阅读说明：本技术 基于超声导波准静态分量的材料性能退化评估方法及装置 (Material performance degradation evaluation method and device based on ultrasonic guided wave quasi-static component ) 是由 李卫彬 肖俊 文放 于 2021-08-24 设计创作，主要内容包括：本发明公开了基于超声导波准静态分量的材料性能退化评估方法,包括：施加一个电脉冲信号,电脉冲信号经过逆压电效应转换形成作为激励的基频超声波信号；基频超声波信号在被检测材料一端的表面耦合进入被检测材料内传播,在另一端通过超低频的超声接收器接收准静态分量信号,将超声接收器接收的准静态分量信号进行傅里叶变换处理,提取频谱信号强度I；使用相同规格的完好的标准材料试件,实施上述步骤,获取信号基准参考强度I-(0),计算I与I-(0)的差值,即可评估被检测材料性能退化程度。本发明还公开了基于超声导波准静态分量的材料性能退化评估装置。本发明适用于高衰减材料,灵敏度高、检测范围广。(The invention discloses a material performance degradation evaluation method based on an ultrasonic guided wave quasi-static component, which comprises the following steps: applying an electric pulse signal, and converting the electric pulse signal through an inverse piezoelectric effect to form a fundamental frequency ultrasonic signal serving as excitation; coupling the fundamental frequency ultrasonic signal on the surface of one end of the detected material to enter the detected material for propagation, receiving the quasi-static component signal at the other end through an ultra-low frequency ultrasonic receiver, performing Fourier transform processing on the quasi-static component signal received by the ultrasonic receiver, and extracting the frequency spectrum signal intensity I; using intact standard material test pieces with the same specification, implementing the steps to obtain the signal reference strength I 0 Calculating I and I 0 The degree of the performance degradation of the detected material can be evaluated. The invention also discloses a material performance degradation evaluation device based on the ultrasonic guided wave quasi-static component. The invention is suitable for high attenuation materials, has high sensitivity and detection rangeWide application.)

1. The material performance degradation evaluation method based on the ultrasonic guided wave quasi-static component is characterized by comprising the following steps:

applying an electric pulse signal, converting the electric pulse signal by inverse piezoelectric effect to form a fundamental frequency ultrasonic signal as excitation, the frequency of the fundamental frequency ultrasonic signal is f_T；

The fundamental frequency ultrasonic wave signal is coupled into the detected material on the surface of one end of the detected material and is propagated, and the quasi-static component signal is received by an ultra-low frequency ultrasonic receiver at the other end, wherein the center frequency of the ultrasonic receiver is f_RWherein f is_RRatio f_TMore than one order of magnitude lower;

carrying out Fourier transform processing on quasi-static component signals received by an ultrasonic receiver, and extracting the frequency f_RThe spectral signal strength I;

using intact standard material test pieces with the same specification, implementing the steps to obtain the signal reference strength I₀Calculating I and I₀The performance degradation degree of the detected material can be evaluated, and the larger the difference is, the more serious the performance degradation degree of the detected material is.

2. The method for evaluating the degradation of the performance of a material based on the quasi-static component of the ultrasonic guided wave according to claim 1, wherein:

reinforcing the quasi-static component signal, and storing the processed signal; processing the stored signals to obtain time domain signals, performing Fourier transform on the time domain signals to obtain corresponding amplitude-frequency characteristic curves, and extracting the frequency f from the amplitude-frequency characteristic curves_RThe spectral signal strength I.

3. The method for evaluating the degradation of the performance of a material based on the quasi-static component of the ultrasonic guided wave according to claim 1, wherein: the method comprises the steps of utilizing a signal generator to generate an electric pulse signal modulated by a Hanning window, carrying out high-pass filtering, improving impedance matching through attenuation, and inputting the electric pulse signal into an ultrasonic excitation transducer, thereby generating a fundamental frequency ultrasonic signal serving as excitation.

