A shape memory alloy based steel structure intelligent active reinforcement system and method

Abstract

The application discloses a kind of steel structure intelligent active reinforcement systems and methods based on shape memory alloy, belong to structural engineering reinforcement technical field.The system includes reinforcement made of iron-based shape memory alloy and monitoring and control unit.The Fe-SMA reinforcement is activated by applying activation energy, thereby generating active compressive stress to steel structure matrix, effectively inhibiting the initiation and propagation of fatigue cracks.The monitoring and control unit includes a sensor assembly and a controller, which can sense the stress, strain and crack state of the structure in real time, and dynamically regulate the activation energy applied to the Fe-SMA reinforcement based on the above information, to achieve intelligent closed-loop control of the reinforcement prestress.The system solves the problem of poor effect and easy failure of traditional reinforcement methods in high temperature and high stress amplitude environment, and realizes self-adaptation, controllability and long-term safety of steel structure reinforcement.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering structural reinforcement technology, and in particular relates to an intelligent active reinforcement system and method for steel structures based on shape memory alloys. Background Technology

[0002] Manufacturing is the lifeblood of my country's economy, and metallurgical plants, as a key link in metal material manufacturing, are crucial for the continuity and safety of their production. Heavy-duty crane beams, commonly found in these plants, bear dynamic cyclic loads for extended periods and are critical structural components. However, in core areas such as smelting, these crane beams not only endure high-amplitude alternating stresses but are also continuously subjected to thermal radiation from furnaces reaching nearly 1500°C, causing localized temperatures to exceed 250°C. This coupling effect of high temperature and high stress amplitude makes fatigue problems in steel crane beams extremely prominent. Fatigue failure is the process by which cracks initiate and gradually propagate in steel under alternating stresses far below its yield strength, ultimately leading to brittle fracture of the component. In recent years, hundreds of cases of fatigue failure of steel crane beams have occurred in metallurgical plants nationwide, even triggering collapses and forcing frequent plant shutdowns for maintenance. Given the complexity of metallurgical production processes and the high cost of restarting, frequent maintenance severely restricts production efficiency and causes significant economic losses.

[0003] Currently, the crack arrestor hole method is commonly used in engineering to treat fatigue cracks in steel structures. This method involves drilling a crack arrestor hole at the crack tip to eliminate stress concentration, achieving a quick, economical, and temporary treatment that does not disrupt traffic. However, under severe working conditions with out-of-plane deformation or high stress amplitude, the stress concentration effect around the crack arrestor hole remains significant, greatly reducing its life-extending effect. Cracks often bypass or penetrate the crack arrestor hole and continue to propagate, thus only addressing the symptoms, not the root cause.

[0004] To improve the fatigue performance of the crack-arresting hole region, cold extrusion technology has been applied to strengthen metal hole structures. This technology applies radial pressure to the hole wall using a mandrel or expansion sleeve, causing plastic deformation and introducing a favorable residual compressive stress field around the hole, thereby effectively delaying the initiation and propagation of fatigue cracks. However, in the high-temperature environment of a metallurgical plant, the metal material undergoes creep, causing the residual stress introduced by cold extrusion to relax, making it difficult to guarantee its long-term strengthening effect.

[0005] In the field of active reinforcement technology, iron-based shape memory alloys (Fe-SMA) have shown great potential due to their unique shape memory effect, excellent mechanical properties, and low cost. Fe-SMA materials can generate significant recovery stress upon activation, providing active reinforcement to damaged structures. Studies have shown that they exhibit good prestress retention under repeated loading, with a prestress loss of only about 14% over 50 years, and their resistance to stress relaxation is far superior to traditional steel, making them particularly suitable for structures subjected to long-term loads. However, how to efficiently and reliably anchor Fe-SMA materials to steel structures operating in high-temperature environments is a key challenge restricting their application. Traditional adhesive bonding methods are greatly affected by temperature and humidity, and are prone to aging and failure in high-temperature environments, resulting in insufficient reliability. Meanwhile, conventional high-strength bolt connections are susceptible to creep damage, decreased fatigue resistance, and prestress relaxation under long-term high-temperature heat radiation and vibration, leading to connection failure.

[0006] Therefore, developing a comprehensive technology and method that can adapt to harsh environments with high temperature and high stress amplitude, integrating rapid crack treatment, long-term active reinforcement and high-performance anchoring, to fundamentally solve the problem of fatigue repair and reinforcement of key components such as steel crane beams in metallurgical plants, has become a technical bottleneck that the engineering community urgently needs to overcome. Summary of the Invention

[0007] To address the aforementioned technical problems, the technical solution adopted by this invention is as follows: According to a first aspect of the present invention, a smart active reinforcement system for steel structures based on shape memory alloys is provided, the system comprising: At least one Fe-SMA reinforcement made of iron-based shape memory alloy, wherein the Fe-SMA reinforcement is activated by an activation energy application method, thereby generating active compressive stress on the steel structure base material to be reinforced; A monitoring and control unit, comprising a sensor assembly disposed on the steel structure base material and / or the Fe-SMA reinforcement, and a controller communicatively connected to the sensor assembly; The controller is configured to dynamically adjust the activation energy applied to the Fe-SMA reinforcement based on monitoring data fed back by the sensor components.

[0008] According to a second aspect of the present invention, a method for intelligent active reinforcement of steel structures based on shape memory alloys is provided, comprising the following steps: S1, at least one Fe-SMA reinforcement made of iron-based shape memory alloy is installed in the area of ​​the steel structure to be reinforced.

[0009] S2, the Fe-SMA reinforcement is activated by applying activation energy, so that the Fe-SMA reinforcement generates active compressive stress on the steel structure base material.

[0010] S3, using sensor components to monitor the status of the steel structure base material and / or the Fe-SMA reinforcement in real time.

