A method for modeling weld structure of a welded steel box under implosion load

Abstract

The application provides a welding seam structure modeling method of a welded steel box under an internal explosion load, comprising: establishing a welded steel box structure and an air domain model; establishing an explosive model in the air domain model; establishing a welding seam structure model in the welded steel box structure model; defining a fluid-solid coupling algorithm; and using LS-DYNA software to perform calculation and analysis based on the welded steel box structure model, the air domain model, the explosive model and the welding seam structure model by using the defined fluid-solid coupling algorithm. The application fills the technical blank of simulating and analyzing the welding structure of the welded steel box, and has the advantages of simple modeling, high calculation efficiency, and the thickness of the shell element being defined by parameters, so that the grid with a high length-width ratio is not formed, and the grid distortion of the welding seam structure under the explosion impact is avoided; the deletion of the welding seam element is controlled by defining the failure plastic strain parameter in the material constitutive of the welding seam structure, so that the welding seam failure behavior of the steel box structure under the explosion impact load can be accurately simulated.

Description

Technical Field

[0001] This invention belongs to the field of mechanical simulation technology, specifically relating to a method for modeling the weld structure of a welded steel box under implosion load. Background Technology

[0002] Welded steel box structures, with their excellent comprehensive mechanical properties, are widely used in transportation, civil engineering, and other fields. Explosive impacts typically cause severe damage to welded box structures, especially when the shock wave from an internal explosion is reflected within the sealed box structure. The reflected waves converge and superimpose within the structure, causing serious damage to the box structure's wall panels. As a common and easily manufactured box structure, welded steel boxes are frequently used in performance studies of box structures under implosion loads. Computer-aided engineering (CAE) technology can accurately simulate and predict structural deformation under loads such as explosions, impacts, and vibrations. Therefore, it is widely used in the simulation process of box structures under implosion loads, which can greatly save experimental costs and shorten the engineering cycle.

[0003] Most current simulation and modeling methods for box-type structures under implosion loads typically ignore the modeling of welded seams, directly treating multiple plates as having common nodes at their intersections. This approach, neglecting weld failure, severely impacts the propagation path and process of the blast shock wave within the structure, leading to significant distortion of the structure's dynamic response and failure characteristics. Other studies have established solid models of the welds, meshed them, and defined the model's material constitutive model. While this method accurately represents the geometric characteristics of the welded structure, under high strain rate conditions such as blast impacts, the welded seam structure inevitably results in excessively high aspect ratio meshes during meshing for implosion simulations of welded steel boxes. Under the influence of the blast shock wave, this can easily cause mesh distortion, leading to computational termination. Therefore, a modeling method for welded structures under implosion loads that can both simulate weld failure behavior, reduce computation time, and avoid mesh distortion under blast impacts is currently lacking. Summary of the Invention

[0004] Therefore, in order to solve the problems existing in the prior art, the present invention provides a method for modeling the weld structure of a welded steel box under implosion load.

[0005] This invention provides a method for modeling the weld structure of a welded steel box under implosion load, comprising:

[0006] Establish a model of the welded steel box structure and air domain;

[0007] Specifically, first, the structure of the welded steel box is obtained, and a geometric model of the welded steel box is established based on the shape, size and other characteristics of the welded steel box structure. The geometric model of the welded steel box is meshed using four-node shell elements, where the mesh size is set to be consistent with the predicted weld width. The thickness of the shell element is defined in the section property settings, and the material constitutive model of the welded steel box structure is defined in the material property settings.

[0008] Then, based on the established welded steel box structure model, an air domain geometric model is established to ensure that it can cover the welded steel box structure model. Then, eight-node hexahedral solid elements are used to mesh the air domain geometric model, the mesh size of the air domain mesh is set, and the material constitutive model of air is defined in the material property settings.

