Search

Backfilling is a promising measure for controlling surface subsidence in mined-out areas and disposing solid wastes from the mineral processing, there are increasing demands of enhanced toughness and anti-cracking properties of backfill materials to prolong the service life under the complex loads. In this study, polypropylene (PP) fibers were employed to improve performance of backfills, four-point bending and uniaxial compression tests were conducted to investigate the failure process and damage evolution of fiber-reinforced aeolian-sand backfill materials (FABs) using Digital Image Correlation (DIC) and Acoustic Emission (AE) techniques. The results show that the compressive strength tends to decrease with the increasing fiber volume fractions, while the four-point bending strength shows a tendency to increase initially and then decrease, and the optimum volume fraction of PP fiber is 0.6%. At the optimal fiber volume fraction, PP fibers with lengths of 3 mm and 9 mm resulted in a 65.25% and 81.62% increase in the four-point bending strength of FABs, respectively. As indicated by DIC measurements, PP fibers with a length of 9 mm were more effective in controlling the horizontal and vertical displacements of FABs under four-point bending loads than that of 3 mm, and the cracks developed more slowly at the same deflection. In addition, PP fibers with a length of 9 mm have stronger crack extension delay characteristics due to longer effective anchorage distance, as evidenced by more frequent acoustic emission ringing counts and higher cumulative ringing counts. The results of the study may provide a theoretical basis for the application of FABs materials in backfilling. [ABSTRACT FROM AUTHOR]

In order to study the dynamic damage evolution law of tunnel‐lining concrete with non‐through crack under single‐side sulfate attack, a 420‐day sulfate attack concrete test was conducted and the uniaxial compression and acoustic emission (AE) tests were carried out on each corrosion time. The test results showed that the compressive strength of each group can be divided into rising stage and falling stage, and the existence of non‐through crack reduced the compressive strength of concrete specimens and accelerated the corrosion of concrete specimens by sulfate. AE ringing count can be divided into compaction stage, elastic stage, yield stage, and post‐peak stage; the variation patterns of AE varied at different stages. Sulfate attack caused the yield point of concrete to advance. With the increase of corrosion time, microcracks increased gradually, cement mortar was consumed continuously, concrete spalling occurred, the proportion of AE cumulative ringing count Stage II decreased gradually, and the proportion of Stage III increased. Non‐through crack changed the energy storage of Stages II and III and reduced the AE activity of concrete after corrosion. The deeper the crack was, the smaller the average cumulative ringing count was and the lower the AE activity was. AE cumulative ringing counts can be used to characterize the damage evolution of corroded concrete. [ABSTRACT FROM AUTHOR]

To study the damage and acoustic emission (AE) energy evolution of basalt under high temperature, a series of tests under uniaxial stress are carried out on basalt heated at 25 °C, 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. Through the comprehensive analysis of AE parameters such as absolute energy and amplitude, the AE characteristics and damage evolution laws of basalt were explored. The results show that high temperature has a significant effect on the characteristics of rock stress–strain curve. With the increase of temperature, the compaction stage of the curve becomes longer, the plasticity increases, and the peak strength of basalt decreases. The higher the heat treatment temperature, the faster the strength decreases, and the strength decreases by 63.91% at 1000 °C. The AE localization points converge from the dispersed state to the aggregated state. With the increase of temperature, the period of convergent nucleation of the AE localization sites is advanced, high amplitude AE signals shifted from a concentrated distribution near the peak stress to a discrete distribution throughout the entire process. The heat treatment of the rock has an additive effect on the burstiness. 600–800 °C can be used as the threshold temperature of basalt to transform from brittle failure to plastic failure. The high temperature effect is responsible for the transition of the AE cumulative absolute energy at 400–600 °C. The influence of high temperature on damage evolution is discussed. The initial damage increases exponentially after 800 °C. With the increase of temperature, the evolution rate of damage variable becomes faster and gradually changes from linear to nonlinear. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) can monitor and evaluate the cracking situations of hydraulic structures for it is real-time and non-destructive. However, a current challenge of this approach is to accurately identify the various stages during the cracking process. The innovation of this paper lies in the application of AE data in analyzing the stage characteristics during the whole process of hydraulic concrete fracture. First, the slope changing of the cumulative ringing count curve was used to determine the cracking stages of hydraulic concrete. Second, the function of inter-event times (denoted as F-function) was used to further investigate the AE characteristics proximity to the final fracture. Last, the spatial-temporal-energy evolution of cracks was studied. The results show that: (1) The whole process of hydraulic concrete failure shows an obvious stage characteristic from the perspective of AE feature and it can be distinguished to five stages by the slope change of the cumulative ringing count curve; (2) The F-function can be used to identify the last two cracking stages, and it is capable of early warning the macroscopic cracking in ahead of b-value; (3) The spatial-temporal-energy distribution of cracks helps to better understanding the generation and evolution for cracks inside hydraulic concrete. [ABSTRACT FROM AUTHOR]

Recently developed multi-scale fiber (i.e., CaCO3 whisker, polyvinyl alcohol (PVA) fiber, and steel fiber) reinforced rubberized concrete exhibits excellent mechanical properties and spalling resistance at high temperatures. Measurement of macro properties such as strength and Young's modulus cannot reveal and characterize damage mechanisms, particularly those relating to the multi-scale fiber strengthening effect. In this study, acoustic emission (AE) technology is applied to investigate the impact of multi-scale fiber on the damage evolution of rubberized concrete exposed to high temperatures, under the uniaxial compression and tension loading processes. The mechanical properties, AE event location, peak frequency, b-value, the ratio of rise time to amplitude (RA), average frequency (AF) values, and AE energy of specimens are investigated. The results show that the number of events observed using AE gradually increases as the loading progresses. The crumb rubber and fibers inhibit the generation and development of the cracks. It is concluded that both the peak frequency and b-value reflect the extension process of cracks. As the cracks develop from the micro scale to the macro scale, the peak frequency tends to be distributed in a lower frequency range, and the b-value decreases gradually. At the peak stress point, the AE energy increases rapidly and the b-value decreases. The specimens without multi-scale fibers exhibit brittle failure, while the specimens with fibers exhibit ductile failure. In addition, adding multi-scale fibers and crumb rubber increases the peak frequency in the medium and high frequency ranges, indicating a positive effect on inhibiting crack development. After being subjected to high temperatures, the maximum and minimum b-values decrease, reflecting an increase in the number of initial cracks due to thermal damage. Meanwhile, the RA and AF values are used to classify tensile and shear cracks. The specimens fracture with more shear cracks under compression, and there are more tensile cracks in specimens with multi-scale fibers under tension. [ABSTRACT FROM AUTHOR]

