A compact induction thermal imaging detection device and testing method for fatigue cracks in steel structures.

Abstract

This invention discloses a compact inductive thermal imaging detection device and testing method for fatigue cracks in steel structures, belonging to the field of mechanical engineering technology. It includes: a data processing terminal, an infrared thermal imaging module, a controller, a uniform field magnetization device, and a steel structure specimen. Firstly, by eliminating the water-cooling system and adopting a magnetic yoke focusing design, this invention achieves overall lightweight and compact design, making it truly suitable for various field environments. Secondly, the adjustable distance of the magnetic yoke base allows a single probe to adapt to various complex geometries, overcoming the limitations of cumbersome coil replacement in traditional methods and improving versatility and economy. Thirdly, the optimized magnetic field distribution ensures effective and uniform heating of the detection area with low power consumption. Finally, the device, combined with a standardized thermal image sequence analysis algorithm, provides a solution for rapid detection of surface defects in metallic materials, successfully engineering and practicalizing high-sensitivity laboratory inductive thermal imaging technology.

Description

Technical Field

[0001] This invention relates to the field of mechanical engineering technology, and more specifically to a compact inductive thermal imaging detection device and testing method for fatigue cracks in steel structures. Background Technology

[0002] Steel structures are prone to fatigue cracks under complex and harsh service environments. As service time increases, the propagation of these fatigue cracks can easily lead to sudden structural failures, posing a serious threat to structural safety. Existing conventional non-destructive testing methods, such as ultrasonic testing and magnetic particle testing, have limited ability to detect early-stage micro-fatigue cracks and hidden defects in steel structures. Inductive thermal imaging, with its non-contact and intuitive imaging characteristics, is an effective detection solution. However, common inductive excitation devices are usually equipped with bulky water-cooling systems, and the heating coils are mostly fixed structures, resulting in problems such as bulkiness, high power consumption, and poor adaptability. This makes them difficult to move and deploy in complex engineering sites such as high altitudes and confined spaces, limiting the technology to laboratory environments and failing to meet the practical needs of engineering sites for lightweight, portable, highly adaptable, and rapid and accurate detection.

[0003] Currently, on-site detection of fatigue cracks in steel structures still mainly relies on traditional non-destructive testing methods such as handheld ultrasonic testing and magnetic particle testing. These methods have low detection efficiency, the results are highly dependent on the operator's experience, and they have limitations in detecting early micro-cracks on the component surface and subsurface hidden defects.

[0004] Inductive thermal imaging technology achieves instantaneous heating of specimens through eddy current induction and captures surface temperature field anomalies caused by defects using an infrared thermal imager. It offers advantages such as non-contact operation, full-field visualization, and intuitive detection results, making it suitable for identifying minute defects. However, existing inductive thermal imaging detection devices generally employ high-power water-cooled induction power supplies and integrated fixed coils to improve heating power and magnetic field uniformity. Water-cooling systems require an external water source or circulating cooling unit, resulting in bulky, heavy, and inconvenient equipment. Fixed coils, with their fixed structure and non-adjustable geometry, struggle to conform closely to detection surfaces of varying curvatures and widths, leading to poor field adaptability and limited application scenarios, failing to meet the diverse and mobile detection needs of complex engineering sites.

