CN117169231A - Composite material nondestructive testing system based on acousto-optic technology - Google Patents
Composite material nondestructive testing system based on acousto-optic technology Download PDFInfo
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Abstract
The invention is suitable for the field of nondestructive testing, and provides a composite nondestructive testing system based on an acousto-optic technology, which comprises an automatic testing robot, wherein an adjusting mechanism and a testing and analyzing operation host are arranged on the automatic testing robot, a distance measuring module and a laser vibration measuring module are arranged on the adjusting mechanism, and the automatic testing robot is also connected with an excitation module. Collecting vibration information data of the composite material through frequency sweep and fixed-frequency excitation, preprocessing and analyzing the vibration information data to obtain vibration response data and structure vibration mode data, and searching feature points to determine defect positions; meanwhile, the defect positions, the defect number and the defect types of the composite material are identified after structural vibration mode data are subjected to a central difference method and wavelet transformation analysis and then are subjected to algorithm processing calculation. According to the nondestructive testing method for the composite material, the vibration is tested by exciting vibration and adopting laser, so that the problems of limitations of the traditional sound vibration method are solved, and the testing efficiency and the sensitivity are improved.
Description
Technical Field
The invention belongs to the field of nondestructive testing, and particularly relates to a composite nondestructive testing system based on an acousto-optic technology.
Background
The composite material has very high strength and rigidity, excellent corrosion resistance and wide application in aerospace and other related industries. Aircraft composites belong to very complex multiphase systems and their structure and shaping are accomplished simultaneously. There are a number of instability factors that can cause problems with the structure of the composite during the forming stage. The composite material has the characteristics of non-uniformity, complex damage type, high production technology difficulty and the like, and the problems of fiber damage, debonding, layering and the like can be inevitably generated in the production and application stages, so that the nondestructive detection of the aircraft composite material component is gradually developed into an indispensable content for ensuring the flight safety.
At present, nondestructive testing methods for composite materials specifically comprise an ultrasonic method, an X-ray method, an acoustic emission method, a microwave detection method and the like. These non-destructive inspection methods, which are commonly used, have significant limitations, such as the difficulty in accurately inspecting defects in thin plates by ultrasonic inspection methods, the significant limitations of X-ray methods in the inspection delamination process, and the difficulty in detecting minor problems by microwave inspection methods, and the requirement that the acoustic emission method place the components under fixed pressure conditions during the inspection process is impractical for partially finished components and components that have been assembled.
As a detection technology which is relatively long in development, the acoustic vibration detection method has the characteristics of simplicity, convenience, rapidness, low cost and the like, can detect and identify layering defects in the carbon fiber composite material, and can further identify dislocation and fracture defects of the carbon fiber composite material after the acoustic emission transducer is introduced. The thickness of the plate, the bit depth, the size and the like of defects such as debonding, layering, air holes and the like in the carbon fiber composite material can be detected by applying the acoustic impedance technology. Compared with an ultrasonic detection method, the ultrasonic vibration method does not need liquid coupling agent when detecting the workpiece, improves the detection convenience and prevents leakage of a part of skin-honeycomb core glued structure caused by defects. Compared with an X-ray method, the operability of the sound vibration method is greatly improved, the harm to human bodies caused by ray radiation is avoided, and the complexity of detection equipment is reduced. Compared with the traditional knocking method, the accuracy and the sensitivity of the sound vibration method are higher, and the detectable defect range is smaller. At present, the acoustic vibration method also has certain limitations, and the requirements on a mechanical device contacted with a workpiece to be detected in the acoustic vibration detection process are high, for example: the acoustic vibration method based on acoustic impedance change detection is greatly influenced by the fixing mode of the detection device, and a workpiece to be detected is in vertical contact with a transducer contact, so that the influence on the detection result is great; the piezoelectric wafer of the vibration measuring device in the transducer is influenced by the property of the material, and the perception sensitivity of weak vibration signals is required to be improved.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a composite nondestructive testing system based on acousto-optic technology, which aims to solve the above technical problems.
