Welding residual stress simulation method

Abstract

The invention provides a welding residual stress simulation method which comprises the following steps: S1, acquiring a metallograph of a welding seam section; s2, according to the metallograph, a welding geometric model containing air holes is established; and S3, welding process simulation is conducted on the geometric model, and the residual stress of the welding joint comprising the air holes is obtained. According to the welding residual stress simulation method provided by the invention, the geometric model containing the air holes is established, so that the problem that the residual stress around the air holes is difficult to test by a conventional simulation method is solved, and a basis is provided for accurately evaluating the influence of the air holes on the mechanical property of a joint.

Description

Technical Field

[0001] The invention relates to the technical field of welding, in particular to a method for simulating welding residual stress. Background Art

[0002] The use of aluminum alloy welding structure is one of the important ways to achieve lightweight high-end equipment. However, during the welding process of aluminum alloy components, hydrogen welding is usually used. The solubility of hydrogen in the liquid phase and solid phase of aluminum alloy is very different, about 20 times, which leads to the formation of pores in the aluminum alloy weld after welding.

[0003] The presence of pores reduces the effective cross-sectional area of ​​the weld on the one hand, and on the other hand, stress is easily concentrated at the pores, causing cracks to initiate at the pores, reducing the static and dynamic mechanical properties of the welded joint. In addition to hydrogen pores, large-sized keyhole-shaped pores will also exist in laser welding and laser-arc hybrid welding welds.

[0004] The presence of pores will affect the magnitude and distribution of residual stress in the joint. However, the current test methods are still difficult to test the residual stress at the pores, which makes it difficult to accurately evaluate the impact of pores on the mechanical properties of the joint.

[0005] Numerical simulation is an effective method to predict welding residual stress. Many scholars have conducted research on related methods. For example, the Chinese patent application number CN202210773696.6 discloses a finite element-based method for predicting welding residual stress of bimetallic composite pipes; the application number CN202211707345.1 discloses a method for measuring ultra-high strength steel welding residual stress by numerical simulation of temperature field. However, the currently disclosed numerical simulation methods for welding residual stress have not yet considered the influence of porosity. Summary of the invention

[0006] The main purpose of the present invention is to solve the above-mentioned problems and shortcomings, and to provide a welding residual stress simulation method. By establishing a geometric model containing pores, the problem that conventional simulation methods are difficult to test the residual stress around the pores is solved, and a basis is provided for accurately evaluating the influence of pores on the mechanical properties of the joint.

[0007] To achieve the purpose of the invention, the present invention provides a method for simulating welding residual stress, which adopts the following technical scheme:

[0008] A welding residual stress simulation method comprises the following steps:

[0009] S1, obtain metallographic photographs of the weld cross section;

[0010] S2, based on the metallographic photographs, establish a welding geometry model including pores;

[0011] S3, the welding process is simulated on the geometric model to obtain the residual stress of the welded joint including pores.

[0012] Furthermore, step S1 includes cutting the weld along its cross section to obtain a metallographic photograph of the weld cross section.

[0013] Furthermore, step S1 includes grinding, polishing and corroding the weld cross section, and then obtaining a metallographic photograph of the weld cross section.

[0014] Furthermore, in step S2, the pores on the cross section are converted into three-dimensional geometric shapes according to the metallographic photographs, and then a welding geometric model including the pores is established.

[0015] Furthermore, in step S2, the welding geometric model includes a local geometric model containing pores, an overall geometric model, and a local-overall geometric model.

[0016] Furthermore, in step S3, before simulating the welding process, welding simulation limiting conditions need to be set on the geometric model.

[0017] Furthermore, setting the welding simulation limitation conditions includes setting the heat source, mesh, material properties and boundary conditions.

[0018] Furthermore, step S3 includes simulating the welding thermal process on the local-global geometric model to obtain the temperature history of each node in the local geometric model containing pores, applying the temperature history of the nodes to the local geometric model for simulation to obtain the residual stress containing pores.

[0019] Furthermore, step S3 includes performing a thermal-mechanical coupling simulation of the welding process on the overall geometric model to obtain the displacement history of the corresponding nodes at the local model boundary, applying the displacement history of the nodes to the local geometric model for simulation, and obtaining the residual stress containing pores.

[0020] Furthermore, in step S2, when establishing a geometric model containing pores, the corresponding position in the overall geometric model is removed according to the cutting position of the weld section, the geometric model containing pores is assembled at the position where the material is removed, and a binding constraint is set at the boundary with the overall geometric model.

