JPH09281084A - Laser ultrasonic flaw detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser ultrasonic flaw detector capable of improving the S/N ratio of detected ultrasonic signal and easily reducing noise. SOLUTION: The laser ultrasonic flow detector comprises an ultrasonic wave generating laser 11 for emitting a laser beam for exciting generating an ultrasonic wave to a specimen, an ultrasonic wave detecting laser 21 for generating a laser beam for a probe for detecting the reflected wave reflected in the specimen A and arriving at the surface, an optical system 23 for converting the beam for the probe into an annular laser beam at the center of the beam for exciting emitted to the surface of the sample as a center, and a photodetector for detecting the change received by the synergistic action of the beam for the probe reflected on the surface of the specimen and the reflected wave. The reflected ultrasonic wave signal from a defect directly under the beam for exciting emitted to the surface of the specimen is strengthened and amplified, and detected. Contrary, scattered noise due to the fine structure in the specimen is canceled by one another to be weakened, and detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser ultrasonic flaw detector used in ultrasonic flaw detection for detecting defects such as internal flaws in materials and products.

[0002]

2. Description of the Related Art In a conventional laser ultrasonic flaw detector, for example, ultrasonic TECHNO May issue: Vol.5, No.5, p38 (1993).
As described in (Nippon Kogyo Shuppan), the detection laser light is irradiated at the same position as the irradiation position of the ultrasonic wave generation laser on the surface of the subject, and propagates through the subject to reach the surface of the subject. Detected ultrasonic waves.

[0003]

By the way, in general, the ultrasonic waves generated as described above are weak because they have low conversion efficiency into ultrasonic waves, and when they propagate through a subject, ultrasonic waves are not generated. Since it is a point sound source, the diffusion attenuation in the material becomes large, and the scattering attenuation of the ultrasonic signal due to the influence of the fine structure in the material (the reflection of the ultrasonic wave in the portion which is not elastically homogeneous structure is meant. For example, in the case of a metal material, it is weak due to the influence of the reflection of ultrasonic waves by the grain boundaries of crystal grains. Therefore, the reflection signal from the flaw in the subject is very weak. In addition to these, since the scattering from the fine structure is superimposed on the weak reflected signal from the flaw as noise, the detected signal cannot obtain a sufficient SN ratio. Therefore, in a conventional laser ultrasonic flaw detector, ultrasonic transmission / reception at the same position is repeated several times to several hundreds of times, and the detected signals are added to improve the SN ratio.

However, there is a problem that the noise due to the scattered reflection ultrasonic waves from the fine structure cannot be removed by adding the signals temporally.
In order to reduce this noise, spatial addition processing of adding the signals obtained by slightly changing the ultrasonic transmission / reception position is necessary, but since spatial movement is performed, the detected signals The addition process requires a complicated computer process and cannot be easily executed.

The present invention has been made in view of the above circumstances, and provides a laser ultrasonic flaw detector capable of easily reducing noise and improving the SN ratio of a detected ultrasonic signal. The purpose is.

[0006]

In order to achieve the above object, a laser ultrasonic flaw detector of the present invention comprises an ultrasonic wave generating laser means for irradiating a subject with a laser beam for excitation for generating an ultrasonic wave, Ultrasonic wave detecting laser means for generating a laser beam for a probe that detects reflected ultrasonic waves that have been reflected in the subject and have reached the surface, and for exciting the laser beam for the probe irradiated to the subject. Optical means for converting the laser light into an annular laser light centered on the center of the laser light, and light for detecting a change that the laser light for the probe reflected on the surface of the subject undergoes by the interaction with the reflected ultrasonic waves. And a detection means.

