A magnetic field type three-dimensional large-stretch flexible strain sensor for crack detection

Abstract

This invention relates to the field of flexible electronic sensor technology, specifically a magnetic field-based three-dimensional large tensile flexible strain sensor for crack detection. It includes a flexible silicone body with a first rigid fixing end and a second rigid fixing end embedded inside. A magnetic sensor module is embedded inside the first rigid fixing end. The magnetic sensor module includes a circuit board, three magnetic transistors, a measurement circuit, and a flexible cable. The three magnetic transistors and the measurement circuit are mounted on the circuit board, and the three magnetic transistors are arranged in three mutually orthogonal directions. A permanent magnet is embedded inside the flexible silicone body near the magnetic sensor module, and an initial gap is established between the permanent magnet and the magnetic sensor module. This invention solves the problems of magnetically based flexible force sensors being unable to be used for large tensile and three-dimensional displacement decoupling measurements of structural cracks, and suffering from insufficient measurement range, severe interdimensional coupling, and difficulty in adapting the packaging structure to long-term deformation of the structural surface.

Description

Technical Field

[0001] This invention relates to the field of flexible electronic sensor technology, specifically a magnetic field-type three-dimensional large tensile flexible strain sensor for crack detection. Background Technology

[0002] Cracks are one of the most common forms of damage in civil engineering structures such as bridges, tunnels, and dams. Real-time monitoring of crack width, depth, and propagation direction is crucial for assessing structural safety and durability. Traditional crack detection methods mainly include mechanical micrometers, vibrating wire crack gauges, and resistance strain gauges. However, these sensors are typically quite stiff, and once fixed to the structural surface, they cannot deform accordingly with the deformation of the substrate being measured. This makes it difficult to accurately measure three-dimensional displacements such as crack opening and misalignment, and they are prone to damage or debonding, especially under conditions of high tension or large deformation.

[0003] In recent years, the development of flexible electronics technology has provided new ideas for strain detection. Existing technologies include flexible force sensors based on magnetic principles. For example, a flexible three-dimensional force sensor (CN113218559B) uses four Hall effect sensors on a PCB circuit board in conjunction with a conductive thin film-circular permanent magnet-rubber hemisphere assembly to sense three-dimensional force by measuring changes in the magnetic field. US9857245 and US20160265985 also disclose technologies that sense soft deformation and force through the relative motion of a Hall sensor in a deformable substrate with a magnet. Furthermore, a flexible magnetic tactile sensing device based on a microstructured elastic layer (CN120927180A) transmits deformation to a flexible magnetic film through the microstructured elastic layer, and then uses a Hall sensor to measure changes in triaxial magnetic field strength to achieve three-dimensional force measurement. However, the aforementioned existing technologies are mainly aimed at the tactile perception of robots. Their design focuses on the measurement of pressure or contact force within a small range. They cannot be used for the decoupled measurement of large tensile stresses on structural cracks (such as millimeter-level or even centimeter-level displacements caused by crack opening) and three-dimensional displacements (opening, shearing, torsion). They suffer from problems such as insufficient measurement range, severe interdimensional coupling, and difficulty in adapting the encapsulation structure to long-term deformation of the structural surface. Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a magnetic field-type three-dimensional large tensile flexible strain sensor for crack detection.

[0005] This invention is achieved using the following technical solution: A magnetic field-type three-dimensional large tensile flexible strain sensor for crack detection includes a long strip-shaped flexible silicone body. The two ends of the flexible silicone body are respectively embedded with a first rigid fixing end and a second rigid fixing end. Both the first rigid fixing end and the second rigid fixing end are provided with through mounting holes. A magnetic sensor module is embedded inside the first rigid fixed end; The magnetic sensor module includes a circuit board, three magnetic transistors, a measurement circuit, and a flexible cable. The three magnetic transistors and the measurement circuit are all mounted on the circuit board, and the three magnetic transistors are arranged in three mutually orthogonal directions. The output terminals of the three magnetic transistors are electrically connected to the input terminal of the measurement circuit, and the output terminal of the measurement circuit is electrically connected to one end of the flexible cable. The other end of the flexible cable extends to the outside of the first rigid fixed end and the flexible silicone body. A permanent magnet is embedded inside the flexible silicone body at one end near the magnetic sensor module, and an initial gap of 1-5mm is set between the permanent magnet and the magnetic sensor module.

