Welding thermal stress simulation method, device and equipment based on crystal plasticity finite element and medium

Abstract

The invention discloses a welding thermal stress simulation method, device, equipment and medium based on a crystal plasticity finite element, and relates to the technical field of welding thermal stress finite element simulation. The method comprises the steps that a sample is prepared according to a specific multi-phase metal material, and phase distribution and crystal orientation information of a two-dimensional plane of the material are obtained through a metallographic experiment; and a three-dimensional multi-grain model is constructed based on the two-dimensional information. According to the method, a crystal plastic constitutive model is adopted to describe the flowing behavior of the material at high temperature, crystal slippage and polycrystal interaction are considered, the influence on the material performance is reflected from the microstructure evolution level, and the problem that the influence on the macroscopic mechanical performance of a microstructure is difficult to capture in welding multiphase metal material simulation is solved; two-dimensional representation is obtained through a metallographic experiment, the Young modulus and rigidity matrix parameters are accurately calculated by combining forward stretching and shear simulation, the rigidity matrix precision is improved, a temperature field area is divided, stress evolution and residual stress are calculated by combining a thermal-elastic-plastic model, and the welding thermal stress calculation precision is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding thermal stress finite element simulation, in particular to a welding thermal stress simulation method, device, equipment and medium based on crystal plasticity finite element. BACKGROUND

[0002] In the field of welding process simulation, thermal stress analysis of multi-phase metal materials is crucial to ensure the safety and reliability of welded structures. Traditional welding thermal stress simulation algorithms are mostly based on macro-scale analysis, treating materials as homogeneous continua and calculating stress distribution only through overall structural parameters, which cannot reflect the influence of internal microstructure on macroscopic properties.

[0003] Currently, researchers have proposed various simulation methods for calculating welding thermal stress to improve the efficiency and accuracy of multi-phase material finite element analysis. For example, microstructure modeling methods use microscope images, three-dimensional reconstruction, and other technologies to construct realistic microstructure models. Element decomposition methods, based on finite element methods or other numerical methods, decompose complex material systems into multiple simple calculation units, independently calculate the physical properties of each unit, and finally synthesize the overall material response. Virtual materials, combining numerical simulation and material science, simulate the microstructure and mechanical properties of computer-generated material models.

[0004] Although the above mainstream thermal stress simulation algorithms have improved the computational efficiency of thermal stress simulation to some extent, they generally have low stiffness matrix calculation accuracy. Since they do not consider crystal slip, twinning, and other micro-deformation behaviors, they cannot accurately describe the flow characteristics of materials at high temperatures, leading to large deviations between thermal stress simulation results and actual welding conditions, making it difficult to meet the high-precision welding process optimization requirements. Although crystal plasticity finite element methods emphasize micro-macro correlation, existing applications lack systematic modeling processes for multi-phase metal welding scenarios, limiting their effectiveness in thermal stress simulation. Therefore, it is of great significance to develop a welding thermal stress simulation method, device, equipment, and medium based on crystal plasticity finite element. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a welding thermal stress simulation method, device, equipment, and medium based on crystal plasticity finite element. It uses a crystal plasticity constitutive model to accurately describe the flow behavior of materials at high temperatures, considers crystal slip and the interaction of polycrystals, reflects the influence of microstructure evolution on material properties, and improves the accuracy of thermal stress calculation results.

[0006] To solve the above technical problems, the present application provides the following technical solutions. The welding thermal stress simulation method based on crystal plasticity finite element includes the following steps: S1, sample preparation according to the specific multiphase metal material, obtain the phase distribution and crystal orientation information of the two-dimensional plane of the material through metallographic experiment.

[0007] S2, according to the two-dimensional metallographic information obtained by metallographic experiment, import the multimodal data processing software and then reconstruct the three-dimensional polycrystalline model.

[0008] S3, import the three-dimensional polycrystalline model into the crystal plastic finite element simulation software, set the boundary conditions according to the different phases of the material, set different characteristic parameters in the elastic stage and plastic stage of the material, set the thermal damage of the material in the high temperature region of the simulation, and complete the setting of the material characteristics and temperature conditions. After that, the crystal is simulated by forward tensile and shear.

[0009] S4, according to the stress and strain data output by the crystal plastic finite element simulation software, calculate the Young's modulus, shear modulus and Poisson's ratio of the metal material, and then obtain the macroscopic stiffness matrix of the material.

[0010] S5, divide the temperature field into base material region, heat affected zone and molten pool region, set the heat conduction differential equation, boundary condition and heat source model.

[0011] S6, calculate the thermal strain according to the thermal-elastic-plastic model.

[0012] S7, calculate the stress evolution according to the thermal-elastic-plastic model.

[0013] S8, characterize the residual stress and evolution according to the temperature field after cooling to complete the welding thermal stress simulation calculation.

[0014] Further, the metallographic experiment adopts electron backscattering experiment, and the obtained information also includes grain size and shape, and the crystal orientation, grain boundary and grain morphology index are extracted, wherein the crystal orientation is used to provide texture analysis, the grain boundary data includes low angle and high angle boundary, the phase recognition part provides basis for the phase change behavior of the material, and the grain morphology part summarizes the grain shape, size and arrangement information.

[0015] Preferably, in step S2, the three-dimensional polycrystalline model reconstruction process specifically includes: In the multimodal data processing software, set the crystal structure and volume fraction, import the grain distribution and size data obtained by metallographic experiment into the software to obtain the probability density function of grain size distribution.

[0016] Extract the grain orientation characteristics from the metallographic experiment output data, import them into the multimodal data processing software, and generate a three-dimensional polycrystal with similar grain orientation distribution characteristics as the two-dimensional metallographic experiment collected data according to the generated microstructure distribution pole figure.

[0017] Set the number of metallographic phases, and set different metallographic phase names and numbers for multiphase materials.

[0018] In the initialization, the number of grid points and the size of grid cell are set, the three-dimensional size and the number of grids of the polycrystal model are determined, and the number of grains of the generated polycrystal model is estimated.

