JP2003149214A - Nondestructive inspecting method and its apparatus using ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nondestructive inspecting method and its apparatus using an ultrasonic sensor capable of highly accurately and easily diagnosing the internal state such as cracks of a concrete structure, etc., even by an unskilled person. SOLUTION: By obtaining a difference spectrum, the difference between the frequency spectrum of reception signals of obtained multiple reflection waves and the frequency spectrum of fundamental reflection waves based on the dynamic characteristics of the ultrasonic sensor, and analyzing the difference spectrum, the internal state of the object to be inspected is inspected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nondestructive inspection method using ultrasonic waves, and particularly to a nondestructive inspection method using ultrasonic waves suitable for nondestructive inspection of concrete structures and the like. Regarding the device.

[0002]

2. Description of the Related Art Concrete structures such as tunnels and bridges need to have their internal condition diagnosed periodically or irregularly from the viewpoint of preventing accidents such as peeling and collapse of concrete and extending the service life. Yes, the diagnosis of such internal conditions is
Conventionally, a diagnosis method using a hammering sound has been adopted, in which a skilled person mainly gives an impact with a hammer and diagnoses cracks and the like by the reaction force and sound. However, the diagnosis by tapping sounds has a background such as a sharp decrease in the number of skilled persons and a rapid increase in the number of objects to be diagnosed, and therefore a diagnostic method that enables even an unskilled person to diagnose the internal state with high accuracy is required.

Therefore, as a diagnostic method replacing the tapping sound,
Non-destructive inspection methods such as X-ray method, electromagnetic wave method, infrared ray method, and ultrasonic method have been tried, but each has its drawbacks, and a solid diagnostic method has not yet been put to practical use. That is, the X-ray method is troublesome to handle, can be used only by qualified personnel, and is risky and expensive. Further, since the transmission is used, there is a problem that it cannot be applied to an inspection target from one side such as a tunnel. On the other hand, the electromagnetic wave method may not be able to be inspected when the reinforcing bar is inside or when there is a lot of water. The infrared method analyzes the temperature distribution, so there is no sunshine and there is no temperature difference inside the tunnel. Etc., there is a problem that it becomes difficult to detect cracks and the like. Further, these methods have a problem that only a shallow crack or the like located within several mm to several cm from the surface can be detected. In the ultrasonic method that directly measures the sound wave round-trip propagation time up to a crack or the like, it is difficult to measure the sound wave round-trip propagation time when the crack or the like is shallow and multiple reflected waves from the crack or the like overlap each other. Regarding these conventional techniques, for example, Japan Highway Public Corporation Testing Research Institute Test Research Promotion Committee Material Enforcement Study Group: Material Enforcement Material (No. 8) Non-Destructive Inspection Method, Japan Highway Public Corporation Testing Laboratory, Testing Laboratory Technical Materials Issue 128, 1
The description can be seen in March 996, etc.

Provided is a nondestructive inspection method using ultrasonic waves and an apparatus therefor, which solves the problems of the ultrasonic method and enables even an unskilled person to diagnose the internal state of a concrete structure such as a crack with high accuracy. In order to achieve the above, the present inventor has previously conducted a time domain measurement method based on a multiple reflection wave model, that is, a predicted received signal waveform and an actual received signal waveform based on the physical characteristics and signal propagation characteristics of the ultrasonic sensor. Proposed a nondestructive inspection method and device for concrete structure using ultrasonic waves, which inspects the internal state of the concrete structure by pattern matching with the wave signal waveform (Japanese Patent Laid-Open No. 2001-201487) did. However,
This technique has a problem that it is slightly difficult to discriminate and it is difficult for an unskilled person to understand.

[0005]

SUMMARY OF THE INVENTION The present invention provides a concrete
Considering the above-mentioned situation related to the non-destructive inspection method for structural objects,
An object of the present invention is to provide a nondestructive inspection method using an ultrasonic sensor and an apparatus therefor, which enables an unskilled person to easily and easily diagnose the internal state of a crack or the like in a concrete structure.

