JPH11281632A - Method and apparatus for measurement of plastic strain ratio by laser ultrasonic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus in which a plastic strain ratio is measured by a laser ultrasonic method in which it is not required to bring the apparatus close to an object to be inspected and in which the value (r) (the plastic strain ratio) of the object to be inspected can be found with high precision even when the distance between the apparatus and the object to be inspected is not kept constant. SOLUTION: A laser beam [at an optical frequency of (f)] which is radiated from a laser 11 for ultrasonic observation is divided into three beams by two polarization beam splitters (PBS's) 16, 17, and the respective laser beams are shifted to optical frequencies f0 , f1 , f2 by corresponding acousto-optic elements 18, 19, 20. The laser beam at f0 is made incident perpendicularly to the surface of an object 1 to be inspected. The laser beam at f1 is made incident at an angle of θ1 from the x-axis inside the x-z plane. The laser beam at f2 is made incident at an angle of from the y-axis inside the y-z plane. A position which is irradiated with the respective laser beams is identical to a point O which is irradiated with a laser beam for ultrasonic generation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for irradiating a test object with a laser beam to generate ultrasonic waves and observing the ultrasonic waves propagated through the test object to obtain a plastic strain ratio of the material. The present invention relates to a method and an apparatus for measuring a plastic strain ratio by an acoustic method.

[0002]

2. Description of the Related Art Cold-rolled steel sheets are used for outer panels of automobiles, electric appliances, etc. by press working. For this reason, in addition to mechanical strength such as tensile strength, press moldability, that is, the characteristic of how much molding can be performed without breaking is important. Generally, a plastic strain ratio (hereinafter, referred to as an “r value”) is used as an index indicating workability when a steel sheet undergoes deep drawing deformation. Products with higher r-values have higher deep drawability and are less likely to crack or the like when pressed. For this reason, specifying the r value can be used for quality control of the product. The r value is usually measured by a destructive method such as a tensile test method or a natural vibration method.

However, these test methods require a sample to be cut out, so that the measurement is troublesome and time-consuming, and there is a problem that only a part of the product can be evaluated. Therefore, a technique for measuring the r value by a non-destructive method using ultrasonic waves has been developed in order to be able to quickly measure the r value of the product without cutting out the sample. Regarding this, Nippon Steel Technical Report No. 364 (1
997), “Online r-value (plastic strain ratio) measurement of cold-rolled steel sheet” (Akagi et al.) (Hereinafter, this paper is referred to as “Reference 1”).

The method for measuring the r _ave value according to the above-mentioned article uses the resonance electromagnetic ultrasonic method. That is, an ultrasonic wave is generated inside the steel plate by an electromagnetic ultrasonic transducer, and it is detected by the electromagnetic ultrasonic transducer that the ultrasonic wave is reflected back on the opposite surface, and the ultrasonic wave is generated. The sound speed of the ultrasonic wave is obtained by measuring the time required to return from the time, and the r value is calculated using this.

[0005]

The above-mentioned reference 1
The technique of measuring the r value described in (1) uses a resonance electromagnetic ultrasonic method. Therefore, it is necessary to bring the electromagnetic ultrasonic transducer close to the subject to a distance of about several millimeters. At such a short distance, if the subject vibrates for some reason, separates from the electromagnetic ultrasonic transducer, or conversely comes too close to it, a proper examination cannot be performed. Therefore, when this method is used in an actual production line, it is necessary to take some measures so that the electromagnetic ultrasonic transducer and the subject are always maintained at a very close constant distance.

The present invention has been made based on the above circumstances, and it is not necessary to bring the apparatus and the subject close to each other, and the r-value of the subject can be obtained with high accuracy even if the distance is not kept constant. It is an object of the present invention to provide a method and an apparatus for measuring a plastic strain ratio by a laser ultrasonic method, which can determine a plastic strain ratio.