Depleted gas reservoirs are important natural gas storage media, thus research on the mechanical properties and damage evolution of reservoir rocks under alternating load conditions has significant practical implications for seal integrity studies. This paper conducted multi-level cyclic loading triaxial compression experiments on medium-porosity medium-permeability sandstone under different confining pressures and used acoustic emission (AE) instruments to detect the AE characteristics during the experiment, analyzing the mechanical characteristics, AE, and damage evolution characteristics. The experimental results show that after cyclic loading, the peak strength of sandstone increased by 14–17%. With the increase in the upper limit stress of cyclic loading, the elastic modulus showed a trend of first increasing and then gradually decreasing. The damage variable of rock samples rose with a rise in the upper limit stress of cyclic loading and confining pressure, and the rock damage was mostly localized at the peak stress. The AE b-value increased generally as confining pressure increased, showing that fractures occurred quicker and more unevenly at lower confining pressures. The distribution of RA-AF values shows that a sudden increase in stress causes the initiation and expansion of cracks in medium-permeability sandstone, and that tensile and shear cracks form continuously during the cyclic loading process, with shear cracks developing more pronounced. This research can provide some theoretical guidance for the long-term stable operation and pressure enhancement expansion of depleted gas reservoir storage facilities. [ABSTRACT FROM AUTHOR]

Abstract Backfilling is a promising measure for controlling surface subsidence in mined-out areas and disposing solid wastes from the mineral processing, there are increasing demands of enhanced toughness and anti-cracking properties of backfill materials to prolong the service life under the complex loads. In this study, polypropylene (PP) fibers were employed to improve performance of backfills, four-point bending and uniaxial compression tests were conducted to investigate the failure process and damage evolution of fiber-reinforced aeolian-sand backfill materials (FABs) using Digital Image Correlation (DIC) and Acoustic Emission (AE) techniques. The results show that the compressive strength tends to decrease with the increasing fiber volume fractions, while the four-point bending strength shows a tendency to increase initially and then decrease, and the optimum volume fraction of PP fiber is 0.6%. At the optimal fiber volume fraction, PP fibers with lengths of 3 mm and 9 mm resulted in a 65.25% and 81.62% increase in the four-point bending strength of FABs, respectively. As indicated by DIC measurements, PP fibers with a length of 9 mm were more effective in controlling the horizontal and vertical displacements of FABs under four-point bending loads than that of 3 mm, and the cracks developed more slowly at the same deflection. In addition, PP fibers with a length of 9 mm have stronger crack extension delay characteristics due to longer effective anchorage distance, as evidenced by more frequent acoustic emission ringing counts and higher cumulative ringing counts. The results of the study may provide a theoretical basis for the application of FABs materials in backfilling.

To study the deformation failure and damage evolution law of weathered granite (WG) under different confining pressures, triaxial compression simultaneous acoustic emission (AE) tests were conducted on WG, and the mechanical and AE parameter characteristics of WG were obtained. It is shown that with the increase of confining pressure, the strength and modulus of elasticity of WG increase, and the failure pattern evolves from splitting failure to shear failure. Using the Mohr-Coulomb criterion, the cohesion c of WG is calculated to be 7.03 MPa, and the angle of internal friction φ is 61.95°. Analysing the AE peak frequency and energy at the characteristic points of the differential stress-axial strain curves, it is evident that the confining pressure limits crack evolution. The fractal characteristics of the WG AE ringing counts at each confining pressure are good, and the correlations between their ln r-ln C(r) curves and the fitted curves are all above 0.90. The WG at each confining pressure showed an increasing growth rate in the values of the damage variables and a rapid and substantial decrease in the fractal dimension before failure occurred. The study's results can provide a theoretical basis for the stability analysis of the WG surrounding rock. [ABSTRACT FROM AUTHOR]

Aiming at effectively utilizing recycled coarse aggregate (RCA) in sustainable construction, it is necessary to study the internal damage evolution of steel fiber–reinforced recycled-aggregate concrete (SFRAC) under dynamic tensile loads and the reinforced mechanism of steel fiber. The influences of the steel fiber content, the recycled-aggregate replacement ratio, and the loading rate on the mechanical properties and dynamic damage of SFRAC were studied using the Brazilian disc splitting test and acoustic emission (AE) technology. Then, the mechanism of crack evolution was investigated by means of the parameter analysis method. The results indicate that the existence of RCA makes the mechanical properties of recycled-aggregate concrete worse than those of normal concrete and weakens the strain rate effect of splitting tensile strength, whereas this negative influence can effectively be improved by steel fiber. The preferable steel fiber contents obtained from the splitting tensile strength and peak displacement are 1.0% and 1.5%, and under these conditions, the SFRAC replaced by 30% RCA has a mechanical performance superior to that of normal concrete. It is also found that the damage degree and energy absorbing capacity of SFRAC can be identified by analyzing the ring and energy counts of the AE signal. Furthermore, the evolution of the crack pattern of SFRAC under dynamic axial tensile load is well reflected by the rise angle and average frequency. Increased steel fiber content and recycled-aggregate replacement ratio can change the failure mode to a complex tensile-shear mixed failure, and the shear crack gradually becomes the main crack with increasing loading rates. Practical Applications: The public environment crisis from the greenhouse effect led to a series of measures from all industries worldwide. The widespread use of concrete has brought with it serious environmental and energy-saving problems. The construction industry preliminarily attempts to replace natural aggregate by recycled aggregate obtained by crushing construction solid waste in green low-carbon buildings, which shows considerable carbon sequestration and emission reduction. However, recycled aggregate has poor mechanical properties such as low strength and high porosity. When participating in concrete configuration, this defect seriously affects the strength of the material and limits its wide application in construction engineering. For a component with strength requirements or special purposes, fiber can be adopted to improve the mechanical properties of recycled-aggregate concrete. This study examines the damage process of fiber-reinforced recycled-aggregate concrete with the microscopic method and proposes a satisfactory mix proportion. Naturally, these analysis methods require more time and effort than a basic macroscopic analysis. Moreover, proper research on the mechanism of damage evolution under dynamic loading is crucial. [ABSTRACT FROM AUTHOR]

Unveiling the mechanical properties and damage mechanism of the complex composite structure, comprising backfill and surrounding rock, is crucial for ensuring the safe development of the downward-approach backfill mining method. This work conducts biaxial compression tests on backfill–rock under various loading conditions. The damage process is analyzed using DIC and acoustic emission (AE) techniques, while the distribution of AE events at different loading stages is explored. Additionally, the dominant failure forms of specimens are studied through multifractal analysis. The damage evolution law of backfill–rock combinations is elucidated. The results indicate that DIC and AE provide consistent descriptions of specimen damage, and the damage evolution of backfill–rock composite specimens varies notably under different loading conditions, offering valuable insights for engineering site safety protection. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Transversely isotropic rocks, which are special anisotropic materials, are widely encountered in civil, mining, petroleum, geothermal, and radioactive waste-disposal engineering. Rock is frequently subject to cyclic loads resulting from natural and human-caused events. However, to date, the fracture mechanism of transversely isotropic rocks under cyclic loading remains poorly understood. To address this gap, uniaxial monotonic-loading and cyclic-loading tests were performed on slate specimens by the MTS815 system, during which acoustic emission (AE) signals inside the rock were monitored, and finally the fracture surfaces of the tested rock were scanned by scanning electron microscopy (SEM). Through these tests, the anisotropic mechanical properties, damage evolution, AE characteristics and fracture pattern of slate as a transversely isotropic rock were studied. The results show that the peak strength of specimens varies with the loading–foliation angle under monotonic and cyclic loading, following a U-shaped trend. The deformation modulus during unloading is more capable of characterizing the damage inside the specimen than that during loading. By defining the damage degree based on dissipation energy, it is found that the damage variable is influenced by the loading–foliation angle and the cyclic stress step. The AE characteristics of specimens exhibit significant anisotropy, closely correlated to the loading condition and loading–foliation angle. Regardless of cyclic stress step, the AE counts of specimens with a loading–foliation angle of 0° are mainly distributed near the peak region, whereas those of specimens with other loading–foliation angles occur primarily in the early stage of each cyclic loading. Finally, it is revealed that the fracture mechanism of slate specimens is determined by the loading–foliation angle, loading condition, and cyclic stress step. [ABSTRACT FROM AUTHOR]

