A method for evaluating fatigue performance of high-strength steel butt joint of dynamic load structure

Abstract

The application discloses a high-strength steel butt joint fatigue performance evaluation method for a dynamic load structure, which considers the influence of welding residual stress on the fatigue behavior of the joint, combines the low notch sensitivity of the high-strength steel box structure commonly used in the dynamic load occasion, and avoids the low cycle period fatigue cracking problem of the small-size edge sharp welding joint fatigue sample caused by the notch stress concentration during the fatigue evaluation to the greatest extent, basically eliminates other internal and external factors that may cause fatigue data dispersion, solves the data dispersion and unevenness problems commonly existing in the high-strength steel welding joint fatigue evaluation, has good usability, and enhances the guiding role of the fatigue evaluation test on engineering application.

Description

Technical Field

[0001] This invention relates to the evaluation technology of high-strength steel welded joints, and more specifically, to a method for evaluating the fatigue performance of high-strength steel butt joints for dynamic load structures. Background Technology

[0002] Welding is a key technology and major process in the on-site production of high-strength steel structural components. However, the non-equilibrium heating and cooling during welding can cause non-equilibrium solid-state phase transformations, making the welded joint a weak point in the entire structure. Various structural failures during manufacturing and service are often related to the weakening of welded joint performance. For low-alloy high-strength steel welded structures used in alternating load applications, such as engineering machinery, marine structures, rail vehicles, and heavy energy equipment, fatigue failure of welded joints is the main form of structural failure, and the dynamic fatigue performance of joints is a technical indicator of great concern in the industry.

[0003] The fatigue behavior of welded joints differs from that of a homogeneous metal matrix. Macroscopic or microscopic discontinuities generated during welding often become initial fatigue crack initiation sites, especially microscopic defects at the weld toe, which can directly propagate without crack initiation. Simultaneously, residual tensile stress generated during welding, weld toe geometry, and stress concentrations arising from microscopic defects during service promote the propagation of initial fatigue cracks, accelerating the fatigue failure process, primarily manifested as a reduction in fatigue strength and fatigue life. GB / T 3075-2008, "Methods for Axial Force Control in Fatigue Testing of Metallic Materials," is a commonly used industry standard for fatigue performance evaluation and testing, specifying the type of small-sized specimens and testing procedures. However, this standard primarily targets homogeneous base metals. If joint fatigue performance evaluation is conducted based on this standard while retaining weld reinforcement, it fails to examine the influence of welding residual stress on joint fatigue behavior. Furthermore, the sharp transitions at specimen edges, especially at the weld toe, increase stress concentration, significantly differing from the dynamic service characteristics of typical high-strength steel box structures. Therefore, it cannot accurately reflect the actual fatigue behavior of high-strength steel welded structures.

[0004] Currently, there are existing technologies for evaluating the fatigue performance of high-strength steel welded joints. For example, application number CN201110047097.8 discloses a method for evaluating the fatigue characteristics of the T-joint portion of a T-type welded joint structure. Based on the influence of factors such as weld toe curvature radius, HAZ uniform elongation, and HAZ actual yield strength on the fatigue behavior of the joint, strain evaluation parameters at the weld toe are fitted, indirectly evaluating the fatigue performance of the T-type joint without actual testing. However, this technology cannot evaluate and predict the fatigue performance of butt joints subjected to normal stress in important structures. Application number CN201510963648.3 discloses a fatigue specimen of a cross-shaped welded joint, which involves welding a fillet weld on a machined, integrally formed substrate and monitoring fatigue cracking after fatigue loading. Application number CN201510273936.6 discloses a method for on-site sample preparation of fatigue specimens for spot welds on vehicle body steel plates, but this method can only be used for spot welds that are not primarily load-bearing and has no reference value for the fatigue evaluation of butt joints subjected to principal stress. Application number CN201611076258.5 discloses a method for preparing fatigue specimens of plate-shaped welded components and its application. By attaching strain gauges to the welded component and cutting it strip by strip to observe changes in welding residual stress, the minimum width of the fatigue specimen retaining residual stress and the maximum width completely releasing residual stress are obtained. This method can reflect the influence of welding residual stress on joint fatigue. However, this method is labor-intensive, the residual stress monitoring procedure is cumbersome, and the cost is high. Furthermore, it does not consider the representativeness of the fatigue evaluation specimens in typical high-strength steel box-type dynamically loaded service structures. Application number CN201810846206.4 discloses a full-scale fatigue test method for welded joints of deep-water steel catenary risers, which can accurately reflect the actual service conditions of steel catenary riser structures. However, this actual pipe evaluation is very costly, inconvenient to operate, and has a long implementation cycle.