[0021] In summary, the welding residual stress simulation method provided by the present invention has the following technical advantages compared with the prior art:

[0022] Based on the metallographic photographs of the weld cross section, the present invention establishes a numerical model of the welding process including pores, which can predict the size and distribution of residual stress in the joint containing pores, solves the problem that the experimental method is difficult to test the residual stress around the pores, and provides a basis for accurately evaluating the influence of pores on the mechanical properties of the joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 : A metallographic photograph of a weld cross section in a welding residual stress simulation method provided by the present invention;

[0024] Figure 2 : A schematic diagram of a local geometric model established based on a metallographic photograph in a welding residual stress simulation method provided by the present invention;

[0025] Figure 3 : A schematic diagram of the overall geometric model of a weldment established in a welding residual stress simulation method provided by the present invention;

[0026] Figure 4 : A schematic diagram of a local-overall geometric model of pores in a welding residual stress simulation method provided by the present invention;

[0027] Figure 5 : A temperature cloud diagram of a welding thermal process simulation performed on a local-global geometric model in a welding residual stress simulation method provided by the present invention;

[0028] Figure 6 : A displacement cloud diagram of a thermal-mechanical coupling simulation of a welding process on an overall geometric model in a welding residual stress simulation method provided by the present invention;

[0029] Figure 7 : A welding residual stress cloud diagram containing pores in a welding residual stress simulation method provided by the present invention.

[0030] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0032] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] The present invention provides a welding residual stress simulation method, a welding residual stress simulation method considering the influence of pores, comprising the following steps:

[0036] S1, obtain metallographic photographs of the weld cross section;

[0037] S2, based on the metallographic photographs, establish a welding geometry model including pores;

[0038] S3, the welding process is simulated on the geometric model to obtain the residual stress of the welded joint including pores.

[0039] In this embodiment, two test plates (hereinafter referred to as test plates) are placed in parallel and welded relative to each other. Figure 3 Taking the state shown in the figure as an example, the simulation method of welding residual stress is introduced. In the simulation process, the influence of pores on welding residual stress is fully considered, including:

[0040] S1, obtain metallographic photographs of the weld cross section.

[0041] For welded components or Figure 3 In the welding test of the integral structure after welding shown, any welding method is used between the two test plates, including but not limited to the hydrogen welding, laser welding, and laser-arc hybrid welding mentioned above, and the components after welding are subjected to conventional correction, cooling and stress release.

[0042] Cut the weld along its cross section (the section perpendicular to the length of the weld) and take a picture of the weld cross section using a metallographic microscope to obtain the following: Figure 1 Preferably, after the weld is cut open, the section to be metallographically photographed is ground, polished and etched to avoid burrs, fine chips and scratches caused by cutting during the cutting operation appearing on the metallographic photograph, forming pores or other welding problems that do not actually exist in the weld, affecting the subsequent simulation calculation of residual stress, and after pretreatment such as grinding, take a photo to obtain a metallographic photograph of the weld cross section.

[0043] Furthermore, after welding (hereinafter referred to as after welding means after correction, cooling and stress release), the weld formed by welding is inspected to obtain the general situation of the entire weld. According to the structure of the inspection, representative positions where the pores are more and more concentrated and the welding effect is weaker are obtained for cutting.

[0044] Preferably, the representative positions can be screened according to pre-set conditions, and the pre-set conditions can be any one or more of the conditions such as pore (diameter) size, pore number, pore density, etc. After obtaining the representative position, the weld is transversely cut at this position to obtain a typical metallographic photograph or a metallographic photograph with a greater influence on stress.

[0045] The representative positions have relatively large and more pores and relatively large residual stress values, which have a greater impact on the residual stress of the entire weld. Therefore, in this embodiment, representative positions are selected for photographing to simulate a more realistic residual stress value of the entire weld.

[0046] S2, based on the metallographic photographs, establish a welding geometry model including pores.

[0047] According to the information obtained in step S1, Figure 1 The metallographic photograph shown in the figure converts all pores on the weld cross section into three-dimensional geometric shapes. Figure 1 The cross-sectional shape of the pores in the metallographic photograph shown is converted into spherical or cylindrical pores. Furthermore, the metallographic photograph can be combined with the flaw detection data to obtain the specific shape of the pores. For the convenience of calculation, the irregular pores can be regularized, and the sharp parts of the pores can be weakened and rounded to convert the pores into relatively regular pore shapes, such as spherical, cylindrical, spherical / cylindrical or other relatively regular shapes that are easy to simulate and calculate stress. Without any restrictions or requirements, the planar pore structure reflected in the metallographic photograph is converted into three-dimensional (quasi) spherical or (quasi) cylindrical pores, thereby establishing a local geometric model of the test plate joint position containing the pores.

