A laser additive reinforcement method for fatigue cracking of steel bridge welds

Abstract

The application discloses a laser additive reinforcement method for steel bridge weld fatigue cracking, comprising the following steps: step S1, performing flaw detection treatment on the top plate-U rib connecting weld of the orthotropic steel bridge deck, and determining the area to be reinforced; step S2, cleaning the area to be reinforced; step S3, performing laser additive printing along an S-shaped track in the corresponding area to be reinforced on the surface of the top plate and the U rib, and then printing a metal additive cladding layer layer by layer, so that the top plate-U rib connecting weld is reinforced by additive manufacturing; step S4, performing penetration flaw detection on the reinforced entity in a completely cooled state; if a damaged defect area to be repaired is detected, the area to be repaired is printed and repaired; the flaw detection and repair process is repeated until the reinforced entity no longer has a detectable defect; and step S5, smoothing the surface of the reinforced entity. The application is suitable for reinforcing the top plate-U rib connecting weld of the orthotropic steel bridge deck.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel structure construction, and particularly relates to a laser additive reinforcement method for fatigue cracking of a steel bridge weld. BACKGROUND

[0002] Orthotropic steel bridge decks have outstanding advantages such as light weight, high strength and convenient construction, and are widely used in large-span bridge engineering in China. However, the orthotropic steel bridge deck has complex structure and more welds, and under the repeated load of the bridge deck vehicle, the weld fatigue problem is more prominent. Among them, the top plate-U rib connecting weld has obvious geometric discontinuity, the stress concentration in this area is more serious, and there are unavoidable initial defect problems in the processing and welding processes, which leads to the fact that this area is one of the most prone to fatigue damage positions of the orthotropic steel bridge deck. Therefore, it is necessary to reinforce the fatigue cracking of the top plate-U rib connecting weld of the orthotropic steel bridge deck.

[0003] At present, the reinforcement methods for the fatigue cracking of the top plate-U rib connecting weld of the orthotropic steel bridge deck mainly include local stiffness reinforcement method and overall stiffness reinforcement method. The local stiffness reinforcement method mainly adds local plates in shape to the weld area through bolt connection and adhesive bonding and the like, and reduces the fatigue crack propagation at the top plate-U rib connecting position by increasing the local stiffness and reducing the stress amplitude at the connecting position. For example, carbon fiber reinforced polymer (CFRP) is bonded at the top plate-U rib connecting weld, and with the increase of the number of bonded layers, the fatigue repair efficiency also increases. Based on this, a method of prestressed CFRP reinforced steel structure is proposed, which reduces the permanent tensile stress in the steel member by introducing prestress to the carbon fiber material, reduces the average stress level and increases the fatigue life of the reinforced member. Angle steel can also be bonded at the top plate-U rib connecting weld to increase the local stiffness and improve the fatigue performance of the structure.

[0004] The overall stiffness reinforcement method needs to lay high-performance concrete on the top plate of the steel bridge deck, and form a combined bridge deck to bear force together with the existing steel bridge deck below through shear nails or structural glue, so as to reduce the fatigue stress amplitude at the weld, that is, to reinforce the weld in the form of increasing the overall stiffness of the orthotropic steel bridge deck. For example, a super-tough concrete layer STC is laid on the top plate of the orthotropic steel bridge deck.

[0005] The two reinforcement methods above effectively reduce the stress amplitude at the top plate-U rib connecting weld of the orthotropic steel bridge deck and prolong the fatigue life of the structure. However, there are still some problems in the reinforcement process. For the overall stiffness reinforcement method, the self-weight of the structure is significantly increased during the laying of high-performance concrete. Therefore, the overall stiffness reinforcement method is not suitable for the repair and reinforcement of old bridges and super-long span bridges that are not suitable for introducing additional self-weight. In addition, in order to reduce the adverse effects of the shrinkage of the laid high-performance concrete on the structure, the overall stiffness reinforcement method involves high-temperature curing of a large amount of concrete, which increases the construction cost. In comparison, the application scenarios of the local stiffness reinforcement method are more extensive. Although the local stiffness reinforcement method uses less material and does not introduce excessive self-weight, it introduces additional stiffness in the local structure through bonding. The reinforcement effect depends largely on the long-term bonding and synergy between the bonding plate and the base material, which is easily affected by the performance of the bonding agent and the construction environment.

