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JPS6355457

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DESCRIPTION JPS6355457
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method and apparatus for generating ultrasonic waves in a noncontacting manner on a material
to be inspected and, for example, in the case of nondestructively inspecting internal defects of
the material to be inspected using ultrasonic waves. It is used. [Prior Art] When the surface of an
object that absorbs light is instantaneously irradiated with a high energy beam such as a laser
beam, an ultrasonic wave is generated on the object by the thermal excitation of the irradiation
unit, and the laser beam is inspected for internal defects. It is known in Japanese Patent
Application Laid-Open No. 54-9679 that an inspection material to be inspected is irradiated with
ultrasonic waves to be generated on the surface of the inspection material and a reflection echo
from a defect is detected to detect an internal defect. FIG. 10 is a schematic view showing the
configuration of a conventional non-contact type ultrasonic wave generator, and in the figure, 1
is an inspection material to be inspected for an internal defect, that is, an ultrasonic wave
generation target. A laser light source 2 for generating a laser beam is provided above the
material to be inspected 1 at an appropriate distance from the material to be inspected 1, and the
drive of the laser light source 2 is adjusted by the controller 6. When the laser light 3 emitted
from the laser light source 2 is irradiated on the surface of the inspection material 1, the
irradiated part of the laser light 3 is thermally expanded instantaneously by the absorption of the
light. As a result, a local thermal stress is caused in the material to be inspected l, 1 mechanical
stress is generated in the material structure of the material to be inspected 1 'by the stress, the
sound source 4 is generated, and an elastic wave, that is, an ultrasonic wave is generated. Occur.
[Problems to be Solved by the Invention] The conventional measuring apparatus and inspection
apparatus using ultrasonic waves have a contact type ultrasonic transducer in contact with the
material to be inspected, and a single mode necessary from the ultrasonic transducer. Was
generated and made to enter the test material. However, in the conventional non-contact type
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ultrasonic wave generator as described above, ultrasonic waves (longitudinal wave, shear wave 1
surface wave) in various modes are simultaneously generated, and the modes can not be
separated. There is a problem that there is an inconvenience in the use of In addition, when an
internal defect is inspected using this ultrasonic wave generator, in particular, a part of the
reflected wave undergoes mode conversion, so the am component and the horizontal i
component can not be identified, and the position of the defect or its size can not be accurately
evaluated. There was a problem of that. . The present invention has been made in view of such
circumstances, and the object of the present invention is the relationship between the
wavelength λ of the ultrasonic wave generated when a high energy beam is irradiated to an
object and the diameter of the sound 11iI of the ultrasonic wave. In order to generate only the
ultrasonic wave of the longitudinal wave component if D / λ> 1, the high energy and a part of
the material to be inspected are irradiated so as to be larger than the value month of the D / λ.
In order to propose a contact type ultrasonic wave generation method and to carry out this
method, means for changing the beam diameter of the high energy beam emitted from the high
energy beam generation means or for intermittently driving the high energy beam generation
means It is an object of the present invention to provide a noncontact ultrasonic wave generation
method for generating a single mode ultrasonic wave consisting of only longitudinal waves by
providing means for changing the time width or fr duration of a signal.
[Means for Solving the Problems] In the non-contact ultrasonic wave generation method for tree
climbing / brighting, the relationship between the wavelength λ of the generated ultrasonic
wave and the diameter of the ultrasonic wave source is set to D / λ> 1. As described above, by
irradiating the test material with a high energy beam, a single-mode ultrasonic wave of only
longitudinal waves is generated in the test material. [Operation] Does the noncontact ultrasonic
wave generation method according to the present invention increase the diameter of the beam
emitted from the high energy beam generation means or shorten the pulse width of the drive
pulse signal applied to the high energy beam generation means? Alternatively, by reducing the
period of the pulse train of the drive pulse signal, the relationship between the wavelength λ of
the generated ultrasonic wave and the diameter of the ultrasonic wave source is D /,! >1にする
。 As a result, a single-mode ultrasonic wave of only longitudinal waves is generated. The present
invention will be specifically described below based on the drawings showing the embodiments.
