CN112765543A - Acoustic time difference algorithm for ultrasonic detection - Google Patents
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Abstract
The invention belongs to the technical field of residual stress testing, and particularly relates to an acoustic time difference algorithm for ultrasonic detection, wherein the acoustic time difference algorithm is arranged between adjacent LCRMultiple data points are inserted between the original wave data to improve the measurement accuracy, and the L in the zero-stress state after the differenceCRWave and detected position LCRCarrying out data processing on the waves, calculating sound time difference, and then carrying out simulation verification; the acoustic time difference is calculated by respectively utilizing a cross-correlation algorithm and a peak algorithm, and the calculation accuracy of different algorithms is analyzed by utilizing numerical simulation, so that the bulk wave which is transmitted at the longitudinal wave speed under the surface of the material is more sensitive to a stress field in a limited thickness and is not limited to the surface of the material.
Description
Technical Field
The invention belongs to the technical field of residual stress testing, and particularly relates to an acoustic time difference algorithm for ultrasonic detection.
Background
The ultrasonic method is one of the most promising techniques in the development direction of nondestructive testing of residual stress. Ultrasonic stress detection is based on a linear relationship between ultrasonic wave velocity and material stress, namely, an acoustic elastic effect which is shown in an elastic limit of a material and shows a linear correlation with stress when in sound. However, the acoustic-elastic effect is a weak effect, and the time difference caused by the change in stress is in the order of nanoseconds. Therefore, the key to detecting stress using ultrasound is the accurate measurement of the acoustic time difference.
Disclosure of Invention
The invention provides an acoustic time difference algorithm for ultrasonic detection, which aims to solve the problems in the prior art, and can process the acquired waveforms by respectively adopting linear difference, cubic difference and spline difference algorithms on the premise of not increasing the hardware cost, then respectively calculating the acoustic time difference by utilizing a cross-correlation algorithm and a peak algorithm, and analyzing the calculation accuracy of different algorithms by utilizing numerical simulation. Meanwhile, an optimized acoustic time difference algorithm is provided in consideration of the influences of the stability of the coupling layer and the thickness of the tested piece during detection.
The invention adopts the specific technical scheme that: the sound time difference algorithm for ultrasonic detection is characterized by comprising the following steps:
acoustic moveout algorithm at adjacent LCRMultiple data points are inserted between the original wave data to improve the measurement accuracy, and the L in the zero-stress state after the differenceCRWave and detected position LCRCarrying out data processing on the waves, and calculating sound time difference;
propagation in the direction of stress LCRThe relationship between wave velocity and stress is as follows:
wherein V is L under stressCRPropagation velocity of wave, p0Is the density, lambda and mu generation of the material to be measuredSecond order elastic constants of the surface material, l and m are third order elastic constants, sigma is a stress value, a positive value represents tensile stress, a negative value represents compressive stress,
and (3) respectively deriving the relationship between the sound velocity variation and the stress variation on two sides of the formula (1):
wherein d σ is the amount of change in stress (MPa), and dV is LCRChange in wave propagation velocity, V0Is the propagation velocity of longitudinal wave under the condition of zero stress, and K is the acoustic elastic constant;
from equation (2), the relationship between stress and sound velocity can be simplified to:
dσ＝K0dt (3)
in the formula (I), the compound is shown in the specification,
is the stress constant; t is t0Is L under zero stress conditionCRThe time required for wave propagation to fix the distance can be known, and the key point for measuring the residual stress by using the sound wave is to accurately measure the sound time difference;
the central frequency of a transducer adopted by an ultrasonic residual stress detection hardware system is 5MHz, the frequency of a high-speed data acquisition card is 100MHz, the time interval of each sampling point is 10ns, and in order to improve the measurement accuracy of the acoustic time difference, adjacent LCRInserting 100 data points between original wave data can be accurate to 0.1ns, and two columns L in a zero-stress state after differenceCRAnd calculating the acoustic time difference by comparing the time at the wave peak value, wherein the cross-correlation calculation formula according to the discrete signals comprises the following steps:
in the formula, N is the number of sampling points, m is the time delay sequence, and the cross-correlation function RxyThe properties of (m) can be represented by fig. 2, where the time shift τ ═ τ is shown0ReflectingThe lag time between x (t) and y (t), i.e., the acoustic time difference, is given.
