Showing papers on "Acoustic emission published in 2016"
TL;DR: In this paper, the authors investigated the energy evolution of rock deformation and failure in uniaxial cyclic loading and unloading compression of 30 sandstone rock specimens under six different loading rates.
Abstract: Characteristics of energy accumulation, evolution, and dissipation in uniaxial cyclic loading and unloading compression of 30 sandstone rock specimens under six different loading rates were explored. Stress–strain relations and acoustic emission characteristics of the deformation and failure of rock specimens were analyzed. The densities and rates of stored energy, elastic energy, and dissipated energy under different loading rates were confirmed, and an effective approach for the equivalent energy surface was presented. The energy evolution of rock deformation and failure were revealed. It turns out that the rock deformation behavior under uniaxial cyclic loading and unloading compression remained almost unchanged compared with that of uniaxial compression. The degree of match between reloading stress–strain curves and previous unloading curves was high, thereby demonstrating the memory function of rock masses. The intensity of acoustic emission fluctuated continually during the entire cyclic process. Emissions significantly increased as the stress exceeded the unloading level. The peak of acoustic emission increased with increasing loading stress level. Relationships between energy density and axial load indicate that the rock mass possesses a certain energy storage limitation. The energy evolution of rock masses is closely related to the axial loading stress, rather than to the axial loading rate. With increasing axial loading stress, stored energy varied most rapidly, followed by that of the elastic energy, then dissipated energy. Energy accumulation dominates prior to the axial load reaching peak strength; thereafter, energy dissipation becomes dominant. The input energy causes the irreversible initiation and extension of microcracks in the rock body. Elastic energy release leads to sudden instability of rock bodies and drives rock damage.
252 citations
TL;DR: In this paper, the authors studied the thermal effect on physical and mechanical properties of rock, such as mass, density, porosity, P-wave velocity, compressive strength, peak strain, elastic modulus, and acoustic emission of rock.
247 citations
TL;DR: In this paper, the characteristics of the acoustic emission (AE) parameters and the evolution of cracking sequences are analyzed for every cracking level, based on micro-and macro-crack damage, a classification of cracking levels is introduced.
Abstract: Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress–strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.
230 citations
TL;DR: In this paper, the effect of adding different types of fibers on the microstructure and the mechanical behavior of cementitious composites, in particular on UHPC, was investigated by using a uni-axial compression test which combines the gas permeability and the acoustic emission (AE) measurement.
Abstract: This study investigates the effect of adding different types of fibers on the microstructure and the mechanical behavior of cementitious composites, in particular on UHPC. These fibers were distinguished mainly by their differing nature (steel, mineral and synthetic), their dimensions (macroscopic or microscopic), and their mechanical properties. The microstructure of the specimens was examined by using SEM observation and by measuring the porosity, the intrinsic permeability and the P-wave velocity. The mechanical behavior under loading has been studied using a uni-axial compression test which combines the gas permeability and the acoustic emission (AE) measurement. This work focuses on the cracking process under mechanical loading. The experimental results show that the fiber has a relatively slight influence on the compressive strength and elastic modulus of concrete, except for the steel fiber which improves the strength because of its intrinsic rigidity. However, The addition of fiber significantly reduces the lateral strain at peak loading and increases the threshold of initial cracking (σk-ci) and that of unstable cracking (σk-pi). Therefore, the fibers clearly restrain the cracking process in concrete under the mechanic loading.
213 citations
TL;DR: In this paper, a modified and effective signal processing algorithm is designed to diagnose localized defects on rolling element bearings components under different operating speeds, loadings, and defect sizes, which is based on optimizing the ratio of Kurtosis and Shannon entropy.
139 citations
TL;DR: In this article, a comprehensive review on fatigue damage assessment of reinforced concrete (RC) structures with the aid of acoustic emission (AE) technique has been carried out, where the reviews were performed on the background, principle, application, monitoring of RC structures, parameter and analysis using AE technique.
135 citations
TL;DR: In this paper, an acoustic emission-based method for the condition monitoring of low speed reversible slew bearings is presented, and several acoustic emission (AE) hit parameters as the monitoring parameters for the detection of impending failure of slew bearings are reviewed first.
135 citations
TL;DR: The semi-circular bend (SCB) method suggested by International Society for Rock Mechanics (ISRM) is demonstrated to yield much conservative mode I fracture toughness as mentioned in this paper, and numerically simulated K-resistance curves are demonstrated to have great potential for determining the fracture toughness at the level II.
128 citations
TL;DR: In this paper, the authors presented the mechanical characterization of an eco composite consisting of a thermoplastic matrix reinforced by flax fibres and used the acoustic emission technique to detect the appearance of damage mechanisms and to follow their evolution.