[0019] After the multi-modal data processing software calculation is completed, a specific format file is output according to a rule, and the file is imported into a visualization software to check the generated three-dimensional polycrystal model.

[0020] Further, in step S3, the crystal plastic finite element simulation setting and simulation process specifically includes: An phenomenological crystal plasticity constitutive model is adopted, and the parameters of the elastic part are determined by experiments. Different elastic moduli are set for different phases of the multi-phase metal material.

[0021] In the material plasticity part, the crystal structure and the corresponding slip system are set, the critical shear stress of the slip system and the twinning system is determined, the Schmid factor is calculated, and the calculation formula is. wherein, is the slip direction, is the normal of the slip plane, is the macroscopic stress tensor.

[0022] For single-slip system calibration of a single crystal sample, a uniaxial tension test is used to obtain a stress-strain curve, and the critical critical shear stress of a single slip system is back calculated according to the Schmid law and the yield stress calculation formula. The yield stress calculation formula is. wherein represents the yield stress, represents the shear stress, is the friction coefficient, is the exponential parameter.

[0023] The multi-slip system calibration of a polycrystal sample is carried out by using a hydrostatic loading test. Different slip systems are activated by loading in different directions to output experimental stress-strain curves. Combined with the macroscopic stress-strain curve and the microcosmic slip system activation, the critical shear stress is adjusted by an optimization algorithm to match the experimental data.

[0024] In the simulation process, the deformation gradient and the stress boundary condition are used in combination, and the deformation gradient rate tensor and characterize the rate of evolution of the deformation gradient in each direction, and the first Piola-Kirchhoff stress tensor represents the stress boundary condition.

[0025] For orthotropic anisotropic materials, the tensile and shear directions are determined when simulating uniaxial tension and shear deformation experiments, and through six calculations, three stress-strain curves of tensile stress and three stress-strain curves of shear stress are obtained.

[0026] Further, in step S4, the stiffness matrix calculation process specifically includes: For the stress-strain curve of the forward stretching, the Young's modulus is calculated according to the formula The Young's modulus is calculated, wherein The Young's modulus is The stress is The strain is, and linear fitting is performed on the data points of this stage, and the slope value obtained is the Young's modulus value.

[0027] For the stress-strain curve of the shear deformation, the shear modulus is calculated according to the formula The shear modulus is calculated, wherein The shear modulus is The stress is The strain is, and linear fitting is performed on the data points of this stage, and the slope value obtained is the shear modulus value.

[0028] The shear modulus has a relationship with the Young's modulus and the Poisson's ratio , wherein The Poisson's ratio is

[0029] According to the above formula, the necessary parameters required for calculating the stiffness matrix are obtained For orthotropic anisotropic materials, the compliance matrix is obtained, the stiffness matrix is obtained, and the compliance matrix is converted as follows , and the elastic matrix of the three-dimensional polycrystalline model is obtained.

[0030] Further, in step S5, the temperature field setting process specifically includes: For the base material region, the temperature does not reach the material solid state phase transition starting temperature, the material microstructure does not change, the original grain structure is maintained, the thermal stress is derived from thermal expansion or contraction, and the linear elastic law is met. In this region, the constitutive model is a linear elastic model.

[0031] For the heat affected zone, the temperature is in the solid state phase transition temperature range, the material undergoes grain coarsening, recrystallization or phase change, and the yield strength and hardening coefficient correction simulation data are introduced in the calculation process.

[0032] In the molten pool region, the temperature exceeds the liquidus temperature of the material, the metal is completely melted at this stage, and presents liquid flow characteristics, and the solidification process is accompanied by microstructure reconstruction, heat dissipation and pore defect formation.

[0033] When establishing the temperature field, the heat conduction differential equation of the orthotropic anisotropic material satisfies , wherein , respectively represent the thermal conductivity of the material in the x, y, z directions, is the specific heat capacity of the material, is the density of the material, is the heat source acting inside the workpiece.

[0034] Define the temperature as a function of the position coordinates and time satisfies For the boundary condition, when the heat loss by convection is known at any position on the material boundary, it satisfies , wherein is the thermal conductivity of the material, is the convection heat transfer coefficient, is the temperature at the metal surface, is the ambient temperature.

[0035] For the heat source model, a Gaussian heat source model is adopted, and the function is , wherein is the surface heat flow at , is the maximum heat flow at the center of the heat source, is the heat flow distribution concentration coefficient, in the welding simulation process, the heat source is in a moving state, and the total heat released is , and the above can be obtained , wherein is the welding input, is the heating area radius, and let .

[0036] In the Cartesian coordinate system, the welding laser light source moves at a uniform speed along the x-axis direction , a moving coordinate system is established , the distance from the center of the heat source in the moving coordinate system is , the effective power of the laser welding material is known , and is obtained.

[0037] Further, in step S6, the temperature calculation of the thermo-elastic-plastic model adopts a time difference, and the temperature difference between the time and the time of a point in the temperature field is For anisotropic materials, the thermal expansion coefficient is a second-order tensor The thermo-elastic-plastic model of anisotropic materials is related to the crystal orientation, and the thermal strain of any point in the temperature field is .

[0038] Further, in step S7, the stress evolution calculation process specifically includes: ​According to the linear elasticity theory, the strain is caused by the temperature change and stress According to the Hooke's law, the stress-strain relationship is .

[0039] For anisotropic material, according to the calculated thermal strain , let , according to the strain energy formula of elastic body, substitute , wherein is the strain-displacement matrix, represents the shape function, represents the displacement amount, and is obtained, wherein the element stiffness matrix and the thermal load are respectively 、 .

[0040] According to the principle of minimum potential energy , the equilibrium equation of the element with free expansion constrained is obtained , the displacement is obtained, and substituted into the equation , the strain is obtained , the strain and the thermal strain are substituted into , and the stress can be obtained.

[0041] Further, in step S8, the residual stress and deformation representation process specifically includes: During the welding process, as the heat source moves, the thermal expansion strain of the metal in the weld and the near-weld area is constrained by the surrounding cooler metal, generating compressive plastic strain, and during the cooling process, the compressive plastic strain is partially stretched to offset, and the residual compressive plastic strain remains after welding. The strain causes residual stress in the material.