[0006]

In order to achieve the above-mentioned object, the present inventor has conducted extensive studies, and as a result, from the frequency spectrum of the received signal of multiple reflected waves, the fundamental reflected wave based on the dynamic characteristics of the ultrasonic sensor is obtained. It was found that the sound wave round-trip propagation time between the surface of the concrete structure, etc. and the internal crack, etc. can be measured with high accuracy by analyzing the difference spectrum from which the frequency spectrum of However, they have found that the internal state of the inspection object can be easily diagnosed and completed the present invention.

That is, the invention of claim 1 is a non-destructive inspection method using the ultrasonic sensor of the present invention, wherein the frequency spectrum of the received signal of the multiple reflected waves obtained and the dynamic characteristics of the ultrasonic sensor are This is a non-destructive inspection method using an ultrasonic sensor that non-destructively inspects the internal state of an inspection target by obtaining a difference spectrum that is the difference from the frequency spectrum of the fundamental reflected wave and analyzing the difference spectrum.

According to a second aspect of the present invention, in the nondestructive inspection method using the ultrasonic sensor of the present invention, the frequency of the multiple reflected wave from the received signal of the multiple reflected wave corresponding to the electric signal input to the ultrasonic sensor is A step of obtaining a spectrum, a step of obtaining a frequency spectrum of a basic reflected wave based on the dynamic characteristics of the ultrasonic sensor, a step of obtaining a difference spectrum which is a difference between the frequency spectrum of the multiple reflected wave and the frequency spectrum of the basic reflected wave, A non-destructive inspection method using an ultrasonic sensor, which comprises a step of obtaining a sound wave round-trip propagation time between a surface of an inspection object and an internal crack or the like from a difference spectrum.

A third aspect of the present invention is a nondestructive inspection method using an ultrasonic sensor, wherein the step of obtaining the frequency spectrum of the multiple reflected waves is the step of obtaining the frequency spectrum of the multiple reflected waves by the maximum entropy method.

According to a fourth aspect of the present invention, the fundamental reflected wave uses the dynamic characteristics of the ultrasonic sensor as parameters of the natural angular frequency and attenuation coefficient of the transmitter, the natural angular frequency and attenuation coefficient of the receiver. A fundamental reflected wave represented by using a modeled transfer function including a parameter, a step of determining a parameter such that the square error between the frequency spectrum of the multiple reflected wave and the frequency spectrum of the fundamental reflected wave is minimized. It is a non-destructive inspection method using an ultrasonic sensor.

According to a fifth aspect of the present invention, the difference spectrum is a difference spectrum obtained by subtracting the frequency spectrum of the fundamental reflected wave from the frequency spectrum of the multiple reflected wave, and the step of obtaining the sound wave round-trip propagation time is performed by the difference spectrum. This is a non-destructive inspection method using an ultrasonic sensor including a process of obtaining a second difference spectrum by extracting only a portion having a negative value.

According to a sixth aspect of the present invention, the step of obtaining the sound wave round-trip propagation time includes the step of obtaining the autocorrelation function of the difference spectrum or the second difference spectrum, and nondestructive using an ultrasonic sensor. The invention is an inspection method, and the invention of claim 7 includes the step of obtaining the sound wave round-trip propagation time, and the step of obtaining the sound wave round-trip propagation time between the surface of the inspection object and an internal crack or the like from the autocorrelation function. Is a non-destructive inspection method using the ultrasonic sensor.

According to an eighth aspect of the present invention, the step of obtaining the sound wave round-trip propagation time is performed by a plurality of pole frequencies related to either the maximum value or the minimum value appearing in the difference spectrum or the second difference spectrum. The invention is a non-destructive inspection method using an ultrasonic sensor, the method including the step of obtaining the repetition frequency from the ultrasonic wave and making the repetition frequency the sound wave reciprocating frequency. There is a non-destructive inspection method using an ultrasonic sensor configured to obtain the repetition frequency by minimizing an error when approximated by an integer multiple of, and the invention of claim 10 provides the difference spectrum or the second Among the pole frequencies appearing in the difference spectrum, the repetition frequency is obtained using a plurality of pole frequencies having relatively large spectrum strength. A nondestructive inspection method using an ultrasonic sensor. Further, the invention of claim 11 is a nondestructive inspection method using the ultrasonic sensor, wherein the nondestructive inspection is performed using ultrasonic waves of approximately 30 KHz.

