Acoustic Emission Monitoring Research Articles

Characteristics of carbon dioxide fracturing in comparison to conventional water hydraulic fracturing: Evidence from acoustic emission monitoring of small-scale field experiments

We conducted small-scale field hydraulic fracturing (HF) experiments using carbon dioxide (CO2) and water as fracturing fluids. A hole was drilled 10–14 m below the tunnel floor into hot granitic rock whose temperature can form CO2 supercritical state at HF pressure. Under the same injection rate of 10 mL/min, the volume of the acoustic emission (AE) hypocenter distribution induced by CO2 HF was approximately 27 times larger than that induced by water HF. In addition, when evaluating injectivity improvement through Injecting/Fall-Off Tests (IFOTs) using gaseous CO2 and water before and after CO2 HF and water HF, respectively, the injectivity of rock around the HF hole was improved by around 400 times larger by CO2 HF in comparison to a few times larger by water HF. The results suggest that CO2 HF can stimulate a much larger region and improve injectivity much more than water HF. In contrast, it has more possibility of leaking injected fluid through the stimulated region. On the other hand, when comparing the focal mechanisms of AE events in both CO2 HF and water HF with their occurrence times and locations, we found a tendency for tensile-dominant events to occur in intact rock, in contrast, shear-dominant events occur with a linkage between cracks, that is, the interaction of cracks. This finding suggests a solution for the paradox of the mechanism of HF in which shear events dominate in AE monitoring in actual production fields where there are various discontinuities and cracks, although the elastic theory expects tensile fractures.

Rheology of hydrated plagioclase at lower crustal conditions: Cataclasis, creep and transformational plasticity

Plagioclase feldspar is one of the main rock-forming minerals of the lower continental crust. Assessing its rheology is therefore of particular importance for understanding the mechanical processes acting in convergence zones, where pressure and strain rate increases are often associated with metamorphic reactions and fluid fluxes. In this prospect, we performed axial shortening experiments on “as-is” (∼0.05 wt% H2O) and water-added (∼0.29 wt% H2O) natural plagioclase samples in a Griggs-type apparatus equipped with an acoustic emission monitoring system. Samples were deformed at ∼ 10−6 and ∼ 10−5 s−1, 700–800 °C, and 1.0 GPa in the plagioclase stability field. Experiments have also been performed at 1.5 GPa in order to study the rheological impact of the breakdown reaction Ca-rich plagioclase + water → zoisite + kyanite + quartz + Na-rich plagioclase. Mechanical data indicate that at the conditions studied, the rheology of plagioclase is strongly affected by water content. Microstructural observations confirm that under dry conditions, plagioclase aggregates deform by cataclastic flow. Under wet conditions, dislocation creep appears to be the dominant deformation mechanism, and plagioclase rheology is best described by the following equation, where strain rate, in s−1, is expressed as:ε·=Aσ3.0exp(−(168kJ/mol)/R/T), where σ is the stress in MPa, R is the gas constant, T is the temperature in K, and the pre-exponential term A=10−3.9MPa−3.0s−1. At 1.5 GPa, the reaction is faster under wet conditions but the rheology observed remains identical to that of wet plagioclase in its stability field. In the low water content experiments, plagioclase breakdown induces transient weakening due to fast zoisite nucleation and significant reaction volume change.

Time-Frequency Response of Acoustic Emission and Its Multi-Fractal Analysis for Rocks with Different Brittleness under Uniaxial Compression

The occurrence of rock burst hazards is closely related to the brittleness of rocks. Current research has paid less attention to the in-depth relationship between rock brittleness and acoustic emission (AE) signal characteristics and precursor information caused by rock fracture. Therefore, in order to further improve the accuracy of the AE monitoring of rockburst hazards, uniaxial compression tests were carried out and AE were monitored for rocks with different brittleness (yellow sandstone, white sandstone, marble, and limestone) in this paper. The relationship between the mechanical properties and the time-frequency characteristics of the AE was analyzed. In addition, the multi-fractal theory was introduced to further deconstruct and mine the AE signals, and the multi-fractal characteristics of AE from rocks with different brittleness were investigated. The results show that the stronger the brittleness of the rock, the higher the main frequency and main frequency amplitude of the AE. Brittleness is positively correlated with the multi-fractal parameter Δα (uniformity of data distribution) and negatively correlated with Δf (frequency difference between large and small data). In addition, the dynamics of Δα and Δf provide new indicators for AE monitoring of rock stability, and their abrupt changes can be regarded as precursors of failure. The weaker the brittleness of the rock, the earlier the failure precursor is and the more significant it is. This has potential engineering application value, which can help identify rockburst precursors and take timely protective measures to ensure engineering safety.

