A tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe

Abstract

This invention discloses a tweezer-shaped focusing magnetization structure leakage magnetic flux detection probe. Magnetic flux generated by a first rectangular permanent magnet is introduced into the ferromagnetic specimen under test via a first tweezer-shaped magnetic yoke foot, forming a local magnetization field in the detection area between the two feet. The magnetic flux then flows back to the second rectangular permanent magnet through the other tweezer-shaped magnetic yoke foot and is closed by a cuboid magnetic yoke, thus forming a short-path closed magnetic loop. When the ferromagnetic specimen under test is free of defects, the magnetic field distribution in the detection area remains balanced, and the magnetic sensor outputs a stable baseline signal. When cracks or corrosion defects are present, the defect area is equivalent to a high magnetic resistance region, causing local distortion of the magnetic circuit. Some magnetic flux escapes above the defect, forming a leakage magnetic field, which in turn causes a change in the sensor output signal. The leakage magnetic flux signal is acquired during the scanning process, and the defect can be identified and quantitatively assessed by processing the acquired signal.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic nondestructive testing technology. More specifically, it relates to a tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe, which can be applied to aerospace, oil and gas pipelines and metal structure health monitoring and other scenarios. Background Technology

[0002] With the rapid development of high-end equipment manufacturing and energy infrastructure, the long-term service safety of ferromagnetic structures under extreme conditions is becoming increasingly prominent. In the aerospace field, critical load-bearing components such as landing gear are prone to fatigue cracking under long-term alternating and impact loads. In the new energy field, ferromagnetic blades or key connecting components in large wind turbine generators may also experience cracking and material degradation under complex stress and environmental conditions. These defects often exhibit small size, irregular shape, and surface / near-surface distribution characteristics, placing higher demands on detection technologies.

[0003] Currently, non-destructive testing methods for ferromagnetic materials mainly include magnetic flux leakage (MFL), eddy current testing (EC), and ultrasonic testing (UT). Among these, magnetic flux leakage technology is widely used in pipeline and structural inspections due to its good applicability to ferromagnetic materials. However, existing MFL testing techniques typically employ large-size magnetic yokes and overall strong magnetization, such as... Figure 1 As shown, it has the following limitations:

[0004] (1) The magnetic circuit structure is long and the magnetic flux utilization rate is low: the traditional magnetization method relies on the closure of a long magnetic circuit. The magnetic flux is severely lost during transmission, resulting in insufficient effective magnetic field strength acting on the detection area.

[0005] (2) Lack of local magnetic field control capability: Existing structures are difficult to achieve effective focusing of magnetic field in local areas, resulting in weak signal response of small defects and limited detection resolution;

[0006] (3) Insufficient sensitivity to microcracks and near-surface defects: For microcracks with a width of less than 0.15 mm, the traditional MFL signal has low amplitude and poor signal-to-noise ratio, and is easily submerged by background noise;

[0007] (4) Large structural volume and heavy weight: difficult to meet the local inspection requirements of complex aerospace components;

[0008] (5) Poor adaptability to complex defects: For irregular cracks, bifurcated cracks and corrosion coupling defects, the existing detection signals are prone to distortion and aliasing, making it difficult to effectively identify and quantitatively evaluate them;

[0009] (6) It is difficult to balance the detection capabilities of near-surface and buried defects: Although increasing the magnetic field strength can enhance the penetration ability, it will lead to a decrease in surface resolution, resulting in a significant performance trade-off.

[0010] Furthermore, the early identification of microcracks is extremely demanding in the inspection of critical load-bearing structures such as aerospace landing gear; in wind power equipment, defects in blades or critical components often have complex geometries, posing even greater challenges to the spatial resolution and adaptability of inspection. Therefore, existing inspection technologies still fall short of meeting the needs of multi-scenario applications in terms of high sensitivity, local high resolution, and structural compactness.

[0011] In summary, there is an urgent need for a new detection structure that can shorten the magnetic circuit, increase the magnetic flux density, achieve local magnetic field focusing, and balance detection sensitivity and penetration capability, in order to meet the high-precision detection requirements of microcracks and complex defects. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of the prior art and provide a tweezer-shaped focusing magnetization structure leakage magnetic field detection probe. By constructing a sensing structure with a short magnetic circuit, high magnetic flux density and controllable distribution of local magnetic field, it can achieve high-resolution detection and quantitative evaluation of microcracks and complex defects on and near the surface of ferromagnetic materials.