[0006] Therefore, in order to solve the problems existing in the reinforcement methods for the fatigue cracking of the top plate-U rib connecting weld of the existing orthotropic steel bridge deck, the local stiffness reinforcement method needs to be optimized and a new technology needs to be used to introduce local stiffness that is well combined with the base material in the local weld. SUMMARY

[0007] The present application aims to at least partially solve one of the above technical problems in the prior art. To this end, the embodiments of the present application provide a laser additive reinforcement method for fatigue cracking of a steel bridge weld, which uses laser additive technology to locally reinforce the top plate-U rib connecting weld of an orthotropic steel bridge deck.

[0008] The laser additive reinforcement method for fatigue cracking of a steel bridge weld according to the embodiments of the present application comprises the following steps:

[0009] Step S1: performing a flaw detection treatment on the top plate-U rib connecting weld of the orthotropic steel bridge deck, and determining the area to be reinforced by additive manufacturing according to the fatigue crack distribution area obtained by the flaw detection;

[0010] Step S2: cleaning the area to be reinforced by additive manufacturing of the top plate and the U rib to remove the protective layer and the oxidation layer on the surface of the steel plate member;

[0011] Step S3: using laser cladding additive technology to perform laser additive printing along an S-shaped trajectory in the area to be reinforced by additive manufacturing corresponding to the surface of the top plate and the U rib, and then layer-by-layer printing to form a cladding layer of metal additive, thereby reinforcing the top plate-U rib connecting weld by additive manufacturing;

[0012] Step S4, cooling the reinforced entity of the cladding layer after additive manufacturing reinforcement, and performing a penetrating inspection on the reinforced entity in a fully cooled state; if a damaged defect area to be repaired is detected, the area is printed and repaired again using the laser cladding additive manufacturing technology; the inspection and repair process is repeated until the reinforced entity no longer has detectable defects.

[0013] Step S5, cooling the reinforced entity of the cladding layer after additive manufacturing reinforcement, and performing a penetrating inspection on the reinforced entity in a fully cooled state; if a damaged defect area to be repaired is detected, the area is printed and repaired again using the laser cladding additive manufacturing technology; the inspection and repair process is repeated until the reinforced entity no longer has detectable defects.

[0014] In an optional or preferred embodiment, the area to be reinforced by additive manufacturing is located in the obtuse angle area formed by the top plate and the U-rib, rather than directly repairing the fatigue cracks in situ by additive manufacturing reinforcement.

[0015] In an optional or preferred embodiment, the area to be reinforced by additive manufacturing is distributed along the length interval of the weld fatigue crack distribution area obtained by inspection, the thickness of the area to be reinforced by additive manufacturing is set to be 1.5 times or greater than the thickness of the U-rib, and the width of the area to be reinforced by additive manufacturing is set to be 20 times or greater than the thickness of the U-rib.

[0016] In an optional or preferred embodiment, the length of the area to be reinforced by additive manufacturing is set according to the location of the fatigue crack: for fatigue cracks located in the middle of the plate, the length of the area to be reinforced by additive manufacturing should completely contain the length of the weld fatigue, and each of the two boundaries relative to the length direction of the weld fatigue should extend outward by at least 5 cm; for fatigue cracks located at the edge of the plate that cannot meet the minimum extension requirement, the thickness of the additive reinforcement layer should be appropriately increased, and the increased thickness should not be less than one-fourth of the thickness of the U-rib.

[0017] In an optional or preferred embodiment, the inspection process in step S1 uses ultrasonic weld inspection technology, and during the inspection process, the probe is always directed at the top plate-U-rib connecting weld, moves along the top plate-U-rib connecting weld in a zigzag manner, and slightly swings the probe at an angle of 10-15° to discover defects of various shapes and orientations, thereby determining the weld fatigue crack distribution area.

[0018] In an optional or preferred embodiment, the cleaning operation in step S2 includes: first, removing impurities from the surface of the top plate and the U-rib with acetone, and removing the protective layer and oxide film on the surface of the steel plate component with a steel wire brush.

[0019] In an optional or preferred embodiment, in step S3, a multi-axis mechanical arm is used to adjust the position of the welding gun head during additive manufacturing reinforcement.

[0020] In an optional or preferred embodiment, in step S3, the additive material used in the laser cladding technology is a metal powder material combined with the steel plate substrate, and the process parameters are as follows: laser power is 2200W, the spot shape is rectangular, the spot size is 5mm*2.2mm, the inter-pass overlap rate is 60%, and the scanning line speed is 1.2m / min.

[0021] In an optional or preferred embodiment, in step S3, during the process of additive manufacturing reinforcement, a multi-layer additive manufacturing process is used, and the thickness of each additive manufacturing reinforcement layer is 0.8-1.0mm.

