CN116660378A - Composite material acoustic excitation terahertz nondestructive testing method - Google Patents

Composite material acoustic excitation terahertz nondestructive testing method Download PDF

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CN116660378A
CN116660378A CN202310646701.1A CN202310646701A CN116660378A CN 116660378 A CN116660378 A CN 116660378A CN 202310646701 A CN202310646701 A CN 202310646701A CN 116660378 A CN116660378 A CN 116660378A
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terahertz
composite material
acoustic excitation
domain spectrum
time
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任姣姣
顾健
张霁旸
杨文韬
崔宗宇
陈奇
薛竣文
李丽娟
张丹丹
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Zhongshan Research Institute Of Changchun University Of Technology
Changchun University of Science and Technology
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Zhongshan Research Institute Of Changchun University Of Technology
Changchun University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
    • G01N29/0654—Imaging
    • G01N29/069—Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
    • G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
    • G01N29/348—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with frequency characteristics, e.g. single frequency signals, chirp signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/46—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by spectral analysis, e.g. Fourier analysis or wavelet analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/023—Solids
    • G01N2291/0231—Composite or layered materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/0289—Internal structure, e.g. defects, grain size, texture

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  • Signal Processing (AREA)
  • Mathematical Physics (AREA)
  • Acoustics & Sound (AREA)
  • Toxicology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

The invention discloses a composite material acoustic excitation terahertz nondestructive testing method, which comprises the following steps: carrying a terahertz time-domain spectrum nondestructive testing system; detecting a composite material sample to be detected loaded by using a terahertz time-domain spectrum nondestructive detection system to obtain terahertz time-domain spectrum Data of silent excitation as reference Data ref The method comprises the steps of carrying out a first treatment on the surface of the Setting acoustic excitation signals with different frequencies; detecting composite material sample to be detected in different acoustic excitation fields by using a terahertz time-domain spectrum nondestructive detection system to obtain terahertz time-domain spectrum data after acoustic excitation loadingFor the reference Data ref Terahertz time-domain spectrum data after acoustic excitation is loadedRespectively imaging and then differential imaging to obtain differential imagesCalculating a difference imageAnd selecting a group of differential images with highest contrast from the group of differential images as a final detection result.

Description

Composite material acoustic excitation terahertz nondestructive testing method
Technical Field
The invention belongs to the field of terahertz nondestructive detection, and particularly relates to a composite material acoustic excitation terahertz nondestructive detection method, which is a nondestructive detection method for composite material defects by using terahertz waves in an acoustic excitation field.
Background
Various processing defects, such as bubbles, holes, interface debonding, microcracks, interlayer cracking, various inclusions and the like, are inevitably generated in the manufacturing process of the composite material sample, the existence of the defects can change the mechanical state of the whole structure, the strength of the material is reduced, the service life is shortened, the defect size in the composite material is different from a few micrometers to a few centimeters [ 10.1016/j.refrigerated.2019.01.013 ], and larger defects can be judged by human eyes, but smaller defects are difficult to find in macroscopic view. When the resonance frequency of the defect area in the composite material is equal to or close to a certain frequency of continuously-changed acoustic excitation, the defect area can generate frequency resonance phenomenon, forced vibration [ DOI:10.11973/wsjc202009016] is generated, the medium amplitude at the defect position is maximum under the resonance condition, the effect of amplifying the defect area is achieved, and at the moment, the data of the sample piece under the resonance condition is detected by adopting another detection mode, so that the internal defect of the sample piece can be better judged.
In the existing defect detection field of composite materials based on acoustic excitation, electronic speckle and laser speckle technologies are mostly adopted to capture vibration generated after the materials are subjected to acoustic excitation. When the measured object is acted by a certain load (force, heat and vibration), the defects of internal debonding, layering and the like can cause the surface of the object to generate larger deformation than normal conditions, and the tiny deformation can be displayed by speckle interference fringes and is expressed as the degree of the density of speckle interference fringe patterns, so that the aim of nondestructive testing is fulfilled. The method is limited by physical characteristics of laser speckle and electronic speckle (J. Vibration detection research based on electronic speckle shearing interference technology; university of vinca university of technology (natural science edition), 2011, 34 (03): 10-12+18.], cannot penetrate through a composite material, directly detects resonance conditions at a defect position, mainly adopts a time average method or a stroboscopic method to measure the difference of image light intensity before and after acoustic excitation, so that the finally identified defect edge is blurred, and cannot be realized more accurately according to the resonance frequency at the defect position of the composite material.
