Shape inversion measurement method and system for asymmetric distribution of residual stress of bending member

Abstract

The invention relates to the technical field of stress measurement, in particular to a form inversion measurement method and system for asymmetric distribution of residual stress of a bent component, and the method comprises the following steps: S1, welding a bent steel component with a box-shaped section, and obtaining the initial curvature of the bent steel component in the length direction of the bent steel component in an unconstrained free state; the method comprises the steps of S1, conducting cutting operation on the middle point in the length direction of the bent steel member or the section with the maximum initial bending rate, releasing the stress of the bent steel member to obtain two symmetrical sections of steel members, S2, conducting form inversion measurement and curvature variation calculation after stress release, S4, conducting residual stress distribution inversion calculation, and S5, conducting deformation calculation. The method is a core method capable of macroscopically and integrally measuring the residual stress distribution of the component and quantitatively verifying the stress asymmetry of the bending concave side and the bending convex side of the component. Meanwhile, a macroscopic measurement method and a local point measurement method can be combined, and mutual verification and correction are carried out, so that more accurate and reliable residual stress field data can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of structural engineering stress measurement, and particularly relates to a method and system for measuring the morphology of residual stress asymmetric distribution of a curved member. BACKGROUND

[0002] Box section steel members are widely used in large space structures such as buildings and bridges due to their high torsional stiffness and load-bearing capacity. In recent years, with the increasing pursuit of complex spatial curved surface morphology in architectural aesthetics, curved steel members have been widely used. Compared with the traditional method of fitting curves with straight bars, curved members can more directly and accurately achieve the architectural modeling intent, and have become key elements in landmark buildings such as large-span stadiums and transportation hubs. This trend has put higher requirements on the processing precision and stress performance control of curved members.

[0003] The manufacturing process of welded box section curved members is much more complex than that of straight members. Specifically, instead of welding straight boxes and then bending them as a whole, the process involves separate processing and assembly welding. First, the two flange plates that make up the concave and convex sides of the curved member are directly processed into the target curved shape through cold bending. At the same time, the two web plates are cut into corresponding fan-shaped segments. Finally, the four plate pieces with curved shapes are assembled into the final box-shaped curved member through welding.

[0004] Therefore, the residual stress field inside such members is a very complex multiple coupling field: it contains plastic deformation stress introduced by cold bending of flange plates, initial stress in the web plate cutting and forming process, and welding residual stress introduced by uneven thermal cycling during welding of the four main welds. The distribution of these residual stresses of different sources and different natures after superposition in the cross section of the member, especially whether the distribution is symmetric on the concave and convex sides of the curve, becomes extremely complex and difficult to predict by traditional theory.

[0005] The existence of residual stress can significantly affect the stability, fatigue life, and overall mechanical properties of steel members. Accurate measurement of the residual stress distribution inside such welded curved box section members made by complex processes, especially quantitative verification of their asymmetry, is crucial for precise structural safety assessment and has been a long-standing technical difficulty in the field.

[0006] Currently, common residual stress measurement methods (such as the sectioning method, blind hole method, and X-ray diffraction method) have obvious limitations when facing such complex curved members:

[0007]

[0008] ​(1) Limitations and high cost of point measurement: These methods (such as blind hole method and X-ray diffraction method) can only obtain the stress values ​​of discrete points on the surface of the component. However, the stress field of welded box-shaped bending components has a large gradient in the weld area and is unevenly distributed on the bending plate. It requires extremely dense measurement points to approximate the stress field, which is inefficient, costly and cannot reflect the overall stress distribution pattern of the cross section macroscopically.

[0009] (2) Unable to identify composite stress sources: Traditional point measurement methods are difficult to distinguish and quantify the contributions of welding stress and bending stress, and are even less able to effectively assess the combined effect of the two on the cross-sectional asymmetry after coupling.

[0010] (3) The principle of classical destructive methods is not applicable: The strip method, as a classical method for measuring residual stress, is based on the principle of inferring stress by measuring the change in distance (i.e., strain) between "marked points" before and after cutting. However, this principle is theoretically seriously inapplicable to bending members with initial curvature, especially their curved flanges:

[0011] Inherent error: When the flange of a curved member is cut into strips, the cut releases not only the elastic strain caused by residual stress, but also the rigid body displacement and rotational components that cause the member to change from its initial bending shape to a new one. After cutting, the strip not only changes in length, but its spatial arc shape also changes. At this point, the change in distance between two marked points is the result of the combined effects of elastic strain, rigid body displacement, and arc deformation, which cannot be effectively separated. This leads to a significant error in the inverse calculation based on the one-dimensional linear strain assumption from the outset, resulting in severely inaccurate results.

[0012] Loss of macroscopic morphological information: The strip cutting process completely destroys the integrity of the component and its initial macroscopic bending shape. The core of this invention lies in using macroscopic morphological changes to invert stress. The strip cutting method loses this key information carrier in the first step, so it cannot be used to verify the influence of residual stress distribution on the overall bending shape of the component, let alone examine the macroscopic effect of the asymmetry between the concave and convex sides of the stress.

[0013] Introducing secondary stress disturbance: The complex cutting process itself introduces new processing stress and thermal stress, which interferes with the original residual stress field and affects the accuracy of the final result.

[0014] Therefore, for welded box-shaped bending members, there is a lack of reliable measurement methods in the prior art that can avoid the limitations of local point measurement, overcome the interference of curved surface geometry, and effectively assess the asymmetry of residual stress in the cross section from a macroscopic perspective. Summary of the Invention

[0015] To address the aforementioned shortcomings of existing technologies, this invention provides a morphological inversion measurement method and system for the asymmetric distribution of residual stress in bending components. This method enables macroscopic and holistic measurement of the residual stress distribution in such components and quantitative verification of the stress asymmetry between the concave and convex sides of the bending structure. Furthermore, it allows for the combination, mutual verification, and correction of macroscopic measurement methods with local point measurement methods to obtain more accurate and reliable residual stress field data.

