Welding method for improving fatigue performance of welding structure of rectangular non-bearing accessory

Abstract

The invention discloses a welding method for improving the fatigue performance of a rectangular non-bearing accessory welding structure. According to welding, a welding seam is formed in the position away from the direction perpendicular to the load transmitting direction in the service process; a roundabout and non-through welding mode of arc starting / arc stopping in the middle area of a welding bead is adopted; according to the welding method, the fatigue characteristic of the welding structure of the rectangular non-bearing accessory is converted into a fatigue strength mechanism which is controlled by the yield strength of the base metal and is represented by cyclic plastic strain accumulated damage of a local micro-area, and then the base metal is set to be high-strength steel, so that the fatigue performance of the welding structure is improved. According to the welding method for improving the fatigue performance of the welding structure of the rectangular non-bearing accessory, the fatigue performance of the welding structure can be converted into a fatigue strength mechanism which is controlled by the yield strength of base metal and is represented by cyclic plastic strain accumulation damage of a local microcell, and the usual concept of the existing industry is broken through.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory. Background Art

[0002] At present, large-scale thick-walled steel structures applied in the industrial field often bear fatigue loads during service, and fatigue failure is also their main failure mode. For a structurally complete rolled or heat-treated material, its fatigue behavior under dynamic load conditions is a typical cumulative damage process from crack initiation, propagation to failure fracture, and there is a significant positive correlation between the conditional fatigue limit and the yield strength of the material. However, for welded joints or structures, due to the influence of three key factors: stress concentration at the weld toe caused by the weld geometry factor, initial fatigue crack sources formed by geometric discontinuities or welding defects in the weld toe and weld, and the superposition of welding residual tensile stress and external load, the fatigue performance will be significantly reduced compared with the base metal material, and the reduction amplitude is related to the influence degree of the above three key factors. In view of this, in the early fatigue design standards for dynamic load structural members, the fatigue S-N curve classification of welded joints was carried out based on a large amount of experimental data accumulation. The fatigue strength level of welded joints or structures of steel materials is not related to the yield strength level of the material, but only related to joint form design, joint detail characteristics, welding quality grade, and post-weld treatment status, etc. For example: in the mainstream EN 1993 standard, IIW-2259-15 standard, DNV-RP-C203 and other standards, a set of S-N curves that can be used for fatigue design are given according to different design forms and quality grades of steel materials, and the stress range values corresponding to the number of cycles of 2*10 6 are extracted from each S-N curve and defined as fatigue strength characteristic values, which are used as the basis for the fatigue design of dynamic load structural members. For example: in the EN1993 standard, for a double-sided welded full-penetration retained weld joint, the S-N curve corresponds to DC90, and the fatigue strength characteristic value is 90 MPa. Other standards have almost the same definition.

[0003] The invention application with the application number: CN2006100155949 discloses a "spray fusing method for improving the fatigue performance of a welded structure", which uses a spray welding or laser spray fusing method to coat a spraying material on the weld toe part of the welded structure to form a smooth-transition metal coating layer with a coating thickness between 1 mm and 6 mm at the weld toe part. The coating thickness at the weld toe part is thicker than that in the nearby area, and the spraying material is in a molten state.

[0004] The invention application with the application number: CN202210206722.7 discloses a "fatigue-resistant welding manufacturing method for the drum of a drum filter press", which includes the following steps: (1) axially fixing axial rib plates on the outer circumference of the shell by welding along the axial direction of the shell, and a plurality of the axial rib plates are evenly distributed; (2) fixing circumferential rib plates to the axial rib plates by welding along the circumferential direction of the shell, and a plurality of groups of the circumferential rib plates are evenly distributed; wherein, the axial rib plates are of an integral structure, the circumferential rib plates are of a segmented structure, and each group of circumferential rib plates includes a plurality of sector rib plates, and the sector rib plates of each group of circumferential rib plates are sequentially welded and fixed between two adjacent axial rib plates along the circumferential direction of the shell.

