An online guided wave monitoring method and device for lightning strike events of a composite material structure

Abstract

The application discloses a lightning stroke event online guided wave monitoring method and device for a composite material structure, and comprises the following steps: arranging a plurality of piezoelectric sheets in a composite material structure to be monitored to form a sparse piezoelectric array; when the outer surface of the composite material structure to be monitored is struck by lightning, lightning impact force guided wave response mechanical quantities are excited, and the generated mechanical quantities are conducted to the piezoelectric sheets; the lightning impact force guided wave response mechanical quantities are converted into lightning impact force guided wave response signals; the lightning impact force guided wave response signals are transmitted to a data acquisition module through an online sensing mode; the lightning impact force guided wave response signals are subjected to direct current component removal and filtering pretreatment; and through a lightning impact force guided wave response signal imaging monitoring mode of the sparse piezoelectric array, lightning attachment point impact force passive imaging results are constructed. The lightning stroke event online guided wave monitoring method and device can not only improve the quality of lightning piezoelectric guided wave response signals, but also can perform high-precision positioning and imaging on lightning attachment points.

Description

Technical Field

[0001] The present invention relates to the technical field of online sensing of lightning guided wave response signals, and in particular to an online guided wave monitoring method and device for lightning strike events on composite material structures. Background Art

[0002] Composite materials are widely used in modern advanced aircraft. However, due to their low electrical conductivity, composite materials are more susceptible to severe structural damage when struck by lightning, thus limiting their application in aircraft. To ensure the safety of modern composite aircraft in the event of lightning strikes, the need for online monitoring of lightning strikes on composite aviation structures is becoming increasingly urgent. However, due to the short duration and high energy of lightning strikes, coupled with the complex and harsh strong electromagnetic field environment, effective technical methods for real-time online monitoring of lightning strikes remain lacking.

[0003] In the field of lightning strike monitoring for composite materials, researchers have been working to achieve online monitoring of key parameters related to the direct effects of a lightning strike, such as the location of the strike (i.e., the lightning attachment point). However, the techniques used often require complex, specialized equipment or are essentially in-situ monitoring methods. These methods are generally limited to basic laboratory observations and are not suitable for online monitoring of aircraft lightning strikes where the actual attachment point is unknown.

[0004] The piezoelectric guided wave monitoring method has the advantages of long signal propagation distance and is very sensitive to surface and internal damage of structures. It has been widely used in the monitoring and imaging research of surface and internal damage of large plate structures. In addition, the related research on using sparse piezoelectric guided wave arrays to monitor impact signals on composite structures is relatively mature. The piezoelectric guided wave monitoring method provides a new and effective way for the online monitoring research of lightning damage characteristic signals during lightning damage of carbon fiber composite materials and the positioning of lightning attachment points.

[0005] The implementation of online monitoring of composite materials using lightning-piezoelectric guided waves needs to face two problems: First, the passive piezoelectric sensing part of the composite materials lightning-piezoelectric guided wave online monitoring system. When performing online sensing of the lightning guided wave response signal, the harsh lightning environment seriously affects the quality of the lightning guided wave response signal, and even causes sensor failure and damage; Second, although the waveform and loading method of the mechanical load of the lightning impact force effect of the composite material are basically the same as the impact load in the external impact event, the lightning guided wave response signal is more complex, with more serious dispersion and easy aliasing of wave packets, which poses a severe challenge to the reliability and accuracy of lightning guided wave imaging monitoring of aviation composite materials structures. Summary of the Invention

[0006] The application aims to provide a lightning strike event online guided wave monitoring method and device for composite material structures, which solves the problem of damage of piezoelectric sheets integrated in composite material structures in a severe lightning strike environment, and solves the problems of too large crosstalk amplitude and too low signal-to-noise ratio of lightning strike piezoelectric guided wave response signals caused by indirect effects of lightning strikes; on the other hand, the lightning strike impact force guided wave response signal imaging monitoring mode of the sparse piezoelectric array can cope with more serious problems such as frequency dispersion and wave packet aliasing of lightning strike piezoelectric guided wave response signals, and can realize accurate positioning and imaging of lightning strike attachment points.

