Fiber reinforced structure damage positioning method based on piezoelectric effect

Abstract

The invention provides a fiber reinforced structure damage positioning method based on a piezoelectric effect, a fiber reinforced structure is widely applied in multiple fields but is easy to damage, an existing positioning method has defects, and the method comprises the steps of piezoelectric composite material preparation, sensor network construction, signal acquisition and processing, positioning based on a time reversal method and the like. During preparation, specific materials are mixed and stirred and then laid with the reinforced fibers, and the processes of curing molding, polarization, packaging and the like are performed; the sensing network is formed by arranging electrodes on the surface of the composite material; signal acquisition is carried out when the composite material deforms or is damaged under load; and the positioning is to re-excite the acquired signal after time reversal processing, and determine a damage point according to a focusing position. The method has the advantages of high-precision positioning, self-energized real-time monitoring, wide applicability, simple and practical structure and the like, can be applied to various fiber reinforced structures, can effectively solve the problems in the prior art, and has important significance for guaranteeing the safety and reliability of the fiber reinforced structures.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber-reinforced structure damage, and particularly to a method for locating fiber-reinforced structure damage based on the piezoelectric effect. Background Art

[0002] In the current era of rapid technological development, fiber-reinforced structures play an indispensable role in many key fields due to their unique performance advantages. In the aerospace field, there are extremely high requirements for the lightweight and high strength of aircraft. Fiber-reinforced structures can reduce weight while ensuring that the structure has sufficient strength and stiffness to withstand various complex stresses during flight, such as extreme temperature changes, strong airflow impacts, and high-load flight loads. In the automotive manufacturing industry, fiber-reinforced structures help improve the fuel efficiency of vehicles, while enhancing the durability and safety of the body, enabling it to better handle bumps, collisions, etc. during daily driving. The construction field also widely benefits from fiber-reinforced structures, which can enhance the seismic performance of buildings, improve the structural stability, and ensure that the buildings remain intact during natural disasters such as earthquakes and strong winds, protecting the lives of people. However, during actual use, these fiber-reinforced structures will inevitably be interfered by various external factors, resulting in damage. Harsh natural environments, such as high temperature, high humidity, and strong ultraviolet radiation, may gradually degrade the performance of fiber-reinforced materials; the action of mechanical external forces, such as the impact force during the takeoff and landing of aircraft, the huge energy transfer during vehicle collisions, and the vibration of building structures during earthquakes or heavy object impacts, may cause damage forms such as fiber breakage, matrix cracking, and delamination inside the fiber-reinforced structure. If these damages cannot be detected and accurately located in a timely manner, they will pose a serious threat to the safety and reliability of the structure. For example, in the aerospace field, if a small damage in the aircraft structure is not detected in time, it may rapidly expand due to stress concentration during flight, ultimately leading to catastrophic consequences; in the construction field, if structural damage cannot be located and repaired in time, the building may face the risk of collapse during subsequent use.

[0003] At present, in order to achieve the localization of damage in fiber-reinforced structures, various methods based on different principles have emerged. The method based on visual inspection is one of the most direct and simple ways. Technicians inspect the surface of the structure by visual observation or with the help of simple tools such as magnifying glasses to check for obvious signs of cracks, deformations, wear, etc. This method can quickly detect surface damage in some cases, but it is powerless for internal damage hidden in the structure, such as microscopic fractures inside the fibers, tiny cracks inside the matrix, and hidden delaminations between layers. Because these internal damages cannot directly present visible signs on the surface of the structure and are thus easily overlooked, which poses a potential safety hazard to the structure. Methods based on traditional sensors, such as strain gauges, accelerometers, etc., have also been applied to a certain extent in the damage detection of fiber-reinforced structures. Strain gauges infer the presence of damage by measuring the strain changes in the structure when it is stressed, and accelerometers judge the damage situation by detecting the changes in the vibration characteristics of the structure. However, these traditional sensors have many problems in practical applications. Their installation process is relatively complex, requiring precise position determination, surface treatment, and reliable fixing methods. A slight mistake may affect the measurement accuracy of the sensors. Moreover, these sensors are usually expensive. Especially when comprehensive monitoring of large or complex structures is required, a large number of sensors need to be arranged, which will undoubtedly significantly increase the cost. In addition, the durability and stability of traditional sensors also have certain limitations. Problems such as drift and failure may occur during long-term use, and regular maintenance and calibration are required, further increasing the use cost and workload.