In this work, a novel method for damage evolution analysis of concrete under uniaxial compression is proposed based on the multi-feature acoustic emission (AE) and the Gaussian mixture model (GMM) clustering. The hierarchical clustering algorithm is adopted to select optimal AE parameters, while multiple features of these parameters are generated through the principal component analysis (PCA). Then the concrete damage signals are separated by using the GMM clustering with multiple features. Meanwhile, the waveform signals associated with concrete damage in each cluster are validated using the Fast Fourier transform (FFT) and the continuous wavelet transform (CWT). Finally, the damage evolution process of concrete under uniaxial compression is divided based on the variation of AE characteristics. The results show that the frequency ranges of signals for micro-cracks, mixed cracks and friction of concrete under uniaxial compression are 20–30 kHz, 20–65 kHz, and 100–120 kHz, respectively. The damage process of concrete under uniaxial compression is divided into three stages according to the inflection points of the cumulative energy curve, namely the initial compaction stage, the crack formation stage and the failure stage. [ABSTRACT FROM AUTHOR]

Nuclear power is a high-quality clean energy source, but nuclear waste is generated during operation. The waste continuously releases heat during disposal, increasing the adjoining rock temperature and affecting the safety of the disposal site. Basalt is widely considered a commonly used rock type in the repository. This study of basalt's mechanical characteristics and damage evolution after thermal damage, with its far-reaching engineering value, was conducted by combining experimental work and theory. Uniaxial compression tests were conducted on basalt exposed to 25 °C, 500 °C, 700 °C, 900 °C, and 1100 °C conditions, and acoustic emission (AE) equipment was utilized to observe the acoustic emission phenomenon during deformation. This study was carried out to examine the mechanical characteristics, the sound emission features, the progression of damage laws, and the stress–strain framework of basalt after exposure to different types of thermal harm. As the temperature rises, the rock's maximum strength declines steadily, the peak strain rises in tandem, the rock sample's ductility is augmented, the failure mode changes from shear to tensile failure, and cracks in the failure area are observed. At room temperature, the acoustic emission signal is more vigorous than in the initial stage of rock sample loading due to thermal damage; however, after the linear elastic stage is entered, its activity is lessened. In cases where the rock approaches collapse, there is a significant surge in acoustic emission activity, leading to the peak frequency of acoustic emission ringing. The cumulative ring count of acoustic emission serves as the basis for the definition of the damage variable. At room temperature, the damage evolution of rock samples can be broken down into four distinct stages. This defined damage variable is more reflective of the entire failure process. After exposure to high temperatures, the initial damage of the rock sample becomes more extensive, and the damage variable tends to be stable with strain evolution. The stress–strain constitutive model of basalt deformation is derived based on the crack axial strain law and acoustic emission parameters. A powerful relationship between theoretical and experimental curves is evident. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The three-point bending damage process of an A7N01 aluminum alloy body material and weld seam in an electric multiple unit train was monitored using acoustic emission (AE) and digital image technology. The AE signal characteristics of static load damage to the aluminum alloy and weld seam were studied using the AE signal parameter and time–frequency analysis. Based on the observation of the microstructure and fracture morphology, the source mechanism of AE signals was analyzed. The experimental results indicate that AE energy, centroid frequency, and peak frequency are effective indices for predicting the initiation of cracks in A7N01 aluminum alloy and weld seams. The digital image monitoring results of the notch tip damage evolution of aluminum alloy samples confirmed the predictions based on AE energy, centroid frequency, and peak frequency for crack initiation. The AE signal source mechanism revealed that the differences in AE characteristics between the base material and weld seam can be attributed to microstructure variations and fracture modes. In summary, the AE technique is more sensitive to changes in the fracture mode and can be utilized to monitor the damage evolution of welded structures. [ABSTRACT FROM AUTHOR]

Quasi-static indentation (QSI) experiments are conducted to investigate the localization, identification and evolution of induced damage in laminate composite up to delamination initiation using acoustic emission (AE) techniques. In this study, we propose a continuous wavelet transform (CWT)-based damage localization method for composites, which can simultaneously identify two damage modes, namely matrix cracking and delamination. The experimental findings demonstrate that the proposed algorithm, which utilizes the arrival time difference within a specific frequency band of the AE signal, effectively reduces the average location error from 3.81% to 2.31% compared to the existing method. Furthermore, the average signal location time has significantly decreased from several minutes to a mere 2 s. Matrix cracking and delamination are identified based on the maximum frequency band of CWT. Both types of damage exhibit prominent peaks within the 40 kHz–50 kHz frequency range, indicating their shared nature as manifestations of matrix damage, albeit with distinct modes of presentation. The first damage pattern that occurs is matrix cracking, succeeded by delamination damage. The nonlinear phase of the mechanical response curve is associated with the rapid aggregation of matrix cracking. Before the onset of macroscopic delamination damage, microscopic delamination damage begins to accumulate. A concentration of high-energy delamination damage signals predicts the initiation of macroscopic delamination. [ABSTRACT FROM AUTHOR]

Ancient masonry constructions and historical buildings, such as cathedrals, are exposed to considerable risks attributed to factors like ageing and long-term exposure to both dynamic and static variations in loading conditions. In this study, an innovative and promising monitoring approach was applied to assess the structural integrity of the vault in the central nave of the Turin Cathedral. Specifically, the outcomes obtained from Acoustic Emissions (AE) are correlated with the insights derived from the Thrust Network Analysis (TNA) conducted on the structure. This analysis considers the structural elements introduced early in the twentieth century to mitigate horizontal forces. Acoustic Emission (AE) is a commonly employed technique in structural monitoring to detect and analyze elastic waves generated by crack formation, providing valuable information about structural damage. The Thrust Network Analysis (TNA) is an approach that applies Heyman's principles to represent stress in masonry vaults. This method models the stresses as a discrete network of forces, achieving equilibrium with gravitational loads. In this context, the results obtained by TNA analysis are strictly correlated with AE localization results.

Unveiling the mechanical properties and damage mechanism of the complex composite structure, comprising backfill and surrounding rock, is crucial for ensuring the safe development of the downward-approach backfill mining method. This work conducts biaxial compression tests on backfill–rock under various loading conditions. The damage process is analyzed using DIC and acoustic emission (AE) techniques, while the distribution of AE events at different loading stages is explored. Additionally, the dominant failure forms of specimens are studied through multifractal analysis. The damage evolution law of backfill–rock combinations is elucidated. The results indicate that DIC and AE provide consistent descriptions of specimen damage, and the damage evolution of backfill–rock composite specimens varies notably under different loading conditions, offering valuable insights for engineering site safety protection.

