A method for evaluating macroscopic welding residual stress in hull structural steel

Abstract

The present invention relates to the technical field of high-quality ship manufacturing. The present invention provides a method for evaluating macroscopic welding residual stress of hull structural steel, comprising the following steps: S1, processing the hull structural steel into two test plates of a certain size, and processing grooves on the butt ends of the two test plates; S2, welding one end of the two test plates away from the butt ends to a fixed component, so that a constrained weld is formed between the test plates and the fixed component; S3, symmetrically welding the two test plates, so that a test plate weld is formed between the test plates; S4, attaching a bidirectional strain gauge on the test plate, wherein the bidirectional strain gauge is used to test the transverse strain ε y , longitudinal strain ε x ; S5, cut one end of the test plate along the flame cutting line and record the data of the bidirectional strain gauge after cutting; S6, calculate the longitudinal section force F according to the change data of the bidirectional strain gauge after cutting x , transverse section force F y The method of the present invention is simple and has a short test period, and can quantitatively characterize the macroscopic welding residual stress of the hull structural steel.

Description

Technical Field

[0001] The invention relates to the technical field of high-quality ship manufacturing, and in particular to a method for evaluating macroscopic welding residual stress of hull structural steel. Background Art

[0002] High-tech ships such as large container ships and luxury cruise ships have an urgent need for high-precision manufacturing technology, and the uneven heating and cooling of the hull structural steel during welding will cause welding residual stress. Residual stress can cause cracks, destroy the strength of the structure, reduce the structural bearing capacity, etc., which will seriously affect the quality of ship construction and service safety. For components such as hull plates, after welding, they often suffer from unstable deformations such as warping and torsion due to the existence of very small welding residual stress, and even cause irreparable losses to the entire project. Therefore, how to predict and control welding residual stress has always been the focus of research by many scholars in the field of shipbuilding.

[0003] There are many methods for testing residual stress at present, which can be roughly divided into two categories: mechanical method and physical method. Mechanical method is generally a destructive test, also known as stress release method, such as drilling method, ring core method and splitting method; physical method is mostly non-destructive test, which can also be non-contact test, such as X-ray diffraction method, neutron diffraction method, magnetic detection method and ultrasonic detection method. The above methods are more effective for measuring welding residual stress in a certain micro area, but they cannot reflect the macroscopic stress of the welded joint, and have disadvantages such as long test cycle and high test cost. For example, the indentation method and X-ray diffraction method can only measure the residual stress within the micrometer range of the surface layer, but cannot obtain the stress in the thickness direction of the steel plate; the neutron diffraction method can obtain the residual stress at a larger depth, but it is also limited to a smaller range, and requires the use of high-end equipment such as large neutron scattering sources, which is not universal.

[0004] In order to meet the low-stress and high-precision construction requirements of various types of ships and marine engineering equipment, welding residual stress can be effectively reduced through welding process optimization or welding material design, but how to quickly evaluate the welding residual stress level of new welding materials and welding processes is a difficult problem that needs to be solved urgently. By characterizing the macroscopic residual stress level within a certain range, the error caused by measurement limitations can be reduced, but current research mainly focuses on local residual stress evaluation methods, and there is no related research on characterizing macroscopic residual stress through simple and easy methods. Summary of the invention

[0005] In view of this, the present invention aims to propose a method for evaluating macro welding residual stress of hull structural steel, so as to solve the problems that the research in the prior art mainly focuses on the local residual stress evaluation method, and there is no related research on characterizing the macro residual stress by a simple and easy-to-obtain method, and the local residual stress evaluation method also has the problems of long test cycle and high test cost.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for evaluating macroscopic welding residual stress of hull structural steel comprises the following steps:

[0008] S1. Processing the hull structural steel into test plates of a certain size, wherein the test plates include a first test plate and a second test plate, and processing grooves on the butt ends of the test plates;

[0009] S2. Weld the end of the test plate away from the butt end to the fixed component, and ensure that the two test plates can be welded symmetrically to form a constrained weld between the test plate and the fixed component;

[0010] S3. After the test plates return to room temperature, the two test plates are symmetrically welded to form a test plate weld between the two test plates;

