Damage monitoring method, readable storage medium and device based on piezoelectric sensing coating in-situ sensor and zero group velocity guided wave

Abstract

The present invention provides a damage monitoring method based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided wave, a readable storage medium and a device, which comprises: preparing a piezoelectric sensing coating on a structure to be tested; connecting two electrodes of the piezoelectric sensing coating to a pulsed ultrasonic signal source and a computer respectively; controlling the pulsed ultrasonic signal source to send an excitation signal to the piezoelectric sensing coating by a computer to stimulate the generation of ultrasonic guided waves; the piezoelectric sensing coating receives the ultrasonic guided waves and transmits them to a data acquisition card and a computer; processing the received ultrasonic guided waves based on a short-time Fourier transform, calculating the energy spectrum of the ultrasonic guided waves in the time-frequency domain, and extracting the frequency of the resonance peak of the ultrasonic guided waves; and judging the damage of the structure to be tested by comparing the frequency of the resonance peak with the value of the zero group velocity guided wave frequency of the structure to be tested in different states. In this way, the piezoelectric sensing coating can conform to a complex structure to be tested, and can realize in-situ online sensing and multi-cycle excitation of zero group velocity guided waves.

Description

Technical Field

[0001] The present invention relates to the field of structural health monitoring, and particularly to damage monitoring of metal, composite material and other structures, and in particular to a damage monitoring method, a readable storage medium and a device based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided waves. Background Art

[0002] With the rapid development of advanced manufacturing technology, bonded structures are playing an increasingly important role in aerospace, automotive, wind energy, pressure vessel and other industries due to their advantages in cost, weight, ease of manufacturing and load-bearing capacity. These structures are prone to debonding damage during processing and service due to the influence of surface quality, impact and fatigue loads, which reduces the load-bearing capacity of the structure and threatens the structural integrity and safety. Therefore, it is very important to develop a method that can monitor the debonding damage in these structures in real time to ensure their safety and reliability.

[0003] Traditional damage monitoring methods include eddy current, X-ray diffraction, optical fiber, ultrasonic guided wave method, etc. Among them, ultrasonic guided wave method is widely used due to its advantages of full thickness detection, simple detection method, and large detection range. The basic principle of ultrasonic guided wave method is to use the phenomena of ultrasonic guided wave reflection, scattering, and mode conversion caused by damage to achieve damage diagnosis. However, the guided waves in the bonded structure have complex multi-modal and dispersion characteristics. In addition, most structures in actual engineering applications have complex forms such as bolt holes, reinforcements, and variable thickness, which leads to the overlap of ultrasonic guided wave signals. It is difficult to extract and analyze the signals of the target guided wave mode. Therefore, the traditional ultrasonic guided wave damage diagnosis method faces problems of applicability and effectiveness in actual engineering applications.

[0004] The method based on zero group velocity guided waves has obvious applicability advantages in complex structural damage diagnosis due to its sensitivity to local health status. However, the existing zero group velocity guided wave measurement method relies on non-contact sensing technology, especially non-contact laser ultrasonic technology, which has limitations such as large equipment size, inconvenient use, and susceptibility to interference from environmental factors. It cannot realize in-situ online sensing of zero group velocity guided waves and is not suitable for real-time online monitoring of structures. In addition, due to the limitations of thermoelastic conditions, the ultrasonic guided waves generated by laser pulses are usually weak, and the signal-to-noise ratio of the obtained guided wave signals is low, resulting in low reliability of damage diagnosis. Summary of the invention

[0005] Aiming at the difficulty of online monitoring of the damage condition and health status of adhesive structures, the present invention proposes a damage monitoring method based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided wave, which is used to solve the problems of low applicability and low robustness of damage diagnosis in engineering applications of the prior art, as well as the inability to realize real-time online measurement of zero group velocity guided wave, and the failure to meet the needs of real-time online monitoring of complex structures.

