Method and system for predicting fatigue life of weld joint of important structure

Abstract

The invention discloses a critical structure weld fatigue life prediction method and system, relates to the technical fields of numerical simulation, weld fatigue analysis and the like, and provides a novel multi-scale numerical simulation method including welding macroscopic finite element simulation, phase field simulation, crystal plasticity finite element simulation and fatigue life simulation. The weld structure is subjected to macroscopic-microscopic-macroscopic multi-scale numerical simulation, the fatigue performance of the weld structure is obtained in the numerical simulation process, and the fatigue life of the weld structure is predicted in combination with a fatigue life simulation analysis method, so that a new method is provided for reliable prediction of the fatigue life of the weld structure. And important guidance is provided for improvement of fatigue life and optimization of a welding process.

Description

Technical Field

[0001] The present application relates to technical fields such as numerical simulation and weld fatigue analysis, and specifically to a method and system for predicting fatigue life of welds in critical structures. Background Art

[0002] In the fields of nuclear industry, shipbuilding industry, energy industry, etc., there are a large number of key equipment composed of welded components. The weld structure, as a key structure, is directly related to the service stability and reliability of the key equipment. Therefore, it is necessary to evaluate its fatigue life and reliability. The fatigue life prediction of weld structures has always been a difficult point in simulation analysis research, especially the acquisition of fatigue performance is one of the core difficulties in current research at home and abroad. Traditional fatigue life prediction methods are usually based on the fatigue properties of materials obtained by fatigue tests, and then use the stress of the service conditions of the welds of key structures to simulate fatigue life, so as to obtain its fatigue life. However, the cost of obtaining fatigue performance is high, and the fatigue test of weld structures is difficult to design compared with the parent material, with many variables to control and difficult to iterate.

[0003] Currently, obtaining fatigue properties of materials through numerical simulation has become one of the research hotspots, but the current methods are mainly based on crack initiation and crack propagation to simulate different states of material cracks to predict fatigue properties. However, this method cannot comprehensively consider the influence of microstructure caused by the process, nor can it consider the influence of microstructure on mechanical properties. Summary of the invention

[0004] In view of the fact that the existing technology of obtaining the fatigue properties of materials through numerical simulation cannot comprehensively consider the influence of the microstructure caused by the process, nor the influence of the microstructure on the mechanical properties, this application proposes a method and system for predicting the fatigue life of key structural welds. This application proposes a multi-scale numerical simulation method of "macro finite element-phase field simulation-crystal plastic finite element-fatigue life prediction", which can comprehensively consider the influence of the microstructure caused by the process, as well as the influence of the microstructure on the mechanical properties, to achieve reliable prediction of the fatigue life of the weld, and provide a reference for improving the fatigue life and optimizing the welding process.

[0005] On the one hand, the present application is implemented through the following technical solutions:

[0006] A fatigue life prediction method for a weld of a critical structure, the fatigue life prediction method comprising:

[0007] Determine the application objects of multi-scale numerical simulation, including: weld forms, structural characteristics and service conditions of key structures;

[0008] Obtain the input data required for multi-scale numerical simulation, including: welding structure and material parameters, welding process parameters and microstructure characteristics;

[0009] Welding macro finite element analysis steps: establish a welding macro finite element model, simulate and analyze the welding process, obtain the temperature field distribution data and residual stress distribution data of the weld structure, and extract the thermal cycle curve of the characteristic points;

[0010] On-site simulation and analysis steps: establishing a phase field model, importing the thermal cycle curve data to simulate the weld solidification process and solid phase transformation process, and obtaining the crystallographic orientation and morphology of the grains;

[0011] Crystal plasticity finite element analysis step: establishing a crystal plasticity finite element model, importing the crystallographic orientation of the grains and the morphology data of the grains to perform tensile-extension and tensile-compression fatigue simulation calculations of the weld structure, obtaining the stress-strain curve of the local microstructure, and thereby obtaining the fatigue performance of the weld structure;

[0012] Fatigue life simulation analysis step: establishing a fatigue simulation model, importing fatigue performance data of the weld structure, realizing fatigue life simulation calculation, and obtaining the fatigue life of the weld structure.

