A method and system for predicting fatigue life of critical structure welds

Abstract

The application discloses a kind of critical structure weld fatigue life prediction method and system, it is related to numerical simulation, weld fatigue analysis and other technical fields, the application proposes a new multiscale numerical simulation method: welding macroscopic finite element simulation-phase field simulation-crystal plastic finite element simulation-fatigue life simulation, the multiscale numerical simulation of "macro-micro-macro" is carried out to weld structure, the fatigue performance of weld structure is obtained in the numerical simulation process, then the fatigue life prediction of weld structure is realized in combination with fatigue life simulation analysis method, so that the fatigue life of weld structure can be reliably predicted to provide new method, also provide important guidance for the improvement of fatigue life and the optimization of welding process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of numerical simulation, weld fatigue analysis, and specifically relates to a critical structure weld fatigue life prediction method and system. BACKGROUND

[0002] In the fields of nuclear industry, shipbuilding industry, energy industry, etc., there are a large number of key equipment composed of welded components, and the weld structure therein is directly related to the service stability and reliability of the key equipment, so the fatigue life and reliability thereof need to be evaluated. The fatigue life prediction of the weld structure has always been a difficulty in simulation analysis research, and the acquisition of fatigue performance is one of the core difficulties in current domestic and foreign research. The traditional fatigue life prediction method is usually based on the fatigue performance of the material acquired through fatigue test, and then the fatigue life of the critical structure weld is simulated by using the stress of the service condition, so as to acquire the fatigue life. However, the acquisition of fatigue performance has a high cost, and the fatigue test of the weld structure has a high design difficulty, many variable controls, and is not easy to iterate.

[0003] At present, the acquisition of material fatigue performance through numerical simulation has become one of the research hotspots, but the current method mainly realizes the prediction of fatigue performance by simulating different states of material cracks based on crack initiation and crack propagation, but this method cannot comprehensively consider the influence of microstructure caused by process, nor can it consider the influence of microstructure on mechanical properties. SUMMARY

[0004] In view of the problems that the existing technology of acquiring material fatigue performance through numerical simulation cannot comprehensively consider the influence of microstructure caused by process, nor can it consider the influence of microstructure on mechanical properties, the present application proposes a critical structure weld fatigue life prediction method and system, and a multi-scale numerical simulation method of "macroscopic finite element-phase field simulation-crystal plastic finite element-fatigue life prediction" is proposed, which can comprehensively consider the influence of microstructure caused by process and the influence of microstructure on mechanical properties, and realize reliable prediction of weld fatigue life, thereby providing a reference for improvement of fatigue life and optimization of welding process.

[0005] In one aspect, the present application realizes the following technical solutions:

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

[0007] determining the application object of multi-scale numerical simulation, including the weld form, structural characteristics and service condition of the critical structure;

[0008] acquiring the input data required by multi-scale numerical simulation, including the parameters of welded structure and material, welding process parameters and microstructure characteristics;

[0009] a welding macro finite element analysis step of establishing a welding macro finite element model, simulating and analyzing a welding process, obtaining temperature field distribution data and residual stress distribution data of a weld structure, and extracting a thermal cycle curve of a feature point;

[0010] a field simulation analysis step of establishing a phase field model, importing the thermal cycle curve data to simulate a weld solidification process and a solid phase transformation process, and obtaining crystallographic orientation of a grain and morphology of the grain;

[0011] a crystal plastic finite element analysis step of establishing a crystal plastic finite element model, importing the crystallographic orientation of the grain and the morphology of the grain to simulate a weld structure tension and tension-compression fatigue, obtaining a stress-strain curve of a local microstructure, and thus obtaining fatigue performance of the weld structure;

[0012] a fatigue life simulation analysis step of establishing a fatigue simulation model, importing the fatigue performance data of the weld structure, simulating and calculating a fatigue life, and obtaining the fatigue life of the weld structure.

