Multifilament rope type structure damage magnetostriction powder coating guided wave detection method

Abstract

The invention discloses a magnetostriction powder coating guided wave detection method for damage of a multi-wire rope type structure. The method comprises the following steps: preparing Fe83Ga17 alloy powder by using a gas atomization method; in the manufacturing stage of the cable of the multi-wire cable type structure of the bridge, the spraying area of a base material of the cable is pretreated, then alloy powder is sprayed, the base material is wrapped with a sheath, and the cable is obtained; a magnetostrictive guided wave transducer is installed outside a sheath, then the intelligent cable is installed on a bridge, and damage detection is conducted on the intelligent cable through a signal excitation receiver by adopting a pulse echo method. The Fe83Ga17 alloy powder with good magnetostrictive property is uniformly sprayed on the surface of the multi-wire cable type structure, and the magnetostrictive guided wave transducer is mounted at the corresponding position, so that the energy conversion efficiency is greatly improved, the detection range of ultrasonic guided waves is enlarged, and the possibility is provided for long-term structural health monitoring of the bridge cable.

Description

Technical Field

[0001] This invention relates to a waveguide detection method for coatings, which falls under the field of nondestructive testing, and specifically to a waveguide detection method for magnetostrictive powder coatings with damage to multi-filament structures. Background Technology

[0002] Multi-wire cables are widely used in various engineering applications, such as stay cables in bridges and power lines in power grids. These structures are characterized by long spans and high tensile stresses. The safety of engineering structures depends on the integrity of these cable structures. However, due to the harsh service conditions, these cable structures have more stringent requirements for non-destructive testing and online structural health monitoring. Currently, there are many non-destructive testing methods, such as visual inspection, X-ray, computed tomography, ultrasonic testing, and magnetic flux leakage. However, existing methods have certain limitations in the application of multi-wire structure inspection and health monitoring.

[0003] In existing methods, magnetic flux leakage (MF) testing can only be used for ferromagnetic materials, and the surface of the specimen cannot have a coating or cladding. Furthermore, MF testing cannot detect internal defects in ferromagnetic materials. Ultrasonic nondestructive testing uses volume waves, which can only cover a small area of ​​the structure under test at a time, i.e., single-point testing, resulting in low efficiency for large or distant structures. Traditional ultrasonic guided wave testing, using piezoelectric and magnetostrictive methods, cannot uniformly generate guided waves in every filament of a multi-filament structure. The most widespread application of magnetostrictive guided wave transducers is to attach pre-magnetized magnetostrictive tape (such as iron-cobalt alloy tape) to the surface of a steel pipe, surrounding it with an excitation coil to generate torsional guided waves. However, due to the irregular surface of the steel strand and the brittleness and hardness of the magnetostrictive tape, it is difficult to bend it at large curvatures, making it impossible to attach the tape to the surface of the steel strand. Therefore, utilizing the magnetostrictive effect of the steel strand itself to excite and receive guided waves is a convenient and efficient method. However, bridge cables have far more steel wire cores than 7-core steel strands, and the outer periphery of the wire bundle is also covered with a polyethylene sheath. This makes it difficult to evenly distribute the bias magnetic field within the cable wires, inevitably affecting the transduction efficiency of the guided wave and the detection sensitivity of individual filaments. The size of the piezoelectric transducer is related to the excitation frequency. In low-frequency applications, piezoelectric transducers are typically large, and the presence of recesses and gaps between the wires makes it difficult for the coupling surface of the piezoelectric transducer to effectively and completely contact the cable surface wires. In practice, point contact or line contact is generally used. This localized contact transduction method makes it difficult to form a uniform excitation wave source in the circumferential direction of the cable, which is detrimental to exciting pure longitudinal modal guided waves. Furthermore, piezoelectric transducers are a contact-based transduction method. To ensure transduction stability, they are generally bonded to the structural surface using coupling agents or epoxy resin adhesives. This installation method carries the risk of detachment or slippage under the influence of wind loads and tension during long-term monitoring applications. Summary of the Invention

[0004] To address the problems existing in the background art, this invention provides a method for detecting guided waves in multi-filament cable structures using magnetostrictive powder coating. This invention designs a novel method for generating and detecting guided waves in multi-filament structures based on the sprayed magnetostrictive powder coating (SMPC). The aim is to overcome the shortcomings of traditional ultrasonic guided wave detection technology in engineering applications, namely, the limitations of piezoelectric transducers in bridge cable inspection due to the rapid dissipation of acoustic energy caused by relying on inter-filament contact to propagate guided waves from the outer layer to the inner layer.

