CN108760798A - Laser ultrasonic testing device and method for linear expansion coefficient of metal material - Google Patents
Laser ultrasonic testing device and method for linear expansion coefficient of metal material Download PDFInfo
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Abstract
The invention discloses a laser ultrasonic testing device and method for linear expansion coefficient of metal material, which accurately calculates wave velocity by detecting surface acoustic waves excited by scanning laser at different positions and adopting a waveform correlation algorithm; according to the characteristic that the surface acoustic wave is always transmitted along the surface of the cylinder, the transmission time of the surface acoustic wave in the excitation and detection process at two ends of the diameter is accurately obtained, so that the radius change of the metal sample at different temperatures is obtained, and the linear expansion coefficient is accurately calculated. The testing device is simple and easy to build; the ultrasonic is excited by the pulse laser, so that nondestructive testing is realized, and the method is suitable for nondestructive requirements and online application. The method has the advantages that materials such as the support and the ejector rod except the test material are not used, errors caused by expansion of other materials are avoided, and the test precision is greatly improved by a scanning laser source method and a multi-signal processing method.
Description
Technical field
The invention belongs to linear expansion coefficient fields of measurement, more particularly to a kind of laser-ultrasound of metal wire expansion coefficient
Test device and method.
Background technology
Linear expansion coefficient indicates material expand or the degree of contraction.By varying with temperature curve to linear expansion coefficient
Measurement, the research of material ensaying, phase transformation, the healing of micro-crack and extension etc. can be carried out.Currently, common line expansion
Coefficient measuring method includes strain gauge method, manometer method, optical lever method, optical fibre displacement sensor method, interferometry etc..And it uses super
The method that sound method carries out linear expansion coefficient measurement is actually rare, and CN103499642A discloses a kind of on-line testing material compression system
The method and apparatus of number and the coefficient of expansion are solved by establishing the regression equation of specific volume, the compressed coefficient or the coefficient of expansion and the velocity of sound
The compressed coefficient and the coefficient of expansion, but the caliberating device of this method Structure of need complexity, and the plunger rod in device is in not equality of temperature
Lower thermally expand of degree is affected to the determination of ultrasound propagation time, so as to cause large error；Patent CN107884434A is disclosed
A kind of SMART METALS linear expansion coefficient measuring device based on ultrasound, the characteristics of propagation along metal bar using ultrasonic longitudinal wave, directly
It connects and calculates length of the metal bar in different temperatures, but the time explanation that longitudinal wave signal is larger according to signal is received, it is difficult to root
Swell increment variation when different temperatures is accurately calculated according to longitudinal wave signal.
Invention content
The purpose of the present invention is to provide the laser-ultrasound test devices and method of a kind of metal wire expansion coefficient, lead to
The surface acoustic wave excited in different location by detection scanning laser is crossed, velocity of wave is accurately calculated using waveform related algorithm；According to
The characteristics of surface acoustic wave is always propagated along periphery is accurately obtained propagation of the surface acoustic wave when diameter both ends excite and detect
Time to obtain the metal sample radius change under different temperatures, and then accurately calculates linear expansion coefficient.
In order to solve the above technical problems, the present invention adopts the following technical scheme that：
A kind of laser-ultrasound test device of metal wire expansion coefficient, including Nd：YAG laser, spectroscope, photoelectricity
Pipe, focus lamp, temperature control heating piece, sonac, oscillograph and computer, wherein Nd：YAG laser swashs as ultrasonic wave
It rises；Spectroscope reflective portion pulse laser；Photoelectric tube receives pulse laser, is converted into electric signal, and number is acquired as oscillograph
According to triggering model；Focus lamp Nd：The pulse laser of YAG laser excitation, the excitaton source as ultrasonic wave；Temperature control heating piece adds
Cylindrical sample both sides are loaded in, metal sample steady temperature is controlled；Sonac loads the fixed position D points in periphery,
The surface acoustic wave of direct impulse laser excitation propagated along cylindrical sample surface；The sound that oscillograph acquisition laser interferometer detects
Wave signal data shows acoustic signals and is converted to digital signal；Computer controls pulse laser, spectroscope and focus lamp in essence
It is rotated with fixed angle on close rotating platform, makes pulse laser in metal cylinder sample surfaces different location (P1、P2、P3……
PN) focus, the data of surface acoustic wave, wave signal that recording impulse laser is excited in different location.