[0005] The invention application with the application number: CN202111459823.7 discloses an "intelligent mechanical grinding method for fatigue life extension of weld toes", which includes the following steps: (1) weld seam scanning; (2) image processing; (3) extracting feature points of each frame of image; (4) determining the starting and ending points of grinding for each frame of image; (5) obtaining the grinding trajectory; (6) determining the pose of the grinding head for each frame of image; (7) weld seam grinding. Summary of the Invention

[0006] The purpose of the present invention is that the purpose of the present technical solution is to break the above conventional cognitions and establish a fatigue strength mechanism of a welded structure characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base metal.

[0007] To achieve the above technical purposes, the present invention provides a welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory, and the specific technical solution is as follows:

[0008] A welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory,

[0009] The welding forms a weld seam at a position avoiding the direction perpendicular to the direction of the transmitted load during service; and adopts a roundabout, non-penetrating welding method with starting / ending arcs in the middle area of the weld bead.

[0010] According to this welding method, the fatigue characteristics of the welded structure of the rectangular non-load-bearing accessory are converted into a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base metal, and then the base metal is set as high-strength steel to improve the fatigue performance of the welded structure.

[0011] Furthermore,

[0012] For the welding, the fillet weld width on the base plate side of the longitudinal fillet weld of the accessory is controlled within the range of 8 - 22 mm, the fillet weld width on the accessory side of the longitudinal fillet weld of the accessory is controlled within the range of 6 - 18 mm, and the fillet weld width on the base plate side of the longitudinal fillet weld of the accessory is controlled within the range of 1.0 - 1.45 times that of the fillet weld width on the accessory side of the longitudinal fillet weld of the accessory.

[0013] Furthermore,

[0014] Forming the weld at a position avoiding the direction perpendicular to the load transfer direction during service, specifically: the welded structure is set as an accessory structure with only longitudinal fillet joints on both sides.

[0015] Furthermore,

[0016] In the non - through - type welding mentioned above, the length of the unwelded area from the weld end to the accessory end is controlled according to the following constraints:

[0017]

[0018] In the above,

[0019] a: The length of the unwelded area from the weld end to the accessory end, unit: mm;

[0020] t: The thickness of the accessory, unit: mm.

[0021] Furthermore,

[0022] In the meandering welding starting / ending at the middle area of the weld bead, the distance between the starting / ending point and the weld end is controlled according to the following constraints:

[0023]

[0024] In the above,

[0025] b: The distance between the starting / ending point and the weld end, unit: mm;

[0026] L: The length of the weld, unit: mm.

[0027] Furthermore,

[0028] The welding is carried out by the process of oscillating welding, and the oscillation residence time in the meandering part after starting and in the meandering part before ending is controlled within 1 - 2 s.

[0029] Furthermore,

[0030] The welding adopts the semi - automatic welding process with solid wire for gas - shielded metal arc welding or the semi - automatic welding process with flux - cored wire for gas - shielded metal arc welding.

[0031] Furthermore,

[0032] When the semi-automatic welding process with a solid wire for gas shielded metal arc welding is adopted, the welding parameters are controlled as follows:

[0033] Wire diameter: 1.2 mm;

[0034] Wire extension length: 13 - 22 mm;

[0035] Welding current: 200 - 290 A;

[0036] Welding voltage: 23 - 32 V;

[0037] Welding speed: 260 - 400 mm / min.

[0038] Furthermore,

[0039] When the semi-automatic welding process with a flux-cored wire for gas shielded metal arc welding is adopted, the welding parameters are controlled as follows:

[0040] Wire diameter: 1.2 mm;

[0041] Wire extension length: 16 - 25 mm;

[0042] Welding current: 160 - 220 A;

[0043] Welding voltage: 21 - 30 V;

[0044] Welding speed: 160 - 250 mm / min.

[0045] Furthermore,

[0046] Before welding, the welding area is polished and cleaned, and the operation ends when the metal luster appears in the welding area.

