CN113324832B - Acoustic emission characteristic-based method for identifying micro-mechanical behavior between particles - Google Patents
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Abstract
The invention discloses a method for identifying micromechanics behaviors among granular particles based on acoustic emission characteristics, which comprises the steps of placing granular particles on a lower load plate of a single-particle loading device, installing an acoustic emission measurement system, controlling an upper load plate of the single-particle loading device to crush the granular particles, acquiring axial load applied to the granular particles by the single-particle loading device in the whole loading process, acquiring axial displacement generated when the granular particles are compressed in the loading process, acquiring original acoustic emission time domain electric signals generated in the crushing process of the granular particles in the whole process by the acoustic emission measurement system, identifying the micromechanics behaviors among the granular particles according to the axial load, the axial displacement and the original acoustic emission time domain electric signals, accurately identifying the micromechanics behaviors among the granular particles, particularly researching the internal micromechanisms of the granular materials in various loading processes, the damage stage of the particles can be continuously judged in real time, the damage degree of the particles can be quantified, the identification process is effectively simplified, and the identification efficiency is improved.
Description
Technical Field
The invention relates to the technical field of geotechnical engineering and acoustics, in particular to an acoustic emission characteristic-based method for identifying micro-mechanical behavior between particles.
Background
Particle breakage is recognized as a key factor affecting the mechanical behavior of bulk aggregates, such as reducing the permeability of the bulk aggregates, reducing the friction angle, changing the position of critical state strands, and inhibiting shear-swell damage. In order to understand the potential micro-mechanical behavior of particle fracture and its relationship with the strength parameters of bulk aggregates, different mineral types and mineral particle sizes are typically studied by combining advanced non-destructive testing techniques with single particle crush tests.
Previous studies have been directed to techniques that have focused primarily on boundary measurements (e.g., high speed microscopy cameras) or local density detection with wide measurement intervals (e.g., X-ray computed tomography), which have difficulty in real-time, continuous assessment of the intensity and pattern of the intrinsic micromechanical behavior of individual particles during crushing.
The acoustic emission technology is used as a nondestructive testing method, can continuously capture elastic waves released inside a stress material, and is widely applied to quasi-continuous body dielectric materials such as metal, rock, concrete and the like at present. When a material is subjected to an external load, microscale degradation processes (e.g., cracking) within the material tend to be accompanied by the release of strain energy, which is mostly released in the form of elastic waves. Such elastic waves may be detected by the acoustic emission sensor and recorded as an acoustic emission signal. Research has shown that by analyzing the information (such as signal arrival time, acoustic emission event rate, acoustic emission frequency, etc.) carried by the acoustic emission waveform, the position of the occurrence of the damage can be accurately located, the fault intensity can be diagnosed, the relevant micro-mechanical behavior patterns can be distinguished, and the like.
The micro-mechanical behavior associated with particle breakage (e.g., particle conditioning, wear and microcracking, etc.) also generates acoustic emission signals, and analysis of the acoustic emission behavior can provide useful information for the disfiguration of the micro-mechanical behavior of the granular aggregate. The research shows that: the acoustic emission characteristics are closely linked to the underlying micromechanical behaviour of the particulate material. For example, regarding the event rate of acoustic emission, Dixon et al and Smith et al establish a linear relationship between the event rate and the displacement rate of acoustic emission, and the linear relationship is used for monitoring and early warning the instability of the soil slope; in terms of acoustic emission frequency, Mao et al found that, regardless of the mineral composition, the process of breaking up the sandy particles was accompanied by a significant increase in the high-frequency acoustic emission component (>100kHz), while the slip process between the particles was dominated by the low-frequency component; recently, Luo et al and Ibraim et al have conducted extensive single particle compression tests, indicating that acoustic emission characteristics can characterize the breakage mechanism and characteristics of the particles. Although the related traditional scheme can realize the detection of the micromechanical behavior among the scattered particles to a certain extent, the detection process is complex.
Disclosure of Invention
Aiming at the problems, the invention provides a method for identifying the micro-mechanical behavior among the particles based on the acoustic emission characteristics.
In order to realize the purpose of the invention, the invention provides a method for identifying the micromechanical behavior among particles based on acoustic emission characteristics, which comprises the following steps:
s10, placing granular particles on a lower loading plate of the single particle loading device;
s20, mounting an acoustic emission measurement system on the base of the single particle loading device;
s30, controlling an upper loading plate of the single particle loading device to crush the granular particles according to a preset loading speed;
s40, acquiring the axial load applied to the granular particles by the single particle loading device in the whole loading process through the pressure sensor, acquiring the axial displacement generated when the granular particles are compressed in the loading process through the displacement sensor, acquiring the original acoustic emission time-domain electrical signal generated in the crushing process of the granular particles in the whole process through the acoustic emission measurement system, and identifying the micromechanical behavior among the granular particles according to the axial load, the axial displacement and the original acoustic emission time-domain electrical signal.
