Optimization method and system for laser ultrasonic saft defect detection

Abstract

This invention relates to an optimized method and system for defect detection based on laser-ultrasonic SAFT. Based on the similarity of signals at nearby detection points, the ultrasonic signals received by the Doppler detector at these points are self-normalized. Then, based on the cross-correlation matching between the ultrasonic signals, the delay time points are located. The detection point data are subtracted according to the delay time points to reduce interference from the incident wave and enhance the amplitude of the echo signal. Finally, the time-domain SAFT algorithm is applied to the difference data of all detection points for imaging. This invention has the following advantages: 1. It avoids artifacts caused by interference from the incident wave in traditional SAFT algorithms, highlighting the imaging quality at the defect location and improving the overall structural imaging quality; 2. It reduces data redundancy, improving imaging quality while requiring only a single real-time experimental acquisition to complete the imaging of the entire structure.

Description

Technical Field

[0001] This invention belongs to the field of laser ultrasonic testing technology, specifically relating to an optimized method and system for laser ultrasonic SAFT defect detection. Background Technology

[0002] Laser ultrasound is a novel, non-contact, high-precision, and non-destructive ultrasonic testing technology. It utilizes laser pulses to generate ultrasonic waves within the workpiece being inspected, and then uses a laser beam to detect the propagation of these waves, thereby identifying defects in the workpiece. Due to its non-destructive nature and non-contact optical inspection capabilities, it is widely used in the field of non-destructive testing.

[0003] SAFT is a novel signal processing technique in the field of ultrasonic imaging, used in laser non-destructive testing (NDT) and serving as an important auxiliary technique for ultrasonic testing. A laser emits pulsed laser light onto the surface of the object being tested. The time-domain SAFT algorithm primarily targets the ultrasonic echo signals from the defects received by the Doppler vibrometer at the detection point. It performs time-delay superposition processing on the echo signals obtained at each detection point to obtain imaging data for the defect.

[0004] In existing laser ultrasonic experiments, the ultrasonic signal received at the detection point includes all the ultrasonic signals of the workpiece being inspected, which can be mainly divided into incident wave signals and reflected wave signals. SAFT imaging primarily relies on reflected wave signals for its imaging. For certain fixed imaging areas (generally near the excitation and detection points), artifacts can occur due to the relatively large amplitude of the incident wave. In existing time-domain SAFT, because interference from the incident wave is not removed and other waveforms besides the reflected wave are not optimized, artifacts cannot be completely eliminated, and the imaging resolution at defects is low, making it difficult to improve the overall imaging quality. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention proposes an optimized method and system for laser ultrasonic SAFT defect detection.

[0006] The technical solution to achieve the purpose of this invention is as follows:

[0007] An optimized system for SAFT-based laser-ultrasonic defect detection includes a vibrometer probe, a pulsed laser emission probe, a sample three-dimensional translation stage, a galvanometer scanning system, a laser, a Doppler vibrometer, a device three-dimensional translation stage, a stepper motor, and a PC control console.

[0008] The vibration meter probe and the Doppler vibration meter form an interferometer. The Doppler vibration meter can emit continuous laser light as a probe light. The pulsed laser emitting probe is used to output Gaussian pulsed laser light. The sample three-dimensional translation stage can move to change the three-dimensional position of the workpiece being inspected. The galvanometer scanning system includes two galvanometers with mutually perpendicular axes, which are used to control the pulsed laser emitting probe to move in two mutually perpendicular translation directions. The equipment three-dimensional translation stage can move to change the horizontal movement of the vibration meter probe. The stepper motor is used to drive the sample three-dimensional translation stage and the equipment three-dimensional translation stage. The PC control console is used to control the laser, the stepper motor, and to acquire and process data.

[0009] Furthermore, the laser is a Q-switched laser.

[0010] Furthermore, the laser operates at a wavelength of 1064 nm, has a pulse width of 2.5 ns, and an energy of 2.6 mJ.

[0011] Furthermore, the Doppler vibrometer can emit a continuous laser beam with a wavelength of 532 nm and a spot radius of 0.5 mm as the probe light.