[0022] In an optional or preferred embodiment, in step S3, the protective gas used in the laser cladding additive technology is argon or helium.

[0023] Based on the above technical solution, the embodiments of the present application have at least the following beneficial effects: in the above technical solution, the cladding layer of the metal additive is formed by layer-by-layer accumulation through the laser cladding additive technology, which can reinforce the roof-U rib connecting weld, change the force transmission path, improve the local stiffness of the weld area, greatly reduce the stress amplitude of the area under the condition of bearing fatigue load, and prolong the fatigue service life of the structure. And the additive reinforcement entity printed by the laser cladding additive technology presents metallurgical bonding with the original metal plate structure, which ensures that the roof-U rib connecting weld has good stress performance and long-term bearing capacity. Compared with the traditional adhesive bonding method, the additional local stiffness introduced by the present application can effectively play a long-term role. BRIEF DESCRIPTION OF DRAWINGS

[0024] The present application will be further described below in conjunction with the drawings and examples;

[0025] Figure 1 is a perspective view of the roof-U rib connecting weld before reinforcement in the embodiment of the present application;

[0026] Figure 2 is a perspective view of the roof-U rib connecting weld after reinforcement in the embodiment of the present application;

[0027] Figure 3 is a side view of the roof-U rib connecting weld after reinforcement in the embodiment of the present application. DETAILED DESCRIPTION

[0028] This part will describe the specific embodiments of the present application in detail, and the preferred embodiments of the present application are shown in the drawings. The drawings serve to supplement the description in the text part of the specification, so that people can intuitively and visually understand each technical feature and the overall technical scheme of the present application. However, it cannot be understood as a limitation on the protection scope of the present application.

[0029] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right and the like, is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0030] In the description of the present application, one or more is understood as one or more, more than two is understood as more than two, greater than, less than, more than and the like are understood as not including the number, above, below, within and the like are understood as including the number. If the first, second is described, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the sequence of technical features indicated.

[0031] In the description of the present application, unless otherwise explicitly limited, the words such as setting, mounting, connecting and the like should be broadly understood, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0032] Reference Figure 1 A structural schematic diagram before reinforcing the top plate-U rib connecting weld is shown, wherein the fatigue crack position at the top plate-U rib connecting weld is shown in a local enlarged manner, as shown in Figure 1 The weld between the U rib 2 and the top plate 1 has a fatigue crack. The U rib refers to a U-shaped rib plate, and the U rib includes a bottom plate and side plates on both sides, which are connected with the top plate.

[0033] Figure 2 A structural schematic diagram after reinforcing the top plate-U rib connecting weld is shown, and Figures 1 to 2 A laser additive reinforcement method for fatigue cracking of a steel bridge weld is described below, comprising the following steps:

[0034] S1, the top plate-U rib connecting weld of the orthotropic steel bridge deck is subjected to flaw detection treatment, and the fatigue crack distribution area of the weld is determined according to the fatigue crack distribution area obtained by the flaw detection. In the flaw detection treatment, the probe is always directed at the top plate-U rib connecting weld, moves along the top plate-U rib connecting weld in a zigzag manner, and slightly swings the probe at an angle of 10-15° to find defects of various shapes and orientations, so as to determine the fatigue crack distribution area of the weld.

[0035] As Figure 1The fatigue crack of the roof-U rib connecting weld is located inside the structure, that is, inside the weld itself or the acute angle area of the roof-U rib connecting position, and the fatigue crack cannot be directly subjected to the additive manufacturing reinforcement treatment. The local stiffness reinforcement method is adopted in the present application, the obtuse angle area of the roof-U rib connecting position is subjected to local additive treatment, additional local stiffness is introduced, and the force transmission path is changed to prolong the fatigue life of the structure. Specifically, the additive reinforcement area is located in the obtuse angle area formed by the roof and the U rib, rather than directly in situ additive reinforcement repair of the fatigue crack.

[0036] In some embodiments, the additive reinforcement area is distributed along the length interval of the fatigue crack distribution area obtained by flaw detection, the thickness of the additive reinforcement area is set to 1.5 times or greater than the U rib thickness, and the width of the additive reinforcement area is set to 20 times or greater than the U rib thickness.

[0037] The length of the additive reinforcement area is set according to the position of the fatigue crack: for the fatigue crack located in the middle of the plate, the length of the additive reinforcement area should be able to completely contain the length of the weld fatigue, and the two boundaries relative to the length direction of the weld fatigue should each extend outward by at least 5 cm; for the fatigue crack located at the edge of the plate that cannot meet the minimum extension requirement, the thickness of the additive reinforcement layer should be appropriately increased, and the increased thickness should not be less than one-fourth of the U rib thickness.