[0005] Therefore, proposing a compact inductive thermal imaging detection device and testing method for fatigue cracks in steel structures to overcome the difficulties of existing technologies is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a compact induction thermal imaging detection device and testing method for fatigue cracks in steel structures. The device adjusts the foot spacing according to the detection location to fit the workpiece, and then applies a short-term induction heating pulse through the controller. The infrared thermal imaging module synchronously records the changes in the surface temperature field and analyzes the abnormal heat flow caused by defects in the thermal image sequence to achieve the visual location and evaluation of defects.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A compact inductive thermal imaging detection device for fatigue cracks in steel structures includes: a data processing terminal, an infrared thermal imaging module, a controller, a uniform field magnetization device, and a steel structure specimen; The uniform field magnetization device integrates a high-frequency inverter power supply, digital control circuit and magnetic yoke probe. The two ends of the magnetic yoke probe are independently linearly movable feet. The feet are attached to the test surface of the steel structure specimen to apply a uniform magnetic field to the steel structure specimen and generate induction heating. The infrared thermal imaging module is fixed to the side of the uniform field magnetization device by a multi-directionally adjustable mechanical bracket. The optical axis of the infrared thermal imaging module's lens is perpendicular to the center of the detection area formed between the two feet of the magnetic yoke probe, and is used to capture dynamic thermal sequence images of the detection area. The controller is electrically connected to the uniform field magnetization device and the infrared thermal imaging module, respectively, and is used to drive the uniform field magnetization device to generate an excitation magnetic field and realize the synchronous acquisition of magnetic field excitation and thermal image. The data processing terminal communicates with the controller, sends control commands to the uniform field magnetization device through the controller, receives data collected by the infrared thermal imaging module, and runs thermal imaging analysis software to perform induction thermal imaging detection and analysis on the steel structure specimen, thereby realizing the visual location and evaluation of defects.

[0008] Optionally, the high-frequency inverter power supply, digital control circuit, and magnetic yoke probe integrated within the uniform field magnetization device include: The digital control circuit is electrically connected to the high-frequency inverter power supply and is used to output control signals to adjust the output frequency and power of the high-frequency inverter power supply. The high-frequency inverter power supply is electrically connected to the excitation coil of the magnetic yoke probe to provide high-frequency excitation current to the excitation coil.

[0009] Optionally, the magnetic yoke probe is a magnetic yoke heating probe, which adopts a split symmetrical layout with two independent magnetic arms. The main body is a magnetic yoke made of high magnetic permeability material. The bottom ends of the two magnetic arms respectively form independently linearly movable feet that fit into the steel structure specimen, realizing continuous adjustment and locking of the spacing. Each foot end is provided with a standardized interface for assembling magnetic yoke end structures of different sizes. The excitation coil and the magnetic yoke probe are integrated into a single structure.

[0010] Optionally, the data processing terminal is a ruggedized tablet computer with industrial-grade protection.

[0011] Optionally, the data processing terminal and the controller can communicate wirelessly or via wired means through Wi-Fi, Bluetooth, or Ethernet.

[0012] Optionally, the uniform field magnetization device can perform magnetic field excitation and induction heating of steel structure specimens without external water cooling / air cooling.

[0013] A compact inductive thermal imaging testing method for fatigue cracks in steel structures, employing any of the aforementioned compact inductive thermal imaging detection devices for fatigue cracks in steel structures, includes the following steps: S1. Based on the geometric features and testing requirements of the steel structure surface to be tested, select a suitable magnetic yoke probe, attach the base of the magnetic yoke probe of the uniform field magnetization device to the area to be tested of the steel structure specimen, and adjust the attitude of the infrared thermal imaging module so that the optical axis of the lens is perpendicular to the center of the testing area. S2. Set the induction heating parameters and infrared thermal imaging module acquisition parameters through the data processing terminal, and send control commands to the controller through the data processing terminal. The controller drives the uniform field magnetization device to apply a uniform magnetic field excitation to the steel structure specimen and generate induction heating. The controller simultaneously triggers the infrared thermal imaging module to acquire dynamic thermal sequence images. S3. Process and analyze the acquired dynamic thermal sequence images using the pulse phase method and principal component analysis algorithm; S4. By processing and analyzing the thermal image data, automatically identify and locate abnormal areas caused by defects, and generate a standardized inspection report containing the defect location, image features and analysis results.

[0014] Optionally, the induction heating parameters set in S2 via the data processing terminal include the amplitude, width, frequency, and repetition period of the pulse current; The parameters acquired by the infrared thermal imaging module include image sampling rate, resolution, and recording duration.