[0012] Furthermore, the workpiece being inspected is made of flat or curved metal material.

[0013] The detection method based on the optimized system for laser-ultrasonic SAFT defect detection described above includes the following steps:

[0014] Step 1: Select the spot radius according to the step size of the detection point. The laser emits pulsed laser light, which is output to the pulsed laser emission probe through the galvanometer scanning system to the preset excitation position on the surface of the workpiece being inspected.

[0015] Step 2: The stepper motor controls the three-dimensional translation stage of the sample to move vertically, so that the surface of the workpiece being inspected is located at the laser focal point;

[0016] Step 3: Plan the movement path of the detection point and determine the movement step size of the detection point. Use a stepper motor to control the three-dimensional translation stage of the device so that the vibration probe of the Doppler vibration meter is at the preset detection point position.

[0017] Step 4: The laser operates, emitting pulsed laser light, while the Doppler vibrometer sends the received ultrasonic data to the PC control console for processing.

[0018] Step 5: Without changing the laser focus and the position of the detection point, repeatedly emit pulsed lasers. Simultaneously, the PC control console averages the ultrasonic data obtained from multiple pulses, using this average as the first detection point data. ;

[0019] Step 6: Select the second detection point along the planned detection path and detection point step size. The PC console drives the stepper motor to control the three-dimensional translation stage of the device, so that the vibration probe of the Doppler vibration meter is translated to the position of the second detection point. Repeat step 5 to obtain the data of the second detection point. ;

[0020] Step 7: The PC console processes the data from the first detection point. and the data from the second detection point Signals were obtained by self-normalization respectively and Then, cross-correlation matching is performed;

[0021] Step 8, SAFT Imaging: All points in the two-dimensional cross-section of the workpiece to be inspected are used as imaging points. Imaging data for all imaging points is acquired. Based on the wave velocity of the reflected wave, the time point determined by the sum of the distances between the detection point and the imaging point, and between the laser focus and the imaging point, is calculated. In the received signal Take the corresponding time point of the reflected wave numerical value As the data for the imaging points, the imaging data of all imaging points can be obtained by calculating all imaging points;

[0022] Step 9: Repeat steps 6 to 8 until all detection points have been detected, and record the difference data for each detection point. As SAFT imaging data, M represents the number of planned inspection points. A total of M-1 inspection point difference data are obtained. All M-1 imaging data are superimposed to obtain the final SAFT imaging image of the inspected workpiece.

[0023] Furthermore, step 7 specifically includes:

[0024] First, define For signal relative signal Time shift, The modulus is the delay time, while The sign represents the direction of time shift, when When, its cross-correlation function is , The total length of the data for each detection point, r, is about When the function r reaches its maximum value, the data from the two detection points reach the optimal cross-correlation matching point. , The optimal time-shift point for matching the data from the two detection points is now complete. ;when At that time, , ,in

[0025] Compared with the prior art, the significant advantages of this invention are:

[0026] This invention allows for direct application of experiments to actual samples without the need to explore ideal sample conditions. It significantly improves efficiency compared to traditional defect-free experimental imaging detection methods and overcomes the shortcomings of traditional laser ultrasound experiments, such as the inability to remove time-domain SAFT artifacts and low imaging quality. This optimized scheme not only removes most artifacts but also improves the imaging resolution at defects. Attached Figure Description

[0027] Figure 1 This is an optimized system diagram based on laser-ultrasound SAFT defect detection.

