A method and structure for detecting bolt stress based on magnetoelectric effect

Abstract

The application discloses a kind of based on magnetoelectric effect bolt stress sensor detection method and structure, it is applied to bolt stress detection field.The present application uses based on magnetoelectric effect stress sensor transmits and receives transverse wave and longitudinal wave transverse, solve the existing electromagnetic ultrasonic transducer in ferromagnetic material excitation longitudinal wave ability is poor, piezoelectric wafer produces transverse wave coupling difficulty causes application limited problem.This sensor includes permanent magnet, transmitting coil, receiving coil, damping insulating layer, magnetoelectric composite wafer, protective layer and thermocouple, thermocouple measures temperature correction temperature influence on sound velocity, using transverse wave and longitudinal wave acoustic time ratio calculation bolt stress.The method and sensor will effectively improve the engineering adaptation of bolt stress measurement.

Description

Technical Field

[0001] This invention belongs to the field of industrial testing technology, specifically relating to a bolt stress sensor detection method and structure based on the magnetoelectric effect. Background Technology

[0002] Bolts are a widely used fastener, extensively used in the fastening of key equipment in industrial fields such as aerospace, marine machinery, chemical equipment, and energy. As an important part of connecting two or more parts, the stress state of bolts is an important aspect of mechanical design.

[0003] The existing technology application (CN202021616324.5) discloses an ultrasonic-based bolt axial stress measuring device. This invention can obtain the ultrasonic measurement characteristics of bolts under arbitrary temperatures and prestresses, and can determine the combined effect of bolt prestress and temperature compensation. It can be applied to preload measurement at any temperature without repeated calibration at different temperatures. However, this patent uses a single longitudinal wave method, not a transverse-to-longitudinal wave time-to-sound ratio method, requiring precise measurement of the bolt length in automatic mode.

[0004] The prior art application, CN202110899485.2, discloses a method and system for temperature compensation in ultrasonic stress testing of in-service high-strength bolts. This invention employs transverse wave piezoelectric crystals and longitudinal wave piezoelectric crystals stacked together. The ultrasonic waves generated by the upper piezoelectric crystal need to penetrate the lower piezoelectric crystal before being transmitted to the bolt. The lower piezoelectric crystal interferes with the ultrasonic signals generated by the upper piezoelectric crystal. Furthermore, the transverse waves are generated by the piezoelectric crystals, not at the bolt end face, requiring a coupling agent to guide them into the bolt. However, transverse waves cannot propagate in liquids, and the choice and effectiveness of the coupling agent will limit its performance.

[0005] The prior art application number is 202010681870.5, which discloses a capacitive electromagnetic ultrasonic transverse and longitudinal wave transducer. This invention makes the test piece the plate of a capacitor and uses the electrostatic force between the capacitor plates to directly induce mechanical vibration on the surface of the test piece, which is different from the conventional ultrasonic technology that uses a coupling agent to transmit the vibration of the sensor to the test piece.

[0006] The existing technology application (CN202011494639.1) discloses a plane stress measurement system and method for specimens with unknown thickness. The electromagnetic ultrasonic transverse and longitudinal wave transducer includes a permanent magnet, orthogonal butterfly coils, a helical coil, and a shell. The permanent magnet, orthogonal butterfly coils, and helical coils are stacked sequentially from top to bottom, with their axial centerlines coinciding. The shell is located outside the permanent magnet, orthogonal butterfly coils, and helical coils. The orthogonal butterfly coils consist of two sets of orthogonally overlapping butterfly coils, each exciting a transverse wave propagating in the thickness direction and with mutually perpendicular polarization directions. The transverse waves are generated using the orthogonal butterfly coils and helical coils. This method only uses transverse waves and does not employ longitudinal wave methods, making it unsuitable for measuring bolt stress.