Mechanical behaviors of backfill-rock composites: Physical shear test and back-analysis

The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence. For exposing the shear failure mechanism of backfill-rock composites, we conducted shear tests on backfill-rock composites under three constant normal loads, compared with the unfilled rock. To investigate the macro- and meso-failure characteristics of the samples in the shear tests, the cracking behavior of samples was recorded by a high-speed camera and acoustic emission monitoring. In parallel with the experimental test, the numerical models of backfill-rock composites and unfilled rock were established using the discrete element method to analyze the continuous-discontinuous shearing process. Based on the damage mechanics and statistics, a novel shear constitutive model was proposed to describe mechanical behavior. The results show that backfill-rock composites had a special bimodal phenomenon of shearing load-deformation curve, i.e. the first shearing peak corresponded to rock break and the second shearing peak induced by the broken of aeolian sand-cement/fly ash paste backfill. Moreover, the shearing characteristic curves of the backfill-rock composites could be roughly divided into four stages, i.e. the shear failure of the specimens experienced: stage I: stress concentration; stage II: crack propagation; stage III: crack coalescence; stage IV: shearing friction. The numerical simulation shows that the existence of aeolian sand-cement/fly ash paste backfill inevitably altered the coalescence type and failure mode of the specimens and had a strengthening effect on the shear strength of backfill-rock composites. Based on damage mechanics and statistics, a shear constitutive model was proposed to describe the shear fracture characteristics of specimens, especially the bimodal phenomenon. Finally, the micro- and meso-mechanisms of shear failure were discussed by combining the micro-test and numerical results. The research can advance the better understanding of the shear behavior of backfill-rock composites and contribute to the safety of mining engineering.

Macroscopic and microscopic mechanical characteristics and crack propagation behavior of sandstone-like samples with single cracks under freeze–thaw cycles: Experimental and numerical simulation

In permafrost regions, rock engineering projects inevitably suffer from the effects of freeze–thaw (F-T) cycles under complex geographical and climatic conditions. Under F-T cycles, the damage and deterioration of macro- and microdefects, such as joints and cracks, in the rock will reduce the structural stability of the rock and even lead to frost damage in rock engineering. In this study, through indoor F-T cycle tests, uniaxial/triaxial compression tests, acoustic emission monitoring, and discrete element method (PFC 3D) modeling, the macro/microscopic mechanical characteristics and crack propagation behavior of sandstone-like samples with single cracks under F-T cycles were investigated. The results show that the compressive strength of sandstone-like samples with single cracks tends to decrease and then increase with an increasing crack angle and exhibits a stable decreasing trend with increasing F-T cycles, indicating a significant crack angle effect and F-T deterioration effect. Additionally, the confining pressure has an inhibiting effect on the F-T deterioration of samples, and there is a mutual inhibition relationship between the F-T deterioration effect and the crack angle effect. The characteristics of the acoustic emission signals during the loading process of sandstone-like samples with single cracks show good consistency with the stress–strain curves. The analysis of fracture mechanisms based on rise time/amplitude (RA) and average frequency (AF) is consistent with the macroscopic failure modes observed in the experiments. Moreover, with an increase in the number of F-T cycles, the number of tension cracks in the sandstone-like samples with single cracks increases, while the number of shear cracks decreases. The crack propagation behavior of sandstone-like samples with single cracks obtained through discrete element simulations (PFC 3D) is mainly divided into four stages: Stage I - initial calm stage, Stage II - crack initiation stage, Stage III - crack propagation stage, and Stage IV - failure stage. The simulated mechanical properties and failure modes agree well with the experimental results, and five crack propagation modes of sandstone-like samples with single cracks under F-T cycles were proposed: direct tension (DT), relative tension (RT), shear-tension (ST), direct shear (DS) and relative shear (RS).