The invention adopts the following technical scheme:
the composite material nondestructive testing system based on the acousto-optic technology comprises an automatic detection robot, wherein an adjusting mechanism and a detection analysis operation host are arranged on the automatic detection robot, a distance measuring module and a laser vibration measuring module are arranged on the adjusting mechanism, and the automatic detection robot is also connected with an excitation module; the excitation module is used for being attached to the composite material to be detected, so that excitation of the composite material is completed, and vibration is generated; the distance measuring module is used for measuring the distance between the laser vibration measuring module and the composite material; the laser vibration measuring module is used for scanning the surface of the composite material at a preset height to collect vibration information of the composite material; the detection analysis operation host is used for performing operation setting on the system and performing data analysis on the received vibration information data.
Further, the scanning track of the laser vibration measuring module is a serpentine grid reciprocating scanning.
Further, there is the microphone wheel automatic detection robot bottom, adjustment mechanism includes horizontal rotation device, horizontal rotation device is last to install up-down slider, horizontal slider is transversely installed about up-down slider, range finding module and laser vibration measurement module install to horizontal slider.
Further, the up-down sliding device is provided with an axial rotating device, and the left-right sliding device is mounted to the axial rotating device.
Further, during detection, the laser vibration measuring module is always perpendicular to the surface of the composite material to be detected, and the composite material to be detected is a planar composite material or a curved composite material with radian.
Further, the process of the detection analysis operation host computer for carrying out data analysis on the vibration information data is as follows:
step S1, controlling an excitation module to perform sweep frequency excitation firstly, analyzing acquired vibration information data to obtain vibration response data, determining the vibration mode frequency of each step, and searching feature points to determine the defect position;
s2, controlling an excitation module to perform fixed frequency excitation of each order according to the vibration mode frequency of each order, analyzing the obtained vibration information data to obtain structural vibration mode data, namely frequency-displacement amplitude data, calculating the curvature of the frequency-displacement amplitude data before and after the structural defect based on a center difference method, processing by using continuous wavelet transformation, calculating the phase difference between a measuring point and an excitation point, and determining the number and the type of the defect;
and S3, integrating the positions of the defects, the number and the types of the defects, and constructing defect identification indexes.
Further, the specific process of step S1 is as follows:
s11, inputting a sweep frequency signal to an excitation module to generate sweep frequency excitation, scanning measuring points on a scanning track by a laser vibration measuring module in a single-point scanning mode, obtaining vibration response data of a single point according to a frequency response function peak value, and finally obtaining vibration mode frequencies of each order of each measuring point of the whole test area of the surface of the composite material structure;
s12, placing the vibration mode frequencies of each step of each measuring point of the composite material in a matrix of the corresponding position of the three-dimensional array according to the space coordinates to obtain the vibration mode frequencies of each step of the surface of the composite material structure under different frequencies in the whole test frequency band;
s13, transforming an original frequency-sweep excitation time domain signal into a frequency domain by utilizing fast Fourier transform to obtain a frequency-displacement amplitude signal of each measuring point, and putting the frequency-displacement amplitude signal into a matrix;
s14, comparing and analyzing the measuring point matrix of the composite material to be measured with the healthy composite material, and acquiring characteristic points through the frequency shift of each order of vibration mode and the change of the amplitude value, so as to determine the defect position.
Further, the specific process of step S2 is as follows:
s21, for each measuring point, performing fixed-frequency excitation on the composite material according to each order of vibration mode frequency control excitation module to obtain structural vibration mode data of each measuring point, namely frequency-displacement amplitude data;
s22, calculating the curvature of frequency-displacement amplitude data of each measuring point before and after the structural defect of the composite material by using a center difference method, namely the curvature of the mode shape;
s23, placing the mode shape curvature of each measuring point into a matrix, comparing the relativity of the measuring point matrix of the defect structure and the healthy structure of the composite material, and processing the mode shape curvature of the composite material by using two-dimensional continuous wavelet transformation to generate a wavelet coefficient to obtain a first matrix norm;
s24, obtaining a frequency response function of each measuring point under fixed frequency excitation, further obtaining the phase of each measuring point and the phase difference between each measuring point and initial excitation, putting the measuring points into a matrix, comparing the singularities of the measuring point matrix of the defect structure and the healthy structure of the composite material, processing the phase difference of the composite material by wavelet transformation, and generating a wavelet coefficient to obtain a second matrix norm;
s25, combining the two matrix norms so as to effectively identify the defect class number and class of the composite material.