[0005] Therefore, there is an urgent need to develop a simple and convenient method for evaluating the fatigue performance of high-strength steel butt joints. This method should be able to objectively reflect the influence of welding residual stress on the fatigue behavior of the joint, eliminate the adverse effects of sharp notch effect on fatigue performance, and reflect the service characteristics of typical dynamic load welded structures of high-strength steel box-type structures. This would allow for a rapid and effective evaluation of the fatigue behavior of high-strength steel welded joints. Summary of the Invention

[0006] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a fatigue performance evaluation method for high-strength steel butt joints in dynamically loaded structures. This method considers the influence of welding residual stress on joint fatigue behavior and leverages the low notch sensitivity of high-strength steel box structures commonly used in dynamically loaded applications. It minimizes the risk of low-cycle fatigue cracking in fatigue evaluation of small-sized, sharply edged welded joint specimens due to notch stress concentration. Furthermore, it largely eliminates other internal and external factors that could cause fatigue data dispersion, thus resolving the common data dispersion and inhomogeneity issues in fatigue evaluation of high-strength steel welded joints. This method offers excellent usability and enhances the guiding role of fatigue evaluation tests in engineering applications.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for evaluating the fatigue performance of high-strength steel butt joints in dynamically loaded structures, comprising the following steps:

[0009] S1, Fatigue Specimen Design: The minimum fatigue specimen for a high-strength steel welded joint can retain at least 90% of the initial welding residual stress. This minimum fatigue specimen includes a clamping section and a working section. The working section includes an arc-shaped transition section and an actual working section. The width W and thickness B of the actual working section satisfy the following formula: In the formula, W is the width of the actual working section of the fatigue specimen in mm, and B is the thickness of the fatigue specimen in mm.

[0010] S2, for usability treatment, the edges and corners of the fatigue specimen working section are smoothed, the weld areas on both sides of the fatigue specimen working section are ground, and the weld reinforcement in the middle area is retained.

[0011] S3, Fatigue Evaluation Test: The fatigue specimens treated in step S2 are subjected to a high-cycle fatigue evaluation test to obtain the conditional fatigue life of the high-strength steel butt joint and complete the fatigue performance evaluation of the high-strength steel butt joint.

[0012] Preferably, in step S1, the size of the minimum fatigue specimen of the high-strength steel welded joint is obtained by finite element calculation.

[0013] Preferably, in step S1:

[0014] The length L of the working section of the fatigue specimen is 200-300 mm;

[0015] The radius R of the arc-shaped transition section satisfies the following formula: R=W / (4~5), where R is the radius of the arc-shaped transition section of the fatigue specimen, in mm;

[0016] The length H of the clamping section is greater than 70 mm.

[0017] Preferably, in step S2, during the smoothing process, the edge corners of the working segment are processed into a smooth transition segment in the shape of an arc. The radius r of the smooth transition segment in the shape of an arc satisfies the following formula: r = (1 / 4 ~ 2 / 5) × B, where r is the radius of the smooth transition segment in the shape of an arc at the edge of the working segment, in mm, and r ≥ 3 mm.

[0018] Preferably, in step S2, during the grinding process, the two ends of the weld area in the width direction of the working section are ground, and the weld grinding length g satisfies: g = (1 / 6 ~ 1 / 4) × W, where g is the weld grinding length in mm, and g ≤ 15 mm.

[0019] Preferably, in step S2, after the weld area of ​​the working section of the fatigue specimen is ground, the surface roughness R is... a ≤12.5.

[0020] Preferably, in step S3, the high-cycle fatigue evaluation test follows the principles of early fatigue fracture and abnormal fracture treatment:

[0021] If fatigue cracking originates at the edge of the fatigue specimen within 50,000 cycles in the high-cycle fatigue evaluation test, the fatigue cracking is caused by notch stress concentration due to abrupt changes in the geometric factors at the edge of the fatigue specimen, and resampling and evaluation are required.

