Friction stir welding numerical simulation predefined stress field method

Abstract

The invention discloses a friction stir welding numerical simulation predefined stress field method, and relates to the technical field of friction stir welding simulation. The technical problems that in existing numerical simulation work for temperature fields, stress fields and plastic deformation behaviors in the friction stir welding process in the prior art, multi-process residual stress is effectively transmitted, model adaptability and consistency are insufficient, and stress field superposition, optimization and regulation are difficult are solved. According to the technical scheme, the method comprises the steps that a welding plate model, a stirring head model and an Euler space model are established in computer-aided simulation software; calculating a quenching residual stress field in the Euler space model; the quenching residual stress field is guided into a friction stir welding simulation model; the pressing, preheating, welding, moving-out and cooling processes of the stirring head are simulated; in the cooling process, complete distribution of a post-welding stress field is obtained. The method is suitable for being applied to numerical simulation work of a temperature field, a stress field and a plastic deformation behavior in the friction stir welding process.

Description

Technical Field

[0001] The invention relates to the technical field of friction stir welding simulation, and in particular to a method for predefining a stress field of friction stir welding based on a CEL method. Background Art

[0002] Friction stir welding (FSW) is an important solid-state welding technology that achieves material connection under heating and plastic flow conditions through the interaction between the rotating stirring head and the weldment. Compared with traditional fusion welding technology, friction stir welding has the advantages of low heat input, small residual stress, and high joint strength. It can effectively avoid defects caused by melting and solidification during welding, such as pores and thermal cracks. Especially for high-strength aluminum alloy materials, such as 2195 aluminum alloy, friction stir welding is widely used in the aerospace field.

[0003] At present, significant progress has been made in the numerical simulation of temperature field, stress field and plastic deformation behavior during friction stir welding. The traditional finite element method (FEM) is widely used to simulate the temperature field and stress field of friction stir welding, which can better reveal the evolution law of thermo-mechanical behavior during welding. For example:

[0004] Research based on the Lagrange method: CN108304657 discloses a multi-process residual stress modeling method for key parts of aerospace machine tools. This method uses the traditional Lagrange method to simulate the superposition of residual stresses between processes, but due to its limited ability to handle large deformation behaviors, it is difficult to accurately describe the complex plastic flow behavior during stir friction welding.

[0005] Research based on the Euler method: In the simulation of welding process for high-temperature alloy materials, the Euler method has gained attention because it can handle large displacement and complex contact problems of materials. However, the Euler method is limited in its expression of the initial stress state of the material and cannot fully consider the influence of residual stress before welding on the welding process.

[0006] In recent years, the Coupled Eulerian-Lagrangian (CEL) method has been gradually applied to the simulation of complex welding processes because it has the advantages of both the Lagrangian method and the Euler method. The CEL method can more accurately describe the large deformation and contact problems of materials during stir friction welding, and is considered to be a potential tool for solving the numerical simulation of complex welding processes. However, existing research based on the CEL method mainly focuses on the calculation of stress and temperature fields during welding, ignoring the residual stress state of the weldment before welding. In practical applications in the aerospace field, weldments often undergo multiple processing steps, and the initial residual stress is significant, and its influence on the performance of stir friction welding joints cannot be ignored.

[0007] For example, CN116090306A proposed a finite element modeling method for stress and deformation under multi-process coupling, which realized multi-process simulation under the same modeling framework. However, due to the significant difference between the CEL modeling method and the traditional finite element method, the existing technology cannot introduce the residual stress field before welding into the CEL friction stir welding simulation, resulting in a deviation between the numerical simulation of the welding process and the actual working conditions.

[0008] In summary, the existing technology still has deficiencies in the following aspects:

[0009] Effective transfer of residual stress in multiple processes: Existing methods make it difficult to predefine and transfer the residual stress field before welding in the CEL method, which limits the accurate simulation of stress evolution throughout the welding process.

[0010] Insufficient model adaptability and consistency: It is difficult for existing technologies to unify the model types and solution methods for quenching and stir friction welding simulation, resulting in inconsistency of models between processes.

[0011] Difficulty in stress field superposition and optimization control: Lack of comprehensive research on the interaction between residual stress before welding and stress field during welding makes it difficult to provide an effective basis for the optimization and control of welding process.