Terahertz waves are high-frequency electromagnetic waves with the frequency range of 0.1-10THz, and compared with the existing infrared speckle method, the terahertz waves have higher spatial resolution, and the detailed vibration conditions of various positions of an object in the vibration process can be measured, including the central vibration frequency, the second harmonic and the frequency distortion condition. The wavelength of terahertz waves is longer than that of optical perception. The adhesive layer between the composite material and the adhesive substrate can generate loss on the terahertz wave, and the scattering effect of the edge of the adhesive defect on the terahertz wave can influence the intensity distribution of the terahertz wave. The characteristics enable terahertz waves to penetrate through the surface of the material to detect fine mechanical vibration inside the object, and the stronger the vibration of the object is, the higher the generated energy field is, and the shape, the defect and the edge position inside the object can be obtained through terahertz signal analysis. The advantages enable the terahertz waves to have wide application prospects in the defect detection and vibration sensing fields.
Disclosure of Invention
The invention provides a composite material defect acoustic excitation terahertz nondestructive testing method, which is based on the continuous change of an acoustic excitation field, and adopts a reflection type terahertz nondestructive testing imaging technology to represent the vibration condition of the composite material defect under the corresponding resonance frequency, so that the identification effect of the micro defect in the composite material is improved, accurate positioning is carried out, and the accurate identification of the micro defect in the multilayer structure is realized.
The invention aims at realizing the following technical scheme:
a composite material acoustic excitation terahertz nondestructive testing method comprises the following steps:
step one, carrying a terahertz time-domain spectrum nondestructive testing system; the terahertz time-domain spectrum nondestructive detection system comprises a terahertz host, a sensor, a terahertz probe, an acoustic excitation generation module, a two-dimensional scanning module and a computer, wherein the terahertz probe is arranged on the two-dimensional scanning module;
step two, detecting a composite material sample to be detected loaded by silent excitation by using a terahertz time-domain spectrum nondestructive detection system to obtain terahertz time-domain spectrum Data of the silent excitation as reference Data ref ；
Step three, setting acoustic excitation signals with different frequencies;
step four, detecting composite material sample to be detected in different acoustic excitation fields by using a terahertz time-domain spectrum nondestructive detection system to obtain terahertz time-domain spectrum data after acoustic excitation loading
Step five, the reference Data obtained in the step two ref The loading sound excitation obtained in the fourth stepTerahertz time-domain spectrum data after excitationRespectively imaging and then differential imaging to obtain differential image +.>
Step six, calculating a difference imageAnd selecting a group of differential images with highest contrast from the group of differential images as a final detection result.
Further, in the terahertz time-domain spectrum nondestructive testing system, a terahertz host generates pumping light and detection light, and the pumping light and the detection light are transmitted into a terahertz probe; the terahertz detection signals acquired by the terahertz probe are transmitted into a computer through a sensor; the acoustic excitation generating module is used for adjusting the frequency of an acoustic excitation field to enable a defect area in the composite material sample to be detected to generate resonance phenomenon.
Further, the second step includes: the terahertz probe carried by the two-dimensional scanning module is used for detecting the composite material sample to be detected in a full-coverage two-dimensional point-by-point scanning mode, data are transmitted into a computer to obtain terahertz time-domain spectrum Data of the composite material sample to be detected, and the terahertz time-domain spectrum Data are used as reference Data ref 。
In the first step, the terahertz host generates the pump light and the probe light, and the pump light and the probe light are transmitted into the terahertz probe, the pump light in the terahertz probe is converted into terahertz waves, and the incident direction of the terahertz waves is perpendicular to the surface of the composite material sample to be measured.
