Metal magnetic memory stress detection method and device based on strong magnetizing enhancement

Abstract

The invention relates to a metal magnetic memory stress detection method and device based on strong magnetization enhancement, and belongs to the technical field of metal component stress detection. According to the invention, the permanent magnet is adopted to carry out strong magnetizing pretreatment on the metal component, so that the residual magnetism signal reference is enhanced. On the basis, the integrated automatic detection device integrates magnetizing, multi-channel magnetic signal acquisition and data processing functions, efficient and automatic stress detection is realized, residual magnetism data of discrete points can be converted into a visual stress distribution cloud picture, and high-sensitivity and high-reliability positioning and evaluation of a stress concentration area are realized. The method can improve the precision and sensitivity of stress detection of the metal component, and is suitable for rapid inspection and health monitoring of a large-scale engineering structure.

Description

Technical Field

[0001] This invention belongs to the field of stress detection technology for metal components, and relates to a method and device for detecting magnetic memory stress in metals based on strong magnetization enhancement. Background Technology

[0002] Metal components play a vital role in modern industry, widely used in bridges, pipelines, pressure vessels, aerospace structures, and railways. Detecting residual and operational stresses in these critical infrastructure components is crucial for ensuring industrial safety, extending service life, and preventing structural failure. The accurate detection of stress states in metal components, widely used in bridge, pipeline, and aerospace structures, is essential for structural health monitoring and lifespan prediction.

[0003] Traditional Metal Magnetic Memory Testing (MMMT) uses the Earth's magnetic field as its excitation source. When ferromagnetic metal components experience internal stress and deformation, the magnetic domains undergo irreversible rearrangement due to stress. This change generates a self-leaking magnetic field on the component's surface, known as the "magnetic memory" effect. This magnetic field records the stress history and concentration state. However, due to the extremely low strength of the Earth's magnetic field (approximately 0.05 mT), it can only induce weak magnetic signals on the order of microtesla, resulting in a generally low signal-to-noise ratio (SNR). Furthermore, the magnetic signals induced by the Earth's magnetic field are highly susceptible to external magnetic interference (such as from electrical equipment or moving ferromagnetic materials), material microstructure inhomogeneities, and electronic noise in the detection system. In other words, the signal is weak and easily interfered with, leading to low sensitivity and reliability in MMMT. Therefore, although MMMT technology possesses advantages such as being non-destructive and rapid, it is difficult to achieve high-precision testing in practical engineering applications. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a metal magnetic memory stress detection method and device based on strong magnetization enhancement. By using permanent magnets for strong magnetization, the residual magnetic signal in the stress region is enhanced. Combined with magnetoelastic effect and force-magnetic coupling theory, stress detection with high signal-to-noise ratio and high sensitivity can be achieved.

[0005] To achieve the above objectives, the present invention provides a method for detecting magnetic memory stress in metals based on strong magnetization enhancement, comprising: A high-intensity excitation magnetic field is applied to the test area of ​​a metal component using a permanent magnet, causing it to reach magnetic saturation or near-magnetic saturation. After removing the permanent magnet, a magnetic sensor is used to collect magnetic signals from the area to be measured, and the collected magnetic signals are then filtered. The stress in the test area of ​​the metal component is calculated based on the collected magnetic signals using a pre-set remanence-stress calculation model. After the calculations are completed, the metal components are subjected to AC demagnetization treatment.

[0006] Furthermore, the remanence-stress calculation model is expressed as:

[0007] In the formula, Residual magnetism, Zero stress remanence The stress sensitivity coefficient, For stress.

[0008] Furthermore, after removing the permanent magnet, a multi-channel magnetic sensor array is used to acquire magnetic signals at multiple locations in the area to be tested, and the spatial coordinates are recorded simultaneously. After calculating the stress value based on the magnetic signals at multiple locations, a two-dimensional or three-dimensional stress distribution cloud map of the area to be tested is generated through an interpolation algorithm.

[0009] Furthermore, a high permeability shield is provided on the multi-channel magnetic sensor array.

[0010] Furthermore, the method also includes acquiring the ambient background magnetic field before acquiring the magnetic signal, and subtracting the background magnetic field during subsequent magnetic signal acquisition to ensure measurement accuracy.

[0011] Furthermore, the method also includes applying a high-intensity excitation magnetic field to the test area of ​​the metal component using a permanent magnet under zero stress load.

[0012] In a second aspect, the present invention provides an apparatus for implementing the method described in the first aspect, the apparatus comprising: A magnetizing probe, which contains at least one permanent magnet for strongly magnetizing the area of ​​the metal component to be tested; A magnetic sensor array is used to collect residual magnetic signals in the area to be measured of a metal component; The motion control unit is used to drive the magnetized probe and magnetic sensor array to move along the surface of the metal component along a preset path. The data processing terminal, connected to the magnetic sensor array and motion control unit, is used to receive the residual magnetism signal collected by the magnetic sensor array and calculate the stress in the test area of ​​the metal component according to the preset residual magnetism-stress calculation model.

