Wind power tower drum circumferential weld fatigue grade evaluation method

Abstract

The invention discloses a wind power tower drum circumferential weld fatigue grade evaluation method, which comprises the following steps of: 1, respectively constructing reference models for a smooth non-welding part model and a smooth welding part model with known IIW standard fatigue grades, and constructing a target wind power tower drum circumferential weld parameterization finite element model; step 2, calibrating a microstress concentration coefficient kt based on the smooth non-welding part model; 3, verifying the precision of the method through a smooth welding part model, and ensuring that an evaluation result meets a preset industrial standard allowance requirement; and 4, evaluating the fatigue grade of the target model by using the kt parameter calibrated in the step 2. By constructing a reference model consistent with a tower base material, calibrating key parameters of comprehensive macro and micro influences and establishing a standardized evaluation process and precision verification mechanism, the efficiency and precision of wind power tower circumferential weld fatigue grade evaluation are remarkably improved. A traditional tedious process depending on an entity experiment is abandoned, rapid evaluation is achieved by means of parameter multiplexing, and the evaluation period is greatly shortened.

Description

TECHNICAL FIELD

[0001] The application relates to a wind power tower cylinder girth weld fatigue grade evaluation method and belongs to the technical field of fatigue grade evaluation. BACKGROUND

[0002] With the iterative development of wind turbines towards large megawatt super-high towers, the multi-axial alternating load borne by the tower cylinder girth weld continuously increases, and in addition to the influence of complex service environments such as offshore high salt mist and mountain strong turbulence, the girth weld has become the main weak link of fatigue crack initiation, directly affecting the safe and stable operation of the wind turbine. At present, the industry mostly uses finite element simulation technology to analyze the weld fatigue performance, but the related research mostly focuses on fatigue life evaluation and stress concentration coefficient calculation, and lacks special in-depth research on fatigue grades that can more comprehensively reflect fatigue performance, and a unified rapid evaluation method has not yet been formed. Traditional weld fatigue grade evaluation mainly relies on physical experiments, which not only has a complicated process and a long cycle, but also is accompanied by high cost investment, and is difficult to adapt to the rapid evaluation needs of batch tower cylinders in the wind power industry. Part of the simulation analysis method does not fully combine the industry general standards, resulting in insufficient accuracy of the evaluation results, which cannot provide reliable support for engineering practice. At the same time, the existing research has not systematically established the internal correlation between the key topographic parameters such as the weld round corner excess and the fatigue grade, so that the weld process optimization lacks clear basis, and it is difficult to realize the targeted improvement of the weld fatigue performance by adjusting the topographic parameters. SUMMARY

[0003] The application aims at: in view of the above-mentioned problems, a wind power tower cylinder girth weld fatigue grade evaluation method is provided, which can solve the problems of "long cycle and high cost" in the traditional wind power tower cylinder girth weld fatigue grade evaluation, provide a rapid evaluation method without repeated experiments, and has high precision.

[0004] The technical scheme adopted by the application is as follows: A wind power tower cylinder girth weld fatigue grade evaluation method, characterized in that it comprises the following steps: Step 1, respectively constructing reference models for a smooth non-welded piece model and a smooth welded piece model with known IIW standard fatigue grades, and constructing a parameterized finite element model of a target wind power tower cylinder girth weld; Step 2, calibrating the micro stress concentration coefficient kt based on the smooth non-welded piece model; Step 3, verifying the method accuracy through the smooth welded piece model, and ensuring that the evaluation result meets the preset industry standard tolerance requirement; Step 4, using the kt parameter calibrated in step 2 to evaluate the fatigue grade of the target model.

[0005] By constructing two types of reference models with known IIW standard fatigue grades and target parameterized finite element models, a unified and accurate analysis foundation is established for subsequent evaluation work. The two types of reference models can provide clear benchmark basis, and the target parameterized model can accurately restore the actual structural characteristics of the wind turbine tower ring weld, avoiding the deviation of the results caused by model distortion in traditional evaluation. Based on the smooth non-welded model, the micro stress concentration coefficient kt is calibrated, which can capture the influence of material micro defects on fatigue performance, filling the gap of existing technology that ignores micro factors leading to insufficient evaluation accuracy, making the evaluation process more in line with the actual service conditions of the material response. The smooth welded model verification method can ensure the reliability and standardization of the entire evaluation process, so that the results meet the tolerance requirements of the preset industry standard, providing reliable decision support for engineering applications. Reusing the calibrated kt parameter to evaluate the fatigue grade of the target model can avoid repeated experiments or complex calculations, and realize efficient promotion of the evaluation process.

