Welding structure stress concentration distribution calculation method and system based on strain energy density

Abstract

The invention discloses a three-dimensional welding structure stress concentration distribution calculation method and system based on strain energy density. A three-dimensional model of a complex welding structure is established based on finite element software; respectively establishing a whole length unit set and a unit length unit set in the three-dimensional model, and establishing a unit set in the two-dimensional model; calculating the radius of a gap part control area based on a strain energy density method; applying an external load to the three-dimensional model, submitting calculation, and calculating strain energy density in each set; failure position and fatigue performance prediction is carried out on the complex welding structure; calculating the three-dimensional strain energy density of the weld toe and the defect to obtain a stress concentration distribution rule of the weld toe and the defect, and determining a specific failure part of the welding structure; through division and respective definition of three-dimensional model grids, the stress concentration distribution condition of the potential failure position of the welding structure is determined, and accurate prediction of the failure position and the fatigue life of the complex welding structure is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of fatigue life prediction of welded structures, and particularly to a method and system for calculating the stress concentration distribution of welded structures based on strain energy density. Background Technique

[0002] Welding technology is widely used in fields such as pressure vessels, vehicle engineering, and high-rise steel structures. It is an important connection method for mechanical structures, and fatigue characteristic analysis based on stress is an important issue among them. The strain energy density method is a method that can analyze the failure mode and fatigue performance of welded structures and has been widely used at present. During the use of the strain energy density method, according to the different structural materials, it is necessary to first calculate the radius of the control area of the notch part with stress concentration, and then establish a corresponding control area at the notch part. Under the action of force, the strain energy of the entire control area is extracted, and then divided by the volume of the entire control area to obtain the average strain energy density at this notch. However, this value can only reflect the average stress concentration degree at the notch and cannot reflect the stress concentration change situation along the notch length.

[0003] In the prior art, Lazzarin proposed a strain energy density method with meshless sensitivity, which has been applied to both two-dimensional and three-dimensional models. However, currently, when conducting three-dimensional model analysis based on the strain energy density method, the average strain energy density along the entire notch length is extracted. For circumferential welds or long welds, extracting the average strain energy density cannot truly and accurately reflect the parts with significant stress concentration. Summary of the Invention

[0004] By providing a method and system for calculating the stress concentration distribution of welded structures based on strain energy density in the embodiments of the present application, the technical problem in the prior art that the strain energy density calculation takes the average value with respect to the weld during the fatigue life prediction of welded structures, resulting in inaccurate stress distribution calculation, is solved, and the accurate calculation and expression of the strain energy density of welded structures are realized.

[0005] The embodiments of the present application provide a method for calculating the stress concentration distribution of welded structures based on strain energy density, including the following steps:

[0006] Step S1, establish a three-dimensional model of a complex welded structure based on finite element software; establish a three-dimensional model based on finite element software. In the finite element software, first set the material properties, loading conditions, and constraint conditions, and then respectively establish a set of elements of the entire length at the defect and a set of elements of unit length at the defect in the three-dimensional model of the weld part; establish a set of elements of the entire length at the weld toe and a set of elements of unit length at the weld toe;

[0007] Step S2: Calculate the radius of the control region at the notch based on the strain energy density method; conduct the failure mode and fatigue performance of the welded structure based on the strain energy density method, taking the notch tip as the origin, and calculate the radius of the control region.

[0008] Step S3: Establish a corresponding control region at the notch of the 3D model; divide the control region into the same unit length, verify and analyze the mesh size of the control region and conduct mesh division, and define the meshes of the unit length control region as sets respectively.

[0009] Step S4: Apply external loads to the 3D model, submit the calculation, calculate the strain energy density within each set, represent the strain energy density distribution along the notch length of the 3D model with an image, and analyze the distribution law of the strain energy density in the entire welded structure.

[0010] Step S5: Predict the failure location and fatigue performance of the complex welded structure; obtain the stress concentration distribution law at the weld toe and defect by calculating the 3D strain energy density at the weld toe and defect, and clarify the specific failure location of the welded structure.