[0016] To achieve the above objectives, the present invention provides the following technical solution:

[0017] A method for morphological inversion measurement of asymmetric residual stress distribution in bending members includes the following steps:

[0018] S1, a bent steel member with a welded box-shaped cross-section, obtaining the initial curvature of the bent steel member along its length in an unconstrained free state. ;

[0019] S2, stress relief, involves cutting the bent steel member at the midpoint of its length or at the section with the largest initial curvature to release the stress and obtain two symmetrical steel members.

[0020] S3, Post-stress release morphological inversion measurement and curvature change calculation, to obtain the curvature of two steel members in an unconstrained free state. Calculate the change in curvature of the component before and after cutting. ,Right now: ;

[0021] S4, Residual stress distribution inversion calculation:

[0022] S41, Calculate the release moment. According to the beam bending theory in mechanics of materials, the change in curvature and the additional bending moment generated by the release of residual stress are considered. A linear relationship exists:

[0023] ;

[0024] in, The elastic modulus of steel. Let be the moment of inertia of the box-shaped cross-section about its neutral axis;

[0025] S42, Establish the inversion model; the additional bending moment is caused by the self-balancing residual stress within the cross section. Integrating, we obtain the moment equilibrium equation:

[0026] ,

[0027] The self-balancing equation is: ,

[0028] in, The cross-sectional area of ​​the box is... The distance from the area of ​​the infinitesimal element on the cross section to the neutral axis;

[0029] S43, Residual stress distribution modeling and inversion solution: Solve the moment equilibrium equations and self-equilibrium equations, and output residual stress distribution contour maps or inverted stress values. A list.

[0030] Optionally, S1 may also include the following steps:

[0031] S11, the bending steel member to be tested is placed on the platform in an unconstrained free state;

[0032] S12, using a 3D laser scanner or photogrammetry system to acquire dense point cloud data of the surface of the curved steel component;

[0033] S13, through point cloud data processing, the spatial curve of the geometric centerline of the curved steel component is extracted and fitted, and its length coordinates are established. Equation of the initial geometric centerline for variables ;

[0034] S14, using the initial geometric equations, calculate the initial curvature of the bent steel member along its length. The calculation formula is: .

[0035] Optionally, straight steel plates are directly processed into the target curved shape through a cold bending process to obtain two flange plates on the concave and convex sides of the curve. At the same time, the two web plates are cut into corresponding fan-shaped segments. Finally, these four plates with curved shapes are assembled into a box-shaped curved steel component by welding.

[0036] Optionally, wire cutting can be used to cut bent steel components.

[0037] Optionally, S3 also includes the following steps:

[0038] S31: Perform the same operation as S12 on the two cut steel components to fit and extract the spatial curves of the geometric center lines of the two steel components, and establish their length coordinates. The equation of the new geometric centerline with variables The curvature corresponding to the new centerline is calculated using the formula in S1. Curvature change It originates directly from the release of residual stress within the bent steel component.

[0039] Optionally, before cutting the bent steel member, a blind hole method measurement is added. According to the standard blind hole method, strain rosettes are attached to the surface of the flange plate of the bent steel member near the weld area in the middle, and holes are drilled and strain measurements are taken to obtain preliminary measurements of the surface residual stress at the measuring points. .

[0040] Optionally, after the blind hole method measurement and the morphological inversion method measurement, the following steps may also be included:

[0041] S5. Data comparison and correction model establishment: Based on the results of residual stress distribution inversion calculation reflecting the overall stress state of the bending steel member, systematic errors in blind hole method measurement are identified and corrected.

[0042] Optional, specifically including:

[0043] S51, Data Preparation and Matching:

[0044] Select all measurement points on the bent steel member that have been measured using the blind hole method and can be covered by the morphological inversion method, ensuring that each measurement point i has two data pairs: the surface residual stress value obtained from the blind hole method measurement and the surface residual stress value obtained from the blind hole method. The residual stress values ​​corresponding to the same location and direction are extracted from the full-field distribution results obtained by the morphological inversion method. ;

[0045] S52, System error analysis and correction model construction, plotting all measurement point pairs on a scatter plot. and with Let x be the x-coordinate. The vertical coordinate is y;

[0046] Error pattern recognition: Observe the distribution trend of data points;

[0047] A. If the point group is evenly distributed near the straight line y=x, it indicates that the blind hole method measurement on the component is accurate and requires no correction or only simple offset correction.

[0048] B, If the point group exhibits a significant systematic deviation, in the high-pressure stress zone (for larger negative values), blind hole method measurement value The absolute value of the system is systematically less than This indicates that the blind hole method underestimates the compressive stress due to the plastic effect and needs to be corrected.

[0049] Establish a quantitative correction model: Based on the identified systematic error patterns, a correction function is established using numerical methods.

[0050] Linear correction model: If the error exhibits a linear relationship, the correction formula can be obtained through linear regression fitting. ,in, The corrected stress value, slope and intercept Determined by fitting;

[0051] Nonlinear correction model: If the error is nonlinear, a piecewise linear function or a quadratic function is used for fitting to obtain an accurate correction;

[0052] S53, Model Validation and Applicability Confirmation: The modified model is applied to all blind hole method measuring points to obtain the corrected stress values. Calculate the corrected and If the residuals between the two are significantly reduced and exhibit a random distribution, it indicates that the modified model is effective and has successfully separated and eliminated systematic errors.

[0053] S54 generates a fused residual stress field. Using a validated correction model, the data of all blind hole measurement points are batch corrected. The corrected local stress data points are used as precise boundary conditions and embedded into the residual stress distribution framework that conforms to the overall mechanical equilibrium obtained by the morphological inversion method to generate the final corrected residual stress field.

[0054] Measurement system, including:

[0055] The three-dimensional topography acquisition unit is used to acquire three-dimensional spatial coordinate point cloud data of the component surface before and after the component is cut.

[0056] The data processing and centerline extraction unit receives point cloud data from the 3D topography acquisition unit, reconstructs the geometric model of the component through a built-in algorithm, and extracts the geometric centerline for calculation.

[0057] The curvature calculation and morphological change analysis unit automatically calculates the curvature and curvature change of the extracted geometric center line.

