CN114689514A - Metal stress distribution detection system based on laser ultrasonic theory - Google Patents

Metal stress distribution detection system based on laser ultrasonic theory Download PDF

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CN114689514A
CN114689514A CN202111499802.8A CN202111499802A CN114689514A CN 114689514 A CN114689514 A CN 114689514A CN 202111499802 A CN202111499802 A CN 202111499802A CN 114689514 A CN114689514 A CN 114689514A
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laser
light
wave
stress distribution
wave plate
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朱明军
熊吉川
张森宇
赵俊杰
李佳铭
张弘毅
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Nanjing University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0047—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to residual stresses
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G01N2021/1706—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in solids

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Abstract

The invention discloses a metal stress distribution detection system based on a laser ultrasonic theory, which comprises a laser emission module, a spectroscope, an attenuation sheet, a lens, a photoelectric detector, a laser ultrasonic detection device and a signal acquisition and processing module. The invention measures the metal stress by using the detection system, measures a series of surface wave signals at different positions, processes the signals, and calculates the stress distribution.

Description

Metal stress distribution detection system based on laser ultrasonic theory
Technical Field
The invention belongs to the field of laser ultrasonic non-contact detection, and particularly relates to a metal stress distribution detection system based on a laser ultrasonic theory.
Background
With the development of times and the progress of science and technology, more and more new materials and new processes appear in the world. The new materials not only promote the further development of science and technology, but also enable people to live better lives, but also provide a great problem for modern researchers, and compared with other destructive measurement methods, the nondestructive detection technology is undoubtedly more practical in modern production life because of the nondestructive detection technology is nondestructive, and the technology is based on subjects such as computer science and technology, mechanical engineering, materials science, physics and the like. In addition, the nondestructive testing technology has been highly evaluated and agreed in various industries along with the use of various systems and equipment in the past, and the nondestructive testing has become an indispensable technology for the Chinese industry after more than twenty years of development.
The ultrasonic detection technology has the advantages of low cost, high speed, high sensitivity, wide detection range, large detection depth, strong directivity and the like.
Because of the benefits of using ultrasonic detection techniques, it has irreplaceable roles in thickness measurement, bioscience, physics, and the like.
When laser light is incident on a metal surface, a surface wave is generated. The ultrasonic wave is received by a receiver after being continuously reflected and refracted in the material, and the information such as the thickness, the stress, the defect and the like of the material is obtained by analyzing the received signal. Methods for experimentally measuring the residual stress of the fabricated part include drilling, X-ray diffraction, magnetic measurements, and the like. Drilling is often used to measure the residual stress distribution in welded structures, but this involves a material separation or cutting process that may compromise the structural integrity. It is therefore destructive, which greatly limits its application in field testing, even though it is relatively low cost. The ring core method allows the evaluation of stresses in the sample to depths of 5-7mm, deeper than the drilling method. However, it causes more damage to the sample. Although the X-ray diffraction method is a nondestructive measurement method, the X-ray diffraction method is applied only to measurement of residual stress on the surface of a material. In addition, appropriate polishing steps and the like are required. The magnetic method applies a magnetic field to the material to measure the residual stress of the material, and the stress of the metal is obtained by converting the transformation quantity of the stress into measurable electric quantity. However, the magnetic measurement method has a certain limitation, and can be only used for measuring ferromagnetic materials.
Disclosure of Invention
The invention aims to provide a metal stress distribution detection system based on a laser ultrasonic theory.