[0011] S4. Based on the monitoring data fed back by the sensor components, the activation energy applied to the Fe-SMA reinforcement is dynamically adjusted by the controller to achieve intelligent control of the active compressive stress.

[0012] The present invention has at least the following beneficial effects: 1. Active Strengthening and Long-Term Effectiveness: Utilizing the shape memory effect of Fe-SMA, active compressive stress is applied to the structure, fundamentally offsetting part of the working tensile stress and significantly improving the fatigue life and strength reserve of the structure. The excellent stress relaxation resistance of Fe-SMA ensures the long-term effectiveness of the strengthening effect.

[0013] 2. Intelligent and Adaptive: By integrating sensors and controllers, the system possesses the ability to perceive, decide, and respond. It can dynamically adjust the prestress magnitude according to the actual load state of the structure, achieving reinforcement as needed, optimizing energy consumption while ensuring safety, and coping with changing load conditions.

[0014] 3. Excellent high-temperature adaptability: The specially designed Fe-SMA material (phase change temperature 70°C-150°C) and optimized anchoring technology (such as ring groove rivets) enable the system to work stably in high-temperature heat radiation environments such as metallurgical plants, effectively solving the problems of traditional adhesive and bolt connections being prone to aging, creep and loosening at high temperatures.

[0015] 4. High repair efficiency and minimal impact: This technology enables rapid reinforcement without interrupting production or with only short-term downtime. It is easy to implement and avoids the long-term downtime caused by traditional welding or large-scale component replacement, greatly reducing economic losses.

[0016] Although the anti-crack hole method, cold extrusion technology, iron-based shape memory alloys (Fe-SMA), and high-performance rivets are all known technologies in their respective fields, it is not obvious to those skilled in the art to systematically integrate them under specific working conditions and endow them with intelligent properties.

[0017] The solution presented in this application is not a simple superposition of the aforementioned technologies, but rather a cross-disciplinary, functionally synergistic systematic creation based on a profound understanding of the complex coupled damage mechanism of high temperature-high stress amplitude-fatigue cracking. Specifically: First, those skilled in the art often hold a technical bias when dealing with fatigue cracks in high-temperature environments: they believe that high temperatures lead to material performance degradation and prestress relaxation, thus rendering active strengthening techniques (such as prestressed cables) ineffective or unreliable in such conditions. This bias prevents them from considering any active strengthening schemes that rely on the thermodynamic properties of the material. This invention reverses this bias by not only actively employing Fe-SMA but also cleverly resolving this contradiction by precisely designing its phase transformation activation temperature (70°C-150°C) within a safe window that is below the base material's performance degradation temperature and above the environmental disturbance temperature.

[0018] Secondly, existing technologies typically treat structural reinforcement and monitoring as two separate processes. This application integrates the Fe-SMA reinforcement component with sensors and controllers into a sensing-decision-execution intelligent closed-loop system, enabling the reinforced structure to shift from passive load-bearing to active adaptation, which exceeds the design paradigm of conventional structural reinforcement. Those skilled in the art are accustomed to providing a static, fixed reinforcement solution and would not readily conceive of creating a dynamic system capable of adjusting its prestress according to actual load conditions.

[0019] In summary, the present invention provides a novel technical concept that achieves a synergistic enhancement effect of "1+1>2" through deep functional coupling and collaboration of multiple components. This solution, which spans multiple technical fields such as materials, mechanics, sensing and control, cannot be directly and unambiguously derived from existing technologies.

[0020] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0022] Figure 1 A structural block diagram of a steel structure intelligent active reinforcement system based on shape memory alloy provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the reinforcement component in implementation method A; Figure 3 This is a schematic diagram of the steel structure's base material; Figure 4a and Figure 4bThese are schematic diagrams of the reinforcement components in Implementation Method B; Figure 5 This is a schematic diagram of the firmware installation in implementation method C; Figure 6 The flowchart illustrates a method for intelligent active reinforcement of steel structures based on shape memory alloys, as provided in this embodiment of the invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] It should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe the steps as sequential processes, many of these steps can be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the steps can be rearranged. A process can be terminated when its operation is complete, but it may also have additional steps not included in the figures. A process can correspond to a method, function, procedure, subroutine, subroutine, etc.

[0026] (Example 1) This embodiment provides an intelligent active reinforcement system for steel structures based on shape memory alloys, used for heavy-duty crane beams in metallurgical plants. For example... Figure 1 As shown, the system includes: at least one reinforcement 1 made of iron-based shape memory alloy (Fe-SMA) and a monitoring and control unit 2.

[0027] (Fe-SMA reinforcement) In this embodiment of the invention, the Fe-SMA reinforcement 1 is activated by applying activation energy, thereby generating active compressive stress on the steel structure base material to be reinforced. Specifically, the Fe-SMA reinforcement 1 generates shape recovery by external energy activation, thereby applying active compressive stress to the steel structure base material to be reinforced (such as the lower flange of a crane beam).

[0028] The Fe-SMA reinforcement is installed in the stress concentration area or fatigue crack damage area of ​​the steel structure base material. The stress concentration area includes crack tips, areas around mechanical holes, or areas of abrupt geometric changes in the steel structure base material. Taking a heavy-duty crane beam in a metallurgical plant as an example, the Fe-SMA reinforcement 1 should be installed in the tension zone of the lower flange of the crane beam, particularly in the upper flange brake truss connection node plate, the end of the stiffening rib weld, or the area along the extension line of a discovered fatigue crack tip. The principle is that under cyclic loading, these areas of the crane beam exhibit high stress concentration, making them the most susceptible locations for fatigue crack initiation and propagation. Precisely installing the Fe-SMA reinforcement (whether a grooved rivet or a patch) at these "critical points" can most effectively apply active compressive stress, offsetting some of the working tensile stress, thereby significantly improving the fatigue life of the structure.