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

[0014] a process iteration step of performing reliability evaluation on the fatigue life of the weld structure, adjusting the welding process parameters if a requirement is not met, and repeating the welding macro finite element analysis step, the phase field simulation analysis step, the crystal plastic finite element analysis step, and the fatigue life simulation analysis step until a corresponding reliability requirement is met.

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

[0016] a checking step of checking the models established in the welding macro finite element analysis step, the phase field simulation analysis step, the crystal plastic finite element analysis step, and the fatigue life simulation analysis step by using real test data to ensure accuracy and reliability of the models.

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

[0018] a welding numerical simulation method is used to sequentially complete weld structure geometric modeling, material attribute assignment, mesh division, heat source model checking, analysis step setting, contact and boundary condition application, and thus the welding macro finite element model is established.

[0019] The welding macro finite element model is used to simulate and analyze a welding process, and obtain temperature field distribution data and residual stress distribution data of the weld structure.

[0020] extracting a thermal cycle curve of a feature point from the temperature field distribution data.

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

[0022] By the phase field method, the system total free energy, the influence of temperature on the interface energy and the volume free energy, the initial microstructure model setting, the formation of the phase field model of the solidification process and the solid state phase transition process are sequentially completed;

[0023] Using the phase field model and the thermal cycle curve data obtained by the macro finite element analysis step, the solidification process and the evolution process of the solid state phase transition of different welding areas of the weld structure are simulated, and the crystallographic orientation of the grain and the morphology of the grain are obtained.

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

[0025] By the crystal plasticity finite element method, the crystal elastic-plastic constitutive model is built, the microstructure numerical information and the hardness data of the welding and surrounding area are inputted, and the crystal plasticity finite element model is built;

[0026] Using the crystal plasticity finite element model, the crystallographic orientation of the grain and the grain morphology obtained by the phase field simulation analysis step are inputted, the tensile and tensile-compressive fatigue simulation of the weld structure is carried out, the stress-strain curve of the local microstructure is calculated, and thus the fatigue performance of the weld structure is obtained.

[0027] In some embodiments, the fatigue life simulation analysis step specifically comprises:

[0028] A fatigue life simulation model is established, the residual stress distribution data obtained by the welding macro finite element analysis step is inputted, and the stress state of the weld structure under the service condition is calculated in combination with the service condition;

[0029] The fatigue performance obtained by the crystal plasticity finite element analysis step is inputted, and the fatigue life of the weld structure is simulated and calculated.

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

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

[0032] a welding macro finite element analysis unit for establishing a welding macro finite element model, simulating a welding process, obtaining temperature field distribution data and residual stress distribution data of a weld structure, and extracting a thermal cycle curve of a feature point;

[0033] a phase field simulation unit for establishing a phase field model, importing the thermal cycle curve data to simulate a weld solidification process and a solid phase transformation process, and obtaining crystallographic orientation of a grain and morphology of the grain;

[0034] a crystal plasticity finite element analysis unit for establishing a crystal plasticity finite element model, importing the crystallographic orientation of the grain and the morphology data of the grain to perform a weld structure tension and compression fatigue simulation calculation, obtaining a stress-strain curve of a local microstructure, and thereby obtaining fatigue performance of the weld structure;

[0035] and a fatigue life simulation unit for establishing a fatigue simulation model, importing the fatigue performance data of the weld structure, performing a fatigue life simulation calculation, and obtaining the fatigue life of the weld structure.

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

[0037] a process iteration unit for performing a reliability evaluation on the fatigue life of the weld structure, adjusting the welding process parameters if a requirement is not met, and driving 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 an iterative analysis until a corresponding reliability requirement is met.

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

[0039] a checking unit for checking the models in the welding macro finite element analysis unit, the phase field simulation unit, the crystal plasticity finite element analysis unit, and the fatigue life simulation unit by using real test data to ensure accuracy and reliability of the models.