[0006] Alternatively, the material of the reference model in step 1 is consistent with the wind turbine tower base material, and the elastic modulus E and Poisson's ratio v of the reference model are set as the standard physical parameters of the corresponding base material; the IIW standard fatigue grades DC of the smooth non-welded model and the smooth welded model are both preset known values. The reference model uses the same material as the wind turbine tower base material, and uses the standard elastic modulus and Poisson's ratio of the corresponding base material, which can make the mechanical response characteristics of the reference model consistent with the actual material performance of the target tower ring weld, avoid introducing additional errors due to material property differences, and make the subsequent parameter calibration and precision verification more in line with the actual engineering scenario. The IIW standard fatigue grades DC of the smooth non-welded model and the smooth welded model are preset as known values, which can provide clear and authoritative benchmark basis for the calibration of the micro stress concentration coefficient, and also provide a directly comparable reference standard for method precision verification, without the need for additional benchmark determination process.

[0007] Alternatively, the construction process of the target wind turbine tower ring weld parameterized finite element model in step 1 includes: Step 1.a, based on the measured topography of the target wind turbine tower ring weld, determine the key geometric parameters of the model; Step 1.b, perform mesh densification processing on the weld toe area of the model; Step 1.c, control the mesh size so that the stress fluctuation rate of the model is less than a preset threshold.

[0008] Based on the measured morphology of the target wind turbine tower ring weld, the key geometric parameters of the model are determined, which can accurately reproduce the actual structural characteristics of the ring weld, and make the finite element model highly consistent with the geometric shape of the real weld, avoiding the stress calculation deviation caused by geometric parameter distortion. The grid encryption processing of the weld toe area of the model can focus on the key area of the weld stress concentration, improve the stress calculation resolution of this part, capture the finer stress distribution changes, and ensure the accuracy of the stress analysis results. Controlling the grid size to make the stress fluctuation rate of the model less than the preset threshold can ensure the convergence of the finite element calculation, eliminate the interference of grid quality on the calculation results, and make the stress data stable and reliable.

[0009] Alternatively, the calibration process of the micro stress concentration coefficient kt in step 2 includes: Step 2.a, apply an axial tension corresponding to the known IIW standard fatigue grade DC of the smooth non-welded model to the model; Step 2.b, obtain the maximum principal stress S1 of the smooth non-welded model through statics calculation; Step 2.c, substitute S1 into the fatigue simulation software and solve the load scaling coefficient k according to the Miner linear damage accumulation rule (formula: D=∑(n_i / N_i(k))=1, where n_i is the preset fatigue cycle number); Step 2.d, combine the known DC value of the smooth non-welded model to inversely derive the micro stress concentration coefficient kt.

[0010] Applying an axial tension corresponding to the known IIW standard fatigue grade DC to the smooth non-welded model can establish a direct correlation between load and standard fatigue performance, provide a load reference that conforms to industry standards for subsequent parameter calibration, and ensure the standardization of the calibration process. Through statics calculation, the maximum principal stress S1 can be obtained, which can capture the key stress response data of the model under the corresponding load, provide the core input parameters for fatigue simulation analysis, and provide clear data support for subsequent iterative calculation. Substitute S1 into the fatigue simulation software and solve the load scaling coefficient k according to the Miner linear damage accumulation rule, which can accurately simulate the fatigue damage accumulation process of the material under cyclic load, make the solution of the load scaling coefficient consistent with the actual law of fatigue failure, and ensure the reasonableness of the coefficient. Combining the known DC value to inversely derive the micro stress concentration coefficient kt can quantify the influence of material micro defects on fatigue performance as a specific parameter, and make the micro factors that are difficult to directly measure clear.

[0011] Alternatively, the verification process of the method accuracy in step 3 includes: Step 3.a, apply a preset axial tension to the smooth welded model; Step 3.b, repeat the operation of obtaining the maximum principal stress S1 and solving the load scaling coefficient k through fatigue iteration. Step 3.c, calculate the evaluation fatigue grade DC of the smooth weldment model according to the formula DC = load value x 2 x k; Step 3.d, compare the evaluation fatigue grade DC with the known IIW standard fatigue grade DC of the smooth weldment model to verify whether the deviation meets the tolerance requirement.

