KR101180151B1 - Measuring method of poisson's ratio and measuring apparatus thereof - Google Patents

Abstract

In the laser ultrasound method, a method and a measuring device for measuring Poisson's ratio using ultrasonic excitation by a thermoelastic effect in which no damage is caused to the surface of the inspected object and no trace of laser irradiation is provided.

By irradiating pulsed laser light on the surface of the test object, ultrasonic waves are generated by the thermoelastic effect.The continuous wave laser light is irradiated on the surface of the test object, and the ultrasonic wave propagating through the test object is received to determine the Poisson's ratio of the test object. As a measuring method, a plate wave ultrasonic wave and surface wave ultrasonic wave propagating to a subject under test are received, the frequency of the plate wave ultrasonic wave is calculated, the propagation time of the surface wave ultrasonic wave is measured, and the surface wave ultrasonic wave propagates from the propagation time and the propagation distance. A speed is calculated, and the Poisson's ratio is calculated based on the frequency of the said wave-wave ultrasonic wave and the propagation speed of the said surface wave ultrasonic wave.

Plate Wave Ultrasound, Surface Wave Ultrasound, Poisson's Ratio

Description

Measuring method and measuring device of Poisson's ratio {MEASURING METHOD OF POISSON'S RATIO AND MEASURING APPARATUS THEREOF}

The present invention relates to a method of measuring the Poisson's ratio by generating ultrasonic waves without damaging the surface of an inspected object by using a thermoelastic effect in a laser ultrasonic method in which ultrasonic waves are generated in a non-contact manner using a laser. It is about.

Poisson's ratio is the ratio of transverse and longitudinal strain when stress is applied to the material, and is an important index of strength of the material, such as Young's modulus, in grasping the strain in the elastic deformation region. By appropriately adjusting the Poisson's ratio, a material with less variation in strength can be produced. In this respect, measuring Poisson's ratio has an important meaning.

In general, Poisson's ratio is obtained through a tensile test. That is, a Poisson's ratio is calculated | required by cutting a tensile test piece from a material, joining a strain gauge, pulling it at a constant speed with a tensile tester, and measuring the strain of the tension direction and the strain of the perpendicular direction.

However, in this method, the measurement accuracy of the tester and the influence of the initial deformation occurring when the test piece is attached to the tensile tester affect the measurement accuracy. In addition, since the tensile test is a destructive test method, the Poisson's ratio cannot be measured for the real object.

Several methods for non-destructively measuring the Poisson's ratio of a subject have been proposed. For example, Patent Documents 1 and 2 disclose ultrasonic wave longitudinal waves and transverse wave speeds (hereinafter, simply longitudinal wave speeds respectively) in which ultrasonic waves are incident on an inspected object from an ultrasonic probe and propagate through the inspected object using a contact ultrasonic probe. And a Young's modulus and Poisson's ratio from the measured longitudinal wave speed, the shear wave speed, and the density of the inspected object. These methods have the advantage that the Young's modulus and Poisson's ratio of the real can be measured without destroying the real. However, in the case of a contact measurement method, there are some difficulties from the viewpoint of speeding up the measurement.

For example, the method of using a piezoelectric transducer requires an ultrasonic wave propagation medium between the inspected object and the transducer, but the radio wave medium deteriorates its function at high temperatures. Moreover, in the method of using an electromagnetic ultrasonic transducer, it is necessary to bring the transducer close to the inspected object to about several mm normally. Therefore, any method has a drawback that it is impossible to use it in a harsh environment, such as a manufacturing line of a steel plate, especially a hot rolling process.

On the other hand, various applications have been proposed for the non-contact measuring method (hereinafter referred to as laser ultrasonic method) in which ultrasonic waves are generated using pulse lasers and the ultrasonic waves propagated inside the inspected object are detected using a continuous wave laser.

For example, the present inventors proposed the inventions related to the defect detection apparatus and the on-line grain size measuring apparatus in the test object in patent documents 3-6.

About the measuring method of the poisson's ratio by the laser ultrasonic method, the non-patent document 1 reports the measuring method of the poisson's ratio, the longitudinal sound velocity, and the transverse sound velocity using the ultrasonic excitation by ablation.

Non-Patent Document 1 discloses a Q-switched Nd: YAG laser beam with a pulse output of about 5.1 mJ / mm ² of fluence (energy amount per unit area) to an object to be ultrasonically excited and generates a group velocity of the generated wave wave ultrasonic wave. The frequency of the S1 mode which is zero (hereinafter, S1f) and the frequency of the A2 mode which is zero, the group speed (hereinafter, A2f) are detected by using the double wave Nd: YAG laser of continuous wave output, and from these values, the Poisson's ratio, the longitudinal sound velocity, and the transverse sound velocity The experimental result of calculating the is described.

Since the non-contact laser ultrasonic method does not require a non-destructive tensile test, various applications are expected as an on-line non-destructive test in a production line requiring high speed and high reliability.

As a method of exciting an ultrasonic wave with a laser, a method of irradiating high energy laser light to the surface of an inspected object and exciting the ultrasonic wave by a thermoelastic effect caused by an instantaneous temperature rise, and part of the surface of the inspected object with higher energy There is a method of exciting ultrasonic waves using a pressure wave generated when vaporizing (ablation).