[0007] The prior art patent application CN202123313551.8 discloses a longitudinal and transverse wave ultrasonic probe for measuring bolt axial force. It includes longitudinal and transverse wave wafers, a magnetic ring, a damping block, longitudinal and transverse wave circuit boards, coaxial cables, connectors, transverse wave ultrasonic wires, longitudinal wave ultrasonic wires, and a packaging shell. The longitudinal and transverse wave wafers consist of a transverse wave wafer, an insulating layer, and a longitudinal wave wafer. The insulating layer is disposed between the transverse and longitudinal wave wafers. The transverse wave ultrasonic wires are connected and disposed on the transverse wave wafer, and the longitudinal wave ultrasonic wires are connected and disposed on the longitudinal wave wafer. The damping block is connected and disposed on the transverse wave wafer, the insulating layer, and the longitudinal wave wafer. The longitudinal and transverse wave wafers are formed by burning the transverse wave wafer, the insulating layer, and the longitudinal wave wafer. The present invention uses longitudinal and transverse wave wafers to generate weak longitudinal waves that are difficult to penetrate the coupling agent, making it difficult to generate longitudinal waves. This patent uses piezoelectric wafers to generate transverse waves, but it does not solve the problem that transverse waves cannot penetrate liquid coupling agents.

[0008] None of the aforementioned existing technologies have been found to use the magnetoelectric effect to generate transverse and longitudinal waves for measuring bolt stress.

[0009] In view of the above factors, a bolt stress sensor detection method and structure based on the magnetoelectric effect are designed. An alternating pulsed strong magnetic field is generated using a permanent magnet and a transmitting coil, forming eddy currents on the bolt surface. The Lorentz force and magnetostrictive force induce mechanical vibrations on the bolt surface, generating transverse waves. Simultaneously, in the strong pulsed alternating magnetic field, the magnetostrictive phase of the magnetoelectric composite wafer experiences strain when sensing the magnetic field along the pre-magnetization direction. This strain is transmitted to the piezoelectric phase through interfacial coupling. Due to the piezoelectric effect, the piezoelectric phase generates a potential difference along the polarization direction, generating longitudinal waves. These longitudinal waves penetrate the protective layer and coupling agent to enter the bolt, overcoming the difficulties in generating longitudinal waves with permanent magnets and coils, and the inability of transverse waves generated by the piezoelectric wafer to penetrate the liquid coupling agent. Summary of the Invention

[0010] The purpose of this invention is to provide a method and structure for detecting bolt stress based on the magnetoelectric effect, so as to solve the problems mentioned in the background art.

[0011] The objective of this invention is achieved through the following technical solution: a bolt stress sensor detection method based on the magnetoelectric effect, wherein the method is implemented using a bolt stress sensor based on the magnetoelectric effect, specifically including the following steps:

[0012] a. Ultrasonic signal transmission process:

[0013] Step 1: The bolt stress sensor is attached vertically to the free end of the bolt to be tested. An alternating pulsed strong magnetic field is generated by a permanent magnet and a transmitting coil, which forms eddy currents on the surface of the bolt. Due to the Lorentz force and magnetostrictive force, mechanical vibration is generated on the surface of the bolt, generating transverse waves.

[0014] Step 2: When the magnetostrictive phase of the magnetoelectric composite wafer senses the magnetic field along the pre-magnetization direction in a strong pulsed alternating magnetic field, it generates strain. This strain is transmitted to the piezoelectric phase through interface coupling. Due to the piezoelectric effect, the piezoelectric phase generates a potential difference along the polarization direction, and the piezoelectric effect generates a longitudinal wave. The longitudinal wave penetrates the protective layer and the coupling agent and enters the bolt.

[0015] b. Ultrasonic signal reception process:

[0016] Step 3: The reflected transverse wave causes the cross-section of the bolt under test to vibrate laterally, changing the magnetic flux density of the receiving coil, and generating an electrical signal by the induced electromotive force; since the transverse wave cannot penetrate the liquid coupling agent, the magnetoelectric composite crystal does not receive the transverse wave, so the reflected transverse wave has no effect on the magnetoelectric composite crystal.

[0017] The time of the first transverse wave reflection inside the bolt under test is marked Ts3, and the time of the second transverse wave reflection inside the bolt under test is marked Ts4; the temperature is measured by thermocouples, and the transverse wave velocity correction coefficient T is calculated. Ts ;

[0018] The reflected longitudinal wave passes through the liquid coupling agent and is conducted to the piezoelectric phase of the magnetoelectric composite wafer. Due to mechanical vibration, the piezoelectric phase generates a potential difference along the polarization direction due to the piezoelectric effect, forming an alternating electromagnetic field. An electrical signal is generated in the receiving coil by the induced electromotive force. The mechanical vibration of the longitudinal wave is perpendicular to the receiving coil, which has little effect on the magnetic flux density of the receiving coil. The amplitude of the electrical signal generated by the receiving coil is less than the threshold. The signal is filtered out by the amplitude height. Therefore, the reflected longitudinal wave is only converted into an electrical signal by the magnetoelectric composite wafer.

[0019] The time of the first longitudinal wave reflection inside the bolt under test is marked as T. L1 The time of the second longitudinal wave reflection inside the bolt to be tested, marked T. L2 The longitudinal wave velocity correction factor T is calculated by measuring the temperature using thermocouples. Tl ;

[0020] Step 4: Calculate the bolt stress by measuring the absolute acoustic time ratio of the transverse / longitudinal waves of the bolt under test and based on the calibrated bolt double-wave stress coefficient;

[0021] Both transverse and longitudinal waves are received by the receiving coil. Since the sound speeds of transverse and longitudinal waves are different, a time-division method can be used to extract the transverse and longitudinal wave signals. At the same time, the transverse and longitudinal wave signals are on the same time axis, which improves the accuracy of the detection signal.

[0022] A bolt stress sensor structure based on the magnetoelectric effect includes a housing, within which are a permanent magnet, a transmitting coil, a receiving coil, a damping insulating layer, a magnetoelectric composite wafer, and a protective layer.

[0023] The transmitting coil is connected to the positive and negative terminals of the transmitting circuit at both ends, the receiving coil is connected to the positive and negative terminals of the receiving circuit, the lower end of the magnetoelectric composite crystal is connected to the negative terminal of the receiving coil, and the upper end is suspended.

[0024] The permanent magnet, transmitting coil, receiving coil, and magnetoelectric composite crystal are all centered on the same straight line, and the main acoustic axes of the generated transverse and longitudinal waves coincide, overcoming the discrete deviation problem of the bolt structure.

[0025] Furthermore, the transmitting coil is a circular coil with a diameter of 20 mm and a thickness of 0.3 mm.

[0026] Furthermore, the receiving coil is a circular coil with a diameter of 25mm and a thickness of 0.3mm.

[0027] Furthermore, the magnetoelectric composite wafer is composed of two layers of materials: an upper layer is a magnetostrictive phase and a lower layer is a piezoelectric phase, wherein the magnetization direction of the magnetostrictive phase is axial and the polarization direction of the piezoelectric phase is axial.

[0028] Furthermore, the magnetostrictive phase material is FeGa, with a diameter of 8 mm and a thickness of 0.8 mm;

[0029] The piezoelectric phase material is PZT, with a diameter of 8 mm, a thickness of 0.6 mm, and a center frequency of 5 MHz.

[0030] Furthermore, the housing also includes a thermocouple, and the housing is fixed to the permanent magnet, transmitting coil, receiving coil, damping insulating layer, magnetoelectric composite wafer, and thermocouple by filling with resin;

[0031] The thermocouple is located between the housing and the permanent magnet.

[0032] Furthermore, the outer wall of the housing is provided with a wiring socket, which is connected to the host end via a connecting wire.

[0033] Furthermore, the thickness of the damping insulation layer is 0.1 to 0.5 mm, wherein the damping insulation layer is a mixture of adhesive and tungsten powder.

[0034] Furthermore, a protective layer is provided on the outer end face of the magnetoelectric composite wafer. The protective layer is a plastic structure and is bonded to the outer end face of the magnetoelectric composite wafer through an adhesive layer.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] This invention addresses the problem that existing electromagnetic ultrasonic transducers have poor ability to excite longitudinal waves in ferromagnetic materials, and that it is difficult to generate transverse wave coupling using piezoelectric wafers, which limits their application.

[0037] This invention utilizes a magnetoelectric composite wafer in a strong pulsed alternating magnetic field. When the magnetostrictive phase senses the magnetic field along the pre-magnetization direction, it generates strain. This strain is transmitted to the piezoelectric phase through interface coupling. Due to the piezoelectric effect, the piezoelectric phase generates a potential difference along the polarization direction, which generates a longitudinal wave. The longitudinal wave penetrates the protective layer and coupling agent and enters the bolt, overcoming the problem of difficulty in generating longitudinal waves in permanent magnets and coils.

[0038] In this invention, the transverse and longitudinal waves are generated in different ways, and they do not interfere with each other. The sound speeds of the transverse and longitudinal waves are different. Although both transverse and longitudinal waves are received by the receiving coil, a time-division multiplexing method can be used to extract the transverse and longitudinal wave signals. At the same time, the transverse and longitudinal wave signals are in the same data stream, which improves the accuracy of the detection signal.

[0039] In this invention, the permanent magnet, coil, and magnetoelectric composite wafer are all centered on the same straight line, and the main acoustic axes of the generated transverse and longitudinal waves coincide, thus overcoming the problem of discrete deviation in bolt structures.

[0040] In this invention, the thermocouple measures the temperature and corrects the effect of temperature on the speed of sound. Therefore, this sensor will effectively improve the engineering applicability of bolt stress measurement. Attached Figure Description

[0041] Figure 1 This is a three-dimensional schematic diagram of the present invention;

[0042] Figure 2 This is the present invention. Figure 1 Partial cross-sectional view;

[0043] Figure 3 This is a schematic diagram of the sensor detection state of the present invention;

[0044] Figure 4 This is a block diagram of the existing host and sensor principles;

[0045] In the diagram: 1. Housing; 2. Permanent magnet; 3. Transmitting coil; 4. Receiving coil; 5. Damping insulation layer; 6. Magnetoelectric composite crystal; 7. Protective layer; 8. Thermocouple; 9. Wiring socket; 10. Bolt to be tested. Detailed Implementation

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0047] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0048] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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, they should not be construed as limitations on this invention. Specific Implementation Example 1:

[0050] like Figure 1-4 As shown, a bolt stress sensor structure based on the magnetoelectric effect includes a housing 1, which contains a permanent magnet 2, a transmitting coil 3, a receiving coil 4, a damping insulating layer 5, a magnetoelectric composite wafer 6, and a protective layer 7. The bolt stress is calculated using the transverse and longitudinal wave acoustic time ratio.

[0051] The two ends of the transmitting coil 3 are connected to the positive and negative terminals of the transmitting circuit, the receiving coil 4 is connected to the positive and negative terminals of the receiving circuit, the lower end of the magnetoelectric composite chip 6 is connected to the negative terminal of the receiving coil 4, and the upper end is suspended, which is actually a suspension in the circuit and is not connected to the external circuit.

[0052] The permanent magnet 2, transmitting coil 3, receiving coil 4, and magnetoelectric composite crystal 6 are all centered on the same straight line, and the main acoustic axes of the generated transverse and longitudinal waves coincide, overcoming the problem of discrete deviation in bolt structure;

[0053] Using permanent magnet 2 and transmitting coil 3 to generate an alternating pulsed strong magnetic field, eddy currents are formed on the surface of the bolt 10 to be tested. Due to Lorentz force and magnetostrictive force, mechanical vibration is generated on the surface of the bolt 10 to be tested, generating transverse waves.

[0054] In a strong pulsed alternating magnetic field, the magnetostrictive phase of the magnetoelectric composite wafer 6 generates strain when it senses the magnetic field along the pre-magnetization direction. This strain is transmitted to the piezoelectric phase through interface coupling. The piezoelectric phase generates a potential difference along the polarization direction through the piezoelectric effect, and longitudinal waves are generated by the piezoelectric effect.

[0055] Since transverse and longitudinal waves are generated in different ways and have different sound velocities, a time-division method can be used to extract transverse and longitudinal wave signals. At the same time, the transverse and longitudinal wave signals are in the same data stream, which improves the accuracy of the detection signal.

[0056] The transmitting coil 3 is a circular coil with a diameter of 20 mm and a thickness of 0.3 mm. The receiving coil 4 is a circular coil with a diameter of 25 mm and a thickness of 0.3 mm.

[0057] The magnetoelectric composite wafer 6 is composed of two layers of materials: an upper layer is a magnetostrictive phase and a lower layer is a piezoelectric phase. The magnetization direction of the magnetostrictive phase is axial, and the polarization direction of the piezoelectric phase is axial.

[0058] The magnetostrictive phase material is FeGa, with a diameter of 8 mm and a thickness of 0.8 mm;

[0059] The piezoelectric phase material is PZT, with a diameter of 8 mm, a thickness of 0.6 mm, and a center frequency of 5 MHz.

[0060] The magnetoelectric composite wafer 6 is coupled to the free end face of the bolt 10 under test through a coupling agent, and a protective layer 7 is provided on the outer end face of the magnetoelectric composite wafer 6. The protective layer 7 is a plastic structure and is attached to the outer end face of the magnetoelectric composite wafer 6 through an adhesive layer.

[0061] The housing 1 also includes a thermocouple 8, which is located between the housing 1 and the permanent magnet 2. The thermocouple 8 uses K-type thermocouple wire.

[0062] The housing 1 is a stainless steel housing structure. The housing 1 is sleeved on the permanent magnet 2, transmitting coil 3, receiving coil 4, damping insulation layer 4, magnetoelectric composite crystal 6 and protective layer 7. The wiring socket 9 is electrically connected to the permanent magnet 2, transmitting coil 3, receiving coil 4 and magnetoelectric composite crystal 6.

[0063] In order to reduce or eliminate noise signals and reduce the influence of the emitted signal on the reflected signal in the application state, the thickness of the damping insulating layer 4 between the permanent magnet 2, the transmitting coil 3, the receiving coil 4 and the magnetoelectric composite wafer 6 is 0.1 to 0.5 mm. The damping layer is an adhesive layer, which includes a mixture of adhesive and tungsten powder in a mixing ratio of 2:0.5.

[0064] The host terminal 11 transmits electrical signals to the permanent magnet 2, transmitting coil 3, receiving coil 4 and magnetoelectric composite crystal 6, converting the electrical signals into transverse and longitudinal waves.

[0065] In the above embodiments, the bolt to be tested 10 includes a bolt head and a screw. The bolt head is disposed at one end or both ends of the screw. The screw includes a smooth section and / or a threaded section. The free end face of the bolt to be tested is the detection part.

[0066] The transmitting coil 3 and the receiving coil 4 are respectively connected to the host terminal 11. The host terminal is existing technology. The two ends of the transmitting coil are connected to the positive and negative terminals of the transmitting circuit / excitation circuit, and the receiving coil is connected to the positive and negative terminals of the receiving circuit. Specific Implementation Example 2:

[0068] A bolt stress sensor detection method based on the magnetoelectric effect includes the following steps:

[0069] a. Ultrasonic signal transmission process:

[0070] Step 1: The bolt stress sensor is attached vertically to the free end of the bolt 10 to be tested. The permanent magnet 2 and the transmitting coil 3 generate an alternating pulsed strong magnetic field, which forms eddy currents on the surface of the bolt 10 to be tested. Due to the Lorentz force and magnetostrictive force, mechanical vibration is generated on the surface of the bolt 10 to be tested, generating transverse waves.

[0071] Step 2: When the magnetostrictive phase of the magnetoelectric composite wafer 6 is in a strong pulsed alternating magnetic field, it generates strain when it senses the magnetic field along the pre-magnetization direction. This strain is transmitted to the piezoelectric phase through interface coupling. Due to the piezoelectric effect, the piezoelectric phase generates a potential difference along the polarization direction, and the piezoelectric effect generates a longitudinal wave. The longitudinal wave penetrates the protective layer 7 and the coupling agent and enters the bolt.

[0072] b. Ultrasonic signal reception process:

[0073] Step 3: The reflected transverse wave causes the cross-section of the bolt 10 under test to vibrate laterally, changing the magnetic flux density of the receiving coil 4, and generating an electrical signal by the induced electromotive force; since the transverse wave cannot penetrate the liquid coupling agent, the magnetoelectric composite crystal does not receive the transverse wave, so the reflected transverse wave has no effect on the magnetoelectric composite crystal.

[0074] The time of the first transverse wave reflection within the bolt 10 under test is marked as Ts3, and the time of the second transverse wave reflection within the bolt 10 under test is marked as Ts4. The temperature is measured by thermocouples, and the transverse wave velocity correction coefficient T is calculated. Ts ;

[0075] The reflected longitudinal wave passes through the liquid coupling agent and is conducted to the piezoelectric phase of the magnetoelectric composite wafer 6. Due to the mechanical vibration, the piezoelectric phase generates a potential difference along the polarization direction due to the piezoelectric effect, forming an alternating electromagnetic field. The induced electromotive force in the receiving coil 4 generates an electrical signal. The mechanical vibration of the longitudinal wave is perpendicular to the receiving coil, and has little effect on the magnetic flux density of the receiving coil (the amplitude of the electrical signal caused by the receiving coil (4) is less than the threshold). The resulting electrical signal is weak, and the signal is filtered out by the amplitude height. Therefore, the reflected longitudinal wave is only converted into an electrical signal through the magnetoelectric composite wafer.

[0076] The time of the first longitudinal wave reflection within the bolt 10 under test is marked as T. L1 The time of the second longitudinal wave reflection within 10 minutes of the bolt under test is marked as T. L2 The longitudinal wave velocity correction factor T is calculated by measuring the temperature using thermocouples. Tl ;

[0077] Step 4: Calculate the bolt stress by measuring the absolute acoustic time ratio of the transverse / longitudinal waves of the bolt 10 under test, based on the calibrated bolt double-wave stress coefficient;

[0078] Both transverse and longitudinal waves are received by the receiving coil. Since the sound speeds of transverse and longitudinal waves are different, a time-division method can be used to extract the transverse and longitudinal wave signals. At the same time, the transverse and longitudinal wave signals are on the same time axis, which improves the accuracy of the detection signal.

[0079] The principle of bolt stress testing using transverse and longitudinal wave methods is as follows:

[0080] When subjected to stress, the propagation speed of ultrasonic waves in a material changes with the stress state; this phenomenon is known as acoustoelasticity. The relationship between the sound velocity in a material and stress can be expressed as follows:

[0081]

[0082]

[0083]

[0084]

[0085] In the formula: V L V T Let be the longitudinal wave velocity and transverse wave velocity of the bolt, respectively; λ and μ are Lamé constants; l, m, and n are third-order elastic constants; K0 is a constant related to the Lamé constant of the material; ρ0 is the material density; is the stress on the bolt; L0, L... σ E represents the length of the bolt before and after it is subjected to force; E is the Young's modulus of the material.

[0086] The impact of changes on test results. According to the theory of acoustic elasticity, there is...

[0087]

[0088]

[0089] In the formula: and These are the longitudinal and transverse wave velocities of the bolt under stress, respectively. and , respectively, are the longitudinal and transverse wave velocities of the bolt under unstressed conditions; A and B are the acoustoelastic coefficients of the longitudinal and transverse waves, respectively.

[0090] By combining equations (4) to (6), we can obtain

[0091]

[0092] In the formula: and These represent the time taken for the longitudinal and transverse waves to propagate their complete paths under bolt stress conditions, respectively. and These represent the time taken for the longitudinal and transverse waves to propagate their complete paths when the bolt is unstressed.

[0093] By performing a Taylor expansion of the acoustic time ratio function of transverse and longitudinal waves and simplifying by taking higher-order terms, we can obtain the following:

[0094]

[0095]

[0096] make: Simplifying, we get

[0097] σ=kx-b (10) Where: k and b can be obtained through calibration tests; x can be measured by equipment.

[0098] The above detection method uses ultrasonic waves to obtain the absolute acoustic time of transverse waves and longitudinal waves in the bolt being tested, thereby eliminating zero-point deviation.

[0099] The transverse and longitudinal wave sensing center axes are aligned, so that the transverse wave incident point coincides with the longitudinal wave incident point, and the transverse wave reflection point coincides with the longitudinal wave reflection point, thereby eliminating the discrete deviation of the bolt structure.

[0100] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0101] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A bolt stress sensor detection method based on the magnetoelectric effect, characterized in that, This method is based on a bolt stress sensor with magnetoelectric effect. The bolt stress sensor includes a housing (1), and the housing (1) contains a permanent magnet (2), a transmitting coil (3), a receiving coil (4), a damping insulation layer (5), a magnetoelectric composite wafer (6), and a protective layer (7). The transmitting coil (3) is connected to the input / output terminals of the transmitting circuit at both ends, the receiving coil (4) is connected to the input / output terminals of the receiving circuit, the lower end face of the magnetoelectric composite crystal (6) is connected to the receiving coil (4), and the circuit on the upper end face is suspended. The permanent magnet (2), transmitting coil (3), receiving coil (4), and magnetoelectric composite crystal (6) are all centered on the same straight line, and the main acoustic axes of the generated transverse and longitudinal waves coincide. The housing (1) also includes a thermocouple (8). The housing (1) is fixed with resin between itself and the permanent magnet (2), transmitting coil (3), receiving coil (4), damping insulation layer (5), magnetoelectric composite crystal (6), and thermocouple (8). The thermocouple (8) is located between the housing (1) and the permanent magnet (2); Specifically, the following steps are included: a. Ultrasonic signal transmission process: Step 1: The bolt stress sensor is attached vertically to the free end of the bolt (10) to be tested. The permanent magnet (2) and the transmitting coil (3) generate an alternating pulsed strong magnetic field, which forms eddy currents on the surface of the bolt (10) to be tested. Due to the Lorentz force and magnetostrictive force, mechanical vibration is generated on the surface of the bolt (10) to be tested, generating transverse waves. Step 2: In a strong pulsed alternating magnetic field, the magnetostrictive phase of the magnetostrictive wafer (6) generates strain when it senses the magnetic field along the pre-magnetization direction. This strain is transmitted to the piezoelectric phase through interface coupling. The piezoelectric phase generates a potential difference along the polarization direction due to the piezoelectric effect. The piezoelectric effect generates longitudinal waves, which penetrate the protective layer (7) and the coupling agent and enter the bolt to be tested (10). b. Ultrasonic signal reception process: Step 3: The reflected transverse wave causes the cross section of the bolt (10) to vibrate laterally, changing the magnetic flux density of the receiving coil (4), and generating an electrical signal by the induced electromotive force; since the transverse wave cannot penetrate the liquid coupling agent, the magnetoelectric composite crystal cannot receive the transverse wave, so the reflected transverse wave has no effect on the magnetoelectric composite crystal. The time of the first transverse wave reflection within the bolt (10) to be tested is marked as Ts3, and the time of the second transverse wave reflection within the bolt (10) to be tested is marked as Ts4; the temperature is measured by thermocouple (8), and the transverse wave velocity correction coefficient T is calculated. Ts ; The reflected longitudinal wave is transmitted through the liquid coupling agent to the piezoelectric phase of the magnetoelectric composite wafer (6). Due to the mechanical vibration, the piezoelectric phase generates a potential difference along the polarization direction due to the piezoelectric effect, forming an alternating electromagnetic field. An electrical signal is generated in the receiving coil (4) by the induced electromotive force. The longitudinal wave is perpendicular to the mechanical vibration of the receiving coil, which has little effect on the magnetic flux density of the receiving coil (4). The amplitude of the electrical signal generated by the receiving coil (4) is less than the threshold. The signal is filtered out by the amplitude height of the signal. Therefore, the reflected longitudinal wave is only converted into an electrical signal through the magnetoelectric composite wafer. The time of the first longitudinal wave reflection inside the bolt (10) to be tested is marked as T. L1 The time of the second longitudinal wave reflection inside the bolt (10) to be tested is marked as T. L2 Temperature is measured using thermocouple (8), and the longitudinal wave velocity correction coefficient T is calculated. Tl ; Step 4: Calculate the bolt stress by measuring the absolute acoustic time ratio of the transverse / longitudinal waves of the bolt (10) under test, based on the calibrated bolt double-wave stress coefficient; Both transverse and longitudinal waves are received by the receiving coil (4). The sound speed of transverse waves is different from that of longitudinal waves. The transverse and longitudinal wave signals can be extracted by using a time-division method. At the same time, the transverse and longitudinal wave signals are on the same time axis, which improves the accuracy of the detection signal.