Using the laser-ultrasound test method of the metal wire expansion coefficient of above-mentioned apparatus, include the following steps：(1) it closes
Temperature control heating piece is closed, at room temperature, pulse laser is in sample surfaces P1Position excites surface acoustic wave, and sonac is in D points
Detection of SAW is set, the surface acoustic wave signal reached for the first time, propagation path P are detected1→D；
(2) keep metal sample temperature-resistant, the position P of pulsed laser excitation source is moved in steppingN(N=2,3 ... ...,
N), the surface acoustic wave that different excitation positions are reached by nearly cambered surface path is separately detected in D points position, and when the propagation of tracer signal
Between t(N)；Laser-excitation source is moved to PMPosition keeps the surface acoustic wave signal by nearly cambered surface path and remote cambered surface propagated complete
Overlapping, the propagation time t of tracer signalM；
(3) start temperature control heating piece, sample temperature is heated to steady temperature T from 20 DEG C1(T1It is molten less than metal sample
Point), step 1 and step 2 are repeated, T is obtained1Different location P when temperatureNThe ultrasonic signal of the position (N=1,2,3 ... ... N, N >=3)
Nearly cambered surface path travel time t(N)1And PMThe propagation time t of positionM1；(4) it is respectively 20 DEG C and T to temperature1When P1It arrives
PNThe ultrasonic signal of position carries out data processing, and series of signal data is handled using waveform related algorithm, calculates surface acoustic wave and passes
Broadcast speed；
(5) according to PMPosition excites the propagation time of surface acoustic wave, in conjunction with acoustic surface wave propagation speed, calculates different temperatures
When sample radius；
(6) linear expansion coefficient of metal cylinder sample is calculated.
Further, in the laser-ultrasound test method of the metal wire expansion coefficient waveform related algorithm calculating
Process is as follows：If phase is normalized in measuring signal r (t) and s (t) by the acoustic signals r (t) and s (t) of adjacent position excitation
Operation is closed, related coefficient is：
In formula, τ indicates signal s (t) time delay relative to reference signal r (t), when B (τ)=1, then s (t) and r (t)
Identical, value τ when B (τ) is maximum value is the time delay of two waveforms.
Further, determining for surface acoustic wave is improved in the laser-ultrasound test method of the metal wire expansion coefficient
The calculating process of position precision is as follows：
Quadratic polynomial fitting is carried out to different measurement points, obtains following formula：
F (x)=ax2+bx+c
τ=b-/2a just corresponds to the maximum value of f (x), i.e., position when correlation function B (τ) is maximized, signal s (t) phases
For the time delay Δ t=-b/2a of r (t), the acoustic surface wave propagation time is determined according to the time delay of adjacent signals.
Further, waveform related algorithm is utilized in the laser-ultrasound test method of the metal wire expansion coefficient
The time relative delay Δ t of each step is calculated the result of detection of N steps, and stepper motor moves step-length of the probe source in cambered surface and is
Δ x obtains the linear fit relationship of the change in location Δ x and Δ t of waveform, and the slope of fitting a straight line is 1/VR, VRAs sound surface
Wave velocity of wave.
Further, increase the step of laser acquisition in the laser-ultrasound test method of the metal wire expansion coefficient
Number N, improves the computational accuracy of surface acoustic wave velocity of wave.
Compared with prior art, the present invention at least has the advantages that：
(1) test device is simple, is easy to build；
(2) it by pulse laser excitation ultrasound, realizes non-destructive testing, is suitble to lossless demand and application on site；
(2) without materials such as holder, mandrils other than test material, error will not be introduced because of the expansion of other materials；
(3) by scanning laser source method and multi signal processing method, measuring accuracy is greatly improved.
Description of the drawings
Fig. 1 is the test device schematic diagram employed in test method of the present invention；
Fig. 2 is Typical laser ultrasonic signal, and wherein R indicates the surface acoustic wave reached by nearly cambered surface path；RR is indicated along remote
The surface acoustic wave that cambered surface path reaches；
Fig. 3 is the acoustic signals that waveform related algorithm extracts that scanning laser source is excited in adjacent position；
Fig. 4 is related algorithm value and fitting of a polynomial；
Fig. 5 is the Linear Fit Chart of Δ x and Δ t (inverse of slope is velocity of wave)；
Fig. 6 is Wen Sheng-strain testing and linear expansion coefficient.
Specific implementation mode
The present invention is described in further detail with comparative example with reference to embodiment.
