Non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors

Abstract

The present application relates to a kind of carbon fiber composite material nondestructive testing methods based on piezoresistive nanofiber sensor, it includes the following steps: 1), preparation spinning solution;2), build electrospinning platform;3), preparation high frequency response piezoresistive nanofiber sensor;4), high frequency response piezoresistive nanofiber sensor is embedded in carbon fiber composite material board;5), to the carbon fiber composite material board vibration response test and ultrasonic guided wave test, to detect the damage condition of carbon fiber composite material board.The present application can guarantee that fiber sensor is embedded in carbon fiber composite material board, can guarantee that the nondestructive testing of carbon fiber composite material is realized under the premise of not affecting the mechanical properties of carbon fiber reinforced composite and not occupying carbon fiber composite material surface space.

Description

Technical Field

[0001] This invention relates to a non-destructive testing method for carbon fiber reinforced composite materials, specifically a non-destructive testing method for carbon fiber composite materials based on a piezoresistive nanofiber sensor, belonging to the field of non-destructive testing technology. Background Technology

[0002] Carbon fiber reinforced composites possess excellent mechanical properties and are widely used in many fields. However, the composite material itself exhibits anisotropy and non-uniformity, making it prone to internal damage that is almost invisible. This damage leads to a significant decrease in performance and poses certain risks to product manufacturing and application.

[0003] To address this issue, composite materials need to be inspected to promptly understand the damage to carbon fibers. Non-destructive testing (NDT) is a method for detecting and assessing internal defects and damage without destroying the structure or material. Currently, many sensors are used for NDT in the composite materials field, such as lead zirconate titanate piezoelectric ceramic sensors and acoustic emission sensors. These sensors can be used to detect structural damage in laminates, but they all need to be attached to the surface of the material, occupying surface space and having poor adaptability to curved structures, thus having certain limitations. Currently, fiber optic grating sensors are the most widely used and technologically mature embedded sensors. The miniaturization design of these sensors does not affect structural performance and is suitable for long-term monitoring of ships, pipelines, etc., but they have drawbacks such as high installation complexity, high risk of breakage, and high maintenance costs.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is indeed necessary to provide an innovative non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors to overcome the defects in the prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a non-destructive testing method for carbon fiber composite materials based on a piezoresistive nanofiber sensor, which can achieve non-destructive testing of carbon fiber reinforced composite materials without affecting the mechanical properties of the carbon fiber reinforced composite materials or occupying the surface space of the materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a non-destructive testing method for carbon fiber composite materials based on a piezoresistive nanofiber sensor, which includes the following steps:

[0007] 1) Preparation of spinning solution;

[0008] 2) Set up an electrostatic spinning table;

[0009] 3) Fabrication of a high-frequency piezoresistive nanofiber sensor;

[0010] 4) Embed a high-frequency response piezoresistive nanofiber sensor into a carbon fiber composite plate;

[0011] 5) Vibration response test and ultrasonic guided wave test were performed on the carbon fiber composite plate to detect the damage of the carbon fiber composite plate.

[0012] The non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors of the present invention is further described as follows: Step 1) specifically involves: weighing polymethyl methacrylate powder and pouring it into a glass screw-top bottle, then sequentially adding graphene dispersion and dimethylformamide solvent, and finally adding a magnetic stir bar for mixing; stirring the prepared solution in a water bath, then placing it in an ultrasonic cleaner, repeating the stirring and ultrasonic cleaning steps three times, and finally obtaining a uniformly mixed polymethyl methacrylate / graphene mixed spinning solution.

[0013] The non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors of the present invention further comprises: in the prepared spinning solution, the mass fraction of polymethyl methacrylate is 28% and the concentration of graphene is 1%.

[0014] The non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors of the present invention further comprises: during magnetic stirring, the stirring speed is set to 800 rpm, the water bath stirring temperature is set to 50°C, and the stirring time is 3 hours; the ultrasonic cleaning temperature is set to 50°C, and the cleaning time is set to 1 hour.