[0006] Furthermore, the magnetic sensing directions of the three magnetic transistors are respectively aligned with the directions of the three mutually orthogonal coordinate axes X, Y, and Z, and the spacing between two adjacent magnetic transistors is 1-5 mm.

[0007] Furthermore, the magnetic transistor is a silicon magnetic transistor.

[0008] Furthermore, the magnetic transistor is soldered onto a circuit board or integrated with the circuit board using semiconductor processes.

[0009] Furthermore, the measurement circuit includes a constant current source bias circuit, a differential amplifier circuit, and a low-pass filter circuit.

[0010] Furthermore, the permanent magnet is cylindrical or cuboid in shape and is made of neodymium iron boron.

[0011] Furthermore, the flexible silicone body is made of a flexible elastomer material, and its maximum elongation is greater than 200%.

[0012] Furthermore, it also includes a signal processing module, the input end of which is electrically connected to the extended end of the flexible ribbon cable.

[0013] A measurement method for a magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection, as described in this invention, includes the following steps: S1: The sensor is installed across the crack to be tested, and its first rigid fixed end and second rigid fixed end are fixed to the structural surfaces on both sides of the crack to be tested by bolts. The extended end of the flexible cable is electrically connected to the signal processing module, and the output voltage of the three magnetic transistors in the initial state is recorded as the reference value. S2: When the crack undergoes three-dimensional displacement, the real-time output voltage of the three magnetic transistors led out from the flexible cable is collected, and the voltage change relative to the reference value is calculated. S3: Based on the pre-calibrated magnetic field-displacement mapping model, the voltage change is calculated as a three-dimensional displacement component of the permanent magnet; S4: Determine the crack opening displacement, vertical misalignment, and horizontal misalignment based on the three-dimensional displacement components of the permanent magnet.

[0014] Furthermore, in step S3, the magnetic field-displacement mapping model is obtained through experimental calibration and is used to establish the correspondence between the voltage change of the magnetic transistor and the three-dimensional displacement components of the permanent magnet.

[0015] The present invention provides a magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection, which has the following advantages compared with the prior art: 1. Three-dimensional large tensile measurement capability: By embedding permanent magnets into a highly elastic flexible silicone body, and utilizing the principle that magnetic flux density changes with distance, it is possible to achieve a large range of measurements from millimeters to centimeters of three-dimensional displacement of crack opening, vertical misalignment, and horizontal misalignment, meeting the needs of large deformation monitoring of structural crack expansion.

[0016] 2. High-sensitivity measurement: The magnetic transistor replaces the traditional Hall element. Utilizing its higher magnetic sensitivity, it can detect weaker magnetic field changes, thereby improving the resolution and accuracy of crack displacement measurement. It is especially suitable for the early monitoring of micro-cracks.

[0017] 3. Three-dimensional decoupled measurement: The three orthogonally arranged magnetic triodes can simultaneously sense the three orthogonal components of the magnetic field. Combined with the decoupling algorithm, it can separate and measure the complex three-dimensional displacement (opening, shearing, torsion) of cracks, avoiding interdimensional coupling.

[0018] 4. Strong anti-interference capability: The magnetic sensor module is fixed to the structure under test by a rigid fixed end, which reduces the measurement error caused by the sensor's own posture change due to the deformation of the structure surface; at the same time, the magnetic field measurement method is not sensitive to environmental temperature, humidity, light, etc., and has good stability.

[0019] 5. Strong installation adaptability: The sensor adopts a split structure. During installation, the rigid fixing end is first fixed through the mounting holes, and the flexible silicone body can adapt to the surface shape of the structure without affecting subsequent deformation. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the sensor structure of the present invention. Figure 1 .

[0021] Figure 2 This is a schematic diagram of the sensor structure of the present invention. Figure 2 .

[0022] Figure 3 This is a schematic diagram of the layout of the magnetic transistor of the present invention on a circuit board.

[0023] Figure 4 This is a top view of the layout of the magnetic transistor of the present invention on a circuit board.

[0024] Figure 5 This is a schematic diagram and response curve of the sensor of the present invention under the crack opening displacement.

[0025] Figure 6 This is a schematic diagram and response curve of the sensor of the present invention under vertical misalignment of a crack.

[0026] Figure 7 This is a schematic diagram and response curve of the sensor of the present invention under horizontal misalignment of a crack.

[0027] Figure 8 This is a flowchart of the signal processing and decoupling process of the sensor of the present invention.

[0028] In the figure: 1. Flexible silicone body; 2. First rigid fixing end; 3. Second rigid fixing end; 4. Mounting hole; 5. Magnetic sensor module; 51. Circuit board; 52. Magnetic transistor; 53. Measurement circuit; 54. Flexible ribbon cable; 6. Permanent magnet. Detailed Implementation

[0029] A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection, such as Figure 1-4 As shown, the device includes a long, flexible silicone body 1. A first rigid fixing end 2 and a second rigid fixing end 3 are embedded at both ends of the flexible silicone body 1, corresponding to each other. Both the first rigid fixing end 2 and the second rigid fixing end 3 are made of rigid materials (such as 3D-printed PLA) and have sufficient rigidity to ensure they do not deform during operation. Both the first rigid fixing end 2 and the second rigid fixing end 3 have through-holes 4 for fixing the sensor across both sides of the crack being measured to the surface of the structure being measured using expansion bolts or high-strength structural adhesive.

[0030] The flexible silicone body 1 is made of a flexible elastomer material, including but not limited to Ecoflex, polydimethylsiloxane, silicone rubber, styrene-ethylene-butene-styrene block copolymer, Dragon Skin, and thermoplastic polyurethane, with a maximum elongation greater than 200%, allowing it to undergo tensile, bending, or torsional deformation as the crack expands. The flexible silicone body 1 completely encapsulates the first rigid fixing end 2 and the second rigid fixing end 3 using a one-piece injection molding process.

[0031] A magnetic sensor module 5 is embedded inside the first rigid fixed end 2.

[0032] The magnetic sensor module 5 includes a circuit board 51, three magnetic transistors 52, a measurement circuit 53, and a flexible cable 54. The three magnetic transistors 52 and the measurement circuit 53 are soldered onto the circuit board 51 or integrated with the circuit board 51 using semiconductor technology. The circuit board 51 is fixed by a first rigid fixing terminal 2. The three magnetic transistors 52 are arranged in three mutually orthogonal directions, and the magnetic sensitivity directions of the three magnetic transistors 52 are respectively aligned with the X, Y, and Z coordinate axes, used to independently measure the magnetic field components in the three directions. The spacing between adjacent magnetic transistors 52 is 1-5 mm. The magnetic transistors 52 are preferably silicon magnetic transistors, which have higher magnetic sensitivity than Hall elements and are suitable for weak magnetic field detection. The output terminals of the three magnetic transistors 52 are electrically connected to the input terminals of the measurement circuit 53. The measurement circuit 53 includes a constant current source bias circuit, a differential amplifier circuit, and a low-pass filter circuit. The constant current source bias circuit provides a stable bias current for the three magnetic transistors 52. The output terminals of the three magnetic transistors 52 are respectively connected to the input terminals of the differential amplifier circuit. The differential amplifier circuit differentially amplifies the received voltage signal, and its output terminal is connected to the input terminal of the low-pass filter circuit. The low-pass filter circuit filters the amplified signal and outputs three analog voltage signals Vx, Vy, and Vz. The output terminal of the measurement circuit 53 is electrically connected to one end of the flexible ribbon cable 54, and the other end of the flexible ribbon cable 54 extends to the outside of the first rigid fixed end 2 and the flexible silicone body 1.

[0033] A permanent magnet 6 is embedded inside the flexible silicone body 1 at one end near the magnetic sensor module 5 (i.e., the end near the first rigid fixed end 2), and an initial gap of 1-5 mm is provided between the permanent magnet 6 and the magnetic sensor module 5. The permanent magnet 6 is cylindrical or cuboid in shape, made of neodymium iron boron material, and magnetized along the axial direction or a specific direction. When the flexible silicone body 1 deforms, the permanent magnet 6 is displaced and deflected accordingly.

[0034] The magnetic field-based three-dimensional high-tensile flexible strain sensor for crack detection also includes a signal processing module. The input of the signal processing module is electrically connected to the extended end of the flexible cable 54. The signal processing module includes an amplification and filtering circuit, an analog-to-digital converter (A / D converter), and a microprocessor (MCU). The input of the amplification and filtering circuit is electrically connected to the extended end of the flexible cable 54 and is used to perform secondary filtering and amplitude adjustment on the received analog voltage signals Vx, Vy, and Vz. The output of the amplification and filtering circuit is connected to the input of the A / D converter. The A / D converter converts the conditioned analog signal into a digital signal, and its output is connected to the input of the microprocessor (MCU). The microprocessor has a built-in magnetic field-displacement mapping model, which can be specifically calculated using a magnetic field theory model or a three-dimensional displacement decoupling algorithm obtained through experimental calibration.

[0035] A measurement method for a magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection includes the following steps: S1: The sensor is installed across the crack to be tested, and its first rigid fixed end 2 and second rigid fixed end 3 are fixed to the structural surfaces on both sides of the crack to be tested by bolts. The extended end of the flexible cable 54 is electrically connected to the signal processing module, and the output voltage of the three magnetic transistors 52 in the initial state is recorded as the reference value.

[0036] S2: When the crack undergoes three-dimensional displacement, the real-time output voltage of the three magnetic sensitive transistors 52 led out from the flexible cable 54 is collected, and the voltage change relative to the reference value is calculated.

[0037] S3: Based on the pre-calibrated magnetic field-displacement mapping model, the voltage change is calculated as a three-dimensional displacement component of the permanent magnet 6.

[0038] S4: Determine the crack opening displacement, vertical misalignment, and horizontal misalignment based on the three-dimensional displacement components of permanent magnet 6.

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example 1

[0040] This embodiment provides a specific magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection. It should be noted that, in this embodiment, structural features, connection relationships, and working principles not explicitly described are consistent with those described in the foregoing specific embodiments, and will not be repeated here.

[0041] The first rigid fixing end 2 and the second rigid fixing end 3 are manufactured using 3D-printed PLA, possessing sufficient rigidity to ensure that they do not deform during sensor operation. The flexible silicone body 1 is made of Smoothon's Ecoflex 0030 silicone rubber, with an elastic modulus of 0.2 kPa and a maximum elongation of 200%. The flexible silicone body 1 completely encapsulates the two rigid fixing ends using a one-piece injection molding process.

[0042] The magnetic sensor module 5 uses a discrete silicon magnetic transistor 52, which is soldered onto three mutually perpendicular surfaces of the circuit board 51 in three orthogonal directions (X, Y, Z), aligning its magnetic sensing direction with the three coordinate axes. The measurement circuit 53 is integrated on the circuit board 51 and includes a constant current source bias circuit, a differential amplifier circuit, and a low-pass filter circuit. The circuit board 51 is mounted inside the first rigid fixing terminal 2. One end of the flexible ribbon cable 54 is electrically connected to the circuit board 51, and the other end extends outside the first rigid fixing terminal 2 for connecting to the signal processing module.

[0043] The permanent magnet 6 is an axially magnetized NdFeB N52 cylindrical magnet with a diameter of 1 mm and a height of 4 mm. Its magnetization direction is along the axial direction of the cylinder (i.e., the length direction of the sensor). An initial distance d0 of 2 mm is set between the permanent magnet 6 and the magnetic sensor module 5. This distance ensures that the permanent magnet 6 and the magnetic transistor 52 do not come into contact within the maximum deformation of the crack, and that the output voltage is within the linear range of the measurement circuit 53.

[0044] The signal processing module includes an amplification and filtering circuit, an analog-to-digital conversion unit, and a microprocessor (MCU). The microprocessor has a built-in magnetic field-displacement mapping model, which can be calculated using a magnetic field theory model or obtained through experimental calibration of a three-dimensional displacement decoupling algorithm.

[0045] The sensor is fabricated as follows: M1: A silicone mold for the sensor, a first rigid fixing end 2, and a second rigid fixing end 3 are made using a 3D printer.

[0046] M2: Three silicon magnetic transistors 52 are soldered onto the circuit board 51 and integrated with the measurement circuit 53 to form a magnetic sensor module 5.

[0047] M3: Fix the magnetic sensor module 5 in the reserved slot of the first rigid fixing end 2, and ensure that one end of the flexible cable 54 is electrically connected to the circuit board 51, and reserve sufficient length for the other end of the flexible cable 54 to be led out later.

[0048] M4: Spray a release agent on the surface of the sensor mold and place the first rigid fixing end 2 (with the magnetic sensor module 5 fixed on it) and the second rigid fixing end 3 into a specific position in the mold.

[0049] M5: Mix the Ecoflex 0030 prepolymer evenly according to the required mass ratio, stir thoroughly and degas, then inject it into the sensor mold. By controlling the injection volume, ensure that only half of the mold is submerged.

[0050] M6: Position the permanent magnet 6 in the cured silicone prepolymer and maintain a set initial distance d0 between it and the magnetic sensor module 5.

[0051] M7: Pour in the remaining silicone prepolymer to fill the entire mold, and obtain the sensor after curing. After curing, ensure that the protruding end of the flexible ribbon cable 54 protrudes outside the first rigid fixing end 2 and the flexible silicone body 1 for subsequent electrical connection with the signal processing module.

[0052] The sensor prepared in this embodiment is used for crack detection, such as... Figure 8 As shown, the specific steps are as follows: S1: Install the sensor: Position and drill holes on the structural surfaces on both sides of the crack to be tested. Fix the mounting holes 4 of the first rigid fixing end 2 and the second rigid fixing end 3 respectively with expansion bolts to ensure that the flexible silicone body 1 spans the crack and is in a naturally straight state. Connect the extended end of the flexible ribbon cable 54 to the signal processing module. Record the output voltage of the three magnetic transistors 52 at this time as the reference values ​​Vx0, Vy0, Vz0.

[0053] S2: Data Acquisition: After the sensor is powered on, the voltage signals Vx, Vy, and Vz output by the three magnetic transistors 52 are first amplified and filtered by the measurement circuit 53 to output conditioned analog voltage signals, which are then sent to the signal processing module.

[0054] S3: Displacement Calculation: The amplification and filtering circuit in the signal processing module further suppresses noise and adjusts the amplitude of the received analog signal. Then, the A / D converter converts the analog signals Vx, Vy, and Vz into digital signals. The digital signals enter the microprocessor (MCU) in the signal processing module. The microprocessor has a built-in magnetic field-displacement mapping model. The microprocessor first calculates the voltage change of the current output voltage relative to the reference value ΔVx = Vx - Vx0, ΔVy = Vy - Vy0, ΔVz = Vz - Vz0. Then, it substitutes these values ​​into the pre-calibrated decoupling matrix or queries the calibration curve to obtain the three-dimensional displacement Δx, Δy, Δz of the permanent magnet 6 in the sensor coordinate system.

[0055] S4: Crack displacement calculation: Since the relative displacement between the permanent magnet 6 and the first rigid fixed end 2 is entirely caused by crack deformation, and the second rigid fixed end 3 is fixed, the three-dimensional displacement of the permanent magnet 6 is the three-dimensional displacement component of the crack: the crack width change is Δx, the vertical displacement of the crack is Δy, and the horizontal displacement of the crack is Δz.

