CN112730613B - Composite board bonding layer performance degradation evaluation method - Google Patents
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Abstract
A composite board bonding layer performance degradation evaluation method belongs to the technical field of material testing. Arranging an ultrasonic excitation transducer capable of exciting an ultrasonic horizontal shear guided wave and a low-frequency ultrasonic receiving transducer capable of receiving the ultrasonic guided wave on the surface of the tested composite plate, and fixing a reasonable distance between the two transducers; modulating an ultrasonic pulse signal with a Hanning window of an ultrasonic pulse period number n by a signal generator and a power amplifier, inputting the ultrasonic pulse signal into an ultrasonic excitation transducer, performing low-pass filtering on the received signal by using a low-pass filter, and observing and extracting the processed signal by using an oscilloscope; performing time domain truncation with the width of tau on the filtered wave packet signals by using a computer, and performing fast Fourier transform to obtain the intensity of static lamb wave signals generated when the ultrasonic horizontal shear guided waves are propagated in the tested composite board; and comparing the detection results in the test intact test piece, and evaluating the performance degradation degree of the bonding layer of the tested composite board. High sensitivity, wide detection range and high efficiency.
Description
Technical Field
The invention belongs to the technical field of material testing, and particularly relates to a composite board bonding layer performance degradation evaluation method based on guided wave nonlinear static response, which utilizes nonlinear ultrasonic waves to perform nondestructive evaluation and characterization on material performance.
Background
Ultrasonic guided waves are a research hotspot which develops more rapidly in the field of ultrasonic nondestructive testing and material evaluation at present. Compared with the body wave (longitudinal wave or transverse wave) detection technology adopted in the traditional ultrasonic detection, the ultrasonic detection method has the following advantages: the ultrasonic wave in the waveguide medium (such as a thin plate, a circular tube and the like) has longer propagation distance, smaller attenuation, wider material area, higher detection efficiency and the like. In addition, nonlinear ultrasonic detection utilizes the nonlinear modulation effect of the material containing the microscopic defects on ultrasonic waves, can detect small defects by using ultrasonic waves with larger wavelengths, and has the advantage of higher detection sensitivity compared with linear ultrasonic detection, thereby realizing early microscopic damage detection and material performance evaluation of the material. However, the current use of guided ultrasound waves for nonlinear ultrasonic inspection of materials also has considerable difficulties. One of the difficulties is that, among the ultrasonic guided waves in the plate, most of the guided wave modes have dispersion characteristics: when the frequency of the fundamental wave changes, the phase velocity and the group velocity of the fundamental wave change; therefore, when using guided waves for non-destructive testing, more complex pre-and post-processing procedures are often required for ultrasonic signal excitation and signal analysis. The second difficulty is that most of the current nonlinear guided wave detection adopts a single ultrasonic excitation source, when fundamental waves are transmitted in a medium, second harmonic waves and even third harmonic waves are generated, and the micro-damage detection and performance evaluation can be performed on the material by using the generation intensity change of the second harmonic waves or the third harmonic waves; however, the method of performing nonlinear ultrasonic detection by using guided wave second harmonic generation often requires that the phase velocity of the second harmonic is equal to the phase velocity of the fundamental guided wave, i.e., a matching condition (or synchronization condition). Under such conditions, the number of guided wave mode pairs capable of realizing nonlinear guided wave nondestructive testing is not large, and some specific testing occasions cannot be met.
Currently, composite materials are increasingly used in the fields of transportation, civil engineering, aerospace, and the like. Aiming at the nondestructive detection problem of the performance degradation of the bonding layer of the composite material plate, the ultrasonic horizontal shear guided wave has certain detection advantages. On one hand, the horizontal shear guided wave is mainly in-plane displacement when propagating in the medium, so that the interference from the out-of-plane medium is less, and the signal-to-noise ratio of the obtained detection signal is relatively high; on the other hand, the nonlinear effect of the horizontal shear guided wave is sensitive to tiny defects in the adhesive layer, and the performance degradation evaluation of the adhesive layer is facilitated. However, based on the guided wave dispersion characteristics and the difficulty in mode selection, the detection mode of generating the second harmonic or the third harmonic by using the horizontal shear guided wave at present has limitations, and flexible and high-sensitivity detection and evaluation of the performance degradation of the composite board bonding layer are difficult to realize.