[0029] This embodiment provides the following typical but non-limiting implementation method: Implementation Method A: Fe-SMA Ring Groove Rivet Reinforcement In this embodiment, the Fe-SMA reinforcement can be an Fe-SMA ring groove rivet 7 (such as...). Figure 2 As shown, after the Fe-SMA ring groove rivet is installed and activated, it can generate recovery deformation in both the axial and radial directions based on its shape memory effect, thereby forming an interference fit in the connection hole of the steel structure base material and applying active compressive stress in both the radial and axial directions to the area around the hole.

[0030] In the Figure 3 Before reinforcing the steel structure base material 3 shown, the specific reinforcement location must first be determined. Non-destructive testing methods such as magnetic particle testing or ultrasonic testing can be used to comprehensively inspect the steel structure base material to accurately identify macroscopic fatigue cracks 4 or potential microscopic crack initiation points. For existing fatigue cracks, arrestor holes 5 should be drilled at the tip of the crack in its expected propagation direction to eliminate stress singularities at the crack tip. For typical areas where no cracks are found but stress analysis using finite element software confirms high stress concentration, connection holes can also be directly drilled at these locations as reinforcement points.

[0031] The installation and activation process of the Fe-SMA ring groove rivet mainly includes the following steps: (1) Installation and pre-tightening: Place the Fe-SMA ring groove rivet into the crack-stopping hole or connecting hole, and use a special rivet gun to perform riveting operation to ensure that it reaches the preset pre-tightening force without damaging the material.

[0032] (2) Activation and Enhancement: Two key preparatory steps are required before performing the activation operation: Base material temperature confirmation: Use non-contact temperature measurement devices such as infrared thermometers to confirm the temperature of the base material in the area to be reinforced, and ensure that it is within a safe range to avoid adverse effects on the mechanical properties of the base material caused by improper heat input.

[0033] Process parameter settings: Strictly follow the temperature-time process card developed for the specific Fe-SMA material used to set heating parameters, aiming to ensure that the material undergoes sufficient austenitic phase transformation while preventing overheating.

[0034] After preparation, the installed rivets are heated using a local heating device. This device raises the temperature above the austenitic phase transformation end temperature (Af point) and maintains it for a predetermined time to complete activation. For Fe-SMA ring groove rivets, a high-frequency induction heating device is preferred. This device is equipped with a dedicated induction coil adapted to the shape of the rivet head, enabling rapid (e.g., within 30 seconds) and precise local heating. This method concentrates energy, has high thermal efficiency, and minimizes the thermal impact on the surrounding base material.

[0035] During activation, the Fe-SMA annular groove rivet undergoes an austenitic phase transformation, which macroscopically manifests as radial expansion and axial contraction. This synergistic deformation effect produces two key effects: Interference fit is formed: the radial expansion between the rivet shank and the hole wall creates a tight interference fit, which enhances the tightness of the connection.

[0036] Applying active stress: Radial compressive stress and axial clamping stress are applied simultaneously to the base material area around the hole, thereby forming a three-dimensional active compressive stress field.

[0037] This compressive stress field can effectively offset part of the external working tensile stress, significantly reduce the stress concentration and stress amplitude in the hole wall area, thereby greatly improving the fatigue strength of the hole structure and effectively suppressing or preventing the propagation of existing fatigue cracks.

[0038] In a preferred embodiment of the present invention, the thermal induction recovery temperature of the Fe-SMA ring groove rivet material, i.e., its austenitic phase transformation end temperature (Af point), is between 70°C and 150°C. To better meet the long-term service requirements of high-temperature environments such as metallurgical plants, a material formulation with an austenitic phase transformation end temperature between 120°C and 150°C is preferred. In actual operation, the corresponding activation heating temperature should be ensured to be higher than the specific Af point of the selected material to ensure that its shape memory effect is fully activated.

[0039] Setting the phase transformation activation temperature (Af point) of iron-based shape memory alloy (Fe-SMA) between 70°C and 150°C is a key and ingenious design of this invention addressing the specific technical challenge of "steel structure reinforcement under high-temperature environments." This temperature range selection brings several synergistic advantages, specifically as follows: 1. A perfect balance between construction feasibility and high-temperature adaptability Lower limit 70°C: Ensure project feasibility Easy to activate: The activation threshold of 70°C is relatively low and can be easily achieved using conventional, low-cost engineering heating equipment (such as heating blankets, hot air guns, or small induction heaters), without the need for special or high-energy-consuming devices, which greatly facilitates on-site construction.

[0040] Fast and efficient: It takes a short time to heat to this temperature range and consumes little energy, meeting the urgent needs of metallurgical plants and other places for rapid repair and reduced downtime.

[0041] Maximum temperature 150°C: Ensures stable performance under high-temperature conditions Resisting Environmental Thermal Interference: In metallurgical plants, crane beams are exposed to high-temperature thermal radiation environments (locally reaching 250°C) for extended periods. Setting the upper limit of the Af point at 150°C ensures that the Fe-SMA reinforced components stably maintain their austenitic state during service. If the Af point is too low (e.g., 50°C), the ambient temperature is sufficient to induce a phase transformation, leading to relaxation of the pre-applied compressive stress and failure of the reinforcement effect. The 150°C Af point provides a safe "temperature redundancy," guaranteeing the long-term stability of the reinforcement effect.

[0042] 2. Effectively protects the structural performance of the parent material. Mitigating the risk of steel "blue brittleness": Ordinary structural steel enters the "blue brittleness" temperature range at around 200°C to 300°C, where its plasticity and toughness significantly decrease, becoming brittle and prone to cracking. This invention strictly controls the activation temperature below 150°C, far below the blue brittleness initiation temperature, thereby completely avoiding any thermal damage to the steel structure base material during the activation process and ensuring the safety of the structure itself.