The principle of the ultrasonic excitation using ablation is schematically shown in FIG. 1A, and the principle of the ultrasonic excitation using the thermoelastic effect is schematically shown in FIG. 1B.

As shown in FIG. 1A, when the laser beam 2 is irradiated to the object 1, a part of the object evaporates by high energy (refer 3 in the figure). At this time, the ultrasonic wave 4 is generated as a pressure wave generated by the reaction force. Here, the arrow of the ultrasonic wave 4 in the figure shows the directivity of the generated ultrasonic wave. On the surface of the object 1, a part of the object evaporates, so that a trace of irradiation with the laser light occurs.

As shown in FIG. 1B, when the laser beam 2 is irradiated to the object 1, the temperature of the surface of the object 1 rises instantaneously by rapid heating by a laser, and the temperature rise area | region 5 And the ultrasonic wave 4 is generated with thermal expansion and contraction in the temperature rise region 5. Here, the arrow of the ultrasonic wave 4 in the figure shows the directivity of the generated ultrasonic wave.

However, when irradiating steel materials, if it is about ² mJ / mm <^{2> of} fluences, the trace of irradiation by an ablation will not generate | occur | produce in an object.

For example, in the measurement technique of the Poisson's ratio by the conventional laser ultrasonic method described in Nonpatent Literature 1, ultrasonic excitation by ablation is used, but irradiation traces on the surface of the subject by ablation are observed. Occurs. Therefore, in the use which does not allow a trace of irradiation, measurement by this method is impossible and there exists a problem that a use is limited.

However, when the same measurement is to be performed using ultrasonic excitation by the thermoelastic effect, it is difficult to detect the generated ultrasonic waves, and there is a problem that A2f measurement of the plate wave ultrasonic waves cannot be performed. That is, due to the difference in the directivity of the ultrasonic wave propagation, it is difficult to detect the ultrasonic wave by the ultrasonic excitation using the thermoelastic effect, and in particular, measurement of A2f with poor S / N is virtually impossible.

Non-patent document 2 describes the directivity of the ultrasonic wave propagation of the ultrasonic excitation by the thermoelastic effect.

Prior art literature

<Patent Literature>

Patent Document 1: Japanese Patent Application Laid-Open No. 5-133861

Patent Document 2: Japanese Patent Application Laid-Open No. 5-126805

Patent Document 3: Japanese Patent Publication No. 2003-121423

Patent Document 4: Japanese Patent Application Laid-Open No. 2003-215110

Patent Document 5: Japanese Patent Application Laid-Open No. 2004-125615

Patent Document 6: Japanese Patent Application Laid-Open No. 2006-084392

<Non-patent Document>

[Non-Patent Document 1] Dominique Clorennec, et., 'Local and non-contact measurements of bulk acoustic wave velocities in thin isotropic plates and shells using zero group velocity Lamb modes', Journal of Applied Physics, 101, 034908, 2007.

[Non-Patent Document 2] C.B. Scruby and L.E.Drain, “Laser Ultrasonic-Techniques and Applications”, ISBN 0-7503-0050-7, Adam Hilger, p. 289, 1990

Non Patent Literature 3: A. Gibson and J.S. Popovics, “Lamb Wave Basis for Impact-Echo Method Analysis”, J. Eng. Mech., Vol. 131 (4), 438-443, (2005).

The present invention has been made in view of the above circumstances, and in the laser ultrasound method, a method for measuring Poisson's ratio using ultrasonic excitation by thermoelastic effect, which does not cause damage to the surface of an object to be examined and does not generate a trace of laser irradiation. And a measuring device.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining about the method of receiving the ultrasonic wave excited by a thermoelastic effect, and calculating the Poisson's ratio, it discovered that the Poisson's ratio can be calculated when receiving a plate wave ultrasonic wave and surface wave ultrasonic wave.

This invention is made | formed based on the said knowledge, The summary is as follows.

(1) Irradiate pulsed laser light to the surface of the test object to generate ultrasonic waves by the thermoelastic effect, irradiate continuous wave laser light to the surface of the test object, and receive ultrasonic waves propagating the test object, As a method of measuring the eddy ratio,

(i) receiving plate wave ultrasonic waves and surface wave ultrasonic waves propagating the subject,

(ii) calculating the frequency of the wave ultrasound;

(iii) measuring the propagation time of the surface wave ultrasonic waves, and calculating the propagation speed of the surface wave ultrasonic waves from the propagation time and the propagation distance;

(iv) A Poisson's ratio is calculated based on the frequency of the said plate wave ultrasonic wave and the propagation speed of the surface wave ultrasonic wave.

(2) The frequency of said wave wave ultrasonic wave is the frequency of the wave wave ultrasonic wave of S1 mode whose group speed is zero, The measuring method of the poisson's ratio of (1) characterized by the above-mentioned.

(3) Measurement of the Poisson's ratio of (1) or (2), wherein the pulsed laser light is irradiated to a point-like spot when the pulsed laser light is irradiated onto the subject to receive the plate wave ultrasonic wave. Way.