Test device schematic diagram used by the laser-ultrasound test method of metal wire expansion coefficient is such as in the present invention
It is specific as follows shown in Fig. 1：
1.Nd：YAG laser：Emission pulse laser (wavelength 1064nm, pulsewidth 5ns), after spectroscope and focus lamp,
It is focused into point source of light (100-300 microns a diameter of), the excitaton source as ultrasonic wave in sample surfaces.
2. spectroscope：Reflective portion pulse laser, makes photoelectric tube receive pulsed laser energy.
3. photoelectric tube：Photoelectric tube receives pulse laser (response time≤5ns), is converted into electric signal, is adopted as oscillograph
Collect the triggering model of data.
4. focus lamp：Focus Nd：The pulse laser of YAG laser excitation, makes it be focused on metal sample surface dotted
Light source (100-300 microns a diameter of), the excitaton source as ultrasonic wave.
5. temperature control heating piece：Load controls metal sample steady temperature, meets under different temperatures in cylindrical sample both sides
Test.
6. sonac：Load periphery fixed position D points, direct impulse laser excitation along cylindrical sample
The surface acoustic wave that surface is propagated.
7. oscillograph：The acoustic data signal that acquisition laser interferometer detects shows acoustic signals and is converted to number
Signal.
8. computer：Control pulse laser, spectroscope and focus lamp are rotated on precision rotation platform with fixed angle, are made
Pulse laser is in metal cylinder sample surfaces different location (P1、P2、P3……PN) focus.Recording impulse laser is in different location
The surface acoustic wave of excitation, the data of wave signal accurately calculate acoustic surface wave propagation speed and propagation according to waveform related algorithm
Time, and calculate propagation path variation.
Using above-mentioned apparatus, in the present invention, the specific steps of the laser-ultrasound test method of metal wire expansion coefficient are such as
Under：
(1) temperature control heating piece is closed, under room temperature (20 DEG C), pulse laser is in sample surfaces P1Swash sound generating surface in position
Wave, sonac detect the surface acoustic wave signal reached for the first time, propagation path P in D points position detection of SAW1→
D；
(2) keep metal sample temperature-resistant, the position P of pulsed laser excitation source is moved in steppingN(N=2,3 ... ...,
N), the surface acoustic wave that different excitation positions are reached by nearly cambered surface path is separately detected in D points position, and when the propagation of tracer signal
Between t(N)；Laser-excitation source is moved to PMPosition keeps the surface acoustic wave signal by nearly cambered surface path and remote cambered surface propagated complete
Overlapping, the propagation time t of tracer signalM；
(3) start temperature control heating piece, sample temperature is heated to steady temperature T from 20 DEG C1(T1It is molten less than metal sample
Point), step 1 and step 2 are repeated, T is obtained1Different location P when temperatureNThe ultrasonic signal of the position (N=1,2,3 ... ... N, N >=3)
Nearly cambered surface path travel time t(N)1And PMThe propagation time t of positionM1；(4) it is respectively 20 DEG C and T to temperature1When P1It arrives
PNThe ultrasonic signal of position carries out data processing, and series of signal data is handled using waveform related algorithm, calculates surface acoustic wave and passes
Broadcast speed；
(5) according to PMPosition excites the propagation time of surface acoustic wave, in conjunction with acoustic surface wave propagation speed, calculates different temperatures
When sample radius；
(6) linear expansion coefficient of metal cylinder sample is calculated.
The present invention test linear expansion coefficient principle be：By detection scanning laser on the sound surface that different location excites
Wave accurately calculates velocity of wave using waveform related algorithm；The characteristics of always being propagated along periphery according to surface acoustic wave, is accurately obtained
Propagation time of the surface acoustic wave when diameter both ends excite and detect becomes to obtain the metal sample radius under different temperatures
Change, and then accurately calculates linear expansion coefficient.
The linear expansion coefficient α of metal cylinder sample is：
Wherein r0For room temperature when cylindrical radius, r1For T1Cylindrical radius when temperature.
In T1At a temperature of, scanning laser source is in P1To PNWhen position, surface acoustic wave velocity of wave (VR) with the relationship of propagation distance
For：
Wherein, LNFor surface acoustic wave along periphery from PNPoint arrives the propagation distance of D points, θNFor PNPoint arrives D point propagation paths
Corresponding angle, tRFor the propagation time of surface acoustic wave.