Preferably, in the first step, the acquisition step sizes of the two-dimensional scanning module rows and columns are set to be m and n respectively; the acquisition step is 0.2mm.
Further, the third step includes: setting the generation adjustable frequency interval (f 1 -Δf,f 1 +Δf)，f 1 Approximating the resonance fundamental frequency of the defect area of the sample to be tested of the composite material, wherein deltaf is the modulation frequency range,f 1 Δf is the lower frequency limit, f 1 +Δf is the upper frequency limit; at the resonant fundamental frequency f 1 And (3) generating resonance in a defect area in the sample to be tested of the composite material under acoustic excitation.
Further, the defect resonance fundamental frequency f in the composite material sample to be measured 1 Calculated from the following formula:
wherein h is the defect thickness, a is the defect radius, ρ is the material density, E is the elastic modulus of the material, and u is the Poisson's ratio.
Further, the fourth step includes:
4.1 Opening the acoustic excitation generating module, and setting the frequency of the acoustic excitation signal to f 1 Δf and generates a frequency f 1 -a sine wave signal of Δf forming an acoustic excitation field surrounding the composite material sample to be measured;
4.2 Using a two-dimensional scanning module to carry a terahertz probe in a full-coverage two-dimensional point-by-point scanning mode, and collecting the data in f 1 Terahertz time-domain spectrum data of composite material sample to be tested in delta f acoustic excitation field
4.3 The sine wave frequency generated by the acoustic excitation generating module is improved, so that the frequency of an acoustic wave field surrounding a sample piece to be tested of the composite material is correspondingly increased, and the step 4.2) is adopted again to collect terahertz time-domain spectrum data of the sample piece
4.4 Repeating step 4.3) to generate f at the acoustic excitation generator 1 When sine wave with +Deltaf frequency is adopted, terahertz time-domain spectrum data of the last sample piece are acquiredK sets of data were obtained together.
Further, the fifth step includes:
5.1 For reference Data ref Terahertz time-domain spectrum data after acoustic excitation is loadedPerforming time-of-flight imaging to obtain a silently excited time-of-flight image IMG ref Image +.>t represents a detection order;
5.2 Using the following formula to image the flight time of terahertz data acquired under acoustic excitation of different frequenciesTime of flight IMG with terahertz data acquired under silent excitation ref Performing differential operation to obtain differential image +.>
Further, in the sixth step, all the differential images obtained in the fifth step are calculated according to the following formulaContrast C of (C):
wherein δ (i, j) = |i-j| is the gray value between adjacent pixels; ρ δ (i, j) is a pixel distribution probability that the gray scale difference between adjacent pixels is δ.
The invention has the following beneficial effects:
the invention provides a composite material acoustic excitation terahertz nondestructive testing method which can be applied to the field of terahertz nondestructive testing and is used for testing nonpolar materials such as foam, resin, rubber and the like. The composite material sample to be tested is positioned in an acoustic wave field with specific frequency in a mode of externally loading an acoustic excitation field to generate a resonance phenomenon, a material defect area can generate tiny off-plane displacement and cause change of an energy field in the material, terahertz nondestructive testing is carried out on the sample by combining a terahertz technology, nondestructive testing is carried out on the sample under the condition of combined excitation of terahertz and acoustic waves, and a novel detection mode is provided for the field of terahertz nondestructive testing.
Compared with detection technologies such as digital speckle, the method can obtain information of each layer in the sample to be detected of the composite material by analyzing terahertz echoes of different depths of the sample, has stronger detection capability on defects such as debonding and weak adhesion, can obtain information such as spatial position, size and shape of the defect by data analysis, and improves recognition capability of tiny defects in the composite material.