[0013] Furthermore, a high-permeability shield is provided outside the magnetic sensor array.

[0014] Furthermore, the device also includes a demagnetization module connected to a data processing terminal, used to perform AC demagnetization on the metal components after the calculation is completed.

[0015] Furthermore, the motion control unit can employ a servo motor to drive the magnetizing probe and magnetic sensor array under the control of the data processing terminal.

[0016] The beneficial effects of this invention are as follows: (1) The present invention introduces permanent magnets to strongly magnetize metal components, which significantly enhances the residual magnetic signal of the tested components and serves as a detection benchmark. This allows the magnetic signal changes caused by stress changes to stand out from the background noise and be clearly and accurately detected, thereby improving the signal-to-noise ratio and detection sensitivity.

[0017] (2) The present invention proposes an automatic detection device integrating magnetization-measurement-demagnetization. This device integrates multiple functional modules, realizes continuous and rapid scanning measurement, avoids the cumbersome manual intervention and repeated positioning in traditional methods, can greatly shorten the detection cycle time, and can realize rapid inspection of large structural components (such as bridges and pipelines). It not only saves a lot of manpower and time costs, but also reduces the error introduced by the difference in operator skills, and ensures the consistency and repeatability of the detection results.

[0018] (3) The present invention scans and records the spatial coordinates of the test component by a multi-channel sensor array, which can reconstruct a two-dimensional or three-dimensional stress distribution cloud map on the surface of the test component. It can intuitively and clearly show the specific area, distribution range and gradient change of stress concentration, and provide a data basis for assessing the health status of the structure and locating potential damage.

[0019] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the magnetic domain structure under a metallographic microscope. Figure 2 This is a schematic diagram of the magnetic domain structure; Figure 3 This is a schematic flowchart of a metal magnetic memory stress detection method based on strong magnetization enhancement according to an embodiment of the present invention. Figure 4 To verify the structural diagram of the steel plate specimen used; Figure 5 This is a comparison chart of actual values ​​and theoretical values ​​tested based on this invention; Figure 6The sensitivity and signal-to-noise ratio of residual magnetism detection for steel plate specimens under magnetized and unmagnetized conditions are determined. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0022] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0023] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0024] The interior of a metallic component consists of numerous tiny magnetized regions called magnetic domains. In these domains, the magnetic moments of each atom are aligned in the same direction, forming a macroscopic magnetized region. In an unmagnetized metallic component, the magnetization directions of the domains are randomly distributed and cancel each other out, resulting in no overall macroscopic magnetism. For example... Figure 1 and Figure 2 As shown, the magnetic domain structure of a ferromagnetic material is illustrated, with arrows indicating domains. The shape of the domains can be observed using a metallographic microscope, and their width is approximately 10. -3 cm, volume approximately 10 -9 cm.

[0025] When an external magnetic field is applied, the magnetization directions of the magnetic domains gradually align with the direction of the external magnetic field, thus magnetizing the metal component. As the strength of the external magnetic field increases, the magnetization directions of the domains gradually become more uniform, eventually reaching magnetic saturation. When the external magnetic field is removed, the magnetization directions of some domains remain aligned, forming macroscopic remanence. This is because the presence of domain walls makes it difficult for the magnetic moments inside the domains to completely reverse back to a zero magnetization state; a certain magnetic field strength is required to achieve complete magnetization reversal.

[0026] Based on the above, the principles by which ferromagnetic materials generate remanence mainly include the following aspects: ① The existence and changes of magnetic domain structure ② Rearrangement of magnetic domains under the influence of an external magnetic field ③ The formation of hysteresis loops and the mechanism for maintaining remanence.

[0027] These principles interact to cause metal components to retain a certain degree of magnetization after the external magnetic field is removed, a phenomenon known as remanence.

[0028] When a material is subjected to an external magnetic field, the energy of the external magnetic field is added to the magnetic crystal of the material, resulting in a steady-state total free energy.

[0029]

[0030] in, For total free energy, It exhibits magnetocrystalline anisotropy. Magnetoelastic properties, For demagnetizing energy, It is external magnetic field energy.

[0031] Under quasi-static conditions, the magnetization direction changes from Decision. To simplify the problem, consider the one-dimensional case, assuming the angle between the magnetization direction and the stress direction is... Then the magnetoelastic energy can be expressed as ,in Let be the saturation magnetostriction coefficient. Combining this with the Boltzmann statistical distribution, the macroscopic remanence along the stress direction can be derived. With stress The relationship satisfies:

[0032] In the formula, The remanence under zero stress is directly determined by the initial magnetization intensity; To match the magnetic properties of the material (such as , The model shows that, under strong magnetization conditions, the relevant stress sensitivity coefficient... The value increases significantly, making It exhibits a larger absolute change when stress changes. Furthermore, its exponential decay relationship ensures that it maintains good sensitivity even in high-stress regions.