According to a twelfth aspect of the present invention, there is provided a non-destructive inspection device using the ultrasonic sensor of the present invention, which is characterized by using any one of the methods of the present invention. It is a destructive inspection device.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a method for measuring a frequency domain based on a multiple reflected wave model. First, the multiple reflected wave model will be described. An ultrasonic sensor mechanically is a transducer having an acoustic transducer in which a transmitter converts an electric signal into a sound pressure signal and a receiver converts the sound pressure signal into an electric signal. Therefore, U (s) As a Laplace transform of the electric signal u (t) input to the wave transmitter, the electric signal r (t) output to the wave receiver can be modeled, for example, as in Expression (1).

[0016]

[Equation 1]

[0017]

[Equation 2]

[0018]

[Equation 3]

Suffix i means a transmitter and a receiver, ω _i is a natural angular frequency, ζ _i is a damping coefficient, K _i is a gain, and T ₀ is from transmission to reception. Represents the round trip propagation time of the sound wave. The natural angular frequency and the like appearing in this model are unknown parameters based on the dynamic characteristics of the ultrasonic sensor such as the shape and material of the acoustic oscillator and the electric circuit connected to it. In equation (1), the reflection waveform with T ₀ = 0 can be said to be a standard form of the electric signal waveform received when an electric signal is input to the ultrasonic sensor, and is referred to as a basic reflection waveform in the present invention. , R ₀ (t) hereinafter.

When ultrasonic waves are emitted from the surface of an object to be inspected, such as a concrete structure, multiple reflected waves are generated between the surface and internal cracks, etc. Received. For example, considering a data window D having an appropriate width except for the initial data which is greatly affected by the transverse wave with one crack or the like, the received signal r _x (t) uses the basic reflection waveform r ₀ (t). Then, it can be modeled as in equation (4). In equation (4), m is the number of reflected waves contained in the data window, k is the reflected wave contained first in the data window is the kth reflected wave, and T is the reflected wave. Is a round-trip sound wave propagation time of p, and p (0 <p <1) represents p = α _a γ _a1 γ _a2 , where α _a is the attenuation rate during one round trip,
γ _a1 and γ _a2 represent reflectances on the surface and cracks, respectively.

[0021]

[Equation 4]

Equation (4) generally has a small p, so
Equation (5) can be approximated by
Equation (6) is obtained, and in order to obtain the frequency spectrum, the equation (7) is obtained by taking the absolute value of equation (6). In addition,
G ₁ (jω) and G ₂ (jω) are respectively s = jω in the equation (3), and j is an imaginary unit.

[0023]

[Equation 5]

[0024]

[Equation 6]

[0025]

[Equation 7]

Next, the logarithm (common logarithm) of the equation (7) is taken to obtain the frequency spectrum of the received signal of the multiple reflected wave, and from this, the frequency spectrum of the basic reflected wave g (ω) = log│G ₁ (jω)
Subtracting G ₂ (jω) |, the difference spectrum s (ω) in Eq. (8)
Is obtained.

[0027]

[Equation 8]

Equation (8) shows that the difference spectrum s (ω) is ω (=
2πf) is a periodic function having a period of 2π / T, and frequency f is a periodic function having a period that is the reciprocal (1 / T) of the sound wave round-trip propagation time. That is, this relationship is obtained by subtracting the frequency spectrum of the basic reflected wave based on the dynamic characteristics of the ultrasonic sensor from the frequency spectrum of the received signal of the multiple reflected waves, and the frequency f
It shows that a spectrum can be obtained with the period being the reciprocal of the sound wave round-trip propagation time between the surface of a structure or the like and an internal crack or the like.

Ideally, from the difference spectrum s (ω),
The frequency f ₁ (Hz) corresponding to the sound wave reciprocating period can be obtained directly, but in reality, not only multiple reflected waves such as cracks but also various disturbances are added to the received signal, so the frequency f 1
It is preferable to obtain an autocorrelation function of s (ω) with the variable as a variable and obtain the periodic frequency f ₁ from this autocorrelation function. If f ₁ is obtained, the sound wave round-trip propagation time is obtained by T = 1 / f ₁ ,
From the relation of L = V (T / 2), the depth L of the crack or the like can be obtained. Note that V is the speed of sound in the inspection object. The autocorrelation function is not limited to the present invention, but can be obtained, for example, by the method described in Arimoto: Linear System Theory, Industrial Book (1977) and the like.