4. The method for evaluating the degradation of the material performance based on the quasi-static component of the ultrasonic guided wave according to claim 1 or 2, wherein: the electric pulse signal is a high-frequency pulse signal with the frequency more than or equal to 10MHz, and the center frequency f of the ultrasonic receiver_R≤0.5MHz。

5. The method for evaluating the degradation of the performance of a material based on the quasi-static component of the ultrasonic guided wave according to claim 1, wherein: the fundamental frequency ultrasonic signal has a period number n and a group velocityThe group velocity of S0 mode guided wave when the frequency is zero in the structure of the detected material isThe distance between the position where the ultrasonic wave enters the surface of the detected material and the receiving position is l, the following formula is required to be satisfied:

6. the method for evaluating the degradation of the material performance based on the quasi-static component of the ultrasonic guided wave according to claim 2, wherein: the time-domain truncation width τ of the aligned static component signal needs to satisfy the following condition:

7. the method for evaluating the degradation of the material performance based on the quasi-static component of the ultrasonic guided wave according to claim 2, wherein: and acquiring the quasi-static component signals through an ultralow frequency transducer, guiding the quasi-static component signals into a computer, and filtering by using MATLAB software to obtain time domain signals.

8. Material performance degradation evaluation device based on supersound guided wave quasi-static component includes: the device comprises a material carrying platform, a signal generator, an ultrasonic excitation transducer, an ultrasonic receiver and a computing system;

the material carrying platform is used for placing the detected material; the signal generator is used for sending an electric pulse signal;

the ultrasonic excitation transducer and the ultrasonic receiver are respectively fixed at two ends of the surface of the detected material, the electric pulse signal is converted into an ultrasonic signal by the ultrasonic excitation transducer, the ultrasonic signal is coupled into the detected material to be transmitted to generate a quasi-static component signal, and the quasi-static component signal is received by the ultrasonic receiver at the other end; and introducing the quasi-static component signal into the computing system for computation and evaluation.

9. The ultrasonic guided wave quasi-static component-based material performance degradation evaluation device according to claim 8, further comprising a filter, an attenuator, a power amplifier, and an oscilloscope;

the filter receives and filters the electric pulse signal of the signal generator, the impedance matching is improved by the attenuator after the electric pulse signal is filtered, and the electric pulse signal is output to the ultrasonic excitation transducer, and the filter and the attenuator are split type or integrated type integrated equipment;

the power amplifier receives and amplifies the quasi-static component signal, the amplified quasi-static component signal is guided into the oscilloscope, the oscilloscope receives and stores the amplified quasi-static component signal, and the received signal is displayed on the oscilloscope screen and simultaneously guided into the computing system.

10. The ultrasonic guided wave quasi-static component-based material performance degradation evaluation device of claim 9, wherein the ultrasonic excitation transducer and the ultrasonic receiver each comprise a piezoelectric ceramic transducer for longitudinal vibration and an angularly adjustable wedge block located above the piezoelectric ceramic transducer, the wedge block comprises a piezoelectric wafer sliding block, a mounting wedge block, a balance block and a mounting piece, a piezoelectric wafer is arranged in the piezoelectric wafer sliding block, the surface of the mounting wedge block is in a circular arc shape, and the piezoelectric wafer sliding block is hinged at the center of the mounting wedge block through the mounting piece so that the piezoelectric wafer sliding block can slide along the surface of the mounting wedge block through the mounting piece; the balance block is fixed on the side edge of the mounting wedge block.

Technical Field

The invention relates to the field of structural material testing, in particular to a method and a device for performing nondestructive evaluation on material performance degradation degree by using an ultrasonic guided wave quasi-static component.

Background

At present, high attenuation materials such as particle reinforced composite materials, polymer materials and the like are widely applied to the fields of aerospace, building engineering, transportation and the like. In the production, manufacturing and engineering service processes of the material, due to the environment such as temperature, humidity, stress and the like, performance degradation of different degrees can be generated, wherein the early performance degradation accounts for more than 80% of the whole fatigue life, and in order to guarantee the safety and reliability of the material, a nondestructive detection technology which is effective and stable for the early performance degradation of the high-attenuation material needs to be developed.

