JP2003269944A - Measurement method and device for crack depth developed in structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measurement method and a measurement device for crack depth capable of nondestructively measuring the depth of a crack developed in a structure, and having high analysis accuracy. <P>SOLUTION: Test sound waves are emitted to a test object 2 from a speaker 1. A vibration velocity of air grains at the front entrance of the crack of the test object 2 is measured by a grain velocity sensor 3. The resonance frequency of resonant sound generated in the inside of the crack of the test object 2 is analyzed by a frequency analysis device 4 based on the measured vibration velocity. The crack depth is obtained from the analyzed resonance frequency. <P>COPYRIGHT: (C)2003,JPO

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 measuring a crack depth generated in a structure for acoustically nondestructively measuring the depth of a crack generated in a building, many structures and materials.

[0002]

2. Description of the Related Art Conventionally, ultrasonic and elastic wave excitation methods have been used to measure the depth of cracks in a structure. That is, some oscillators and geophones were attached to concrete, and the crack depth was estimated from the arrival time of ultrasonic waves or elastic waves (mainly surface waves).

However, in the method of measuring the crack depth using ultrasonic waves, there is a problem in that it is difficult to measure the crack depth generated in thick concrete or the like because the ultrasonic waves are largely attenuated inside the concrete. .

In addition, in the method of measuring the crack depth using elastic waves, even if thick concrete (deep crack) can be measured as compared with the method using ultrasonic waves, if the analysis frequency is lowered, the wavelength can be measured. However, there is a problem in that the accuracy of analysis is reduced because of the long length.

Further, if the cracking depth is measured by increasing the analysis frequency, the analysis accuracy is improved, but the attenuation becomes large as in the case of ultrasonic waves, and there is a problem that measurement becomes difficult with thick concrete. is there.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a crack depth measuring means capable of measuring the depth of deep cracks formed in a structure and having high analysis accuracy. The challenge is to provide.

[0007]

In the present invention, the crack depth is not obtained from the acoustic and vibration propagation characteristics of the material, but the resonance phenomenon occurring inside the crack is utilized.

First, the resonance theory, which is the principle of the present invention, will be briefly described. When a sound wave is sent to the inside of a crack of a cracked structure of a certain thickness, an incident wave and a reflected wave are superposed inside the crack, and an interfering wave is formed. Further, at a specific crack depth, the intensity of the interference wave inside the crack is maximized and a strong sound is generated.
This is called sound wave resonance. The frequency (resonance frequency) of the resonating wave inside the crack (stationary wave) is determined by the depth of the crack. This is called acoustic resonance theory.

Here, if the tip of the crack does not reach the back side of the structure and is closed, a characteristic as a closed tube appears as shown in FIG. That is, the wavelength is λ, the resonance frequency is f,
Assuming that the crack depth is L, the speed of sound is c, and the natural number is n,
3, the equation (n-1) λ / 2 + λ / 4 = L holds. Since c = λf, from the above equation, the resonance frequency f
= {(N-1) / 2 + 1/4} c / L.

If the tip of the crack reaches the back side of the structure, a characteristic as an open tube appears as shown in FIG. That is, assuming that the wavelength is λ, the resonance frequency is f, the crack depth is L, the sound velocity is c, and the natural number is n, in FIG. 14, nλ / 2 = L formula is established, and the resonance frequency f = nc /
It becomes 2L.

FIG. 15 shows an impedance model under the plane wave incidence condition for a closed tube and an open tube having a length of 100 mm.
An example of calculating sound pressure and admittance around the opening is shown. It can be seen from FIG. 15 that peaks and dips due to the resonance phenomenon appear at different frequencies for each condition. In this way, the resonance frequency of the resonating sound is determined by the crack depth. Therefore, the crack depth of the structure can be calculated by calculating backward from the resonance frequency. Therefore, the method for measuring the crack depth generated in the structure of the present invention comprises the steps of radiating a test sound wave to the target test body, and measuring the vibration velocity of air particles at the surface entrance of the crack of the target test body. And analyzing the resonance frequency of the resonance sound wave generated inside the crack of the target test body based on the measured vibration speed, and determining the crack depth from the analyzed resonance frequency.

