which is the independent variable. It is the radius of curvature at the root of the notch in the sample; This refers to the range of cyclic loads applied to the specimen. It is the crack shape factor. The long crack propagation threshold is obtained by regression using equation (1); (8); n is a material constant representing the effect of stress ratio R on crack propagation rate, where n = 0.5; In equation (3), The initial crack size can be obtained from the effective size of the printed defect based on the metallographic analysis of the material; l is the critical crack length value for the transition between the PSC stage and the LC stage. In equation (4), f(a) is the crack length correlation coefficient, which is obtained by consulting the stress intensity factor handbook.

[0029] In equation (5), The critical final crack size, without loss of generality. =5mm.

[0030] In equation (7), d is the fatigue limit of a smooth sample of additive manufacturing printed material; d is the critical crack size of microcracks, d=0.02mm.

[0031] This invention extends the small crack propagation threshold model into a model that can predict finite fatigue life. It links the crack propagation threshold values ​​of the small crack stage and the long crack stage, establishes a functional relationship between crack length and crack propagation threshold value, and comprehensively considers the influence of notch stress concentration and mean stress of fatigue specimens. The fatigue life prediction results have small errors compared with experimental results.

[0032] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0033] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0034] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The function specified in one or more boxes.

[0035] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely prisms of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for printing a fatigue life scatter prediction of defects based on additive manufacturing materials, characterized by: The specific steps are as follows: Step S1: Fracture analysis: Through fracture analysis, determine the critical crack size d for small cracks in the microstructure of ideal additive manufacturing titanium alloy materials, and determine the crack shape factor Y for crack propagation; Step S2: Fatigue test: By fatigue test, the fatigue limit of the ideal material under a given stress ratio R is determined ; Step S3: Crack propagation rate measurement test: By the crack propagation rate measurement test, the material constants C, m and long crack propagation threshold value expressing the long crack propagation rate are acquired, and the Paris formula of long crack propagation is constructed . Step S4: Constructing the model: Constructing the PSC stage small crack growth effective stress intensity factor range Function model on small crack length a; Step S5: Model integration: Integrate the function model in step S4 to obtain the propagation life of small cracks in the PSC stage ;​ Step S6: Function model: build the effective stress intensity factor range of long crack propagation using the corresponding model in the stress intensity factor manual Function model on long crack length a; Step S7: Extension life: Integrating the function model in step S6, the extension life of long crack in LC stage is obtained Step S7: Extension life: Integrating the function model in step S6, the extension life of long crack in LC stage is obtained Step S7: Extension life: Integrating the function model in step S6, the extension life of long crack in LC stage is obtained Step S8: Final fatigue life: Based on steps S5 and S7, the final fatigue life is obtained by summing the number of cycles in the small crack and long crack stages.

2. The method of predicting the scatter of fatigue life of a print defect based on an additive manufacturing material according to claim 1, characterized in that: The method further includes: Step S9: Analyze the printing defect characteristics of the fracture surface of the additive manufacturing sample, obtain the maximum equivalent printing defect size of different samples, analyze the obtained printing defect characteristics, set its initial crack, calculate its fatigue life under the corresponding fatigue load, and obtain the comparison data of predicted life and fatigue test life. Step S10, according to the printing defect characteristics obtained by analyzing step S9, set different initial crack sizes of the small crack propagation, and set a series of monotonically changing cyclic loads , using steps S4-S8, the fatigue life dispersion band under different defect sizes is calculated, and the influence degree of the printing defects of the additive manufacturing titanium alloy material on the fatigue life dispersion is quantified by the graphical method; Step S11: If the stress level of the material application environment is low, perform the reverse operation by selecting different... Size analysis reveals the maximum allowable critical defect size d, enabling relaxed defect control in additive manufacturing processes and improving the processability of additive manufacturing materials.

3. The fatigue life dispersion prediction method based on additive manufacturing material printing defects according to claim 1, characterized in that: In step S1, the Paris formula for stable crack propagation is established: (1) in, Indicates crack length The rate of change of fatigue cycle number N, where C is a material constant, is called the Paris constant. It is the effective stress intensity factor range, also known as the stress intensity factor range of a crack.

4. The fatigue life dispersion prediction method based on additive manufacturing material printing defects according to claim 1, characterized in that: In step S4, the effective stress intensity factor range of the equivalent crack corresponding to the printing defect in the PSC stage is established. Computational model: (2) In formula (2), It is the stress concentration factor of the specimen; This is the crack length, which is the independent variable. It is the radius of curvature at the root of the notch in the sample; This refers to the range of cyclic loads applied to the specimen. Y is the crack shape factor. The long crack propagation threshold is obtained by regression using formula (1); ; n is a material constant representing the effect of stress ratio R on crack propagation rate, where n = 0.

5.

5. The fatigue life dispersion prediction method based on additive manufacturing material printing defects according to claim 1, characterized in that: In step S5, a calculation model for the small crack propagation life of printing defects in the PSC stage is established using formula (3). (3) In formula (3), The initial crack size can be obtained from the effective size of the printed defect based on the metallographic analysis of the material; l is the critical crack length value for the transition between the PSC stage and the LC stage.

6. The fatigue life dispersion prediction method based on additive manufacturing material printing defects according to claim 1, characterized in that: Step S6 specifically includes: Using knowledge from the stress intensity factor handbook, the effective stress intensity factor range for crack propagation to the LC stage corresponding to printing defects is established. Computational model: (4) In formula (4), f(a) is the crack length correlation coefficient, which is obtained by consulting the stress intensity factor handbook.

7. The fatigue life dispersion prediction method based on additive manufacturing material printing defects according to claim 1, characterized in that: In step S7, a calculation model for the number of cycles required to determine the critical final crack size when the crack corresponding to the printing defect expands to the final abrupt structural failure state is established using formula (5): (5) In formula (5), The critical final crack size, without loss of generality. =5mm.

8. The fatigue life dispersion prediction method based on additive manufacturing material printing defects according to claim 1, characterized in that: In step S8, the final fatigue life is obtained by summing the number of cycles in the small crack and long crack stages. （6）。 9. The fatigue life dispersion prediction method based on additive manufacturing material printing defects according to claim 1, characterized in that: Step S11 specifically includes: Using the MSC stage microstructure small crack propagation threshold calculation model shown in formula (7), maintain No change, adjustment The size of the critical defect size d under different cyclic loads is obtained. Functional relationship; when the maximum equivalent defect size of the surface layer is less than the critical defect size d, it is confirmed that the defect has no direct impact on the fatigue life of the material, and the life of the specimen tends to be the fatigue life of the ideal material. Then, based on the applied cyclic load level... Determine the maximum acceptable equivalent defect size for a printing defect; (7) In formula (7), d is the fatigue limit of a smooth sample of additive manufacturing printed material; d is the critical crack size of microcracks, d=0.02mm.

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