[0012] Therefore, a new method is urgently needed to realize the pre-definition and transfer of the residual stress field before welding in the CEL method, so as to accurately simulate the stress evolution behavior during friction stir welding. Summary of the invention

[0013] In order to solve the technical problems existing in the prior art, in the existing numerical simulation work of temperature field, stress field and plastic deformation behavior in the process of friction stir welding, there are effective transmission of residual stress in multiple processes, insufficient model adaptability and consistency, and difficulty in superposition and optimization control of stress fields, the technical solution provided by the present invention is:

[0014] A method for numerical simulation of predefined stress field in friction stir welding, comprising:

[0015] Steps for establishing welding plate model, stirring head model and Euler space model in computer-aided simulation software;

[0016] In the Euler space model, a step of calculating the quenching residual stress field;

[0017] The step of introducing the quenching residual stress field into a friction stir welding simulation model;

[0018] Steps to simulate the stirring head pressing, preheating, welding, removal and cooling process;

[0019] During the cooling process, a complete distribution of the stress field after welding is obtained.

[0020] Furthermore, a preferred embodiment is provided, wherein the welding plate model and the stirring head model are three-dimensional deformable body models, the Euler space model is a three-dimensional Euler body model, and the Euler space model is meshed.

[0021] Furthermore, a preferred embodiment is provided, which uses the birth-death unit method, retains units consistent with the size of the weld plate model to simulate the quenching residual stress, assigns material physical properties and sets the initial temperature field and thermal boundary conditions, and calculates the quenching residual stress field.

[0022] Furthermore, a preferred embodiment is provided, which also includes the steps of matching the discrete fields of the weld plate model and the Euler space model through the volume fraction tool of Abaqus, and assigning values ​​in the predefined field.

[0023] Furthermore, a preferred embodiment is provided, which simulates the processes of pressing down, preheating, welding, removing and cooling the stirring head by setting material properties, contact properties and load boundary conditions for the welding plate model and the stirring head model.

[0024] Furthermore, a preferred embodiment is provided, in which the complete distribution of the post-welding stress field is obtained by setting the initial temperature field to room temperature and defining fixed boundary conditions.

[0025] Based on the same inventive concept, the present invention also provides a device for numerical simulation of friction stir welding with a predefined stress field, comprising:

[0026] Modules for establishing welding plate model, stirring head model and Euler space model in computer-aided simulation software;

[0027] In the Euler space model, a module for calculating the quenching residual stress field;

[0028] A module for importing the quenching residual stress field into a friction stir welding simulation model;

[0029] Modules for simulating the stirring head pressing, preheating, welding, removal and cooling processes;

[0030] Module that obtains the complete distribution of the stress field after welding during the cooling process.

[0031] Based on the same inventive concept, the present invention also provides a computer storage medium for storing a computer program. When the computer program is read by a computer, the computer executes the described method.

[0032] Based on the same inventive concept, the present invention also provides a computer, including a processor and a storage medium. When the processor reads a computer program stored in the storage medium, the computer executes the method described.

[0033] Based on the same inventive concept, the present invention also provides a computer program product, which is a computer program. When the computer program is executed, the method described above is implemented.

[0034] Compared with the prior art, the technical solution provided by the present invention is beneficial in that:

[0035] The CEL method combined with the birth-death unit method effectively eliminates the influence of redundant units in the numerical simulation of the quenching process, and realizes the accurate transmission of the residual stress field after quenching. Compared with the existing multi-process continuous modeling method that cannot distinguish the stress field error caused by invalid units, this solution ensures the one-to-one correspondence between the weld plate model and the Euler model unit, greatly improving the simulation accuracy.

[0036] By establishing a unified model including welding plate, stirring head and Euler space in ABAQUS, the problem of inconsistent model types and solution methods in different processes is solved. Compared with the traditional finite element method of separate modeling, this solution connects the quenching and stir friction welding processes through a unified model framework, which significantly improves the consistency and computational efficiency of multi-process simulation.

[0037] By introducing the predefined stress field and volume fraction tool, the quenching residual stress field is introduced into the CEL method friction stir welding simulation, realizing the accurate transfer of residual stress between processes. The influence of pre-welding stress is often ignored in existing studies, but this scheme uses an effective stress field superposition method to make the simulation of the welding process closer to the actual working conditions, thereby improving the credibility of the simulation results.