[0058] The stress inversion calculation unit is used to convert morphological changes into residual stress distribution results;

[0059] The control and visualization human-computer interaction interface unit is used to integrate and control the collaborative work of various units and provide intuitive results display.

[0060] Optionally, the 3D topography acquisition unit is a laser 3D scanner or a photogrammetry system; the data processing and centerline extraction unit includes a point cloud processing software module. This module employs a curve fitting algorithm based on non-uniform rational B-splines to process the discrete point cloud data and reconstruct a smooth, continuous geometric centerline equation that conforms to the actual bending shape of the component. and The curvature calculation and morphological change analysis unit includes a symbolic computation and numerical differentiation module, capable of performing calculations on the centerline equation. Perform automatic differentiation and calculate the first derivative. and second derivative Subsequently, the curvature is automatically calculated at each point along the length of the component according to the curvature calculation formula, and the curvature change is finally output. The stress inversion calculation unit has a built-in inversion calculation engine that receives... Input the moment of inertia of the box section about its neutral axis and the elastic modulus of the steel to calculate the released bending moment. The inversion engine solves the bending moment balance and self-balancing equations and outputs the final residual stress distribution cloud map or a list of inverted stress values. It also automatically calculates and identifies the maximum stress amplitude of the concave and convex flanges.

[0061] The technical solution provided by this invention has the following advantages compared with the known prior art:

[0062] 1. The morphological inversion method of this invention breaks through the limitations of traditional point measurement techniques. It does not rely on limited local strain data to infer the overall stress, but uses the overall geometry of the component itself as the measurement signal. It releases stress through a single cutting operation and accurately measures the resulting stress.

[0063] The macroscopic morphological changes (curvature changes) are observed, and the residual stress distribution on the cross-section is directly inverted using a mechanical model. For verifying the macroscopic distribution characteristics of the asymmetry between residual stress on the concave and convex sides of a bend, this invention provides direct and quantitative measurement results, a problem that traditional methods cannot effectively solve due to their localized nature.

[0064] 2. Through high-precision three-dimensional measurement and rigorous mathematical modeling, the residual stress can be quantitatively determined.

[0065] The measurement provides precise input for subsequent structural calculations by providing specific numerical values ​​and distribution cloud maps, rather than qualitative or semi-quantitative judgments. The measurement results reflect the overall, average stress state of the component, effectively avoiding...

[0066] In areas with large stress gradients (such as near welds), even slight deviations in the measurement point location can lead to significant differences in results, making the results more representative and reliable for engineering applications. This method, based on elasticity theory, is unaffected by the absolute value of residual stress. Even when the residual stress approaches or reaches the material's yield strength, it can still be accurately measured, effectively overcoming the measurement errors caused by plastic effects in high-stress areas by traditional methods such as the blind hole method.

[0067] 3. The dedicated measurement system integrates and automates the complex measurement process, greatly reducing the difficulty of operation and the technical dependence on operators, reducing human error, and improving the repeatability and consistency of measurement results. The system can generate animations of component shape changes, curvature change curves, and distribution cloud maps of residual stress on the cross section, making abstract stress data intuitive and visible, and facilitating the understanding and analysis of asymmetry and other characteristics. This method provides a clear and repeatable operating procedure and data processing standard, laying the foundation for establishing a standard measurement method for residual stress of such complex components in the future.

[0068] 4. The method of integrating blind hole measurement leverages the advantages of macroscopic accuracy of morphological inversion and local precision of blind hole measurement, forming a unique complementary enhancement effect. It uses the overall results to verify and correct local measurements, greatly improving the reliability of the final data. It is especially suitable for scientific research and key engineering projects with extremely high precision requirements. This integrated scheme provides a reliable benchmark method for evaluating and calibrating the applicability of other residual stress measurement methods on complex components, and has important industry guidance value. Attached Figure Description

[0069] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0070] Figure 1 This is a schematic diagram of the process of the present invention;

[0071] Figure 2 This is a structural schematic diagram of a bent steel component;

[0072] Figure 3 This is a schematic diagram showing the morphological changes of a bent steel component before and after it is cut.

[0073] Figure 4 A schematic diagram comparing the centerlines of a bent steel component before and after cutting;

[0074] Figure 5 This is a schematic diagram of the system structure of the present invention;

[0075] Figure 6 The residual stress distribution at the intended cut-off location of the bent steel member, as measured by the blind hole method;

[0076] Figure 7 This is a schematic diagram of the residual stress distribution in the welded box section of the existing ECCS model;

[0077] Figure 8To improve the schematic diagram of residual stress distribution in the welded box-section bending steel member in the model;

[0078] Figure 9 A schematic diagram of the process for measurement using the blind hole method;

[0079] Figure 10 This is a schematic diagram of the cross-sectional structure of a bent steel member.

[0080] Reference numerals: 1-bent steel member, 2-flange plate, 3-web plate. Detailed Implementation

[0081] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0082] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0083] The present invention will be further described below with reference to embodiments.

[0084] A method for morphological inversion measurement of asymmetric residual stress distribution in bending members includes the following steps:

[0085] S1, Welding a box-shaped curved steel member 1, obtaining the initial curvature of the curved steel member 1 along its length in an unconstrained free state. ;

[0086] S2, stress relief, is achieved by cutting at the midpoint of the length of the bent steel member 1 or at the section with the largest initial curvature to release the stress in the bent steel member 1 and obtain two symmetrical steel members.

[0087] S3, Post-stress release morphological inversion measurement and curvature change calculation, to obtain the curvature of two steel members in an unconstrained free state. Calculate the change in curvature of the component before and after cutting. ,Right now: ;

[0088] This represents the initial curvature of the bent steel member 1 before it is cut. Indicates the curvature of the two segments after cutting;

[0089] S4, Residual stress distribution inversion calculation:

[0090] S41, Calculate the release moment. According to the beam bending theory in mechanics of materials, the change in curvature and the additional bending moment generated by the release of residual stress are considered. A linear relationship exists:

[0091] ;

[0092] in, The elastic modulus of steel. Let be the moment of inertia of the box-shaped cross-section about its neutral axis;

[0093] S42, Establish the inversion model; the additional bending moment is caused by the self-balancing residual stress within the cross section. Integrating, we obtain the moment equilibrium equation:

[0094] ,

[0095] The self-balancing equation is: ,

[0096] in, The cross-sectional area of ​​the box is... The distance from the area of ​​the infinitesimal element on the cross section to the neutral axis;

[0097] S43, Residual stress distribution modeling and inversion solution: Solve the moment equilibrium equations and self-equilibrium equations, and output residual stress distribution contour maps or inverted stress values. A list.

