JP2000241397A - Surface defect detection method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly detect a flaw present on a surface layer of a material online by a transmission method using an ultrasonic surface wave and to accurately estimate the depth of the surface defect. To SOLUTION: An ultrasonic probe for transmission 3 for generating an ultrasonic surface wave on a surface layer of a device under test 1, and a ultrasonic probe for reception receiving a surface wave transmitted through a surface layer of the device under test. A probe 6 for detecting a defect 2 in the surface layer of a material, a transmission waveform 11 in which two or more burst waves having different frequencies are collected in a time-sequential manner and transmitted by an arbitrary waveform generator 10 for ultrasonic probe for transmission When the transmitting ultrasonic wave is transmitted to the probe 3 and the receiving ultrasonic probe 6 receives the transmitted surface waves at the respective frequencies, the transmitted ultrasonic waves are detected by the gate circuit 15 in accordance with the respective arrival times, and the transmission intensity at the respective frequencies is further determined. Peak hold circuit 16
a, 16b, 16c,..., and the depth estimating unit 18 estimates the defect depth from the transmission intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting a surface defect in a surface layer of a material using ultrasonic surface waves.

[0002]

2. Description of the Related Art Ultrasonic surface waves are well known as a means for detecting flaws on a surface layer of a material. For example, Japanese Unexamined Patent Publication
In Japanese Patent No. 331603, a variable-angle vibrator that enables a tire to move on the surface of a steel plate via a fixed shaft through a fixed shaft, seals the filling liquid inside the tire, and changes the angle by an angle adjuster is used. There has been proposed a method for detecting a surface flaw on a steel sheet in which ultrasonic waves are oscillated at an angle of 30 ° to 38 °. However, since this method is a reflection method, there are problems that the defect detection ability changes depending on the direction of the defect and that the depth of the detected defect cannot be estimated.

Therefore, a flaw detection method for a surface layer of a material by a transmission method has been invented as disclosed in JP-A-10-213573. FIG. 8 shows a surface layer flaw detection method described in this publication, wherein 1 is an object to be inspected, 2 is a surface defect to be detected,
Reference numeral 21 denotes a burst wave oscillator that generates a tone burst wave of a predetermined frequency, 22 denotes a transmission ultrasonic probe that oscillates an ultrasonic surface wave, and 23 denotes a transmitted surface wave transmitted through the surface layer of the DUT 1. Receiving ultrasonic probe for receiving, 24 is defect 2
This is a receiver for detecting the presence / absence, depth, etc. According to the present invention, utilizing the fact that the penetration depth of a surface wave changes depending on the wavelength (frequency), the defect depth is estimated from the frequency distribution of the surface wave transmitted through the defect in the surface layer of the material. Is going. In other words, a high-frequency surface wave with a short wavelength utilizes the fact that wave energy is concentrated and propagated near the surface,
The defect depth can be estimated by examining how much high-frequency energy is contained in the surface wave transmitted through the defect. Further, the present invention has a feature that by using the transmission method, it is possible to obtain an attenuation waveform that depends only on the depth without depending on the direction of the defect.

However, the method disclosed in this publication indicates that in order to estimate the defect depth, it is necessary to repeatedly perform transmission and reception while switching between several different tone burst waves. In this case, it is necessary to perform transmission and reception several times in order to estimate the depth of one defect, so that it takes a lot of time and is not suitable for quick online inspection. Also, as another method, this publication uses a waveform obtained by adding the number of tone burst waves required for measurement as a transmission signal, divides a reception signal by a band-pass filter, and measures an attenuation amount of a transmission wave of each frequency. In this method, the defect depth is estimated by one transmission / reception. However, this method has a problem that the defect depth cannot be accurately estimated for the following reason. That is, in order to accurately estimate a defect, it is necessary to transmit a large number of tone burst waves of different frequencies having a wavelength approximately equal to the depth of the defect. , The bandpass filter
One reason is that it becomes impossible to separate only frequency components. Further, in this publication, as another method, a method of digitally performing frequency analysis by FFT or the like instead of a band-pass filter is disclosed, but since FFT takes time, it is also necessary to perform online analysis. Not suitable for testing.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and is intended to remove a scratch existing on a surface layer of a material.
It is an object of the present invention to quickly detect online by a transmission method using an ultrasonic surface wave and to accurately estimate the depth of the surface defect.