Drawings
FIG. 1 is a flow chart of a terahertz acoustic excitation defect detection method for a composite material according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a terahertz time-domain spectroscopy nondestructive testing system used in the method for detecting terahertz acoustic excitation defects of the composite material according to the embodiment of the invention;
FIG. 3 is a terahertz time-domain image;
FIG. 4 (a) is a terahertz time-of-flight differential image of a composite sample under acoustic excitation at a frequency of 30 Hz;
FIG. 4 (b) is a terahertz time-of-flight differential image of a composite sample under acoustic excitation at a frequency of 50 Hz;
FIG. 4 (c) is a terahertz time-of-flight differential image of a composite sample under acoustic excitation at a frequency of 70 Hz;
in the figure:
1-terahertz host computer; 2-a sensor; 3-terahertz probes; a 4-acoustic excitation generation module; 5-a two-dimensional scanning module; 6-a sample piece to be tested of the composite material; 7-computer.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent.
As shown in fig. 1, this embodiment takes a composite material to-be-detected sample 6 with preset defects as an example, and provides a method for detecting terahertz acoustic excitation defects of a composite material, which includes the following steps:
step one, carrying a terahertz time-domain spectrum nondestructive testing system:
as shown in fig. 2, the terahertz time-domain spectrum nondestructive detection system mainly comprises a terahertz host 1, a sensor 2, a terahertz probe 3, an acoustic excitation generation module 4, a two-dimensional scanning module 5 and a computer 7; the terahertz host 1 generates pumping light and detection light, the pumping light and the detection light are transmitted into the terahertz probe 3, and the terahertz probe 3 is arranged on the two-dimensional scanning module 5; the terahertz detection signal acquired by the terahertz probe 3 is transmitted into a computer 7 through a sensor 2; the acoustic excitation generating module 4 is used for adjusting the frequency of an acoustic excitation field to enable a defective area in the composite material sample piece 6 to be tested to generate resonance phenomenon.
Step two, detecting a composite material sample to be detected loaded by silent excitation by using a terahertz time-domain spectrum nondestructive detection system, and obtaining terahertz time-domain spectrum data of the silent excitation as reference data:
the terahertz host 1 generates pumping light and detection light, the pumping light and the detection light are transmitted into the terahertz probe 3, the pumping light in the terahertz probe 3 is converted into terahertz waves, the incidence direction of the terahertz waves is required to be perpendicular to the surface of the composite material sample piece 6 to be detected, namely, the terahertz waves are required to be normally incident to the surface of the composite material sample piece 6 to be detected; the two-dimensional scanning module 5 carries the terahertz probe 3 to detect the sample 6 to be tested of the composite material in a full-coverage two-dimensional point-by-point scanning mode; setting the row and column acquisition step length of the two-dimensional scanning module 5 to be m and n respectively, wherein the acquisition step length is 0.2mm; terahertz detection signals acquired by the terahertz probe 3 are transmitted into a computer 7 through the sensor 2 to obtain terahertz time-domain Data of a composite material sample piece 6 to be detected, and the terahertz time-domain Data is used as reference Data ref 。
Step three, setting acoustic excitation signals with different frequencies:
setting acoustic excitation generation module4 (f) 1 -Δf,f 1 +Δf)，f 1 Approximating the resonance fundamental frequency of the defect area of the sample 6 to be tested of the composite material, wherein Deltaf is the modulation frequency range, f 1 Δf is the lower frequency limit, f 1 +Δf is the upper frequency limit. Defective resonance fundamental frequency f in composite material sample 6 to be measured 1 As shown in formula (1), h is defect thickness, a is defect radius, ρ is material density, E is elastic modulus of the material, and u is poisson's ratio.
At the resonant fundamental frequency f 1 And the defective area in the sample 6 to be tested of the composite material generates resonance under the acoustic excitation.
Detecting composite material sample pieces to be detected in different acoustic excitation fields by using a terahertz time-domain spectrum nondestructive detection system, and obtaining terahertz time-domain spectrum data after acoustic excitation loading:
4.1 Opening the acoustic excitation generating module 4 to set the acoustic excitation signal frequency to f 1 Δf and generates a frequency f 1 -a sine wave signal of Δf forming an acoustic excitation field surrounding the composite material sample piece 6 to be measured.