[0011] Preferably, in step S1, the 3D model is built in a dog-bone shape with the notch as the center.

[0012] Preferably, in step S2, the notch locations are: the weld toe, the weld root, and the defect locations.

[0013] Preferably, the formula for calculating the radius of the control region at the notch in step S2 is:

[0014]

[0015] where ΔK 1A is the reference stress intensity factor of the material; Δσ A is the reference fatigue strength; (λ1, e1) are angular parameters.

[0016] Preferably, the mesh division principles in step S3 are as follows:

[0017] Mesh division principle for the control region: Divide it using the optimal mesh size.

[0018] Mesh division principle for the transition region: Divide the meshes near the control region using a transition size between the optimal mesh size and other mesh sizes.

[0019] Mesh division principle for other regions: Divide them using other mesh sizes.

[0020] Preferably, the mesh size in the plate width direction in step S3 is determined according to the length in the plate width direction.

[0021] Preferably, the set in step S3 is defined as follows: The control region is divided into 100 cylinders, with 4 cylinders as a unit, and each unit is defined as a set in the finite element.

[0022] Preferably, the stress concentration distribution law at the weld toe and the defect in step S5 is as follows: The strain energy density value is symmetric about the entire length of the weld toe, showing a nearly M-shaped distribution law. The strain energy density is the smallest at the middle part of the weld toe, and the strain energy value reaches the maximum at both ends close to the weld toe.

[0023] The present application also proposes a calculation system for stress concentration distribution of a welded structure based on strain energy density, including the following modules:

[0024] Model construction module: Establish a three-dimensional model of a complex welded structure based on finite element software; establish a three-dimensional model based on finite element software. In the finite element software, first set the material properties, loading conditions and constraint conditions, and then establish a set of elements of the entire length of the defect and a set of elements of the unit length of the defect in the three-dimensional model of the weld area; establish a set of elements of the entire length of the weld toe and a set of elements of the unit length of the weld toe.

[0025] Region calculation module: Calculate the radius of the control region of the notch part based on the strain energy density method; when carrying out the failure mode and fatigue performance of the welded structure based on the strain energy density method, with the notch tip as the origin, calculate the radius of the control region.

[0026] Region establishment module: Establish a corresponding control region at the notch part of the three-dimensional model; divide the control region into the same unit length, verify and analyze the mesh size of the control region and carry out mesh division, and define the meshes of the unit length control region as sets.

[0027] Strain energy density calculation module: Apply an external load to the three-dimensional model, submit the calculation, calculate the strain energy density in each set, and use an image to represent the strain energy density distribution on the notch length of the three-dimensional model, and analyze the distribution law of the strain energy density in the entire welded structure.

[0028] Analysis and prediction module: Predict the failure position and fatigue performance of the complex welded structure; through the calculation of the three-dimensional strain energy density at the weld toe and the defect, obtain the stress concentration distribution law at the weld toe and the defect, and clarify the specific failure parts of the welded structure.

[0029] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0030] In this application, the welds in the three-dimensional welding structure model are divided by finite element software into equal unit lengths, the strain energy density per unit length is calculated, the strain energy density distribution at the notch is clarified, and then the stress concentration significant parts under the action of force on the welding structure are accurately determined and the fatigue life of the structure is predicted; the problem of unclear stress concentration distribution at the notch in complex components is solved, and at the same time, the problem of inaccurate prediction of the failure position and fatigue life in large components is solved. This application mainly studies the distribution of the three-dimensional strain energy density at the potential failure position of the butt joint three-dimensional model, not only determines the specific differences between the calculation results of the three-dimensional model and the two-dimensional model, but also clarifies the specific positions of the structure failure parts. When the structure under study is relatively complex, the present invention can provide us with more accurate positions for attention and analysis. Description of the Drawings

[0031] Figure 1 It is a flow chart of the calculation method for stress concentration distribution of a welding structure based on strain energy density in Embodiment 1 of this application;