[0022] If fatigue cracking occurs at the weld root position of the back weld within 100,000 cycles in the high-cycle fatigue evaluation test, the fatigue cracking is related to the welding quality of the weld root. The weld root quality needs to be analyzed and evaluated, and then re-sampled for evaluation.

[0023] If fatigue cracking occurs in the base material outside the welded joint during the high-cycle fatigue evaluation test, the fatigue cracking is an abnormal result. The cause needs to be identified by analyzing the fracture characteristics, and then sampling should be repeated for evaluation until the fatigue cracking is located at the welded joint.

[0024] Preferably, in step S3, the fatigue performance evaluation principle of the high-strength steel butt joint is as follows:

[0025] At least three fatigue evaluation failure specimens were obtained in the same group under the same fatigue stress level, and the fatigue evaluation failure specimens were opened to show the fatigue cracks of the fatigue evaluation failure specimens.

[0026] Introducing fatigue crack propagation deviation parameter E syn To determine the validity of the fatigue evaluation test results for the high-strength steel butt joint, if the fatigue crack propagation deviation parameter E... synIf the value is ≤0.2, the results of the fatigue evaluation test of the high-strength steel butt joint are valid; otherwise, it is necessary to calculate the individual fatigue crack propagation deviation parameter E of each fatigue specimen in the same group. syn-i For E syn-i Fatigue specimens with a strength >0.2 were subjected to repeat testing under the same test conditions until the E value of each fatigue specimen was reached. syn-i ≤0.2, and E syn Until it is ≤0.2.

[0027] Preferably, in step S3, the fatigue crack propagation deviation parameter E syn The calculation formula is:

[0028]

[0029] In the formula, E syn The parameter for fatigue crack propagation deviation is dimensionless.

[0030] L f The length of the lateral fatigue crack is measured in mm to indicate rapid propagation.

[0031] L s The length of fatigue crack propagation on the slow-progressing side is expressed in mm.

[0032] n is the number of fatigue evaluation failure samples in the same group, n≥3.

[0033] Preferably, in step S3, the individual fatigue crack propagation deviation parameter E syn-i The calculation formula is:

[0034]

[0035] In the formula, E syn-i Let be the individual fatigue crack propagation deviation parameter for the i-th fatigue specimen, which is dimensionless;

[0036] L fi The fatigue crack propagation length on the rapid propagation side of the i-th fatigue specimen is expressed in mm.

[0037] L si Let be the fatigue crack propagation length on the slow-propagation side of the i-th fatigue specimen, in mm.

[0038] The fatigue performance evaluation method for high-strength steel butt joints in dynamically loaded structures provided by this invention has the following advantages:

[0039] 1. The fatigue performance evaluation method for high-strength steel butt joints in dynamic load structures of the present invention considers the influence of welding residual stress on the fatigue behavior of the joint, and combines the low notch sensitivity of high-strength steel box structures commonly used in dynamic load applications. It avoids the problem of low-cycle fatigue cracking caused by notch stress concentration in fatigue evaluation of small-sized welded joint specimens with sharp edges to the greatest extent. At the same time, it basically eliminates other internal and external factors that may cause fatigue data dispersion, solves the data dispersion and non-uniformity problems that are common in fatigue evaluation of high-strength steel welded joints, has good usability, and enhances the guiding role of fatigue evaluation tests in engineering applications.

[0040] 2. The fatigue performance evaluation method for high-strength steel butt joints in dynamic load structures of the present invention is a suitable fatigue performance evaluation method that closely resembles the dynamic load service state of high-strength steel box structures commonly used in dynamic load applications. It obtains the minimum sample size that maximizes the retention of welding residual stress through finite element calculations. Considering the low notch sensitivity of typical high-strength steel closed box welded structures, it optimizes the design of high-strength steel fatigue evaluation samples. Furthermore, it comprehensively applies the principles for handling early fatigue fracture and abnormal fracture of high-strength steel butt joints, as well as suitable fatigue performance evaluation principles. This effectively eliminates stress concentration caused by edge notch effects in fatigue evaluation samples and other internal and external factors that may cause fatigue data dispersion, resulting in a more uniform distribution of welded joint fatigue performance evaluation test data. Consequently, it closely resembles the fatigue characteristics of box structures with low notch sensitivity commonly used in actual dynamic load structures.

