CN105403623A - Extraction method for sound emission main frequency of rock under single-axis compression condition - Google Patents

Abstract

The invention belongs to the field of acoustic emission detection, and relates to a method for extracting the main frequency of acoustic emission of rocks under the condition of uniaxial compression. The rock is prepared as a cuboid sample; the acoustic emission sensor is attached to the prepared cuboid sample; the rock mechanics testing machine is used to apply load to the sample, and the acoustic emission sensor is used to receive the acoustic emission signal generated by the internal damage of the sample. The test process The acoustic emission monitoring system is used to monitor the rupture process of the sample in real time and synchronously; the fast Fourier transform is performed on the acoustic emission signal received in the step to obtain a two-dimensional spectrogram; all the acoustic emission waveform signals of the sample from loading to destruction are collected , perform Fourier transform on all waveforms to obtain main frequency information at different times, and draw the relationship curve between load, main frequency and time. The invention uses fast Fourier transform to extract the main frequency of the acoustic emission signal, which is simple, efficient and easy to popularize; it can obtain all-round main frequency information of the rock catastrophe process.

Description

Acoustic emission main frequency extraction method of rock under uniaxial compression

technical field

The invention belongs to the field of acoustic emission detection, and relates to a method for extracting the main frequency of acoustic emission of rocks under the condition of uniaxial compression.

Background technique

Acoustic Emission (AE) technology is to use the ultrasonic information radiated by the generation of internal cracks and the friction and sliding between the cracked surfaces during the rock deformation process to continuously observe the dynamic evolution of micro-cracks inside the rock material, so as to Study the microscopic mechanism of rock deformation and failure. It plays an important role in the study of the stability of rock mass, and is widely used in the study of the failure of materials such as rocks. In recent years, scholars have begun to study the mechanism of rock fracture from the perspective of acoustic emission spectrum analysis, seeking the necessary and sufficient conditions for rock fracture. Acoustic emission waveforms carry all information such as rock stress state, structure, physical and mechanical properties, etc. Analyzing the spectral information can better understand the rock failure mechanism and failure precursors.

According to the characteristics of rock acoustic emission signals, it is particularly important to use spectrum analysis technology to accurately and effectively extract the frequency characteristics of acoustic emission signals and determine the main frequency of acoustic emission signals. However, up to now, there is no definite suggested method to determine the dominant frequency of rock AE signals in the world.

Contents of the invention

The invention provides a method for extracting main frequency of acoustic emission of rock under uniaxial compression condition.

The technical scheme that the present invention adopts is as follows:

A method for extracting the dominant frequency of acoustic emission from rocks under uniaxial compression, characterized in that the steps are as follows:

a. Prepare the rock as a cuboid sample;

b. Paste the acoustic emission sensor on the prepared cuboid sample;

c. Use the rock mechanics testing machine to apply load to the sample, use the acoustic emission sensor to receive the acoustic emission signal generated by the internal damage of the sample, and use the acoustic emission monitoring system to monitor the rupture process of the sample synchronously in real time during the test;

d. Using the acoustic emission spectrum analysis system, fast Fourier transform is performed on the acoustic emission signal received in step c to obtain a two-dimensional spectrogram; the frequency corresponding to the maximum amplitude in the two-dimensional spectrogram is the main frequency of the acoustic emission;

e. Collect all the acoustic emission waveform signals of the sample from loading to destruction, perform Fourier transform on all waveforms, obtain the main frequency information at different times, draw the relationship curve between load, main frequency and time, and use the main frequency The uniaxial compression damage characteristics of rocks are described.

The present invention provides a new method for obtaining the main frequency of the acoustic emission signal of the rock under the condition of uniaxial compression, and its advantages are as follows: the method uses fast Fourier transform to extract the main frequency of the acoustic emission signal, which is simple, efficient and easy to popularize; This method can realize the fast Fourier transform of all acoustic emission waveforms in the rock catastrophe process, and obtain all-round main frequency information of the rock catastrophe process.

Preferred version of the present invention is:

The rock in step a is granite, basalt or coal gangue.