[0028] Figure 2 This is a schematic diagram of the scanning method of the detection point using laser detection and Doppler vibration meter. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0030] Combination Figure 1 An optimized system for laser-ultrasonic SAFT defect detection includes an interferometer probe 1, a pulsed laser emission probe 2, a workpiece to be inspected 3, a sample three-dimensional translation stage 4, a galvanometer scanning system 5, a laser 6, a Doppler vibrometer 7, a device three-dimensional translation stage 8, a stepper motor 9, and a PC control console 10. The vibration meter probe 1 and the Doppler vibration meter 7 form an interferometer. The Doppler vibration meter 7 emits a continuous laser beam of 532nm with a spot radius of 0.5mm as the probe beam. The pulsed laser 2 outputs a Gaussian pulsed laser. The workpiece 3 being inspected is a planar or curved metal material. The sample three-dimensional translation stage 4 can move to change the three-dimensional position of the workpiece being inspected. The galvanometer scanning system 5 includes two galvanometers with mutually perpendicular axes, which can control the pulsed laser emitting probe 2 to move in two mutually perpendicular translation directions. The laser 6 is a Q-switched laser with a working wavelength of 1064nm, a pulse width of 2.5ns, and an energy of 2.6mJ. The equipment three-dimensional translation stage 8 can move to change the horizontal movement of the interferometer probe 1. The stepper motor 9 is responsible for driving the two translation stages. The PC 10 is responsible for controlling the laser, the stepper motor, and acquiring and processing data.

[0031] The SAFT-optimized system detection method based on a laser ultrasonic detection system of the present invention includes the following steps:

[0032] Step 1: Select an appropriate spot radius based on the step size of the detection point. Generally, it should not be larger than the step size of the detection point. The pulsed laser emitted by the laser 6 is output to the laser probe 2 at the preset excitation position on the surface of the sample after passing through the galvanometer scanning system 5.

[0033] Step 2: Stepper motor 9 controls the vertical movement of sample three-dimensional translation stage 4 so that the surface of the workpiece 3 being inspected is located at the laser focal point.

[0034] Step 3: Plan the movement path of the detection point and determine the movement step length of the detection point. Control the three-dimensional translation stage 8 of the equipment through the stepper motor 9 so that the vibration probe 1 of the Doppler vibration meter 7 is at the position of the preset detection point.

[0035] Step 4: Laser 6 operates, emitting pulsed laser light, while Doppler vibration meter 7 sends the received ultrasonic data to PC terminal 10 for processing.

[0036] Step 5: Without changing the laser focus and the position of the detection point, repeatedly emit pulsed lasers. Simultaneously, the PC calculates the average of the ultrasonic data obtained from the multiple pulses, using this average as the first detection point data. .

[0037] Step 6: Select the second detection point along the planned detection path and detection point step size. PC10 drives stepper motor 9 to control the three-dimensional translation stage 8 of the device, so that the vibration probe 1 of the Doppler vibration meter 7 is translated to the position of the second detection point. Repeat step 5 to obtain the data of the second detection point. .

[0038] Step 7: Data from the first detection point on the PC. and the data from the second detection point Signals were obtained by self-normalization respectively and Then, perform cross-correlation matching: First, define... For signal relative signal Time shift, The modulus is the delay time, while The sign represents the direction of time shift, when When, its cross-correlation function is , The total length of the data for each detection point, r, is about When the function r reaches its maximum value, the data from the two detection points reach the optimal cross-correlation matching point. , The optimal time-shift point for matching the data from the two detection points is now complete. ;when At that time, , ,in .

[0039] Step 8, SAFT Imaging: All points in the two-dimensional cross-section of the workpiece to be inspected are used as imaging points. Taking one imaging point as an example, based on the wave velocity of the reflected wave being determined by the material properties of the workpiece, the time point determined by the sum of the distances between the detection point and the imaging point, and between the laser focus and the imaging point, is calculated. In the received signal Take the corresponding time point of the reflected wave numerical value This serves as the data for this imaging point. Calculations can be performed on all imaging points to obtain the imaging data for all imaging points.

[0040] Step 9: Repeat steps 6 to 8 until all detection points have been detected, and record the difference data for each detection point. As SAFT imaging data, M represents the number of planned inspection points. A total of M-1 inspection point difference data are obtained. All M-1 imaging data are superimposed to obtain the final SAFT imaging image of the inspected workpiece, and the defects are discussed and analyzed.