The traditional ultrasonic guided wave detection technology is widely applied to the industry due to the long propagation distance and high efficiency. However, for the early performance degradation detection of a high attenuation material, the traditional ultrasonic guided wave detection needs to improve the detection sensitivity by increasing the frequency of ultrasonic waves, but the increase of the frequency inevitably leads to the increase of the attenuation of the ultrasonic waves in the material, and in addition, the signal-to-noise ratio requirement of a detection signal cannot be met because a detection object is originally a high attenuation material.

The nonlinear ultrasonic guided wave technology is one of research hotspots in the field of current nondestructive testing, and by utilizing the microstructure change in the material and the nonlinear effect generated by the ultrasonic guided wave, the early performance degradation of the material can be effectively evaluated. However, for the early performance degradation detection of the high attenuation material, the ultrasonic detection means based on the nonlinear physical characteristics such as the second order harmonic and the higher order harmonic still has certain disadvantages, on one hand, under the excitation of the ultrasonic signal with higher fundamental frequency, the attenuation of the ultrasonic wave in the high attenuation material is larger, and the attenuation of the second order harmonic and the higher order harmonic is more severe, which leads to the difficulty in receiving the effective signal; on the other hand, when the ultrasonic guided waves propagate in the medium, only when physical quantities such as second-order harmonics and higher-order harmonics satisfy a synchronism condition (harmonic phase velocity is equal to fundamental frequency phase velocity), the nonlinear characteristic quantities can have an accumulation effect, and the evaluation of the performance degradation of the material is suitable for utilizing the intensity change of the nonlinear characteristic quantities. However, the guided wave modes strictly satisfying this condition are not many, and it is difficult to achieve wide and effective detection.

For the problem of nondestructive detection of early performance degradation of a high-attenuation material, although a detection means based on nonlinear components such as ultrasonic guided wave second-order harmonic waves and high-order harmonic waves is effective to micro damage, the detection means is affected by material attenuation and limited by the phase velocity matching conditions, and flexible and efficient performance degradation detection of the high-attenuation material is difficult to realize.

Disclosure of Invention

The invention aims to provide a method and a device for evaluating the performance degradation of a material, which are used for representing the performance degradation degree of the material by measuring an ultrasonic guided wave quasi-static component, are suitable for high-attenuation materials, and have high sensitivity and wide detection range. In order to achieve the purpose, the invention adopts the following technical scheme:

the invention discloses a material performance degradation evaluation method based on an ultrasonic guided wave quasi-static component, which comprises the following steps:

applying an electric pulse signal, converting the electric pulse signal by inverse piezoelectric effect to form a fundamental frequency ultrasonic signal as excitation, the frequency of the fundamental frequency ultrasonic signal is f_T. The fundamental frequency ultrasonic wave signal is coupled on the surface of one end of the detected material through a high-pass filter and enters the detected material to be transmitted, and a quasi-static component signal is received at the other end of the detected material through an ultra-low frequency ultrasonic receiver, wherein the center frequency of the ultrasonic receiver is f_R，Wherein f is_RRatio f_TMore than one order of magnitude lower. Carrying out Fourier transform processing on quasi-static component signals received by an ultrasonic receiver, and extracting the frequency f_RThe spectral signal strength I. Using intact standard material test pieces with the same specification, implementing the steps to obtain the signal reference strength I₀Calculating I and I₀The performance degradation degree of the detected material can be evaluated, and the larger the difference is, the more serious the performance degradation degree of the detected material is.

Further, the quasi-static component signal is strengthened, and the processed signal is stored; processing the stored signals to obtain time domain signals, performing Fourier transform on the time domain signals to obtain corresponding amplitude-frequency characteristic curves, and extracting the frequency f from the amplitude-frequency characteristic curves_RThe spectral signal strength I.