Disclosure of Invention
The invention aims to provide a composite board bonding layer performance degradation evaluation method based on guided wave nonlinear static response, which has high sensitivity, large detection range, high efficiency and flexibility, and aims to solve the problems of low efficiency of point-by-point ultrasonic detection, difficult ultrasonic guided wave mode selection and analysis and the like.
The invention comprises the following steps:
1) arranging an ultrasonic excitation transducer capable of exciting an ultrasonic horizontal shear guided wave and a low-frequency ultrasonic receiving transducer capable of receiving the ultrasonic guided wave on the surface of the tested composite board, and fixing a reasonable distance d between the ultrasonic excitation transducer and the low-frequency ultrasonic receiving transducer;
2) modulating an ultrasonic pulse signal with a Hanning window of an ultrasonic pulse period number n by a signal generator and a power amplifier, inputting the ultrasonic pulse signal into an ultrasonic excitation transducer, performing low-pass filtering on the signal received by the transducer by using a low-pass filter, and observing and extracting the processed signal by using an oscilloscope;
3) performing time domain truncation with the width of tau on the filtered wave packet signals by using a computer, and performing fast Fourier transform on the filtered wave packet signals to obtain the intensity of static lamb wave signals generated when the ultrasonic horizontal shear guided waves are propagated in the tested composite board;
4) and comparing the detection results in the test intact test piece, and evaluating the performance degradation degree of the bonding layer of the tested composite board.
In steps 1) and 2), the reasonable distance d and the number n of ultrasonic pulse periods satisfy the following relation:
wherein f is1For the centre frequency, f, of the ultrasonic excitation transducer2Is the center frequency of the low frequency ultrasound receiving transducer,
for the group velocity of the fundamental SH wave guide,
the group velocity of the S0 mode guided wave of the tested composite plate at zero frequency is shown.
In step 3), performing time domain truncation with a width τ on the filtered wave packet signal, where τ needs to satisfy:
wherein f is2The center frequency of the low frequency ultrasonic receiving transducer.
In the step 4), the specific steps of comparing the detection results in the test piece with the detection results in the test piece to evaluate the performance degradation degree of the bonding layer of the tested composite board are as follows: using intact composite board test pieces with the same specification, implementing the steps 1) to 3) to obtain a reference measurement result M0Then, howeverComparing the result M of the composite board with the performance degradation result M0，M/M0The larger the size, the more severe the degradation of the composite board bonding layer.
The basic principle of the invention is as follows: measuring the nonlinear static response intensity generated when the horizontal shear guided wave is propagated in the composite plate by using an ultrasonic transducer to represent the performance degradation degree of the bonding layer of the composite plate; the greater the nonlinear static response intensity generated by the test piece, the higher the performance degradation degree of the test piece. The invention belongs to nonlinear ultrasonic guided wave detection, but the horizontal shear guided wave without fundamental frequency meets the conditions of specific phase velocity and group velocity, and the detection sensitivity is higher.
Compared with the prior art, the invention has the following outstanding advantages:
1. when the ultrasonic horizontal shear guided wave propagates in the composite material plate, nonlinear static response of ultrasonic waves is caused due to microscopic defects (such as gaps, closed debonding and the like) in the bonding layer of the composite material plate, and the response intensity of the ultrasonic horizontal shear guided wave is in direct proportion to the degradation degree (or damage degree) of the material performance in the region where the ultrasonic guided wave is experienced; the invention is based on the positive correlation relationship between the nonlinear static response of the ultrasonic horizontal shear guided wave and the performance degradation of the composite board bonding layer, and utilizes the measurement of the static response signal of zero frequency generated by the horizontal shear guided wave in the weak nonlinear medium to detect and evaluate the material to be detected.
2. The invention combines the advantages of ultrasonic guided wave and nonlinear ultrasonic detection, improves the efficiency of ultrasonic detection and evaluation of the performance degradation of the bonding layer of the composite board, and simultaneously fully utilizes the characteristic that nonlinear response in ultrasonic detection is sensitive to the microstructure change and early damage of the material.
3. The invention obtains the nonlinear static response signal generated when the ultrasonic wave propagates in the tested test piece through a certain ultrasonic guided wave excitation and measurement means, and evaluates the performance degradation degree of the bonding layer of the tested composite board by comparing the result measured in a complete test piece.