[0098] In this embodiment, as Figure 1 As shown, the classical residual stress distribution model (often referred to as the ECCS model or Birkeland model), a recognized model in the field of welded structural mechanics, is adopted as the benchmark model. This model has been verified through numerous experiments and is suitable for the welded box section, as shown below. Figure 7 As shown in the existing classic welded box section residual stress distribution mode,

[0099] Tensile stress zone: A band-shaped area of ​​a certain width distributed near the four welds, where the stress value is the constant maximum residual tensile stress. .

[0100] Compressive stress zone: distributed in the middle of the plate (the area far from the weld), where the stress value is the constant maximum residual compressive stress. .

[0101] Transition zone: The linear transition zone between the tensile and compressive stress zones.

[0102] Geometric parameters: the width of the tensile stress zone b, the width of the transition zone c, and the width of the compressive stress zone a are constants related to the plate thickness, the width-to-thickness ratio of the plate, and the welding process.

[0103] Symmetry: In the baseline model, the residual stress distribution patterns of the four plates (two flange plates 2 and two web plates 3) of the box section are the same, and the stress amplitudes are... and The constant is used, meaning the model is symmetric.

[0104] Model Innovation: The model introduces the asymmetry in stress amplitude between the concave and convex sides due to bending effects, and does not treat the stress amplitude as a constant in the classical model. For components that have undergone bending, the effects of the bending process are coupled with the welding effects, resulting in unequal residual stress amplitudes in the corresponding regions of the concave and convex sides. Figure 6, a residual stress distribution diagram of the middle part (the proposed cut-off position) of the bent steel component measured by the blind hole method, verifies this viewpoint. It can be seen that the residual tensile stress amplitude of the concave flange at this location is significantly greater than that of the convex side. Simultaneously, based on a considerable amount of experimental data, a residual stress distribution model for the welded box-section bent steel component 1 is proposed, such as... Figure 8 (The improved residual stress distribution pattern of the welded box-section bending steel member) is shown: Based on the existing classic distribution pattern (i.e., the region divisions a, b, and c remain unchanged), the stress amplitudes on the concave and convex sides are allowed to be independent parameters to be determined. Taking flange plate 2 as an example:

[0105] The maximum residual tensile stress amplitude on the concave side of the curved flange 2 is denoted as P1, and the maximum residual compressive stress amplitude is denoted as P2. The maximum residual tensile stress amplitude on the convex side of the curved flange 2 is denoted as P3, and the maximum residual compressive stress amplitude is denoted as P4. The residual stress distribution pattern of the two web plates 3 still adopts the classic symmetrical ECCS model.

[0106] Model parameters and solutions: The improved model established based on parameter correlation and inversion according to physical assumptions introduces four key magnitude parameters (P1, P2, P3, P4), but the inversion solution is based on only two independent equations:

[0107] Moment equilibrium equation;

[0108] Self-balancing equation;

[0109] To ensure the system of equations is closed and solvable, reasonable physical assumptions need to be introduced to correlate the parameters and reduce the number of unknowns. Based on existing technology and research findings, for a given welding process (heat input, plate thickness, width-to-thickness ratio, material, etc.), there exists a relatively stable proportional relationship between the tensile stress amplitude generated near a weld and the compressive stress amplitude generated in the middle of the plate. Therefore, the following key assumptions are introduced:

[0110] For the same flange plate 2, the ratio of the absolute value of the tensile stress amplitude in the weld zone to the absolute value of the compressive stress amplitude in the middle of the plate is approximately a constant. (generally This assumption can be expressed as:

[0111] , ;

[0112] in, and The proportionality constant can be obtained in advance through finite element simulation or experimental calibration of the specimen. Under this assumption, the four amplitude parameters (P1, P2, P3, P4) are reduced to two independent parameters (e.g., P2 and P4). The tensile stress parameters P1 and P3 can be calculated from P2 and P4, respectively. Thus, the two equilibrium equations are sufficient to solve for the two independent parameters, making the inversion problem mathematically closed and solvable.

[0113] Model Solving and Asymmetry Verification:

[0114] Substituting the above parameterized improved model into the moment equilibrium equation and the self-equilibrium equation allows for numerical inversion and solution. The solution process is a constrained optimization problem, with the goal of finding a set of parameters (P2, P4) such that the released moment calculated by the model is closest to the measured moment. The self-balancing equation is strictly satisfied. After inversion calculation, the residual stress asymmetry introduced by the bending process can be quantitatively verified by directly comparing the stress amplitudes of the corresponding characteristic regions on the concave and convex sides solved by the model (e.g., comparing P2 (concave compressive stress) and P4 (convex compressive stress)). If P2≠P4, the existence of asymmetry is confirmed, and the degree of difference can be accurately calculated.

[0115] Furthermore, S1 also includes the following steps:

[0116] S11, the bending steel member 1 to be tested is placed on the platform in an unconstrained free state;

[0117] S12, Use a 3D laser scanner or photogrammetry system to acquire dense point cloud data of the surface of the curved steel component 1;

[0118] S13, through point cloud data processing, the spatial curve of the geometric centerline of the curved steel component 1 is extracted and fitted, and its length coordinates are established. Equation of the initial geometric centerline for variables ;

[0119] S14, using the initial geometric equations, calculate the initial curvature of the bent steel member 1 along its length. The calculation formula is: .

[0120] Furthermore, the flat steel plate is directly processed into the target curved shape through cold bending process to obtain two flange plates 2 on the concave and convex sides of the curve. At the same time, the two web plates 3 are cut into corresponding fan-shaped segments. Finally, these four plates with curved shapes are assembled into a box-shaped curved steel component 1 by welding.