[0006] The invention provides a damage monitoring method based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided wave, which comprises the following steps: step 1: preparing a piezoelectric sensing coating on a structure to be tested (bonded structure); step 2: connecting one electrode in the piezoelectric sensing coating to a pulse ultrasonic signal source, and connecting the other electrode to a data acquisition card and a computer; step 3: controlling the pulse ultrasonic signal source to send an excitation signal by a computer, and transmitting the excitation signal to the piezoelectric sensing coating to excite the structure to be tested to generate ultrasonic guided waves; step 4: the piezoelectric sensing coating receives the ultrasonic guided waves, and transmits the ultrasonic guided waves to the data acquisition card and the computer through a wireless network; step 5: processing the received ultrasonic guided waves based on short-time Fourier transform, calculating the energy spectrum of the ultrasonic guided waves in the time-frequency domain, and extracting the frequency of the resonance peak of the ultrasonic guided waves; step 6: judging the damage of the structure to be tested by comparing the frequency of the resonance peak with the value of the zero group velocity guided wave frequency of the structure to be tested in different states.

[0007] In some embodiments, the preparation process of the piezoelectric sensing coating in step 1 is: by dissolving PVDF-TrFE powder in dimethylformamide DMF and acetone solvent with a percentage concentration of 5%, and then stirring with a magnetic stirrer for at least 10 hours to mix the powder and the solvent evenly, and then spraying the mixed solution on the surface of the structure to be tested with a spray gun to form a coating, placing the structure to be tested in an oven at 133-135°C for annealing for 1-2 hours, and then brushing a conductive electrode pair on the surface of the coating by a mask method, and the structure to be tested itself serves as the negative electrode, and then performing corona polarization treatment at a voltage of 20kV to polarize the coating covered by the electrode pair along the thickness direction to form the piezoelectric sensing coating.

[0008] In some embodiments, in step 1, the piezoelectric sensing coating is prepared in both the healthy area and the damaged area of ​​the structure to be measured, and the prepared piezoelectric sensing coating forms several in-situ sensor pairs, one in-situ sensor in each pair of in-situ sensors is an excitation sensor, and the other is a receiving sensor, and the excitation sensor and the receiving sensor are spaced a certain distance apart.

[0009] In some embodiments, in step 3, the frequency of the excitation signal is the frequency of the zero group velocity guided wave mode, and the excited ultrasonic guided waves include multiple modes.

[0010] In some embodiments, in step 3 and step 4, the excitation and reception of the ultrasonic guided wave can be achieved by a single sensor, and the single sensor is connected to the pulse ultrasonic signal source and the data acquisition card through a duplexer.

[0011] In some embodiments, in step 5, the zero group velocity guided wave frequency values ​​of the structure to be tested in a healthy state and a damaged state are obtained by a semi-analytical finite element method, and the dispersion curves of each mode of the ultrasonic guided wave are obtained by the semi-analytical finite element method to obtain the frequency values ​​of each zero group velocity guided wave mode.

[0012] In some embodiments, damage is set at different thickness positions, and the frequency value of the zero group velocity guided wave caused by damage at different thickness positions is obtained using a semi-analytical finite element method.

[0013] In some embodiments, the process of preparing the structure to be tested is: using a 0.2 mm thick epoxy film to bond two upper and lower aluminum plates with a thickness of 1 mm and a size of 300 mm×300 mm, and by placing a polytetrafluoroethylene film between an aluminum plate and the adhesive layer to form an unbonded surface, thereby introducing debonding damage.

[0014] The present invention also provides a computer-readable storage medium, on which is stored a program for implementing a damage monitoring method, and the program for implementing the damage monitoring method is executed by a processor to implement the steps of the damage monitoring method based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided wave as described in any of the above embodiments.

[0015] The present invention also provides a device, which includes a memory for storing an embedded software program; a processor for executing the embedded software program stored in the memory, and when the embedded program is executed, the steps of the damage monitoring method based on piezoelectric sensing coating in-situ sensor and zero group velocity guided wave described in any of the above embodiments are implemented.

[0016] The present invention provides a damage monitoring method, a readable storage medium and a device based on an in-situ sensor of a piezoelectric sensing coating and zero group velocity waveguide. For the first time, a PVDF-TrFE piezoelectric sensing coating is used as an in-situ sensor for in-situ excitation and reception of zero group velocity waveguide. The piezoelectric sensing coating has the advantages of being light, flexible and ultra-thin. Compared with the traditional laser ultrasonic technology, it has the advantages of higher reliability, simple manufacture and use, high signal-to-noise ratio, large-area deployment and real-time online sensing. A damage diagnosis method based on zero group velocity waveguide is adopted. The waveguide mode is only sensitive to the structural health status within a local range, and the problem of signal analysis difficulties caused by complex structural forms can be avoided, so that it can be applicable to various complex structures such as metal bonding structures and composite material structures. The method of using the resonance peak frequency of the zero group velocity waveguide signal for damage diagnosis can eliminate the uncertainty influence of signal measurement caused by various interference factors, improve the robustness of damage diagnosis, and is suitable for real-time online monitoring of complex structures.

[0017] Other features and beneficial effects of the present invention will be described in the following description, and some of the features and beneficial effects can be understood by implementing the present invention. The purpose and other beneficial effects of the present invention can be achieved and obtained by the structures specifically pointed out in the description, claims, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. The positional relationships described in the drawings in the following description are based on the directions in which the components are drawn in the diagrams, unless otherwise specified.

[0019] Figure 1 It is a flow chart of a damage monitoring method based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided waves provided by an embodiment of the present invention;

[0020] Figure 2 It is a schematic diagram of the arrangement of a structure to be tested (bonding structure) and a piezoelectric sensing coating provided in one embodiment of the present invention;

[0021] Figure 3 is a schematic diagram of a structure to be tested with debonding damage provided by an embodiment of the present invention;

[0022] Figure 4 It is a schematic diagram of the preparation process of the PVDF-TrFE piezoelectric sensing coating provided by one embodiment of the present invention;

[0023] Figure 5 is a schematic diagram of signals obtained in a healthy area provided by an embodiment of the present invention;

[0024] Figure 6 This is a schematic diagram of signals obtained in a 20 mm debonding damage area provided by an embodiment of the present invention;

[0025] Figure 7 This is a schematic diagram of signals obtained in a 40 mm debonding damage area provided by an embodiment of the present invention;

[0026] Figure 8 This is a schematic diagram of a time-frequency spectrum obtained by short-time Fourier transform of a signal acquired in a healthy area provided by an embodiment of the present invention;

[0027] Fig. 9 This is a schematic diagram of a time-frequency spectrum obtained by short-time Fourier transform of a signal acquired in a 20 mm debonding damage area provided by an embodiment of the present invention;

[0028] Fig.10 This is a schematic diagram of a time-frequency spectrum obtained by short-time Fourier transform of a signal acquired in a 40 mm debonding damage area provided by an embodiment of the present invention;

[0029] Fig.11 It is a schematic diagram of spectrum comparison of signals obtained in a healthy area, a 20 mm debonding damage area, and a 40 mm debonding damage area provided by an embodiment of the present invention;

[0030] Fig.12 is a schematic diagram of a dispersion curve of ultrasonic guided waves in a healthy area of ​​a bonding structure provided by an embodiment of the present invention;

[0031] Fig.13 It is a schematic diagram of a dispersion curve of ultrasonic guided waves in a debonding region of a bonding structure provided by an embodiment of the present invention.

[0032] Markings in the figure:

[0033] 1-function generator; 2-data acquisition card; 3-20mm debonding damage area; 4-40mm debonding damage area; 5-electrode pair; 6-structure to be measured; 7-piezoelectric sensing coating; 8-computer. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; the technical features designed in different implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be understood that the terms "center", "lateral", "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In addition, the term "including" and any variation thereof all mean "at least including".

[0036] See also Figure 1 , Figure 2 and Figure 3 , Figure 1 1 is a flow chart of a damage monitoring method based on an in-situ sensor of a piezoelectric sensing coating 7 and a zero group velocity guided wave provided by an embodiment of the present invention. Figure 2 Schematic diagram of the arrangement of the structure to be tested 6 (bonding structure) and the piezoelectric sensing coating 7 provided in one embodiment of the present invention. Figure 3 Schematic diagram of a structure to be tested 6 with debonding damage provided by an embodiment of the present invention. In order to achieve at least one of the above advantages or other advantages, an embodiment of the present invention provides a damage monitoring method based on an in-situ sensor of a piezoelectric sensing coating 7 and a zero group velocity guided wave. As shown in the figure, the damage monitoring method includes the following steps:

[0037] Step 1: Prepare a piezoelectric sensing coating 7 on the structure to be measured 6.

[0038] Step 2: Connect one electrode in the piezoelectric sensing coating 7 to a pulsed ultrasonic signal source, and the other electrode to a data acquisition card 2 and a computer 8. One electrode in the piezoelectric sensing coating 7 is connected to a function generator 1, which has a pulsed ultrasonic signal source.

[0039] Step 3: The computer 8 controls the pulse ultrasonic signal source to send out an excitation signal, and transmits the excitation signal to the piezoelectric sensing coating 7 to excite the structure to be measured 6 to generate ultrasonic guided waves.

[0040] Step 4: The piezoelectric sensing coating 7 receives the ultrasonic guided wave and transmits it to the data acquisition card 2 and the computer 8 via the wireless network.

[0041] Step 5: Process the received ultrasonic guided waves based on short-time Fourier transform, calculate the energy spectrum of the ultrasonic guided waves in the time-frequency domain, and extract the frequency of the resonance peak of the ultrasonic guided waves.

[0042] Step 6: By comparing the frequency of the resonance peak with the value of the zero group velocity guided wave frequency of the structure 6 under different states, the damage condition of the structure 6 under test is determined.

[0043] In this embodiment, the structure to be tested 6 is a multi-layer bonding structure, such as Figure 3 As shown, the process of preparing a multilayer bonding structure (structure to be tested 6) is as follows: two upper and lower aluminum plates with a thickness of 1 mm and a size of 300 mm × 300 mm are bonded with an epoxy film with a thickness of 0.2 mm, and a polytetrafluoroethylene film is placed between an aluminum plate and the adhesive layer to form an unbonded surface, thereby introducing debonding damage. The sizes of the debonding damage are 20 mm × 20 mm and 40 mm × 40 mm, respectively. However, the present case is not limited to this, and the monitoring object of the damage monitoring method can also be other structures, such as damage monitoring of single-layer structures, damage monitoring of composite layered structures, etc.

[0044] like Figure 4 As shown, the preparation process of the piezoelectric sensing coating 7 in step 1 is: by dissolving PVDF-TrFE powder (72 / 28, Solvay, Belgium) in dimethylformamide DMF (N,N-Dimethylformamide) and acetone solvent, the percentage concentration is 5%, which refers to the concentration of the PVDF-TrFE powder after it is dissolved in the solvent. Then, stir with a magnetic stirrer for at least 10 hours to mix the powder and the solvent evenly. Then, use a spray gun to spray the mixed solution on the surface of the structure to be tested 6 to form a coating (thickness is about 80μm). Then place the structure to be tested 6 in an oven at 133-135°C for 1-2 hours of annealing to improve the crystallinity of the coating. Then, a long conductive electrode pair 5 (the length of the electrode pair 5 can be 10 mm, the width is 2 mm, and the spacing is 6 mm) is brushed on the coating surface by a mask method, and the structure to be measured 6 itself serves as the negative electrode. Then, through a corona polarization treatment with a voltage of 20 kV, the coating covered by the electrode pair 5 is polarized along the thickness direction to form a piezoelectric sensing coating 7, so that the piezoelectric sensing coating 7 has piezoelectric properties and has the ability to in-situ sense ultrasonic guided waves.

[0045] The effective piezoelectric coefficient of the piezoelectric sensing coating 7 is measured by scanning with a laser vibrometer. An AC voltage with a frequency of 1 kHz and a peak value of 20 Vpp is applied to the electrode pair 5. The areas with electrodes and without electrodes are scanned. The effective piezoelectric coefficient D33 value of the prepared piezoelectric sensing coating 7 can be 18 pm / V.

[0046] The sensors of the piezoelectric sensing coating 7 can be arranged on the surface of the structure in a large area. In order to excite and receive the zero-group-velocity guided wave, the sensors of the piezoelectric sensing coating 7 are prepared in the healthy area and the damaged area of ​​the structure 6 to be measured. That is, the prepared piezoelectric sensing coating 7 forms several in-situ sensor pairs ( Figure 2 There are 3 pairs of in-situ sensors in total), one in-situ sensor in each pair is an excitation sensor, and the other is a receiving sensor. The excitation sensor and the receiving sensor are separated by a certain distance, which can be within a wavelength. The wavelength refers to the wavelength of the zero-group-velocity guided wave for damage detection. Normally, the interval range can be 2 mm to 2 cm. The subsequent excitation and reception of ultrasonic guided waves are respectively responsible for the excitation sensor and the receiving sensor. However, the present case is not limited to this. In steps 3 and 4, the excitation and reception of ultrasonic guided waves can also be achieved by a single sensor, which is connected to the pulse ultrasonic signal source and the data acquisition card 2 through a duplexer.

[0047] In step 3, a computer 8 control system can be used to generate a 10-cycle Hanning window modulated sine wave signal with a center frequency of 3 MHz, the signal amplitude is amplified to 200 Vpp by a power amplifier, and the signal is input to the piezoelectric sensing coating 7 to excite the ultrasonic guided waves in the structure to be tested 6. The excited ultrasonic guided waves include multiple modes, and the energy of the remaining modes except the zero group velocity guided wave mode propagates and disperses in the specimen, while the zero group velocity guided wave mode is maintained in the local area around the sensor due to its characteristic of zero energy velocity, causing local resonance.

[0048] In step 4, the ultrasonic guided wave signal (the signal contains ultrasonic guided waves) is collected by the receiving sensor and input into the data acquisition card 2 and the computer 8. The received ultrasonic guided wave signal is averaged 512 times to obtain an ultrasonic guided wave signal with a high signal-to-noise ratio, such as Figure 5 The ultrasonic guided wave signal obtained in the healthy area is shown. Figure 6 and Figure 7 These are the ultrasonic guided wave signals obtained in the 20mm damage area and the 40mm damage area respectively.

[0049] In step 5, the received ultrasonic guided wave signal is processed by short-time Fourier transform to calculate the energy spectrum of the ultrasonic guided wave signal in the time-frequency domain. The energy spectrum is as follows: Figure 8 , Fig. 9 , Fig.10 Select a suitable time window and extract the frequency of the resonance peak of the ultrasonic guided wave signal within the time window. The frequency of the resonance peak is shown in Fig.11 shown.

[0050] In step 5, the zero group velocity guided wave frequency values ​​of the structure to be tested 6 in the healthy state and the damaged state are obtained by the semi-analytical finite element method. The dispersion curves of each mode of the ultrasonic guided wave signal are obtained by the semi-analytical finite element method, and then the frequency values ​​of each zero group velocity guided wave mode are obtained. By setting damage at different thickness positions, the frequency values ​​of the zero group velocity guided waves caused by damage at different thickness positions are obtained by the semi-analytical finite element method. For example, in the healthy area of ​​the multilayer adhesive structure (structure to be tested 6) prepared by the above method, there are three zero group velocity guided wave modes with frequencies of 2.57 MHz, 2.78 MHz and 3.2 MHz, respectively, as shown in FIG. Fig.12 In the debonding damage area, there is only one zero group velocity guided wave mode with a frequency of 2.89 MHz, as shown in Fig.13 shown.