[0015] As can be seen from the above technical solution, compared with the prior art, the present invention provides a compact induction thermal imaging detection device and testing method for fatigue cracks in steel structures, which has the following beneficial effects: (1) First, by abandoning the water cooling system and adopting the magnetic yoke focusing design, the invention achieves overall lightweight and small size of the device, and is truly applicable to a variety of field environments; second, the adjustable distance of the magnetic yoke feet allows a single probe to adapt to a variety of complex geometric structures, solving the limitation of cumbersome replacement of traditional coils and improving versatility and economy; third, the optimized magnetic field distribution ensures effective and uniform heating of the detection area with low power consumption; finally, the device, in conjunction with a standardized thermal image sequence analysis algorithm, can realize a solution for rapid detection of surface defects of metal materials, and successfully engineered and put into practical use the high-sensitivity laboratory inductive thermal imaging technology. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 A schematic diagram of a compact inductive thermal imaging detection device for fatigue cracks in steel structures provided by the present invention. Figure 2 This is a schematic diagram of the magnetic flux density of the induced magnetic field under a conventional magnetic yoke heating coil in the prior art. Figure 3 A schematic diagram of the magnetic flux density of the induced magnetic field under the heating coil provided by the present invention; Figure 4 The temperature response diagram of a defect-free steel structure specimen under conventional magnetic yoke heating coil in the prior art; Figure 5 Temperature response diagram of a defect-free steel structure specimen under a heating coil provided by the present invention; Figure 6 A comparison diagram of the temperature response at the midpoint of the weld seam under the heating coil of the present invention between a conventional magnetic yoke and the present invention. Figure 7 This is a temperature response diagram of weld defects under conventional magnetic yoke heating coils in the prior art; Figure 8 The temperature response diagram of weld defects under the heating coil provided by the present invention; Figure 9 A flowchart of a compact induction thermal imaging testing method for fatigue cracks in steel structures provided by the present invention; Figure 10 A flowchart of image processing using principal component analysis (PCA) provided for this invention; Among them, 1-data processing terminal, 2-infrared thermal imaging module, 3-controller, 4-uniform field magnetization device, and 5-steel structure specimen. Detailed Implementation

[0018] 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.

[0019] See Figure 1 As shown, the present invention discloses a compact inductive thermal imaging detection device for fatigue cracks in steel structures, comprising: a data processing terminal 1, an infrared thermal imaging module 2, a controller 3, a uniform field magnetization device 4, and a steel structure specimen 5; The uniform field magnetization device 4 integrates a high-frequency inverter power supply, digital control circuit and magnetic yoke probe. The two ends of the magnetic yoke probe are independently linearly movable feet. The feet are attached to the surface to be tested of the steel structure specimen 5 and are used to apply a uniform magnetic field to the steel structure specimen 5 to generate induction heating. The infrared thermal imaging module 2 is fixed to the side of the uniform field magnetization device 4 by a multi-directionally adjustable mechanical bracket. The optical axis of the lens of the infrared thermal imaging module 2 is perpendicular to the center of the detection area formed between the two feet of the magnetic yoke probe, and is used to capture dynamic thermal sequence images of the detection area. The controller 3 is electrically connected to the uniform field magnetization device 4 and the infrared thermal imaging module 2 respectively, and is used to drive the uniform field magnetization device 4 to generate an excitation magnetic field and realize the synchronous acquisition of magnetic field excitation and thermal image. Data processing terminal 1 is connected to controller 3. Controller 3 sends control commands to uniform field magnetization device 4, receives data collected by infrared thermal imaging module 2, and runs thermal imaging analysis software to perform inductive thermal imaging detection and analysis on steel structure specimen 5, thereby realizing the visual location and evaluation of defects.

[0020] Specifically, infrared thermal imaging module 2 is an infrared thermal imager.

