Symmetrical path-based Lamb wave reference-free damage detection imaging method and system

Abstract

The invention discloses a symmetric path-based Lamb wave non-reference damage detection imaging method and system, and relates to the technical field of ultrasonic Lamb wave non-destructive detection and imaging, and the method comprises the steps: obtaining a preset symmetrically arranged sensor array, obtaining a response signal of a receiving sensor of each path based on a preset excitation signal, the response signals of the symmetrical paths are subjected to difference processing to obtain difference signals; calculating a wave packet of the difference signal by adopting Hilbert transform on the difference signal, extracting a scattered wave packet and a direct wave packet based on the wave packet of the difference signal, and respectively calculating the flight time of the scattered wave packet and the flight time of the direct wave packet; based on the flight time of the scattered wave packet and the flight time of the direct wave packet, calculating an elliptical orbit of the defect on each path, and based on the elliptical orbit of the defect on each path and by utilizing a spatial distribution function, obtaining defect pixel points in the imaging area; and the defect pixel points in the imaging area are subjected to weighted fusion to obtain a damage positioning imaging picture, so that the Lamb wave non-reference imaging of the damage is realized, and the detection efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic Lamb wave non-destructive testing and imaging, and specifically to a Lamb wave benchmark-free damage detection imaging method and system based on a symmetric path. Background Art

[0002] Plate-like structures are widely used in life and various engineering fields. During long-term use, defects that are not easily detectable, such as cracks and corrosion, are likely to occur. Therefore, it is necessary to regularly inspect these structures to timely detect and locate defects. Ultrasonic Lamb waves are widely used in non-destructive testing and structural health monitoring due to their advantages of long propagation distance, low attenuation, and sensitivity to defects. This technology analyzes the Lamb wave signals collected by sensors and uses algorithms to image and intuitively display the detection results.

[0003] Currently, commonly used Lamb wave damage detection imaging methods include time reversal imaging, delay and sum imaging, tomography imaging, and probability imaging, etc. Some of the above methods achieve defect detection by quantifying the difference between the response signal and the reference signal, and some extract defect information for detection by using the scattered signal obtained by subtracting the response signal from the reference signal. However, in practical applications, due to reasons such as environmental changes, probe errors, and human errors, it is difficult to maintain consistent measurement conditions between the measured response signal and the reference signal, thus affecting the imaging accuracy. Therefore, benchmark-free imaging methods have been proposed, but the current benchmark-free imaging algorithms are difficult to balance between the detection area and the detection efficiency. Summary of the Invention

[0004] To solve the deficiencies mentioned in the above background art, the purpose of the present invention is to provide a Lamb wave benchmark-free damage detection imaging method and system based on a symmetric path, which realizes benchmark-free imaging of Lamb waves for damage and improves the detection efficiency.

[0005] In a first aspect, the purpose of the present invention can be achieved by the following technical solutions: A Lamb wave benchmark-free damage detection imaging method based on a symmetric path, the method comprising the following steps:

[0006] Obtain a sensor array arranged symmetrically as preset, obtain the response signals of each path receiving sensors based on a preset excitation signal, and obtain a difference signal by taking the difference between the response signals of the symmetric paths;

[0007] Perform Hilbert transform on the difference signal to calculate the wave packet of the difference signal, extract the scattered wave packet and the direct wave packet based on the wave packet of the difference signal, and calculate the flight time of the scattered wave packet and the flight time of the direct wave packet respectively;

[0008] Calculate the elliptical trajectory of the defect on each path based on the flight time of the scattered wave packet and the flight time of the direct wave packet. Obtain the defect pixel points in the imaging area based on the elliptical trajectory of the defect on each path and use the spatial distribution function. Perform weighted fusion on the defect pixel points in the imaging area to obtain the damage location imaging map.

[0009] Combined with the first aspect, in some implementation manners of the first aspect, the method further includes: the calculation process of the preset excitation signal:

[0010] The excitation signal Y(t) is a sine signal modulated by a Hanning window, and the expression is as follows:

[0011]

[0012] In the formula, f c represents the center frequency of the excitation signal, N is the number of wave peaks, and t is time.

[0013] Combined with the first aspect, in some implementation manners of the first aspect, the method further includes: the calculation process of obtaining the difference signal by taking the difference of the response signals of the symmetric paths:

[0014] Obtain the signals X AB and X AD of the symmetric paths, then there is a symmetric path difference signal:

[0015] D A = X AB - X AD

[0016] where D A is the difference signal of paths AB and AD.