The research aimed to examine the impact of different pH solutions on the tensile mechanical properties of saturated and natural sandstone specimens. The study utilized the WHY-300/10 microcomputer-controlled pressure testing machine to conduct Brazil splitting tests and employed acoustic emission and local dynamic strain testing techniques. The results indicated the tensile strength and split tensile modulus of the sandstone specimens gradually decreased with the polarisation of the solution pH, and the acoustic emission signal ring number monitoring values showed an increasing trend. The pH of the soaking solution followed an exponential decay pattern over time, eventually tending towards weak alkalinity. A new damage variable based on the cumulative ring count after chemical corrosion was defined to indirectly analyze the degree of corrosion degradation. It was discovered that in acidic or alkaline environments, the internal crystals of the rock are dissolved, weakening the mineral interconnections and causing a deterioration in tensile stress and strength. These findings can provide valuable insights for ensuring the safety and stability of the Denglou Mountain Tunnel in Yunnan Province. [ABSTRACT FROM AUTHOR]

It is helpful to study the creep process of rock by modeling the process of damage evolution in triaxial creep test. Based on the statistical distribution of strength of representative element, a dynamic damage model suitable for the initial loading stage is established. From the perspective of strength deterioration of representative element, the similarity of damage characteristics between characteristic representative element and rock sample during creep is found, and a time-dependent damage model suitable for the constant loading stage is also obtained. And the quantitative identification of parameters in the damage model is realized based on the cumulative acoustic emission (AE) count, which reveals the whole process of damage evolution in triaxial creep test. In addition, the power-law dashpot suitable for the accelerated creep stage is proposed, and the fractional non-Newtonian creep model considering the damage evolution is further established. The parameters of creep model are also identified by the stepwise least square fitting (LSF), and the applicability and superiority of the models are verified. [ABSTRACT FROM AUTHOR]

The three-point bending damage process of an A7N01 aluminum alloy body material and weld seam in an electric multiple unit train was monitored using acoustic emission (AE) and digital image technology. The AE signal characteristics of static load damage to the aluminum alloy and weld seam were studied using the AE signal parameter and time–frequency analysis. Based on the observation of the microstructure and fracture morphology, the source mechanism of AE signals was analyzed. The experimental results indicate that AE energy, centroid frequency, and peak frequency are effective indices for predicting the initiation of cracks in A7N01 aluminum alloy and weld seams. The digital image monitoring results of the notch tip damage evolution of aluminum alloy samples confirmed the predictions based on AE energy, centroid frequency, and peak frequency for crack initiation. The AE signal source mechanism revealed that the differences in AE characteristics between the base material and weld seam can be attributed to microstructure variations and fracture modes. In summary, the AE technique is more sensitive to changes in the fracture mode and can be utilized to monitor the damage evolution of welded structures.

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The essence of rockburst is the sudden release of energy accumulated in the rock. High-strength energy-absorbing anchoring bolt is an effective means for rockburst control. We conducted rockburst tests on the intact rock and rocks anchored by a new type of energy-absorbing material with high-strength, high-elongation, and high-energy-absorbing characteristics. Subsequently, we analyzed the damage evolution and acoustic emission characteristics of the intact, single-anchored, and double-anchored rocks. Then we explored the control mechanism of the constant-resistance energy-absorbing (CREA) bolt to rockburst. Our experimental results show that the rockburst process includes two stages: gradual damage stage and accelerated damage stage. The time and stress at the beginning of the damage acceleration are about 80% of the rockburst time and peak stress. Compared with the intact rock, the high-amplitude and high-energy signals are significantly reduced in the rocks reinforced by the CREA bolts, indicating that the CREA reinforcement can effectively control the energy release from rockburst. Considering rockburst energy criterion, we find that the rockburst peak stress in single-anchored and double-anchored rocks is 2.0 times and 2.2 times of the uniaxial compressive strength, respectively. The energy required for rockburst in these two anchored rocks is increased by 15.8% and 37.1%, respectively, compared with the intact rock. Therefore, CREA reinforcement can effectively reduce the risk of rockburst. The findings from this work can provide a reference for designing energy-absorbing reinforcing system for rockburst prevention in underground engineering. Highlights: A new type of constant resistance energy-absorbing (CREA) material is developed. The rockburst tests of rocks anchored by CREA material are conducted. The damage evolution of rock anchored by CREA material are obtained. The burst resistance mechanism of rock with different anchoring quantity is clarified. [ABSTRACT FROM AUTHOR]

When subjected to significant loading, damage occurs in rock, leading to degradation of mechanical properties and increased wave attenuation. Although wave propagation in porous and jointed rocks has been extensively studied, influences of damage evolution on wave propagation are not fully understood. In this study, damage evolution and its influence on ultrasonic wave propagation in unconfined uniaxially loaded granite specimens were experimentally investigated. Granite specimen was firstly compressed to a certain load to generate damage and then unloaded immediately. The stress-driven damages in granite specimens during and after loading were quantified by acoustic emission and micro-CT scanning, respectively. Meanwhile, ultrasonic wave propagation in granite specimen along the loading direction was measured during and after loading, respectively. Results showed that the stress-driven damage in granite specimen is highly nonlinear, it increases drastically to the peak when the axial stress approaches the peak point. The stress-driven damage during loading is higher than that after loading. Wave propagation in granite is stress-dependent during compression. Both wave amplitude and velocity increase first and then decrease before the axial stress increasing to approximately 60 and 90% of the uniaxial compressive strength of the granite, respectively. However, compared with wave velocity, wave amplitude is more sensitive to stress and the stress-driven damage. The findings of this study could facilitate a better understanding of the relationship between damage evolution and wave propagation and attenuation in rocks. Highlights: The acoustic emission and micro-CT scanning can be adopted to quantify stress-driven damage in granite specimens. Wave amplitude is much more sensitive to stress and the stress-driven damage than wave velocity. Wave propagation is affected by the competition between the enhancing effect due to closure of initial cracks and the weakening effect due to generation of new cracks. [ABSTRACT FROM AUTHOR]

This paper discusses the combined application of the lattice discrete element method (LDEM) and the acoustic emission (AE) technique to analyze damage in quasi-brittle materials. These methods were used to study the damage in a concrete slab under pure-shear stress and a pre-fissured sandstone beam subjected to three-point bending. The first test was restricted to simulation results, whereas the second included experimental data. The discrete element method was used to perform the simulations for both tests, whereas the corresponding results and the information from the experiments were assessed using AE analysis tools. It was shown that the synergistic use of these two methods led to a comprehensive understanding of the two analyzed cases and offered an effective, generalizable approach for assessing damage processes in quasi-brittle materials. [ABSTRACT FROM AUTHOR]