[0047] Furthermore,

[0048] After welding, post-welding treatment is carried out on the weld end for the purpose of smooth transition and reducing the height difference between the weld end and the base metal bottom plate;

[0049] The post-welding treatment is carried out by grinding or by mechanical impact.

[0050] A welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to the present invention can convert the fatigue performance of the welded structure into a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base material, breaking through the conventional concepts of the existing industry. Based on the mechanism that the stress concentration at the weld toe of the longitudinal fillet welds transmitting loads in the accessory welded structure reduces the fatigue grade of the overall structure, it creatively proposes a welding technology with only longitudinal fillet welds on both sides. Compared with the existing technology, without making complex changes and increasing costs, it can ensure the fatigue performance of the accessory welded structure, thus giving full play to the potential of the fatigue performance of the base material of the thick-walled high-strength steel structure, realizing the application of high-strength steel and lightweight operation, and helping to improve the overall manufacturing level and reduce costs in related industries. Based on the existing fatigue test standards, and based on the unique characteristics of the fatigue behavior of high-strength steel welded joints, by adopting scientific and reasonable technical measures, it has obtained the result that the fatigue strength characteristic value of the accessory welded structure has been significantly improved, subverting the understanding of the fatigue performance of welded joints in the industry for many years. Compared with the existing standards and technologies, it has significant creativity. It provides technical support for the application and popularization of high-strength steel in multiple industrial fields involving dynamic load service. Replacing ordinary carbon steel with high-strength steel will have the effect of green and low-carbon in both the manufacturing process and the service process in the long run, and it will make a lasting contribution to energy conservation and carbon reduction in the industrial field. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the accessory structure with only longitudinal corner joints in the present invention;

[0052] Figure 2 is Figure 1 top view of;

[0053] Figure 3 Schematic diagram of the unwelded area at both ends of the longitudinal fillet weld of the accessory in the present invention;

[0054] Figure 4 Schematic diagram of the weld leg size of the longitudinal fillet weld of the accessory in the present invention;

[0055] Figure 5 Schematic diagram of the meandering weld starting / ending at the middle area of the weld bead in the present invention;

[0056] Figure 6 Schematic diagram of the before-and-after comparison of the post-weld treatment of mechanically impacting the weld end in the present invention;

[0057] Figure 7 Schematic diagram of the type and size of the fatigue evaluation specimen of the welded structure of the rectangular accessory on the Q500MD high-strength steel base plate in the embodiment of the present invention;

[0058] Figure 8 is Figure 7 top view of.

[0059] In the figure,

[0060] 1 - Large steel structure base plate;

[0061] 2 - Rectangular accessory;

[0062] 3 - Longitudinal fillet weld of the accessory. Specific implementation manner

[0063] Next, according to the accompanying drawings of the specification and the specific implementation manner, a welding method for improving the fatigue performance of a welded structure of a rectangular non - load - bearing accessory of the present invention will be further specifically described.

[0064] To fully understand this technical solution, the following will specifically introduce this technical solution in two parts. The first part refers to the overview of this technical solution, and the second part refers to the specific process and principle based on the overview.

[0065] Technical overview:

[0066] The R & D team of the applicant found through research that: under certain conditions, when establishing control and optimization of the welding stress concentration effect, establishing control and optimization of the initial fatigue crack source, and establishing control and optimization of the welding residual tensile stress, a comprehensive control and optimization effect can be found, so that the fatigue performance of the welded structure is converted to the fatigue strength mechanism characterized by the cumulative damage of local micro - area cyclic plastic strain controlled by the yield strength of the base material. Then, based on the positive correlation between the fatigue strength and static load strength of the metal, the material to be welded is set as high - strength steel, thereby improving the fatigue performance of the welded structure. In specific practice, only by controlling the process and setting the working conditions in advance to make the duration of the residual stress relaxation effect generated by the superposition of the welding residual tensile stress and the external load meet the set requirements, can the fatigue performance of the welded structure be improved through the welding of this technical solution. The duration of the residual stress relaxation effect generated by the superposition of the welding residual tensile stress and the external load meeting the set requirements specifically means that no fatigue failure occurs when the early fatigue crack cycle is 1000 - 5000 times.