[0017] Combined with the first aspect, in some implementation manners of the first aspect, the method further includes: the process of calculating the wave packet of the difference signal by performing Hilbert transform on the difference signal:

[0018] Construct an analytic signal Z(t) = d(t) + jh(t) about the difference signal d(t), where h(t) is the signal after Hilbert transform of d(t), and the expression is as follows:

[0019]

[0020] * represents convolution, j is the imaginary symbol, and the wave packet of the difference signal is obtained by taking the modulus of Z(t).

[0021] Combined with the first aspect, in some implementation manners of the first aspect, the method further includes: the calculation process of the flight time of the scattered wave packet:

[0022] The flight times Tof1 and Tof2 of the scattered wave packets on paths AB and AD are respectively obtained by using local similarity matching. The flight time is the difference between the peak of the scattered wave packet and the peak of the excitation signal wave packet. The local similarity formula is as follows:

[0023]

[0024] In the formula, t1 and t2 respectively represent the start and end times of the scattered signal, and respectively represent the average values of the original signal and the scattered signal in this time period.

[0025] Combined with the first aspect, in some implementation manners of the first aspect, the method further includes: the size of the elliptical trajectory where the defect exists is described by the shape factor β on path ij ij and is ij as follows:

[0026] In the formula, Tof is the flight time of the scattered wave packet on path ij, and t d is the flight time of the direct wave packet on path ij.

[0027] Combined with the first aspect, in some implementation manners of the first aspect, the method further includes: the process of obtaining the defect pixel points in the imaging area based on the elliptical trajectories where the defects exist on each path and using the spatial distribution function:

[0028] Define the ratio of the sum of the distances from the pixel point (x, y) to the transmitting sensor S i (x i , y i ) and the receiving sensor S j (x j , y j ) to the distance between the sensors as:

[0029]

[0030] Then the distance of the point (x, y) from the ellipse of path ij is:

[0031] X ij (x, y) = |R(x, y) - β ij |

[0032] In the formula, β ij represents the shape factor on path ij;

[0033] Define the spatial distribution function as follows:

[0034]

[0035] The formula is a normal distribution with a mean of 0 and a variance of σ2 Gaussian probability density function

[0036] Combined with the first aspect, in some implementations of the first aspect, the method further includes: the process of weighted fusion of defective pixel points in the imaging area:

[0037]

[0038] In the formula, k represents the kth path, n is the total number of paths, and n is greater than or equal to 3, and P(x, y) represents the probability value that the pixel point is defective.

[0039] In a second aspect, to achieve the above object, the present invention discloses a Lamb wave benchmark-free damage detection imaging system based on symmetric paths, including:

[0040] A signal processing module, configured to obtain a sensor array arranged symmetrically by preset, obtain response signals of each path receiving sensor based on a preset excitation signal, and obtain a difference signal by taking the difference of the response signals of the symmetric paths;

[0041] A time acquisition module, configured to calculate the wave packet of the difference signal by performing Hilbert transform on the difference signal, extract the scattered wave packet and the direct wave packet based on the wave packet of the difference signal, and calculate the flight time of the scattered wave packet and the flight time of the direct wave packet respectively;

[0042] A defect imaging module, configured to calculate the elliptical trajectory of the existence of defects on each path based on the flight time of the scattered wave packet and the flight time of the direct wave packet, obtain defective pixel points in the imaging area based on the elliptical trajectory of the existence of defects on each path and using a spatial distribution function, and perform weighted fusion on the defective pixel points in the imaging area to obtain a damage location imaging map.

[0043] In another aspect of the present invention, to achieve the above object, a terminal device is disclosed, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. The memory stores a computer program capable of running on the processor. When the processor loads and executes the computer program, the above-mentioned Lamb wave benchmark-free damage detection imaging method based on symmetric paths is adopted.

[0044] Advantages of the present invention:

[0045] The present invention does not need to measure the reference signal in a defect-free structure of the same material in advance, directly analyzes the response signal in the structure to be detected, realizes Lamb wave benchmark-free imaging of damage, and improves the detection efficiency; it can not only realize area detection within the array but also area detection outside the array; it also reduces the number of detection sensors, and at least only three sensors are required. Description of the Drawings

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0047] Figure 1 is a schematic flowchart of the method of the present invention;

[0048] Figure 2 is a schematic diagram of square array detection;

[0049] Figure 3 is a schematic diagram of a set of wave packet extraction;

[0050] Figure 4 is a defect location map within the array;

[0051] Figure 5 is a defect location map outside the array;

[0052] Figure 6 is a schematic diagram of the system structure of the present invention. Detailed implementation manners

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0054] Embodiment 1:

[0055] As Figure 1 shown, a Lamb wave damage detection imaging method without a reference based on a symmetric path, the method includes the following steps:

[0056] S101: Obtain a sensor array arranged symmetrically as preset, obtain the response signals of each path receiving sensors based on a preset excitation signal, and obtain a difference signal by taking the difference between the response signals of the symmetric paths;

[0057] Process of setting a symmetric sensor array layout:

[0058] Set a symmetrically arranged sensor array on the board to be detected. As Figure 2Shown is a square array of 4 sensors, where A and C are excitation sensors, and B and D are receiving sensors. Four path signals can be obtained by transmitting through A and receiving at B and D, and transmitting through C and receiving at B and D. Each path is represented by the letters of the transmitting sensor and the receiving sensor. For example, AB refers to the straight-line path from A to B when A is the transmitting sensor and B is the receiving sensor.

[0059] The calculation process of the preset excitation signal:

[0060] Excitation signal Y ( t ) is a sine signal modulated by a Hanning window, and the expression is as follows:

[0061]

[0062] In the formula, f c represents the center frequency of the excitation signal, N is the number of wave peaks, and t is the time.

[0063] Subtract the two signals of the symmetric path to obtain a difference signal.

[0064] Obtain the signals X AB , X AD and X CB , X CD of two groups of symmetric paths, then there are symmetric path difference signals:

[0065] D A = X AB - X AD

[0066] D C = X CB - X CD

[0067] where D A is the difference signal of paths AB and AD, and D C is the difference signal of paths CB and CD.

[0068] S102: Perform Hilbert transform on the difference signal to calculate the wave packet of the difference signal, extract the scattered wave packet and the direct wave packet based on the wave packet of the difference signal, and calculate the flight time of the scattered wave packet and the flight time of the direct wave packet respectively;

[0069] The process of performing Hilbert transform on the difference signal to calculate the wave packet of the difference signal:

[0070] Construct an analytic signal Z(t) = d(t) + jh(t) about the difference signal d(t), where h(t) is the signal after Hilbert transform of d(t), and the expression is as follows:

[0071]

[0072] * represents convolution, j is the imaginary symbol, and the wave packet of the difference signal is obtained by taking the modulus of Z(t).

[0073] Extract the scattered wave packet and calculate the flight time.

[0074] There will be two wave peaks in the wave packet of the difference signal, corresponding to the scattered wave packets of two paths. For the difference signal D A Using local similarity, the flight times Tof1 and Tof2 on paths AB and AD are respectively obtained by matching. For the difference signal D C Using local similarity, the flight times Tof3 and Tof4 on paths CB and CD are respectively obtained by matching.

[0075] Among them, the flight time is the difference between the peak of the scattered wave packet and the peak of the excitation signal wave packet. The local similarity formula is as follows:

[0076]

[0077] In the formula, t1 and t2 respectively represent the start and end times of the scattered signal, and respectively represent the average values of the original signal and the scattered signal in this time period. When r is the largest, the scattered wave packet at this time is matched with its corresponding path.

[0078] Calculate the flight time t of the direct wave d .

[0079] Similarly, the wave packet of the direct wave is extracted by Hilbert transform, and the difference is made between the peak point and the peak point of the envelope of the excitation signal, and the flight time t of the direct wave can be obtained. Since the square structure is adopted in this scheme, the flight time of each path is the same.

[0080] S103: Calculate the elliptical trajectory where the defect exists on each path based on the flight time of the scattered wave packet and the flight time of the direct wave packet. Based on the elliptical trajectory where the defect exists on each path and using the spatial distribution function, obtain the defect pixel points in the imaging area, and perform weighted fusion on the defect pixel points in the imaging area to obtain the damage location imaging map.

[0081] Specifically, the solution of the present invention will be further elaborated through the following embodiments:

[0082] Calculate the elliptical trajectory where the defect exists on each path using the flight time.

[0083] The size of the elliptical trajectory where the defect is located on path ij is described by the shape factor β ij as follows:

[0084] In the formula, Tof is the flight time of the scattered wave packet on path ij, td is the flight time of the direct wave packet on path ij.

[0085] The probability value that the point (x, y) in the imaging area is a defect is calculated using the spatial distribution function.

[0086] Define the distance sum from the pixel point (x, y) to the transmitting sensor S i (x i , y i ) and the receiving sensor S j (x j , y j ) and the ratio of the distance between the sensors is

[0087]

[0088] Then the distance of the point (x, y) from the ellipse of path ij is:

[0089] X ij (x, y) = |R(x, y) - β ij |

[0090] β in the formula ij represents the shape factor on path ij;

[0091] Define its spatial distribution function as follows:

[0092]

[0093] σ used in this method is 0.05.

[0094] Fuse three or more paths to achieve defect location imaging.

[0095] Perform weighted fusion on the pixel points in the imaging area to obtain the damage location imaging map:

[0096]

[0097] In the formula, k represents the k-th path, n is the total number of paths and n is greater than or equal to 3, and P(x, y) represents the probability value that the pixel point is a defect.

[0098] To verify the detection effect of this method, on a steel plate with a typical rectangular through defect, the rectangular through defect was imaged using the Figure 2 shown array, where as Figure 3 shown is a schematic diagram of a set of wave packet extraction, and the imaging results are as Figure 4 and 5 shown.

[0099] Figure 4It is a defect location map within the array. The actual defect size is 10mm * 10mm, the defect center is located at (-100, 50), the defect center of the positioning result is (-93, 49), and the absolute error is approximately 7.07mm, where the error in the x direction is 7mm and the error in the y direction is 1mm. Accurate defect location imaging can be achieved.

[0100] Figure 5 It is a defect location map outside the array. The actual defect size is 10mm * 10mm, the defect center is located at (100, 250), the defect center of the positioning result is (101, 243), and the absolute error is approximately 7.07mm, where the error in the x direction is 1mm and the error in the y direction is 7mm. Accurate defect location imaging can be achieved.

[0101] Embodiment 2: As Figure 6 shown, to achieve the above object, the present invention discloses a Lamb wave non-reference damage detection imaging system based on a symmetric path, including:

[0102] A signal processing module 11, configured to obtain a sensor array arranged in a preset symmetric manner, obtain the response signals of each path receiving sensor based on a preset excitation signal, and obtain a difference signal by taking the difference of the response signals of the symmetric paths;

[0103] A time acquisition module 12, configured to calculate the wave packet of the difference signal by performing a Hilbert transform on the difference signal, extract the scattered wave packet and the direct wave packet based on the wave packet of the difference signal, and calculate the flight time of the scattered wave packet and the flight time of the direct wave packet respectively;

[0104] A defect imaging module 13, configured to calculate the elliptical trajectories of the defects existing on each path based on the flight time of the scattered wave packet and the flight time of the direct wave packet, obtain the defect pixel points in the imaging area by using a spatial distribution function based on the elliptical trajectories of the defects existing on each path, and perform weighted fusion on the defect pixel points in the imaging area to obtain a damage location imaging map.

[0105] Based on the same inventive concept, the present invention further provides a computer device, which includes: one or more processors, and a memory for storing one or more computer programs; the program includes program instructions, and the processor is configured to execute the program instructions stored in the memory. The processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is used to implement one or more instructions. Specifically, it is used to load and execute one or more instructions in the computer storage medium to implement the above method.

[0106] It should be further noted that, based on the same inventive concept, the present invention further provides a computer storage medium, on which a computer program is stored, and the computer program, when run by a processor, executes the above method. The storage medium may adopt any combination of one or more computer-readable media. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may, for example, but not be limited to, be an electrical, magnetic, optical, electrical, magnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above. More specific examples (non-exhaustive list) of the computer-readable storage medium include: an electrical connection having one or more wires, a portable computer disk, a hard disk, a Random Access Memory (RAM), a Read-Only Memory (ROM), an Erasable Programmable Read-Only Memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the present invention, the computer-readable storage medium may be any tangible medium that contains or stores a program, and the program may be used by or combined with an instruction execution system, apparatus, or device.

[0107] In the description of this specification, the descriptions referring to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0108] The foregoing has shown and described the basic principles, main features and advantages of the present disclosure. Those skilled in the art should understand that the present disclosure is not limited by the above embodiments, and what is described in the above embodiments and the specification only illustrates the principles of the present disclosure. Without departing from the spirit and scope of the present disclosure, the present disclosure will have various changes and improvements, and these changes and improvements fall within the scope of the present disclosure claimed.

Claims

1. A Lamb wave non-reference damage detection imaging method based on a symmetric path, characterized in that The method includes the following steps: Obtain a sensor array with a preset symmetric arrangement, obtain the response signals of the receiving sensors for each path based on a preset excitation signal, and obtain a difference signal by taking the difference between the response signals of the symmetric paths; Perform a Hilbert transform on the difference signal to calculate the wave packet of the difference signal, extract the scattered wave packet and the direct wave packet based on the wave packet of the difference signal, and calculate the flight time of the scattered wave packet and the flight time of the direct wave packet respectively; Calculate the elliptical trajectories where defects exist on each path based on the flight time of the scattered wave packet and the flight time of the direct wave packet, obtain the defective pixel points in the imaging area based on the elliptical trajectories where defects exist on each path and using the spatial distribution function, and perform weighted fusion on the defective pixel points in the imaging area to obtain a damage location imaging map.