[0012] Applying a preset axial tension to the smooth weldment model can provide stable and repeatable load conditions, establish a unified calculation basis for subsequent precision verification, and ensure the objectivity of the verification process. Repeating the operation of obtaining the maximum principal stress S1 and iteratively solving the load scaling coefficient k through statics calculation can continue the calculation logic of the parameter calibration stage, maintain the consistency of the entire evaluation process, and avoid introducing additional errors due to differences in calculation methods. Calculating the evaluation fatigue grade DC of the smooth weldment model according to the formula DC = load value x 2 x k can convert the load parameters and fatigue iteration results into intuitive fatigue grade indicators, form a standardized calculation path, and ensure the traceability and reproducibility of the results. Comparing the evaluation fatigue grade DC with the known IIW standard fatigue grade DC of the smooth weldment model can directly judge the calculation accuracy of the entire evaluation method, screen situations that do not meet the tolerance requirement, and ensure the reliability of the method in engineering applications.

[0013] Alternatively, the preset industry standard in step 3 includes the International Institute of Welding (IIW) standard and the BS7608:2014 standard, and the deviation of the evaluation result needs to be controlled within the corresponding tolerance range specified by the above industry standards. This can provide a unified and rigorous technical basis for the evaluation process, ensure that the evaluation process, index definition, and result determination all meet the industry general requirements, and avoid differences or incomparability of evaluation results due to non-uniform standards. Controlling the deviation of the evaluation result within the corresponding tolerance range specified by the above standards can directly ensure that the accuracy of the evaluation result reaches the required level for engineering applications, making the result have sufficient credibility and being directly used as a decision support for wind turbine tower ring weld design, construction, and maintenance.

[0014] Alternatively, the evaluation process of the target model fatigue grade in step 4 includes: Step 4.a, apply a preset axial tension to the ring weld model to be evaluated; Step 4.b, obtain the maximum principal stress S1 of the target model through statics calculation; Step 4.c, reuse the kt parameter calibrated in step 2, which comprehensively considers the effects of macroscopic stress concentration and microscopic defects, to iteratively solve the load scaling coefficient k; Step 4.d, calculate the fatigue grade of the target model according to the formula DC = load value x 2 x k.

[0015] The preset axial tension is applied to the girth weld model to be evaluated, which can continue the load application logic of the reference model, provide uniform and stable stress conditions for the target model, ensure that the fatigue rating is carried out under consistent load conditions, and avoid affecting the objectivity of the results due to differences in load conditions. The maximum principal stress S1 of the target model is obtained through statics calculation, which can accurately capture the stress response of the key area of the target girth weld, provide core data support for subsequent fatigue rating calculation, and provide a clear stress basis for the evaluation process. The kt parameter calibrated in step 2 can be reused to consider the comprehensive effect of material micro-characteristics and girth weld macro-structure on fatigue performance, without the need for complex parameter calibration for the target model, which significantly simplifies the evaluation process and makes the evaluation results more comprehensive.

[0016] Alternatively, it also includes the following steps: Step 5, based on the evaluation results of step 4, analyze the influence law of girth weld morphology parameters on fatigue rating, and then complete the girth weld morphology optimization. Based on the fatigue rating evaluation results of the target model obtained in step 4, the influence law of girth weld morphology parameters on fatigue rating can be analyzed to quantify the internal relationship between morphology parameters and fatigue performance, form a clear rule of the influence relationship which is difficult to determine, and get rid of the limitations of traditional morphology optimization relying on experience. Further complete the girth weld morphology optimization, which can adjust the key morphology parameters, strengthen the fatigue resistance of the girth weld, and make the optimization measures more suitable for actual needs, avoiding resource waste or insufficient performance improvement caused by blind adjustment.

[0017] Alternatively, the analysis process of the influence law of girth weld morphology parameters on fatigue rating in step 5 includes: Step 5.a, select the corner radius R and the excess height H3 in the girth weld morphology parameters as the key analysis parameters; Step 5.b, change the value of the corner radius R within a predetermined range, record the maximum principal stress S1 corresponding to each value, and analyze the correlation between R and S1; Step 5.c, change the value of the excess height H3 within a predetermined range, record the maximum principal stress S1 corresponding to each value, and determine the value of H3 that makes S1 reach a minimum value.