In one embodiment, identifying the inter-mitochondrial micromechanical behavior from the axial load, the axial displacement, and the raw acoustic emission time domain electrical signal comprises:
determining a curve of the axial load of the granular particles changing along with time in the crushing process according to the axial load;
determining a curve of the change of the axial displacement of the granular particles along with time in the crushing process according to the axial displacement;
and determining the micro-mechanical behavior of the granular particles among the granular particles identified in the crushing process according to the curve of the axial load changing along with time, the curve of the axial displacement changing along with time and the original acoustic emission time-domain electrical signal.
In one embodiment, the process of crushing the particulate granules includes five stages; the five phases include:
at the initial stage of loading, the axial load of the granular particles grows in a concave shape, the axial load of partial granules grows in a concave shape in an oscillation mode, at the moment, the acoustic emission event rate is in a bead shape and is accompanied by a low-frequency signal of about 50kHz, and the granules under pressure are judged to be in the stage (I): adjusting the position of the particles and compacting the pores/fractures;
when the axial load is linearly and elastically increased, the acoustic emission event rate is in a dispersion state and is accompanied by a frequency signal of 100-200kHz, and the pressed particles are judged to be in the stage (II): an elastic deformation stage;
when the axial load continues to increase linearly and elastically, the acoustic emission event rate begins to increase rapidly again, and the compressed particles are judged to be in the stage (III) along with sporadic high-frequency signals higher than 200 kHz: a microcrack stable growth phase;
when the axial load is increased in an oscillating manner, the acoustic emission event rate is increased in an accelerating manner, and a large number of high-frequency signals with the frequency of 200-700kHz accompany the acoustic emission event rate, and the pressed particles are judged to be in the stage (IV): a microcrack unstable growth phase;
when the axial load is reduced in a cliff-breaking mode, the acoustic emission event rate is still continuously and rapidly increased in a low-stress state, and the pressed particles are judged to be in a stage (V) along with a large number of high-frequency signals with the frequency of 200-700 kHz: and (4) a destruction stage.
In one embodiment, the upper and lower load plates of the single particle loading apparatus comprise a rigid solid ram.
In one embodiment, before step S10, the method further includes:
and sound insulation barriers are respectively attached to the upper load plate and the lower load plate of the single-particle loading device so as to reduce the static noise of the environment and the loading system, and each sound insulation barrier comprises a rubber film and a steel plate with a smooth plane.
The method for identifying the micromechanical behavior among the granules based on the acoustic emission characteristics comprises the steps of placing granules on a lower load plate of a single-granule loading device, installing an acoustic emission measurement system on a base of the single-granule loading device, controlling an upper load plate of the single-granule loading device to crush the granules according to a preset loading speed, obtaining an axial load applied to the granules by the single-granule loading device in the whole loading process through a pressure sensor, obtaining an axial displacement generated when the granules are compressed in loading through a displacement sensor, obtaining an original acoustic emission time domain electric signal generated in the crushing process of the granules through the acoustic emission measurement system in the whole process, identifying the micromechanical behavior among the granules according to the axial load, the axial displacement and the original acoustic emission time domain electric signal, and accurately identifying the micromechanical behavior among the granules, effectively simplifying the identification process and improving the identification efficiency.
Drawings
FIG. 1 is a flow chart of a method for identifying micromechanical behavior between particles based on acoustic emission characteristics according to an embodiment;
FIG. 2 is a schematic view of a single particle crush load test apparatus and a high accuracy acoustic emission measurement system in one embodiment;
FIG. 3 is a flow diagram of a method for identifying the micro-mechanical behavior of the particulate and granular material based on the acoustic emission characteristic information according to an embodiment;
FIG. 4 is a schematic illustration of acoustic emission raw time domain electrical signals excited during particle crushing according to one embodiment;
FIG. 5 is a schematic diagram illustrating acoustic emission events, acoustic emission peak frequency definitions, according to one embodiment;
FIG. 6 is a graphical representation of the axial load as a function of axial displacement during particle crushing according to one embodiment;
FIG. 7 is an axial load-axial displacement-acoustic emission event rate relationship established from experimental data in one embodiment;
FIG. 8 is a graph of axial load versus axial displacement versus acoustic emission frequency characteristics established from experimental data in one embodiment.