[0005] The technical solution adopted in this invention is: The present invention provides a guided wave detection method for magnetostrictive powder coating damage in multi-filament structures, characterized in that: Step 1) Prepare Fe with good magnetostrictive properties using gas atomization method. 83 Ga 17 alloy powder.

[0006] Step 2) In the cable manufacturing stage of multi-wire cable structures for bridges, the spraying areas of each base material of the cable are first pretreated, and then Fe is uniformly sprayed. 83 Ga 17 Alloy powder is used to completely wrap each base material with a sheath to obtain a cable.

[0007] Step 3) Install a magnetostrictive guided wave transducer on the outside of the sheath in the sprayed area of ​​the cable to obtain a smart cable.

[0008] Step 4) Install the smart cable on the bridge and use the pulse echo method to detect damage to the smart cable by exciting the receiver with a signal.

[0009] In step 1), during the preparation of Fe 83 Ga 17 When making alloy powder, first, Fe 83 Ga 17 The alloy ingot is heated in a high-purity argon (Ar) atmosphere to completely melt it into Fe. 83 Ga 17 The alloy was molten; then heating was stopped, pressure was applied, and the alloy was broken up and solidified to obtain Fe. 83 Ga 17 Alloy particles, selecting Fe particles within a preset particle size range. 83 Ga 17 The alloy particles were removed from the argon (Ar) environment, then subjected to a secondary heating treatment, and finally cooled to room temperature to obtain Fe. 83 Ga 17 alloy powder.

[0010] The initial heating process specifically involves heating to a temperature not lower than 1580℃ and holding for 5 minutes; the pressurization process specifically involves pressurizing argon gas (Ar) to a pressure not lower than 3.4 MPa, during which the temperature is gradually reduced to room temperature until the Fe is broken down. 83 Ga 17 The alloy liquid solidifies; the secondary heating treatment specifically involves heating to no less than 800℃ and holding at that temperature for 4 to 8 hours.

[0011] The Fe 83 Ga 17 The preset particle size range for the alloy particles is 30~50μm.

[0012] In step 2), for each base material of the cable, the sprayed area of ​​the base material is sandblasted with corundum powder to increase the surface roughness of the base material. Then, the sprayed area of ​​the base material is cleaned in acetone solution, dried, and preheated to 100~200℃ to complete the pretreatment. The length of the sprayed area is generally 55-65mm.

[0013] In step 2), for each base material of the cable, the pretreated base material is straightened and rotated uniformly around its own central axis, and then Fe is applied using an oxygen fuel spraying device. 83 Ga 17 Alloy powder is heated and accelerated in a high-temperature, high-pressure supersonic flame and then sprayed onto the coating area of ​​the base material to form a high-quality magnetostrictive powder coating. After the coating is completed and cooled to room temperature, the base materials are stacked in a cylindrical shape, with the coating area of ​​each base material located at the same length position, and wrapped with a polyethylene sheath to finally form a cable.

[0014] The temperature of the supersonic flame is not lower than 2600℃, and the pressure is not lower than 8 bar. After the nozzle of the oxygen fuel spraying equipment is adjusted to a preset distance from the surface of the spraying area, Fe is propelled by the supersonic flame. 83 Ga 17 Alloy powder is sprayed onto the spraying area at a spray flow rate of 1000-1200 m / s, ultimately forming a magnetostrictive powder coating with a thickness of 320-380 μm.

