JP2013088421A - Nondestructive inspection method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nondestructive inspection device for exciting an object to be measured in a thin planar shape including a defect by low frequency vibrations while transmitting/receiving ultrasonic waves in a non-contact manner and identifying presence/absence of the defect on the basis of the spectrum of ultrasonic signals modulated by the vibrations.SOLUTION: While giving vibrations to an object 10 to be measured in a thin planar shape placed on a support part 13 by a low frequency vibration exciter 14, large amplitude burst waves of a fixed frequency are transmitted by an air ultrasonic transmission probe 11, and ultrasonic signals modulated by low frequency vibrations are received by an air ultrasonic reception probe 12. Fast Fourier transformation is executed on the ultrasonic signals in a selected time range by a high-pass filter of a waveform processing/display part 6, an alarm is issued when the intensity of the spectrum in a selected frequency range exceeds a preset value, and thus a minute defect or an unsound area inside the object to be measured is detected.

Description

  The present invention relates to a method and apparatus for nondestructively detecting minute defects or unhealthy portions in a thin plate component by combining low-frequency excitation and non-contact ultrasonic transmission / reception.

  An ultrasonic method is widely used for nondestructively detecting defects in metal materials, various parts, and structures using ultrasonic waves.

As described in Non-Patent Document 1, in the normal pulse reflection method, it is necessary to apply an oil or jelly-like acoustic binder between the ultrasonic probe and the object to be measured. An increase in inspection time for removing the binder becomes a problem, and it is difficult to apply to inspection on a production line. In addition, it is extremely difficult to apply to detection of defects contained in curved parts welded after press working.
JIS Handbook 43 Nondestructive Inspection, Japanese Standards Association, 2005

  As a non-contact ultrasonic defect inspection method, an electromagnetic ultrasonic method, a laser ultrasonic method, or an air ultrasonic method is used.

However, it is difficult to reduce the area of the electromagnetic ultrasonic probe to 1 cm ² or less. In the laser ultrasonic method, waves of various modes are excited by the laser incident angle. In the air ultrasonic method, the frequency is low. Therefore, there is a problem that the spatial function is low.

  Further, in any of these methods, when the defect position is unknown, it is necessary to inspect the object to be measured by scanning the defect detection sensor, and there is a problem that the inspection time increases.

In addition to the above, a device has been developed in which the object to be measured is vibrated with a vibrator, the change in the natural frequency is detected using an ultrasonic probe, a laser vibrometer, etc., and the presence or absence of an internal defect is identified. .
Patent Publication 2006-105680 Patent Publication 9-159681 Patent Publication 5-87780

  However, the method of Patent Document 1 is a method for reducing noise in ultrasonic nondestructive inspection for thick-walled concrete structures used in water, and is applicable to thin-walled parts having a thickness of several millimeters or less. Can not. On the other hand, in Patent Document 2, the cantilever is scanned along the surface of the object to be measured while the object to be measured is vibrated, and the minute displacement at that time is measured by a laser to detect a very small defect on the surface or just below the surface. It is a method for detecting and imaging, and it is too precise to be used at the manufacturing site. Furthermore, Patent Document 3 is a method of measuring the thickness of a pipe by a resonance method using an electromagnetic ultrasonic probe, and is difficult to apply to inspection of minute defects of thin parts.

  In addition to the above, a resonance inspection apparatus RI3000 developed by Quasar, USA is commercially available in Japan. This device detects changes in the natural frequency due to the presence or absence of internal defects for a small number of natural vibration modes, so that relatively simple objects such as discs, rectangular plates, cylinders, and cuboids with limited dominant natural vibration modes are detected. Although it is effective for inspection, it is not suitable for nondestructive inspection of minute defects in welds in thin plate parts.