[0013] In some embodiments, the weld fatigue life prediction method further includes:

[0014] Process iteration step: perform reliability evaluation on the fatigue life of the weld structure, adjust the welding process parameters if the requirements are not met, repeat the welding macro finite element analysis step, phase field simulation analysis step, crystal plasticity finite element analysis step and fatigue life simulation analysis step until the corresponding reliability requirements are met.

[0015] In some embodiments, the weld fatigue life prediction method further includes:

[0016] Verification step: The models established in the welding macroscopic finite element analysis step, the phase field simulation analysis step, the crystal plasticity finite element analysis step and the fatigue life simulation analysis step are verified by real test data to ensure the accuracy and reliability of the models.

[0017] In some embodiments, the welding macro finite element analysis step specifically includes:

[0018] Through the welding numerical simulation method, the weld structure geometric modeling, material property assignment, meshing, heat source model verification, analysis step setting, contact and boundary condition application are completed in sequence, so as to establish the welding macroscopic finite element model;

[0019] Using the welding macro finite element model, the welding process is simulated and analyzed to obtain the temperature field distribution data and residual stress distribution data of the weld structure;

[0020] A thermal cycle curve of characteristic points is extracted from the temperature field distribution data.

[0021] In some embodiments, the phase field simulation analysis step specifically includes:

[0022] Through the phase field method, the total free energy of the system, the influence of temperature on the interface energy and volume free energy, and the initial microstructure model setting are completed in sequence to form a phase field model of the solidification process and the solid phase change process;

[0023] The phase field model is used, and the thermal cycle curve data obtained in the macroscopic finite element analysis step is imported to simulate the solidification process and the evolution process of the solid phase transformation of different welding areas of the weld structure, so as to obtain the crystallographic orientation and morphology of the grains.

[0024] In some embodiments, the crystal plasticity finite element analysis step specifically includes:

[0025] Through the crystal plasticity finite element method, the construction of the crystal elastic-plastic constitutive model, the input of microstructure numerical information, and the hardness data of the welding and surrounding areas are completed in sequence to complete the construction of the crystal plasticity finite element model;

[0026] The crystal plasticity finite element model is used to import the crystallographic orientation and grain morphology of the grains obtained in the phase field simulation analysis step, and the tension-extension and tension-compression fatigue simulations of the weld structure are performed to calculate the stress-strain curve of the local microstructure, thereby obtaining the fatigue performance of the weld structure.

[0027] In some implementations, the fatigue life simulation analysis step specifically includes:

[0028] Establishing a fatigue life simulation model, importing the residual stress distribution data obtained in the welding macroscopic finite element analysis step, and calculating the stress state of the weld structure under the service condition in combination with the service condition;

[0029] The fatigue performance obtained by the crystal plasticity finite element analysis step is introduced, and the fatigue life of the weld structure is obtained by simulation calculation.

[0030] On the other hand, the present application also proposes a critical structure weld fatigue life prediction system, the weld fatigue life prediction system comprising:

[0031] An input unit, the input unit is used to determine the application type of the multi-scale numerical simulation, including: the weld form, structural characteristics and service conditions of the key structure; and obtain the input data required for the multi-scale numerical simulation, including: welding structure and material parameters, welding process parameters and microstructure characteristics;

[0032] A welding macro finite element analysis unit, which is used to establish a welding macro finite element model, perform simulation analysis on the welding process, obtain temperature field distribution data and residual stress distribution data of the weld structure, and extract thermal cycle curves of characteristic points;

[0033] A phase field simulation unit, which is used to establish a phase field model, import the thermal cycle curve data to simulate the weld solidification process and the solid phase change process, and obtain the crystallographic orientation and morphology of the grains;

[0034] A crystal plasticity finite element analysis unit, which is used to establish a crystal plasticity finite element model, import the crystallographic orientation of the grains and the morphology data of the grains to perform tensile-extension and tensile-compression fatigue simulation calculations of the weld structure, obtain the stress-strain curve of the local microstructure, and thereby obtain the fatigue performance of the weld structure;

[0035] And, a fatigue life simulation unit, which is used to establish a fatigue simulation model, import the fatigue performance data of the weld structure, realize the simulation calculation of fatigue life, and obtain the fatigue life of the weld structure.