[0067] A welding method for improving the fatigue performance of a welded structure of a rectangular non - load - bearing accessory of this technical solution forms a weld at a position avoiding the direction perpendicular to the direction of the transmitted load during service; adopts a round - about, non - through welding method starting / ending at the middle area of the weld bead; according to this welding method, the fatigue characteristics of the welded structure of the rectangular non - load - bearing accessory are converted to the fatigue strength mechanism characterized by the cumulative damage of local micro - area cyclic plastic strain controlled by the yield strength of the base material, and then the base material is set as high - strength steel to improve the fatigue performance of the welded structure.

[0068] Here, the weld is formed at a position that avoids the direction perpendicular to the load transfer direction during service, which is achieved by setting the welding structure as an accessory structure with only two longitudinal corner joints. Here, "circumventive welding with arc starting / ending in the middle area of ​​the weld" means: the arc is started in the middle area of ​​the weld, and then the arc is ended after circling welding from the arc starting position, and the arc starting and arc ending positions are closer to the inner circle of the accessory. Here, "non-through welding" means: the length of the weld is set in a way that is less than the length of the accessory, so that the end of the weld forms an unwelded length at a certain distance from the end of the accessory.

[0069] On the basis of the above settings, in order to take into account the firmness and reliability of welding and to curb the introduction of additional stress concentration, this technical solution also controls the welding angle width of the parent material bottom plate side of the accessory longitudinal fillet weld and the welding angle width of the accessory side of the accessory longitudinal fillet weld. At the same time, in order to better serve the technical purpose, the pre-welding treatment and post-welding treatment processes are adopted for operators to select according to actual conditions.

[0070] Specific process and principle:

[0071] The technical solution is a welding method for improving the fatigue performance of rectangular non-load-bearing accessory welded structure. It is aimed at rectangular non-load-bearing accessories commonly used on large thick-walled steel structures for pipe or cable arrangement and fixation, operation monitoring and maintenance, decoration and other purposes. Under the objective condition that the stress concentration effect of the accessory fillet weld cannot be avoided to significantly reduce the fatigue level of the thick-walled steel structure parent material, the accessory fillet weld welding method and weld bead arrangement form are optimized. The method of welding only the fillet welds on the longitudinal sides of the accessory and the matching fillet weld bead arrangement, welding process technology, weld bead end processing technology, etc. are mainly adopted to avoid the accessories perpendicular to the load transfer direction during service. The transverse fillet weld has, to a certain extent, significantly reduced the stress concentration caused by the traditional transverse fillet weld of the accessory and its adverse effect on the fatigue performance of the overall structure. Combined with the control of the duration of the aforementioned residual stress relaxation effect, the fatigue performance of the welded structure can be converted to a fatigue strength mechanism characterized by the cumulative damage of local micro-area cyclic plastic strain controlled by the yield strength of the parent material, thereby giving full play to the fatigue performance potential of the parent material of the thick-walled high-strength steel structure, improving the overall fatigue level of the large thick-walled steel structure, ensuring the fatigue service safety of the overall structure, and providing technical support for the design and application of high-strength steel in the field of dynamic load structural parts and lightweight weight reduction of structural materials. The specific technical solution is as follows:

[0072] Step 1: Layout of fillet welds of accessories

[0073] In dynamic load service scenarios, the fillet welds of the accessories on large thick-walled steel structures do not bear normal stress, but the transverse fillet welds of the accessories perpendicular to the normal stress direction play a role in transferring the load. The presence of the fillet welds causes stress concentration at the weld toe, which often becomes a failure risk point for fatigue service of the overall structure, reducing the fatigue level of the overall structure. However, the longitudinal fillet welds on both sides of the accessories only play a connecting role, and their role in transferring loads and causing stress concentration during service is very small, and have little adverse effect on the fatigue performance of the overall structure. In view of this, the accessory structure is designed with only longitudinal fillet welds on both sides, such as Figure 1 , 2 As shown in the figure, 1 is the base plate of the large steel structure; 2 is the rectangular accessory; 3 is the longitudinal fillet weld of the accessory. In order to avoid the stress concentration effect caused by the superposition of the arc starting and arc ending positions of the longitudinal fillet weld and the width of the accessory, the longitudinal fillet weld of the accessory is welded non-through, leaving a certain unwelded area at both ends to buffer the stress concentration. Figure 3 As shown. Let t be the thickness of the accessory, a be the unwelded area left at both ends of the longitudinal fillet weld, and limit a = 0.35 ~ 0.80t, and a> 5mm. At the same time, certain restrictions are imposed on the size of the longitudinal fillet weld of the accessory, which can ensure that the accessory is firmly connected to the thick-walled base plate without causing additional stress concentration effects. Figure 4 As shown. is the longitudinal fillet weld parent material bottom plate side weld angle width, The width of the longitudinal fillet weld accessory side weld angle, limit and

[0074] Step 2: Welding direction of longitudinal fillet weld of accessory

[0075] In order to ensure the welding quality of the contact area between the two ends of the longitudinal fillet weld of the accessory and the reserved unwelded area, and to avoid the stress concentration effect caused by the uncontrollable changes in the geometric shapes of the arc starting and arc ending areas during the load transfer process, the following method is used: Figure 5 The welding method shown is to start the arc in the middle part and end the arc in the middle part of the other end, thereby avoiding the uneven arc pit at the end of the longitudinal fillet weld and the stress concentration effect that may be caused, which is beneficial to the overall fatigue performance of the accessory structure during service. In order to ensure the quality of the end of the longitudinal fillet weld and minimize the area of ​​secondary welding, the detour distance b between the arc starting / ending point and the end is limited, b = 3 ~ 10mm, and b < 0.15L, L is the length of the longitudinal fillet weld.

[0076] Step 3: Welding process specifications for longitudinal fillet welds of accessories

[0077] Considering the operating habits, implementation convenience and economy in the field of large steel structure manufacturing, the longitudinal fillet welds of rectangular accessories are welded by semi-automatic welding with solid wire or flux-cored wire using gas shielded metal arc welding. To avoid defects during welding, it is necessary to grind and clean the two sides of the accessory towards the welding area before welding according to the actual situation. The grinding and cleaning should be carried out until the metal luster is exposed on the surface of the base plate and the bottom of the accessory. The welding process specifications for the longitudinal fillet welds of the accessory are as follows:

[0078] Process 1: Semi-automatic welding with solid wire using gas shielded metal arc welding

[0079] Use the commonly used and cost-effective AWS A5.18 ER70S-G gas shielded solid wire in the industrial field. The wire diameter is 1.2 mm, the welding current I = 200 - 290 A, the welding voltage U = 23 - 32 V, the welding speed v = 260 - 400 mm / min, and the welding shielding gas is 80% Ar + 20% CO 2 argon-rich mixed gas or 100% pure CO 2 , and the gas flow rate f = 20 - 28 L / min. The wire extension length is 13 - 22 mm. To ensure the uniform spreading of the longitudinal fillet welds of the accessory, a welding method with appropriate oscillation is adopted during welding, especially at the turning points at both ends after starting the arc and before stopping the arc. The residence time during oscillation is 1 - 2 s, so as to ensure the smooth transition and complete spreading of the turning points at both ends to the base plate of the parent material in the reserved unwelded area.

[0080] Process 2: Semi-automatic welding with flux-cored wire using gas shielded metal arc welding

[0081] Use the commonly used and cost-effective AWS A5.29 E71T1 gas shielded flux-cored wire in the industrial field, with a diameter of 1.2 mm, the welding current I = 160 - 220 A, the welding voltage U = 21 - 30 V, the welding speed v = 160 - 250 mm / min, and the welding shielding gas is 80% Ar + 20% CO 2 argon-rich mixed gas, and the gas flow rate f = 18 - 26 L / min. The wire extension length is 16 - 25 mm. To ensure the uniform spreading of the longitudinal fillet welds of the accessory, a welding method with appropriate oscillation is adopted during welding, especially at the turning points at both ends after starting the arc and before stopping the arc. The residence time during oscillation is 1 - 2 s, so as to ensure the smooth transition and complete spreading of the turning points at both ends to the base plate of the parent material in the reserved unwelded area.