[0006]

According to a first aspect of the present invention, there is provided a method for detecting a surface defect of a material by a transmission method using an ultrasonic surface wave. A set of burst waves of different frequencies divided in time is used as a transmission waveform, and at the time of reception, a transmitted surface wave of each frequency is detected and detected using a gate circuit adapted to each arrival time. The depth of a defect is obtained (estimated) from the transmission intensity of each frequency of a transmitted surface wave.

According to the surface wave detecting method of the present invention configured as described above, a waveform including two or more different frequencies necessary for estimating the depth of a defect in one transmission is used. And the frequency components in the transmitted waveform are separated in time, so that there is no need for close proximity to accurately estimate the depth of the defect to be detected. Even if such frequencies are used, the received signal can be completely separated and detected for each frequency by the gate circuit, so that the amount of attenuation for each frequency can be accurately measured from the transmission intensity of each frequency. For this reason, the accuracy of estimating the defect depth is equivalent to the estimated value of the conventional method of measuring by switching between a number of tone burst waves.

Further, a surface defect detecting apparatus for carrying out the method according to the present invention comprises a transmitting ultrasonic probe for generating an ultrasonic surface wave on a surface layer of an object to be inspected, and a surface layer of the object to be inspected. An apparatus for detecting a defect in a surface layer of a material, comprising a receiving ultrasonic probe for receiving a transmitted surface wave, and transmitting a transmission waveform in which two or more burst waves having different frequencies are divided in time and collected. An arbitrary waveform generator for transmitting to a trusted ultrasonic probe, a gate circuit for detecting a transmitted surface wave of each frequency received by the receiving ultrasonic probe in accordance with each arrival time, and the gate circuit And a peak hold circuit for determining the transmission intensity of each frequency of the transmitted surface acoustic wave detected by the method. Further, the apparatus is provided with a depth estimating means for calculating the depth of the defect from the transmission intensity of each frequency obtained by the peak hold circuit.

The surface defect detection apparatus of the present invention includes an arbitrary waveform generator capable of arbitrarily creating and transmitting a burst wave having a frequency required for measurement (inspection), thereby providing a defect depth with one transmission waveform. The surface wave of the frequency only to estimate the frequency can be transmitted, and the received waveform is divided by the gate circuit for each arrival time, and for each time,
That is, a signal for each frequency can be obtained, and a measurement amount for estimating the defect depth can be obtained at a time.
However, the waveform in the gate circuit is output as a peak value by the peak hold circuit, and the transmission intensity of the surface wave of each frequency becomes a measured amount.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of a surface defect detecting method according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an inspection object such as a steel plate, and 2 denotes a surface defect to be detected. 1
Numeral 0 denotes an arbitrary waveform generator which creates a frequency band capable of generating a surface wave having a wavelength of 2.5 to 10 times the defect depth to be detected. This arbitrary waveform generator 1
The transmission waveform 11 formed at 0 is a set of two or more burst waves of different frequencies necessary for measurement or inspection separated by time and arranged in a time series and separated. Preferably, there is. Numeral 3 denotes an ultrasonic probe on the transmitting side, and its transducer 4 has a surface acoustic wave 5
Are inclined at the incident angle that causes When the arbitrary waveform generator 10 generates a waveform like 11 and sends it to the probe 3, a surface wave 5a having a wavelength corresponding to the frequency is generated.
Is generated on the surface layer of the test object 1 and propagates through the test object 1, passes through the surface defect 2, and the transmitted surface wave 5 b is detected by the ultrasonic probe 6 on the receiving side. Probe 6 on the receiving side
Is arranged to face the transmission-side probe 3 and is the same as the transmission-side probe 3. Here, assuming that the frequency characteristics of the transmitting and receiving vibrators are flat for the sake of simplicity, the received waveform has a short wavelength, that is, a high frequency, corresponding to the depth of the surface defect of the inspected portion. It becomes the form that received a large attenuation. Therefore, the received waveform is detected by the gate circuit 15 which is adjusted to the arrival time of each frequency, and the RF circuit divided by the gate circuit 15 for each frequency is extracted by the gate and the peak hold circuit 16
a, 16b, 16c,..., the peak value in each gate can be obtained as an output, so that the amount of attenuation for each frequency can be obtained.