[0038] By setting up local encrypted grids and the Johnson-Cook constitutive model, this scheme accurately describes the thermo-mechanical behavior during welding. Compared with the common grid division method in existing research, the high-precision modeling of this scheme ensures that the interaction between the stirring head movement, the plastic flow of the weld plate and the heat input is carefully characterized, which improves the guiding value of the simulation data for the optimization of the welding process.

[0039] Combining the advantages of the CEL method in dealing with large deformation and complex contact problems, this scheme successfully realizes the transfer and redistribution of the quenching residual stress field during the welding process. Compared with the simplified assumptions on the influence of residual stress in traditional methods, this scheme provides effective support for the design and performance prediction of high-performance welded structures through accurate calculation of the entire process of stress evolution.

[0040] It is suitable for numerical simulation of temperature field, stress field and plastic deformation behavior in the process of friction stir welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the aluminum alloy welding process model;

[0042] Figure 2 Deactivate the model element schematic for the birth-death element method;

[0043] Figure 3 Schematic diagram of residual stress in quenching simulation;

[0044] Figure 4 Assemble the schematic diagram for the model;

[0045] Figure 5 It is a schematic diagram of the overall stress field during the downward pressure stage of the mixing head;

[0046] Figure 6 Schematic diagram of the overall residual stress field after welding;

[0047] Figure 7 Flowchart of a method for pre-defining stress fields in numerical simulation of friction stir welding. DETAILED DESCRIPTION

[0048] In order to make the advantages and benefits of the technical solution provided by the present invention more clearly reflected, the technical solution provided by the present invention is now further described in detail in conjunction with the accompanying drawings, specifically:

[0049] Embodiment 1: This embodiment provides a method for numerically simulating a predefined stress field of friction stir welding, including:

[0050] Steps for establishing welding plate model, stirring head model and Euler space model in computer-aided simulation software;

[0051] In the Euler space model, a step of calculating the quenching residual stress field;

[0052] The step of introducing the quenching residual stress field into a friction stir welding simulation model;

[0053] Steps to simulate the stirring head pressing, preheating, welding, removal and cooling process;

[0054] During the cooling process, a complete distribution of the stress field after welding is obtained.

[0055] Implementation method 2. This implementation method is a further limitation of the method for predefining stress field of stir friction welding numerical simulation provided in implementation method 1. The welding plate model and stirring head model are three-dimensional deformable body models, and the Euler space model is a three-dimensional Euler body model. The Euler space model is meshed.

[0056] Specific, combined Figure 7 , the solution provided in this embodiment includes:

[0057] Step 1: Build an initial model

[0058] An initial model including welding plate, stirring head and Euler space was established in ABAQUS to provide a unified geometric framework for subsequent simulation.

[0059] Detailed description: In the ABAQUS modeling module, three models are established: welding plate model, stirring head model and Euler space model. The welding plate model and stirring head model select the three-dimensional deformable body type, and the Euler space model selects the three-dimensional Euler body type. The size of the Euler space model is designed to be consistent with the length and width of the welding plate model, and the thickness direction is higher than the welding plate model to simulate the flow extrusion behavior of the welding plate material, and the area with the same thickness as the welding plate model is pre-divided in the Euler space model. The model is meshed, and the center position of the weld of the Euler space model needs to be locally encrypted to improve the calculation accuracy. The welding plate model and stirring head model use standard meshing rules to ensure that the mesh density is sufficient to reflect the material properties and welding behavior.

[0060] Step 2: Quenching process simulation

[0061] The redundant elements in the Euler space model are processed by the birth-death element method, and the residual stress field of the weld plate during quenching is calculated.

[0062] Detailed description: Based on the Euler space model established in the first step, its model type is changed from a three-dimensional Euler body to a three-dimensional deformable body, and material properties are assigned, including density, specific heat capacity, thermal conductivity, elastic modulus, plasticity, thermal expansion coefficient, and Poisson's ratio. Use the assembly module to create an Euler space model instance and establish a quenching analysis step. Set the thermal boundary conditions for quenching, including an ambient temperature of 20°C and heat transfer coefficients on different surfaces. Through the birth and death unit method, the regional units outside the weld plate in the Euler space model are inactive, and only the units with the same size as the weld plate model are retained for calculation. When defining the initial temperature field, the initial temperature of the activated unit is set to 515°C, and the unit type is C3D8T eight-node thermally coupled hexahedral unit. Finally, through quenching simulation, the quenching residual stress field is calculated and obtained.