[0041] 3. The fatigue performance evaluation method for high-strength steel butt joints in dynamic load structures of the present invention can be used to evaluate the fatigue performance of butt joints of high-strength steel of various strength grades based on different welding methods and processes. Under the condition that fatigue evaluation of large structural components is not required, it can quickly and indirectly evaluate the fatigue behavior of welded joints in dynamic load situations at a low cost, which has important guiding significance for the application of high-strength steel in dynamic load situations.

[0042] 4. The fatigue performance evaluation method for high-strength steel butt joints in dynamic load structures of the present invention provides technical guidance for the safe service of structures and has the advantages of good reliability of evaluation results, low dispersion, high efficiency and low cost.

[0043] 5. The fatigue performance evaluation method for high-strength steel butt joints in dynamic load structures of the present invention is a common technology for joint fatigue behavior. It has good universal applicability in related products in various industrial fields that are subjected to dynamic load fatigue service, with wide coverage and broad prospects for promotion. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of the fatigue specimen of the welded joint used in the fatigue performance evaluation method of high-strength steel butt joints for dynamic load structures of the present invention.

[0045] Figure 2 In the figure, (a) is a plan view of the welding area after the parallel test section has been ground, and (b) is a cross-sectional view of the parallel test section after the edges and corners have been smoothed.

[0046] Figure 3 This is a schematic diagram of the fatigue crack propagation deviation model for high-strength steel welded joints of the present invention. Detailed Implementation

[0047] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0048] This invention provides a fatigue performance evaluation method for high-strength steel butt joints in dynamic load structures. It uses finite element analysis to obtain the minimum specimen size for high-strength steel welded joints that maximizes the retention of welding residual stress, despite the influence of thickness. It also fully considers the characteristics of high-strength steel box-type welded structures typically used in dynamic load applications, such as their closed-loop structure and low fatigue cracking sensitivity due to edge notch effects. An optimized fatigue specimen design for high-strength steel joints is developed, preserving welding residual stress while avoiding the low-cycle edge cracking problem caused by notch effects in fatigue evaluation of small-sized, sharply edged welded joint specimens. By comprehensively applying the principles of early fatigue fracture and abnormal fracture treatment for high-strength steel butt joints, as well as the principles of usability-appropriate fatigue performance evaluation, the method effectively eliminates stress concentration caused by edge notch effects and other internal and external factors that may cause dispersion in fatigue data. This results in a more uniform distribution of fatigue performance evaluation test data for welded joints, closely resembling the fatigue characteristics of box-type structures with low notch sensitivity commonly used in actual dynamic load structures, thus enhancing the guiding role of fatigue evaluation tests in engineering applications. Without requiring fatigue evaluation of large structural components, this method enables rapid and indirect evaluation of the fatigue performance of welded joints in dynamic load applications at a lower cost, providing important guidance for the application of high-strength steel welded structures in dynamic load applications.

[0049] The present invention provides a method for evaluating the fatigue performance of high-strength steel butt joints in dynamically loaded structures, comprising the following steps:

[0050] S1, Fatigue Specimen Design: The minimum fatigue specimen for a high-strength steel welded joint capable of retaining at least 90% of the initial weld residual stress includes a clamping section and a working section. The width W and thickness B of the actual working section satisfy the following formula: In the formula, W is the width of the actual working section of the fatigue specimen in mm, and B is the thickness of the fatigue specimen in mm.

[0051] Specifically, the residual tensile stress generated during the welding process of high-strength steel, combined with external loads during structural service, theoretically increases the tendency of welded structures to fatigue failure. However, since the residual stress in standard small fatigue specimens is largely released during the paper-based testing process, it cannot accurately reflect the influence of residual stress on the fatigue behavior of the joint. Using excessively large specimens or structural components for fatigue performance evaluation is impractical and costly. Therefore, for high-strength steel welded joints of typical thickness, a finite element numerical model needs to be established to simulate and calculate the residual stress field under certain welding conditions. The width of the specimen that retains 90% of the initial residual stress is taken as the actual working section width W (in mm) of the welded joint fatigue specimen. This width is obtained through the following relationship with the fatigue specimen thickness B (i.e., the original thickness of the high-strength steel plate, in mm):

[0052]

[0053] In the formula, W is the width of the actual working section of the fatigue specimen in mm, and B is the thickness of the fatigue specimen in mm.