FIG. 2 is a diagram showing an example of the configuration of an apparatus for specifically inspecting the surface of a steel sheet using the method of the present invention. In FIG. 2, 8 is a transmission / reception integrated surface wave probe, 10 is the above-mentioned arbitrary waveform generator, and 12 is an arbitrary waveform generator 10
, An arbitrary waveform parameter input means for generating a transmission waveform at, an amplification circuit, a preamplifier, a gate circuit, a peak hold circuit, and a peak hold circuit.
Denotes an AD converter, 18 denotes a depth estimating unit for calculating a defect depth, and 19 denotes an output unit for outputting the depth estimation value obtained by the depth estimating unit 8 to a display device, a recording device, or the like (not shown).

First, the frequency and wave number of a surface wave used for inspection of a steel plate or the like are input from the arbitrary waveform parameter input means 12. This is a value that changes depending on the inspection target,
In the case of this embodiment, since a surface defect having a depth of 0.1 mm to 1 mm is to be inspected, 8 MHz, 5.0 MHz, 3.
5MHz, 5MHz, 2MHz, 1MHz
A wave burst wave was used. The arbitrary waveform generator 10 transmits a waveform in which burst waves of the input parameters are arranged in time series as shown in FIG. At this time, if the frequency characteristics of the probe are known, if the amplitude of each frequency is corrected so that the sensitivity of the inspection from low frequency to high frequency in transmission and reception of the surface wave becomes constant, evaluation can be easily performed later.

The transmitted waveform leaving the arbitrary waveform generator 10 is:
The signal is amplified by the amplifier circuit 13 so that the ultrasonic probe can generate an ultrasonic wave sufficient for the inspection (in this embodiment, 400 V _pp ). The amplified transmission signal is sent to the surface acoustic wave probe on the transmission side. However, if the transmission side and the reception side probes are separate and independent as shown in FIG. In this embodiment, it is difficult to hold and move the probes on both sides so as to face each other during use.
As shown in FIG. 7, the surface wave probe 8 integrated for transmission and reception was used. In FIG. 4, the vibrators 8a and 8b of the surface wave probe 8 are shown.
Is designed such that an ultrasonic wave enters the steel plate at an incident angle of about 30 ° so as to generate a surface wave on the steel plate (surface wave acoustic velocity 2890 m / s). The space between the vibrators 8 a and 8 b and the test object (steel plate) 1 is filled with the acoustic contact medium 9.
In the case of this embodiment, the medium is water, but another medium may be used.
In this case, it is necessary to change the inclination of the vibrators 8a and 8b depending on the sound velocity of the medium.

The surface wave propagated through the device under test 1 by the surface wave probe 8 is received after receiving an attenuation depending on the depth of the surface defect 2 when the device under test 1 has a surface defect 2. The received signal is amplified by a preamplifier 14, time-separated for each burst wave by a gate circuit 15, and sent to a peak hold circuit 16. Figure 5
It was shown to. The peak hold circuits 16a to 16e output the waveforms A to E in the respective gates to the AD converter 17, and the AD converter 17 outputs the peak value of each gate to the depth estimating unit 18.

