JPS61225646A - Noncontact ultrasonic conversion for defect and acoustic discontinuous detection - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ultrasonic transduction, and more particularly to the field of ultrasonic transduction, and more particularly to the remote and non-contact transduction of test objects with respect to acoustic discontinuities and defects, such as solid-gas or liquid-solid interfaces. The present invention relates to a method and apparatus for non-destructively testing using ultrasonic waves.

X-ray inspection of test objects such as jets and reusable rocket engines for cracks and other defects has various drawbacks, including cost and
They may be complex, harmful to humans, or unable to detect cracks or delaminations perpendicular to the beam. Non-destructive testing can also be performed by using a piezoelectric transducer to transmit ultrasound waves into the test object and analyzing the ultrasound waves after they have passed through the test object. However, such ultrasonic transducers must be held against the test object using a wet or grease compound, and it is therefore necessary to clean the test object and the transducer after testing. This adds effort, time, and expense to the testing procedure, and often produces undesirable residues. Additionally, the device must be disassembled if internal parts such as wings or impellers are to be checked. Inspection for other types of defects requires cutting and inspecting the test object, in which case the test object is destroyed and cannot be used thereafter.

The present invention has been made in view of the above points, and an object of the present invention is to inspect a test object for defects using a non-destructive testing method. It is another object of the present invention to acoustically inspect a test object by using ultrasonic waves that cannot be induced into the test object by mechanically mounted transducers. . Yet another object of the invention is to eliminate the use of wetting or greasing the test object and/or the transducer when performing ultrasonic testing of the test object. Yet another object of the present invention is to provide a flexible coogle that is inserted through a port in an engine for non-destructive testing without disassembling the engine.

According to the invention, the formation of ultrasound waves is induced within the test object by creating stress zones that emit ultrasound energy through the test object. This stress is generated by an intense laser pulse and preferably by a radar dP4 pulse from a beam array whose beam propagating elements are separated from each other by a distance equal to the acoustic wavelength. The laser pulse rate is the same as the frequency of the acoustic wave.

After passing through the test object or being partially or wholly reflected from the test object, the ultrasound waves are derived from the test object by an electro-optical derivative system without physically contacting the test object.

Therefore, both the guidance and derivation systems are contactless and non-destructive with respect to the test object.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows how ultrasonic waves 18 are induced and propagated within a test object 16, such as a turbine blade of a jet engine. The localized heating induced in the test object 16 by the intense laser pulse creates photon-phonon traps and thermal elastic waves. 11 a single/maternal Lede peak 12 from a separated Lede source 10
Although it is possible to induce ultrasound waves 18 by direct impingement, preferably a series of parallel spaced apart laser beams is used. Accordingly, FIG. 1 shows a plurality of partially reflective and partially transmissive mirrors 14-14'', which mirrors are connected to the incident light source 10 which is the output of the laser-operated radar source 10. It is set to provide parallel beams 13 to 13'' from a powerful A-Russled beam 12. These mirrors 14-14n are separated from each other by a distance d, which distance d is preferably equal to the wavelength λ of the ultrasound wave 18 induced in the test object 16, so that in this case d= It is λ.

With such spacing, each successive mirror 14
The duck beam 13 makes it possible to reinforce the ultrasound waves 18, in other words to keep them at a constant amplitude. This means that each colliding beam 13
This can be achieved by keeping the intensity of ~13n equal to the intensities of the other beams. The optimal number of mirrors 14 is approximately 5
The number ranges from 1 to 10, but of course it is possible to use a smaller number or a larger number. Obviously, at ultrasonic frequencies λ is extremely small, so the total extent of the array (vertical height in Figure 1) is extremely small compared to the dimensions of the test object, perhaps 0.5 mils long. That's about it.

A second and preferred type of collimated laser beam source is a bundle 32 of optical fibers separated from each other by a distance d (see FIG. 2). In this case, the output beams from each optical fiber 21 have the same energy. The diameter of bundle 32 is on the order of 1716' to 1718 inches.

Ultrasonic waves 18 are derived from test object 16 by any suitable sensing method, generally illustrated by ultrasonic sensing means 34 . A preferred contactless means is shown in FIG.