[0054] Combination Figure 1 The fatigue specimens of the high-strength steel butt joints shown are as follows: the minimum fatigue specimen of the high-strength steel welded joint includes a clamping section and a working section. The working section includes an arc-shaped transition section and an actual working section, that is, a plate-shaped specimen with a parallel test working section processed in the middle. The width W of the actual working section is determined by formula (1), and the length L of the working section is 200-300 mm. The radius R of the arc-shaped transition section satisfies the following formula: R = W / (4-5), where R is the radius of the arc-shaped transition section of the fatigue specimen in mm, and W is the width of the actual working section of the fatigue specimen in mm. The length H of the clamping section is greater than 70 mm, and is determined according to the clamping characteristics of the testing machine.

[0055] S2, for usability treatment, the edges and corners of the fatigue specimen working section are smoothed, the weld areas on both sides of the fatigue specimen working section are ground, and the weld reinforcement in the middle area is retained.

[0056] Given that fatigue evaluation of fatigue specimens of high-strength steel butt joints with sharp edges of small size is prone to local stress concentration due to the notch effect, which can easily lead to edge-priority cracking in low-cycle periods, while the edge notch effect of high-strength steel closed box welded structures actually in dynamic load conditions is relatively low, it is necessary to perform usability treatment on the joint area of ​​fatigue specimens of high-strength steel welded joints to make the evaluation results closer to the actual service conditions and thus have a more direct guiding role.

[0057] Specifically, such as Figure 1The fatigue specimen of the high-strength steel butt joint shown has its working section's edges smoothed out, that is, the four edges of the working section are rounded into smooth transition sections (see...). Figure 2 As shown in (b), this reduces the low-cycle fatigue cracking caused by stress concentration at the sharp edges of the fatigue specimen during fatigue loading, making its fatigue behavior similar to the low edge fatigue cracking sensitivity of general high-strength steel closed box welded structures. The radius r of the smooth transition section with an arc shape satisfies the following formula: r = (1 / 4 ~ 2 / 5) × B, where r is the radius of the smooth transition section with an arc shape at the edge of the working section, in mm, and r ≥ 3 mm; B is the thickness of the fatigue specimen, in mm.

[0058] Then, the weld areas on both sides of the working section of the fatigue specimen are ground down, while retaining the weld reinforcement in the middle area. Specifically, for the working section, a certain length of weld reinforcement at both ends of the width direction of the fatigue specimen's weld area is ground down to be flush with the base material. This minimizes or avoids the presence of weld toes at the edges of the fatigue specimen and the stress concentration caused by sharp corner effects, similar to the fatigue service characteristics of typical high-strength steel enclosed box-type welded structures. Combined with... Figure 1 , Figure 2 As shown in (a), during the grinding process, both ends of the weld area in the width direction of the working section are ground. The grinding length g of the weld satisfies: g = (1 / 6 ~ 1 / 4) × W, where g is the grinding length of the weld in mm, and g ≤ 15 mm, and W is the width of the actual working section of the fatigue specimen in mm. After the weld area of ​​the working section of the fatigue specimen is ground, in order to ensure the machining accuracy of the specimen cross-section and the grinding position of the weld reinforcement on both sides, the surface roughness R is... a ≤12.5, and after grinding, no visible grooves or scratches should appear in the weld area, especially transverse grooves or scratches perpendicular to the loading direction.

[0059] S3, Fatigue Evaluation Test: The fatigue specimens treated in step S2 are subjected to a high-cycle fatigue evaluation test to obtain the conditional fatigue life of the high-strength steel butt joint and complete the fatigue performance evaluation of the high-strength steel butt joint.