In this study, the characteristics of the fracture evolution of argillaceous shale under increasing-amplitude loading were investigated. The GCTS RTR-2000 test system and in-situ acoustic emission (AE) monitoring were employed to execute the tests. The following results were observed. (1) The strength, deformation, and fatigue life increased with the frequency, and the morphology of the hysteresis curve changed regularly with time. (2) The cumulative damage of the rock at the location in which the stress amplitude suddenly increased exceeded that at the fatigue loading stage. The AE count and AE energy were affected by the loading frequency. (3) The secant modulus exhibited different values for different loading frequencies; the smaller the loading frequency, the fewer loading stages the samples experienced, and the faster the secant modulus decreased. The change in Poisson's ratio over the entire process was composed of a steady growth stage and a rapid growth stage. (4) The rock exhibited two stages of damage evolution, with rapid damage accumulation occurring at the beginning of the loading and relatively smooth damage occurring thereafter. This study developed a cumulative fatigue damage model that can adequately fit the accumulated damage during the fracturing process. The experiments revealed that variable amplitude fatigue loading at different frequencies significantly influences the damage deterioration and the failure law of the rock. The results are expected to improve the understanding of the frequency effect on the fracture behavior and help predict the lifespan of rock structures. This is of great significance to the promotion of slope management, landslide disaster prevention, and mine reuse at the West Open-pit Mine. [ABSTRACT FROM AUTHOR]

Soft sandstones are known to deteriorate with increasing water saturation. This study explores the effects of different immersion heights on the failure characteristics of soft sandstone obtained from the second member of the Paleogene Eocene Lushi Formation. Uniaxial compression strength (UCS) tests are performed on the rock samples with acoustic emission (AE) monitoring. The results show that water reduces the required stress level for initiating and expanding microcracks within the samples, severely affecting the damage characteristics. With an increase in immersion height, soft sandstone’s uniaxial compressive strength and elastic modulus linearly decrease. The P-wave propagation velocity also gradually decreases, and the number, activity, main peak frequency, energy, and amplitude peak of AE events decrease. There is a negative correlation between the main peak frequency of acoustic emission and the crack scale in the rock samples, and the AE characteristics better reflect the damage and failure characteristics of rock samples. In general, raising the immersion height increases the deterioration effect on the soft sandstone. Furthermore, the results of UCS and AE monitoring are then used to establish a simplified damage constitutive relationship of soft sandstone with different water immersion heights and the instantaneous and cumulative damage variables calculation method. [ABSTRACT FROM AUTHOR]

Detecting welding defects is a key aspect in the safety assessment of pressure vessels. Using non-destructive testing methods to reveal influences of welding defects on the evolution of material damage is of great significance. In this paper, the damage evolution of Q245R steel with different welding defects was monitored by acoustic emission and infrared thermography technology. First, cluster analysis was used to reduce the effects of noise on acoustic emission signals. Then, differences in the characteristic parameters during the damage evolution were compared. Furthermore, the predominant peak frequency and time-frequency spectrum using fast Fourier transform and wavelet transform were investigated for acoustic emission waveforms, and temperature changes were monitored during damage evolution using thermal conductivity. The results indicated that the effects of different welding defects on the damage evolution of Q245R steel can be effectively revealed through the non-destructive testing technology combining acoustic emission and infrared thermography, which can provide a reference for evaluating the overall structural health of pressure vessels and reducing the failure risk. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The variation of pore structure results in a significant difference in physical–mechanical properties within coral reef limestone (CRL). The acoustic emission (AE) and digital volume correlation (DVC) techniques were utilized to investigate the damage evolution characteristics of four structural types of CRL under uniaxial compression. The influence of pore structure on the fracture mechanism of CRL was revealed from the microscopic perspective. The results suggested that the failure patterns of CRL specimens gradually transferred from brittle tensile failure to ductile shear failure with the increase of porosity. Based on the AE technique, the damage evolution process of CRL was comparatively analyzed. The AE evolution characteristics of the coral framework limestone (CFL) and coral boulder limestone (CBL) were similar to conventional brittle rocks. Furthermore, the coral gravel limestone (CGL) and coral calcarenite limestone (CCL) stimulated a considerable amount of AE signal during the initial compression stage by adjustment of sand particles. Using the computerized tomography (CT) scanning-based DVC method, the strain field distribution after the failure of CRLs with different structures was revealed, and the interaction mechanism between pore and crack was analyzed. Finally, the crack volume strain (CVS), lateral strain response (LSR), and AE cumulative energy were used to determine the crack initiation stress range in CRLs of four structures. According to the range of crack initiation stress, the results obtained by the on-site microseismic monitoring and in-situ stress measurement can be used to determine the stress state and plastic zone extent in the coral reef strata, which provides a reference for the design of support schemes in the construction of island reefs. Highlights: With the increase of porosity, the failure pattern of coral reef limestone gradually changed from brittle tensile failure to ductile shear failure. The strain field anisotropy of coral framework, coral boulder, and coral gravel limestones was more pronounced. The speckle quality of coral boulder and coral gravel limestones was more robust than that of coral framework and coral calcarenite limestones. [ABSTRACT FROM AUTHOR]

The stability and safety of rock mass in underground constructions are influenced by the damage processes of cracks evolution caused by the excavation under coupled hydro-mechanical loading conditions. In this paper, to understand the crack development and damage evolution of sandstone under different seepage conditions, a series of triaxial compression tests with acoustic emission under different water pressures (5, 10, 15 MPa) are carried out. The stress-strain behavior, crack stress thresholds, failure mode, AE characteristics and micromechanical mechanisms are analyzed and discussed. The experimental results demonstrate that the crack stress thresholds and the mechanical property of studied sandstone decrease with the increase of water pressure. Moreover, the water pressure has an important influence on and deformation behavior of sandstone, for instance, the elastic modulus and deformation modulus decreased when the water pressure increased. Based on the result of accumulated ring counts, the damage evolution of sandstone gradually increased with increasing water pressure. Finally, the micro-structural evolution under the coupling effects of water pressure and applied stress is discussed. The obtained results can be used to identify the initiation and propagation of studied sandstone in the engineering applications. [ABSTRACT FROM AUTHOR]

In this study, cyclic loading–unloading experiments on coal samples with different moisture contents were conducted. The damage mechanism was investigated through acoustic emission (AE) monitoring. The validity of the average frequency and rise angle (RA–AF) correlation for the fracture evolution of water-bearing coal samples under cyclic loading was verified. The damage evolution equation of coal samples based on energy dissipation theory was proposed. The results show that at the same growth rates of damage variables for the three water-bearing coal samples, there is a characteristic stress σ' (σ' = 5.36 MPa, N = 3) in the evolution of damage variables of the samples. Under cyclic loading, the moisture content was negatively correlated with the damage variable during the initial damage stage, while the two were positively correlated during the accelerated damage stage. The total strain energy of the water-bearing coal samples increases with the increase in the loading cycles, and the higher the moisture content, the greater is the total strain energy. The results of cyclic loading–unloading experiments demonstrate that there is a correlation between the damage process caused by moisture content and stress in coal samples, and the evolution of dissipation energy and the development of hysteresis loops are both related to the presence of the characteristic stress σ'. The RA–AF scatter plot and probability density plot feedback of each period correspond to the characteristics of damage evolution. This study verifies the feasibility of RA–AF qualitative evaluation of fracture type evolution mode of water-bearing coal samples under cyclic loading. Highlights: The coal pillar dams of the underground reservoir are simplified to the model of coal samples with different moisture contents under cyclic loading. There is a characteristic stress σ' in the evolution of damage variables of the water-bearing coal samples under cyclic loading–unloading. Based on energy dissipation theory, the equations describing the damage evolution of water-bearing coal samples are established. Qualitative characterization of the evolution of fracture types within each cycle using RA–AF correlation was studied. [ABSTRACT FROM AUTHOR]