The reference numerals in fig. 2 include:
the device comprises a single particle loading device base 1, a loading system reaction frame 2, an upper loading plate 3, a lower loading plate 4, an upper sound-proof barrier 5, a lower sound-proof barrier 6, a loading rod 7, a pressure sensor 8, a displacement sensor 9, a servo control system 10, an acoustic emission sensor 11, an acoustic emission signal amplifier 12, a data recorder 13, a data memory 14 and a granular material 15.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.
Referring to fig. 1, fig. 1 is a flowchart of an embodiment of a method for identifying micromechanical behavior between particles based on acoustic emission characteristics, including the following steps:
and S10, placing the granular particles on a lower loading plate of the single particle loading device.
The single particle loading device comprises a base, a reaction frame, an upper loading plate, a lower loading plate, an upper sound insulation barrier, a lower sound insulation barrier, a pressure sensor arranged on the single particle loading device, a displacement sensor arranged on the single particle loading device, a loading rod and a servo control loading system.
And S20, installing an acoustic emission measurement system on the base of the single particle loading device.
The acoustic emission measurement system is a high-performance acoustic emission measurement system and comprises an acoustic emission sensor, a signal amplifier, a data recorder and a data memory. The high-performance acoustic emission measurement system should have the characteristics of high sensitivity, high signal-to-noise ratio, broadband working frequency and high sampling rate.
Specifically, the original acoustic emission time-domain electrical signal received by the acoustic emission measurement system should be analyzed by setting a voltage threshold according to the voltage level caused by electrical and environmental noise, once the signal exceeds the threshold, the acoustic emission signal is identified and defined as an acoustic emission event, and the acoustic emission event quantity is accumulated at fixed time intervals and defined as an acoustic emission event rate. The method comprises the steps that an original acoustic emission time domain electric signal received by an acoustic emission sensor is converted from a time domain to a frequency domain by a Fast Fourier Transform (FFT) method, and a frequency component with a peak amplitude value in a spectrum is used as a peak frequency so as to analyze the frequency characteristic of the detected acoustic emission signal.
And S30, controlling an upper loading plate of the single particle loading device according to a preset loading speed to crush the granular particles.
The preset loading speed can be controlled by a conventional servo control loading device.
Specifically, before crushing granular particles, two sound insulation barriers are respectively attached to a loading platform to reduce the static noise of the environment and a loading system, and before crushing target particles, the upper surface and the lower surface of a loading plate which are in contact with the particles need to be fully polished to reduce the frictional resistance between the particles and the loading plate. During the single particle crush test, the test particles were placed in dry condition at all times.
S40, acquiring the axial load applied to the granular particles by the loading device in the whole loading process through the pressure sensor, acquiring the axial displacement generated when the granular particles are compressed in the loading process through the displacement sensor, acquiring the original acoustic emission time-domain electrical signal generated in the crushing process of the granular particles in the whole process through the acoustic emission measurement system, and identifying the micromechanical behavior among the granular particles according to the axial load, the axial displacement and the original acoustic emission time-domain electrical signal.
The method for identifying the micromechanical behavior among the particles based on the acoustic emission characteristics comprises the steps of placing particles on a lower load plate of a single particle loading device, installing an acoustic emission measurement system on a base of the single particle loading device, controlling an upper load plate of the single particle loading device to crush the particles according to a preset loading speed, obtaining an axial load applied to the particles by the single particle loading device in the whole loading process through a pressure sensor, obtaining an axial displacement generated when the particles are compressed in loading through a displacement sensor, obtaining an original acoustic emission time domain electric signal generated in the crushing process of the particles through the emission measurement system in the whole process, identifying the micromechanical behavior among the particles according to the axial load, the axial displacement and the original acoustic emission time domain electric signal, and accurately identifying the micromechanical behavior among the particles, the method can be used for researching the internal micro mechanism of the granular material in various loading processes, can continuously judge the damage stage of the granules in real time and quantify the damage degree of the granules, effectively simplifies the identification process and improves the identification efficiency.
In one embodiment, identifying the inter-mitochondrial micromechanical behavior from the axial load, the axial displacement, and the raw acoustic emission time domain electrical signal comprises:
determining a curve of the axial load of the granular particles changing along with time in the crushing process according to the axial load;
determining a curve of the change of the axial displacement of the granular particles along with time in the crushing process according to the axial displacement;
and determining the micro-mechanical behavior of the granular particles among the granular particles identified in the crushing process according to the curve of the axial load changing along with time, the curve of the axial displacement changing along with time and the original acoustic emission time-domain electrical signal.
The embodiment can analyze the characteristics of the axial load, the axial displacement, the acoustic emission event rate and the acoustic emission frequency, and establish the corresponding relation among the mechanical parameters, the displacement parameters and the acoustic emission parameters of the single particles in the crushing process so as to respectively obtain various curves of the required changes of the axial load, the acoustic emission event rate and the acoustic emission frequency characteristic along with the axial displacement.
