CN113092591A - Method for extracting acoustic emission dominant frequency of rock under uniaxial heating condition - Google Patents
Method for extracting acoustic emission dominant frequency of rock under uniaxial heating condition Download PDFInfo
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- CN113092591A CN113092591A CN202110273267.8A CN202110273267A CN113092591A CN 113092591 A CN113092591 A CN 113092591A CN 202110273267 A CN202110273267 A CN 202110273267A CN 113092591 A CN113092591 A CN 113092591A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/14—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object using acoustic emission techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
- G01N29/46—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by spectral analysis, e.g. Fourier analysis or wavelet analysis
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/023—Solids
- G01N2291/0232—Glass, ceramics, concrete or stone
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/028—Material parameters
- G01N2291/0289—Internal structure, e.g. defects, grain size, texture
Abstract
The invention provides a method for extracting acoustic emission dominant frequency of a rock under a uniaxial heating condition, and relates to the technical field of rock mechanical tests. The method comprises the following steps: preparing a cylindrical rock test piece, attaching an acoustic emission sensor on the test piece, heating the rock test piece by using a rock unidirectional heating test device, receiving an acoustic emission signal in the rock test piece by using the acoustic emission sensor, and monitoring a cracking process; carrying out fast Fourier transform on the acoustic emission signal to obtain a two-dimensional spectrogram, and determining the acoustic emission dominant frequency; collecting acoustic emission waveform signals of the sample at a constant temperature, carrying out Fourier transform on the waveform to obtain main frequency information at each moment, drawing a temperature, main frequency and time relation graph, and determining the damage characteristic of the rock. The method also has the advantages of simple and convenient operation, accurate data and the like, and provides convenience for the research of the temperature distribution and the heat damage characteristics of the rock mass.
Description
Technical Field
The invention relates to the technical field of rock mechanics tests, in particular to a method for extracting acoustic emission dominant frequency of a rock under a uniaxial heating condition.
Background
In industries such as nuclear waste storage, geothermal utilization, underground coal gasification and the like, a high-temperature heat source exists, surrounding rock masses are generally in a one-way heating state in the environment, the high temperature can generate heat damage to the rock masses, the temperature distribution, the heat damage characteristic and the like of the rock masses can also present a one-way distribution rule, and the acquisition of the heat fracture rule characteristic of the rock masses has great significance for researching the stability, the air tightness and the like of the rock masses.
In the prior art, the research on the thermal damage of the rock mass usually comprises the steps of putting the whole test piece into a heating furnace for programmed heating or constant-temperature heating, and then researching the thermal damage characteristic of the test piece, wherein the heating mode ignores the real heating state of the rock; meanwhile, the development conditions and rules of cracks, pores and the like in the rock in the thermal damage process cannot be obtained by performing later analysis on the thermally treated rock. Acoustic Emission (AE) is a technique for non-destructive testing of materials or components by receiving ultrasonic information generated by internal cracking or friction of the material or component during the application of force or heat.
In order to continuously observe the dynamic evolution of micro-fractures in rock materials, so that the research on thermal damage of the rock provides accurate data, further improvement on the existing research method is needed.
Disclosure of Invention
In order to simulate the one-way heating state of the rock and accurately obtain the change rule of the microscopic fracture of the rock in the heating process, the invention provides a method for extracting the acoustic emission dominant frequency of the rock under the condition of a single-axis heating, and the specific technical scheme is as follows.
A method for extracting acoustic emission dominant frequencies of rock under uniaxial heating conditions comprises the following steps:
s1, preparing a cylindrical rock test piece;
s2, pasting an acoustic emission sensor on the rock test piece;
s3, heating the rock test piece by using a rock unidirectional heating test device, receiving an acoustic emission signal in the rock test piece by using an acoustic emission sensor, and synchronously monitoring the cracking process of the rock test piece;
s4, performing fast Fourier transform on the acoustic emission signal to obtain a two-dimensional spectrogram, and determining the frequency corresponding to the maximum amplitude in the two-dimensional spectrogram as an acoustic emission dominant frequency;
s5, collecting all acoustic emission waveform signals of the rock test piece under a fixed temperature heating condition, carrying out Fourier transform on all waveforms to obtain main frequency information at each moment, drawing a relation graph of temperature, main frequency and time, and determining the damage characteristic of the rock.
Preferably, the rock unidirectional heating test device comprises an upper cushion block, a loading device, a heating device, thermocouples, a signal receiver and a sound emission detector, wherein the rock test piece is placed below the upper cushion block, the loading device loads the rock test piece through the upper cushion block, the thermocouples are connected with the signal receiver, the sound emission detector is connected with a sound emission sensor, and the sound emission sensor is fixedly connected to the rock test piece.