[0015] The non-destructive testing method for carbon fiber composite materials based on a piezoresistive nanofiber sensor of the present invention further comprises: the electrospinning table includes a base, an injection pump, a syringe, an asynchronous motor, and a bearing; wherein, the injection pump is installed on one side of the base and can move along the base; the syringe is installed on the injection pump and is pushed by the injection pump to inject; the needle of the syringe is an electrospinning flat-tipped needle; the asynchronous motor and the bearing are arranged opposite to each other; the two ends of a bare copper wire are respectively fixed between the asynchronous motor and the bearing, so that the position of the bare copper wire and the syringe are perpendicular to each other.

[0016] The non-destructive testing method for carbon fiber composite materials based on a piezoresistive nanofiber sensor of the present invention is further described as follows: the needle end of the syringe is connected to the positive terminal of a 10kV DC high voltage power supply; the asynchronous motor end of the bare copper wire is connected to the negative terminal of a 10kV DC high voltage power supply, and the bearing end is grounded; the rotational speed of the asynchronous motor is set to 300 rpm; and the spinning distance between the bare copper wire and the syringe is set to 15 cm.

[0017] The non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors of the present invention is further described as follows: Step 3) specifically involves: pushing the syringe with an injection pump at a speed of 0.002 mm / s; the injection pump moving left and right at a uniform speed, with the spinning time set to 30 s; the spun solution passing through the electric field forms a layer of polymethyl methacrylate / graphene piezoresistive nanofibers on a uniformly rotating bare copper wire, thereby obtaining a high-frequency response piezoresistive nanofiber sensor.

[0018] The non-destructive testing method for carbon fiber composite materials based on a piezoresistive nanofiber sensor of the present invention further comprises: step 4) specifically includes:

[0019] 4-1) The high-frequency response piezoresistive nanofiber sensor is wound into a "bow" shape and distributed in the middle of the edge of the 3rd and 4th layers of carbon fiber plain weave fabric, exposing a part of bare copper wire. The carbon fiber plain weave fabric is stacked in a total of 6 layers.

[0020] 4-2) Using vacuum-assisted resin transfer molding process, the resin is transferred from one end to the closed cavity of the plain weave fabric structure by using the negative pressure of the vacuum pump. The resin impregnates the fabric structure, and then the resin is cured. Finally, the carbon fiber composite board is demolded.

[0021] 4-3) The upper surface of the carbon fiber composite plate is polished to expose the carbon fiber yarn, and conductive silver paste is used to couple the wires to the surface of the carbon fiber composite plate as the upper electrode. The exposed copper wires of the high-frequency response piezoresistive nanofiber sensor are polished to serve as the lower electrode. The upper electrode, the lower electrode and the signal amplifier are connected.

[0022] The non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors of the present invention is further described as follows: The specific method for vibration response testing in step 4) is as follows:

[0023] The signal generator emits different sinusoidal signals, which are transmitted to the exciter through the power amplifier. The exciter's punch drives the carbon fiber composite plate embedded with the piezoresistive nanofiber sensor to vibrate at high frequency. The piezoresistive nanofiber sensor vibrates at high frequency along with the sample to measure the resistance change of the fiber sensor.

[0024] Based on the linear relationship between the rate of change of resistance ΔR / R0 and the strain ε, i.e. Where: ΔR is the change in resistance. R(t) is the instantaneous resistance during vibration, R0 is the initial resistance, and G is the piezoresistive coefficient; ε is the strain experienced by the fiber sensor; by monitoring abnormal changes in ΔR in real time, early warning of microcracks caused by fatigue vibration in the structure can be provided.