[0007]

According to a first aspect of the present invention, there is provided an apparatus for measuring a plastic strain ratio by a laser ultrasonic method, which comprises a Fabry-Perot interferometer. At the second and third optical frequencies,
Fabry-Perot interference means with the characteristic that the absolute value of the value obtained by differentiating the transmitted light intensity with the optical frequency is locally maximum, and the first laser that emits a laser beam for generating ultrasonic waves on the subject Light source, the respective optical frequency is the first, second, third optical frequency or its vicinity,
A second laser light source that emits first, second, and third laser beams for observing ultrasonic waves that have propagated through the subject;
Normal (which the -y to the plane) and z-axis) and parallel to, the second laser beam at an incident angle of theta ₁ from the z-axis in the z-x plane and said third laser The beam z
At an incident angle theta ₂ from the z-axis and the -y plane, a first optical means to be incident on the same position of each of the subject surface,
Second optical means for causing the reflected light of the first, second, and third laser beams from the subject to be incident on the Fabry-Perot interference means; and Light detection means for detecting a change in the intensity of light emitted from the Fabry-Perot drying means due to shifting the optical frequency of the reflected light of the second and third laser beams, and outputting a signal to that effect, While irradiating the subject with the laser light emitted from the first laser light source to determine the propagation time from when the predetermined ultrasonic wave is observed by the light detection means, the sound velocity of each ultrasonic wave from the propagation time And calculating means for calculating the plastic strain ratio of the subject based on a predetermined formula using the calculated value.

According to a second aspect of the present invention, in the first aspect of the present invention, the Fabry-Perot interference means has a value obtained by differentiating the transmitted light intensity with the optical frequency at least at the first, second, and third optical frequencies. Consisting of a single Fabry-Perot interferometer having the characteristic that the absolute value of the local maximum is obtained, wherein the second optical means transmits the first, second, and third laser beams from the subject. The reflected light is integrated into a single path to be incident on the Fabry-Perot interferometer, and further, the output light from the Fabry-Perot interferometer is split into laser beams of respective optical frequencies, And a branching unit for causing the laser beam to enter each of the photodetecting units capable of detecting a change in the intensity of the laser beam.

According to a third aspect of the present invention, in the first or second aspect of the invention, the second laser light source emits a single laser beam having a single optical frequency, and radiates from the laser. Laser beam
The first, the second, the first branching means to make a third laser beam, the first, the second, the optical frequency of the third laser beam, the first, the second, respectively And an optical frequency converting means for converting the optical frequency to an optical frequency in the third or third optical frequency range.

A fourth aspect of the present invention is characterized in that, in the third aspect of the present invention, the optical frequency conversion means is an acousto-optical element. According to a fourth aspect of the present invention, there is provided a method for measuring a plastic strain ratio by a laser ultrasonic method, comprising: irradiating a laser beam emitted by a first laser light source onto a surface of an object to generate ultrasonic waves on the object. Process and
The respective optical frequencies are the first, second, and third optical frequencies or in the vicinity thereof, to generate first, second, and third laser beams for observing the ultrasonic wave transmitted through the subject. The second laser beam in the z-x plane in parallel with the normal (this is the z-axis) of the first laser beam to the object surface (this is the xy plane) at an incident angle theta ₁ from the axis, and wherein a third angle of incidence theta ₂ from the z-axis of a laser beam in the z-y plane, the laser beam incidence step of entering the same position of each of the subject surface The absolute value of the value obtained by differentiating the transmitted light intensity by the optical frequency at least in the first, second, and third optical frequencies of the reflected light of each laser beam applied to the subject in the laser beam incident step is Fabs with locally maximal properties And Fabry-Perot interferometer means incident step of entering the-Perot interferometer means, based on the laser beam output from the Fabry-Perot interferometer means, wherein said ultrasonic propagating within the object first, second,
A light detection step of detecting a change in the intensity of light emitted from the Fabry-Perot interference means due to shifting the optical frequency of the reflected light of the third laser beam, and outputting a signal to that effect; and the first laser An ultrasonic wave propagation time measuring step of measuring a propagation time from irradiating the light source to the subject until a predetermined ultrasonic wave is observed by the light detecting means, and calculating a sound speed of each ultrasonic wave from the propagation time. Calculating a plastic strain ratio of the subject based on a predetermined formula using the value.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of one embodiment of a laser ultrasonic device according to the present invention.
In FIG. 1, an ultrasonic wave generation laser 10 is a laser light source that emits a laser beam for generating an ultrasonic wave inside a steel material 1 whose r value is to be measured. It is a laser light source that emits a laser beam for observing an ultrasonic wave propagating through the subject 1. For example, an Nd: YAG laser is used as the ultrasonic wave generation laser 10, and a He—Ne laser whose frequency is stable is used as the ultrasonic wave observation laser 11, for example.