And after the acoustic time difference is obtained through calculation, carrying out numerical simulation verification of the algorithm, and carrying out stress detection on the residual compressive stress test block preset by shot blasting by using a 100MHz data acquisition card, a 2.5MHz ultrasonic detection probe and a stress detection software algorithm and adopting a detection mode that two ultrasonic probes obliquely enter a transmitting wave and a receiving wave.
Preferably, the hardware is designed into a constant magnetic attraction structure, so that the contact force between the sound transmission wedge and the surface of the measured piece is constant, and the liquid coupling film is uniform; adopting a delay + stability criterion on software, delaying for 2min, and circularly reading L after the coupling agent is stabilizedCRWave data, a plurality of LCRPerforming cross-correlation analysis on the wave data, if absolute value<When 0.5ns, the system is considered to be stable, and stress analysis is started.
Preferably, zero stress is separately calibrated for different thickness of the measured piece, and only L is interceptedCRAnd calculating the position of the first wave trough of the wave by a peak method.
The invention has the beneficial effects that: under the existing hardware environment, Lagrange linear interpolation is adopted to be 0.5ns, then the acoustic time difference calculated through cross correlation can be accurate to 0.5ns, and the theoretical detection precision of the residual stress reaches within 10 MPa. The interpolation point of the combined algorithm is moderate, the calculation speed is high, and the precision is high; calculating the acoustic time difference by using a linear interpolation to 0.1ns + cross-correlation algorithm; or spline interpolation is selected to be 0.1ns + peak value algorithm to calculate the acoustic time difference, so that the precision of 0.1ns is obtained;
and processing the acquired waveforms by adopting linear difference, cubic difference and spline difference algorithms respectively, calculating the acoustic time difference by utilizing a cross-correlation algorithm and a peak algorithm respectively, and analyzing the calculation accuracy of different algorithms by utilizing numerical simulation. Meanwhile, in the process of detecting residual stress on site, the thickness unevenness of a couplant film and the thickness difference of a detected piece bring great errors and even singular dataCRWave can be atBulk waves propagating at longitudinal wave velocities below the surface of a material are more sensitive to stress fields within a limited thickness and are not confined to the surface of the material.
Drawings
FIG. 1 is a functional block diagram of an acoustic time difference optimization algorithm;
FIG. 2 is a cross-correlation waveform diagram;
FIG. 3 is two columns of analog sinusoidal signals;
FIG. 4 is a comparison of the accuracy of the cross-correlation method and the peak method when the difference reaches 0.5 ns;
FIG. 5 is a comparison of the accuracy of the cross-correlation method and the peak method when the difference reaches 0.1 ns;
fig. 6 shot peening presets residual stress values.
Detailed Description
The invention will be further described with reference to the following drawings and specific embodiments:
LCRa wave is a bulk wave that propagates at longitudinal wave velocities below the surface of a material, is more sensitive to stress fields within a limited thickness, and is not limited to the surface of the material.
The research shows that the L is propagated along the stress directionCRThe relationship between the wave velocity and the stress is as follows[6]：
Wherein V is L under stressCRPropagation velocity of wave, p0In the density of the measured material, λ and μ represent the second-order elastic constants of the material, l and m are the third-order elastic constants, σ represents the stress value, positive values represent tensile stress, and negative values represent compressive stress.
And (3) respectively deriving the relationship between the sound velocity variation and the stress variation on two sides of the formula (1):
wherein d σ is the amount of change in stress (MPa), and dV is LCRWave propagationAmount of change in speed, V0Is the propagation velocity of longitudinal wave under the condition of zero stress, and K is the acoustic elastic constant.
From equation (2), the relationship between stress and sound velocity can be simplified to:
dσ＝K0dt (3)
in the formula (I), the compound is shown in the specification,
is the stress constant; t is t0Is L under zero stress conditionCRThe time required for the wave to travel a fixed distance. It can be seen that the key to measuring residual stress with acoustic waves is to accurately measure acoustic time differences.
The central frequency of a transducer adopted by the ultrasonic residual stress detection hardware system is 5MHz, the frequency of a high-speed data acquisition card is 100MHz, and the time interval of each sampling point is 10 ns. In order to improve the measurement accuracy of the acoustic time difference, adjacent LCRThe interpolation of 100 data points between the wave raw data can be accurate to 0.1 ns. Two columns L in a zero-stress state after the differenceCRAnd calculating the acoustic time difference by comparing the time at the wave peak value, wherein the cross-correlation calculation formula according to the discrete signals comprises the following steps:
in the formula, N is the number of sampling points, and m is the time delay sequence. Cross correlation function RxyThe properties of (m) can be represented by FIG. 2. Time shift τ ═ τ in the figure0Reflecting the lag time between x (t) and y (t), i.e. the acoustic time difference.