[0007] To achieve the above-mentioned purpose, the application provides a lightning strike event online guided wave monitoring method for composite material structures, which comprises the following steps:

[0008] S1, a plurality of piezoelectric sheets are bonded or arranged inside the inner surface of a composite material structure to be monitored to form a sparse piezoelectric array;

[0009] S2, the outer surface of the composite material structure to be monitored is subjected to lightning strikes, and lightning strike impact force guided wave response mechanical quantities are excited;

[0010] S3, the lightning strike impact force guided wave response mechanical quantities are conducted in the composite material structure to be monitored to each piezoelectric sheet;

[0011] S4, each piezoelectric sheet converts the lightning strike impact force guided wave response mechanical quantities into lightning strike impact force guided wave response signals;

[0012] S5, the lightning strike impact force guided wave response signals of the sparse piezoelectric array are transmitted to a data acquisition module through an online sensing mode;

[0013] S6, the lightning strike impact force guided wave response signals of the sparse piezoelectric array collected in the data acquisition module are acquired, and direct current component removal and filtering pretreatment are performed;

[0014] S7, after the pretreatment in step S6 is completed, the lightning strike impact force guided wave response signal imaging monitoring mode of the sparse piezoelectric array is used to construct a lightning strike attachment point impact force passive imaging result.

[0015] Further, in the step S1, the cathode of the piezoelectric sheet is short-circuited with the short-circuit point of the composite material to be monitored.

[0016] Further, in the step S5, the online sensing mode adopts one or more of a shielding cable direct transmission mode and an optical-electric conversion indirect transmission mode.

[0017] Further, in the step S7, the lightning strike impact force guided wave response signal imaging monitoring mode of the sparse piezoelectric array adopts a virtual time reversal imaging processing or a delay and stack imaging processing.

[0018] The online guided wave monitoring device for lightning strike event of composite material structure comprises piezoelectric sheets arranged on the inner surface of the composite material structure to be monitored, a data acquisition module arranged on the outer side of the composite material structure to be monitored, a pretreatment module connected to the output end of the data acquisition module, and an imaging processing module connected to the output end of the pretreatment module.

[0019] Further, the cathode of the piezoelectric sheet is electrically connected to a shorting point on the composite material structure to be monitored, and the shorting point is arranged on the inner surface of the composite material structure to be monitored near the position of the piezoelectric sheet.

[0020] Further, the connection mode between the cathode of the piezoelectric sheet and the shorting point adopts a conductor insertion mode, a conductive glue bonding mode or a wire connection mode.

[0021] Therefore, the online guided wave monitoring method and device for lightning strike event of composite material structure adopt the above method and device, which solve the problem of damage of the piezoelectric sheet integrated in the composite material structure under a severe lightning strike environment, and solve the signal quality problems of the lightning strike piezoelectric guided wave response signal, such as too large crosstalk amplitude and too low signal-to-noise ratio caused by indirect effects of lightning strike; on the other hand, the lightning strike impact force guided wave response signal imaging monitoring mode using the sparse piezoelectric array can cope with more serious problems of the lightning strike piezoelectric guided wave response signal, such as frequency dispersion and wave packet aliasing, and realize accurate positioning and imaging of the lightning strike attachment point.

[0022] The technical solutions of the present application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a flowchart of the online guided wave monitoring method for lightning strike event of composite material structure of the present application;

[0024] Figure 2 is a structural principle diagram of the online guided wave monitoring device for lightning strike event of composite material structure of the present application;

[0025] Figure 3 is a structural principle diagram of the online guided wave monitoring device for lightning strike event of composite material structure of the present application;

[0026] Figure 4 is a coordinate position diagram of the piezoelectric sheets P1-P4 and lightning strike impact sources e1-e2 in the embodiment one of the present application;

[0027] Figure 5 is a time domain waveform diagram of the piezoelectric sheets P1-P4 in the embodiment one of the present application;

[0028] Figure 6This is the common imaging result of the lightning impulse sources e1 to e2 in the first embodiment of the present invention;

[0029] Figure 7 This is the high-contrast imaging result of the VTR-based lightning impulse sources e1-e2 in the first embodiment of the present invention.