[0011] S4. After the welded test plate returns to room temperature, a bidirectional strain gauge is attached to the test plate. The bidirectional strain gauge is located on either the first test plate or the second test plate, and the bidirectional strain gauge is close to the restrained weld of the corresponding test plate. The bidirectional strain gauge is used to test the transverse strain ε y , longitudinal strain ε x ;

[0012] S5, connecting the bidirectional strain gauge to the strain acquisition device, returning the bidirectional strain gauge record to zero, cutting one end of the test plate along the flame cutting line, and recording the data of the bidirectional strain gauge after cutting, wherein the flame cutting line and the bidirectional strain gauge are located on different test plates;

[0013] S6. Calculate the longitudinal section force F according to the data of the bidirectional strain gauge after cutting. x , transverse section force F y .

[0014] The method of the invention is simple and has a short test period, and can quantitatively characterize the macro welding residual stress of the hull structural steel, thereby improving the accuracy of measuring the residual stress.

[0015] Furthermore, the bidirectional strain gauge is pasted on a first parallel line, the first parallel line is parallel to the center of the test plate weld, and the distance between the first parallel line and the center of the test plate weld is L, where L≥(2~3)·H, where H is the thickness of the test plate, in mm.

[0016] This setting can ensure that the area measured by the bidirectional strain gauge is relatively far away from the direct interference of the welding heat affected zone by sticking the bidirectional strain gauge at a specific position, thereby more accurately reflecting the residual stress state of the test plate away from the weld area; it can also reduce the measurement error caused by changes in material properties and improve the stability of the measurement results.

[0017] Furthermore, the longitudinal section force F x According to formula (3), the transverse section force F y Calculated by formula (4);

[0018] F x= A.σ x (3)

[0019] F y= A.σ y (4)

[0020] In the formula, σ x is the longitudinal stress, unit: MPa; σ y is the transverse stress, unit is MPa, A is the cross-sectional area of ​​the test plate where the bidirectional strain gauge is located, that is, the product of the width and thickness of the test plate, unit is mm².

[0021] This setting can more intuitively reflect the stress state of the test plate in different directions, and can more comprehensively evaluate the residual stress distribution and magnitude of the test plate in these two main directions.

[0022] Furthermore, the longitudinal stress σ x According to formula (1), the transverse stress σ y Calculated by formula (2);

[0023] σ x =E / (1- v 2 )·(ε x + v ·ε y ) (1)

[0024] σ y =E / (1- v 2 )·(ε y + v ·ε x ) (2)

[0025] In the formula, ε x is the longitudinal strain; ε y is the lateral strain; E is the elastic modulus, unit: MPa; v is Poisson's ratio.

[0026] This setup can significantly improve the accuracy of the evaluation by calculating the stress through the formula, and some measurement errors can be eliminated by calculating the stress through the strain compared to measuring the stress directly.

[0027] Furthermore, a plurality of bidirectional strain gauges may be provided, and the plurality of bidirectional strain gauges are located on the first parallel line.

[0028] This setup can improve the accuracy of the evaluation and provide a more detailed understanding of the distribution of residual stress on the test plate. This is particularly important for identifying high stress areas, stress gradient changes, and stress concentration phenomena. The measurement data of multiple strain gauges can be verified with each other, thus improving the reliability of the evaluation results.

[0029] Furthermore, the fixing assembly is a rigid frame. The rigid frame is set according to the length, width and height of the test plate, and the size of the rigid frame satisfies that two test plates can be butt-jointed and can be welded on the test plate.

[0030] This setting can firmly fix the test plate through a rigid frame to prevent the test plate from deformation or movement due to welding thermal stress during welding. This fixing and restraining effect helps to maintain the stability and consistency of the test plate, thereby ensuring the quality of the welded joint. During the welding process, the welded joint will generate large thermal stress and residual stress;

[0031] Furthermore, the test plate is welded at the middle position of the rigid frame.

[0032] Furthermore, the first test plate and the second test plate are symmetrical about the test plate weld.

[0033] Furthermore, the distance between the flame cutting line and the nearest restrained weld on the test plate is 8-12 mm.

[0034] This setting can ensure that the evaluation area is relatively far away from the direct interference of the heat-affected zone. In this way, the evaluation results can better reflect the residual stress state of the test plate under normal service conditions, rather than the residual stress affected by the heat of the flame cutting process. The thermal stress and residual stress generated during the flame cutting process will affect the accuracy of the evaluation results. By reasonably setting the distance between the flame cutting line and the constrained weld, this influence can be reduced, thereby improving the accuracy of the evaluation. In addition, maintaining a certain distance can also avoid the vibration and impact generated during the cutting process causing additional stress changes in the evaluation area.