The method for obtaining the frequency spectrum is not particularly limited to the present invention. For example, FFT (fast Fourier transform method), MEM (maximum entropy method) or the like can be used. It is excellent in frequency resolution, which is preferable. However, MEM uses the number M of recurrence calculations as a parameter, and if M is small, only a rough frequency spectrum can be obtained.If M is made larger than necessary, it also reacts to the waveform due to disturbance and the spectrum peak is broken. Since a disturbance peak appears, it is necessary to properly select M in order to achieve highly accurate detection. Relatedly, the present inventor has found through a number of experiments that the negative part of s (ω) is not easily affected by the value of M, and it is not possible to directly apply the autocorrelation function to s (ω). However, it was found that it is preferable to obtain the autocorrelation function of the second difference spectrum h (ω) by extracting only the part of s (ω) having a negative value.

Next, a method of obtaining unknown parameters such as the natural angular frequency appearing in the model of the equation (1) will be described. Ideally, this parameter is the shape, material,
Such as the electrical circuit connected to this, is determined by the dynamic characteristics of the ultrasonic sensor, for example, as shown in JP 2001-201487, the actual received signal waveform and the predicted received signal waveform It can be experimentally obtained by the pattern matching of, and approximately this can be used as a constant thereafter.

However, in practice, the basic reflection waveform may slightly change depending on the degree of contact between the ultrasonic sensor and the surface of the object to be inspected. Therefore, it is necessary to obtain unknown parameters such as the natural angular frequency at each inspection. desirable. For example, using an optimization method (Tanaka: Measurement System Engineering, Asakura Shoten, 1994, or J. Kowarik, MR Osbourne (Yamamoto and Koyama): Nonlinear Optimization Problem, Baifukan, 1976, etc.) may be a square error is determined as the minimum | of the frequency spectrum log | R _x (jω) | and fundamental wave reflected frequency spectrum _{log | G 1 (jω) G} 2 (jω).

Next, a suitable analysis method of the autocorrelation function will be described. The analysis of the autocorrelation function is ideally a simple matter of finding the frequency f ₁ that gives the first maximum value of the autocorrelation function, but in general, the maximum value is found at the integral multiple of the repetition frequency. Therefore, when the first maximum value cannot be clearly detected, it is necessary to obtain the repetition frequency by comprehensively using the second maximum value, the third maximum value, and the like.

Next, an analysis method using the difference spectrum or the second difference spectrum in the case where it is difficult to judge only by the autocorrelation function will be described. That is, in the difference spectrum or the second difference spectrum, for example, when considering a group of maximum values (a group having a frequency represented by an integer multiple of a certain reference frequency), the frequency giving the maximum value in the group is Although it is not always expressed exactly as an integral multiple, and in general, there may be variations or lacks, but a more accurate method of obtaining a reference frequency (repetition frequency) will be described. That is, the frequencies that give N maximum values that form a group of certain maximum values are f ₁ , f ₂ ,
, F _N , if the reference frequency is f, and f that minimizes the error when the frequency at each point is approximated by an integer multiple of f is obtained, it becomes the reference frequency f of the maximum point group. . Specifically, if [•] is a Gaussian symbol, then f _i is
[F _i / f] f ≦ f _i ≦ ([f _i / f] +1) f, and the error of the entire group is expressed by equation (10). Where α
_i is defined by the equation (9) as δ _i = f _i / f- [f _i / f].

[0035]

[Equation 9]

[0036]

[Equation 10]

As described above, the repetition frequency as the first approximate solution can be obtained using the difference spectrum or the second difference spectrum, but the peak value (polar value) appearing in the difference spectrum or the second difference spectrum can be obtained. It is also possible to obtain a more accurate second approximate solution by a similar analysis using only a plurality of peaks having relatively large spectral intensities among the (values).