[0060] Specifically, the fatigue specimens processed in step S2 are placed on a testing machine and then subjected to high-cycle fatigue evaluation tests. To ensure the effectiveness of the fatigue performance evaluation of high-strength steel butt joints and their basic consistency with the service characteristics of box structures commonly used in dynamic load applications, the high-cycle fatigue evaluation tests must adhere to the principles of early fatigue fracture and abnormal fracture treatment.

[0061] If fatigue cracking originates at the edge of the fatigue specimen within 50,000 cycles in a high-cycle fatigue evaluation test, the fatigue cracking is caused by notch stress concentration due to abrupt changes in the geometric factors at the edge of the fatigue specimen, and resampling and evaluation are required.

[0062] If fatigue cracking occurs at the weld root position of the back weld within 100,000 cycles in the high-cycle fatigue evaluation test, the fatigue cracking is related to the welding quality of the weld root. After analyzing and evaluating the quality of the weld root, it is necessary to resample and evaluate.

[0063] If fatigue cracking occurs in the base material outside the welded joint during high-cycle fatigue evaluation tests, regardless of the number of cycles, the cracking is an abnormal result. The fracture characteristics need to be analyzed to determine the cause, and then samples need to be taken again for evaluation until the fatigue cracking is located at the welded joint.

[0064] After the aforementioned steps, and following the principles of early fatigue fracture and abnormal fracture treatment, the fatigue performance evaluation principles for high-strength steel butt joints are as follows:

[0065] 1. Under the same fatigue stress level, at least three fatigue evaluation failure specimens are obtained in the same group. The fatigue evaluation failure specimens are opened by means of tension, bending or crushing to show clear and uncontaminated fatigue cracks.

[0066] 2. Due to the aforementioned design of fatigue specimen dimensions and the usability treatment to reduce or eliminate notch effects in the edge regions of the fatigue specimens, theoretically, fatigue cracks should initiate from a certain area in the middle of the fatigue specimen with retained weld reinforcement and propagate substantially synchronously. Therefore, in order to correlate with the low edge notch sensitivity of box-type welded structures actually in dynamic load applications and to reduce the impact of fatigue specimen edge notch effects on the dispersion of fatigue evaluation, a fatigue crack propagation deviation parameter E is introduced. syn To determine the validity of the fatigue evaluation test results for the high-strength steel butt joint, in combination with... Figure 3 As shown, the fatigue crack propagation deviation parameter E syn The calculation formula is:

[0067]

[0068] In the formula, E syn The parameter for fatigue crack propagation deviation is dimensionless.

[0069] L fi The fatigue crack propagation length on the rapid propagation side of the i-th fatigue specimen is expressed in mm.

[0070] L si The length of the fatigue crack on the slow-propagation side of the i-th fatigue specimen is in mm.

[0071] n is the number of fatigue evaluation failure samples in the same group, n≥3.

[0072] Under ideal conditions, if, under external fatigue load, fatigue cracks originate in a region within the specimen retaining the weld and propagate uniformly and synchronously, eventually leading to failure, the fatigue crack propagation deviation parameter E... syn =0. However, due to the influence of many internal and external factors on the fatigue performance of welded joints, even with suitable use treatments such as fatigue specimen size design and reduction or elimination of notch effects in the specimen edge region, fatigue cracks cannot propagate completely synchronously during fatigue testing. The fatigue crack propagation deviation parameter E syn It must be greater than 0. Based on extensive experimental verification, the following fatigue crack propagation deviation parameter E was established. syn Necessary criterion:

[0073] If the fatigue crack propagation deviation parameter E syn If the coefficient of performance is ≤0.2, the fatigue crack propagation synchronization of the high-strength steel butt joint is considered good, and the results of the fatigue evaluation test of the high-strength steel butt joint are considered valid.

[0074] Conversely, if the fatigue crack propagation deviation parameter E syn If the value is greater than 0.2, then unforeseen internal and external factors may affect the fatigue test results of the high-strength steel butt joint. In this case, it is necessary to calculate the individual fatigue crack propagation deviation parameter E of each fatigue specimen in the same group. syn-i The individual fatigue crack propagation deviation parameter E syn-i The calculation formula is:

[0075]

[0076] In the formula, E syn-i Let be the individual fatigue crack propagation deviation parameter for the i-th fatigue specimen, which is dimensionless;

[0077] L fi The fatigue crack propagation length on the rapid propagation side of the i-th fatigue specimen is expressed in mm.