[0035] Furthermore, the distance between the flame cutting line and the nearest restrained weld on the test plate is 10 mm.

[0036] Furthermore, the method further includes step S7, which is to conduct experiments on different welding materials or processes to quickly evaluate the magnitude of welding residual stress by comparing the cross-sectional force or strain change.

[0037] Furthermore, in steps S2 and S3, the welding process is a welding current of 180-200 A, a voltage of 15-25 V, and a welding speed of 30-50 cm / min.

[0038] Furthermore, in steps S2 and S3, the welding process is a welding current of 190A, a voltage of 20V, and a welding speed of 40cm / min.

[0039] Furthermore, in step S1, the processing groove angle is 50-70°.

[0040] Furthermore, in step S1, the processing groove angle is 60°.

[0041] Furthermore, the finite element method simulation method is used to determine the position where the bidirectional strain gauge is pasted, that is, the first parallel line.

[0042] Furthermore, in the finite element method simulation method, the boundary load force of the rigid frame on the welded test plate is obtained and compared with the load force calculated by cross-sectional stress and cross-sectional area, verifying the feasibility of characterizing the boundary load by cross-sectional stress method. The constraint effect of the rigid frame is used to simulate some of the constraint conditions of the hull structure in the actual construction process. Through this simulation, the stress state and performance of the welded joint during the shipbuilding process can be more realistically evaluated.

[0043] Furthermore, in the finite element method simulation method, the following steps are included;

[0044] S100. Establish a finite element model, which includes a rigid frame, a test plate, a test plate weld, and a constrained weld. The simulation calculation in the finite element model is to obtain the boundary load force of the test plate. One end of the test plate is connected to the rigid frame through a constrained weld, and the other end is a fixed constraint. By releasing the fixed constraint, the post-welding cutting process can be simulated to obtain the change in the cross-sectional load force. By carrying out finite element simulation of the welding process and the constraint removal process, the stress distribution at different longitudinal cross sections at the distances from the weld center L1, L2...Ln is obtained;

[0045] S200, according to the stress distribution in step S100, determining the position of the first parallel line at a distance L from the center of the weld, that is, the detection position of the strain gauge;

[0046] S300, obtain the boundary load force of the rigid frame for welding test, which can be directly obtained by extracting the "boundary load" option in the MSC.MARC software;

[0047] S400, comparing the boundary load force obtained in step S300 with the load force calculated by the cross-sectional stress and cross-sectional area in steps S1-S6, and verifying the feasibility of characterizing the boundary load by the cross-sectional stress method.

[0048] Compared with the prior art, the method for evaluating macroscopic welding residual stress of hull structural steel described in the present invention has the following advantages:

[0049] (1) The present invention can quantitatively characterize the macroscopic welding residual stress of hull structural steel; the present invention intuitively characterizes the welding residual stress level of different welding materials or processes through cross-sectional force or strain, avoiding the disadvantage that traditional methods can only obtain tiny local features, which is directly related to the safety of the structure. For example, the cross-sectional force can be used to simply calculate whether the structure will be unstable and damaged due to residual stress, which has important guiding significance for structural safety;

[0050] (2) The method of the present invention is simple, has low requirements for tooling and equipment, and has accurate measurement results. The present invention can obtain macro welding residual stress by only using the most commonly used bidirectional strain gauge and strain acquisition device combined with flame cutting. The principle is clear, the method is simple and easy to obtain, and many laboratories have these conditions. In addition, the rigid frame used in the present invention can be obtained by using the most commonly used thick plate through simple mechanical processing, which is fast to process and low in cost.

[0051] (3) The method of the present invention has a short test cycle and a fast effect, and can timely evaluate the welding process or materials. After the test plate is welded, the macro residual stress of each design condition can be immediately obtained by cooling it to room temperature and cutting it. However, traditional welding residual stress test methods such as the X-ray method and the blind hole method have a long test cycle and require various protective measures, which are difficult to meet the requirements of rapid iteration of materials and processes.