[0021] Furthermore, the high-frequency inverter power supply, digital control circuit, and magnetic yoke probe integrated within the uniform field magnetization device 4 include: The digital control circuit is electrically connected to the high-frequency inverter power supply and is used to output control signals to adjust the output frequency and power of the high-frequency inverter power supply. The high-frequency inverter power supply is electrically connected to the excitation coil of the magnetic yoke probe to provide high-frequency excitation current to the excitation coil.

[0022] Furthermore, the magnetic yoke probe is a magnetic yoke heating probe, which adopts a split symmetrical layout with two independent magnetic guide arms. The main body is a magnetic yoke made of high magnetic permeability material. The bottom ends of the two magnetic guide arms respectively form independently linearly movable feet that fit into the steel structure specimen 5, realizing continuous adjustment and locking of the spacing. Each foot end is provided with a standardized interface for assembling magnetic yoke end structures of different sizes. The excitation coil and the magnetic yoke probe are integrated into a single structure.

[0023] Specifically, the design of the magnetic yoke probe achieves two key functions: First, the magnetic yoke structure guides and constrains the alternating magnetic field generated by the excitation coil. Based on the basic principles of electromagnetic fields, the magnetic yoke can more effectively concentrate and guide magnetic lines of force to the detection area between the two feet, thereby forming a stronger and more uniformly distributed induced magnetic field in this area. This characteristic can be optimized through numerical simulation. The direct result is that the distribution of induced eddy currents on the surface of steel components is more uniform, providing a thermal excitation signal with a higher signal-to-noise ratio for thermal imaging detection and improving the detection capability of minute defects. Secondly, the adjustable distance between the two feet gives the probe high adaptability: for cylindrical surfaces with different curvatures or planar structures with different widths on site, by adjusting the distance between the feet, the working surface of the coil can be made to fit closely and parallel to the surface to be measured. This significantly reduces the lift-off effect, ensures that the magnetic field energy is efficiently coupled into the workpiece, and overcomes the problem of unstable detection caused by poor coupling of traditional fixed coils. During operation, the foot spacing is first adjusted according to the detection area to fit the workpiece. Then, a short-term induction heating pulse is applied through the controller 3, and the infrared thermal imaging module 2 synchronously records the changes in the surface temperature field. By analyzing the abnormal heat flow caused by the defect in the thermal image sequence, the defect can be visualized, located, and evaluated.

[0024] Furthermore, the data processing terminal 1 is a ruggedized tablet computer with industrial protection rating.

[0025] Furthermore, the data processing terminal 1 and the controller 3 can achieve wireless or wired two-way communication via Wi-Fi, Bluetooth or Ethernet.

[0026] Furthermore, the uniform field magnetization device 4 completes the magnetic field excitation and induction heating of the steel structure specimen 5 without external water cooling / air cooling.

[0027] In one specific embodiment, the following is included: The device includes: a data processing terminal 1, an infrared thermal imaging module 2, a controller 3, a uniform field magnetization device 4, and a steel structure specimen 5; The uniform field magnetization device 4 integrates a high-frequency inverter power supply, digital control circuit and magnetic yoke probe. The two ends of the magnetic yoke probe are independently linearly movable feet. The feet are attached to the surface to be tested of the steel structure specimen 5 and are used to apply a uniform magnetic field to the steel structure specimen 5 to generate induction heating. The infrared thermal imaging module 2 is fixed to the side of the uniform field magnetization device 4 by a multi-directionally adjustable mechanical bracket. The optical axis of the lens of the infrared thermal imaging module 2 is perpendicular to the center of the detection area formed between the two feet of the magnetic yoke probe, and is used to capture dynamic thermal sequence images of the detection area. The controller 3 is electrically connected to the uniform field magnetization device 4 and the infrared thermal imaging module 2 respectively, and is used to drive the uniform field magnetization device 4 to generate an excitation magnetic field and realize the synchronous acquisition of magnetic field excitation and thermal image. Data processing terminal 1 is connected to controller 3. Controller 3 sends control commands to uniform field magnetization device 4, receives data collected by infrared thermal imaging module 2, and runs thermal imaging analysis software to perform inductive thermal imaging detection and analysis on steel structure specimen 5, thereby realizing the visual location and evaluation of defects.

