A method for numerical simulation of friction stir welding by predefining stress field

Abstract

The application discloses a pre-defined stress field method for numerical simulation of friction stir welding, and relates to the technical field of friction stir welding simulation. In order to solve the technical problems of the existing numerical simulation of temperature field, stress field and plastic deformation behavior in the process of friction stir welding, such as effective transmission of multi-process residual stress, insufficient model adaptability and consistency, and difficulty in stress field superposition and optimization control, the technical scheme provided by the application is as follows: a welding plate model, a stir head model and an Euler space model are established in computer-aided simulation software; in the Euler space model, a quenching residual stress field is calculated; the quenching residual stress field is introduced into a friction stir welding simulation model; a stir head pressing, preheating, welding, moving-out and cooling process is simulated; and a complete distribution of a post-welding stress field is obtained in the cooling process. The application is suitable for numerical simulation of temperature field, stress field and plastic deformation behavior in the process of friction stir welding.

Description

TECHNICAL FIELD

[0001] The application relates to the field of friction stir welding simulation, in particular to a method for predefining a stress field in friction stir welding based on a CEL method. BACKGROUND

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

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

[0004] Research based on Lagrange method: CN108304657 discloses a multi-process residual stress modeling method for key parts of aerospace machine tools. The 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 behavior, it is difficult to accurately describe the complex plastic flow behavior during the friction stir welding process.

[0005] Research based on Euler method: In the simulation of the welding process of high-temperature alloy materials, the Euler method has attracted attention because it can handle large displacement and complex contact problems of materials. However, the Euler method has limitations in expressing the initial stress state of materials, and cannot fully consider the influence of pre-welding residual stress on the welding process.

[0006] In recent years, the coupled Eulerian-Lagrangian (CEL) method has gradually been applied to the simulation of complex welding processes due to its advantages of combining the Lagrange method and the Euler method. The CEL method can more accurately describe the large deformation and contact problems of materials during the friction stir welding process, and is considered as 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 the welding process, ignoring the residual stress state of the workpiece before welding. In actual applications in the aerospace field, the workpiece often undergoes multiple machining processes, and the initial residual stress is significant, which cannot be ignored in the influence on the performance of the friction stir welded joint.

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

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

[0009] Effective transmission of multi-process residual stress: the existing method is difficult to realize the predefinition and transmission of the residual stress field before welding in the CEL method, which limits the accurate simulation of the stress evolution in the whole welding process.

[0010] Insufficient model adaptability and consistency: the existing technology is difficult to unify the model type and solution method of quenching and friction stir welding simulation, resulting in inconsistency between the models of different processes.

[0011] Stress field superposition and optimization control difficulty: lacking comprehensive research on the interaction between the residual stress before welding and the stress field during welding, it is difficult to provide effective basis for the optimization and control of the welding process.

[0012] Therefore, a new method is needed to realize the predefinition and transmission of the residual stress field before welding in the CEL method, so as to accurately simulate the stress evolution behavior in the friction stir welding process. SUMMARY

[0013] To solve the technical problems of effective transmission of multi-process residual stress, insufficient model adaptability and consistency, and difficulty in stress field superposition and optimization control in the existing numerical simulation of temperature field, stress field and plastic deformation behavior in the friction stir welding process, the technical solution provided by the present application is:

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

[0015] establishing a welding plate model, a stirrer model and an Euler space model in a computer-aided simulation software;

[0016] calculating the quenching residual stress field in the Euler space model;

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

[0018] simulating the processes of stirrer pressing, preheating, welding, moving out and cooling;

[0019] In the cooling process, the step of obtaining the complete distribution of the post-weld stress field.

[0020] Further, a preferred embodiment is provided, wherein the welding sheet model and the stir model are three-dimensional deformation body models, and the Euler space model is a three-dimensional Euler body model, and the Euler space model is meshed.

[0021] Further, a preferred embodiment is provided, wherein the live and dead cell method is used to retain cells consistent with the size of the welding sheet model for quenching residual stress simulation, material physical properties are assigned and an initial temperature field and thermal boundary conditions are set, and the quenching residual stress field is calculated.