[0052] (4) The test cost of the present invention is low; the present invention only requires a few strain gauges and other consumables, and can be completed in a laboratory environment. There is no need to entrust relevant institutions to conduct residual stress testing, thus saving a lot of money. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A residual stress test assembly for the test plate of the present invention;

[0054] Figure 2 It is a schematic diagram of the structure of the test plate after welding of the present invention;

[0055] Figure 3 It is a schematic diagram of the arrangement of the first strain gauge and the second strain gauge on the test plate of the present invention;

[0056] Figure 4 The finite element model diagram used for the test plate welding of the present invention;

[0057] Figure 5 The lateral residual stress distribution of the test plate under the constraint state of the present invention;

[0058] Figure 6 The longitudinal residual stress distribution of the test plate under the constraint state of the present invention;

[0059] Figure 7 The lateral residual stress distribution of the test plate after the restraint is removed according to the present invention;

[0060] Figure 8 The longitudinal residual stress distribution of the test plate after the restraint is removed according to the present invention;

[0061] Fig. 9 The transverse stress of the cross section of the bidirectional strain gauge of the present invention set at 80 mm from the center of the weld of the test plate;

[0062] Fig.10 The transverse stress of the cross section of the bidirectional strain gauge of the present invention set at 100 mm from the center of the weld of the test plate;

[0063] Fig.11 The transverse stress of the cross section of the bidirectional strain gauge of the present invention set at 120 mm from the center of the weld of the test plate;

[0064] Fig.12 The curve diagram of transverse load variation when the bidirectional strain gauge of the present invention is set at 80mm, 100mm and 120mm from the center of the weld of the test plate;

[0065] Fig.13 It is a curve diagram of strain value variation on the strain gauge at the cross section of position A and position B of the present invention;

[0066] Fig.14 It is a schematic diagram of a Y-shaped groove formed when two test plates of the present invention are butt-jointed;

[0067] Fig.15 It is a schematic diagram of a V-shaped groove formed when two test plates of the present invention are butt-jointed;

[0068] Fig.16 It is a strain curve diagram of the stress release process of the test plate of the Y-shaped groove and the V-shaped groove of the present invention.

[0069] Description of reference numerals:

[0070] 1-rigid frame, 2-test plate, 21-first test plate, 22-second test plate, 3-restraint weld, 4-test plate weld, 5-bidirectional strain gauge, 6-flame cutting line, 7-first parallel line, 8-weld center, 9-test plate length center line. DETAILED DESCRIPTION

[0071] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0072] When building a hull structure, it is of great significance to select welding materials and processes with low welding residual stress, small deformation tendency and strong crack resistance. There are many types of welding materials for hull structures, and various forms of welding joints and welding processes. There is a great practical demand for rapid evaluation of the macroscopic residual stress of welding joints. Based on this demand, this paper proposes a method for evaluating the macroscopic welding residual stress of hull structural steel, and verifies it through numerical simulation and experiments.

[0073] The object of the present invention is achieved by: referring to the window type welding crack resistance test, in a frame with greater rigidity, the two ends of the butt test plate are fixed in the frame by constrained welds, such as Figure 1 As shown. The macroscopic effect of the transverse residual stress caused by the welding of the test plate weld is to generate an extrusion or tensile load on the constraint weld at the boundary of the test plate, that is, the boundary force. The magnitude of the boundary force can reflect the magnitude of the macroscopic residual stress. According to the law of force transmission, the force of each section of the test plate is equal to the boundary force. Under the action of the macroscopic residual stress, a certain strain will be generated in various parts of the test plate. When the constraint weld at one end of the test plate is cut off, the boundary force will be released, and the macroscopic manifestation is that the transverse residual stress on the test plate is released. Therefore, the strain gauge pasted at the appropriate position of the test plate will capture the strain change. When the distance between the bidirectional strain gauge pasting position and the center of the test plate weld exceeds 2 to 3 times the plate thickness, the residual stress distribution on the cross section parallel to the weld direction is relatively uniform. Strain gauges are pasted at these cross-sectional positions to measure the strain of the test plate. The cross-sectional stress can be obtained according to the stress-strain relationship, and the cross-sectional stress can be further obtained by multiplying the cross-sectional area by the cross-sectional stress to obtain the cross-sectional load, or directly based on the strain change to achieve the characterization of the macroscopic residual stress or strain of the entire weld joint. See the schematic diagram of the strain gauge detection position and the cut end. Figure 2 .

