JP2003106830A - How to measure the length of elastic material - Google Patents

Abstract

(57) [Summary] [Problem] To improve measurement accuracy. SOLUTION: In a measuring method, a pair of probes T, on both sides of a crack B generated in an elastic material A is sandwiched.
R is set, and the propagation time T of the elastic wave propagated between the probes T and R is measured to determine the depth d of the crack. At this time, the distances Lc between the centers of the probes T and R are made different by at least three or more, and the propagation time T is measured for each. And The correction value α of the center-to-center distance Lc between the probes T and R, the propagation velocity v of the elastic wave in the elastic material A, and the depth of the crack B are calculated by the least squares approximation method based on Calculate d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a length such as a depth from a surface of a crack existing in an elastic material such as concrete, and particularly to measuring a propagation time of an elastic wave propagating in the elastic material. The present invention relates to a measuring method for measuring the length of an elastic material such as a crack depth by measuring from the surface side.

[0002]

2. Description of the Related Art As a method for measuring the depth of cracks generated in an elastic material such as concrete, a method utilizing elastic waves such as ultrasonic waves is known. FIG. 8 shows a typical example of a crack depth measuring method for concrete.

In this type of measuring method, the sound area is previously measured.
The cleat's ultrasonic velocity is measured. In this case, the figure
As shown in FIG. 8 (A), a pair of transmitter and receiver probes
Child T _T, T_RWith a center-to-center distance of 2a, on the surface of concrete
Installed on the transmitter T_TReceives ultrasonic waves emitted from
Side probe T_RReceived at, propagation time T₀To measure.

The propagation velocity v in this case is obtained by 2a / T ₀ . Next, as shown in FIG. 8 (B), a pair of probes T _T and T _R are placed on both sides of the crack across the crack, and the propagation time of the ultrasonic pulse diffracted by the crack is set. Measure T _c .

Then, the propagation time T _c is multiplied by the measured propagation velocity v to be converted into an ultrasonic propagation distance, and the equation d = a
From {(T _c / T ₀ ) ² −1} ^0.5 , the crack depth d
Is calculated. However, such a conventional crack depth measuring method has technical problems described below.

[0006]

That is, in the above-described crack depth measuring method, it is necessary to measure the propagation velocity of elastic waves in an elastic material such as concrete in advance. However, there are variations that are not uniform, and accurate measurement of the propagation velocity is difficult, resulting in a large measurement error, and there is a problem to be solved in measurement accuracy.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a method for measuring the length of an elastic material with which high accuracy can be obtained. .

[0008]

In order to achieve the above object, the present invention provides a crack depth existing in an elastic material such as concrete, a reflecting surface existing in the elastic material, and a cavity. In the method of measuring the distance from the surface of the elastic material, or the length L such as the thickness of the elastic material, the center-to-center distance is L at a predetermined distance from the surface of the elastic material to be measured.
When a pair of probes c are installed and the propagation time T of the elastic wave propagated between the probes is measured to calculate the length L, the distance between the centers of the pair of probes is The distance Lc is varied by at least 3 or more, the propagation time T is measured for each,

【formula】 Based on the least square approximation method, the correction value α of the inter-probe distance and the propagation velocity v of the elastic wave in the elastic material,
Also, the length L is obtained.

According to the method of measuring the length of the elastic material having such a structure, unlike the conventional measuring method, the distance Lc between the centers of the probes is at least determined without previously obtaining the propagation velocity of the elastic wave. By measuring three or more different propagation times T, based on the measurement results,

【formula】

As a result, the correction value α of the distance between the probes, the propagation velocity v of the elastic wave in the elastic material, and the length L are calculated by the least-squares approximation method. The crack depth can be determined.