Preferably, the acoustic emission sensor is fixed on the upper part of the rock test piece through a coupling agent, and the acoustic emission detector is connected with a computer.
Preferably, a plurality of rock test pieces are manufactured, and each rock test piece is used for testing; vaseline is coated between the rock test piece and the acoustic emission sensor.
Further preferably, the rock test piece is heated for 2 hours under the condition of fixed temperature, the acoustic emission sensor adopts a resonant high-sensitivity sensor, and the working frequency is 35-100 kHz.
More preferably, the heating part of the heating device uses a nickel-chromium alloy heating pipe, and the nickel-chromium alloy heating pipe is inserted into the hastelloy heating plate, and the maximum heating temperature is 1100 ℃.
It is further preferred that the processing of the acoustic emission signal uses MATLAB software.
The method for extracting the acoustic emission dominant frequency of the rock under the uniaxial heating condition has the beneficial effects that:
(1) the method utilizes the acoustic emission sensor to receive acoustic emission signals generated by internal damage of the rock test piece, and adopts the acoustic emission monitoring system to synchronously monitor the cracking process of the test piece in real time in the unidirectional heating process.
(2) In the method, the received acoustic emission signals can be subjected to fast Fourier transform to obtain a two-dimensional spectrogram; collecting all acoustic emission waveform signals of the whole process from the beginning to the end of heating of the test piece, carrying out Fourier transform on all waveforms to obtain main frequency information at different moments, drawing a relation curve of temperature, main frequency and time, and providing accurate data for the research of the thermal damage of the rock; the method also has the advantages of simplicity, high efficiency, accurate data and the like.
Drawings
FIG. 1 is a schematic diagram of the steps of a method for acoustic emission dominant frequency extraction of rock under uniaxial heating conditions;
FIG. 2 is a schematic diagram of the composition of a rock unidirectional heating test device;
FIG. 3 is a schematic view of an arrangement of acoustic emission sensors;
FIG. 4 is a graph of an original acoustic emission waveform signal in a dominant frequency extraction process plot of an acoustic emission signal;
FIG. 5 is a two-dimensional spectrogram of a waveform signal after a fast Fourier transform from an original acoustic emission waveform signal plot;
FIG. 6 is a graph of sandstone thermal stress, dominant frequency and time under the condition of unidirectional heating at 200 ℃;
FIG. 7 is a graph of sandstone thermal stress, dominant frequency and time under the condition of unidirectional heating at 300 ℃;
FIG. 8 is a graph of sandstone thermal stress, dominant frequency and time under the condition of unidirectional heating at 400 ℃;
FIG. 9 is a graph of sandstone thermal stress, dominant frequency and time under the condition of unidirectional heating at 500 ℃;
FIG. 10 is a graph of sandstone thermal stress, dominant frequency and time under the condition of unidirectional heating at 600 ℃;
in the figure: 1, arranging a cushion block; 2-a rock test piece; 3-a coupling agent; 4-an acoustic emission sensor; 5-a loading device; 6-a thermocouple; 7-a signal receiver; 8-a computer; 9-a heating device; 10-acoustic emission detector.
Detailed Description
The method for extracting the acoustic emission main frequency of the rock under the uniaxial heating condition provided by the invention is described by combining with the method shown in fig. 1 to 10.
Example 1
Because the traditional heating treatment mode of the rock test piece is to put the whole rock test piece into a heating furnace for temperature programming or constant temperature heating, and then to research the heat damage characteristic of the test piece, the whole heating mode of the rock is not suitable for simulating the real state of the one-way heating of the rock in industries such as nuclear waste storage, geothermal research, underground coal gasification and the like. In addition, in the existing research method, a heated rock test piece is generally analyzed, and the change rule of micro-fracture in the rock in the heating process cannot be accurately obtained, so that the research on the thermal fracture mechanism of the rock subjected to unidirectional heating is incomplete.
Therefore, the method for extracting the acoustic emission dominant frequency of the rock under the uniaxial heating condition comprises the following specific steps:
s1, preparing a cylindrical rock test piece 2.
A plurality of rock test pieces 2 can be manufactured, and each rock test piece 2 is used for testing; of course, standard rock test pieces of other shapes can be made according to the test requirements.
S2, an acoustic emission sensor 4 is attached to the rock test piece 2. Vaseline is smeared between the rock test piece 2 and the acoustic emission sensor 4, and the acoustic emission sensor 4 is fixed on the upper part of the rock test piece 2 through a coupling agent, so that the whole rock test piece 2 can be better monitored.
