An early warning method for intergranular damage behavior based on acoustic emission characteristics

Abstract

The present invention discloses an early warning method for the destructive behavior of granular materials based on acoustic emission characteristics, involving the fields of geotechnical engineering and acoustic technology. The method comprises obtaining the deviation stress applied to the specimen by a loading device during the entire loading process, obtaining the axial strain generated by the specimen during the entire loading process, and obtaining the original acoustic emission time-domain electrical signal generated by the specimen during the destructive process through an acoustic emission measurement system; processing and analyzing the original acoustic emission time-domain electrical signal, extracting the acoustic emission characteristic parameter acoustic emission event rate, and judging the destructive behavior of the specimen based on the peak deviation stress and the peak acoustic emission event rate. The destructive behavior of the granular material specimen is judged based on the peak deviation stress and the peak acoustic emission event rate, and early warning information of the destructive behavior of the granular material can be issued timely and effectively based on the time sequence of the occurrence of the peak deviation stress and the peak acoustic emission event rate, thereby simplifying the warning process and improving the warning efficiency.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering and acoustic technology, and in particular to an early warning method for destructive behavior between granular bodies based on acoustic emission characteristics. Background Art

[0002] With rapid economic development, my country's infrastructure construction has flourished. Super-high-rise buildings and ultra-deep foundation pits continue to emerge, but various engineering problems, such as foundation instability, pit collapse, and embankment collapse, also occur frequently. These engineering accidents not only cause significant loss of life and property but also have a negative impact on my country's infrastructure. Research has shown that the mechanical failure of geotechnical materials characterized by granular structures develops gradually, generally progressing from strain localization to shear bands, and then to complete failure as the shear bands further develop. The development of shear bands controls the mode and scale of granular failure, and the initiation of shear bands (i.e., initial strain localization) can provide useful information for early warning of granular failure. Therefore, understanding the initiation and evolution of shear bands is crucial for exploring the nature of granular failure mechanisms, providing early warning information for granular failure, and preventing engineering accidents.

[0003] In recent years, numerous researchers have employed technologies such as borehole inclinometers, fiber optic sensors, geomagnetic induction, and three-dimensional laser scanning to achieve early warning of granular failure. However, borehole inclinometers can only measure deformation at the sensor location, lacking a comprehensive and intuitive understanding of the deformation of the entire granular soil mass. This results in low measurement accuracy and poor early warning effectiveness. Fiber optic sensing offers advantages such as high precision and distributed monitoring, but is limited to surface monitoring and cannot effectively reflect the internal deformation and damage of granular materials. Technologies such as geomagnetic induction and three-dimensional laser scanning can monitor internal deformation of granular materials in an automated, fully monitored, real-time, and highly accurate manner. However, data processing is complex and susceptible to environmental influences, significantly impacting the timeliness and accuracy of early warnings of granular failure.

[0004] Acoustic emission (AE) refers to elastic body waves generated by the sudden release of stored strain energy due to stress concentration or strain localization in stressed materials. These elastic waves can be captured continuously and in real time by AE sensors and used to diagnose the degradation and failure process of stressed materials. Research has shown that materials exhibit certain characteristics during failure, such as progressive failure, with the weakest parts often breaking first. During this process, they produce precursory "microcracks" and associated elastic waves that propagate through the material. Based on this, the rapidly developing AE method is expected to provide new insights into impending material instabilities.

[0005] Therefore, we propose an early warning method for intergranular destruction behavior based on acoustic emission characteristics to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide an early warning method for destructive behavior between granular bodies based on acoustic emission characteristics, so as to solve any of the problems currently occurring in the market raised by the above background technology.