[0074] Specifically, the present invention proposes a method for evaluating macroscopic welding residual stress of hull structural steel, comprising the following steps:

[0075] S1, processing the hull structural steel into a test plate 2 of a certain size, wherein the test plate 2 comprises a first test plate 21 and a second test plate 22, and processing a groove on the butt end of the test plate;

[0076] S2. Weld the end of the test plate away from the butt end to the fixed component, while ensuring that the two test plates can be welded symmetrically, forming a constrained weld 3 between the test plate and the fixed component;

[0077] Specifically, the fixing component is a rigid frame 1, which is set according to the length, width and height of the test plate, and the size of the rigid frame satisfies that two test plates can be butt-jointed and can be welded on the test plates.

[0078] Specifically, the welding end of the test plate is welded at the middle position of the rigid frame.

[0079] S3, after the test plates return to room temperature, the two test plates are symmetrically welded to form a test plate weld 4 between the two test plates;

[0080] Specifically, the two ends of the welded test plate in the width direction are welded to the rigid frame respectively, such as Figure 1 As shown; after the test plate returns to room temperature, the test plate is symmetrically welded according to the welding process requirements. The rigid frame is made of thick steel plate, which will not be significantly deformed during the whole process, thus improving the accuracy of the test. The thickness of the thick steel plate is ≥150mm.

[0081] S4, after the welded test plate returns to room temperature, a bidirectional strain gauge 5 is attached to the test plate. The bidirectional strain gauge is located on any one of the first test plate and the second test plate, and the bidirectional strain gauge is close to the restrained weld of the corresponding test plate. The bidirectional strain gauge is used to test the transverse strain ε y , longitudinal strain ε x ;

[0082] Specifically, the bidirectional strain gauge may be provided in plurality, and the plurality of bidirectional strain gauges are located on the first parallel line 7;

[0083] Specifically, the bidirectional strain gauge includes transverse and longitudinal stresses, and the stress and strain parallel to the weld axis are respectively referred to as longitudinal stress σ x and the longitudinal strain ε x ; The stress and strain perpendicular to the weld axis are called transverse stress σ y and the transverse strain ε y The arrangement of the bidirectional strain gauges is as follows: Figure 3 As shown;

[0084] S5, connecting the bidirectional strain gauge to the strain acquisition device, returning the bidirectional strain gauge record to zero, cutting one end of the test plate along the flame cutting line 6, and recording the data of the bidirectional strain gauge after cutting, wherein the flame cutting line and the bidirectional strain gauge are located on different test plates;

[0085] S6. Calculate the longitudinal section force F according to the data of the bidirectional strain gauge after cutting. x , transverse section force F y .

[0086] Specifically, the bidirectional strain gauge is pasted on a first parallel line, the first parallel line is parallel to the center 8 of the test plate weld, and the distance between the first parallel line and the center 8 of the test plate weld is L, where L≥(2~3)·H, where H is the thickness of the test plate in mm.

[0087] Specifically, the longitudinal section force F x According to formula (3), the transverse section force F y Calculated by formula (4);

[0088] F x= A.σ x (3)

[0089] F y= A.σ y (4)

[0090] Where F x、 F y The unit of σ is N. x is the longitudinal stress, unit: MPa; σ y is the transverse stress, unit is MPa, A is the cross-sectional area of ​​the test plate where the bidirectional strain gauge is located, that is, the product of the width and thickness of the test plate, unit is mm².

[0091] Specifically, the longitudinal stress σ x According to formula (1), the transverse stress σ y Calculated by formula (2);

[0092] σ x =E / (1- v 2 )·(ε x + v ·ε y ) (1)

[0093] σ y =E / (1- v 2 )·(ε y + v ·ε x ) (2)

[0094] In the formula, ε x is the longitudinal strain; ε y is the lateral strain; E is the elastic modulus, unit: MPa; v is Poisson's ratio.

[0095] Specifically, a plurality of bidirectional strain gauges may be provided, and the plurality of bidirectional strain gauges are located on the first parallel lines.

[0096] Specifically, the distance between the flame cutting line and the nearest restrained weld is 8-12 mm, preferably 10 mm.