The laser beam emitted from the ultrasonic wave generation laser 10 is transmitted to a mirror 12, half mirrors 13,
The light is irradiated onto the surface of the subject 1 via the light sources 4 and 15. When the subject 1 is irradiated with the laser beam, an ultrasonic wave is generated in that part by thermal stress or evaporation reaction force. The ultrasonic waves include those that propagate inside the subject and those that propagate on the surface of the subject around the point irradiated with the laser beam. Consider only an ultrasonic wave propagating in a direction perpendicular to the direction (this is the z-axis direction; see FIG. 3).

On the other hand, a laser beam (optical frequency f) emitted from the ultrasonic observation laser 11 is divided into three laser beams by two polarizing beam splitters (PBS) 16 and 17, and each laser beam is divided into three laser beams. The beams are directed to corresponding acousto-optic elements 18, 19, 20. The acousto-optic devices 18, 19, and 20 are devices utilizing an acousto-optic effect, and in this case, an acousto-optic frequency shifter (Acousto-Optical FrequencyS).
hifter: AOFS). That is,
In the acousto-optic device, a medium provided therein performs ultrasonic vibration by a signal supplied from an external oscillator or the like, and its elastic strain and pressure change depending on the location. Due to this, a refractive index fluctuation having a cycle of the wavelength of the ultrasonic wave occurs in the medium, and the light incident on the fluctuation region causes diffraction. At this time, the diffracted light undergoes Doppler shift due to the ultrasonic wave, and the optical frequency of the first-order diffracted light has a value shifted from the optical frequency of the incident light by the frequency of the ultrasonic wave. That is,
The optical frequency of the incident light [nu _i, the first-order diffracted light of the light frequency [nu _d, the frequency of the ultrasonic wave and f _a, the _{ν d = ν i ± f a} . Here, the sign of ± is determined by the direction of diffraction.

In the description of this embodiment, the ultrasonic observation laser
Laser beam of frequency f emitted from the laser light source 11
By the acousto-optic elements 18, 19, 20₀,
f₁, F _TwoTo the optical frequency of this frequency shift
The obtained laser beam is used for observation of ultrasonic waves. Super sound
Observation of the waves indicates that these laser beams
Dopped by ultrasonic vibrations on the surface of the subject when projected
And the optical frequency is f₀, F₁, F
_TwoThe slight displacement about the center frequency
This is done by capturing with a Perot interferometer.

A laser beam for ultrasonic observation, which has been diffracted by the acousto-optic devices 18, 19 and 20 and has undergone a frequency shift, is applied to the subject 1 by appropriate optical elements. The positions on the subject 1 where these laser beams are irradiated are the same as the positions where the laser beams emitted from the ultrasonic wave generation laser 10 are irradiated. However, the angles of incidence on the surface of the subject 1 are different. How to set the incident angle will be described later. Among the laser beams for ultrasonic observation applied to the subject 1, those reflected on the surface of the subject 1 are reflected by the half mirror 5 and the mirror 21, and are reflected by the Fabry-Perot interferometer 30.
Incident on.

FIG. 2 is a graph showing the characteristics of the Fabry-Perot interferometer 30. The horizontal axis indicates the optical frequency of the incident light, and the vertical axis indicates the output light intensity (transmitted light intensity). As shown in the figure,
In the Fabry-Perot interferometer, the output light intensity reaches a peak at a certain optical frequency, and greatly decreases before and after that. Although such peaks of the emitted light intensity appear at substantially constant optical frequency intervals, FIG. 2 shows only two peaks.

As described above, the optical frequencies f ₀ , f ₁ , f ₂
Depends on the frequency of a signal supplied from the outside to the acousto-optic elements 18, 19 and 20, respectively. Therefore, in the present embodiment, the three optical frequencies f ₀ , f ₁ , and f ₂ are locally determined by differentiating the transmitted light intensity (vertical axis) of the Fabry-Perot interferometer 30 with the optical frequency (horizontal axis). The signals supplied to the acousto-optical elements 18, 19, and 20 are set so that the optical frequency becomes the maximum or the minimum, in other words, the optical frequency at which the slope of the characteristic curve in FIG. Adjust the frequency. These optical frequencies are located before and after the optical frequency at which the transmitted light intensity peaks in FIG.
By selecting the optical frequencies f ₀ , f ₁ , and f ₂ at such a value that the change in the intensity of the emitted light is greatest, the slight light received by the laser beam for ultrasonic observation due to the ultrasonic vibration of the surface of the subject is obtained. The displacement of the frequency can be detected with high sensitivity as a change in the output light intensity of the Fabry-Perot interferometer.