[0025] The non-destructive testing method for carbon fiber composite materials based on piezoresistive nanofiber sensors of the present invention can also be described as follows: The specific method of ultrasonic guided wave testing in step 4) is as follows: a laser emitter emits a pulsed laser, and the pulsed laser is aligned and focused on the polished center part of the surface of the carbon fiber composite material plate; the laser pulse instantly heats a small area on the surface of the material, causing the area to expand rapidly. At the same time, constrained by the surrounding cold material, this restricted expansion generates strong transient mechanical stress, which propagates into the material and around it in the form of a Lamb wave; the high-frequency Lamb wave generated by the pulsed laser is received by the fiber sensor; the signal received by the fiber sensor is amplified by a signal amplifier and displayed on an oscilloscope. The damage to the carbon fiber composite material plate is detected by observing the change in the amplitude of the Lamb wave mode on the oscilloscope.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The piezoresistive nanofiber sensor used in the non-destructive testing method for carbon fiber composite materials of the present invention is embedded in the carbon fiber composite material plate, unlike some other sensors that need to be pasted on the surface of the material plate and occupy space; at the same time, the piezoresistive nanofiber sensor is small in size and has little impact on the mechanical properties of the carbon fiber composite material plate.

[0028] 2. The high-frequency response piezoresistive nanofiber sensor used in this invention is simple to prepare, the raw materials are readily available and inexpensive, and the sensor can be embedded in carbon fiber laminates relatively quickly. It is applicable to both planar and curved laminates and can perform real-time structural health monitoring of carbon fiber composite materials. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the electrospinning table in step 2) of the present invention.

[0030] Figure 2 This is a schematic diagram of the structure of the high-frequency response piezoresistive nanofiber sensor obtained in step 3) of the present invention.

[0031] Figure 3 This is a schematic diagram of the vibration response test performed in step 5) of the present invention.

[0032] Figure 4 This is a schematic diagram of the ultrasonic guided wave test performed in step 5) of the present invention.

[0033] Figure 5 This is a response diagram of a high-frequency piezoresistive nanosensor to different high-frequency vibrations during vibration response testing in step 5) of the present invention.

[0034] Figure 6This is a schematic diagram of the self-made Wheatstone bridge used in step 5) of the present invention for ultrasonic guided wave testing.

[0035] Figure 7 This is the frequency domain diagram of the signal received by the high-frequency response piezoresistive nanosensor during the ultrasonic guided wave test in step 5) of the present invention. Detailed Implementation

[0036] Please refer to the instruction manual appendix. Figure 1 To be continued Figure 7 As shown, this invention provides a non-destructive testing method for carbon fiber composite materials based on a piezoresistive nanofiber sensor, which includes the following steps:

[0037] 1) Preparation of spinning solution, specifically as follows:

[0038] After weighing the polymethyl methacrylate powder, pour it into a glass screw-top bottle, then add graphene dispersion and dimethylformamide solvent dropwise, and finally add a magnetic stir bar to mix.

[0039] To obtain a spinning solution with suitable concentration, different concentrations of polymethyl methacrylate (PMMA) were added to dimethylformamide solvent, and then mixed evenly with a certain amount of graphene dispersion before electrospinning experiments were conducted. The microstructure of the sensor fiber layers prepared at different concentrations was observed under a microscope, and the optimal values ​​were determined to be 28% mass fraction of PMMA and 1% concentration of graphene in the spinning solution.

[0040] Furthermore, the prepared solution is stirred in a water bath, and then placed in an ultrasonic cleaner. The stirring and ultrasonic cleaning steps are repeated three times to finally obtain a uniformly mixed polymethyl methacrylate / graphene hybrid spinning solution.

[0041] In this embodiment, during magnetic stirring, the stirring speed is set to 800 rpm, the water bath stirring temperature is set to 50°C, and the stirring time is 3 hours; the ultrasonic cleaning temperature is set to 50°C, and the cleaning time is set to 1 hour.

[0042] 2) Set up an electrostatic spinning table.

[0043] The electrospinning table is assembled from several parts, including a base 3, a syringe pump 2, a syringe 1, an asynchronous motor 5, and a bearing 6. The syringe pump 2 is mounted on one side of the base 3 and can move along it. The syringe 1 is used to draw up the uniformly mixed spinning solution obtained in step 1), and is mounted on the syringe pump 2, which pushes it for injection. The needle of the syringe 1 is a flat-tipped electrospinning needle. The asynchronous motor 5 and the bearing 6 are positioned opposite each other. Both ends of a bare copper wire 4 are fixed between the asynchronous motor 5 and the bearing 6, and the asynchronous motor 5 drives the bare copper wire 4 to rotate. The bare copper wire 4 is perpendicular to the syringe 1.