[0036] In some embodiments, the weld fatigue life prediction system further includes:

[0037] A process iteration unit, wherein the process iteration unit is used to perform reliability evaluation on the fatigue life of the weld structure. If the requirements are not met, the welding process parameters are adjusted to drive the welding macro finite element analysis unit, the phase field simulation analysis unit, the crystal plasticity finite element analysis unit and the fatigue life simulation analysis unit to perform iterative analysis until the corresponding reliability requirements are met.

[0038] In some embodiments, the weld fatigue life prediction system further includes:

[0039] A verification unit is used to verify the models in the welding macroscopic finite element analysis unit, the phase field simulation unit, the crystal plasticity finite element analysis unit and the fatigue life simulation unit using real test data to ensure the accuracy and reliability of the models.

[0040] The present application proposes a method and system for predicting fatigue life of welds in important structures, and proposes a new multi-scale numerical simulation method: welding macroscopic finite element simulation-phase field simulation-crystal plastic finite element simulation-fatigue life simulation, and performs "macro-micro-macro" multi-scale numerical simulation on the weld structure. The numerical simulation process realizes the acquisition of fatigue performance of the weld structure, and then combines the fatigue life simulation analysis method to realize fatigue life prediction of the weld structure, thereby providing a new method for reliable prediction of fatigue life of weld structure, and also provides important guidance for improvement of fatigue life and optimization of welding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the embodiments of the present application, constitute a part of the present application, and do not constitute a limitation on the embodiments of the present application. In the drawings:

[0042] Figure 1 A flow chart of a weld fatigue life prediction method proposed in an embodiment of the present application;

[0043] Figure 2 This is a principle block diagram of the weld fatigue life prediction system proposed in the embodiment of the present application;

[0044] Figure 3 A welding macroscopic finite element model of a pipe butt weld established for an embodiment of the present application;

[0045] Figure 4 The temperature field distribution result of the pipe butt weld obtained in the embodiment of the present application;

[0046] Figure 5 The residual stress distribution result of the pipe butt weld obtained in the embodiment of the present application;

[0047] Figure 6 The thermal cycle curve extracted from the embodiment of the present application;

[0048] Figure 7 The phase field simulation result of the pipe butt weld of the embodiment of the present application;

[0049] Figure 8 The crystal plastic finite element analysis results of the pipe butt weld of the embodiment of the present application; wherein (a) is the true stress-true strain diagram, (b) is the change of plastic work with cycle, and (c) is the cumulative change of plastic work with true stress;

[0050] Fig. 9 The stress distribution result of the pipe butt weld in the embodiment of the present application under the service condition is obtained;

[0051] Fig.10 This is the fatigue life result of the pipe butt weld of the embodiment of the present application obtained under service conditions. DETAILED DESCRIPTION

[0052] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with examples and drawings. The illustrative implementation scheme of the present application and its description are only used to explain the present application and are not intended to limit the present application.

[0053] Example 1

[0054] Traditional fatigue life prediction methods rely on fatigue tests to obtain the fatigue properties of materials. However, fatigue tests are more difficult to design than parent materials, have more variables to control, and are not easy to iterate. Existing technologies based on numerical simulation technology to obtain fatigue properties of materials cannot comprehensively consider the impact of microstructures caused by processes, nor can they consider the impact of microstructures on mechanical properties, resulting in poor reliability of prediction results. In response to this, this embodiment proposes a fatigue life prediction method for critical structure welds.

[0055] like Figure 1 As shown, the prediction method proposed in this embodiment includes the following steps:

[0056] Step 1: Determine the application objects of multi-scale numerical simulation, including: weld forms, structural characteristics and service conditions of key structures.

[0057] Step 2: Obtain the input data required for multi-scale numerical simulation, including: welding structure and material parameters, welding process parameters and microstructure characteristics.