[0004] In existing patents related to the localization of damage in fiber-reinforced structures based on the piezoelectric effect, although certain research results have been achieved, there are still some deficiencies. Some patents may be optimized only for specific types of fiber-reinforced structures at the beginning of the design, resulting in limited applicability.

[0005] The Chinese invention patent with the application number CN202410093333.7 discloses a thermosetting-thermoplastic core-shell nanofiber self-healing carbon fiber reinforced material, a composite material and a preparation method thereof. This method is only applicable to one or several specific fiber reinforced materials, such as only applicable to carbon fiber reinforced composites, while for other common fiber reinforced materials, such as glass fiber reinforced composites, basalt fiber reinforced composites, etc., it cannot be effectively applied. This makes it difficult for these patented technologies to play a role and meet diverse needs in actual engineering when faced with the coexistence of multiple different types of fiber reinforced materials. The lack of positioning accuracy is also an important problem faced by existing related patents. For fiber reinforced components with complex structures, especially those with curved surface structures, some existing damage positioning methods are also difficult to achieve effective detection. Fiber reinforced components with curved surface structures widely exist in engineering, such as the wings of airplanes and the body shells of cars. The shapes of these curved surface structures are irregular and the stress distributions are uneven, making damage positioning more difficult. When some traditional piezoelectric effect-based methods are applied to curved surface structures, signal attenuation may be serious and positioning errors may increase due to reasons such as poor fitting between the sensor and the curved surface and complex signal propagation characteristics on the curved surface, and the position and degree of damage cannot be accurately detected. Some piezoelectric effect-based technologies also have problems of high cost and large system complexity in actual applications.

[0006] The Chinese invention patent with the application number CN202210340128.7 discloses damage location and imaging of composites based on Lamb wave spectra. In order to achieve high detection accuracy and reliability, a large number of piezoelectric sensors are arranged on the structure, which not only increases the procurement cost of the sensors, but also makes the wiring and installation of the system extremely complex. A large number of sensors require a complex signal acquisition and processing system to support, which further increases the cost and complexity of the system. Moreover, too many sensors may interfere with each other, affecting the accuracy of the measurement results, and at the same time increasing the maintenance difficulty and workload of the system, reducing the overall reliability and practicality of the system.

[0007] In summary, although existing fiber reinforced structure damage location methods can meet some needs to a certain extent, there are still many problems and challenges. Therefore, the technical problem to be solved urgently at present is: how to develop a piezoelectric effect-based fiber reinforced structure damage location method with wide applicability, high precision, capable of dealing with complex structures and low cost. Summary of the Invention

[0008] The present invention is made to solve the above problems, and the purpose is to provide a piezoelectric effect-based fiber reinforced structure damage location method.

[0009] The present invention provides a method for locating damage in a fiber-reinforced structure based on the piezoelectric effect, which has the following characteristics, including: Step S1, preparing a piezoelectric composite material: at room temperature, adding polyvinylidene fluoride-trifluoroethylene copolymer and zinc oxide nanoparticles into a resin solution, adding a curing agent at the same time, stirring, performing a laminating process on the obtained mixture and reinforcing fibers, the number of laminating layers meeting the principle of symmetric laminating, curing and forming the obtained laminated structure by a curing and forming process to obtain a composite material, polarizing the composite material in a strong electric field, cutting it into a suitable shape according to actual application requirements after polarization, pasting electrodes at corresponding positions on both of its side surfaces, and wrapping an electromagnetic shielding layer around the electrode wiring, and finally encapsulating it with an insulating encapsulating material to obtain a piezoelectric composite material; Step S2, constructing a sensing network: arranging a plurality of electrodes on the surface of the piezoelectric composite material to form an electrode array sensing network; Step S3: signal acquisition and processing, when the piezoelectric composite material is deformed or damaged under a load, an electric signal is generated, and the change of the electric signals of each electrode is collected by a data acquisition system; and Step S4: locating based on the time reversal method, performing time reversal processing on the collected electric signals, and then re-exciting them into the piezoelectric composite material, and determining the damage position according to the position where the time reversal signal focuses in the piezoelectric composite material.

[0010] In the method for locating damage in a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may also have the following characteristics: wherein, by weight, the polyvinylidene fluoride-trifluoroethylene copolymer is 0.1 to 15 wt%, and the zinc oxide nanoparticles are 0.1 to 8 wt%.

[0011] In the method for locating damage in a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may also have the following characteristics: wherein, the resin solution includes at least one of epoxy resin, phenolic resin, unsaturated polyester and polyurethane.