(4) When the pulsed laser beam is irradiated to the object under test to receive the plate wave ultrasonic wave, the continuous wave laser beam is irradiated into the point-shaped spot area irradiated with the pulsed laser beam (3) Method of Poisson's ratio

(5) The Poisson's ratio of any one of (1) to (4), wherein the pulsed laser beam is irradiated linearly when the pulsed laser beam is irradiated onto the subject to receive the surface wave ultrasonic waves. Method of measurement.

(6) The method for receiving the plate wave ultrasonic wave and the surface wave ultrasonic wave, wherein the continuous wave laser beam is irradiated onto the surface of the subject and subjected to a Doppler shift by the vibration of the plate wave ultrasonic wave and the surface wave ultrasonic wave. A method of measuring the Poisson's ratio according to any one of (1) to (5), wherein the reflected light of the continuous wave laser light is received, the reflected light is interfered with an interferometer, and a change in intensity of light output from the interferometer is detected. .

(7) Irradiate pulsed laser light to the surface of the test object to generate ultrasonic waves by the thermoelastic effect, irradiate continuous wave laser light to the surface of the test object, and receive ultrasonic waves propagating the test object. As a device for measuring Poisson's ratio,

(i) an ultrasonic wave generator including a laser light source for generating ultrasonic waves by irradiating pulsed laser light on the surface of the object to be ultrasonically excited;

(ii) a receiving unit including a laser light source for receiving plate wave ultrasound and surface wave ultrasound propagating the object by irradiating continuous wave laser light onto the surface of the object,

(iii) a first processing unit for calculating the frequency of the plate wave ultrasonic wave from the received plate wave ultrasonic wave,

(iv) a second processor for measuring the propagation time of the received surface wave ultrasonic waves and calculating the propagation speed of the surface wave ultrasonic waves from the propagation time and the propagation distance;

(v) A Poisson's ratio measuring device, comprising: a third processing unit for calculating the Poisson's ratio of the object under test from the frequency of the plate wave ultrasound and the propagation speed of the surface wave ultrasound.

(8) The fraudulence ratio measurement device according to (7), wherein the frequency of the wave wave ultrasonic wave is the frequency of the wave wave ultrasonic wave of the S1 mode in which the group speed is zero.

(9) The apparatus for measuring Poisson's ratio according to (7) or (8), wherein the ultrasonic wave generation unit further comprises an irradiation optical system for irradiating the pulsed laser light to the test subject with a spot shape spot.

(10) The poisson's ratio measuring device according to (9), wherein the continuous wave laser light is irradiated into the point spot area for irradiating the pulsed laser light.

(11) The apparatus for measuring Poisson's ratio according to (9) or (10), wherein the ultrasonic wave generation unit further comprises an irradiation optical system for irradiating the pulsed laser light to the subject under a linear spot.

(12) The apparatus for measuring Poisson's ratio of (11), wherein the ultrasonic wave generation unit further includes a mechanism for switching the irradiation optical system irradiated with the point spot and the irradiation optical system irradiated with the linear spot. .

(13) The receiving unit includes an interferometer for receiving the reflected light of the continuous wave laser light subjected to the Doppler shift by the vibration of the plate wave ultrasound and the surface wave ultrasound, and interfering the reflected light of the received continuous wave laser light, and the light output from the interferometer. The photodetector of any one of (7)-(12) characterized by further including the light-detecting part which outputs a intensity change as an electrical signal.

According to the present invention, since the ultrasonic energy is excited by the thermoelastic effect by using a laser energy of a low energy level such that no ablation occurs, no damage is caused to the surface of the inspected object, so that no trace of the laser light is generated. Poisson's ratio can be measured non-destructively and non-destructively.

Hereinafter, the principle of the measurement method using the ultrasonic excitation by the thermoelastic effect in the present invention will be described in comparison with the measurement method using the ultrasonic excitation by ablation (hereinafter, referred to as a conventional method).

In the conventional method, ultrasonic waves are generated and propagated to an inspected object by ultrasonic excitation using ablation.

At this time, when the object to be inspected is a relatively thin plate, waves called plate wave ultrasonic waves, which are elastic waves propagating along the plane, in addition to the longitudinal and transverse waves, are generated.

In the wave ultrasound, there are many modes divided into symmetrical modes (S0, S1, S2, ...) and asymmetrical modes (A0, A1, A2, ...) by the symmetry of vibration. In addition, the phase velocity of the plate wave ultrasound varies depending on the mode, and also depends on the product of the frequency and the plate thickness. That is, the phase velocity has the characteristic of velocity dispersion. In addition, the group velocity exists by phase velocity dispersion, and the group velocity also depends on the product of the frequency and the plate thickness. It is known that there is a relationship shown in FIG. 2 between the group speed [m / s] of the plate wave ultrasonic wave and the product of the frequency and the plate thickness.

The plate wave ultrasound is a mode in which the S1 mode and the A2 mode are easily detected from the viewpoints of S / N and the ultrasonic attenuation, and the frequency measurement of the plate wave ultrasound is mainly performed for the S1 mode and the A2 mode.

It is known that the relationship between S1f and A2f of the plate wave ultrasonic wave, the Poisson's ratio ν, the longitudinal wave velocity V _L , and the transverse wave velocity V _S is the same as that of Equation 1. However, β1 (υ) and β2 (υ) are existing functions that take the Poisson's ratio υ as a parameter (Non Patent Literature 3). The relationship between Poisson's ratio and β1 (υ) is shown in FIG. 3A, and the relationship between Poisson's ratio and β2 (υ) is shown in FIG. 3B.

Equation 3 can be obtained from the relationship between Poisson's ratio ν and the longitudinal sound speed V _L and the transverse sound speed V _S shown in the equations (1) and (2). When the values of S1f and A2f are obtained, the Poisson's ratio ν can be calculated from Equation 3, and the longitudinal wave speed V _L and the shear wave sound speed V _S can be calculated from Equation 1.

That is, in the conventional method, the plate wave ultrasonic waves generated by ablation are detected by using a continuous wave laser or the like, and the detected waveforms are processed by fast Fourier transform (hereinafter referred to as FFT) to thereby detect S1f and A2f is simultaneously measured to calculate the Poisson's ratio υ, the longitudinal wave speed V _L and the transverse wave speed V _S.

Next, the measuring method of this invention is demonstrated.

When the laser beam is excited by irradiating the laser beam with the laser beam, energy is concentrated at a depth of about one wavelength from the surface of the surface layer in addition to the longitudinal wave, transverse wave, and plate wave ultrasonic wave, and an acoustic wave called surface wave ultrasonic wave propagates along the surface. Occurs.

In the present invention, S1f of the plate wave ultrasonic wave and the sound velocity V _SAW of the surface wave ultrasonic wave are measured using ultrasonic excitation by the thermoelastic effect.

There is a relationship of Equation 4 between the sound velocity V _SAW of the surface wave ultrasonic wave and the shear wave sound velocity V _S. Equation 5 may be derived from Equations 1, 3, and 4. In other words, if the values of S1f and V _SAW are obtained, the Poisson's ratio ν can be calculated from the expression (5).

When the Poisson's ratio ν is calculated, the transverse wave speed V _S can be calculated again from Equation 4, and the longitudinal wave speed V _L can be calculated from Equation 1.

As described above, in the measurement using the ultrasonic excitation by the thermoelastic effect, measurement of A2f is virtually impossible, but the sound velocity V _SAW of the plate wave ultrasonic wave and the surface wave ultrasonic wave can be measured. That is, it is a feature of the present invention that the Poisson's ratio can be calculated by measuring the sound velocity V _SAW of S1f and surface wave ultrasonic waves without measuring A2f.

An apparatus for performing measurement according to the present invention includes an ultrasonic wave generator, a receiver, a first processor, a second processor, and a third processor.

The ultrasonic wave generation unit includes a laser light source for generating ultrasonic waves by irradiating pulsed laser light on the surface of the object to be ultrasonically excited to generate an ultrasonic wave, and, if necessary, switching an irradiation optical system made of a lens, a mirror or the like and a plurality of irradiation optical systems. Additional equipment.

The receiver includes a laser light source for receiving plate wave ultrasound and surface wave ultrasound that propagates the object by irradiating continuous wave laser light onto the surface of the object, and, for example, such as a Fabry-Perot interferometer, An interferometer for receiving and interfering reflected light from an object under test of continuous wave laser light, and an optical signal outputting an intensity change of light output from the interferometer as an electrical signal, for example, an avalanche photodiode (APD) or the like. Further equipped with a detector.

The first processing unit includes an electronic calculator or the like, and calculates a frequency of the plate wave ultrasonic wave from the received plate wave ultrasonic wave.

The second processing unit includes an electronic calculator and the like, measures the propagation time of the received surface wave ultrasonic waves, and calculates the propagation speed of the surface wave ultrasonic waves from the propagation time and the propagation distance.

The third processing unit is composed of an electronic calculator or the like and calculates the Poisson's ratio of the inspected object from the frequency of the plate wave ultrasound and the propagation speed of the surface wave ultrasound.

Note that the first processing unit, the second processing unit, and the third processing unit do not necessarily need to be constituted by physically different devices, respectively. For example, the first processing unit, the second processing unit, and the third processing unit may have a program for performing each processing in the same electronic calculator.

Hereinafter, an example of the measurement by this invention is demonstrated in detail using drawing.

4A shows an outline of the measurement of S1f of the plate wave ultrasonic wave. The measurement of S1f is performed by analyzing the waveform of the ultrasonic wave wave ultrasonic wave generated by irradiating a pulsed laser light to the surface of the inspected object 11.

As the laser light source 12 for generating ultrasonic waves for generating ultrasonic waves, for example, a Q-switched Nd: YAG laser with a pulse output can be used.

As for the laser beam PL emitted from the laser light source 12 for ultrasonic generation, the beam diameter is enlarged in the condensing lens 17a through the mirror 14a, the filter 16, and the mirror 14b, and the test subject 11 ) Is irradiated to the surface. At this time, the transmittance of the filter 16 is determined or the output of the ultrasonic wave generation laser light source 12 is adjusted so that the fluence in the irradiated area on the surface of the test object is about ² mJ / mm ² or less.

The laser light PL depends on the characteristics of the Q-switched Nd: YAG laser of the pulse output used, but the repetition frequency is about 10 Hz to 200 Hz. In addition, the irradiation angle of the laser beam PL irradiated to the surface of the inspected object 11 is not specifically limited, but practically, it is about within +/- 30 degree perpendicular to a plane.

On the surface of the inspected object 11, a sudden temperature rise occurs by laser light irradiation, and ultrasonic waves are excited by the thermoelastic effect.

In this case, the wave wave ultrasound at the frequency at which the group velocity is zero resonates locally at the irradiation position of the laser beam, which is the source of generation, without the energy of the wave wave propagating in the inspected object. It is possible to measure the frequency of the plate wave ultrasonic wave with a group speed of zero.

In addition, when the plate wave ultrasound mode is a low-dimensional mode such as S0 mode or A0 mode, as shown in FIG. 2, there is no frequency domain of group speed zero or zero Hz, and in the high-dimensional mode, the attenuation of the ultrasonic wave becomes large. Therefore, it is preferable that the detected wave wave ultrasonic wave is a wave wave ultrasonic wave of the S1 mode.

As the laser light source 13 for ultrasonic detection, the double wave Nd: YAG laser of continuous wave output can be used, for example.

The laser light CL emitted from the laser light source 13 for ultrasonic detection transmits the P-polarized light component CLP through a polarization beam splitter (hereinafter referred to as PBS) 19a, and the S-polarized light component ( CLS) is reflected. The P-polarized component CLP of the laser light CL is irradiated onto the surface of the inspected object 11 through the mirrors 14c and 14d. As shown in FIG. 5, it is preferable that the irradiation area | region of the test subject surface is in the irradiation area | region of the said laser for ultrasonic generation.

The P-polarized component CLP of the laser light CL irradiated onto the inspected object 11 shifts the Doppler shift according to the surface displacement velocity V of the inspected object 11 by the ultrasonic wave generated in the inspected object 11. It is reflected by receiving Δf = 2 V / λ. Is the wavelength of the laser beam for ultrasonic detection.

The reflected laser light passes through the PBS 19b through the condensing lenses 17b and the mirrors 14e and 14f and is incident on the Febrier ferot interferometer 20.

Although the irradiation angle of the P-polarization component CLP of the laser beam CL irradiated to the to-be-tested object 11 is not specifically limited, For practical use, it is about less than +/- 30 degree perpendicular to a plane.

On the other hand, the S-polarized component CLS of the laser light CL divided by the PBS 19a is reflected by the PBS 19b and is incident on the Fabry-Perot interferometer 20.

The Fabry Perot Interferometer 20 serves as a wavelength filter. The transmittance of the Fabry-Perot interferometer greatly varies with the frequency of light as shown in FIG. 6.

The P-polarized component CLP of the laser light CL incident on the Fabry-Perot interferometer 20 is the magnitude of the Doppler effect received from the ultrasound wave propagating the object 11, that is, the surface displacement of the object 11. The frequency changes slightly with speed, which translates into a relatively large change in transmitted light intensity by transmitting the Fabry Perot interferometer 20.

And the vibration state of the surface of the to-be-tested object 11 can be calculated | required by measuring the intensity change of the P-polarization component CLP of the laser beam CL which permeate | transmitted the Fabry-Perot interferometer 20.

Here, the size of the Doppler shift Δf is approximately 0.01 to 0.1 Hz, and the ultrasonic detection laser light source 13 preferably uses a laser light source with high frequency stability, and is not particularly limited, but the frequency deviation is about 100 Hz / s. It is preferable that it is the following.

Moreover, as for the permeation | transmission characteristic of the Fabry-Perot interferometer 20, about 1 MHz-10 MHz of FWHM (Full Width Half Max), and about 100 MHz-1 GHz of FSR (Free Spectral Range) are preferable. In addition, FWHM means the width | variety value of x range in which f (x) becomes a value more than half of the maximum value, when a certain function f (x) shows the shape of the local function of a mountain shape. In addition, FSR is an abbreviation of the free spectral region, and is a value defined as a difference between neighboring resonance peak frequency values.

The S-polarized light component CLS of the laser light CL is emitted from the Fabry-Perot interferometer 20 and then reflected by the PBS 19c, converted into an electrical signal ES1 by the APD 21a, and stabilized. Is sent to 22.

The intensity of the S-polarized light component CLS of the laser light CL incident on the APD 21a will not change because the path of the laser light in the middle is always in the same state. When the intensity is changed, the distance between two reflection mirrors (not shown) constituting the resonator of the Fabry-Perot interferometer 20 changes due to disturbance such as external vibration, and the Fabry-Perot interferometer 20 It is possible to consider the cause of change in the characteristics of the laser beam or fluctuation in the oscillation frequency of the laser light source 13 for ultrasonic detection.

In that case, the Fabry-Perot interferometer is provided by the electrical signal ES2 from the stabilizing element 22 so that the intensity of the S-polarized component CLS of the laser light CL incident on the APD 21a becomes constant. The reflection mirror at 20 is adjusted to an optimal position. For example, a piezo element etc. can be used for position adjustment of a reflection mirror.

The P-polarized component CLP of the laser light CL is emitted from the Fabry-Perot interferometer 20, then passes through the PBS 19c, is converted into an electrical signal ES3 by the APD 21b, and is calculated. Is sent to 23. Then, the vibration state of the surface of the test object 11 is calculated from the intensity of the electric signal ES3 input from the S1f value calculating unit 23a which is the first processing unit in the calculating unit 23, and the obtained waveform is subjected to FFT processing. The value of S1f is calculated.

Next, sound velocity measurement of surface wave ultrasonic waves will be described with reference to FIG. 4B. The measurement of the sound velocity of surface wave ultrasonic waves is computed from the waveform of surface wave ultrasonic waves which generate | occur | produced by irradiating a pulse laser to the surface of the to-be-tested object 11.

As the laser light source for generating surface wave ultrasonic waves, the laser light source 12 for ultrasonic generation can be used as the laser light source for detection, and the laser light source 13 for ultrasonic detection can be used as it is.

However, in the sound velocity measurement of surface wave ultrasonic waves, the ultrasonic wave generation position and the detection position of the surface of the inspected object 11 for measuring the propagation time from the ultrasonic wave generation position to the ultrasonic wave detection position need a constant distance. Therefore, it is necessary to change the irradiation optical system of the laser light source 12 for ultrasonic generation, as shown, for example in FIG. 4B.

Specifically, the laser light PL emitted from the laser light source 12 for ultrasonic generation is reflected by the mirror 14g after passing through the mirror 14a and the filter 16, and the surface of the subject 11 Is irradiated to a position different from the irradiation position of the ray light CLP emitted from the laser light source 13 for ultrasonic detection.

In the example shown in FIG. 4A and FIG. 4B, by moving the mirror 14g on the linear stage 15, the irradiation optical system for S1f measurement and the irradiation optical system for the sound velocity measurement of surface wave ultrasonic wave can be switched mutually. The linear stage 15 may be replaced automatically using a motor or the like. You may provide another mechanism for changing an irradiation optical system.

In addition, since the surface wave ultrasonic waves are radiated in all directions around the laser irradiation position, it is effective to irradiate the laser beam PL after converting it into a linear beam by, for example, a cylindrical lens or the like, as shown in FIG. 7. . When the linear beam is irradiated, the energy of the surface wave ultrasonic waves propagating in the direction perpendicular to the beam increases, so that the detection sensitivity of the surface wave ultrasonic waves can be increased.

In the example shown in FIG. 4B, the laser beam PL reflected by the mirror 14g is converted into a linear beam by the cylindrical lens 18, and then irradiated onto the surface of the inspected object 11. At this time, the output of the ultrasonic wave generation laser light source 12 is adjusted so that the fluence in the irradiation area on the surface of the subject may be about ² mJ / mm ² or less.

The laser light PL depends on the characteristics of the Q-switched Nd: YAG laser of the pulse output used, but the repetition frequency is about 10 Hz to 200 Hz. In addition, the irradiation angle of the laser beam PL irradiated to the surface of the inspected object 11 is not specifically limited, but practically, it is about within +/- 30 degree perpendicular to a plane.

The generated surface wave ultrasonic wave causes the P-polarized component of the laser beam CL irradiated to the surface of the inspected object 11 in accordance with the surface displacement. The intensity of the P-polarized light component of the laser beam CL subjected to the Doppler shift is changed by the Doppler shift through the Fabry-Perot interferometer 20, and the intensity is converted from the APD 21b to the electrical signal ES3. It is sent to the calculator 23.

In the calculation unit 23, the surface wave ultrasonic sound speed calculation unit 23b which is the second processing unit calculates the vibration state of the surface of the test object 11 from the intensity of the input electric signal ES3, and uses the surface wave from the obtained waveform. Sound velocity V _{SAW of} ultrasound Is calculated.

Then, using the calculated values of S1f and V _SAW, the Poisson's ratio υ is calculated from Equation 5 in the Poisson's Ratio calculation unit 23c which is the third processing unit in the calculator 23.

The calculated result can also be provided by displaying the display apparatus 24, for example.

As mentioned above, although an example of the measurement by this invention was demonstrated, of course, this invention is not limited to this, It can also be implemented with another aspect in the range of the technical idea of this invention.

<Examples>

Hereinafter, the example which implemented this invention is demonstrated concretely.

The Poisson's ratio of steel material SK85 was measured using the system shown to FIG. 4A and FIG. 4B. As a laser light source for ultrasonic generation, a Q-switched Nd: YAG laser of pulse output was used, and a double wave Nd: YAG laser of continuous wave output was used as a laser light source for ultrasonic detection.

Measurement conditions are shown in Table 1.

Shown in Table 1, S1f of the irradiation optical system for measuring fluence ^{1.8mJ / mm 2, 2.0mJ / mm} 2 of the surface wave acoustic velocity measuring ultrasonic irradiation optical system for all the energy of the extent to which ablation will occur. In addition, the distance of a to-be-tested object and an irradiation optical system in Table 1 means the shortest distance of a to-be-tested object and an irradiation optical system, and is a distance of the to-be-tested object 11 and the mirror 14f in the example of FIG. 4A.

First, S1f was measured by the irradiation optical system for S1f measurement shown in FIG. 4A. 8 shows the waveform detected by the APD 21b. In Fig. 8, reference numeral 51 denotes a pulse YAG oscillation timing (ultrasound generation time). In addition, the result of FFT processing the waveform shown in FIG. 8 is shown in FIG. The spectrum 61 showing S1f at the position of the frequency 1.38 MHz was clearly measured. However, when detected, A2f, which was thought to be visible at a position of about 2.4 MHz, was not detected.

Next, the mirror 14g on the linear stage 15 was advanced, and switched and measured with the irradiation optical system for surface wave ultrasonic measurement shown in FIG. 4B.

10 shows the waveform detected by the APD 21b. From this waveform, if the propagation time of surface wave ultrasound is measured by the zero-cross method, it becomes 3.590μs, and the sound velocity of surface wave ultrasound is 2980m / s. Saved.

Table 2 shows the results of calculating the Poisson's ratio υ, the longitudinal wave speed V _L , and the transverse wave speed V _S from the measured values of S1f = 1.38 MHz and V _SAW = 2980 m / s.

Moreover, as a result of observing the test subject after measurement, no irradiation trace by laser light irradiation was observed.

Comparative Example

In order to examine the validity of the results obtained in the examples, the Poisson's ratio υ, the longitudinal wave speed V _L , and the transverse wave speed V _S were calculated by a measurement method using ablation, which is a known method. In a comparative example, the intensity | strength of the ultrasonic wave generation pulse laser beam irradiated to the to-be-tested object is 3.5 mmJ / mm <^2> , which is the intensity | strength which the micro ablation produces.

11 shows the detection results of the frequency component 61 of S1f and the frequency component 62 of A2f. In addition, a measurement result is shown in Table 2 with the result of an Example.

Moreover, when the surface of the test subject measured after the measurement in the comparative example was observed, the trace of irradiation by ablation was observed.

Longwave Sound Velocity (m / s) Shear sound speed (m / s) Poisson's Measurement result according to the present invention 5920 3228 0.2884 Measurement result by conventional method 5913 3219 0.2894 Measurement results according to the present invention,
Difference (%) of measurement result by conventional method 0.1 0.3 0.3

From the results shown in Table 2, the measurement results using the measurement method according to the present invention and the measurement results according to the conventional method are in good agreement, and the measurement method of the present invention is suitable measurement without causing traces of laser irradiation on the inspected object. It was confirmed that the results can be obtained.

According to the present invention, in the laser ultrasonic method, the ultrasonic wave excitation can be performed using the thermoelastic effect, and the Poisson's ratio can be calculated without creating traces of laser irradiation on the surface of the object, so that it can be applied to nondestructive inspection of various materials. have.

In addition, since the present invention is a non-destructive and non-contact measuring method, by applying the present invention to, for example, a metal manufacturing process, it is possible to measure physical properties such as the Poisson's ratio of the actual product being manufactured online. It can also be used for feedback.

1A is a diagram schematically illustrating the principle of ultrasonic excitation using ablation by laser light.

FIG. 1B is a diagram schematically illustrating the principle of ultrasonic excitation using a thermoelastic effect by laser light.

Fig. 2 is a diagram showing the relationship between the group speed of plate wave ultrasonic waves and the frequency × plate thickness.

3A is a diagram illustrating a relationship between Poisson's ratio and β1.

3B is a diagram illustrating a relationship between Poisson's ratio and β2.

4A is a block diagram showing the outline of the entire system for measuring the frequency of the wave ultrasonic wave when measuring Poisson's ratio using the measurement method of the present invention.

4B is a schematic configuration diagram of the entire system for measuring the sound velocity of surface wave ultrasonic waves when measuring Poisson's ratio using the measurement method of the present invention.

Fig. 5 is a diagram showing the relationship between the irradiation spot positions of the preferable ultrasonic wave generation laser and the ultrasonic wave detection laser when detecting the plate wave ultrasonic wave with zero group velocity in the present invention.

FIG. 6 is a diagram illustrating an example of a relationship between a frequency and transmittance of a Fabry Perot interferometer.

7 is a diagram showing an outline of a preferable irradiation method of a laser for generating ultrasonic waves when measuring the sound velocity of surface wave ultrasonic waves in the present invention.

8 is a diagram showing waveforms of plate wave ultrasonic waves detected in the embodiment of the present invention.

9 is a diagram showing a result of processing the waveform of the plate wave ultrasonic wave detected by the embodiment of the present invention by a fast Fourier transform (FFT).

Fig. 10 is a diagram showing waveforms of surface wave ultrasonic waves detected in the embodiment of the present invention.

It is a figure which shows the result of having processed the waveform of the plate wave ultrasonic wave detected by the conventional method by a fast Fourier transform (FFT).

Description of the Related Art [0002]

1 object

2 laser light

3 evaporation of the object

4 ultrasound

5 temperature rise zone

11 Subjects

12 Laser light source for ultrasonic generation

13 Laser Light Source for Ultrasonic Detection

14a, 14b, 14c, 14d, 14e, 14f mirror

15 linear stage

16 filters

17a, 17b condensing lens

18 cylindrical lens

19a, 19b, 19c polarizing beam splitter

20 Febri Ferot Interferometer

21a, 21b, 21c avalanche photodiode (photodetector)

22 stabilization circuit

23 output

23a S1f value calculating unit (first processing unit)

23b surface wave ultrasonic sound velocity calculating part (the second processing part)

23c Poisson's ratio calculation part (the third processing part)

24 display

31 Irradiation spot of laser light for ultrasonic generation

32 Irradiation Spot of Laser Light for Ultrasonic Detection

33 Direction of Ultrasound

Irradiation spot of laser beam for ultrasonic wave generation at the sound speed measurement of 41 surface wave ultrasonic waves

51 pulse YAG oscillation timing (ultrasonic generation time)

Frequency components of plate wave ultrasound in S1 mode

62 Frequency component of wave ultrasound in A2 mode

Laser light for CL ultrasonic detection (continuous wave laser light)

P-polarized component of laser light (continuous wave laser light) for CLP ultrasonic detection

S-polarized component of laser light (continuous wave laser light) for CLS ultrasonic detection

PL Ultrasound Laser Light (Pulse Laser Light)

Claims (13)

By irradiating pulsed laser light on the surface of the test object, ultrasonic waves are generated by the thermoelastic effect.The continuous wave laser light is irradiated on the surface of the test object, and the ultrasonic wave propagating through the test object is received to determine the Poisson's ratio of the test object. As a measuring method, (i) receiving plate wave ultrasound and surface wave ultrasound that propagate the subject, (ii) calculating the frequency of the wave ultrasound; (iii) The propagation time of the surface wave ultrasonic waves is measured, and the propagation speed of the surface wave ultrasonic waves is calculated from the propagation time and the propagation distance. (iv) A Poisson's ratio is calculated based on the frequency of the said plate wave ultrasonic wave and the propagation speed of the surface wave ultrasonic wave. The method of claim 1, The frequency of said wave-wave ultrasound is the frequency of the wave-wave ultrasound of S1 mode whose group speed is zero, The Poisson's ratio measuring method. The method of claim 1, And irradiating the pulsed laser light to the inspected object to receive the plate wave ultrasonic wave, wherein the pulsed laser light is irradiated to a spot shape spot. The method of claim 3, The continuous wave laser light is irradiated into the point-shaped spot area irradiated with the pulsed laser light when the pulsed laser light is irradiated to the test object to receive the plate wave ultrasonic wave. . The method of claim 1, The pulsed laser beam is irradiated linearly when the pulsed laser beam is irradiated to the test object to receive the surface wave ultrasonic waves. 6. The method according to any one of claims 1 to 5, The method for receiving the plate wave ultrasonic wave and the surface wave ultrasonic wave includes irradiating the continuous wave laser light onto the surface of the test object, receiving the reflected light of the continuous wave laser light subjected to Doppler shift by vibration of the plate wave ultrasonic wave and the surface wave ultrasonic wave. And a method of interfering the reflected light with an interferometer and detecting a change in intensity of light output from the interferometer. By irradiating pulsed laser light on the surface of the test object, ultrasonic waves are generated by the thermoelastic effect, and irradiating continuous wave laser light on the surface of the test object, and receiving the ultrasonic wave propagating through the test object, As a measuring device, (i) an ultrasonic wave generator including a laser light source for generating ultrasonic waves by irradiating pulsed laser light on the surface of the object to be ultrasonically excited; (ii) a receiving unit including a laser light source for receiving plate wave ultrasound and surface wave ultrasound propagating the object by irradiating continuous wave laser light onto the surface of the object, (iii) a first processing unit for calculating the frequency of the plate wave ultrasonic wave from the received plate wave ultrasonic wave, (iv) a second processor for measuring the propagation time of the received surface wave ultrasonic waves and calculating the propagation speed of the surface wave ultrasonic waves from the propagation time and the propagation distance; (v) A Poisson's ratio measuring device, comprising: a third processing unit for calculating the Poisson's ratio of the object under test from the frequency of the plate wave ultrasound and the propagation speed of the surface wave ultrasound. The method of claim 7, wherein The frequency of the said plate wave ultrasonic wave is the frequency of the plate wave ultrasonic wave of S1 mode whose group speed is zero, The Poisson's ratio measuring apparatus. The method of claim 7, wherein The said ultrasonic wave generation part further includes the irradiation optical system which irradiates the said pulse laser beam to a said to-be-tested object in a spot shape, The measuring apparatus of the Poisson's ratio characterized by the above-mentioned. 10. The method of claim 9, The continuous wave laser beam is irradiated into the point-shaped spot region for irradiating the pulsed laser beam, Posson's ratio measuring device. 10. The method of claim 9, The said ultrasonic wave generation part further includes the irradiation optical system which irradiates the said pulse laser beam to a said to-be-tested object in a linear spot, The Poisson's ratio measuring apparatus characterized by the above-mentioned. 12. The method of claim 11, The ultrasonic generator further includes a mechanism for switching the irradiation optical system irradiated with the point spot and the irradiation optical system irradiated with the linear spot. The method according to any one of claims 7 to 12, The receiving unit receives an reflected light of the continuous wave laser light subjected to the Doppler shift by vibrations of the plate wave ultrasonic wave and the surface wave ultrasonic wave, and interferes the reflected light of the received continuous wave laser light and changes in intensity of light output from the interferometer. And a photodetector for outputting the signal as an electrical signal.

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