Further, the method of measuring the crack depth generated in the structure of the present invention comprises the steps of radiating a test sound wave to the target test body and receiving a resonance sound wave generated inside the crack of the target test body. And a step of analyzing the resonance frequency of the received resonance sound wave, and is configured to obtain the crack depth from the analyzed resonance frequency.

Further, the method of measuring the crack depth generated in the structure of the present invention comprises the steps of blowing compressed air to the target test body, and receiving the resonance sound waves generated inside the crack of the target test body. And a step of analyzing the resonance frequency of the received resonance sound wave, and the crack depth is obtained from the analyzed resonance frequency.

Further, the apparatus for measuring the crack depth generated in the structure of the present invention measures the means for radiating the test sound wave to the target test body and the vibration velocity of the air particles at the surface entrance of the crack of the target test body. Based on the means and the measured vibration velocity,
It is configured to include a means for analyzing the resonance frequency of the resonance sound wave generated inside the crack of the target test body and a means for obtaining the crack depth from the analyzed resonance frequency.

Further, the measuring device for the crack depth generated in the structure of the present invention comprises means for radiating a test sound wave to the target test body and means for receiving the resonance sound wave generated inside the crack of the target test body. And a means for analyzing the resonance frequency of the received resonance sound wave and a means for obtaining the crack depth from the analyzed resonance frequency.

In the case of adopting such a constitution, the means for receiving the resonance sound wave generated inside the crack of the target test body eliminates the test radiated sound as much as possible, and resonates through the inside of the crack of the target test body. A blocking device (cover or the like) for strongly responding to sound waves may be provided.

The crack depth measuring device of the structure of the present invention comprises means for blowing compressed air to the target test body and means for receiving the resonance sound waves generated inside the crack of the target test body. And a means for analyzing the resonance frequency of the received resonance sound wave and a means for obtaining the crack depth from the analyzed resonance frequency.

According to the present invention, by adopting the above configuration,
It is possible to capture the resonance frequency of the resonance sound wave generated inside the crack generated in the structure, and the crack depth can be measured by analyzing the resonance frequency.

In addition to the fundamental resonance frequency, higher order resonance frequencies can be detected to improve the accuracy of measurement.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an outline of a crack depth measuring method according to a first embodiment of the present invention. In the crack depth measuring method according to the first embodiment of the present invention, attention is paid to the fact that the movement of the air particles at the surface entrance of the crack becomes active when the resonance phenomenon occurs. Uses a particle velocity sensor to detect.

Reference numeral 1 is a speaker which emits a test sound wave toward the inside of a crack formed in the structure, and 2 is a target test body in which the crack is generated. A particle velocity sensor 3 detects the velocity of vibrating air particles at the surface entrance of the crack and converts it into an electric signal. Reference numeral 4 is a frequency analysis device for performing frequency analysis based on the electric signal transmitted from the particle velocity sensor to measure the magnitude of the resonance frequency component, and 5 is for capturing a sound wave and converting acoustic energy into electric energy. It is a microphone.

First, a test sound wave having a frequency characteristic having a bandwidth large enough to measure the crack depth by frequency is radiated from the speaker 1 toward the target test body 2. By the test sound wave radiated from the speaker 1, the target test body 2
Inside the crack, the incident wave and the reflected wave interfere with each other to cause a resonance phenomenon. Then, the particle velocity sensor 3 that detects the movement of the air particles brought close to the surface measures the velocity of the air particles that vibrate due to the resonance phenomenon and converts them into an electric signal.

Next, the frequency analyzer 4 measures the magnitude of each frequency component based on the electric signal transmitted from the particle velocity sensor 3. Then, the frequency at which the amplitude shows a peak is detected as the resonance frequency, and the crack depth is obtained based on the resonance theory.