In this specification, the optical frequency at which the value obtained by differentiating the transmitted light intensity with respect to the optical frequency is locally maximum or minimum is referred to as "maximum change frequency". In the case of FIG. 2, the optical frequencies corresponding to the three consecutive maximum change frequencies are respectively f
₀ , f ₁ , f ₂ , but there are actually more maximum changing frequencies, and therefore, the optical frequencies f ₀ , f 2
₁ and f ₂ can be any arbitrary maximum change frequency, provided that they do not have the same optical frequency. Note that the term “local” is used as described above because, as described above, the peak of the emitted light intensity appears at a substantially constant optical frequency interval, and the maximum changing frequency is the optical frequency before and after each peak. It takes into account the existence.

The laser beam emitted from the Fabry-Perot interferometer 30 enters the interference filters 31 and 32. These interference filters have the property of reflecting incident light of a certain range of optical frequencies and transmitting another range of incident light. By utilizing such characteristics, the path of a laser beam according to the optical frequency is utilized. Can be divided. As a result, the laser beam of the optical frequency f ₀ is
Then, the laser beam of the optical frequency f ₁ is a photodetector 41,
Laser beam of the optical frequency f ₂ is to be detected, respectively by the optical detector 42. Photodetectors 40, 41, 42
Converts an incident laser beam into an electric signal corresponding to the intensity and outputs the electric signal.

Next, the laser beam for ultrasonic observation at the optical frequencies f ₀ , f ₁ , f ₂ is applied to the subject 1 at any incident angle.
Will be described. FIG. 3 is an enlarged view showing the vicinity of a point where each laser beam is irradiated on the subject 1. The x-axis and the y-axis are taken on the surface of the subject 1 as shown in FIG. Take in a direction perpendicular to the subject 1. FIG.
As shown in the figure, a laser beam having an optical frequency f ₀ is perpendicularly incident on the surface of the subject 1 (parallel to the z axis), and a laser beam having an optical frequency f ₁ is shifted from the x axis in the xz plane. θ
Is incident at _first angle, the laser beam of the optical frequency f ₂ is to be incident at theta ₂ angle from the y axis in the y-z plane.
The irradiation position of each laser beam is the same as the irradiation position of the laser beam for generating the ultrasonic wave as described above.

When each ultrasonic observation laser beam is irradiated in the manner shown in FIG. 3, a laser beam f ₀ irradiating the surface of the subject 1 vertically (hereinafter, similarly, f ₀ , which represents an optical frequency, Each of the laser beams is distinguished by using f ₁ and f ₂ ) is subjected to Doppler shift by ultrasonic waves vibrating perpendicularly to the surface of the subject, that is, longitudinal ultrasonic waves. A laser beam (f) incident at an angle of θ ₁ from the x-axis
₁ ) is subjected to Doppler shift by a longitudinal ultrasonic wave vibrating perpendicularly to the surface of the subject and a transverse ultrasonic wave displacing the surface of the subject in the x-axis direction. And from the y-axis
_The laser beam (f ₂ ) incident at an angle of ₂ is subjected to a Doppler shift by a longitudinal ultrasonic wave displaced perpendicular to the surface of the subject and a transverse ultrasonic wave displaced in the y-axis direction on the subject surface. .

When an ultrasonic observation laser beam whose irradiation direction is inclined by a predetermined angle from the normal direction of the subject, such as the laser beams f ₁ and f ₂ , is used, the surface of the subject becomes parallel to the surface. Vibrating transverse waves can be captured. For the observation of a transverse wave using such a laser beam, see, for example, Nakamura and Ueba “Non-contact Measurement Method of Vibration” (Ultrasonic T
ECHNO (May 1997) (this paper is hereinafter referred to as “Reference 2”).

By the way, even with the ultrasonic wave propagating in the same z-axis direction, the sound velocity V _{ZZ of} the longitudinal wave vibrating perpendicularly to the surface of the subject,
The sound velocity V _{ZX of} the transverse wave whose wavefront is in the xz plane (the surface of the subject is displaced in the x-axis direction), and the wavefront is in the yz plane (the surface of the subject is displaced in the y-axis direction) The sound velocity V _ZY of the shear wave is
Generally not the same. Therefore, the time required for these ultrasonic waves generated at the moment of irradiating the point O of the subject 1 with the laser beam for generating an ultrasonic wave to be reflected on the back surface of the subject and returned to the point O again is extremely long. It depends on the type of sound wave. Further, when the ultrasonic wave of the longitudinal wave is reflected on the back surface of the subject 1, a part of the ultrasonic wave becomes a transverse wave.