Mechanical response of sandstone exposed to monotonic and multilevel fatigue loading: Insights from deformation, energy and acoustic emission characteristics

Rock masses containing intermittent discontinues under dynamic loading have rarely been investigated, although step-path failure frequently occurs in field engineering. This work aims to explore the action mechanism of dynamic cyclic loading and discontinuities on step-path failure. Four treatments including the control (Intact sandstone), pre-flawed samples with assemblage of two 30° dip fissures (type-I), assemblage of 10° and 65° dip fissures (type-II) and assemblage of two 65° dip fissures (type-III) were replicated. Laboratory experiments consisted of conventional uniaxial compression tests (UCT) and multilevel constant-amplitude fatigue tests (MLFT). Real-time acoustic emission (AE) monitoring was conducted along with scanning electron microscopy (SEM) observation on the fractured surfaces. Results indicated that the mechanical properties, energy evolution, AE characteristics and microscopic features of sandstones were significantly influenced by pre-existing fissures. The weakened rates of peak strength ranged from 2.80% to 85.63%, and regardless of loading methods, always followed the sequence of type-I > type-II > type-III. We contribute the weakening effect to the reduction in the effective bearing area and the increase in the dip angle of the rock bridge. With the same pre-fissure morphology, the sandstone under MLFT has enhanced its deformation resistance compared to under UCT. In addition, the maximum AE count/energy during the whole cyclic stage were always significantly lower than those during the monotonic rising process. SEM images revealed that long-term fatigue loading lead to numerous micro pores and transgranular cracks. Ultimately, a simple constitutive model was proposed based on the statistical damage mechanics and geometric damage theory.

Correlational fractal characteristics and damage progression of granite with different grain sizes based on acoustic emission monitoring

Mineral grain size caused by the geological diagenetic process is one of the fundamental reasons leading to the differences in rock mechanical behaviors, which brings challenges to the stability of underground engineering, especially in rock masses with continuous grain size changes. This study conducted uniaxial compression tests on granite samples obtained from the same invaded anticline with different grain sizes. During the tests, the acoustic emission (AE) signals were acquired synchronously. The correlation between damage evolution and AE data was then studied by frequency-spectrum analysis, fractal theory methods, and G-P algorithms. The mechanism of grain size effect on granite failure evolution was discussed. The results reveal that as the grain size increases, the strength and the elastic modulus decrease while the plastic deformation characteristic is enhanced. Grain size also affects the frequency distribution of AE signals and its time-varying characteristics. With the increase in grain size, the proportion of high-frequency signals declines during loading. The fractal dimension value of dominant frequency during loading fluctuates within the range from 0.5 to 2.25 and generally shows an overall ‘rise-fall-rise-fall’ mode. In addition, as the grain size increases from fine-grained to medium-grained, the fractal dimension changes from an increasing to a decreasing trend earlier in the compaction and elastic stages. Especially in coarse-grained samples, after a brief increase, the fractal dimension decreases continuously until approaching the overall failure. The frequency domain characteristics and correlation fractal variation of granites reflect the damage and crack evolution inside the rock sample. More scattered and unordered micro-cracks generated in samples with finer grains facilitate the dispersion of applied stress and the reduction of local stress concentration, resulting in higher strength and stiffness of the sample.

Evaluation of EDZ characterization technology for URL based on field investigation at BET