[0033] In summary, the traditional MMMT method uses the Earth's magnetic field as a weak excitation source, and based on the magnetoelastic effect, stress concentration areas will exhibit weak remanent magnetization anomalies. However, if an artificial strong permanent magnet is used to generate a high-intensity controllable excitation magnetic field, it will significantly increase zero-stress remanent magnetization, ultimately leading to a substantial enhancement of remanent magnetization in stress concentration areas. This makes stress-induced changes easier to detect, thus overcoming the core defect of weak signals in traditional methods.

[0034] Based on this, one embodiment of the present invention provides a method for detecting magnetic memory stress in metals based on strong magnetization enhancement, the method being described below: 1. A permanent magnet is used to actively and intensely magnetize the test area of ​​a metal component under zero stress load. The strong magnetic field aligns the magnetic domains within the component, achieving or nearing magnetic saturation. As a result, the component retains a strong residual magnetism even after the external magnetic field is removed.

[0035] By strongly magnetizing, the remanent magnetization reference value of metal components is greatly increased, making the stress-induced changes more significant, thereby improving the signal-to-noise ratio and detection sensitivity.

[0036] 2. Integrated automatic detection and data acquisition To improve detection efficiency, this embodiment designs an integrated automatic detection device for magnetization and data acquisition. This device integrates a permanent magnet magnetization probe, a multi-channel magnetic sensor array, a motion control unit, and a data processing terminal, achieving full automation of the magnetization, measurement, and demagnetization process. Details are as follows: ①Automated magnetization and data acquisition: The magnetization probe and sensor array are driven by servo motors to scan along the surface of the test piece. The magnetization time is optimized to 1-5 minutes (originally 10 minutes) based on the material thickness and residual magnetism saturation characteristics. The demagnetization time is optimized to within 30 seconds by high-frequency AC pulses, which greatly shortens the detection cycle.

[0037] ② Real-time data processing: The acquired magnetic signals are transmitted to the data processing terminal in real time, and processed using the formula described above. Calculate the remanence-stress relationship and generate a stress distribution map to avoid errors caused by human intervention.

[0038] This device is suitable for rapid inspection of large structures (such as bridges and pipelines), supports continuous multi-point measurement, and is more than 3 times more efficient than manual operation.

[0039] 3. Stress signal processing and interference suppression During and after data acquisition, multiple measures are employed to ensure that the acquired magnetic signals accurately reflect the stress state and reduce environmental interference.

[0040] In this embodiment, the following measures are taken: ①Active magnetic shielding: A high-permeability shielding cover is installed outside the magnetic sensor array to reduce the influence of external stray magnetic fields (such as power equipment and geomagnetic fluctuations).

[0041] ② Differential Measurement and Signal Processing: A differential method is used to cancel common-mode noise. A dedicated sensor is placed outside the array area, far from the target, and theoretically only senses ambient common-mode noise. The output of each main channel in the array is differentially analyzed with the output of this dedicated sensor, and then processed using digital filtering algorithms such as wavelet denoising to effectively extract stress-related magnetic signals.

[0042] ③ Adaptive calibration: The background magnetic field of the environment is collected before the test, and then subtracted from the background magnetic field during the subsequent magnetic signal acquisition process to ensure measurement accuracy.

[0043] Tests showed that, under typical industrial conditions (magnetic field noise ≤ 0.5 mT), the system signal-to-noise ratio could still be maintained above 20 dB, meeting the requirements for on-site testing.

[0044] 4. Regional stress distribution detection and visualization To address the issue that traditional stress-remanence curves only reflect overall stress, this embodiment uses scanning measurement to obtain the load conditions in different regions of the test piece, as detailed below: 1) When acquiring magnetic signals from the test piece, the residual magnetic signals at multiple locations on the surface of the test piece are acquired synchronously using a multi-channel magnetic sensor array, and the spatial coordinates are recorded in real time by a position encoder during the acquisition process.

[0045] 2) Stress distribution reconstruction: based on calculation formula The residual magnetism values ​​at each point are converted into stress values, and two-dimensional or three-dimensional stress cloud maps are generated through interpolation algorithms to intuitively display the stress concentration area and load gradient.

[0046] In this embodiment, 45# steel is used as the test specimen to verify the detection method proposed in this invention.

[0047] First, multiple plate-like structures, each 200 mm long, 20 mm wide, and 5 mm thick, are fabricated as test specimens. Figure 4 As shown in the figure. At the same time, six N35 grade neodymium iron boron permanent magnets with dimensions of 30 mm × 10 mm × 2 mm were selected to construct different magnetic field sources.