In order to achieve the purpose, the invention adopts the following technical scheme: the utility model provides a metal stress distribution detecting system based on laser ultrasonic theory, includes laser emission module, spectroscope, decay piece, lens, photoelectric detector, laser ultrasonic detection device and signal acquisition and processing module, and is set up to:
the laser emission module sends out laser and divides into two bundles of light through the spectroscope, and a bundle of light incides the metal sample surface through lens, gathers the signal on the metal sample and transmits signal acquisition and processing module through laser ultrasonic device, and another bundle of light passes through the decay piece after, gathers through photoelectric detector and transmits signal acquisition and processing module, and signal acquisition and processing module handles the signal of gathering, obtains metal stress distribution.
Preferably, the laser emission module adopts a first Nd: YAG laser, and the wavelength of the first Nd: YAG laser is 1064 nm.
Preferably, the laser ultrasonic detection device adopts a photorefractive crystal dual-wave hybrid interferometer, which comprises a second Nd, a YAG laser, a first quarter-wave plate, a first polarization beam splitter prism (PBS1), a second polarization beam splitter prism, a third polarization beam splitter prism, a photorefractive crystal (PRC), a first quarter-wave plate, a second quarter-wave plate, a microscope objective and a photodetector, and is set as follows:
the second Nd is that laser emitted by the YAG laser is incident on the metal sample through the first half-wave plate, the second polarization beam splitter prism, the second quarter-wave plate and the microscope objective;
the signal beam reflected from the surface of the metal sample passes through a second polarization beam splitter prism according to the original optical path and is focused to a photorefractive crystal (PRC), and the reflected signal beam and the reference beam are overlapped at the same position of the photorefractive crystal (PRC); two bundles of light interfere each other in the photorefractive crystal and then take place double wave and mix, and the signal light that comes out behind the photorefractive crystal including the reference beam is on passing through first quarter wave plate and third polarization beam splitting prism, incidenting on the photoelectric detector.
Compared with the prior art, the invention has the following remarkable advantages: the invention is based on the acoustic elastic effect, and completes the stress measurement by accurately measuring the speed of ultrasonic waves transmitted in the material, and the ultrasonic waves have good directionality, strong penetrability and no damage.
Drawings
FIG. 1 is a schematic diagram of a photorefractive crystal two-wave hybrid interferometer.
Fig. 2 is a schematic structural diagram of a photorefractive crystal dual-wave hybrid interferometer.
Fig. 3 is a schematic diagram of a metal stress distribution detection system based on a laser ultrasonic theory.
Fig. 4 is a sample model.
FIG. 5 is a time domain signal acquired by scanning the sample surface along the X-axis.
Fig. 6 is a schematic diagram of a sound velocity distribution on a scan line with reference to a first point.
Fig. 7 is a schematic diagram of the sound velocity distribution.
Fig. 8 is a schematic diagram of the time domain signals obtained by extracting each column in fig. 7.
FIG. 9 is a graph showing normalized stress distribution at scanned points along the surface of a sample.
Detailed Description
As shown in fig. 3, a metal stress distribution detection system based on laser ultrasonic theory includes a laser emitting module, a spectroscope, an attenuation sheet, a lens, a photodetector, a laser ultrasonic detection device, and a signal collecting and processing module, and is configured as follows:
the laser emitting module emits laser which is divided into two beams of light through the spectroscope, one beam of light enters the surface of the metal sample through the lens, the signal on the metal sample is collected through the laser ultrasonic device and transmitted to the signal collecting and processing module, and the other beam of light passes through the attenuation sheet, passes through the photoelectric detector and then is collected and processed through the signal collecting and processing module.
In a further embodiment, the laser emission module adopts a first Nd: YAG laser, and the wavelength of the first Nd: YAG laser is 1064 nm.
In a further embodiment, as shown in fig. 1, the laser ultrasonic detection apparatus employs a photorefractive crystal dual-wave hybrid interferometer, which includes a second Nd, a third Nd, a fourth Nd, a fifth Nd, a sixth, a seventh, a sixth and a seventh half-wave plates (HWP1, HWP2, HWP3), a first polarization splitting prism (PBS1), a second polarization splitting prism (PBS2), a third polarization splitting prism (PBS3), a photorefractive crystal (PRC), a first quarter-wave plate (QWP1), a second quarter-wave plate (QWP2), a microscope objective lens (MO), and a photodetector (D), and is configured to:
the laser beam from the second Nd: YAG laser is first split into a signal beam and a reference beam by a first half-wave plate (HWP1) and then by a first polarization beam splitter prism (PBS 1). The reference light then passes through a second half-wave plate (HWP2) and is reflected by the mirror into the photorefractive crystal (PRC). The signal light is reflected by the reflector and then sequentially enters a third half wave plate (HWP3), a second polarization beam splitter prism (PBS2), a second quarter wave plate (QWP2) and a microscope objective lens (MO) to be incident on the metal sample;
the signal light beam reflected from the surface of the metal sample passes through a second polarization beam splitter prism (PBS2) according to the original light path and is focused to a photorefractive crystal (PRC), and the reflected signal light and the reference light are overlapped at the same position of the photorefractive crystal (PRC); the two beams interfere with each other inside the photorefractive crystal and then double wave mixing occurs. Then, the signal light containing the reference light coming out after passing through the photorefractive crystal passes through a first quarter-wave plate (QWP1) and a third polarization beam splitter prism (PBS3) and then enters a photodetector (D). Finally, the ultrasonic signal is detected by a photoelectric detector (D).
The second Nd: YAG laser, the first quarter wave plate (HWP1), and the first polarization beam splitter prism (PBS1) are located on the same optical axis, and the first polarization beam splitter prism (PBS1) splits the laser light into a signal beam and a reference beam. The metal sample, the Microscope Objective (MO), the second quarter-wave plate (QWP2), the second polarization beam splitter prism (PBS2), the photorefractive crystal (PRC), the third polarization beam splitter prism (PBS3), the first quarter-wave plate (QWP1) and the photodetector (D) are positioned on the same optical axis. A second quarter wave plate (QWP2) and a micro objective lens (MO) are added between a second polarization beam splitter prism (PBS2) and a metal sample, and the second quarter wave plate (QWP2) can be used for adjusting the polarization direction of signal light incident on the surface of the sample, and when the signal light returns, the direction of the signal light can be continuously adjusted to enable the light beam to completely pass through the second polarization beam splitter prism (PBS2) to reach the photorefractive crystal and then form interference with reference light inside the photorefractive crystal. The Microscope Objective (MO) can focus the light beam into a light spot, so that the detection is more accurate, and the optical system can compress the reflected signal light beam, so that the size of the signal light beam is approximately consistent with that of the reference light, and the signal light beam enters the photorefractive crystal through various optical elements.
Specifically, the second Nd-YAG laser is used for emitting laser, the beam splitter is used for splitting incident laser into two beams, the photorefractive crystal is used for mixing the two beams of light, high-efficiency interference can be generated, the reference light can be better matched with signal light after the two beams of light are mixed, the high-efficiency interference has the advantages that the tiny deformation of the surface of a metal test block can be measured, and the influence of tiny change of a propagation path and sample movement can not be generated, so that the interferometer has a high signal-to-noise ratio.
Specifically, the signal acquisition and processing module comprises an oscilloscope, computer software LabView and a three-dimensional mobile platform (motor). And the computer software LabView controls the motion of the three-dimensional mobile platform and processes data acquired by the oscilloscope, and the sample is arranged on the three-dimensional mobile platform, so that a series of surface wave signals can be conveniently acquired at different positions on one line along the x direction of the sample.
The detection principle of the invention is as follows:
the ultrasonic residual stress measurement method is based on the acoustic elastic effect. In the weld, the resulting residual stress changes the speed of movement of the rayleigh wave, which corresponds to different material stress states. As shown in fig. 4. The sensor can collect only xi1Rayleigh waves propagating in the direction (weld direction). It is assumed that rayleigh waves can propagate freely at the welded plate surface. For simplicity, assume plate thickness direction ξ3The above stress is a zero plane stress condition. Thus, only two stress components are considered, longitudinal ξ1σ of (a)11And transverse xi2Sigma of22. This assumption is valid based on the free boundary conditions in the thickness direction of the welded steel sheet. The invention takes into account only the principal stress component σ11And σ22Since the rayleigh wave velocity variation is assumed to be independent of the material shear stress.