[0043] 3. Achieve optimization of reinforcement performance and long-term durability. Sufficient recovery stress is generated: Within this temperature range, Fe-SMA can be fully activated to generate high recovery stress, which is sufficient to effectively strengthen the steel structure.

[0044] Excellent resistance to stress relaxation: As described in the background section, Fe-SMA effectively maintains prestress even after repeated loading. This temperature range is selected to ensure stable performance under normal operating conditions (even short-term exposure to 70-80°C), with minimal prestress loss over 50 years, guaranteeing the durability of the reinforcement effect.

[0045] 4. Optimal solution for high-temperature operating conditions (120°C-150°C) Based on this, to further optimize performance under extreme high-temperature conditions such as in metallurgical plants, this invention particularly prefers materials with an Af point of 120°C to 150°C. This preferred option has decisive advantages: It further widens the gap with the highest ambient temperature, ensuring that even in areas with the strongest heat radiation, Fe-SMA reinforced components will never spontaneously anneal or experience stress relaxation due to ambient heat, fundamentally solving the industry problem of active reinforcement technology failure caused by high-temperature environments.

[0046] It should be noted that the Fe-SMA ring groove rivet used in this embodiment does not require separate cold extrusion (cold expansion) treatment after drilling during its activation process.

[0047] The radial expansion effect generated by the Fe-SMA ring groove rivet after thermal activation is equivalent to or even better than that of the traditional cold expansion process. Furthermore, it can simultaneously apply axial active compressive stress, which is impossible to achieve with traditional cold expansion, thus forming a more effective three-dimensional compressive stress field. This not only simplifies the construction process, realizing a one-stop operation of "hole making-installation-activation," but also significantly improves the strengthening effect and fatigue resistance of the crack-arresting hole from a mechanistic perspective.

[0048] Implementation Method B: Fe-SMA Patch / Bushing Reinforcement In this embodiment, the reinforcement is a strip patch 6 made of Fe-SMA (such as...). Figure 4a (as shown) or curved bushing 10 (as shown) Figure 4b As shown). Figure 4a As shown, the strip patch 6 can be provided with two mounting holes. Figure 4b As shown, the arc-shaped bushing 10 may include a square base block and a cylindrical portion connected to the square base block, with communicating mounting holes formed on the base block and the cylindrical portion. The bushing or liner is anchored to the surface of the steel structure base material or a pre-drilled groove using high-strength short-tailed groove rivets or activated Fe-SMA groove rivets (as described in Embodiment A) as fasteners; after activation, the Fe-SMA patch or bushing applies a uniformly distributed active compressive stress field larger than a preset area to the target area on the steel structure base material.

[0049] In a preferred embodiment of the present invention, the high-strength short-tailed groove rivet has a performance grade of not less than 8.8, preferably 10.9 or higher. This strength grade ensures that the rivet does not yield or break when subjected to huge clamping forces and structural vibrations, thereby providing reliable anchoring for the Fe-SMA reinforcement.

[0050] The area covered by the active compressive stress field (i.e., the preset area) needs to be designed according to the reinforcement target, and the basic principle is: (1) For crack repair: the area should at least completely cover the region centered on the crack tip and extending along the crack propagation direction several times the crack length. In a preferred embodiment, the length of the Fe-SMA patch should be no less than twice the original crack length, and the width should fully cover the plastic zone and high stress influence zone on both sides of the crack.

[0051] (2) Preventive reinforcement of stress concentration areas: The area should at least completely cover the high stress concentration areas determined by finite element analysis, and extend outward with a certain safety margin to ensure that the stress level of the critical area is reduced below the fatigue limit.

[0052] The safety margin refers to the dimension extending outward from the boundary of the high stress concentration region, and its size should ensure that the contour lines of the critical stress level (e.g., the fatigue strength limit or allowable stress amplitude of the base material) are completely contained within the reinforced region. The determination of this safety margin must be based on one or a combination of the following principles: Based on stress field analysis: A stress distribution cloud map of the base material is obtained through finite element analysis. The safety margin should ensure that the reinforced area covers the entire region above the fatigue strength threshold of the base material and extends outwards to a sufficient distance where the stress has significantly attenuated. In a specific design, this distance can be determined by the width of the high stress gradient zone.

[0053] Based on specifications or empirical coefficients: When precise analysis is not possible, the safety margin can be selected based on relevant engineering specifications or mature design experience. As a non-limiting example, its size can be set to be no less than 0.5 times the thickness of the reinforced member, or no less than 50 mm, and the larger of the two values ​​can be used to ensure effective stress transfer and coverage.

[0054] Through the above design, the active compressive stress field can effectively reduce the stress intensity factor at the crack tip and change its stress ratio, thereby significantly delaying or preventing the initiation and propagation of fatigue cracks.

[0055] Implementation Method B1: Fe-SMA Patch In one illustrative embodiment, the installation and activation process of the Fe-SMA patch mainly includes the following steps: (1) Surface treatment and preheating: The areas of the steel structure base material to be reinforced (such as cracked areas or stress concentration areas) are cleaned and pretreated, and then preheated to about 80°C to reduce thermal shock during thermal activation and ensure good heat transfer.

[0056] (2) Positioning and Fixing: The pre-deformed Fe-SMA patch is directly attached to the treated surface of the steel structure base material. Subsequently, according to the design position, anchoring holes are drilled simultaneously on the Fe-SMA patch and the steel structure base material below. Then, several fasteners (short-tailed groove rivets or Fe-SMA groove rivets) are passed through the anchoring holes to firmly anchor the two ends and key parts of the patch to the surface of the base material.