When the length L is the crack depth d existing in the elastic material, the pair of probes are placed on both sides of the crack so as to avoid the crack. Based on the wave, the propagation time T of the elastic wave
The crack depth d can be calculated by measuring

If the length L is the thickness t of the elastic material, the elastic wave propagates in the thickness direction of the elastic material, and based on the reflected wave from the bottom surface of the elastic material,
The thickness t can be calculated by measuring the propagation time T of the elastic wave.

When the length L is the distance d1 from the surface to the reflecting surface or the cavity existing in the elastic material, the elastic wave propagates in the thickness direction of the elastic material, The distance d1 can be calculated by measuring the propagation time T of the elastic wave based on the reflected wave from the reflecting surface or the cavity present therein.

In the present invention, when measuring the propagation time T, it is desirable to confirm that the center-to-center distance Lc of the probe and the propagation time T of the elastic wave are in a substantially proportional relationship.

When the measurement is performed according to such conditions,
Since the correctness of the measurement state can be ensured and clear erroneous measurement can be eliminated, the crack depth can be obtained with even higher accuracy.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Figure 1
Shows a first embodiment of a method for measuring the length of an elastic material according to the present invention.

In the measuring method shown in the figure, the length L to be measured is the depth d of the crack B generated in the elastic material A such as concrete, and when the depth d is calculated. , A pair of probes T and R are installed on the surface of the elastic material A.

The pair of probes T and R are placed with the crack B as the center, sandwiching the probe B at the same intervals on both sides,
The basic configuration is to determine the crack depth d by measuring the propagation time T ₀ of the elastic wave propagated between the probes T and R.

At this time, in the present embodiment, the center-to-center distance Lc of the pair of probes T and R is varied by at least 3 or more, and the propagation time T ₀ is measured for each. And

[Formula 1] Based on the above, the correction value α of the center-to-center distance Lc between the probes T and R, the propagation velocity v of the elastic wave in the elastic material A, and the depth of the crack B are calculated by the least square approximation method. Calculate d.

Here, the center-to-center distance Lc between the probes T and R is
The correction value α of was considered by the following consideration. That is, when the probes T and R are installed on the surface of the elastic material a and the elastic wave is propagated between them, the incident or emission point of the elastic wave is the center point of each of the probes T and R. Rather, it is based on the knowledge that these points are positions displaced by a predetermined distance.

In the measuring method of this embodiment, the elastic material is
A propagation time T of an elastic wave propagating in A ₀Is a broken line in FIG.
As shown, the elastic wave emitted from the probe T on the launch side
Circumvents the tip of the crack B, and
It takes time to reach and diffraction that bypasses the crack B
Based on the wave, the propagation time T of the elastic wave₀To measure
Become.

Furthermore, when measuring the propagation time T _0, probe T, and a propagation time T ₀ of the center-to-center distance Lc and the elastic wave R, and to be sure that the general proportional relationship .

This is because when the depth d of the crack B at the same point is measured, the relationship between the center-to-center distance Lc between the probes T and R and the propagation time T ₀ is as shown in equation 1. Since there is a substantially proportional relationship, this relationship is confirmed during measurement, for example, by plotting it on a graph.

When the propagation time T ₀ is measured by changing the center-to-center distance Lc of the pair of probes T and R in accordance with such conditions, the correctness of the measurement state can be ensured. The crack depth d can be obtained with high accuracy.

According to the method for measuring the crack depth d of the elastic material A having the above-described structure, unlike the conventional measuring method, the probe T, The distance Lc between the centers of R is made different by at least 3 to measure a plurality of propagation times T ₀ , and based on the measurement result,

[Formula 1] As a result, the variables of the inter-probe distance correction value α, the propagation velocity v of the elastic wave in the elastic material, and the crack depth d are calculated by the least-squares approximation method. As described above, the crack depth d can be obtained with high accuracy.

In order to confirm the effectiveness of the present invention, the present inventors set a concrete model as the elastic material A, and even if the distribution of ultrasonic wave propagation velocity is generated inside the concrete member, Whether the invention can be applied, ultrasonic analysis by a two-dimensional finite element difference method was performed to confirm the applicability.