[0040] The application provides a welded joint fatigue life prediction method and system, and a new multi-scale numerical simulation method: welded joint macro finite element simulation-phase field simulation-crystal plastic finite element simulation-fatigue life simulation, which is used for multi-scale numerical simulation of the welded joint structure in a macro-micro-macro mode, realizes acquisition of fatigue performance of the welded joint structure in the numerical simulation process, realizes fatigue life prediction of the welded joint structure in combination with a fatigue life simulation analysis method, and thus provides a new method for reliable prediction of the fatigue life of the welded joint structure and important guidance for improvement of the fatigue life and optimization of the welding process. BRIEF DESCRIPTION OF DRAWINGS

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

[0042] Figure 1 A welded joint fatigue life prediction method flowchart provided by the embodiments of the application;

[0043] Figure 2 A welded joint fatigue life prediction system principle block diagram provided by the embodiments of the application;

[0044] Figure 3 A welded joint macro finite element model of a pipe butt joint established by the embodiments of the application;

[0045] Figure 4 Temperature field distribution results of the pipe butt joint obtained by the embodiments of the application;

[0046] Figure 5 Residual stress distribution results of the pipe butt joint obtained by the embodiments of the application;

[0047] Figure 6 A thermal cycle curve extracted by the embodiments of the application;

[0048] Figure 7 A phase field simulation result of the pipe butt joint of the embodiments of the application;

[0049] Figure 8 A crystal plastic finite element analysis result of the pipe butt joint of the embodiments of the application; wherein (a) is a true stress-true strain diagram, (b) is plastic work change with cycles, and (c) is plastic work cumulative change with true stress;

[0050] Figure 9 A stress distribution result of the pipe butt joint of the embodiments of the application under a service condition;

[0051] Figure 10 A fatigue life result of the pipe butt joint of the embodiments of the application under the service condition. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the present application clearer, further detailed description of the present application is made below in combination with examples and drawings, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0053] Example 1

[0054] The conventional fatigue life prediction method needs to rely on fatigue test to obtain the fatigue performance of the material, however, the fatigue test has high difficulty, many variable controls and is not easy to iterate compared with the parent material design; the existing technology based on numerical simulation technology to obtain the fatigue performance of the material cannot comprehensively consider the influence of the microstructure caused by the process, and also cannot consider the influence of the microstructure on the mechanical performance, resulting in poor reliability of the prediction result. In view of this, the present embodiment proposes a fatigue life prediction method for critical structure weld.

[0055] As shown in Figure 1 The prediction method proposed by the present embodiment includes the following steps:

[0056] Step 1, determining the application object of multi-scale numerical simulation, specifically including: the form of critical structure weld, structural characteristics and service conditions.

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

[0058] Among them, the welding structure and material parameters include: welding structure size, material performance of the structure to be welded and thermal physical performance, mechanical performance and the like of the material; the welding process parameters include: welding current, voltage, clamping mode and welding speed and the like; the microstructure characteristics include: the initial and post-weld microstructure characteristics obtained by metallography, scanning electron microscopy and the like.

[0059] Step 3, welding macro finite element analysis: establishing a welding macro finite element model, simulating and analyzing the welding process, obtaining the temperature field distribution data and residual stress distribution data of the weld structure, and extracting the thermal cycle curve of the feature points.

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

[0061] Through the welding numerical simulation method, the welding macro finite element model is established by means of ABAQUS or SYSWELD software to sequentially complete the weld structure geometric modeling, material attribute assignment, mesh division, heat source model checking, analysis step setting, contact and boundary condition application.

[0062] A welding macro finite element model is used to simulate the welding process, and temperature field distribution data and residual stress distribution data of the weld structure are obtained.

[0063] A thermal cycle curve of a feature point is extracted from the welding temperature field distribution result; the feature point is selected according to the analysis focus, and the center point of the weld and the heat affected zone is usually selected.

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

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

[0066] Through the phase field method, the system total free energy, the influence of temperature on the interface energy and the volume free energy, and the initial microstructure model are sequentially completed, and the phase field model is formed;

[0067] Using the phase field model, the thermal cycle curve obtained by the welding macro finite element analysis is imported to simulate the weld solidification process and solid state phase transformation process in different welding areas of the weld structure, and the crystallographic orientation of the grain and the morphology of the grain, such as crystal distribution, average grain size, and distribution of different variants, are obtained.