Tekriwal and Mazumder deduced the dependence of acoustic velocity on two main state cases. Rayleigh wave on free surface (xi) of isotropic material1-ξ2Plane) upper edge xi1The change in velocity of the directional propagation may be related to the biaxial stress state in the following equation:
Figure RE-GDA0003664043400000051
wherein VRIs the Rayleigh wave velocity, Δ VRIs the change in rayleigh wave velocity between the unstressed solid and the stressed medium. Beta is a1And beta2Is the acoustic spring constant in the longitudinal and transverse directions. This equation provides the rayleigh wave velocity change in a stressed solid with two material basis constants. It can also be seen from this equation that the effect of shear stress on rayleigh wave propagation in thin welded plates is neglected.
Weld induced residual stress σ in the longitudinal direction11Greater than the transverse stress sigma22. In addition, if the propagation direction is along ξ1Go forward, the material coefficient beta2Less than beta1. Therefore, the rayleigh wave velocity variation caused by the transverse stress component is negligible. In this case, the variation in the propagation velocity of the rayleigh wave shown in equation (1) can be simplified and expressed as follows:
Figure RE-GDA0003664043400000052
wherein, is Δ VRIs the change in the velocity of the rayleigh wave,
Figure RE-GDA0003664043400000053
is the rayleigh wave velocity in the unstressed region. A is the coefficient of acoustic elasticity associated with a material, which can be determined by the second and third order coefficients of elastic constants of the material.
Figure RE-GDA0003664043400000054
Representing the relative change in the rayleigh wave propagation velocity.
As can be readily seen from equation (2), an increase in the fluctuation speed indicates a tensile residual stress state, and a decrease indicates a compressive stress state. If the distance is determined to be d0Velocity of Rayleigh wave
Figure RE-GDA0003664043400000055
The relative change in (c) corresponds to the ToF,
Figure RE-GDA0003664043400000061
relative change of (c). Thus, ToF changes can be correlated with stress conditions as follows:
Figure RE-GDA0003664043400000062
wherein
Figure RE-GDA0003664043400000063
Figure RE-GDA0003664043400000064
Xi representing Rayleigh wave in unstressed steel plate1Directionally propagating ToF, tRIs expressed in weld zone xi1The direction of (2) is transmitted.
From equations (1) and (2), the variation in the rayleigh wave velocity depends linearly on the magnitude of the residual stress state in the weld bead direction. The ToF of the rayleigh wave traveling along distance d0 is measured indirectly with a photorefractive crystal two-wave hybrid interferometer. The acoustic elastic constant a links the speed change and the longitudinal residual stress. A normalization procedure is implemented by dividing the velocity measurement data by the maximum value. The residual stress due to welding can be obtained from the normalized distribution of the velocity change of the rayleigh wave.
By using the invention, a series of surface wave signals are taken at different positions on a line along the x direction of a sample, and each signal can extract the time t of the wave crest of the surface wave from an excitation point to a detection pointRAcoustic velocity (V) at the first measurement point, since the stress distribution of the sample is unknownR) For reference, other points are normalized with respect to the first point
Figure RE-GDA0003664043400000065
The arrival time is processed in the same way
Figure RE-GDA0003664043400000066
Thereby calculating the stress distribution obtained on the basis of the first point on the line, wherein R is the peak position of the Rayleigh wave.
FIG. 5 shows a sound wave time domain signal obtained from a certain point on a sample, the signal is obtained by an oscilloscope, the ordinate is signal intensity, the unit is V, the abscissa is time, and in an experiment, the time t corresponding to the peak value (shown by a circle) with the maximum amplitude is takenR。
FIG. 6 is a graph that combines all the signals obtained along each point on the X-axis. The horizontal axis is position (unit m), the vertical axis is time (unit s), and color is signal intensity. The pixels in each column of the graph are taken out to obtain a time domain signal graph as the first one.
The stress distribution is calculated as follows: each column in fig. 7 is taken out to obtain a time domain signal as in fig. 2, and then the arrival time t of the highest peak (surface wave) in the time domain signal is calculatedRAccording to the point sound velocity
Figure RE-GDA0003664043400000067
Figure RE-GDA0003664043400000071
After the sound velocity of each point is obtained, the stress distribution is calculated according to the following formula:
Figure RE-GDA0003664043400000072
Figure RE-GDA0003664043400000073
the normalized stress distribution at the scanning points along the sample surface is shown in fig. 8.