[0007]

[Function] A reflected ultrasonic signal from a defect such as a flaw or a cavity directly below the excitation laser beam is emitted at any position in the annular portion of the surface of the subject irradiated with the probe laser beam. It becomes an in-phase component. Therefore, the reflected ultrasonic signal detected by the annular laser light is constructively amplified and detected. On the other hand, the scattering noise due to the fine structure in the subject, at a certain point of the annular portion, a constant phase component is always detected, but the scattering noise at that one point and the scattering noise at other points are Topologically unrelated. Therefore, the phase-random scattering noises detected by the annular laser light are canceled and weakened and detected.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a laser ultrasonic flaw detection apparatus according to a first embodiment of the present invention, FIG. 2 is a schematic perspective view of laser light with which a subject is irradiated, and FIG. 3 shows reflected ultrasonic waves from a defect portion. It is a schematic diagram which shows a mode at the time of detecting. The laser ultrasonic flaw detector of the first embodiment shown in FIG. 1 includes an ultrasonic wave generation laser device 11 that generates a laser beam 10 that excites ultrasonic waves on a subject A, and a reflection ultrasonic wave reflected in the subject A. Laser light for probe to detect sound waves 2
Ultrasonic wave detecting laser device 21 for generating 0, and cylindrical laser light 2 emitted from the ultrasonic wave detecting laser device 21
An optical system 23 for converting 0 into an annular laser beam, and a photodetector 31 for detecting a change in the probe laser beam reflected on the surface of the subject A due to the interaction with the reflected ultrasonic wave. It is equipped with.

The ultrasonic wave generating laser device 11 is provided for the subject A.
The device 11 uses a Q-switch YAG laser or the like, which is capable of outputting a relatively large pulsed laser beam, because it generates a laser beam for exciting ultrasonic waves on its surface. The laser light emitted from the ultrasonic wave generating laser device 11 is reflected by the mirror 13 and then irradiated onto the subject A.

The ultrasonic detecting laser device 21 is provided for the subject A.
Laser light for a probe for detecting the reflected ultrasonic waves reflected by the defective portion inside and returning to the surface of the subject A is generated. As the device 21, for example, a He-Ne laser or the like that outputs laser light having a stable frequency is used. The optical system 23 converts a cylindrical laser light into a circular laser light, and the ultrasonic detection laser device 21.
Beam expander 23a that expands the beam diameter of the laser beam 20 emitted by the laser beam, and conical mirror 23b that reflects the laser beam expanded by the beam expander 23a.
And a hat-shaped ring-shaped mirror 23c that further reflects the laser reflected by the conical mirror to irradiate the subject A. The conical mirror 23b is supported and fixed by a support member 23d provided at the center of a half mirror 33 described later.

The photodetector 31 is provided with a half mirror 33 provided in the optical path of the annular laser light for extracting the laser light 20 for the probe reflected by the surface of the subject A.
And a condensing lens 35 that condenses the laser light reflected by the half mirror 33, and a photodetector 37 that detects the laser light condensed by the condensing lens 35. The photodetector 37 is the same as that used in the conventional laser ultrasonic flaw detector.

Further, as shown in FIGS. 2 and 3, the ultrasonic wave generating laser device 11, the ultrasonic wave detecting laser device 21, the optical system 23, etc., have an annular laser beam 20 irradiated on the surface of the subject. Are arranged so as to have an annular shape centered on the center O point of the excitation laser light 10 with which the surface of the subject is irradiated. The parts are equidistant from the center O point. The dotted line shown in FIG. 3 is the axis X perpendicular to the surface of the subject at the center O thereof.

Next, the operation of the first embodiment will be described. The laser light 20 emitted from the ultrasonic detection laser device 21 is emitted by the beam expander 23a.
After the beam diameter is expanded, it is incident on the conical mirror 23b. The conical mirror 23b reflects the incident laser light to the shade ring mirror 23c. At this time, the cylindrical laser light incident on the conical mirror 23b is converted into an annular laser light. The hat-shaped ring-shaped mirror 23c receives the incident annular laser beam as shown in FIG.
Irradiation perpendicular to If the diameter of the annular laser light 20 is too large, the detection signal becomes weak. Therefore, when using a He-Ne laser currently on the market, the beam diameter (about 2 mm) of the excitation laser light 10 is It is considered that the same size or two to three times larger size is suitable.