2. The bolt stress sensor detection method based on magnetoelectric effect according to claim 1, characterized in that: The transmitting coil (3) is a circular coil with a diameter of 20 mm and a thickness of 0.3 mm.

3. The bolt stress sensor detection method based on magnetoelectric effect according to claim 2, characterized in that: The receiving coil (4) is a circular coil with a diameter of 25 mm and a thickness of 0.3 mm.

4. The bolt stress sensor detection method based on magnetoelectric effect according to claim 2, characterized in that: The magnetoelectric composite wafer (6) consists of two layers of material, with the upper layer being a magnetostrictive phase and the lower layer being a piezoelectric phase. The magnetization direction of the magnetostrictive phase is axial, and the polarization direction of the piezoelectric phase is axial.

5. The bolt stress sensor detection method based on magnetoelectric effect according to claim 4, characterized in that: The magnetostrictive phase material is FeGa, with a diameter of 8 mm and a thickness of 0.8 mm; The piezoelectric phase material is PZT, with a diameter of 8 mm, a thickness of 0.6 mm, and a center frequency of 5 MHz.

6. The bolt stress sensor detection method based on magnetoelectric effect according to claim 5, characterized in that: The outer wall of the housing (1) is provided with a wiring socket (9), which is connected to the host end (11) via a connecting wire.

7. The bolt stress sensor detection method based on magnetoelectric effect according to claim 6, characterized in that: The thickness of the damping insulation layer (5) is 0.1 to 0.5 mm, wherein the damping insulation layer (5) is a mixture of adhesive and tungsten powder.

8. The bolt stress sensor detection method based on magnetoelectric effect according to claim 7, characterized in that: The outer end face of the magnetoelectric composite wafer (6) is provided with a protective layer (7), wherein the protective layer (7) is a plastic structure and is attached to the outer end face of the magnetoelectric composite wafer (6) through an adhesive layer.

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