[0082] Step 4: End treatment technology for longitudinal fillet welds of accessories

[0083] Compared with the transverse fillet welds of accessories perpendicular to the direction of the principal stress during service, the longitudinal fillet welds cause little stress concentration during the load transfer process. However, for the accessory structure designed in the present invention without transverse fillet welds and only longitudinal fillet joints on both sides, certain stress concentration effects will also occur in the area of the turning points at both ends of the longitudinal fillet welds, especially at the longitudinal weld toes where they meet the reserved unwelded area, which will have an adverse impact on the fatigue performance of the overall structure during service. In view of this, for the accessory structure with longitudinal fillet joints welded on both sides, post-weld treatment can be carried out on the ends of the longitudinal fillet welds on both sides according to the actual situation; the specific limits of the following treatment belong to the category that those skilled in the art can fully grasp based on their own experience. The post-weld treatment includes the following two optional mechanical treatment methods:

[0084] Post-weld treatment method 1: Mechanical impact on both ends of the longitudinal fillet weld

[0085] By means of mechanical energy-induced hammering or high-frequency-induced steel ball impact, the relatively sharp longitudinal weld toes in the turning point areas at both ends of the longitudinal fillet weld are transformed into concave arc shapes or gentle transition slopes, as Figure 6 shown. There are no special restrictions on the specific shape and size of the mechanical impact area, as long as the principle of transforming the sharp transition into a smooth transition and reducing the height difference between the weld end and the base metal floor is followed.

[0086] Post-weld treatment method 2: Uniform grinding treatment on both ends of the longitudinal fillet weld

[0087] Using a special mechanical grinding tool with a spherical or conical end, uniformly grind the turning point areas at both ends of the longitudinal fillet weld, and transform the longitudinal weld toes with a significant height difference from the base metal floor and sharp transition into concave arc shapes or gentle transition slopes, as Figure 5 shown. There are no special restrictions on the specific shape and size of the uniform grinding treatment area, as long as the principle of transforming the sharp transition into a smooth transition and reducing the height difference between the weld end and the base metal floor is followed.

[0088] Embodiment

[0089] The welding method for improving the fatigue performance of the welded structure of rectangular non-load-bearing accessories of the present invention is implemented to verify the feasibility of the technical solution. A Q500MD high-strength steel base plate with a wall thickness of 20 mm is used as the base material. According to the specific steps described in the present invention, the fillet weld bead arrangement of the accessory, the intermediate starting and ending arc and the detour welding at both ends of the longitudinal fillet weld of the accessory are completed in sequence, and mechanical impact or homogenizing grinding treatment is performed on both ends of the longitudinal fillet weld after welding, to obtain an accessory welded structure with good welding quality and only longitudinal fillet joints on both sides. For this accessory welded structure, a pull-pull dynamic fatigue performance verification test is carried out under the conditions of stress ratio R = 0.5 and fatigue stress range Δσ = 80 MPa. The test stop condition is that the specimen generates fatigue cracks resulting in a significant decrease in the test frequency or the number of cycles reaches 1*10 7 times. By comparing and contrasting the test results under this fatigue test condition with the current mainstream standard design values, the optimization effect of the method described in the present invention on the fatigue performance of the accessory welded structure is comprehensively evaluated.