[0121] Furthermore, the bending steel component 1 is cut using wire cutting, with a cutting accuracy better than 0.1mm.

[0122] Specifically, such as Figure 2 , Figure 3 , Figure 10 As shown, the cutting operation is performed at the critical location of the bent steel member 1 (usually selected at the midpoint of the member's length direction, or at the section with the largest initial bending curvature). To ensure complete stress release and avoid introducing new processing stress, it is preferable to use cold working methods such as wire cutting or water jetting to completely separate the member.

[0123] Furthermore, S3 also includes the following steps:

[0124] S31, perform the same operation as S12 on the two cut steel components respectively, such as... Figure 4 As shown, the spatial curves of the geometric centerlines of the two steel components are extracted by fitting, and their length coordinates are established. The equation of the new geometric centerline with variables The curvature corresponding to the new centerline is calculated using the formula in S1. Curvature change It originates directly from the release of residual stress inside the bent steel member 1.

[0125] Furthermore, before cutting the bent steel member 1, a blind hole method measurement was added. According to the standard blind hole method, strain gauges were attached to the surface of the flange plate 2 of the bent steel member 1 in the middle area near the weld, and drilling and strain measurements were performed to obtain preliminary measurements of the surface residual stress at the measuring points. .

[0126] Specifically, such as Figure 9 As shown, the blind hole method is a mature local stress measurement technique that is widely used, but it has inherent limitations, especially when measuring welded box-section bending members:

[0127] Limited measurement depth: The blind hole method can only measure the residual stress in the shallow layer of the component surface. For thicker steel plates, the stress gradient along the thickness direction inside cannot be captured, so the measurement results cannot represent the stress state of the entire plate thickness.

[0128] High-stress measurement distortion: When the residual stress level is high (e.g., close to or exceeding a certain percentage of the material's yield strength), the plastic deformation caused by stress release during drilling can cause significant errors in the measurement results, hence the so-called limitation that "residual stress value / yield strength" cannot be too high.

[0129] Lack of overall representativeness: The stress values ​​of a single or a few measuring points are difficult to truly reflect the macroscopic overall residual stress distribution law of the component, especially the specific numerical value of the asymmetry of residual stress amplitude at the cross-section level.

[0130] The purpose of combining the blind hole method is to fully leverage the respective advantages of the blind hole method ("precise local measurement") and the morphological inversion method ("realistic overall reflection") to form a complementary measurement strategy. The overall results of the morphological inversion method are used to verify and correct the local measurement values ​​of the blind hole method, thereby obtaining more accurate and reliable residual stress distribution data.

[0131] First, perform blind hole method measurements: Before cutting the component, according to the conventional blind hole method standard (such as ASTM E837), strain gauges are attached to the surface of critical parts of the component (such as the middle of flange plate 2 and the area near the weld), and drilling and strain measurements are performed to obtain preliminary measurements of the surface residual stress at these measuring points. .

[0132] Then, the morphological inversion method is performed: as mentioned earlier, the entire process from initial morphological measurement to cutting and then to stress inversion calculation is completed to obtain the overall residual stress distribution of the component, especially the stress distribution pattern on the cross section (such as concave compressive stress and convex tensile stress) and the inversion stress values ​​at key locations (corresponding to blind hole measurement points). .

[0133] Furthermore, following the blind hole method measurement and morphological inversion method measurement, the following steps are also included:

[0134] S5. Data comparison and correction model establishment: Based on the results of the residual stress distribution inversion calculation reflecting the overall stress state of the bending steel member 1, systematic errors in blind hole method measurement are identified and corrected.

[0135] This step aims to establish a quantitative relationship based on reliable results obtained by the morphological inversion method that reflect the overall stress state of the component, in order to identify and correct the systematic errors that may exist in the blind hole method in specific application scenarios (such as high stress levels and thick plates).

[0136] Furthermore, specifically including:

[0137] S51, Data Preparation and Matching:

[0138] Select all key measurement points on the component that have been measured by the blind hole method and can be covered by the morphological inversion method. These measurement points should be representative, such as those located in the middle of the flange or near the weld area.

[0139] Ensure that each measuring point i has two data pairs: the surface residual stress value measured by the blind hole method. The residual stress values ​​corresponding to the same location and direction (such as along the component axis) are extracted from the full-field distribution results obtained by the morphological inversion method. ;

[0140] S52, System error analysis and correction model construction, plotting all measurement point pairs on a scatter plot. and with Let x be the x-coordinate. The vertical coordinate is y;

[0141] Error pattern recognition: Observe the distribution trend of data points;

[0142] A. If the point group is evenly distributed near the straight line y=x, it indicates that the blind hole method measurement on the component is accurate and requires no correction or only simple offset correction.

[0143] B, If the point group exhibits a significant systematic deviation, in the high-pressure stress zone (for larger negative values), blind hole method measurement value The absolute value of the system is systematically less than This indicates that the blind hole method underestimates the compressive stress due to the plastic effect and needs to be corrected.

[0144] Establish a quantitative correction model: Based on the identified systematic error patterns, a correction function is established using numerical methods.

[0145] Linear correction model: If the error exhibits a linear relationship, the correction formula can be obtained through linear regression fitting. ,in, The corrected stress value. The corrected stress value, slope and intercept Determined by fitting;

[0146] Nonlinear correction model: If the error is nonlinear, a piecewise linear function or a quadratic function is used for fitting to obtain an accurate correction;

[0147] S53, Model Validation and Applicability Confirmation: The modified model is applied to all blind hole method measuring points to obtain the corrected stress values. Calculate the corrected and If the residuals between the two are significantly reduced and exhibit a random distribution, it indicates that the modified model is effective and has successfully separated and eliminated systematic errors.

[0148] S54 generates a fused residual stress field. Using a validated correction model, the data of all blind hole measurement points are batch corrected. The corrected local stress data points are used as precise boundary conditions and embedded into the residual stress distribution framework that conforms to the overall mechanical equilibrium obtained by the morphological inversion method to generate the final corrected residual stress field.