[0012] In the method for locating damage in a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may also have the following characteristics: wherein, the stirring is carried out by a laboratory electric stirrer, the stirring speed is 600 to 1000 r / min, and the stirring time is 25 to 45 min.

[0013] In the method for locating damage in a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may also have the following characteristics: wherein, the reinforcing fiber is at least one of carbon fiber, glass fiber, basalt fiber and aramid fiber, and the weaving method of the reinforcing fiber is unidirectional fiber, plain fiber or twill fiber.

[0014] In the method for locating damage in a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may also have the following characteristics: wherein, the curing and forming process is a hot pressing process, a vacuum assisted resin transfer molding process or an autoclave process.

[0015] In the method for locating damage of a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may further have the following characteristics: among them, the voltage of the polarization strong electric field is 18 - 30 kV, and the polarization treatment time is 5 - 9 h.

[0016] In the method for locating damage of a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may further have the following characteristics: among them, the shape of the electrode is rectangular, the length of the electrode is 0.6 - 1.2 cm, the width is 0.6 - 1.2 cm, the shape of the insulating encapsulation material is rectangular, the length of the insulating encapsulation material is 0.6 - 2.5 cm, and the width is 0.6 - 2.5 cm.

[0017] In the method for locating damage of a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may further have the following characteristics: among them, the spacing between the electrodes is determined according to the size of the composite material and the required positioning accuracy, and the spacing between the electrodes is 2 - 10 cm.

[0018] In the method for locating damage of a fiber-reinforced structure based on the piezoelectric effect provided by the present invention, it may further have the following characteristics: among them, the calculation process of the time reversal processing is specifically as follows: let the electrical signal collected by the i-th electrode be S i (t), perform time reversal on it to obtain S i (-t), superimpose all the reversed signals and then excite them into the composite material, and the response signal at a certain point (x, y, z) in the composite material is where τ i is the time required for the signal to propagate from the i-th electrode to the point (x, y, z). When the response signal R(x, y, z, t) reaches the maximum value at a certain point, this point is the damage location.

[0019] Functions and effects of the invention

[0020] According to the method for locating damage of a fiber-reinforced structure based on the piezoelectric effect involved in the present invention, the present invention is based on an electrode array sensing network and the time reversal method, can accurately determine the damage location, overcome the problem of inaccurate positioning in the prior art, and achieve high-precision positioning; it does not require an external power supply, uses the self-power generation characteristics of the piezoelectric composite material to achieve real-time online monitoring, can continuously provide electrical energy for the monitoring system, and meets the requirements of sustainable development; it can be applied to various fiber-reinforced structures, has a simple structure, is easy to integrate into various composite material structures, has a relatively simple preparation process, low cost, and wide applicability. Brief description of the drawings

[0021] Figure 1 It is an example of the electrode paste position and encapsulation on the carbon fiber piezoelectric composite material in Embodiments 1 - 2 of the present invention. Detailed implementation manners

[0022] In the description of the present application, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a connection that allows mutual communication; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0023] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the following embodiments will specifically describe the fiber-reinforced structure damage location method based on the piezoelectric effect of the present invention in conjunction with the accompanying drawings.

[0024] Embodiment 1

[0025] In this embodiment, the fiber-reinforced structure damage location method based on the piezoelectric effect specifically includes the following steps:

[0026] Step S1, prepare a piezoelectric composite material.

[0027] S1-1, Mix epoxy resin of type E51 and curing agent T31 in a mass ratio of 100:28, and stir with a laboratory electric stirrer at a speed of 800 r / min for 35 min to obtain a mixed solution A;

[0028] S1-2, Add P(VDF-TrFE) with a mass fraction of 8 wt% and zinc oxide nanoparticles with a mass fraction of 5 wt% to the above mixed solution A, and continue to stir at a speed of 800 r / min for 30 min to obtain a mixed solution B.

[0029] S1-3, Lay up the mixed solution B with 10 layers of unidirectional carbon fiber fabric, and cure and form it by a hot pressing process. First, keep it at 0.25 MPa and 95 °C for 35 min, then raise the pressure to 1.3 MPa and the temperature to 125 °C, and keep it for 130 min. Finally, cool it with the furnace to obtain a cooled composite laminate.

[0030] S1-4, Polarize the cooled composite laminate in an electric field of 22 kV for 7 h, and then cut it into a square composite material of 120 mm × 120 mm.