The annular laser beam applied to the subject A is reflected by the surface of the subject A and enters the half mirror 33. The half mirror 33 reflects a part of the incident laser light and makes it enter the condenser lens 35. The condenser lens 35 condenses the incident annular laser light on the photodetector 37. The laser light incident on the photodetector 37 is first converted by the Fabry-Perot interferometer (not shown) into a change in the wavelength of the light into a change in the intensity of the light. The converted light is further photoelectrically converted by a photodiode (not shown), and the electric signal is amplified by an amplifier and then output to an oscilloscope or the like for display.

As described above, the laser beam 2 for the probe is used.
While irradiating the subject A with 1, the subject A is irradiated with the pulsed laser light 10 from the ultrasonic wave generation laser device 11. As a result, the temperature of the surface of the object A is instantaneously locally increased or evaporated, and thermal stress or evaporation reaction force at this time generates a wide-band ultrasonic wave. The generated ultrasonic wave travels along the axis X shown by the dotted line in FIG. 3, propagates inside the subject A, reaches the back surface of the subject A, is reflected here, and again reaches the surface of the subject A. Return.

When the surface of the subject A is ultrasonically vibrated by the reflected ultrasonic waves reflected and returned, the spatial position of the surface of the subject A is displaced at the cycle of the reflected ultrasonic waves. Therefore, when the circular laser light for the probe is reflected on the surface of the subject A, it undergoes the Doppler shift accompanying this displacement, and the wavelength of the circular laser light fluctuates. The annular laser light whose frequency changes in this way is condensed on the photodetector 37 by the half mirror 33 and the condenser lens 35. The photodetector 37 first converts incident laser light into a change in light intensity by a Fabry-Perot interferometer. Further, the converted light is photoelectrically converted by a photodiode, amplified by an amplifier, passed through a high pass filter to remove low frequency noise, and then the signal is output to an oscilloscope or the like.

The signal output from the photodetector 37 is the object A
Each time the reflected ultrasonic wave that is repeatedly reflected on the front surface and the back surface returns to the front surface, it greatly changes. When this output signal is displayed on an oscilloscope with time on the horizontal axis and signal intensity on the vertical axis, if there is no defect in the subject, it will be a constant value determined by the speed of sound in the subject and the thickness of the subject. The signal strength changes at time intervals. On the other hand, if there is a defect such as a flaw or a cavity inside the subject, the ultrasonic waves are reflected by this defect and the signal intensity changes in a time shorter than the above time. Therefore, by examining this time interval, it is possible to inspect the presence or absence of a defective portion inside the subject.

By the way, the conventional laser ultrasonic flaw detector has carried out point sensing on the axis X shown by the dotted line in FIG. In such conventional point sensing, ultrasonic waves that are noise are simultaneously detected in addition to the reflected ultrasonic waves from the defective portion, and as described above, it is not easy to remove this noise. On the other hand, in the present embodiment, the ultrasonic wave generation laser device 11 and the ultrasonic wave detection laser device 21 are used.
The optical system 23 and the like are arranged so that the annular laser light 20 with which the subject surface is irradiated has an annular shape with the center O point of the excitation laser light 10 with which the subject surface is irradiated. Has been done. That is, the laser light 20 on the surface of the subject A
The annular portion irradiated with is located equidistant from the center O point. Therefore, the reflected ultrasonic waves reflected by the defect portion on the axis X in FIG. 3 are detected at the annular portion located at the same distance from the axis X, and thus become the in-phase component, which is integrated and strengthened by amplification. Is detected. On the contrary, since the noises have different phases, they are canceled out by integration and detected. As a result, the SN ratio can be improved.

According to the present embodiment described above, spatial addition can be easily executed in addition to the conventional temporal addition of the reflected ultrasonic signals, and the conventional temporal addition alone can reduce the spatial addition. It is possible to easily reduce the scattering noise due to the difficult microstructure of the subject, and improve the SN ratio of the detection signal. As a result, application to a material having a fine structure, which has been difficult to apply in the past, and detection of a finer defect portion can be realized.