4. The invention provides a specific measurement method for measuring nonlinear static response generated when horizontal shear guided waves propagate in a composite board, the nonlinear static response is sensitive to performance degradation of a bonding layer of the composite board, and a measurement system and a signal processing means of the method are relatively simple and effective.
5. The invention overcomes the problem of low efficiency of point-by-point ultrasonic detection, simultaneously overcomes the problem of difficult selection and analysis of ultrasonic guided wave modes, and can realize high-efficiency detection and evaluation of the performance degradation of the bonding layer of the composite board with higher sensitivity.
Drawings
FIG. 1 is a schematic diagram of a system and wiring for implementing the present invention.
FIG. 2 is a schematic diagram of a windowed, horizontally sheared guided-wave fundamental frequency signal excited in an excitation transducer of the present invention and a guided-wave signal received by a low frequency receiving transducer after passing through a composite slab with degraded performance of the bonding layer.
Detailed Description
The following examples will further illustrate the present invention with reference to the accompanying drawings.
Referring to fig. 1, a system for use in the ultrasonic excitation and measurement process of an embodiment of the present invention includes: the ultrasonic signal generator 1, the power amplifier 2, the ultrasonic excitation transducer 3, the low-frequency ultrasonic receiving transducer 4, the filter 5, the oscilloscope 6 and the computer 7. The ultrasonic signal generator 1 is used for exciting horizontal shear guided waves, the output end of the ultrasonic signal generator 1 is connected with the power amplifier 2, the output end of the power amplifier 2 is connected with the ultrasonic excitation transducer 3, the ultrasonic excitation transducer 3 and the low-frequency ultrasonic receiving transducer 4 are arranged on the composite board test piece P, the output end of the low-frequency ultrasonic receiving transducer 4 is connected with the filter 5, the filter 5 is used for performing low-pass filtering on signals received by the low-frequency ultrasonic receiving transducer 4, the output end of the filter 5 is connected with the oscilloscope 6, the oscilloscope 6 is used for observing and extracting the processed signals, and the oscilloscope 6 is connected with the computer 7.
The embodiment of the invention comprises the following steps:
1) an ultrasonic excitation transducer 3 capable of exciting horizontal shear guided waves is arranged on a composite board test piece P with degraded measured performance, and the center frequency of the ultrasonic excitation transducer is f1；
2) A position which is arranged on the tested composite board test piece P and is a certain distance d away from the ultrasonic excitation transducer 3 is provided with an energy sensing transducerLow frequency ultrasonic receiving transducer 4 vibrating in the direction of propagation of guided waves and having a center frequency f2；
3) Modulating a frequency f by means of an ultrasonic signal generator 1 and a power amplifier 21The ultrasonic pulse signal with the number of cycles of n and the Hanning window is input into the ultrasonic excitation transducer 3 set in the step 1);
4) performing low-pass filtering on the signal received by the low-frequency ultrasonic receiving transducer 4 by using a filter 5, and observing and extracting the processed signal by using an oscilloscope 6;
5) the filtered wave packet signal is subjected to a time domain truncation with width tau by using a computer 7, subjected to a fast Fourier transform, and extracted with frequency f2The spectral signal strength M;
6) using intact composite board test pieces with the same specification, carrying out the above steps 1) to 5) to obtain a reference measurement result M0Comparing the result M of the composite panel with the measured performance degradation to M0，M/M0The larger the size, the more the deterioration of the adhesive layer is.
In the detection process, in order to ensure the consistency of the measurement process of different composite board test pieces, the coupling state between the excitation and reception ultrasonic transducer and the test piece needs to be stable and consistent. Two ultrasound transducers need to be placed at the same fixed position on different specimens in the measurement. The ultrasonic signal generator used in the detection process is at least dual-channel, so that the excitation signal can be windowed. The number n of cycles of the excited ultrasonic pulse signal and the distance d between the exciting transducer and the receiving transducer should satisfy:
the width of the time domain truncated wave packet signal before Fourier transform is satisfied
Wherein f is1For the centre frequency, f, of the ultrasonic excitation transducer2As the center frequency of a low frequency ultrasonic receiving transducerThe ratio of the total weight of the particles,
for the group velocity of the fundamental SH wave guide,
the group velocity of the S0 mode guided wave at zero frequency of the composite plate is shown.