[0044] Since the spinning voltage and distance both affect the state of the spun fibers, experiments with a control group showed that a 10kV DC high voltage and a spinning distance of 15cm resulted in a more stable jet. Therefore, the needle end of the syringe 1 was connected to the positive terminal of the 10kV DC high voltage. The bare copper wire 4 was placed horizontally, with both ends fixed between an asynchronous motor 5 and a bearing 6, ensuring that the bare copper wire 4 and the syringe 1 were perpendicular. The vertical distance between the needle of the syringe 1 and the bare copper wire 4 was set to 15cm. The asynchronous motor end of the bare copper wire 4 was connected to the negative terminal of the 10kV DC high voltage, and the bearing end was grounded. The rotational speed of the asynchronous motor 5 was set to 300 rpm.

[0045] 3) To prepare a high-frequency response piezoresistive nanofiber sensor, a layer of polymethyl methacrylate / graphene piezoresistive nanofiber 7 is coated on a bare copper wire 4, which is the high-frequency response piezoresistive nanofiber sensor 8 to be prepared.

[0046] Specifically, during spinning, the syringe pump 2 pushes the syringe 1, which remains stationary while the syringe pump 2 moves horizontally at a constant speed. The spun spinning solution is passed through an electric field and forms a piezoresistive nanofiber layer on the uniformly rotating bare copper wire 4. In this embodiment, the injection speed of the syringe 1 is set to 0.002 mm / s, and the spinning time is set to 30 s.

[0047] 4) Embedding a high-frequency response piezoresistive nanofiber sensor into a carbon fiber composite plate, the specific method is as follows:

[0048] 4-1) The high-frequency response piezoresistive nanofiber sensor 8 is wound into a "bow" shape and distributed in the middle of the edge of the 3rd and 4th layers of carbon fiber plain weave fabric, exposing a part of bare copper wire 4. The carbon fiber plain weave fabric is stacked in a total of 6 layers.

[0049] 4-2) Using the Vacuum Assisted Resin Transfer Molding (VARTM) process, resin is transferred from one end to the closed cavity of a plain weave fabric structure using the negative pressure of a vacuum pump. The resin impregnates the fabric structure, then cures, and finally demolds to obtain the carbon fiber composite plate 9. In this embodiment, the dimensions of the carbon fiber composite plate 9 are 500×500×2mm.

[0050] 4-3) The upper surface of the carbon fiber composite plate 9 is polished to expose the carbon fiber yarn, and conductive silver paste is used to couple the wires to the surface of the carbon fiber composite plate 9 as the upper electrode. The copper wires of the exposed part of the high-frequency response piezoresistive nanofiber sensor 8 are polished to serve as the lower electrode. The upper electrode, the lower electrode and the signal amplifier are connected.

[0051] 5) Vibration response test and ultrasonic guided wave test were performed on the carbon fiber composite plate to detect the damage of the carbon fiber composite plate.

[0052] The specific method for the vibration response test is as follows: a signal generator emits different sinusoidal signals, which are transmitted to the exciter through a power amplifier. The exciter's punch 10 drives the carbon fiber composite plate 9, which is embedded with a piezoresistive nanofiber sensor 8, to vibrate at high frequency. The piezoresistive nanofiber sensor 8 vibrates at high frequency along with the sample, thereby measuring the resistance change of the fiber sensor 8. The corresponding data is acquired by a data acquisition card.

[0053] The core of the above process is the piezoresistive effect, meaning that the resistance of the fiber sensor 8 changes significantly under the mechanical strain generated by vibration. This resistance change is determined by the deformation of its internal conductive network. Graphene, as a conductive phase, is uniformly dispersed in the polymethyl methacrylate matrix, forming conductive pathways. When the fiber is subjected to strain, the distance, contact area, and arrangement of the graphene sheets change, generating a quantum tunneling effect, which leads to a change in the resistance of the conductive pathways. This resistance change converts the intangible high-frequency vibration parameters into quantifiable electrical signals, allowing the fiber sensor 8 to be integrated into carbon fiber composite structures such as those used in aerospace and wind turbine blades.