Preferably, the electrical pulse signal modulated by the hanning window is generated by a signal generator, high-pass filtered and input to the ultrasonic excitation transducer after impedance matching is improved by attenuation, so as to generate a fundamental frequency ultrasonic signal as excitation.

Wherein the electric pulse signal is a high-frequency pulse signal with the frequency more than or equal to 10MHz, and the center frequency f of the ultrasonic receiver_R≤0.5MHz。

Wherein, the period number of the fundamental frequency ultrasonic signal is n, the group velocity isThe group velocity of S0 mode guided wave when the frequency is zero in the structure of the detected material isThe distance between the position where the ultrasonic wave enters the surface of the detected material and the receiving position is l, the following formula is required to be satisfied:

preferably, the time-domain truncation width τ of the aligned static component signal needs to satisfy the following condition:

preferably, the quasi-static component signal is introduced into a computer, and filtering processing is performed by using MATLAB software to obtain a time domain signal.

The invention also discloses a material performance degradation evaluation device based on the ultrasonic guided wave quasi-static component, which comprises the following components: the device comprises a material carrying platform, a signal generator, an ultrasonic excitation transducer, an ultrasonic receiver and a computing system. The material carrying platform is used for placing the detected material; the signal generator is used for sending an electric pulse signal; the ultrasonic excitation transducer and the ultrasonic receiver are respectively fixed at two ends of the surface of the detected material, the electric pulse signal is converted into an ultrasonic signal by the ultrasonic excitation transducer, the ultrasonic signal with high-pass filtering enters the detected material by coupling to be transmitted to generate a quasi-static component signal, and the quasi-static component signal is received by the ultrasonic receiver at the other end; and introducing the quasi-static component signal into the computing system for computation and evaluation.

Preferably, the device further comprises a filter, an attenuator, a power amplifier and an oscilloscope. The filter receives and filters the electric pulse signal of the signal generator, the impedance matching is improved by the attenuator after the electric pulse signal is filtered, the electric pulse signal is output to the ultrasonic excitation transducer, and the filter and the attenuator are split type or integrated type integrated equipment. The power amplifier receives and amplifies the quasi-static component signal, the amplified quasi-static component signal is guided into the oscilloscope, the oscilloscope receives and stores the amplified quasi-static component signal, and the received signal is displayed on the oscilloscope screen and simultaneously guided into the computing system.

The ultrasonic excitation transducer and the ultrasonic receiver respectively comprise a piezoelectric ceramic transducer which vibrates longitudinally and an angle-adjustable wedge block positioned above the piezoelectric ceramic transducer. The wedge block comprises a piezoelectric wafer sliding block, an installation wedge block, a balance block and an installation piece, wherein a piezoelectric wafer is arranged in the piezoelectric wafer sliding block, the surface of the installation wedge block is arc-shaped, and the piezoelectric wafer sliding block is hinged at the circle center of the installation wedge block through the installation piece so that the piezoelectric wafer sliding block can slide along the surface of the installation wedge block through the installation piece; the balance block is fixed on the side edge of the mounting wedge block.

Due to the adoption of the structure, the invention has the following beneficial effects:

1. the performance degradation degree of the material is represented by measuring the amplitude of the nonlinear quasi-static component generated when the high-frequency ultrasonic guided wave is transmitted in the material, and the larger the amplitude of the generated nonlinear quasi-static component is, the higher the performance degradation degree of the test piece is. The method belongs to nonlinear ultrasonic guided wave detection, but does not need guided waves of fundamental frequency to meet specific phase velocity conditions, overcomes the problems of serious attenuation and low signal-to-noise ratio of the traditional nonlinear ultrasonic in a high-attenuation material, expands the mode selection of ultrasonic guided waves, and can realize the evaluation of the early-stage performance degradation and micro-damage of the high-attenuation material structure with higher detection sensitivity.