Detailed characterization of the Excavation Damage Zone (EDZ) is an important issue for the high-level radioactive waste (HLW) geological disposal engineering, which is closely related to the long-term safety of the HLW repository. With drill-blast experiment in Beishan Exploration Tunnel (BET, a platform for the field experiment and validation of potential technologies used for China’s HLW disposal engineering in crystalline rock), systematic field tests were carried out to evaluate the suitability of techniques in characterizing EDZ, and to study EDZ characteristic in crystalline tunnel. A series of investigation technologies were used to delineate EDZ and to examine the process of its formation, which includes: p-wave velocity measurement, ground penetrating radar (GPR), acoustic emission (AE) monitoring and borehole televiewer. P-wave velocity measurement along borehole reveal that wave velocity decreased significantly (more than 10%) in 30 cm to 50 cm from the excavation surface, and this zone is defined as EDZ. Clear images of borehole televiewer were obtained, which is helpful for EDZ delineation. GPR and borehole radar were also used for EDZ delineation. Strong reflection signals were detected in the range of 10 cm to 25 cm by GPR with high frequency antenna, indicating significant changes of physical properties of rock-mass in the zone, which is defined as Highly Damaged Zone (HDZ). Moreover, the formation process of EDZ induced by blast in crystalline rock tunnel was analyzed using AE monitoring. Damage process of surrounding rock was divided into blasting damage stage and progressive damage stage. AE events location show the induced cracking activities were clustering within 30 cm to 100 cm from excavation surface. With the experience from field investigation and result analysis, the feasibility and suitability of the techniques for EDZ characterization is evaluated. Finally a specialized EDZ characterization technique system is proposed for underground research laboratory construction in crystalline host rock in Beishan area.

Influence of freeze–thaw cycles on mechanical properties of pervious concrete: From experimental studies to discrete element simulations

In this paper, pervious concrete (PC) was prepared using fly ash, granulated blast furnace slag, and rice husk ash as supplementary cementitious materials (SCMs), and the mechanical properties, water permeability, and freeze–thaw durability of permeable concrete were mainly investigated. Discrete elements (DEM) were used to mimic the freeze–thaw cycle process of pervious concrete to assess better how freeze–thaw cycles affect the mechanical properties of pervious concrete. To allow water particles of various sizes to fill the model pores, new algorithms were developed. However, since some connected pores release some of the pressure generated by water expansion when undergoing FTCs, two different water particles must be defined. Meanwhile, an elastoplastic parallel bond contact model (EPPBM) was created to account for any residual strain brought on by water freeze–thaw expansion at the aggregate bond. Through experiments, it was determined that adding SCMs increased the compressive strength of the pervious concrete by 1.22 %, 15.32 %, 32.34 %, and 35.20 % at 7, 28, 56, and 90 days compared to the control group. The microstructure of the hydrated calcium silicate (C-S-H) gel could be relatively dense by SEM. The width of the interfacial transition zone (ITZ) was found to have been effectively shortened by further scanning using EDS. As a result, in the tests of mechanical properties after freeze–thaw cycles (25, 50, 75, and 100 cycles), there was a significant improvement in the loss of strength compared to the control group, which was 2.13 %, 6.91 %, 10.04 %, and 17.40 %, respectively. Using numerical simulation to correct the functional correlation between FTCs and the mechanical characteristics of permeable concrete, the trend essentially aligns with the experiment's results, demonstrating the model's viability. Acoustic emission monitoring of model rupture location and strain energy loss after FTCs were utilized and the effect of different porosity and initial uniaxial compressive strength (UCS) on the attenuation constant of the freeze–thaw resistance of pervious concrete was analyzed. The decay constant of UCS increased with increasing porosity and elastic modulus while decreasing with increasing initial UCS. Therefore, the decay constant of UCS and elastic modulus after arbitrary FTCs can be easily estimated using the initial parameters of the pervious concrete.

Systematic Uncertainty Quantification of First-Polarity-Based Moment Tensor Inversion Due to Sparse Coverage of Sensor Arrays in Laboratory Acoustic Emission Monitoring

Systematic Uncertainty Quantification of First-Polarity-Based Moment Tensor Inversion Due to Sparse Coverage of Sensor Arrays in Laboratory Acoustic Emission Monitoring

Mechanical properties of additive-manufactured hydroxyapatite porous scaffolds and follow-up of damage process under compression loading

In this work, the mechanical response and the damage process during compressive loading tests of hydroxyapatite scaffolds processed by stereolithography and designed for biomedical applications were investigated. Damage is followed by acoustic emission monitoring, Scanning Electron Microscopy observations at different loading stages and by In-situ X-ray tomography. A significant and progressive damage evolution is observed at stress value superior to 25 MPa. The cracks responsible for the damage are initiated from the edge of the sample and propagate parallel to the applied force, which explains the small variation of the Young's modulus, initially of 85 GPa, during loading/unloading sequences. Finite element analysis confirmed that the stress is non-uniform and maximum at the edge of the sample, which confirms the scenario of damage evolution.

