Group velocity mismatch based closed defect referenceless positioning method and system

Abstract

The application relates to a group velocity mismatch-based closed defect reference-free positioning method and system, which comprises the following steps: acquiring attribute information of a sample to be tested, determining ultrasonic excitation parameters based on the attribute information; generating an ultrasonic signal based on the ultrasonic excitation parameters, and propagating into one end of the sample to be tested; receiving a receiving signal generated at the other end of the sample to be tested; performing time-frequency analysis on the receiving signal to determine whether a fundamental frequency signal and a double frequency signal exist simultaneously, if yes, extracting peak times of the fundamental frequency signal and the double frequency signal, and if no, determining that there is no closed defect; and determining the position of the closed defect in the sample to be tested based on the peak times and a group velocity curve of the sample to be tested. Compared with the prior art, the application can reference-free identify and position the closed defect by using the contact acoustic nonlinear effect of the closed defect without damaging the sample to be tested, and has the advantages of fast detection, high defect positioning accuracy and the like.

Description

Technical Field

[0001] This invention relates to the field of structural health monitoring, and in particular to a non-reference-based method and system for locating closed defects based on group velocity mismatch. Background Technology

[0002] Ultrasonic testing technology has been widely used in industrial non-destructive testing and structural health monitoring due to its ability to rapidly and extensively inspect plate-like structures non-destructively. Currently, traditional ultrasonic testing techniques primarily rely on linear characteristics (scattering, reflection, etc.) to detect macroscopic defects. Since the interaction between closed defects and ultrasonic waves exhibits less pronounced linear characteristics, closed defects within materials are more difficult to identify by ultrasonic waves. Although closed defects are difficult to characterize using traditional ultrasonic methods, the nonlinear contact acoustic effect generated during the interaction between closed defects and ultrasonic waves produces spectral components different from the incident wave frequency, such as higher harmonics and mixing components. Therefore, the nonlinear contact acoustic characteristics of the interaction between ultrasonic waves and closed defects represent a promising supplementary method for detecting closed defects.

[0003] Current technologies for ultrasonic defect localization mainly include baseline localization methods, multi-element transducer array methods, and phased array technology. Baseline localization identifies and locates defects by comparing the ultrasonic signal obtained in the current state with the signal obtained in the original state. However, constantly changing environmental and operating conditions, such as temperature variations and noise levels, can significantly affect baseline-based identification, thus impacting the accuracy of the localization technology and even leading to false alarms. Multi-element transducer array and phased array technologies require the excitation and reception of multiple elements at both the excitation and reception ends, placing high demands on equipment. Furthermore, the large volume of received data and the complex and time-consuming data processing make them difficult to apply to practical rapid on-site inspections. Therefore, existing localization methods, to some extent, limit the practical application of ultrasonic defect detection technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art by providing a referenceless positioning method and system for closed defects based on group velocity mismatch.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A referenceless method for locating closed defects based on group velocity mismatch includes the following steps:

[0007] Obtain the attribute information of the sample to be tested, and determine the ultrasonic excitation parameters based on the attribute information;

[0008] An ultrasonic signal is generated based on the ultrasonic excitation parameters and propagated into one end of the test sample.

[0009] Receive the received signal generated at the other end of the test sample;

[0010] The received signal is subjected to time-frequency analysis to determine whether a fundamental frequency signal and a second harmonic signal exist simultaneously. If so, the peak times of the fundamental frequency signal and the second harmonic signal are extracted. If not, it is determined that there is no closure defect.

[0011] The location of the closure defect in the test sample is determined based on the peak time and the group velocity curve of the test sample.

[0012] Furthermore, the attribute information includes material parameters and geometric dimensions.

[0013] Furthermore, the ultrasonic excitation parameters include ultrasonic excitation frequency, excitation mode, and excitation angle.

[0014] Furthermore, the principle for selecting the ultrasonic excitation frequency is determined as follows: the fundamental frequency signal of the excitation and the second harmonic signal generated by the closed defect have unequal group velocities.

[0015] Furthermore, the excitation angle conforms to Snell's law.

[0016] Furthermore, determining the location of the closure defect in the test sample based on the peak time and the group velocity curve of the test sample specifically involves:

[0017] The location of the closed defect is determined by the distance from the signal receiving position to the closed defect. The formula for calculating the distance from the closed defect to the signal receiving position is as follows:

[0018]

[0019] Among them, t f and t 2f c represents the peak time of the fundamental frequency signal and the second harmonic signal generated by the closure defect. g (f) represents the group velocity that excites the fundamental frequency, c g (2f) is the group velocity that generates a second harmonic from a closed defect.