On the other hand, as described in Non-Patent Document 2, when a thin plate-shaped object to be measured including a defect is vibrated at a frequency (F) of about several KHz, an ultrasonic wave having a higher frequency (f) is transmitted and received. It is known that ultrasonic vibration called a side band having a frequency of f ± nF (n: integer) is excited.
Hayashi et al., 3 non-destructive inspections, 58-5 (2009), pp. 196-201

  However, in Non-Patent Document 2, the object to be measured is fixed to the support with a bolt and a contact ultrasonic transmitter is used, so that it is difficult to apply to a manufacturing site where inspection in a short time is required. .

  In view of the above circumstances, the present invention provides a nondestructive inspection apparatus capable of inspecting the presence of minute defects or unhealthy parts in thin-walled parts, particularly automobile thin plate parts, in a short time of about 10 seconds. The purpose is to provide.

  In order to achieve the above object, the solution adopted by the present invention is an ultrasonic signal generator that generates an electrical signal for ultrasonic excitation in response to a trigger signal from a control PC, and the ultrasonic signal generator generates the ultrasonic signal. A transmission signal amplifier that electrically amplifies the ultrasonic signal that has been transmitted, converts the transmission signal transmitted from the ultrasonic signal amplifier into an ultrasonic wave, and enters the thin plate-like object to be measured in a non-contact manner via air. An air ultrasonic transmission probe, an air ultrasonic reception probe that receives an ultrasonic signal from the thin plate-like object to be measured via the air, and a reception signal that amplifies the signal detected by the ultrasonic probe Amplification unit, waveform storage unit for converting analog signal amplified by reception signal amplification unit into digital signal by high-speed A / D conversion board and digital recording of the digital signal waveform, selection of waveform stored in waveform storage unit Fast over a given time range A waveform processing / display unit that displays a spectrum within a selected frequency range by performing a Fourier transform process, a support unit that supports the thin plate-like object to be measured, and the thin plate-like object to be measured based on a command from the control PC Including a low-frequency vibrator that applies low-frequency vibration for a certain period of time to the ultrasonic signal amplifying unit that generates an ultrasonic excitation electrical signal generated by the ultrasonic signal generating unit based on a command from the control PC. At the same time, the ultrasonic wave is incident on the object to be measured through the air from the air ultrasonic transmission probe, and at the same time, the object to be measured is vibrated using a low-frequency vibrator in the previous period and modulated by the low-frequency vibration. The received ultrasonic signal is received by the air ultrasonic reception probe, the ultrasonic reception signal is amplified by the reception signal amplifying unit, and then the waveform digitally converted by the high-speed A / D conversion board is stored in the waveform memory. Recorded in the department A digital bandpass filter process is performed on the selected time range for the waveform stored in the waveform storage unit, and then a fast Fourier transform process is performed to display a spectrum within the selected frequency range. An inspection method and an inspection apparatus characterized by detecting a minute defect or an unhealthy part inside an object to be measured by issuing an alarm when a set value is exceeded.

  The area of the ultrasonic irradiation area can be adjusted by selecting either the focal type or the planar type for the air ultrasonic transmission probe and the air ultrasonic transmission probe.

  In place of the air ultrasonic probe, the ultrasonic wave modulated by the low-frequency vibration is received by a laser Doppler vibrometer, so that finer defects can be detected than when the air ultrasonic probe is used. .

  According to the present invention, a means for detecting in a short time a minute defect or an unhealthy part existing inside a thin plate-like object to be measured, which has been difficult to detect by a conventional nondestructive inspection method, has been established.

  By optimizing the position of the vibrator that gives low-frequency vibration, the position of the transmitting and receiving air ultrasonic probe, and the orientation with respect to the object to be measured with respect to the expected defect position included in the object to be measured, Sensitivity for nondestructively detecting defects or unhealthy parts inside the measurement object can be improved.

  In addition, by setting the nominal frequency of the transmitting and receiving air ultrasonic probe and the frequency and excitation output of the low frequency exciter appropriately with respect to the thickness of the non-measured object, defects or unhealthy parts can be eliminated. Sensitivity for destructive detection can be improved.