Therefore, the laser beam f ₀ is transmitted
On the return path, it undergoes Doppler shift only by longitudinal ultrasonic waves. Laser beam f ₁ includes ultrasonic longitudinal wave with the forward-backward, and ultrasonic backward path transverse forward path by a longitudinal wave (shear wave wavefront in the x-z plane), both forward-backward wavefront x- z
A Doppler shift is caused by a transverse ultrasonic wave in the plane. Then, the laser beam f ₂ includes the ultrasonic longitudinal wave with the forward-backward, forward the backward by vertical wave shear (wavefront y-
The wavefront undergoes a Doppler shift due to the ultrasonic wave of the transverse wave in the z plane and the ultrasonic wave of the transverse wave in the forward and backward paths both in the yz plane.

By the way, as is well known, the Doppler shift Δf ₀ of the laser beam f ₀ is expressed as Δf ₀ = 2Vf ₀ / c (1). Here, V is the displacement speed of the surface of the subject 1, and c is the speed of light. According to the above-mentioned Document 2,
The Doppler shifts Δf ₁ and Δf ₂ of the laser beam f ₁ and the laser beam f ₂ are given by Δf ₁ ∝V sin θ ₁ −U _x cos θ ₁ (2) Δf ₂ ∝V sin θ ₂ −U _y cos θ ₂ (3) Is done. Here, U _x is the speed of displacement of the surface of the subject 1 in the x-axis direction, and U _y is the speed of displacement of the surface of the subject 1 in the y-axis direction.

FIGS. 4 (a), 4 (b), and 4 (c) are the same as FIGS.
FIG. 4 is a diagram schematically showing output waveforms of the photodetectors 40, 41, and 42, and the horizontal axis represents the time after irradiating the laser beam for generating an ultrasonic wave to the surface of the subject. (A)
The large change in the output of the photodetector 40 at time t _{0ll indicates} that longitudinal ultrasonic waves were observed on both the outward and return paths. In (b), the output of the photodetector 41 is at time t
_Significant changes in _1ll , _t1tl , and _t1tt are caused by longitudinal ultrasonic waves on both the forward and return paths, and transverse waves on the outward _path (transverse waves with wavefronts in the xz plane). This shows that a transverse wave ultrasonic wave whose wavefront is within the xz plane was observed for both the sound wave and the outward and return paths. Further, in (c), the photodetector 4
2 outputs the time t _2LL, t _2TL, the largely changes at t _2Tt, respectively, the longitudinal ultrasonic wave with the forward-backward,
This indicates that ultrasonic waves were observed in which the forward path was a longitudinal wave and the backward path was a transverse wave (a transverse wave having a wavefront in the yz plane), and both the forward and return paths were transverse wave ultrasonic waves in which the wavefront was in the yz plane. .

In FIGS. 4A, 4B and 4C, at time t
_0ll , _t1ll , and _t2ll are all the same. this is,
This is because these ultrasonic waves are all composed only of longitudinal waves. However, at each time, each photodetector 40,
The magnitudes of the changes in the output waveforms of 41 and 42 are different. on the other hand,
t _1TL and t _2TL, for t _1Tt and t _2Tt, since there is anisotropy in acoustic velocity generally different.

Therefore, for example, t _0ll , t _1tt , t
By measuring _2tt (the thickness d of the subject 1 is measured in advance), the sound velocity V _{ZZ of} the longitudinal wave and the wavefront are in the xz plane (the surface of the subject is displaced in the x-axis direction). ) It is possible to calculate the sound velocity V _{ZX of} the shear wave and the sound velocity V _ZY of the shear wave whose wavefront is in the yz plane (the surface of the subject is displaced in the y-axis direction).

Once V _ZZ , V _ZX , and V _ZY have been determined, the r value can be determined from them. This is described in detail in the above document 1. here,
The fact that the r value is obtained from V _ZZ , V _ZX , and V _ZY based on the description in Document 1 will be briefly described. The annealed cold-rolled steel sheet is considered to be an aggregate of iron cubic iron single crystals,
The distribution of each crystal orientation with respect to the material axis is biased, forming a so-called texture. The quality of this texture has a great influence on its plastic properties, and the r-value is also strongly governed by it.

On the other hand, the texture is deeply related to the elastic properties of the steel sheet. The degree of the preferred orientation of each crystal that determines the texture is represented by a crystal orientation distribution coefficient that gives the probability of a crystal orientation having a characteristic orientation with respect to the material axis. For polycrystalline samples with symmetry orthorhombic as cold rolled steel sheet, the crystal orientation distribution factor of three lower order W _{40 0,} W ₄₂₀ W ₄₄₀ is, has important implications, the three one of the values, and the three modulus C ⁰ ₁₁ of a single crystal, C ⁰ _12, C ⁰
_{Since 44} is considered to be a physical constant, W ₄₀₀ and W _{42 are} eventually obtained.
₀ W ₄₄₀ determines the elastic properties of the steel sheet, and also determines the Young's modulus.

The texture also affects the ultrasonic waves propagating through the steel sheet, and the ultrasonic waves also exhibit velocity anisotropy according to the anisotropy due to the texture. Therefore, five types of ultrasonic waves as shown in FIG. 5, that is, a longitudinal wave U _ZZ propagating in the thickness direction (Z direction) and a transverse wave U _ZX propagating in the thickness direction and polarized in the rolling direction (X direction). Using the transverse wave U _ZY propagating in the plate thickness direction and polarized in the width direction (Y direction) and the SH ₀ plate wave propagating in two directions, the ratio K ₁ of the thickness resonance frequencies of the preceding three types of ultrasonic waves, K ₂
From and after two ultrasonic sound speed ratio K _3, W _400, W
_The need for _{420 W440} is clarified as follows. That is,

[0032]

(Equation 1)

Here, m and n are arbitrary orders, and f
_ZZm is the m-th thickness resonance frequency of the longitudinal ultrasonic wave U _ZZ , f _ZYn is the n-th thickness resonance frequency of the transverse ultrasonic wave U _ZY polarized in the width direction f _ZXn is the transverse ultrasonic wave U polarized in the rolling direction The nth-order thickness resonance frequencies V _SH0 (0 °) and V _SH0 (45 °) of _ZX are the speed of sound of the SH ₀ plate wave propagating in the rolling direction, the rolling direction and the 45 ° direction, respectively.

At this time,

[0035]

(Equation 2)

As follows:

[0037]

(Equation 3)

Is represented by Where C⁰= C⁰ ₁₁-C⁰
₁₂-2C⁰ ₄₄It is. As mentioned above, nine cold-rolled steel sheets
Elastic modulus C_ij, And the Young's modulus E (θ) in the rolling plane θ direction
Is the above W₄₀₀, W₄₂₀W₄₄₀And C⁰ ₁₁, C⁰ ₁₂, C
⁰ ₄₄Can be represented by Therefore, the ultrasonic measurement
Variable K obtained by_P, K_M, K_ThreeAnd three iron single crystals
Thus, the Young's modulus E (θ) can be obtained. E (θ) = Func₁(W₄₀₀, W₄₂₀W₄₄₀, C⁰ ₁₁, C⁰ ₁₂, C⁰ ₄₄, Θ) = Func_Two(K_P, K_M, K_Three, C⁰ ₁₁, C⁰ ₁₂, C⁰ ₄₄, Θ) (5) In the ultrasonic measurement, SH propagating in two directions₀
K indicating the sound speed ratio of the plate wave _ThreeIs the Young's modulus E in each direction_ave=
[E (0 °) + 2E (45 °) + E (90 °)] / 4
On the other hand, it has little effect.

The K obtained as a result of measuring a large number of cold-rolled steel sheets
_1, in the range of K _2, K _3, was evaluated error in the case where the K ₃ a constant value, the change in E _ave is the largest 0.05G
It was about Pa and found to be very small. _{Thus, E ave = Func 3 (K} P, K M, C 0 11, C 0 12, C 0 44) become (6).