Then when in PMIt, can be according to the propagation time t of surface acoustic wave when positionMCalculate metal cylinder radius when different temperatures：
r1=(VR1tM1)/π (3)
In step (1) to the test process of step (5), the surface acoustic wave signal of scanning laser source excitation different location, essence
Really measure the velocity of wave of surface acoustic wave and propagation time under different temperatures, can calculate different temperatures when metal cylinder sample half
Diameter substitutes into the linear expansion coefficient that metal material can be obtained in formula (1).
It should be further noted that surface acoustic wave velocity of wave and the measuring accuracy in propagation time determine linear expansion coefficient
Computational accuracy.
The propagation time of surface acoustic wave is directly read by waveform signal, due to being less than the photoelectric tube of 5ns using the response time
It triggers oscillograph and receives signal, can ensure propagation starting time high-precision enough, therefore the error in propagation time is mainly deposited
It is waveform value error on a timeline.Ultrasonic signal as shown in Figure 2, surface acoustic wave (R is labeled as in figure) is in time
Broadening is less than 0.05 μ s (more than 20 data points), and due to the propagation characteristic of surface acoustic wave, and signal has significant
Sharp peak, therefore be reference with the time of the peak position, the propagation time error of surface acoustic wave is can guarantee in signal value
Less than 2.5ns.
To lasing light emitter in P1To PNThe Series ultrasonic signal of position excitation, surface wave is accurately calculated using waveform related algorithm
Speed and velocity variations.Calculating process is as follows：If the acoustic signals r (t) and s (t) of adjacent position excitation, as shown in Figure 3.
Related operation is normalized in measuring signal r (t) and s (t), related coefficient is：
τ indicates time delays of this signal s (t) relative to reference signal r (t) in formula.For two sound of arbitrary continuation
Surface wave waveform, according to formula (4), related coefficient occurs to change accordingly between 0 to 1, when related coefficient reaches maximum value
When, i.e. signal s (t) and reference signal r (t) is most like, such as B (τ)=1, then s (t) is identical with r (t).At this point, B (τ)
For maximum value when value τ be two waveforms time delay.Since the positioning accuracy of surface acoustic wave is up to oscillograph
Sampling period T carries out quadratic polynomial fitting to further increase this precision to different measurement points, as shown in figure 4,
Obtain following formula：
F (x)=ax2+bx+c (5)
τ=- b/2a so just corresponds to the maximum value of f (x), this value is also position when correlation function B (τ) is maximized
It sets namely time delay Δ t=-b/2as of the signal s (t) relative to r (t), sound table is determined according to the time delay of adjacent signals
The surface wave propagation time.
The time relative delay Δ t of each step, stepper motor are calculated using above-mentioned waveform related algorithm the N result of detection walked
Step-length of the mobile probe source in cambered surface is Δ x, can obtain the linear fit relationship of the change in location Δ x and Δ t of waveform,
As shown in figure 5, the slope of fitting a straight line is 1/VR, VRAs surface acoustic wave velocity of wave.The step number N for increasing laser acquisition, can improve
The computational accuracy of surface acoustic wave velocity of wave.
By the acoustic surface wave speed V of accurate measureRAnd tM, metal sample material can be calculated to obtain by formula (1) and (3)
Linear expansion coefficient.
The linear expansion coefficient for now measuring aluminium alloy cylindrical sample (radius of machining 10mm) is tested using step (1)-(5) and is swashed
Light activated surface acoustic wave signal, and accurately calculate the spread speed V of surface acoustic wave at different temperaturesR, in conjunction with arrival time
tM, radius change of the derived sample in different temperatures is as shown in table 1, and the relation curve of fit radius variation and temperature can obtain material
The linear expansion coefficient of material is 20.7 × 10-6/℃。
The test data of 1 aluminium alloy cylindrical sample (r=10mm) of table
Specific implementation mode of the invention above described embodiment only expresses, but can not be therefore understands that for the present invention
The limitation of the scope of the claims.Any variation that those skilled in the art is the present invention under the enlightenment of present inventive concept is fallen
Within the scope of the present invention.
Claims (6)
1. a kind of laser-ultrasound test device of metal wire expansion coefficient, including Nd：YAG laser, spectroscope, photoelectricity
Pipe, focus lamp, temperature control heating piece, sonac, oscillograph and computer, which is characterized in that Nd：YAG laser is as ultrasound
The excitaton source of wave；Spectroscope reflective portion pulse laser；Photoelectric tube receives pulse laser, electric signal is converted into, as oscillograph
The triggering model of gathered data；Focus lamp Nd：The pulse laser of YAG laser excitation, the excitaton source as ultrasonic wave；Temperature control adds
Backing load controls metal sample steady temperature in cylindrical sample both sides；Sonac loads the fixed bit in periphery
Set D points, the surface acoustic wave of direct impulse laser excitation propagated along cylindrical sample surface；Oscillograph acquires laser interferometer detection
The acoustic data signal arrived shows acoustic signals and is converted to digital signal；Computer controls pulse laser, spectroscope and focusing
Mirror is rotated on precision rotation platform with fixed angle, makes pulse laser in metal cylinder sample surfaces different location (P1、P2、
P3……PN) focus, the data of surface acoustic wave, wave signal that recording impulse laser is excited in different location.
2. a kind of laser-ultrasound test method of metal wire expansion coefficient, which is characterized in that include the following steps：
(1) temperature control heating piece is closed, at room temperature, pulse laser is in sample surfaces P1Position excites surface acoustic wave, sonac
In D points position detection of SAW, the surface acoustic wave signal reached for the first time, propagation path P are detected1→D；
(2) keep metal sample temperature-resistant, the position P of pulsed laser excitation source is moved in steppingN(N=2,3 ... ..., N), in D
Point position separately detects the surface acoustic wave that different excitation positions are reached by nearly cambered surface path, and the propagation time t of tracer signal(N)；
Laser-excitation source is moved to PMPosition keeps the surface acoustic wave signal by nearly cambered surface path and remote cambered surface propagated completely overlapped,
The propagation time t of tracer signalM；
(3) start temperature control heating piece, sample temperature is heated to steady temperature T from 20 DEG C1(T1Less than metal sample fusing point), weight
Multiple step 1 and step 2, obtain T1Different location P when temperatureNThe nearly arc of the ultrasonic signal of the position (N=1,2,3 ... ... N, N >=3)
Face path travel time t(N)1And PMThe propagation time t of positionM1；
(4) it is respectively 20 DEG C and T to temperature1When P1To PNThe ultrasonic signal of position carries out data processing, using waveform related algorithm
Series of signal data is handled, acoustic surface wave propagation speed is calculated；
(5) according to PMPosition excites the propagation time of surface acoustic wave, in conjunction with acoustic surface wave propagation speed, when calculating different temperatures
Sample radius；
(6) linear expansion coefficient of metal cylinder sample is calculated.
3. the laser-ultrasound test method of metal wire expansion coefficient according to claim 2, which is characterized in that waveform
The calculating process of related algorithm is as follows：If the acoustic signals r (t) and s (t) of adjacent position excitation, by measuring signal r (t) and s
(t) related operation is normalized, related coefficient is：
In formula, τ indicates signal s (t) time delay relative to reference signal r (t), and when B (τ)=1, then s (t) and r (t) is complete
Identical, value τ when B (τ) is maximum value is the time delay of two waveforms.
4. the laser-ultrasound test method of metal wire expansion coefficient according to claim 3, which is characterized in that improve
The calculating process of the positioning accuracy of surface acoustic wave is as follows：
Quadratic polynomial fitting is carried out to different measurement points, obtains following formula：
F (x)=ax2+bx+c
τ=- b/2a just corresponds to the maximum value of f (x), i.e., position when correlation function B (τ) is maximized, signal s (t) is relative to r
(t) time delay Δ t=-b/2a, the acoustic surface wave propagation time is determined according to the time delay of adjacent signals.
5. the laser-ultrasound test method of metal wire expansion coefficient according to claim 3 or 4, which is characterized in that
The time relative delay Δ t of each step is calculated using waveform related algorithm the N result of detection walked, and stepper motor moves probe source
Step-length in cambered surface is Δ x, obtains the linear fit relationship of the change in location Δ x and Δ t of waveform, the slope of fitting a straight line is
1/VR, VRAs surface acoustic wave velocity of wave.
6. the laser-ultrasound test method of metal wire expansion coefficient according to claim 5, which is characterized in that increase
The step number N of laser acquisition improves the computational accuracy of surface acoustic wave velocity of wave.
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| CN111239243A (en) * | 2020-01-20 | 2020-06-05 | 南京大学 | Nondestructive testing method for longitudinal defects of small-caliber thin-walled tube based on laser ultrasound and circumferential guided wave |
| CN111257237A (en) * | 2020-02-10 | 2020-06-09 | 金陵科技学院 | High-rise building security system design method based on surface acoustic waves |
| CN114935547A (en) * | 2022-06-01 | 2022-08-23 | 国家石油天然气管网集团有限公司 | Pipeline hardness internal inspection method and system |
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