[0020] Furthermore, the closure defect includes closed cracks, closed segments of microcracks, closed interfaces of adhesive structures, or weak adhesion.

[0021] Furthermore, the test sample has a plate-like structure.

[0022] The present invention also provides a referenceless positioning system for closed defects based on group velocity mismatch, including a high-energy ultrasonic module, an excitation transducer, a wedge block, a receiving transducer and a display processing module. The excitation transducer and the receiving transducer are respectively placed at both ends of the test sample via the wedge block. The high-energy ultrasonic module is connected to the excitation transducer and the display processing module is connected to the receiving transducer.

[0023] The high-energy ultrasonic module generates a sinusoidal signal, which excites the transducer to generate an ultrasonic signal that propagates into one end of the test sample based on the sinusoidal signal. The receiving transducer collects the received signal at the other end of the test sample. The display processing module performs time-frequency analysis on the received signal to determine whether a fundamental frequency signal and a second harmonic signal exist simultaneously. If so, the peak times of the fundamental frequency signal and the second harmonic signal are extracted. If not, it is determined that there is no closure defect. Based on the peak times and the group velocity curve of the test sample, the location of the closure defect in the test sample is determined.

[0024] Furthermore, the inclined block is an acrylic inclined block.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Based on the principle of nonlinear contact sound of closed defects, this invention achieves referenceless identification and detection of closed defects by extracting and judging the second harmonic signal in the received signal and using group velocity. It overcomes the shortcomings of traditional ultrasound in being insensitive to closed defects, avoids complex and large amounts of data, is more suitable for rapid detection under actual working conditions, and can realize the detection of early degradation of plate-like structures.

[0027] 2. This invention uses a non-referenced positioning method based on group velocity mismatch to locate closed defects, which can eliminate noise interference and improve the accuracy of closed defect positioning.

[0028] 3. This invention can complete the detection based on a common ultrasonic transducer with one transmitter and one receiver, which reduces the detection cost and avoids the complex and large amount of data, enabling rapid detection under actual working conditions. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the method of the present invention.

[0030] Figure 2 This is a system schematic diagram of the present invention;

[0031] Figure 3 This is a schematic diagram showing the relative position of the closed defect and the transducer.

[0032] Figure 4 The time-domain signal diagram for nonlinear detection of contact sound;

[0033] Figure 5 This is a time-frequency domain characteristic map of nonlinear detection of contact sound. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] like Figure 1 As shown, this embodiment provides a referenceless method for locating closed defects based on group velocity mismatch, including the following steps:

[0036] S1. Obtain the attribute information of the test sample, and determine the ultrasonic excitation parameters based on the attribute information. Specifically, the attribute information includes the material parameters and geometric dimensions of the test sample, and the determined ultrasonic excitation parameters include the ultrasonic excitation frequency, excitation mode, and excitation angle.

[0037] The principle for selecting the ultrasonic excitation frequency is as follows: the fundamental frequency signal of the excitation and the second harmonic signal generated by the closed defect have unequal group velocities, i.e., c g (f)≠c g (2f), where f is the excitation frequency and c g (f) represents the group velocity that excites the fundamental frequency, c g (2f) is the group velocity that generates a second harmonic from a closed defect.

[0038] The excitation angle can be generated by a wedge, and the determined excitation angle conforms to Snell's law:

[0039]

[0040] Among them, c wedge-L Let c be the longitudinal wave velocity of the inclined block. p The phase velocity of the selected excitation mode under the current detection environment.

[0041] S2. Based on the ultrasonic excitation parameters, a positioning system is built to perform ultrasonic testing on the test sample. Specifically, an ultrasonic signal is generated and propagated into one end of the test sample to generate an ultrasonic signal of selected frequency and mode as a detection signal. The detection signal interacts with the closed defect to generate a nonlinear contact sound effect, and the received signal generated at the other end of the test sample is received.

[0042] S3. Perform time-frequency analysis on the received signal to determine whether a fundamental frequency signal and a second harmonic signal exist simultaneously. If yes, proceed to step S4; otherwise, determine that there is no closure defect.

[0043] S4. Extract the peak times of the fundamental frequency signal and the second harmonic signal, and determine the location of the closure defect in the test sample based on the peak times and the group velocity curve of the test sample. Specifically, a receiving transducer is used to collect the received signal, and the arrival times of the fundamental frequency signal and the second harmonic signal at the receiving transducer are used as the corresponding peak times of the fundamental frequency signal and the second harmonic signal.