[0056] S5: Data Output and Early Warning: The calculated three-dimensional displacement data of the crack is uploaded to the monitoring center via wired or wireless means. When the displacement in any direction exceeds the preset threshold, an early warning signal is issued.

[0057] When the sensor is working, in the initial state, the permanent magnet 6 and the magnetic sensor module 5 maintain a fixed initial positional relationship, including the initial spacing, and the three magnetic transistors 52 output a stable reference voltage value. When the crack expands, the relative position between the first rigid fixed end 2 and the second rigid fixed end 3 changes, and the flexible silicone body 1 undergoes stretching, bending, or torsional deformation, causing the permanent magnet 6 to produce three-dimensional displacement and attitude changes relative to the magnetic sensor module 5. Since the magnetic flux density B is inversely proportional to the square of the distance r (B ∝ 1 / r),... 2 The change in the spatial position of the permanent magnet 6 will cause the magnetic flux density components (Bx, By, Bz) at the positions of the three magnetic transistors 52 to change accordingly, thereby causing the output voltage signals Vx, Vy, Vz of the three magnetic transistors 52 to change accordingly.

[0058] Figure 5 The sensor state is shown when the crack opens (normal displacement), at which time the permanent magnet 6 moves away from the magnetic sensor module 5 mainly along the X direction; Figure 6 The sensor status is shown when the crack is vertically misaligned (tangential displacement), at which time the permanent magnet 6 is mainly offset along the Y direction; Figure 7 The sensor status is shown when the crack is horizontally misaligned (another tangential displacement), at which point the permanent magnet 6 is mainly offset along the Z direction. Figure 5-7 In the diagram, D0 represents the initial length of the sensor; ΔDx, ΔDy, and ΔDz represent the displacement of the sensor along the x, y, and z directions, respectively; and Δd represents the displacement change between the permanent magnet 6 and the magnetic sensor module 5.

[0059] Flexible cable 54 leads the three-channel magnetic transistor voltage signals to an external signal processing module. The microprocessor in the signal processing module has a built-in magnetic field-displacement mapping model. This model can be pre-established through calibration experiments to establish the mapping relationship between the magnetic transistor voltage changes (ΔVx, ΔVy, ΔVz) and the three-dimensional displacement (Δx, Δy, Δz) of the permanent magnet. In actual measurement, the microprocessor, based on the real-time acquired ΔVx, ΔVy, and ΔVz, obtains the corresponding three-dimensional displacement through interpolation or calculation, and finally outputs the three-dimensional displacement data of the crack. Example 2

[0060] This embodiment is a magnetic field-type three-dimensional large tensile flexible strain sensor for crack detection. The main difference from Embodiment 1 is that the initial distance between the permanent magnet 6 and the magnetic sensor module 5 is 1 mm. The rest of the structure is the same as the magnetic field-type three-dimensional large tensile flexible strain sensor in Embodiment 1. Example 3

[0061] This embodiment is a magnetic field-type three-dimensional large tensile flexible strain sensor for crack detection. The main difference from Embodiment 1 is that the initial distance between the permanent magnet 6 and the magnetic sensor module 5 is 5mm. The rest of the structure is the same as the magnetic field-type three-dimensional large tensile flexible strain sensor in Embodiment 1. Example 4