In one embodiment, the process of crushing the particulate granules includes five stages; the five phases include:
at the initial stage of loading, the axial load of the granular particles grows in a concave shape, the axial load of partial granules grows in a concave shape in an oscillation mode, at the moment, the acoustic emission event rate is in a bead shape and is accompanied by a low-frequency signal of about 50kHz, and the granules under pressure are judged to be in the stage (I): adjusting the position of the particles and compacting the pores/fractures;
when the axial load is linearly and elastically increased, the acoustic emission event rate is in a dispersion state and is accompanied by a frequency signal of 100-200kHz, and the pressed particles are judged to be in the stage (II): an elastic deformation stage;
when the axial load continues to increase linearly and elastically, the acoustic emission event rate begins to increase rapidly again, and the compressed particles are judged to be in the stage (III) along with sporadic high-frequency signals higher than 200 kHz: a microcrack stable growth phase;
when the axial load is increased in an oscillating manner, the acoustic emission event rate is increased in an accelerating manner, and a large number of high-frequency signals with the frequency of 200-700kHz accompany the acoustic emission event rate, and the pressed particles are judged to be in the stage (IV): a microcrack unstable growth phase;
when the axial load is reduced in a cliff-breaking mode, the acoustic emission event rate is still continuously and rapidly increased in a low-stress state, and the pressed particles are judged to be in a stage (V) along with a large number of high-frequency signals with the frequency of 200-700 kHz: and (4) a destruction stage.
In one example, the five stages may not occur sequentially in order, and the particles do not have to go through the complete five fracturing stages; some stages may overlap partially or completely, while individual or certain stages may be present for a short time or even disappear during the fracturing of the particles.
Further, after the target particles (particulate particles) are crushed, the method further includes:
setting a voltage threshold value for an original acoustic emission time-domain electrical signal received by an emission sensor according to a voltage level caused by electrical and environmental noises, identifying and defining an acoustic emission signal as a primary acoustic emission event once the signal exceeds the threshold value, accumulating acoustic emission event quantity at fixed time intervals, and defining the acoustic emission event quantity as an acoustic emission event rate;
for an original acoustic emission time domain electric signal received by an acoustic emission sensor, a Fast Fourier Transform (FFT) method is adopted to convert the signal from a time domain to a frequency domain, and a frequency component with a peak amplitude in a frequency spectrum is used as a peak frequency so as to analyze the frequency characteristic of the acoustic emission signal.
In one embodiment, the upper and lower load plates of the single particle loading apparatus comprise a rigid solid ram.
Specifically, sound-proof barriers may be attached to upper and lower load plates of the single particle loading device, respectively, to reduce electrostatic noise of the environment and the loading system, and the sound-proof barriers may be formed by combining rubber films and steel plates having smooth planes. The above single particle crush test should be conducted under dry conditions.
In one embodiment, before step S10, the method further includes:
and sound insulation barriers are respectively attached to the upper load plate and the lower load plate of the single-particle loading device so as to reduce the static noise of the environment and the loading system, and each sound insulation barrier comprises a rubber film and a steel plate with a smooth plane.
The method for identifying the micromechanical behavior among particles of the particulate material based on the acoustic emission characteristic information according to the embodiment of the present invention is further described in detail with reference to fig. 2 to 8.
In order to more clearly describe the method for identifying the micro-mechanical behavior among particles of the particulate material based on the acoustic emission characteristic information according to the embodiment of the present invention, a loading test apparatus and a high-precision acoustic emission measurement system are described below.
FIG. 2 is a schematic diagram of the single particle crushing load test device and a high-precision acoustic emission measurement system. As shown in fig. 2, the loading test apparatus includes: the device comprises a base 1, a reaction frame 2, an upper load plate 3, a lower load plate 4, an upper sound-proof barrier 5, a lower sound-proof barrier 6, a loading rod 7, a pressure sensor 8, a displacement sensor 9, a servo control system 10, an acoustic emission sensor 11, an acoustic emission signal amplifier 12, a data recorder 13 and a data memory 14.
The upper and lower load plates refer to solid pressure heads made of metal materials or non-metal materials.
The upper sound-insulating barrier 5 is arranged on the lower surface of the upper load plate, and the lower sound-insulating barrier 6 is arranged on the lower surface of the lower load plate, so that the electric noise generated by the environment and a loading system is avoided.
In this embodiment, the sound-insulating barriers 5 and 6 are formed by stacking a plurality of layers of latex films and thin metal plates with glue.
