Self-repairing smart connector based on shape memory alloy and installation method thereof

Abstract

The application relates to a self-repairing intelligent connecting piece based on a shape memory alloy and a mounting method thereof, and belongs to the technical field of civil engineering structures and mechanical connection. The self-repairing intelligent connecting piece comprises an SMA composite bushing composed of a steel sleeve and an SMA bushing with a circular hole, and first and second SMA functional gaskets with the same structure. The first and second SMA functional gaskets are both composed of an elliptical insertion part and a convex part above the elliptical insertion part, the diameter of the convex part being slightly larger than that of the elliptical insertion part. The SMA bushing with a compensation gap, the first SMA gasket and the second SMA gasket are used to realize damage self-repairing, solve the core problems that a traditional node bolt hole cannot be restored under a 400-ton heavy load, the dismounting efficiency is low, there is no intelligent sensing, and the service life is short, and the service life of the traditional node under heavy load is improved.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering structure and mechanical connection technology, and specifically relates to a self-healing intelligent connector based on shape memory alloy and its installation method. Background Technology

[0002] The passage of 400-ton super-heavy trucks and the relocation of steel structures in mining areas place stringent requirements on the load-bearing capacity, damage repairability, and reusability of connectors. Existing connectors face numerous technical bottlenecks in their application in mining areas: 1. Irreversible damage and high maintenance costs: Under heavy fatigue loads, traditional high-strength bolt joints are prone to plastic deformation of ≥0.5mm in bolt holes. Repair requires on-site hole enlargement (damaging the integrity of the connecting plate) or replacement of parts. The repair time for a single joint is ≥72 hours, the material loss rate is ≥40%, and the average number of maintenance times per year is ≥3. 2. Difficult to disassemble and reassemble, poor reusability: The bolts and holes are misaligned due to deformation of the nodes, and disassembly requires violent cutting (damage rate ≥35%). The success rate of secondary installation and docking is less than 50%, which cannot meet the requirements of "rapid relocation and cyclic reuse" of movable steel structures. 3. Lack of intelligent sensing and high safety risks: The lack of a damage monitoring mechanism and reliance on periodic visual inspections to identify problems can easily lead to missing the opportunity for early repair. In extreme cases, this may cause node failure and threaten structural safety. 4. Insufficient weather resistance and fatigue resistance: In the dusty and low-temperature (-40℃) environment of the mining area, the salt spray resistance of ordinary epoxy paint anti-corrosion layer is ≤2500 hours, and the fatigue life of nodes is ≤8 years, which is far lower than the 15-year design life of the main structure. Moreover, the stress concentration factor is as high as 1.8, which easily leads to bolt breakage problems.

[0003] The existing nodes are not specifically optimized for the "overload + self-healing + relocation and reuse" scenario, and there is an urgent need for a dedicated connection device that integrates high strength, self-healing and easy disassembly and assembly. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a self-healing intelligent connector based on shape memory alloy and its installation method, solving the core problems of traditional node bolt hole deformation that cannot be recovered under 400-ton heavy loads, low disassembly and assembly efficiency, lack of intelligent sensing, and short lifespan.

[0005] The technical solution adopted in this invention is: a self-healing intelligent connector based on shape memory alloy, the key technical points of which are: a high-strength bolt, an SMA composite bushing, a first SMA functional washer, and a second SMA functional washer; the SMA composite bushing includes a steel sleeve and an SMA bushing with a round hole, the SMA bushing being fitted inside the steel sleeve; the first SMA functional washer and the second SMA functional washer have the same structure, both consisting of an elliptical insertion part and a protrusion located above the elliptical insertion part with a diameter slightly larger than the elliptical insertion part.

[0006] Furthermore, resistance wires are embedded in the SMA bushing, the first SMA functional washer, and the second SMA functional washer. The resistance wires are adapted to a handheld electromagnetic induction heating device to heat the SMA bushing, the first SMA functional washer, and the second SMA functional washer to restore their deformation.