[0062] This embodiment is a magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection. The main difference from Embodiment 1 lies in the integration method of the magnetic transistor 52. To reduce sensor size and improve integration and consistency, this embodiment uses an integrated magnetic transistor chip. Specifically, a monolithic integrated spatial magnetic vector sensor chip is selected. This chip integrates six silicon magnetic transistors in a three-dimensional structure, which are combined in pairs to form three magnetic sensing units, used for detecting magnetic fields in the X, Y, and Z directions, respectively. By directly mounting this chip onto the circuit board 51, triaxial magnetic field measurement can be achieved without the need for manual orthogonal mounting of discrete components, which is beneficial to improving measurement accuracy and consistency, while reducing sensor size. The remaining structure is the same as that of the magnetic field-type three-dimensional high-tensile flexible strain sensor in Embodiment 1.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection, characterized in that: It includes a long strip of flexible silicone body (1), with a first rigid fixing end (2) and a second rigid fixing end (3) embedded in the two ends of the flexible silicone body (1) respectively, and mounting holes (4) are opened through the first rigid fixing end (2) and the second rigid fixing end (3). A magnetic sensor module (5) is embedded inside the first rigid fixed end (2); The magnetic sensor module (5) includes a circuit board (51), three magnetic transistors (52), a measurement circuit (53), and a flexible cable (54). The three magnetic transistors (52) and the measurement circuit (53) are both mounted on the circuit board (51), and the three magnetic transistors (52) are arranged in three mutually orthogonal directions. The output terminals of the three magnetic transistors (52) are electrically connected to the input terminals of the measurement circuit (53), and the output terminals of the measurement circuit (53) are electrically connected to one end of the flexible cable (54). The other end of the flexible cable (54) extends to the outside of the first rigid fixed end (2) and the flexible silicone body (1). A permanent magnet (6) is embedded in the interior of the flexible silicone body (1) near the magnetic sensor module (5), and an initial gap of 1-5mm is provided between the permanent magnet (6) and the magnetic sensor module (5).

2. The magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection according to claim 1, characterized in that: The magnetic sensing directions of the three magnetic transistors (52) are respectively aligned with the directions of the three mutually orthogonal coordinate axes X, Y, and Z, and the distance between two adjacent magnetic transistors (52) is 1-5 mm.

3. A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection according to claim 1, characterized in that: The magnetic transistor (52) is a silicon magnetic transistor.

4. A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection according to claim 1, characterized in that: The magnetic transistor (52) is soldered onto the circuit board (51) or integrated into the circuit board (51) through semiconductor processes.

5. A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection according to claim 1, characterized in that: The measurement circuit (53) includes a constant current source bias circuit, a differential amplifier circuit, and a low-pass filter circuit.

6. A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection according to claim 1, characterized in that: The permanent magnet (6) is cylindrical or cuboid in shape and is made of neodymium iron boron.

7. A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection according to claim 1, characterized in that: The flexible silicone body (1) is made of flexible elastomer material and its maximum elongation is greater than 200%.

8. A magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection according to claim 1, characterized in that: It also includes a signal processing module, the input of which is electrically connected to the extended end of the flexible ribbon cable (54).

9. A measurement method for a magnetic field-type three-dimensional high-tensile flexible strain sensor for crack detection as described in claim 8, characterized in that: Includes the following steps: S1: The sensor is installed across the crack to be tested, and its first rigid fixed end (2) and second rigid fixed end (3) are fixed to the structural surfaces on both sides of the crack to be tested by bolts. The extended end of the flexible cable (54) is electrically connected to the signal processing module, and the output voltage of the three magnetic transistors (52) in the initial state is recorded as the reference value. S2: When the crack undergoes three-dimensional displacement, the real-time output voltage of the three magnetic transistors (52) led out from the flexible cable (54) is collected, and the voltage change relative to the reference value is calculated. S3: Based on the pre-calibrated magnetic field-displacement mapping model, the voltage change is calculated as the three-dimensional displacement component of the permanent magnet (6); S4: Determine the crack opening displacement, vertical misalignment and horizontal misalignment based on the three-dimensional displacement components of the permanent magnet (6).

10. The measurement method of a magnetic field-type three-dimensional large tensile flexible strain sensor for crack detection according to claim 9, characterized in that: In step S3, the magnetic field-displacement mapping model is obtained through experimental calibration and is used to establish the correspondence between the voltage change of the magnetic transistor (52) and the three-dimensional displacement components of the permanent magnet (6).

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