[0030] Reference numerals

[0031] 1. Composite material to be monitored; 2. Piezoelectric sheet; 3. Lightning attachment point; 4. Piezoelectric sheet anode; 5. Piezoelectric sheet cathode; 6. Short-circuit point; 7. Data acquisition module; 8. Preprocessing module; 9. Imaging processing module; 10. Lightning impact force guided wave response signal; 11. Optical transmitting module; 12. Optical fiber; 13. Optical receiving module. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0033] like Figure 1 As shown, an online guided wave monitoring method for lightning strike events on composite material structures includes the following steps:

[0034] S1, bonding or arranging a plurality of piezoelectric sheets 2 on the inner surface of the composite material 1 structure to be monitored to form a sparse piezoelectric array;

[0035] S2, the outer surface of the composite material structure 1 to be monitored is struck by lightning, which stimulates the mechanical quantity of the guided wave response of the lightning impact force;

[0036] S3, the mechanical quantity of the guided wave response of the lightning impulse force is transmitted to each piezoelectric piece 2 in the structure of the composite material 1 to be monitored;

[0037] S4, each piezoelectric piece 2 converts the mechanical quantity of the lightning impulse force guided wave response into a lightning impulse force guided wave response signal 10;

[0038] S5, transmitting the lightning impulse force guided wave response signal 10 of the sparse piezoelectric array to the data acquisition module 7 through an online sensing method;

[0039] S6, obtaining the lightning impulse force guided wave response signal 10 of the sparse piezoelectric array collected in the data acquisition module 7, and performing DC component removal and filtering preprocessing;

[0040] S7. After completing the pre-processing work of step S6, a passive imaging result of the lightning strike attachment point impact force is constructed by imaging and monitoring the lightning strike impact force guided wave response signal of the sparse piezoelectric array.

[0041] Specifically, in step S1, the piezoelectric sheet cathode 5 is short-circuited with the short-circuiting point 6 of the composite material 1 to be monitored.

[0042] Specifically, in step S5, the on-line sensing mode adopts one or more of the direct transmission mode of shielded cable and the indirect transmission mode of photoelectric conversion.

[0043] Specifically, in step S7, the lightning strike impact force guided wave response signal imaging monitoring mode of the sparse piezoelectric array adopts virtual time reversal imaging processing or delay and superposition imaging processing.

[0044] As shown in Figure 2 , an on-line guided wave monitoring device for lightning strike events of a composite material structure includes a piezoelectric sheet 2 arranged on the inner surface of the composite material 1 structure to be monitored, a data acquisition module 7 arranged on the outer side of the composite material 1 structure to be monitored, the output end of the data acquisition module 7 is connected with a preprocessing module 8, and the output end of the preprocessing module 8 is connected with an imaging processing module 9.

[0045] Specifically, a glue layer is arranged below the piezoelectric sheet 2 and connected with the inner surface of the composite material 1 structure to be monitored.

[0046] Specifically, the piezoelectric sheet cathode 5 is electrically connected with the short-circuiting point 6 on the composite material 1 structure to be monitored, and the short-circuiting point 6 is arranged on the inner surface of the composite material 1 structure to be monitored near the position of the piezoelectric sheet 2.

[0047] Specifically, the connection mode of the piezoelectric sheet cathode 5 and the short-circuiting point 6 adopts a conductor insertion mode, a conductive glue bonding mode or a wire connection mode.

[0048] The technical solutions of the present application will be described below through a specific embodiment.

[0049] Example 1

[0050] In this embodiment, an on-line guided wave monitoring device for lightning strike events of a composite material structure adopts an optical conversion indirect transmission mode, as shown in Figure 3 , the on-line guided wave monitoring device includes a piezoelectric sheet 2 arranged on the inner surface of the composite material 1 structure to be monitored, a data acquisition module 7 arranged on the outer side of the composite material 1 structure to be monitored, the output end of the data acquisition module 7 is connected with a preprocessing module 8, and the output end of the preprocessing module 8 is connected with an imaging processing module 9. A glue layer is arranged below the piezoelectric sheet 2 and connected with the inner surface of the composite material 1 structure to be monitored. The cathode of the piezoelectric sheet 2 is electrically connected with the short-circuiting point 6 on the composite material 1 structure to be monitored through a wire. The piezoelectric sheet anode 4 is connected with a light emitting module 11, which can convert the lightning strike impact force guided wave response signal 10 into an optical signal, which is transmitted to a light receiving module 13 through an optical fiber 12. The specific steps are as follows:

[0051] (1) A sparse piezoelectric array is arranged on the surface of the carbon fiber reinforced composite material, and each piezoelectric sheet 2 converts the mechanical quantity of the lightning strike guided wave response into a lightning strike piezoelectric guided wave response signal:

[0052] The piezoelectric sheet 2 is arranged on the inner surface of the carbon fiber reinforced composite material by gluing, the inner surface of the carbon fiber reinforced composite material in the peripheral area of the piezoelectric sheet is covered with a 0.2mm-0.4mm thick copper foil, a short-circuit point 6 is selected at a distance of 80mm from the piezoelectric sheet arrangement position, the cathode of the piezoelectric sheet 2 is connected to the light emitting module 11 through an electromagnetic shielding connector and a wire, and the electromagnetic shielding layer of the wire is connected to the short-circuit point 6 of the carbon fiber reinforced composite material through the 0.2mm thick copper foil.