The utilization of deep mineral resources is severely restricted by dynamic disasters, such as rock burst, caused by mining disturbances. This study is aimed at investigating the instability failure mechanism and precursory response of coal specimen, with the aid of acoustic emission (AE) monitoring, under triaxial loading and unloading disturbance. The AE time-varying characteristics were analyzed, the crack propagation mode was explored, and the statistical b value and βt value (damage parameters) of AE events were introduced to evaluate the damage state of the loaded coal under disturbance. The results show that: the dynamic disturbance loads will accelerate the deformation process of coal specimen under high static confining stress, resulting in a positive relation between the AE characteristic parameters (AE counts and energy) and the increasing disturbance amplitude. The proportion of low-frequency and high-amplitude AE signals increases with the disturbance amplitude, indicating the disturbance with large amplitude will promote the formation of large-magnitude cracking events. Those stress-induced cracks, judged from the RA-AF value of AE signals, are mainly tensile mode (i.e., mode-I) under the applied disturbance load, but shear cracks are the critical factor affecting the instability and failure of the loaded coal specimen. Both the b value and βt value can reflect the time-varying evolution process of internal damage for the loaded coal specimen. The sudden decreasing of the b value together with the exponential increasing of the βt value can be regarded as a short-impending precursor indicator for the coal instability and failure. The results of this study will provide some experiment basic and theoretical guidance for dynamic disaster monitoring and early-warning during the deep coal mining. Highlights: The instability failure mechanism and the precursory response of coal specimens under triaxial loading and unloading disturbance were investigated. By analyzing the AE characteristic parameters, the internal damage evolution processes, crack propagation mode and the mechanisms of disturbance were studied. The damage accumulation process and precursor warning information of coal instability failure are extracted by the b and βt values. [ABSTRACT FROM AUTHOR]

Quasi-static indentation (QSI) experiments are conducted to investigate the localization, identification and evolution of induced damage in laminate composite up to delamination initiation using acoustic emission (AE) techniques. In this study, we propose a continuous wavelet transform (CWT)-based damage localization method for composites, which can simultaneously identify two damage modes, namely matrix cracking and delamination. The experimental findings demonstrate that the proposed algorithm, which utilizes the arrival time difference within a specific frequency band of the AE signal, effectively reduces the average location error from 3.81% to 2.31% compared to the existing method. Furthermore, the average signal location time has significantly decreased from several minutes to a mere 2 s. Matrix cracking and delamination are identified based on the maximum frequency band of CWT. Both types of damage exhibit prominent peaks within the 40 kHz–50 kHz frequency range, indicating their shared nature as manifestations of matrix damage, albeit with distinct modes of presentation. The first damage pattern that occurs is matrix cracking, succeeded by delamination damage. The nonlinear phase of the mechanical response curve is associated with the rapid aggregation of matrix cracking. Before the onset of macroscopic delamination damage, microscopic delamination damage begins to accumulate. A concentration of high-energy delamination damage signals predicts the initiation of macroscopic delamination.

• Compression-shear fracturing experiments on thermally-treated granites are performed. • Thermal effects on physical properties and response of AEs, EPs and strain fields are analyzed. • Damage evolution and precursors are explored quantitively by multiparameter analysis. • Microcracking modes are determined by AE parameter and DIC displacement components. • The micromechanics of thermal effects are discussed using XRD and SEM tests. Shear-dominant instability disasters in high-temperature conditions pose a significant challenge for deep underground rock projects, necessitating a thorough understanding of rock fracture evolution and the impacts of thermal damage. To investigate how thermal damage influences shear fracturing behavior and geophysical responses, experiments were conducted on thermally-treated granite under compression-shear loading conditions. The detailed failure process was meticulously monitored using integrated acoustic emission (AE), electric potential (EP), and digital image correlation (DIC) techniques. The effects of thermal treatment on the patterns of AEs, EPs, and DIC strain fields during the loading process were analyzed. Micromechanics related to the influence of thermal treatment on mechanical properties and geophysical responses were explored using X-ray diffraction (XRD) and scanning electron microscopy (SEM). By defining damage variables through multiparameter analysis using AE, EP, and DIC, the study delved into predictive insights on the failure process of thermal-damage granite. The results indicate that the physical properties of granite undergo significant changes as the treatment temperature increases, with the peak stress gradually decreasing and the plastic characteristics increasing. These changes can be attributed to thermal damage, which causes internal water escape, expansion of mineral particles, and crack formation. Additionally, increasing the thermal treatment temperature leads to a decrease in both AE and EP intensity, as well as a reduction in the occurrence of high-magnitude AE events, while the cumulative AE count rapidly increases during the plastic stage. Notably, thermal treatment induces significant alterations in mineral composition, intergranular fractures, and the formation of a gradual zigzag crack path, resulting in the intensified development of shear microcracks. This observation is supported by the varying of AE characteristic parameter AF/RA and the analysis of DIC displacement decomposition. Moreover, the three defined damage variables exhibit accelerated growth prior to catastrophic failure, with the order of precursor occurrence observed as AE, DIC, and EP. However, the occurrence of the precursor time for these three geophysical signals becomes earlier with increasing treatment temperature. These research findings shed light on the mechanism of compression-shear failure of thermal-damage rock and provide valuable references for predicting precursors of the shear-dominant instability disasters such as induced earthquakes. [ABSTRACT FROM AUTHOR]

• The influence of mechanical properties and damage process of sandstone with 0°-90° cracks was studied. • The number of cracks, extension mode and damage mode of single-fractured sandstone were analyzed. • The stage characteristics of acoustic emission of fractured sandstone and the failure precursor criterion of multi-parameter response were revealed. • The differences of acoustic emission parameters and precursor response time of crack inclination were discussed. Cracks are generally the weakest position in engineering rock mass. It is of great practical significance to study the influence of cracks on the fracture process of rock mass and the precursor criterion of failure for disaster prevention and mitigation projects. In this paper, particle flow program (PFC2D) is used to analyze the mechanical strength and damage evolution of fractured rock. The multi-parameter stage characteristics of acoustic emission (AE) and the difference of fracture precursor information of fractured rock mass under uniaxial compression (UC) are explored. The results are as follows: (1) The strength and modulus of elasticity of fractured rock samples are smaller than that of intact rock mass, and increase in quadratic function with the increase of fracture angle, and the strength of B-90 sample is closest to intact rock samples; (2) The PFC analysis shows that the cracks in the defective rock samples all originate from the tip of the prefabricated crack, and the crack initiation angle is basically in the range of 60°∼90°. The loading process mainly produces tensile damage, and the number of tensile cracks are far more than that of shear cracks. Compressive stress and tensile stress increase with the increase of load, but the force chain of failure surface is the smallest after complete failure of rock; (3) The acoustic emission ringing number, RA/AF value, b value and entropy value of sandstone have obvious stage characteristics, the main frequency signal is mainly low frequency signal, and large-scale cracks are mainly produced in the failure process. The sudden increase point of AE ringing times and RA/AF value accumulation curve can be used as critical failure point. The fluctuation of B value and entropy value reflects the instability of fracture development, and "cliff-like" descending point and ascending point can be regarded as the precursor of critical failure of rock; (4) The failure precursor of acoustic emission parameters of sandstone appears in the peak load period of 85 %–98 %. The order of response time of different parameters is: cumulative RA/AF value, cumulative event number, entropy value, B value. The response time of B-45 and B-15 is earlier, while that of B-60 and B-30 is later. The research results are expected to deepen the understanding of the relevant standards of damage evolution and failure precursors of defective rocks in engineering applications. [ABSTRACT FROM AUTHOR]