[0022] Further, a preferred embodiment is provided, further comprising the step of matching the discrete fields of the welding sheet model and the Euler space model by the volume fraction tool of Abaqus, and assigning values in the predefined field.

[0023] Further, a preferred embodiment is provided, wherein the stir down, preheating, welding, moving out and cooling processes are simulated by setting material properties, contact properties and load boundary conditions for the welding sheet model and the stir model.

[0024] Further, a preferred embodiment is provided, wherein the complete distribution of the post-weld 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 application further provides a device for simulating a predefined stress field in friction stir welding, comprising:

[0026] a module for establishing a welding sheet model, a stir model and an Euler space model in computer-aided simulation software;

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

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

[0029] a module for simulating stir down, preheating, welding, moving out and cooling processes;

[0030] a module for obtaining the complete distribution of the post-weld stress field in the cooling process.

[0031] Based on the same inventive concept, the present application further provides a computer storage medium for storing a computing program, wherein when the computing program is read by a computer, the computer executes the method.

[0032] Based on the same inventive concept, the present application further provides a computer comprising a processor and a storage medium, wherein when the processor reads the computer program stored in the storage medium, the computer executes the method.

[0033] Based on the same inventive concept, the application also provides a computer program product, which is a computer program and realizes the method when the computer program is executed.

[0034] Compared with the prior art, the technical scheme provided by the application has the advantages that:

[0035] By using the CEL method combined with the birth and death element method, the influence of redundant elements is effectively eliminated in the numerical simulation of the quenching process, and accurate transmission of the residual stress field after quenching is realized. Compared with the stress field error caused by the invalid element in the multi-process continuous modeling method in the prior art, the present scheme ensures one-to-one correspondence between the welding plate model and the Euler model element, and greatly improves the simulation accuracy.

[0036] By establishing a unified model including the welding plate, the stirring head and the Euler space in ABAQUS, the problem of inconsistent model types and solving methods in different processes is solved. Compared with the traditional finite element method of separate modeling, the present scheme connects the quenching and friction stir welding processes through a unified model framework, significantly improving the consistency and calculation 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 simulation of friction stir welding, and accurate transmission of the residual stress between processes is realized. The influence of the pre-welding stress is often ignored in existing research, but the present scheme effectively superimposes the stress field, making the simulation of the welding process more close to the actual working condition, and improving the credibility of the simulation results.

[0038] By setting local encryption grids and Johnson-Cook constitutive models, the present scheme accurately describes the thermal-mechanical behavior in the welding process. Compared with the ordinary grid division method in existing research, the high-precision modeling of the present scheme ensures that the interaction between the stirring head movement, plastic flow of the welding plate and heat input is finely described, and the guiding value of the simulation data for welding process optimization is improved.

[0039] By combining the advantages of the CEL method in handling large deformation and complex contact problems, the present scheme successfully realizes the transmission and redistribution of the quenching residual stress field in the welding process. Compared with the simplification assumption of the influence of residual stress in the traditional method, the present scheme accurately calculates the whole process of stress evolution, providing effective support for the design and performance prediction of high-performance welded structures.

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

[0041] Figure 1 It is a schematic diagram of an aluminum alloy welding process model.

[0042] Figure 2 Schematic diagram for deactivating model unit for birth-death unit method

[0043] Figure 3 Schematic diagram for quenching simulation residual stress

[0044] Figure 4 Schematic diagram for model assembly

[0045] Figure 5 Schematic diagram for overall stress field in plunge phase of stirring head

[0046] Figure 6 Schematic diagram for overall residual stress field after welding

[0047] Figure 7 Flow chart of a method for predefining stress field in numerical simulation of friction stir welding. DETAILED DESCRIPTION

[0048] In order to make the advantages and beneficial effects of the technical solutions provided by the present application more clear, the technical solutions provided by the present application are further described in detail below in combination with the drawings, and the specific embodiments are as follows:

[0049] Embodiment one, the embodiment provides a method for predefining stress field in numerical simulation of friction stir welding, comprising:

[0050] The steps of establishing the welding plate model, the stirring head model and the Euler space model in the computer-aided simulation software;

[0051] The step of calculating the quenching residual stress field in the Euler space model;

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

[0053] The step of simulating the processes of plunge, preheating, welding, moving out and cooling of the stirring head;

[0054] The step of obtaining the complete distribution of the post-welding stress field in the cooling process.