[0063] Step 3: Establishing Friction Stir Welding Analysis Model

[0064] The Euler space model and the weld plate model are integrated in ABAQUS to form a complete friction stir welding analysis model.

[0065] Detailed description: Assemble the welding plate model into the pre-divided area in the Euler space model, and assemble the stirring head model to the starting position of the weld and suspend it above the welding plate model. Assign material properties to the Euler space model and the stirring head model, including density, specific heat capacity, thermal conductivity, elastic modulus, thermal expansion coefficient and Poisson's ratio, and set the Johnson-Cook constitutive model of the material for the welding plate and stirring head models respectively. Define the Euler space model and the stirring head model as instances, and ensure their geometric overlap and alignment in the assembly module, so as to provide an accurate geometric basis for the analysis of friction stir welding.

[0066] Step 4: Set up friction stir welding analysis conditions

[0067] Define the contact properties, thermal boundary conditions, load boundary conditions, and initial field parameters during the friction stir welding process.

[0068] Detailed description: Set the contact properties between the Euler space model and the stirring head model, use a penalty function for tangential contact, use hard contact for normal contact, and apply a rigid body constraint to the stirring head. The thermal boundary conditions include the heat transfer coefficient and thermal radiation coefficient of different surfaces of the Euler space model. The load boundary conditions include the fixed constraint of the welding plate, the downward pressure and moving load of the stirring head, and the rotation speed and welding speed of the stirring head during welding. The discrete field of the Euler space model and the welding plate model is established through the volume fraction tool of Abaqus, and the material assignment of the discrete field is created in the predefined field. At the same time, the quenching residual stress field calculated in the second step is imported to form the initial stress state of stir friction welding.

[0069] Step 5: Friction stir welding simulation calculation

[0070] The CEL method is used to carry out friction stir welding simulation and obtain the evolution results of the welding stress field.

[0071] Detailed description: In the simulation, five analysis steps are established, corresponding to the pressing, preheating, welding, removal and cooling processes of the stirring head. The mesh type is set to EC3D8RT eight-node thermally coupled Euler hexahedron element in the Euler space model. At the beginning of the simulation, the stress state of the welding area includes the pre-applied quenching residual stress and the dynamic stress introduced by the stirring head movement. As the simulation proceeds, the high temperature and severe plastic deformation during the welding process cause the quenching residual stress to be redistributed, and the stress field in the weld and near-weld area gradually evolves to be dominated by the stir friction welding residual stress, while the parent material area still mainly retains the quenching residual stress.

[0072] Step 6: Analyze the residual stress field after welding

[0073] The simulation results of friction stir welding are analyzed to verify the effectiveness of residual stress transfer and the engineering applicability of the simulation.

[0074] Detailed description: Through post-processing analysis, the distribution data of the residual stress field during and after welding are extracted. The results show that the quenching residual stress is successfully transferred to the welding model before welding, and superimposed with the stress field generated during the welding process to form a complete residual stress distribution. The stress in the weld and near-weld area is mainly caused by the stress introduced by stir friction welding, while the stress level in the parent material area is lower than that in the weld area, which is mainly composed of quenching residual stress. By comparing with the existing technology, the significant advantages of this scheme in multi-process stress transfer, consistent modeling and accurate simulation are verified.

[0075] Implementation method three. This implementation method is a further limitation of the method for predefined stress field of stir friction welding numerical simulation provided in implementation method one. It uses the birth and death unit method, retains units with the same size as the weld plate model to simulate the quenching residual stress, assigns physical properties to the material, sets the initial temperature field and thermal boundary conditions, and calculates the quenching residual stress field.

[0076] Implementation method 4: This implementation method further limits the method of predefined stress field for numerical simulation of stir friction welding provided in implementation method 1, and also includes the steps of matching the discrete fields of the weld plate model and the Euler space model through the volume fraction tool of Abaqus, and assigning values ​​in the predefined field.

[0077] Implementation method five. This implementation method is a further limitation of the method for predefined stress field of stir friction welding numerical simulation provided in implementation method one. By setting material properties, contact properties and load boundary conditions for the welding plate model and the stirring head model, the stirring head pressing down, preheating, welding, removal and cooling process are simulated.