[0044] The aforementioned one-dimensional, reference-free positioning principle based on the mismatch between the group velocities of the fundamental frequency and the second harmonic is as follows: The incident wave of the test sample interacts with the closed defect along its propagation path, generating a second harmonic signal. Then, the fundamental frequency signal and the second harmonic signal propagate forward and reach the receiving transducer, respectively. When the group velocities of the fundamental frequency and the second harmonic signal are different, their arrival times at the receiving transducer are also different. The arrival times of the incident fundamental frequency signal and the second harmonic signal generated by the closed defect at the receiving transducer are t0 and t1, respectively. f and t 2f The values ​​were obtained at frequencies f and 2f in the time-frequency domain, respectively.

[0045] The time it takes for the incident fundamental frequency signal to travel from the excitation transducer to the closed defect and then to the receiving transducer is:

[0046]

[0047] Where, d a-c To excite the distance from the transducer to the closed defect, d c-d The distance from the closed defect to the receiving transducer;

[0048] The time it takes for the second harmonic signal generated by the closed defect to reach the receiving transducer is

[0049]

[0050] The location of the closed defect on the propagation path can be determined from the two time differences mentioned above:

[0051]

[0052] The above method is applied to plate-like test samples, and applicable closure defects include, but are not limited to, closed cracks, closed segments of microcracks, interface closures of bonded structures, or weak adhesions. This method can identify and locate closure defects in plate-like structures without damaging the test sample, utilizing the nonlinear contact acoustic effect of the closure defects.

[0053] The above method can be achieved through, for example Figure 2The illustrated closed defect localization system includes a high-energy ultrasonic module, an excitation transducer 3, a first inclined block 4, a second inclined block 6, a receiving transducer 7, and a display and processing module. The excitation transducer 3 is placed at one end of the test sample via the first inclined block 4, and the receiving transducer 7 is placed at the other end of the test sample via the second inclined block 6. The high-energy ultrasonic module is connected to the excitation transducer 3, and the display and processing module is connected to the receiving transducer 7. The high-energy ultrasonic module generates a sinusoidal signal, and the excitation transducer 3 generates an ultrasonic signal that propagates into one end of the test sample based on the sinusoidal signal. The receiving transducer 7 acquires the received signal at the other end of the test sample. The display and processing module performs time-frequency analysis on the received signal to determine whether a fundamental frequency signal and a second harmonic signal are present simultaneously. If so, the peak times of the fundamental frequency signal and the second harmonic signal are extracted; otherwise, it is determined that there is no closed defect. The location of the closed defect in the test sample is determined based on the peak times and the group velocity curve of the test sample.

[0054] Specifically, the high-energy ultrasound module includes a signal generator 1 and a power amplifier 2. The display and processing module includes an oscilloscope 8 and a computer 9. The oscilloscope 8 is used to display and store the received signals, and the computer 9 is used to analyze the received signals to achieve reference-free localization of closed defects.

[0055] In a specific implementation, the first inclined block 4 and the second inclined block 6 are made of plexiglass.

[0056] In this embodiment, the test sample is 7075 aluminum alloy with the following material parameters: density 2773.11 kg / m³. 3 The metal plate has a Young's modulus of 73.1 GPa, a Poisson's ratio of 0.34, and geometric dimensions of 200 mm (length), 45 mm (width), and 2 mm (thickness). Based on the material parameters and geometric dimensions of the metal plate under test, the selected excitation frequency is 600 kHz, the excitation mode is S0 mode, and the excitation angle is 31°.

[0057] Based on the excitation frequency, a narrowband transducer with a center frequency of 600KHz was selected as the excitation transducer, and a narrowband transducer with a frequency of 1MHz was selected as the receiving transducer.

[0058] The excitation and receiving transducers are installed on both sides of the sample to be tested, such as... Figure 3 As shown, a 600kHz sine wave with a period of 10 is generated by a signal generator. After being amplified by a power amplifier, a voltage signal is applied to the excitation transducer to generate an ultrasonic signal. This ultrasonic signal is transmitted to the test sample through a 31° angled plexiglass bevel to generate a selected mode ultrasonic signal as a detection signal. The detection signal interacts with the closed defect to produce a nonlinear contact sound effect. The detection signal is acquired by a receiving transducer and displayed and stored on an oscilloscope. Figure 4The image shows the time-domain signal received by the receiving transducer. The time-frequency characteristics of the received signal are obtained by performing a short-time Fourier transform on the time-domain signal, as shown below. Figure 5 As shown.

[0059] analyze Figure 5 The time-frequency signal has a second harmonic with a frequency of 1.2MHz, indicating that there is a closed defect in the test sample along the propagation path.