[0055] Embodiment two, the embodiment is a further limitation of the method for predefining stress field in numerical simulation of friction stir welding provided by embodiment one, wherein the welding plate model and the stirring head model are three-dimensional deformation body models, the Euler space model is a three-dimensional Euler body model, and the Euler space model is meshed.

[0056] Specifically, in combination with Figure 7 The scheme provided by the embodiment comprises:

[0057] First step: establishing an initial model

[0058] An initial model including the welding plate, the stirring head and the 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 were established: a welding plate model, a stirring head model and an Euler space model. The welding plate model and the stirring head model were selected as three-dimensional deformation body types, and the Euler space model was selected as a three-dimensional Euler body type. The size of the Euler space model was designed to be consistent with the length and width of the welding plate model, and the thickness direction was higher than the welding plate model to simulate the flow extrusion behavior of the welding plate material, and a region with the same thickness as the welding plate model was pre-segmented in the Euler space model. The model was meshed, and the welding seam center position of the Euler space model needed to be locally encrypted to improve the calculation accuracy. The welding plate model and the stirring head model used standard meshing rules to ensure that the mesh density was sufficient to reflect the material properties and welding behavior.

[0060] Second step: quenching process simulation

[0061] The excess elements in the Euler space model were processed using the birth and death element method to calculate the residual stress field of the welding plate quenching process.

[0062] Detailed description: Based on the Euler space model established in the first step, the model type was changed from a three-dimensional Euler body to a three-dimensional deformation body, and material properties were assigned, including density, specific heat capacity, thermal conductivity, elastic modulus, plasticity, thermal expansion coefficient and Poisson's ratio. The assembly module was used to create an instance of the Euler space model and establish a quenching analysis step. The thermal boundary conditions of quenching were set, including an environment temperature of 20°C and different surface heat transfer coefficients. Through the birth and death element method, the elements in the Euler space model outside the welding plate were in an inactive state, and only the elements consistent with the size of the welding plate model were retained for calculation. In defining the initial temperature field, the initial temperature of the activated elements was set to 515°C, and the element type was C3D8T eight-node thermal coupling hexahedral element. Finally, through quenching simulation, the quenching residual stress field was calculated and obtained.

[0063] Third step: establishing a friction stir welding analysis model

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

[0065] Detailed description: Assemble the welding plate model into the pre-segmented region of the Euler space model, and assemble the stir head model into the starting position of the weld, suspended above the welding plate model. Assign material properties to the Euler space model and the stir 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 for the material of the welding plate and the stir head model, respectively. Define the Euler space model and the stir head model as instances, and ensure their geometric coincidence and alignment in the assembly module to provide an accurate geometric basis for the analysis of friction stir welding.

[0066] Fourth step: Set the friction stir welding analysis conditions

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

[0068] Detailed description: Set the contact properties between the Euler space model and the stir head model, with tangential contact using a penalty function and normal contact using hard contact, and apply rigid body constraints to the stir head. The thermal boundary conditions include the heat transfer coefficient and the 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 and moving load of the stir head, and the rotation speed and welding speed of the stir head during welding. Establish the discrete field of the Euler space model and the welding plate model using the volume fraction tool of Abaqus, create the material assignment of this discrete field in the pre-defined field, and import the calculated quenching residual stress field in the second step to form the initial stress state of friction stir welding.

[0069] Fifth step: Friction stir welding simulation calculation

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

[0071] Detailed description: In the simulation, five analysis steps are established, corresponding to the downward pressure, preheating, welding, moving out, and cooling processes of the stir head. Set the grid type in the Euler space model to EC3D8RT eight-node thermal coupled Euler hexahedron element. 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 movement of the stir head. As the simulation progresses, the high temperature and severe plastic deformation during welding cause the redistribution of quenching residual stress, and the stress field in the weld and near the weld gradually evolves into a friction stir welding residual stress, while the base material area still mainly retains the quenching residual stress.