[0149] Specifically, using a validated correction model, the data of all blind hole method measurement points (including those detailed locations not directly covered by the morphological inversion method) are batch corrected. These corrected, more reliable local stress data points are used as precise boundary conditions and embedded into the residual stress distribution framework obtained by the morphological inversion method, which conforms to the overall mechanical equilibrium. This is then integrated with the overall stress distribution pattern obtained by the morphological inversion method, ultimately generating a high-confidence residual stress field that is accurate in both macroscopic distribution and local details. This provides top-quality input data for subsequent fatigue analysis, ultimate bearing capacity assessment, and other tasks.

[0150] The combination of blind hole measurement and morphological inversion measurement leverages their complementary advantages, resulting in more reliable results. It overcomes the limitations of the blind hole method in measuring high stress and thick plates, and compensates for the shortcomings of the morphological inversion method in reflecting local stress concentration. This allows for mutual verification and correction of point and surface measurement results. A new measurement paradigm under high stress conditions has been established, providing an effective solution for obtaining accurate data in measurement scenarios where traditional methods may result in distortions (such as high-strength steel and thick plate components). The usability of the data has been improved; the final fused stress field model includes both macroscopic distribution and local details, providing higher-quality input data for subsequent finite element analysis, fatigue life prediction, and structural safety assessment.

[0151] Measurement system, including:

[0152] The three-dimensional topography acquisition unit is used to acquire three-dimensional spatial coordinate point cloud data of the component surface before and after the component is cut.

[0153] The data processing and centerline extraction unit receives point cloud data from the 3D topography acquisition unit, reconstructs the geometric model of the component through a built-in algorithm, and extracts the geometric centerline for calculation.

[0154] The curvature calculation and morphological change analysis unit automatically calculates the curvature and curvature change of the extracted geometric center line.

[0155] The stress inversion calculation unit is used to convert morphological changes into residual stress distribution results;

[0156] The control and visualization human-computer interaction interface unit is used to integrate and control the collaborative work of various units and provide intuitive results display.

[0157] Furthermore, the 3D topography acquisition unit is a laser 3D scanner or photogrammetry system; the data processing and centerline extraction unit includes a point cloud processing software module. This module employs a curve fitting algorithm based on non-uniform rational B-splines to process the discrete point cloud data and reconstruct a smooth, continuous geometric centerline equation that conforms to the actual bending shape of the component. and The curvature calculation and morphological change analysis unit includes a symbolic computation and numerical differentiation module, capable of performing calculations on the centerline equation. Perform automatic differentiation and calculate the first derivative. and second derivative Subsequently, the curvature is automatically calculated at each point along the length of the component according to the curvature calculation formula, and the curvature change is finally output. The stress inversion calculation unit has a built-in inversion calculation engine that receives... Input the moment of inertia of the box section about its neutral axis and the elastic modulus of the steel to calculate the released bending moment. The inversion engine solves the bending moment balance and self-balancing equations and outputs the final residual stress distribution cloud map or a list of inverted stress values. It also automatically calculates and identifies the maximum stress amplitude of the concave and convex flange plates 2.

[0158] In this embodiment, as Figure 5 As shown, the 3D topography acquisition unit is responsible for acquiring high-precision and rapid 3D spatial coordinate point cloud data of the component's surface before and after cutting. This unit includes a high-precision optical scanning device, such as a laser 3D scanner or an industrial-grade photogrammetry system. To maintain a consistent measurement benchmark, the system can integrate an automatic positioning platform for fixing and precisely moving the scanning device, ensuring strict consistency of the coordinate systems between the two scans. Its core performance indicator lies in its ability to capture minute morphological changes in the component; therefore, its absolute accuracy should be better than 0.1 mm.

[0159] The data processing and centerline extraction unit receives point cloud data from the 3D topography acquisition unit and reconstructs the geometric model of the component using a built-in algorithm, accurately extracting the geometric centerline for calculation. This unit is one of the "brains" of the system and contains a dedicated point cloud processing software module. This module uses a curve fitting algorithm based on non-uniform rational B-splines (NURBS) to process discrete point cloud data, accurately reconstructing a smooth, continuous geometric centerline mathematical model that conforms to the actual bending shape of the component. and The core of this unit lies in the robustness of its algorithm, which can effectively filter measurement noise and accurately handle the edge features of the box-shaped cross-section, ensuring the accuracy of centerline positioning.

[0160] The curvature calculation and morphological change analysis unit automatically calculates curvature and its changes based on the extracted centerline equation. This unit includes a symbolic computation and numerical differentiation module, which can perform symbolic computation and numerical differentiation on the centerline equation. Perform automatic differentiation and calculate the first derivative. and second derivative Subsequently, the curvature is automatically calculated at each point along the length of the component based on the precise formula for curvature, and the change in curvature is finally output. .

[0161] The stress inversion calculation unit is the core calculation unit of the system, responsible for converting morphological changes into residual stress distribution results. This unit has a built-in dedicated inversion calculation engine. It receives data from upstream... The user-input material parameters (elastic modulus) and cross-sectional geometric parameters (moment of inertia) are first processed according to the formula... Calculate the release moment.

[0162] The key is that it includes a pre-defined residual stress distribution model for welded box-section bending members, introducing the asymmetry in stress amplitude between the concave and convex sides caused by the bending effect, and not treating the stress amplitude in the classical model as constant. Instead, it recognizes that for bending members, the effects of the bending process are coupled with the welding effect, resulting in unequal residual stress amplitudes in corresponding regions on the concave and convex sides of the bend. Figure 6 This is a residual stress distribution map of the middle part (the proposed cut-off position) of a bent steel component, measured by the blind hole method in the laboratory. It can be seen that the residual tensile stress amplitude of the flange 2 on the concave side of the bend is greater than that on the convex side, while its residual compressive stress amplitude is smaller. The distribution pattern of residual stress in each flange 2 and web 3 conforms to the aforementioned model benchmark. Therefore, the final distribution model used for inversion is based on the classical distribution model, allowing the stress amplitudes on the concave and convex sides to be treated as independent parameters. For example, the compressive stress in the middle of the flange has different values ​​on the concave and convex sides; similarly, the tensile stress amplitude near the weld is also different on the concave and convex sides. The inversion engine solves the moment balance and self-balancing equations, outputting the final residual stress distribution cloud map or numerical list, and automatically calculates and identifies the maximum stress amplitudes on the concave and convex sides, thus directly providing a quantitative conclusion on the asymmetry.