[0015] In step 3), the magnetostrictive guided wave transducer includes an ultrasonic guided wave transducer coil and a permanent bias magnet. The ultrasonic guided wave transducer coil is fitted outside the sheath of the cable where the spraying area is located and fixed with iron hoops and located at the center position. The axial length of the ultrasonic guided wave transducer coil is less than the axial length of the spraying area. The bias magnet includes a yoke and two permanent magnets with opposite polarities. The yoke is magnetically attracted and fixed to the cable and fixed with iron hoops and located at the center position outside the ultrasonic guided wave transducer coil. The two permanent magnets are symmetrically installed at the upper and lower ends of the yoke.

[0016] The ultrasonic waveguide transducer coil generates a dynamic magnetic field. The magnetic field direction of the permanent magnet is perpendicular to the axial direction of the cable and the length direction of the yoke, so that the bias magnet generates a static magnetic field that is consistent with the direction of the dynamic magnetic field. The parallel dynamic and static magnetic fields cause the magnetostrictive powder coating and each base material to alternately expand and contract according to the magnetostrictive effect, thereby generating longitudinal guided waves.

[0017] In step 4), the signal excitation receiver includes a preamplifier and a signal generator connected in sequence, as well as a filter, a digital oscilloscope, and a host computer connected in sequence. The preamplifier and the filter are both connected to the ultrasonic guided wave transducer coil. When performing damage detection on the smart cable, the magnetostrictive guided wave transducer is used as both an excitation transducer and a receiving transducer using the pulse echo method. A 30 kHz-150 kHz sine wave excitation signal is generated by the signal generator, and then transmitted to the ultrasonic guided wave transducer coil via the preamplifier and propagates in the cable. When the sine wave excitation signal passes through the damage, a guided wave echo signal is generated. The guided wave echo signal is received by the filter and transmitted to the digital oscilloscope for display. Finally, it is stored in the host computer after analog-to-digital conversion.

[0018] The beneficial effects of this invention are: Traditional ultrasonic guided wave testing technology, when used for bridge cable inspection, suffers from drawbacks. Due to the large number of steel wire cores in the cable and the polyethylene sheath covering the wire bundle, the bias magnetic field is difficult to distribute uniformly within the cable wires. This inevitably affects the transduction efficiency of the guided wave and the detection sensitivity of individual filaments, resulting in rapid energy dissipation with increasing distance and limiting its suitability for long-term, long-distance health monitoring. In contrast, the method of this invention enables reliable inspection of multi-filament cable structures by utilizing Fe, which possesses excellent magnetostrictive properties. 83 Ga 17 Alloy powder is uniformly sprayed onto the surface of a multi-wire cable structure, and a new type of magnetostrictive guided wave transducer consisting of an ultrasonic guided wave transducer coil and a bias magnet is installed at the corresponding position. This greatly improves the energy conversion efficiency (2000%), increases the detection range of ultrasonic guided waves, and provides the possibility for long-term structural health monitoring of bridge cables. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the magnetostrictive powder coating guided wave detection for damage to multi-filament structures according to the present invention. Figure 2 This is a diagram of the detection system of the present invention; Figure 3 This is a processed diagram of the bridge cable system; Figure 4 The diagram shows the sensor location, the L(0,1) waveguide path, and the experimental setup. Figure 5 This is a graph of the signal received by the uncoated end of the sensor at 50kHz. Figure 6 The signal received by the sensor with the coating at 50kHz is a graph. Figure 7 This is a graph of the signal received by the uncoated end of the sensor at 100kHz. Figure 8 The signal received by the sensor with the coating at 100kHz is a graph. Figure 9 The diagram shows the group velocity dispersion curve of the steel wire rope. In the diagram: 1. Cable, 11. Wire rope, 12. Sheath, 2. Ultrasonic guided wave transducer coil, 3. Spraying area, 4. Bias magnet, 41. Yoke, 42. Permanent magnet, 5. Magnetostrictive powder coating, 6. Signal excitation receiver, 61. Preamplifier, 62. Signal generator, 63. Filter, 64. Digital oscilloscope, 65. Host computer. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1:

[0022] The guided wave detection method for magnetostrictive powder coating damage in multi-filament structures according to the present invention is as follows: First, Fe with good magnetostrictive properties was prepared using a gas atomization method. 83 Ga 17 Alloy powder; in the preparation of Fe 83 Ga 17 When making alloy powder, first, Fe 83 Ga 17 The alloy ingot is subjected to a heat treatment in a high-purity argon atmosphere (Ar) with a purity of at least 99.999% (5N grade) to 1580℃ and held for 5 minutes, thereby completely melting it into Fe. 83 Ga 17 The alloy was slurried; then heating was stopped and argon (Ar) gas was pressurized to 3.4 MPa. During the pressurization process, the temperature was gradually reduced to room temperature until the Fe alloy broke apart. 83 Ga 17 Fe is obtained by solidification of alloy liquid. 83 Ga 17 Alloy particles are formed when a high-pressure, high-speed argon gas stream acts on the molten Fe83Ga17 alloy. This process converts the kinetic energy of the high-pressure gas jet into the surface energy of the melt. During this process, the alloy stream is broken into tiny droplets and solidifies into powder particles. Fe particles within a predetermined particle size range are then selected. 83 Ga17 The alloy particles were removed from the argon (Ar) environment and then subjected to a secondary heating treatment, heated to 800°C and held for 6 hours. Finally, they were cooled to room temperature to obtain Fe. 83 Ga 17 The alloy powder was screened into three different particle sizes: ① less than 30 μm; ② 30~50 μm; ③ greater than 50 μm. The second particle size was selected, and Fe was chosen as the appropriate particle size. 83 Ga 17 The preset particle size range for the alloy particles is 30~50μm. The Fe83Ga17 alloy powder prepared by gas atomization has the advantages of uniform composition, controllable particle size, high particle sphericity, and low oxygen content.

[0023] Then, during the manufacturing stage of the cable 1 in the multi-wire cable structure of the bridge, the spraying areas 3 of each base material of the cable 1 are pre-treated. For each base material of the cable 1, the spraying area 3 is sandblasted with corundum powder to increase the surface roughness of the base material. Then, the spraying area 3 of the base material is cleaned in acetone solution, dried, and preheated to 150℃ to complete the pretreatment. The base material is a single steel wire rope 11 with a diameter of Φ=7mm. Since the surface of the steel wire rope 11 is smooth and the coating adhesion is poor, each steel wire rope 11 is sandblasted during the factory production stage. The distance from the center of the spraying area 3 to the end face of the steel wire rope 11 is P=100mm, and the length of the spraying area 3 is 60mm. After installation, the spraying area 3 is located at the bottom of the cable 1 to facilitate the installation of the transducer.

[0024] Then evenly spray Fe 83 Ga 17 For each base material of cable 1, the pre-treated base material is straightened and rotated uniformly around its central axis. Specifically, both ends of the steel wire rope 11 are clamped to the spraying table. Due to the poor rigidity of the workpiece, a certain tension force needs to be applied to the clamps at both ends to straighten the workpiece. The table speed is set to 30 rpm. Then, the Fe alloy powder is applied using an SX-JP8000™ oxygen fuel spraying device. 83 Ga 17 After being heated and accelerated in a high-temperature, high-pressure supersonic flame, the alloy powder is sprayed onto the coating area 3 of the base material. The temperature of the supersonic flame is not lower than 2600℃, and the pressure is not lower than 8 bar, meaning the combustion chamber pressure of the oxy-fuel spraying equipment is above 8 bar. After the nozzle of the oxy-fuel spraying equipment is adjusted to a preset distance from the surface of the coating area 3, Fe is propelled by the supersonic flame. 83 Ga 17Alloy powder is sprayed onto the spraying area 3 at a spraying flow rate of 1200 m / s, ultimately forming a high-quality magnetostrictive powder coating 5 with a thickness of 350 μm. After spraying, the coating is cooled to room temperature, and then the various base materials are stacked in a cylindrical shape, with the spraying area 3 of each base material located at the same length position. A polyethylene sheath is then wrapped around each base material to ultimately form the cable 1.

