阅读说明：本技术 基于同侧超声混频小波的板状结构疲劳裂缝定位系统及方法 (Plate-shaped structure fatigue crack positioning system and method based on same-side ultrasonic frequency mixing wavelet ) 是由 李一博 王晢 芮小博 綦磊 刘嘉玮 于 2019-08-26 设计创作，主要内容包括：本发明涉及一种基于同侧超声混频小波的板状结构疲劳裂缝定位系统,其特征在于：包括计算机、非线性超声仪、衰减器、低通滤波器、信号激励传感器、待测样件、双工器、高通滤波器及示波器。本发明还涉及一种基于同侧超声混频小波的板状结构疲劳裂缝定位方法,其特征在于：该方法的步骤为：1)系统搭建；2)激励信号调节；3)激励信号传输；4)信号处理；5)疲劳裂缝定位。本发明涉及科学合理,能够快速准确的现并确定板状结构中疲劳裂缝的位置,降低因过早对不含损伤结构的材料进行替换而造成的浪费,提高材料的利用率,同时也避免因未能及时发现损伤结构的存在而引发的安全事故,此外本发明对预测金属材料剩余寿命的研究具有很好的借鉴意义。(The invention relates to a plate-shaped structure fatigue crack positioning system based on ipsilateral ultrasonic frequency mixing wavelets, which is characterized in that: the device comprises a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, a signal excitation sensor, a sample to be tested, a duplexer, a high-pass filter and an oscilloscope. The invention also relates to a plate-shaped structure fatigue crack positioning method based on the same-side ultrasonic frequency mixing wavelet, which is characterized by comprising the following steps of: the method comprises the following steps: 1) building a system; 2) excitation signal conditioning; 3) excitation signal transmission; 4) signal processing; 5) and (5) positioning fatigue cracks. The method is scientific and reasonable, can quickly and accurately present and determine the position of the fatigue crack in the plate-shaped structure, reduces waste caused by replacing materials without damaged structures too early, improves the utilization rate of the materials, and simultaneously avoids safety accidents caused by failing to find the damaged structures in time.)

1. The utility model provides a plate-like structure fatigue crack positioning system based on homonymy supersound frequency mixing wavelet which characterized in that: comprises a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, a signal excitation sensor, a sample piece to be tested, a duplexer, a high-pass filter and an oscilloscope, the computer is connected with the nonlinear ultrasonic instrument which is provided with two paths of radio frequency output ends and one path of radio frequency input end, the two paths of radio frequency output ends are respectively connected with attenuators which are respectively connected with a low pass filter and a duplexer, two signal excitation sensors are arranged on one side of the sample piece to be detected in parallel, the low-pass filter is connected to one of the signal excitation sensors, the duplexer is connected to another signal excitation sensor, the other end of the duplexer is connected to the high-pass filter, the high-pass filter is connected to the radio frequency input end of the nonlinear ultrasonic instrument, and the nonlinear ultrasonic instrument is connected to the oscilloscope.

2. The method for positioning the fatigue crack of the plate-shaped structure based on the ipsilateral ultrasonic mixed wavelet as recited in claim 1, wherein: the positioning method comprises the following steps:

1) system construction: adhering a signal excitation sensor to two sides of a sample piece to be detected through a high vacuum silicone grease coupling agent, and connecting a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, the signal excitation sensor, the sample piece to be detected, a duplexer, a high-pass filter and an oscilloscope;

2) excitation signal conditioning: the computer generates an excitation signal and transmits the excitation signal to the nonlinear ultrasonic instrument, the excitation signal is respectively acted on a sample to be tested through two radio frequency output ends, and one radio frequency output emission frequency of the two radio frequency output ends of the nonlinear ultrasonic instrument is set as S₁₀And setting the frequency scanning range and scanning step length to make another path of radio frequency output the transmitting frequency S₁₁Applying different frequency excitations according to the range and step length, and recording the transmitting frequency S with the best mixing effect₁₁The signal is used as an excitation source of the other path of radio frequency output end, and the frequency of a target characteristic mixing signal to be extracted is S₁₀+S₁₁；

3) Excitation signal transmission: exciting the sensor by a signal applying a frequency S₁₀After the signal is propagated to the other end of the plate to be tested, continuously applying 20 continuous signals with the period frequency of S₁₁A short-period signal of (a);

4) signal processing: selecting proper wavelet basis functions and scale functions according to the principle of wavelet transformation, analyzing the acquired signals by using MATLAB software, fully utilizing the advantages of the wavelet transformation in time-frequency analysis, extracting characteristic frequencies and the corresponding time of the characteristic frequencies to realize the purpose of positioning defects;

5) positioning fatigue cracks: the fatigue crack position calculation formula is as follows:

X＝c_g·t_sum/2

wherein: c. C_gIs lamb wave group velocity;

x is the distance between the fatigue crack and the signal excitation sensor;

t_sumis the sum frequency signal return time.