[0078] L si The length of the slow-propagation fatigue crack on the i-th fatigue specimen is denoted as mm.

[0079] For E syn-i Fatigue specimens with a strength >0.2 were subjected to repeat testing under the same test conditions until the E value of each fatigue specimen was reached. syn-i ≤0.2, and E syn Until it is ≤0.2.

[0080] This treatment method can effectively eliminate stress concentration caused by the notch effect at the edge of fatigue specimens, as well as other internal and external factors that may cause dispersion in fatigue data. This makes the distribution of fatigue evaluation data for welded joints more uniform, thus closely resembling the fatigue characteristics of box structures with low notch sensitivity commonly used in actual dynamic load structures. This enhances the guiding significance of fatigue evaluation tests for engineering applications.

[0081] The fatigue performance evaluation method for high-strength steel butt joints used in dynamic load structures according to the present invention will be further described below with specific examples.

[0082] Example

[0083] Hot-rolled Q550E steel plates with wall thicknesses of 8mm, 12mm, and 20mm were selected respectively. Butt welding tests were conducted using the mainstream solid wire gas shielded automatic welding (GMAW) process for on-site structural component manufacturing, ensuring joint welding quality. Then, the technology of this invention was applied to design fatigue specimens for the butt joints and evaluate their usability. Table 1 shows the design dimensions of the high-strength steel butt joint fatigue specimens. A fixed maximum stress value of 0.5 to 0.6 times the specified minimum yield strength of the Q550E steel plate was selected as the maximum stress value for conditional fatigue life evaluation; here, 300MPa was chosen, with a stress ratio R = 0.1, for the fatigue performance evaluation of this butt joint. Considering the dispersion of fatigue performance data, three samples were tested in each set of examples, and the fatigue evaluation results are shown in Table 2. After calculating the fatigue crack propagation deviation parameter for each specimen and each set of specimens after the test, it was found that E... syn-i and E syn All values ​​were less than 0.2, indicating that the test results were all valid and the uniformity of the test results was also relatively good.

[0084] Table 1 Design dimensions of fatigue specimens for high-strength steel butt joints

[0085] B(mm) W(mm) L(mm) R(mm) H(mm) g(mm) r(mm) Example 1 8 42 200 8 70 8 3 Example 2 12 63 230 14 80 11 4 Example 3 20 104 280 22 100 18 6

[0086] Table 2. Fatigue performance evaluation results of high-strength steel butt joints

[0087]

[0088] As shown in Tables 1 and 2, the conditional fatigue life gradually decreases with the increase of the wall thickness of the high-strength steel plate, which is consistent with the actual situation. Meanwhile, the data from the three samples in each group show good consistency, overcoming the problem of large dispersion in fatigue evaluation results.

[0089] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for evaluating the fatigue performance of high-strength steel butt joints in dynamically loaded structures, characterized in that... This includes the following steps: S1, Fatigue Specimen Design: The minimum fatigue specimen for a high-strength steel welded joint can retain at least 90% of the initial welding residual stress. This minimum fatigue specimen includes a clamping section and a working section. The working section includes an arc-shaped transition section and an actual working section. The width W and thickness B of the actual working section satisfy the following formula: ， In the formula, W is the width of the actual working section of the fatigue specimen, in mm, and B is the thickness of the fatigue specimen, in mm. The length L of the working section of the fatigue specimen is 200-300 mm; The radius R of the arc-shaped transition section satisfies the following formula: R=W / (4~5), where R is the radius of the arc-shaped transition section of the fatigue specimen, in mm; The length H of the clamping section is greater than 70 mm; S2, for usability treatment, the edges and corners of the working section of the fatigue specimen are smoothed, the weld areas on both sides of the working section of the fatigue specimen are ground, and the weld reinforcement in the middle area is retained. During the smoothing process, the edges and corners of the working segment are processed into smooth, rounded transition segments. The radius r of the rounded transition segment satisfies the following formula: r = (1 / 4 ~ 2 / 5) × B, where r is the radius of the rounded transition segment at the edge of the working segment, in mm, and r ≥ 3 mm. During the grinding process, the two ends of the weld area in the width direction of the working section are ground. The grinding length g of the weld satisfies: g = (1 / 6 ~ 1 / 4) × W, where g is the grinding length of the weld in mm, and g ≤ 15 mm. S3, Fatigue Evaluation Test: The fatigue specimens treated in step S2 are subjected to a high-cycle fatigue evaluation test to obtain the conditional fatigue life of the high-strength steel butt joint and complete the fatigue performance evaluation of the high-strength steel butt joint.