[0090] Figure 7 、 8 Figure 8 shows an example of the type and size of a fatigue evaluation specimen for a welded structure with only longitudinal fillet joints on both sides of a rectangular accessory located on a Q500MD high-strength steel base plate. The Q500MD thick-walled base plate is machined to ensure that the surface roughness Ra of the two cross-sections parallel to the loading direction is ≤ 3.2. The rectangular accessory is also machined to ensure the flatness of the contact surface between the bottom of the accessory and the thick-walled base plate, and the fitting gap is less than 1 mm. In order to ensure the welding quality of the subsequent longitudinal fillet weld of the accessory, the relevant areas including the thick-walled base plate and the accessory are polished and cleaned before welding to remove contaminants such as rust and oil that may cause a decrease in weld quality, and the area to be welded shows obvious metallic luster.

[0091] In this embodiment, considering the operating habits and implementation convenience in the field of large steel structure manufacturing, the shielded metal arc welding with solid wire and the shielded metal arc welding with flux-cored wire are respectively used to complete the welding of the welded structure with only longitudinal fillet joints on both sides of the rectangular accessory. The welding process specifications are as follows:

[0092] Process 1: Shielded metal arc welding with solid wire

[0093] The commonly used and cost-effective AWS A5.18 ER70S-G gas shielded solid wire in the industrial field is adopted. The wire diameter is 1.2 mm, the welding current I = 230 - 250 A, the welding voltage U = 26 - 28 V, the welding speed v = 290 - 320 mm / min, and the welding shielding gas is 80% Ar + 20% CO 2Argon-rich mixed gas, with gas flow rate f = 22 - 24 L / min. The wire extension length is 18 - 20 mm. To ensure uniform spreading of the longitudinal fillet weld of the accessory, a welding method with appropriate oscillation is adopted during welding. Especially at the detour points at both ends after starting arc and before stopping arc, the residence time during oscillation is 1.5 - 2 s to ensure smooth transition and complete spreading from the detour points at both ends to the base metal floor of the reserved unwelded area.

[0094] Process 2: Semiautomatic flux-cored wire gas shielded arc welding

[0095] Adopt the commonly used AWS A5.29 E71T1 gas shielded flux-cored wire in the industrial field, with a diameter of 1.2 mm, welding current I = 170 - 190 A, welding voltage U = 22 - 24 V, welding speed v = 180 - 200 mm / min, and the welding shielding gas is 80% Ar + 20% CO 2 Argon-rich mixed gas, with gas flow rate f = 20 - 21 L / min. The wire extension length is 20 - 22 mm. To ensure uniform spreading of the longitudinal fillet weld of the accessory, a welding method with appropriate oscillation is adopted during welding. At the detour points at both ends after starting arc and before stopping arc, the residence time during oscillation is 1 - 1.5 s, so as to ensure smooth transition and complete spreading from the detour points at both ends to the base metal floor of the reserved unwelded area.

[0096] Table 1 shows the longitudinal fillet weld characteristic parameters of the longitudinal fillet welded structure of the accessory with only two-sided longitudinal fillet welding obtained by the two different welding methods in the examples. Table 2 shows the conditional fatigue life of the longitudinal fillet welded structure of the accessory with only two-sided longitudinal fillet welding when the stress ratio R = 0.5 obtained by the examples. It can be seen that under the condition of the design stress range Δσ = 80 MPa commonly used in the current mainstream standards, the number of cycles obtained by the test of the welded structure of the accessory in the examples is much higher than the corresponding number of cycles in the design standards. Through the implementation of the welding method of the non-load-bearing accessory structure described in the present invention and comparing the fatigue performance data under its specific conditions with the design values of the current mainstream standards, it is confirmed that the fatigue performance optimization technology for the welded structure of non-load-bearing accessories in dynamic load scenarios described in the present invention has significant effects.

[0097] Table 1 Longitudinal fillet weld characteristic parameters of the welded structure of the accessory with two different welding methods

[0098]

[0099] Remarks:

[0100] 1. The length a of the unwelded area left at both ends of the longitudinal fillet weld and the detour distance b between the starting / stopping arc point and the end are the average values of the measured values on both sides;

[0101] 2. GMAW stands for semi-automatic gas metal arc welding with solid wire, and FCAW stands for semi-automatic flux cored arc welding with gas metal arc welding.