[0009] Establish an explosive model within the air domain model;

[0010] Specifically, an explosive model is established in the air domain model. On the one hand, the geometric model of the explosive model is established according to the preset shape, size and other characteristics. On the other hand, the type, amount and starting position information of the explosive model are set, and the initial point position information of the detonation point of the explosive is defined.

[0011] Establish a weld structure model in the welded steel box structure model;

[0012] Specifically, in the welded steel box structure model, mesh elements at preset welding positions are selected and divided into independent parts distinct from the welded steel box structure itself, namely the weld structure. When establishing the welded steel box structure model, four-node shell elements are used to mesh the geometric model of the welded steel box, with the mesh size set to match the predicted weld width. Therefore, the weld width is the mesh width of the welded steel box structure model; that is, the width of the mesh elements at the selected welding positions can characterize the width features of the weld structure. Then, the thickness of the weld structure is defined by setting the cross-sectional thickness, and the material constitutive model of the weld structure is defined using material properties. The failure plastic strain in the material constitutive model of the weld structure is defined to simulate the failure behavior of the weld structure under explosive impact loads.

[0013] Define a fluid-structure interaction algorithm;

[0014] Specifically, the air domain model and the explosive model are placed in a multi-group group, and the welded steel box structure model and the weld seam structure model are placed in a component set. The air domain model and the explosive model adopt the ALE algorithm, and the welded steel box structure model and the weld seam structure model adopt the Lagrange algorithm to complete the definition of the fluid and solid coupling algorithm.

[0015] Using the LS-DYNA software, based on the welded steel box structure model, air domain model, explosive model, and weld structure model, a defined fluid-structure interaction algorithm is employed for calculation and analysis.

[0016] Specifically, based on the established welded steel box structure model, air domain model, explosive model, and weld structure model, a k-file is generated. This k-file is then imported into the dynamic simulation software LS-DYNA for calculation and analysis to simulate the failure behavior of the weld structure of the steel box structure under explosive impact load.

[0017] Through the above technical solution, this application can achieve the following technical effects:

[0018] 1. This application provides a method for modeling the weld structure of a welded steel box under implosion load, which can simulate and analyze the weld structure of the welded steel box under implosion load, greatly saving the cost of the test, shortening the engineering cycle, and filling the current technical gap in simulating and analyzing the welded structure of the welded steel box.

[0019] 2. This application uses four-node shell elements to mesh the geometric model of the welded steel box, with the mesh size set to match the predicted weld width. The weld width is the mesh width of the welded steel box structural model, meaning that the width of the mesh elements at the welding location can characterize the width of the weld structure. The thickness of the weld structure is defined by setting the cross-sectional thickness of the weld structure. Eight-node hexahedral solid elements are used to mesh the geometric model of the air domain, with the mesh size set for the air domain mesh. This modeling method is simple, computationally efficient, and the thickness of the shell elements is defined by parameters, preventing meshes with excessively high aspect ratios and avoiding mesh distortion of the weld structure under explosive impact.

[0020] 3. This application controls the deletion of weld elements by defining the failure plastic strain parameter in the material constitutive model of the weld structure, which can accurately simulate the failure behavior of the weld structure under explosive impact. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a flowchart of the application;

[0023] Figure 2 These are renderings of an embodiment of this application; Detailed Implementation

[0024] This invention provides a method for modeling the weld structure of a welded steel box under implosion load, such as... Figure 1 ,include:

[0025] Establish a model of the welded steel box structure and air domain;

[0026] The establishment of the welded steel box structure and air domain model here refers to the establishment of the finite element model of the welded steel box structure and air domain, including the establishment of geometric model, mesh generation, definition of dimensions, material properties, etc.

[0027] Furthermore, establishing the geometric model of the welded steel box structure involves acquiring the structure of the welded steel box, establishing the geometric model of the welded steel box based on its shape, size, and other characteristics, and then using four-node shell elements to mesh the geometric model of the welded steel box. After meshing, the mesh size is set to be consistent with the predicted weld width. The thickness of the shell element is then defined in the section property settings, and the material constitutive model of the welded steel box structure is defined in the material property settings.