[0072] Sixth step: Analysis of the post-weld residual stress field

[0073] Analyze the simulation results of friction stir welding 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 the welding process and after the welding is extracted. The results show that the quenching residual stress is successfully transferred to the welding model before welding, and is superimposed with the stress field generated during the welding process to form a complete residual stress distribution. The stress in the weld and the near-weld zone is mainly introduced by friction stir welding, while the stress level in the base material area is lower than that in the weld zone, which is mainly composed of quenching residual stress. By comparing the prior art, the significant advantages of the present scheme in multi-process stress transfer, consistent modeling and accurate simulation are verified.

[0075] Embodiment three, the present embodiment is a further limitation of the pre-defined stress field method for numerical simulation of friction stir welding provided in embodiment one, using the birth and death element method, preserving the elements consistent with the size of the welding plate model for quenching residual stress simulation, assigning material physical properties and setting initial temperature field and thermal boundary conditions, calculating the quenching residual stress field.

[0076] Embodiment four, the present embodiment is a further limitation of the pre-defined stress field method for numerical simulation of friction stir welding provided in embodiment one, further comprising the steps of matching the discrete field of the welding plate model and the Euler space model by the volume fraction tool of Abaqus, and assigning values in the pre-defined field.

[0077] Embodiment five, the present embodiment is a further limitation of the pre-defined stress field method for numerical simulation of friction stir welding provided in embodiment one, by setting material properties, contact properties and load boundary conditions for the welding plate model and the stir head model, simulating the processes of stir head pressing down, preheating, welding, moving out and cooling.

[0078] Embodiment six, the present embodiment is a further limitation of the pre-defined stress field method for numerical simulation of friction stir welding provided in embodiment one, by setting the initial temperature field to room temperature and defining the fixed boundary condition, obtaining the complete distribution of the post-weld stress field.

[0079] Embodiment seven, the present embodiment provides a pre-defined stress field device for numerical simulation of friction stir welding, comprising:

[0080] a module for establishing a welding plate model, a stir head model and an Euler space model in computer-aided simulation software;

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

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

[0083] a module for simulating the processes of stir head pressing down, preheating, welding, moving out and cooling;

[0084] A module for obtaining a complete distribution of a post-weld stress field during the cooling process.

[0085] Embodiment eight, the 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 by embodiment one.

[0086] Embodiment nine, the embodiment provides a computer, comprising a processor and a storage medium, when the processor reads the computer program stored in the storage medium, the computer executes the method provided by embodiment one.

[0087] Embodiment ten, the embodiment provides a computer program product as a computer program, when the computer program is executed, the method provided by embodiment one is realized.

[0088] Embodiment eleven, in combination Figures 1-6 The embodiment is described in detail by specific examples, and the above-mentioned technical solutions are further described in detail.

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

[0090] (1) the type selection of the welding plate model and the stirring head model is three-dimensional deformation body, and the Euler space model selects three-dimensional Euler body.

[0091] (2) the length and width dimensions of the Euler space model are the same as those of the welding plate model, and the thickness dimension is higher than that of the welding plate model to realize the simulation of material flow extrusion of the welding plate model, and the region with the same thickness as the welding plate model is pre-segmented.

[0092] (3) the Euler space model and the stirring head model are divided into grids, and the welding seam center position in the Euler space model needs to be locally encrypted.

[0093] 2, the main process of the quenching process simulation is as follows:

[0094] (1) the quenching model selects the Euler space model in the model established in the last step, and changes the model type from three-dimensional Euler body to three-dimensional deformation body;

[0095] (2) attribute of the Euler space model is given. The physical quantities including density, specific heat capacity, thermal conductivity, elastic modulus, plasticity, thermal expansion coefficient, Poisson's ratio and the like are set, and the model instance is created in the assembly module to establish the analysis step of the quenching process;

[0096] (3) set the corresponding thermal boundary condition of quenching, use the birth-death element method, and cancel the activation of the element in the Euler space model which is segmented out of the welding plate area in the calculation;

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

[0098] (5) At this time, the activated part of the Euler space model is the same size as the welding plate model. The quenched stress field is obtained by using the Euler space model processed by the birth and death element method for quenching simulation.