[0018] Selecting the fillet radius R and the excess height H3 as the key analysis parameters in the weld profile parameters can focus on the geometric factors that play a core role in the weld fatigue performance, avoid scattered analysis of irrelevant parameters, make the research direction more targeted, and ensure that the analysis results can directly serve the profile optimization. Changing the value of the fillet radius R within a predetermined range, recording the maximum principal stress S1 corresponding to each value, and analyzing the correlation between them can clearly present the influence trend of the change of R on the stress state of the weld through systematic variable adjustment and data accumulation, and convert the original implicit correlation into quantifiable and traceable rule cognition. Changing the value of the excess height H3 within a predetermined range, recording the corresponding maximum principal stress S1, and determining the value of H3 that makes S1 reach a minimum value can accurately locate the optimal interval of the excess height parameter and provide a clear numerical target for subsequent profile optimization.

[0019] Alternatively, the implementation process of the weld profile optimization in step 5 includes: Step 5.d, based on the obtained correlation between R and S1 and the correlation between H3 and S1, selecting the combination of the fillet radius R and the excess height H3 that minimizes the maximum principal stress S1 as the optimal profile parameter; Step 5.e, substituting the optimal profile parameter into the target model to re-execute the fatigue level evaluation of step 4 and obtain the optimized target model fatigue level.

[0020] Based on the correlation between the fillet radius R, the excess height H3, and the maximum principal stress S1, selecting the parameter combination that minimizes S1 as the optimal profile parameter can make the parameter selection fully meet the core requirement of minimizing stress, abandon the traditional scattered adjustment method that relies on experience, achieve precise matching of parameter combinations, and ensure that the optimization direction directly targets the key to improving fatigue performance. Substituting the optimal profile parameter into the target model and re-executing the fatigue level evaluation can directly quantify the performance improvement effect after optimization and verify the effectiveness of the optimization measures.

[0021] In summary, due to the adoption of the above technical solutions, the present application has the following advantages: The wind turbine tower ring weld fatigue level evaluation method provided by the present application significantly improves the efficiency and accuracy of the wind turbine tower ring weld fatigue level evaluation by constructing a reference model consistent with the tower base material, calibrating key parameters that comprehensively consider macro and micro influences, establishing a standardized evaluation process and precision verification mechanism. It abandons the traditional cumbersome process that relies on physical experiments, achieves rapid evaluation with the help of parameter reuse, significantly shortens the evaluation period, and relies on internationally recognized industry standards to ensure the credibility of the results, solving the core problems of low evaluation efficiency, insufficient accuracy, and lack of unified standards in the prior art, providing scientific and efficient technical support for engineering decision-making. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1is a flow chart of the method.

[0023] Figure 2 is a schematic diagram of S-N curve and fatigue class definition.

[0024] Figure 3 is a flow chart of the calculation of the load scaling factor k.

[0025] Figure 4 is a curve graph of the relationship between the weld fillet and S1.

[0026] Figure 5 is a curve graph of the relationship between the excess height and S1. DETAILED DESCRIPTION

[0027] The present application will be described in detail below with reference to the accompanying drawings.

[0028] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0029] A wind power tower ring weld fatigue class evaluation method, for the butt joint scene of the super large land wind turbine tower cylinder with different thickness plates (the thickness of the cylinder sections is 25mm and 30mm respectively, and the outer diameter of the bottom section is 4500mm), as shown in Figure 1 The method comprises the following steps: Step 1: Reference model construction: two types of reference models are constructed: Smooth non-welded part (material Q345, E=210GPa, v=0.3, known IIW standard fatigue class DC=160MPa), used to calibrate the micro stress concentration coefficient kt; wherein, according to the definition of the weld fatigue class (Detail Category, abbreviated as DC), the DC is the stress range when the stress cycle number on the S-N curve is 2x106, as shown in Figure 2 The present method is based on this to develop the calculation of the weld fatigue class.

[0030] Smooth welded part (only containing weld macro geometry, known IIW standard fatigue class DC=112MPa), used to verify the accuracy.

[0031] Target model construction: Based on the measured profile of the tower drum uneven plate (25mm / 30mm) circumferential weld, a finite element model containing 11 key geometric parameters is established: T1=30mm (thickness of thick cylinder segment), T2=25mm (thickness of thin cylinder segment), bottom segment outer diameter D=4500mm, initial fillet R=1mm, initial remaining height H3=3mm, weld contact area width H5=2mm, etc.; the mesh in the weld toe area is encrypted to 0.05-0.8mm, and the stress fluctuation rate is controlled within 1.5%, meeting the convergence requirements.

[0032] Step 2: An axial tension of 80MPa (corresponding to the load requirement of IIW standard DC=160MPa) is applied to the upper end face of the smooth non-welded model, and the maximum principal stress S1=99.8MPa is solved by static analysis.