[0097] Furthermore, the first test plate and the second test plate are symmetrical about the test plate weld.

[0098] S7. Experiment with different welding materials or processes to quickly evaluate the magnitude of welding residual stress by comparing the changes in cross-sectional force or strain.

[0099] Specifically, in step S7, different parameters are compared by the control variable method to quickly obtain the lowest residual stress of the welded joint. For example, for two groove designs, in order to explore which groove brings the smallest macro welding residual stress, the method of the present invention is adopted, and a welding test is first carried out. Except for the different grooves, all welding parameters are kept consistent. After welding, the test plate is cut and the stress is released, and the strain value is recorded at the same time. According to the test results, a cross-sectional load change curve is drawn, and according to the curve, the cross-sectional load released by different grooves is determined, so as to determine which groove can produce smaller cross-sectional welding residual stress.

[0100] More specifically, in steps S2 and S3, the welding process is a welding current of 180-200A, a voltage of 15-25V, and a welding speed of 30-50cm / min; preferably, the welding process is a welding current of 190A, a voltage of 20V, and a welding speed of 40cm / min.

[0101] Specifically, in step S1, the groove angle is 50-70°, preferably the groove angle is 60°.

[0102] Specifically, the finite element method simulation method is used to determine the position where the bidirectional strain gauge is pasted, that is, the first parallel line.

[0103] Specifically, in the finite element simulation method, the boundary load force of the rigid frame on the welded test plate is obtained and compared with the load force calculated by cross-sectional stress and cross-sectional area to verify the feasibility of characterizing the boundary load by the cross-sectional stress method.

[0104] Specifically, the finite element method simulation method includes the following steps:

[0105] S100, establishing a finite element model, wherein the finite element model includes a rigid frame, a butted test plate, a test plate weld, and a constrained weld, and performing finite element simulation of a welding process and a constraint removal process to obtain stress distribution at different longitudinal cross sections at distances L1, L2, ..., Ln from the weld center;

[0106] S200, determining a detection position of a bidirectional strain gauge at a distance L from the center of the weld according to the stress distribution in step S100, wherein the detection position of the bidirectional strain gauge is located on a first parallel line;

[0107] S300, obtain the boundary load force of the rigid frame for welding test, which can be directly obtained by extracting the "boundary load" option in the MSC.MARC software;

[0108] S400, comparing the boundary load force obtained in step S300 with the load force calculated by the cross-sectional stress and cross-sectional area in steps S1-S6, and verifying the feasibility of characterizing the boundary load by the cross-sectional stress method.

[0109] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0110] According to the requirements of the method for evaluating the macroscopic welding residual stress of hull structural steel, the present invention selects a high-strength hull structure, conducts a welding test on the high-strength hull structure, affixes a bidirectional strain gauge to a test plate to test the strain data of the test plate after cutting, and then obtains the welding residual stress by calculation. The method is simple and has a short cycle. In addition, the rationality of the cross-sectional load characterization of the residual stress is verified again by the finite element method simulation method. Finally, the method is used to carry out welding tests with different groove sizes, and the welding residual stresses are compared, which shows that the method has high applicability.

[0111] The specific working process is as follows:

[0112] 1. Welding process:

[0113] The high-strength hull structural steel is processed into the first test plate and the second test plate. The first test plate and the second test plate are two identical plates, and their length × width × height are 250 × 150 × 18 mm. 3 , the test plate is processed into Fig.14 The groove; using φ1.2mm gas shielded welding wire, the welding process is welding current 190A, voltage 20V, welding speed 40cm / min, one end of the two test plates are respectively welded to the rigid frame to form a constrained weld, and then the two test plates are symmetrically welded to form a test plate weld. The welding process parameters used to form the constrained weld and the test plate weld are consistent, and before welding, the test plates must be at room temperature;

[0114] After the two test plates are welded, wait for the test plates to cool to room temperature, and attach two bidirectional strain gauges on the first test plate. The two bidirectional strain gauges are located on the first parallel line. The first parallel line is parallel to the center of the test plate weld. The distance between the first parallel line and the center of the test plate weld is 120 mm. The two bidirectional strain gauges include a first strain gauge and a second strain gauge. The first strain gauge is located at position A, and the second strain gauge is located at position B. Position A is located on the center line 9 of the length of the test plate, that is, perpendicular to the center of the weld and intersecting with the first parallel line. Position B is 10 mm away from the edge of the test plate.