3. The method for positioning the fatigue crack of the plate-shaped structure based on the ipsilateral ultrasonic mixed wavelet as recited in claim 2, wherein: the specific steps of signal processing in step 4) are as follows:

1) parameter optimization using MATLAB tool: the method comprises the steps of selecting five common wavelet basis functions of Harr wavelets, Daubechies wavelets, Mexican Hat wavelets, Meyer wavelets and Morlet wavelets, trying different scales a under different wavelet bases to process and analyze extracted simulation mixing signals by using MATLAB, obtaining the optimal wavelet basis and scale a capable of representing the extracted mixing signals, achieving the purpose of optimizing parameters through software, and further applying the parameters to engineering practice.

2) Performing time-frequency analysis on the mixing signals and completing feature extraction: based on the MATLAB wavelet basis function and the wavelet scale optimization parameter which are built and obtained by the nonlinear ultrasonic homonymy excitation positioning system, the frequency mixing signals extracted by the experiment are analyzed to obtain a time-frequency spectrum, the characteristic frequency amplitude and the time for the characteristic frequency to appear are read and recorded, and the subsequent comparison and verification work is facilitated.

Technical Field

The invention belongs to the field of metal nondestructive testing, and relates to a plate-shaped structure fatigue crack positioning system and method based on homonymy ultrasonic frequency mixing wavelets.

Background

The metal plate is widely applied to the fields of military affairs, industry, medical treatment, aerospace and the like, the material is inevitably influenced by external factors such as repeatedly applied load, temperature change, corrosion and the like in the using process, fatigue is further generated, and when the fatigue is accumulated to a certain degree, a macrocrack is developed, so that safety accidents and great economic loss are caused.

There are four major categories of currently mature methods for nondestructive testing of metals: ultrasonic flaw detection, which mainly detects metallurgical defects such as slag inclusion, holes, cracks and the like; x-ray flaw detection, detecting high-density inclusions in parts, such as defects of tungsten inclusion and the like; a fluorescent penetrant inspection method for detecting surface opening defects; eddy current inspection, the detection of surface and near-surface defects. These conventional non-destructive inspection methods are feasible and effective for conventional open cracks, but are ineffective for fatigue cracks caused by fatigue damage. With the development of lamb wave theory and nonlinear ultrasonic frequency mixing theory, a new idea is provided for the nondestructive testing of the fatigue crack of the metal plate structure.

According to a Dun clear team, the generation condition of secondary lamb waves in a plate structure is researched by a waveguide excitation mode analysis method on the basis of a second order perturbation theory, the result shows that the generation efficiency of the secondary harmonic waves is related to the constant of an interface, and the result lays a foundation for the application of the secondary harmonic waves of the lamb waves in the aspect of nondestructive testing of a thin plate structure. ChristohpPruell experimentally demonstrated that lamb wave nonlinearity has similar results in interaction with plastic materials as longitudinal and transverse waves, thus indicating that lamb wave higher harmonics can be used to evaluate plastic-driven material damage. Thereafter, Christoph Pruell continues to excite and receive lamb waves and second harmonics by using a pair of wedge-shaped sensors, and the results show that the acoustic nonlinearity measured based on the lamb waves is directly related to fatigue damage, so that an experimental program for representing the fatigue damage of the metal sheet by using the nonlinearity of the lamb waves is developed. H Xu et al studied the evaluation of lamb nonlinear effect characterization structural damage, and proposed a time-frequency analysis algorithm to process the acquired nonlinear lamb signals. When the XWan is simulated by using a finite element analysis method, the fact that the lamb wave generates second harmonic when acting with the micro-size cracks in the thin plate is found, and further, a structural damage detection method of applying the nonlinear lamb wave to the thin plate is provided. In the same year, Z Su extracts linear and nonlinear signals from almost invisible fatigue cracks of the metal plate, and proves the feasibility, accuracy and practicability of the lamb wave nonlinearity in micro-damage structure detection. In 2017, a team of the worship products completes the frequency mixing ultrasonic detection of the closed cracks by utilizing body waves, and makes a positive search for the evaluation of the fatigue cracks in the structure.

Through a search for a patent publication, no patent publication that is the same as the present patent application is found.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, and provides a method for carrying out frequency-frequency analysis on a frequency mixing signal and extracting characteristic frequency and corresponding time when the frequency mixing signal occurs, aiming at solving the problem that fatigue damage existing in a metal plate is difficult to identify and position. The method has the advantages that the position of the fatigue crack in the structure is discovered and determined as soon as possible, the waste caused by replacing the material without the damaged structure too early is reduced, the utilization rate of the material is improved, meanwhile, the safety accident caused by the fact that the damaged structure cannot be discovered in time is avoided, and in addition, the method has good reference significance for the research of predicting the residual life of the metal material.