[0028] Furthermore, since this application is a modeling method for welded steel boxes under implosion loads, the air domain geometry model should be established based on the established welded steel box structure model to ensure that it can cover the welded steel box structure model or wrap around the explosion center area of ​​the welded steel box. Then, the air domain geometry model is meshed using eight-node hexahedral solid elements, and the mesh size of the air domain mesh is set. The material constitutive model of air is defined in the material property settings.

[0029] Establish an explosive model within the air domain model;

[0030] Furthermore, establishing an explosive model within the air domain model involves two aspects: firstly, creating a geometric model of the explosive based on pre-defined explosive shape, size, and other characteristics; and secondly, setting the explosive model's type, quantity, and initial position information, as well as defining the initial detonation point. Specifically, the explosive model is defined within the air domain model mesh using the keyword *INITIAL_VOLUME_FRACTION_GEOMETRY, the explosive model's type and quantity are set using explosive materials, and the initial detonation point is determined using the keyword *INITIAL_DETONATION.

[0031] Establish a weld structure model in the welded steel box structure model;

[0032] Furthermore, establishing a weld structure model within the welded steel box structure model involves selecting mesh elements at preset welding positions within the welded steel box structure model and dividing them into independent parts distinct from the welded steel box structure itself—the weld structure. Since four-node shell elements are used to mesh the geometric model of the welded steel box when establishing the model, with the mesh size set to match the predicted weld width, the weld width is essentially the mesh width of the welded steel box structure model. In other words, the width of the mesh elements at the selected welding positions characterizes the width of the weld structure. Then, the thickness of the weld structure is defined by setting its cross-sectional thickness, and its material constitutive model is defined using material properties. This material constitutive model characterizes the tearing failure of the weld under explosive impact. The failure behavior of the weld structure under explosive impact loads is simulated by defining the failure plastic strain within the material constitutive model.

[0033] Furthermore, the failure plastic strain in the material constitutive model of the weld structure is calculated according to formula (1):

[0034] (1)

[0035] in, For the failure plastic strain of the weld structure, For the true strain of the weld structure, For actual stress, It is the elastic modulus.

[0036] Nominal strain can be obtained through weld structure performance testing. Nominal stress With elastic modulus The following formula can be used to calculate the actual stress and actual strain at failure based on the nominal strain and nominal stress at failure of the weld structure in the test. In the formula, l is the current length of the measurement part of the performance test, l0 is the initial length of the measurement part of the performance test, F is the force applied to the weld structure, and A is the current cross-sectional area.

[0037]

[0038] (2)

[0039]

[0040] Substituting into formula (1), the failure plastic strain in the material constitutive model of the weld structure can be calculated. .

[0041] Define a fluid-structure interaction algorithm;

[0042] Furthermore, the air domain model and the explosive model are placed in a multi-group group, and the welded steel box structure model and the weld seam structure model are placed in a component set. The air domain model and the explosive model adopt the ALE algorithm, while the welded steel box structure model and the weld seam structure model adopt the Lagrange algorithm, thus completing the definition of the fluid-solid coupling algorithm. Specifically, by defining the LS-DYNA software keyword *ALE_MULTI_MATERIAL_GROUP, the air domain model and the explosive model are defined as multi-fluid material group 1. By defining the Part set, the welded steel box structure model and the weld seam structure model are placed in Part set 1. The air domain model and the explosive model in multi-fluid material group 1 adopt the ALE algorithm, while the welded steel box structure model and the weld seam structure model in Part set 1 adopt the Lagrange algorithm. By defining the LS-DYNA software keywords *CONSTRAIED_LARGANGE_IN_SOLID and *CONTROL_ALE, the coupling mechanism of the fluid-structure interaction model is defined, thus completing the definition of the fluid-solid coupling algorithm.