[0041] In the simulation of laser ultrasound systems, to improve imaging quality, two sets of control models with and without defects are generally set up. The corresponding data of the same detection points are subtracted to cancel the incident wave signal. Although this method is effective, it is only suitable for simulation because it is difficult to find the same defect-free control model in actual engineering applications, so it is not practical. In all existing laser ultrasound experiments, the laser ultrasound signal used for SAFT imaging is not processed or the incident wave part is directly windowed in the original detection point signal. Although the latter method can completely remove the incident wave, it has two main drawbacks: First, due to the windowing of the incident wave, the imaging data at some positions in the SAFT image is 0. If these positions are defect points, reflected wave signals will be generated. For a certain detection point data, the windowed part of the signal not only contains the incident wave but also the reflected wave. Therefore, the reflected wave is filtered out along with the incident wave by the window, resulting in the defect image at these positions not being displayed in the SAFT image, causing missed detection. Second, for data at a certain detection point, the incident wave exists in the entire band, but the amplitude decays over time. However, this does not mean that it does not exist. Windowing only filters out artifacts at certain locations. If there are defects in the unwindowed part, the presence of the incident wave will result in low imaging resolution at the defect location.

[0042] To address the issue of low resolution caused by artifacts in laser ultrasonic experiments, and aiming to reduce the influence of incident waves and improve the signal strength of reflected waves, this invention proposes an optimization method. This method incorporates synchronous preprocessing of the detection point data before each laser ultrasonic experiment. The laser 6 operates, causing the laser probe 2 to emit pulsed laser light that excites the ultrasonic bulk wave signal of the workpiece 3 under test. Simultaneously, the Doppler vibrometer 7 sends the received ultrasonic data to the PC 10 for processing. Firstly, the detection point data is essentially acoustic signal data, containing both incident and reflected waves. The reflected wave represents the desired waveform, distributed across any time period of the detection point data, with a relatively small amplitude. The incident wave, however, is noise, present throughout the entire time period, with its amplitude decreasing from large to small. The artifacts in the SAFT imaging are primarily caused by the large amplitude incident wave. On the PC, cross-correlation matching is performed based on the similarity of data from nearby detection points. The result of cross-correlation matching is mainly affected by the amplitude of the signal. Since the incident wave is relatively large at the beginning, during the full-band matching process of signals from nearby detection points, the incident wave signal matches well and cancels out due to subtraction. The small-amplitude reflected wave signal, due to poor matching, is relatively amplified after subtraction, resulting in a wider overall distribution. When applying SAFT imaging, this amplified reflected wave data is used as the image at the defect point, improving the imaging resolution at the defect. Since the incident wave is canceled out, no artifacts are produced. If the subtraction of the incident wave also highlights the reflected wave that might have originally existed, and if there is a reflected wave, the defect in the original artifact area will also be imaged, so no missed detection will occur. PC 10 controls the acquisition of laser ultrasonic signal data according to the number and path of detection points planned in step 6. Doppler vibration meter 7 receives the data of the next detection point and transmits it back to PC 10. Throughout the process, PC 10 ensures that the data of each detection point is processed synchronously. If there are M original detection point data, there will be M-1 effective detection point data after processing.