[0028] To achieve excellent testing adaptability and solve the problem of traditional fixed coils being unable to fit components with different geometric features, each working foot is connected to the magnetic yoke probe mounting base via a high-precision linear slide rail. It can slide independently along a direction perpendicular to the surface of the steel structure specimen 5, and the linear slide rail has precise spacing graduations engraved on its side for easy visual reference during adjustment. The foot spacing is manually adjusted via a dedicated knob on the main unit, enabling stepless, precise, and continuous adjustment of the distance between the two feet. After adjustment, it can be securely fixed by a built-in mechanical locking device. This design allows the probe to fit closely to steel structure surfaces of different thicknesses and curvatures, effectively reducing the lift-off effect, ensuring efficient coupling of magnetic field energy into the workpiece, and guaranteeing the excitation efficiency of induction heating.

[0029] In terms of magnetic field design, the yoke probe employs magnetic field homogenization technology based on the principle of magnetic circuit optimization. Considering the structural characteristics of the integrated coil, the excitation coil is wound on the yoke arm, and a low-resistivity magnetic path is constructed using a high-permeability yoke body, effectively guiding and concentrating the divergent magnetic field generated by the coil into the working area between the two bases. For example... Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8As shown, modeling verification and parameter optimization were performed using multiphysics simulation software. Simulation results show that, compared with the traditional magnetic yoke coil excitation method, the optimized structure adopted in this invention can generate a significantly stronger induced magnetic field in the detection area. The temperature under 200ms heating is 0.65K higher than that of the traditional magnetic yoke structure, and the spatial distribution uniformity of the magnetic field is improved. This lays a physical foundation for obtaining high-quality and highly consistent thermal imaging data in the future.

[0030] In another specific embodiment, the following is included: The testing method includes the following steps: The first step is the preparation stage. Operators must select a suitable magnetic yoke probe based on the specific geometric characteristics of the component to be tested, such as the plane, the radius of curvature of the pipe, and the type and size of the weld. Then, by rotating the adjustment knob, the distance between the two feet is adjusted to accommodate the component's thickness or surface curvature, ensuring close and uniform physical contact between the coil's working surface and the component's detection surface. Finally, all mechanical fixing devices are locked to ensure stable coupling between the probe and the workpiece during the testing process.

[0031] Next, the parameter setting and scanning excitation phase begins. The operator sends commands to the controller 3 via the dedicated software interface of the data processing terminal 1 to set the induction heating parameters, including the amplitude, width, frequency, and repetition period of the pulse current. Simultaneously, the operator sets the image sampling rate, resolution, and recording duration of the infrared thermal imaging module 2. After parameter setting, the calibrated probe is smoothly placed at the starting position of the detection area. The induction heating pulse and the video recording function of the infrared thermal imaging module 2 are simultaneously activated via software or hardware triggers. The controller 3 achieves precise synchronization between heating excitation and image acquisition, enabling efficient acquisition of on-site data.

[0032] Finally, the data analysis and report generation stage begins. The acquired infrared thermal imaging video data is transmitted to data processing terminal 1 in real time or post-processing. The dedicated analysis software in data processing terminal 1 first performs thermal processing on the data: subtracting the initial temperature image to improve thermal contrast and suppress background interference such as ambient temperature and radiation; further, it uses principal component analysis (PCA) to reduce the dimensionality of the thermal image data and enhance spatial thermal feature information; combined with advanced processing algorithms such as pulse phase method, it further suppresses interference such as uneven heating and background noise, highlighting the thermal signals of defects; the software automatically identifies and marks abnormal thermal response areas caused by typical defects such as fatigue cracks, and finally automatically generates a structured inspection report, which includes the precise location of the defects, characteristic thermal images, and preliminary quantitative analysis results.