[0058] Among them, welding structure and material parameters include: welding structure size, material properties of the structure to be welded, and thermal physical properties and mechanical properties of the material; welding process parameters include: welding current, voltage, clamping method and welding speed; microstructure characteristics include: obtaining initial and post-welding microstructure characteristics through metallographic, scanning electron microscopy and other methods.

[0059] Step 3, welding macro finite element analysis: establish a welding macro finite element model, simulate and analyze the welding process, obtain the temperature field distribution data and residual stress distribution data of the weld structure, and extract the thermal cycle curve of the characteristic points.

[0060] In this step, the welding macro finite element analysis process specifically includes:

[0061] Through the welding numerical simulation method, with the help of ABAQUS or SYSWELD software, the weld structure geometric modeling, material property assignment, meshing, heat source model verification, analysis step setting, contact and boundary condition application are completed in sequence, so as to establish a welding macro finite element model;

[0062] Use the welding macro finite element model to simulate and analyze the welding process and obtain the temperature field distribution data and residual stress distribution data of the weld structure;

[0063] The thermal cycle curve of the characteristic points is extracted from the welding temperature field distribution results; wherein the characteristic points are selected according to the focus of the analysis, usually the center points of the weld and the heat affected zone are selected.

[0064] Step 4, phase field simulation analysis: Establish a phase field model, import thermal cycle curve data to simulate the weld solidification process and solid phase transformation process, and obtain the crystallographic orientation and morphology of the grains.

[0065] In this step, the phase field simulation analysis process specifically includes:

[0066] Through the phase field method, the total free energy of the system, the influence of temperature on the interface energy and volume free energy, the initial microstructure model and other settings are completed in sequence to form a phase field model;

[0067] By using the phase field model and importing the thermal cycle curve obtained from the welding macroscopic finite element analysis, the weld solidification process and solid-state phase transformation process of different welding areas of the weld structure are simulated to obtain the crystallographic orientation and morphology of the grains, such as crystal distribution, average grain size, and distribution of different variants.

[0068] Step 5, crystal plasticity finite element analysis: establish a crystal plasticity finite element model, import the phase field simulation analysis results to perform tension-extension and tension-compression fatigue simulation calculations, obtain the stress-strain curve of the local microstructure, and thus obtain the fatigue performance of the weld structure.

[0069] In this step, the crystal plasticity finite element analysis process specifically includes:

[0070] Through the crystal plasticity finite element method, the construction of the crystal elastic-plastic constitutive model, the microstructure numerical information, the hardness data of the weld and the surrounding area and other structural inputs are completed in sequence, and the crystal plasticity finite element model is built with the help of ABAQUS;

[0071] By using the constructed crystal plasticity finite element model and importing the data obtained from the phase field simulation analysis, the tension-extension and tension-compression fatigue simulations of the weld structure are carried out, and the stress-strain curve of the local microstructure is calculated, thereby obtaining the fatigue performance of the weld structure.

[0072] Step 6, fatigue life simulation analysis: Establish a fatigue simulation model, import the fatigue performance obtained by crystal plasticity finite element analysis, realize the simulation calculation of fatigue life, and obtain the fatigue life of the weld structure.

[0073] In this step, based on the welding residual stress field obtained by the welding macroscopic finite element analysis and combined with the service conditions, the stress state of the weld structure under the service conditions is calculated. Combined with the fatigue performance obtained by the crystal plasticity finite element analysis, a fatigue life simulation model is established through ABAQUS and FE-SAFE software to realize the simulation calculation of fatigue life and obtain the fatigue life of the weld structure.

[0074] Furthermore, the method proposed in this embodiment also includes:

[0075] Step 7, process iteration: Evaluate the reliability of fatigue life. If the requirements are not met, adjust the welding process parameters and repeat steps 3 to 6 until the corresponding reliability requirements are met.

[0076] In this step, iterative optimization is performed according to the fatigue life simulation calculation results until a welding process solution that meets the optimization objectives is obtained, and finally the optimal welding process parameters are obtained.

[0077] Furthermore, the method proposed in this embodiment also includes:

[0078] The models established in steps 3 to 6 are calibrated using real test data to ensure the accuracy and reliability of the models.