As the frequency of the ultrasonic wave used in the present invention, according to various experiments by the present inventor, the center frequency is approximately
By using ultrasonic waves of 30 KHz, it is possible to detect cracks and the like in a wide range of depth, and the present invention can be preferably implemented.

Next, a nondestructive inspection apparatus using the ultrasonic sensor of the present invention will be described. A nondestructive inspection apparatus using the ultrasonic sensor of the present invention is an apparatus using the nondestructive inspection method of the present invention, and the detailed configuration thereof does not particularly limit the present invention. As shown in the conceptual configuration diagram of FIG. 1, an ultrasonic sensor including a wave transmitter that transmits an ultrasonic wave having a predetermined center frequency and a wave receiver that receives a multiple reflected wave that has passed through an inspection object and converts it into an electric signal, A computer having a program as a means for realizing the method of the present invention such as a means for obtaining the frequency spectrum of multiple reflected waves from a wave signal, an amplifier for signal conversion between the ultrasonic sensor and the computer, a display or printer attached to the computer , And the like.

The present invention is not limited to the non-destructive inspection of concrete structures by detecting multiple reflected waves generated between cracks and the surface of concrete structures, but the size of basic reflected waves can be changed. It is also effective for abnormality diagnosis that can result in the measurement of the difference between the reception time or propagation time of each fundamental reflected wave when they appear successively.

[0041]

EXAMPLES The present invention will be specifically described below with reference to examples, but it goes without saying that the present invention is not limited to these examples.

First, a specimen as an inspection object used in the examples described below will be described. The specimens are two cubic concrete blocks with a side of about 600 mm, and the mixing ratios of coarse aggregate, cement, fine aggregate and water are 40%, 10%, 30% and 20% respectively by volume. The standard size of the coarse aggregate is 10 mm or less. A plurality of pseudo-cracks having different depths from the surface were created in this concrete block to prepare a test piece. Pseudo crack is made of Styrofoam plate (60 mm × 100 mm × thickness 5 mm)
It was created by vertically embedding a 100 mm side on the upper surface, and FIG. 2 is a layout view of pseudo cracks when viewed from the upper surface of the test piece. The black circle shown in FIG. 2B is a reinforcing bar having a diameter of 9 mm, and is provided in front of a crack having a depth of 310 mm and at a position of a depth of 153 mm.

The ultrasonic sensor used in this embodiment is an ESP-10 manufactured by Toyoko Hermes, and has a center frequency of 30 KHz.
Is an ultrasonic sensor. The laptop is the Dell Inspiron 7500.

As a first embodiment, an example in which a nondestructive inspection method using the ultrasonic sensor of the present invention is applied to a crack at a relatively shallow position (parallel crack 41 mm from the surface) will be described. FIG. 3 is an example of the measured received signal,
Ideally, since the sound velocity in concrete is 3,000 m / s, multiple reflected waves will appear at a period of 27 μs, but in reality, superposition of intensities will occur and the basic reflected waveform will be read from Fig. 3. It is difficult. The large waveform (peak-cut) appearing in the initial stage of reception in FIG. 3 is due to the influence of transverse waves.

FIG. 4 is a diagram showing an analysis process of the first embodiment. FIG. 4A shows multiple reflections obtained by applying MEM to the received signal data (data window: 0 to 2 ms) shown in FIG. Wave frequency spectrum log | R _x (jω) | (where M = 900) and the frequency spectrum lo of the fundamental reflected wave obtained by the least squares method
g | G ₁ (jω) G ₂ (jω) | (displayed by a broken line), and (b) is a negative region waveform of these difference spectra (second difference spectrum, but inverted positive display). Yes, (c) is the autocorrelation function of the negative region waveform of (b). From (c) of Figure 4, 33.3k
It shows a maximum value with a large peak value at Hz, and also shows a peak at 66.8 kHz, which is about twice this peak frequency, indicating that 33.3 kHz is the repetition frequency of the differential spectrum. From this, the sound wave round-trip propagation time T is 30.0
μs, and the crack measurement depth is 45.0 mm. That is, Example 1 proves that highly accurate measurement close to the actual 41 mm is possible.