The particle velocity sensor 3 and the microphone 5 are arranged side by side because the frequency characteristic of the radiated sound of the speaker 1 is not flat, and if only the particle velocity sensor 3 is used, there is a risk of measuring the frequency characteristic of the speaker 1. Because,
Particle velocity sensor 3 with the output of microphone 5
This is to solve the problem that the frequency characteristic of the speaker 1 is not flat by making the output of the above relative. This relativized value is called acoustic admittance.

FIG. 2 is a block diagram of the frequency analyzer 4 used in the first embodiment. When the particle velocity sensor 3 converts the air particle velocity at the inlet of the crack surface into an electric signal, the electric signal is converted into a frequency analysis device
Is transmitted to the A / D converter 41 and is converted into a digital signal.

On the other hand, the output of the microphone 5 is transmitted to the A / D converter 42 of the frequency analyzer 4 and converted into a digital signal. The digital signals are Fourier transformed by the Fourier transform unit 43 and the Fourier transform unit 44, respectively, and then the acoustic admittance calculation unit 4
5, the acoustic admittance is calculated, and the frequency information output unit 46 outputs the magnitude of each frequency component.
The method of extracting the resonance frequency from the output frequency information and estimating the crack depth is to numerically analyze the frequency information, calculate the peak value of the frequency, and then determine the crack depth corresponding to the resonance frequency. Or you can output the frequency information as a graph on a display or printer,
The measurer may read the graph.

3 to 7 are diagrams showing detailed experimental examples in the first embodiment. Fig. 3 shows an example in which the crack depth is changed, Fig. 4 shows a comparative example with closed and open pipes,
FIG. 5 is a graph showing an example in which the inside of the groove is not smooth, FIG. 6 is an example in which the groove width is changed, and FIG.

FIG. 3 is a graph obtained by making a test body in which the groove depth can be changed with an aluminum material and using an acoustic admittance in which a heat ray type particle velocity sensor and a microphone are arranged directly above the groove. As a result of observing in this way, in the graph shown in FIG. 3, the groove depth is 80 m.
Spectral peaks were observed for m, 40 mm, and 20 mm. Then, in the graph, a vertical line is drawn downward from the peak of each spectrum and the intersection with the horizontal axis is read to detect the resonance frequency.

The present embodiment is based on the case of a closed tube having a fundamental vibration of n = 1, and an expression f = {(n-1) / 2 + 1 / for obtaining a resonance frequency in the case of a closed tube based on the acoustic resonance theory.
4} c / L is applicable, and the resonance theory can be applied.

Next, an example of an experiment conducted under the two conditions of opening and closing the other end of the aluminum material groove having a depth of 100 mm is shown in the graph of FIG.
In this example, the first-order mode appears at 700 Hz in the case of the closed tube, and appears in the vicinity of 1.5 kHz which is about twice the case of the closed tube in the case of the open tube, and it is judged that the application of the resonance theory is appropriate.

Next, for a concrete crack test body in which the inside of the groove of the structure is not smooth, the groove depth is 10 mm and 20 m.
An example of observations with m, 30 mm, and 40 mm test specimens is shown in the graph of FIG. In this example as well, spectral peaks are observed at different frequencies, demonstrating that the application of resonance theory is appropriate.

Next, referring to FIG. 6, the groove width of the aluminum material is set to 0.
An example of observation when changing from 6 to 1 mm is shown. In this observation example, the peak tends to be observed as the groove width decreases, and it is considered that the sensitivity of the fine crack must be improved, but the resonance theory is considered to be valid.

Next, a graph of FIG. 7 shows an observation example of a non-linear cross-section length void in which a 40-mm-thick concrete paving stone plate is cut, the fracture surfaces are brought into close contact, and the lower surface is closed with oil soil. In this observation example, the characteristic as an open tube in the acoustic resonance theory appears and a peak is observed near 1.5 kHz, so the resonance theory is valid.

Here, in the first embodiment, the test sound wave having a wide bandwidth is radiated from the speaker.
The resonance frequency can also be measured by sweeping the test sound wave emitted from the speaker and gradually increasing the frequency with time. FIG. 8 shows a configuration example of the frequency analysis device 6 when sweeping the test sound wave.