[0054] Based on the linear relationship between the rate of change of resistance ΔR / R0 and the strain ε, i.e. Where: ΔR is the change in resistance. R(t) is the instantaneous resistance during vibration, R0 is the initial resistance, and G is the piezoresistive coefficient; ε is the strain experienced by the fiber sensor. By monitoring abnormal changes in ΔR in real time, microcracks caused by fatigue vibration in the structure can be predicted in advance.

[0055] Please refer to the instruction manual appendix. Figure 5As shown, this is a response graph of the high-frequency piezoresistive nanosensor to different high-frequency vibrations during vibration response testing of this invention. During the vibration response test, the vibration frequencies of the exciter were 2Hz, 5Hz, 10Hz, 20Hz, and 50Hz, with an amplitude of 1.5mm. The response data of the fiber sensor 8 to different vibration signals show that the sensor can effectively distinguish signals of different frequencies. However, it was also found that once the frequency of the signal generator exceeded 50Hz, the collected data became distorted and could not accurately reflect the excitation signal frequency. Analysis suggests that the possible reason is that the exciter vibrates too rapidly at this point, causing the test sample to potentially re-contact the exciter's punch 10 during the period between deformation and restoration of its shape. This results in multiple irregular collisions between the test sample and the vibrating end, thus causing data distortion.

[0056] The specific method for ultrasonic guided wave testing is as follows:

[0057] First, use sandpaper to sand the center of the upper surface of the carbon fiber composite plate 9 to expose the carbon fiber yarns. Since the resin matrix usually has weak absorption of specific wavelengths of laser light, this can enhance the absorption efficiency of the pulsed laser energy in this area.

[0058] Then, a pulsed laser is emitted using laser emitter 11, and the pulsed laser is aligned and focused on the polished center area of ​​the upper surface of the carbon fiber composite plate 9. The main mechanism utilized in this method is the thermoelastic effect: the laser pulse instantaneously heats a small area on the material surface, causing rapid thermal expansion in that area. Simultaneously constrained by the surrounding cold material, this restricted expansion generates strong transient mechanical stress, which propagates into and around the material in the form of a Lamb wave. The high-frequency Lamb wave generated by the pulsed laser is received by the fiber sensor 8, resulting in a dynamic strain ε(t) on the surface of the carbon fiber composite plate 9. Since the nanofibers are tightly attached to the surface of the carbon fiber composite plate 9, they also generate the same strain ε(t). The piezoresistive effect causes a change in the resistance of the fiber sensor 8. Where: ΔR is the change in resistance, R0 is the original resistance, G is the piezoresistive coefficient, which measures the resistive response sensitivity of a material to strain. Due to their small size and special structure, nanofibers typically have a high G value, and ε(t) is the strain as a function of time. Since the deformation of the carbon fiber composite plate 9 caused by the Lamb wave signal is extremely small, resulting in a very small change in the resistance of the conductive filler, a Wheatstone bridge was fabricated to amplify the signal received by the fiber sensor 8 during the test.

[0059] Please refer to the instruction manual appendix. Figure 6 The diagram shown is a schematic of a self-made Wheatstone bridge used in ultrasonic guided wave testing according to this invention. The required circuit component is an adjustable resistor. , , The AD8336 is a variable gain amplifier and a steady-state voltage source. The AD8336 can amplify signals up to 100MHz, meeting the testing requirements. Several formulas can be derived from the bridge circuit:

[0060]

[0061]

[0062]

[0063] If the bridge circuit is balanced and the bridge output voltage is... If it is 0, then

[0064]

[0065] Test bridge output voltage A value of 0 ensures that the output starting voltage will not exceed the oscilloscope's range. Therefore, during testing, the resistance of fiber sensor 8 is measured using a multimeter. In the future, adjustable resistors can be... , , Adjustment of resistance value and Same. And external voltage source. The larger the resistance, the greater the change in voltage signal converted from the change in resistance of fiber sensor 8. In this embodiment, It is 15V.