[0032] Figure 2 It is a schematic diagram of three-dimensional modeling of a butt joint with defects in Embodiment 1 of this application;

[0033] Figure 3 It is a schematic diagram of the stress and control area near the notch tip in Embodiment 1 of this application;

[0034] Figure 4 It is a detailed diagram of the mesh division of the three-dimensional finite element model in Embodiment 1 of this application;

[0035] Figure 5 It is a detailed diagram of the mesh division of the two-dimensional finite element model in Embodiment 1 of this application;

[0036] Figure 6 It is the three-dimensional and two-dimensional strain energy density results at the weld toe in Embodiment 1 of this application;

[0037] Figure 7 It is the three-dimensional and two-dimensional strain energy density results at the defect in Embodiment 1 of this application. Detailed Implementation Modes

[0038] In the embodiment of this application, by providing a calculation method for stress concentration distribution of a welding structure based on strain energy density, the technical problem of inaccurate calculation of strain energy density at the weld during the fatigue life test of the welding structure in the prior art is solved. In this application, the welds in the three-dimensional welding structure model are divided by finite element software into equal unit lengths, the strain energy density per unit length is calculated, the strain energy density distribution at the notch is clarified, and then the stress concentration significant parts under the action of force on the welding structure are accurately determined and the fatigue life of the structure is predicted.

[0039] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0040] Example 1

[0041] As Figure 1 shown, a method for calculating the stress concentration distribution of a welded structure based on strain energy density according to the present invention includes the following steps:

[0042] Step S1, establish a three-dimensional model of a complex welded structure based on finite element software.

[0043] As Figure 2 shown, establish a dog-bone-shaped three-dimensional model 1 and a two-dimensional model 2 based on finite element software. In the finite element software, first set the material properties, loading conditions and constraint conditions, and then establish the entire length element set 4 and the unit length element set 5 at the defect location in the three-dimensional model of the weld area 3, and establish the element set 6 at the defect location in the two-dimensional model; use the same method to establish the entire length element set 7 and the unit length element set 8 at the weld toe, and establish the element set 9 at the weld toe in the two-dimensional model, and submit the job for calculation.

[0044] Step S2, calculate the radius of the control area of the notch part based on the strain energy density method.

[0045] As Figure 3 shown, the welding process will cause the welded structure to have a reinforcement and defects, which will in turn lead to stress concentration. When carrying out the failure mode and fatigue performance of the welded structure based on the strain energy density method, the weld toe, weld root and defect location can be equivalent to notches. Taking the notch tip as the origin and the notch bisector as the polar axis, establish a polar coordinate system (r, θ). The notch opening angle is expressed as 2α. The stress components near the notch include the circumferential stress σ θθ , radial stress σ rr and shear stress τ rθ . The radius R C of the control area is affected by the material properties, and the calculation formula is as follows:

[0046]

[0047] Among them, ΔK 1A is the reference stress intensity factor of the material; Δσ A is the reference fatigue strength; (λ1, e1) is the angle parameter.

[0048] The theoretical basis of the strain energy density method:

[0049] For a structure with a stress concentration part, the strain energy density method can equivalent the stress concentration area to a sharp notch. According to Figure 3Schematic diagram of a notch. Under the action of a load, the stress at the notch will exhibit singularity. Therefore, we can use the notch stress intensity factor to characterize the stress concentration at the notch. The calculation formula for the notch stress concentration factor is as follows:

[0050]

[0051] Where, and are the notch stress intensity factors corresponding to the opening-mode and sliding-mode cracks respectively; λ1 and λ2 represent the characteristic values of the opening-mode and sliding-mode cracks.

[0052] According to Williams' formula, the strain energy of the control region R c at the notch tip can be calculated by the following formula:

[0053]

[0054] Based on the volume or area of the control region, the strain energy density at the notch can be obtained by dividing the strain energy at the notch by the control region:

[0055]

[0056] Where, e1 and e2 are the angular functions for calculating the strain energy density respectively.