2. The Lamb wave non-reference damage detection imaging method based on a symmetric path according to claim 1, wherein The calculation process of the preset excitation signal: The excitation signal Y(t) is a sine signal modulated by a Hanning window, and the expression is as follows: where f c represents the center frequency of the excitation signal, N is the number of wave peaks, and t is the time.

3. The method for Lamb wave benchmark-free damage detection imaging based on symmetric paths according to claim 1, wherein The calculation process of obtaining the difference signal by taking the difference between the response signals of the symmetric paths: Obtain the signal X of the symmetric path AB , X AD , then there is a symmetric path difference signal: D A = X AB - X AD D A is the differential signal of paths AB and AD.

4. The Lamb wave non-reference damage detection imaging method based on a symmetric path according to claim 1, characterized in that The process of performing a Hilbert transform on the difference signal to calculate the wave packet of the difference signal: Construct an analytic signal Z(t) = d(t) + jh(t) for the difference signal d(t), where h(t) is the signal after the Hilbert transform of d(t), and the expression is as follows: * represents convolution, j is the imaginary symbol, and the wave packet of the difference signal is obtained by taking the modulus of Z(t).

5. The Lamb wave non-reference damage detection imaging method based on a symmetric path according to claim 1, wherein The calculation process of the flight time of the scattered wave packet: Use local similarity to respectively match and obtain the flight times Tof1 and Tof2 of the scattered wave packets on paths AB and AD. The flight time is the difference between the peak of the scattered wave packet and the peak of the excitation signal wave packet. The local similarity formula is as follows: where \(t_1\) and \(t_2\) respectively represent the start and end times of the scattered signal, and respectively represent the average values of the original signal and the scattered signal over this time period.

6. The Lamb wave benchmark-free damage detection imaging method based on a symmetric path according to claim 1, wherein The size of the defect with an elliptical locus is described by the shape factor β on path ij ij which is ij as follows: where Tof is the flight time of the scattered wave packet along path ij, and t d is the flight time of the direct wave packet along path ij.

7. The Lamb wave benchmark-free damage detection imaging method based on symmetric paths according to claim 1, wherein The process of obtaining the defective pixel points in the imaging area based on the elliptical trajectories where defects exist on each path and using the spatial distribution function: Define the ratio of the sum of the distances from the pixel point (x, y) to the transmitting sensor S i (x i , y i ) and the receiving sensor S j (x j , y j ) to the distance between the sensors as: Then the distance of the point (x, y) from the ellipse of the ij path is: X ij (x,y) = |R(x,y) - β ij | β in the formula ij represents the shape factor on the ij path; Define the spatial distribution function as follows: The formula is a Gaussian probability density function with a mean of 0 and a variance of σ 2 .

8. The Lamb wave benchmark-free damage detection imaging method based on a symmetric path according to claim 1, characterized in that The process of performing weighted fusion on the defective pixel points in the imaging area: In the formula, k represents the kth path, n is the total number of paths, and n is greater than or equal to 3. P(x, y) represents the probability value that the pixel point is defective.

9. A Lamb wave non-reference damage detection imaging system based on a symmetric path, characterized in that Includes: A signal processing module, configured to obtain a sensor array with a preset symmetric arrangement, obtain the response signals of the receiving sensors for each path based on a preset excitation signal, and obtain a difference signal by taking the difference between the response signals of the symmetric paths; A time acquisition module, configured to perform a Hilbert transform on the difference signal to calculate the wave packet of the difference signal, extract the scattered wave packet and the direct wave packet based on the wave packet of the difference signal, and calculate the flight time of the scattered wave packet and the flight time of the direct wave packet respectively; A defect imaging module, configured to calculate the elliptical trajectories where defects exist on each path based on the flight time of the scattered wave packet and the flight time of the direct wave packet, obtain the defective pixel points in the imaging area based on the elliptical trajectories where defects exist on each path and using the spatial distribution function, and perform weighted fusion on the defective pixel points in the imaging area to obtain a damage location imaging map.

10. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, A computer program capable of running on a processor is stored in the memory. When the processor loads and executes the computer program, the method for detecting and imaging damage without a reference based on symmetric path Lamb waves described in any one of claims 1 to 8 is adopted.

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