[0057] In this invention, different types of ring groove rivets can be selected as fasteners according to engineering needs, and the installation process is as follows: When using traditional high-strength short-tailed groove rivets, installation requires a special collar (or locking ring). A pulling force is applied using a rivet gun, causing plastic deformation of the rivet shank and squeezing the collar, forming a mechanical interlock on the back side of the connecting plate, thus achieving a permanent mechanical bond.

[0058] When using the Fe-SMA ring groove rivet of this invention, the initial mechanical installation steps are compatible with or the same as those of traditional short-tail ring groove rivets, and initial pre-tightening can also be achieved through collar and riveting operations. However, the fundamental difference and core technology lies in the fact that after riveting is completed, it must be thermally activated. The thermal activation process causes the Fe-SMA material to undergo an austenitic phase transformation, resulting in significant radial expansion and axial contraction. This shape memory effect not only greatly enhances the interference fit effect between the rivet shank and the hole wall, but also applies active compressive stress to the base material around the hole, thereby achieving a qualitative leap from "passive locking" to "active reinforcement".

[0059] (3) Activation and molding: The fixed Fe-SMA patch is heated as a whole using a large-area uniform heating device. Preferably, a tracked resistance heating blanket is used for covering heating, or a laser scanner is used to scan along a predetermined path to heat the patch / bushing as a whole to above its austenitic phase transformation end temperature (Af point) (e.g., 100°C), and the temperature is maintained for a period of time to complete the activation.

[0060] During activation, driven by the shape memory effect, the Fe-SMA patch strongly tends to recover its initial flatness or preset shape. Since its deformation is constrained by the parent material, this tendency to recover translates into a large-area, uniform active compressive stress on the surface of the parent material. This active compressive stress field can: It significantly reduces the actual stress ratio at the crack tip, effectively delaying or even preventing the propagation of fatigue cracks.

[0061] It improves the fatigue strength of the entire reinforced area and inhibits the initiation of new cracks in the stress concentration zone.

[0062] Compared with the point reinforcement in Implementation A, this implementation achieves planar reinforcement, resulting in a more uniform stress distribution. It is particularly effective for treating long cracks or widely distributed fatigue damage areas.

[0063] Implementation Method B2: Fe-SMA Bushing The key difference between the installation method of Fe-SMA bushings and patches lies in their embedded design: first, a groove matching the shape of the bushing must be milled or cut into the area of ​​the steel structure to be reinforced; then, the pre-deformed bushing is embedded and placed in the groove; finally, it is anchored using fasteners. This embedded installation method allows the reinforcement to ultimately remain flush or nearly flush with the surface of the base material, with minimal impact on the original shape and clearance dimensions of the structure, making it particularly suitable for areas requiring surface flatness.

[0064] The activation process for Fe-SMA bushings is the same as that for Fe-SMA patches. After installation and fixing, a large-area uniform heating device (such as a tracked resistance heating blanket or a laser scanner) is used to heat the entire reinforcement, raising its temperature above its austenitic phase transformation end temperature (Af point) and maintaining it for a predetermined time. After activation, both the bushing and patch apply a large-area, uniformly distributed active compressive stress field to the target area of ​​the base material beneath them, based on the shape memory effect.

[0065] Implementation method C: Tension reinforcement based on pre-stretched Fe-SMA and anchor blocks This embodiment provides a reinforcement path different from the aforementioned embodiments. By tensioning the linear Fe-SMA member, it is suitable for scenarios that require applying large-scale, high-precision active tension forces to steel structures, such as for reinforcing large-span members, main load-bearing members with macroscopic cracks, or structures that require overall reinforcement.

[0066] In this embodiment, the system further includes independent anchor blocks 8 respectively disposed on both sides of the area to be reinforced of the steel structure base material 3. The Fe-SMA reinforcement is a pre-stretched Fe-SMA component 9 (which can be in bundle or strip form), with both ends anchored to the anchor blocks 8. After undergoing a two-stage process of mechanical pre-tensioning and thermal activation, this component can apply an active tension force to the steel structure base material 3 that far exceeds the level of simple mechanical tensioning. In this embodiment, the anchor block 8 can be implemented as a bushing.

[0067] The reinforcement process of this implementation method mainly includes the following steps: C1. Surface treatment and anchor block positioning First, the surface of the area to be reinforced on the steel structure base material 3 (such as both sides of fatigue crack 4) is treated to ensure flatness and cleanliness. Then, as... Figure 5As shown, independent anchor blocks 8 are precisely installed on both sides of the damaged area. The anchor blocks 8 are firmly fixed to the steel structure base 3 via a connection pair consisting of high-strength bolts and friction pads. The use of friction pads effectively improves the anti-slip performance of the connection and the reliability of the overall anchoring system.

[0068] C2. Installation and Mechanical Pre-tensioning of Fe-SMA Components The pre-stretched Fe-SMA component 9 is passed through or around the damaged area to be reinforced, and its two ends are anchored to two pre-installed anchor blocks 8. At room temperature, a predetermined initial pretension is applied to the Fe-SMA component 9 using a mechanical tensioning device (such as a hydraulic jack). Once the predetermined tension is reached, it is locked by a locking mechanism on the anchor blocks 8, thus completing the mechanical pretensioning stage and laying the foundation for subsequent thermal activation enhancement.

[0069] C3. Thermal activation and formation of active tension force After mechanical pretensioning, a specific thermal excitation area of ​​the tensioned and locked Fe-SMA member 9 is locally heated using a thermal excitation device (such as an induction heating coil or a tracked heating blanket) to raise its temperature above its austenitic phase transformation end temperature (Af point) and maintain it for a period of time. During thermal excitation, the Fe-SMA material, based on its shape memory effect, will generate additional, substantial recovery strain. Because this recovery strain is constrained by the anchor block 8, the previously applied mechanical pretension is significantly increased into a higher, more stable active tension force.