[0048] Furthermore, by using modeling, Figure 1 The two-dimensional weld cross section shown in the metallographic photograph is transformed into Figure 2 The local geometric model of the joint position of the two test plates containing pores is shown in the three-dimensional Figure 2 As shown, the local geometric model includes the test plates on both sides, the groove shape of the test plates at the weld, the weld structure shape and multiple pores in the weld. The distribution and number of pores in the local geometric model correspond to the metallographic photographs one by one.

[0049] Furthermore, the structural form of the test plate after welding is transformed into Figure 3The overall geometric model of the welded test plate shown does not include pores.

[0050] Then according to the cutting position on the test plate after welding, Figure 2 The local geometry shown is similar to Figure 3 The overall geometric models shown are integrated to form Figure 4 The local-global geometry model is shown.

[0051] Thus, the overall structure of the test plate after welding, the metallographic photographs obtained after the weld is cut open, and, if necessary, the flaw detection data can be integrated into a local, overall, and local-overall geometric model of the weld, which is used for simulation calculation of weld residual stress.

[0052] When establishing a local-global geometric model containing pores, the corresponding position in the overall geometric model is removed according to the cutting position of the weld section corresponding to the metallographic photograph on the test plate (on the entire weld), the geometric model containing the pores is assembled at the position where the material is removed, and binding constraints are set at the boundary with the overall geometric model.

[0053] It should be noted that the metallographic photograph can be converted into a local geometric model by using an existing, conventional modeling method, or any other method that can achieve the conversion, and the metallographic photograph can be converted into a geometric model in combination with flaw detection data when necessary, without any limitation or requirement. The conversion method is not the focus of the invention and will not be described in detail.

[0054] S3, the welding process is simulated on the geometric model to obtain the weld residual stress including pores.

[0055] The welding process is simulated on the obtained geometric models (including local, overall and local-overall geometric models), and the residual stress of the weld including the pores is calculated based on the historical data obtained during the simulation.

[0056] Before simulating the welding process, it is necessary to set simulation limitation conditions on the geometric model. By setting the simulation limitation conditions, the simulated welding process can be close to or consistent with the actual welding process.

[0057] The simulation constraints include any one or more of the heat source, mesh, material properties, and boundary conditions.

[0058] Heat source, which simulates the heat provided during the welding process and the correction process after welding;

[0059] Meshing, setting up meshes on local-global geometry, especially meshing welds;

[0060] Material properties, including but not limited to material name, material characteristics during welding, such as thermal deformation, welding deformation, thermal expansion, etc.;

[0061] Boundary conditions, including mechanical boundaries and / or thermal boundaries of the welding process, are combined with the grid set in the previous text to determine the mechanical boundaries and / or thermal boundaries on the test plate. Preferably, it can also include setting mechanical and self-contact conditions in the pores, especially in the pores at the cross-section of the weld.

[0062] It should be noted that the simulation limit condition is set on the geometric model established by transformation, which is equivalent to a virtual limit condition. For example, the heat source is combined with the material properties to simulate the corresponding deformation, temperature and other changes at different positions of the test plate under different welding conditions, welding progress and welding temperature.

[0063] According to the actual material, welding method and welding conditions of the test plate, set the corresponding simulation limit conditions. After setting, simulate the welding process, obtain the welding history data corresponding to the node at the welding section in step S1, apply the welding history data to the local geometric model for simulation, and obtain the residual stress of the weld containing pores. Specifically:

[0064] The welding thermal process simulation is performed on the local-global geometric model to obtain the temperature history of each node in the local geometric model of the joint containing pores. The welding thermal process simulation is performed on the geometric model to simulate the welding process, and the temperature change process of the node position corresponding to the weld section in the time sequence before welding, reaching the temperature required for the welding process, and the end of welding, that is, the temperature history. If necessary, it also includes the temperature change process during the correction and stress release process after the welding is completed, so as to obtain Figure 5 Shown is the temperature contour of the nodes in the local-global model;

[0065] Thermomechanical coupling simulation of the welding process is performed on the overall geometric model to obtain the displacement history of the corresponding node at the local model boundary; on the overall geometric model, any node position is selected, preferably, the corresponding node at the local model boundary is selected, such as any point of a pore wall at the local model boundary as the test node, and the displacement change of the node with the welding process is obtained in time sequence, that is, the displacement history of the node with the welding process and temperature change is obtained, so as to understand the displacement history of the node with the temperature change and the progress of the welding process, and obtain the following Figure 6 The displacement cloud diagram of the nodes on the overall geometric model is shown in Figure 1. By setting the grid, the node displacement and displacement boundary can be determined more accurately.