[0078] Embodiment 6: This embodiment further limits the method for pre-defining stress field of stir friction welding numerical simulation provided in embodiment 1. By setting the initial temperature field to room temperature and defining fixed boundary conditions, the complete distribution of the stress field after welding is obtained.

[0079] Embodiment 7: This embodiment provides a device for numerical simulation of friction stir welding with a predefined stress field, comprising:

[0080] Modules for establishing welding plate model, stirring head model and Euler space model in computer-aided simulation software;

[0081] In the Euler space model, a module for calculating the quenching residual stress field;

[0082] A module for importing the quenching residual stress field into a friction stir welding simulation model;

[0083] Modules for simulating the stirring head pressing, preheating, welding, removal and cooling processes;

[0084] Module that obtains the complete distribution of the stress field after welding during the cooling process.

[0085] Embodiment 8: This embodiment provides a computer storage medium for storing a computer program. When the computer program is read by a computer, the computer executes the method provided in embodiment 1.

[0086] Embodiment 9: This embodiment provides a computer, including a processor and a storage medium. When the processor reads a computer program stored in the storage medium, the computer executes the method provided in embodiment 1.

[0087] Embodiment 10: This embodiment provides a computer program product, which is a computer program. When the computer program is executed, the method provided in embodiment 1 is implemented.

[0088] Implementation Method XI: Combination Figure 1-6 This embodiment is described in detail by using specific examples to further describe the technical solution provided above. Specifically:

[0089] 1. Establish a model in ABAQUS, including welding plate model, stirring head model and Euler space model.

[0090] (1) Select the type of welding plate model and stirring head model as 3D deformable body, and select the type of Euler space model as 3D Euler body.

[0091] (2) The length and width of the Euler space model are the same as those of the weld plate model, and the thickness is larger than that of the weld plate model to simulate the flow extrusion of the weld plate model material, and the area with the same thickness as the weld plate model is pre-divided.

[0092] (3) The Euler space model and the stirring head model are meshed, and the center position of the weld in the Euler space model needs to be locally encrypted.

[0093] 2. The main process of quenching process simulation is as follows:

[0094] (1) Quenching model selection uses the Euler space model in the model established in the previous step and changes the model type from 3D Euler body to 3D deformable body;

[0095] (2) Assign material properties to the Euler space model. Set physical quantities including density, specific heat capacity, thermal conductivity, elastic modulus, plasticity, thermal expansion coefficient, Poisson's ratio, etc., create a model instance in the assembly module, and establish the analysis steps of the quenching process;

[0096] (3) Set the thermal boundary conditions corresponding to quenching, and use the birth-death unit method to deactivate the regional units outside the weld plate segmented in the Euler space model in the calculation;

[0097] (4) Establish displacement constraints for the Euler space model, define the initial temperature field, and set the unit type to C3D8T eight-node thermally coupled hexahedral unit;

[0098] (5) At this time, the activated part of the Euler space model has the same size as the weld plate model. The Euler space model processed by the birth and death element method is used to perform quenching simulation to obtain the stress field after quenching.

[0099] 3. The main process of CEL friction stir welding simulation is as follows:

[0100] (1) Assign material properties to the Euler space model and the mixing head model established in the first step. The Euler space model needs to set physical quantities including density, specific heat capacity, thermal conductivity, elastic modulus, thermal expansion coefficient, Poisson's ratio, and the Johnson-Cook constitutive model of the material. The mixing head model needs to set material properties except plasticity.

[0101] (2) Create a model instance in the assembly module, assemble the welding plate model into the pre-divided area in the Euler space model, assemble the stirring head model into the pre-pressing position, and establish the analysis step corresponding to the friction stir welding process;

[0102] (3) Set the contact properties of the Euler model and the stirring head model, and apply thermal boundary conditions and load boundary conditions: First, set the contact properties, where the tangential contact uses a penalty function, the normal contact uses hard contact, and a rigid body constraint is applied to the stirring head. The contact type between the stirring head and the welding plate is general contact; then apply thermal boundary conditions, including the heat transfer coefficient and thermal radiation coefficient of the Euler model. Finally, apply load boundary conditions, including the fixation of the welding plate, the downward pressure and movement of the stirring head, and the rotation speed and welding speed of the stirring head during welding.