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

[0100] (1) Assign material properties to the Euler space model and the stir head model established in the first step. The Euler space model needs to be set to include physical quantities such as density, specific heat capacity, thermal conductivity, elastic modulus, thermal expansion coefficient, and Poisson's ratio, as well as the Johnson-Cook constitutive model of the material. The stir head model needs to be set to material properties other than plasticity;

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

[0102] (3) Set the contact properties of the Euler model and the stir head model, and apply the thermal boundary condition and the load boundary condition: first, set the contact properties, where the tangential contact uses the penalty function, the normal contact uses the hard contact, and the stir head is subjected to rigid body constraints. The contact type between the stir head and the welding plate is general contact; then apply the thermal boundary condition, including the heat transfer coefficient and the thermal radiation coefficient of the Euler model. Finally, apply the load boundary condition, including the fixation of the welding plate, the pressing and movement of the stir head, and the rotation speed and welding speed of the stir head during welding.

[0103] (4) Set the mesh type of the Euler space to EC3D8RT: 8-node thermal coupled Euler hexahedral element. Establish the discrete field of the Euler space model and the welding plate model through the volume fraction tool of Abaqus. Create the material assignment of the discrete field in the pre-defined field, and set the pre-defined stress field through the pre-defined field setting. Import the residual stress field after quenching. Due to the application of the birth and death element method in the previous step, the elements in the Euler space model that overlap with the welding plate model contain all the residual stress data after quenching, and the other elements are in a stress-free state, solving the problem of mismatch between the welding part model and the Euler space model;

[0104] (5) Use the above established model to simulate friction stir welding based on the CEL method, and obtain the friction stir welding stress field result with pre-applied quenching stress.

[0105] In the specific implementation work:

[0106] Take two 200mm x 100mm x 16mm butt welding flat plate as an example for illustration; Figure 1 The center of (a) is the Euler space model, with a size of 200mm x 200mm x 20mm; (b) is the welding plate model, with a size of 200mm x 200mm x 16mm, and the center is divided into a welding seam; (c) is the stirrer head model. The Euler space model is divided into two parts in the thickness direction, the light color part has the same size as the welding plate model, and the dark color part is a pre-set area considering the material flow out of the Euler space. The characteristic line is divided at the welding seam to facilitate the refinement of the grid. (d) and (e) are the grid models of the Euler space model and the stirrer head model respectively. The Euler space model uses hexahedral grid, and the welding position is locally encrypted; the stirrer head model uses tetrahedral grid, and the size is consistent.

[0107] (1) First, the quenching process simulation: this process uses the Euler space model, sets the model type to three-dimensional deformation body; the material properties of the Euler space model are selected according to the parameters corresponding to 2195 aluminum alloy, including density, specific heat capacity, thermal conductivity, elastic modulus, plasticity, thermal expansion coefficient, Poisson's ratio and other physical quantities; and create a model instance in the assembly module to establish the analysis step of the quenching process; set the corresponding thermal boundary conditions of quenching, set the environment temperature to 20℃, define different surface heat transfer coefficients; as shown in Figure (2), use the birth-death element method, use the birth-death element method in the interaction module to make Figure 1 The dark area units in (a) are in active and inactive states, and the remaining active unit models are consistent with the size of the welding plate model; three-point displacement constraints are established for the Euler space model, and the initial temperature field is defined, with a uniform temperature of 515℃; set the element type to C3D8T eight-node thermal coupled hexahedral element; at this time Figure 2 The selected units in (a) do not participate in the calculation simulation of the quenching process simulation, while the information of this part of the units in the model is retained, so that the model units used in the two processes are one-to-one correspondence, and finally the Euler space model after the birth-death element method is used for quenching simulation, and the quenching residual stress is calculated, as shown in Figure 3 ;

[0108] (2) Then, the friction stir welding simulation is carried out: the Euler space model and the stirrer head model are given the material properties of 2195 aluminum alloy, which need to set the density, specific heat capacity, thermal conductivity, elastic modulus, thermal expansion coefficient, Poisson's ratio and Johnson-Cook constitutive model of the material. Then assemble the model, as shown in Figure 4 The Euler space model coincides with the welding plate model, with a space reserved for material flow in the thickness direction, and the stirrer is assembled at one end of the welding seam, suspended above the welding plate model.