[0163] Finally, the control and visualization human-machine interface integrates the control of the collaborative work of each unit and provides an intuitive display of results. The system provides a graphical user interface for setting measurement parameters (such as component size and material) and starting the measurement process. The interface can visualize the comparison of the three-dimensional model before and after cutting, the curvature change curve, and the distribution cloud map of the final residual stress on the cross section, making the asymmetry results clear at a glance.

[0164] Compared with existing technologies, the three-in-one technical solution provided by this invention brings significant and multi-layered positive effects, specifically reflected in the following aspects:

[0165] (1) This invention represents a fundamental breakthrough by realizing a paradigm shift from "local inference" to "global inversion." The "morphological inversion method" pioneered in this invention breaks through the limitations of traditional point measurement techniques. It does not rely on limited local strain data to "predict" the overall stress, but instead uses the overall geometric shape of the component itself as a measurement signal. It releases stress through a single cutting operation and accurately measures the resulting macroscopic morphological changes (curvature changes). Then, it uses a mechanical model to directly invert the distribution of residual stress on the cross-section. For the problem of "verifying the asymmetry of residual stress on the concave and convex sides of bending," this invention can provide a technical means for direct and quantitative measurement results. Traditional methods cannot effectively solve this problem due to their locality.

[0166] (2) Significant improvement in measurement performance: accurate, macroscopic, and capable of measuring high stress

[0167] Through high-precision three-dimensional measurement and rigorous mathematical modeling, this method can quantitatively provide the specific values ​​and distribution cloud maps of residual stress, rather than qualitative or semi-quantitative judgments, thus providing accurate input for subsequent structural calculations. The measurement results reflect the overall, average stress state of the component, effectively avoiding significant differences in results caused by small deviations in the measurement point location in areas with large stress gradients (such as near welds), making the results more representative and reliable for engineering applications. Based on the theory of elasticity, the measurement accuracy of this method is unaffected by the absolute value of the residual stress. Even when the residual stress approaches or reaches the yield strength of the material, it can still be accurately measured, effectively overcoming the measurement errors caused by plastic effects in high-stress areas by traditional methods such as the blind hole method.

[0168] (3) Key advantages of technology integration: automation, visualization, and standardization

[0169] The dedicated measurement system integrates and automates the complex measurement process, greatly reducing operational difficulty and reliance on operator skills, minimizing human error, and improving the repeatability and consistency of measurement results. The system can generate animations of component morphological changes, curvature variation curves, and residual stress distribution cloud maps on cross-sections, making abstract stress data intuitive and facilitating the understanding and analysis of characteristics such as asymmetry. This method provides a clear and repeatable operational procedure and data processing standard, laying the foundation for establishing a standard measurement method for residual stress in such complex components in the future.

[0170] (4) Significant expansion of application value: from detection to guiding design and optimization

[0171] The measurement results can be directly used to provide feedback and evaluate the rationality of manufacturing processes such as bending and welding. By comparing the residual stress levels and asymmetries of components under different process parameters, a scientific basis for decision-making can be provided to optimize manufacturing processes and reduce harmful residual stresses at the source. The accurate residual stress data obtained can be used as an initial state and input into finite element analysis software to predict stress redistribution, creep deformation, and fatigue performance of components during long-term use, providing key data support for the safety and durability assessment of structures. By realizing a "measurement-evaluation-control" closed loop, this invention transforms residual stress from a difficult-to-quantify "implicit" parameter into an "explicit" indicator that can be accurately measured, evaluated, and controlled, providing a core technology for achieving a closed-loop quality control system in high-end steel structure manufacturing.

[0172] (5) Multiplier effect of integrated solutions: integration and complementarity, multiplying value

[0173] The fusion measurement method leverages the advantages of the macroscopic accuracy of the "morphological inversion method" and the local precision of the "blind hole method," forming a unique complementary enhancement effect. It uses the overall results to verify and correct local measurements, greatly improving the reliability of the final data. It is especially suitable for scientific research and key engineering projects with extremely high precision requirements.

[0174] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for morphological inversion measurement of asymmetric residual stress distribution in bending members, characterized in that, Includes the following steps: S1, Weld a box-shaped curved steel member (1) and obtain the initial curvature of the curved steel member (1) along its length in an unconstrained free state. ; S2, stress release, cut off at the midpoint of the length of the bent steel member (1) or at the section with the largest initial curvature to release the stress of the bent steel member (1) and obtain two symmetrical steel members; S3, Post-stress release morphological inversion measurement and curvature change calculation, to obtain the curvature of two steel members in an unconstrained free state. Calculate the change in curvature of the component before and after cutting. ,Right now: ; S4, Residual stress distribution inversion calculation: S41, Calculate the release moment. According to the beam bending theory in mechanics of materials, the change in curvature and the additional bending moment generated by the release of residual stress are considered. A linear relationship exists: ； in, The elastic modulus of steel. Let be the moment of inertia of the box-shaped cross-section about its neutral axis; S42, Establish the inversion model; the additional bending moment is caused by the self-balancing residual stress within the cross section. Integrating, we obtain the moment equilibrium equation: ， The self-balancing equation is: , in, The cross-sectional area of ​​the box is... The distance from the area of ​​the infinitesimal element on the cross section to the neutral axis; S43, Residual stress distribution modeling and inversion solution: Solve the moment equilibrium equations and self-equilibrium equations, and output residual stress distribution contour maps or inverted stress values. A list.