• An acoustic emission (AE) method from multi-dimensional perspectives is proposed to intuitively characterize the spatio-temporal evolution of rock damage. • From the spatial characteristics of the velocity field evolution, the stress environment controls the spatial heterogeneity of the velocity field. • From the temporal characteristics of the velocity field evolution, there are the continuous decrease and extension of low-velocity regions and the transformation from the high velocity to the low velocity during rock failure. • The mutation trend coefficient (MTC) and deformation coefficient (DC) of the velocity field are proposed as precursor indicators for rock instability. Stress redistribution and crack development are prominent features in rock failure. However, these processes are complex and challenging to analyze, making early warning of instability in rock engineering difficult. To characterize the rock failure process and obtain reliable precursory indicators, the imaging method that combines active and passive sources was employed to construct the velocity field during the rock failure process in this study. The micro-crack propagation law and its potential connection with the stress environment were investigated by mapping the velocity field, the acoustic emission (AE) density field, and the energy field. Moreover, the Mutation Trend Coefficient (MTC) and Deformation Coefficient (DC) were proposed as precursory indicators of instability based on the spatio-temporal correlation and directional differences of velocity evolution. Results show that the nucleation of AE sources and the release of energy accumulation are key to the formation of the velocity gradient, and progressive rock failure is accompanied by the intensification of velocity anisotropy. Additionally, low-velocity regions usually preferentially extend in the direction parallel to the principal stress, while expansion in the direction vertical to the principal stress is dominant in the plastic stage, indicating that the stress environment controls the spatial heterogeneity of the velocity field. The evolution trend of precursor indicators shows that the increase of MTC from a low value and the continuous decrease of DC can be regarded as the initiation of rock secondary cracks. The proposed indicators and method not only provide beneficial complements to the understanding of the evolution mechanism of rock damage but also have potential in the early warning and identification of the early stage of crack propagation, offering references for the safety prevention and control of rock engineering disasters. [ABSTRACT FROM AUTHOR]

• The coal-rock combination with primary interface structure characteristics were prepared. • Mechanical properties and damage evolution patterns of combinations were investigated. • A uniaxial compression model for coal-rock combinations was established. Indirect fracturing technology of coal seam roofs is a crucial method to enhance coalbed methane extraction efficiency in broken soft coal seams. The cracks formed significantly increase permeability by extending from the rock-coal interface into the coal seam. The structural features of the coal-rock interface are pivotal in determining the path of crack propagation, highlighting the importance of studying the mechanical properties and damage evolution in coal-rock combinations. Industrial CT, three-dimensional (3D) reconstruction, and 3D printing technology are utilized to create physical models with authentic interface structure features. Subsequently, coal-rock combination samples exhibiting smooth and original interface characteristics are produced through a layered pouring method. Uniaxial compression experiments are conducted on various interface feature combinations to examine the impact of primary interface structure characteristics on the mechanical properties and damage evolution of the combinations. Real-time monitoring is performed using acoustic emission (AE) equipment. The results show that the compressive strength of coal-rock combinations treated with glue and pouring is significantly higher than those treated with vaseline, while the axial strain shows an opposite trend. The presence of an interface constraint effect weakens the strength of the rock near the coal-rock interface, while enhancing the strength of the coal. The damage in coal-rock combinations initially occurs in the middle and lower parts of the coal, then progresses towards the interface and rock. Finally, a uniaxial compression model considering the interface constraint effect explains and theoretically demonstrates the phenomenon observed in the experiment, where more complex coal-rock interface structures result in higher compressive capacities of samples. It provides insights for further investigation into fracture trans -media expansion and permeability enhancement during the indirect fracturing of coal seam roofs. [ABSTRACT FROM AUTHOR]

The research aimed to examine the impact of different pH solutions on the tensile mechanical properties of saturated and natural sandstone specimens. The study utilized the WHY-300/10 microcomputer-controlled pressure testing machine to conduct Brazil splitting tests and employed acoustic emission and local dynamic strain testing techniques. The results indicated the tensile strength and split tensile modulus of the sandstone specimens gradually decreased with the polarisation of the solution pH, and the acoustic emission signal ring number monitoring values showed an increasing trend. The pH of the soaking solution followed an exponential decay pattern over time, eventually tending towards weak alkalinity. A new damage variable based on the cumulative ring count after chemical corrosion was defined to indirectly analyze the degree of corrosion degradation. It was discovered that in acidic or alkaline environments, the internal crystals of the rock are dissolved, weakening the mineral interconnections and causing a deterioration in tensile stress and strength. These findings can provide valuable insights for ensuring the safety and stability of the Denglou Mountain Tunnel in Yunnan Province.

To explore the fatigue characteristics of self-compacting rubberized concrete (SCRC) pavement, notched slabs with a 10% rubber content were fabricated. Monotonic and fatigue tests were carried out, including incremental amplitude tests controlled by crack mouth opening displacement (CMOD), load, and alternative constant and incremental amplitude loads. Meanwhile, the fracture process was dynamically monitored with acoustic emission (AE), and the failure characteristics were analyzed based on AE parameters. Under monotonic loads, cracks mainly develop along with the interface between aggregates or rubber particles and cement. The cumulative ring counts and damage evolution show a three-stage distribution. The b-value fluctuates dramatically initially and less in the middle and later stages under monotonic tests. Under fatigue loads, brittle fractures are significant and fatigue life increases. Only one inflection point appears in the cumulative ringing counts curve and damage evolution curve, the critical damage is lower. The fluctuation range of the b-value are higher. The cumulative ringing counts, AE signal intensity, damage parameter based on AE energy, and b-value can dynamically reflect the crack growth and damage evolution of SCRC slabs. The fracture mode analysis based on AF-RA manifests cracks are mainly tensile, and the fracture mode is the type I. [ABSTRACT FROM AUTHOR]