[0079] The method proposed in this embodiment adopts a multi-scale numerical simulation method through "welding macroscopic finite element-phase field simulation-crystal plastic finite element simulation-fatigue life simulation". This multi-scale numerical simulation method comprehensively considers the influence of microstructure caused by the process and the influence of microstructure on mechanical properties. It can effectively realize the fatigue life prediction of key structural welds, ensure the prediction accuracy and reliability, and provide a new technical idea for improving fatigue life and optimizing welding process.

[0080] Based on the same technical concept as above, this embodiment also proposes a fatigue life prediction system for key structural welds, such as Figure 2 As shown, the prediction system proposed in this embodiment includes:

[0081] The input unit is used to determine the application object of the multi-scale numerical simulation and obtain the input data required for the multi-scale numerical simulation. The application object includes: the weld form, structural characteristics and service conditions of the key structure; the input data includes: welding structure and material parameters, welding process parameters and microstructure characteristics.

[0082] The welding macro finite element analysis unit is used to establish a welding macro finite element model, simulate and analyze the welding process, obtain the temperature field distribution data and residual stress distribution data of the weld structure, and extract the thermal cycle curve of the characteristic points.

[0083] The phase field simulation unit is used to establish a phase field model, import thermal cycle curve data to simulate the weld solidification process and solid phase change process, and obtain the crystallographic orientation and morphology of the grains.

[0084] The crystal plasticity finite element analysis unit is used to establish a crystal plasticity finite element model, import the phase field simulation analysis results to perform tension-extension and tension-compression fatigue simulation calculations, obtain the stress-strain curve of the local microstructure, and thus obtain the fatigue performance of the weld structure.

[0085] And, a fatigue life simulation unit, which is used to establish a fatigue simulation model, import the fatigue performance obtained by crystal plasticity finite element analysis, realize the simulation calculation of fatigue life, and obtain the fatigue life of the weld structure.

[0086] Furthermore, the system proposed in this embodiment also includes:

[0087] The process iteration unit is used to adjust the welding process parameters when the fatigue life reliability does not meet the requirements, and drive the welding macro finite element analysis unit, the phase field simulation analysis unit, the crystal plasticity finite element analysis unit and the fatigue life simulation analysis unit to perform iterative analysis to obtain a reliable fatigue life of the weld structure and determine the optimal welding process parameters.

[0088] Furthermore, the system proposed in this embodiment also includes:

[0089] A verification unit uses real experimental data to verify the models in the welding macro finite element analysis unit, phase field simulation unit, crystal plasticity finite element analysis unit and fatigue life simulation unit to ensure the accuracy and reliability of the models.

[0090] Example 2

[0091] This embodiment uses the weld fatigue life prediction method or system proposed in the above embodiment 1 to predict the fatigue life of a pipe butt weld structure, wherein the pipe butt weld is welded by two different titanium alloy materials, and its service stability has a significant impact on the entire equipment. Once fatigue failure occurs, it will cause adverse effects. Therefore, it is necessary to complete the weld fatigue life prediction at the beginning of the process design to provide a technical reference for the improvement of the welding process. The specific process is as follows:

[0092] S1, determine the application object of multi-scale numerical simulation. The pipe butt weld is mainly connected by welding two butt pipes. Its service conditions include high temperature and high pressure, and repeated cycles.

[0093] S2, obtain the input data required for multi-scale numerical simulation, which specifically includes three aspects of data: (1) structural and material parameters, including the size of the welding structure, the material grade of the structure to be welded, and the thermal physical properties and mechanical properties of the material; (2) welding process parameters, including welding current, voltage, clamping method, welding speed, etc.; (3) microstructural characteristics, obtain the initial (before welding) and post-weld microstructural characteristics through metallographic, scanning electron microscopy, etc.

[0094] S3, welding macro finite element analysis. Through the welding numerical simulation method, a welding macro finite element model is established. Figure 3 As shown, the welding process is simulated and analyzed to obtain the temperature field distribution data of the weld structure (such as Figure 4 as shown) and residual stress distribution data (as shown Figure 5 ), extract the thermal cycle curve of the characteristic points in the temperature field (as shown in Figure 6 and imported into the phase field model.