[0007] Furthermore, light-absorbing nano-coatings are coated on the outside of the SMA bushing, the first SMA functional washer, and the second SMA functional washer. The light-absorbing nano-coatings work in conjunction with near-infrared laser remote directional excitation to restore the deformation of the SMA bushing, the first SMA functional washer, and the second SMA functional washer.

[0008] An installation method for a self-healing smart connector based on shape memory alloy, which utilizes the self-healing smart connector based on shape memory alloy, includes the following steps: Factory prefabrication steps: Oval holes adapted to the first SMA functional washer are drilled on the main bridge connector, and oval holes adapted to the second SMA functional washer are drilled on the auxiliary connector; the round holes on the SMA bushing should provide ±20mm displacement buffer space to realize the deformation self-repair of the SMA bushing. The SMA composite bushing is pre-pressed into the bolt holes on the stiffening rib, and the two are in an interference fit relationship. The SMA bushing, the first SMA functional washer, and the second SMA functional washer were subjected to three heating-cooling shape memory training cycles to ensure that the phase transition temperature was stable at 45-75℃. On-site installation steps: Insert the first SMA6 functional washer into the elliptical hole of the main bridge connector and the second SMA functional washer into the auxiliary connector; use high-strength bolts to screw the main bridge connector, stiffening ribs and auxiliary connector together. The steps of damage repair: After the first and second SMA washers are installed, if the preload loss of the high-strength bolt is no more than 20% or the first SMA washer, second SMA washer, and SMA bushing are deformed by compression, the first SMA washer and second SMA washer are heated to restore them to their initial shape; the SMA bushing is heated to restore it to its initial shape.

[0009] Furthermore, resistance wires are embedded inside the SMA composite bushing, the first SMA functional washer, and the second SMA functional washer. A handheld electromagnetic induction heating device is used to heat the SMA composite bushing, the first SMA functional washer, and the second SMA functional washer to restore their deformation.

[0010] Furthermore, the SMA composite bushing, the first SMA functional washer, and the second SMA functional washer are coated with a light-absorbing nano-coating. Near-infrared laser remote directional excitation is used to restore the deformation of the SMA composite bushing, the first SMA functional washer, and the second SMA functional washer.

[0011] The beneficial effects of this invention are: the self-healing intelligent connector based on shape memory alloy and its installation method achieve damage self-repair through SMA bushing with compensation gap, first SMA washer and second SMA washer, which solves the core problems of traditional node bolt hole deformation that cannot be recovered under 400-ton heavy load, low disassembly and assembly efficiency, lack of intelligent sensing and short life, and improves the life of traditional nodes under heavy load. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a 3D diagram of the bridge structure in an embodiment of the present invention; Figure 2 This is an exploded view of the SMA composite bushing in an embodiment of the present invention; Figure 3 This is a schematic diagram of the SMA composite bushing assembly in an embodiment of the present invention; Figure 4 This is a schematic diagram of the first SMA functional washer in an embodiment of the present invention; Figure 5 This is an exploded view of the first SMA functional washer in an embodiment of the present invention; The numbers in the diagram are explained as follows: 1-Main bridge connector; 2-Auxiliary bridge connector; 3-SMA composite bushing; 31-Steel sleeve; 32-SMA bushing; 33-Bolt hole; 4-Reinforcing rib; 5-High-strength bolt; 6-First SMA functional washer; 7-Nut; 8-Second SMA functional washer. Detailed Implementation

[0014] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the following description is provided in conjunction with the accompanying drawings. Figures 1-5 The present invention will be further described in detail below with reference to specific embodiments.