Ultrasonic waves 18 are detected by directing a second laser beam, preferably a continuous laser beam with Δ las, through an optical eyeper 22 or a group of optical fibers onto the test object 16. Is possible. The second laser beam 23 is preferably aligned with the first loop beam 13-13° when both are on opposite sides of the test object 16, as in FIG. 1, and when both are on opposite sides of the test object 16, as in FIG. 13, they are oriented to irradiate the same spot as the beam from the first pulse radar 10.

In either embodiment, the two laser beams may be somewhat mismatched, but in a preferred method of operation, they are made to coincide. The reflected beam 24 is a modulated beam, i.e. the frequency F0 of the radar 20 is equal to the ultrasonic wave 18.
is modulated by the frequency F1 of , and encompasses the frequencies of F0+F. The reflected optical beam 24 is received by an optical fiber bundle 42 and fed to an optical heterodyne means 26 which separates out the Rade frequency F0 and passes the beam 28 with the ultrasonic frequency F& to an optical detector 30. . Optical detector 30 may be a photodetector, for example representative of the amplitude of the ultrasound frequency beam. The optical fibers in this system may be a fiber bundle 32 as shown in FIG. 5, in which case one or more central fibers 22 and 2
5 is used to propagate a laser beam for acoustic wave generation and to receive a detection laser beam, and is spaced apart from each other by a distance of λ/2.Detection system fibers 22 and 2
A group of fibers 21 surrounding the fibers 5 are used to propagate a laser beam for ultrasound induction. FIG. 5 shows that the optical 7 eyeper cable 32 is
This shows a state in which the device and the detection device are connected. cable 3
2 can be introduced, for example, through a hole 44 in the engine housing 46 to scan the turbine blade 48 for defects.

It should be noted that both the ultrasonic induction input beam means, eg optical fiber 21, and the detection system input beam means, eg optical fiber 22, are simultaneously scanned along the test object 16. These can be placed on either side of the test object 16; in this embodiment, upon encountering a defect 36 (or an acoustic discontinuity, such as a liquid-solid or solid-gas interface) in the test object 16, the optical The output signal from detector 30 is reduced. In transmission mode, defects (or liquid-
Acoustic discontinuities (such as solid or solid-gas interfaces) reduce the amplitude of the ultrasound waves 18.

The scanning means are known and may be mechanical or electrical, for example a Bragg cell, through which the beams 13 and 23 pass before impinging on the test object 16. Voltage variations applied to each Bragg cell move the direction of the beam exiting that cell. It is also possible to scan these beams by mechanical means 40, 40' to which mirrors 14-14n or optical fiber bundles 32 are attached.

The detection system input beam 23 is as shown in FIG.
The laser beams are directed to closely spaced spots and scanned together, which can be on the same side of the test object 16. In this mode of operation (reflection mode), reflected signals from defects 36 (or acoustic discontinuities such as liquid-solid or solid-gas interfaces) typically increase the signal reflected from test object 16 and cause optical The output of target detector 30 increases if defect 36 is present.

The above detailed description of a novel optical ultrasound system for detecting defects and acoustic discontinuities such as liquid-solid or solid-gas interfaces in a test object requires physical contact with the test object. It is therefore possible to avoid wet or grease coatings, cleaning, undesired residues, etc., which are inherent problems when coupling the transducer to the test object. .

Although specific embodiments of the present invention have been described in detail above, the present invention should not be limited only to these specific examples, and various modifications may be made without departing from the technical scope of the present invention. Of course, it is possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of one embodiment of the present invention, FIG. 2 is a schematic diagram showing bundles of optical fibers and their spacing from each other, and FIG. A schematic diagram of the sensing system; Figure 4 is a cross-sectional view of an optical fiber bundle that can be used for both propagation and reception of the laser beam; Figure 5 is a cross-sectional view of an optical fiber bundle that can be used for both propagation and reception of the laser beam; 1 is a schematic diagram of a defect detection system using a single optical fiber cable introduced through a hole in the housing; FIG. (Explanation of symbols) lO: Rade source 12: Pulse laser beam 16
: Test object 18: Ultrasonic wave 22 Niogutical fiber 26: Optical heterodyne means 30: Optical detector 34: Acoustic wave detection means 36: Missing
M40: Scanning means] - Poration same Masaaki Kobashi. 1゛, 2