[0095] S4, phase field simulation analysis. Through the phase field method, a phase field model (including the phase field model of the solidification process and the phase field model of the solid phase transformation process) is established to simulate the microstructural evolution process of the weld solidification and solid phase transformation in different welding areas of the welding structure, obtain the crystallographic orientation and morphology of the grains and import them into the crystal plasticity finite element model, such as Figure 7 shown.

[0096] S5, crystal plasticity finite element analysis. Through the crystal plasticity finite element method, a crystal plasticity finite element model is built, and the established model is used to perform tension-extension and tension-compression fatigue simulations, and the stress-strain curve of the local microstructure is calculated to obtain the fatigue performance of the weld structure and import it into the fatigue life simulation model, such as Figure 8 shown.

[0097] S6, establish a fatigue life simulation model, import the residual stress distribution data of the welded structure obtained by welding macro finite element analysis, and calculate the stress state of the weld structure under the service conditions in combination with the service conditions (such as Fig. 9 As shown in Figure 2), combined with the fatigue performance obtained by crystal plasticity finite element analysis, the fatigue life of the weld structure is obtained by simulation calculation, as shown in Figure 2. Fig.10 shown.

[0098] S7, process iteration. Based on the predicted fatigue life, the welding process is fed back for optimization, and the above steps are repeated, iterating according to the simulation analysis results until a welding process solution that meets the optimization objectives is obtained, and finally reasonable welding process parameters are output.

[0099] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0100] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0101] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0102] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0103] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only the specific implementation method of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for predicting fatigue life of welds of important structures, characterized in that: The fatigue life prediction method includes: Determine the application objects of multi-scale numerical simulation, including: weld forms, structural characteristics and service conditions of key structures; Obtain the input data required for multi-scale numerical simulation, including: welding structure and material parameters, welding process parameters and microstructure characteristics; Welding macro finite element analysis steps: establish a welding macro finite element model, simulate and analyze the welding process, obtain the temperature field distribution data and residual stress distribution data of the weld structure, and extract the thermal cycle curve of the characteristic points; On-site simulation and analysis steps: establishing a phase field model, importing the thermal cycle curve data to simulate the weld solidification process and solid phase transformation process, and obtaining the crystallographic orientation and morphology of the grains; Crystal plasticity finite element analysis step: establishing a crystal plasticity finite element model, importing the crystallographic orientation of the grains and the morphology data of the grains to perform tensile-extension and tensile-compression fatigue simulation calculations of the weld structure, obtaining the stress-strain curve of the local microstructure, and thereby obtaining the fatigue performance of the weld structure; Fatigue life simulation analysis step: establishing a fatigue simulation model, importing fatigue performance data of the weld structure, realizing fatigue life simulation calculation, and obtaining the fatigue life of the weld structure.

2. A method for predicting fatigue life of a critical structure weld according to claim 1, characterized in that: The weld fatigue life prediction method further includes: Process iteration step: perform reliability evaluation on the fatigue life of the weld structure, adjust the welding process parameters if the requirements are not met, repeat the welding macro finite element analysis step, phase field simulation analysis step, crystal plasticity finite element analysis step and fatigue life simulation analysis step until the corresponding reliability requirements are met.

3. The method for predicting fatigue life of a critical structure weld according to claim 1, characterized in that: The weld fatigue life prediction method further includes: Verification step: The models established in the welding macroscopic finite element analysis step, the phase field simulation analysis step, the crystal plasticity finite element analysis step and the fatigue life simulation analysis step are verified by real test data to ensure the accuracy and reliability of the models.

4. A method for predicting fatigue life of a critical structure weld according to any one of claims 1 to 3, characterized in that: The welding macroscopic finite element analysis steps specifically include: Through the welding numerical simulation method, the weld structure geometric modeling, material property assignment, meshing, heat source model verification, analysis step setting, contact and boundary condition application are completed in sequence, so as to establish the welding macroscopic finite element model; Using the welding macro finite element model, the welding process is simulated and analyzed to obtain the temperature field distribution data and residual stress distribution data of the weld structure; A thermal cycle curve of characteristic points is extracted from the temperature field distribution data.

