CN115062456B - Laser welding joint strength simulation analysis method based on tensile fracture evaluation - Google Patents
Laser welding joint strength simulation analysis method based on tensile fracture evaluation Download PDFInfo
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Abstract
The invention discloses a laser welding joint strength simulation analysis method based on tensile fracture evaluation, which is based on a finite element analysis method and comprises the steps of firstly simulating a laser welding process and a natural cooling process by adopting a thermo-elastic-plastic transient coupling method, then loading a physical state after natural cooling to a tensile model by adopting a predefined physical field method, respectively endowing different material properties to a welding seam area, a heat affected area and a base metal, and finally analyzing the tensile process by adopting a display dynamics method. The simulation method disclosed by the invention can simulate the tensile test of the laser welding joint, fully analyzes the influence of the cooled physical field and the inconsistency of the material properties of different areas on the tensile result, has more accurate calculation result, and can simulate and calculate the tensile strength of the laser welding joint with various shapes.
Description
Technical Field
The invention belongs to the technical field of simulation methods, and particularly relates to a simulation analysis method for the strength of a laser welding joint based on tensile fracture evaluation.
Background
The laser welding is that the light beam emitted from the laser passes through the focusing system to form a focusing light spot, the workpiece to be welded is arranged at a defocusing position with a certain distance from the focal point, the workpiece to be welded reaches a melting point to form a molten state under the action of high-energy beam laser with relatively uniform power density distribution, and the workpiece to be welded is connected into a whole after being naturally cooled. As a connecting method, laser welding is widely applied to many fields of industrial production, such as aerospace field, automobile industry, ship industry and the like, because of its advantages of high efficiency, high material utilization rate, good joint sealing performance, strong corrosion resistance and the like.
According to different weld shapes, the weld can be divided into penetration, non-penetration, wide weld and narrow weld, and the structure performance, plastic deformation, residual stress and the like of different welds have influence on the weld strength, so that the judgment of the strength of different welds through a tensile test is particularly important. The steps required for completing a tensile test of the welded joint comprise sample cutting, welding, cooling and stretching, particularly the welding process needs to be debugged, so that a long time is needed, and the steps are repeated if the strength of the welded joint with different shapes is analyzed. By adopting the simulation method, the tensile test phenomenon which is difficult to observe can be simulated, and the simulation time is short. At present, a simulation method for stretching a welding joint is generally similar to that described in 'elasto-plastic evolution and fracture numerical analysis of 301L overlap laser welding joint stretching process', a welding sample grid model is established, material attributes are given, a displacement boundary is set, and statics or dynamics calculation is carried out.
Disclosure of Invention
The invention aims to solve the existing problems and provides a laser welding joint strength simulation analysis method based on tensile fracture evaluation, which introduces the influence of a physical field after welding and cooling on a tensile result, so that the initial physical state of a welding sample is more practical, and a calculation result is more accurate.
The technical solution of the invention is as follows:
the laser welding joint strength simulation analysis method based on the tensile fracture evaluation comprises the following steps of:
welding, cooling and analyzing:
(1) importing a grid model: importing the grid model into nonlinear finite element analysis software;
(2) and (3) changing the grid property: setting the imported grid attributes as temperature-displacement coupling units under an implicit solver;
(3) endowing the material with the following properties: assigning all cells to the same isotropic material properties;
(4) setting an analysis step: setting analysis steps of a welding process and a cooling process, wherein the analysis steps are implicit transient thermodynamic coupling analysis;
(5) setting load and boundary conditions: loading a heat source load on the whole grid model, and performing full constraint on partial nodes at a certain distance from a welding line;
(6) solving and analyzing: submitting and calculating the settings to obtain a solving result;
step (2) tensile analysis:
(1) importing a grid model: importing a grid model into nonlinear finite element analysis software;
(2) and (3) changing the grid attribute: the imported grid attributes are set as temperature-displacement coupling units under an explicit solver, the display solver does not need balance iteration, and the calculation speed is high and convergence is easy;
(3) endowing the material with the following properties: respectively endowing corresponding material properties to the welding seam area, the heat affected zone and the base metal;
(4) setting an analysis step: setting the analysis step of the stretching process as explicit kinetic analysis;
(5) setting a predefined physical field and boundary conditions: loading the final solution result in the step (1) to a stretching grid model in a predefined physical field mode, fully constraining one end of the stretching grid model, and setting a displacement boundary at the other end of the stretching grid model, namely, stretching on one side;
(6) solving and analyzing: and submitting and calculating the settings to obtain a simulation result.