[0103] (4) Set the mesh type of the Euler space to EC3D8RT:8-node thermally coupled Euler hexahedron unit, establish the discrete fields of the Euler space model and the weld plate model through the volume fraction tool of Abaqus, create the material assignment of the discrete field in the predefined field, and at the same time establish the predefined stress field through the predefined field setting, and import the residual stress field after quenching. Due to the application of the birth and death unit method in the previous step, the units in the Euler space model that overlap with the weld plate model contain all the residual stress data after quenching, and the other units are in a stress-free state, which solves the problem of mismatch between the weldment model and the Euler space model;

[0104] (5) The stir friction welding simulation based on the CEL method was carried out using the model established above, and the stir friction welding stress field results with pre-applied quenching stress were obtained.

[0105] In the specific implementation work:

[0106] Take two 200mm×100mm×16mm butt-welded flat plates as an example; Figure 1 (a) shows the Euler space model, with a size of 200mm×200mm×20mm; (b) is the weld plate model, with a size of 200mm×200mm×16mm, and a centrally divided weld; (c) is the stirring head model. The Euler space model is divided into two parts in the thickness direction. The light-colored part has the same size as the weld plate model, and the dark-colored part is the area pre-set to consider the material outflow in the Euler space. The characteristic lines are divided at the weld to facilitate mesh refinement. (d) and (e) are the mesh models of the Euler space model and the stirring head model, respectively. The Euler space model uses a hexahedral mesh, and the welding position is locally encrypted; the stirring head model uses a tetrahedral mesh with the same size.

[0107] (1) First, the quenching process is simulated: this process uses the Euler space model, and the model type is set to a three-dimensional deformable body; the material properties of the Euler space model select the parameters corresponding to the 2195 aluminum alloy, and set physical quantities including density, specific heat capacity, thermal conductivity, elastic modulus, plasticity, thermal expansion coefficient, Poisson's ratio, etc.; and create a model instance in the assembly module to establish the analysis step of the quenching process; set the thermal boundary conditions corresponding to the quenching, set the ambient temperature to 20°C, and define the heat transfer coefficients of different surfaces; as shown in Figure (2), the birth and death unit method is used in the interaction module. Figure 1 (a) The dark-colored area units are in an inactive state, and the remaining active unit models are consistent with the size of the weld plate model. A three-point displacement constraint is established for the Euler space model, and the initial temperature field is defined. The temperature is set to be uniform and the size is 515°C. The unit type is set to C3D8T eight-node thermally coupled hexahedral unit. Figure 2 The selected units do not participate in the calculation simulation of the quenching process simulation, and the information of this part of the units in the model is retained, so that the model units used in the two processes correspond one to one. Finally, the Euler space model processed by the birth and death unit method is used for quenching simulation, and the quenching residual stress is calculated, such as Figure 3 As shown;

[0108] (2) Then perform friction stir welding simulation: assign material properties of 2195 aluminum alloy to the Euler space model and the stir head model, including physical quantities such as density, specific heat capacity, thermal conductivity, elastic modulus, thermal expansion coefficient, Poisson's ratio, and the Johnson-Cook constitutive model of the material. Then assemble the model, such as Figure 4 As shown, the Euler space model overlaps with the welding plate model, and space is reserved in the thickness for material outflow. The stirring head is assembled to one end of the weld and suspended above the welding plate model.

[0109] (3) The analysis step settings, contact type settings, thermal boundary condition settings, Euler space model and weld plate model discrete field settings, load boundary condition settings, predefined stress field settings, initial temperature field settings and Euler space model mesh type settings are performed in sequence: five analysis steps are established corresponding to the stirring head pressing down-preheating-welding-removal-cooling process of stir friction welding; the contact properties of the Euler model and the stirring head model are set to general contact, in which the tangential contact adopts a penalty function and the normal contact adopts hard contact; the thermal boundary conditions include the heat transfer coefficient and thermal radiation coefficient of different surfaces of the Euler model; the discrete fields of the Euler space model and the weld plate model are established through the volume fraction tool of Abaqus, and the material assignment of the discrete field is created in the predefined field; the load boundary conditions include the fixation of the weld plate, the pressing down and removal of the stirring head, and the rotation speed and welding speed of the stirring head during welding; a predefined stress field is established in the predefined field setting, and the residual stress field after quenching is imported, and the overall temperature is predefined as room temperature 20℃; the mesh type of the Euler space is set to EC3D8RT. Due to the application of the birth-and-death unit method in the previous step, the units overlapping with the weld plate model in the Euler space model now contain all the residual stress data after quenching, and the other units are in a stress-free state, which solves the problem of mismatch between the weldment model and the Euler space model. The stir friction welding simulation based on the CEL method was performed using the above established model to obtain the stir friction welding stress field results with pre-applied quenching stress.