[0013] To achieve the above-mentioned objectives, the present invention provides a tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe, characterized in that it comprises: a rectangular magnetic yoke, a rectangular magnet, tweezer-shaped magnetic yoke feet, and a magnetic sensor;

[0014] The rectangular magnetic yoke is located at the top of the probe and serves as the dominant magnetic flux channel in the magnetic flux circuit.

[0015] There are two rectangular magnets, labeled as the first rectangular magnet and the second rectangular magnet. The two rectangular magnets are vertically installed at both ends of the rectangular yoke and are flush with the left and right end faces of the rectangular yoke. The two rectangular magnets are in opposite magnetization directions, i.e., arranged in the NS and SN manner.

[0016] There are two tweezer-type magnetic yoke boots, which are respectively labeled as the first tweezer-type magnetic yoke boot and the second tweezer-type magnetic yoke boot;

[0017] The two tweezer-shaped magnetic yoke feet are mirror-symmetrical. The top end face of each tweezer-shaped magnetic yoke foot is the same size as the end face of the rectangular magnet, and the bottom end face is inclined to the top end face. After the two tweezer-shaped magnetic yoke feet are connected to the rectangular magnet, they are arranged in a symmetrical "tweezer" shape. A non-magnetic support structure plastic base is set on the feet of the tweezer-shaped magnetic yoke feet to fix the magnetic sensor.

[0018] The magnetic sensor is located between the feet of the two tweezer-shaped magnetic yoke feet, and is flush with the bottom end face of the tweezer-shaped magnetic yoke feet after being fixed by a non-magnetic support structure plastic base.

[0019] The objective of this invention is achieved as follows:

[0020] This invention discloses a tweezer-shaped focusing magnetization structure leakage magnetic flux detection probe. Magnetic flux generated by a first rectangular permanent magnet is introduced into the ferromagnetic specimen under test via a first tweezer-shaped magnetic yoke foot. A local magnetization field is formed in the detection area between the two feet. Subsequently, the magnetic flux flows back to the second rectangular permanent magnet through the other tweezer-shaped magnetic yoke foot and is closed by a cuboid magnetic yoke, thus forming a short-path closed magnetic loop. Due to the opposing structure of the tweezer-shaped feet, the magnetic flux is constrained and concentrated in the middle region, forming a detection area with high magnetic field strength. When the ferromagnetic specimen under test is defect-free, the material's permeability is uniform, and the magnetic flux stably closes along a predetermined path. The magnetic field distribution within the detection area remains balanced. The magnetic sensor outputs a stable baseline signal. When cracks or corrosion defects are present, the defect area is equivalent to a high magnetoresistance region, causing local distortion of the magnetic circuit. Some magnetic flux escapes from the surface of the tested ferromagnetic specimen, forming a leakage magnetic field above the defect, which causes a change in the sensor output signal. During the scanning process, the magnetic sensor collects the leakage magnetic signal. The leakage magnetic signal generated by the defect usually exhibits bipolar and unipolar waveform characteristics in the axial and normal components of the scanning direction, respectively. The amplitude of the obtained signal is related to the defect depth, the signal width is related to the defect size, and the signal gradient reflects the defect boundary change characteristics. Finally, the defect can be identified and quantitatively evaluated by processing the signal.

[0021] Meanwhile, the tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe of the present invention also has the following beneficial effects:

[0022] (1) Compared with the traditional U-shaped magnetic yoke flux leakage detection probe, the present invention has the following significant advantages:

[0023] 1) Traditional U-shaped probes use an open magnetic circuit structure, resulting in a long and dispersed magnetic flux path; while the present invention constructs a short closed magnetic circuit through a tweezer-like magnetic yoke structure, which significantly reduces magnetic flux loss and improves magnetic flux utilization efficiency.

[0024] 2) Traditional U-shaped probes have a large magnetic field distribution range, making it difficult to achieve local enhancement; this invention forms a narrow gap region by using two tweezer-shaped feet, which makes the magnetic flux highly concentrated in the detection area, achieving local high-intensity magnetization.

[0025] 3) Traditional U-shaped probes have a weak response to microcracks (especially 0.15 mm); the present invention can significantly improve the amplitude of the leakage magnetic signal of microcracks due to the enhancement of the local magnetic field, thus achieving higher sensitivity detection.

[0026] 4) Traditional structures struggle to maintain surface resolution while simultaneously ensuring penetration depth; this invention enhances the detection capability of buried defects by increasing the local magnetic field strength, thereby enabling the magnetic field to penetrate more deeply.