[0057] According to linear elastic fracture mechanics, when the elastic strain energy ΔW reaches the critical value ΔW C , the material will fail (Equation (7)). For

[0058] For welded structures that undergo in-plane failure, and when the geometric shape or loading condition is symmetric, the nominal stress range Δσ a and the reference stress intensity factor range ΔK 1A can be used to determine the control radius, as shown in Equations (8) and (9). The control radius of aluminum alloy is Rc = 0.12 mm.

[0059]

[0060] Step S3, establish a corresponding control region at the notch of the three-dimensional model; divide the control region into the same unit length, verify and analyze the mesh size of the control region and perform mesh division, and define the meshes of the unit length control region as sets respectively;

[0061] The mesh division principle is as follows:

[0062] Mesh division principle of the control region: Divide it using the optimal mesh size,

[0063] Mesh generation principle for the transition region: The meshes near the control region are generated with a transition size between the optimal mesh size and other mesh sizes;

[0064] Mesh generation principle for other regions: The meshes are generated with other mesh sizes.

[0065] The sets are defined as follows: The control region is divided into 100 cylinders respectively; Four cylinders are taken as one unit; Each unit is defined as a set in the finite element.

[0066] Taking the double-sided welded aluminum alloy butt joint with defects as an example, lack of fusion defects are set inside the model, and a control region with a radius of 0.12 mm is established at the lack of fusion defect and the weld toe.

[0067] Since the evaluation process of the strain energy density method is to carry out the fatigue behavior analysis of the joint by calculating the strain energy density in the control region, therefore. The radius of the control region of the aluminum alloy material can be calculated as 0.12 mm through the above calculation formula. Although the strain energy density method has mesh insensitivity, when analyzing based on the ABAQUS finite element software, first, the mesh size of the control region needs to be verified and analyzed to determine that the optimal mesh size is not greater than 0.05 mm. The mesh size adopted in the control region of this invention patent is 0.03 mm. If the same mesh size is adopted in the plate width direction, the number of meshes of the butt joint model will be very large and the calculation efficiency will be greatly reduced. Therefore, in this study, the mesh size in the plate width direction of the finite element model is adopted as 1 mm. Since the length in the plate width direction is 100 mm, according to Figure 2 the meshes of the control region at the defect and the weld toe, in order to more clearly display the meshes of these two regions, Figure 2 in ④⑦ only the meshes at the internal defect and a partial length of the weld toe are shown for a clearer display of the mesh generation. In this way, the internal defect and the weld toe control regions can be divided into 100 cylinders respectively (each cylinder is defined as a cylinder with unit length), as shown in ⑤⑧ in Figure 2 In order to accurately obtain the strain energy density distribution law of the internal defect and the weld toe in the plate width direction and reduce the calculation efficiency, this invention takes four cylinders as one unit (the length of each cylinder in the unit is 4 mm, and the control region with a length of 100 mm is divided into 25 units), defines each unit as a set in the finite element, calculates the strain energy density of each set respectively, and then the strain energy density distribution laws of the internal defect and the weld toe can be obtained. The mesh generation principle for the regions outside the internal defect and the weld toe control regions is as follows: The meshes near the control region are generated with a transition size. Such generation can make the meshes smoothly transition from small to large, ensuring the accuracy of the finite element analysis. The transition mesh size transitions from 0.03 mm in the control region to 3 mm. The specific details of the mesh generation of the three-dimensional finite element model are as shown in Figure 4as shown

[0068] To effectively compare the results calculated based on the two-dimensional model and the three-dimensional model, the present invention patent also uses a grid of 0.03 mm for the internal defects and the control area at the weld toe in the two-dimensional model, and the grid near the control area also transitions from 0.03 mm to 3 mm. The specific grid division details of the two-dimensional finite element model are as Figure 5 shown

[0069] Step S4: Apply an external load to the three-dimensional model, submit the calculation, calculate the strain energy density within each set, and clarify the strain energy density distribution along the notch length of the three-dimensional model.