In particular, in order to reduce the frictional resistance between the particles and the contact surface, the load surfaces (i.e., the lower surface of the sound-insulating barrier 5 and the upper surface of the lower load-carrying plate) contacting the particles need to be sufficiently polished;
the pressure sensor 8 is arranged at the propelling end of the loading rod 7 and is used for measuring the axial load applied to the target particles 15 by the loading rod 7;
the displacement sensor 9 is arranged at the pushing end of the loading rod 7 and is used for measuring the axial displacement generated by the loading rod 7 crushing the target particles 15;
in this embodiment, the thrust loading rod 7 can be any loading rod capable of applying an axial load;
the servo control system 10 is arranged at the end part of the loading rod 7 and is used for controlling the loading rod 7 to advance up and down at a preset loading speed;
the acoustic emission sensor 11 is arranged on the outer surface, namely the free surface, of the lower metal load plate 3 and is used for continuously measuring acoustic emission original time domain electric signals excited in the whole process of crushing the target particles 15 in real time;
the acoustic emission signal amplifier 12 is connected with an acoustic emission sensor and is used for improving the signal-to-noise ratio of the received acoustic emission signal;
the data recorder 13 is connected with the acoustic emission signal amplifier and is used for continuously recording an acoustic emission original time domain electric signal;
the morphology, size, texture of the target particle 15 is not limited;
in this embodiment, in the process that the loading rod 7 crushes the target particles 15, the pressure sensor 8 obtains the axial load applied to the target particles 15 by the loading test device, the displacement sensor 9 obtains the axial displacement generated when the target particles 15 are compressed during loading, and the acoustic emission measurement system obtains the original acoustic emission time-domain signal generated in the crushing process of the target particles 15.
Fig. 3 is a flowchart of a method for identifying the micromechanical behavior among particles of the particulate material based on acoustic emission characteristics according to an embodiment of the present invention. As shown in fig. 3, the method for identifying the micromechanical behavior among particles of the particulate/granular material based on the acoustic emission characteristics may include the following steps:
step 1: placing single-particle sand on a single-particle loading test device, as shown in figure 2;
in this example, five kinds of single-particle siliceous sandy soils with different sizes were selected, and the test particle sizes were: 6.79mm × 5.36mm × 4.53mm, 4.61mm × 4.26mm × 3.62mm, 3.57mm × 3.26mm × 2.50mm, 2.95mm × 2.46mm × 2.06mm, 2.18mm × 1.85mm × 1.53 mm;
in this embodiment, the optical image of the different sized single particle sand grains shows: the roundness of larger particles is higher, the surface is smoother, and the surface has primary micro defects; smaller particles have more edges and corners and rougher surfaces;
in this example, the target particles 15 were placed in dry condition before and during the test, and 10 tests were performed for each size of particles, for a total of 50 tests for all particles;
step 2: installing a high-performance acoustic emission measurement system on the testing device, as shown in FIG. 2;
in the embodiment, in order to reduce the energy attenuation of the acoustic emission signal in the granular material, the acoustic emission measurement system comprises a high-performance acoustic emission sensor 11, a signal amplifier 12, a high-performance data collector 13 and a data memory 14. The acoustic emission sensor 11 is a piezoelectric ceramic sensor manufactured by fuji ceramics: M304A, a preamplifier with gain of 20 +/-2 dB is arranged in the sensor probe, the working frequency of the sensor is 10kHz-5MHz (the resonant frequency is 300kHz), and the sensitivity is 115 +/-3 dB (the reference: 0dB is 1V/M/s); the acoustic emission signal amplifier 12 is a signal amplifier manufactured by fuji ceramics: a1201, the gain of which is 53 +/-3 dB; the data acquisition instrument 13 is PXIe-6366 manufactured by NI corporation in America, and the sampling rate is set to be 2 MS/s;
and step 3: controlling a loading test device to crush the target particles according to a preset loading speed;
in this embodiment, the predetermined loading rate is constant at 0.2mm/min to propel the loading rod 7 downward, simulating a target particle crushing process. Specifically, with the advance of the loading rod 7, the target particle firstly undergoes particle position adjustment and primary pore/fracture closure, linear elastic compression, stable growth of microcracks, unstable growth of microcracks, and finally fracturing of particles caused by fusion and penetration of microcracks.