The technical problem to be solved by the invention is realized by the following technical scheme:

the utility model provides a plate-like structure fatigue crack positioning system based on homonymy supersound frequency mixing wavelet which characterized in that: comprises a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, a signal excitation sensor, a sample piece to be tested, a duplexer, a high-pass filter and an oscilloscope, the computer is connected with the nonlinear ultrasonic instrument which is provided with two paths of radio frequency output ends and one path of radio frequency input end, the two paths of radio frequency output ends are respectively connected with attenuators which are respectively connected with a low pass filter and a duplexer, two signal excitation sensors are arranged on one side of the sample piece to be detected in parallel, the low-pass filter is connected to one of the signal excitation sensors, the duplexer is connected to another signal excitation sensor, the other end of the duplexer is connected to the high-pass filter, the high-pass filter is connected to the radio frequency input end of the nonlinear ultrasonic instrument, and the nonlinear ultrasonic instrument is connected to the oscilloscope.

A plate-shaped structure fatigue crack positioning method based on same-side ultrasonic frequency mixing wavelets is characterized by comprising the following steps: the positioning method comprises the following steps:

1) system construction: adhering a signal excitation sensor to two sides of a sample piece to be detected through a high vacuum silicone grease coupling agent, and connecting a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, the signal excitation sensor, the sample piece to be detected, a duplexer, a high-pass filter and an oscilloscope;

2) excitation signal conditioning: the computer generates an excitation signal and transmits the excitation signal to the nonlinear ultrasonic instrument, the excitation signal is respectively acted on a sample to be tested through two radio frequency output ends, and one radio frequency output emission frequency of the two radio frequency output ends of the nonlinear ultrasonic instrument is set as S₁₀And setting the frequency scanning range and scanning step length to make another path of radio frequency output the transmitting frequency S₁₁Applying different frequency excitations according to the range and step length, and recording the transmitting frequency S with the best mixing effect₁₁The signal is used as an excitation source of the other path of radio frequency output end, and the frequency of a target characteristic mixing signal to be extracted is S₁₀+S₁₁；

3) Excitation signal transmission: exciting the sensor by a signal applying a frequency S₁₀After the signal is propagated to the other end of the plate to be tested, continuously applying 20 continuous signals with the period frequency of S₁₁A short-period signal of (a);

4) signal processing: selecting proper wavelet basis functions and scale functions according to the principle of wavelet transformation, analyzing the acquired signals by using MATLAB software, fully utilizing the advantages of the wavelet transformation in time-frequency analysis, extracting characteristic frequencies and the corresponding time of the characteristic frequencies to realize the purpose of positioning defects;

5) positioning fatigue cracks: the fatigue crack position calculation formula is as follows:

X＝c_g·t_sum/2

wherein: c. C_gIs lamb wave group velocity;

x is the distance between the fatigue crack and the signal excitation sensor;

t_sumis the sum frequency signal return time.

Moreover, the specific steps of the signal processing in the step 4) are as follows:

1) parameter optimization using MATLAB tool: the method comprises the steps of selecting five common wavelet basis functions of Harr wavelets, Daubechies wavelets, Mexican hat wavelets, Meyer wavelets and Morlet wavelets, trying different scales a under different wavelet bases to process and analyze extracted simulation mixing signals by using MATLAB, obtaining the optimal wavelet basis and scale a capable of representing the extracted mixing signals, achieving the purpose of optimizing parameters through software, and further applying the parameters to engineering practice;

2) performing time-frequency analysis on the mixing signals and completing feature extraction: based on the MATLAB wavelet basis function and the wavelet scale optimization parameter which are built and obtained by the nonlinear ultrasonic homonymy excitation positioning system, the frequency mixing signals extracted by the experiment are analyzed to obtain a time-frequency spectrum, the characteristic frequency amplitude and the time for the characteristic frequency to appear are read and recorded, and the subsequent comparison and verification work is facilitated.

The invention has the advantages and beneficial effects that:

1. the invention builds a nonlinear ultrasonic same-side excitation experimental platform and completes further exploration of the application of a same-side frequency mixing effect in fatigue crack detection in a metal plate structure on the basis of a body wave frequency mixing theory.

2. The invention applies wavelet transform theory and MATLAB software to the field of nondestructive testing, and provides an algorithm for detecting and positioning fatigue cracks in metal plates from the time-frequency analysis angle.

3. The method is scientific and reasonable, can quickly and accurately present and determine the position of the fatigue crack in the plate-shaped structure, reduces waste caused by replacing materials without damaged structures too early, improves the utilization rate of the materials, and simultaneously avoids safety accidents caused by failing to find the damaged structures in time.

Drawings

FIG. 1 is an overall flow chart of the technical solution of the present invention;

FIG. 2 is a schematic diagram of the connection of the positioning system of the present invention.