[0043] Using the LS-DYNA software, based on the welded steel box structure model, air domain model, explosive model, and weld structure model, a defined fluid-structure interaction algorithm is employed for calculation and analysis.

[0044] Furthermore, based on the established welded steel box structure model, air domain model, explosive model, and weld structure model, a k-file is generated. This k-file is then imported into the dynamic simulation software LS-DYNA for calculation and analysis to simulate the failure behavior of the weld structure of the steel box structure under explosive impact load.

[0045] To better understand the technical solution of this application, the following description is provided in conjunction with specific embodiments.

[0046] In this embodiment, a large-sized welded steel box structure of 2.2m*2.3m*2.9m, composed of multiple stiffened plates, is simulated. The geometric model of the welded steel box structure can be established using the modeling software SolidWorks. The geometric model of the welded steel box structure is meshed using the software HyperMesh. The mesh of the welded steel box structure is generated using four-node shell elements with a mesh size of 10mm*10mm. The thickness of the shell elements is defined in the section properties of the geometric model of the welded steel box structure, and the material constitutive model is defined in the material properties.

[0047] Furthermore, based on the established welded steel box structure model, the geometric model of the air domain is created using the modeling software SolidWorks. This ensures that the model can cover the welded steel box structure model or enclose the explosion center area of ​​the welded steel box. Then, the geometric model of the air domain is meshed using the software HyperMesh. Eight-node hexahedral solid elements are used to mesh the geometric model of the air domain, with a mesh size of 5mm*5mm*5mm. The material constitutive model of the air is defined in the material property settings, thus completing the establishment of the welded steel box structure and the air domain model.

[0048] Furthermore, using the LS-DYNA simulation software, the keyword *INITIAL_VOLUME_FRACTION_GEOMETRY was used to fill the air domain model mesh inside the welded steel box structure model with a size of 5mm*5mm*5mm and a 2kg explosive equivalent cube model. The keyword was then used to define the initial position of the detonation point as the center point of the cube side of the explosive model.

[0049] Furthermore, the meshes at the intersections of multiple stiffened plates were separated into independent components as weld structures. The width of the weld structure, i.e., the mesh width of the welded steel box structure model, was 10mm. The thickness of the weld structure was then defined as 2mm by setting the cross-sectional thickness. The material constitutive models of the steel box structure and the weld structure were defined using material type 3, *MAT_PLASTIC_KINEMATIC, an isotropic kinematic hardening plastic material model in LS-DYNA software. Except for the failure plastic strain, the material parameters of the steel box structure and the weld structure remained consistent. No failure plastic strain was set for the steel box structure. The failure plastic strain of the weld structure was calculated using the calculation formula for weld failure in the experiment. The experimentally measured tensile stress at weld tearing failure was 246MPa, the strain was 0.094, and the elastic modulus E was 27400MPa, i.e., the nominal stress. =246MPa, nominal strain =0.094, calculate the true strain = True stress Substituting the actual stress of 269 MPa, the actual strain of 0.0898, and the elastic modulus of 27400 MPa into equation (1), the failure plastic strain of the weld failure is... 0.08. Therefore, a failure plastic strain of 0.08 is defined in the material properties of the weld structure model, and a section thickness of 2 mm is defined in the section properties of the weld structure.

[0050] Furthermore, calculation formulas are selected for the solid medium and fluid elements. The formulas for the air domain model and the explosive model adopt the ALE algorithm, while the formulas for the welded steel box structure model and the weld structure model adopt the Lagrange algorithm. The air domain model and the explosive model are placed in multiple groups, group 1, and the welded steel box structure model and the weld structure model are placed in Part 1. The keywords *CONSTRAINED_LAGRANG_IN_SOLID and *CONTROL_ALE are used to couple the fluid and solid components.

[0051] Furthermore, the established welded steel box structure model, air domain model, explosive model, and weld structure model are exported as k-files using HyperMesh software, and then imported into the dynamic simulation software LS-DYNA for calculation and analysis.