And 4, step 4: acquiring an axial load applied to target particles by a single particle loading device through a pressure sensor, acquiring axial displacement generated when the target particles are compressed during loading through a displacement sensor, and acquiring an original acoustic emission time domain signal generated in the crushing process of the target particles through a high-performance acoustic emission measuring system;
in the embodiment, the sampling frequency of the pressure sensor is set to be 1S/S, the sampling frequency of the displacement sensor is set to be 1S/S, and the sampling frequency of the acoustic emission measurement system is set to be 2 MS/S;
in this embodiment, the original acoustic emission time domain signal is as shown in fig. 4;
in this embodiment, the acoustic emission signals mainly originate from the initiation and development of cracks inside the particles, the breakage of edges and corners of the particles, the dislocation friction of the broken parts of the particles, the friction and abrasion between the surfaces of the particles and the upper and lower load plates, and the like;
and 5: in order to effectively distinguish the acoustic emission signals from the environmental electrical noise, a voltage threshold is preset according to the voltage level caused by the electrical and environmental noise to filter the acoustic emission signal noise, once the signal exceeds the threshold, the acoustic emission signals are identified and defined as a primary acoustic emission event, the acoustic emission event quantity accumulated at fixed time intervals is defined as an acoustic emission event rate, the acoustic emission event rate in the loading process is counted, and the acoustic emission parameters are defined as shown in the attached figure 5;
in the embodiment, the noise of the acoustic emission signal is about 20dB (reference: 0dB ═ 1mV/m/s), and the preset voltage threshold is 29.54dB (reference: 0dB ═ 1 mV/m/s); the acoustic emission event rate is defined as the cumulative number of acoustic emission events in 1 second;
further, a Fast Fourier Transform (FFT) method is adopted to convert the recorded original acoustic emission time domain electrical signal from a time domain to a frequency domain, and a frequency component with a peak amplitude in a spectrum is taken as a peak frequency to acquire a frequency characteristic of the detected acoustic emission signal.
Step 6: by establishing a relation curve among characteristics of axial load, axial displacement, acoustic emission event rate and acoustic emission frequency, the indoor test method for identifying the micro-mechanical behavior among particles of the granular material based on the acoustic emission characteristic information is provided.
Further, the specific relationship curve established in step 6 includes:
the curve of the axial load-axial displacement variation during the particle crushing process is shown in fig. 6;
the relationship curve of axial load-axial displacement-acoustic emission event rate in the particle crushing process is shown in FIG. 7;
the characteristic relation curve of axial load-axial displacement-acoustic emission frequency in the particle crushing process is shown in figure 8.
As can be seen from fig. 6 to 8, the single particle crushing process is divided into five stages;
the five stages are respectively: the method comprises the following steps of (I) adjusting the position of particles and compacting primary micropores/fractures, (II) performing linear elastic deformation, (III) performing stable microcrack growth, (IV) performing unstable microcrack growth, and (V) performing destruction.
Specifically, in the stage (I), the position of the particles between the particles and the upper and lower load plates is adjusted in a rotating and sliding mode, and the primary cracks/pores are closed, so that the rigidity of the particles is gradually increased, and an axial load-axial displacement curve is concave; on the other hand, the acoustic emission event rate appears as a bead and is accompanied by a low frequency signal of around 50 kHz. Along with the loading, the particles enter a linear elasticity stage, and the axial load is linearly and elastically increased; on the other hand, the acoustic emission event rate is in a dispersion state and is accompanied by a higher frequency signal with the frequency of 100-200kHz, and at the moment, the particles are in a stage (II): and (5) an elastic deformation stage. Subsequently, the axial load continues to increase linearly elastically, but the acoustic emission event rate begins to increase rapidly and with sporadic high frequency signals above 200kHz, when the compressed particles are in phase (III): microcracking and a plateau growth phase. With the advancing of the loading rod, particle microcracks continuously develop and rapidly fuse, weak corners can also break, so that the load tends to increase in an undulating manner, on the other hand, the acoustic emission event rate increases in an accelerated manner, and is accompanied by more high-frequency signals with the frequency of 200-700kHz, and the pressed particles are in a stage (IV): unstable micro-crack growth phase. Finally, with the complete coalescence of the microcracks, the axial load is reduced in a cliff-broken manner, on the other hand, the acoustic emission event rate still continuously and rapidly increases in a low-stress state, and the pressed particles can be judged to be in the stage (V) along with a large number of high-frequency signals with the frequency of 200-700 kHz: and (4) a destruction stage. It should be noted that: the five stages do not necessarily occur sequentially throughout the particle crushing process, and the particles do not have to undergo the entire five fracturing stages, some stages may overlap partially or completely, and individual or some stages may be present for a short time or even disappear during the particle fracturing process.
In particular, before the final failure (i.e.: phase IV), a rapid increase in the acoustic emission event rate is observed with a large number of high frequency signals (>200kHz), which is closely related to the initiation and evolution of microcracks. On one hand, the phenomenon of sound emission is expected to be regarded as precursor information of material damage, and advanced early warning is realized; on the other hand, when the internal micro mechanism of the bulk and granular material aggregate is researched in various loading processes, the real-time continuous evaluation of the strength and the mode of the interaction among the particles in the particle aggregate can be realized by carrying out classification statistics (such as separation of high-frequency and low-frequency signals) on the acoustic emission characteristic information.