[0007] To achieve the above-mentioned object, the present invention provides the following technical solution: an early warning method for destructive behavior between granular bodies based on acoustic emission characteristics, comprising the following steps:

[0008] S01 places the prefabricated specimen on the base inside the triaxial loading device;

[0009] S02 installs the acoustic emission measurement system on the side wall of the sample placed in S01, waiting for the test;

[0010] S03 controls the confining pressure system of the triaxial device and the loading system of the triaxial device to destroy the specimen in S02;

[0011] S04 obtains the deviation stress applied to the sample by the loading device during the entire loading process, obtains the axial strain generated by the sample during the entire loading process, and obtains the original acoustic emission time domain electrical signal generated by the sample during the destruction process through the acoustic emission measurement system;

[0012] S05 processes and analyzes the original time-domain electrical signals of acoustic emission, extracts the characteristic parameters of acoustic emission, namely the acoustic emission event rate, and determines the sample failure behavior based on the peak deviation stress and the peak acoustic emission event rate. By analyzing the chronological order of the data after analysis, early warning information of material failure is issued in a timely and effective manner.

[0013] Preferably, judging the sample failure behavior by the peak deviation stress and the peak acoustic emission event rate in S05 includes:

[0014] The deviation stress is used to determine the curve of the deviation stress changing with the axial strain during the failure of the specimen;

[0015] The curve of acoustic emission event rate changing with axial strain during the specimen failure process was determined by the original acoustic emission time-domain electrical signal.

[0016] Preferably, the peak deviation stress is determined by the axial strain relationship curve; the peak acoustic emission event rate is determined by the axial strain relationship curve;

[0017] The failure behavior of the specimens was determined by the peak deviatoric stress and the peak acoustic emission event rate.

[0018] Preferably, the time sequence of the data analyzed in S05 and the issuance of early warning information of material damage include:

[0019] Determine the axial strain corresponding to the peak deviation stress through the axial strain relationship curve;

[0020] The axial strain corresponding to the peak acoustic emission event rate was determined through the axial strain relationship curve.

[0021] Preferably, the time sequence of the peak deviation stress and the peak acoustic emission event rate is compared to issue early warning information of material damage.

[0022] Preferably, the time sequence of occurrence of the peak deviation stress and the peak acoustic emission event rate of the sample includes three stages: post-peak stage, peak stage and pre-peak stage.

[0023] Preferably, when the confining pressure applied to the specimen by the confining pressure system of the triaxial apparatus is low, the peak acoustic emission event rate occurs later than the peak deviation stress, which is the post-peak stage.

[0024] Preferably, when the confining pressure applied to the sample by the confining pressure system of the triaxial apparatus is moderate, the peak stage occurs when the peak acoustic emission event rate and the peak deviation stress appear simultaneously.

[0025] Preferably, when the confining pressure applied to the specimen by the confining pressure system of the triaxial apparatus is high, the peak acoustic emission event occurs before the peak deviation stress, which is the pre-peak stage;

[0026] When the confining pressure system of the triaxial device applies high confining pressure to the specimen, the peak acoustic emission event occurs before the peak deviation stress. This phenomenon can provide early warning information of the specimen's failure behavior based on the acoustic emission characteristics.

[0027] Preferably, the sample is a granular body.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention places a cylindrical granular sample on the bottom base of a triaxial device, installs an acoustic emission measurement system on the side wall of the sample, controls the confining pressure system of the triaxial device, controls the loading system of the triaxial device to destroy the granular sample, obtains the deviation stress applied to the granular sample by the loading device during the entire loading process, obtains the axial strain generated by the granular sample during the entire loading process, and obtains the original acoustic emission time domain electrical signal generated by the granular sample during the destruction process through the acoustic emission measurement system. The original acoustic emission time domain electrical signal is processed and analyzed, and the acoustic emission characteristic parameter acoustic emission event rate is extracted. The destruction behavior of the granular sample is judged according to the peak deviation stress and the peak acoustic emission event rate. According to the time sequence of the peak deviation stress and the peak acoustic emission event rate, early warning information of granular material destruction can be timely and effectively issued, thereby simplifying the warning process and improving the warning efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of an early warning method for destructive behavior between granular bodies based on acoustic emission characteristics according to the present invention;