[0025] In practice, an oxygen fuel spraying system (SX-JP8000™) is used. Kerosene is atomized with oxygen to form a combustible mixture that enters the combustion chamber. The ignition system ignites this mixture, generating a high-temperature, high-pressure flame. This flame is accelerated through a Laval nozzle to form a high-temperature, high-pressure supersonic jet. The distance between the nozzle and the workpiece is adjusted to 300mm. Fe... 83 Ga 17 Alloy powder is loaded into the feed port, and the powder feeder sends the alloy powder from the low-pressure zone into the flame stream. After heating and acceleration, it is sprayed onto the surface of the substrate to form a high-quality magnetostrictive powder coating 5. The coating should be uniformly deposited on the surface of the steel wire rope 11.

[0026] like Figure 1 and Figure 2 As shown, a magnetostrictive guided wave transducer is then installed outside the sheath 12 at the spraying area 3 of cable 1 to obtain a smart cable. The magnetostrictive guided wave transducer includes an ultrasonic guided wave transducer coil 2 and a permanent bias magnet 4. The ultrasonic guided wave transducer coil 2 is fitted outside the sheath 12 at the spraying area 3 of cable 1 and fixed with an iron hoop, and is located at the center position. The axial length of the ultrasonic guided wave transducer coil 2 is less than the axial length of the spraying area 3. Specifically, an ultrasonic guided wave transducer coil with an axial length of 50.8 mm is used. 2. The bias magnet 4 includes a yoke 41 and two Nd-Fe-B permanent magnets 42 with opposite polarities. The yoke 41 is magnetically attracted and fixed to the cable 1 and secured with an iron hoop, located at the center outside the ultrasonic wave guide transducer coil 2. The two permanent magnets 42 are symmetrically mounted at the upper and lower ends of the yoke 41, respectively. The 30×30mm end face of the permanent magnet 42 is parallel to the 120×25mm plane of the yoke 41, and the 30×40mm end face of the permanent magnet 42 coincides with the 25×25mm end face of the yoke 41. The length direction of the bias magnet 4 is parallel to the axis of the cable 1. The ultrasonic wave guide transducer coil 2, the bias magnet 4, and the spraying area 3 coincide at their centers along the length direction of the cable 1. The dimensions of the yoke 41 are 120×25×25mm. 3 The permanent magnet 42 has dimensions of 30×40×30mm. 3 .

[0027] The ultrasonic waveguide transducer coil 2 generates a dynamic magnetic field. The magnetic field direction of the permanent magnet 42 is perpendicular to the axial direction of the cable 1 and the length direction of the yoke 41, so that the bias magnet 4 generates a static magnetic field that is consistent with the direction of the dynamic magnetic field. The parallel dynamic magnetic field and static magnetic field cause the magnetostrictive powder coating 5 and each base material to expand and contract alternately according to the magnetostrictive effect, thereby generating longitudinal guided waves.

[0028] like Figure 3 As shown, the total length of the bridge cable 1 is L = 1.6m, and the axial length of the ultrasonic guided wave transducer coil 2 is... l =50.8mm, the distance P from the center of the sprayed area 3 to the end face of the steel wire rope 11 of the cable 1 is 100mm, and the diameter of a single steel wire rope 11 is Φ=7mm. For example Figure 4 The diagram shows the sensor location, L(0,1) waveguide path, and experimental setup of this invention. For easy comparison with the method of this invention, one end of cable 1 is coated with the novel sensor of this invention, while the other end is not coated with magnetostrictive powder but only fitted with an ultrasonic waveguide transducer of the same specification, forming a conventional sensor. The novel sensor and the conventional sensor are respectively placed at two L(0,1) points near the end face of the 1.6m long cable 1. T =0.1m, the distance from the sensor to the other end of cable 1 is L e =1.5m.