2. The fatigue performance evaluation method for high-strength steel butt joints used in dynamic load structures according to claim 1, characterized in that: In step S1, the dimensions of the minimum fatigue specimen for the high-strength steel welded joint are obtained through finite element calculation.

3. The fatigue performance evaluation method for high-strength steel butt joints used in dynamic load structures according to claim 1, characterized in that: In step S2, after the weld area of ​​the working section of the fatigue specimen is ground, the surface roughness R is... a ≤12.

5.

4. The fatigue performance evaluation method for high-strength steel butt joints used in dynamic load structures according to claim 1, characterized in that: In step S3, the high-cycle fatigue evaluation test follows the principles of early fatigue fracture and abnormal fracture treatment: If fatigue cracking originates at the edge of the fatigue specimen within 50,000 cycles in the high-cycle fatigue evaluation test, the fatigue cracking is caused by notch stress concentration due to abrupt changes in the geometric factors at the edge of the fatigue specimen, and resampling and evaluation are required. If fatigue cracking occurs at the weld root position of the back weld within 100,000 cycles in the high-cycle fatigue evaluation test, the fatigue cracking is related to the welding quality of the weld root. The weld root quality needs to be analyzed and evaluated, and then re-sampled for evaluation. If fatigue cracking occurs in the base material outside the welded joint during the high-cycle fatigue evaluation test, the fatigue cracking is an abnormal result. The cause needs to be identified by analyzing the fracture characteristics, and then sampling should be repeated for evaluation until the fatigue cracking is located at the welded joint.

5. The fatigue performance evaluation method for high-strength steel butt joints used in dynamic load structures according to claim 1, characterized in that: In step S3, the fatigue performance evaluation principle of the high-strength steel butt joint is as follows: At least three fatigue evaluation failure specimens were obtained in the same group under the same fatigue stress level, and the fatigue evaluation failure specimens were opened to show the fatigue cracks of the fatigue evaluation failure specimens. Introducing fatigue crack propagation deviation parameter E syn To determine the validity of the fatigue evaluation test results for the high-strength steel butt joint, if the fatigue crack propagation deviation parameter E... syn If the value is ≤0.2, the results of the fatigue evaluation test of the high-strength steel butt joint are valid; otherwise, it is necessary to calculate the individual fatigue crack propagation deviation parameter E of each fatigue specimen in the same group. syn-i For E syn-i Fatigue specimens with a strength >0.2 were subjected to repeat testing under the same test conditions until the E value of each fatigue specimen was reached. syn-i ≤0.2, and E syn Until it is ≤0.

2.

6. The fatigue performance evaluation method for high-strength steel butt joints used in dynamic load structures according to claim 5, characterized in that: In step S3, the fatigue crack propagation deviation parameter E syn The calculation formula is: ； In the formula, E syn The parameter for fatigue crack propagation deviation is dimensionless. L f The length of the lateral fatigue crack is measured in mm to indicate rapid propagation. L s The length of fatigue crack propagation on the slow-progressing side is expressed in mm. n is the number of fatigue evaluation failure samples in the same group, n≥3.

7. The fatigue performance evaluation method for high-strength steel butt joints used in dynamic load structures according to claim 5, characterized in that: In step S3, the individual fatigue crack propagation deviation parameter E syn-i The calculation formula is: ； In the formula, E syn-i Let be the individual fatigue crack propagation deviation parameter for the i-th fatigue specimen, which is dimensionless; L fi The fatigue crack propagation length on the rapid propagation side of the i-th fatigue specimen is expressed in mm. L si Let be the fatigue crack propagation length on the slow-propagation side of the i-th fatigue specimen, in mm.

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