[0031] Figure 2 Schematic diagram of the triaxial loading test device and high-precision acoustic emission measurement system in the present invention;

[0032] Figure 3 This is a flow chart of an early warning method for the destructive behavior of granular silica sand based on acoustic emission characteristics of the present invention;

[0033] Figure 4 Schematic diagram of the original time-domain electrical signal of acoustic emission excited during the destruction process of granular silica sand in the present invention;

[0034] Figure 5 A schematic diagram of the definition of an acoustic emission event of the present invention;

[0035] Figure 6 Schematic diagram of the curve of deviation stress versus axial strain during the destruction of granular silica sand according to the present invention;

[0036] Figure 7 Schematic diagram of the curve of acoustic emission event rate versus axial strain during the destruction of granular silica sand according to the present invention;

[0037] Figure 8 This is a peak deviation stress-peak acoustic emission event rate-axial strain relationship curve established by the present invention based on experimental data. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] See also Figures 1-8 The present invention provides a technical solution: an early warning method for destructive behavior between granular bodies based on acoustic emission characteristics, comprising the following steps:

[0040] S01 places the prefabricated specimen on the base inside the triaxial loading device;

[0041] S02 installs the acoustic emission measurement system on the side wall of the sample placed in S01, waiting for the test;

[0042] S03 controls the confining pressure system of the triaxial device and the loading system of the triaxial device to destroy the specimen in S02;

[0043] S04 obtains the deviation stress applied to the sample by the loading device during the entire loading process, obtains the axial strain generated by the sample during the entire loading process, and obtains the original acoustic emission time domain electrical signal generated by the sample during the destruction process through the acoustic emission measurement system;

[0044] S05 processes and analyzes the original time-domain electrical signals of acoustic emission, extracts the characteristic parameters of acoustic emission, namely the acoustic emission event rate, and determines the sample failure behavior based on the peak deviation stress and the peak acoustic emission event rate. By analyzing the chronological order of the data after analysis, early warning information of material failure is issued in a timely and effective manner.

[0045] The peak deviation stress and peak acoustic emission event rate in S05 determine the failure behavior of the specimen, including:

[0046] The deviation stress is used to determine the curve of the deviation stress changing with the axial strain during the failure of the specimen;

[0047] The curve of acoustic emission event rate changing with axial strain during the specimen failure process was determined by the original acoustic emission time-domain electrical signal.

[0048] Determine the peak deflection stress from the axial strain relationship curve; determine the peak acoustic emission event rate from the axial strain relationship curve;

[0049] The failure behavior of the specimens was determined by the peak deviatoric stress and the peak acoustic emission event rate.

[0050] The chronological order of the data analyzed in S05, and the early warning information of material damage, includes:

[0051] Determine the axial strain corresponding to the peak deviation stress through the axial strain relationship curve;

[0052] The axial strain corresponding to the peak acoustic emission event rate was determined through the axial strain relationship curve.

[0053] By comparing the time sequence of peak deviation stress and peak acoustic emission event rate, early warning information of material damage is issued.

[0054] The time sequence of the peak deviation stress and peak acoustic emission event rate of the specimen includes three stages: post-peak stage, peak stage and pre-peak stage.

[0055] When the confining pressure applied to the specimen by the confining pressure system of the triaxial apparatus is low, the peak acoustic emission event rate occurs later than the peak deflection stress, which is the post-peak stage.

[0056] When the confining pressure system of the triaxial device applies moderate confining pressure to the specimen, the peak stage is when the peak acoustic emission event rate and the peak deviation stress appear simultaneously.

[0057] When the confining pressure applied to the specimen by the confining pressure system of the triaxial apparatus is high, the peak acoustic emission event precedes the peak deflection stress, which is the pre-peak stage;

[0058] When the confining pressure system of the triaxial device applies high confining pressure to the specimen, the peak acoustic emission event occurs before the peak deviation stress. This phenomenon can provide early warning information of the specimen's failure behavior based on the acoustic emission characteristics.

[0059] The sample is a granular material.