  Furthermore, the defect or unhealthy part is detected nondestructively by appropriately setting the upper and lower cutoff frequencies of the digital bandpass filter corresponding to the nominal frequency of the transmission and reception air ultrasonic probes described above. Sensitivity can be improved.

  In the present invention, inspection can be performed by placing a weak force such that the object to be measured placed on the support base is not separated from the support base by low-frequency vibration, for example, an appropriate weight, and the inspection time can be shortened.

It is a figure explaining the modulation | alteration of the ultrasonic signal by the low frequency excitation of a thin plate-shaped to-be-measured object containing an internal defect, and ultrasonic transmission / reception. It is a whole block explanatory view of the inspection device which combined low frequency excitation and ultrasonic transmission and reception. It is a figure which shows the received waveform and spectrum with respect to the stainless steel thin plate to-be-measured object using the low frequency vibrator of frequency 15kHz. It is a figure which shows the spectrum with respect to the stainless steel thin plate to-be-measured object containing a defect-free and a defect using the low frequency shaker of frequency 15kHz. It is a figure which shows the sideband spectrum of the stainless steel thin plate to-be-measured object containing a defect-free and a defect using the low frequency shaker of frequency 60kHz. It is a figure which shows the spectrum with respect to the aluminum thin plate to-be-measured object containing a defect-free and a defect using the low frequency shaker of frequency 15kHz.

  Hereinafter, after describing the measurement principle of the present invention, the configuration, operation, test results, and the like of the apparatus according to the present invention will be described.

[Measurement principle]
As shown in FIG. 1, when an ultrasonic wave is transmitted and received while applying bending stress to a plate-like object including a crack-like defect inside by low-frequency vibration, the rigidity decreases when the crack surface opens, As shown in the upper part, the received ultrasonic amplitude decreases. On the other hand, when the crack surface is closed, the rigidity increases and the received ultrasonic amplitude increases as in the middle stage. Thus, the received ultrasonic amplitude is subjected to amplitude modulation by the low frequency vibration.

  Thus, with respect to the plate-like object to be measured including a crack-like defect, f ± nF (n: integer) as shown in the lower part of FIG. 1 by superimposing the vibration by the low frequency (F) and the ultrasonic signal of the frequency f. ) Is excited by an ultrasonic vibration called a sideband.

  Further, when a harmonic having an integral multiple of the frequency f is extracted from a plate-shaped object including a crack-like defect using a bandpass or high-pass filter, a sideband of mf ± nF (m, n: integer) Is also known to be observed.

  On the other hand, it is known that a side band does not occur or only a very low intensity side band peak is observed for a plate-like object to be measured that does not contain defects.

  Next, a nondestructive inspection apparatus applying the above measurement principle will be described.

  FIG. 2 shows a configuration of a defect inspection apparatus in a plate-like object to be measured using an air ultrasonic probe for ultrasonic transmission and reception. The plate-like object to be measured 10 is placed on the support part 13 and the height of the object to be measured is adjusted so as to be in contact with the head part of the low-frequency vibrator 13. With an appropriate weight, the object to be measured is held away from the support portion by vibration. After the electrical signal from the ultrasonic signal generating unit 2 is amplified by the transmission signal amplifying unit 3, the air ultrasonic transmission probe 11 is excited and ultrasonic waves are incident on the object to be measured through the air. In this state, the object to be measured is vibrated for a certain period of time by the low frequency exciter 14, the ultrasonic wave modulated by the low frequency vibration is received by the air ultrasonic reception probe 12, and amplified by the reception signal amplifying unit 4. Thereafter, A / D conversion is performed and the waveform storage unit 5 stores the result.