4.2 Using the two-dimensional scanning module 5 to carry the terahertz probe 3 to collect the probe at f in a full-coverage two-dimensional point-by-point scanning mode 1 Terahertz time-domain spectrum data of composite material sample 6 to be tested in delta f acoustic excitation field
4.3 Increasing the sine wave frequency generated by the acoustic excitation generating module 4 to correspondingly increase the frequency of the acoustic wave field surrounding the sample 6 to be tested made of the composite material, and collecting terahertz time-domain spectrum data of the sample again by adopting the steps in 4.2)
4.4 With such a push, repeating the detection step in 4.3), in the case of acoustic excitationThe generator generates f 1 When sine wave with +Deltaf frequency is adopted, terahertz time-domain spectrum data of the last sample piece are acquiredK sets of data were obtained together.
Step five, imaging the reference data obtained in the step two and the terahertz time-domain spectrum data obtained in the step four after acoustic excitation loading respectively, and performing differential imaging to obtain a differential image:
5.1 For silence excitation terahertz detection Data ref Terahertz detection data of composite material sample 6 to be detected under acoustic wave fields of various frequenciesPerforming time-of-flight imaging to obtain images +.>And silent excitation time-of-flight image IMG ref T represents the detection order. When terahertz propagates in different media, reflection and transmission occur, which are reflected in the time domain as troughs and peaks, and the distance between different peaks or troughs, i.e. the time of flight T, is shown in fig. 3.
5.2 Using formula (2) to acquire the flight time images of terahertz data acquired under different frequency acoustic excitationTime of flight IMG with terahertz data acquired under silent excitation ref Performing differential operation to obtain differential image +.>As shown in fig. 4.
Step six, calculating a difference imageAnd selecting a group of differential images with highest contrast from the group of differential images, and taking the differential images as a final detection result.
Calculating all the difference images obtained in step 5.2 according to formula (3)Contrast C of (C):
wherein δ (i, j) = |i-j| is the gray value between adjacent pixels, ρ δ (i, j) is a pixel distribution probability that a gray scale difference between adjacent pixels is δ; and adopting a group of data with highest contrast as a final detection result.
In order to illustrate the effect of the invention, the method is adopted to detect the composite material containing preset defects, and terahertz flight time difference images of 30 Hz-70 Hz are obtained. The imaging contrast of the preset defect of the sample piece to be tested of the composite material in the 50Hz acoustic excitation field is the highest, and then 50Hz is the resonance fundamental frequency of the debonding defect area of the composite material, and the defect imaging effect is better than the imaging results at the rest frequencies at the frequency, so that the image is adopted as the final detection result.

Claims (10)

1. The composite material acoustic excitation terahertz nondestructive testing method is characterized by comprising the following steps of:
step one, carrying a terahertz time-domain spectrum nondestructive testing system; the terahertz time-domain spectrum nondestructive detection system comprises a terahertz host, a sensor, a terahertz probe, an acoustic excitation generation module, a two-dimensional scanning module and a computer, wherein the terahertz probe is arranged on the two-dimensional scanning module;
step two, detecting a composite material sample to be detected loaded by silent excitation by using a terahertz time-domain spectrum nondestructive detection system to obtain terahertz time-domain spectrum data of the silent excitation as a reference numberData of Data ref ；
Step three, setting acoustic excitation signals with different frequencies;
step four, detecting composite material sample to be detected in different acoustic excitation fields by using a terahertz time-domain spectrum nondestructive detection system to obtain terahertz time-domain spectrum data after acoustic excitation loading
Step five, the reference Data obtained in the step two ref And terahertz time-domain spectrum data obtained in the fourth step after acoustic excitation loadingRespectively imaging and then differential imaging to obtain differential image +.>
Step six, calculating a difference imageAnd selecting a group of differential images with highest contrast from the group of differential images as a final detection result.
2. The composite material acoustic excitation terahertz nondestructive testing method as set forth in claim 1, wherein the terahertz time-domain spectroscopy nondestructive testing system, a terahertz host generates pump light and probe light, and the pump light and probe light are transmitted into a terahertz probe; the terahertz detection signals acquired by the terahertz probe are transmitted into a computer through a sensor; the acoustic excitation generating module is used for adjusting the frequency of an acoustic excitation field to enable a defect area in the composite material sample to be detected to generate resonance phenomenon.