[0051] Continue to step 6, by comparing the frequency of the resonance peak of the measured signal with the theoretical value of the zero group velocity guided wave frequency under different structural states, the health status and damage of the structure can be judged, thereby realizing long-term real-time online monitoring of the health status of the structure. By comparison, it can be seen that Figure 8 The resonance peak frequencies shown match the theoretically calculated values ​​of the healthy area (2.57 MHz, 2.78 MHz, and 3.2 MHz), which indicates that no damage has occurred in the vicinity of the sensor. Fig. 9 The resonance peak shown is not obvious, which indicates that there is debonding damage close to the wavelength of the zero group velocity waveguide in the vicinity of the sensor. This is because when the damage size is comparable to the wavelength of the zero group velocity waveguide, the damage causes modal conversion, causing the energy of the zero group velocity waveguide to be transferred to other waveguide modes and thus spread out, resulting in the rapid attenuation of the zero group velocity waveguide energy and the inability to form an obvious resonance peak. Fig.10 The resonance peak frequency shown matches the theoretical value of the zero group velocity waveguide frequency within the debonding damage (2.89 MHz), and it is determined that there is a debonding damage with a size larger than the zero group velocity waveguide wavelength near the sensor. This is because when the debonding damage size is larger than the zero group velocity waveguide wavelength, a new zero group velocity waveguide mode is formed in the damage area, and the signal resonance peak frequency of this mode is related to the thickness parameter of the damage.

[0052] That is to say, the existence of damage will lead to significant changes in the characteristics of zero group velocity waveguide. When the damage size is comparable to the wavelength of the zero group velocity waveguide, the damage causes modal conversion, which transfers the energy of the zero group velocity waveguide to other waveguide modes and spreads them out, resulting in rapid attenuation of the zero group velocity waveguide energy. When the damage size is larger than the wavelength of the zero group velocity waveguide, a new zero group velocity waveguide mode can be formed in the damage area, which means that the signal resonance peak frequency of this mode is related to the thickness parameter of the damage.

[0053] The present invention also provides a computer-readable storage medium, on which a program for implementing a damage monitoring method is stored. The program for implementing the damage monitoring method is executed by a processor to implement the steps of the damage monitoring method based on an in-situ sensor of a piezoelectric sensing coating 7 and zero group velocity guided waves as described in any of the above embodiments.

[0054] The present invention also provides a device, which includes a memory for storing an embedded software program; a processor for executing the embedded software program stored in the memory, and when the embedded program is executed, the steps of the damage monitoring method based on the piezoelectric sensing coating 7 in-situ sensor and zero group velocity guided wave described in any of the above embodiments are implemented.

[0055] In summary, the present invention provides a damage monitoring method, a readable storage medium and a device based on an in-situ sensor of a piezoelectric sensing coating 7 and zero group velocity waveguide. For the first time, a PVDF-TrFE piezoelectric sensing coating 7 is used as an in-situ sensor for in-situ excitation and reception of zero group velocity waveguide. This piezoelectric sensing coating 7 has the advantages of being lightweight, flexible and ultra-thin. Compared with traditional laser ultrasonic technology, it has the advantages of higher reliability, easy manufacture and use, high signal-to-noise ratio, large-area deployment and real-time online sensing. A damage diagnosis method based on zero group velocity waveguide is adopted. The waveguide mode is only sensitive to the structural health status within a local range, and can avoid the problem of signal analysis difficulties caused by complex structural forms, so that it can be applicable to various complex structures such as metal bonding structures and composite material structures. The method of damage diagnosis using the resonant peak frequency of the zero group velocity waveguide signal can eliminate the uncertainty of signal measurement caused by various interference factors, improve the robustness of damage diagnosis, and is suitable for real-time online monitoring of complex structures.