[0031] Figure 1 It is an example of the electrode pasting position and encapsulation on the carbon fiber piezoelectric composite material in Embodiment 1-2 of the present invention.

[0032] S1-5, As Figure 1As shown, silver electrodes 20 are pasted on the upper and lower surfaces of the square composite material 10. The size of the electrodes 20 is 0.8 cm × 0.8 cm, and the distance between the electrodes 20 is 5 cm. Copper foil is wrapped around the wiring of the electrodes 20. The pasting pressure of the electrodes 20 is controlled at 0.2 MPa to ensure the cleanliness of the pasting surface. Finally, it is encapsulated with a 3 cm × 3 cm polyimide film 30 to obtain a piezoelectric composite material.

[0033] Step S2, arrange a plurality of electrodes on the surface of the piezoelectric composite material to form an electrode array sensing network and construct a sensing network.

[0034] Step S3, apply a slight impact on the surface of the piezoelectric composite material as a simulated damage, and use a data acquisition system to collect the change in the electrical signals of the electrode array.

[0035] Step S4, perform time reversal processing on the collected electrical signals and re-excite them into the composite material, and determine the damage location by calculating the focal point coordinates of the response signal.

[0036] Let the electrical signal collected by the i-th electrode be S i (t), perform time reversal on it to obtain S i (-t). After superimposing all the reversed signals, excite them into the composite material. The response signal at a certain point (x, y, z) in the piezoelectric composite material is where τ i is the time required for the signal to propagate from the i-th electrode to the point (x, y, z). When the response signal R(x, y, z, t) reaches the maximum value at a certain point, this point is the damage location.

[0037] Example Two

[0038] In this example, the method for locating damage in a fiber-reinforced structure based on the piezoelectric effect specifically includes the following steps:

[0039] Step S1, prepare a piezoelectric composite material.

[0040] S1-1, weigh 100 g of PF9305 type phenolic resin as the basic amount, add 10 wt% of P(VDF-TrFE) and 3 wt% of zinc oxide nanoparticles based on the mass of the PF9305 type phenolic resin, and 10 wt% of hexamethylenetetramine curing agent based on the mass of the PF9305 type phenolic resin. Use a laboratory electric stirrer to stir at a speed of 700 r / min for 40 min to obtain a mixed liquid A.

[0041] S1-2, perform a layup treatment on the mixed liquid A and 8 layers of plain weave fiberglass fabric, and cure and mold it using the vacuum-assisted resin transfer molding process. Cure it at a vacuum degree of -0.08 MPa and a temperature of 85 °C for 120 min to obtain a cured composite material.

[0042] S1-3. Polarize the solidified composite material in an electric field of 18 kV for 8 h, and cut it into a rectangle with dimensions of 100 mm × 150 mm to obtain a rectangular composite material.

[0043] S1-4, as Figure 1 shown, paste silver electrodes 20 on the surface of the rectangular composite material 10. The size of the electrodes 20 is 1.0 cm × 1.0 cm, the spacing between the electrodes 20 is 6 cm, and they are wrapped with tinned copper braided mesh. The pasting pressure of the electrodes 20 is 0.25 MPa. Package it with an epoxy resin encapsulation material 30 with dimensions of 2.5 cm × 3.5 cm to obtain a piezoelectric composite material.

[0044] Step S2. Arrange a plurality of electrodes on the surface of the piezoelectric composite material to form an electrode array sensing network and construct a sensing network.

[0045] Step S3. Conduct a tensile test on the composite material to cause damage, and use a data acquisition system to collect the change in the electrical signals of the electrode array.

[0046] Step S4. Perform time reversal processing on the collected electrical signals and re-excite them into the composite material, and determine the damage location by calculating the focal point coordinates of the response signal.

[0047] Let the electrical signal collected by the i-th electrode be S i (t), perform time reversal on it to obtain S i (-t), superimpose all the reversed signals and then excite them into the composite material. The response signal at a certain point (x, y, z) in the piezoelectric composite material is where τ i is the time required for the signal to propagate from the i-th electrode to the point (x, y, z). When the response signal R(x, y, z, t) reaches the maximum value at a certain point, this point is the damage location.

[0048] The working principles of the above two embodiments of the present invention are as follows:

[0049] The piezoelectric composite material of the present invention works based on the piezoelectric effect and the inverse piezoelectric effect. After polarization, the dipoles inside the composite material are arranged orderly along the thickness direction. When an external force acts, the material deforms, the orientation of the internal dipoles changes, resulting in the destruction of the electrostatic balance between the upper and lower electrodes and generating an electrical signal.