Next, as a second embodiment, an example in which a non-destructive inspection method using the ultrasonic sensor of the present invention is applied to a parallel crack having a depth of 274 mm will be described. FIG. 5 shows the first embodiment.
4 is an example of a measured received signal of Example 2 similar to FIG.

FIG. 6 is a view showing the analysis process of the second embodiment, which is similar to FIG. 4 of the first embodiment. It can be seen from FIG. 6 (c) that the repetition frequency is approximately 6.5 kHz, but since the subsequent peaks are not clear integer multiples, the values from the first to sixth peaks in FIG. 6 (b) are used. Then, the above first approximate solution is calculated to be 7.46 kHz. Furthermore, in the vicinity of the periodic frequency based on the first approximate solution, a peak (~) with large spectral intensity
Using, the above-mentioned second approximate solution is calculated to be 6.30 kHz.
The sound wave round-trip propagation time corresponding to a repetition frequency of 6.30 kHz is 1
It is 59 μs, and the crack measurement depth is 238 mm. That is, even in Example 2 where the crack is deep, it is possible to perform relatively high-precision measurement.

Next, as a third embodiment, an example in which a non-destructive inspection method using the ultrasonic sensor of the present invention is applied to a parallel crack having a depth of 490 mm will be described. FIG. 7 shows the first embodiment.
FIG. 5 is a diagram showing an analysis process of Example 3 similar to FIG.
In this embodiment, it is quite difficult to determine the repetition frequency from the autocorrelation function of FIG. 7C, but the first to the first of FIG.
When the first approximate solution is calculated using the value of the 10th peak, it is 3.55kH
z is obtained, and the corresponding sound wave round-trip propagation time is 282μ.
s, the measurement depth of cracks is 423 mm. That is, in this embodiment, even a crack at a very deep position of 490 mm,
This shows that relatively high precision measurement is possible.

Next, as a fourth embodiment, an example in which a nondestructive inspection method using the ultrasonic sensor of the present invention is applied to a parallel crack having a reinforcing bar at a depth of 153 mm and a depth of 310 mm will be described. FIG. 8 shows a fourth embodiment similar to FIG. 4 of the first embodiment.
It is a figure which shows the analysis progress of. From FIG. 8C, it can be seen that there are two types of multiple reflection waves, a relatively small peak having a repetition frequency of about 10 kHz and a relatively large peak having a repetition frequency of about 5 kHz. Since the latter has a considerably larger peak value and a smaller repetition frequency than the former, it can be seen that the latter corresponds to multiple reflection waves reflected by a large reflecting surface at a deeper place than the former. Specifically, when the first approximate solution is obtained, the former is 10.2 kHz and the latter is
5.12 kHz was obtained, and the corresponding sound wave round-trip propagation times were 98.4 μs and 195 μs, and the measurement depths were 148 mm and 292 mm, which indicate that they correspond to a reinforcing bar with a depth of 153 mm and a parallel crack with a depth of 310 mm, respectively. That is, the present example shows that cracks can be detected even when reinforcing bars are present, and that their positions can be measured simultaneously and with high accuracy. Since the position of the reinforcing bar can be known in advance from a design drawing or the like, cracks can be detected regardless of the presence or absence of the reinforcing bar.

In this embodiment, if the center frequency of the ultrasonic sensor (30 kHz in this embodiment) is increased, the reflected wave from the cracks weakens and the reflected wave of the reinforcing bar near the surface strengthens. This shows that the measurement can be performed with high accuracy.

Next, as a fifth embodiment, an example in which a non-destructive inspection method using the ultrasonic sensor of the present invention is applied to a crack inclined with respect to the concrete surface will be described.
FIG. 9 is an example of the result applied to the crack inclined at 45 degrees in FIG. 2A, and is a diagram showing the analysis progress of Example 5 similar to FIG. 4 of Example 1.