[0102] Table 2 Fatigue life of the welding structure conditions of accessories for two different welding methods

[0103]

[0104] Note: The corresponding number of cycles of the design standard is the number of cycles corresponding to the fatigue stress range Δσ = 80 MPa on the typical rectangular accessory fatigue S-N curve specified in the EN 1993 standard. This stress range value is also commonly used in the fatigue design of structural components.

Claims

1. A welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory, characterized in that: the weld is formed at a position avoiding the direction perpendicular to the load transfer direction during service; the welding is carried out by a roundabout and non-penetrating welding method starting / ending at the middle area of the weld bead; according to this welding method, the fatigue characteristics of the welded structure of the rectangular non-load-bearing accessory are converted into a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base material, and then the base material is set as high-strength steel to improve the fatigue performance of the welded structure.

2. The welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to claim 1, characterized in that: for the welding, the fillet weld width on the base plate side of the longitudinal fillet weld of the accessory is controlled within the range of 8 - 22 mm, the fillet weld width on the accessory side of the longitudinal fillet weld of the accessory is controlled within the range of 6 - 18 mm, and the fillet weld width on the base plate side of the longitudinal fillet weld of the accessory is controlled within the range of 1.0 - 1.45 times that of the fillet weld width on the accessory side of the longitudinal fillet weld of the accessory.

3. The welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to claim 1, characterized in that: forming the weld at a position avoiding the direction perpendicular to the load transfer direction during service specifically means: setting the welded structure as an accessory structure with only longitudinal corner joints on both sides.

4. The welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to claim 1, characterized in that: in the non-penetrating welding, the length of the unwelded area from the weld end to the accessory end is controlled according to the following constraints: wherein, a: the length of the unwelded area from the weld end to the accessory end, unit: mm; t: the thickness of the accessory, unit: mm.

5. The welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to claim 1, characterized in that: in the roundabout welding starting / ending at the middle area of the weld bead, the distance between the starting / ending point and the weld end is controlled according to the following constraints: wherein, b: the distance between the starting / ending point and the weld end, unit: mm; L: the length of the weld, unit: mm.

6. The welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to claim 1, characterized in that: the welding is carried out by the process of oscillating welding, and the oscillation residence time in the roundabout part after starting and in the roundabout part before ending is controlled within 1 - 2 s.

7. The welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to claim 2, characterized in that: the welding adopts the semi-automatic welding process of a solid wire with gas shielded metal arc welding or the semi-automatic welding process of a flux-cored wire with gas shielded metal arc welding.

8. The welding method for improving the fatigue performance of a welded structure of a rectangular non-load-bearing accessory according to claim 7, characterized in that: when adopting the semi-automatic welding process of a solid wire with gas shielded metal arc welding, the welding parameters are controlled as follows: wire diameter: 1.2 mm; Wire extension length: 13 - 22 mm; Welding current: 200 - 290 A; Welding voltage: 23 - 32 V; Welding speed: 260 - 400 mm / min.

9. A welding method for improving the fatigue performance of a welded structure of a rectangular non - load - bearing accessory according to claim 7, characterized in that: When using the semi - automatic welding process with a flux - cored wire for gas shielded arc welding, the welding parameters are controlled as follows: Wire diameter: 1.2 mm; Wire extension length: 16 - 25 mm; Welding current: 160 - 220 A; Welding voltage: 21 - 30 V; Welding speed: 160 - 250 mm / min.

10. A welding method for improving the fatigue performance of a welded structure of a rectangular non - load - bearing accessory according to claim 1, characterized in that: Before welding, the welding area is polished and cleaned, and the operation ends when the metal luster appears in the welding area.

11. A welding method for improving the fatigue performance of a welded structure of a rectangular non - load - bearing accessory according to claim 1, characterized in that: After welding, post - welding treatment is carried out on the weld end for the purpose of smooth transition and reducing the height difference between the weld end and the base metal bottom plate; The post - welding treatment is carried out by grinding or by mechanical impact.

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