3. The method for acoustically exciting a terahertz non-destructive testing of a composite material according to claim 1, wherein the second step comprises: carrying too much with two-dimensional scanning moduleThe terahertz probe detects a composite material sample to be detected in a full-coverage two-dimensional point-by-point scanning mode, and Data is transmitted into a computer to obtain terahertz time-domain spectrum Data of the composite material sample to be detected as reference Data ref 。
4. The method for the terahertz nondestructive testing of the acoustic excitation of the composite material according to claim 3, wherein in the first step, pump light and detection light are generated by a terahertz host computer and are transmitted into a terahertz probe, the pump light in the terahertz probe is converted into terahertz waves, and the incident direction of the terahertz waves is perpendicular to the surface of a sample piece to be tested of the composite material.
5. The method for the acoustic excitation terahertz nondestructive testing of composite materials according to claim 3, wherein in the first step, acquisition step sizes of rows and columns of the two-dimensional scanning module are respectively m and n; the acquisition step is 0.2mm.
6. The method for acoustically exciting a terahertz non-destructive testing of a composite material according to claim 1, wherein the step three includes: setting the generation adjustable frequency interval (f 1 -Δf,f 1 +Δf)，f 1 Approximating the resonance fundamental frequency of the defect area of the sample to be tested of the composite material, wherein Deltaf is the modulation frequency range, f 1 Δf is the lower frequency limit, f 1 +Δf is the upper frequency limit; at the resonant fundamental frequency f 1 And (3) generating resonance in a defect area in the sample to be tested of the composite material under acoustic excitation.
7. The method for the nondestructive testing of the terahertz of the acoustic excitation of the composite material according to claim 6, wherein the defect resonance fundamental frequency f in the sample piece to be tested of the composite material 1 Calculated from the following formula:
wherein h is the defect thickness, a is the defect radius, ρ is the material density, E is the elastic modulus of the material, and u is the Poisson's ratio.
8. The method for acoustically exciting a terahertz non-destructive testing of a composite material according to claim 1, wherein the fourth step comprises:
4.1 Opening the acoustic excitation generating module, and setting the frequency of the acoustic excitation signal to f 1 Δf and generates a frequency f 1 -a sine wave signal of Δf forming an acoustic excitation field surrounding the composite material sample to be measured;
4.2 Using a two-dimensional scanning module to carry a terahertz probe in a full-coverage two-dimensional point-by-point scanning mode, and collecting the data in f 1 Terahertz time-domain spectrum data of composite material sample to be tested in delta f acoustic excitation field
4.3 The sine wave frequency generated by the acoustic excitation generating module is improved, so that the frequency of an acoustic wave field surrounding a sample piece to be tested of the composite material is correspondingly increased, and the step 4.2) is adopted again to collect terahertz time-domain spectrum data of the sample piece
4.4 Repeating step 4.3) to generate f at the acoustic excitation generator 1 When sine wave with +Deltaf frequency is adopted, terahertz time-domain spectrum data of the last sample piece are acquiredK sets of data were obtained together.
9. The method for acoustically exciting a terahertz non-destructive testing of a composite material according to claim 1, wherein the fifth step comprises:
5.1 For reference Data ref Terahertz time-domain spectrum data after acoustic excitation is loadedPerforming time-of-flight imaging to obtain a silently excited time-of-flight image IMG ref Image +.>t represents a detection order;
5.2 Using the following formula to image the flight time of terahertz data acquired under acoustic excitation of different frequenciesTime of flight IMG with terahertz data acquired under silent excitation ref Performing differential operation to obtain differential image +.>
10. The method for acoustically exciting a terahertz non-destructive testing of a composite material according to claim 1, wherein in step six, all differential images obtained in step five are calculated according to the following formulaContrast C of (C):
wherein δ (i, j) =i-j is a gray value between adjacent pixels; ρ δ (i, j) is a pixel distribution probability that the gray scale difference between adjacent pixels is δ.
CN202310646701.1A 2023-06-02 2023-06-02 Composite material acoustic excitation terahertz nondestructive testing method Pending CN116660378A (en)

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