Claims (1)

[Claims] 1. In a device for inducing ultrasonic waves in a test object,
means for providing a plurality of spaced apart laser beams directed to impinge on the test object;
An apparatus characterized in that each beam is separated from an adjacent beam by a distance equal to the wavelength of the ultrasound beam. 2. In paragraph 1 above, the supply means is arranged to include a laser pulse means for providing a series of laser pulses and to transmit and reflect the output of the laser pulse means within the spaced parallel beam. a plurality of spaced apart partially transmissive and partially reflective mirrors. 3. In paragraph 2 above, the ratio of transmittance to reflectance of the mirrors is such that each mirror directs the same amount of energy onto the test object in order to maintain the amplitude of the acoustic wave at a constant level. A device characterized by: 4. In the above item 2, the number of mirrors is 5 to 10.
A device characterized in that it is within the range of 5. In the above item 1, the supply means has a laser pulse generation means for applying a series of laser pulses, and an optical fiber means for directing the output of the laser pulse generation means onto the test object. , wherein the optical fiber means comprises a bundle of optical fibers, each separated from its neighbor by a distance equal to half the wavelength of the ultrasound beam. 6. In a manner of detecting acoustic discontinuities such as defects and solid-liquid or solid-gas interfaces in a possible test object with sustaining the generation and propagation of ultrasound waves into said test object. The method is characterized by comprising an optical means for inducing the ultrasonic wave, which does not need to be coupled to the test object, and an optical means for detecting the ultrasonic wave in the test object, which does not need to be coupled to the test object. method to do. 7. The method of claim 6, wherein the wave inducing means comprises optical fiber means for directing laser beam pulses onto the test object. 8. The method of claim 6, wherein the wave detection means includes optical fiber means for directing a laser beam onto the test object so that the beam is modulated by the ultrasound waves. 9. In clause 6 above, the wave inducing means comprises optical fiber means for directing laser beam pulses towards the test object, and the wave detecting means directs the laser beam towards the test object. A system characterized in that it comprises optical fiber means for causing said beam to be modulated by said ultrasound. 10. The method of claim 6, wherein the wave inducing means directs an intense light pulse onto the test object as a source of the ultrasound waves. 11. The method according to item 10 above, wherein the optical pulse is a laser pulse. 12. In paragraph 6 above, the wave inducing means comprises optical fiber means for directing the output of the laser pulse generating means onto the test object, each optical fiber means directing the output of the laser pulse generating means onto the test object, each optical fiber means A system characterized in that it has a bundle of optical fibers separated by a distance equal to the wavelength of the ultrasound beam. 13. The method of claim 12, wherein the wave inducing means comprises means for generating intense laser pulses and means for propagating and directing the laser pulses. 14. As defined in paragraph 13 above, said means for propagating and directing comprises means for providing a plurality of spaced parallel laser beams directed to impinge on said test object, each beam being different from its adjacent beam. A method characterized in that the ultrasonic beam is separated from the ultrasonic beam by a distance equal to the wavelength of the ultrasonic beam. 15. As defined in paragraph 13 above, the propagating and directing means comprises a plurality of spaced apart segments arranged to transmit and reflect the output of the laser pulsing means in the spaced apart collimated beams. 1. A method characterized in that the laser pulse generating means comprises a transparent and partially reflective mirror. 16. In paragraph 15 above, the ratio of the transmittance and reflectance of the mirrors is such that each mirror is placed on the test object to compensate for the energy loss incurred during the propagation time of the preceding wavelength of the ultrasound wave. A method characterized by directing sufficient energy. 17. The method according to item 15 above, wherein the number of mirrors is within a range of 5 to 10. 18. In the above item 13, the detection means includes a laser beam generation means and a laser beam generated from the laser beam generation means on a spot on the test object whose laser beam frequency can be modulated by the frequency of the ultrasonic wave. and second means for propagating and directing the laser beam. 19. The system according to item 18 above, further comprising optical heterodyning means for supplying the modulated laser beam and separating an ultrasonic component from the modulated laser beam. 20. The method according to item 19 above, characterized in that the two laser beams directed onto the test object are synchronously scanned over the test object.