[0053] (2) The front surface of the composite material structure to be monitored is subjected to a lightning signal

[0054] (3) The piezoelectric sheet 2 converts the mechanical quantity of the lightning strike guided wave response into a lightning strike piezoelectric guided wave response signal, and transmits it to the light emitting module 11 through a wire for short distance transmission;

[0055] (4) The light emitting module 11 converts the lightning strike piezoelectric guided wave response signal into a lightning strike piezoelectric guided wave response optical signal, and transmits the lightning strike piezoelectric guided wave response optical signal through the optical fiber 12 for long distance transmission;

[0056] The lightning strike piezoelectric guided wave response optical signal is transmitted through a 62.5 / 125μm multimode optical fiber for long distance transmission, at the same time, an ST connector is used for the optical fiber connector to ensure the fastening of the connection, and a metal aluminum material is used for the shell of the optical fiber connector to enhance the anti-electromagnetic interference capability.

[0057] (5) The lightning strike piezoelectric guided wave response optical signal is received by the light receiving module 13, which is converted into a lightning strike impact force guided wave response signal 10 and output to the data acquisition module 7.

[0058] (6) The lightning strike impact force guided wave response signal 10 in the data acquisition module 7 is processed by the preprocessing module 8 and transmitted to the imaging processing module 9 for imaging, and the imaging method adopts virtual time reversal imaging processing.

[0059] In order to facilitate verification, the laying direction of the test piece in this embodiment is P[-45 / 0 / 45 / 90] 4s , and the size is selected as 600mmx600mmx2mm. The center of the aviation composite material structure is set as the coordinate origin O, four piezoelectric sheets P1-P4 are used for lightning impact online monitoring array, the lightning impact source is e1 and e2, and a rectangular coordinate system is established as shown in Figure 4 .

[0060] Table 1 is a coordinate table of piezoelectric sheets P1-P4 and lightning impact sources e1-e2

[0061]

[0062] Using the lightning impact source e1 (100, 50) in this embodiment as an example, the time-domain waveform diagram of the piezoelectric patches P1-P2 is obtained as shown in the figure, from which it can be seen that: Figure 5

[0063] (1) The P1 piezoelectric patch can clearly see two wave packets showing the propagation characteristics of the first anti-symmetry mode (A0 mode) of Lamb wave in the frequency range of 0-30 kHz and the time range of 400-1000 μs. According to the time domain position, the two wave packets are obviously the direct wave packet and the boundary reflected wave packet of the A0 mode.

[0064] (2) Similarly, the direct wave packet and the boundary reflected wave packet of the A0 mode can be seen in the P2, P3, and P4 piezoelectric patches in the frequency range of 0-30 kHz. Due to the different distances of the piezoelectric patches from the lightning attachment point, the positions of the direct wave packets are different.

[0065] (3) According to the time-frequency analysis of the external impact response signals of the P1-P4 piezoelectric patches, a three-peak sinusoidal modulation signal with a center frequency of 15 kHz is selected to participate in the virtual time reversal (VTR) imaging signal processing process.

[0066] In this embodiment, the lightning impact sources e1-e2 are subjected to ordinary imaging processing, and the imaging results are obtained as shown in the figure, wherein "X" is the actual impact source position, and "O" is the position of the piezoelectric patch. From the figure, it can be seen that the lightning impact sources e1-e2 are far away from the center region of the composite material structure and the monitoring array, and their signals are relatively complex, and there are many false images. Through the VTR imaging method, the imaging results are obtained as shown in the figure, and it can be seen that the VTR can realize relatively accurate lightning impact positioning imaging. Figure 6 Figure 7

[0067] In order to further investigate the lightning positioning imaging results based on the carbon fiber plate and the piezoelectric array, the threshold value is set to 95% of the maximum energy value, the pixel points with pixel values higher than the set threshold value are extracted, and the connected pixel points are classified as the same lightning point. According to the Euclidean distance between the positioning monitoring results and the lightning coordinates, the corresponding error value can be obtained, and the corresponding coordinates and error values of the e1 and e2 lightning positioning imaging results are shown in Table 2.