In particular, after the particles are fragmented or disintegrated, the broken "new particles" will become more emissive, even at very low loading levels, and exhibit a large high frequency signal (>200kHz), as shown in fig. 6-8, indicating that: compared with mechanical parameters and displacement parameters, the acoustic emission parameters can better reflect the historical damage degree of the particles;
by combining the 50 single-particle crushing tests in this example, the axial load-axial displacement relationship curve, the axial load-axial displacement-acoustic emission event rate relationship curve, and the axial load-axial displacement-acoustic emission frequency characteristic relationship curve are analyzed, and it can be seen that the low-frequency acoustic emission component (below 100kHz), the medium-high frequency acoustic emission component (100 + 200kHz), and the high-frequency component (200 + 700kHz) are closely related to the micro-mechanical behavior modes such as particle adjustment, particle surface grinding, and micro-cracks, respectively, and the internal micro-mechanical characteristics of the loaded single-particle sandy soil can be further judged through the acoustic emission frequency characteristics.
According to the method for identifying the micro-mechanical behavior among the particles of the bulk and granular material based on the acoustic emission characteristics, the bulk and granular particles are placed on a single particle loading device; installing a high-performance acoustic emission measurement system on the single particle loading device; controlling a single particle loading device to crush the target particles according to a preset loading speed; acquiring an axial load applied to the target particles by a loading test device through a pressure sensor, acquiring axial displacement generated when the target particles are compressed during loading through a displacement sensor, and acquiring an original acoustic emission time domain signal generated in the crushing process of the target particles through a high-performance acoustic emission measurement system; filtering the noise of the acoustic emission electrical signal through a preset voltage threshold, extracting and counting the acoustic emission event rate in the loading process, converting an original acoustic emission time domain signal into a frequency domain signal through Fourier transform, and acquiring the frequency domain characteristic of the acoustic emission signal generated in the crushing process; the relationship among the characteristics of axial load, axial displacement, acoustic emission event rate and acoustic emission frequency is established. By providing the indoor test method for identifying the micro-mechanical behavior among the particles of the granular material based on the acoustic emission characteristic information, the identification and research of the internal micro-mechanism of the granular material in various loading processes can be carried out, and the damage stage and the damage degree of the granular material in the particle fracturing process can be continuously judged in real time; the problem of high attenuation of acoustic signal propagation in the granular material is effectively solved by adopting a high-precision acoustic emission measurement system; the sound insulation barrier is adopted, so that the problems of environment and electric noise of a loading system are effectively reduced; the method can synchronously measure mechanical parameters, displacement parameters and acoustic parameters (including acoustic emission event rate and acoustic emission frequency characteristics) in the particle fracturing process, integrates acoustics-mechanics-statistics, and can realize real-time and continuous internal microscopic monitoring of the whole material fracturing process. A large number of test results prove that: the acoustic emission event rate and the acoustic emission frequency characteristic have strong correlation with axial load, axial displacement, material destruction stage and material internal micromechanics behavior. At the initial stage of loading, the axial load of the particles is increased in an upper concave shape, the axial load of part of the particles is increased in an oscillating upper concave shape, the acoustic emission event rate is in a bead shape and is accompanied by a low-frequency signal about 50kHz, and at the moment, the pressed particles can be judged to be in the particle position adjustment and pore/fracture compaction stages; when the axial load is linearly and elastically increased, the acoustic emission event rate is in a dispersion state and is accompanied by a higher-frequency signal with the frequency of 100-200kHz, and the pressed particles can be judged to be in an elastic deformation stage; when the axial load continues to increase linearly and elastically, the acoustic emission event rate starts to increase rapidly, and the pressurized particles can be judged to be in a stable microcrack increasing stage along with a high-frequency signal with the sporadic frequency of 200-700 kHz; when the axial load is increased in a vibration mode, the acoustic emission event rate is increased in an accelerated mode, and the pressure particles can be judged to be in the stage of unstable microcrack growth along with more high-frequency signals of 200-700 kHz; when the axial load is reduced in a cliff-breaking manner, the acoustic emission event rate is still continuously and rapidly increased in a low-stress state, and the compressed particles can be judged to be in a damage stage along with a large number of high-frequency signals with the frequency of 200-700 kHz. It should be noted that: throughout the particle crushing process, the five stages do not necessarily occur sequentially in order, and the particles do not have to undergo the complete five fracturing stages; some stages may overlap partially or completely, while individual or certain stages may be present for a short time or even disappear during the fracturing of the particles. Particularly, in the early stage of material damage, the acoustic emission event rate is increased rapidly and is accompanied by the generation of more high-frequency signals (>200kHz), the unstable development of the internal cracks of the material is better reflected, and the characteristic information is expected to be used as precursor information of the material damage on one hand, so that the advance early warning is realized; on the other hand, when the internal micro mechanism of the bulk and granular aggregates in various loading processes is researched, the strength and the mode of the interaction among the particles in the bulk and granular aggregates can be continuously evaluated in real time by counting different acoustic emission parameters carrying different frequency components, so that the detection process is simpler and more convenient.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
It should be noted that the terms "first \ second \ third" referred to in the embodiments of the present application merely distinguish similar objects, and do not represent a specific ordering for the objects, and it should be understood that "first \ second \ third" may exchange a specific order or sequence when allowed. It should be understood that "first \ second \ third" distinct objects may be interchanged under appropriate circumstances such that the embodiments of the application described herein may be implemented in an order other than those illustrated or described herein.
