Nondestructive testing method for debonding defect of laminated plate based on non-simple harmonic excitation

Abstract

The invention discloses a laminated plate debonding defect nondestructive testing method based on non-simple harmonic excitation, which comprises the following steps: sweep frequency excitation is performed on a laminated plate to be tested, a speckle interference image of the laminated plate to be tested is acquired through a speckle interferometer, and non-simple harmonic waves such as square waves, triangular waves or pulses are adopted as sweep frequency excitation signals; before detection, a camera of the speckle interferometer is adjusted to be in a real-time subtraction mode; during frequency sweeping, observing a real-time subtraction picture, and when an annular stripe is detected, marking the stripe as the debonding position of the laminated plate; continuously increasing the excitation frequency and observing whether a new position of the real-time subtraction picture has an annular stripe, and if so, continuously marking; and continuously sweeping the frequency and detecting the stripes until the stripes do not appear, storing the picture marked with the defect position, and ending the detection. According to the method, non-simple harmonic excitation is adopted, so that the debonding defect detection of the laminated plate is short in time consumption and high in efficiency, missing detection can be reduced, and the effect is more obvious especially when multiple defects exist.

Description

Technical Field

[0001] The invention relates to a nondestructive detection method for debonding defects of laminated plates, and in particular to a nondestructive detection method for debonding defects of laminated plates based on anharmonic excitation. Background Art

[0002] The laminated plate-like bonding structure has the advantages of low density, high strength and rigidity, good stability and reliability, etc. However, due to the limitations of factors such as the bonding process, the bonding structure will produce damages such as poor bonding, bubbles, pores, and local debonding during bonding or use. The existence of these damages will cause a decrease in structural strength and rigidity. Under the action of external forces, when the damage expands to a certain extent in the bonding structure, the mechanical properties of the bonding structure will deteriorate and there is a high probability that the entire structure will fail, posing a huge safety hazard. Therefore, it is crucial to conduct real-time and accurate quality assessment of the bonding surface.

[0003] At present, the main non-destructive testing method used is resonance combined with shear speckle interferometry. Vibration modes are inherent and integral characteristics of elastic structures. The resonance method can accurately test the mechanical behavior of materials under different excitation amplitudes. Shear speckle interferometry technology uses coherent light to illuminate the surface of a rough object to form speckles in space, thereby realizing the displacement and deformation detection of the object surface. It has the characteristics of full-field measurement, simple optical path, convenient adjustment, and low environmental requirements. During the inspection, the defective plate is excited by an external excitation force, the excitation frequency is slowly adjusted, and then the speckle interferometry method is used to observe whether it resonates. When resonating, the surface deformation becomes larger and the stripes become denser. If the plate is defective, the stripes are locally not smooth.

[0004] The technical problems of existing nondestructive testing methods are: using simple harmonic excitation (sinusoidal excitation signal), on the one hand, the resonance frequencies of defects of different sizes (debonding areas) are different, and a simple harmonic wave can only produce one frequency and can only excite one defect. It is necessary to continuously scan the frequency to excite defects in different positions, which is time-consuming and inefficient; on the other hand, it is necessary to continuously change the frequency, which may result in missed detection. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a nondestructive detection method for debonding defects of laminates based on anharmonic excitation, which is time-saving, efficient and can reduce missed detections.

[0006] Technical solution: The nondestructive detection method for debonding defects of laminates based on non-harmonic excitation described in the present invention includes performing frequency sweeping excitation on the laminate to be tested and collecting the speckle interference image of the laminate to be tested by a speckle interferometer, and the frequency sweeping excitation signal adopts a non-harmonic wave.

[0007] Furthermore, the non-harmonic wave is a square wave.

[0008] Furthermore, the non-harmonic wave adopts a triangular wave.

[0009] Furthermore, the non-harmonic wave adopts a pulse.