2. The invention combines the advantages of ultrasonic nonlinear response signals and quasi-static response signals, not only utilizes the characteristic that the ultrasonic nonlinear response is sensitive to the material performance degradation, but also fully exerts the advantages that the quasi-static component carrier wave center frequency is close to zero and the attenuation is small.

3. The invention provides a specific measuring device for nonlinear static components generated by ultrasonic guided wave propagation in materials, and the device has the advantages of simple structure and strong applicability.

Drawings

FIG. 1 is a schematic diagram of the structure of the apparatus of the present invention.

Fig. 2 is a schematic view of the wedge structure.

FIG. 3 is a graph of time versus amplitude of the transmitted signal in an embodiment.

Fig. 4 is an amplitude-frequency characteristic of a transmission signal.

FIG. 5 is a graph of time versus amplitude of a received signal in an embodiment.

Fig. 6 shows the amplitude-frequency characteristic curve corresponding to fig. 5 obtained by fourier transform processing.

FIG. 7 is an electron micrograph of a standard acrylic plate without damage.

FIG. 8 is an electron micrograph of a tested acrylic plate with thermal damage.

Description of the main component symbols:

1: material stage, 2: signal generator, 3: filter attenuation integrator, 4: ultrasonic excitation transducer, 41/51: piezoelectric ceramic transducer, 42/52: wedge, 421: piezoelectric wafer slider, 422: mounting wedge block, 423: weight, 424: mounting piece, 5: ultrasonic receiver, 6: power amplifier, 7: an oscilloscope, 8: computing system, 9: the material is detected.

Detailed Description

In order to make the technical solutions of the present invention better understood by those skilled in the art, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1, the invention discloses a material performance degradation evaluation device based on an ultrasonic guided wave quasi-static component, which comprises: the device comprises a material carrying platform 1, a signal generator 2, a filtering attenuation integrator 3, an ultrasonic excitation transducer 4, an ultrasonic receiver 5, a power amplifier 6, an oscilloscope 7 and a computing system 8.

The material carrying platform 1 is used for placing the material 9 to be detected, and the material 9 to be detected in this embodiment is a high attenuation material, such as a particle-reinforced composite material, a polymer material, and the like.

The signal generator 2 is used for sending out electric pulse signals. Frequency f of pulse signal from signal generator 2_TGreater than or equal to 10 MHz.

The filtering attenuation integrator 3 receives the electric pulse signal of the signal generator 2, improves impedance matching through high-pass filtering, and outputs the electric pulse signal to the ultrasonic excitation transducer 4. The filtering attenuation integrator 3 integrates the functions of filtering and attenuating signals at the same time, and in other embodiments, a filter and an attenuator which are connected in a split manner can be adopted to perform the same function.

An ultrasonic excitation transducer 4 and an ultrasonic receiver 5 are fixed to both ends of the surface of the material to be detected, respectively. The ultrasonic excitation transducer 4 and the ultrasonic receiver 5 each comprise a longitudinally vibrating piezoceramic transducer 41/51 and an angularly adjustable wedge 42/52 located thereabove. As shown in fig. 2, each wedge 42/52 includes a piezoelectric wafer sliding block 421, a mounting wedge 422, a balance block 423, and a mounting member 424, wherein a piezoelectric wafer is disposed in the piezoelectric wafer sliding block 421, and a transducer signal line is disposed on the piezoelectric wafer. The surface of the mounting wedge 422 is arc-shaped, and the piezoelectric wafer sliding block 421 is hinged at the center of the mounting wedge 422 through the mounting piece 424, so that the piezoelectric wafer sliding block 421 can slide along the surface of the mounting wedge 422 through the mounting piece 424. The balance block 423 is fixed on the side of the mounting wedge 422, and the balance block 423 can be integrally formed with the mounting wedge 422, so as to play a role of balance and stability when the piezoelectric wafer sliding block 421 slides. When ultrasonic waves pass through the ultrasonic excitation transducer 4, according to Snell's law, electric pulse signals firstly enter from the wedge block 42, ultrasonic guided waves of a specific mode are excited through the piezoelectric ceramic transducer 41, and then the ultrasonic guided waves enter a detected material. When the ultrasonic receiver 5 receives the ultrasonic signal, the ultrasonic signal is converted into an electric signal by the piezoelectric ceramic transducer 51 and then emitted from the wedge 52.