[0042] For the calculation of residual stress and deformation, after obtaining the specific temperature field distribution of each welding time step in the welding thermal stress simulation process, the temperature difference value is calculated in sequence according to the time step order.

[0043] The compressive plastic strain is obtained from the temperature difference value and the linear expansion coefficient, and the stress value calculated by introducing the constitutive model is the residual stress value under the cooled temperature field.

[0044] The welding thermal stress simulation device based on the crystal plastic finite element includes: The sample preparation module is used for sample preparation according to specific multi-phase metal materials, and the phase distribution and crystal orientation information of the two-dimensional plane of the material are obtained through metallographic experiments.

[0045] The reconstruction module is used to import the two-dimensional metallographic information obtained by the metallographic experiment into the multi-modal data processing software to reconstruct a three-dimensional polycrystalline model.

[0046] The simulation module is used for importing the three-dimensional multi-grain model into a crystal plastic finite element simulation software, setting boundary conditions according to different phases of the material, setting different characteristic parameters of the material in the elastic stage and the plastic stage, setting thermal damage of the material in a high temperature region of the simulation, and performing forward tensile and shear simulation on the crystal after setting the material properties and the temperature condition.

[0047] The rigidity module is used for calculating the Young's modulus, the shear modulus and the Poisson's ratio of the metal material according to stress and strain data output by the crystal plastic finite element simulation software, and further obtaining a macroscopic rigidity matrix of the material.

[0048] The division and setting module is used for dividing a temperature field into a base material region, a heat affected zone and a molten pool region, setting a heat conduction differential equation, a boundary condition and a heat source model.

[0049] The thermal strain module is used for calculating thermal strain according to a thermal-elastic-plastic model.

[0050] The stress module is used for calculating stress evolution according to the thermal-elastic-plastic model.

[0051] The residual stress module is used for characterizing residual stress and evolution according to a temperature field after cooling, so as to complete the welding thermal stress simulation calculation.

[0052] The welding thermal stress simulation device based on the crystal plastic finite element includes a processor, a memory and a computer program stored in the memory. The computer program can be executed by the processor to implement the welding thermal stress simulation method based on the crystal plastic finite element.

[0053] A computer readable storage medium includes a stored computer program, wherein the computer readable storage medium controls the device where the computer readable storage medium is located to execute the welding thermal stress simulation method based on the crystal plastic finite element when the computer program runs.

[0054] Compared with the prior art, the welding thermal stress simulation method, device, equipment and medium based on the crystal plastic finite element have the following beneficial effects.

[0055] This invention employs a crystal plastic constitutive model to accurately describe the flow behavior of materials at high temperatures. It considers crystal slip and polycrystalline interactions, reflecting the impact on material properties from the perspective of microstructure evolution. This addresses the difficulty in capturing the influence of microstructure on macroscopic mechanical properties in simulations of welded multiphase metallic materials. Two-dimensional characterization is obtained through metallographic experiments, and a three-dimensional polycrystalline model is reconstructed using multimodal data processing software. Combined with forward tensile and shear simulations, parameters such as Young's modulus and stiffness matrix are accurately calculated, improving the accuracy of the stiffness matrix. By dividing the temperature field into regions and combining it with a thermo-elastic-plastic model to calculate stress evolution and residual stress, the accuracy of welding thermal stress calculation is improved, effectively reflecting the correlation between microstructure and macroscopic stress.

[0056] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0057] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the specific embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some specific embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0058] Figure 1 This is a flowchart of a welding thermal stress simulation method based on crystal plastic finite element method.

[0059] Figure 2 This is a schematic diagram of grain coordinates.

[0060] Figure 3 The flowchart for solving the stiffness matrix.

[0061] Figure 4 The flowchart is for solving the residual stress. Detailed Implementation

[0062] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structure, features and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0063] The welding thermal stress simulation method based on crystal plastic finite element method disclosed in this invention has the following specific steps.

[0064] Initiate the simulation calculation and, based on the specific type of multiphase metal material, formally begin the welding thermal stress simulation calculation process.

[0065] S1. Metallographic experimental data acquisition: Sample preparation is carried out according to the specific multiphase metal material. Metallographic experimental methods such as electron backscattering experiments are used to obtain the phase distribution and crystal orientation information of the material in two-dimensional plane. At the same time, indicators such as grain size and shape, grain boundaries (including low-angle and high-angle boundaries) and grain morphology (covering grain shape, size and arrangement) are extracted. Among them, crystal orientation is used for texture analysis, and the phase identification results provide a basis for phase transformation behavior.

[0066] S2. Reconstruction of the three-dimensional polycrystalline model: Import the two-dimensional metallographic information obtained in step S2 into the multimodal data processing software to reconstruct the three-dimensional polycrystalline model.

[0067] Set the crystal structure and volume fraction in the software, and import the grain distribution and size data to obtain the probability density function of the grain size distribution.

[0068] Extract grain orientation features and import them into the software. Based on the generated microstructure distribution pole map, the generated three-dimensional polycrystal possesses grain orientation distribution features similar to those of the two-dimensional data.

[0069] Set the number of metallographic phases, and assign different metallographic names and numbers to multiphase materials.

[0070] During initialization, set the number of grid points and the size of grid cells to determine the three-dimensional dimensions of the model, the number of grids, and the estimated number of grains.

[0071] After the software completes the calculation, it outputs a file in a specific format, which is then imported into visualization software to check whether the model meets the requirements.

[0072] S3. Crystal Plasticity Finite Element Simulation Setup and Simulation: Import the three-dimensional polycrystalline model into the crystal plasticity finite element simulation software.

[0073] Boundary conditions are set according to different phases of the material, and different characteristic parameters are set for the elastic and plastic stages respectively. Material thermal damage is simulated in the high-temperature region. The high-temperature region specifically refers to the local area where the temperature significantly exceeds the critical value of material phase transformation during welding. Among them, the molten pool region is the absolute high-temperature region, the heat-affected zone is the medium-high temperature region, and the base material region is the non-high-temperature region.