[0070] This implementation method utilizes a composite process of mechanical pre-tensioning and heating activation to synergistically leverage the dual advantages of mechanical tensioning and intelligent material response. This process not only achieves precise control of the active tension force but also yields a significantly higher amplitude of active tension force than simple mechanical tensioning. This results in an extremely efficient and reliable active reinforcement effect on the steel structure base material, providing an innovative technical means to solve the challenges of reinforcing large structures.

[0071] (Monitoring and Control Unit) In this embodiment of the invention, the monitoring and control unit 2 is the core of realizing intelligent active hardening, and may include sensor component 21 and controller 22.

[0072] The sensor components 21 are distributed at key locations of the steel structure substrate and / or the Fe-SMA reinforcement, preferably around the reinforcement points, along the extension line of the crack tip, and in high-stress areas. The sensor components 21 include, but are not limited to, one or more of the following: Fiber Bragg grating sensors are used to monitor the dynamic strain amplitude and distribution on the surface of steel structure base materials in real time, and have the ability to detect crack initiation. Piezoelectric sensors are used to monitor the vibration characteristics and acoustic emission signals of the steel structure base material in order to identify damage events such as crack propagation. Temperature sensor, used to sense ambient temperature and temperature field when firmware is activated in real time.

[0073] The controller 22 (such as a PLC, embedded system, or dedicated industrial computer) and the sensor assembly 21 are connected by wired or wireless means to form a closed-loop feedback system.

[0074] The controller 22 has pre-stored strain thresholds, temperature thresholds, and other relevant parameters set according to the structural design safety requirements. The controller 22 is configured to dynamically adjust the activation energy applied to the Fe-SMA reinforcement based on the monitoring data fed back by the sensor assembly.

[0075] The activation energy described in this invention refers to the total thermal energy applied to the Fe-SMA reinforcement via an external heating device. Specific control parameters of the activation energy can be expressed as a combination of heating power, heating time, and / or heating temperature. The function of the activation energy is to rapidly and uniformly raise the Fe-SMA material to above its austenitic phase transformation end temperature (Af point) and complete the phase transformation.

[0076] Specifically, the controller 22 is configured to execute at least one of the following intelligent control strategies: (1) Adaptive strengthening strategy: When the dynamic strain amplitude of the monitored steel structure parent material or the calculated load exceeds the first preset threshold, the controller 22 instructs the heating system to increase the activation energy applied to the Fe-SMA reinforcement 1 (such as increasing the heating power or extending the heating time) to improve the applied pre-compression stress level and actively enhance the structural stiffness and bearing capacity.

[0077] The calculated load mentioned in this article refers to the equivalent dynamic load (such as crane wheel pressure, bending moment, etc.) or its stress amplitude acting on the structure, calculated in real time by the controller based on the dynamic strain signals of the steel structure base material monitored in real time by the sensor components (especially fiber optic grating sensors), combined with the mechanical model of the structure (such as pre-inputted geometric and physical parameters such as section moment of inertia and material elastic modulus), and through a built-in algorithm. The technical principle is as follows: based on the fundamental formulas of mechanics of materials σ=E·ε and M=σ·W, where E is the elastic modulus, ε is the strain, M is the bending moment, and W is the section modulus, the system can directly calculate the stress σ from the measured strain ε, and further calculate the load M that causes this stress. This provides a control parameter that is more intuitive than the original strain data and directly corresponds to the structural safety assessment specifications for control decision-making.

[0078] The first preset threshold is a control parameter pre-set based on the design allowable stress, fatigue strength limit, and specific service conditions of the steel structure base material. This first preset threshold is associated with the structure's safety warning status, and its value can be set to 1.2 to 1.5 times the stress generated by the base material under standard working load, or 80% to 95% of the allowable stress amplitude set according to design specifications. When monitoring data exceeds this threshold, it indicates that the structure is experiencing abnormally high loads, posing a risk of accelerated fatigue damage, and requiring reinforcement.

[0079] (2) Reversible energy dissipation strategy: When the monitored dynamic strain amplitude of the structure or the calculated load is lower than the second preset threshold, the controller 22 can reduce or cut off the activation energy. In this state, the Fe-SMA reinforcement 1 can make full use of its hyperelastic properties to undergo a reversible martensitic phase transformation under load to absorb and dissipate energy, thus acting as a passive damper, and returning to its original state after the load is unloaded.

[0080] The second preset threshold is a control parameter pre-set based on the design allowable stress, fatigue strength limit, and specific service conditions of the steel structure base material. The second preset threshold is associated with the structure's low-load or normal service state, and its value can be set close to the structure's fatigue limit stress amplitude or average working stress level. When the monitoring data is below this threshold, it indicates that the structure is in a safe or low-load state, and the system can reduce intervention or activate a reversible energy consumption mode to optimize energy consumption and utilize hyperelasticity.

[0081] In this embodiment of the invention, the controller is configured to perform closed-loop feedback control, which dynamically adjusts the pre-stress applied by the Fe-SMA reinforcement by regulating the activation energy (specifically manifested as the output power of the heating device, the heating time, or a combination thereof).

[0082] The correlation between the increase and decrease of the activation energy and the monitoring data (strain or estimated load) is realized through a pre-set control algorithm within the controller. This control algorithm includes, but is not limited to, one or more of the following strategies: Proportional control: The adjustment amount ΔE of the activation energy is proportional to the deviation Δε of the monitored strain amplitude relative to a preset threshold, or the deviation ΔP of the calculated load relative to a preset threshold. That is: ΔE = K p ×Δε or ΔE=K p ×ΔP, where K p This is the proportionality coefficient.