[0050] By detecting the change in the electrical signals of the electrode array, the precise location of the damage is achieved using the time reversal method. The principle lies in that the time reversal signal can automatically focus on the signal source (i.e., the damage location) during the propagation process, and the damage location is determined by calculating the coordinates of the focal point.

[0051] Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for locating damage in a fiber-reinforced structure based on the piezoelectric effect, characterized in that, Specifically, it includes the following steps: Step S1, preparing a piezoelectric composite material: At room temperature, adding poly(vinylidene fluoride-trifluoroethylene) copolymer and zinc oxide nanoparticles into a resin solution, and simultaneously adding a curing agent, stirring, laminating the obtained mixture with reinforcing fibers, the number of laminations meeting the principle of symmetric lamination, curing the obtained laminated structure by a curing and forming process to obtain a composite material, polarizing the composite material in a strong electric field, cutting it into a suitable shape according to actual application requirements after polarization, pasting electrodes at corresponding positions on its two side surfaces, and wrapping an electromagnetic shielding layer around the electrode wiring, and finally encapsulating it with an insulating encapsulation material to obtain a piezoelectric composite material; Step S2, constructing a sensing network: Arranging a plurality of electrodes on the surface of the piezoelectric composite material to form an electrode array sensing network; Step S3, signal acquisition and processing: When the piezoelectric composite material is deformed or damaged under a load, an electrical signal is generated, and the change of the electrical signals of each electrode is collected through a data acquisition system; And Step S4, positioning based on the time reversal method: Performing time reversal processing on the collected electrical signals, and then re-exciting them into the piezoelectric composite material, and determining the damage location according to the position where the time reversal signal focuses in the piezoelectric composite material.

2. The fiber-reinforced structure damage location method based on the piezoelectric effect according to claim 1, wherein: Among them, By weight, the poly(vinylidene fluoride-trifluoroethylene) copolymer is 0.1 - 15 wt%, and the zinc oxide nanoparticles are 0.1 - 8 wt%.

3. The fiber-reinforced structure damage location method based on the piezoelectric effect according to claim 1, wherein: Among them, The resin solution includes at least one of epoxy resin, phenolic resin, unsaturated polyester, and polyurethane.

4. The fiber-reinforced structure damage location method based on the piezoelectric effect according to claim 1, wherein: Among them, The stirring is carried out with a laboratory electric stirrer, the stirring speed is 600 - 1000 r / min, and the stirring time is 25 - 45 min.

5. The fiber-reinforced structure damage location method based on the piezoelectric effect according to claim 1, wherein: Among them, The reinforcing fiber is at least one of carbon fiber, glass fiber, basalt fiber, and aramid fiber, and the weaving method of the reinforcing fiber is unidirectional fiber, plain fiber, or twill fiber.

6. The fiber-reinforced structure damage location method based on the piezoelectric effect according to claim 1, wherein: Among them, The curing and forming process is a hot pressing process, a vacuum-assisted resin transfer molding process, or an autoclave process.

7. The fiber-reinforced structure damage location method based on the piezoelectric effect according to claim 1, wherein: Among them, The voltage of the polarizing strong electric field is 18 - 30 kV, and the polarization treatment time is 5 - 9 h.

8. The fiber-reinforced structure damage location method based on the piezoelectric effect according to claim 1, wherein: Among them, The shape of the electrode is rectangular, the length of the electrode is 0.6 to 1.2 cm, the width is 0.6 to 1.2 cm, the shape of the insulation encapsulation material is rectangular, the length of the insulation encapsulation material is 0.6 to 2.5 cm, and the width is 0.6 to 2.5 cm.

9. The method for locating damage to a fiber-reinforced structure based on the piezoelectric effect according to claim 1, wherein: Among them, The spacing of the electrodes is determined according to the size of the composite material and the required positioning accuracy, and the spacing of the electrodes is 2 to 10 cm.

10. The method for locating damage to a fiber-reinforced structure based on the piezoelectric effect according to claim 1, wherein: Among them, The calculation process of the time reversal processing is specifically as follows: Let the electrical signal collected by the i-th electrode be S i (t), perform time reversal on it to obtain S i (-t), superimpose all the reversed signals and then excite them into the composite material. The response signal at a certain point (x, y, z) in the composite material is where τ i is the time required for the signal to propagate from the i-th electrode to the point (x, y, z). When the response signal R(x, y, z, t) reaches the maximum value at a certain point, this point is the damage location.

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