When the excited ultrasonic guided wave enters the detected material 9 with degraded performance for transmission, nonlinear interaction occurs, so that a quasi-static component (nonlinear characteristic quantity) with the carrier center frequency close to zero is generated.

The quasi-static component signal is received at the other end by an ultrasonic receiver 5. The ultrasonic receiver 5 is an ultra-low frequency ultrasonic guided wave receiver with a center frequency f_R。f_RRatio f_TBy more than an order of magnitude, in order to receive the quasi-static component signal.

The power amplifier 6 receives and amplifies the quasi-static component signal sent from the ultrasonic receiver, the amplified quasi-static component signal is guided into the oscilloscope 7, the oscilloscope 7 receives and stores the amplified quasi-static component signal, and the received signal is displayed on a screen of the oscilloscope 7 and is guided into the computing system 8 at the same time. The computing system 8 is a computer having a computing and analyzing function.

The invention also discloses a material performance degradation evaluation method based on the ultrasonic guided wave quasi-static component, and the evaluation method is based on the principle that: when the high-energy ultrasonic guided wave is transmitted in the material, the high-energy ultrasonic guided wave interacts with some microscopic defects (such as fatigue, creep, old thermal degradation and the like) in the structure to cause quasi-static nonlinear response, the quasi-static component carrier frequency is close to zero, the attenuation is small, and the strength of the quasi-static nonlinear response is positively correlated with the degradation degree of the material performance in the ultrasonic guided wave transmission region. And acquiring a quasi-static nonlinear response signal generated by the action of the ultrasonic guided wave and the tested piece through a proper ultrasonic guided wave excitation and measurement device, and then comparing the detection result of the intact and nondestructive test piece under the same test condition to evaluate the performance degradation degree of the tested high attenuation material. The larger the amplitude of the generated nonlinear quasi-static component is, the higher the performance degradation degree of the test piece is.

The evaluation method of the present invention will be described in detail below with reference to the apparatus of the present invention.

The material performance degradation evaluation method based on the ultrasonic guided wave quasi-static component comprises the following steps:

s1, applying electric pulse signals

According to the priori knowledge that the intensity of the quasi-static component of the ultrasonic guided wave is in direct proportion to the square of the excitation ultrasonic frequency, a high-frequency pulse signal is selected as an excitation fundamental frequency ultrasonic signal. Generating a frequency f by means of a signal generator 2_TN, a Hanning window, where f_TIs more than or equal to 10 MHz. In this embodiment, the transmitted electric pulse signals are as shown in fig. 3 and 4.

S2, converting the electric pulse signal into an excited base frequency ultrasonic signal

The high attenuation material to be detected is fixed on the material carrier 1. An ultrasonic excitation transducer 4 and an ultrasonic receiver 5 are respectively fixed at two ends of the surface of the detected material 9, wherein the center frequency of the ultrasonic excitation transducer 4 is f_TThe center frequency of the ultrasonic receiver 5 is f_R。

The ultrasonic excitation transducer 4 is spaced from the ultrasonic receiver 5 by l.

The electric pulse signal is high-pass filtered and impedance matching improved by the filtering attenuation integrator 3 and then is input into the ultrasonic excitation transducer 4, and the electric pulse signal is converted into a fundamental frequency ultrasonic signal by the inverse piezoelectric effect of the ultrasonic excitation transducer 4.

In this embodiment, an acrylic plate with a thermal damage defect is selected as the material to be detected.