Furthermore, the grid model adopts a transition grid dividing method, the number of grids is reduced, the calculation speed is improved, the grids are divided into hexahedral grids, and the appearance of the welding seam is calculated by utilizing a stress gradient algorithm in the hexahedral grids.
Furthermore, the stress inside the hexahedral mesh adopts a gradient algorithm, and a plurality of stress and strain integral points exist inside the unit and are used for accurately describing the region of stress-strain gradient change.
Further, the nonlinear finite element analysis software is ABAQUS.
Furthermore, the introduced grid models in the step (1) and the step (2) are the same grid model, so that the accuracy of the introduced predefined physical field is ensured.
Further, in the step of giving material properties in the step (1) and the step (2), the material properties include an elastic modulus, a poisson's ratio, a thermal conductivity coefficient, a thermal expansion coefficient, a plasticity parameter, a specific heat and a density which change with temperature.
Further, in the step of setting a predefined physical field and boundary conditions in step (2), the solution result finally obtained in step (1) is loaded to the tensile grid model in the manner of the predefined physical field, that is, the physical state of the stress strain finally solved in step (1) is taken as the initial state of step (2).
Further, in the step of setting load and boundary conditions in the step (1), the used heat source model is a double-ellipsoid heat source, a double-ellipsoid heat source subprogram is set by using finite element analysis software, and the double-ellipsoid heat source subprogram adopts a formula as follows:
f 1 +f 2 ＝2
wherein, f 1 、f 2 Is a coefficient, q 1 、q 2 To power, a 1 、a 2 The half axis length of the front half ellipsoid and the half axis length of the back half ellipsoid in the x direction are respectively, and the b and the c are the half axis lengths of the front half ellipsoid and the back half ellipsoid in the y direction and the z direction respectively.
Further, the length of the half axis b of the front half ellipsoid y and the z direction is equal to the length of the half axis c of the rear half ellipsoid y and the z direction.
The invention has the advantages that:
1. the tensile test sample is endowed with physical properties such as residual stress, plastic strain and the like after welding and cooling, so that the initial physical state of the tensile test sample is more consistent with the actual state, and the calculation result is more accurate.
2. And the weld appearance of the tensile sample is endowed while the predefined physical field is loaded.
Drawings
The technical solution and other advantages of the present application will become apparent from the detailed description of the embodiments of the present application with reference to the accompanying drawings.
Fig. 1 is a flow chart of a simulation analysis method for laser welding joint strength based on tensile fracture evaluation according to the present invention.
FIG. 2 is a schematic structural diagram of a mesh model of the present invention.
Fig. 3 shows a tensile plastic strain distribution to which physical properties such as residual stress and plastic strain are not imparted in the present invention.
Fig. 4 shows a tensile plastic strain distribution to which physical properties such as residual stress and plastic strain are imparted according to the present invention.
Detailed Description
The technical solutions of the present invention are further described below with reference to the accompanying drawings and examples, but the scope of the present invention should not be limited thereby.
The invention discloses a laser welding joint strength simulation analysis method based on tensile fracture evaluation, which is based on a finite element analysis method and comprises the steps of firstly simulating a laser welding process and a natural cooling process by adopting a thermo-elastic-plastic transient coupling method, then loading a physical state after natural cooling to a tensile model by adopting a predefined physical field method, respectively endowing different material properties to a welding seam area, a heat affected area and a base metal, and finally analyzing the tensile process by adopting a display solver.
Specifically, referring to fig. 1, fig. 1 is a flow chart of a simulation analysis method for laser welding joint strength based on tensile fracture evaluation, which includes the following steps:
welding, cooling and analyzing:
(1) importing a grid model: and (3) carrying out meshing on the geometric model, dividing the divided mesh model into an upper plate, a lower plate, a welding seam area and a heat affected zone as shown in figure 2, reducing the number of meshes by using a transitional meshing method, wherein all the meshes are hexahedrons, and introducing the mesh model into nonlinear finite element analysis software because the stress in the hexahedron meshes adopts a gradient algorithm. A plurality of stress and strain integral points exist inside the hexahedral mesh, and can be used for accurately describing the region of stress-strain gradient change; the hexahedron grid means a literal meaning, and six faces are solid units of eight nodes. The solid elements have hexahedral elements and tetrahedral elements. The meaning of "cell" and "grid". The nonlinear finite element analysis software is ABAQUS.
(2) And (3) changing the grid attribute: the imported grid attributes are set as temperature-displacement coupling units under an implicit solver, and the grid units must have corresponding physical attributes because transient thermo-elastic-plastic coupling analysis is adopted in the analysis process.