[0010] Furthermore, the speckle interferometer includes a laser, a beam expander, a CCD camera, a first reflector, a beam splitter and a second reflector. A piezoelectric ceramic drive device is fixed behind the first reflector. By changing the drive voltage, the first reflector can be driven to translate along the normal direction to achieve time phase shift; the second reflector is fixed on a rotating table and can be tilted in various directions to adjust the shear direction and shear amount; the laser output laser is irradiated to the laminate to be tested after passing through the beam expander, and the diffusely reflected light on its surface is divided into two coherent light beams by the beam splitter prism. One beam of coherent light is reflected by the first reflector and passes through the beam splitter prism again. The other beam of coherent light is reflected by the second reflector and the beam splitter prism. The two beams of light are imaged on the image plane of the CCD camera and interfere with each other.

[0011] Furthermore, the camera is adjusted to a real-time subtraction mode, that is, the image at the moment when the real-time subtraction mode is turned on is subtracted from the subsequent real-time image, and the absolute value is taken, and then displayed in real time.

[0012] Furthermore, when sweeping the frequency, observe the real-time subtraction image. When annular stripes are detected, mark the stripes as the debonding position of the laminate; continue to increase the excitation frequency and observe whether there are new positions of annular stripes in the real-time subtraction image. If so, continue to mark; continue to sweep the frequency and detect the stripes until no stripes appear, save the image of the marked defect position, and the detection is completed.

[0013] Furthermore, a vibration excitation device is fixed on the back side of the laminate to be tested to excite the laminate to be tested, and the vibration excitation device is connected to a driving circuit, which is used to provide a waveform signal for the vibration excitation device.

[0014] Furthermore, the vibration excitation device is adhered to the back side of the laminate to be tested by double-sided adhesive or quick-drying adhesive.

[0015] Furthermore, the excitation device adopts a piezoelectric ceramic buzzer; and the driving circuit adopts a function generator or a signal generator.

[0016] The technical principle of the present invention is:

[0017] The present invention uses non-harmonic excitation, and the non-harmonic vibration signal can be decomposed into several harmonic signals (the decomposition here should be understood as the non-harmonic wave can be decomposed into several harmonic waves through Fourier transform, but there is no artificial decomposition in the detection process, but when the object is subjected to non-harmonic excitation and resonates, the object vibrates in a sinusoidal form, and only one harmonic component in the non-harmonic resonates with the object. By default, only this harmonic component works, and other components do not work for resonance). This means that when using non-harmonic excitation of a certain frequency, the object will respond to vibrations of multiple frequencies, and when the local natural frequency of a defect is close to one of the frequencies, resonance will occur.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention adopts non-harmonic excitation, and the detection of debonding defects of laminates is time-saving and efficient, which can reduce missed detections, especially when there are multiple defects, the effect is more obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flowchart of a method for nondestructive detection of debonding defects of laminates based on anharmonic excitation provided by an embodiment of the present invention;

[0020] Figures 2 to 7 is a square wave excitation laminate defect detection image in an embodiment of the present invention, Figure 2 The frequency is 64Hz, Figure 3 The frequency is 96.2Hz, Figure 4 The frequency is 106.8Hz, Figure 5 The frequency is 160.3Hz, Figure 6 The frequency is 320Hz, Figure 7 The frequency is 481Hz;

[0021] Figures 8 to 13 is a defect detection image of a laminated plate excited by triangle wave in an embodiment of the present invention, Figure 8 The frequency is 80.1Hz, Fig. 9 The frequency is 120.25Hz, Fig.10 The frequency is 160.3Hz, Fig.11 The frequency is 240.5Hz, Fig.12 The frequency is 320Hz, Fig.13 The frequency is 481Hz;

[0022] Figures 14 to 16 is a pulse excitation laminate defect detection image in an embodiment of the present invention, Fig.14 The frequency is 96.2Hz, Fig.15 The frequency is 160.3Hz, Fig.16 The frequency is 481Hz;

[0023] Figure 17 to Figure 18is a defect detection image of a laminated plate excited by a simple harmonic wave (sine wave) in an embodiment of the present invention, Fig.17 The frequency is 320Hz, Fig.18 The frequency is 481Hz. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings.