[0033] like Figure 10As shown, the specific content of using principal component analysis (PCA) to reduce the dimensionality of thermal image data and enhance spatial thermal feature information is as follows: Image sequence acquisition and region cropping: The infrared thermal image sequence (total number of frames t, single frame pixels MxN) during the weld inspection process is acquired by the infrared thermal imaging module 2; in order to reduce the PCA computation load, only the image data of the core area of ​​the weld is cropped for subsequent processing, and invalid background areas are removed; 3D matrix to 2D matrix conversion (vectorization): Convert the single-frame MxN dimensional image matrix into column vectors, and then combine the column vectors of all frames into a 2D matrix adapted to the PCA algorithm; complete the format conversion; Data standardization preprocessing: Standardize the transformed two-dimensional matrix to distribute the data around the origin, eliminate the influence of dimensions, and improve the efficiency of algorithm operation and data visualization. Calculate the covariance matrix: Solve for the covariance matrix of the standardized matrix to reflect the correlation between different dimensions of the image data, which provides a certain basis for subsequent feature extraction; Solving for eigenvalues ​​and eigenvectors: Perform eigenvalue decomposition on the covariance matrix to obtain eigenvalues ​​and corresponding eigenvectors sorted from largest to smallest. The magnitude of the eigenvalues ​​corresponds to the proportion of thermal information in the image, and the eigenvectors correspond to different thermal response trends. Image reconstruction and defect feature analysis: The first four key feature vectors are selected and operated on with the original matrix. The result is then reversed to restore the two-dimensional image matrix to obtain the principal component reconstructed image. The first and second principal components highlight the weld edge + defect edge and the pure defect area, respectively, thereby enhancing the defect features.

[0034] A compact induction thermal imaging testing method for fatigue cracks in steel structures, such as... Figure 9 As shown, a compact inductive thermal imaging detection device for fatigue cracks in steel structures, applying any of the above-mentioned methods, includes the following steps: S1. Based on the geometric features and testing requirements of the steel structure surface to be tested, select a suitable magnetic yoke probe, attach the base of the magnetic yoke probe of the uniform field magnetization device 4 to the area to be tested of the steel structure specimen 5, and adjust the orientation of the infrared thermal imaging module 2 so that the optical axis of the lens is perpendicular to the center of the testing area. S2. Set the induction heating parameters and the infrared thermal imaging module 2 acquisition parameters through the data processing terminal 1, and send control commands to the controller 3 through the data processing terminal 1. The controller 3 drives the uniform field magnetization device 4 to apply a uniform magnetic field excitation to the steel structure specimen 5 and generate induction heating; the controller 3 synchronously triggers the infrared thermal imaging module 2 to acquire dynamic thermal sequence images. S3. Process and analyze the acquired dynamic thermal sequence images using the pulse phase method and principal component analysis algorithm; S4. By processing and analyzing the thermal image data, automatically identify and locate abnormal areas caused by defects, and generate a standardized inspection report containing the defect location, image features and analysis results.

[0035] Furthermore, the induction heating parameters set by the data processing terminal 1 in S2 include the amplitude, width, frequency, and repetition period of the pulse current; The infrared thermal imaging module 2 acquires parameters including image sampling rate, resolution, and recording duration.

[0036] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the apparatus disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the apparatus description.