The terms "comprising" and "having" and any variations thereof in the embodiments of the present application are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product, or device that comprises a list of steps or modules is not limited to the listed steps or modules but may alternatively include other steps or modules not listed or inherent to such process, method, product, or device.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (5)
1. A microscopic mechanical behavior identification method between particles based on acoustic emission characteristics is characterized by comprising the following steps:
s10, placing granular particles on a lower loading plate of the single particle loading device;
s20, mounting an acoustic emission measurement system on the base of the single particle loading device;
s30, controlling an upper loading plate of the single particle loading device to crush the granular particles according to a preset loading speed;
s40, acquiring the axial load applied to the granular particles by the single particle loading device in the whole loading process through the pressure sensor, acquiring the axial displacement generated when the granular particles are compressed in the loading process through the displacement sensor, acquiring the original acoustic emission time-domain electrical signal generated in the crushing process of the granular particles in the whole process through the acoustic emission measurement system, and identifying the micromechanical behavior among the granular particles according to the axial load, the axial displacement and the original acoustic emission time-domain electrical signal.
2. The acoustic emission feature-based method for identifying micromechanical behavior between particles according to claim 1, wherein identifying micromechanical behavior between particles according to axial load, axial displacement and original acoustic emission time domain electrical signal comprises:
determining a curve of the axial load of the granular particles changing along with time in the crushing process according to the axial load;
determining a curve of the change of the axial displacement of the granular particles along with time in the crushing process according to the axial displacement;
and determining the micro-mechanical behavior of the granular particles among the granular particles identified in the crushing process according to the curve of the axial load changing along with time, the curve of the axial displacement changing along with time and the original acoustic emission time-domain electrical signal.
3. The acoustic emission feature-based method for identifying micromechanical behavior between particles according to claim 1, wherein the process of crushing the particles comprises five stages; the five phases include:
at the initial stage of loading, the axial load of the granular particles grows in a concave shape, the axial load of partial granules grows in a concave shape in an oscillation mode, at the moment, the acoustic emission event rate is in a bead shape and is accompanied by a low-frequency signal of about 50kHz, and the granules under pressure are judged to be in the stage (I): adjusting the position of the particles and compacting the pores/fractures;
when the axial load is linearly and elastically increased, the acoustic emission event rate is in a dispersion state and is accompanied by a frequency signal of 100-200kHz, and the pressed particles are judged to be in the stage (II): an elastic deformation stage;
when the axial load continues to increase linearly and elastically, the acoustic emission event rate begins to increase rapidly again, and the compressed particles are judged to be in the stage (III) along with sporadic high-frequency signals higher than 200 kHz: a microcrack stable growth phase;
when the axial load is increased in an oscillating manner, the acoustic emission event rate is increased in an accelerating manner, and a large number of high-frequency signals with the frequency of 200-700kHz accompany the acoustic emission event rate, and the pressed particles are judged to be in the stage (IV): a microcrack unstable growth phase;
when the axial load is reduced in a cliff-breaking mode, the acoustic emission event rate is still continuously and rapidly increased in a low-stress state, and the pressed particles are judged to be in a stage (V) along with a large number of high-frequency signals with the frequency of 200-700 kHz: and (4) a destruction stage.
4. The acoustic emission feature-based method for identifying micromechanical behavior between particles according to claim 1, wherein the upper and lower load plates of the single particle loading device comprise a rigid solid indenter.
5. The method for identifying micromechanical behavior among particles based on acoustic emission characteristics according to claim 1, wherein before step S10, the method further comprises:
and respectively attaching sound insulation barriers to an upper load plate and a lower load plate of the single-particle loading device to reduce the static noise of the environment and a loading system, wherein each sound insulation barrier comprises a rubber film and a steel plate with a smooth plane.
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