The frequency control unit 60 of the frequency analyzer 6 is
The frequency information that sweeps with time is transmitted to the speaker output frequency control unit 61, and the speaker output frequency control unit 6
1 transmits this frequency information to the D / A converter 62. Then, the D / A converter 62 converts the digital signal into an analog signal, which is radiated as a sound wave from the speaker 1. Next, the output from the particle velocity sensor 3 is transmitted to the A / D converter 63 of the frequency analyzer 6. The digital signal converted by the A / D converter 63 is transmitted to the frequency information output unit 64, and the frequency information output unit 64 detects each frequency information.

FIG. 9 is a diagram showing an outline of a crack depth measuring method according to the second embodiment of the present invention. Second
In the above embodiment, the fine microphone 5 that enters the inside of the crack is used.

First, a test sound wave having a frequency characteristic having a bandwidth large enough to measure the crack depth by frequency is radiated from the speaker 1 toward the target test body. By the test sound wave radiated from the speaker 1, the target test body 2
Inside the crack, the incident wave and the reflected wave interfere,
Resonance phenomenon occurs. Next, the fine microphone 5 installed inside the crack or the entrance portion of the target test body 2 receives the resonance sound wave inside the crack and converts the acoustic energy into electric energy.

Then, the frequency analyzer 4 measures the magnitude of each frequency component based on the electric signal transmitted from the microphone 5. Then, the frequency at which the amplitude shows a peak is detected as the resonance frequency, and the crack depth is calculated based on the resonance theory.

Also in the second embodiment, the crack depth can be calculated by analyzing the resonance frequency as in the first embodiment. Note that the crack depth can also be obtained in the same way by observing the sound waves emitted by the radiation test.

FIG. 10 is a diagram showing an outline of a crack depth measuring method according to the third embodiment of the present invention. In the third embodiment, a cover 7 is attached to the microphone 5 to eliminate the test radiated sound as much as possible, and a sound receiving device is used that is sensitive to the sound wave passing through the inside of the crack. By making such a device, the sensitivity to resonance sound waves can be improved and the accuracy of crack depth measurement can be improved.

First, a test sound wave having a frequency characteristic having a bandwidth large enough to measure the crack depth by frequency is radiated from the speaker 1 toward the target test body. By the test sound wave radiated from the speaker 1, the target test body 2
Inside the crack, the incident wave and the reflected wave interfere,
Resonance phenomenon occurs. Next, the microphone 5 receives the resonance sound wave inside the crack and converts the acoustic energy into electric energy. Then, based on the electric signal transmitted from the microphone 5, the frequency analysis device 4 measures the magnitude of each frequency component. Then, the frequency at which the amplitude shows a peak is detected as the resonance frequency, and the crack depth is calculated based on the resonance theory.

Also in the third embodiment, the crack depth can be calculated by analyzing the resonance frequency as in the first embodiment. Note that the crack depth can also be obtained in the same way by observing the sound waves emitted by the radiation test.

FIG. 11 is a diagram showing an outline of a crack depth measuring method according to the fourth embodiment of the present invention. In the fourth embodiment, compressed air 9 is used.

First, the compressed air 9 is blown from the nozzle 8 toward the inside of the crack of the test specimen 2. The blown compressed air 9 causes a resonance phenomenon inside the crack of the target test body 2. Next, the microphone 5 receives the resonance sound wave inside the crack and converts the acoustic energy into electric energy. Then, based on the electric signal transmitted from the microphone 5, the frequency analysis device 4 measures the magnitude of each frequency component. Then, the frequency at which the amplitude shows a peak is detected as the resonance frequency, and the crack depth is calculated based on the resonance theory.