[0060] extract Figure 5 The time intervals of the fundamental frequency and second harmonic frequency in a time-frequency signal: t f =2.78e -5 s,t 2f =3.67e -5 s. The group velocities of the S0 mode at 600 kHz and 1.2 MHz were obtained from the group velocity curves of 7075 aluminum alloy plates, respectively: c g (600kHz)=5246m / s, c g (1.2MHz) = 1758m / s.

[0061] The location of the closed defect in the specimen without a reference is determined based on the time difference between the fundamental frequency and the second harmonic frequency signals: d c-d =23.53mm. The actual distance from the closed defect to the receiving transducer is 20mm. The absolute error of the positioning by this method is 3.53mm, and the relative error is 17.6%.

[0062] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A group velocity mismatch based closed defect referenceless positioning method, characterized in that, The method comprises the following steps: acquiring attribute information of a sample to be tested, determining ultrasonic excitation parameters based on the attribute information, the ultrasonic excitation parameters comprising an ultrasonic excitation frequency, an excitation mode and an excitation angle; generating an ultrasonic signal based on the ultrasonic excitation parameters, the ultrasonic signal propagating into one end of the sample to be tested; receiving a receiving signal generated at the other end of the sample to be tested; performing time-frequency analysis on the receiving signal to determine whether a fundamental frequency signal and a double frequency signal exist simultaneously, if so, extracting peak times of the fundamental frequency signal and the double frequency signal, if not, determining that there is no closed defect; determining a position of the closed defect in the sample to be tested based on the peak times and a group velocity curve of the sample to be tested; the selection principle of the ultrasonic excitation frequency is that the group velocity of the excited fundamental frequency signal is not equal to that of the double frequency signal generated by the closed defect; the determination of the position of the closed defect in the sample to be tested based on the peak times and the group velocity curve of the sample to be tested is: the position of the closed defect is located according to a distance from the closed defect to a receiving position of the receiving signal, and a calculation formula of the distance from the closed defect to the receiving position of the receiving signal is: wherein and is the peak time of the fundamental signal and the second harmonic signal generated by the closing defect, is the group velocity of the excited fundamental, is the group velocity of the second harmonic generated by the closing defect.

2. The group velocity mismatch based closed defect referenceless positioning method of claim 1, wherein, the attribute information comprises material parameters and geometric dimensions.

3. The group velocity mismatch based closed defect referenceless positioning method of claim 1, wherein, The excitation angle meets the Snell law.

4. The group velocity mismatch based closed defect referenceless positioning method of claim 1, wherein, The closed defect comprises a closed crack, a micro-crack closed segment, a bonding structure interface closure or a weak bonding.

5. The group velocity mismatch based closed defect referenceless positioning method of claim 1, wherein, The sample to be tested is a plate-like structure.

6. A group velocity mismatch based closed defect referenceless positioning system, characterized in that, The method comprises a high-energy ultrasonic module, an excitation transducer, an inclined block, a receiving transducer and a display processing module, the excitation transducer and the receiving transducer are respectively placed at two ends of the sample to be tested through the inclined block, the high-energy ultrasonic module is connected with the excitation transducer, and the display processing module is connected with the receiving transducer. The high-energy ultrasonic module generates a sinusoidal signal, the excitation transducer generates an ultrasonic signal propagating into one end of the sample to be tested based on the sinusoidal signal, the receiving transducer collects a receiving signal at the other end of the sample to be tested, the display processing module performs time-frequency analysis on the receiving signal to determine whether a fundamental frequency signal and a double frequency signal exist simultaneously, if so, extracts peak times of the fundamental frequency signal and the double frequency signal, if not, determines that there is no closed defect, and determines a position of the closed defect in the sample to be tested based on the peak times and a group velocity curve of the sample to be tested. The ultrasonic signal is generated based on determined ultrasonic excitation parameters, the ultrasonic excitation parameters comprising an ultrasonic excitation frequency, an excitation mode and an excitation angle; the selection principle of the ultrasonic excitation frequency is that the group velocity of the excited fundamental frequency signal is not equal to that of the double frequency signal generated by the closed defect. The determination of the position of the closed defect in the sample to be tested based on the peak times and the group velocity curve of the sample to be tested is: the position of the closed defect is located according to a distance from the closed defect to a receiving position of the receiving signal, and a calculation formula of the distance from the closed defect to the receiving position of the receiving signal is: wherein and is the peak time of the fundamental signal and the second harmonic signal generated by the closing defect, is the group velocity of the excited fundamental, is the group velocity of the second harmonic generated by the closing defect.

7. A group velocity mismatch based closed defect referenceless positioning system according to claim 6, characterized in that, The inclined block is an organic glass inclined block.

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