[0033] S1 is introduced into the fatigue simulation module, and the load scaling coefficient k is initially set to 1. According to the Miner linear damage accumulation rule (D=Σ(n_i / N_i(k))=1, n_i=2×10^6 cycles), the load scaling coefficient k is iterated: when the fatigue life reaches 2×10^6 cycles, as shown in Figure 3 , k=1.002 is obtained; combined with the known DC=160MPa, the micro stress concentration coefficient kt is finally derived to be 1.258 (reflecting the stress concentration effect of micro defects such as material grain boundaries and inclusions) through the formula "DC=load value×2×k / kt".

[0034] Step 3: An axial tension of 100MPa is applied to the upper end face of the smooth welded model, and S1=112.3MPa is obtained by repeating static analysis; k value is iterated in the fatigue module: when the fatigue life is 2×10^6 times, k=0.565.

[0035] According to the formula "DC=load value×2×k", the evaluation DC of the model is calculated to be 113MPa; compared with the IIW standard DC=112MPa, the deviation is only +0.9%, meeting the A-level tolerance requirement (±5%) of BS7608:2014, proving that the method is accurate and reliable.

[0036] Step 4: An axial tension of 100MPa is applied to the target model, and S1=142.5MPa is obtained by static analysis; kt is 1.258, which is calibrated in step 2, and is corrected to 1.798 (comprehensive influence of micro defects and macro geometry) combined with the stress concentration effect of macro geometry of the weld; k=0.46 is iterated in the fatigue module, and the initial fatigue grade DC of the target model is calculated to be 92MPa according to the formula "DC=100×2×0.46".

[0037] Step 5: Analysis of the influence of the shape parameters on S1: The influence of the fillet R: As shown in the figure, adjust R in the range of 0.5mm-1.5mm, and record the corresponding S1: when R=0.5mm, S1=123MPa; when R=1.0mm, S1=108MPa; when R=1.5mm, S1=104MPa, with a decrease of 15% (the fitting function is y=12.737x²-46.088x+143.64, R²=0.9978, with excellent fitting degree). Figure 4 The influence of the remaining height H3: As shown in the figure, adjust H3 in the range of 1.5mm-3.0mm, when H3=3.0mm, S1=115MPa; when H3=2.0mm, S1=110MPa; when H3=1.56mm, S1 reaches the minimum value of 108.85MPa (with the weakest stress concentration effect).

[0038] Figure 5 Select the optimal shape parameter combination: R=1.5mm, H3=1.56mm, and substitute it into the target model to recalculate; apply an axial tension of 50MPa, and obtain S1=103.5MPa through statics solution; through fatigue iteration, k=1.0 (fatigue life of 2.01x10^6 times), according to the formula "DC=50x2x1.0", the optimized fatigue grade DC=100MPa, which is 8.8% higher than the initial grade.

[0039] In this embodiment, the fatigue grade evaluation time of a single sample is shortened from 7 days in traditional experiments to 1 day, and the deviation of the optimized grade evaluation is 0.8% (which meets the A-level tolerance of BS7608:2014). The optimal shape parameters (R=1.5mm, H3=1.56mm) can be directly adapted to the SAW (submerged arc welding) and GMAW (gas metal arc welding) processes in the manufacturing of the tower, without the need to adjust the welding equipment parameters. After optimization, the fatigue grade of the weld is improved by 8.8%, which is expected to reduce the probability of weld cracking maintenance during the service of the tower by more than 30%, and reduce the life cycle cost of the wind power project by about 12%.

[0040]

[0041] ​​The above merely describes preferred embodiments of the present application and is not intended to limit the present application. The present application extends to any novel features or any new combinations disclosed in the specification and any modifications, equivalent replacements and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application. It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the details of the technical features not disclosed in the embodiments, such as specific structures, can be obtained from the prior art. The connection mode can be fixed connection, detachable connection or integral; it can be fixed connection, movable connection or hinged connection, and it can be directly connected or indirectly connected through an intermediate medium. Those skilled in the art can understand the specific mode of the above terms in the embodiments of the present application according to the specific circumstances, and the embodiments of the present disclosure do not specifically limit the above terms.