[0115] Before cutting the test plate, the strain data is cleared, and the test plate is cut along the flame cutting line to release the stress. The distance of the flame cutting line to the constraint weld is 10 mm. The change in strain value Δε before and after cutting at A and B is recorded. The strain value change curve drawn according to the test results is shown in the figure below: Fig.13As shown in the figure, when the test plate is cut and the stress is released, the longitudinal and transverse strain curves of point A and point B basically coincide. After release, the final longitudinal strain value of point A is about 116 microstrain, and the final transverse strain value is about -613 microstrain. The final longitudinal strain value of point B is about 110 microstrain, and the final transverse strain value is about -568 microstrain. The strain conditions at the two points are basically the same. This shows that the strain at the cross-section position 120mm away from the center line of the test plate weld determined by the test has good uniformity.

[0116] 2. Finite element model simulation process:

[0117] A high-strength hull structural steel butt joint test plate was selected. The test plate size, groove, welding parameters, flame cutting line position, test plate connected components, etc. were consistent with the above welding process. The finite element model is shown in Figure 4 As shown in the figure, in the finite element model, one side of the test plate is fixed to the rigid base by a constraint weld, and a rigid constraint is set on the other side of the test plate to replace the rigid base. In the simulation analysis, the rigid constraint belongs to the boundary condition and can be removed at any time. This operation can simulate the subsequent cutting process. Three bidirectional strain gauges are pasted on one of the test plates. The pasting positions of the three bidirectional strain gauges are 80mm, 100mm, and 120mm away from the center of the test plate weld. The constraint weld welding simulation is performed first, and then the test plate weld welding simulation is performed.

[0118] When the constraint is not removed, the residual stress distribution of the test plate is as follows: Figures 5 and 6 As shown in the figure, the stress in the X direction is the transverse stress perpendicular to the weld axis, and the stress in the Z direction is the longitudinal stress parallel to the weld axis.

[0119] When the left restraint weld is removed, the residual stress changes of the test plate are as follows: Figure 7-8 The numerical simulation results show that when the constraint on one end of the test plate is removed, the test plate will produce a more obvious stress change.

[0120] Figure 5 Before the test plate was cut, the bidirectional strain gauge was pasted 120 mm away from the center of the test plate weld to measure the transverse residual stress. From the simulation result cloud map, it can be seen that the residual stress is about 446 MPa (the orange area in the figure); Figure 6 After cutting the test plate, Figure 6 The transverse residual stress in the weld zone drops to almost 0 MPa (orange area), and the macroscopic residual stress in the cross section away from the weld zone is basically completely released. Figure 8 The phenomenon that the load drops to 0 after flame cutting indicates that the strain value of the test plate can be captured by the bidirectional strain gauge.

[0121] Figure 9-11The bidirectional strain gauges are pasted on the transverse stress of the three longitudinal sections at 80mm, 110mm, and 120mm from the center of the test plate weld. The stress of each node of the longitudinal section is extracted and the average value is obtained. At the same time, the left boundary constraint load is extracted. The load of each section changes with the start of welding, cooling, and cutting stages. Fig.12 As shown in the figure. From the load variation diagram, it can be seen that with the increase of cooling time, the boundary load and the load of each section change in the same law, the load size is consistent, especially after the cooling is completed, the section load and the boundary load are almost the same, and it decreases sharply to 0 after cutting the restrained weld, which can prove that the section load is equal to the restrained load. The bidirectional strain gauge is set away from the weld area to reduce welding heat and welding magnetic field interference. Finally, the section 120mm away from the center line of the test plate weld is selected as the bidirectional strain gauge pasting position.

[0122] 3. Compare different grooves to determine the minimum macro welding residual stress

[0123] Based on the welding process of the above-mentioned Y-shaped groove, the strain curve of the stress release process of the Y-shaped groove specimen was obtained. For the design of Y-shaped groove and V-shaped groove, in order to explore which groove brings the smallest macro welding residual stress, in order to obtain the strain curve of the stress release process of the V-shaped groove specimen, when carrying out the welding test, except for the groove and Y-shaped groove, all welding parameters were kept consistent. After welding, the test plate was cut and the stress was released, and the strain value change was recorded at the same time. The transverse section load change curve drawn according to the test results is shown in the figure. Fig.16 As shown, the V-shaped groove design is as follows Fig.15 As shown. Fig.16 It can be seen that the cross-sectional load caused by the residual stress of V-groove welding is significantly greater than that caused by the residual stress of Y-groove welding, indicating that when other welding process conditions are the same, the transverse welding residual stress of the Y-groove welded joint is smaller than that of the V-groove, and the Y-groove can be given priority in ship design.