[0043] Compared with existing laser ultrasonic inspection systems, this invention, for the first time, applies the correlation between data from different inspection points to the processing of laser ultrasonic signals and combines it with SAFT imaging. In experiments, defect imaging can be completed with only one complete data acquisition and processing of the workpiece under inspection, eliminating the need for a defect-free comparison experiment. This not only improves inspection efficiency and overcomes the shortcomings of windowing methods but also significantly improves imaging quality.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A detection method based on an optimized system for laser-ultrasonic SAFT defect detection, the system comprising a vibrometer probe (1), a pulsed laser emission probe (2), a sample three-dimensional translation stage (4), a galvanometer scanning system (5), a laser (6), a Doppler vibrometer (7), a device three-dimensional translation stage (8), a stepper motor (9), and a PC control console (10). The vibration meter probe (1) and the Doppler vibration meter (7) form an interferometer. The Doppler vibration meter (7) can emit continuous laser light as a probe light. The pulse laser emission probe (2) is used to output Gaussian pulse laser light. The sample three-dimensional translation stage (4) can move to change the three-dimensional position of the workpiece (3) being tested. The galvanometer scanning system (5) includes two galvanometers with mutually perpendicular axes, which are used to control the pulse laser emission probe (2) to move in two mutually perpendicular translation directions. The equipment three-dimensional translation stage (8) can move to change the horizontal movement of the vibration meter probe (1). The stepper motor (9) is used to drive the sample three-dimensional translation stage (4) and the equipment three-dimensional translation stage (8). The PC control console (10) is used to control the laser (6), the stepper motor (9), and the data acquisition and processing. Its features are, The detection method includes the following steps: Step 1: Select the spot radius according to the step size of the detection point. The laser (6) emits pulsed laser and outputs it to the pulsed laser emitting probe (2) through the galvanometer scanning system (5) to the preset excitation position on the surface of the workpiece (3) to be detected. Step 2: The stepper motor (9) controls the three-dimensional translation stage (4) of the sample to move in the vertical direction so that the surface of the workpiece (3) being inspected is located at the laser focus; Step 3: Plan the movement path of the detection point and determine the movement step length of the detection point. Control the three-dimensional translation stage (8) of the equipment through the stepper motor (9) so that the vibration probe (1) of the Doppler vibration meter (7) is at the position of the preset detection point. Step 4: The laser (6) operates and emits pulsed laser light. At the same time, the Doppler vibration meter (7) sends the received ultrasonic data to the PC control console (10) for processing. Step 5: Without changing the laser focus and the position of the detection point, repeatedly emit pulsed lasers. At the same time, the PC control console (10) averages the ultrasonic data obtained multiple times and uses it as the data for the first detection point. ; Step 6: Select the second detection point along the planned detection path and detection point step size. The PC console (10) drives the stepper motor (9) to control the three-dimensional translation stage (8) of the device, so that the vibration probe (1) of the Doppler vibration meter (7) is translated to the position of the second detection point. Repeat step 5 to obtain the data of the second detection point. ; Step 7: PC console (10) processes the data of the first detection point. and the data from the second detection point Signals were obtained by self-normalization respectively and Then, cross-correlation matching is performed; Step 8, SAFT imaging: Take all points in the two-dimensional cross-section of the workpiece (3) to be inspected as imaging points, acquire imaging data of all imaging points, and calculate the time point determined by the sum of the distances between the detection point and the imaging point and between the laser focus and the imaging point based on the wave velocity of the reflected wave. In the received signal Take the corresponding time point of the reflected wave numerical value As the data for the imaging points, the imaging data of all imaging points can be obtained by calculating all imaging points; Step 9: Repeat steps 6 to 8 until all detection points have been detected, and record the difference data for each detection point. As SAFT imaging data, M represents the number of planned inspection points. A total of M-1 inspection point difference data are obtained. All M-1 imaging data are superimposed to obtain the final SAFT imaging image of the inspected workpiece.

2. The detection method of the optimized system based on laser-ultrasonic SAFT defect detection according to claim 1, characterized in that, The laser (6) is a Q-switched laser.

3. The detection method of the optimized system based on laser-ultrasonic SAFT defect detection according to claim 2, characterized in that, The laser (6) has a working wavelength of 1064 nm, a pulse width of 2.5 ns, and an energy of 2.6 mJ.

4. The detection method of the optimized system based on laser-ultrasonic SAFT defect detection according to claim 1, characterized in that, The Doppler vibration meter (7) can emit a continuous laser with a wavelength of 532nm and a spot radius of 0.5mm as a probe light.

5. The detection method of the optimized system based on laser-ultrasonic SAFT defect detection according to claim 1, characterized in that, The workpiece (3) being inspected is a flat or curved metal material.

6. The detection method of the optimized system based on laser-ultrasonic SAFT defect detection according to claim 1, characterized in that, Step 7 specifically includes: First, define For signal relative signal Time shift, The modulus is the delay time, while The sign represents the direction of time shift, when When, its cross-correlation function is , The total length of the data for each detection point, r, is about When the function r reaches its maximum value, the data from the two detection points reach the optimal cross-correlation matching point. , The optimal time shift point for matching the data from the two detection points is now complete. ;when At that time, , ,in .

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