[0015] This embodiment employs a self-healing intelligent connector based on shape memory alloy, including a high-strength bolt 5, an SMA composite bushing 3, and an SMA functional washer 4. The high-strength bolt 5 is an M22×100 10.9 grade shear-resistant high-strength bolt, with a thread length increased by 15mm compared to traditional bolts, resulting in an improved effective engagement length and increasing shear bearing capacity by over 22%. This embodiment can also be equipped with an R15 spherical washer, whose concave surface adapts to the bolt head, adaptively adjusting to a maximum bolt deflection angle of 3°, further optimizing deformation adaptability.

[0016] The SMA composite bushing 3 in this embodiment includes a steel sleeve 31 and an SMA bushing 32, with the SMA bushing 32 fitted inside the steel sleeve 31. The steel sleeve 31 is made of Q355qD material with a wall thickness of 2mm. The SMA bushing 32 is a nickel-titanium-based SMA bushing, and bolt holes 33 are pre-pressed on the nickel-titanium-based SMA bushing.

[0017] In this embodiment, the main bridge connector 1, stiffening rib 4, and auxiliary bridge connector 2 are arranged sequentially from top to bottom and connected by high-strength bolts 5. SMA composite bushings 3 are installed in the bolt holes on the stiffening rib 4. The high-strength bolts 5 pass through the bolt holes on the main bridge connector 1 and the stiffening rib 4, and then exit through the bolt hole on the lowest auxiliary bridge connector 2. A first SMA functional washer 6 is installed in the bolt hole on the main bridge connector 1, and a second SMA functional washer 8 is installed in the bolt hole on the auxiliary bridge connector. The upper end of the high-strength bolt 5 exits through the first SMA functional washer 6 of the main bridge connector, and the lower end of the high-strength bolt 5 exits through the second SMA functional washer 8 of the auxiliary bridge connector 2, and is then locked in place by nuts 7. In this embodiment, both the first SMA functional washer 6 and the second SMA functional washer 8 are made of iron-based material. The thickness of the first SMA functional washer 6 is the same as that of the main bridge connector 1, and the thickness of the second SMA functional washer is the same as that of the auxiliary bridge connector 2. They are used as washers during installation. When the bolt preload loss is ≥20% or the inner hole is deformed, heating can compensate for ≥80% of the preload and restore the roundness of the inner hole, thus preventing the high-strength bolt 5 from getting stuck.

[0018] In this embodiment, the outer surfaces of the SMA composite bushing 3, the first SMA functional washer 6, and the second SMA functional washer 8 are all coated with a composite anti-corrosion layer. The composite anti-corrosion layer includes: a Sa2.5 grade sandblasting rust removal layer, a 60μm thick fluorocarbon primer layer applied over the rust removal layer, and an 80μm thick fluorocarbon topcoat layer sprayed over the fluorocarbon primer layer. The total thickness of the composite anti-corrosion layer reaches 140μm. The salt spray resistance of this composite anti-corrosion layer is ≥5000 hours, which is twice that of traditional epoxy paint, and the dust adhesion resistance is improved by 32%, making it suitable for dusty and humid environments in mining areas.

[0019] This embodiment restores the deformation of the SMA bushing 32, the first SMA functional washer 6, and the second SMA functional washer 8 in two ways: The first method involves pre-embedding miniature copper-nickel alloy resistance wires within the SMA bushing 32, the first SMA functional washer 6, and the second SMA functional washer 8. A handheld electromagnetic induction heating device (power 1.2-1.8kW, frequency 25-45kHz) used in conjunction with the resistance wires is used to adjust the phase change of the SMA material, i.e., heating the SMA bushing 32, the first SMA functional washer 6, and the second SMA functional washer 8 to restore their shape, release the bolt preload, and ensure that the bolt can be easily removed.

[0020] The second method involves coating the SMA bushing 32, the first SMA functional washer 6, and the second SMA functional washer 8 with a light-absorbing nano-coating. The thickness of the light-absorbing nano-coating is 6-8 μm, and the absorption rate is not less than 92%. Near-infrared laser is used for remote directional excitation to regulate the phase transition of the SMA material, thereby restoring its shape.