Incidentally, the reason why such a model is set is that
It is known that concrete, which is an elastic material to which the measuring method of the present invention is applied, is not uniform in internal compressive strength when it is used as an actual structure, based on the following reasons.

For example, when concrete with a large amount of bleeding is used, the compressive strength at the upper part of the driven member is lower than that at the lower part, or the concrete dries due to the effect of premature demolding of the formwork, and The compressive strength and elastic modulus may be lower than those of the inside.

Under such circumstances, the elastic wave, that is,
When measuring the propagation velocity of ultrasonic waves and calculating the crack depth, the propagation velocity is partially different, and the effectiveness of the measuring method of the present invention is confirmed even when the propagation velocity is not uniform. It is necessary to do so, and for this purpose, the analysis is performed using the model described below.

In this analysis, assuming that a crack B as shown in FIG. 2 exists in the concrete model,
The crack depth d was determined by applying the measuring method of the present invention.

The concrete model shown in FIG.
It is a two-layer concrete model consisting of b
The layer has a thickness of 50 mm, and the b layer below the layer has a thickness of 150 mm.
It has a thickness.

In this case, the ultrasonic wave propagation velocity of the layer a is set to 405.
0m / sec, ultrasonic wave velocity of layer b is 4400m /
sec, width 1.0m across the a and b layers in the center
A crack B having an m and a depth d of 100 mm was arranged.

The analysis conditions are as shown in FIG.
A sine gaussian pulse wave of 00 kHz was applied, the mesh size was 1 mm in both length and width, and the analysis step was 0.19 μsec pitch.

In FIG. 4, a concrete model specimen shown in FIG. 2 was actually produced, and in this specimen, the value of the center distance Lc between the probes T and R was about 40 to 130 mm.
The graph shows the measurement results when the propagation time is actually measured for each center-to-center distance by changing the distance eight times within the range.

From this measurement result,

[Formula 1] By substituting that value into the equation, a simultaneous equation including the unknown correction value α of the probe distance, the propagation velocity v of the elastic wave in the elastic material, and the crack depth d was obtained. Then, the simultaneous equations were solved by the least-squares approximation method to obtain the approximate values of the variables with respect to the correction value α of the inter-probe distance, the propagation velocity v of the elastic wave in the elastic material, and the crack depth d. However, the correction value α is 37.6 mm and the propagation velocity v of the elastic wave is 43
05m / sec, crack depth d is 104.0mm
Became.

The error of the crack depth d in this case is 4% with respect to the set value, and it is possible to measure the crack depth with high accuracy even if the propagation velocity of ultrasonic waves is distributed inside the concrete. I was able to confirm that

In the above-mentioned analysis, the distance Lc between the centers of the probes T and R is made to differ eight times, and a plurality of propagation times T _{0 are obtained.}
Was measured and the crack depth d was calculated based on this measurement result. However, in the present invention, since the unknowns are three, the crack depth d is calculated if three or more simultaneous equations are obtained. Will be possible.

5 and 6 show a second embodiment of the method for measuring the length of an elastic material according to the present invention. In addition,
In the following description, parts that are the same as or correspond to those in the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted, and only the characteristic points will be described below.

In the measuring method shown in the figure, the length L to be measured is the thickness t of the elastic material A such as concrete, and when calculating this thickness t, it is the same as in the first embodiment. A pair of probes T and R are installed on the surface of the elastic material A.

In this embodiment, as in the first embodiment,
The distance Lc between the centers of the pair of probes T and R is at least 3
By measuring the propagation time T ₁ differently for each of the above,

[Formula 2] Based on the above, the correction value α of the center-to-center distance Lc between the probes T and R, the propagation velocity v of the elastic wave in the elastic material A, and the thickness t are calculated by an approximate calculation by the least squares approximation method. .
The expression 2 is substantially the same as the expression 1 of the first embodiment.