[0037] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A compact induction thermography detection device for fatigue cracks in steel structures, characterized by, include: Data processing terminal, infrared thermal imaging module, controller, uniform field magnetization device, and steel structure specimen; The uniform field magnetization device integrates a high-frequency inverter power supply, digital control circuit and magnetic yoke probe. The two ends of the magnetic yoke probe are independently linearly movable feet. The feet are attached to the test surface of the steel structure specimen to apply a uniform magnetic field to the steel structure specimen and generate induction heating. The infrared thermal imaging module is fixed to the side of the uniform field magnetization device by a multi-directionally adjustable mechanical bracket. The optical axis of the infrared thermal imaging module's lens is perpendicular to the center of the detection area formed between the two feet of the magnetic yoke probe, and is used to capture dynamic thermal sequence images of the detection area. The controller is electrically connected to the uniform field magnetization device and the infrared thermal imaging module, respectively, and is used to drive the uniform field magnetization device to generate an excitation magnetic field and realize the synchronous acquisition of magnetic field excitation and thermal image. The data processing terminal communicates with the controller, sends control commands to the uniform field magnetization device through the controller, receives data collected by the infrared thermal imaging module, and runs thermal imaging analysis software to perform induction thermal imaging detection and analysis on the steel structure specimen, thereby realizing the visual location and evaluation of defects.

2. The compact inductive thermal imaging detection device for fatigue cracks in steel structures according to claim 1, characterized in that, The high-frequency inverter power supply, digital control circuit, and magnetic yoke probe integrated within the uniform field magnetization device include: The digital control circuit is electrically connected to the high-frequency inverter power supply and is used to output control signals to adjust the output frequency and power of the high-frequency inverter power supply. The high-frequency inverter power supply is electrically connected to the excitation coil of the magnetic yoke probe to provide high-frequency excitation current to the excitation coil.

3. A compact inductive thermal imaging detection device for fatigue cracks in steel structures according to claim 1, characterized in that, The magnetic yoke probe is a magnetic yoke heating probe with a split symmetrical layout of two independent magnetic arms. The main body is a magnetic yoke made of high magnetic permeability material. The bottom ends of the two magnetic arms form independently linearly movable feet that fit into the steel structure specimen, realizing continuous adjustment and locking of the spacing. Each foot end is equipped with a standardized interface for assembling magnetic yoke end structures of different sizes. The excitation coil and the magnetic yoke probe are integrated into a single structure.

4. A compact inductive thermal imaging detection device for fatigue cracks in steel structures according to claim 1, characterized in that, The data processing terminal is a ruggedized tablet computer with industrial-grade protection.

5. A compact inductive thermal imaging detection device for fatigue cracks in steel structures according to claim 1, characterized in that, The data processing terminal and the controller can communicate wirelessly or via wired means through Wi-Fi, Bluetooth or Ethernet.

6. A compact inductive thermal imaging detection device for fatigue cracks in steel structures according to claim 1, characterized in that, The uniform field magnetization device completes the magnetic field excitation and induction heating of the steel structure specimen without external water / air cooling.

7. A compact thermographic testing method for fatigue cracks in steel structures, characterized by, The compact inductive thermal imaging detection device for fatigue cracks in steel structures according to any one of claims 1-6 includes the following steps: S1. Based on the geometric features and testing requirements of the steel structure surface to be tested, select a suitable magnetic yoke probe, attach the base of the magnetic yoke probe of the uniform field magnetization device to the area to be tested of the steel structure specimen, and adjust the attitude of the infrared thermal imaging module so that the optical axis of the lens is perpendicular to the center of the testing area. S2. Set the induction heating parameters and infrared thermal imaging module acquisition parameters through the data processing terminal, and send control commands to the controller through the data processing terminal. The controller drives the uniform field magnetization device to apply a uniform magnetic field excitation to the steel structure specimen and generate induction heating. The controller simultaneously triggers the infrared thermal imaging module to acquire dynamic thermal sequence images. S3. Process and analyze the acquired dynamic thermal sequence images using the pulse phase method and principal component analysis algorithm; S4. By processing and analyzing the thermal image data, automatically identify and locate abnormal areas caused by defects, and generate a standardized inspection report containing the defect location, image features and analysis results.

8. A compact induction thermal imaging testing method for fatigue cracks in steel structures according to claim 7, characterized in that, The induction heating parameters set in S2 via the data processing terminal include the amplitude, width, frequency, and repetition period of the pulse current. The parameters acquired by the infrared thermal imaging module include image sampling rate, resolution, and recording duration.

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