From FIG. 9 (c), large peaks (13.0 kHz, 44.6 kHz, 57.8 kHz) having a repetition frequency of about 13 kHz are obtained.
) And many small peaks having a repetition frequency of about 4 kHz, it can be seen that there are two types of multiple reflection waves. Specifically, when the first approximate solution is obtained, the former is
14.5kHz, the latter 4.44kHz is obtained, corresponding to these,
The sound wave round-trip propagation times are 68.8 μs and 223 μs, and the measurement depths are 103 mm and 335 mm. The former is equivalent to the distance to the center of the crack, even if the crack is diagonal,
It shows that the crack position can be measured with high accuracy according to the present invention. On the other hand, the latter corresponds to the distance to the side surface of the sample through the crack from FIG. 2 (a), and the ultrasonic waves reaching the side surface of the sample through the crack are reflected there.
It shows multiple reflected waves between the side surface of the specimen and can be separated according to the shape of the inspection object. This example is an example showing that even an inclined crack can be measured with high accuracy.

Next, as a sixth embodiment, the characteristics of the fundamental reflected wave will be described with reference to FIG. FIG. 10 shows Example 1 (41 mm deep parallel cracks) and Example 2 (depth 27 mm).
It is a diagram showing the basic reflected wave of a 4 mm parallel crack), but it can be seen that the waveforms of the two are slightly different. As described above, the fundamental reflected wave is based on the dynamic characteristics of the ultrasonic sensor, and ideally is unique to the ultrasonic sensor. However, in reality, as shown in the example of FIG. There may be some differences depending on the measurement situation, such as differences in the propagation distance inside, and this embodiment shows that it is desirable to obtain the basic reflected wave each time a nondestructive inspection is performed. that's all,
According to the embodiment described in detail, even an unskilled person can easily and easily diagnose the internal state such as a crack of a concrete structure, and a wide range can be obtained only by ultrasonic waves having a center frequency of 30 kHz. It is possible to measure depth cracks and the like, and it is also possible to measure inclined cracks and the like, or cracks having reinforcing bars in the front. Furthermore, the covering of the reinforcing bars can be measured with high accuracy. Although the embodiments of the present invention have been described above, it is obvious that various changes may be made in the form and details without departing from the spirit and scope of the present invention defined in the claims. .

For example, in the embodiments, the analysis process of multiple reflected waves is described in detail for convenience of explanation, but these analyzes are performed by a program incorporated in the computer, and the results of each analysis process or the final Such results can be displayed on the CRT, etc., either sequentially or in response to the inspector's request, and the inspector can set the data window to be used and select the peak to be used when obtaining an approximate solution. It is also possible to carry out the present invention more suitably.

[0055]

According to the present invention, the concrete structure is analyzed by analyzing the difference spectrum between the frequency spectrum of the received signal of the multiple reflected waves and the frequency spectrum of the basic reflected wave based on the dynamic characteristics of the ultrasonic sensor. It is possible to accurately and easily determine the sound wave reciprocating propagation time between the surface such as a crack and the inside crack, and to easily and accurately diagnose the internal state of a crack such as a concrete structure even by an unskilled person. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is a conceptual diagram for explaining a configuration of a nondestructive inspection device using an ultrasonic sensor of the present invention.

FIG. 2 is an explanatory diagram of a test piece used as an inspection object used in an example, and is a layout diagram of pseudo cracks when viewed from the top surface of the test piece.

FIG. 3 is an example of a measured received signal of Example 1 (parallel crack having a depth of 41 mm).

FIG. 4 is a diagram showing an analysis process of Example 1, (a)
Shows the frequency spectrum of the multiple reflected wave obtained by applying MEM to the received signal data of FIG. 3 and the frequency spectrum of the basic reflected wave obtained by the least squares method (displayed by the broken line). These are the negative-region waveforms of these difference spectra (however, the inverted positive display), and (c) is the autocorrelation function of (b).

FIG. 5 is an example of a measured received signal of Example 2 (parallel crack having a depth of 274 mm).

FIG. 6 is a diagram similar to FIG. 4 of the first embodiment, showing the analysis process of the second embodiment.

7 is a third embodiment (depth 490 m) similar to FIG. 4 of the first embodiment.
It is a figure which shows the analysis progress of (parallel crack of m).

8 is the same as FIG. 4 of the first embodiment, the fourth embodiment (depth 153m;
It is a figure which shows the analysis progress of the parallel crack of 310 mm in depth which has a reinforcing bar in m.

FIG. 9 is a diagram showing an analysis process of Example 5 (gradient crack) similar to FIG. 4 of Example 1.