Claims (7)

1. The utility model provides a metal stress distribution detecting system based on laser supersound theory which characterized in that, includes laser emission module, spectroscope, decay piece, lens, photoelectric detector, laser supersound detection device and signal acquisition and processing module, and is set up to:
the laser emitting module emits laser which is divided into two beams of light through the spectroscope, one beam of light enters the surface of the metal sample through the lens, the laser ultrasonic device collects signals on the metal sample and transmits the signals to the signal collecting and processing module, the other beam of light passes through the attenuation sheet and then is collected and transmitted to the signal collecting and processing module through the photoelectric detector, and the signal collecting and processing module processes the collected signals to obtain metal stress distribution.
2. The laser ultrasonic theory-based metal stress distribution detection system according to claim 1, wherein the laser emission module employs a first Nd: YAG laser, and the wavelength of the first Nd: YAG laser is 1064 nm.
3. The laser ultrasonic theory-based metal stress distribution detection system according to claim 1, wherein the laser ultrasonic detection device adopts a photorefractive crystal two-wave hybrid interferometer, comprises a second Nd, a YAG laser, a first half-wave plate (HWP1), a second half-wave plate (HWP2), a third half-wave plate (HWP3), a first polarization beam splitter prism (PBS1), a second polarization beam splitter prism (PBS2), a third polarization beam splitter prism (PBS3), a photorefractive crystal (PRC), a first quarter-wave plate (QWP1), a second quarter-wave plate (QWP2), a Microscope Objective (MO), a photodetector (D), and is arranged as follows:
YAG laser beam emitted from the laser device is divided into signal light and reference light by the first half-wave plate (HWP1) and the first polarization beam splitter prism (PBS1), the reference light is reflected by the reflector into the light refraction crystal (PRC) after passing through a second half-wave plate (HWP 2); the signal light is reflected by a reflecting mirror and is incident on the metal sample through a third half wave plate (HWP3), a second polarization beam splitter prism (PBS2), a second quarter wave plate (QWP2) and a microscope objective lens (MO) in sequence;
the signal light beam reflected from the surface of the metal sample passes through a second polarization beam splitter prism (PBS2) according to the original light path and is focused to a photorefractive crystal (PRC), and the reflected signal light and the reference light are overlapped at the same position of the photorefractive crystal (PRC); two beams of light interfere with each other in the photorefractive crystal and then are subjected to double-wave mixing, and signal light which is emitted from the photorefractive crystal and contains reference light passes through a first quarter-wave plate (QWP1) and a third polarization beam splitter prism (PBS3) and is incident on a photoelectric detector (D).
4. The system for detecting the metal stress distribution based on the laser ultrasonic theory according to claim 3, wherein the wavelength of the second Nd: YAG laser is 532 nm.
5. The laser ultrasonic theory-based metal stress distribution detection system as claimed in claim 1, wherein the signal acquisition and processing module comprises an oscilloscope, computer software LabView, and a three-dimensional moving platform, wherein the computer software LabView controls the movement of the three-dimensional moving platform and processes data acquired by the oscilloscope, and the three-dimensional moving platform is used for placing a sample.
6. The laser ultrasonic theory-based metal stress distribution detection system according to claim 1, wherein the signal acquisition and processing module processes the signal by:
acquiring the ToF of the Rayleigh wave which travels along the distance d0 indirectly by using the optical refractive crystal double-wave hybrid interferometer;
the weld-induced residual stress in the longitudinal direction is solved from the ToF of the rayleigh wave.
7. The laser-ultrasonic-theory-based metal stress distribution detection system according to claim 6, wherein the obtained weld-induced residual stress in the longitudinal direction is:
Figure FDA0003401066780000021
Figure FDA0003401066780000022
a is the acoustic elastic coefficient associated with the material,
Figure FDA0003401066780000023
xi representing Rayleigh wave in unstressed steel plate1Directionally propagating ToF, tRIs shown in weldingZone xi·1The direction of (2) is transmitted.
CN202111499802.8A 2021-10-10 2021-12-09 Metal stress distribution detection system based on laser ultrasonic theory Pending CN114689514A (en)

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