A non-contact laser ultrasonic method for assessing damage in tubular structures

Abstract

This invention discloses a non-contact laser ultrasonic method for assessing damage in tubular structures. First, a scanning laser ultrasonic system is used to acquire wavefield signals from the pipe structure. The resulting signals are then analyzed using conventional signal processing methods such as forward and inverse Fourier transforms and windowed filtering to determine the damage distribution within the scanned tubular structure. Compared to conventional planar damage detection, this method can locate damage on curved tubular surfaces and provide global, high-resolution characterization of any damage morphology, ultimately achieving the goal of assessing damaged areas within tubular structures and enabling targeted repair.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic detection technology, and in particular to a laser ultrasonic method for non-contact evaluation of tubular structure damage. Background Art

[0002] Tubular structures are widely used in aerospace, petroleum, chemical, and storage tank industries. Over long periods of service, they are subject to environmental influences such as rainwater erosion, natural material aging, seismic loads, and the effects of internal and external forces, inevitably leading to accumulated damage and weakening of their resistance. This can directly lead to pipeline leaks, impacting the natural environment and, in worse cases, causing unforeseen losses. To ensure the healthy operation of pipeline systems, timely inspection, monitoring, and maintenance are essential. Nondestructive testing (NDT) of pipeline structures plays a crucial role in eliminating structural safety hazards and ensuring reliable operation.

[0003] Ultrasonic guided waves, with their advantages of long propagation distance and high speed, hold a significant position in the field of nondestructive testing. Damage localization based on ultrasonic guided wave technology is currently well established, and damage imaging has become a research hotspot within ultrasonic guided wave testing in recent years. However, damage patterns in tubular structures are complex, and the principles of damage imaging remain unclear. Curved pipe surfaces, in particular, further complicate ultrasonic testing. While damage imaging has matured in plate-like structures with the recent rise of laser ultrasonic guided wave technology, the mechanism of damage imaging in curved tubular structures remains under investigation.

[0004] Therefore, for tubular structures, how to design a method that can quickly locate the damage position of its curved surface and characterize the damage morphology of the structure in a global and high-resolution manner, and ultimately achieve the purpose of evaluating the damaged area of the material and targeted repair, has become a technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a non-contact laser ultrasonic method for evaluating damage to tubular structures. Through the present invention, the damage to the structure can be quickly located and the damaged position of the material can be characterized in a full range and high resolution, ultimately achieving the purpose of evaluating the damaged area of the tubular structure and targeted repair.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A non-contact laser ultrasound method for assessing damage to tubular structures, the method comprising the following steps:

[0008] Step S1: Place the sample to be tested with the AE sensor attached on a fixed rack; configure the PC hardware address, complete the selection of the serial port, acquisition card, and acquisition channel, and set the sampling rate and number of sampling points of the excitation signal;

[0009] Step S2: Setting the starting and ending coordinates of the laser scan according to the area to be detected of the sample, and using a two-dimensional deflecting mirror to control the laser beam to move and scan in the x and y directions of the plane, and setting the scanning step length;

[0010] Step S3: The laser beam is mainly emitted by a Nd:YAG laser, and its excitation energy determines the intensity of the ultrasonic wave in the structure; the Nd:YAG laser is controlled by a computer, and its interface communicates via RS-232 to USB;

[0011] Step S4: When the Nd:YAG laser emits laser light, the excitation unit generates a trigger signal, which triggers the data acquisition unit to perform data acquisition to ensure synchronization between the excitation and acquisition times. The response signal received by the AE sensor is amplified and processed by the data acquisition unit, then collected by the acquisition card and stored in the control unit.

[0012] Step S5: The control unit performs data analysis on the signal and performs wavefield damage visualization processing to complete the storage of wavefield data of the damaged area, thereby obtaining a three-dimensional time-space wavefield signal;

[0013] Step S6: performing fast Fourier transform on the obtained time-space domain signal to obtain a frequency-wavenumber domain signal; and simultaneously performing windowing filtering to obtain a narrowband frequency-wavenumber three-dimensional signal;

[0014] Step S7: performing wavenumber domain windowing processing on the obtained narrowband frequency-wavenumber three-dimensional signal to obtain three-dimensional signals at different center wavenumbers;

[0015] Step S8: Perform inverse Fourier transform on the three-dimensional signals at different central wavenumbers, and accumulate the transformed signals in the time dimension to obtain space-wavenumber signals; then extract the wavenumber value corresponding to the maximum energy at each spatial point, that is, finally obtain the wavenumber distribution of each spatial point;

[0016] Furthermore, in the step S1 , the sample to be detected with the AE sensor attached should be attached directly below the area to be detected to prevent the sensor from being burned due to excessive laser energy during scanning.