FIG. 1 is a schematic view showing the configuration of an embodiment of the non-contact type
ultrasonic wave generator according to the present invention, and in the figure, 1 is a test
material to be ultrasonically generated. An intermittently driven laser light source 2 that
generates a laser beam 3 at an appropriate distance from the test material 1 is provided above
the test material l. In addition, a lens 7 for enlarging the beam diameter of the laser beam 3
emitted from the laser light source 2 is provided between the inspection material 1 and the laser
light source 2, and the laser beam 3 from the laser light source 2 is provided. The diameter of the
lens 7 is enlarged by the lens 7 so that the material to be inspected 1 is irradiated. The laser light
source 2 is connected to a controller 6 that controls the drive of the laser light source 2, and the
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laser light source 2 is driven by a switch signal from the controller 6. Next, the operation will be
described. When a switch signal from the controller 6 is input to the laser light source 2, the
laser light: a 2 emits the laser light 3 in synchronization with the switch signal. The beam
diameter of the laser beam 3 is expanded to d by the lens 7 and momentarily illuminates the
surface of the inspection object 1. As a result, a local heat stress generated on the surface of the
test-metal member 1 generates a sound source 4 with a diameter, and an ultrasonic wave is
generated radially from the sound source 4. Here, the relationship between the wave length and
the wavelength 2 of the ultrasonic wave is set to D / λ> 1, and the ultrasonic wave generated in
the test material 1 becomes a single mode of only the longitudinal wave. Here, in the case of D /
λ> 1, the reason why the generated ultrasonic wave is a single mode of only longitudinal waves
will be described. Fig. 2 cited from "Ultrasonic test technology" by Toloud Kramer shows the
sound field characteristics of ultrasonic waves emitted from point sources when D / λ 関係 1.
The solid wave represents the sound field of longitudinal waves, B represents the sound field of
transverse waves. !
As shown in FIG. 1, the sound field of the shear wave has a component having a phase increase,
and the phase of the part of the mode shown by hunting and the part of the mode without
hatching differ by 90 °. FIG. 3 shows the sound field characteristic of the ultrasonic wave
emitted from the sound source when D / λ> l, and only longitudinal waves exist. When the
diameter of the sound fR4 is large, it is considered that the ultrasonic waves generated from a
plurality of point sound sources 4c as shown in FIG. 2 are synthesized. In the sound field radiated
from each point sound source 4c, there is a sod sound source 4c in which the ultrasonic waves of
the components of the transverse wave are substantially in the stated phase. Therefore, the
sound field of the transverse wave is canceled out and ceases to exist when the diabetics of all
the point sound sources 4c are synthesized. On the other hand, since the longitudinal wave has
only the in-phase component, it becomes an added value of each point sound source. 4 shows the
surface wave generated from the point sound source, and FIG. 4 (a) shows the surface wave 10a
generated from the point sound source 4a, and the surface wave 10a is in the direction of the
arrow in the drawing. To propagate. Further, FIG. 4 (b) shows a state in which the surface waves
10a and 10b are generated from the individual sound sources by separating two point sound
sources 4a and 4b by% wavelength (〃λ) N. The surface vibration due to surface waves when
ultrasonic waves are simultaneously generated from the point sound sources 4a and 4b is the
sum of these two surface waves 10a and 10b. Here, since the phases of the surface waves IDa
and 10b differ by 180 ', the sum of the two types of surface waves 10a and job is 0 (see FIG. 4
(C)). Since the sound source of the inspection and the material surface when the relationship
between the wavelength λ of the sound source and the diameter is D / λ> 1 can be regarded as
a set of point sound sources 4a and 4b shown in FIG. If / λ> 1, as in the case of FIG. 4 (b), the
surface waves cancel each other out at point sound sources having sound fields of substantially
opposite phase to each other, and no surface waves are generated. Therefore, for the reason
described above, when D / λ> 1, no shear wave and surface wave are generated, and a 串 -mode
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ultrasonic wave of only the longitudinal wave is generated. The above is the reason why the
transverse wave and the surface wave are not generated when D / λ> 1. Next, the operation of
the means for achieving the relationship D 1 λ> 1 will be described. In order to obtain a
relationship of D / λ> 1, D may be increased or λ may be decreased. The relationship between
the diameter of the ultrasonic wave source and the beam diameter d of the laser light can be
expressed by the following equation (1). In order to increase the diameter of the sound source
according to D = −d (1) (where K is the light-source conversion coefficient = 1), the beam
diameter d of the laser light may be enlarged. The lens 7 is provided for this purpose.
In addition, not only the lens 7 but a beam expander. A means for enlarging the beam diameter
such as a pinhole may be provided. If the laser light is convergent light or diffused light, the
beam diameter can be enlarged even if the distance between the inspection material 1 and the
laser light source 2 is adjusted without providing the lens 7. FIG. 5 shows the switch signal (FIG.