The beneficial effects of the invention are as follows: according to the invention, the laser vibration measuring module is matched with the distance measuring module and the adjusting mechanism to realize reciprocating grid motion on the surface of the composite material detecting piece, vibration information data of the composite material is collected through frequency sweeping and fixed-frequency excitation, the detection and analysis operation host machine is used for preprocessing and analyzing the received vibration information data, vibration response data and structure vibration type data are obtained, and characteristic points are searched for to determine defect positions; meanwhile, the defect positions, the defect number and the defect types of the composite material are identified after structural vibration mode data are subjected to a central difference method and wavelet transformation analysis and then are subjected to algorithm processing calculation. The invention adopts a non-contact and more sensitive composite material nondestructive testing technology, adopts laser to test vibration by exciting vibration, solves some limitation problems of the traditional acoustic vibration method, and improves the detection efficiency and sensitivity.
Drawings
FIG. 1 is a schematic diagram of a composite nondestructive testing system provided by an embodiment of the present invention;
FIG. 2 is a block diagram of an automatic inspection robot according to an embodiment of the present invention;
fig. 3 is a flow chart of data analysis of vibration information data.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In order to illustrate the technical scheme of the invention, the following description is made by specific examples.
As shown in fig. 1 and 2, the composite nondestructive testing system based on the acousto-optic technology provided by the embodiment comprises an automatic testing robot 100, wherein an adjusting mechanism and a detection analysis operation host 8 are installed on the automatic testing robot 100, a distance measuring module 3 and a laser vibration measuring module 5 are installed on the adjusting mechanism, and the automatic testing robot 1 is also connected with an excitation module 2; the excitation module 2 is used for being attached to the composite material 200 to be detected, so that excitation of the composite material 200 is completed and vibration is generated; the distance measuring module 3 is used for measuring the distance between the laser vibration measuring module 4 and the composite material 200; the laser vibration measuring module 4 is used for scanning the surface of the composite material at a preset height to collect vibration information of the composite material. In the illustration, the scan trajectory 300 of the laser vibration measuring module is a serpentine grid reciprocating scan. The detection and analysis operation host computer 8 is used for performing operation setting on the system and performing data analysis on the received vibration information data.
In this structure, automatic detection robot bottom has the microphone wheel 1, adjustment mechanism includes horizontal rotation device 7, install up-and-down slider 6 on the horizontal rotation device 7, horizontal slider 4 is transversely installed to up-and-down slider 6, range finding module 3 and laser vibration measurement module 5 install to horizontal slider 4. The automatic detection robot mainly enables the laser vibration measuring module to conduct grid reciprocating scanning movement on the surface of the composite material, and therefore vibration information of the composite material is collected. The detection robot can run autonomously, and the Mecanum wheels are adopted to carry motors to drive the front, back, left and right movements. The detection analysis operation host is provided with a data acquisition host. The detection robot is provided with an up-and-down sliding device through a horizontal rotating device, so that rotation and up-and-down movement can be realized; the left and right sliding devices are mounted on the up and down sliding devices, and the laser vibration measuring module and the ranging module are mounted on the left and right sliding devices. The up-down sliding device and the ranging module are mutually matched to finish proper measurement height on the surface of the composite material, and the left-right sliding module, the laser vibration measuring module and the detection robot move so as to finish grid reciprocating movement on the surface of the composite material.