Investigation of crack recognition and spatio-temporal evolution pattern in coal samples damage

Understanding the evolution mechanism of cracks helps to evaluate the behavior and performance of rock masses and provides a theoretical basis for the mechanism of crack propagation and instability. For this purpose, a rock mechanics testing system and an acoustic emission monitoring system were used to conduct acoustic emission positioning experiments on coal samples under uniaxial compression. According to clustering theory, the distribution pattern of microcracks and the dynamic evolution process of multiple cracks were studied. Subsequently, the reasons for the change in the spatio-temporal entropy (H) and fractal dimension (D) of a single crack were revealed. The research results show that microcracks present a statistical equilibrium distribution, the Gaussian distribution model is applicable to cluster crack distribution patterns, and a machine learning method can effectively identify cracks. The fractal dimension reflects the spatial characteristics of three-dimensional elliptical cracks, and low-dimensional cluster cracks are more likely to develop into macroscopic cracks. The change of H is related to the formation process of cracks, and an abnormal H (sudden increase and sudden decrease) could provide precursor information for the instability of coal samples. This research provides a new method to study crack distributions and formations and shows the competitiveness of the method in evaluating the damage state of coal.

Tracing fracture damage evolution and identifying damage patterns in cast steel using advanced acoustic emission analysis

The application of advanced acoustic emission signal analysis techniques can facilitate the identification of fracture damage modes in ductile materials and enable the provision of fracture precursor warnings. Given the vast array of acoustic emission signal characteristic parameters, there must be a systematic and comprehensive basis for selection and a deep comparison among different fracture warning indicators. This study uses G20Mn5QT cast steel material fracture acoustic emission monitoring tests under different in-plane constraints as an example. We adopted principal component analysis and k-means++ to select acoustic emission feature parameters and cluster damage modes. Additionally, we conducted a comparative analysis of several fracture precursor warning indicators and influencing factors, including fractal dimensions, b/Ib values, and natural time analysis. Our findings show that shear and tensile fracture damage modes are present in type-I fracture tests when applying the k-means++ cluster to the rise angle-average frequency-energy parameter, but tensile fracture modes dominate. Fractal dimensions, b-values, and Ib-values show a strong trend correlation with the fracture damage evolution process. Natural time analysis can quantitatively provide the moment of fracture precursor warnings, but the sliding window length inversely affects the absolute value sizes. Through acoustic emission signal analysis, our research provides a reference for identifying and examining the evolution of fracture damage in ductile materials and engineering components.

Progressive damage process and destabilization precursor recognition of sulfate tailing-cemented paste backfill based on acoustic emission

Sulfate-rich tailings are commonly used as aggregate materials for mine filling, and the sulfate retained within them significantly affects the structural characteristics of cemented paste backfill (CPB). A series of microstructure tests, uniaxial compressive strength (UCS) tests, and acoustic emission (AE) monitoring were carried out on CPB and sulfate tailing-cemented paste backfill (ST-CPB) to investigate the progressive damage pattern and identify the destabilization precursor information of the backfill. The results showed that the UCS of the backfill increased and then decreased with the increase in sulfate content, and 1.5% was the optimal content. The AE counts, energy, amplitude, and peak frequency time series corresponded to each other, exhibited the stage characteristics of a stress curve and were significantly affected by sulfate content. CPB and 0.5% ST-CPB displayed more active AE counts and energy during the initial loading stage, with high amplitude and low-frequency signals. However, the 1.5% ST-CPB exhibited active AE events and medium-high amplitude and medium-low frequency signals only during the plastic yielding and damage stages. 2.5% ST-CPB exhibited more active AE signals during the entire loading process. RA-AF values indicate that CPB and 2.5% ST-CPB reached 93.12 and 96.62% of tensile cracks at final failure, respectively. Meanwhile, the percentages of tensile cracks at the final failure of 0.5 and 1.5% ST-CPB were 76.65 and 76.86%, respectively. The sudden increase in the variance curve and the rapid decrease in the b value of AE in the critical slowdown theory were identified as the precursor characteristics of the backfill instability. This investigation can provide technical and theoretical support for the progressive damage characteristic and stability assessment of ST-CPB.