[0074] A phenomenological crystal plastic constitutive model is adopted, and the elastic parameters are determined experimentally. For multiphase materials, different elastic moduli need to be set for different phases.

[0075] The crystal structure and corresponding slip system are defined, the decomposition shear stress of the slip system and twin system is determined, the single slip system of the single crystal sample is calibrated by uniaxial tensile test, and the multi-slip system of the polycrystalline sample is calibrated by hydrostatic loading test.

[0076] In the simulation, the deformation gradient and stress boundary conditions are combined to simulate uniaxial tensile and shear deformation experiments on orthotropic materials and determine the direction. The corresponding stress-strain curves are obtained through multiple calculations, and the forward tensile and shear simulation is completed.

[0077] S4. Stiffness matrix calculation, based on stress and strain data output by crystal plasticity finite element simulation software.

[0078] Young's modulus is calculated from the tensile stress-strain curve, and shear modulus is calculated from the shear deformation stress-strain curve.

[0079] The Poisson's ratio is obtained by using the relationship between shear modulus, Young's modulus and Poisson's ratio.

[0080] Based on the obtained parameters such as Young's modulus, shear modulus, and Poisson's ratio, the compliance matrix is ​​first obtained for orthotropic materials, and then the macroscopic stiffness matrix is ​​obtained through the transformation relationship between the compliance matrix and the stiffness matrix.

[0081] S5. Temperature field setting: Divide the temperature field into the base material region, the heat-affected zone, and the molten pool region.

[0082] The parent material region adopts a linear elastic constitutive model. Since the temperature has not reached the solid phase transition initiation temperature, the thermal stress originates from thermal expansion or contraction and conforms to the linear elastic law.

[0083] Since the temperature in the heat-affected zone is within the solid-state phase transition range, the calculation incorporates corrective data for yield strength and hardening coefficient that vary with temperature.

[0084] When the temperature in the molten pool region exceeds the liquidus line, the characteristics of the molten metal flow and the microstructure reconstruction, heat dissipation, and porosity defects during the solidification process must be considered.

[0085] Define the differential equations for heat conduction, boundary conditions (such as convective heat release conditions), and a moving Gaussian heat source model for orthotropic materials.

[0086] S6. Thermal strain calculation: Based on the thermo-elastic-plastic model, the time difference method is used to calculate the temperature difference at a certain point in the temperature field at different times. For anisotropic materials, the thermal strain at that point is calculated by combining its thermal expansion coefficient (second tensor) related to the crystal orientation.

[0087] S7. Stress evolution calculation, based on the thermo-elastic-plastic model.

[0088] Based on the theory of linear elasticity, it is clear that strain is caused by both temperature change and stress, and the stress-strain relationship is established using Hooke's law.

[0089] Using thermal strain as the initial strain, and combining the strain-displacement matrix, shape function, and displacement, the element stiffness matrix and thermal load are obtained through the elastic body strain energy formula.

[0090] The equilibrium equations are established based on the principle of minimum potential energy. After solving for the displacement, the strain is obtained, and then the stress evolution is calculated.

[0091] S8. Characterization of residual stress and deformation during welding thermal stress simulation.

[0092] As the heat source moves, the thermal expansion of the weld and the metal near the weld zone is constrained, resulting in compressive plastic strain. After cooling, some of the strain remains, forming residual stress.

[0093] For each welding time step, the temperature field distribution is acquired, and the temperature difference after cooling is calculated in the order of the time steps.

[0094] Compressional plastic strain is obtained by combining temperature difference and linear expansion coefficient, and then imported into constitutive model to calculate residual stress value under temperature field after cooling, thus completing the characterization of residual stress and deformation.

[0095] The welding thermal stress simulation device based on crystal plastic finite element method includes: sample preparation module, reconstruction module, simulation module, stiffness module, partitioning and setting module, thermal strain module, stress module and residual stress module.

[0096] The sample preparation module is used to prepare samples based on specific multiphase metal materials and obtain information on the phase distribution and crystal orientation of the material in a two-dimensional plane through metallographic experiments.

[0097] The reconstruction module is used to import the two-dimensional metallographic information obtained from metallographic experiments into multimodal data processing software to reconstruct a three-dimensional polygrain model.

[0098] The simulation module is used to import the three-dimensional polycrystalline model into the crystal plasticity finite element simulation software, set boundary conditions according to different phases of the material, set different characteristic parameters for the material in the elastic and plastic stages, set the thermal damage of the material in the high-temperature region of the simulation, and perform forward tensile and shear simulation of the crystal after the material properties and temperature conditions are set.

[0099] The stiffness module is used to calculate the Young's modulus, shear modulus, and Poisson's ratio of the metallic material based on the stress-strain data output by the crystal plasticity finite element simulation software, and then obtain the macroscopic stiffness matrix of the material.

[0100] The partitioning and setting module is used to divide the temperature field into the base material region, the heat-affected region, and the molten pool region, and to set the heat conduction differential equation, boundary conditions, and heat source model.

[0101] The thermal strain module is used to calculate thermal strain based on a thermo-elastoplastic model.

[0102] The stress module is used to calculate stress evolution based on a thermo-elastic-plastic model.

[0103] The residual stress module is used to characterize residual stress and its evolution based on the temperature field after cooling, in order to complete the simulation calculation of welding thermal stress.

[0104] The welding thermal stress simulation device based on crystal plasticity finite element method includes a processor, a memory, and a computer program stored in the memory. The computer program can be executed by the processor to implement the aforementioned welding thermal stress simulation method based on crystal plasticity finite element method.

[0105] A computer-readable storage medium includes a stored computer program, wherein, when the computer program is executed, it controls the device on which the computer-readable storage medium is located to perform the welding thermal stress simulation method based on crystal plastic finite element method as described above.