Description of the reference numerals

The method comprises the following steps of 1-left side attenuator, 2-right side attenuator, 3-low pass filter, 4-upper end signal excitation sensor of a sample to be tested, 5-fatigue crack, 6-high pass filter, 7-lower end signal excitation sensor of the sample to be tested, 8-computer, 9-oscilloscope, 10-first radio frequency output end, 11-second radio frequency output end, 12-radio frequency input end, 13-nonlinear ultrasonic instrument, 14-sample to be tested and 15-duplexer.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.

A plate-shaped structure fatigue crack positioning system based on same-side ultrasonic frequency mixing wavelets is innovative in that: the device comprises a computer 8, a nonlinear ultrasonic instrument 13, attenuators, a low-pass filter 3, signal excitation sensors, a sample piece to be tested 14, a duplexer 15, a high-pass filter 6 and an oscilloscope 9, wherein the computer is connected to the nonlinear ultrasonic instrument which is provided with two radio frequency output ends and a radio frequency input end 12, the two radio frequency output ends comprise a first radio frequency output end 10 and a second radio frequency output end 11, the first radio frequency output end and the second radio frequency output end are respectively connected with a left attenuator 1 and a right attenuator 2, the left attenuator and the right attenuator are respectively connected to the low-pass filter and the duplexer, two signal excitation sensors are arranged on one side of the sample piece to be tested in parallel, the low-pass filter is connected to a signal excitation sensor 4 on the upper end of the sample piece to be tested, the duplexer is connected to a, the high-pass filter is connected to the radio frequency input end of the nonlinear ultrasonic instrument, and the nonlinear ultrasonic instrument is connected to the oscilloscope.

A plate-shaped structure fatigue crack positioning method based on same-side ultrasonic frequency mixing wavelets is characterized in that: the positioning method comprises the following steps:

1) system construction: adhering a signal excitation sensor to two sides of a sample piece to be detected through a high vacuum silicone grease coupling agent, and connecting a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, the signal excitation sensor, the sample piece to be detected, a duplexer, a high-pass filter and an oscilloscope;

2) excitation signal conditioning: generating exciting signal by computer and transmitting to the nonlinear ultrasonic instrument, acting on the sample to be measured via two RF output ends, setting one RF output emission frequency of the two RF output ends of the nonlinear ultrasonic instrument to S10, and setting frequency scanning range and scanning step length to make the other RF output emission frequency S₁₁Applying different frequency excitations according to the range and step length, and recording the transmitting frequency S with the best mixing effect₁₁The signal is used as an excitation source of the other path of radio frequency output end, and the frequency of a target characteristic mixing signal to be extracted is S₁₀+S₁₁；

3) Excitation signal transmission: exciting the sensor by a signal applying a frequency S₁₀After the signal is propagated to the other end of the plate to be tested, continuously applying 20 continuous signals with the period frequency of S₁₁A short-period signal of (a);

4) signal processing: selecting proper wavelet basis functions and scale functions according to the principle of wavelet transformation, analyzing the acquired signals by using MATLAB software, fully utilizing the advantages of the wavelet transformation in time-frequency analysis, extracting characteristic frequencies and the corresponding time of the characteristic frequencies to realize the purpose of positioning defects;

5) positioning fatigue cracks: the calculation formula of the fatigue crack 5 position is as follows:

X＝c_g·t_sum/2

wherein: c. C_gIs lamb wave group velocity;

x is the distance between the fatigue crack and the signal excitation sensor;

t_sumis the sum frequency signal return time.

The specific steps of signal processing in step 4) are as follows:

1) parameter optimization using MATLAB tool: the method comprises the steps of selecting five common wavelet basis functions of Harr wavelets, Daubechies wavelets, Mexican hat wavelets, Meyer wavelets and Morlet wavelets, trying different scales a under different wavelet bases to process and analyze extracted simulation mixing signals by using MATLAB, obtaining the optimal wavelet basis and scale capable of representing the extracted mixing signals, achieving the purpose of optimizing parameters through software, and further applying the parameters to engineering practice.

2) Performing time-frequency analysis on the mixing signals and completing feature extraction: based on the MATLAB wavelet basis function and the wavelet scale optimization parameter which are built and obtained by the nonlinear ultrasonic homonymy excitation positioning system, the frequency mixing signals extracted by the experiment are analyzed to obtain a time-frequency spectrum, the characteristic frequency amplitude and the time for the characteristic frequency to appear are read and recorded, and the subsequent comparison and verification work is facilitated.

Although the embodiments of the present invention and the accompanying drawings are disclosed for illustrative purposes, those skilled in the art will appreciate that: various substitutions, changes and modifications are possible without departing from the spirit and scope of the invention and the appended claims, and therefore the scope of the invention is not limited to the disclosure of the embodiments and the accompanying drawings.