Claims

1. A method for evaluating the fatigue level of circumferential welds in wind turbine towers, characterized in that: Includes the following steps: Step 1: Construct reference models for smooth non-welded parts and smooth welded parts with known IIW standard fatigue levels, and construct a parametric finite element model of the target wind turbine tower circumferential weld. Step 2: Calibrate the micro-stress concentration factor kt based on the smooth non-welded component model; Step 3: Verify the accuracy of the method using a smooth welded part model to ensure that the evaluation results meet the preset industry standard tolerance requirements; Step 4: Use the kt parameters calibrated in Step 2 to evaluate the fatigue level of the target model.

2. The method as described in claim 1, characterized in that, The material of the reference model mentioned in step 1 is the same as that of the wind turbine tower substrate, and the elastic modulus E and Poisson's ratio ν of the reference model are set as the standard physical parameters of the corresponding substrate; the IIW standard fatigue level DC of the smooth non-welded part model and the smooth welded part model are both preset known values.

3. The method as described in claim 1, characterized in that, The process of constructing the parametric finite element model of the target wind turbine tower circumferential weld in step 1 includes: Step 1.a. Based on the measured morphology of the circumferential weld of the target wind turbine tower, determine the key geometric parameters of the model; Step 1.b: Refine the mesh in the weld toe area of ​​the model; Step 1.c: Control the mesh size so that the stress fluctuation rate of the model is less than the preset threshold.

4. The method as described in claim 1, characterized in that, The calibration process for the micro-stress concentration factor kt in step 2 includes: Step 2.a: Apply an axial tensile force to the smooth, non-welded part model, corresponding to the known IIW standard fatigue grade DC of the model; Step 2.b: Obtain the maximum principal stress S1 of the smooth non-welded part model through static calculations; Step 2.c: Substitute S1 into the fatigue simulation software and iteratively solve the load scaling factor k according to Miner's linear damage accumulation rule (the formula is D=Σ(n_i / N_i(k))=1, where n_i is the preset number of fatigue cycles); Step 2.d: Using the known DC value of the smooth non-welded part model, the micro-stress concentration factor kt is derived in reverse.

5. The method as described in claim 1, characterized in that, Step 3, the verification process for method accuracy, includes: Step 3.a: Apply a preset axial tensile force to the smooth welded part model; Step 3.b: Repeat the static calculation to obtain the maximum principal stress S1 and the fatigue iteration to solve for the load scaling factor k; Step 3.c: Calculate the fatigue rating DC of the smooth welded part model according to the formula DC = load value × 2 × k; Step 3.d: Compare the assessed fatigue grade DC with the known IIW standard fatigue grade DC of the smooth welded part model to verify whether the deviation meets the tolerance requirements.

6. The method as described in claim 5, characterized in that, The preset industry standards mentioned in step 3 include the International Institute of Welding (IIW) standard and the BS7608:2014 standard, and the deviation of the evaluation results must be controlled within the corresponding tolerance range specified in the above industry standards.

7. The method as described in claim 1, characterized in that, Step 4, the evaluation process for the fatigue level of the target model, includes: Step 4.a: Apply a preset axial tensile force to the weld model to be evaluated; Step 4.b: Obtain the maximum principal stress S1 of the target model through static calculations; Step 4.c: Reuse the kt parameters calibrated in Step 2, which integrate the effects of macroscopic stress concentration and microscopic defects, and iteratively solve for the load scaling factor k; Step 4.d: Calculate the fatigue level of the target model using the formula DC = load value × 2 × k.

8. The method as described in claim 1, characterized in that, It also includes the following steps: Step 5: Based on the evaluation results of Step 4, analyze the influence of weld morphology parameters on fatigue level, and then complete the weld morphology optimization.

9. The method as described in claim 8, characterized in that, Step 5, the analysis of the influence of weld morphology parameters on fatigue grade, includes: Step 5.a: Select the fillet radius R and reinforcement height H3 from the weld morphology parameters as key analysis parameters; Step 5.b: Change the value of the fillet radius R within the preset range, record the maximum principal stress S1 corresponding to each value, and analyze the correlation between R and S1. Step 5.c: Change the value of the excess height H3 within the preset range, record the maximum principal stress S1 corresponding to each value, and determine the value of H3 that makes S1 reach its minimum value.

10. The method as described in claim 8 or 9, characterized in that, The implementation process of weld morphology optimization in step 5 includes: Step 5.d: Based on the obtained correlation between R and S1, and H3 and S1, select the combination of fillet radius R and excess height H3 that minimizes the maximum principal stress S1 as the optimal morphology parameters. Step 5.e. Substitute the optimal morphology parameters into the target model and re-execute the fatigue level assessment in step 4 to obtain the fatigue level of the optimized target model.

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