Because the acoustic emission waveform carries all information such as rock thermal stress, structure, physical and mechanical properties and the like, the rock thermal damage mechanism can be better known by analyzing the spectrum information, and thus the microscopic mechanism of deformation and damage of the rock which is heated in a single direction in a special industry can be researched.
S3, heating the rock test piece 2 by using the rock unidirectional heating test device, receiving an acoustic emission signal inside the rock test piece by using the acoustic emission sensor 4, and synchronously monitoring the cracking process of the rock test piece 2.
The rock unidirectional heating test device comprises an upper cushion block 1, a loading device 5, a heating device 9, a thermocouple 6, a signal receiver 7, an acoustic emission detector 10 and the like, a rock test piece 2 is placed below the upper cushion block 1, the loading device 5 loads the rock test piece through the upper cushion block, and the heating device 9 is arranged below the rock test piece. A plurality of thermocouples are connected to the signal receiver so that changes in the temperature of the rock specimen can be monitored. The acoustic emission detector 10 is connected with the acoustic emission sensor 4, the acoustic emission sensor 4 is fixedly connected to the rock test piece 2, and the rock test piece is monitored in real time by the acoustic emission detector 10. The acoustic emission sensor 4 is fixed on the upper part of the rock test piece through a coupling agent, and the acoustic emission detector 10 is connected with the computer 8; the coupling agent 3 is aqueous polymer gel, the pH value of the coupling agent is neutral, and the coupling agent is non-toxic, harmless, not easy to dry and rancid, clear in ultrasonic development, proper in viscosity and free of greasy property. The heating part of the heating device 5 uses a nickel-chromium alloy heating pipe and is inserted into the Hastelloy heating plate, the heating part can be prevented from being damaged by pressure, the Hastelloy has good oxidation resistance, comprehensive mechanical property and tissue stability, the highest heating temperature is 1100 ℃, and the heating device is enough for simulating the unidirectional heating state of the lower surface of the rock.
The rock test piece 2 is heated for 2 hours under the condition of fixed temperature, the fixed temperature can be 200 ℃, 300 ℃, 400 ℃, 500 ℃, 600 ℃, 1000 ℃ and the like, the specific temperature can be selected according to the test requirement, the acoustic emission sensor 4 adopts a resonant high-sensitivity sensor, and the working frequency is 35-100 kHz.
And S4, performing fast Fourier transform on the acoustic emission signal to obtain a two-dimensional spectrogram, and determining the frequency corresponding to the maximum amplitude in the two-dimensional spectrogram as the acoustic emission dominant frequency. The acoustic emission signal was processed using MATLAB software.
S5, collecting all acoustic emission waveform signals of the rock test piece under a fixed temperature heating condition, carrying out Fourier transform on all waveforms to obtain main frequency information at each moment, drawing a relation graph of temperature, main frequency and time, and determining the damage characteristic of the rock.
A two-dimensional spectrogram can be obtained by performing fast Fourier transform on the received acoustic emission signals; the method has the advantages that all acoustic emission waveform signals of the whole process from the beginning to the end of heating of the test piece are collected, Fourier transform is carried out on all waveforms, main frequency information at different moments is obtained, a relation curve of temperature, main frequency and time is drawn, accurate data are provided for research of rock thermal damage, and the method is simple, efficient, accurate in data and the like.
Example 2
On the basis of the example 1, a method for extracting the acoustic emission dominant frequency of the rock under the uniaxial heating condition provided by the invention is described by taking a specific test as an example.
Step 1: the rock to be tested is prepared into standard rock test pieces, cylinders with the size of phi 50mm multiplied by 100mm, and the standard rock test pieces are numbered respectively.
Step 2: as shown in fig. 3, the acoustic emission sensor is fixed and the test piece is placed.
And (3) placing the test piece in a rock unidirectional heating experimental device, and installing an acoustic emission probe at the top of the rock test piece.
During the experiment, a couplant is coated between the acoustic emission probe and the rock test piece, so that the coupling property of the acoustic emission probe and the rock test piece is enhanced, and the attenuation of acoustic emission signals is reduced. The acoustic emission probe is connected with an acoustic emission detector through a line, and the acoustic emission detector is connected with a computer.
And step 3: and heating the rock test piece by adopting a rock unidirectional heating test device, and collecting acoustic emission signals of the whole heating process of the rock test piece.
The rock one-way heating test device that adopts in the experiment specifically is, and the device can realize heating standard rock test piece lower terminal surface constant temperature, and the heating portion adopts Cr20Ni80 nichrome heating tube, interpolates in the hastelloy heating plate, can prevent that the piece that generates heat from the compression destruction. The Hastelloy heating plate is made of Hastelloy188 high-temperature-resistant alloy, the service temperature of the alloy is high and can reach 1100 ℃, and the Hastelloy heating plate has good oxidation resistance, comprehensive mechanical property and structural stability. The test device can simulate the one-way heated state of the lower surface of the rock.