[0068] Table 2 Coordinates and error values of e1 and e2 lightning impact sources based on virtual time reversal method

[0069]

[0070] ​​​From the experimental results, the lightning impact force guided wave response signal high reliable online sensing technology of the application, combined with the lightning guided wave imaging monitoring method based on virtual time reversal, can use four piezoelectric sheets to form a monitoring array of 400mm*400mm, and can perform high reliable lightning event online monitoring on an aviation CFRP structure of 600mm*600mm, and can perform accurate lightning impact positioning imaging on a lightning attachment point far away from the plate structure and the center area of the monitoring array, and the positioning error is less than or equal to 15mm.

[0071] Therefore, the online guided wave monitoring method and device for lightning event of the composite material structure adopt the above-mentioned method, which solves the problem of damage of the piezoelectric sheet integrated in the composite material structure in a harsh lightning environment, solves the problem of too large crosstalk amplitude, too low signal-to-noise ratio, and inaccurate wave arrival time extraction of the lightning piezoelectric guided wave response signal caused by indirect effects of lightning, and directly affects the signal quality, and can also perform accurate lightning impact positioning imaging on the lightning attachment point.

[0072] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: the technical solutions of the present application can still be modified or replaced by equivalent, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. An online guided wave monitoring method for lightning strike events on composite materials, characterized by: The following steps are involved: S1. Adhere multiple piezoelectric sheets to the inner surface of the composite material structure to be monitored or arrange them inside to form a sparse piezoelectric array; S2, the outer surface of the composite material structure to be monitored is struck by lightning, which stimulates the mechanical quantity of the guided wave response of the lightning impact force; S3, the mechanical quantity of the guided wave response of the lightning impact force is transmitted to each piezoelectric piece in the composite material structure to be monitored; S4, each piezoelectric piece converts the mechanical quantity of the lightning impulse force guided wave response into a lightning impulse force guided wave response signal; S5, transmitting the guided wave response signal of the lightning impulse force of the sparse piezoelectric array to the data acquisition module through an online sensing method; S6. Acquire the guided wave response signal of the lightning impulse force of the sparse piezoelectric array collected in the data acquisition module, and perform DC component removal and filtering preprocessing; S7. After completing the pre-processing work of step S6, a passive imaging result of the lightning strike attachment point impact force is constructed by imaging and monitoring the lightning strike impact force guided wave response signal of the sparse piezoelectric array.

2. The online guided wave monitoring method for lightning strike events on composite materials according to claim 1, characterized in that: In the step S1, the cathode of the piezoelectric sheet is short-circuited with the short-circuit point of the composite material to be monitored.

3. The online guided wave monitoring method for lightning strike events on composite materials according to claim 1, characterized in that: In step S5, the online sensing method adopts one or more of a shielded cable direct transmission method and a photoelectric conversion indirect transmission method.

4. The online guided wave monitoring method for lightning strike events on composite materials according to claim 1, characterized in that: In step S7, the imaging monitoring method of the guided wave response signal of the lightning impulse force of the sparse piezoelectric array adopts virtual time reversal imaging processing or delayed superposition imaging processing.

5. The online guided wave monitoring method for lightning strike events on composite material structures according to any one of claims 1 to 4, characterized in that: The monitoring device includes a piezoelectric piece arranged on the inner surface of the composite material structure to be monitored and a data acquisition module arranged on the outside of the composite material structure to be monitored. The output end of the data acquisition module is connected to a preprocessing module, and the output end of the preprocessing module is connected to an imaging processing module.

6. The online guided wave monitoring method for lightning strike events on composite materials according to claim 5, characterized in that: The cathode of the piezoelectric sheet is electrically connected to a short-circuit point on the composite material structure to be monitored, and the short-circuit point is arranged on the inner surface of the composite material structure to be monitored near a position of the piezoelectric sheet.

7. The online guided wave monitoring method for lightning strikes on composite materials according to claim 6, characterized in that: The connection between the cathode of the piezoelectric sheet and the short-circuit point is achieved by conductor plugging, conductive adhesive bonding or wire connection.

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