[0017] Furthermore, the laser in step S3 is computer-controlled, using a USB-to-RS-232 interface to communicate with the laser. Manual control, however, only allows for single-point laser irradiation, making it difficult to scan the entire structure. Furthermore, the laser can adjust the pulsed laser energy by adjusting the delay time of the Q switch. Reducing the Q switch delay time can yield higher laser energy.

[0018] Furthermore, the windowing filter in step S6 specifically uses a Tukey window function and a one-dimensional Gaussian window function to perform wavenumber domain and frequency domain filtering on the frequency-wavenumber domain signal, respectively, to obtain a single-mode narrowband frequency-wavenumber domain signal. The Tukey window function W m [k x ,k y ,f] and one-dimensional Gaussian window function W F [f c ] are shown as follows:

[0019]

[0020] in, k R is the wave number in the R direction of the original signal, K B (f,m) for different k R The wave number change under B M is the Tukey window bandwidth, k x With k y are the wave numbers in the X and Y directions, f is the original frequency, m is the selected guided wave mode, K H With K L are the upper and lower limits of the wavenumber at the maximum value of the Tukey window function.

[0021]

[0022] Where f1 is the selected center frequency, f c is the frequency of the one-dimensional Gaussian window function, B F is the bandwidth of the one-dimensional Gaussian window function.

[0023] Furthermore, in step S7, the obtained narrowband frequency-wavenumber three-dimensional signal is subjected to wavenumber domain windowing processing, and the selected window function is a two-dimensional Gaussian window W K [k x ,k y ,k c ], the formula is as follows:

[0024]

[0025] Among them, k c is the central wave number, B K is the two-dimensional Gaussian window bandwidth.

[0026] The wave value corresponding to the maximum energy value at each spatial point in step S8 is shown in the following formula:

[0027]

[0028] in, It is a two-dimensional wavenumber signal, where x and y represent the coordinate points in space, and k is the wavenumber corresponding to the maximum value of the spatial point.

[0029] Beneficial Effects: This invention provides a non-contact laser ultrasonic method for assessing damage in tubular structures. First, a scanning laser ultrasonic system is used to acquire wavefield signals from the pipe structure. The resulting signals are then analyzed using conventional signal processing methods such as forward and inverse Fourier transforms and windowed filtering to determine the damage distribution within the scanned tubular structure. Compared to conventional planar damage detection, this method can locate damage on curved tubular surfaces and provide global, high-resolution characterization of any damage morphology, ultimately achieving the goal of assessing damaged areas within tubular structures and enabling targeted repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart of a non-contact laser ultrasonic method for assessing damage to tubular structures provided by the present invention;

[0031] Figure 2 Schematic diagram of the laser ultrasonic experiment for damage detection of tubular structures;

[0032] Figure 3(a) shows the wave field signal at 40μs;

[0033] Figure 3(b) shows the wave field signal at 100 μs;

[0034] Figure 4(a) shows the frequency-wavenumber domain signal before filtering;

[0035] Figure 4(b) shows the frequency-wavenumber domain signal after filtering;

[0036] Figure 5 This is a two-dimensional wavenumber diagram of the damage imaging results of the tubular structure. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments of the present invention.

[0038] A non-contact laser ultrasonic method for evaluating damage in tubular structures. Figure 1 As shown, the present invention can not only quickly locate damage to the structure, but also perform global, high-resolution morphological characterization of the damaged position of the material, ultimately achieving the purpose of evaluating the damaged area of the tubular structure and targeted repair.

[0039] like Figure 2As shown in the figure, the scanning area is roughly determined based on the damage location of the damaged multi-layer pipe structure (the inner layer is aluminum, the outer layer is carbon fiber reinforced resin-based material), and the AE sensor is attached to the right end of the scanning area. It is important to note that the AE sensor should be attached outside the laser scanning area to prevent the laser energy from ablating the sensor.

[0040] After fixing the pipe with the AE sensor in the appropriate position, first configure the hardware address on the computer, complete the selection of the serial port, acquisition card, and acquisition channel, and set the appropriate sampling rate and number of sampling points according to the needs of signal analysis. In this example, the sampling rate is set to 10MHz and the number of sampling points is set to 1000.

[0041] Next, set the parameters for the laser excitation module and the scanning setup module. The key parameters are the laser energy, the starting coordinates of the scanning area, and the step size. The laser energy primarily determines whether waveguides can form in the tube. Laser energy should be kept low, so set the energy value based on the specific material. The step size of the scanning area primarily determines the spatial resolution; a resolution of 0.5mm or 1mm is generally sufficient.

[0042] After setting the relevant parameters, the excitation unit emits a laser pulse. Simultaneously, it generates a trigger signal, triggering the data acquisition unit to collect data, ensuring synchronization between excitation and acquisition. The response signal received by the AE sensor is amplified and processed by the data acquisition unit before being collected by the acquisition card and stored in the control unit. The control unit then analyzes the signal and visualizes the wavefield damage, completing the wavefield data storage of the damaged area and generating a three-dimensional time-space wavefield signal.

[0043] After the obtained three-dimensional time-space wave field signal is processed by Matlab software, the results shown in Figure 3(a) and Figure 3(b) are obtained.

[0044] In order to analyze the transformation of the wave during propagation, the collected time-space domain signal v[x, y, t] is first subjected to a three-dimensional fast Fourier transform based on Matlab software, as shown in Figure 4(a), to obtain the frequency-wavenumber domain signal V[k x ,k y ,f]. Then, the Tukey window function is used to filter the frequency-wavenumber domain signal in the wavenumber domain, with the single waveguide mode as the research object. The formula of the Tukey window function is shown in the following formula (1):

[0045]

[0046] in, k R is the wave number in the R direction of the original signal, K B(f,m) for different k R The wave number change under B M is the Tukey window bandwidth, k x With k y are the wave numbers in the X and Y directions, f is the original frequency, m is the selected guided wave mode, K H With K L are the upper and lower limits of the wavenumber at the maximum value of the Tukey window function.

[0047] Secondly, the one-dimensional Gaussian window function W is used F [f c ] Perform frequency domain filtering on the above wavenumber signal, and finally obtain the narrowband frequency-wavenumber three-dimensional signal V1[k x ,k y ,f], the result is shown in Figure 4(b). The formula of Gaussian window function is shown in the following formula (2):

[0048]

[0049] Where f1 is the selected center frequency, f c is the frequency of the one-dimensional Gaussian window function, B F is the bandwidth of the one-dimensional Gaussian window function.

[0050] V1[k x ,k y ,f c ]=W F [f c ]*W m [k x ,k y ,f]*V[k x ,k y ,f] (3)

[0051] After filtering, in order to show the change of global structural wavenumber, as shown in formula (4), a group of central wavenumbers k is introduced. c Two-dimensional Gaussian window function W (including the wave number of the guided wave passing through the lossless and lossy parts) k [k x ,k y ,k c ], and the obtained narrowband frequency-wavenumber three-dimensional signal V2[k x ,k y ,f c ] is windowed to obtain the four-dimensional narrowband frequency-wavenumber signal Z[k x ,k y ,f c ,k c]. Then for each wave number k c The three-dimensional signal Z under c [k x ,k y ,f c ] performs a three-dimensional inverse Fourier transform to obtain the signal z[x,y,t,k c ], and finally, by accumulating in the third dimension time t, we get the three-dimensional signal z1[x,y,k c ].

[0052]

[0053]

[0054]

[0055] Among them, B K is the bandwidth of the two-dimensional Gaussian window function, V1[k x ,k y ,f c ] is a narrowband frequency-wavenumber three-dimensional signal.

[0056] Extract the wave number corresponding to the maximum value of the three-dimensional signal at each spatial point to obtain the two-dimensional wave number signal as shown in formula (7): That is Figure 5 The wave number corresponding to each spatial point is used to evaluate the morphology of the damaged area based on the wave number characteristics.

[0057]

[0058] Where k is the wave number corresponding to the maximum value of the spatial point.

[0059] It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. A non-contact laser ultrasonic method for assessing damage in tubular structures, characterized by: The method comprises the following steps: Step S1: Place the sample to be tested with the AE sensor attached on a fixed rack; configure the PC hardware address, complete the selection of the serial port, acquisition card, and acquisition channel, and set the sampling rate and number of sampling points of the excitation signal; Step S2: Setting the starting and ending coordinates of the laser scan according to the area to be detected of the sample, and using a two-dimensional deflecting mirror to control the laser beam to move and scan in the x and y directions of the plane, and setting the scanning step length; Step S3: The laser beam is mainly emitted by a Nd:YAG laser, and its excitation energy determines the intensity of the ultrasonic wave in the structure; the Nd:YAG laser is controlled by a computer, and its interface communicates via USB to RS-232; Step S4: When the Nd:YAG laser emits laser light, the excitation unit generates a trigger signal, which triggers the data acquisition unit to perform data acquisition to ensure synchronization between the excitation and acquisition times. The response signal received by the AE sensor is amplified and processed by the data acquisition unit, then collected by the acquisition card and stored in the control unit. Step S5: The control unit performs data analysis on the signal and performs wavefield damage visualization processing to complete the storage of wavefield data of the damaged area, thereby obtaining a three-dimensional time-space wavefield signal; Step S6: performing fast Fourier transform on the obtained time-space domain signal to obtain a frequency-wavenumber domain signal; and simultaneously performing windowing filtering to obtain a narrowband frequency-wavenumber three-dimensional signal; Step S7: performing wavenumber domain windowing processing on the obtained narrowband frequency-wavenumber three-dimensional signal to obtain three-dimensional signals at different center wavenumbers; Step S8: Perform inverse Fourier transform on the three-dimensional signals at different central wavenumbers, and accumulate the transformed signals in the time dimension to obtain space-wavenumber signals; then extract the wavenumber value corresponding to the maximum energy at each spatial point, that is, finally obtain the wavenumber distribution of each spatial point; The windowing filtering in step S6 specifically uses a Tukey window function and a one-dimensional Gaussian window function to perform wavenumber domain and frequency domain filtering on the frequency-wavenumber domain signal, respectively, to obtain a single-mode narrowband frequency-wavenumber domain signal; the Tukey window function W m [k x ,k y ,f] and one-dimensional Gaussian window function W F [f c ] are shown as follows: in, k R is the wave number in the R direction of the original signal, K B (f,m) for different k R The wave number change under B M is the Tukey window bandwidth, k x With k y are the wave numbers in the X and Y directions, f is the original frequency, m is the selected guided wave mode, K H With K L They are the upper and lower limits of the wave number at the maximum value of the Tukey window function; Where f1 is the selected center frequency, f c is the frequency of the one-dimensional Gaussian window function, B F is the bandwidth of the one-dimensional Gaussian window function; In step S7, the obtained narrowband frequency-wavenumber three-dimensional signal is subjected to wavenumber domain windowing processing, and the selected window function is a two-dimensional Gaussian window W K [k x ,k y ,k c ], the formula is as follows: Among them, k c is the central wave number, B K is the two-dimensional Gaussian window bandwidth; The wave value corresponding to the maximum energy value at each spatial point in step S8 is shown in the following formula: in, It is a two-dimensional wavenumber signal, where x and y represent the coordinate points in space, and k is the wavenumber corresponding to the maximum value of the spatial point.

2. The non-contact laser ultrasonic method for assessing damage to tubular structures according to claim 1, characterized in that: In the step S1 , the sample to be tested with the AE sensor attached should be attached directly below the area to be tested.

3. The non-contact laser ultrasonic method for assessing damage to tubular structures according to claim 1, characterized in that: The laser beam energy in step S3 determines the ultrasonic intensity in the structure. The Nd:YAG laser adjusts the energy of the pulsed laser by adjusting the delay time of the Q switch. Reducing the delay time of the Q switch can obtain higher laser energy.

Images