[0025] like Figure 1 As shown, an embodiment of the present invention provides a nondestructive detection method for debonding defects of laminates based on anharmonic excitation, which specifically includes the following steps:

[0026] (1) Install the vibration equipment.

[0027] The excitation device of this embodiment adopts a piezoelectric ceramic buzzer, and the frequency range and vibration mode of the piezoelectric ceramic buzzer should meet the excitation requirements of the laminate to be tested.

[0028] Use double-sided tape or quick-drying adhesive to stick the piezoelectric ceramic buzzer on the back of the laminate to be tested, and ensure that it is firmly attached so that the vibration can be effectively transmitted to the laminate to be tested.

[0029] The piezoelectric ceramic buzzer is connected to a driving circuit, which can be a function generator or a signal generator. In this embodiment, a signal generator is used. The signal generator can provide the piezoelectric ceramic buzzer with any waveform signal, including square wave, sine wave, triangle wave, pulse and user input waveform.

[0030] The piezoelectric ceramic buzzer is stimulated to vibrate the laminate to be tested, causing the local defect position to resonate and generate a large amplitude, which is used as a signal for defect detection.

[0031] (2) The laminate to be tested is subjected to frequency sweeping excitation and a speckle interferometer is used to collect a speckle interference image of the laminate to be tested, and the frequency sweeping excitation signal adopts a non-harmonic wave.

[0032] Non-simple harmonic waves use square waves, triangle waves or pulses.

[0033] The speckle interferometer includes a laser, a beam expander, a CCD camera, a first reflector, a beam splitter and a second reflector. A piezoelectric ceramic drive device is fixed behind the first reflector. By changing the drive voltage, the first reflector can be driven to translate along the normal direction to achieve time phase shift; the second reflector is fixed on a rotating table and can be tilted in various directions to adjust the shear direction and shear amount; the laser output laser is irradiated to the laminate to be tested after passing through the beam expander, and the diffusely reflected light on its surface is divided into two coherent light beams by the beam splitter prism. One coherent light beam is reflected by the first reflector and passes through the beam splitter prism again. The other coherent light beam is reflected by the second reflector and the beam splitter prism. The two light beams are imaged on the image plane of the CCD camera and interfere with each other.

[0034] During the specific inspection, run the camera control software, display the picture taken by the camera in real time, adjust the components of the speckle interferometer according to the picture, make the light intensity moderate, ensure the image display is clear, and set the shear amount in the image to about 5mm. Then, set the output waveform of the signal generator to a non-simple harmonic waveform (triangle wave, square wave or pulse wave). In order to obtain the maximum excitation force, adjust the voltage of the signal generator to the maximum. Then, control the camera to enter the real-time subtraction mode through the camera control software, that is, the image at the moment when the real-time subtraction mode is turned on is subtracted from the subsequent real-time image, and the absolute value is taken, and then displayed in real time. Adjust the signal generator frequency, sweep from 1Hz, and observe the real-time subtraction screen on the computer. When the ring stripes are detected, the marked stripes are the debonding position of the laminate. Continue to increase the excitation frequency and observe whether there are new positions of ring stripes in the real-time subtraction screen. If so, continue to mark. Continue to sweep and detect stripes until the sweep frequency reaches 10,000 Hz, save the picture of the marked defect position, and the inspection is completed.

[0035] Experimental verification:

[0036] The defects of wood laminates were detected by square wave, triangle wave and pulse (non-harmonic wave) excitation respectively, and simple harmonic wave excitation was used for comparison. The experimental results show that the defects of laminates detected by non-harmonic wave are more numerous and more accurate, while simple harmonic wave can only detect the existence of defects. Figures 2 to 18 , annular fringes begin to appear at 64Hz for square wave excitation frequency, 80.1Hz for triangle wave, 96.2Hz for pulse, and 320Hz for simple harmonic wave. This is enough to show that the excitation effect of non-simple harmonic wave is better than that of simple harmonic wave.