[0070] Extract the strain energy density in the entire length element set 4 at the defect, the unit length element set 5 at the defect, the element set 6 at the defect in the two-dimensional model, the entire length element set 7 at the weld toe, the unit length element set 8 at the weld toe, and the element set 9 at the weld toe in the two-dimensional model. The results are as Figure 6 and Figure 7 shown. It can be seen that the strain energy density calculated based on the entire length element set 4 at the defect and the entire length element set 7 at the weld toe is the average of the calculation results of the unit length element set 5 at the defect and the unit length element set 8 at the weld toe. From the results calculated by the unit length element set 5 at the defect, it can be seen that the strain energy density value is symmetric about the entire length of the weld toe, showing an approximate "M"-shaped distribution law, with the minimum strain energy density at the middle part of the weld toe and the maximum strain energy value at both ends close to the weld toe. From the results calculated by the entire length element set 7 at the weld toe, it can be seen that the strain energy density value is symmetric about the entire length of the defect, showing an approximate "U"-shaped distribution law, with the maximum strain energy density at both ends of the defect, and this value is significantly higher than the three-dimensional average strain energy density and the two-dimensional strain energy density.

[0071] Step S5: Predict the failure location and fatigue performance of the complex welded structure.

[0072] By calculating the three-dimensional strain energy density at the weld toe and the defect, the stress concentration distribution law at the weld toe and the defect is obtained, and it is determined that the stress concentration is the most significant at both ends close to the weld toe, and the stress concentration is the most obvious at both ends of the defect, thereby clarifying the specific failure parts of the welded structure.

[0073] Embodiment 2

[0074] The present application also provides a calculation system for stress concentration distribution of a welded structure based on strain energy density, including the following modules:

[0075] The model construction module establishes a three-dimensional model of a complex welded structure based on finite element software; when establishing a three-dimensional model based on finite element software, in the finite element software, first set the material properties, loading conditions and constraint conditions, and then establish a set of elements of the entire length at the defect and a set of elements of the unit length at the defect in the three-dimensional model of the weld area; establish a set of elements of the entire length at the weld toe and a set of elements of the unit length at the weld toe;

[0076] The area calculation module calculates the radius of the control area of the notch part based on the strain energy density method; when carrying out the failure mode and fatigue performance of the welded structure based on the strain energy density method, the weld toe, weld root and defect are equivalent to notches, and taking the notch tip as the origin, calculate the radius of the control area;

[0077] The area establishment module uses the calculated radius of the control area to establish a corresponding control area at the notch part of the three-dimensional model;

[0078] The strain energy density calculation module applies an external load to the three-dimensional model, submits the calculation, calculates the strain energy density in each set, and the image represents the distribution of the strain energy density on the notch length of the three-dimensional model, and analyzes the distribution law of the strain energy density in the entire welded structure;

[0079] The analysis and prediction module predicts the failure location and fatigue performance of the complex welded structure; by calculating the three-dimensional strain energy density at the weld toe and the defect, obtain the stress concentration distribution law at the weld toe and the defect, and clarify the specific failure part of the welded structure.

[0080] The embodiments of the specific implementation manners are all preferred embodiments of the present invention, and do not limit the protection scope of the present invention accordingly. Therefore, all equivalent changes made according to the structure, shape and principle of the present invention shall be covered within the protection scope of the present invention. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A calculation method for stress concentration distribution of a welded structure based on strain energy density, characterized in that, It includes the following steps: Step S1: Establish a three-dimensional model of a complex welded structure based on finite element software; Establish a three-dimensional model based on finite element software. In the finite element software, first set the material properties, loading conditions, and constraint conditions, and then establish a set of elements for the entire length of the defect and a set of elements per unit length of the defect in the three-dimensional model of the weld area; establish a set of elements for the entire length of the weld toe and a set of elements per unit length of the weld toe; Step S2: Calculate the radius of the control area of the notch part based on the strain energy density method; carry out the failure mode and fatigue performance of the welded structure based on the strain energy density method. Taking the notch tip as the origin, calculate the radius of the control area; Step S3: Establish a corresponding control area at the notch part of the three-dimensional model; Divide the control area into the same unit length, verify and analyze the mesh size of the control area and carry out mesh division, and define the meshes of the unit length control area as sets respectively; Step S4: Apply external loads to the three-dimensional model, submit the calculation, calculate the strain energy density in each set, use an image to represent the strain energy density distribution along the notch length of the three-dimensional model, and analyze the distribution law of the strain energy density in the entire welded structure; Step S5: Predict the failure location and fatigue performance of the complex welded structure; by calculating the three-dimensional strain energy density at the weld toe and the defect, obtain the stress concentration distribution law at the weld toe and the defect, and clarify the specific failure parts of the welded structure.

2. The calculation method for the stress concentration distribution of the welding structure according to claim 1, characterized in that, In step S1, the three-dimensional model is established in the shape of a dog bone with the notch part as the center.

3. The method for calculating the stress concentration distribution of the welding structure according to claim 1, characterized in that, In step S2, the notch parts are: the weld toe, the weld root, and the defect.

4. The method for calculating the stress concentration distribution of the welding structure according to claim 1, wherein In step S2, the calculation formula for the radius of the control area of the notch part is: Among them, ΔK 1A is the reference stress intensity factor of the material; Δσ A is the reference fatigue strength; (λ1, e1) are angular parameters.

5. The method for calculating the stress concentration distribution of the welding structure according to claim 1, characterized in that, In step S3, the mesh division principle is as follows: Mesh division principle for the control area: Divide it using the optimal mesh size; Mesh division principle for the transition area: The meshes near the control area are divided using a transition size between the optimal mesh size and other mesh sizes; Mesh division principle for other areas: Divide it using other mesh sizes.

6. The method for calculating the stress concentration distribution of the welding structure according to claim 4, characterized in that In step S3, the mesh size in the plate width direction is determined according to the length in the plate width direction.

7. The method for calculating the stress concentration distribution of the welding structure according to claim 1, wherein In step S3, the set definition is as follows: The control area is divided into 100 cylinders respectively, take 4 cylinders as a unit, and define each unit as a set in the finite element.

8. The method for calculating the stress concentration distribution of the welding structure according to claim 1, characterized in that, In step S5, the stress concentration distribution law at the weld toe and the defect is: The strain energy density value is symmetric about the entire length of the weld toe, showing an approximate M-shaped distribution law. The strain energy density is the smallest at the middle part of the weld toe, and at both ends near the weld toe, the strain energy value reaches the maximum.

9. A calculation system for stress concentration distribution of a welded structure based on strain energy density, characterized in that It includes the following modules: Model construction module: Establish a three-dimensional model of a complex welded structure based on finite element software; establish a three-dimensional model based on finite element software. In the finite element software, first set the material properties, loading conditions, and constraint conditions, and then establish a set of elements for the entire length of the defect and a set of elements per unit length of the defect in the three-dimensional model of the weld area; establish a set of elements for the entire length of the weld toe and a set of elements per unit length of the weld toe; The region calculation module calculates the radius of the control region at the notch part based on the strain energy density method; when carrying out the failure mode and fatigue performance of the welded structure based on the strain energy density method, with the notch tip as the origin, calculate the radius of the control region. The region establishment module establishes the corresponding control region at the notch part of the three-dimensional model. Divide the control region into the same unit length, verify and analyze the mesh size of the control region and conduct mesh division, and define the meshes of the control region with unit length as sets respectively. The strain energy density calculation module applies external loads to the three-dimensional model, submits the calculation, calculates the strain energy density in each set, represents the strain energy density distribution on the notch length of the three-dimensional model by an image, and analyzes the distribution law of the strain energy density in the whole welded structure. The analysis and prediction module predicts the failure position and fatigue performance of the complex welded structure; by calculating the three-dimensional strain energy density at the weld toe and defect, obtain the stress concentration distribution law at the weld toe and defect, and clarify the specific failure parts of the welded structure.

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