[0060] Example 1

[0061] The granular sample tested in this embodiment is a cylindrical granular silica sand sample with a particle size of 0.075 mm to 5 mm. The sample is prepared by the falling sand method. The size of the cylindrical granular silica sand sample is: diameter 50 mm × height 100 mm, and a rubber film with a thickness of 0.3 mm is wrapped on the side wall of the cylindrical granular sample.

[0062] The initial relative density of the cylindrical granular silica sand sample tested in a loose state is about 60%, and the initial relative density of the cylindrical granular silica sand sample tested in a dense state is about 90%;

[0063] The cylindrical granular silica sand samples were placed in dry conditions before and during the test, and the samples of each density were tested three times.

[0064] The acoustic emission measurement system includes: an acoustic emission sensor and an aluminum plate with a size of 10mm×10mm×1mm attached to the head of the acoustic emission sensor. At the same time, it is equipped with a signal amplifier, a high-performance data acquisition instrument and a data storage device to process, analyze and store the collected data.

[0065] The acoustic emission sensor (model: M304A) is a piezoelectric ceramic sensor produced by Fuji Ceramics. The probe has a built-in preamplifier with a gain of 20±2dB. The sensor operates at a frequency of 10kHz-5MHz (resonant frequency of 300kHz) and has a sensitivity of 115±3dB (reference: 0dB=1V / m / s). The acoustic emission signal amplifier (model: A1201) is a signal amplifier produced by Fuji Ceramics, with a gain of 53±3dB. The data acquisition instrument (model: PXIe-6366) is produced by National Instruments of the United States and has a sampling rate of 2MS / s.

[0066] Combine Figure 2 The loading test device includes: a base, a permeable stone, a loading rod, a top pressure plate, a load sensor, a plexiglass cylinder, a limit device, a loading piston, an external displacement sensor, a locking device, an acoustic emission sensor, an acoustic emission signal amplifier, a data acquisition instrument, and a data storage device.

[0067] Among them, the base and the top pressure plate are used as solid pressure heads, and the base and the top pressure plate are made of metal materials, but are not limited to metal materials. Those skilled in the art can make appropriate choices according to actual needs, and will not be described in detail here;

[0068] A closed loading chamber is formed by installing a plexiglass cylinder on the shell, and the set confining pressure stress can be applied through the bottom inflation valve;

[0069] A load sensor is provided at the propulsion end of the loading piston and is used to measure the axial load applied by the loading piston to the target sample;

[0070] The limiting device is provided at the end of the loading rod and the loading piston, and is used to control the loading rod and the loading piston to advance up and down at a predetermined loading speed;

[0071] The acoustic emission signal amplifier is connected to the acoustic emission sensor to further amplify the received acoustic emission signal and improve the signal-to-noise ratio of the signal;

[0072] The data acquisition instrument is connected to the acoustic emission signal amplifier to continuously record the original time domain electrical signal of the acoustic emission;

[0073] The data storage device is connected to the data acquisition device and is used for continuously storing the original time-domain electrical signals of the acoustic emission.

[0074] The working principle is as follows: the confining pressure stress is controlled by the bottom inflation valve, and in the process of destroying the sample by the loading rod and loading piston, the deviatoric stress applied to the target sample by the loading test device is obtained by the load sensor, the axial strain generated when the target sample is destroyed during loading is obtained by the external displacement sensor, and the original acoustic emission time domain signal generated by the target sample during the destruction process is obtained by the high-performance acoustic emission measurement system.

[0075] See also Figures 1-8 An early warning method for intergranular destructive behavior based on acoustic emission characteristics includes the following steps:

[0076] S01 places the prefabricated granular sample on the base inside the triaxial loading device;

[0077] S02 installs the sampling parts of the acoustic emission measurement system on the side wall of the granular sample placed in S01, waiting for the test; the sampling parts are the acoustic emission sensor and the aluminum plate, and the aluminum plate on the acoustic emission sensor is glued to the rubber membrane on the side wall of the cylindrical sample by glue.