Also in this embodiment, the correction value α of the center distance Lc between the probes T and R is adopted for the same reason as in the first embodiment.

In the measuring method of this embodiment, the elastic material
A propagation time T of an elastic wave propagating in A ₁Is a broken line in FIG.
As shown, the elastic wave emitted from the probe T on the launch side
Propagates in the thickness direction of the elastic material A and is reflected at the bottom surface of
The time it takes for the reflected wave to reach the receiving probe R.
And the propagation time T of the elastic wave based on the reflected wave₁To measure
Will be.

FIG. 6 shows a waveform of an elastic wave received by the probe R when the elastic wave having a predetermined frequency is emitted from the probe T. The reception waveform shown in this figure is a waveform diagram when the crack B shown in the first embodiment exists in the elastic material A.

A pair of probes T and R are arranged on the surface of the elastic material A at a predetermined interval to generate an elastic wave having a predetermined frequency.
When the probe R is fired from the first, a waveform that propagates on the surface of the elastic material A or in the vicinity thereof and reaches the probe R in a short time appears on the probe R on the receiving side.

After that, after a lapse of a predetermined interval T ₀ , a waveform of a diffracted wave that bypasses the crack B appears, and after a predetermined time, a waveform of a reflected wave reflected by the bottom surface of the elastic material A appears. In this embodiment, , The time until the appearance of this waveform is measured as the propagation time T ₁ . Since the received waveform of the reflected wave has a larger amplitude than the waveform of the diffracted wave, it can be easily detected.

Then, from the obtained measured values of the propagation times T ₁ , a plurality of simultaneous equations are obtained according to the equation 2, and the thickness t of the elastic material a is calculated. Also in the case of the present embodiment, it can be confirmed that the distance Lc between the centers of the probes T and R and the propagation time T _{1 of the} elastic wave have the relationship of Expression 1. When the thickness t of the elastic material A is measured in this manner, a highly accurate measured value can be obtained as in the first embodiment.

FIG. 7 shows a third embodiment of the method for measuring the length of an elastic material according to the present invention. In the following description, parts that are the same as or correspond to those in the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted, and only the characteristic points will be described below.

In the measuring method shown in the figure, the length L to be measured is such that the cavity C exists in the elastic material A such as concrete, and the distance d from the surface of the elastic material A to the cavity C is d.
The present invention is applied when measuring 1.

When calculating the distance d1 to the cavity C,
Similar to the first embodiment, a pair of probes T and R are installed on the surface of the elastic material A.

In this embodiment, as in the first embodiment,
The distance Lc between the centers of the pair of probes T and R is at least 3
By measuring the propagation time T ₂ differently for each of the above,

[Formula 3] Based on the above, the correction value α of the center-to-center distance Lc between the probes T and R, the propagation velocity v of the elastic wave in the elastic material A, and the distance d1 are calculated by an approximate calculation by the least-squares approximation method. .
The expression 3 is substantially the same as the expression 1 of the first embodiment.

Also in the case of this embodiment, the correction value α of the center distance Lc between the probes T and R is adopted for the same reason as in the first embodiment.

In the measuring method of this embodiment, the elastic material
A propagation time T of an elastic wave propagating in A _TwoIs a dashed line in Figure 7.
As shown, the elastic wave emitted from the probe T on the launch side
Propagated in the thickness direction of the elastic material A and were reflected by the cavity C
It is the time it takes for the reflected wave to reach the probe R on the receiving side.
And the propagation time T of the elastic wave based on the reflected wave_TwoTo measure
Will be.

The measurement of the propagation time T ₂ is the time until a reflected wave substantially the same as that in the second embodiment appears. Then, from the obtained plurality of measured values of the propagation time T ₂ , a plurality of simultaneous equations are obtained according to Expression 3, and the distance d1 to the cavity C existing in the elastic material A is calculated.

Also in the case of this embodiment, it can be confirmed that the distance Lc between the centers of the probes T and R and the propagation time T _{2 of the} elastic wave have the relation of the expression 1. In this way the cavity C
When the distance d1 to is measured, a highly accurate measurement value can be obtained as in the first embodiment.

In the embodiment shown in FIG. 7, instead of the cavity C, when the elastic wave reflection surface D exists in the elastic material A as shown by the phantom line in FIG. It can also be applied when measuring the distance.

[0055]

As described above in detail, according to the method for measuring the length of the elastic material according to the present invention, the length such as the crack depth and the thickness can be calculated with high accuracy.

[Brief description of drawings]

FIG. 1 is a side view for explaining a propagation time when a method for measuring a length of an elastic material according to the present invention is applied to a crack depth measurement.

FIG. 2 is an explanatory diagram of a concrete model set by an analysis performed to confirm the effect of the present invention.

FIG. 3 is a waveform diagram of ultrasonic waves applied to the concrete model shown in FIG.

FIG. 4 is a measurement result when ultrasonic wave propagation time is measured by the model shown in FIG.

FIG. 5 is a side view for explaining the propagation time when the method for measuring the length of the elastic material according to the present invention is applied to the thickness measurement.

6 is an explanatory diagram of a propagation waveform that appears on the receiving side of the probe shown in FIG.

FIG. 7 is a side view for explaining the propagation time when the method for measuring the length of the elastic material according to the present invention is applied to the measurement of the cavity distance.

FIG. 8 is an explanatory diagram of conventional crack depth measurement.

[Explanation of symbols]

A elastic material B crack T probe R probe L Length in elastic material d crack depth t Elastic material thickness l Distance from surface to cavity

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takayoshi Hirata             4-640 Shimoseido, Kiyose-shi, Tokyo Dai Inc.             Hayashigumi Institute of Technology F term (reference) 2F068 AA06 AA24 AA28 AA48 BB14                       BB26 EE01 FF11 FF12 FF16                       FF25 KK14 QQ34                 2G047 AA08 AA10 BA03 BB02 BC08                       BC18 EA10 GA14 GA15 GG30

Claims (5)

[Claims] 1. A crack depth existing in an elastic material such as concrete, a reflecting surface existing in the elastic material, a distance from a surface to a cavity, or a length such as a thickness of the elastic material. In the method of measuring L, a pair of probes having a center-to-center distance of Lc are installed on a surface of an elastic material to be measured with a predetermined interval, and a propagation time T of an elastic wave propagated between the probes is set. To calculate the length L, the center-to-center distance Lc of the pair of probes is varied by at least 3 or more, and the propagation time T is measured for each of: Based on the least square approximation method, the correction value α of the inter-probe distance, the propagation velocity v of the elastic wave in the elastic material, and the length L of the elastic material are obtained. How to measure length. 2. The length L is a crack depth d existing in the elastic material, and the pair of probes are placed on both sides of the crack so as to bypass the crack. The method for measuring the length of an elastic material according to claim 1, wherein the propagation time T of the elastic wave is measured based on the wave. 3. The length L is a thickness t of the elastic material, and the elastic wave propagates in a thickness direction of the elastic material, and the elastic wave is generated based on a reflected wave from a bottom surface of the elastic material. The method for measuring the length of an elastic material according to claim 1, wherein the propagation time T of the wave is measured. 4. The length L is a distance d1 from a surface to a reflecting surface or a cavity existing in the elastic material, and the elastic wave propagates in a thickness direction of the elastic material, The method for measuring the length of an elastic material according to claim 1, wherein the propagation time T of the elastic wave is measured based on the reflected wave from the reflection surface or the cavity present therein. 5. When measuring the propagation time T, it is confirmed that the center-to-center distance Lc of the probe and the propagation time T of the elastic wave are in a substantially proportional relationship. 4. The method for measuring the length of the elastic material according to any one of 1 to 3.