By the way, the average r value in the rolling plane (r _ave =
[R (0 °) + 2r (45 °) + r (90 °)] / 4)
It is known that there is a strong correlation between the in-plane average Young's modulus E _ave (see Stickel for this).
s. C. A. , Mould. P. R. : Metall.
Trans. 1, 1303 (1970)). Thus, if the Young's modulus E _ave as described above is obtained, empirical formula, for example, ^{_{r ave = aE av e 2 +}} bE ave + c (a,
b, c, based on the quadratic equation, such as appropriate coefficient) r _{av e}
Value can be obtained. From the above, among the five types of ultrasonic waves in FIG. 5, the measurement of the sound velocity of the SH ₀ plate wave relating to K ₃ is omitted, and the Young's modulus is obtained only by measuring the thickness resonance frequency of the three types of ultrasonic waves propagating in the plate pressure direction. It can be seen that E _ave can be obtained, and further that the r _ave value can be obtained.

By the way, the sound speeds V _ZZ , V _ZX , V
And _ZY, between its _{frequency, f ZZm = (m / 2d} ) V ZZ (7) f ZYn = (n / 2d) V ZY (8) f ZXn = (n / 2d) V ZX (9) There is a relationship. Where d is the thickness of the subject,
m and n are orders of the resonance frequency. This (7)-
By substituting equation (9) into equation (3), K ₁ , K
₂ is determined, K _p by substituting this into equation (4), K _M is obtained, the Young's modulus E _ave is obtained by substituting this into (6), further, the Young's modulus E _The r _ave value is calculated from _ave as described above. Therefore, when the sound velocities V _ZZ , V _ZX , and V _ZY of each ultrasonic wave are obtained in the configuration of the present embodiment shown in FIG. 1, the r _ave value is calculated by performing the calculation according to the procedure described above. be able to.

As described above, in the present embodiment, since the laser ultrasonic method is used, the apparatus (an electromagnetic ultrasonic transducer in the case of the resonant electromagnetic ultrasonic method) is used as in the case of using the resonant electromagnetic ultrasonic method. No need to approach the specimen,
For example, the laser can be irradiated from a place several meters away from the subject. Further, even if the distance changes, the specific result is not affected. Therefore, operability in an actual production line is improved as compared with the resonance electromagnetic ultrasonic method.

In the present embodiment, the laser beam emitted from one ultrasonic observation laser light source 11 is divided into three, and the optical frequency f of each laser beam is changed to acousto-optic elements 18 and 19. , 20 to shift to the optimal frequencies f ₀ , f ₁ , f ₂ for the observation of the Doppler shift, and three different optical frequencies f ₀ ,
Ultrasound waves are observed using laser beams f ₁ and f ₂ using separate photodetectors. Thus, even when the times at which the three ultrasonic waves are observed are very close, the propagation time of each ultrasonic wave can be accurately obtained.

Further, in this embodiment, three ultrasonic observation laser beams are obtained by splitting a laser beam emitted from a single laser light source 11. Further, the laser beam reflected by the subject 1 is detected using a single Fabry-Perot interferometer 30.
As described above, since only one relatively expensive laser light source 11 and one Fabry-Perot interferometer 30 can be used, it is cost effective.

The present invention is not limited to the above embodiment, and various changes can be made within the scope of the invention.

[0046]

As described above, according to the present invention,
Unlike resonant electromagnetic ultrasound, which requires the electromagnetic ultrasound transducer to be very close to the subject, a laser that can non-destructively examine the inside of the subject while the device is sufficiently far away from the subject Using the ultrasonic method, the sound velocity of the longitudinal wave and two transverse waves in the subject can be measured, and the plastic strain ratio of the subject can be calculated from a predetermined formula from these, so that the plastic strain in the actual production line can be calculated. It is possible to provide a method and an apparatus for measuring a plastic strain ratio by a laser ultrasonic method in which the ratio can be easily measured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a laser ultrasonic device according to the present invention.

FIG. 2 is a characteristic diagram of a Fabry-Perot interferometer in which the horizontal axis represents the optical frequency of incident light and the vertical axis represents the intensity of outgoing light (transmitted light intensity).

FIG. 3 is an enlarged view showing the vicinity of a point where each laser beam is irradiated on a subject.

FIG. 4 is a diagram schematically illustrating output waveforms of three photodetectors.