[0124] In summary, the method for rapidly characterizing the macroscopic welding residual stress of hull structural steel welded joints of the present invention is based on welding experiments and model simulations, and can rapidly characterize the residual stress of different welding processes or welding materials through simple test fixtures and strain measurement devices, thereby significantly improving the application of new materials and new processes for hull structural steel in the field of high-precision shipbuilding.

[0125] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for evaluating macroscopic welding residual stress of hull structural steel, characterized in that: The steps include: S1. Processing the hull structural steel into test plates of a certain size, wherein the test plates include a first test plate and a second test plate, and processing grooves on the butt ends of the test plates; S2. Weld the end of the test plate away from the butt end to the fixed component, and ensure that the two test plates can be welded symmetrically to form a constrained weld between the test plate and the fixed component; S3. After the test plates return to room temperature, the two test plates are symmetrically welded to form a test plate weld between the two test plates; S4. After the welded test plate returns to room temperature, a bidirectional strain gauge is attached to the test plate. The bidirectional strain gauge is located on either the first test plate or the second test plate, and the bidirectional strain gauge is close to the restrained weld of the corresponding test plate. The bidirectional strain gauge is used to test the transverse strain ε y , longitudinal strain ε x ; S5, connecting the bidirectional strain gauge to the strain acquisition device, returning the bidirectional strain gauge record to zero, cutting one end of the test plate along the flame cutting line, and recording the data of the bidirectional strain gauge after cutting, wherein the flame cutting line and the bidirectional strain gauge are located on different test plates; S6. Calculate the longitudinal section force F according to the data of the bidirectional strain gauge after cutting. x , transverse section force F y ; Longitudinal section force F x According to formula (3), the transverse section force F y Calculated by formula (4); F x= A·s x (3) F y= A·s y (4) In the formula, σ x is the longitudinal stress, unit: MPa; σ y is the transverse stress, in MPa, A is the cross-sectional area of ​​the test plate where the bidirectional strain gauge is located, in mm²; Longitudinal stress σ x According to formula (1), the transverse stress σ y Calculated by formula (2); s x =E / (1- v 2 )·(e x + v ·e y (1) s y =E / (1- v 2 )·(e y + v ·e x ) (2) In the formula, ε x is the longitudinal strain; ε y is the lateral strain; E is the elastic modulus, unit: MPa; v is Poisson's ratio.

2. A method for evaluating macro welding residual stress of hull structural steel according to claim 1, characterized in that: The bidirectional strain gauge is pasted on a first parallel line, the first parallel line is parallel to the center of the test plate weld, and the distance between the first parallel line and the center of the test plate weld is L, where L≥(2~3)·H, where H is the thickness of the test plate, in mm.

3. A method for evaluating macro welding residual stress of hull structural steel according to claim 1, characterized in that: The bidirectional strain gauge may be provided in plurality, and the plurality of bidirectional strain gauges are located on the first parallel line.

4. A method for evaluating macro welding residual stress of hull structural steel according to claim 1, characterized in that: The fixing assembly is a rigid frame.

5. The method for evaluating macro welding residual stress of hull structural steel according to claim 1, characterized in that: The first test plate and the second test plate are symmetrical about the test plate weld.

6. A method for evaluating macro welding residual stress of hull structural steel according to claim 1, characterized in that: The distance between the flame cutting line and the nearest restrained weld on the test plate is 8-12 mm.

7. A method for evaluating macro welding residual stress of hull structural steel according to claim 1, characterized in that: The distance between the flame cutting line and the nearest restrained weld on the test plate is 10 mm.

8. A method for evaluating macro welding residual stress of hull structural steel according to claim 1, characterized in that: The method further includes step S7, which is to conduct experiments on different welding materials or processes to quickly evaluate the magnitude of welding residual stress by comparing cross-sectional forces or strains.

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