[0029] Finally, the smart cable was installed on the bridge, and damage detection of the smart cable was performed using the pulse echo method through the signal excitation receiver 6. The signal excitation receiver 6 includes a preamplifier 61 and a signal generator 62 connected in sequence, as well as a filter 63, a digital oscilloscope 64, and a host computer 65 connected in sequence. The preamplifier 61 and the filter 63 are both connected to the ultrasonic guided wave transducer coil 2. When performing damage detection on the smart cable, the magnetostrictive guided wave transducer is used as both an excitation transducer and a receiving transducer using the pulse echo method. A 50 kHz sinusoidal excitation signal is generated by the signal generator 62, that is, the longitudinal L(0,1) mode guided wave with a center frequency of 50 kHz is selected for detection and the detection echo signal is obtained. Then, it is transmitted to the ultrasonic guided wave transducer coil 2 through the preamplifier 61 and propagates in the cable 1. When the sinusoidal excitation signal passes through the damage, a guided wave echo signal is generated. The guided wave echo signal is received by the filter 63 and transmitted to the digital oscilloscope 64 for display. Finally, it is stored in the host computer 65 after analog-to-digital conversion. Because the contact and frictional stress between adjacent steel wire ropes 11 in cable 1 will cause the signal-to-noise ratio to decrease significantly after multiple reflections between the end faces, the first end-face reflected wave packet was recorded at the signal median, such as... Figure 5 and Figure 6 As shown, the first wave packet received is the initial electromagnetic pulse, and the other wave packet is the echo from the end face. The waveguide propagation time ToF The time history of the guided wave from excitation to reception is represented by the abscissa of the wave signal. The propagation distance d of the wave packet is as follows: d=t(f)×v g (f) Where t is the waveguide propagation time, f is the center frequency, and v g Group velocity.

[0030] Based on the dispersion curve of the group velocity, such as Figure 9 As shown, the group velocity v at 50kHz can be obtained. g It is 5100 m / s.

[0031] like Figure 5 and Figure 6 As shown, the waveguide propagation time of a 50kHz transducer is T. oF =0.587ms, estimated distance 2.99m, amplitude measured in the uncoated section is almost zero because Fe 83 Ga 17 The high magnetostriction coefficient significantly improves the energy exchange efficiency at the coated end, with an amplitude value of 0.552V measured at the coated section.

[0032] Example 2:

[0033] Similar to Example 1, but a longitudinal L(0,1) mode guided wave with a center frequency of 100kHz is selected for detection and the detection echo signal is obtained, such as... Figure 7 and Figure 8 As shown, the first wave packet received is the initial electromagnetic pulse, and the other wave packet is the echo from the end face. According to the dispersion curve of the group velocity, as... Figure 9 As shown, the group velocity v at 100kHz can be obtained. g It is 5065 m / s.

[0034] like Figure 7 and Figure 8 As shown, the waveguide propagation time of a transducer with a frequency of 100 kHz is T. oF =0.585ms, estimated distance is 2.963m, the amplitude value measured in the uncoated section is almost zero, and the amplitude value measured in the coated section is 2.486V.

[0035] Because higher guided wave frequencies result in faster energy attenuation during propagation through materials and are more susceptible to scattering from surface features (such as rust, coatings, and grease), and the detection of steel wire rope 11 typically requires covering a long distance; furthermore, according to the group velocity dispersion curve of steel wire rope 11, ultrasonic group velocities below 150 kHz are less affected by frequency changes, which can reduce the time difference between the detection of echo signals from different frequencies and prevent excessively wide wave packets. Therefore, when using ultrasonic guided waves generated by the magnetostrictive effect to detect defects in steel wire rope 11, the commonly used frequency range is typically between 30 kHz and 150 kHz. In specific implementations of this invention, longitudinal L(0,1) mode guided waves with center frequencies of 50 kHz and 100 kHz are selected. For signal excitation and processing, a sine wave with five cycles modulated by a Hanning window is first generated by signal generator 62. The excitation signal is then fed into the ultrasonic guided wave transducer coil 2 after passing through RAM-5000 power amplifier 61. The ultrasonic guided wave transducer coil 2 is an axial array coil, and the bias magnet 4 is provided by a permanent magnet bias magnetizer. The guided wave echo signal is then fed into an oscilloscope 64 for display after passing through filter 63 and voltage amplifier. Simultaneously, the voltage signal is stored in a computer after A / D conversion. On the other hand, the voltage signal detected in the coil is bandpass filtered and amplified by approximately 45dB.

[0036] Furthermore, the addition of non-magnetic Ga elements to the magnetic material Fe can effectively improve the magnetostriction coefficient of the magnetic material, generally by more than ten times. Spraying Fe83Ga17 alloy powder with giant magnetism can greatly improve the energy conversion efficiency (approximately 2000%) and increase the detection range of ultrasonic guided waves.