For determining the L collected by a 100MHz data acquisition cardCRAnd (4) after the wave data pass through different difference algorithms, carrying out peak value method or cross-correlation method operation to judge whether the expected acoustic time difference measurement precision can be achieved, and carrying out simulation verification. Two arrays of sinusoidal signals were simulated using MATLAB software, as shown in fig. 3.
And respectively adopting three difference algorithms to enable the sound time precision difference to reach 0.5ns and 0.1ns, and calculating the interpolated data by a cross correlation method and a peak method to respectively calculate the sound time difference. And performing cross-correlation method and peak method calculation on the interpolated data, and respectively calculating the acoustic time difference. With a large amount of simulation data, the acoustic time difference accuracy compared to different algorithms is shown in fig. 4 and 5.
The comprehensive analysis can obtain that the precision of the cross-correlation algorithm for calculating the sound time difference is only related to the number of interpolation points and is not related to which interpolation method is adopted, so that the linear interpolation and the cross-correlation algorithm are adopted for calculating the sound time difference very properly. The method for calculating the sound time difference by linear interpolation to 0.5ns and then cross-correlation can be accurate to the accuracy of 0.5ns, and the method has moderate interpolation point, high calculation speed and high accuracy.
In the process of experimental verification, the stress value of the test block sometimes measures singular data with large deviation. The test is carried out at room temperature, and the test process is considered to be a constant temperature state. Even with a 1 ℃ temperature change, only about 70MPa of stress change is caused, so that the test temperature change is not the main cause of the generation of singular data. The reason for analyzing the method is mainly as follows: the influence of the thickness of the coupling layer and the influence of the thickness of the measured piece.
The effect of the coupling layer thickness can be reduced by optimization of the mechanical structure and software algorithms. If the hardware is designed into a constant magnetic attraction structure, the contact force between the sound transmission wedge and the surface of the tested piece is constant, so that the uniformity of the liquid coupling film is ensured; the software adopts a delay + stability criterion, namely delaying for 2min first, so that the couplant is stabilized and then read L circularlyCRWave data, a plurality of LCRPerforming cross-correlation analysis on the wave data, if absolute value<When 0.5ns, the system is considered to be stable, and stress analysis is started.
In the generation of LCRWhen the wave is generated, the refracted transverse wave is transmitted to the bottom surface of the tested piece and can be reflected back, when the reflected transverse wave is reflected to the surface from the bottom surface, the wave form conversion can be generated, and a part of the reflected transverse wave is converted into the longitudinal wave transmitted along the surface, so that the L pair is formedCRInfluence of the wave shape. The solution is as follows: firstly, separately calibrating zero stress for measured pieces with different thicknesses, and secondly, only intercepting LCRAnd calculating the position of the first wave trough of the wave by a peak method.
The experimental verification is carried out by detecting the residual compressive stress of the test block, which specifically comprises the following steps: stress detection is carried out on the residual compressive stress test block preset by shot blasting by utilizing a 100MHz data acquisition card, a 2.5MHz ultrasonic detection probe and a stress detection software algorithm and adopting a detection mode that two ultrasonic probes obliquely enter a transmitting wave and a receiving wave. The test block was annealed (heated to 450 ℃ for 2 hours at constant temperature and then furnace-cooled) before shot blasting to relieve initial stress. And after the heat treatment, cleaning an oxide film on the surface of the workpiece. And respectively leaving one test block with different thicknesses for zero stress calibration, and then carrying out shot blasting treatment on the other test blocks by adopting a single nozzle. All test blocks are put into a constant temperature box (the temperature is 18-22 ℃), and the natural release of the stress of the test blocks caused by long-time day and night temperature difference is prevented. The results of ultrasonic stress measurement of the shot blast region for 9 consecutive days are shown in fig. 6.