[0078] S03 controlled the confining pressure system and the loading system of the triaxial apparatus to destroy the granular specimens in S02. The target confining pressure stresses were set to 100kPa, 200kPa, 400kPa, and 600kPa. The specimens were isotropically loaded at a loading rate of 5kPa / min to the target confining pressure stresses. During the test, the loading system of the triaxial apparatus subjected the specimens to drained triaxial compression tests at a constant strain rate of 0.10% / min. Loading was stopped at an axial strain of 30%.

[0079] S04 obtains the deviation stress applied to the granular sample by the loading device during the entire loading process, obtains the axial strain generated by the granular sample during the entire loading process, and obtains the original acoustic emission time domain electrical signal generated by the granular sample during the destruction process through the acoustic emission measurement system;

[0080] The deflection stress can be calculated by dividing the current axial load measured by the load cell by the current cross-sectional area, which can be corrected by dividing the constant sample volume by the current sample height.

[0081] The calculation formula is:

[0082] The axial strain can be calculated from the axial displacement. The axial strain is calculated by dividing the axial displacement by the original height of the specimen.

[0083] The sampling frequency of the load sensor of the loading device is set to 1S / s, the sampling frequency of the external displacement sensor is set to 1S / s, and the sampling frequency of the acoustic emission measurement system is set to 2MS / s; the original acoustic emission time domain signal collected is as follows Figure 4 As shown in the figure, the main sources of the acoustic emission signals collected at the same time are particle sliding, particle friction, initiation and development of cracks inside particles, etc.

[0084] S05 processes and analyzes the original time-domain electrical signal of acoustic emission, extracts the characteristic parameter of acoustic emission, acoustic emission event rate, and judges the failure behavior of granular sample according to the peak deviation stress and peak acoustic emission event rate;

[0085] The original acoustic emission time domain electrical signal received by the acoustic emission measurement system should be analyzed according to the voltage level caused by electrical and environmental noise, and the voltage threshold should be set. The judgment logic is that once the signal exceeds the threshold, the acoustic emission signal is identified and defined as an acoustic emission event (such as Figure 5 The acoustic emission events are accumulated at fixed time intervals and defined as the acoustic emission event rate.

[0086] Among them, the deviation stress during the failure process of the granular sample is the axial strain change curve;

[0087] The curve of acoustic emission event rate changing with axial strain during the failure process of granular silica sand sample;

[0088] Determine the peak deviation stress based on the deviation stress and axial strain relationship curve. (e.g. Figure 6 shown)

[0089] The peak stress obtained above reflects the magnitude of the shear stress that the sand can withstand, which is usually related to the initial failure of the sand.

[0090] The peak acoustic emission event rate is determined based on the relationship curve between the acoustic emission event rate and the axial strain. (e.g. Figure 7 shown)

[0091] The peak acoustic emission hit rate, representing the most severe particle interaction, is associated with the failure of the sand; the failure behavior of the bulk silica sand specimens is determined based on the peak deviation stress and the peak acoustic emission event rate.

[0092] By analyzing the chronological order of the data, early warning information of material damage can be issued in a timely and effective manner.

[0093] Among them, the time sequence of the analyzed data to issue early warning information of material damage includes: deviation stress and acoustic emission event rate;

[0094] The deviation stress is determined by the axial strain relationship curve to determine the axial strain corresponding to the peak deviation stress;

[0095] The acoustic emission event rate is determined by the axial strain relationship curve to determine the axial strain corresponding to the peak acoustic emission event rate.

[0096] Establish and compare the time sequence of peak deviation stress and peak acoustic emission event rate, and issue early warning information of material damage. (e.g. Figure 8 shown)

[0097] Among them, the time sequence of the peak deviation stress and peak acoustic emission event rate of granular samples includes:

[0098] The first stage: the post-peak stage, when the confining pressure system of the triaxial device applies a low confining pressure to the granular specimen (such as 100kPa, 200kPa), the peak acoustic emission event rate occurs later than the peak deviation stress, which is the post-peak stage.