[0037] The coating on the outer layer of cable 1 undergoes magnetostriction under the influence of a bias magnetic field and an excitation magnetic field that are parallel to each other. The resulting magnetostrictive force is along the cable axis. The inner core steel wire rope 11 in cable 1 also undergoes magnetostriction. Thus, the axial magnetostrictive force can excite longitudinal modal guided waves in cable 1. Due to the eddy current effect, eddy currents of equal magnitude and opposite direction to the excitation current are induced on the inner side of the coating. The direction of the eddy currents is counterclockwise around the cable. Under the action of the bias magnetic field, the eddy currents generate Lorentz force. According to the left-hand rule, the direction of the Lorentz force is radial, pointing from the outside to the inside along the radial direction towards the center of the cross-section of cable 1. Since the longitudinal modal guided waves have both radial and axial vibration displacements, the radial Lorentz force can also excite longitudinal modal guided waves. The coating generates longitudinal modal vibration displacement under the superposition of radial and axial forces, which is transmitted to the steel wire rope 11 on the surface of cable 1. During the propagation of the guided wave, it is further transmitted to the inner layer. The vibration displacement of the guided wave eventually covers the entire cross section of cable 1 and forms a stable longitudinal modal wave group that propagates forward.

[0038] As can be seen from the two embodiments above, the estimated distance of the wave packet is very close to the precise distance, which demonstrates the accuracy of the theoretical dispersion curve. Compared with the guided wave generated by the magnetostriction of the steel wire rope 11 itself, the amplitude of the reflected wave at the coating end is significantly improved, with the maximum increase being nearly 2000 times that at 100 kHz. This shows that the method can greatly improve energy conversion efficiency, increase the detection range of ultrasonic guided waves, and provide feasibility for long-term online structural health monitoring.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A guided wave detection method for magnetostrictive powder coating damage in multi-filament cable-like structures, characterized in that, include: Step 1) Prepare Fe with magnetostrictive properties using gas atomization method 83 Ga 17 alloy powder; Step 2) In the manufacturing stage of the cable (1) of the multi-wire cable structure of the bridge, the spraying areas (3) of each base material of the cable (1) are first pretreated, and then Fe is uniformly sprayed. 83 Ga 17 Alloy powder is then used to completely wrap each base material with a sheath (12) to obtain a cable (1). Step 3) Install a magnetostrictive waveguide transducer outside the sheath (12) at the spraying area (3) of the cable (1) to obtain a smart cable; Step 4) Install the smart cable on the bridge and use the pulse echo method to detect damage to the smart cable through the signal excitation receiver (6).

2. The method for detecting magnetostrictive powder coating damage in multi-filament structures according to claim 1, characterized in that: In step 1), during the preparation of Fe 83 Ga 17 When making alloy powder, first, Fe 83 Ga 17 The alloy ingot is heated in an argon atmosphere (Ar) to completely melt it into Fe. 83 Ga 17 The alloy was molten; then heating was stopped, pressure was applied, and the alloy was broken up and solidified to obtain Fe. 83 Ga 17 Alloy particles, selecting Fe particles within a preset particle size range. 83 Ga 17 The alloy particles were removed from the argon (Ar) environment, then subjected to a secondary heating treatment, and finally cooled to room temperature to obtain Fe. 83 Ga 17 alloy powder.

3. The method for detecting magnetostrictive powder coating damage in multi-filament structures according to claim 2, characterized in that: The initial heating process specifically involves heating to a temperature not lower than 1580℃ and holding for 5 minutes; the pressurization process specifically involves pressurizing argon gas (Ar) to a pressure not lower than 3.4 MPa, during which the temperature is gradually reduced to room temperature until the Fe is broken down. 83 Ga 17 The alloy liquid solidifies; the secondary heating treatment specifically involves heating to no less than 800℃ and holding at that temperature for 4 to 8 hours.

4. The method for detecting magnetostrictive powder coating damage in multi-filament structures according to claim 2, characterized in that: The Fe 83 Ga 17 The preset particle size range for the alloy particles is 30~50μm.