[0106] Example 1: This example focuses on the laser welding process of austenitic stainless steel multiphase metal materials. It employs a welding thermal stress simulation method based on crystal plasticity finite element method to accurately simulate the microstructure evolution and macroscopic stress distribution during the welding process. Austenitic stainless steel is widely used in welded structural components in chemical, aerospace and other fields due to its excellent corrosion resistance and mechanical properties. However, during the welding process, defects such as cracks and deformation are easily generated due to thermal stress concentration. Traditional simulation methods are difficult to reflect the influence of microscopic grain orientation and phase distribution on macroscopic stress. This example achieves cross-scale simulation of welding thermal stress from micro to macro through crystal plasticity modeling and multi-field coupling analysis, providing a precise theoretical basis for welding process optimization.

[0107] The specific implementation process is as follows.

[0108] S1. Simulation initialization: Based on the characteristics of the austenitic stainless steel material to be welded, the simulation object is determined to be a multiphase metal system. The welding thermal stress simulation calculation process is then initiated (see...). Figure 1 The simulation objective is to obtain the stress evolution law during the welding process and the distribution of residual stress after welding.

[0109] S2. Metallographic Data Acquisition: Austenitic stainless steel samples were prepared, and electron backscatter diffraction (EBSD) experiments were used to obtain microscopic information about the material. The distribution characteristics of the austenitic and ferrite phases in a two-dimensional plane were acquired through metallographic experiments, and crystal orientation data were extracted for texture analysis. Grain size, shape parameters, and arrangement were recorded (see [reference]). Figure 2 (Schematic diagram of grain coordinate distribution), distinguishing between low-angle (<15°) and high-angle (≥15°) grain boundaries. Phase identification technology is used to determine the distribution regions of different phases, providing fundamental data for subsequent phase transformation behavior analysis.

[0110] S3. Three-dimensional polygrain model reconstruction: Import two-dimensional metallographic data into multimodal data processing software for three-dimensional reconstruction.

[0111] The crystal structures and volume fractions of austenite and ferrite are set, and grain size distribution data is imported to generate a probability density function. Crystal orientation features are extracted to generate a microstructure distribution pole map, ensuring the grain orientation distribution of the 3D model matches the 2D experimental data. The multiphase materials are named and numbered, the number of mesh points and element size are initialized, and the 3D dimensions of the model and the estimated number of grains are determined. After the software calculation is complete, a standard format file is output and imported into visualization software to verify whether the grain morphology and boundary distribution of the model conform to the characteristics of the actual material.

[0112] S4. Crystal plasticity finite element simulation settings: Import the three-dimensional polycrystalline model into the crystal plasticity finite element software and configure the simulation parameters.

[0113] A phenomenological crystal plastic constitutive model was adopted, and elastic modulus parameters were set for the austenite and ferrite phases respectively. A slip system for a face-centered cubic crystal structure was defined, and the Schmid factor was calculated. ,in The direction of sliding. For the normal direction of the slip surface, This represents the macroscopic stress tensor. Stress-strain curves of single-crystal specimens were obtained through uniaxial tensile tests, based on the yield stress formula. Inversely derive the critical shear stress of a single-slip system, where For yield stress, For shear stress, The friction coefficient is used. Hydrostatic loading tests were conducted on the polycrystalline samples, and the critical shear stress was adjusted using an optimization algorithm to match the simulated stress-strain curve with the experimental data. The deformation gradient rate tensor was used in the simulation. With the first type of Piola-Kirchhoff stress tensor To characterize the boundary conditions, six tensile-shear calculations were performed on the orthogonal anisotropic region to obtain complete stress-strain curves of tensile stress and shear stress in three directions.

[0114] S5. Stiffness matrix calculation: Key parameters are calculated based on the stress-strain data output from the simulation (see...). Figure 3 (Stiffness matrix solution process).

[0115] Linear fitting was performed on the positive tensile curve, according to Young's modulus formula. The slope value of the elastic stage is the Young's modulus. Similarly, the shear deformation curve is treated as follows: Calculate the shear modulus Using relationships Derivation of Poisson's ratio ,in Let Poisson's ratio be the material value. Solve for the compliance matrix of the orthotropic material. ,pass Calculating the stiffness matrix using transformation relationships , obtain Complete parameters, etc.

[0116] S6. Temperature field region division and parameter setting: The welding area is divided into three characteristic regions.

[0117] The base material region has a temperature below the solid-state phase transition temperature. A linear elastic model is used, and thermal stress is caused only by thermal expansion and contraction.

[0118] Heat-affected zone. The temperature is in the phase transition range, so a modified model is introduced to adjust the yield strength and hardening coefficient as they vary with temperature.

[0119] Molten pool region. Temperature exceeds the liquidus line; consider liquid metal flow and solidification structure reconstruction.

[0120] Establish the differential equation for heat conduction. ,in For each thermal conductivity, For specific heat capacity, The density is given. The boundary conditions adopt a convection-exothermic model. , Thermal conductivity, The heat transfer coefficient is given. The heat source model uses a moving Gaussian heat source. ,in For the speed at which the heat source moves, This refers to the laser power.

[0121] S7. Thermal strain calculation: The time difference method is used to calculate the thermal strain.

[0122] Select any point within the temperature field and calculate and Temperature difference over time Considering the anisotropic characteristics of austenitic stainless steel, the coefficient of thermal expansion... For a second-order tensor, according to Calculate thermal strain, where the coefficient of thermal expansion is related to crystal orientation.

[0123] S8. Stress evolution calculation, stress analysis based on a thermo-elastoplastic model.

[0124] According to linear elasticity theory, strain is decomposed into ,in Establish relationships through Hooke's Law. Substituting into the strain-displacement equation ,in The strain matrix, For shape functions, This is the displacement. Based on the principle of minimum potential energy. Equilibrium equations are established, and after solving for displacement, strain is calculated inversely to obtain stress evolution data.

[0125] S9. Residual stress characterization: During welding, the movement of the heat source causes constrained thermal expansion in the weld zone, resulting in compressive plastic strain. After cooling, the remaining portion forms residual stress (see...). Figure 4 (Residual stress solution process).

[0126] The temperature field difference after cooling is calculated sequentially over time. The compressive plastic strain is then determined using the coefficient of linear expansion. The strain data is imported into the constitutive model to calculate the residual stress distribution after cooling, thus completing the entire welding thermal stress simulation process.

