A piezoelectric fiber-based composite material non-destructive testing method

Abstract

The application relates to a piezoelectric fiber-based composite material nondestructive testing method, which comprises the following process steps: 1) preparing a piezoelectric fiber; 2) embedding the piezoelectric fiber into a carbon fiber composite material plate; 3) connecting a signal amplifier to a measurement end of the copper wire in the piezoelectric fiber and the carbon fiber composite material plate, and connecting the signal amplifier to an oscilloscope; 4) using a laser to emit laser light, aiming and focusing the laser light on the surface of the carbon fiber composite material plate, and receiving a Lamb wave generated by pulsed laser light by the piezoelectric fiber; amplifying the signal through the signal amplifier, and then displaying the signal on the oscilloscope; and detecting the damage of the carbon fiber composite material plate by observing the amplitude change of the Lamb wave mode of the oscilloscope. The application can realize the nondestructive testing of the composite material based on the Lamb wave under the premise of guaranteeing the mechanical properties of the carbon fiber reinforced composite material and not occupying the surface space of the carbon fiber composite material.

Description

TECHNICAL FIELD

[0001] The application relates to a material detection method, in particular to a piezoelectric fiber-based composite material nondestructive detection method, and belongs to the technical field of material performance detection.

BACKGROUND

[0002] Carbon fiber reinforced composite materials have good mechanical properties and are widely used in many fields. However, in practical applications, the composite materials are often damaged and the damage is almost invisible, resulting in a decrease in mechanical strength. If the damage cannot be found and repaired in time, disastrous consequences may occur.

[0003] In order to solve this problem, many nondestructive detection methods have been developed, such as lead zirconate titanate piezoelectric ceramic sensors (PZT) which can be used for structural detection. It can be used to emit and receive signals, but needs to be placed on the surface of the material, occupying the surface space of the measured material.

[0004] Therefore, in order to solve the above problems, it is necessary to provide an innovative piezoelectric fiber-based composite material nondestructive detection method to overcome the defects in the prior art.

SUMMARY

[0005] The purpose of the present application is to provide a piezoelectric fiber-based composite material nondestructive detection method which can realize nondestructive detection of carbon fiber reinforced composite materials without affecting the mechanical properties of carbon fiber reinforced composite materials and without occupying the surface space of carbon fiber composite materials.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a piezoelectric fiber-based composite material nondestructive detection method, comprising the following process steps:

[0007] 1) preparing piezoelectric fibers;

[0008] 2) embedding the piezoelectric fibers into the carbon fiber composite material plate;

[0009] 3) connecting the copper wire in the piezoelectric fiber and the carbon fiber composite material plate to the signal amplifier measurement end, and connecting the signal amplifier to the oscilloscope;

[0010] 4) using a laser to emit laser light, aiming and focusing the laser light on the surface of the carbon fiber composite material plate, and receiving the Lamb wave generated by the pulsed laser by the piezoelectric fiber; amplifying the signal through the signal amplifier, and then displaying the signal on the oscilloscope; detecting the damage of the carbon fiber composite material plate by observing the change of the Lamb wave mode amplitude of the oscilloscope.

[0011] The piezoelectric fiber-based composite material nondestructive detection method of the present application further comprises the following steps in step 1):

[0012] 1-1), covering the copper wire with PVDF piezoelectric paint by electro-infiltration method;

[0013] 1-2), winding the copper wire into a comb shape, wherein each comb head distance is an odd multiple of half a wavelength.

[0014] The piezoelectric fiber-based composite material nondestructive testing method of the present application further comprises that each comb head distance is 12 mm, each comb head width is 3 mm, and each comb head length is 30 mm.

[0015] The piezoelectric fiber-based composite material nondestructive testing method of the present application further comprises that in step 2), the piezoelectric fibers are distributedly embedded in the middle of the edge of the carbon fiber composite material plate, and a part of the wire head is exposed to facilitate connection with the signal amplifier.

[0016] The piezoelectric fiber-based composite material nondestructive testing method of the present application further comprises that in step 4), the processing process of the Lamb wave is as follows:

[0017] 4-1), calculating the signal difference coefficient SDC of the Lamb wave ij :

[0018]

[0019] wherein t0 is the direct arrival time from the laser excitation point to the copper wire measurement point, μ x , μ y is the signal average value after damage and before damage, x ij (t) is the signal after damage, y ij (t) is the signal before damage, and ΔT is the signal window, the time length of which at least contains one symmetric Lamb wave signal and one anti-symmetric Lamb wave signal.