For laser vibration measurement, the laser beam is perpendicular to the measured object as much as possible, and accurate data are acquired. In the structure, the laser vibration measuring module is required to be always vertical to the surface of the composite material to be measured during detection. The composite material to be tested is a planar composite material or a curved composite material with radian. For curved surface composite materials, as shown in fig. 1 and 2, the vertical sliding device 6 is further provided with an axial rotating device 9, and the horizontal sliding device 5 is mounted on the axial rotating device 9, so that the axial angle rotation of the laser vibration measuring module can be controlled, the laser vibration measuring module can be adapted to the condition that the laser of the laser vibration measuring module is perpendicular to the surface of the detected curved surface composite materials, nondestructive detection can be performed, and accurate data can be obtained.
The excitation module can adopt a PZT piezoelectric ceramic plate (or a piezoelectric stack), and the principle is a piezoelectric effect. The piezoelectric ceramic is an information functional ceramic material capable of mutually converting mechanical energy and electric energy-piezoelectric effect; when a voltage is applied to the piezoelectric ceramic, mechanical deformation occurs with changes in voltage and frequency. By using this principle, when an electric signal is applied to a vibrator composed of two pieces of piezoelectric ceramics or one piece of piezoelectric ceramics and one piece of metal sheet, vibration occurs due to bending. So that it can be vibrated by applying a pulse voltage thereto. The specific process is as follows: sine waves with different frequencies are generated by a signal generator, then are amplified by a signal amplifier, and then are applied to the PZT piezoelectric ceramic plate to generate vibration.
The laser vibration measuring module is mainly based on the interference principle of light, and obtains the relation of vibration speed, displacement and the like of the measured object and calculates corresponding parameters by processing and analyzing the phase change, the light intensity change and the like of the surface of the object and the reference before and after deformation. Laser vibration measurement is currently the best measurement method for obtaining displacement and velocity resolution. The device can realize pm-level amplitude resolution, has high linearity, and can ensure the consistency of the amplitude in an extremely high frequency range (exceeding 1 GHz). Compared with the traditional piezoelectric sensor, the laser energy can finish measurement under the condition of not contacting an object to be measured, and the problems caused by poor stability of a mechanical device to the detection effect and sensitivity are greatly reduced. Meanwhile, due to the characteristics of good directivity, monochromaticity, coherence and the like of laser, the method has good effect in measuring various weak vibration, movement speed and small change.
In this embodiment, since the mounting position of the excitation module is fixed, the frequency response function of the measurement point can be obtained by the laser vibration measurement module, and the phase difference can be obtained by comparing two signals, one is the measured vibration signal and the other is the reference signal, and then the phase difference can be obtained after comparing the two signals.
Based on the composite material nondestructive detection system, after the vibration excitation module is installed, the laser vibration detection module scans according to the set height and track. The signal generator of the excitation module is used for generating signals, and the embodiment selects sweep frequency signals and fixed frequency sinusoidal signals. The method comprises the steps of firstly obtaining the frequency of each order of vibration mode of a single point according to the peak value of a frequency response function by using a single-point scanning mode, and then scanning each measuring point under a fixed-frequency sinusoidal signal according to each order of frequency, so that the vibration mode of the whole composite material under the frequency is obtained. The signal generated by the signal generator is amplified by a voltage signal amplifier. The input end of the voltage amplifier is connected with the output end of the signal generator, the amplification factor is adjusted, and the voltage is amplified in multiple. The amplified signal is output to the PZT piezoelectric ceramic plate from the output end of the voltage amplifier, so that the composite material is excited to vibrate. And the detection and analysis operation host machine performs data analysis on the received vibration information data.
The existing sound vibration method has to require vertical close contact with the detection object, and the contact area is large, so that the resolution of detection is low. The invention has simple structural design, adopts non-contact detection perpendicular to the composite material to be detected, and has high local resolution of single-point laser pair detection. Therefore, when detecting tiny damage, the defect position of the composite material is roughly detected, and then the laser is used for finely detecting the initial defect position by the method.
For the specific process of data analysis described above, with reference to fig. 3, the process is as follows:
s1, controlling an excitation module to perform sweep frequency excitation, analyzing the acquired vibration information data to obtain vibration response data, determining the vibration mode frequency of each step, and searching for characteristic points to determine the defect position.