[0127] In summary, this embodiment achieves accurate simulation of welding thermal stress in austenitic stainless steel using the crystal plasticity finite element method. Compared with traditional macroscopic simulation, this method captures the influence of microstructure characteristics on macroscopic properties through three-dimensional multigrain modeling, improving the accuracy of stiffness matrix calculation. The use of a partitioned temperature field model coupled with a moving heat source accurately reflects the differences in mechanical behavior between the molten pool, heat-affected zone, and base material. This embodiment verifies the effectiveness of the crystal plasticity finite element method for welding thermal stress simulation in the welding analysis of multiphase metallic materials, providing a reliable numerical simulation tool for the process optimization of high-precision welded structures.

[0128] Example 2: This example focuses on the laser welding process of high-strength aluminum alloys (including aluminum-copper-magnesium multiphase systems). It employs a welding thermal stress simulation method based on crystal plasticity finite element method, focusing on analyzing the influence mechanism of microscopic grain evolution on macroscopic residual stress during welding. High-strength aluminum alloys, due to their high specific strength and significant lightweight characteristics, are widely used in structural welded components in fields such as rail transportation and new energy vehicles. However, during welding, thermal deformation and residual stress can easily lead to a decline in joint performance. Traditional simulation methods struggle to accurately describe the high-temperature mechanical behavior of their multiphase structure (including the matrix phase and strengthening phase). This example utilizes micro-macro coupled modeling to achieve precise transfer of thermal stress from the crystal scale to the structural scale, providing numerical support for optimizing welding process parameters and controlling welding deformation.

[0129] The specific implementation process is as follows.

[0130] S1. Simulation initialization: Based on the multiphase composition characteristics of high-strength aluminum alloys (including Al matrix phase, Al2Cu strengthening phase, and trace amounts of Mg), the welding thermal stress simulation calculation process is initiated (see...). Figure 1 It is clear that the simulation should focus on capturing the grain coarsening phenomenon in the heat-affected zone and the stress accumulation law during the solidification process of the molten pool.

[0131] S2. Metallographic experimental data acquisition: High-strength aluminum alloy samples were prepared, and microstructure information was obtained using electron backscattering experiments. The distribution characteristics of the matrix phase (Al) and strengthening phase (Al₂Cu) in the two-dimensional plane were identified through metallographic analysis, and crystal orientation data was extracted for texture evolution analysis. Grain size and shape parameters of different phases were recorded, and low-angle subgrain boundaries and high-angle grain boundaries were distinguished (see...). Figure 2 (Medium grain coordinates and stress component distribution). Phase identification technology is used to determine the precipitation location and density of strengthening phases, providing basic parameters for subsequent plastic deformation analysis.

[0132] S3. Reconstruction of a three-dimensional polycrystalline model: Based on two-dimensional metallographic data, the reconstruction of the three-dimensional polycrystalline model is completed using multimodal data processing software.

[0133] Crystal parameters and volume fractions of the Al matrix phase (face-centered cubic structure) and Al₂Cu phase (face-centered cubic structure) were set separately, and grain size distribution data were imported to generate probability density functions. Crystal orientation features were extracted to generate microstructure pole figures, ensuring that the grain orientation distribution of the 3D model was consistent with the 2D experimental data. The two phases were named and numbered, mesh parameters were initialized to determine the model size and grain number, and the grain morphology and boundary features of the model were verified using visualization software.

[0134] S4. Crystal plasticity finite element simulation settings: Import the 3D model into the crystal plasticity finite element software for parameter configuration.

[0135] A phenomenological crystal plastic constitutive model was adopted, with different elastic moduli assigned to the matrix and reinforcing phases. The slip systems of the matrix and reinforcing phases were defined, and the Schmid factor was calculated. ,in The direction of sliding. The slip plane is normal. The stress-strain curve of the single crystal was obtained through uniaxial tensile testing, based on... The critical shear stress was calculated by reverse engineering. Hydrostatic loading was applied to the polycrystalline sample, and the critical shear stress was adjusted using an optimization algorithm to match the experimental curve. The deformation gradient rate tensor was used in the simulation. With stress tensor Characterize the boundary conditions and perform six tensile-shear calculations on the orthotropic region to obtain complete stress-strain data.

[0136] S5. Stiffness matrix calculation, based on stress-strain data output from simulation, according to... Figure 3 The process calculates the stiffness matrix parameters.

[0137] Linear fitting of the forward stretching curve, according to Calculate Young's modulus. Apply the shear curve according to... Calculate the shear modulus using Derivation of Poisson's ratio Solve for the orthogonal anisotropic compliance matrix. ,pass The stiffness matrix is ​​obtained by transformation. .

[0138] S6: Temperature field region division and parameter setting, dividing the welding area into three characteristic regions.

[0139] The base material region. The temperature is below the recrystallization temperature, and a linear elastic model is used, with thermal stress originating from thermal expansion and contraction.

[0140] Heat-affected zone. The temperature is within the recrystallization range, so a modified model for yield strength and hardening coefficient that varies with temperature is introduced.

[0141] Molten pool region. Temperature exceeds the liquidus line; consider liquid metal flow and solidification shrinkage.

[0142] Establish the heat conduction equation. Boundary conditions adopted The heat source model uses a moving Gaussian heat source. This simulates the heating process of a laser moving along the x-axis.

[0143] S7: Thermal strain calculation, based on a thermo-elastoplastic model, using the time difference method. and Temperature difference over time Combining the anisotropic thermal expansion coefficient (second-order tensor) according to Calculate thermal strain.

[0144] S8: Stress evolution calculation, using a thermo-elasto-plastic model to calculate stress evolution: in accordance with and Establish the stress-strain relationship. Substitute... Through the principle of minimum potential energy The stress evolution data are obtained by solving for the displacement and then calculating the strain.

[0145] S9: Residual stress characterization, according to... Figure 4 The process calculates residual stress.