[0083] Lookup table method: The controller has a pre-stored database of the correspondence between strain / load and optimal activation energy. The system queries this database based on real-time monitoring data and directly outputs the corresponding activation energy command.

[0084] Fuzzy logic control: To address the fuzziness of strain and load changes, fuzzy logic rules are used for intelligent decision-making. For example, if the strain is large, a stronger activation energy is applied.

[0085] By combining one or more of the above algorithms, the system achieves accurate and automatic mapping from structural state perception to dynamic adjustment of reinforcement force.

[0086] (3) Temperature compensation strategy: Based on the temperature data of the steel structure base material, i.e. the environment, monitored by the temperature sensor, the controller 22 performs real-time compensation control on the application of activation energy. For example, when the ambient temperature rises, the activation heating temperature is appropriately reduced to avoid overheating; conversely, it is appropriately increased to ensure sufficient activation. This strategy aims to maintain the long-term stability of the pre-compression stress applied by the Fe-SMA reinforcement 1 under different ambient temperatures.

[0087] In this embodiment of the invention, the temperature compensation strategy aims to eliminate the influence of ambient temperature fluctuations on the prestressing effect of Fe-SMA. Its core is to maintain the effective temperature rise of the Fe-SMA reinforcement (i.e., the difference between the final and initial temperatures) within a constant or optimal range by dynamically adjusting the activation parameters. The specific implementation of the temperature compensation strategy is as follows: When the monitored ambient temperature or base material temperature T0 increases, the controller will correspondingly reduce the target heating temperature (T0) applied to the Fe-SMA reinforcement. target (or heating power) to prevent overheating and prestress relaxation. Its compensation logic can follow: T target =T 基准 +(T 基准 -T0)×K, or determined by a lookup table. Where T 基准 The optimal activation temperature is determined experimentally at room temperature (20℃), and K is a compensation coefficient set according to the material properties (0<K≤1).

[0088] When the monitored ambient temperature or base material temperature T0 decreases, the controller will correspondingly increase the target heating temperature (T). target The heating power is adjusted to ensure that the Fe-SMA receives sufficient heat energy to fully complete the phase transformation and generate adequate recovery stress. Its compensation logic remains consistent with that during heating, following the same control law: T target =T 基准 +(T 基准 -T0)×K, at this time, since T0 decreases, the term (T 基准 The value of -T0) increases, thus causing the calculated T to... target Increase.

[0089] The essence of this unified formula is that, regardless of changes in ambient temperature, the system strives to make the Fe-SMA reinforced member achieve a state relative to T. 基准A stable "overheating state". The controller dynamically sets T using a lookup table method or the calculation method described above. target To ensure that Fe-SMA undergoes an effective temperature rise (T) during activation. target -T0) is sufficient to activate its full shape memory effect, thus enabling it to output stable and consistent preload stress under different environmental conditions.

[0090] This temperature compensation strategy ensures that the effective temperature rise (i.e., the superheat above its Af point) of the Fe-SMA reinforcement is essentially consistent under different initial temperatures, thereby maintaining the resulting recovery stress (i.e., prestress) within a stable design range and avoiding prestress relaxation due to high ambient temperatures or insufficient activation due to low ambient temperatures. Assuming that at a room temperature of 20°C, the Fe-SMA rivet needs to be heated to 150°C (i.e., a temperature rise of 130°C) to generate ideal prestress. In a hot environment of 50°C, if it is still heated to 150°C (a temperature rise of only 100°C), the generated prestress will be insufficient. After compensation: the system will automatically adjust the target temperature to approximately 180°C based on the ambient temperature of 50°C, thus ensuring that the actual temperature rise remains around 130°C, ultimately maintaining a stable prestress output.

[0091] Through the aforementioned closed-loop control that integrates perception, decision-making, and execution, this system can achieve dynamic perception and adaptive maintenance of the reinforcement effect, enabling the reinforced structure to possess "intelligent" characteristics and respond to changing loads and environments, thereby significantly improving the reliability, safety, and durability of reinforcement under complex variable loads and harsh environments.

[0092] To verify the long-term durability of the present invention, a systematic accelerated environmental aging and fatigue performance test was conducted.

[0093] (1) Environmental durability verification The specimens reinforced using the system described in this invention were placed in a constant temperature and humidity chamber at 85°C and 85% relative humidity for a continuous 1000-hour accelerated aging test. The test results showed that after this rigorous environmental testing, the prestress loss rate of the Fe-SMA reinforced component applied to the base material was less than 10%. This performance is far superior to traditional mechanical reinforcement methods (where prestress loss typically exceeds 30% under the same conditions), fully demonstrating the superior stress relaxation resistance and long-term operational reliability of this invention under high temperature and high humidity conditions.

[0094] (2) Fatigue resistance verification After strengthening the specimen with fatigue cracks, a high-frequency fatigue load test of 2 million cycles was conducted. The test data showed that: Crack propagation suppression effect: Compared with the unreinforced reference specimen, the crack propagation rate was reduced by more than 85% after reinforcement with the present invention.

[0095] Fatigue life improvement effect: The fatigue life of the reinforced area was increased by more than 5 times, significantly delaying the failure time of the structure.

[0096] (3) Establishment of the design model Based on the above experiments and a series of parametric test data, an accurate prediction model for the fatigue life of this reinforced system was constructed. This model can provide a reliable theoretical basis and calculation tool for engineering design and life assessment under different load conditions, environmental factors, and crack sizes.

[0097] (Example 2) This embodiment provides a smart active reinforcement method for steel structures based on shape memory alloys, such as... Figure 6 As shown, this method corresponds to the system described in Embodiment 1 and includes the following steps: S1. At least one Fe-SMA reinforcement made of iron-based shape memory alloy is installed in the area of ​​the steel structure base material to be reinforced. In one specific embodiment, the Fe-SMA reinforcement is an Fe-SMA ring groove rivet, which is installed in the crack arrest hole drilled at the tip of the fatigue crack in the steel structure, or in other connection holes that need to be reinforced.

