JPH09243615A - Crack detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crack detector capable of detecting the position of the crack developed in a material to be tested without being affected by noise. SOLUTION: A crack detector is constituted of a pair of AE detection means 5X, 5Y detecting AE waves generated from a material W to be tested, a cross- correlation processing circuit 6 subjecting the signals from the AE detection means 5X, 5Y to cross-correlation processing to calculate correlation characteristics and a crack position measuring means 7 detecting the developed position of the crack of the material W to be tested on the basis of the correlation characteristics from the cross-correlation processing circuit 6. The operation of cross-correlation is performed with respect to the signals from both AE detection means 5X, 5Y to calculate correlation characteristics. Here, a noise signal becomes non-impulse data to be canceled. The crack position measuring means 7 operates the shift from the center of correlation characteristics to detect the position of the crack developed in the material to be tested.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crack detecting device for detecting a crack generated in a test material.

[0002]

2. Description of the Related Art A crack may occur in a test material during quenching or strain relief, and a crack detector is used to detect the occurrence of the crack. As an example of a conventional crack detection device, as disclosed in Japanese Patent Laid-Open No. 60-135861, acoustic radiation having a high periodicity as shown in FIG. 4 which is generated when a crack occurs in a test material. (Acoustic Emission, hereinafter referred to as AE) Techniques using waves are known. When this AE wave is subjected to frequency analysis, as shown in FIG. 6A, a waveform diagram having a sensitivity peak in a specific frequency band is obtained.

The crack detection device described in the above publication detects an AE wave by a sensor, converts it into a pulse signal corresponding to this AE wave, and sets a preset threshold value (see FIG. 4).
The number of pulse signals exceeding the reference number is counted, and the quality of the crack is determined by the number of pulses.

[0004]

However, for example, at the time of cooling during quenching, as shown in FIG. 5, noise with low periodicity (so-called white noise) has the same strength as the AE wave at substantially the same time. appear. When this noise is subjected to frequency analysis, as shown in FIG. 6B, no peak of sensitivity appears in the specific frequency band in the waveform diagram. In the case of measuring the number of AE waves above the threshold value as in the above-mentioned conventional technique, noise above the threshold value is detected by
Since it is confused with the wave and counted, it is possible that the detection of the crack is erroneously determined.

Further, depending on the type of the test material, the position of the crack may be an important factor for judging the quality. In the conventional technique for detecting the crack by using the AE wave as described above, Could not detect the position where the crack occurred.

The present invention has been made in view of the above circumstances. It is possible to accurately detect cracks in a test material without being affected by noise, and moreover, to detect the position where the crack in the test material occurs. It is an object of the present invention to provide a crack detection device that can detect the crack.

[0007]

In order to achieve the above object, a feature of the first invention is a crack detecting device for detecting a crack based on an acoustic radiation wave generated from a test material,
A pair of detecting means for detecting an acoustic radiation wave generated from the test material, a cross-correlation processing means for performing a cross-correlation processing on a signal from the detecting means to obtain a correlation characteristic, and a cross-correlation processing means And a crack position measuring means for detecting a crack occurrence position of the test material based on the correlation characteristic.

In order to achieve the above object, the feature of the second invention resides in that, in the first invention, a plurality of pairs of means for detecting acoustic waves generated from the test material are provided.

In the first aspect of the present invention, the acoustic radiation waves generated from the test material are detected by the detection means provided in pairs, and both detection signals are subjected to cross-correlation processing by the cross-correlation processing means to obtain correlation characteristics. The crack position measuring means detects the crack occurrence position of the sample material based on the correlation characteristics of both acoustic radiation waves.