[0110] (4) At the beginning of the friction stir welding process simulation, Figure 5 is the stress field of the overall model during the downward pressure stage of the mixing head, Figure 5 (a) It can be seen that the quenching residual stress is transferred to the initial state of the model of the welding process, and the residual stress exists only in the units of the Euler space model that overlap with the weld plate model, that is, the base material area. Figure 5 (b) It can be seen that after removing the grid without material filling, the stress generated by the downward pressure of the stirring head and the quenching residual stress exist simultaneously.

[0111] (5) After the friction stir welding process simulation is completed, Figure 6 This is the overall residual stress field after welding. It can be seen that the quenching residual stress and the residual stress of the stir friction welding process exist at the same time; the weld and near-seam area are dominated by stir friction welding residual stress, and the original quenching residual stress re-evolves under the influence of high temperature and severe plastic deformation; the parent material area is still dominated by quenching residual stress, and the stress level is lower than that of welding residual stress; the transfer of quenching residual stress from the three-dimensional deformed body model to the stir friction welding simulation of the Euler body model is realized.

[0112] The technical solution provided by the present invention is further described in detail above through several specific implementation modes in order to highlight the advantages and benefits of the technical solution provided by the present invention. However, the several specific implementation modes described above are not intended to be used as limitations on the present invention. Any reasonable modification and improvement of the present invention, combination of implementation modes and equivalent substitution within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for numerical simulation of predefined stress field in friction stir welding, characterized in that: include: Steps for establishing welding plate model, stirring head model and Euler space model in computer-aided simulation software; In the Euler space model, a step of calculating the quenching residual stress field; The step of introducing the quenching residual stress field into a friction stir welding simulation model; Steps to simulate the stirring head pressing, preheating, welding, removal and cooling process; During the cooling process, a complete distribution of the stress field after welding is obtained.

2. A method for predefined stress field of friction stir welding numerical simulation according to claim 1, characterized in that: The welding plate model and the stirring head model are three-dimensional deformable body models, the Euler space model is a three-dimensional Euler body model, and the Euler space model is meshed.

3. A method for predefined stress field of friction stir welding numerical simulation according to claim 1, characterized in that: Using the birth-and-death unit method, the units with the same size as the weld plate model are retained to simulate the quenching residual stress. The physical properties of the material are given, the initial temperature field and thermal boundary conditions are set, and the quenching residual stress field is calculated.

4. A method for predefining stress field for numerical simulation of friction stir welding according to claim 1, characterized in that: It also includes the steps of matching the discrete fields of the weld plate model and the Euler space model through the volume fraction tool of Abaqus and assigning values ​​in the predefined fields.

5. The method for predefining stress field for numerical simulation of friction stir welding according to claim 1, characterized in that: By setting material properties, contact properties, and load boundary conditions for the welding plate model and the stirring head model, the stirring head pressing, preheating, welding, removal, and cooling processes are simulated.

6. A method for predefining stress fields for numerical simulation of friction stir welding according to claim 1, characterized in that: By setting the initial temperature field to room temperature and defining fixed boundary conditions, the complete distribution of the stress field after welding is obtained.

7. A device for numerical simulation of predefined stress field of friction stir welding, characterized in that: include: Modules for establishing welding plate model, stirring head model and Euler space model in computer-aided simulation software; In the Euler space model, a module for calculating the quenching residual stress field; A module for importing the quenching residual stress field into a friction stir welding simulation model; Modules for simulating the stirring head pressing, preheating, welding, removal and cooling processes; Module to obtain the complete distribution of the stress field after welding during the cooling process.

8. A computer storage medium for storing a computing program, characterized in that: When the computer program is read by a computer, the computer executes the method of claim 1 .

9. A computer, comprising a processor and a storage medium, characterized in that: When the processor reads the computer program stored in the storage medium, the computer executes the method of claim 1 .

10. A computer program product, being a computer program, characterized in that When the computer program is executed, the method of claim 1 is implemented.

Images