In order to verify that the measured signal is really a nonlinear static response signal generated when the fundamental frequency horizontal shear guided wave propagates in the composite board, the invention can be implemented to carry out measurement of different propagation distances for many times. If the wave packet group velocity of the measured signal is the group velocity of the S0 mode in the test piece at zero frequency, and the static response signal strength increases along with the increase of the propagation distance, the measured signal is confirmed to be the static response signal needing to be measured.
The schematic diagram of the windowed horizontal shear guided wave fundamental frequency signal excited in the excitation transducer and the guided wave signal received by the low-frequency receiving transducer after passing through the composite board with degraded performance of the bonding layer is shown in figure 2. If the received signal is directly Fourier transformed, the frequency spectrum is at frequency f2The signal intensity can be used as an index of a static response signal and is used for evaluating the performance degradation of the composite board adhesive layer.
The principle of the invention is given below: when ultrasonic waves propagate in a medium material with uneven microstructure, such as dislocation, slippage, holes, corrosion, cracks and the like, waveform distortion occurs, double-frequency second harmonic, triple-frequency third harmonic, zero-frequency static response signals and the like are generated, and the newly generated signals except the fundamental frequency ultrasonic signals are called nonlinear response of the ultrasonic waves. Generally, the more non-uniform the microstructure of the material (the more microscopic defects or the more severe the degradation of the properties), the more pronounced the nonlinear response of the ultrasound waves. The related mechanical properties of the composite board material can be inverted based on the ultrasonic signal after the interaction of the bonding layer and the guided wave when the ultrasonic horizontal shear guided wave is transmitted in the composite board.
The invention can utilize the advantage that the detection efficiency of the horizontal shear guided wave is higher than that of the ultrasonic bulk wave on one hand, and improve the capability of ultrasonic detection and evaluation of the generation of early micro-damage and performance degradation of the material by measuring the nonlinear response of the ultrasonic on the other hand. When the strength of the guided wave static response signal measured by the method is higher, the bonding layer of the composite board to be measured contains more microscopic damage, and the performance degradation is more serious. In addition, the method is based on the method for measuring the nonlinear static response generated by the horizontal shear guided wave in the composite board, is not limited by the problems of mode selection, phase velocity matching and the like of the guided wave, and is simple and effective in the measuring process.
Claims (2)
1. A composite board bonding layer performance degradation evaluation method is characterized by comprising the following steps:
1) arranging an ultrasonic excitation transducer capable of exciting an ultrasonic horizontal shear guided wave and a low-frequency ultrasonic receiving transducer capable of receiving the ultrasonic guided wave on the surface of the tested composite board, and fixing a reasonable distance d between the ultrasonic excitation transducer and the low-frequency ultrasonic receiving transducer;
2) modulating an ultrasonic pulse signal with a Hanning window of an ultrasonic pulse period number n by a signal generator and a power amplifier, inputting the ultrasonic pulse signal into an ultrasonic excitation transducer, performing low-pass filtering on the signal received by the transducer by using a low-pass filter, and observing and extracting the processed signal by using an oscilloscope;
in steps 1) and 2), the reasonable distance d and the number n of ultrasonic pulse periods satisfy the following relation:
wherein n is more than or equal to 6, f1For the centre frequency, f, of the ultrasonic excitation transducer2Is the center frequency of the low frequency ultrasound receiving transducer,
for the group velocity of the fundamental SH wave guide,
the group velocity of the S0 mode guided wave of the tested composite plate at zero frequency;
3) performing time domain truncation with the width of tau on the filtered wave packet signals by using a computer, and performing fast Fourier transform on the filtered wave packet signals to obtain the intensity of static lamb wave signals generated when the ultrasonic horizontal shear guided waves are propagated in the tested composite board;
and performing time domain truncation with the width of tau on the filtered wave packet signal, wherein tau needs to satisfy the following conditions:
wherein f is2Is the center frequency of the low-frequency ultrasonic receiving transducer;
4) and comparing the detection results in the test intact test piece, and evaluating the performance degradation degree of the bonding layer of the tested composite board.
2. The method for evaluating the performance degradation of the bonding layer of the composite board according to claim 1, wherein in the step 4), the specific steps of evaluating the performance degradation degree of the bonding layer of the tested composite board according to the detection result of the test piece in the comparative test are as follows: using intact composite board test pieces with the same specification, implementing the steps 1) to 3) to obtain a reference measurement result M0Then comparing the result M of the composite board with the measured performance degradation result M0，M/M0The larger the size, the more severe the degradation of the composite board bonding layer.
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