[0027] 5) Traditional U-shaped probes have a large volume; this invention adopts a tweezer-like compact structure, which has the advantages of smaller volume and lighter weight.

[0028] (2) Compared with the prior art, the present invention has the following advantages: it can effectively detect microcracks as small as about 0.15 mm with a signal-to-noise ratio of more than 20 dB; it can detect defects with a depth of about 4 mm; it can achieve high-intensity magnetization only in the detection area, thereby improving the contrast of defect signals; and it has good response capability to irregular cracks and complex corrosion. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a specific implementation of a traditional U-shaped magnetic flux leakage probe;

[0030] Figure 2 This is a schematic diagram of a specific embodiment of the magnetic flux leakage detection probe with a tweezer-shaped focusing magnetization structure according to the present invention;

[0031] Figure 3 yes Figure 1 The diagram shows the magnetic circuit of the magnetic flux leakage detection probe.

[0032] Figure 4 This is a simulation diagram of the magnetic field distribution of a traditional U-shaped magnetic flux leakage probe and a magnetic flux leakage detection probe;

[0033] Figure 5 These are schematic diagrams of specimens with cracks of different lengths;

[0034] Figure 6 These are images showing the detection results of cracks of different lengths;

[0035] Figure 7 These are schematic diagrams of crack specimens at different burial depths;

[0036] Figure 8 These are images showing the results of crack detection at different burial depths. Detailed Implementation

[0037] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0038] Example

[0039] Figure 2 This is a schematic diagram of a specific embodiment of the magnetic flux leakage detection probe with a tweezer-shaped focusing magnetization structure according to the present invention.

[0040] In this embodiment, as Figure 2As shown, the present invention provides a tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe, comprising: a rectangular magnetic yoke, a rectangular magnet, tweezer-shaped magnetic yoke feet, and a magnetic sensor;

[0041] The rectangular magnetic yoke 1 is located at the top of the probe and serves as the dominant magnetic flux channel in the magnetic flux circuit.

[0042] There are two rectangular magnets, labeled as the first rectangular magnet 2 and the second rectangular magnet 3 respectively. The two rectangular magnets are vertically installed at both ends of the rectangular yoke and are flush with the left and right end faces of the rectangular yoke 1. The two rectangular magnets are in opposite magnetization directions, i.e., arranged in the NS and SN manner.

[0043] There are two tweezer-type magnetic yoke boots, which are respectively labeled as the first tweezer-type magnetic yoke boot 4 and the second tweezer-type magnetic yoke boot 5;

[0044] The two tweezer-shaped magnetic yoke feet are mirror-symmetrical. The top end face of each tweezer-shaped magnetic yoke foot is the same size as the end face of the rectangular magnet, and the bottom end face is inclined to the top end face. After the two tweezer-shaped magnetic yoke feet are connected to the rectangular magnet, they are arranged in a symmetrical "tweezer" shape. A non-magnetic support structure plastic base is provided on the feet of the tweezer-shaped magnetic yoke feet to fix the magnetic sensor 6.

[0045] In this embodiment, the magnetic sensor adopts a linear array structure, with multiple Hall magnetic sensors arranged along or perpendicular to the scanning direction to form a linear array structure;

[0046] The magnetic sensor is located between the feet of the two tweezer-shaped magnetic yoke feet, and is flush with the bottom end face of the tweezer-shaped magnetic yoke feet after being fixed by a non-magnetic support structure plastic base.

[0047] The following is an analysis of the defect detection process of the tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe. The specific process is as follows:

[0048] The tweezer-shaped focusing magnetization structure leakage magnetic field detection probe is placed above the ferromagnetic specimen under test. The magnetic flux generated by the first rectangular permanent magnet is introduced into the ferromagnetic specimen under test through the first tweezer-shaped magnetic yoke foot. A local magnetization field is formed in the detection area between the two feet. Then the magnetic flux flows back to the second rectangular permanent magnet through the other tweezer-shaped magnetic yoke foot and is closed by the cuboid magnetic yoke, thus forming a short-path closed magnetic loop.