5. The guided wave detection method for magnetostrictive powder coating damage in multi-filament structures according to claim 1, characterized in that: In step 2), for each base material of the cable (1), the base material is sandblasted with corundum powder in the spraying area (3), then the spraying area (3) of the base material is cleaned in acetone solution, and then dried and preheated to 100~200℃ to complete the pretreatment.

6. The method for detecting magnetostrictive powder coating damage in multi-filament structures according to claim 1, characterized in that: In step 2), for each base material of the cable (1), the pretreated base material is straightened and rotated at a constant speed around its own central axis, and then Fe is applied using an oxygen fuel spraying device. 83 Ga 17 Alloy powder is heated and accelerated in a high-temperature and high-pressure supersonic flame stream and then sprayed onto the spraying area (3) of the base material to form a magnetostrictive powder coating (5). After spraying, it is cooled to room temperature, and then each base material is stacked and arranged into a cylindrical shape. The spraying area (3) of each base material is located at the same length position and wrapped with a polyethylene sheath to form a cable (1).

7. The method for detecting magnetostrictive powder coating damage in multi-filament structures according to claim 6, characterized in that: The temperature of the supersonic flame is not lower than 2600℃ and the pressure is not lower than 8 bar. After the nozzle of the oxygen fuel spraying equipment is adjusted to a preset distance from the surface of the spraying area (3), Fe is sprayed under the action of the supersonic flame. 83 Ga 17 Alloy powder is sprayed onto the spraying area at a spraying flow rate of 1000-1200 m / s (3), and finally a magnetostrictive powder coating with a thickness of 320-380 μm is formed (5).

8. The method for detecting magnetostrictive powder coating damage in multi-filament structures according to claim 1, characterized in that: In step 3), the magnetostrictive waveguide transducer includes an ultrasonic waveguide transducer coil (2) and a bias magnet (4). The ultrasonic waveguide transducer coil (2) is fitted outside the sheath (12) where the sprayed area (3) of the cable (1) is located and is located at the center position. The axial length of the ultrasonic waveguide transducer coil (2) is less than the axial length of the sprayed area (3). The bias magnet (4) includes a yoke (41) and two permanent magnets (42) with opposite polarities. The yoke (41) is magnetically attracted and fixed on the cable (1) and is located at the center position outside the ultrasonic waveguide transducer coil (2). The two permanent magnets (42) are symmetrically installed at the upper and lower ends of the yoke (41).

9. The method for detecting magnetostrictive powder coating damage in multi-filament structures according to claim 8, characterized in that: The ultrasonic waveguide transducer coil (2) generates a dynamic magnetic field. The magnetic field direction of the permanent magnet (42) is perpendicular to the axial direction of the cable (1), so that the bias magnet (4) generates a static magnetic field that is consistent with the direction of the dynamic magnetic field. The parallel dynamic magnetic field and static magnetic field cause the magnetostrictive powder coating (5) and each base material to expand and contract alternately according to the magnetostrictive effect, thereby generating longitudinal guided waves.

10. The method for detecting magnetostrictive powder coating damage in multi-filament cable-like structures according to claim 8, characterized in that: In step 4), the signal excitation receiver (6) includes a preamplifier (61) and a signal generator (62) connected in sequence, as well as a filter (63), a digital oscilloscope (64), and a host computer (65) connected in sequence. The preamplifier (61) and the filter (63) are both connected to the ultrasonic guided wave transducer coil (2). When performing damage detection on the smart cable, the magnetostrictive guided wave transducer is used as both an excitation transducer and a receiving transducer by means of the pulse echo method. The signal generator (62) generates a 30kHz-150kHz sine wave excitation signal, which is then transmitted to the ultrasonic guided wave transducer coil (2) through the preamplifier (61) and propagates in the cable (1). When the sine wave excitation signal passes through the damage, a guided wave echo signal will be generated. The guided wave echo signal is received by the filter (63) and transmitted to the digital oscilloscope (64) for display. Finally, it is stored in the host computer (65) after analog-to-digital conversion.

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