In the step, the excitation module is excited by a sweep frequency signal to obtain vibration information data (such as amplitude, frequency, displacement, speed and phase) of the composite material, performs preprocessing analysis to obtain vibration response data, finally obtains vibration type frequencies of each order, and searches for characteristic points to determine defect positions. In specific implementation, the method specifically comprises the following steps:
s11, inputting a sweep frequency signal to an excitation module to generate sweep frequency excitation, scanning measuring points on a scanning track by a laser vibration measuring module in a single-point scanning mode, obtaining vibration response data of a single point according to a frequency response function peak value, and finally obtaining the vibration mode frequencies of the single point in each order of each measuring point of the whole test area of the surface of the composite material structure.
In the embodiment, the sweep frequency signal is amplified and then input into the piezoelectric ceramic plate for excitation, and single-point scanning is performed on each measuring point according to the scanning track. For the current measuring point single point, obtaining the vibration mode frequency of each order of the single point according to the frequency response function peak value; for each measuring point, the frequency of each order of vibration mode can be acquired for multiple times and the linear average is taken, so that the accuracy is improved. After the acquisition of the single point is completed, the scanning head of the laser vibration measuring module moves to the next measuring point according to the point distribution sequence of the measuring points on the track to complete the acquisition of vibration response data and acquire the vibration mode frequency of each order. And finally obtaining the vibration mode frequencies of each step of each measuring point of the whole test area of the surface of the composite material structure.
S12, placing the vibration mode frequencies of each order of each measuring point of the composite material in a matrix of the corresponding position of the three-dimensional array according to the space coordinates, and obtaining the vibration mode frequencies of each order of the surface of the composite material structure under different frequencies in the whole test frequency band.
S13, transforming the original frequency-sweep excitation time domain signal into a frequency domain by utilizing fast Fourier transform to obtain a frequency-displacement amplitude signal of each measuring point, and putting the frequency-displacement amplitude signal into a matrix.
S14, comparing and analyzing the measuring point matrix of the composite material to be measured with the healthy composite material, and acquiring characteristic points through the frequency shift of each order of vibration mode and the change of the amplitude value, so as to determine the defect position.
And S2, controlling an excitation module to perform fixed frequency excitation of each order according to the vibration mode frequency of each order, analyzing the obtained vibration information data to obtain structural vibration mode data, namely frequency-displacement amplitude data, calculating the curvature of the frequency-displacement amplitude data before and after the structural defect based on a center difference method, processing by using continuous wavelet transformation, calculating the phase difference between a measuring point and an excitation point, and determining the number and the type of the defect.
And (2) exciting the composite material by using the vibration mode frequencies of each step obtained in the step (S1) as fixed frequencies to obtain structural vibration mode data, analyzing by a central difference method and wavelet transformation, and identifying the defect number and the defect type of the composite material after algorithm processing and calculation. Specifically, the process of the step is as follows:
s21, for each measuring point, performing fixed-frequency excitation on the composite material according to each order of vibration mode frequency control excitation module to obtain structural vibration mode data of each measuring point, namely frequency-displacement amplitude data;
s22, calculating the curvature of frequency-displacement amplitude data of each measuring point before and after the structural defect of the composite material by using a center difference method, namely the curvature of the mode shape;
s23, placing the mode shape curvature of each measuring point into a matrix, comparing the relativity of the measuring point matrix of the defect structure and the healthy structure of the composite material, and processing the mode shape curvature of the composite material by using two-dimensional continuous wavelet transformation to generate a wavelet coefficient to obtain a first matrix norm;
s24, obtaining a frequency response function of each measuring point under fixed frequency excitation, further obtaining the phase of each measuring point and the phase difference between each measuring point and initial excitation, putting the measuring points into a matrix, comparing the singularities of the measuring point matrix of the defect structure and the healthy structure of the composite material, processing the phase difference of the composite material by wavelet transformation, and generating a wavelet coefficient to obtain a second matrix norm;
s25, combining the two matrix norms so as to effectively identify the defect class number and class of the composite material.