In practical engineering, concrete is often under continuous stress conditions and there are limitations in considering the effect of wet–dry cycles alone on the strength deterioration of concrete. In order to study the deterioration of concrete strength under the coupling of load and wet-dry cycles, concrete specimens were loaded with 0%, 10%, 20%, and 35% stress levels and coupled to undergo one, three, and seven wet–dry cycles. The strength deterioration of the concrete was obtained by uniaxial compression and the regression equation was established. The strength deterioration mechanism of the concrete under the coupled conditions was analyzed and revealed through an AE acoustic emission technique and nuclear magnetic resonance technique. The results of the study show that, with the same number of wet–dry cycles, there are two thresholds of a and b for the uniaxial compressive strength of concrete with the stress level, and with the progression of wet–dry cycles, the length of the interval from a to b gradually shortens until it reaches 0. The cumulative AE energy of concrete decreases with the progression of wet–dry cycles; using the initiating crack stress as the threshold, the calm phase of concrete acoustic emission, the fluctuating phase, and the NMR T2 spectral peak area show different patterns of variation with the increase in the number of wet–dry cycles. [ABSTRACT FROM AUTHOR]

Negative temperature has an important influence on rock deformation and failure process. In a negative temperature environment, the pore water in rock partially turns into ice lenses. These changes in rock microstructure and components cause the frozen rock to exhibit temperature-related mechanical behavior. To disclose the mechanical damage process and failure mechanism of rock at different negative temperatures, we carried out acoustic emission (AE) tests on frozen sandstone. Results reveal that the cumulative AE count increases exponentially with increasing load, and the AE count mainly occurs in the yield and failure stages. According to the number and density of the AE count rate, the deformation process of frozen sandstone can be divided into four stages: compaction stage, elastic stage, yield stage, and failure stage. A sharp increase in the AE count rate implies that the rock deformation enters an unstable crack propagation section and macroscopic failure will occur. In addition, assuming that the microelement strength of rock obeys the Weibull distribution and the microelement failure conforms to the Drucker–Prager criterion, a constitutive model considering the negative temperature is proposed. A comparison between the experimental curve and the model curve shows that the model can accurately reflect the deformation process of frozen sandstone. This study is expected to improve the understanding of the damage mechanism and failure progress of frozen rock, and the constitutive model can provide a basis for calculating the deformation of frozen rock. [ABSTRACT FROM AUTHOR]

In order to explore the mechanical characteristics of confined-pressure soaking (CPS) sandstone during the damage-fracture process, the uniaxial compression and acoustic emission (AE) experiment of CPS sandstone was conducted. The mechanical parameters, fracture morphology, AE and energy characteristics under uniaxial stress were researched. The results show that the uniaxial compressive strength and elastic modulus decrease as a logarithmic function with CPS parameters, corresponding to the inflection point of modification. The fracture mode gradually changes from brittleness to toughness with the increase in moisture content. The difference between fracture fragmentation and mechanical behavior mainly depends on the degree of CPS. The evolution of AE characteristics and energy dissipation has a good correspondence with CPS specimens. The higher the CPS degree is, the less the AE cumulative number is and the longer the excitation time is. Based on the phase variation of AE events and energy dissipation, the CPS damage variables are proposed to quantify the weakening degree and reveal the damage evolution process. The results provide a useful foundation for evaluating rock failure and improving service life. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) is often accompanied by the propagation of internal microcracks in loaded rock samples, and it essentially reflects microinstability phenomena driven by energy redistribution under stress. In this paper, loading and unloading tests were carried out to investigate the internal nonlinear damage evolution characteristics of diorite samples under different unloading confining-pressure rates. The nonlinear mechanical characteristics of the strain energy sequence of diorite were studied by applying nonlinear dynamics and basic chaos theory and MATLAB software. Moreover, the evolution characteristics of AE counts and AE energy of rock samples were investigated, and their microcrack-propagation modes were analyzed based on the RA–AF scatter distribution of AE and a two-dimensional Gaussian mixture model. Finally, according to the evolution characteristics of energy and AE, the nonlinear damage evolution mechanism of diorite under loading and unloading conditions was revealed. The results show that, before the loading and unloading peak strength, when the strain-energy-promotion coefficient, r, is equal to 1 or changes in the ranges of 1–3, 3–3.57, and ≥3.57, the strain-energy evolution of diorite presents the characteristics of supercritical stability, nonlinear stability, period-doubling stability, and chaos, respectively. Meanwhile, the greater the rate of the unloading confining pressure, the earlier the period-doubling bifurcation and chaotic mechanical behavior will occur. After loading and unloading peak strength, the sudden decrease of high-density AE counts and AE energy or the sudden transition of the strain-energy-promotion coefficient from >0 to <0 can be used as an important criterion for the complete failure of rock samples. [ABSTRACT FROM AUTHOR]

The stability of the backfilling body–coal pillar–backfilling body (BPB) composite structure in coal mines is of great significance for the rock strata control after backfilling along both sides of the coal pillars. Uniaxial compression tests were conducted on different BPB composite samples to explore their acoustic emission (AE) characteristics and damage evolution process. The results show that the strength of the BPB composite samples is lower than that of the backfilling body sample of the same size. When increasing the coal element width, the peak stress of the BPB composite samples gradually decreases, the stress–strain curve changes from a single peak to multiple peaks, and the AE events transition from a uniform distribution to a regional concentrated distribution. The concentrated areas of AE energy during BPB composite sample failure are mainly distributed in the coal elements, and the maximum AE energy values all appear on the coal elements. The reduction of the backfilling body element width in the BPB composite sample reduces its binding force on the coal element. Larger coal element widths are thus associated with poorer sample integrity after uniaxial compression. The study of the AE ringing count clarifies the relationship between the strain and damage variable during uniaxial compression. This study provides an important foundation for understanding the disaster evolution process of BPB composite structures. [ABSTRACT FROM AUTHOR]

In order to reveal the fracture development and damage evolution law of marble under the influence of temperature, the deformation and failure characteristics and acoustic emission activity of marble under the conditions of 30, 60, 90, 120 ℃ and 150 ℃ were studied by using triaxial servo testing machine and acoustic emission testing system. The results show that the triaxial compression failure of marble under high temperature goes through four stages: compaction and elastic deformation stage, plastic deformation stage, ductile failure stage and instability failure stage. The higher the test temperature is, the longer the compaction deformation stage and ductile failure stage are, and the rock gradually transforms from elastic brittle failure to elastic-plastic failure. The peak strength, elastic modulus and internal friction angle of marble decrease with the increase of temperature. The acoustic emission activity of rock and the correspondence between AE location and macroscopic crack decrease with the increase of test temperature. By analyzing the characteristics of acoustic emission signal amplitude, impact, ring down count, acoustic emission energy, peak frequency and b value in the damage evolution process of marble, it is found that the amplitude fluctuation of acoustic emission is small and the temperature sensitivity is poor, but the peak frequency and b value parameters can better characterize the crack development inside the rock. The peak frequency has the highest temperature sensitivity, which is favorable as the prediction index of rock failure and instability. In the process of triaxial compression failure, tension-shear composite cracks appear in marble, of which shear cracks are dominant. High temperature inhibits the initiation of internal cracks in rock mass. The higher the test temperature is, the weaker the tensile failure and the stronger the shear failure are. The test results shed light on the study of rock thermal damage mechanism and engineering thermal damage monitoring and prediction.

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)