[0066] The temperature history and displacement history of the node are applied to the local geometric model for simulation, and the following is obtained: Figure 7The residual stress of the porous joint (weld) shown. Preferably, the conversion of the metallographic photograph into a three-dimensional geometric model, the setting of boundary conditions and the welding simulation can be completed in the same software, and the software that can perform stress calculation is suitable, such as abaqus software (finite element software for engineering simulation), the boundary data of the local model and the data of the overall model are input into the software, so that the geometric model containing pores is generated in the software simulation, and the welding process is simulated in the software to obtain the temperature history and displacement history of the node, and the stress calculation method provided by the software is used to obtain the stress value of the weld.

[0067] In this embodiment, welding thermal process simulation and thermal-mechanical coupling simulation are performed separately to obtain the temperature history and displacement history required for stress calculation. In practical applications, different welding simulations can be performed separately according to the needs of different simulation software to obtain the corresponding data required for stress calculation, including but not limited to the temperature history and / or displacement history mentioned above.

[0068] In summary, the welding residual stress simulation method provided by the present invention has the following technical advantages compared with the prior art:

[0069] Based on the metallographic photographs of the weld cross section, the present invention establishes a numerical model of the welding process including pores, which can predict the size and distribution of residual stress in the joint containing pores, solves the problem that the experimental method is difficult to test the residual stress around the pores, and provides a basis for accurately evaluating the influence of pores on the mechanical properties of the joint.

[0070] As described above, similar technical solutions can be derived from the given solution content. However, any simple modification, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A welding residual stress simulation method, characterized in that: The following steps are included: S1, obtain metallographic photographs of the weld cross section; S2, based on the metallographic photographs, establish a welding geometry model including pores; S3, the welding process is simulated on the geometric model to obtain the residual stress of the weld including the pores.

2. A welding residual stress simulation method according to claim 1, characterized in that: Step S1 includes cutting the weld along its cross section to obtain a metallographic photograph of the weld cross section.

3. A welding residual stress simulation method according to claim 1, characterized in that: Step S1 includes grinding, polishing and corroding the weld cross section, and then obtaining a metallographic photograph of the weld cross section.

4. A welding residual stress simulation method according to claim 1, characterized in that: In step S2, the pores on the cross section are converted into three-dimensional geometric shapes according to the metallographic photographs, and then a welding geometric model including the pores is established.

5. A welding residual stress simulation method according to claim 4, characterized in that: In the step S2, the welding geometric model includes a local geometric model containing pores, a global geometric model and a local-global geometric model.

6. A welding residual stress simulation method according to claim 1, characterized in that: In step S3, before simulating the welding process, welding simulation limiting conditions need to be set on the geometric model.

7. A welding residual stress simulation method according to claim 6, characterized in that: Setting the welding simulation limit conditions includes setting the heat source, mesh, material properties and boundary conditions.

8. A welding residual stress simulation method according to any one of claims 1 to 7, characterized in that: Step S3 includes simulating the welding thermal process on the local-global geometric model to obtain the temperature history of each node in the local geometric model containing pores, applying the temperature history of the nodes to the local geometric model for simulation to obtain the residual stress containing pores.

9. A welding residual stress simulation method according to any one of claims 1 to 7, characterized in that: Step S3 includes performing a thermal-mechanical coupling simulation of the welding process on the overall geometric model to obtain the displacement history of the corresponding nodes at the local model boundary, applying the displacement history of the nodes to the local geometric model for simulation, and obtaining the residual stress containing pores.

10. A welding residual stress simulation method according to any one of claims 1 to 7, characterized in that: In step S2, when establishing a geometric model containing pores, the corresponding position in the overall geometric model is removed according to the cutting position of the weld section, the geometric model containing pores is assembled at the position where the material is removed, and a binding constraint is set at the boundary with the overall geometric model.

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