[0066] As one arm of the Wheatstone bridge, the fiber sensor 8 causes the bridge to become unbalanced when the resistance changes, outputting a differential voltage signal V that is proportional to ΔR. Therefore, the voltage signal V output by the fiber sensor 8 is directly proportional to the dynamic strain ε(t) on the plate surface at the sensor location, which is also proportional to the amplitude of the strain field of the Lamb wave reaching that location.

[0067] Finally, the signal received by fiber sensor 8 is amplified by a signal amplifier and displayed on an oscilloscope. Observing the signal directly received by the oscilloscope reveals significant ambient noise. This is because the Lamb wave signal received by fiber sensor 8 is completely submerged by ambient noise, making further analysis impossible. Therefore, the signal needs to be filtered. A Fast Fourier Transform (FFT) is performed on the excitation signal from laser emitter 11 and the signal received by fiber sensor 8 to obtain the frequency domain diagram. For the frequency domain diagram of the signal received by fiber sensor 8, please refer to the appendix of the instruction manual. Figure 7As shown in the diagram. In this embodiment, the excited Lamb wave signal is mainly below 150kHz, and the signal frequency received by the fiber sensor 8 is also within 150kHz, indicating that the fiber sensor 8 has a good response to high-frequency Lamb wave signals. In order to filter out irrelevant noise signals, the received signal needs to be bandpass filtered. The ambient noise signal is mainly below 1kHz, so the cutoff frequency of the bandpass filter is 1kHz to 150kHz, and the filtered signal can be obtained. Based on the above analysis, this test can detect the damage 12 of the carbon fiber composite plate 9 by observing the change in the amplitude of the Lamb wave mode on the oscilloscope.

[0068] In this embodiment, damage 12 is simulated by placing a weight on the surface of the carbon fiber composite plate 9, which can simulate the local impedance change caused by actual damage (such as delamination, debonding, and impact damage). When a Lamb wave encounters damage 12, scattering, reflection, mode conversion, and energy attenuation occur, causing a change in the amplitude of the wave packet propagating to the fiber sensor 8. By monitoring the change in the amplitude of a specific mode of Lamb wave, the presence and extent of damage 12 can be inferred.

[0069] The above-described specific embodiments are merely preferred embodiments of this invention and are not intended to limit this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A method for non-destructive testing of carbon fiber composites based on piezoresistive nanofiber sensors, characterized in that: It comprises the following steps: 1) preparing a spinning solution; 2) building an electrostatic spinning platform; 3) preparing a high-frequency response piezoresistive nanofiber sensor; 4) embedding the high-frequency response piezoresistive nanofiber sensor into a carbon fiber composite plate; 5) testing the carbon fiber composite plate for vibration response and ultrasonic guided wave to detect the damage of the carbon fiber composite plate; The specific method of the vibration response test is as follows: The signal generator sends different sinusoidal signals, which are transmitted to the exciter through the power amplifier. The punch of the exciter drives the carbon fiber composite plate embedded with the piezoresistive nanofiber sensor to vibrate at a high frequency. The piezoresistive nanofiber sensor vibrates at a high frequency with the sample to measure the resistance change of the fiber sensor. Based on the linear relationship between the resistance change rate ΔR / R0 and the strain ε, that is ; wherein: ΔR is the resistance change amount, , R(t) is the instantaneous resistance when vibrating, R0 is the initial resistance, G is the piezoresistive coefficient; ε is the strain received by the fiber sensor; by monitoring the abnormal change of ΔR in real time, the micro cracks generated by the fatigue vibration of the structure are warned; The specific method of the ultrasonic guided wave test is as follows: a laser emitter is used to emit pulsed laser, which is aimed at and focused on the polished center of the upper surface of the carbon fiber composite plate. The laser pulse instantaneously heats a small area of the material surface, causing rapid thermal expansion of the area. At the same time, it is constrained by the surrounding cold material, and the constrained expansion generates transient mechanical stress, which propagates to the interior and surrounding of the material in the form of Lamb waves. The high-frequency Lamb waves generated by the pulsed laser are received by the fiber sensor. The signal received by the fiber sensor is amplified through a Wheatstone bridge and displayed on an oscilloscope. The damage of the carbon fiber composite plate is detected by observing the amplitude change of the Lamb wave mode of the oscilloscope. The Wheatstone bridge comprises an adjustable resistance , , a variable gain amplifier AD8336 and a steady voltage source.