[0038] In the present embodiment, fatigue cracks exist along the entire length of the weld, and additive reinforcement treatment is required for the entire length of the weld, wherein the width s of the additive reinforcement area is 20 times the U rib thickness, the length of the additive reinforcement area is along the entire length of the weld, and the thickness of the additive reinforcement area should be thickened to 1.75 times the U rib thickness. The U rib thickness refers to the thickness of the side plate in the U-shaped rib plate.

[0039] Step S2, clean the additive reinforcement area of the roof and the U rib, and remove the protective layer and the oxide layer on the surface of the steel plate member. The cleaning operation includes: first, remove the impurities on the surface of the roof and the U rib with acetone, and remove the protective layer and the oxide film on the surface of the steel plate member with a stainless steel wire brush. The steel plate member refers to the roof and the U rib.

[0040] Step S3, laser cladding additive technology is adopted to perform laser additive printing along the S-shaped trajectory in the corresponding additive reinforcement area on the surface of the roof and the U rib, and then layer-by-layer printing is performed to form a cladding layer of metal additive, thereby reinforcing the roof-U rib connecting weld by additive manufacturing. In the process of laser additive printing, the layer-by-layer printing direction is perpendicular to the side plate of the U rib.

[0041] It should be noted that after the completion of the additive printing of a layer, the welding torch head is lifted to maintain a constant distance from the laser cladding reinforcement layer, and the scanning printing path of each layer is completed layer by layer, and finally a metal additive reinforcement body 3 is formed. At the same time, it should be noted that the difference between the interlayer printing direction and the layer-by-layer printing direction, the reinforcement body 3 as shown in Figure 3 is formed in a single layer, and the weld bead is perpendicular to the top plate-U rib connecting weld.

[0042] Step S4, cooling the additive manufacturing reinforced cladding layer of the reinforcement body, and performing penetration detection on the reinforcement body in a completely cooled state; if a damaged defect area to be repaired is detected, that is, the reinforcement body has defects, the damaged area to be repaired is repaired again by using the laser cladding additive manufacturing technology.

[0043] Repeat the detection and repair process until the reinforcement body no longer has detectable defects. The detection and repair process refers to the process of detecting defects by detection and repairing.

[0044] Step S5, cooling the additive manufacturing reinforced cladding layer of the reinforcement body, and performing grinding and softening treatment on the reinforcement body in a completely cooled state to smooth the surface of the reinforcement body.

[0045] In this example, the metal additive manufacturing technology used is laser cladding additive manufacturing technology, and the additive material used is a metal powder material that is well combined with the steel plate material in this example. The process parameters used are: laser power is 2200W, spot shape is rectangular, spot size is 5mm x 2.2mm, weld bead overlap rate is 60%, and scanning line speed is 1.2m / min. During the additive manufacturing reinforcement process, a multi-layer additive manufacturing process is used, and the thickness of each additive manufacturing reinforcement layer is 0.8-1.0mm, and argon or nitrogen is used as the protective gas. A multi-axis mechanical arm is used to adjust the position of the welding torch head during additive manufacturing reinforcement.

[0046] The laser additive reinforcement method for fatigue cracking of steel bridge welds provided by the application is suitable for additive reinforcement of fatigue cracking of the top plate-U rib connecting weld of the orthotropic steel bridge deck, the application improves the deficiencies of the traditional reinforcement method, a new technology, i.e., laser cladding additive technology, is adopted to enhance the connecting effect between the reinforcement solid layer and the original structure, metallurgical bonding is formed at the connecting surface, and the problems of poor reinforcement effect and short duration caused by aging or insufficient bonding force of the traditional local stiffness reinforcement method are solved. In the embodiments of the application, the crack is in the acute angle area of the weld inside or the top plate-U rib connecting area, the position is hidden, and the in-situ repair cannot be directly performed on the structural damage area (crack) according to the traditional laser additive repair method, therefore, the application does not directly perform in-situ repair on the crack, but performs additive reinforcement on the obtuse angle area of the top plate-U rib connecting area, the force transmission path is changed, and the fatigue life of the original structure is effectively prolonged. In addition, due to the flexibility inherent in the laser cladding additive technology, targeted reinforcement of the top plate-U rib weld can be realized, i.e., through weld detection, additive reinforcement is performed at the fatigue cracking area, and the weld area without fatigue cracking remains unchanged, the use of materials is minimized, and the material utilization rate is improved.