In step a, the size of the sample is a cuboid of 50mm×50mm×100mm, the error of the unevenness of the two ends of the sample is less than 0.05mm, and the length error of the two opposite sides along the height is less than 0.3mm.

The acoustic emission sensor in step b is an R6a resonant high-sensitivity sensor, and its operating frequency is 35-100 kHz.

During the test in step b, apply petroleum jelly between the sensor and the sample.

The rock mechanics testing machine in step c is a microcomputer-controlled electro-hydraulic servo rock mechanics testing machine.

In step c, the uniaxial compression test is loaded in an axial equidisplacement control mode, first preloaded to 1.5KN, and then loaded at a rate of 0.2mm/min until failure.

Sensors are placed on two opposing faces of the sample.

Description of drawings

Fig. 1 is a flow chart of a method for extracting the main frequency of acoustic emission under rock uniaxial compression condition provided by the present invention.

Fig. 2 is a position diagram of an acoustic emission sensor under uniaxial compression condition in the present invention.

Fig. 3 is the scene diagram of the experiment under the uniaxial compression condition in the present invention.

Fig. 4 is a diagram of the original AE waveform signal in the main frequency extraction process of an AE signal in the present invention.

Fig. 5 is a two-dimensional spectrogram obtained by performing fast Fourier transform on a waveform signal in the main frequency extraction process diagram of an acoustic emission signal in the present invention.

Fig. 6 is a graph showing the relationship between granite load, main frequency and time under uniaxial compression in the present invention.

Fig. 7 is a graph showing the relationship between basalt load, dominant frequency and time under uniaxial compression conditions in the present invention.

Fig. 8 is a graph showing the relationship between gangue load, main frequency and time under uniaxial compression conditions in the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, a method for extracting the dominant frequency of acoustic emission under uniaxial compression of rocks is carried out in sequence as follows:

Step a: Prepare the rock to be tested into a standard cuboid sample.

Granite, basalt and coal gangue No. 1, No. 2 and No. 3 were selected as test samples respectively. Granite, basalt and coal gangue were respectively taken from a mining area in Laizhou, Shandong, Chifeng, Inner Mongolia, and Tangshan, Hebei. Samples and numbered.

Step b: As shown in Figure 2, place the sample and fix the acoustic emission sensor.

Install the test piece on the sample table 1 of the press, install two acoustic emission sensors 3 in the middle of the sample 2, and place the two acoustic emission sensors on two opposite surfaces of the sample 2, as shown in the figure It is two opposite sides of left and right.

During the test, Vaseline 4 is applied between the acoustic emission sensor 3 and the sample to enhance the coupling between the two and reduce the attenuation of the acoustic emission signal.

The acoustic emission sensor 3 is connected to the acoustic emission instrument 5 by a line, and the acoustic emission instrument 5 is connected to the acoustic emission detection system 6 system. The sample stage 1 is connected with the control cabinet 7 through lines.

Step c: as shown in Figure 3. A press is used to load the specimen uniaxially, and the acoustic emission signals of the whole process of rock specimen fracture are collected.

The loading system used in the test is the TAW-3000 servo rock mechanics testing machine produced by Changchun Chaoyang Test Instrument Co., Ltd. The uniaxial loading adopts the axial equal displacement control method to ensure the complete contact between the sample and the loading surface and avoid the occurrence of The contact noise affects the acoustic emission monitoring results, first preloaded to 1.5KN, and then loaded to destruction at a rate of 0.2mm/min. During the test, an acoustic emission monitoring system was used to monitor the rupture process of the sample in real time and synchronously. The acoustic emission monitoring was a PCI-2 multi-channel acoustic emission monitoring system produced by PAC, an American physical acoustics company.