5. A method for predicting fatigue life of a critical structure weld according to any one of claims 1 to 3, characterized in that: The phase field simulation analysis step specifically includes: Through the phase field method, the total free energy of the system, the influence of temperature on the interface energy and volume free energy, and the initial microstructure model setting are completed in sequence to form a phase field model of the solidification process and the solid phase change process; The phase field model is used, and the thermal cycle curve data obtained in the macroscopic finite element analysis step is imported to simulate the solidification process and the evolution process of the solid phase transformation of different welding areas of the weld structure, so as to obtain the crystallographic orientation and morphology of the grains.

6. A method for predicting fatigue life of a weld of a critical structure according to any one of claims 1 to 3, characterized in that: The crystal plasticity finite element analysis step specifically includes: Through the crystal plasticity finite element method, the construction of the crystal elastic-plastic constitutive model, the input of microstructure numerical information, and the hardness data of the welding and surrounding areas are completed in sequence to complete the construction of the crystal plasticity finite element model; The crystal plasticity finite element model is used to import the crystallographic orientation and grain morphology of the grains obtained in the phase field simulation analysis step, and the tension-extension and tension-compression fatigue simulations of the weld structure are performed to calculate the stress-strain curve of the local microstructure, thereby obtaining the fatigue performance of the weld structure.

7. A method and system for predicting fatigue life of welds of critical structures according to any one of claims 1 to 3, characterized in that: The fatigue life simulation analysis steps specifically include: Establishing a fatigue life simulation model, importing the residual stress distribution data obtained in the welding macroscopic finite element analysis step, and calculating the stress state of the weld structure under the service condition in combination with the service condition; The fatigue performance obtained by the crystal plasticity finite element analysis step is introduced, and the fatigue life of the weld structure is obtained by simulation calculation.

8. A fatigue life prediction system for critical structural welds, characterized in that: The weld fatigue life prediction system comprises: An input unit, the input unit is used to determine the application type of the multi-scale numerical simulation, including: the weld form, structural characteristics and service conditions of the key structure; and obtain the input data required for the multi-scale numerical simulation, including: welding structure and material parameters, welding process parameters and microstructure characteristics; A welding macro finite element analysis unit, which is used to establish a welding macro finite element model, perform simulation analysis on the welding process, obtain temperature field distribution data and residual stress distribution data of the weld structure, and extract thermal cycle curves of characteristic points; A phase field simulation unit, which is used to establish a phase field model, import the thermal cycle curve data to simulate the weld solidification process and the solid phase change process, and obtain the crystallographic orientation and morphology of the grains; A crystal plasticity finite element analysis unit, which is used to establish a crystal plasticity finite element model, import the crystallographic orientation of the grains and the morphology data of the grains to perform tensile-extension and tensile-compression fatigue simulation calculations of the weld structure, obtain the stress-strain curve of the local microstructure, and thereby obtain the fatigue performance of the weld structure; And, a fatigue life simulation unit, which is used to establish a fatigue simulation model, import the fatigue performance data of the weld structure, realize the simulation calculation of fatigue life, and obtain the fatigue life of the weld structure.

9. A system for predicting fatigue life of welds of critical structures according to claim 8, characterized in that: The weld fatigue life prediction system further includes: A process iteration unit, wherein the process iteration unit is used to perform reliability evaluation on the fatigue life of the weld structure. If the requirements are not met, the welding process parameters are adjusted to drive the welding macro finite element analysis unit, the phase field simulation analysis unit, the crystal plasticity finite element analysis unit and the fatigue life simulation analysis unit to perform iterative analysis until the corresponding reliability requirements are met.

10. The system for predicting fatigue life of welds of critical structures according to claim 8, characterized in that: The weld fatigue life prediction system further includes: A verification unit is used to verify the models in the welding macroscopic finite element analysis unit, the phase field simulation unit, the crystal plasticity finite element analysis unit and the fatigue life simulation unit using real test data to ensure the accuracy and reliability of the models.

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