[0098] S2, the Fe-SMA reinforcement is activated by applying activation energy, causing it to generate active compressive stress on the steel structure base material. Activation energy can be applied to the Fe-SMA reinforcement through localized heating, raising its temperature above the austenitic phase transformation end temperature and maintaining it for a predetermined time. When the reinforcement is an Fe-SMA ring groove rivet, during activation, it simultaneously undergoes radial expansion and axial contraction within the hole, forming an interference fit and applying radial and axial active compressive stress to the hole periphery. The localized heating method is preferably induction heating or laser scanning heating.

[0099] S3, using sensor components to monitor in real time the state parameters of the steel structure base material and / or the Fe-SMA reinforcement, including strain, temperature and vibration signals.

[0100] S4. Based on the monitoring data fed back by the sensor components, the activation energy applied to the Fe-SMA reinforcement is dynamically adjusted by the controller to achieve intelligent closed-loop control of the active compressive stress and ensure the adaptive maintenance of the reinforcement effect under different working conditions.

[0101] Furthermore, before step S1, step S0 is also included: surface treatment of the area to be reinforced of the steel structure parent material to remove rust and oil stains, and preheating treatment, wherein the preheating temperature is lower than the phase transformation activation temperature of the Fe-SMA reinforcement.

[0102] This method achieves efficient and intelligent reinforcement of steel structures through a closed-loop process of installation-activation-monitoring-control, and is particularly suitable for fatigue repair and reinforcement in high-temperature and heavy-load environments such as metallurgical plants.

[0103] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0104] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A smart active reinforcement system for steel structures based on shape memory alloys, characterized in that, The system includes: At least one Fe-SMA reinforcement made of iron-based shape memory alloy, wherein the Fe-SMA reinforcement is activated by an activation energy application method, thereby generating active compressive stress on the steel structure base material to be reinforced; A monitoring and control unit, comprising a sensor assembly disposed on the steel structure base material and / or the Fe-SMA reinforcement, and a controller communicatively connected to the sensor assembly; The controller is configured to dynamically adjust the activation energy applied to the Fe-SMA reinforcement based on monitoring data fed back by the sensor components.

2. The reinforcement system according to claim 1, characterized in that, The Fe-SMA reinforcement is a Fe-SMA ring groove rivet. After installation and activation, the Fe-SMA ring groove rivet undergoes simultaneous axial and radial recovery deformation, thereby forming an interference fit in the connection hole of the steel structure base material and applying active compressive stress in the radial and axial directions to the area around the hole.

3. The reinforcement system according to claim 2, characterized in that, The Fe-SMA reinforcement is a Fe-SMA patch or bushing, which is anchored to the surface of the steel structure base material or a pre-drilled groove by a short-tailed ring groove rivet or an activated Fe-SMA ring groove rivet. After activation, the Fe-SMA patch or bushing applies an active compressive stress field larger than the preset area and uniformly distributed to the target area on the steel structure base material.

4. The reinforcement system according to any one of claims 1 to 3, characterized in that, The sensor assembly includes at least one of the following: Fiber Bragg grating sensors used to monitor strain or cracks; Piezoelectric sensors used to monitor vibration or acoustic emissions; Temperature sensor.

5. The reinforcement system according to claim 4, characterized in that, The controller is configured to perform at least one of the following operations: When the strain or load of the steel structure parent material exceeds the first preset threshold, the activation energy applied to the Fe-SMA reinforcement is increased to enhance the pre-compression stress. When the strain or load of the steel structure parent material is detected to be lower than the second preset threshold, the activation energy is reduced or turned off, so that the Fe-SMA reinforcement enters a reversible phase transition state to dissipate energy. Based on the monitored temperature data, the application of the activation energy is compensated and controlled to maintain the stability of the prestress.

6. The reinforcement system according to claim 1, characterized in that, Also includes: Independent anchor blocks are respectively set on both sides of the area to be reinforced of the steel structure parent material. The Fe-SMA reinforcement is a pre-stretched Fe-SMA component, and both ends of the Fe-SMA component are respectively anchored to the anchor blocks.

7. A method for intelligent active reinforcement of steel structures based on shape memory alloys, characterized in that, Includes the following steps: S1, In the area of ​​the steel structure base material to be reinforced, install at least one Fe-SMA reinforcement made of iron-based shape memory alloy; S2, the Fe-SMA reinforcement is activated by applying activation energy, so that the Fe-SMA reinforcement generates active compressive stress on the steel structure base material; S3, using sensor components to monitor the status of the steel structure base material and / or the Fe-SMA reinforcement in real time; S4. Based on the monitoring data fed back by the sensor components, the activation energy applied to the Fe-SMA reinforcement is dynamically adjusted by the controller to achieve intelligent control of the active compressive stress.

8. The method according to claim 7, characterized in that, In S1, the Fe-SMA reinforcement is a Fe-SMA grooved rivet, which is installed in the crack arrest hole drilled at the tip of the fatigue crack in the steel structure or in the connection hole that needs to be reinforced; in S2, the Fe-SMA grooved rivet is activated by local heating, so that the Fe-SMA grooved rivet simultaneously expands radially and contracts axially in the hole, forming an interference fit and applying active compressive stress in the radial and axial directions.

9. The method according to claim 8, characterized in that, The local heating method is induction heating or laser scanning heating.

10. The method according to claim 7, characterized in that, Before S1, there is also S0: surface treatment and preheating treatment of the area to be reinforced of the steel structure parent material, wherein the preheating temperature is lower than the phase transformation activation temperature of the Fe-SMA reinforcement.

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