[0056] In addition, those skilled in the art should understand that, although there are many problems in the prior art, each embodiment or technical solution of the present invention can be improved in only one or several aspects, without having to solve all the technical problems listed in the prior art or background technology at the same time. Those skilled in the art should understand that the content not mentioned in a claim should not be used as a limitation on the claim.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A damage monitoring method based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided waves, characterized in that: The damage monitoring method comprises the following steps: Step 1: Prepare a piezoelectric sensing coating on the structure to be tested; Step 2: connecting one electrode in the piezoelectric sensing coating to a pulsed ultrasonic signal source, and connecting the other electrode to a data acquisition card and a computer; Step 3: The computer controls the pulsed ultrasonic signal source to send out an excitation signal, and transmits the excitation signal to the piezoelectric sensing coating to excite the structure to be tested to generate ultrasonic guided waves; Step 4: The piezoelectric sensing coating receives the ultrasonic guided wave and transmits it to the data acquisition card and the computer through a wireless network; Step 5: Processing the received ultrasonic guided wave based on short-time Fourier transform, calculating the energy spectrum of the ultrasonic guided wave in the time-frequency domain, and extracting the frequency of the resonance peak of the ultrasonic guided wave; Step 6: Determine the damage of the structure to be tested by comparing the frequency of the resonance peak with the value of the zero group velocity guided wave frequency of the structure to be tested in different states; Wherein, the preparation process of the piezoelectric sensing coating in step 1 is: dissolving PVDF-TrFE powder in dimethylformamide DMF and acetone solvent with a percentage concentration of 5%, and then stirring with a magnetic stirrer for at least 10 hours to mix the powder and the solvent evenly, and then spraying the mixed solution on the surface of the structure to be tested with a spray gun to form a coating, placing the structure to be tested in an oven at 133-135°C for 1-2 hours of annealing, and then brushing a conductive electrode pair on the surface of the coating by a mask method, the structure to be tested itself as a negative electrode, and then through a corona polarization treatment with a voltage of 20kV, the coating covered by the electrode pair is polarized in the thickness direction to form the piezoelectric sensing coating; In step 1, the piezoelectric sensing coating is prepared in both the healthy area and the damaged area of ​​the structure to be measured, and the prepared piezoelectric sensing coating forms several in-situ sensor pairs, one in-situ sensor in each pair of in-situ sensors is an excitation sensor, and the other is a receiving sensor, and the excitation sensor and the receiving sensor are spaced a certain distance apart; The process of preparing the structure to be tested is as follows: two upper and lower aluminum plates with a thickness of 1 mm and a size of 300 mm×300 mm are bonded with an epoxy film with a thickness of 0.2 mm, and a polytetrafluoroethylene film is placed between an aluminum plate and the adhesive layer to form an unbonded surface, thereby introducing debonding damage.

2. The damage monitoring method based on piezoelectric sensing coating in-situ sensor and zero group velocity guided wave according to claim 1 is characterized in that: In step 3, the frequency of the excitation signal is the frequency of the zero group velocity guided wave mode, and the excited ultrasonic guided waves include multiple modes.

3. The damage monitoring method based on piezoelectric sensing coating in-situ sensor and zero group velocity guided wave according to claim 1 is characterized in that: In step 3 and step 4, the excitation and reception of the ultrasonic guided wave can be realized by a single sensor, and the single sensor is connected to the pulse ultrasonic signal source and the data acquisition card through a duplexer.

4. The damage monitoring method based on piezoelectric sensing coating in-situ sensor and zero group velocity guided wave according to claim 1 is characterized in that: In step 5, the zero group velocity guided wave frequency values ​​of the structure to be tested in a healthy state and a damaged state are obtained by a semi-analytical finite element method, and the dispersion curves of each mode of the ultrasonic guided wave are obtained by the semi-analytical finite element method, thereby obtaining the frequency values ​​of each zero group velocity guided wave mode.

5. The damage monitoring method based on piezoelectric sensing coating in-situ sensor and zero group velocity guided wave according to claim 4 is characterized in that: By setting damage at different thickness positions, the semi-analytical finite element method is used to obtain the frequency values ​​of zero group velocity guided waves caused by damage at different thickness positions.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a program for implementing the damage monitoring method, and the program for implementing the damage monitoring method is executed by a processor to implement the steps of the damage monitoring method based on a piezoelectric sensing coating in-situ sensor and zero group velocity guided wave as described in any one of claims 1-5.

7. A device, characterized in that: The device comprises: A memory for storing embedded software programs; A processor is used to execute the embedded software program stored in the memory, and when the embedded software program is executed, the steps of the damage monitoring method based on the piezoelectric sensing coating in-situ sensor and zero group velocity guided wave as described in any one of claims 1-5 are implemented.

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