[0109] (3) Analysis step setting, contact type setting, thermal boundary condition setting, Euler space model and weld sheet model discrete field setting, load boundary condition setting, predefined stress field setting, initial temperature field setting and Euler space model grid type setting are set in sequence: five analysis steps are established for the process of the pin pressing-preheating-welding-moving out-cooling of the friction stir welding; the contact properties of the Euler model and the pin model are set as general contact, in which the tangential contact adopts penalty function and the normal contact adopts hard contact; the thermal boundary conditions include the heat transfer coefficients and thermal radiation coefficients of different surfaces of the Euler model; the discrete field of the Euler space model and the weld sheet model is established by 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 sheet, the pin pressing and moving out, and the rotation speed and welding speed of the pin during the welding process; the predefined stress field is established in the predefined field setting, the residual stress field after quenching is imported, and the overall temperature is set as room temperature 20℃; the grid type of the Euler space is set as EC3D8RT. Due to the application of the birth and death element method in the previous step, the elements of the Euler space model that overlap with the weld sheet model contain all the residual stress data after quenching, and the other elements are in a stress-free state, solving the problem of mismatch between the weld model and the Euler space model; the above established model is used for the simulation of friction stir welding based on the CEL method, and the stress field result of the friction stir welding with pre-applied quenching stress is obtained.

[0110] (4) At the beginning of the simulation of the friction stir welding process, Figure 5 the stress field of the overall model for the pin pressing stage is shown in FIG. 6, in which the residual stress after quenching is pre-applied to the Euler space model, and the stress field of the Euler space model is shown in FIG. 7. 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 elements of the Euler space model that overlap with the weld sheet model, i.e. the base material region. Figure 5 (b) It can be seen that after removing the grid without material filling, the stress generated by the pin pressing exists simultaneously with the quenching residual stress.

[0111] (5) After the simulation of the friction stir welding process is completed, Figure 6 the overall residual stress field after welding is shown in FIG. 8, in which the quenching residual stress and the residual stress of the friction stir welding process exist simultaneously; the residual stress of the weld and the near weld region is mainly the residual stress of the friction stir welding, and the original quenching residual stress is re-evolved under the influence of high temperature and severe plastic deformation; the quenching residual stress is mainly in the base material region, and the stress level is lower than the welding residual stress; the transfer of the quenching residual stress of the three-dimensional deformed body model to the Euler body model of the friction stir welding simulation is realized.

[0112] The technical solutions of the present application are described in further detail through several specific embodiments above, in order to highlight the advantages and benefits of the technical solutions provided by the present application. However, the above several specific embodiments are not used as a limitation to the present application, and any reasonable modifications and improvements, combinations and equivalent replacements, etc. of the present application within the scope of the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A friction stir welding numerical simulation pre-defined stress field method, characterized by, The method comprises the following steps: establishing a welding plate model, a stir head model and an Euler space model in computer-aided simulation software; calculating a quenching residual stress field in the Euler space model; introducing the quenching residual stress field into a friction stir welding simulation model; simulating a stir head pressing, preheating, welding, moving out and cooling process; obtaining a complete distribution of a post-welding stress field during the cooling process; Specifically: by means of a live and dead element method, elements outside the welding plate in the Euler space model are in a non-activated state, and only elements consistent with the size of the welding plate model are reserved for calculation; when defining an initial temperature field, the initial temperature of the activated elements is set to 515 DEG C, and the element type is C3D8T eight-node thermal coupling hexahedral element; finally, the quenching residual stress field is calculated and obtained through quenching simulation; the live and dead element method is used to process the redundant elements in the Euler space model, and the residual stress field of the welding plate in the quenching process is calculated; a discrete field of the Euler space model and the welding plate model is established by means of the volume fraction tool of Abaqus, a material assignment of the discrete field is created in a pre-defined field, and the quenching residual stress field is introduced to form an initial stress state of the friction stir welding; in the simulation, five analysis steps are established, which correspond to the stir head pressing, preheating, welding, moving out and cooling process respectively; the grid type is set to EC3D8RT eight-node thermal coupling Euler hexahedral 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 stir head movement; through post-processing analysis, the distribution data of the residual stress field during the welding process and after the welding are extracted; the quenching residual stress is transmitted to the welding model before the welding, and is superimposed with the stress field generated in the welding process to form a complete residual stress distribution.