FIG. 5 is a diagram schematically showing various ultrasonic waves generated in a subject.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Subject 10 Laser for ultrasonic generation 11 Laser for ultrasonic observation 12,21 Mirror 13,14,15 Half mirror 16,17 Polarization beam splitter (PBS) 18,19,20 Acousto-optic element 30 Fabry-Perot interferometer 31 , 32 Interference filters 40, 41, 42 Photodetector

Claims (5)

[Claims] 1. Using a Fabry-Perot interferometer, a characteristic in which the absolute value of the value obtained by differentiating the transmitted light intensity with the optical frequency at least at the first, second, and third optical frequencies is locally maximum. Fabry-Perot interference means, and a first laser light source that emits a laser beam for generating an ultrasonic wave on the subject, and each optical frequency is the first, second, third optical frequency or its In the vicinity, a second laser light source that emits first, second, and third laser beams for observing ultrasonic waves that have propagated through the subject; and xy
The second laser beam is shifted from the z-axis in the z-x plane by θ _{1 in} parallel with the normal (which is the z-axis) of the plane.
At an incident angle of, also the third laser beam at an incident angle of theta ₂ from the z-axis in the z-y plane, a first optical means to be incident on the same position of each of the subject surface, said first First, second, and third optical means for causing reflected light of the subject of the laser beam from the subject to enter the Fabry-Perot interference means, and the ultrasonic waves propagated in the subject are the first and second ultrasonic beams. Light detecting means for detecting a change in the intensity of light emitted from the Fabry-Perot drying means due to shifting the optical frequency of the reflected light of the second and third laser beams, and outputting a signal to that effect; While irradiating the object with the laser light emitted from one laser light source to determine the propagation time from when the predetermined ultrasonic wave is observed by the light detection means, calculate the sound speed of each ultrasonic wave from the propagation time. , Using that value A calculating means for calculating a plastic strain ratio of the subject based on a constant calculation formula; and a plastic strain ratio measuring apparatus by a laser ultrasonic method. 2. The Fabry-Perot interference means has a characteristic in which the absolute value of the value obtained by differentiating the transmitted light intensity with respect to the optical frequency at least at the first, second, and third optical frequencies is locally maximum. A second Fabry-Perot interferometer, wherein the second optical means integrates reflected light of the first, second, and third laser beams from the subject into a single path to produce the Fabry-Perot interferometer. Further, the light emitted from the Fabry-Perot interferometer is split into laser beams having respective optical frequencies, and the respective laser beams can be detected for their intensity change. 2. The plastic strain ratio measuring apparatus according to claim 1, further comprising a branching means for entering the light into the light detecting means. 3. The second laser light source, comprising: a laser emitting a single laser beam having a single optical frequency; and a laser beam emitted from the laser divided into three, The first, second branching means to be a third laser beam, the first, second, the optical frequency of the third laser beam,
3. An optical frequency conversion means for converting each of the first, second, and third optical frequencies or an optical frequency in the vicinity thereof into the first, second, and third optical frequencies. Ratio measuring device. 4. The plastic strain ratio measuring apparatus according to claim 3, wherein the optical frequency conversion means is an acousto-optic device. 5. An ultrasonic wave generating step of irradiating a laser beam emitted from a first laser light source to a surface of a subject to generate an ultrasonic wave on the subject, wherein the respective optical frequencies are equal to the first, second, and A first, second, and third laser beams for observing an ultrasonic wave that has propagated through the subject at or near a third optical frequency are generated, and the first laser beam is applied to the subject surface ( This is a normal line (which z-axis of the the x-y plane)) and parallel to, the second laser beam at an incident angle of theta ₁ from the z-axis in the z-x plane, and the second the third laser beam at an incident angle of theta ₂ from the z-axis in the z-y plane, the laser beam incidence step of entering the same position of each of the surface of the object, is applied to the specimen at the laser beam incident step The reflected light of each laser beam Both the first,
Second, at the third optical frequency, Fabry-Perot interference means incident step to enter the Fabry-Perot interference means having the characteristic that the absolute value of the value obtained by differentiating the transmitted light intensity with the optical frequency is locally maximum, Based on the laser beam output from the Fabry-Perot interference unit, the ultrasonic wave propagated in the subject shifts the optical frequency of the reflected light of the first, second, and third laser beams. A light detection step of detecting a change in the intensity of the emitted light of the Fabry-Perot interference means and outputting a signal to that effect, and irradiating the subject with the first laser light source and then performing a predetermined process by the light detection means. An ultrasonic propagation time measuring step of measuring a propagation time until an ultrasonic wave is observed, calculating a sound speed of each ultrasonic wave from the propagation time, and using the value thereof based on a predetermined calculation formula. Plastic strain ratio measurement method by laser ultrasonic method, characterized by comprising: a calculation step of calculating a plastic strain ratio of the sample.