[0037] Take square wave and sine wave as examples:

[0038] The first-order natural frequency of wood is 320Hz. If a sinusoidal signal is used for excitation, the frequency of the signal generator needs to be gradually adjusted from 0 to 320Hz to see the stripes corresponding to the resonant vibration mode, and then determine whether there is a defect from the stripes. If a square wave is used, then when the frequency of the signal generator is adjusted from 0 to 64Hz (one-fifth of 320Hz), stripes can be seen, and it can be determined whether there is a defect. When it is adjusted to 106.8Hz (one-third of 320Hz), vibration mode stripes can also be seen, and it can also be determined whether there is a defect. When it is adjusted to 320Hz, vibration mode stripes can also be obtained, and it can also be determined whether there is a defect. Compared with sinusoidal excitation (simple harmonic wave excitation), square wave excitation (non-simple harmonic wave excitation) can generate resonant stripes at more excitation frequencies, increase the number of vibration mode stripe diagrams used as reference for defect detection, and thus improve the efficiency of defect detection.

Claims

1. A non-destructive detection method for debonding defects of laminates based on anharmonic excitation, comprising performing frequency sweeping excitation on the laminate to be tested and collecting a speckle interferometer image of the laminate to be tested, It is characterized in that The sweep frequency excitation signal uses a non-harmonic wave.

2. According to claim 1, the non-destructive detection method for laminate debonding defects based on anharmonic excitation, It is characterized in that The non-simple harmonic wave adopts a square wave.

3. The nondestructive detection method for debonding defects of laminates based on anharmonic excitation according to claim 1, It is characterized in that The non-simple harmonic wave adopts a triangular wave.

4. The nondestructive detection method for laminate debonding defects based on anharmonic excitation according to claim 1, It is characterized in that The non-harmonic wave adopts pulse.

5. The nondestructive detection method for debonding defects of laminates based on anharmonic excitation according to claim 1, It is characterized in that The speckle interferometer includes a laser, a beam expander, a CCD camera, a first reflector, a beam splitter and a second reflector. A piezoelectric ceramic drive device is fixed behind the first reflector. By changing the drive voltage, the first reflector can be driven to translate along the normal direction to achieve time phase shift. The second reflector is fixed on a rotating table and can be tilted in various directions to adjust the shear direction and shear amount. The laser emitted by the laser is irradiated to the laminate to be tested after passing through a beam expander. The diffusely reflected light on its surface is divided into two coherent light beams by a beam splitter prism. One coherent light beam is reflected by the first reflector and passes through the beam splitter prism again. The other coherent light beam is reflected by the second reflector and the beam splitter prism. The two light beams are imaged on the image plane of the CCD camera and interfere with each other.

6. The nondestructive detection method for debonding defects of laminates based on anharmonic excitation according to claim 5, It is characterized in that The camera is adjusted to the real-time subtraction mode, that is, the image at the moment when the real-time subtraction mode is turned on is subtracted from the subsequent real-time image, and the absolute value is taken, and then displayed in real time.

7. The nondestructive detection method for debonding defects of laminated plates based on anharmonic excitation according to claim 6, It is characterized in that During the frequency sweep, observe the real-time subtraction screen. When annular fringes are detected, mark the fringes as the debonding position of the laminate. Continue to increase the excitation frequency and observe whether there are new positions of annular fringes in the real-time subtraction screen. If so, continue to mark. Continue to scan and detect stripes until no stripes appear. Save the image marking the defect location and the detection is complete.

8. The nondestructive detection method for debonding defects of laminated plates based on anharmonic excitation according to claim 1, It is characterized in that The excitation device is fixed on the back of the laminate to be tested to excite the laminate to be tested. The excitation device is connected to a driving circuit, and the driving circuit is used to provide a waveform signal for the excitation device.

9. The nondestructive detection method for debonding defects of laminated plates based on anharmonic excitation according to claim 8, It is characterized in that The excitation device is adhered to the back side of the laminate to be tested by double-sided adhesive or quick-drying adhesive.

10. The nondestructive detection method for debonding defects of laminated plates based on anharmonic excitation according to claim 8, It is characterized in that The excitation device adopts a piezoelectric ceramic buzzer; the driving circuit adopts a function generator or a signal generator.

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