According to the second aspect of the present invention, since a plurality of pairs of detecting means are required to obtain a plurality of correlation characteristics of the AE waves generated in the test material, the accuracy of crack detection is improved and the position of the crack is detected. It is detected in two or more dimensions.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a crack detecting device according to the present invention will be described below with reference to FIGS. 1 and 3.
In the drawings, the same reference numerals denote the same or corresponding parts.
In this embodiment, the crack detection device 1 according to the present invention will be described in the case of being used in the induction hardening device 2, but the present invention is not limited to this and can be used in other hardening devices, strain relief machines, and the like. You can also In the induction hardening device 2,
The test material W is placed in the induction hardening coil 4 while being supported by the chuck 3, and is induction hardened.

The crack detecting device 1 according to the present invention is roughly related to a pair of AE detecting means 5X and 5Y for detecting an AE wave generated from a sample material W and signals from the AE detecting means 5X and 5Y. A cross-correlation processing circuit 6 as a cross-correlation processing means for performing a cross-correlation processing to obtain a correlation characteristic, and a crack position for detecting a crack generation position of the test material W based on the correlation characteristic from the cross-correlation processing circuit 6. And measuring means 7.

The respective AE detecting means 5X and 5Y are respectively
The AE sensors CH1 and CH2 that detect the AE wave of the crack generated in the sample material W, the preamplifier 10 and the main amplifier 11 that amplify the AE wave signals of the AE sensors CH1 and CH2, and the low level of the amplified AE wave signal. A filter 12 for removing a level noise component, a sample hold circuit 13 for sampling and maintaining an AE wave signal at a set sampling period, an A / D converter 14 for digitizing the sampled AE wave signal, The memory 15 for storing the digitized AE wave signals x (t) and y (T) is sequentially connected and configured. A pair of AE sensors CH1 and CH2 are provided inside the chuck so as to face each other at a position equidistant from the center of the test material, and detect AE waves generated from the test material during quenching through the chuck.

The signals detected by the AE sensors CH1 and CH2 are amplified by a preamplifier 10 and a main amplifier 11, respectively, and low-level noise is removed by a filter 12, and then input to a sample hold circuit 13.

The sample hold circuit 13 samples and maintains the input signal at a preset sampling period. The signal (analog signal) maintained in the sample hold circuit 13 is converted into digital detection signals x (t) and y (t) by the A / D converter 14 and output, and stored in the memory 15.

The cross-correlation processing circuit 6 has a digital detection signal x (t) and a detection signal y stored in the memory 15.
For (t), the cross-correlation function of the following equation (1), which is generally used for obtaining the impulse response of the measuring instrument, is calculated to obtain the correlation characteristic (CQ Publishing Co., “Interface”, 1983 2). (See the monthly issue, pages 258-260).

[0017]

[Equation 1]

By the calculation of the equation (1), the detection signals x (t) and y output from both the AE detecting means 5X and 5Y.
The correlation characteristic of (t) is obtained. Each detecting means 5
Detection signals x (t) and y output from X and 5Y
(T) shows the same waveform in the case of the AE wave due to the crack of the test material.

If the detection signals x (t) and y (t) are signals corresponding to the cracked AE wave, and the AE sensor CH1,
When a crack occurs at the center of CH2, that is, at the center of the sample material W, the signal obtained by the cross-correlation processing circuit 6 becomes the correlation characteristic data (impulse data for convenience) indicating the impulse response. , Fig. 3 (a)
As shown in, the peak of the waveform appears at τ = 0.

Further, it is assumed that the detection signals x (t) and y are
When (t) is a signal corresponding to a cracked AE wave and a crack is generated at a position deviated from the center of the AE sensors CH1 and CH2, the signal obtained by the cross-correlation processing circuit 6 is the impulse data. However, as shown in FIG. 3B, the position of the peak of the pulse waveform appears in a state having a time difference (t) from τ = 0.

If the test material is not cracked and the detection signals x (t) and y (t) are output, that is, if noise is generated, the noise has periodicity. The signal obtained by the cross-correlation processing circuit 6 is canceled because it is low, and becomes the correlation characteristic data (for convenience, referred to as non-impulse data) that does not show an impulse response as shown in FIG.