Step d: Based on the matlab platform, the acoustic emission spectrum analysis system is compiled to extract the main frequency of the acoustic emission signal. Taking the No. 5408 acoustic emission waveform of the No. 3 coal gangue sample as an example, the extraction process of the main frequency of the acoustic emission signal is illustrated. Based on the matlab platform, the acoustic emission spectrum analysis system is compiled to extract the original acoustic emission waveform signal, as shown in Figure 4. Perform fast Fourier transform (FFT) on the waveform signal to obtain a two-dimensional spectrogram, as shown in Figure 5. The main frequency is defined as the frequency corresponding to the maximum amplitude in the two-dimensional spectrogram. Observing the two-dimensional spectrogram of this waveform, we can see that its main frequency is 37.11kHz.

Step e: As shown in Fig. 6, Fig. 7 and Fig. 8, fast Fourier transform is performed on all acoustic emission signals during the rock failure process, and the load, main frequency and time curves of the entire failure process of the rock sample are drawn.

According to the results obtained in step d, select all the acoustic emission waveform signals of the sample from loading to destruction, perform fast Fourier transformation on all waveforms, obtain the main frequency information at different times, and draw the relationship curve of load, main frequency and time , using the main frequency to describe the rock uniaxial compression damage characteristics.

This embodiment proposes to use the fast Fourier transform method to obtain the main frequency of the acoustic emission signal, to further reveal the characteristics of the frequency domain change of the acoustic emission during the rock catastrophe process, and to provide a new idea for analyzing the rock catastrophe process from the perspective of frequency spectrum.

Claims (8)

1. rock acoustic emission dominant frequency extracting method under Uniaxial Compression, is characterized in that, carry out as follows:

A, rock is prepared into rectangular parallelepiped sample;

B, calibrate AE sensor is attached on the rectangular parallelepiped sample for preparing;

C, utilize rock mechanics experiment machine to sample imposed load, the acoustic emission signal utilizing calibrate AE sensor to receive sample internal injury to produce, adopts acoustic emission monitoring system real-time synchronization to monitor the rupture process of sample in process of the test;

D, utilizing acoustic emission spectrum analytic system, carrying out Fast Fourier Transform (FFT) to receiving acoustic emission signal in step c, obtain 2-d spectrum figure; The frequency that in 2-d spectrum figure, maximum amplitude is corresponding is the dominant frequency of this acoustic emission;

E, collection sample are from being loaded into the whole acoustic emission waveform signals destroying whole process, Fourier transform conversion is carried out to all waveforms, obtain not dominant frequency information in the same time, draw load, dominant frequency and the relation curve of time, utilize dominant frequency to be described Rock Under Uniaxial Compression compressive damage characteristic.

2. rock according to claim 1 acoustic emission dominant frequency extracting method under Uniaxial Compression, it is characterized in that, in step a, rock selects grouan, Irish touchstone or gangue.

3. rock according to claim 1 acoustic emission dominant frequency extracting method under Uniaxial Compression, it is characterized in that, in step a, sample is of a size of the rectangular parallelepiped of 50mm × 50mm × 100mm, and sample both ends of the surface irregularity degree error is less than 0.05mm, is less than 0.3mm along height two opposite side error in lengths.

4. rock according to claim 1 acoustic emission dominant frequency extracting method under Uniaxial Compression, is characterized in that, in step b, calibrate AE sensor is R6 α type resonant mode high sensor, and its frequency of operation is 35 ~ 100kHz.

5. rock according to claim 1 acoustic emission dominant frequency extracting method under Uniaxial Compression, is characterized in that,

Between sensor and sample, vaseline is scribbled when testing in step b.

6. rock according to claim 1 acoustic emission dominant frequency extracting method under Uniaxial Compression, is characterized in that, in step c, rock mechanics experiment machine is microcomputer controlled electro-hydraulic servo rock mechanics experiment machine.

7. rock according to claim 1 acoustic emission dominant frequency extracting method under Uniaxial Compression, it is characterized in that, in step c, uniaxial compression test adopts and axially waits displacement-control mode to load, and is first preloaded into 1.5kN, is loaded on destruction subsequently with the speed of 0.2mm/min.

8. rock according to claim 5 acoustic emission dominant frequency extracting method under Uniaxial Compression, is characterized in that, sensor setting is on two opposite faces of sample.