  The stored waveform is displayed in the waveform display window in the upper part of FIG. In consideration of the propagation time between the air ultrasonic probes and the propagation time within the object to be measured, a time range to be subjected to fast Fourier transform (FFT) is set. Furthermore, by setting the upper and lower cutoff frequencies of the bandpass filter included in the waveform processing unit, the frequency spectrum at the lower left of FIG. 3 is displayed. A frequency range to be monitored is set as indicated by a thick white horizontal line in FIG. When the object to be measured includes a defect or an unhealthy part, as shown in the right of FIG. 4, the spectrum intensity in the monitoring frequency region is displayed large. Incidentally, the left of FIG. 4 is a spectrum for a defect-free measured object. If the monitoring level of the spectrum intensity is set in advance as shown by the thin horizontal line on the right side of FIG. 4, when an intensity exceeding that level appears, the FFT alarm on the upper right of the lower part of FIG. As a result, the presence or absence of defects or unhealthy parts can be inspected.

Using the nondestructive inspection apparatus shown in FIG. 2, frequency spectra for the object to be measured in which a groove-like defect is introduced into a 3 mm-thick stainless steel plate welded part and the object to be measured without a defect are shown on the right and left in FIG. . The vibration frequency range that can be set by the used vibrator is 2 kHz to 20 kHz. In this measurement, the vibration frequency was set to 15 kHz. An air ultrasonic probe with a nominal frequency of 200 kHz was used, and the lower limit frequency of the bandpass filter was set to 500 kHz and the upper limit was set to 900 kHz.
The normalized amplitude (intensity) of the spectrum in the frequency range in the defect-free measured object is about 0.1, but the normalized amplitude of the measured object including the defect reaches 0.6. Thus, it was confirmed that a significant difference appears in the normalized spectrum depending on the presence or absence of defects.

  The spectrum of the object to be measured including the same defect and defect as described above when the transmission frequency of the air ultrasonic probe is set to 220 kHz using a low-frequency vibrator having a resonance frequency of 60 kHz is shown in the left of FIG. And shown on the right. In the spectrum including the defects, sidebands of 80 kHz and 360 kHz, that is, 220 ± 2 × 70 kHz are clearly observed.

  Using the nondestructive inspection apparatus shown in FIG. 2, the frequency spectrum for the object to be measured in which a groove-like defect is introduced into a 1.5 mm-thick aluminum alloy plate welded part and the object to be measured without a defect is shown on the right side of FIG. Shown on the left. The normalized spectrum amplitude in the evaluation frequency range of the defect-free measurement object is 0.2 or less, but the amplitude of the measurement object including the defect exceeds 0.6. Thereby, the presence or absence of a defect can be identified.

  If a laser Doppler vibrometer is used instead of the air ultrasonic reception probe of the nondestructive inspection apparatus shown in FIG. 2, finer defects can be detected.

  The air ultrasonic transmission and reception probe of the nondestructive inspection apparatus shown in FIG. 2 is arranged so as to sandwich the assumed defect position, but the defect can be detected even if they are arranged at other positions.

  The air ultrasonic transmission / reception probe of the nondestructive inspection apparatus shown in FIG. 2 is arranged on one side of the object to be measured, and a defect can be detected by transmitting / receiving a bending mode plate wave.

  Instead of the configuration of the non-destructive inspection apparatus for the thin flat plate-like object shown in FIG. 2, it is possible to detect defects by using a three-point support for the curved thin plate-like object.

1 Control PC
DESCRIPTION OF SYMBOLS 2 Ultrasonic signal generation part 3 Transmission signal amplification part 4 Reception signal amplification part 5 Waveform memory | storage part 6 Waveform processing / display part 10 Measured object 11 Air ultrasonic transmission probe 12 Air ultrasonic reception probe 13 Support part 14 Low frequency exciter

Claims (5)