Here, the depth estimating unit 18 compares the peak value of each frequency with the peak value of the sound part, calculates the transmittance of the received surface wave, and estimates the depth of the surface defect. In estimating the depth of the surface defect, the relationship between the surface wave wavelength and the defect depth and the surface wave transmittance is used. The relationship is as shown in FIG. 6. When the wavelength-normalized defect depth (= defect depth h / wavelength λ) is plotted on the horizontal axis, the value is between 0.1 and 0.4. It is proportional to the surface wave transmittance. That is,
The estimated value of the defect depth h is represented by h = (100−x ′) · λ ′ / 165 by the wavelength λ ′ and the transmittance x ′ when the surface wave transmittance is 35 to 90%. (Equation 1).

In this embodiment, the transmittance of a surface wave transmitted through a surface defect having a depth of 0.28 mm is as shown in FIG. 2 MHz (λ ≒) when the transmittance is 35 to 90%
1.5 mm, transmittance 70%) and 3.5 MHz (λ
(0.86 mm, transmittance 51%) From the measured value of the frequency, the defect depth was calculated using Equation 1 to obtain 0.27.
mm and 0.26 mm, and in this example, the defect depth could be estimated with sufficient measurement accuracy. Finally, the estimated value of the defect depth is output by the output unit 19 to a display device, a recording device, or the like.

[0017]

As described above, according to the present invention,
The surface defects existing in the surface layer of the material can be quickly inspected online, which has been considered impossible, and the defect depth can be accurately estimated.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a surface defect detection method of the present invention.

FIG. 2 is a diagram showing a configuration of a surface defect detection device of the present invention.

FIG. 3 is a diagram showing a profile of a transmission waveform used in the embodiment.

FIG. 4 is an enlarged view of a transmission / reception integrated surface wave probe used in the embodiment.

FIG. 5 is a diagram showing how to apply a gate and an RF waveform after a gate circuit in the example.

FIG. 6 is a diagram showing the relationship between the surface wave transmission intensity after a surface wave has passed through a surface defect and the wavelength-normalized defect depth (h / λ).

FIG. 7 is a diagram showing the surface wave intensity at each frequency after passing through a surface defect in the example.

FIG. 8 is a diagram showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inspection object 2 Surface defect 3 Transmission ultrasonic probe 4 Transducer of probe 3 5a Surface wave 5b Transmitted surface wave 6 Ultrasonic probe for reception 7 Transducer of probe 6 8 Integrated transmission and reception Surface wave probe 9 Acoustic contact medium 10 Arbitrary waveform generator 11 Transmission waveform 12 Arbitrary waveform parameter input means 13 Amplification circuit 14 Preamplifier 15 Gate circuit 16 Peak hold circuit 17 AD converter 18 Depth estimating unit 19 Output unit

Continued on the front page (72) Inventor Akira Murayama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Yu Yu 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock In-house F term (reference) 2G047 BA01 BC03 BC04 BC08 BC10 BC18 CB03 EA09 GF08 GF21 GG01 GG09 GG12 GG24

Claims (3)

[Claims] 1. A method of detecting a defect in a surface layer of a material by a transmission method using a surface wave of an ultrasonic wave, wherein a set of burst waves of two or more different frequencies divided in time is used as a transmission waveform. Detects transmitted surface waves of each frequency using a gate circuit that matches the arrival time at the time of reception, and determines the depth of defects from the transmission intensity of each frequency of the detected transmitted surface waves. Surface defect detection method. 2. A transmitting ultrasonic probe for generating an ultrasonic surface wave on a surface layer of an object to be inspected, and a receiving ultrasonic probe for receiving a surface wave transmitted through the surface layer of the object to be inspected. An apparatus for detecting a defect in a surface layer portion of a material, comprising: an arbitrary waveform generator for transmitting a transmission waveform obtained by temporally dividing and collecting two or more burst waves having different frequencies to the transmission ultrasonic probe; A gate circuit that detects the transmitted surface wave of each frequency received by the receiving ultrasonic probe in accordance with each arrival time, and a transmission intensity of each frequency of the transmitted surface wave detected by the gate circuit. And a peak hold circuit to be obtained. 3. The surface defect detecting device according to claim 1, further comprising a depth estimating unit that calculates a depth of the defect from the transmission intensity of each frequency obtained by the peak hold circuit.