2. The method of claim 1, wherein, The welding plate model and the stir head model are three-dimensional deformation body models, and the Euler space model is a three-dimensional Euler body model, and the Euler space model is meshed.

3. The method of claim 1, wherein, By means of the live and dead element method, the elements consistent with the size of the welding plate model are reserved for quenching residual stress simulation, the material physical properties are given, and the initial temperature field and thermal boundary conditions are set to calculate the quenching residual stress field.

4. The method of claim 1, wherein, It also comprises the steps of matching the discrete field of the welding plate model and the Euler space model by means of the volume fraction tool of Abaqus, and assigning values in the pre-defined field.

5. The method of claim 1, wherein, By setting the material properties, contact properties and load boundary conditions of the welding plate model and the stir head model, the stir head pressing, preheating, welding, moving out and cooling process are simulated.

6. The method of claim 1, wherein, By setting the initial temperature field to room temperature and defining the fixed boundary conditions, the complete distribution of the post-welding stress field is obtained.

7. A friction stir welding numerical simulation pre-defined stress field apparatus, characterized by, The method comprises the following steps: establishing a welding plate model, a stir head model and an Euler space model in computer-aided simulation software; calculating a quenching residual stress field in the Euler space model; introducing the quenching residual stress field into a friction stir welding simulation model; simulating a stir head pressing, preheating, welding, moving out and cooling process; obtaining a complete distribution of a post-welding stress field during the cooling process; Specifically: The Euler space model is used to make the units outside the welding plate inactive by the birth and death unit method, and only the units consistent with the size of the welding plate model are reserved to participate in the calculation; when defining the initial temperature field, the initial temperature of the activated unit is set to 515℃, and the unit type is C3D8T eight-node thermal coupling hexahedral unit; finally, the quenching residual stress field is calculated and obtained through quenching simulation; The Euler space model is used to make the units outside the welding plate inactive by the birth and death unit method, and only the units consistent with the size of the welding plate model are reserved to participate in the calculation; when defining the initial temperature field, the initial temperature of the activated unit is set to 515℃, and the unit type is C3D8T eight-node thermal coupling hexahedral unit; finally, the quenching residual stress field is calculated and obtained through quenching simulation; The discrete field of the Euler space model and the welding plate model is established by the volume fraction tool of Abaqus, the material assignment of the discrete field is created in the predefined field, and the quenching residual stress field is imported to form the initial stress state of the friction stir welding; In the simulation, five analysis steps are established, corresponding to the pressing, preheating, welding, moving out and cooling processes of the stir head respectively; In the Euler space model, the grid type is set to EC3D8RT eight-node thermal coupling Euler hexahedral unit; 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 movement of the stir head; Through post-processing analysis, the distribution data of the residual stress field during and after welding is extracted; The quenching residual stress is transferred to the welding model before welding, and is superimposed with the stress field generated during welding to form a complete residual stress distribution.

8. Computer storage medium for storing a computing program, characterized in that The computer executes the method of claim 1 when the computer program is read by the computer.

9. A computer comprising a processor and a storage medium, characterized in that The computer executes the method of claim 1 when the computer program stored in the storage medium is read by the processor.

10. Computer program product as computer program, characterized in that The method of claim 1 is implemented when the computer program is executed.

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