An ultrasonic signal generator for generating an electrical signal for ultrasonic excitation in response to a trigger signal from the control PC, a transmission signal amplifier for electrically amplifying the ultrasonic signal generated by the ultrasonic signal generator, An air ultrasonic transmission probe that converts the transmission signal transmitted from the transmission signal amplification unit into ultrasonic waves and enters the thin plate-like object to be measured in a non-contact manner via air, from the thin plate-like object to be measured An air ultrasonic receiving probe that receives ultrasonic signals via the air, a received signal amplifying unit that amplifies signals detected by the ultrasonic receiving probe, and an analog signal amplified by the received signal amplifying unit at high speed A waveform storage unit that performs A / D conversion and digitally records the waveform of the digital signal, and displays a spectrum within the specified frequency range by applying fast Fourier transform to the specified time range of the waveform stored in the waveform storage unit Waveform processing / display , And a supporting portion, a low-frequency vibrator that provides a constant time low-frequency vibration to the thin plate-like measuring object based on a command from the controlling PC which supports the thin plate-like object to be measured,
The ultrasonic excitation electrical signal generated by the ultrasonic signal generation unit based on the command from the control PC is amplified by the transmission signal amplification unit, and the air is transmitted from the air ultrasonic transmission probe via the air. At the same time as the ultrasonic wave is incident on the object to be measured, the object to be measured is vibrated using a low frequency vibrator in the previous period, and the ultrasonic signal modulated by the low frequency vibration is received by the air ultrasonic receiving probe. After the reception ultrasonic signal is amplified by the reception signal amplification unit, the waveform digitally converted by the high-speed A / D conversion board is recorded in the waveform storage unit, and the waveform stored in the waveform storage unit is selected. Perform fast Fourier transform on the time range, display the spectrum within the selected frequency range after applying digital bandpass filter processing, and alarm when the intensity of the spectrum exceeds a preset value It allows testing method characterized by detecting a minute defect or the unsound part inside the measured object to. An ultrasonic signal generator for generating an electrical signal for ultrasonic excitation in response to a trigger signal from the control PC, a transmission signal amplifier for electrically amplifying the ultrasonic signal generated by the ultrasonic signal generator, An air ultrasonic transmission probe that converts the transmission signal transmitted from the transmission signal amplification unit into ultrasonic waves and enters the thin plate-like object to be measured in a non-contact manner via air, from the thin plate-like object to be measured An air ultrasonic receiving probe that receives ultrasonic signals via the air, a received signal amplifying unit that amplifies signals detected by the ultrasonic receiving probe, and an analog signal amplified by the received signal amplifying unit at high speed A waveform storage unit that performs A / D conversion and digitally records the waveform of the digital signal, and displays a spectrum within the specified frequency range by applying fast Fourier transform to the specified time range of the waveform stored in the waveform storage unit Waveform processing / display , And a supporting portion, a low-frequency vibrator that provides a constant time low-frequency vibration to the thin plate-like measuring object based on a command from the controlling PC which supports the thin plate-like object to be measured,
The ultrasonic excitation electrical signal generated by the ultrasonic signal generation unit based on the command from the control PC is amplified by the transmission signal amplification unit, and the air is transmitted from the air ultrasonic transmission probe via the air. At the same time as the ultrasonic wave is incident on the object to be measured, the object to be measured is vibrated using the low frequency vibrator, and the ultrasonic signal modulated by the low frequency vibration is received by the air ultrasonic receiving probe. After the ultrasonic reception signal is amplified by the reception signal amplification unit, the waveform digitally converted by the high-speed A / D conversion board is recorded in the waveform storage unit, and the waveform stored in the waveform storage unit is designated. After applying fast Fourier transform processing to the time range, applying digital bandpass filter processing, the spectrum within the specified frequency range is displayed, and an alarm is issued when the intensity of the spectrum exceeds a preset value. By non-destructive inspection apparatus characterized by detecting a minute defect or the unsound part inside the measured object.   The nondestructive inspection apparatus according to claim 2, wherein the air ultrasonic transmission probe and the air ultrasonic transmission probe are of a focal type or a planar type.   3. The nondestructive inspection apparatus according to claim 2, wherein an ultrasonic wave is received by a laser Doppler vibrometer instead of the air ultrasonic wave receiving probe.   The nondestructive inspection apparatus according to claim 2, wherein the ultrasonic excitation electrical signal generated by the ultrasonic signal generator is a burst wave.