(3) Endowing the material with the following properties: all units are endowed with the same isotropic material properties, the material properties comprise a series of elastic modulus, poisson's ratio, heat conduction coefficient, thermal expansion coefficient, plasticity parameters, specific heat, density and the like which change along with the temperature, and because the temperature change is large in the analysis process, the highest temperature is above 1000 ℃, and under the condition of severe temperature change, the material properties under different temperatures must be loaded.
(4) Setting an analysis step: and setting analysis steps of the welding process and the cooling process, wherein the analysis steps are implicit transient thermal coupling analysis, the analysis time of the welding process is calculated according to the total length of a welding path and the welding speed, and the analysis time of the cooling process takes the model temperature reduced to room temperature as a standard.
(5) Setting load and boundary conditions: the heat source load is loaded on the whole grid model, the heat source model used in the embodiment is a double-ellipsoid heat source, a double-ellipsoid heat source subprogram is developed by utilizing the secondary development function of finite element analysis software, and the double-ellipsoid formula is as follows:
f 1 +f 2 ＝2
wherein f is 1 、f 2 Is a coefficient, q 1 、q 2 Is power, a 1 、a 2 The half shaft length of the front half ellipsoid and the half shaft length of the back half ellipsoid in the x direction, and the half shaft length of the front half ellipsoid and the half shaft length of the back half ellipsoid in the y direction and the z direction, b and c are the half shaft length of the front half ellipsoid and the half shaft length of the back half ellipsoid in the z direction。
General rule f 1 The value of 2/3, f 2 Taking a value of 4/3; the semi-axes of the front and back semi-ellipsoids in the y and z directions are consistent, namely the length of the semi-axis b of the front semi-ellipsoid in the y and z directions is equal to the length of the semi-axis c of the back semi-ellipsoid in the y and z directions, and b = c.
At a certain distance from the welding line, namely the position of a clamp in the welding process, fully restricting partial nodes;
(6) solving and analyzing: establishing an analysis task for the welding and cooling processes, submitting the analysis task to calculation, obtaining a solving result, and analyzing the solving result;
step (2) tensile analysis:
(1) importing a grid model: loading the grid model in the step (1) into nonlinear finite element analysis software, and using the same grid model to ensure that the loading result of the subsequent predefined physical field is completely consistent with the final analysis result in the step (1);
(2) and (3) changing the grid property: the imported grid attributes are set as temperature-displacement coupling units under an explicit solver, and the explicit solver does not need to carry out balance iteration, so that the solution speed is higher and convergence is easy compared with the implicit dynamics analysis;
(3) endowing the material with the following properties: the welding seam area, the heat affected zone and the base metal are distinguished during grid division, three areas are determined by test tests, corresponding grids of the three areas are selected respectively, corresponding material attributes such as elastic modulus, plastic parameters, density and the like are given, after welding and cooling processes are carried out, the material attributes of the welding seam area and the heat affected zone are changed, and the calculation result is more accurate after the corresponding material attributes are given respectively;
(4) setting an analysis step: setting an analysis step of a stretching process as explicit dynamics analysis, and setting a mass amplification coefficient on the premise of ensuring undistorted calculation results to improve the calculation speed;
(5) setting a predefined physical field and boundary conditions: loading the final solution result in the step (1) to the stretching grid model in a predefined physical field mode, namely taking the physical state of the stress strain finally solved in the step (1) as the initial state of the step (2), namely assigning all information contained in the result file in the step (1) to the stretching grid model, wherein the initial physical state of the step (2) is the final physical state of the step (1), one end of the stretching grid model is fully constrained, and the other end of the stretching grid model is provided with a displacement boundary, namely unilateral stretching;
(6) solving and analyzing: an analysis task is created and submitted for the stretching process, a simulation result is obtained, and a plastic strain distribution is checked, as shown in fig. 3, the average value (Avg) of the plastic strain (PEEQ) is 75%, the plastic strain (PEEQ) of a heat affected zone is the maximum, the maximum value (Max) is 0.7978, and the area is most prone to fracture.
Fig. 4 shows the distribution of plastic strain in the tensile simulation of the sample to which physical properties such as residual stress after welding and cooling are not given, the maximum value is 0.5924, which is smaller than the maximum value in fig. 3, and the calculation result underestimates the fracture risk.
According to the welding joint tensile test simulation method disclosed by the invention, physical characteristics such as residual stress, plastic strain and the like which are unevenly distributed after welding and cooling are loaded on a welding sample, a simulation model is more in line with the reality, and a calculation result is more in line with the reality.