[0048] The experimental verification was conducted in an electromagnetically shielded room to minimize interference from stray magnetic fields in the environment. The laboratory temperature was controlled at (25 ± 2) °C. The entire experimental procedure covered four main stages: pretreatment, loading, magnetization measurement, and demagnetization.

[0049] In the pretreatment stage, all specimens were subjected to AC demagnetization to ensure that their initial magnetic state was zero (the residual magnetic field strength was less than 0.1 mT).

[0050] During the loading phase, the specimen was kept under a constant load for 30 seconds at each set load level, then unloaded to 0 kN and left to stand for 30 seconds to release elastic deformation energy. This cyclic loading and unloading process is designed to ensure that the experimental results accurately reflect the material properties under different stress levels.

[0051] During the magnetization stage, N35 grade neodymium iron boron permanent magnets are tightly attached to the predetermined measurement point area of ​​the specimen for strong magnetization, which lasts for 1-5 minutes to ensure that the magnetization process reaches a steady state. During the demagnetization phase, after completing a single magnetization measurement, the specimen is demagnetized using AC to ensure that its magnetic state is restored to its initial state.

[0052] like Figure 5 , Figure 6 As shown, the method proposed in this invention not only maintains the same signal strength as the theoretical value, which is superior to traditional methods, but also performs well in terms of sensitivity and anti-interference ability.

[0053] Strong magnetization significantly enhanced the magnetization of stress concentration regions, resulting in a stronger remanent magnetization signal. According to magnetoelastic theory, the magnetization intensity of stress concentration regions is positively correlated with the stress level, and this positive correlation is even more pronounced under strong magnetization conditions.

[0054] In summary, the metal magnetic memory stress detection method based on strong magnetization enhancement provided by this invention lays a solid foundation for achieving high-sensitivity stress detection by enhancing the magnetization degree of stress concentration areas through strong magnetization. This allows the magnetic field changes in stress concentration areas to be detected more clearly and accurately, thereby improving the accuracy and reliability of stress detection.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A metal magnetic memory stress detection method based on strong magnetization enhancement, characterized in that, The permanent magnet is used to apply a high-intensity excitation field to the to-be-measured region of the metal component, so that the to-be-measured region reaches a magnetic saturation or near magnetic saturation state; After the permanent magnet is removed, a magnetic sensor is used to collect magnetic signals of the to-be-measured region, and the collected magnetic signals are filtered; A preset residual magnetism-stress calculation model is used to calculate the stress of the to-be-measured region of the metal component based on the collected magnetic signals; After the calculation is completed, the metal component is subjected to alternating current demagnetization treatment.

2. The method of claim 1, wherein, The residual magnetism-stress calculation model is represented as: wherein is the remanence, is the zero-stress remanence, is the stress sensitivity coefficient, is the stress.

3. The method of claim 1, wherein, After the permanent magnet is removed, a multi-channel magnetic sensor array is used to collect magnetic signals of multiple positions of the to-be-measured region, and spatial position coordinates are recorded at the same time; after the stress values of the multiple positions are calculated based on the magnetic signals, an interpolation algorithm is used to generate a two-dimensional or three-dimensional stress distribution cloud diagram of the to-be-measured region.

4. The method of claim 3, wherein, A high magnetic permeability shield is arranged on the multi-channel magnetic sensor array.

5. The method of claim 1, wherein, The method further includes, before the magnetic signal collection, collecting an environmental background magnetic field, and subtracting the background magnetic field in the subsequent magnetic signal collection process, so as to ensure the measurement accuracy.

6. The method of claim 1, wherein, The method further includes, under a zero stress load, applying a high-intensity excitation field to the to-be-measured region of the metal component by the permanent magnet.

7. An apparatus for implementing the method of any one of claims 1 to 6, characterized in that, The method comprises: The magnetizing probe is provided with at least one permanent magnet, and is used to strongly magnetize the to-be-measured region of the metal component; The magnetic sensor array is used to collect residual magnetic signals of the to-be-measured region of the metal component; The motion control unit is used to drive the magnetizing probe and the magnetic sensor array to move along a preset path on the surface of the metal component; The data processing terminal is connected with the magnetic sensor array and the motion control unit, and is used to receive the residual magnetic signals collected by the magnetic sensor array, and calculate the stress of the to-be-measured region of the metal component based on a preset residual magnetism-stress calculation model.

8. The apparatus of claim 7, wherein, A high magnetic permeability shield is arranged outside the magnetic sensor array.

9. The apparatus of claim 7, wherein, The device further includes a demagnetization module connected with the data processing terminal, and is used to perform alternating current demagnetization treatment on the metal component after the calculation is completed.

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