Cavitation in an antivascular cancer therapy setting

Focused ultrasound in combination with circulating microbubbles is being widely investigated as a means to promote spatially targeted drug delivery. This approach has considerable potential in oncology for a range of therapeutic agents. At sufficiently high pressures, above those typically employed in drug delivery, tumor microvessel damage can be induced to an extent that leads to perfusion shutdown and subsequent ischemic tissue necrosis. This approach is often referred to as antivascular ultrasound (AVUS), which has been shown in preclinical work to be capable of enhancing the effects of radiation therapy, antiangiogenic therapy, chemotherapy, and immunotherapy. At present, the mechanisms of AVUS are not well established. It is important to gain a more detailed understanding of the bubble–microvessel interactions that lead to perfusion shutdown, along with the cavitation signatures associated with these behaviors to enable the rational development of effective cavitation based control methods. This talk will provide a brief overview of AVUS therapy in oncology and highlight recent efforts employing two-photon microscopy, high speed optical imaging, and acoustic emission monitoring to gain insights into bubble behavior within small channels and in vivo microvessels under AVUS exposure conditions.

Research on acoustic emission multi-parameter characteristics in the failure process of imitation steel fiber reinforced concrete

Studies of the damage process of fiber-reinforced concrete through acoustic emission are very significant for concrete structural health monitoring. In this study, three specifications of fiber concrete and one group of plain concrete were prepared to carry out the uniaxial compression test and acoustic emission monitoring test; then, b value, entropy H, and variance D, were calculated and compared their characterization effect. The main results showed that fibers increased the degree of internal inhomogeneity of the specimens, making the acoustic emission response more active. For every 2% increase in fiber content, the total acoustic emission count and energy increased by about 20%, the acoustic emission precursor parameters changed more significantly, the b-value decreased by 2%–10%, the entropy and variance increased by 3%–5% and 2%–22%, respectively. The variation of b value, entropy, and variance can be divided into three phases: initial rising/falling, unstable transition, and fluctuating slow-rising/falling, which had good consistency with the stress curve. According to the linear fitting results, the b value that dropped below the envelope in the post-peak phase can be taken as the damage precursor point, and its accuracy and generalizability were better. The entropy at the failure moment was around 0.6, but the value close to or above 0.6 occurred several times during the damage process, and taking the entropy value beyond the envelope range as the failure precursor point may lead to the error early warning. The variance was slightly worse to distinguish small-scale fracture, but was not susceptible to high-energy events. Therefore, variances close to 5 or beyond the envelope interval can be regarded as the precursor of final failure. As for studying concrete damage processes with acoustic emission, it is suggested to combine multiple parameters for comprehensive discrimination.

Effect of weakening characteristics of mechanical properties of granite under the action of liquid nitrogen

Liquid nitrogen fracturing and hot dry rock geothermal development are both emerging technologies in the field of energy. However, during the extraction of geothermal energy, it can cause the evolution of geological fractures, leading to the diffusion of groundwater and pollutants, thereby causing environmental pollution issues. Currently, geothermal energy has become a focal point in the global development of renewable energy. However, traditional hydraulic fracturing methods used in harnessing geothermal resources suffer from limitations such as limited fracture creation, uncertain initiation points, and environmental pollution. In contrast, liquid nitrogen has emerged as a promising reservoir stimulation technique, exhibiting significant effects on rock fracturing. In this study, we conducted three-point bending tests on granite samples subjected to liquid nitrogen treatment at temperatures of 300°C, with varying numbers of cooling cycles. Changes in fundamental mechanical parameters were analyzed. Additionally, through acoustic emission monitoring, we studied the variations in characteristic parameters of acoustic emissions under different cooling cycle conditions. Furthermore, based on the theory of energy evolution, we analyzed the energy evolution process during sample failure under different cooling cycle conditions. Using a compact scanning electron microscope, we observed changes in the microstructure of granite and analyzed the influence of cooling treatment on its surface characteristics and failure modes, thereby revealing the thermal damage process of granite. Moreover, by employing a non-metallic ultrasonic testing analyzer, we scanned the fracture surface morphology of granite and investigated the variations in fracture surface morphology features and surface roughness parameters caused by cooling treatment. The results indicate that liquid nitrogen cooling treatment can more effectively reduce the mechanical properties of rocks, and this effect is further enhanced at high temperatures. Under the condition of 300°C, after undergoing different cycles of liquid nitrogen cooling, granite will exhibit a more diverse macroscopic and microscopic structural failure characteristics, consistent with the expected formation of fluid flow channels in high-temperature rock formations.

Technologies for acoustic emission monitoring of concrete and reinforced concrete structures

Introduction. The acoustic emission (AE) method is successfully used for diagnostics and monitoring in various industries including oil and gas, nuclear, aerospace as well as in welding processes and structural corrosion. However, inspection of reinforced concrete structures seldom involves the AE method. The main reason behind is the lack of regulatory documents and specific control procedures.State Standard R 59938-2021 “Concretes. Acoustic emission testing method” was issued in 2021. Over the past few years, new data on effective application of the acoustic emission method for non-destructive testing and technical diagnostics of the building structures have been obtained. The studies were carried out on specimens and fragments of structures (reinforced concrete beams, concrete samples in the form of slabs, wall panels, etc.) in NIIZHB named after A.A. Gvozdev. The studies were conducted on the structures under construction at Kursk NPP-2.Aim. To present the results of the recently developed methods of technical diagnostics and non-destructive AE testing of concrete and reinforced concrete structures.Materials and methods. The investigations were carried out on concrete and reinforced concrete specimens made of both normal (B15–B40) and high-strength (B60–B100) concrete. A number of beams were made of fiber concrete. Structures were tested in the power unit. AE monitoring of concrete hardening involved concrete mixtures made of heavy, fine-grained, cement concrete with mineral and chemical additives. Concrete hardening was investigated remotely, with online data transmission.Results. Based on the results of the conducted study, the technologies for acoustic emission monitoring and technical diagnostics of the structures under construction and in operation have been developed.Conclusions. The given acoustic emission technologies can be used for monitoring and technical diagnostics of structures under construction and in operation. The implementation of technologies in construction will lead to the increase in safety and reliability of building structures due to the introduction of acoustic emission monitoring.

Spatio-temporal evolution of acoustic emission events and initiation of stress fields in the fracturing of rock mass around a roadway under cyclic high-stress loading.

To study fracture mechanisms and initiation of stress fields in the rock mass around a roadway subjected to cyclic stress, a series of loading and unloading tests were conducted on the rock mass around the roadway by using high-precision acoustic emission (AE) monitoring. The results show that intense AE activities occur in a specimen during cyclic load-holding at different levels. With the increase in the number of cycles, the overall stability of the specimen gradually decreases. In the cyclic loading and unloading process, the specimen exhibits a Kaiser effect. As the number of cycles increases, more AE events occur in the unloading stage and a Felicity effect is manifest. The spatial distribution of AE events is related to the stress regime and structure of the specimen, crack propagation in the roadway exhibits directionality due to effects of the principal stress. High stress is conducive to microcrack initiation and propagation in the specimen, which accelerates damage accumulation and macrofracture formation in a rock mass. The research provides a reference for roadway support work and disaster prevention and control in deep mines.

Investigating apparent plateau phases in fatigue after impact damage growth in CFRP with ultrasound scan and acoustic emissions

In previous literature, a plateau phase in fatigue growth of impact delamination projected area in CFRP was found. Explaining this plateau phase still represents a knowledge gap. In the present work, echo-pulse and through thickness transmission ultrasonic scan inspections were combined with acoustic emission monitoring to explain this plateau phase. Before the onset of growth outside of projected area, growth of delamination in the central impact cone and growth of smaller delamination was observed. Low-frequency acoustic emissions localized in the impact damage were recorded even before any type of growth was measured. The provided evidence suggests that an actual plateau phase may not exist if all the damage mechanisms are properly considered.