S3. Signal transmission and reception

The fundamental frequency ultrasonic wave signal is coupled into the detected material to propagate on the surface of one end of the detected material 9, and the quasi-static component signal is received by the ultra-low frequency ultrasonic receiver 5 at the other end.

After entering the material to be detected 9, the fundamental frequency ultrasonic signal interacts with the material in a nonlinear way, so that a quasi-static component (nonlinear characteristic quantity) with the carrier center frequency close to zero is generated, and is received by the ultra-low frequency ultrasonic receiver 5 at the other end. The center frequency of the ultrasonic receiver 5 is f_R。

The ultra low frequency ultrasonic receiver 5 is chosen to facilitate reception of quasi-static components with carrier frequencies close to zero. Requirement f_RRatio f_TLower by more than one order of magnitude, e.g.：f_TFor a 10MHz signal, then f is required_RBelow 1 MHZ. Theoretically, it is better to set the reception carrier frequency lower, and f is preferably set for better reception_RLess than or equal to 0.5 MHz. The quasi-static component generated by the 10MHz excitation signal can be received by arranging a 0.5MHz low-frequency ultrasonic receiver 5 in a laboratory.

f_T、f_RThe signal modulation conforms to the following equation (1):

wherein the group velocity of the fundamental frequency ultrasonic wave isThe group velocity of S0 mode guided wave when the frequency is zero in the structure of the detected material isThe signal modulation conforms to the formula 1, quasi-static components can be propagated along with the main wave packet all the time, energy loss is reduced, and the signal-to-noise ratio of the obtained result is optimal.

S4, extracting signal intensity

The quasi-static component signal is strengthened by a power amplifier 6, and the processed signal is observed and stored by an oscilloscope 7. The signal pattern received after passing through the acrylic plate in this example is shown by the gray line in fig. 5.

The received signal is led into the computing system 8, and the MATLAB software is used to perform fast fourier transform processing on the filtered and stored time domain signal to obtain a corresponding amplitude-frequency characteristic curve, as shown by the gray line in fig. 6. Extracting the frequency f from the_RI.e. the amplitude of the signal strength corresponding to 0.5MHZ in fig. 6 is about 2.8.

The time-domain truncation width τ of the aligned static component signal needs to satisfy the following equation (2):

s5, comparing with a standard material test piece

Using intact standard material test pieces with the same specification, implementing the steps to obtain the signal reference strength I₀. In this embodiment, the nondestructive acrylic plate is used as a standard material test piece, and is observed through an electron microscope to obtain fig. 7, and it can be seen from the figure that the surface of the standard acrylic plate is relatively smooth under the electron microscope without damage defects. The diagram of the quasi-static component signal received by the same excitation signal through a standard acrylic plate is shown as a black line in fig. 5. The amplitude-frequency characteristic curve obtained by the Fourier transform processing is extracted as shown by the black line in FIG. 6, and the frequency f is extracted from the curve_RReference intensity of₀(i.e., amplitude), i.e., corresponding to a signal strength amplitude of about 2.3 at 0.5MHZ in fig. 6.

Calculating I and I₀I.e. Δ I ═ I-I₀And evaluating the performance degradation degree of the detected material. In this example,. DELTA.I.2.8-2.3.0.5. The detected acrylic plate is verified and observed through an electron microscope to obtain a graph 8, and as is obvious from the graph 8, the surface of the detected acrylic plate has a plurality of defect traces.

The larger the difference Δ I, the more serious the degree of deterioration (damage) of the performance of the material to be tested. According to the evaluation method, the performance degradation degree of the detected materials with different damages can be rapidly compared.

In conclusion, the invention uses the ultralow frequency ultrasonic receiver to measure the nonlinear quasi-static component amplitude generated when the high frequency ultrasonic guided wave propagates in the high attenuation material, so as to represent the performance degradation degree of the high attenuation material. The method belongs to nonlinear ultrasonic guided wave detection, has high detection sensitivity and strong practicability, and is suitable for popularization and application.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.