And 4, step 4: and extracting the dominant frequency of the acoustic emission signal based on an acoustic emission frequency spectrum analysis system compiled by a Matlab platform. The acoustic emission waveform of the sandstone test piece at 400 ℃ is taken as an example to explain the dominant frequency extraction process of the acoustic emission signal. And compiling an acoustic emission frequency spectrum analysis system based on the matlab platform, and extracting an original acoustic emission signal. And performing Fast Fourier Transform (FFT) on the waveform signal to obtain a two-dimensional spectrogram. The dominant frequency is defined as the frequency corresponding to the maximum amplitude in the two-dimensional spectrogram, and the dominant frequency is 24.42kHz by observing the two-dimensional spectrogram of the waveform.
And 5: as shown in fig. 6 to 10, all acoustic emission signals in the thermal damage process of the rock are subjected to fast fourier transform, and thermal stress, dominant frequency and time curves of the whole thermal damage process of the rock specimen at 200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃ respectively are drawn.
According to the test result, all acoustic emission waveform signals of the sample in the thermal damage process are selected, fast Fourier transform is carried out on all waveforms, main frequency information at different moments is obtained, a relation curve of thermal stress, main frequency and time is drawn, and the characteristic of rock uniaxial thermal damage is described by using the main frequency.
According to the method, the dominant frequency of the acoustic emission signal is obtained by using a fast Fourier transform method, the acoustic emission frequency domain change characteristics in the rock thermal damage process are further disclosed, and convenience is provided for analyzing the rock fracture process from the frequency spectrum angle.
It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make modifications, alterations, additions or substitutions within the spirit and scope of the present invention.
Claims (7)
1. A method for extracting acoustic emission dominant frequency of a rock under a uniaxial heating condition is characterized by comprising the following steps:
s1, preparing a cylindrical rock test piece;
s2, pasting an acoustic emission sensor on the rock test piece;
s3, heating the rock test piece by using a rock unidirectional heating test device, receiving an acoustic emission signal in the rock test piece by using an acoustic emission sensor, and synchronously monitoring the cracking process of the rock test piece;
s4, performing fast Fourier transform on the acoustic emission signal to obtain a two-dimensional spectrogram, and determining the frequency corresponding to the maximum amplitude in the two-dimensional spectrogram as an acoustic emission dominant frequency;
s5, collecting all acoustic emission waveform signals of the rock test piece under a fixed temperature heating condition, carrying out Fourier transform on all waveforms to obtain main frequency information at each moment, drawing a relation graph of temperature, main frequency and time, and determining the damage characteristic of the rock.
2. The method for extracting acoustic emission dominant frequency of the rock under the uniaxial heating condition of claim 1, wherein the rock unidirectional heating test device comprises an upper cushion block, a loading device, a heating device, thermocouples, a signal receiver and an acoustic emission detector, the rock test piece is placed below the upper cushion block, the loading device loads the rock test piece through the upper cushion block, the thermocouples are connected with the signal receiver, the acoustic emission detector is connected with the acoustic emission sensor, and the acoustic emission sensor is fixedly connected to the rock test piece.
3. The method for extracting acoustic emission dominant frequency of rock under uniaxial heating condition of claim 2, wherein the acoustic emission sensor is fixed on the upper part of the rock test piece through a coupling agent, and the acoustic emission detector is connected with a computer.
4. The method for extracting the acoustic emission dominant frequency of the rock under the uniaxial heating condition of claim 2, wherein a plurality of rock test pieces are manufactured, and each rock test piece is used for testing; vaseline is coated between the rock test piece and the acoustic emission sensor.
5. The method for extracting acoustic emission dominant frequency of rock under uniaxial heating condition of claim 3 or 4, characterized in that the rock specimen is heated for 2 hours under fixed temperature condition, the acoustic emission sensor is a resonance type high sensitivity sensor, and the working frequency is 35-100 kHz.
6. The method for extracting acoustic emission dominant frequency of rock under uniaxial heating condition of claim 3 or 4, wherein the heating part of the heating device uses a nickel-chromium alloy heating tube and is inserted into a Hastelloy heating plate, and the maximum heating temperature is 1100 ℃.
7. A method for acoustic emission dominant frequency extraction of rock under uniaxial heating conditions according to claim 3 or 4, characterized in that the acoustic emission signal is processed using MATLAB software.
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