2. The method for morphological inversion measurement of asymmetric residual stress distribution in bending members according to claim 1, characterized in that, S1 also includes the following steps: S11, the bending steel member (1) to be tested is placed on the platform in an unconstrained free state; S12, use a 3D laser scanner or photogrammetry system to acquire dense point cloud data of the surface of the curved steel component (1); S13, through point cloud data processing, the spatial curve of the geometric center line of the curved steel member (1) is extracted and fitted, and its length coordinates are established. Equation of the initial geometric centerline for variables ; S14, combined with the initial geometric equation, calculate the initial curvature of the bent steel member (1) along the length direction. The calculation formula is: .

3. The method for morphological inversion measurement of asymmetric residual stress distribution in bending members according to claim 2, characterized in that, The flat steel plate is directly processed into the target curve shape through cold bending process to obtain two flange plates (2) on the concave and convex sides of the curve. At the same time, the two web plates (3) are cut into corresponding fan-shaped segments. Finally, these four plates with the curved shape are assembled into a box-shaped curved steel component (1) by welding.

4. The method for morphological inversion measurement of asymmetric residual stress distribution in bending members according to claim 3, characterized in that, (1) Cutting bent steel components by wire cutting.

5. The method for morphological inversion measurement of asymmetric residual stress distribution in bending members according to claim 4, characterized in that, S3 also includes the following steps: S31: Perform the same operation as S12 on the two cut steel components to fit and extract the spatial curves of the geometric center lines of the two steel components, and establish their length coordinates. The equation of the new geometric centerline with variables The curvature corresponding to the new centerline is calculated using the formula in S1. Curvature change The direct cause is the release of residual stress inside the bent steel member (1).

6. The method for morphological inversion measurement of asymmetric residual stress distribution in bending members according to claim 5, characterized in that, Before cutting the bent steel member (1), a blind hole method measurement was added. According to the standard blind hole method, strain rosettes were pasted on the surface of the flange plate (2) of the bent steel member (1) in the middle and near the weld area, and drilling and strain measurement were carried out to obtain the preliminary measurement value of the surface residual stress at the measuring point. .

7. The method for morphological inversion measurement of asymmetric residual stress distribution in bending members according to claim 6, characterized in that, Following the blind hole method measurement and the morphological inversion method measurement, the following steps are also included: S5, Data comparison and correction model establishment, based on the results of the inversion calculation of residual stress distribution reflecting the overall stress state of the bending steel member (1), to identify and correct the systematic errors in the blind hole method measurement.

8. The method for morphological inversion measurement of asymmetric residual stress distribution in bending members according to claim 7, characterized in that, Specifically, it includes: S51, Data Preparation and Matching: Select all measurement points on the bent steel member (1) that have been measured by the blind hole method and can be covered by the morphological inversion method, ensuring that each measurement point i has two data pairs: the surface residual stress value obtained by the blind hole method. ; The residual stress values ​​corresponding to the same location and direction are extracted from the full-field distribution results obtained by the morphological inversion method. ; S52, System error analysis and correction model construction, plotting all measurement point pairs on a scatter plot. and with Let x be the x-coordinate. The vertical coordinate is y; Error pattern recognition: Observe the distribution trend of data points; A. If the point group is evenly distributed near the straight line y=x, it indicates that the blind hole method measurement on the component is accurate and requires no correction or only simple offset correction. B, If the point group deviates, it is in the high-pressure stress zone. Negative values ​​indicate values ​​measured using the blind hole method. The absolute value is less than It needs to be corrected; Establish a quantitative correction model: Based on the identified systematic error patterns, a correction function is established using numerical methods. Linear correction model: If the error exhibits a linear relationship, the correction formula can be obtained through linear regression fitting. ,in, The corrected stress value, slope and intercept Determined by fitting; Nonlinear correction model: If the error is nonlinear, a piecewise linear function or a quadratic function is used for fitting to achieve correction; S53, Model Validation and Applicability Confirmation: The modified model is applied to all blind hole method measuring points to obtain the corrected stress values. Calculate the corrected and If the residuals decrease and exhibit a random distribution, it indicates that the modified model is effective and has successfully separated and eliminated systematic errors. S54 generates a fused residual stress field. Using a validated correction model, the data of all blind hole measurement points are batch corrected. The corrected local stress data points are used as boundary conditions and embedded into the residual stress distribution framework that conforms to the overall mechanical equilibrium obtained by the morphological inversion method to generate the final corrected residual stress field.

9. A measurement system for implementing the morphological inversion measurement method for the asymmetric distribution of residual stress in a bending member as described in any one of claims 1-8, characterized in that, include: The three-dimensional topography acquisition unit is used to acquire three-dimensional spatial coordinate point cloud data of the component surface before and after the component is cut. The data processing and centerline extraction unit receives point cloud data from the 3D topography acquisition unit, reconstructs the geometric model of the component through a built-in algorithm, and extracts the geometric centerline for calculation. The curvature calculation and morphological change analysis unit automatically calculates the curvature and curvature change of the extracted geometric center line. The stress inversion calculation unit is used to convert morphological changes into residual stress distribution results; The control and visualization human-computer interaction interface unit is used to integrate and control the collaborative work of various units and provide intuitive results display.

10. The measurement system according to claim 9, characterized in that, The 3D topography acquisition unit is a laser 3D scanner or photogrammetry system; the data processing and centerline extraction unit includes a point cloud processing software module. This module employs a curve fitting algorithm based on non-uniform rational B-splines to process discrete point cloud data and reconstruct a smooth, continuous geometric centerline equation that conforms to the actual bending shape of the component. and The curvature calculation and morphological change analysis unit includes a symbolic computation and numerical differentiation module, capable of performing calculations on the centerline equation. Perform automatic differentiation and calculate the first derivative. and second derivative Subsequently, the curvature is automatically calculated at each point along the length of the component according to the curvature calculation formula, and the curvature change is finally output. ; The stress inversion calculation unit's built-in inversion calculation engine receives... Input the moment of inertia of the box section about its neutral axis and the elastic modulus of the steel to calculate the released bending moment. The inversion engine solves the bending moment balance and self-balancing equations, outputs the final residual stress distribution cloud map or a list of inverted stress values, and automatically calculates and identifies the maximum stress amplitude of the concave and convex flanges (2).

Images