[0047] The embodiments of the application are described in detail above in combination with the drawings, but the application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art in the technical field without departing from the purpose of the application.

Claims

1. A laser additive reinforcement method for fatigue cracking of steel bridge welds, characterized in that, Includes the following steps: Step S1: Perform flaw detection on the top plate-U rib connection weld of the orthotropic steel bridge deck. Determine the area to be reinforced by additive manufacturing based on the fatigue crack distribution area of ​​the weld obtained from the flaw detection. The fatigue crack of the top plate-U rib connection weld is located inside the weld itself or in the acute angle area of ​​the top plate-U rib connection. Step S2: Clean the area to be reinforced by additive manufacturing of the top plate and U-rib, and remove the protective layer and oxide layer on the surface of the steel plate component; Step S3: Using laser cladding additive manufacturing technology, laser additive printing is performed along an S-shaped trajectory in the area to be reinforced on the surface of the top plate and U-rib, and then layer by layer is printed to form a cladding layer of metal additive manufacturing, thereby reinforcing the weld of the top plate-U-rib connection by additive manufacturing. The area to be reinforced by additive manufacturing is located in the obtuse angle area formed by the top plate and U-rib, rather than directly reinforcing and repairing fatigue cracks in situ. Step S4: Cool the reinforced entity of the cladding layer after additive manufacturing reinforcement, and perform penetrant testing on the reinforced entity in a fully cooled state; if a damaged area is detected to be repaired, the area to be repaired is repaired again using laser cladding additive manufacturing technology. Repeat the flaw detection and repair process until no detectable defects are found in the reinforced entity; Step S5: Cool the reinforced entity of the cladding layer after additive manufacturing reinforcement, and perform a grinding and softening treatment on the reinforced entity in a completely cooled state to smooth the surface of the reinforced entity. The region to be reinforced by additive manufacturing is distributed along the length range of the weld fatigue crack distribution area obtained by flaw detection. The thickness of the region to be reinforced by additive manufacturing is set to 1.5 times or greater than the thickness of the U-rib, and the width of the region to be reinforced by additive manufacturing is set to 20 times or greater than the thickness of the U-rib. The length of the area to be reinforced by additive manufacturing is set according to the location of the fatigue crack: for fatigue cracks located in the middle of the plate, the length of the area to be reinforced by additive manufacturing should completely include the length of the weld fatigue, and extend outward by at least 5 cm from each of the two boundaries relative to the weld fatigue length direction; for fatigue cracks located at the edge of the plate that cannot meet the minimum extension requirement, the thickness of the additive reinforcement layer should be appropriately increased, and the increased thickness should not be less than one-quarter of the thickness of the U-rib.

2. The laser additive reinforcement method for fatigue cracking of steel bridge welds according to claim 1, characterized in that: The flaw detection process in step S1 uses ultrasonic weld flaw detection technology. During the flaw detection process, the probe is always facing the top plate-U rib connection weld and moves in a sawtooth pattern along the top plate-U rib connection weld. The probe is also slightly swung at an angle of 10~15° to detect defects of various shapes and orientations, thereby determining the distribution area of ​​weld fatigue cracks.

3. The laser additive reinforcement method for fatigue cracking of steel bridge welds according to claim 1, characterized in that, The cleaning operation in step S2 includes: first, removing impurities from the surface of the top plate and U-rib with acetone, and then removing the protective layer and oxide film from the surface of the steel plate component with a wire brush.

4. The laser additive reinforcement method for fatigue cracking of steel bridge welds according to claim 1, characterized in that: In step S3, a multi-axis robotic arm is used to adjust the position of the welding torch head during additive manufacturing reinforcement.

5. The laser additive reinforcement method for fatigue cracking of steel bridge welds according to claim 1, characterized in that, In step S3, the additive material used in the laser cladding additive technology is a metal powder that is bonded to the steel plate substrate. The process parameters are as follows: laser power is 2200W, the spot shape is rectangular, the spot size is 5mm×2.2mm, the overlap rate between weld beads is 60%, and the scanning line speed is 1.2m / min.

6. The laser additive reinforcement method for fatigue cracking of steel bridge welds according to claim 1, characterized in that: In step S3, during the additive manufacturing reinforcement process, a multi-layer additive manufacturing process is adopted, and the thickness of each additive manufacturing reinforcement layer is 0.8~1.0mm.

7. The laser additive reinforcement method for fatigue cracking of steel bridge welds according to claim 1, characterized in that: In step S3, the protective gas used in laser cladding additive manufacturing technology is argon or helium.

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