[0020] 4-2), the signal difference coefficient SDC ij is multiplied by the spatial distribution function s ij (x, y), wherein the spatial distribution function s ij (x, y) is as follows:

[0021]

[0022]

[0023] x i ,y i are the coordinate positions of the transmitter (laser excitation point), x j ,y j are the coordinate positions of the exposed measurement part of the receiver (copper wire head);

[0024] 4-3), the probability P(x, y) can be calculated according to the formula as follows:

[0025]

[0026] After imaging according to the probability P(x,y), the damage position is roughly located by tomography using the spatial distribution function.

[0027] The nondestructive testing method of the piezoelectric fiber-based composite material of the application further has that in the step 4-2), β is 1.005.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] 1. The nondestructive testing method of the piezoelectric fiber-based composite material of the application uses piezoelectric polymer piezoelectric fibers as sensors for nondestructive testing of carbon fiber composite material plates, on the one hand, the sensors are embedded in the carbon fiber composite material plates, without occupying space like some other sensors that need to be pasted on the surface of the material plate, on the other hand, the piezoelectric polymer piezoelectric fibers are small in size and have little effect on the mechanical properties of the carbon fiber composite material plate.

[0030] 2. The nondestructive testing method of the piezoelectric fiber-based composite material of the application embeds piezoelectric fibers in carbon fiber reinforced composite materials to realize nondestructive testing, and the Lamb wave signal is generated by laser, so it also does not need to occupy the surface space of the carbon fiber composite material plate, when the laser is aligned and focused above the carbon fiber composite material plate to generate Lamb waves, the sensor will receive the Lamb wave signal, and the damage condition of the carbon fiber composite material plate can be found by observing the signal change of the Lamb wave, so that the nondestructive testing of the carbon fiber reinforced composite material can be realized without affecting the mechanical properties of the carbon fiber reinforced composite material. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a schematic diagram of the three-dimensional structure of the piezoelectric fiber in step 1) of the application.

[0032] Figure 2 It is a schematic diagram of the piezoelectric fiber embedded in the carbon fiber composite material plate in step 2) of the application.

[0033] Figure 3 It is a schematic diagram of the connection of the piezoelectric fiber and the carbon fiber composite material plate to the signal amplifier and the oscilloscope.

[0034] Figure 4 It is a schematic diagram of the laser irradiating the carbon fiber composite material plate and being received by the piezoelectric fiber. DETAILED DESCRIPTION

[0035] Please refer to the drawings in the specification Figure 1 to the drawings Figure 4 shown, the application is a nondestructive testing method of a piezoelectric fiber-based composite material, which comprises the following process steps:

[0036] 1), piezoelectric fiber 1 is prepared as a sensor, and the specific preparation method is as follows:

[0037] 1-1), polyvinyl fluoride (PVDF) piezoelectric coating 2 is covered on the copper wire by using the electro-wetting method;

[0038] 1-2), the copper wire is wound into a comb shape by using a steel wire clamp, and in order to generate the wavelength coordination phenomenon, the distance d between each comb head is an odd multiple of half the wavelength. In this embodiment, the distance d between each comb head is 12 mm, the width of each comb head is 3 mm, and the length is 30 mm, so as to generate the wavelength coordination phenomenon.

[0039] 2), the piezoelectric fiber is embedded in the carbon fiber composite material plate;

[0040] In this embodiment, the piezoelectric fiber 1 is distributedly embedded in the middle of the edge of the carbon fiber composite material plate 3 during the laying of the carbon fiber cloth, and a part of the wire head is exposed to facilitate connection with the signal amplifier.

[0041] 3), the copper wire in the piezoelectric fiber and the carbon fiber composite material plate are connected to the measurement end of the signal amplifier, and the signal amplifier is connected to the oscilloscope.

[0042] 4) a laser 4 is used to emit laser, and the laser is aligned and focused on the surface of the carbon fiber composite material plate 3. When the energy of the laser is focused and irradiated on the surface of the elastic material, part of it will be transferred to the material itself and will be in the form of thermal energy and stress wave energy. By using the instantaneous thermal action of high-energy laser pulse on the surface of the material, the strain and stress field is generated on the surface of the carbon fiber composite material plate through the thermoelastic effect, so that the particles produce fluctuations, and then the Lamb wave signal is generated in the carbon fiber composite material plate and scattered into several symmetric Lamb wave signals and anti-symmetric Lamb wave signals. The Lamb wave signal will be received by the piezoelectric fiber 1 embedded in the carbon fiber composite material plate 3, and will be amplified by the signal amplifier and displayed on the oscilloscope. By observing the amplitude change of the Lamb wave mode of the oscilloscope, the damage 5 of the carbon fiber composite material plate can be known.