[0052] The simulation effect of this modeling method is as follows: Figure 2 As shown, the modeling method of this patent can effectively simulate the typical failure characteristics of steel box structures under implosion loads, such as large plastic deformation, weld tearing, and edge tearing.

[0053] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0054] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for modeling the weld structure of a welded steel box under implosion load, characterized in that, include: Establish a model of the welded steel box structure and air domain; Establish an explosive model within the air domain model; In the welded steel box structure model, select the mesh elements at the preset welding position and divide them into weld structures; the width of the weld structure is the same as the mesh width of the welded steel box structure model. The thickness of the weld structure is defined by setting the cross-sectional thickness of the weld structure. The material constitutive model of the weld structure is defined in the material property settings. The failure plastic strain in the material constitutive model of the weld structure is defined. Define a fluid-structure interaction algorithm; Using LS-DYNA software, based on the welded steel box structure model, air domain model, explosive model, and weld structure model, a defined fluid-structure interaction algorithm was used for calculation and analysis.

2. A method for modeling the weld structure of a welded steel box under implosion load according to claim 1, characterized in that, The establishment of the welded steel box structure model includes: Obtain the structure of the welded steel box, establish a geometric model of the welded steel box based on its shape and size, mesh the geometric model of the welded steel box using four-node shell elements, set the mesh size to be the same as the predicted weld width, define the thickness of the four-node shell elements in the section property settings, and define the material constitutive model of the welded steel box structure in the material property settings.

3. The method for modeling the weld structure of a welded steel box under implosion load according to claim 2, characterized in that, The establishment of the air domain model includes: An air domain model is established based on the existing welded steel box structure model. The air domain model covers the welded steel box structure model. The air domain geometry model is meshed using eight-node hexahedral solid elements. The mesh size is set, and the material constitutive model of air is defined in the material property settings.

4. The method for modeling the weld structure of a welded steel box under implosion load according to claim 3, characterized in that, The establishment of the explosive model in the air domain model includes: In the air domain model, a geometric model of the explosive model is established based on the preset shape and size characteristics of the explosive. The type, quantity, and starting position information of the explosive model are set, and the initial point position information for detonating the explosive is defined.

5. The method for modeling the weld structure of a welded steel box under implosion load according to claim 1, characterized in that, The failure plastic strain in the material constitutive model defining the weld structure includes: The nominal strain at the point of weld failure was measured through material property testing. Nominal stress With elastic modulus The actual strain is calculated using formula (2). and actual stress , ； （2）； ； For the failure plastic strain of the weld structure, For the true strain of the weld structure, For actual stress, It is the elastic modulus; Real response and actual stress Substituting into formula (3), the failure plastic strain is calculated. ; （3） ； In the formula, l is the current length of the measurement part in the performance test, l0 is the initial length of the measurement part in the performance test, F is the force applied to the weld structure, and A is the current cross-sectional area.

6. The method for modeling the weld structure of a welded steel box under implosion load according to claim 5, characterized in that, The defined fluid-structure interaction algorithm includes: The air domain model and the explosive model are placed in a multi-group group, and the welded steel box structure model and the weld seam structure model are placed in a component set. The air domain model and the explosive model are subjected to the ALE algorithm, and the welded steel box structure model and the weld seam structure model are subjected to the Lagrange algorithm, thus completing the definition of the fluid and solid coupling algorithm.

7. The method for modeling the weld structure of a welded steel box under implosion load according to claim 6, characterized in that, Using LS-DYNA software, based on the welded steel box structure model, the air domain model, the explosive model, and the weld structure model, a defined fluid-structure interaction algorithm is employed for computational analysis, including: Based on the established welded steel box structure model, air domain model, explosive model, and weld structure model, a k-file is generated. The k-file is then imported into the dynamic simulation software LS-DYNA for calculation and analysis to simulate the failure behavior of the weld structure of the welded steel box structure under explosive impact load.

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