FIG. 12 shows a concrete crack test with a 40 mm thick concrete paving slab, the fracture surfaces of which are adhered to each other, and the bottom surface of which is closed with oil soil to form a void having a non-linear section length and a groove depth of 30 mm. An example of an experiment in which compressed air was blown to the opening of the body and the generated sound was frequency analyzed is shown. As shown in the graph of FIG. 12, a blunted peak was observed at the same frequency as the peak observed by radiating the test sound wave from the speaker. From this result, in the fourth embodiment as well, although the peak becomes slower by analyzing the resonance frequency than in the first embodiment, the crack depth is calculated similarly to the first embodiment. It was confirmed that it can be done.

FIG. 13 is a diagram showing an outline of a crack depth measuring method according to the fifth embodiment of the present invention. In the fifth embodiment, a test sound wave is radiated using an acoustic tube, the impedance and sound absorption coefficient of the cracked surface are obtained by the acoustic tube method, and the sound absorption coefficient is measured to compare with other embodiments described above. Similarly, the peak of the resonance frequency,
Estimate the resulting crack depth.

First, the acoustic tube 10 is erected vertically so as to look into the crack surface of the target test body 2, and two microphones 5A and 5B are arranged in the acoustic tube 10 in the vicinity of the crack with a slight distance therebetween. A test sound wave such as white noise is radiated from the speaker 1 arranged above the acoustic tube 10, the outputs of the microphones 5A and 5B are guided to the frequency analyzer 4, and the sound pressure is measured. By performing a calculation process such as a time delay on the outputs of the two microphones, the ratio of the sound pressure incident on the surface of the target test body 2 and the sound pressure reflected from the surface, that is, the sound pressure reflection coefficient is obtained. From this, the acoustic impedance (reciprocal of acoustic admittance) and sound absorption coefficient of the cracked surface can be obtained.

If the sound pressure reflection coefficient is r, the acoustic impedance Z of the surface and the sound absorption coefficient α are Z = (1 + r) / (1-r), α = 1-r ² be able to.

That is, two mylophones 5A and 5B are installed inside the acoustic tube 10, the sound pressure at each point is simultaneously observed, and the phase delay calculation corresponding to the distance to either one of the sound pressure measurement values. When the difference between the two is obtained by performing the above, the traveling wave or backward wave components cancel each other out, and either component can be removed. From this, it becomes possible to calculate the sound pressure reflection coefficient by the resonance phenomenon of cracks. The method of measuring the normal incidence sound absorption characteristics using such an acoustic tube is a well-known technique (reference: "Noise Control Engineering Handbook" (Company, Japan Society for Noise Control Engineering)).

The reason why the sound absorption coefficient changes due to the resonance phenomenon is as follows. When the resonance phenomenon occurs inside the target test body 2 due to the emission of the test sound wave, the air particles move violently. As a result, viscous friction occurs near the surface of the crack and consumption of kinetic energy (conversion into heat energy)
The sound absorption effect appears due to, and the sound absorption coefficient peaks at the resonance frequency. Therefore, the crack depth can be estimated by measuring a peak having a high sound absorption coefficient from this frequency characteristic and performing the same analysis as in the above-described embodiment.

[0051]

According to the present invention, it is possible to detect the resonance frequency of the resonance sound wave generated inside the crack generated in the structure, analyze the resonance frequency, and measure the crack depth by applying the resonance theory. can do.
In addition to the fundamental resonance frequency, higher order resonance frequencies can be detected to improve the accuracy of measurement.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a crack depth measuring method according to a first embodiment.

FIG. 2 is a configuration diagram of a frequency analysis device.

FIG. 3 is a graph showing an experimental example in the first embodiment.

FIG. 4 is a graph showing an experimental example in the first embodiment.

FIG. 5 is a graph showing an experimental example in the first embodiment.

FIG. 6 is a graph showing an experimental example in the first embodiment.

FIG. 7 is a graph showing an experimental example in the first embodiment.

FIG. 8 is a configuration diagram of a frequency analysis device.

FIG. 9 is a diagram showing an outline of a crack depth measuring method according to the second embodiment.

FIG. 10 is a diagram showing an outline of a crack depth measuring method according to a third embodiment.