Wavelet transformation has evolved into one of the most efficient time-frequency analysis methods in signal processing and spatial domain analysis with extremely strong detail resolution. And processing the curvature of the mode shape of the composite material by using the definition of two-dimensional continuous wavelet transformation, and obtaining matrix norms of the generated wavelet coefficients. Meanwhile, as the installation position of the excitation module, namely the excitation point is fixed, the distance between the measurement point and the excitation point can be known; the frequency response function of each measuring point can be obtained under fixed frequency excitation, so that the phase of each measuring point and the phase difference between each measuring point and initial excitation are obtained; and then putting the composite material into a matrix, comparing the singularities of the measuring point matrix of the defect structure and the singularities of the measuring point matrix of the healthy structure, and simultaneously processing the phase difference of the composite material by wavelet transformation, and obtaining the matrix norms of the generated wavelet coefficients. And further effectively identifying the defect number and the defect type of the composite material.
And S3, integrating the positions of the defects, the number and the types of the defects, and constructing defect identification indexes.
The defect identification index is mainly analysis of experimental data and results, the defect detection of the composite material is realized through the method of the embodiment, and finally the defect identification index of the composite material is realized through data processing.
In summary, when the defect detection of the composite material is performed by the method of the embodiment, firstly, a PZT piezoelectric ceramic sheet or a piezoelectric stack is attached to a composite material detection piece; the automatic detection robot carries a microphone wheel to perform omnidirectional movement, the laser vibration measurement module performs reciprocating grid movement on the surface of a composite material detection part under the cooperation of the ranging module, the vertical sliding device and the horizontal sliding device, vibration information data of the composite material are collected through sweep frequency excitation and fixed frequency excitation, and then the vibration information data are transmitted to a detection analysis operation host computer through a data bus, and the collected structure vibration pattern diagram of the composite material can be displayed firstly through processing, and then the defect position, the number and the category of the composite material are identified after the processing and calculation of an algorithm through a central difference method and wavelet transformation analysis.
Compared with the traditional nondestructive detection by the acoustic vibration method, the laser vibration detection can realize high-sensitivity detection of micro defects or deformation in the composite material, and can detect weak vibration signals and accurately measure the weak vibration signals, so that potential problems can be found early. And can detect fine deformation or damage, and can accurately measure hidden defects.
The laser vibration detection does not need to be in direct contact with the composite material, and can be detected under the condition of not damaging the material by scanning or aiming through laser beams, so that the laser vibration detection device is particularly suitable for detecting the composite material with higher sensitivity, and further damage is avoided. In addition, the laser vibration measurement has advantages in the frequency response range, can cover a wide range from low frequency to high frequency from structural vibration to acoustic signal, and is very suitable for detecting vibration conditions of different frequencies in the composite material. Meanwhile, the nondestructive testing task of the composite material can be rapidly and accurately executed by combining an automatic robot. Compared with manual operation, the robot can measure more stably, reduce human errors and improve the consistency and accuracy of detection.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (8)
1. The nondestructive testing system for the composite material based on the acousto-optic technology is characterized by comprising an automatic testing robot, wherein an adjusting mechanism and a testing and analyzing operation host are arranged on the automatic testing robot, a distance measuring module and a laser vibration measuring module are arranged on the adjusting mechanism, and the automatic testing robot is further connected with an excitation module; the excitation module is used for being attached to the composite material to be detected, so that excitation of the composite material is completed, and vibration is generated; the distance measuring module is used for measuring the distance between the laser vibration measuring module and the composite material; the laser vibration measuring module is used for scanning the surface of the composite material at a preset height to collect vibration information of the composite material; the detection analysis operation host is used for performing operation setting on the system and performing data analysis on the received vibration information data.
2. The acousto-optic technology based composite nondestructive testing system of claim 1 wherein the scan trajectory of the laser vibration measuring module is a serpentine grid reciprocating scan.