[0049] Because the tweezer-shaped feet are in an opposing structure, the magnetic flux is constrained and concentrated in the middle region, forming a detection area with a high magnetic field strength. When the ferromagnetic specimen being tested is free of defects, the material has uniform magnetic permeability, and the magnetic flux closes stably along a predetermined path. The magnetic field distribution within the detection area remains balanced, and the Hall magnetic sensor outputs a stable baseline signal. However, when cracks or corrosion defects are present, the defect area is equivalent to a high magnetic resistance region, causing local distortion of the magnetic circuit. Some magnetic flux escapes from the surface of the ferromagnetic specimen being tested, forming a leakage magnetic field above the defect, which in turn causes a change in the sensor output signal.

[0050] During the scanning process, the magnetic sensor collects the leakage magnetic signal. The leakage magnetic signal generated by the defect usually exhibits bipolar and unipolar waveform characteristics in the axial and normal components of the scanning direction, respectively. The amplitude of the obtained signal is related to the defect depth, the signal width is related to the defect size, and the signal gradient reflects the defect boundary change characteristics. Finally, the defect can be identified and quantitatively evaluated by processing the signal.

[0051] In this embodiment, as Figure 2 As shown, a narrow gap is provided between the feet of the tweezer-type magnetic yoke boot, with a spacing of 2–5 mm. In this embodiment, the spacing is set to 3 mm.

[0052] Figure 3 The magnetic circuit of the tweezer-shaped magnetic leakage probe is described. When the probe acts on the surface of the specimen, the magnetic flux flows to the specimen, forming a closed-loop magnetic circuit diagram: magnet NS - tweezer-shaped magnetic conductive structure - specimen - tweezer-shaped magnetic conductive structure - magnet SN - rectangular magnetic yoke.

[0053] Figure 4 Simulation diagrams of the magnetic field distribution of a traditional U-shaped magnetic flux leakage probe and a magnetic flux leakage detection probe are presented. The left diagram shows the magnetic field distribution of the traditional U-shaped magnetic flux leakage probe, while the right diagram shows the magnetic field distribution of the magnetic flux leakage detection probe proposed in this invention. The comparison reveals that the magnetic field lines of the traditional magnetic flux leakage probe in the left diagram are more dispersed, the magnetic flux density in the detection area is relatively low, and the magnetic field is diffused in space. In contrast, the tweezer-shaped magnetic focusing probe of this invention, due to its opposing tweezer-shaped magnetic yoke structure, effectively confines and concentrates the magnetic flux in a local area between the two "shoe feet," resulting in a significantly denser distribution of magnetic field lines. These results demonstrate that this invention, by shortening the magnetic circuit and achieving local magnetic flux concentration, significantly improves the magnetic field strength and magnetic flux density in the detection area, thereby enhancing the material's internal defect response to magnetic field disturbances. Especially for buried defects, the increased local magnetization leads to a significantly larger magnetic flux leakage signal amplitude compared to the traditional structure, which is beneficial for improving the signal-to-noise ratio and defect identification capability.

[0054] Therefore, the simulation results verify the effectiveness of the tweezer-like focusing magnetization structure of the present invention in terms of magnetic field enhancement and defect response amplification, providing a theoretical basis for achieving high-sensitivity defect detection.

[0055] In this embodiment, Figure 5 This is a schematic diagram of the structure of a specimen with cracks of different lengths. The specimen contains nine artificial crack defects, all with a crack spacing of 30 mm. The crack lengths are 2 mm, 3 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, and 35 mm, respectively, with crack widths and depths of 0.15 mm and 2 mm, respectively. Based on the above specimens, the tweezers-shaped focusing magnetization probe described in this invention was used for detection. The detection results are as follows: Figure 6 As shown. Figure 6 The original detection signal and the signal after low-pass filtering are presented respectively. As can be seen from the figure, all nine cracks of different lengths can be clearly detected, and the corresponding signals all exhibit a stable "one valley, one peak" characteristic. With the increase of crack length, the signal amplitude gradually increases, and the signals corresponding to each defect show good consistency and distinguishability, indicating a stable correspondence between the detection signal and the crack size. Experimental results further demonstrate that this invention can effectively detect cracks with a minimum size of 0.15 mm × 2 mm × 2 mm, verifying its high sensitivity detection capability for minute defects.