2. The piezoresistive nanofiber sensor based carbon fiber composite non-destructive testing method of claim 1, wherein: The step 1) is specifically as follows: the polymethyl methacrylate powder is weighed and poured into a glass screw neck bottle, then the graphene dispersion liquid and dimethylformamide solvent are added dropwise, and finally a magnetic stirrer is added for mixing. The prepared solution is stirred in a water bath, then put into an ultrasonic cleaning machine, and the stirring and ultrasonic cleaning are repeated for three times. Finally, a uniformly mixed polymethyl methacrylate / graphene mixed spinning solution is obtained.

3. The piezoresistive nanofiber sensor based carbon fiber composite non-destructive testing method of claim 2, wherein: The mass fraction of polymethyl methacrylate in the prepared spinning solution is 28%, and the concentration of graphene is 1%.

4. The piezoresistive nanofiber sensor based carbon fiber composite non-destructive testing method of claim 2, wherein: During magnetic stirring, the stirring speed is set to 800 rpm, the water bath stirring temperature is set to 50℃, and the stirring time is 3 hours. The ultrasonic cleaning temperature is set to 50℃, and the cleaning time is set to 1 hour.

5. The piezoresistive nanofiber sensor based carbon fiber composite non-destructive testing method of claim 1, wherein: The electrostatic spinning platform comprises a base, an injection pump, an injector, an asynchronous motor and a bearing. The injection pump is installed on one side of the base and can move along the base. The injector is installed on the injection pump and is pushed by the injection pump for injection. The needle of the injector is a flat needle for electrostatic spinning. The asynchronous motor and the bearing are oppositely arranged. One end of a bare copper wire is fixed between the asynchronous motor and the bearing, so that the bare copper wire and the injector are perpendicular to each other.

6. The piezoresistive nanofiber sensor based carbon fiber composite non-destructive testing method of claim 5, wherein: The needle end of the injector is connected to the positive electrode of a 10kV direct current high voltage. The asynchronous motor end of the bare copper wire is connected to the negative electrode of a 10kV direct current high voltage, and the bearing end is connected to the ground. The rotating speed of the asynchronous motor is set to 300rmp. The spinning distance between the bare copper wire and the injector is set to 15cm.

7. The piezoresistive nanofiber sensor based carbon fiber composite non-destructive testing method of claim 1, wherein: The step 3) is specifically: pushing the syringe by means of the injection pump, the pushing speed of which is set to 0.002 mm / s; the injection pump is uniformly translated left and right, and the spinning time is set to 30 s; the pushed spinning solution forms a layer of polymethyl methacrylate / graphene piezoresistive nanofiber on the uniformly rotating bare copper wire in an electric field, that is, the high-frequency response piezoresistive nanofiber sensor is prepared.

8. The piezoresistive nanofiber sensor based carbon fiber composite non-destructive testing method of claim 1, wherein: The step 4) is specifically: 4-1), the high-frequency response piezoresistive nanofiber sensor is wound into a "bow" shape and distributedly placed in the middle of the edges of the 3rd and 4th layers of carbon fiber plain weave fabric, exposing a part of the bare copper wire, wherein the carbon fiber plain weave fabric is stacked in 6 layers; 4-2), a vacuum-assisted resin transfer molding process is used, resin is transferred from one end to the closed cavity of the plain weave fabric structure by means of negative pressure of a vacuum pump, the resin infiltrates the fabric structure, then the resin is cured, and finally the carbon fiber composite plate is demolded; 4-3), the upper surface of the carbon fiber composite plate is polished to expose the carbon fiber yarn, and the lead wire is coupled to the surface of the carbon fiber composite plate as the upper electrode using conductive silver glue, and the exposed part of the copper wire of the high-frequency response piezoresistive nanofiber sensor is polished as the lower electrode; the upper electrode, the lower electrode and the signal amplifier are connected.

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