[0146] The temperature difference after cooling is calculated according to the time step sequence, and the compressive plastic strain is obtained by combining the linear expansion coefficient. The strain is imported into the constitutive model to obtain the residual stress distribution after cooling, and the stress gradient in the weld zone and heat-affected zone is analyzed in detail.

[0147] In summary, this embodiment achieves accurate simulation of welding thermal stress in high-strength aluminum alloys using the crystal plasticity finite element method. Compared to traditional methods, this approach accurately captures the influence of the relative stress distribution during strengthening through three-dimensional multi-grain modeling, improving the accuracy of stiffness matrix calculation. The grain coarsening effect in the heat-affected zone is accurately simulated using a partitioned temperature field model. This embodiment verifies the applicability of this invention in the welding simulation of multiphase aluminum alloys, providing reliable micromechanical analysis for optimizing the welding process of lightweight structures and effectively reducing the risk of welding deformation and cracking.

[0148] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A simulation method for welding thermal stress based on crystal plasticity finite element method, characterized in that, Includes the following steps: Samples are prepared based on specific multiphase metallic materials, and the phase distribution and crystal orientation information of the material in two-dimensional plane are obtained through metallographic experiments. Based on the two-dimensional metallographic information obtained from the metallographic experiment, the data is imported into multimodal data processing software to reconstruct a three-dimensional polygrain model. The three-dimensional polycrystalline model was imported into the crystal plasticity finite element simulation software. Boundary conditions were set according to different phases of the material. Different characteristic parameters were set for the material in the elastic and plastic stages. Thermal damage of the material was set in the high-temperature region of the simulation. After the material properties and temperature conditions were set, the crystal was subjected to forward tensile and shear simulation. Based on the stress-strain data output by the crystal plasticity finite element simulation software, the Young's modulus, shear modulus and Poisson's ratio of the metal material are calculated, and then the macroscopic stiffness matrix of the material is obtained. The temperature field is divided into the base material region, the heat-affected region, and the molten pool region. The heat conduction differential equation, boundary conditions, and heat source model are set. Calculate thermal strain based on the thermo-elastic-plastic model; Stress evolution was calculated using a thermo-elastic-plastic model; The residual stress and its evolution are characterized by the temperature field after cooling, so as to complete the simulation calculation of welding thermal stress.

2. The welding thermal stress simulation method based on crystal plasticity finite element method according to claim 1, characterized in that, The metallographic experiment uses electron backscattering experiments, and the information obtained also includes grain size and shape. It focuses on extracting crystal orientation, grain boundary and grain morphology indicators. Among them, crystal orientation is used to provide texture analysis, grain boundary data includes low-angle and high-angle boundaries, phase identification provides a basis for the phase transformation behavior of the material, and grain morphology summarizes the grain shape, size and arrangement information. The reconstruction process of the three-dimensional polygrain model specifically includes: In the multimodal data processing software, the crystal structure and volume fraction are set, and the probability density function of the grain size distribution is obtained by importing the grain distribution and size data obtained from the metallographic experiment into the software. Grain orientation features were extracted from the metallographic experimental output data and imported into multimodal data processing software. Based on the generated microtexture distribution pole map, the generated three-dimensional polycrystal has grain orientation distribution features similar to those of the two-dimensional metallographic experimental data. Set the number of metallographic phases, and assign different metallographic names and numbers for multiphase materials; In the initialization, the number of grid points and the size of grid cells are set to determine the three-dimensional dimensions and number of grids of the polycrystalline model, and the number of grains in the generated polycrystalline model is estimated. After the multimodal data processing software finishes its calculations, it outputs a file in a specific format according to the rules. This file is then imported into visualization software to check the generated three-dimensional polycrystalline model.

3. The welding thermal stress simulation method based on crystal plasticity finite element method according to claim 1, characterized in that, The specific setup and simulation process for crystal plasticity finite element simulation include: A phenomenological crystal plastic constitutive model was adopted, and the parameters of the elastic part were determined experimentally. For multiphase metallic materials, different elastic moduli were set for different phases. In the material plasticity section, the crystal structure and corresponding slip system are defined, the decomposition shear stress of the slip system and twin system is determined, and the Schmid factor is calculated using the following formula: ,in, The direction of sliding. For the normal direction of the slip surface, For macroscopic stress tensor; For the calibration of a single-slip system in a single-crystal specimen, a uniaxial tensile test is used to obtain the stress-strain curve. The critical shear stress of a single slip system is then calculated using Schmid's law and the yield stress calculation formula. The yield stress calculation formula is as follows: ,in Indicates yield stress. Represents shear stress. The coefficient of friction, For exponential parameters; The calibration of the multi-slip system of the polycrystalline specimen was carried out by hydrostatic loading test. The experimental stress-strain curves output by different slip systems were activated by loading in different directions. The critical shear stress was adjusted to match the experimental data by combining the macroscopic stress-strain curves and the microscopic slip system activation status through optimization algorithm. The deformation gradient and stress boundary conditions are used together in the simulation process, using the deformation gradient rate tensor. and The rate of evolution of the deformation gradient in each direction is characterized using the first-type Piola-Kirchhoff stress tensor. Indicates stress boundary conditions; For orthotropic materials, the tensile and shear directions are determined in the simulation of uniaxial tensile and shear deformation experiments. After six calculations, stress-strain curves for three tensile stresses and three shear stresses are obtained.

4. The welding thermal stress simulation method based on crystal plasticity finite element method according to claim 1, characterized in that, The stiffness matrix calculation process specifically includes: For the stress-strain curve under normal tension, the Young's modulus is calculated using the formula... Calculate Young's modulus, where For Young's modulus, For stress, To adapt, a linear fit was performed on the data points of this stage, and the slope value obtained was the value of Young's modulus. For the stress-strain curve of shear deformation, the shear modulus is calculated using the formula... Calculate the shear modulus, where Shear modulus For stress, To adapt to the strain, a linear fit was performed on the data points of this stage, and the slope value obtained was the value of the shear modulus. It is known that the shear modulus is related to Young's modulus and Poisson's ratio. ,in Poisson's ratio; The necessary parameters for calculating the stiffness matrix can be obtained from the above formula. For orthogonal anisotropic materials, the compliance matrix is ​​obtained. stiffness matrix With the flexibility matrix The conversion relationship is as follows: Then, the elastic matrix of the three-dimensional polycrystalline model is obtained.