[0056] In this embodiment, Figure 7 Schematic diagrams of crack specimens with different burial depths are shown. The length and width of each crack are 25 mm and 0.35 mm, respectively, and the burial depths are 1 mm, 2 mm, 3 mm, and 4 mm, respectively. The probe of this invention was used to test the above specimens, and the test results are as follows: Figure 8 As shown. Figure 8 The original signal and the filtered signal curves are also presented. The detection results show that all four types of cracks with different burial depths can be effectively identified, exhibiting a "peak-valley" waveform, opposite to the signal polarity characteristics of surface cracks. As the crack depth increases, the signal amplitude gradually decreases, but the overall trend remains stable, and the signals corresponding to defects at different burial depths show good consistency and an approximately linear relationship. This indicates that while ensuring the sensitivity of surface defect detection, this invention also possesses stable response capabilities and good quantitative potential for buried defects within a certain depth range.

[0057] In summary, the analysis of the detection results of cracks of different lengths and burial depths shows that the tweezer-shaped focusing magnetization detection probe of the present invention can achieve stable identification of multi-scale defects. The detection signal has a good correspondence and variation law with the defect size and burial depth, which further verifies the effectiveness of the structure in improving detection sensitivity and quantitative evaluation capability.

[0058] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe, characterized in that, include: Rectangular magnetic yoke, rectangular magnet, tweezer-type magnetic yoke feet, and magnetic sensor; The rectangular magnetic yoke is located at the top of the probe and serves as the dominant magnetic flux channel in the magnetic flux circuit. There are two rectangular magnets, labeled as the first rectangular magnet and the second rectangular magnet. The two rectangular magnets are vertically installed at both ends of the rectangular yoke and are flush with the left and right end faces of the rectangular yoke. The two rectangular magnets are in opposite magnetization directions, i.e., arranged in the NS and SN manner. There are two tweezer-type magnetic yoke boots, which are respectively labeled as the first tweezer-type magnetic yoke boot and the second tweezer-type magnetic yoke boot; The two tweezer-shaped magnetic yoke feet are mirror-symmetrical. The top end face of each tweezer-shaped magnetic yoke foot is the same size as the end face of the rectangular magnet, and the bottom end face is inclined to the top end face. After the two tweezer-shaped magnetic yoke feet are connected to the rectangular magnet, they are arranged in a symmetrical "tweezer" shape. A non-magnetic support structure plastic base is set on the feet of the tweezer-shaped magnetic yoke feet to fix the magnetic sensor. The magnetic sensor is located between the feet of the two tweezer-shaped magnetic yoke feet, and is flush with the bottom end face of the tweezer-shaped magnetic yoke feet after being fixed by a non-magnetic support structure plastic base.

2. The tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe according to claim 1, characterized in that, The tweezer-type magnetic yoke boot feet are provided with a narrow gap between the boot feet, with a spacing of 2–5 mm.

3. The tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe according to claim 1, characterized in that, The magnetic sensor adopts a linear array structure, with multiple Hall magnetic sensors arranged along or perpendicular to the scanning direction to form a linear array structure.

4. The tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe according to claim 1, characterized in that, The defect detection process of the tweezer-shaped focusing magnetization structure magnetic flux leakage detection probe is as follows: The tweezer-shaped focusing magnetization structure leakage magnetic field detection probe is placed above the ferromagnetic specimen under test. The magnetic flux generated by the first rectangular permanent magnet is introduced into the ferromagnetic specimen under test through the first tweezer-shaped magnetic yoke foot. A local magnetization field is formed in the detection area between the two feet. Then the magnetic flux flows back to the second rectangular permanent magnet through the other tweezer-shaped magnetic yoke foot and is closed by the cuboid magnetic yoke, thus forming a short-path closed magnetic loop. Because the tweezer-shaped feet are in an opposing structure, the magnetic flux is constrained and concentrated in the middle region, forming a detection area with a high magnetic field strength. When the ferromagnetic specimen being tested is free of defects, the material has uniform magnetic permeability, and the magnetic flux closes stably along a predetermined path. The magnetic field distribution within the detection area remains balanced, and the Hall magnetic sensor outputs a stable baseline signal. However, when cracks or corrosion defects are present, the defect area is equivalent to a high magnetic resistance region, causing local distortion of the magnetic circuit. Some magnetic flux escapes from the surface of the ferromagnetic specimen being tested, forming a leakage magnetic field above the defect, which in turn causes a change in the sensor output signal. During the scanning process, the magnetic sensor collects the leakage magnetic signal. The leakage magnetic signal generated by the defect usually exhibits bipolar and unipolar waveform characteristics in the axial and normal components of the scanning direction, respectively. The amplitude of the obtained signal is related to the defect depth, the signal width is related to the defect size, and the signal gradient reflects the defect boundary change characteristics. Finally, the defect can be identified and quantitatively evaluated by processing the signal.

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