FIG. 4 is a schematic configuration diagram of a laser ultrasonic flaw detector according to a second embodiment of the present invention. The difference between the second embodiment and the first embodiment is that the shaded ring-shaped mirror 23
0c has four slit-shaped non-reflecting portions 231c. The non-reflecting portion 231c may absorb the laser light or may transmit the laser light. Further, in the first embodiment, the laser light 10 for excitation is irradiated onto the subject A from an oblique direction, whereas in the second embodiment, the laser light 100 for excitation is emitted.
Is vertically irradiated to the subject A. Since other configurations are similar to those of the first embodiment, those having the same functions as those of the first embodiment are designated by the same or corresponding reference numerals, and detailed description thereof will be omitted.

In the second embodiment, the shaded ring-shaped mirror 23 is used.
0c is provided with four slit-shaped non-reflecting portions 231c. Therefore, by providing four support rods (not shown) in the horizontal direction on the conical mirror 23b, and by associating each support rod with the non-reflecting portion 231c, the optical path of the annular laser light is not blocked, It is possible to fix the conical mirror 23b to the main body of the apparatus by pulling the support rod to the outside of the annular laser beam. Other operations and effects are the same as those of the first embodiment.

The present invention is not limited to the above embodiment, but various modifications can be made within the scope of the gist thereof. For example, in the above embodiment, the case where the diameter of the laser light for excitation is smaller than the diameter of the laser light for probe as shown in FIG. 2 has been described, but the present invention is not limited to this. For example, the beam diameter of the laser light for excitation may be increased to be equal to or larger than the diameter of the annular laser light. As a result, even if the surface of the subject is not a mirror surface, the annular portion for constantly detecting the reflected ultrasonic waves on the surface of the object by the laser light for excitation is made a mirror surface and the reflected ultrasonic waves are detected. You can

[0023]

As described above, according to the present invention,
Since the laser light for the probe is an annular laser light centered on the center of the laser light for excitation applied to the surface of the subject, it is directly below the laser light for excitation applied to the surface of the subject. The reflected ultrasonic signal from the defect portion is detected by being strengthened and amplified, and conversely, the scattered noise caused by the fine structure in the subject is canceled and weakened and detected. Therefore, it becomes possible to improve the SN ratio and extract the reflected ultrasonic signal from a defect such as a flaw or a cavity required for flaw detection.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a laser ultrasonic flaw detector according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view of laser light with which a subject is irradiated.

FIG. 3 is a schematic diagram showing a state when detecting reflected ultrasonic waves from a defective portion.

FIG. 4 is a schematic configuration diagram of a laser ultrasonic flaw detector according to a second embodiment of the present invention.

[Explanation of symbols]

 A subject 10 laser light 11 ultrasonic wave generation laser device 13 mirror 21 ultrasonic wave detection laser device 23 optical system 23a beam expander 23b conical mirror 23c cap ring mirror 23d support member 31 photodetector 33 half mirror 35 Optical lens 37 Photodetector 230c Cap ring-shaped mirror 231c Non-reflection part

Claims (4)

[Claims] 1. An ultrasonic wave generating laser means for irradiating a subject with an exciting laser beam for generating an ultrasonic wave, and a laser beam for a probe for detecting reflected ultrasonic waves reflected in the subject and reaching the surface. Laser means for generating ultrasonic waves,
Optical means for converting the laser light for the probe into an annular laser light centered on the center of the laser light for excitation applied to the subject, and for the probe reflected on the surface of the subject A laser ultrasonic flaw detector, comprising: a light detecting unit that detects a change that the laser light undergoes due to the interaction with the reflected ultrasonic wave. 2. The optical means includes a diameter enlarging means for enlarging the diameter of the laser beam for the probe, and a conical shape for reflecting the cylindrical laser beam with the enlarged diameter and converting it into an annular laser beam. The laser ultrasonic flaw detector according to claim 1, further comprising: a reflecting unit; and an annular reflecting unit that reflects the annular laser beam to irradiate the subject. 3. The laser ultrasonic flaw detector according to claim 2, wherein the annular reflecting means has at least one slit-shaped non-reflecting portion. 4. A laser ultrasonic flaw detection method for irradiating a subject with laser light for an annular probe to detect reflected ultrasonic waves reflected from a defective portion inside the subject.