The method for simulation analysis of the strength of the laser welding joint based on tensile fracture evaluation provided by the embodiment of the application is described in detail, a specific example is applied in the method for description of the principle and the implementation mode of the application, and the description of the embodiment is only used for helping understanding the technical scheme and the core idea of the application; those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications or substitutions do not depart from the spirit and scope of the present disclosure as defined by the appended claims.
Claims (10)
1. A laser welding joint strength simulation analysis method based on tensile fracture evaluation is characterized by comprising the following steps:
welding, cooling and analyzing:
(1) importing a grid model: importing the grid model into nonlinear finite element analysis software;
(2) and (3) changing the grid property: setting the imported grid attributes as temperature-displacement coupling units under an implicit solver;
(3) endowing the material with the following properties: assigning all units to the same isotropic material properties;
(4) setting an analysis step: setting analysis steps of a welding process and a cooling process, wherein the analysis steps are implicit transient thermodynamic coupling analysis;
(5) setting load and boundary conditions: loading a heat source load on the whole grid model, and performing full constraint on partial nodes at a certain distance from a welding line;
(6) solving and analyzing: submitting and calculating the settings to obtain a solving result;
step (2) tensile analysis:
(1) importing a grid model: importing a grid model into nonlinear finite element analysis software;
(2) and (3) changing the grid property: setting the imported grid attributes as temperature-displacement coupling units under an explicit solver;
(3) endowing the material with the following properties: respectively endowing corresponding material properties to the welding seam area, the heat affected zone and the base metal;
(4) setting an analysis step: setting the analysis step of the stretching process as explicit kinetic analysis;
(5) setting a predefined physical field and boundary conditions: loading the final solution result in the step (1) to a stretching grid model in a predefined physical field mode, fully constraining one end of the stretching grid model, and setting a displacement boundary at the other end of the stretching grid model, namely, stretching on one side;
(6) solving and analyzing: and submitting and calculating the settings to obtain a simulation result.
2. The method for simulation analysis of the strength of the laser welding joint based on the tensile failure evaluation as claimed in claim 1, wherein the grid model adopts a division method of transition grids.
3. The method of claim 1, wherein the mesh model is divided into hexahedral meshes.
4. The method for simulation analysis of the strength of the laser welding joint based on the tensile fracture evaluation as claimed in claim 3, wherein a gradient algorithm is adopted for the stress inside the hexahedral mesh, and a plurality of stress and strain integral points exist inside the unit, so as to accurately describe the area of the stress-strain gradient change.
5. The method as claimed in claim 1, wherein the nonlinear finite element analysis software is ABAQUS.
6. The method for simulation analysis of the strength of the laser welding joint based on the tensile failure evaluation as claimed in claim 1, wherein the introduced mesh models in the step (1) and the step (2) are the same mesh model.
7. The method for simulation analysis of the strength of the laser welding joint based on the tensile failure evaluation as claimed in claim 1, wherein in the step of giving the material properties in the steps (1) and (2), the material properties comprise elastic modulus, poisson's ratio, thermal conductivity coefficient, thermal expansion coefficient, plasticity parameter, specific heat and density which change along with temperature.
8. The method for simulation analysis of the strength of the laser welding joint based on the tensile failure evaluation according to claim 1, wherein in the step of setting the predefined physical field and the boundary condition in step (2), the final solution result in step (1) is loaded to the tensile grid model in the manner of the predefined physical field, that is, the physical state of the stress strain finally solved in step (1) is used as the initial state of step (2).
9. The method for simulation analysis of the strength of the laser welding joint based on the tensile fracture evaluation as claimed in claim 1, wherein in the step of setting the load and the boundary conditions in step (1), the heat source model used is a double-ellipsoid heat source, a double-ellipsoid heat source subroutine is set by using finite element analysis software, and the double-ellipsoid heat source subroutine adopts the formula:
f 1 +f 2 ＝2
wherein f is 1 、f 2 Is a coefficient, q 1 、q 2 Is power, a 1 、a 2 The half axis length of the front half ellipsoid and the half axis length of the back half ellipsoid in the x direction are respectively, and b and c are the half axis lengths of the front half ellipsoid and the back half ellipsoid in the y direction and the z direction respectively.
10. The method for simulation analysis of the strength of the laser welding joint based on the tensile failure evaluation as claimed in claim 9, wherein the length of the half axis b in the y and z directions of the front half ellipsoid is equal to the length of the half axis c in the y and z directions of the rear half ellipsoid.
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