Claims (4)
1. The acoustic time difference algorithm for ultrasonic detection is characterized by comprising the following steps of:
acoustic moveout algorithm at adjacent LCRMultiple data points are inserted between the original wave data to improve the measurement accuracy, and the L in the zero-stress state after the differenceCRWave and detected position LCRCarrying out data processing on the waves, and calculating sound time difference;
propagation in the direction of stress LCRThe relationship between wave velocity and stress is as follows:
wherein V is L under stressCRPropagation velocity of wave, p0The density of the tested material is shown, lambda and mu represent the second-order elastic constant of the material, l and m are the third-order elastic constants, sigma is the stress value, positive value represents tensile stress, negative value represents compressive stress,
and (3) respectively deriving the relationship between the sound velocity variation and the stress variation on two sides of the formula (1):
wherein d σ is the amount of change in stress (MPa), and dV is LCRChange in wave propagation velocity, V0Is the propagation velocity of longitudinal wave under the condition of zero stress, and K is the acoustic elastic constant;
from equation (2), the relationship between stress and sound velocity can be simplified to:
dσ＝K0dt (3)
in the formula (I), the compound is shown in the specification,
is the stress constant; t is t0Is L under zero stress conditionCRThe time required for wave propagation to fix the distance can be known, and the key point for measuring the residual stress by using the sound wave is to accurately measure the sound time difference;
the central frequency of a transducer adopted by an ultrasonic residual stress detection hardware system is 5MHz, the frequency of a high-speed data acquisition card is 100MHz, the time interval of each sampling point is 10ns, and in order to improve the measurement accuracy of the acoustic time difference, adjacent LCRInserting 100 data points between original wave data can be accurate to 0.1ns, and two columns L in a zero-stress state after differenceCRAnd calculating the acoustic time difference by comparing the time at the wave peak value, wherein the cross-correlation calculation formula according to the discrete signals comprises the following steps:
in the formula, N is the number of sampling points, m is the time delay sequence, and the cross-correlation function RxyThe properties of (m) can be represented by fig. 2, where the time shift τ ═ τ is shown0Reflecting the lag time between x (t) and y (t), i.e. the acoustic time difference.
2. The acoustic moveout algorithm for ultrasonic detection according to claim 1 or 2, wherein: the hardware is designed into a constant magnetic attraction structure, so that the contact force between the sound transmission wedge and the surface of a measured piece is constant, and the liquid couplingThe combined film is uniform and consistent; adopting a delay + stability criterion on software, delaying for 2min, and circularly reading L after the coupling agent is stabilizedCRWave data, a plurality of LCRPerforming cross-correlation analysis on the wave data, if absolute value<When 0.5ns, the system is considered to be stable, and stress analysis is started.
3. The acoustic moveout algorithm for ultrasonic detection of claim 3, wherein: separately calibrating zero stress for measured parts with different thicknesses, and only intercepting LCRAnd calculating the position of the first wave trough of the wave by a peak method.
4. The acoustic moveout algorithm for ultrasonic detection of claim 1, wherein: and after the acoustic time difference is obtained through calculation, carrying out numerical simulation verification on the algorithm, and carrying out stress detection on the shot-peening preset residual compressive stress test block by utilizing a selected hardware system and a software algorithm and adopting a one-sending-one-receiving mode.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115144112A (en) * | 2022-06-23 | 2022-10-04 | 武汉中科创新技术股份有限公司 | Residual stress detection method and device, electronic equipment and storage medium |
| CN117968904A (en) * | 2024-04-02 | 2024-05-03 | 晗煊科技(成都)有限公司 | Ultrasonic testing system and method for axial stress of anchor rod |
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| CN106679872A (en) * | 2017-01-25 | 2017-05-17 | 大连理工大学 | Surface residual stress ultrasonic detection method capable of achieving direct coupling wave generation |
| US20200158585A1 (en) * | 2018-11-16 | 2020-05-21 | Beijing Institute Of Technology | Non-destructive detecting method for weld residual stress and a probe using the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106679872A (en) * | 2017-01-25 | 2017-05-17 | 大连理工大学 | Surface residual stress ultrasonic detection method capable of achieving direct coupling wave generation |
| US20200158585A1 (en) * | 2018-11-16 | 2020-05-21 | Beijing Institute Of Technology | Non-destructive detecting method for weld residual stress and a probe using the same |
Non-Patent Citations (1)
| Title |
|---|
| 宋文涛: "残余应力超声无损检测与调控技术研究", 《博士学位论文电子期刊 工程科技I辑》 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115144112A (en) * | 2022-06-23 | 2022-10-04 | 武汉中科创新技术股份有限公司 | Residual stress detection method and device, electronic equipment and storage medium |
| CN117968904A (en) * | 2024-04-02 | 2024-05-03 | 晗煊科技(成都)有限公司 | Ultrasonic testing system and method for axial stress of anchor rod |
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Application publication date: 20210507 |