FIG. 10 is a diagram showing fundamental reflected waves of Example 1 (parallel crack with a depth of 41 mm) and Example 2 (parallel crack with a depth of 274 mm).

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Claims (12)

[Claims] 1. A difference spectrum, which is the difference between the frequency spectrum of the received signal of the multiple reflected waves obtained and the frequency spectrum of the basic reflected wave based on the dynamic characteristics of the ultrasonic sensor, is obtained, and the difference spectrum is analyzed. A nondestructive inspection method using an ultrasonic sensor, which is characterized by performing a nondestructive inspection of the internal state of an inspection object by means of. 2. A step of obtaining a frequency spectrum of the multiple reflected wave from a received signal of the multiple reflected wave corresponding to an electric signal input to the ultrasonic sensor, and a frequency of the basic reflected wave based on the dynamic characteristic of the ultrasonic sensor. Between the step of obtaining a spectrum, the step of obtaining a difference spectrum which is the difference between the frequency spectrum of the multiple reflection wave and the frequency spectrum of the basic reflection wave, and the step of obtaining a difference between the inspection object surface and an internal crack or the like from the difference spectrum. A nondestructive inspection method using an ultrasonic sensor according to claim 1, further comprising a step of obtaining a sound wave round-trip propagation time. 3. The ultrasonic sensor according to claim 1, wherein the step of obtaining the frequency spectrum of the multiple reflected waves is a step of obtaining the frequency spectrum of the multiple reflected waves by the maximum entropy method. Non-destructive inspection method used. 4. The basic reflected wave was modeled by including the dynamic characteristics of the ultrasonic sensor as parameters including the natural angular frequency and attenuation coefficient of the transmitter, the natural angular frequency and attenuation coefficient of the receiver, and gain. A fundamental reflected wave represented by using a transfer function, the method including the step of determining the parameter so that a squared error between the frequency spectrum of the multiple reflected wave and the frequency spectrum of the fundamental reflected wave is minimized. A nondestructive inspection method using the ultrasonic sensor according to any one of claims 1 to 3. 5. The difference spectrum is a difference spectrum obtained by subtracting the frequency spectrum of the fundamental reflected wave from the frequency spectrum of the multiple reflected wave, and the step of obtaining the sound wave round-trip propagation time is a negative spectrum of the difference spectrum. The nondestructive inspection method using the ultrasonic sensor according to any one of claims 2 to 4, which is a step including a process of obtaining a second difference spectrum in which only a portion having a value is extracted. 6. The step of obtaining the sound wave round-trip propagation time comprises:
The non-destructive inspection method using the ultrasonic sensor according to claim 2, which is a step including a process of obtaining an autocorrelation function of the difference spectrum or the second difference spectrum. . 7. The step of determining the sound wave round-trip propagation time comprises:
The non-destructive inspection method using an ultrasonic sensor according to claim 6, which is a step including a process of obtaining a sound wave round-trip propagation time between a surface of an inspection object and an internal crack or the like from the autocorrelation function. . 8. The step of obtaining the sound wave round-trip propagation time comprises:
A step including a process of obtaining the repeating frequency from a plurality of extreme point frequencies related to any of the maximum values or the minimum values appearing in the difference spectrum or the second difference spectrum, and setting the repeating frequency as a sound wave reciprocating frequency. The nondestructive inspection method using the ultrasonic sensor according to any one of claims 2 to 7. 9. The repeating frequency is obtained by minimizing an error when the plurality of pole frequencies are approximated by an integral multiple of the repeating frequency.
A nondestructive inspection method using the described ultrasonic sensor. 10. The repeating frequency is obtained by using a plurality of pole frequencies having relatively large spectrum strength among the pole frequencies appearing in the difference spectrum or the second difference spectrum. A nondestructive inspection method using the ultrasonic sensor according to claim 8. 11. The nondestructive inspection method using the ultrasonic sensor according to claim 1, wherein the nondestructive inspection is performed using ultrasonic waves of approximately 30 KHz. 12. A nondestructive inspection apparatus using an ultrasonic sensor, characterized by using the method according to any one of claims 1 to 11.