Method and system for evaluating propagation life of fatigue crack on surface of welding structure

Abstract

The invention provides a welding structure surface fatigue crack propagation life evaluation method and system, and relates to the technical field of crack life evaluation and prediction.The method comprises the steps that generalized structural stress in a tensile load mode and generalized structural stress in a bending load mode are calculated through numerical simulation; a welding seam gauge is used for actually measuring the geometrical characteristics of the welding joint, and geometrical characteristic parameters of the welding joint are extracted; generating a tensile load geometric correction factor and a bending load geometric correction factor associated with the crack characteristic parameters through multivariate nonlinear regression analysis; constructing a stress intensity amplification factor correction model in a shallow surface crack stage, and further generating a full-thickness stress intensity amplification factor in the shallow crack stage; and iteratively calculating the evolution of the crack depth, and outputting a fatigue life prediction result of the welding joint. According to the method, the stress intensity factor of the crack on the surface of the welded joint is accurately solved, and the efficiency of crack propagation life evaluation is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of crack life assessment and prediction, and in particular to a method and system for assessing the surface fatigue crack propagation life of a welded structure. Background Art

[0002] Welded joints are often vulnerable to fatigue failure due to high temperatures, stress concentrations, and geometric imperfections during welding. Surface fatigue crack growth in welded structures is a key factor affecting the fatigue life of welded structures, particularly in localized areas such as the weld toe, where the crack propagation process significantly impacts structural performance. Existing fatigue crack growth models for welded joints mostly focus on the overall structural stress distribution but fail to adequately consider local geometric characteristics, notch effects, and variations in crack depth during surface crack growth. Structural stress is a crucial mechanical parameter for studying fatigue failure mechanisms in welded structures. It is a comprehensive measure of the stress concentration at the weld toe or weld root caused by external loads. It is also the driving stress for crack propagation at the weld interface. The fracture mechanics derivation of this method reveals that structural stress has a limited ability to capture local characteristics of welded joints. Although the equations for calculating stress intensity factors for welded joints have been incorporated into the BS7910 standard, the evaluation process does not consider the evolution of crack morphology, and the prediction results are somewhat conservative.

[0003] At present, under the fracture mechanics evaluation system, it is necessary to further construct a complete fracture mechanics parameter analysis model based on the geometric characteristics, load form, stress state, surface crack evolution, etc. of the weld joint. Under the premise of ensuring the accuracy of the solution, the computational efficiency of the finite element iterative crack extension can be effectively improved. In the existing technology, most fracture mechanics models and crack extension evaluation methods, such as traditional models based on structural stress and weight function methods, although they can provide a certain degree of prediction accuracy, still have many shortcomings. First, the existing fatigue crack extension models often ignore the significant influence of the geometric characteristics of the weld joint (such as weld angle and weld toe radius) on crack extension, resulting in certain limitations in the accuracy and applicability of the model. Secondly, the traditional fatigue crack extension evaluation method of welded joints, especially when the crack depth is small (shallow crack stage), fails to effectively consider the local stress concentration effect, which makes the prediction results of the crack extension process more conservative and cannot accurately reflect the actual crack extension behavior. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for evaluating the fatigue crack growth life of welded structures to improve the above-mentioned problems. To achieve the above-mentioned purpose, the technical solutions adopted by the present invention are as follows:

[0005] In a first aspect, the present application provides a method for evaluating the surface fatigue crack growth life of a welded structure, comprising:

[0006] A three-dimensional finite element model of the welded joint was established, and the generalized structural stress under the tensile load mode and the generalized structural stress under the bending load mode were calculated through numerical simulation;

[0007] The geometric characteristics of the weld joint are measured using a weld gauge to extract the geometric characteristic parameters of the weld joint, including the weld angle, weld toe radius and plate thickness.

[0008] Based on the geometric characteristic parameters, a geometric correction factor function associated with the crack characteristic parameters is established through multivariate nonlinear regression analysis, and the tensile load geometric correction factor and bending load geometric correction factor associated with the crack characteristic parameters are generated. The crack characteristic parameters include crack depth, half-length, weld angle and weld toe radius.

[0009] Combining the geometric correction factors of tensile load and bending load, a stress intensity amplification factor correction model for the shallow surface crack stage is constructed to determine the tensile correction coefficient and bending correction coefficient for the shallow surface crack stage, thereby generating the full-thickness stress intensity amplification factor for the shallow crack stage.

[0010] The generalized structural stress, tensile load geometric correction factor, bending load geometric correction factor, and full-thickness stress intensity amplification factor in the shallow crack stage are input into the crack growth rate equation. The evolution of the crack depth is iteratively calculated to output the fatigue life prediction results of the welded joint.

[0011] Preferably, based on the geometric characteristic parameters, a geometric correction factor function associated with the crack characteristic parameters is established through multivariate nonlinear regression analysis to generate a tensile load geometric correction factor and a bending load geometric correction factor associated with the crack characteristic parameters, which include:

[0012] Based on the geometric characteristic parameters and crack morphology parameters of the welded joint, multiple finite element models were established and numerically simulated with tensile / bending loads to obtain stress intensity factor data sets under different crack depths, half-lengths, and geometric parameters. The geometric characteristic parameters include weld angle, weld toe radius, and plate thickness, and the crack morphology parameters include depth and half-length.

[0013] Based on the stress intensity factor data set, the tensile load geometric correction factor is obtained by using the multivariate nonlinear regression model under the tensile load mode.

[0014] According to the stress intensity factor dataset and the multivariate nonlinear regression model, the bending load geometric correction factor was obtained by polynomial fitting under the bending load mode.

[0015] Preferably, the tensile load geometric correction factor and the bending load geometric correction factor are combined to construct a stress intensity magnification factor correction model for the shallow surface crack stage, determine the tensile correction coefficient and the bending correction coefficient for the shallow surface crack stage, and then generate the full-thickness stress intensity magnification factor for the shallow crack stage, which includes:

[0016] Combining the tensile load geometric correction factor, bending load geometric correction factor and weld joint geometric parameters, the stress concentration effect parameters at the shallow surface crack stage are determined through correlation analysis and processing of the notch self-balancing force amplification factor and finite element data, thereby obtaining the tensile correction factor and bending correction factor.

[0017] Based on the tensile correction factor, bending correction factor and geometric parameters, the full-thickness amplification factor benchmark value of the shallow crack stage associated with the weld angle and weld toe radius is generated through the generalized structural stress driving parameter construction processing;

[0018] Based on the benchmark values ​​and crack morphology parameters, the stress intensity amplification factors of tensile load and bending load at the shallow surface crack stage are solved through multivariate regression analysis.

[0019] In a second aspect, the present application also provides a system for evaluating the surface fatigue crack growth life of a welded structure, comprising:

[0020] Calculation module: used to establish a three-dimensional finite element model of the welded joint and calculate the generalized structural stress under the tensile load mode and the generalized structural stress under the bending load mode through numerical simulation;

[0021] Extraction module: used to measure the geometric characteristics of welded joints using weld gauges and extract the geometric characteristic parameters of welded joints, including weld angle, weld toe radius and plate thickness;

[0022] Generation module: used to establish a geometric correction factor function associated with the crack characteristic parameters through multivariate nonlinear regression analysis based on the geometric characteristic parameters, and generate the tensile load geometric correction factor and bending load geometric correction factor associated with the crack characteristic parameters, where the crack characteristic parameters include crack depth, half-length, weld angle and weld toe radius;

[0023] Construction module: used to combine the tensile load geometric correction factor and the bending load geometric correction factor to construct a stress intensity amplification factor correction model for the shallow surface crack stage, determine the tensile correction coefficient and bending correction coefficient for the shallow surface crack stage, and then generate the full-thickness stress intensity amplification factor for the shallow crack stage;

[0024] Iterative calculation module: It is used to input the generalized structural stress, tensile load geometric correction factor, bending load geometric correction factor and shallow crack stage full thickness stress intensity magnification factor into the crack growth rate equation, and output the fatigue life prediction results of the weld joint by iteratively calculating the evolution of crack depth.

[0025] In a third aspect, the present application further provides a device for evaluating the surface fatigue crack growth life of a welded structure, comprising:

[0026] Memory for storing computer programs;

[0027] A processor is configured to implement the steps of the method for evaluating the surface fatigue crack growth life of a welded structure when executing the computer program.

[0028] In a fourth aspect, the present application also provides a readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-mentioned method for evaluating the life of fatigue crack propagation based on the surface of a welded structure.

[0029] The beneficial effects of the present invention are:

[0030] The present invention proposes a two-stage model for surface fatigue crack propagation of welded joints based on generalized structural stress. By introducing geometric contours and notch effects, the model accurately describes the propagation behaviors of shallow surface cracks (a / t≤0.2) and long cracks (a / t>0.2). The model also effectively corrects the local stress concentration effect through the multivariate regression method, significantly improving the prediction accuracy of the crack propagation process. This model not only realizes the accurate solution of the stress intensity factor of the surface crack of the welded joint, but also improves the efficiency of the crack propagation life assessment, providing a more reliable theoretical basis for the crack propagation behavior of welded joints under complex service load conditions.

[0031] The present invention improves the traditional structural stress model by considering the geometric characteristics of the weld joint (such as weld angle, weld toe radius, etc.) and the notch effect, so that the expansion process of the surface crack of the weld joint can more accurately reflect the actual situation. Especially in the shallow crack stage (a / t≤0.2), this scheme effectively corrects the local stress concentration effect and significantly improves the accuracy of the stress intensity factor solution.

[0032] Compared with traditional complex finite element simulation and parametric crack propagation simulation, the present invention avoids the tedious numerical iteration process through multivariate regression analysis and calculation of geometric correction factors, simplifies the solution process of crack propagation, and thus greatly improves the calculation efficiency. It is particularly suitable for rapid evaluation under complex load conditions.

[0033] The two-stage crack propagation model can clearly distinguish the propagation behaviors of shallow surface cracks (a / t≤0.2) and long cracks (a / t>0.2), the staged modeling method can more accurately capture the influence of crack morphology evolution on the stress intensity factor, and more accurate crack propagation prediction can be provided.

[0034] The application can provide more reliable theoretical basis and technical support for the crack propagation life assessment of the welded joint under complex service loads by accurately describing the propagation process of the surface crack of the welded joint, in particular, on the basis of considering the geometric features, load mode, stress state and crack morphology evolution, and the reliability of the fatigue life prediction is improved.

[0035] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows, it should be understood that the following drawings only show some of the embodiments of the present application, therefore should not be regarded as a limitation to the scope, for those skilled in the art, without paying creative labor, other related drawings can also be obtained according to these drawings.

[0037] Figure 1 The flow chart of the surface fatigue crack propagation life assessment method of the welded structure described in the embodiments of the present application is shown in the figure.

[0038] Figure 2 The structure schematic diagram of the surface fatigue crack propagation life assessment system of the welded structure described in the embodiments of the present application is shown in the figure.

[0039] Figure 3 The structure schematic diagram of the surface fatigue crack propagation life assessment equipment of the welded structure described in the embodiments of the present application is shown in the figure.

[0040] Figure 4 The geometric feature schematic diagram of the welded joint described in the embodiments of the present application is shown in the figure.

[0041] Figure 5 The semi-elliptical surface crack schematic diagram described in the embodiments of the present application is shown in the figure.

[0042] In the figure: 701, a calculation module; 702, an extraction module; 703, a generation module; 704, a construction module; 705, an iterative calculation module; 800, a welded structure surface fatigue crack propagation life evaluation device; 801, a processor; 802, a memory; 803, a multimedia assembly; 804, an I / O interface; 805, a communication assembly. DETAILED DESCRIPTION

[0043] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work, fall within the scope of protection of the present application.

[0044] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. Meanwhile, in the description of the present application, the terms "first", "second" and the like are only used to distinguish description, and cannot be understood as indicating or implying relative importance.

[0045] Embodiment 1

[0046] The embodiment provides a welded structure surface fatigue crack propagation life evaluation method.

[0047] Although existing fatigue crack growth assessment methods for welded joints can predict crack growth behavior to a certain extent, they still have technical defects in the following aspects: (1) Insufficient influence of geometric characteristics and notch effect: Most traditional crack growth models ignore the influence of geometric characteristics of welded joints (such as weld angle, weld toe radius, etc.) and notch effect on crack growth, resulting in low crack growth prediction accuracy. (2) Insufficient stage-by-stage treatment of shallow cracks and long cracks: Most existing models do not distinguish between the growth behavior of cracks in the shallow surface (a / t≤0.2) and long cracks (a / t>0.2) stages, and cannot accurately simulate the effect of crack depth changes on stress intensity factors. (3) Low model calculation efficiency: Although some existing methods can predict crack growth more accurately, due to the need for complex finite element analysis and parametric simulation, their calculation efficiency is low and they cannot quickly provide reliable evaluation results under complex loading conditions. The present invention aims to address the shortcomings of existing welded structure fatigue crack propagation prediction models when considering the geometric characteristics of welded joints, notch effects, and stage changes in crack depth, thereby improving the prediction accuracy and computational efficiency of the surface crack propagation process of welded structures.

[0048] See also Figure 1 , the figure shows that the method includes step S100, step S200, step S300, step S400 and step S500.

[0049] S100. Establish a three-dimensional finite element model of the weld joint, and calculate the generalized structural stress under the tensile load mode and the generalized structural stress under the bending load mode through numerical simulation.

[0050] It is understandable that in this step, first, it is necessary to establish a three-dimensional model using professional finite element analysis software (such as ANSYS, ABAQUS, etc.) based on the actual geometric shape and size of the weld joint. This model needs to reflect all the key features of the weld joint in detail, including the shape, size, position of the weld, and the physical properties of the welding material and substrate. After the model is established, the model needs to be meshed. The density and quality of the mesh directly affect the accuracy and computational efficiency of the simulation results. Usually, finer meshes are used near the welding area and cracks to capture the stress concentration effect. Secondly, numerical simulation is performed using finite element software to calculate the stress distribution under different load modes. After the simulation is completed, the results need to be analyzed in detail, including stress distribution diagrams, identification of stress concentration areas, etc.

[0051] S200, using a weld gauge to measure the geometric characteristics of the weld joint and extract the geometric characteristic parameters of the weld joint, wherein the geometric characteristic parameters of the weld joint include weld angle, weld toe radius and plate thickness.

[0052] It can be understood that in this step, the angle information is directly measured by using a gauge or extracted from the image of the welded joint by image processing technology, and the profile of the weld toe is measured by using a feeler gauge or laser scanning technology, so as to calculate the weld toe radius, and then the thickness of the plate is measured by using a caliper or an ultrasonic thickness gauge.

[0053] In this embodiment, the initial surface crack parameters a0 and c0 of the welded structure are input, and the welded structure plate thickness t = 10 mm, the reinforcement angle θ = 20°, the weld toe radius ρ / t = 0.15, and the structure stress 50 MPa.

[0054] S300, based on the geometric feature parameters, a geometric correction factor function associated with the crack feature parameters is established by multivariate nonlinear regression analysis, and a tensile load geometric correction factor and a bending load geometric correction factor associated with the crack feature parameters are generated, wherein the crack feature parameters include crack depth, half length, weld angle and weld toe radius.

[0055] It can be understood that the step S300 includes S301, S302 and S303.

[0056] S301, based on the geometric feature parameters and the crack morphology parameters of the welded joint, a stress intensity factor dataset under different crack depths, half lengths and geometric parameters is obtained by establishing a plurality of finite element models and loading numerical simulation processing of tensile / bending load, wherein the geometric feature parameters include weld angle, weld toe radius and plate thickness, and the crack morphology parameters include depth and half length;

[0057] S302, according to the stress intensity factor dataset, a multivariate nonlinear regression model under the tensile load mode is used for processing to obtain a tensile load geometric correction factor;

[0058] S303, according to the stress intensity factor dataset and the multivariate nonlinear regression model, a polynomial fitting processing under the bending load mode is adopted to obtain a bending load geometric correction factor.

[0059] The calculation formula of the tensile load geometric correction factor is as follows:

[0060]

[0061] In the formula, Fm is the tensile load geometric correction factor, Q is the semi-elliptical surface crack shape coefficient, and Y0 is the spatial parameter of the tensile load mode.

[0062] The calculation formula of the bending load geometric correction factor is as follows:

[0063]

[0064] Where Fb is the bending load geometric correction factor, Q is the semi-elliptical surface crack shape coefficient, and Y1 is the bending load space parameter.

[0065] It should be noted that the above steps are to establish the geometric correction factors Fm and Fb of welded joints with different geometric characteristics under tensile and bending load modes, and to solve the stress intensity factor K of the deepest point of the surface crack under a given arbitrary crack depth a. n , stress intensity factor K at the deepest point of surface crack n The solution is shown in formula (1):

[0066]

[0067] where K n is the stress intensity factor at the surface crack front, including K under tensile load m and K under bending load b , two physical parameters σ obtained by finite element calculation based on structural stress under tensile load and bending load modes m and σ b Finally, given the value of the current crack depth parameter a, the stress intensity factor Kn of different crack depths on the surface of any welded structure can be solved, where Fm is the geometric correction factor under the tensile load mode and Fb is the geometric correction factor under the bending load mode.

[0068] The key is to solve the geometric correction factors Fm and Fb for weld joints with different geometric characteristics under the tensile and bending load modes in the above steps. It is necessary to fully reflect the influence of different weld joint geometric characteristics and different crack morphologies on the geometric correction factors. Therefore, separate solution models are established for Fm and Fb.

[0069] In the above steps, the surface crack growth process of the weld joint is divided into two stages: the shallow surface crack stage (a / t ≤ 0.2) and the long crack stage (a / t > 0.2). For the shallow crack stage, the influence of the weld joint geometry and notch effect on crack growth is considered, and a geometric correction factor correction model based on generalized structural stress is established.

[0070] Therefore, by establishing a series of different weld joint finite element models to solve the stress intensity factor regression under different crack depths and weld joint geometric characteristics under tensile and bending load modes, the geometric correction factors Fm and Fb are obtained. The geometric correction factors are associated with the crack depth, morphology and geometric characteristics of the weld joint (weld angle, weld toe radius), and can provide accurate stress intensity factor correction at different stages of crack propagation.

[0071] Under the tensile loading mode, the stress intensity factor of the deepest point of the surface crack of the welded joint under different geometric characteristics and surface crack depths under the tensile loading mode is extracted. Then the solution of Fm is shown in equation (1-2):

[0072]

[0073] where Y0 is the spatial parameter under tensile loading mode, Q is the shape coefficient of semi-elliptical surface crack, thus Q = [1 + 1.464(a / c) 1.65 ] 0.5 Therefore, the key is to solve the spatial parameter Y0 under tensile loading mode. The finite element simulation results of different cracks in the long crack stage are extracted, and the multi-element nonlinear regression of the geometric correction factor of the semi-elliptical surface crack of the welded joint under tensile loading mode is carried out, and the polynomial function containing the crack depth and the evolution of the shape characteristics is obtained, so as to calculate the stress intensity factor of the deepest point of the weld toe surface crack. The spatial parameter under tensile loading mode is shown in equations (1-3) to (1-6):

[0074] Y0 = [M1 + M2(a / t) 2 + M3(a / t) 4 ] (1-3)

[0075] M1 = 1.01741 - 0.12234(a / c) - 0.02248(a / c) 2 (1-4)

[0076] M2 = 2.69040 - 7.02955(a / c) + 7.85329(a / c) 2 - 3.15008(a / c) 3 (1-5)

[0077] M3 = -0.46253 + 0.57159(a / c) - 0.22068(a / c) 2 + 0.03811(a / c) 3 (1-6)

[0078] Therefore, by inputting the depth a and half length c of the current surface semi-elliptical crack, the current geometric correction factor Fm can be obtained, and then the geometric characteristic parameters of the welded joint obtained by actually measuring in step S100 and the generalized structural stress of the welded joint obtained by finite element calculation can be input to iteratively solve the stress intensity factor of the surface semi-elliptical crack under different crack depths a and lengths c. Next, after completing step S300, the stress intensity factor of the surface crack of the welded joint under bending loading mode is extracted in the same way Then the solution of Fb is shown in equation (1-7):

[0079]

[0080] Among them, Y1 is the spatial parameter of the bending loading mode, Q is the shape coefficient of the semi-elliptical surface crack, so Q=[1+1.464(a / c) 1.65 ] 0.5 , which can be obtained by inputting the depth a and half-length c of the current surface semi-elliptical crack. Therefore, the key lies in solving for the spatial parameter Y1 under the bending load mode. The finite element simulation results for different cracks in the long crack stage in step 300 are extracted. A multivariate nonlinear regression is performed on the geometric correction factor for the semi-elliptical surface crack of the weld joint under the tensile loading mode. This polynomial function that includes the evolution of crack depth and morphological characteristics is obtained. This function is then used to calculate the stress intensity factor at the deepest point of the crack on the weld toe surface, resulting in the spatial parameters under the pure bending load mode.

[0081] Based on the calculation results of the geometric correction factors for different weld joint geometric parameters, the geometric correction factors Fm and Fb can be further expressed as functions of the geometric characteristics a / t, a / c, θ, and ρ / t. Here, c is the half-length of the surface semi-elliptical crack, a is the crack depth, θ is the weld angle, ρ is the weld toe radius, and t is the plate thickness. The geometric correction factors for weld joints with different geometric characteristics approach the asymptote of the long crack stage when a / t ≈ 0.2. The stress intensity amplification effect disappears at a / t = 0.2, so a / t = 0.2 is selected as the segmentation point for the two-stage crack growth model.

[0082] S400. Combining the tensile load geometric correction factor and the bending load geometric correction factor, a stress intensity amplification factor correction model for the shallow surface crack stage is constructed, the tensile correction coefficient and the bending correction coefficient for the shallow surface crack stage are determined, and then the full-thickness stress intensity amplification factor for the shallow crack stage is generated.

[0083] It can be understood that step S400 includes S401, S402 and S403, wherein:

[0084] S401. Determine the stress concentration effect parameters at the shallow surface crack stage by combining the tensile load geometric correction factor, the bending load geometric correction factor, and the weld joint geometric parameters through correlation analysis and processing of the notch self-balancing force amplification factor and finite element data, thereby obtaining the tensile correction factor and the bending correction factor.

[0085] S402, generating a full-thickness amplification factor baseline value for a shallow crack stage associated with a weld angle and a weld toe radius through a generalized structural stress driven parameter construction process based on a stretch correction coefficient, a bending correction coefficient, and geometric parameters;

[0086] S403. Based on the reference values ​​and crack morphology parameters, the tensile load stress intensity amplification factor and the bending load stress intensity amplification factor at the shallow surface crack stage are solved through multivariate regression analysis.

[0087] It should be noted that the calculation formulas for the tensile load stress intensity magnification factor and the bending load stress intensity magnification factor at the shallow surface crack stage are as follows:

[0088] MknT * =λ·f(θ,ρ / t,a / t,a / c)

[0089] MknB * =γ·g(θ,ρ / t,a / t,a / c)

[0090] Where, MknT * is the tensile load stress intensity magnification factor, MknB * is the bending load stress intensity amplification factor, λ is the first correction coefficient, γ is the second correction coefficient, f(θ,ρ / t,a / t,a / c) is the first function, g(θ,ρ / t,a / t,a / c) is the second function, θ is the weld angle, ρ is the weld toe radius, t is the plate thickness, a is the crack depth, and c is the half length of the semi-elliptical crack.

[0091] It can be understood that based on the long crack stage model in the above steps, a generalized structural stress two-stage welded structure crack growth model is constructed, and the full thickness stress intensity magnification factor M is given on the basis of the long crack stage. kn Step S400 is to solve the stress intensity magnification factor M at the shallow surface crack stage. kn * , which also includes the stress intensity magnification factor for shallow surface cracks under tensile loading mode and the stress intensity magnification factor of shallow surface cracks under bending load mode Taking into account the stress concentration effect caused by the local geometric characteristics and notch effect at the weld toe of the weld joint, the geometric correction factor calculation result of a / t≤0.2 is regressed with the notch self-balancing force amplification factor derived from the theory to obtain the stress intensity factor correction tensile coefficient λ and bending coefficient γ at the shallow surface crack stage. Therefore, the generalized structural stress full thickness amplification stress intensity amplification factor at the shallow surface crack stage is first constructed. knT * and M knB * are the amplification correction factors of the stress intensity in the shallow surface crack stage driven by generalized structural stress under tensile and bending load modes respectively. With the weld angle and weld toe radius as geometric characteristic parameters, the generalized structural stress driving parameters are constructed, and the full thickness M is used as the kn *The amplification factor characterizes the influence of geometric characteristics and notch effect on the stress intensity factor of the deepest point of the surface crack of the weld toe of the weld joint, and realizes the accurate solution of the stress intensity factor of the deepest point of any crack shape in the shallow surface crack stage (a / t≤0.2).

[0092] S500: Input the generalized structural stress, tensile load geometric correction factor, bending load geometric correction factor, and shallow crack stage full-thickness stress intensity amplification factor into the crack growth rate equation, and output the fatigue life prediction result of the welded joint by iteratively calculating the evolution of the crack depth.

[0093] It is understandable that in this step, the long crack stage function and shallow crack stage amplification factor of the above steps are described in a unified manner. That is, by inputting the initial crack parameters, structural stress, geometric characteristics and load conditions, the crack growth depth is updated in real time using an iterative calculation method, and the fatigue life is calculated based on the stress intensity factor and crack growth rate. Referring to the Paris crack growth rate form, the two stages can be further described in a unified manner to achieve the solution of the fatigue crack growth life of the welded joint. The two-stage unified description of the surface crack growth of the welded joint is shown in formula (1-8):

[0094] da / dN=C[f1(ΔK) a / t≤0.2 ×f2(ΔK) a / t＞0.2 ] m (1-8)

[0095] Where da / dN is the crack growth rate, and the local stress concentration effect caused by the weld joint contour is included in the geometric correction factor F at the shallow crack stage. m (θ, ρ / t, a / t, a / c), F b (θ, ρ / t, a / t, a / c) further reflects the influence of local characteristics on surface cracks, C and m are crack growth rate parameters, and n is the shallow crack growth rate coefficient. Figure 4 and Figure 5 As shown in FIG, the geometric characteristics of the welding structure of the present invention and the schematic diagram of the semi-elliptical surface crack, wherein c is the half length of the surface semi-elliptical crack, a is the crack depth, θ is the weld angle and ρ is the weld toe radius, t is the plate thickness, S is the distal stress, 2w is the weld width, is the crack direction angle of the semi-elliptical surface. The semi-elliptical surface crack solved in this method is That is the stress intensity factor at the deepest point.

[0096] The structural stress σ m and σ b As well as the geometric correction factor of the long crack stage, ΔK can be solved nThe equation for solving the stress intensity factor of the weld joint surface crack based on generalized structural stress is shown in formula (1-9):

[0097]

[0098] For shallow surface cracks, the geometric characteristics of the weld joint (weld angle, weld toe radius) obtained by actual measurement with a weld gauge can be substituted into step S400 as the input of the model parameters to solve the full-thickness magnified stress intensity magnification factor Mkn* to achieve the solution of the shallow surface crack stress intensity factor as shown in the following formula (1-10):

[0099]

[0100] Example 2:

[0101] like Figure 2 As shown, this embodiment provides a system for evaluating the surface fatigue crack growth life of a welded structure, see Figure 2 The system comprises:

[0102] Calculation module 701: used to establish a three-dimensional finite element model of the weld joint and calculate the generalized structural stress under the tensile load mode and the generalized structural stress under the bending load mode through numerical simulation;

[0103] Extraction module 702: used to measure the geometric features of the weld joint using a weld gauge and extract the geometric feature parameters of the weld joint, wherein the geometric feature parameters of the weld joint include weld angle, weld toe radius and plate thickness;

[0104] Generation module 703: used to establish a geometric correction factor function associated with the crack characteristic parameters through multivariate nonlinear regression analysis based on the geometric characteristic parameters, and generate a tensile load geometric correction factor and a bending load geometric correction factor associated with the crack characteristic parameters, wherein the crack characteristic parameters include crack depth, half length, weld angle, and weld toe radius;

[0105] Construction module 704: for combining the tensile load geometric correction factor and the bending load geometric correction factor to construct a stress intensity magnification factor correction model for the shallow surface crack stage, determine the tensile correction coefficient and the bending correction coefficient for the shallow surface crack stage, and then generate the full-thickness stress intensity magnification factor for the shallow crack stage;

[0106] Iterative calculation module 705: is used to input the generalized structural stress, tensile load geometric correction factor, bending load geometric correction factor and shallow crack stage full thickness stress intensity magnification factor into the crack growth rate equation, and output the fatigue life prediction result of the weld joint by iteratively calculating the evolution of the crack depth.

[0107] Specifically, the generating module 703 includes:

[0108] The first processing unit is used to obtain stress intensity factor data sets under different crack depths, half-lengths and geometric parameters based on the geometric characteristic parameters and crack morphological parameters of the weld joint by establishing multiple finite element models and applying tensile / bending loads for numerical simulation processing. The geometric characteristic parameters include weld angle, weld toe radius and plate thickness, and the crack morphological parameters include depth and half-length.

[0109] The second processing unit is used to process the stress intensity factor data set using a multivariate nonlinear regression model under a tensile load mode to obtain a tensile load geometric correction factor;

[0110] The third processing unit is used to obtain the bending load geometric correction factor by using the polynomial fitting process under the bending load mode according to the stress intensity factor data set and the multivariate nonlinear regression model.

[0111] Specifically, the building block 704 includes:

[0112] Determination unit: used to combine the tensile load geometric correction factor, the bending load geometric correction factor and the weld joint geometric parameters, and determine the stress concentration effect parameters in the shallow surface crack stage through the correlation analysis and processing of the notch self-balancing force amplification factor and the finite element data, thereby obtaining the tensile correction factor and the bending correction factor;

[0113] The fourth processing unit is used to generate a reference value of the full-thickness amplification factor in the shallow crack stage associated with the weld angle and weld toe radius through a generalized structural stress driving parameter construction process based on the stretch correction factor, the bending correction factor and the geometric parameters;

[0114] Solving unit: used to solve the tensile load stress intensity amplification factor and the bending load stress intensity amplification factor at the shallow surface crack stage based on the benchmark value and crack morphology parameters through multiple regression analysis.

[0115] It should be noted that, regarding the system in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated on here.

[0116] Example 3:

[0117] Corresponding to the above method embodiment, this embodiment also provides a welding structure surface fatigue crack growth life assessment device. The welding structure surface fatigue crack growth life assessment device described below and the welding structure surface fatigue crack growth life assessment method described above can refer to each other.

[0118] Figure 3FIG. 8 is a block diagram of a device 800 for evaluating the surface fatigue crack growth life of a welded structure according to an exemplary embodiment. Figure 3 As shown, the device 800 for evaluating the lifespan of fatigue crack growth on a welded structure surface includes a processor 801 and a memory 802. The device 800 also includes one or more of a multimedia component 803, an I / O interface 804, and a communication component 805.

[0119] The processor 801 is used to control the overall operation of the device 800 for assessing the fatigue crack growth life of a welded structure surface, so as to complete all or part of the steps in the aforementioned method for assessing the fatigue crack growth life of a welded structure surface. The memory 802 is used to store various types of data to support the operation of the device 800. This data may include, for example, instructions for any application or method operating on the device 800, as well as application-related data such as contact information, sent and received messages, images, audio, and video. The memory 802 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk. The multimedia component 803 may include a screen and an audio component. The screen may be, for example, a touch screen, and the audio component is used to output and / or input audio signals. For example, the audio component may include a microphone for receiving external audio signals. The received audio signal may be further stored in the memory 802 or transmitted via the communication component 805. The audio component also includes at least one speaker for outputting audio signals. The I / O interface 804 provides an interface between the processor 801 and other interface modules, and the above-mentioned other interface modules can be a keyboard, a mouse or buttons, etc. These buttons can be virtual buttons or physical buttons. The communication component 805 is used for wired or wireless communication between the welding structure surface fatigue crack growth life assessment device 800 and other devices. Wireless communication, such as Wi-Fi, Bluetooth, near field communication (NFC), 2G, 3G or 4G, or a combination of one or more of them, so the corresponding communication component 805 may include: a Wi-Fi module, a Bluetooth module or an NFC module.

[0120] In an exemplary embodiment, the welding structure surface fatigue crack growth life assessment device 800 can be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors, or other electronic components to perform the above-mentioned welding structure surface fatigue crack growth life assessment method.

[0121] In another exemplary embodiment, a computer-readable storage medium including program instructions is also provided. When executed by a processor, the program instructions implement the steps of the aforementioned method for assessing the surface fatigue crack growth life of a welded structure. For example, the computer-readable storage medium may be the aforementioned memory 802 including the program instructions. The program instructions may be executed by the processor 801 of the device 800 for assessing the surface fatigue crack growth life of a welded structure to perform the aforementioned method for assessing the surface fatigue crack growth life of a welded structure.

[0122] Example 4:

[0123] Corresponding to the above method embodiment, this embodiment further provides a readable storage medium. The readable storage medium described below and the method for evaluating the surface fatigue crack growth life of a welded structure described above can refer to each other.

[0124] The readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for evaluating the surface fatigue crack growth life of a welded structure of the above method embodiment.

[0125] The readable storage medium may specifically be any readable storage medium that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0126] The present invention solves these technical bottlenecks through the following innovations: (1) Introduction of generalized structural stress: Based on the theoretical model of structural stress of welded joints, the present invention takes into account the geometric characteristics of welded joints (weld angle, weld toe radius, etc.) and notch effect, and proposes a two-stage model of surface fatigue crack growth of welded joints based on generalized structural stress, so that the stress intensity factor during crack growth can more accurately reflect the actual situation. (2) Staged modeling of shallow cracks and long cracks: The present invention divides the crack growth process into the shallow surface crack stage (a / t≤0.2) and the long crack stage (a / t>0.2). By accurately modeling the crack growth behavior of different stages, it ensures that the crack growth process at different depth stages can be accurately described. (3) Efficient calculation method: The geometric correction factor and full thickness amplification factor under tensile and bending load modes are obtained by multivariate regression method to solve the stress intensity factor. The present invention improves the calculation accuracy and efficiency of the stress intensity factor during crack growth, avoids the complex simulation of parametric crack growth of welded joints in traditional methods, and thus improves the calculation efficiency.

[0127] The present invention not only considers the geometric characteristics of the overall structure and the stress distribution caused by the load, but also pays special attention to the influence of local geometric contours and notch stress. The two-stage model of surface fatigue crack growth of welded joints based on generalized structural stress can accurately describe the growth behavior of shallow surface cracks (a / t≤0.2) and long crack stages (a / t>0.2) by introducing geometric contours and notch effects. The model obtains the geometric correction factor F and full thickness M of welded joints with different geometric characteristics under tensile and bending load modes through multivariate regression. kn The amplification factor can effectively correct the local stress concentration effect and improve the prediction accuracy of the crack growth process. The model has good consistency with the calculation results of the weighted function method, and achieves the accurate solution of the stress intensity factor of the entire process of surface fatigue crack growth in welded joints. The full-thickness stress intensity amplification factor of shallow surface cracks is derived based on the notch self-balancing force. For welded structures with different plate thicknesses, when the relative crack depth reaches a / t≈0.2, the amplification effect of the notch effect on the surface crack stress intensity factor disappears. By introducing a modified geometric correction factor regression parameter, the influence of the surface geometric characteristics of the welded joint and the local notch effect on the stress intensity factor is further considered, and the solution accuracy of the surface crack stress intensity factor is further improved compared with the analytical model in the BS7910 standard. The relative error between the calculation results of the welded joint surface crack growth model driven by generalized structural stress and the weighted function geometric correction factor is less than 5%. At the same time, the model avoids the parametric crack growth simulation of the welded joint and improves the efficiency of solving the surface crack stress intensity factor of the welded joint.

[0128] The present invention considers the influence of weld profile and notch stress on the basis of structural stress parameters, and defines the entire process of fatigue crack propagation on the weld joint surface as two stages: shallow surface (a / t≤0.2) and long crack (a / t>0.2), thus realizing the accurate solution of fatigue crack stress intensity factor on the weld joint surface. The relative error of the calculation result with the weighted function method is within 5%. At the same time, the model avoids the parameterized crack propagation simulation of the weld joint, improves the solution efficiency of the stress intensity factor on the weld joint surface crack, and provides theoretical support for the evaluation of the crack propagation life of the weld joint under complex service loads; and based on the two-stage model of fatigue crack propagation on the surface of the weld joint of generalized structural stress, by introducing geometric profile and notch effect, it can accurately describe the propagation behavior of shallow surface crack (a / t≤0.2) and long crack stage (a / t>0.2), and obtains the geometric correction factor F and full thickness M of weld joints with different geometric characteristics under tensile and bending load modes through multivariate regression. kn The amplification factor can effectively correct the local stress concentration effect and improve the prediction accuracy of the crack growth process. The model has good consistency with the calculation results of the weight function method, and achieves the accurate solution of the stress intensity factor of the entire process of fatigue crack growth on the welded joint surface.

[0129] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

[0130] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for evaluating the surface fatigue crack growth life of a welded structure, characterized in that: include: A three-dimensional finite element model of the welded joint was established, and the generalized structural stress under the tensile load mode and the generalized structural stress under the bending load mode were calculated through numerical simulation; The geometric characteristics of the weld joint are measured using a weld gauge to extract the geometric characteristic parameters of the weld joint, including the weld angle, weld toe radius and plate thickness. Based on the geometric characteristic parameters, a geometric correction factor function associated with the crack characteristic parameters is established through multivariate nonlinear regression analysis, and the tensile load geometric correction factor and bending load geometric correction factor associated with the crack characteristic parameters are generated. The crack characteristic parameters include crack depth, half-length, weld angle and weld toe radius. Combining the geometric correction factors of tensile load and bending load, a stress intensity amplification factor correction model for the shallow surface crack stage is constructed to determine the tensile correction coefficient and bending correction coefficient for the shallow surface crack stage, thereby generating the full-thickness stress intensity amplification factor for the shallow crack stage. The generalized structural stress, tensile load geometric correction factor, bending load geometric correction factor, and full-thickness stress intensity amplification factor in the shallow crack stage are input into the crack growth rate equation. The evolution of the crack depth is iteratively calculated to output the fatigue life prediction results of the welded joint.

2. The method for evaluating the surface fatigue crack growth life of a welded structure according to claim 1, characterized in that: Based on the geometric characteristic parameters, a geometric correction factor function associated with the crack characteristic parameters is established through multivariate nonlinear regression analysis to generate a tensile load geometric correction factor and a bending load geometric correction factor associated with the crack characteristic parameters, which include: Based on the geometric characteristic parameters and crack morphology parameters of the welded joint, multiple finite element models were established and numerically simulated with tensile / bending loads to obtain stress intensity factor data sets under different crack depths, half-lengths, and geometric parameters. The geometric characteristic parameters include weld angle, weld toe radius, and plate thickness, and the crack morphology parameters include depth and half-length. Based on the stress intensity factor data set, the tensile load geometric correction factor is obtained by using the multivariate nonlinear regression model under the tensile load mode. According to the stress intensity factor dataset and the multivariate nonlinear regression model, the bending load geometric correction factor was obtained by polynomial fitting under the bending load mode.

3. The method for evaluating the surface fatigue crack growth life of a welded structure according to claim 2, wherein: The calculation formula for the tensile load geometric correction factor is as follows: Where Fm is the tensile load geometric correction factor, Q is the semi-elliptical surface crack shape coefficient, and Y0 is the spatial parameter of the tensile loading mode; The calculation formula of the bending load geometric correction factor is as follows: Where Fb is the bending load geometric correction factor, Q is the semi-elliptical surface crack shape coefficient, and Y1 is the bending load space parameter.

4. The method for evaluating the surface fatigue crack growth life of a welded structure according to claim 1, wherein: The tensile load geometric correction factor and the bending load geometric correction factor are combined to construct a stress intensity amplification factor correction model for the shallow surface crack stage, determine the tensile correction coefficient and the bending correction coefficient for the shallow surface crack stage, and then generate the full-thickness stress intensity amplification factor for the shallow crack stage, which includes: Combining the tensile load geometric correction factor, bending load geometric correction factor and weld joint geometric parameters, the stress concentration effect parameters at the shallow surface crack stage are determined through correlation analysis and processing of the notch self-balancing force amplification factor and finite element data, thereby obtaining the tensile correction factor and bending correction factor. Based on the tensile correction factor, bending correction factor and geometric parameters, the full-thickness amplification factor benchmark value of the shallow crack stage associated with the weld angle and weld toe radius is generated through the generalized structural stress driving parameter construction processing; Based on the benchmark values ​​and crack morphology parameters, the stress intensity amplification factors of tensile load and bending load at the shallow surface crack stage are solved through multivariate regression analysis.

5. The method for evaluating the surface fatigue crack growth life of a welded structure according to claim 4, characterized in that: The calculation formulas for the tensile load stress intensity magnification factor and the bending load stress intensity magnification factor at the shallow surface crack stage are as follows: MknT * =λ·f(θ,ρ / t,a / t,a / c) MknB * =γ·g(θ,ρ / t,a / t,a / c) Where, MknT * is the tensile load stress intensity magnification factor, MknB * is the bending load stress intensity amplification factor, λ is the first correction coefficient, γ is the second correction coefficient, f(θ,ρ / t,a / t,a / c) is the first function, g(θ,ρ / t,a / t,a / c) is the second function, θ is the weld angle, ρ is the weld toe radius, t is the plate thickness, a is the crack depth, and c is the half length of the semi-elliptical crack.

6. A welding structure surface fatigue crack growth life assessment system based on the welding structure surface fatigue crack growth life assessment method according to claim 1, characterized in that: include: Calculation module: used to establish a three-dimensional finite element model of the welded joint and calculate the generalized structural stress under the tensile load mode and the generalized structural stress under the bending load mode through numerical simulation; Extraction module: used to measure the geometric characteristics of welded joints using weld gauges and extract the geometric characteristic parameters of welded joints, including weld angle, weld toe radius and plate thickness; Generation module: used to establish a geometric correction factor function associated with the crack characteristic parameters through multivariate nonlinear regression analysis based on the geometric characteristic parameters, and generate the tensile load geometric correction factor and bending load geometric correction factor associated with the crack characteristic parameters, where the crack characteristic parameters include crack depth, half-length, weld angle and weld toe radius; Construction module: used to combine the tensile load geometric correction factor and the bending load geometric correction factor to construct a stress intensity amplification factor correction model for the shallow surface crack stage, determine the tensile correction coefficient and bending correction coefficient for the shallow surface crack stage, and then generate the full-thickness stress intensity amplification factor for the shallow crack stage; Iterative calculation module: It is used to input the generalized structural stress, tensile load geometric correction factor, bending load geometric correction factor and shallow crack stage full thickness stress intensity magnification factor into the crack growth rate equation, and output the fatigue life prediction results of the weld joint by iteratively calculating the evolution of crack depth.

7. The welded structure surface fatigue crack growth life assessment system according to claim 6, characterized in that: The generation module includes: The first processing unit is used to obtain stress intensity factor data sets under different crack depths, half-lengths and geometric parameters based on the geometric characteristic parameters and crack morphological parameters of the weld joint by establishing multiple finite element models and applying tensile / bending loads for numerical simulation processing. The geometric characteristic parameters include weld angle, weld toe radius and plate thickness, and the crack morphological parameters include depth and half-length. The second processing unit is used to process the stress intensity factor data set using a multivariate nonlinear regression model under a tensile load mode to obtain a tensile load geometric correction factor; The third processing unit is used to obtain the bending load geometric correction factor by using the polynomial fitting process under the bending load mode according to the stress intensity factor data set and the multivariate nonlinear regression model.

8. The welded structure surface fatigue crack growth life assessment system according to claim 6, characterized in that: The building blocks include: Determination unit: used to combine the tensile load geometric correction factor, the bending load geometric correction factor and the weld joint geometric parameters, and determine the stress concentration effect parameters in the shallow surface crack stage through the correlation analysis and processing of the notch self-balancing force amplification factor and the finite element data, thereby obtaining the tensile correction factor and the bending correction factor; The fourth processing unit is used to generate a reference value of the full-thickness amplification factor in the shallow crack stage associated with the weld angle and weld toe radius through a generalized structural stress driving parameter construction process based on the stretch correction factor, the bending correction factor and the geometric parameters; Solving unit: used to solve the tensile load stress intensity amplification factor and the bending load stress intensity amplification factor at the shallow surface crack stage based on the benchmark value and crack morphology parameters through multiple regression analysis.

9. A device for evaluating the surface fatigue crack growth life of a welded structure, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the method for evaluating the surface fatigue crack growth life of a welded structure as claimed in any one of claims 1 to 5 when executing the computer program.

10. A readable storage medium, characterized in that: The readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for evaluating the surface fatigue crack growth life of a welded structure according to any one of claims 1 to 5 is implemented.

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