[0021] The installation method of the self-healing connector based on shape memory alloy used in this embodiment is as follows: Factory prefabrication steps: The main bridge connector 1, auxiliary connector 2, and stiffening rib 4 are cut using CNC plasma cutting. Elliptical holes are drilled in the main bridge connector 1; these holes serve as bolt holes and are compatible with the first SMA functional washer 6. Similarly, elliptical holes are drilled in the auxiliary bridge connector 2; these holes serve as bolt holes and are compatible with the second SMA functional washer 8. The SMA composite bushing 3 is press-fitted into the circular bolt holes of the stiffening rib 4.

[0022] In this embodiment, the SMA composite bushing 3 is pre-pressed into the round bolt hole on the stiffening rib 4 at the factory, and the SMA bushing 32 and the round bolt hole are in an interference fit relationship. The steel sleeve 31 set on the outside of the SMA bushing 32 ensures the static load-bearing strength. When the extrusion deformation of the round hole on the SMA bushing 32 is no more than 2mm, it can be 100% restored to its original shape after excitation.

[0023] In this embodiment, the SMA bushing 3, the first SMA functional washer 6, and the second SMA functional washer 8 are subjected to three heating-cooling shape memory training cycles to ensure that the phase transition temperature is stable at 45-75℃.

[0024] In this embodiment, lifting lugs are pre-installed on the main bridge connector 1 to facilitate on-site hoisting.

[0025] Step 2: On-site installation steps: Using a crane with lifting lugs, the node consisting of the main bridge connector 1, auxiliary connector 2, and stiffening rib 4 is hoisted to the main beam docking position and its levelness is adjusted.

[0026] Use compressed air to blow away the dust from the surfaces of the first SMA functional gasket 6 and the second SMA functional gasket 8.

[0027] A first SMA6 functional washer is inserted into the elliptical hole of the main bridge connector 1, and a second SMA functional washer 8 is inserted into the auxiliary connector 2.

[0028] Connect the main bridge connector 1, stiffening rib 4, and auxiliary connector 2 using M22×100 high-strength bolts 5 in a top-to-bottom order. Initially tighten the high-strength bolts 5 to 50% of the design value using a torque wrench. Check the fit between the circular bolt holes on the main bridge connector 1 and the high-strength bolts, and the fit between the elliptical holes on the auxiliary connector 2 and the high-strength bolts. The bolt holes and elliptical holes should provide ±20mm of displacement buffer space to cooperate with the SMA bushing 32, the first SMA functional washer 6, and the second SMA functional washer 8 to achieve deformation self-repair, providing a foundation for subsequent damage repair. After achieving the required fit, tighten the high-strength bolts 5 to 100% of the design value, approximately 400 N·m.

[0029] Step 3: Damage repair steps.

[0030] After the first and second SMA washers are installed, if the preload loss of the high-strength bolt 5 is not less than 20% or the elliptical hole is deformed, use a handheld electromagnetic induction heating device to heat the first and second SMA washers. The power should be 1.2-1.8kW and the frequency 25-45kHz. When the first and second SMA functional washers reach their phase transition temperature, hold them at that temperature for 4 minutes. After cooling, use ultrasonic testing to check the deformation of the elliptical hole. An error of no more than 0.1mm in the deformation of the elliptical hole is considered acceptable.

[0031] Restoring the elliptical inner hole can prevent jamming during the disassembly or installation of high-strength bolts. After repair, tighten the bolts to the design preload, and ultrasonic testing confirms that the welded areas are free of cracks and the coating integrity is not less than 95%.

[0032] Step 4: Steps for relocation and reuse.

[0033] After the first and second SMA washers are restored to their original shapes, the elliptical holes that fit them are restored, thereby releasing the bolt preload and allowing the high-strength bolt 5 to be easily removed without jamming.

[0034] The main structure was hoisted to the new work station, and compressed air was used to blow away the dust from the surfaces of the first and second SMA functional washers.