The crack position measuring means 7 obtains a time difference (t) from τ = 0 based on the impulse data obtained as described above, and based on this time difference (t), the following equation (2) is obtained.
And the crack position is obtained by (3).

[0023]

[Equation 2]

(Equation 3) Here, L: sample material length, v: sound velocity, l: crack position, respectively.

A plurality of pairs of AE sensors CH1 and CH
2 and SH3 / CH4 ... In the case where each pair of AE sensors CH1 / CH2, SH3 / CH4 ...
Since the respective signals output by the above are subjected to the calculation of the cross-correlation function by the cross-correlation processing circuit 6 and the crack position measuring means 7 calculate based on the respective impulse data, the position of the crack can be obtained in a multidimensional manner. .

In the crack detecting device 1 configured as described above, the AE detecting means 5X and 5Y detect the signals from the sample material W, respectively, and detect the signals as x (t) and y.
It is stored in the memory 15 as (t). Then, the cross-correlation processing circuit 6 calculates the cross-correlation function of Expression (1) with respect to the detection signals x (t) and y (t) to obtain the detection signals x (t) and y (t). Obtain the correlation characteristics.

The cross-correlation processing circuit 6 detects the detection signal x (t).
And y (t) are signals corresponding to the crack AE wave, impulse data (FIGS. 3A and 3B) are output to the crack position measuring means 7. When the impulse data is input, the crack position measuring means 7 performs a calculation for detecting the crack occurrence position to detect the crack occurrence position.

As described above, for the detection signals x (t) and y (t) corresponding to the signal from the test material W, the cross-correlation function of the equation (1) is calculated to obtain the correlation characteristic. Therefore, the signals x (t) and y detected from the test material W are
If (t) is noise, it is canceled. When the signal corresponds to the crack AE wave, the position of the crack is detected based on the output impulse data.

[0028]

According to the present invention, since the crack detecting device is constructed as described above, the correlation characteristic calculating means can mutually detect the detection signal from the sample material detected by the pair of detecting means. Since correlation processing is performed to obtain correlation characteristics,
It is possible to accurately detect cracks in the test material without being affected by noise, and it is possible to detect the position where the cracks occur based on the correlation characteristics.

[Brief description of drawings]

FIG. 1 is a circuit diagram schematically showing an embodiment of a crack detection device according to the present invention.

FIG. 2 is a circuit diagram showing a main part of the crack detection device.

3A is a waveform diagram schematically showing an example of impulse data output from a cross-correlation processing circuit of the crack detection device when a crack occurs in the center of the test material; FIG. A waveform diagram schematically showing an example of impulse data output by the cross-correlation processing circuit of the crack detection device when a crack is generated by shifting from the center of the same, (c) Non-impulse data output by the cross-correlation processing circuit It is a wave form diagram which shows an example of typically.

FIG. 4 is a waveform diagram showing an example of an AE wave.

FIG. 5 is a waveform diagram showing an example of noise.

6A is a frequency analysis diagram showing an example of an AE wave having a sensitivity peak in a specific frequency band, and FIG. 6B is a frequency analysis diagram showing an example of noise in which a sensitivity peak does not appear in the specific frequency band.

[Explanation of symbols]

 1 crack detection device 5X, 5Y AE detection means 6 cross-correlation processing circuit 7 crack position measurement means

Claims (2)

[Claims] 1. A crack detection device for detecting cracks based on acoustic radiation waves generated from a test material, comprising a pair of detection means for detecting acoustic radiation waves generated from the test material, and the detection means. From the cross-correlation processing means for performing the cross-correlation processing on the signal to obtain the correlation characteristic, and the crack position measuring means for detecting the crack generation position of the sample material based on the correlation characteristic from the cross-correlation processing means. Crack detection device. 2. The crack detecting device according to claim 1, wherein a plurality of pairs of means for detecting acoustic waves generated from the test material are provided.