3. The composite nondestructive testing system based on the acousto-optic technology according to claim 1, wherein the automatic testing robot is provided with a microphone wheel at the bottom, the adjusting mechanism comprises a horizontal rotating device, an up-and-down sliding device is arranged on the horizontal rotating device, a left-and-right sliding device is transversely arranged on the up-and-down sliding device, and the ranging module and the laser vibration testing module are arranged on the left-and-right sliding device.
4. A composite nondestructive inspection system based on acousto-optic technology as set forth in claim 3 wherein said up and down slide has an axial rotation device thereon, said left and right slide being mounted to said axial rotation device.
5. The composite nondestructive testing system based on the acousto-optic technology according to claim 4, wherein the laser vibration testing module is always vertical to the surface of the composite to be tested during the testing, and the composite to be tested is a planar composite or a curved composite with radian.
6. The composite nondestructive testing system based on acousto-optic technology as set forth in any one of claims 1 to 5, wherein the process of data analysis of vibration information data by the testing operation host machine is as follows:
step S1, controlling an excitation module to perform sweep frequency excitation firstly, analyzing acquired vibration information data to obtain vibration response data, determining the vibration mode frequency of each step, and searching feature points to determine the defect position;
s2, controlling an excitation module to perform fixed frequency excitation of each order according to the vibration mode frequency of each order, analyzing the obtained vibration information data to obtain structural vibration mode data, namely frequency-displacement amplitude data, calculating the curvature of the frequency-displacement amplitude data before and after the structural defect based on a center difference method, processing by using continuous wavelet transformation, calculating the phase difference between a measuring point and an excitation point, and determining the number and the type of the defect;
and S3, integrating the positions of the defects, the number and the types of the defects, and constructing defect identification indexes.
7. The composite nondestructive testing system based on acousto-optic technology as set forth in claim 6, wherein the specific process of the step S1 is as follows:
s11, inputting a sweep frequency signal to an excitation module to generate sweep frequency excitation, scanning measuring points on a scanning track by a laser vibration measuring module in a single-point scanning mode, obtaining vibration response data of a single point according to a frequency response function peak value, and finally obtaining vibration mode frequencies of each order of each measuring point of the whole test area of the surface of the composite material structure;
s12, placing the vibration mode frequencies of each step of each measuring point of the composite material in a matrix of the corresponding position of the three-dimensional array according to the space coordinates to obtain the vibration mode frequencies of each step of the surface of the composite material structure under different frequencies in the whole test frequency band;
s13, transforming an original frequency-sweep excitation time domain signal into a frequency domain by utilizing fast Fourier transform to obtain a frequency-displacement amplitude signal of each measuring point, and putting the frequency-displacement amplitude signal into a matrix;
s14, comparing and analyzing the measuring point matrix of the composite material to be measured with the healthy composite material, and acquiring characteristic points through the frequency shift of each order of vibration mode and the change of the amplitude value, so as to determine the defect position.
8. The composite nondestructive testing system based on acousto-optic technology as set forth in claim 7, wherein the specific process of the step S2 is as follows:
s21, for each measuring point, performing fixed-frequency excitation on the composite material according to each order of vibration mode frequency control excitation module to obtain structural vibration mode data of each measuring point, namely frequency-displacement amplitude data;
s22, calculating the curvature of frequency-displacement amplitude data of each measuring point before and after the structural defect of the composite material by using a center difference method, namely the curvature of the mode shape;
s23, placing the mode shape curvature of each measuring point into a matrix, comparing the relativity of the measuring point matrix of the defect structure and the healthy structure of the composite material, and processing the mode shape curvature of the composite material by using two-dimensional continuous wavelet transformation to generate a wavelet coefficient to obtain a first matrix norm;
s24, obtaining a frequency response function of each measuring point under fixed frequency excitation, further obtaining the phase of each measuring point and the phase difference between each measuring point and initial excitation, putting the measuring points into a matrix, comparing the singularities of the measuring point matrix of the defect structure and the healthy structure of the composite material, processing the phase difference of the composite material by wavelet transformation, and generating a wavelet coefficient to obtain a second matrix norm;
s25, combining the two matrix norms so as to effectively identify the defect class number and class of the composite material.
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