[0068] Step 5, crystal plastic finite element analysis: establish a crystal plastic finite element model, import the phase field simulation analysis results for tensile and tensile-compressive fatigue simulation calculation, and obtain the stress-strain curve of the local microstructure, thereby obtaining the fatigue performance of the weld structure.

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

[0070] Through the crystal plastic finite element method, the crystal elastic-plastic constitutive model is built, the microstructure numerical information, the hardness data of the weld and the surrounding area are sequentially input, and the crystal plastic finite element model is built with the help of ABAQUS;

[0071] Using the built crystal plastic finite element model, the data obtained by the phase field simulation analysis are imported, and the tensile and tensile-compressive fatigue simulation of the weld structure is performed, 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 the crystal plastic finite element analysis, realize the simulation calculation of the fatigue life, and obtain the fatigue life of the weld structure.

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

[0074] Further, the method proposed in this embodiment further comprises:

[0075] Step 7, process iteration: the reliability of the fatigue life is evaluated, and if the requirement is not met, the welding process parameters are adjusted, and steps 3-6 are repeated until the corresponding reliability requirement is met.

[0076] In this step, the fatigue life simulation calculation result is iteratively optimized until the welding process scheme meeting the optimization target is obtained, and finally the optimal welding process parameters are obtained.

[0077] Further, the method proposed in this embodiment further comprises:

[0078] The model established in steps 3-6 is checked through real test data to ensure the accuracy and reliability of the model.

[0079] The method proposed in this embodiment adopts a multi-scale numerical simulation method of "welding macroscopic finite element-phased field simulation-crystal plastic finite element simulation-fatigue life simulation", which comprehensively considers the influence of the process on the microstructure and the influence of the microstructure on the mechanical properties, can effectively realize the fatigue life prediction of the critical structure weld, ensures the prediction accuracy and reliability, and provides a new technical idea for the improvement of the fatigue life and the optimization of the welding process.

[0080] Based on the same technical concept, this embodiment also proposes a critical structure weld fatigue life prediction system, as shown in Figure 2 The prediction system proposed in this embodiment comprises:

[0081] An input unit is configured to determine the application object of the multi-scale numerical simulation and obtain the input data required by the multi-scale numerical simulation. The application object includes the weld form, structure characteristics and service condition of the critical structure; the input data includes the welding structure and material parameters, welding process parameters and microstructure characteristics.

[0082] A welding macroscopic finite element analysis unit is configured to establish a welding macroscopic finite element model, simulate and analyze the welding process, obtain temperature field distribution data and residual stress distribution data of the weld structure, and extract the thermal cycle curve of the feature point.

[0083] a phase field simulation unit, which is configured to establish a phase field model, import thermal cycle curve data to simulate a weld solidification process and a solid phase transformation process, and obtain crystallographic orientation of a grain and a morphology of the grain.

[0084] a crystal plasticity finite element analysis unit, which is configured to establish a crystal plasticity finite element model, import a phase field simulation analysis result to perform tensile and tensile-compressive fatigue simulation calculation, obtain a stress-strain curve of a local microstructure, and thus obtain a fatigue performance of a weld structure.

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

[0086] Further, the system provided in the embodiment further includes:

[0087] a process iteration unit, which is configured to adjust a welding process parameter in a case where fatigue life reliability does not meet a requirement, 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, so as to obtain reliable fatigue life of a weld structure and determine an optimal welding process parameter.

[0088] Further, the system provided in the embodiment further includes:

[0089] a checking unit, which is configured to check models in the welding macro finite element analysis unit, the phase field simulation unit, the crystal plasticity finite element analysis unit, and the fatigue life simulation unit by using real experimental data, so as to ensure accuracy and reliability of the models.

[0090] Embodiment 2

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

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

[0093] S2, obtain the input data required for multi-scale numerical simulation, specifically including three aspects of data: (1) structure and material parameters, including the size of the welded structure, the material grade of the structure to be welded, and the thermal and mechanical properties of the material; (2) welding process parameters, including welding current, voltage, clamping method, welding speed, etc.; (3) microstructure characteristics, which are obtained by metallography, scanning electron microscopy, etc.