[0035] Heating the first and second SMA functional washers allows them to automatically compensate for preload, completing a "blind connection" with a 100% success rate for secondary installation.

[0036] Repeat steps 2-4. Example

[0037] The difference between this embodiment and Embodiment 1 is that the method of coating the surface of the first SMA functional gasket and the second SMA functional gasket with a light-absorbing nano-coating is used instead of embedding a micro copper-nickel alloy resistance wire inside them.

[0038] In this embodiment, the thickness of the light-absorbing nano-coating is 6-8 μm, the absorption rate is not less than 92%, and it is remotely directionally excited by a near-infrared laser with a wavelength of 1064 nm and a power of 60-90 W, with a repair range accuracy of ±1.5 mm.

[0039] Performance evaluation of self-healing smart connectors based on shape memory alloys and their installation methods: This intelligent connector was applied to the transverse links of prefabricated steel box girders bearing the load of a 400-ton mining truck. When overload was detected causing a 1.2mm deformation in the bolt holes of the main bridge connector and auxiliary bridge connectors, the system alarmed. An induction-driven heating device was used to heat the node area; after 3 minutes, the SMA phase transition restored the bolt holes to their original roundness with an error of 0.07mm, allowing the bolts to be removed with a force of 38N. The node was hoisted to a new work station, high-strength bolts were inserted, and the SMA washers were heated, automatically compensating for the preload to 400N·m. The total time was 5.5 hours, with a 100% success rate. This connector can withstand temperatures as low as -40℃ and dusty environments, with a fatigue life of no less than 2 million cycles and a structural life of no less than 15 years.

[0040] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An installation method for a self-healing smart connector based on shape memory alloy, characterized in that, The specific structure of the self-healing smart connector based on shape memory alloy is as follows: it includes a high-strength bolt, an SMA composite bushing, a first SMA functional washer, and a second SMA functional washer; the SMA composite bushing includes a steel sleeve and an SMA bushing with a round hole, with the SMA bushing fitted inside the steel sleeve; the first SMA functional washer and the second SMA functional washer have the same structure, both consisting of an elliptical insertion part and a protrusion located above the elliptical insertion part with a diameter slightly larger than the elliptical insertion part. Its installation method includes the following steps: Factory prefabrication steps: Oval holes adapted to the first SMA functional washer are drilled on the main bridge connector, and oval holes adapted to the second SMA functional washer are drilled on the auxiliary connector; the round holes on the SMA bushing should provide ±20mm displacement buffer space to realize the deformation self-repair of the SMA bushing. The SMA composite bushing is pre-pressed into the bolt holes on the stiffening rib, and the two are in an interference fit relationship. The SMA bushing, the first SMA functional washer, and the second SMA functional washer were subjected to three heating-cooling shape memory training cycles to ensure that the phase transition temperature was stable at 45-75℃. On-site installation steps: Insert the first SMA functional washer into the elliptical hole of the main bridge connector and the second SMA functional washer into the auxiliary connector; use high-strength bolts to screw the main bridge connector, stiffening ribs and auxiliary connector together. The steps of damage repair: After the first and second SMA functional washers are installed, if the preload loss of the high-strength bolt is no more than 20% or the first SMA functional washer, the second SMA functional washer, and the SMA bushing are deformed by compression, the first SMA functional washer and the second SMA functional washer are heated to restore their initial shape; the SMA bushing is heated to restore its initial shape. The SMA bushing, the first SMA functional washer, and the second SMA functional washer are embedded with resistance wires. A handheld electromagnetic induction heating device is used to heat the SMA composite bushing, the first SMA functional washer, and the second SMA functional washer to restore their deformation. The SMA bushing, the first SMA functional washer, and the second SMA functional washer are coated with a light-absorbing nano-coating. Near-infrared laser remote directional excitation is used to restore the deformation of the SMA composite bushing, the first SMA functional washer, and the second SMA functional washer.

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