[0043] Among them, the processing process of the Lamb wave is as follows:

[0044] 4-1), the signal difference coefficient SDC of the Lamb wave is calculated ij :

[0045]

[0046] Among them, t0 is the direct arrival time from the laser excitation point to the copper wire measurement point, μ x ,μ y is the average value of the signal before and after damage, x ij (t) is the signal after damage, y ij(t) is the signal before damage, ΔT is the signal window, the time length contains at least one symmetric Lamb wave signal and one anti-symmetric Lamb wave signal;

[0047] 4-2), signal difference coefficient SDC ij times the spatial distribution function s ij (x, y). After calculating the SDC ij value of all sensor pairs, the next step of the fast algorithm is image reconstruction. The image is generated by the spatial distribution function on the image plane, which is an ellipse, and the two foci of the ellipse are the positions of the two sensors.

[0048] The spatial distribution function s ij (x, y) is as follows:

[0049]

[0050] Where β is a shape factor that controls the size of the ellipse distribution, which can be any value, but must be greater than 1.0. If the value of β is larger, the ellipse will be larger, and through experiments it is found that when β is 1.005, the results of tomography are closest to the true value.

[0051]

[0052] x i ,y i is the coordinate position of the transmitter (laser excitation point), x j ,y j is the coordinate position of the exposed measurement part of the receiver (copper wire end); therefore, in the experiment, the above formula denominator is a constant value, and the numerator part is an ellipse formula, so R ij (x, y) is actually imaged as an ellipse with the laser excitation point and the copper wire measurement point as the foci, and through the adjustment of β in s ij (x, y), it can only image inside the ellipse, i.e. it can determine the damage on this path.

[0053] 4-3), according to the formula, the probability P(x, y) can be calculated, and the formula is as follows:

[0054]

[0055] Therefore, the larger the SDC ij , the larger the P(x, y) obtained, and the larger the damage probability value on this path, and then according to the probability P(x, y) imaging is performed using the spatial distribution function to roughly locate the damage position.

[0056] The above detailed description is merely exemplary in nature and is not intended to limit the application or the application and uses of the application. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding description of the application.

Claims

1. A non-destructive testing method for composite materials based on piezoelectric fibers, characterized in that: The process includes the following steps: 1) Preparation of piezoelectric fibers, the specific preparation method is as follows: 1-1), PVDF piezoelectric coating is applied to copper wire using an electro-impregnation method; 1-2) Wind the copper wire into a comb shape, wherein the distance between each comb head is an odd multiple of half the wavelength; the distance between each comb head is 12mm, and each comb head is 3mm wide and 30mm long; 2) Embed piezoelectric fibers into a carbon fiber composite plate; the piezoelectric fibers are distributedly embedded in the middle of the edge of the carbon fiber composite plate, with a portion of the wire ends exposed for easy connection to a signal amplifier; 3) The copper wires inside the piezoelectric fiber and the carbon fiber composite plate are connected to the measurement end of the signal amplifier, and the signal amplifier is connected to the oscilloscope; 4) Use a laser to emit a laser, aim and focus the laser onto the surface of the carbon fiber composite plate. The pulsed laser generates a Lamb wave which is received by the piezoelectric fiber. The signal is amplified by a signal amplifier and then displayed on an oscilloscope. The damage to the carbon fiber composite plate is detected by observing the change in the amplitude of the Lamb wave mode on the oscilloscope. The processing procedure for the Lamb wave is as follows: 4-1) Calculate the Lamb wave signal difference coefficient SDC ij : Where t0 is the direct arrival time from the laser excitation point to the copper wire measurement point, μ x ,μ y x is the average signal value before and after the injury. ij (t) represents the signal after damage, y ij (t) represents the signal before damage, ΔT is the signal window, and the time length includes at least one symmetric Lamb wave signal and one antisymmetric Lamb wave signal; 4-2), Signal Difference Coefficient (SDC) ij Multiply by the spatial distribution function s ij (x,y), where the spatial distribution function s ij The formula for (x,y) is as follows: x i ,yi represents the coordinates of the laser excitation point, x j ,y j The coordinates of the exposed portion of the copper wire end being measured; β is set to 1.005; 4-3), calculate the probability P(x,y) according to the formula, as follows: Then, based on the probability P(x,y) imaging, tomography using the spatial distribution function is used to roughly locate the damage location.

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