5. The welding thermal stress simulation method based on crystal plasticity finite element method according to claim 1, characterized in that, The temperature field setting process specifically includes: For the parent material region, the temperature has not reached the material's solid-state phase transformation initiation temperature, the material's microstructure has not undergone a phase transformation, and it retains its original grain structure. The thermal stress comes from thermal expansion or contraction, which conforms to the linear elastic law. In this region, the constitutive model is a linear elastic model. For the heat-affected zone, the temperature is within the solid-state phase transition temperature range. At this temperature, the material undergoes grain coarsening, recrystallization, or phase transformation. In the calculation process, the yield strength and hardening coefficient, which vary with temperature, are introduced to correct the simulation data. In the molten pool region, the temperature exceeds the liquidus temperature of the material. At this stage, the metal is completely melted and exhibits liquid flow characteristics. The solidification process is accompanied by microstructure reconstruction, heat dissipation, and the formation of porosity defects. When establishing the temperature field, the differential equation for heat conduction of orthotropic materials satisfies In the formula , These represent the thermal conductivity of the material in the x, y, and z directions, respectively. It is the specific heat capacity of the material. It is the density of the material. It is a heat source acting inside the workpiece; Define temperature Position coordinates and time The function satisfies For boundary conditions, the convective heat release at any known location on the material boundary satisfies the following conditions. In the formula The thermal conductivity of the material The convective heat transfer coefficient is... The temperature at the metal surface. The ambient temperature; For the heat source model, a Gaussian heat source model is adopted, and the function is: ,in for Surface heat flow at the location, This represents the maximum heat flux at the center of the heat source. Let be the heat flux concentration factor. During the welding simulation, the heat source is in a moving state, and the total heat released is . In summary, we can conclude that In the formula For welding input, Let be the radius of the heating area. ; In a Cartesian coordinate system, the welding laser source moves along the x-axis at... Move at a constant speed, and establish a coordinate system for the movement. The distance from the center of the heat source in the moving coordinate system is The effective power of the laser welding material is known to be ,have to .

6. The welding thermal stress simulation method based on crystal plasticity finite element method according to claim 1, characterized in that, Temperature calculations in the thermo-elastoplastic model use time differences to calculate the temperature at a point within the temperature field. Time and The temperature difference at time is For anisotropic materials, the coefficient of thermal expansion is... For second-order tensors The thermo-elastoplastic model of anisotropic materials is related to crystal orientation, and the thermal strain at any point in the temperature field is: ; The stress evolution calculation process specifically includes: According to linear elasticity theory, strain is caused by both temperature change and stress. According to Hooke's Law, the stress-strain relationship is: ; For anisotropic materials, based on the calculated thermal strain ,make According to the strain energy formula for elastic bodies, Substitute into the formula. The strain-displacement matrix, Represents shape functions, To express the displacement, we get The element stiffness matrix and thermal load are respectively 、 ; By the principle of minimum potential energy The equilibrium equations for the freely expanding constrained element are obtained. Find the displacement and substitute it into the equation. Get adaptable Substituting strain and thermal strain into The stress can be obtained.

7. The welding thermal stress simulation method based on crystal plasticity finite element method according to claim 1, characterized in that, The residual stress and deformation characterization process specifically includes: During the welding process, as the heat source moves, the thermal expansion strain of the weld and the near-weld zone is constrained by the surrounding cooler metal, resulting in compressive plastic strain. During the cooling process, this compressive plastic strain is partially offset by stretching, leaving a residual compressive plastic strain after welding. This strain causes residual stress inside the material. For the calculation of residual stress and deformation, in the welding thermal stress simulation process, after obtaining the specific temperature field distribution at each welding time step, the temperature difference of the cooled temperature field is calculated sequentially according to the time step order. The compressive plastic strain is obtained from the temperature difference and the coefficient of linear expansion. The stress value calculated by importing it into the constitutive model is the residual stress value under the temperature field after cooling.

8. A welding thermal stress simulation device based on crystal plasticity finite element method, characterized in that, Include: The sample preparation module is used to prepare samples based on specific multiphase metallic materials and obtain information on the phase distribution and crystal orientation of the material in a two-dimensional plane through metallographic experiments. The reconstruction module is used to import the two-dimensional metallographic information obtained from metallographic experiments into multimodal data processing software to reconstruct the three-dimensional polygrain model. The simulation module is used to import the three-dimensional polycrystalline model into the crystal plasticity finite element simulation software, set boundary conditions according to different phases of the material, set different characteristic parameters for the material in the elastic and plastic stages, set the thermal damage of the material in the high-temperature region of the simulation, and perform positive tensile and shear simulation of the crystal after the material properties and temperature conditions are set. The stiffness module is used to calculate the Young's modulus, shear modulus and Poisson's ratio of the metal material based on the stress and strain data output by the crystal plasticity finite element simulation software, and then obtain the macroscopic stiffness matrix of the material. The partitioning and setting module is used to divide the temperature field into the base material region, the heat-affected region, and the molten pool region, and to set the heat conduction differential equation, boundary conditions, and heat source model. The thermal strain module is used to calculate thermal strain based on a thermo-elastoplastic model. The stress module is used to calculate stress evolution based on a thermo-elasto-plastic model; The residual stress module is used to characterize residual stress and its evolution based on the temperature field after cooling, in order to complete the simulation calculation of welding thermal stress.

9. A welding thermal stress simulation device based on crystal plasticity finite element method, characterized in that, It includes a processor, a memory, and a computer program stored in the memory; the computer program can be executed by the processor to implement the welding thermal stress simulation method based on crystal plastic finite element method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein, when the computer program is executed, it controls the device on which the computer-readable storage medium is located to perform the welding thermal stress simulation method based on crystal plastic finite element method as described in any one of claims 1 to 7.

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