[0099] The second stage is the peak stage. When the confining pressure system of the triaxial device applies moderate confining pressure to the granular sample, the peak acoustic emission event rate and the peak deviation stress appear at the same time.

[0100] The third stage is the pre-peak stage. When the confining pressure system of the triaxial device applies a high confining pressure to the granular sample (e.g., 600 kPa), the peak acoustic emission event occurs before the peak deviation stress occurs.

[0101] When the confining pressure system of the triaxial device applies high confining pressure to the granular sample, the peak acoustic emission event occurs before the peak deviation stress. This phenomenon can be used to issue early warning information on the failure behavior of the granular sample based on the acoustic emission characteristics.

[0102] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0103] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An early warning method for intergranular destructive behavior based on acoustic emission characteristics, characterized in that: The steps include: S01 places the prefabricated specimen on the base inside the triaxial loading device; S02 installs the acoustic emission measurement system on the side wall of the sample placed in S01, waiting for the test; S03 controls the confining pressure system of the triaxial device and the loading system of the triaxial device to destroy the specimen in S02; S04 obtains the deviation stress applied to the sample by the loading device during the entire loading process, obtains the axial strain generated by the sample during the entire loading process, and obtains the original acoustic emission time domain electrical signal generated by the sample during the destruction process through the acoustic emission measurement system; S05 processes and analyzes the original time-domain electrical signals of acoustic emission, extracts the characteristic parameters of acoustic emission, namely the acoustic emission event rate, and determines the sample failure behavior based on the peak deviation stress and the peak acoustic emission event rate. By analyzing the chronological order of the data after analysis, early warning information of material failure is issued in a timely and effective manner.

2. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 1 is characterized by: The peak deviation stress and peak acoustic emission event rate in S05 are used to determine the failure behavior of the sample, including: The deviation stress is used to determine the curve of the deviation stress changing with the axial strain during the specimen failure process; The curve of acoustic emission event rate changing with axial strain during the specimen failure process was determined by the original acoustic emission time-domain electrical signal.

3. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 2 is characterized by: Determine the peak deflection stress from the axial strain relationship curve; determine the peak acoustic emission event rate from the axial strain relationship curve; The failure behavior of the specimens was determined by the peak deviatoric stress and the peak acoustic emission event rate.

4. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 1 is characterized by: The time sequence of the data analyzed in S05 and the early warning information of material damage are as follows: Determine the axial strain corresponding to the peak deviation stress through the axial strain relationship curve; The axial strain corresponding to the peak acoustic emission event rate was determined through the axial strain relationship curve.

5. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 4 is characterized by: By comparing the time sequence of peak deviation stress and peak acoustic emission event rate, early warning information of material damage is issued.

6. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 5 is characterized by: The time sequence of the peak deviation stress and peak acoustic emission event rate of the specimen includes three stages: post-peak stage, peak stage and pre-peak stage.

7. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 6 is characterized by: When the confining pressure applied to the specimen by the confining pressure system of the triaxial apparatus is low, the peak acoustic emission event rate occurs later than the peak deflection stress, which is the post-peak stage.

8. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 6 is characterized by: When the confining pressure system of the triaxial apparatus applies moderate confining pressure to the specimen, the peak stage is when the peak acoustic emission event rate and the peak deviation stress appear simultaneously.

9. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to claim 6 is characterized by: When the confining pressure system of the triaxial apparatus applies a high confining pressure to the specimen, the peak acoustic emission event occurs before the peak deflection stress, which is the pre-peak stage; When the confining pressure system of the triaxial device applies high confining pressure to the specimen, the peak acoustic emission event occurs before the peak deviation stress. This phenomenon can provide early warning information of the specimen's failure behavior based on the acoustic emission characteristics.

10. The early warning method for intergranular destructive behavior based on acoustic emission characteristics according to any one of claims 1 to 9, characterized in that: The sample is a granular body.

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