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

[0095] S4, phase field simulation analysis. By the phase field method, a phase field model (including a solidification process organization phase field model and a solid state phase transformation process phase field model) is established to simulate the microstructure evolution process of the weld solidification and solid state phase transformation in different welding areas of the welded structure, and the crystallographic orientation of the grain and the morphology of the grain are obtained and imported into the crystal plastic finite element model, as shown in Figure 7 .

[0096] S5, crystal plastic finite element analysis. By the crystal plastic finite element method, a crystal plastic finite element model is built, and tensile and tensile-compressive fatigue simulation is performed using the established model to calculate the stress-strain curve of the local microstructure, thereby obtaining the fatigue performance of the weld structure and importing it into the fatigue life simulation model, as shown in Figure 8 .

[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 condition (as shown in Figure 9 ), combined with the fatigue performance obtained by the crystal plastic finite element analysis, to simulate and calculate the fatigue life of the weld structure, as shown in Figure 10 .

[0098] S7, process iteration. Based on the predicted fatigue life, the welding process is optimized and the above steps are repeated, and the simulation analysis results are iterated until the welding process scheme that meets the optimization target is obtained, and finally the reasonable welding process parameters are output.

[0099] Those skilled in the art will appreciate that embodiments of the application can be readily used as software, hardware, or a combination of software and hardware. In one

[0100] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or a combination thereof. These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. Figure 1 an apparatus to perform the functions specified in the flowchart block or blocks.

[0101] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or a combination thereof. These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. Figure 1 an apparatus to perform the functions specified in the flowchart block or blocks.

[0102] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or a combination thereof. These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. Figure 1 an apparatus to perform the functions specified in the flowchart block or blocks.

[0103] The above detailed description has shown, described, and pointed out the aspects of the application in sufficient detail, that others skilled in the art can follow the present application. It is understood that changes in the above detailed description do not depart from the scope of the application, which is defined by the appended claims, and their equivalents.

Claims

1. A method for predicting fatigue life of a weld in a critical structure, characterized by, The fatigue life prediction method comprises: determining the application object of multi-scale numerical simulation, including the weld form of the critical structure, the structural characteristics and the service conditions thereof; obtaining the input data required by the multi-scale numerical simulation, including the welding structure and material parameters, the welding process parameters and the microstructure characteristics; a welding macro finite element analysis step: establishing a welding macro finite element model, simulating and analyzing the welding process, obtaining the temperature field distribution data and the residual stress distribution data of the weld structure, and extracting the thermal cycle curve of the characteristic point; a field simulation analysis step: establishing a phase field model, importing the thermal cycle curve data to simulate the solidification process and the solid-state phase transformation process of the weld, and obtaining the crystallographic orientation of the grain and the morphology of the grain; a crystal plastic finite element analysis step: establishing a crystal plastic finite element model, importing the crystallographic orientation of the grain and the morphology of the grain to simulate the tensile and tensile-compressive fatigue of the weld structure, obtaining the stress-strain curve of the local microstructure, and thus obtaining the fatigue performance of the weld structure; a fatigue life simulation analysis step: establishing a fatigue simulation model, importing the fatigue performance data of the weld structure, realizing the simulation calculation of the fatigue life, and obtaining the fatigue life of the weld structure.

2. The method of claim 1, wherein, The weld fatigue life prediction method further comprises: a process iteration step: reliability evaluation is performed on the fatigue life of the weld structure, the welding process parameters are adjusted if the requirements are not met, and the welding macro finite element analysis step, the phase field simulation analysis step, the crystal plastic finite element analysis step and the fatigue life simulation analysis step are repeated until the corresponding reliability requirements are met.

3. The method of claim 1, wherein, The weld fatigue life prediction method further comprises: a checking step: the models established in the welding macro finite element analysis step, the phase field simulation analysis step, the crystal plastic finite element analysis step and the fatigue life simulation analysis step are checked through real test data to ensure the accuracy and reliability of the models.

4. The method of predicting the fatigue life of a girth weld according to any one of claims 1 to 3, characterized in that, The welding macro finite element analysis step specifically comprises: a welding numerical simulation method is used to sequentially complete the weld structure geometry modeling, material attribute assignment, mesh division, heat source model checking, analysis step setting, contact and boundary condition application, and thus the welding macro finite element model is established; the welding process is simulated and analyzed by using the welding macro finite element model, and the temperature field distribution data and the residual stress distribution data of the weld structure are obtained; the thermal cycle curve of the characteristic point is extracted from the temperature field distribution data.

5. The method of predicting the fatigue life of a girth weld of any one of claims 1-3, wherein, The phase field simulation analysis step specifically comprises: a phase field method is used to sequentially complete the system total free energy, the influence of temperature on the interface energy and the volume free energy, the initial microstructure model setting, the phase field model of the solidification process and the solid-state phase transformation process is formed; the phase field model is used, and the thermal cycle curve data obtained in the macro finite element analysis step is imported to simulate the solidification process and the evolution process of the solid-state phase transformation of different welding areas of the weld structure, and the crystallographic orientation of the grain and the morphology of the grain are obtained.

6. The method of predicting the fatigue life of a girth weld of any one of claims 1-3, wherein, The crystal plastic finite element analysis step specifically comprises: The crystal plasticity finite element model is built by sequentially completing the crystal elastic-plastic constitutive model building, the microstructure numerical information input, the welding and the surrounding area hardness data input, and the crystal plasticity finite element model building. The crystal plasticity finite element model is used to import the crystallographic orientation and the grain morphology of the grain obtained by the phase field simulation analysis step, to perform the weld structure tension and compression fatigue simulation, to calculate the stress-strain curve of the local microstructure, and to obtain the fatigue performance of the weld structure.

7. A method and system for fatigue life prediction of a girth weld according to any one of claims 1-3, characterized in that, The fatigue life simulation analysis step specifically includes: A fatigue life simulation model is established, the residual stress distribution data obtained by the welding macroscopic finite element analysis step is imported, the stress state of the weld structure under the service condition is calculated in combination with the service condition, and the fatigue life of the weld structure is simulated and calculated. The weld fatigue life prediction system includes:

8. A critical structure weld fatigue life prediction system, characterized by, An input unit is configured to determine the application stack of the multi-scale numerical simulation, including the weld form of the critical structure, the structural characteristics and the service condition, and to obtain the input data required by the multi-scale numerical simulation, including the welding structure and material parameters, the welding process parameters and the microstructure characteristics. A welding macroscopic finite element analysis unit is configured to establish a welding macroscopic finite element model, to simulate and analyze the welding process, to obtain the temperature field distribution data and the residual stress distribution data of the weld structure, and to extract the thermal cycle curve of the feature point. A phase field simulation unit is configured to establish a phase field model, to import the thermal cycle curve data to simulate the weld solidification process and the solid state phase change process, and to obtain the crystallographic orientation and the morphology of the grain. A crystal plasticity finite element analysis unit is configured to establish a crystal plasticity finite element model, to import the crystallographic orientation and the morphology data of the grain to perform the weld structure tension and compression fatigue simulation calculation, to obtain the stress-strain curve of the local microstructure, and to obtain the fatigue performance of the weld structure. A fatigue life simulation unit is configured to establish a fatigue simulation model, to import the fatigue performance data of the weld structure, to realize the fatigue life simulation calculation, and to obtain the fatigue life of the weld structure. The weld fatigue life prediction system further includes:

9. The system for fatigue life prediction of a critical structural weld according to claim 8, wherein, A process iteration unit is configured to perform reliability evaluation on the fatigue life of the weld structure, to adjust the welding process parameters if the requirements are not met, to drive the welding macroscopic 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. The weld fatigue life prediction system further includes:

10. The system for fatigue life prediction of a critical structural weld according to claim 8, wherein, A checking unit is configured to check 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 by using the real test data, to ensure the accuracy and reliability of the models. ​

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