FIG. 11 is a diagram showing an outline of a crack depth measuring method according to a fourth embodiment.

FIG. 12 is a graph showing an experimental example in the fourth embodiment.

FIG. 13 is a diagram showing an outline of a crack depth measuring method according to a fifth embodiment.

FIG. 14 is a diagram showing an example of resonance sound waves in a closed tube.

FIG. 15 is a diagram showing an example of resonance sound waves in an open tube.

FIG. 16 is a graph showing a resonance phenomenon.

[Explanation of symbols]

1 speaker 2 Target specimen 3 Particle velocity sensor 4 Frequency analyzer 5 microphones 6 Frequency analyzer 7 cover 8 nozzles 9 compressed air 10 sound tube 41 A / D converter 42 A / D converter 43 Fourier transform unit 44 Fourier transform unit 45 Acoustic admittance calculator 46 Frequency information output section 60 Frequency controller 61 Speaker output frequency controller 62 D / A converter 63 A / D converter 64 Frequency information output section

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroto Yasuoka             518-1 Komagaki, Nagareyama-shi, Chiba Mitsui Construction Co., Ltd.             Company Technology Research Center (72) Inventor Takeshi Iwamoto             518-1 Komagaki, Nagareyama-shi, Chiba Mitsui Construction Co., Ltd.             Company Technology Research Center F term (reference) 2F068 AA24 BB01 BB09 CC11 FF23                       GG05 GG09 QQ05 QQ06 QQ10                 2G047 AA10 BC04 BC07 BC18 EA10                       GA18 GF11 GG09 GG12

Claims (6)

[Claims] 1. A method for measuring the depth of cracks in a structure, the method comprising: radiating a test sound wave to a target test body; and measuring the vibration velocity of air particles at the surface entrance of the crack of the target test body. And a step of analyzing the resonance frequency of the resonance sound wave generated inside the crack of the target test body based on the measured vibration velocity, and a step of outputting information for calculating or estimating the crack depth from the analyzed resonance frequency. A method for measuring a crack depth generated in a structure, characterized by having. 2. A method of measuring a crack depth generated in a structure, comprising: radiating a test sound wave to a target test body; and receiving a resonance sound wave generated inside the crack of the target test body. Crack depth generated in a structure, characterized by having a step of analyzing the resonance frequency of the received resonance sound wave and a step of outputting information for calculating or estimating the crack depth from the analyzed resonance frequency. Measurement method. 3. A method for measuring a crack depth generated in a structure, comprising: blowing compressed air to a target test body; receiving a resonance sound wave generated inside the crack of the target test body; A crack depth generated in a structure, characterized by having a step of analyzing the resonance frequency of the sounded resonance sound wave and a step of outputting information for calculating or estimating the crack depth from the analyzed resonance frequency. Measuring method. 4. A device for measuring a crack depth generated in a structure, comprising means for radiating a test sound wave to a target test body and means for measuring the vibration velocity of air particles at the surface entrance of the crack of the target test body. And means for analyzing the resonance frequency of the resonance sound wave generated inside the crack of the target test body based on the measured vibration velocity, and means for outputting information for calculating or estimating the crack depth from the analyzed resonance frequency. An apparatus for measuring a crack depth generated in a structure, comprising: 5. A device for measuring a crack depth generated in a structure, comprising means for radiating a test sound wave to a target test body, and means for receiving a resonance sound wave generated inside the crack of the target test body. Crack depth in a structure, characterized by comprising means for analyzing the resonance frequency of the received resonance sound wave and means for outputting information for calculating or estimating the crack depth from the analyzed resonance frequency. Measuring device. 6. A device for measuring a crack depth generated in a structure, which comprises means for blowing compressed air to a target test body,
A means for receiving the resonance sound wave generated inside the crack of the target test body, a means for analyzing the resonance frequency of the received resonance sound wave, and the output of information for calculating or estimating the crack depth from the analyzed resonance frequency. An apparatus for measuring a crack depth generated in a structure, comprising: