CN111965651B - Method for testing plate thickness - Google Patents

Method for testing plate thickness Download PDF

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CN111965651B
CN111965651B CN202010783247.0A CN202010783247A CN111965651B CN 111965651 B CN111965651 B CN 111965651B CN 202010783247 A CN202010783247 A CN 202010783247A CN 111965651 B CN111965651 B CN 111965651B
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胡新发
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only

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  • Radar, Positioning & Navigation (AREA)
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  • Acoustics & Sound (AREA)
  • Computer Networks & Wireless Communication (AREA)
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  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
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Abstract

The invention discloses a method for testing plate thickness, which is characterized in that compression waves, shear waves and Rayleigh waves which are transmitted to the periphery are generated in stress waves excited by initial excitation, the Rayleigh waves occupy most of energy, the shear waves are second, the energy carried by the compression waves is minimum, the energy is attenuated in the process that all the waves are transmitted to the periphery at different speeds by taking an excitation point as a circle center, but the attenuation rate is the slowest with the Rayleigh waves, and because the energy of echo signals of the compression waves after being reflected by the bottom of a plate is very small, the influence of stimulated signaling is avoided. In order to avoid the influence of different wave velocities of compression waves of different concrete plates on a detection result due to different matching ratios, strengths, ages and the like, avoid the influence of different wave velocities of the compression waves on the detection result due to different plate sizes and different compression wave wavelengths and reduce the error of the detection result, the invention provides a method for measuring the plate thickness independent of the wave velocities of the compression waves of the plates.

Description

Method for testing plate thickness
Technical Field
The invention relates to the technical field of concrete plate thickness testing, in particular to a method for testing plate thickness.
Background
Concrete slabs, slabs made of reinforced concrete materials, are basic components in house buildings and various engineering structures, are commonly used as roof covers, floor systems, platforms, walls, retaining walls, foundations, terraces, pavements, pools and the like, have extremely wide application range, are divided into square slabs, circular slabs and special-shaped slabs according to planar shapes, are divided into unidirectional slabs and bidirectional slabs according to the stress action mode of the structure, are most commonly provided with the unidirectional slabs, the four-side supported bidirectional slabs and beamless flat slabs supported by columns, and need to be subjected to thickness detection before the completion of the engineering acceptance of the concrete slabs.
The invention provides a method for separating an excitation signal from an echo signal in a time domain and a method for measuring the plate thickness irrelevant to the compression wave velocity of a plate, aiming at the problems that the thickness of the structure such as the concrete plate is thin, the excitation signal and the echo signal are often interwoven together and cannot be separated in the time domain, the echo signal is separated by using a frequency spectrum analysis means such as FFT (fast Fourier transform algorithm), the effect is not ideal generally, the compression wave velocity of the concrete is preset according to experience, but the wave velocities of different concretes are not constant values, and the error caused by the fixed value is large.
In order to solve the problems, innovative design based on the original method for testing the thickness of the plate is urgently needed.
Disclosure of Invention
The invention solves the problems that the concrete slab and other structures are thin in thickness, excitation signals and echo signals of an acoustic echo method are often interwoven together and cannot be separated in a time domain, the echo signals are separated by means of frequency spectrum analysis means such as FFT (fast Fourier transform algorithm) and the like, but the effect is not ideal generally, the compression wave velocity of the concrete is preset according to experience, but the wave velocities of different concretes are not constant, and the error is large.
In order to solve the above technical problems, the present invention provides a method for measuring a sheet thickness, wherein a compression wave, a shear wave and a rayleigh wave are generated in a stress wave excited by an initial excitation, the rayleigh wave occupies most of energy, the shear wave has the lowest energy, the energy carried by the compression wave is the smallest, the energy is attenuated when each wave is transmitted to the periphery at different speeds with the excitation point as a center, but the attenuation rate is the slowest with the rayleigh wave, and the propagation speeds of the compression wave (P wave), the shear wave (S wave) and the rayleigh wave (R wave) are respectively:
velocity of compressional wave
Figure BDA0002620978840000021
Shear wave velocity
Figure BDA0002620978840000022
Wave velocity of Rayleigh wave
Figure BDA0002620978840000023
Wherein E-is the modulus of elasticity of the concrete;
g-shear modulus of concrete;
mu-Poisson's ratio of concrete, generally 0.2;
rho-mass density of the concrete,
the wave velocity is related to cP＞cS＞cR，
Because the excitation energy occupied by the compression wave is very small, the longitudinal motion speed of the particle is mainly influenced by the shear wave and Rayleigh waveWithout loss of generality, the excitation point and the receiving point are positioned on the same side of the board, in order to make the receiving point R1Firstly, receiving an echo signal of a P wave reflected by a plate bottom, and then receiving an S wave signal propagated along a surface, wherein the following steps are required:
Figure BDA0002620978840000024
where a-is the excitation point and the reception point R1The distance of (d);
h is the thickness of the plate,
and then have
Figure BDA0002620978840000031
The Poisson's ratio of concrete can be generally 0.2, but various special concretes are continuously emerged at present, and the Poisson's ratio of concrete is 0.10-0.30 calculated according to the formula (1) and the formula (2) in conclusion of previous researches
Figure BDA0002620978840000032
Is between 0.535 and 0.667, formula (5) can be simplified as:
a＞1.8h (6)
for plates of other media, which typically have a Poisson ratio greater than 0.1, the above formula is also applicable,
from the equation (6), it can be seen that, as long as the distance between the excitation point and the receiving point is greater than 1.8 times the plate thickness, the receiving point receives the P-wave echo signal first, and separates the P-wave echo signal from the excitation signal, and for a material with a known poisson's ratio, for example, a steel plate with a poisson ratio of 0.25, according to the above calculation, the distance between the excitation point and the receiving point is greater than 1.5 times the plate thickness,
solves the problem of separating the excitation signal from the echo signal in the time domain, provides a method for testing the thickness of the plate,
excitation point and 1# receiving point R1A distance from the 2# reception point R2Has a distance of ka, k > 1, of
Figure BDA0002620978840000033
Figure BDA0002620978840000034
In the formula, t1、t2Respectively receiving points R1、R2The travel time of the echo signal of the P wave reflected by the bottom of the plate is received,
is represented by the formulae (7) and (8)
Figure BDA0002620978840000035
Further comprise
4(t2 2-t1 2)h2＝(k2t1 2-t2 2)a2 (10)
Let λ be t2/t1Is provided with
Figure BDA0002620978840000041
It can be seen from equation (11) that the plate thickness h is only related to the receiving-transmitting distance ratio k and the ratio λ of the travel time of the two compression waves, and is not related to the wave velocity, so that the influence of different wave velocities of compression waves of different concrete plates on the detection result due to different matching ratios, strengths, ages and the like is avoided, and the influence of different wave velocities of compression waves on the detection result due to different plate sizes and compression wave wavelengths is also avoided.
Has the advantages that: the method for testing the plate thickness avoids the influence of different wave velocities of the compression waves of different concrete plates on the detection result due to different matching ratios, strengths, ages and the like, also avoids the influence of different wave velocities of the compression waves on the detection result due to different plate sizes and compression wave wavelengths, improves the accuracy of the plate thickness test, and reduces the error of the detection result.
Detailed Description
The present invention will be further illustrated below with reference to specific embodiments, which are to be understood as merely illustrative and not limitative of the scope of the present invention.
A method for testing plate thickness is disclosed, wherein compression waves, shear waves and Rayleigh waves which propagate to the periphery are generated in stress waves excited by initial excitation, the Rayleigh waves occupy most of energy, the shear waves are the second order, the energy carried by the compression waves is the smallest, the energy is attenuated when each wave is transmitted to the periphery at different speeds by taking an excitation point as a circle center, but the attenuation rate is the slowest by the Rayleigh waves, and the propagation speeds of the compression waves (P waves), the shear waves (S waves) and the Rayleigh waves (R waves) are respectively as follows:
velocity of compressional wave
Figure BDA0002620978840000042
Shear wave velocity
Figure BDA0002620978840000043
Wave velocity of Rayleigh wave
Figure BDA0002620978840000051
Wherein E-is the modulus of elasticity of the concrete;
g-shear modulus of concrete;
mu-Poisson's ratio of concrete, generally 0.2;
rho-mass density of the concrete,
the wave velocity is related to cP＞cS＞cR，
Because the excitation energy occupied by the compression wave is very small, the longitudinal motion speed of the particle is mainly influenced by the shear wave and Rayleigh wave, the generality is not lost, and the excitation point and the receiving point are positioned on the same plane of the plateIn order to receive the point R1Firstly, receiving an echo signal of a P wave reflected by a plate bottom, and then receiving an S wave signal propagated along a surface, wherein the following steps are required:
Figure BDA0002620978840000052
where a-is the excitation point and the reception point R1The distance of (d);
h is the thickness of the plate,
and then have
Figure BDA0002620978840000053
The Poisson's ratio of concrete can be generally 0.2, but various special concretes are continuously emerged at present, and the Poisson's ratio of concrete is 0.10-0.30 calculated according to the formula (1) and the formula (2) in conclusion of previous researches
Figure BDA0002620978840000054
Is between 0.535 and 0.667, formula (5) can be simplified as:
a＞1.8h (6)
for plates of other media, which typically have a Poisson ratio greater than 0.1, the above formula is also applicable,
from the equation (6), it can be seen that, as long as the distance between the excitation point and the receiving point is greater than 1.8 times the plate thickness, the receiving point receives the P-wave echo signal first, and separates the P-wave echo signal from the excitation signal, and for a material with a known poisson's ratio, for example, a steel plate with a poisson ratio of 0.25, according to the above calculation method, the distance between the excitation point and the receiving point is greater than 1.5 times the plate thickness,
solves the problem of separating the excitation signal from the echo signal in the time domain, provides a method for testing the thickness of the plate,
excitation point and 1# receiving point R1A distance from the 2# reception point R2Has a distance of ka, k > 1, of
Figure BDA0002620978840000061
Figure BDA0002620978840000062
In the formula, t1、t2Respectively receiving points R1、R2The travel time of the echo signal of the P wave reflected by the bottom of the plate is received,
is represented by the formulae (7) and (8)
Figure BDA0002620978840000063
Further comprise
4(t2 2-t1 2)h2＝(k2t1 2-t2 2)a2 (10)
Let λ be t2/t1Is provided with
Figure BDA0002620978840000064
From the formula (11), the plate thickness h is only related to the receiving-transmitting distance ratio k and the ratio lambda of the travel time of the two compression waves, and is not related to the wave velocity, so that the influence of different compression wave velocities of different concrete plates on the detection result due to different matching ratios, strengths, ages and other factors is avoided, and the influence of different compression wave velocities on the detection result due to different plate sizes and compression wave wavelengths is also avoided.
The method for testing the plate thickness has the following advantages:
the method for testing the plate thickness avoids the influence of different wave velocities of the compression waves of different concrete plates on the detection result due to different matching ratios, strengths, ages and the like, also avoids the influence of different wave velocities of the compression waves on the detection result due to different plate sizes and compression wave wavelengths, improves the accuracy of the plate thickness test, and reduces the error of the detection result.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (1)

1. A method of testing sheet thickness, characterized by: in the stress wave excited by the initial excitation, compression wave, shear wave and Rayleigh wave which propagate to the periphery are generated, the Rayleigh wave occupies most energy, the shear wave is the second time, the energy carried by the compression wave is the minimum, in the process that all the waves are transmitted to the periphery at different speeds by taking an excitation point as the center of a circle, the energy is attenuated, but the attenuation rate is the slowest by the Rayleigh wave, the compression wave is marked as P wave, the shear wave is marked as S wave and the Rayleigh wave is marked as R wave, and the propagation speeds are respectively:
velocity of compressional wave
Figure DEST_PATH_IMAGE002
（1）
Shear wave velocity
Figure DEST_PATH_IMAGE004
（2）
Wave velocity of Rayleigh wave
Figure DEST_PATH_IMAGE006
（3）
In the formula (I), the compound is shown in the specification,
Figure DEST_PATH_IMAGE008
-is the modulus of elasticity of the concrete;
Figure DEST_PATH_IMAGE010
-shear modulus of the concrete;
Figure DEST_PATH_IMAGE012
-poisson's ratio of concrete;
Figure DEST_PATH_IMAGE014
-the mass density of the concrete,
the wave velocity relationship is as follows:
Figure DEST_PATH_IMAGE016
，
because the excitation energy occupied by the compression wave is very small, the longitudinal motion speed of the particle is mainly influenced by the shear wave and Rayleigh wave, the excitation point and the receiving point are positioned at the same side of the plate, and in order to ensure that the receiving point R is positioned at the same side of the plate1Firstly, receiving an echo signal of a P wave reflected by a plate bottom, and then receiving an S wave signal propagated along a surface, wherein the following steps are required:
Figure DEST_PATH_IMAGE018
(4)
in the formula (I), the compound is shown in the specification,
Figure DEST_PATH_IMAGE020
for the excitation point and the reception point R1The distance of (d);
Figure DEST_PATH_IMAGE022
-the thickness of the sheet is taken as the sheet,
and then have
Figure DEST_PATH_IMAGE024
(5)
The Poisson's ratio of the concrete is between 010 to 0.30, calculated according to the formulae (1) and (2)
Figure DEST_PATH_IMAGE026
Between 0.535 and 0.667, formula (5) is simplified as:
Figure DEST_PATH_IMAGE028
（6）
as can be seen from equation (6), as long as the distance between the excitation point and the receiving point is greater than 1.8 times of the plate thickness, the receiving point receives the P wave echo signal first, so that the P wave echo signal is separated from the excitation signal,
excitation point and 1# receiving point R1A distance of
Figure 410748DEST_PATH_IMAGE020
And 2# reception point R2A distance of
Figure DEST_PATH_IMAGE030
Is provided with
Figure DEST_PATH_IMAGE032
(7)
Figure DEST_PATH_IMAGE034
(8)
In the formula (I), the compound is shown in the specification,
Figure DEST_PATH_IMAGE036
、
Figure DEST_PATH_IMAGE038
respectively receiving points R1、R2The travel time of the echo signal of the P wave reflected by the bottom of the plate is received,
is represented by the formulae (7) and (8)
Figure DEST_PATH_IMAGE040
(9)
Further comprise
Figure DEST_PATH_IMAGE042
（10）
Order to
Figure DEST_PATH_IMAGE044
Is provided with
Figure DEST_PATH_IMAGE046
(11)
As can be seen from the formula (11), the sheet thickness
Figure 888740DEST_PATH_IMAGE022
Ratio of transmitting-receiving distance only
Figure DEST_PATH_IMAGE048
And the ratio of travel time of two compression waves
Figure DEST_PATH_IMAGE050
The method is independent of the wave velocity, so that the influence of different compression wave velocities of different concrete plates on the detection result due to different factors such as mixing proportion, strength and age is avoided, and the influence of different compression wave velocities on the detection result due to different plate sizes and compression wave wavelengths is also avoided.
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