5 (a)) output from the controller 6 and the vibration waveform (15 (b)) of the generated
ultrasonic wave. The frequency fa of the ultrasonic wave is determined by the pulse width Δta of
the switch signal from the controller 6, that is, the driving time of the laser light source 2. Since
the wavelength λ of the ultrasonic wave which is a problem in the present invention is
calculated by the following equation (2), the value of the wavelength λ of the ultrasonic wave
can be adjusted by controlling the pulse width of the switch signal. λ-c / f (2) (where C:
propagation speed of ultrasonic wave in the test material l: ultrasonic frequency) In other words,
if it is intended to reduce the wavelength λ of the ultrasonic wave, the frequency of the
ultrasonic wave In other words, it is sufficient to make the pulse width of the switch signal large.
Accordingly, the controller 6 acts to shorten the pulse width of the output trigger signal. 5 (C)
shows the frequency-modulated switch signal, and FIG. 5 (d) shows the vibration waveform of the
ultrasonic wave generated corresponding to the switch signal shown in FIG. 5 (C). The vibration
waveform of (b) corresponding to the switch signal (a) is ultrasonic vibration of a high band,
while the vibration waveform (d) corresponding to the frequency-modulated switch signal (C) is
the following (3) As shown by the equation, it is a narrow band ultrasonic vibration proportional
to the modulation width of the pulse. Therefore, if the pulse train period Δtc is reduced in this
case, the frequency fc becomes large, that is, λ decreases. As mentioned above, although the
case where a single laser light source was used was demonstrated, the other Example using
several laser light source is described next. FIG. 6 is a schematic view showing the construction
of another embodiment, and in this embodiment, laser light sources 2a, 2b... Consisting of a large
number of semiconductor lasers are provided at an appropriate distance from the material to be
inspected 1 It is installed in the laser light source installation part 9 which makes a dome shape.
The center position of the dome shape is a surface portion to be generated of the ultrasonic wave
of the inspection object l. FIG. 7 is a plan view showing the arrangement of laser light sources in
the case where the arrangement of the laser light sources provided in the laser light source
setting unit 9 is annular, and the laser light sources are provided on the circumference of
concentric circles. The laser light from each laser light source is condensed in the vicinity of the
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surface portion of the test material 1 to be generated ultrasonic waves, but here the test object 1
is changed by changing the curvature of the dome or the distance to the test material l. The
irradiation beam diameter d of the laser beam irradiated to the inspection material 1 can be
changed.
Therefore, if d is increased, the relationship of D can be maintained based on the equation (1)
and D / λ> 1. Further, FIG. 8.9 shows another arrangement example of a plurality of laser light
sources, and in this example, the laser light source setting unit 9 for setting the laser light source
has an opening facing the inspection material 1 side. Make a semi-cylindrical shape. FIG. 8 is a
developed plan view when the laser light sources are arranged in a grid, and FIG. 9 is a developed
plan view when the laser light sources are arranged in only one row in the longitudinal direction
of the inspection object l. In the embodiment shown in FIG. 8.9, a linear sound source can be
obtained instead of a point sound source. In addition, although the case where the installation
surface is installed in the laser light source installation unit 9 having a curved surface shape has
been described, the present invention is not limited to this. A plurality of laser light sources may
be provided by adjusting the installation angle to light. [Effects] As described in detail above, in
the method of the present invention, the relationship between the wavelength λ of the
generated ultrasonic wave and the diameter of the sound source of the ultrasonic wave is always
maintained at D / λ> 1. Ultrasonic waves can be generated in a noncontacting manner on a
material to be inspected, and can be used as a measuring device, an inspection device,
particularly a device for inspecting internal defects, and the measurement and inspection errors
can be reduced.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a schematic view of the non-contact type ultrasonic wave generator according to the
present invention, FIG. 2.3 is a sound field characteristic view of the ultrasonic wave emitted
from the point sound source, and FIG. 4 is a surface wave generated from the point sound source
Sound field characteristic diagram, FIG. 5 is a signal diagram of a switch signal output from the
controller and a vibration waveform diagram of an ultrasonic wave generated corresponding to
this switch signal, FIG. 6 rf!
J is a schematic view showing the configuration of another embodiment, and FIGS. 7, 8 and 9 are
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schematic views showing the arrangement pattern of the laser light source, and FIG. 10 is a
schematic view of a conventional noncontact ultrasonic wave generator FIG. 1 · · · · · · · · · · · · · · · · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 7 Indicates a
part.
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