Abstract: This article presents the mechanical characterization of an eco composite consisting of a thermoplastic matrix reinforced by flax fibres. Different configurations of specimens were tested with uniaxial tensile loading and their mechanical behaviours were discussed. Moreover, the acoustic emission technique was used to detect the appearance of damage mechanisms and to follow their evolution. In addition, a list of these mechanisms was established by means of macroscopic and microscopic observations. The acoustic emission records were post processed by the k-means unsupervised pattern recognition algorithm. Depending on the specimen configuration, three or four classes of events were obtained. The acoustic characteristics of these classes were compared. Then, a correlation between these AE events classes and the damage mechanisms observed was proposed. Their effects on the mechanical behaviour of the material were investigated by means of a variable called the Sentry Function.
118 citations
TL;DR: In this paper, the authors explored the influence of methane to coal and studying fractal characteristics and acoustic emission (AE) features in the damage evolution, the triaxial compression experiments of coal containing methane were conducted, and the acoustic emission response was collected simultaneously in the loading process.
113 citations
TL;DR: In this paper, the authors studied the effect of water intrusion on crack propagation and calculated the mechanical properties of coal such as the elastic modulus and post-peak modulus, and quantified the percentage of the stress thresholds for crack closure, crack initiation and crack damage that constitutes the peak stress.
Abstract: Studying the mechanical properties of and crack propagation in coal after water intrusion is necessary to tackle a number of geological engineering problems such as those associated with underground water storage in collieries and support for underground roadways in coal mines. To study the mechanical properties and crack development, 12 coal samples with moisture contents of 0, 2.37, 3.78 and 5.29 % were prepared for acoustic emission tests under uniaxial compression. Over about 6 days, the coal samples absorbed moisture from a humidifier in three different phases. In this period, uniaxial tests show that the peak stress, elastic modulus, strain softening modulus and post-peak modulus decreased with rising moisture content in the samples while the peak strain increased. It was further found that, by analysing the relationship between the stiffness and stress and the accumulated acoustic emission counts, all the phases of crack development can be evaluated. This is useful for studying the effect of water intrusion on crack propagation and for calculating the mechanical properties of the coal such as the elastic modulus. This investigation also quantifies the percentage of the stress thresholds for crack closure, crack initiation, and crack damage that constitutes the peak stress. These stress thresholds do not change with moisture content. Our results are of great significance for water storage in coal mines, for determination of pillar dimensions in coal mines, and for expanding the knowledge base of the mechanical properties of coal and the characteristics of crack propagation.
TL;DR: In this article, the authors present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite.
Abstract: Most studies of thermally induced cracking in rocks have focused on the generation of cracks formed during heating and thermal expansion. Both the nature and the mechanism of crack formation during cooling are hypothesized to be different from those formed during heating. We present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite. Results show that both the rate and the energy of acoustic emission are consistently much higher during cooling than during heating. Seismic velocity comparisons and crack morphology analysis of our heated and cooled samples support the contemporaneous acoustic emission data and also indicate that thermal cracking is largely isotropic. These new data are important for assessing the contribution of cooling-induced damage within volcanic structures and layers such as dikes, sills, and lava flows.
TL;DR: In this article, an analysis of the acoustic emission and energy fields of concrete beams with respect to three-point bending (TPB) tests on concrete beams of different sizes is carried out.
TL;DR: In this article, a new and improved fully automatic delta T mapping technique is presented, where a clustering algorithm is used to automatically identify and select the highly correlated events at each grid point whilst the minimum difference approach is employed to determine the source location.
TL;DR: In this article, an acoustic emission (AE) sensor has been employed to measure the signal frequency in machining and the frequency of tool wear was found to lie between 67 kHz and 471 kHz.
TL;DR: In this article, a method based on the acoustic emissions (AE) b-value was developed to predict stress drops and the fault-slip rockbursts induced by the stress drops.
TL;DR: In this paper, an unsupervised pattern recognition procedure is applied to identify damage mechanisms from acoustic signals, and a spatial and time analysis of acoustic events and heat sources is developed and some correlation range in the acoustic and IT events amplitude are identified.
Abstract: Acoustic emission (AE) and infrared thermography (IT) are simultaneously combined to identify damage evolution in carbon fibre reinforced composites. Samples are subjected to tensile static loads while acoustic emission sensors and an infrared camera record the acoustic signals and the temperature variations respectively. Unsupervised pattern recognition procedure is applied to identify damage mechanisms from acoustic signals. Thermodynamic arguments are introduced to estimate global heat source fields from thermal measurements and anisotropic heat conduction behavior is taken into account by means of homogenization technique. A spatial and time analysis of acoustic events and heat sources is developed and some correlation range in the AE and IT events amplitude are identified.
TL;DR: In this article, the authors conducted hydraulic fracturing (HF) experiments on 170mm cubic granite specimens with a 20mm diameter central hole to investigate how fluid viscosity affects HF process and crack properties.
Abstract: We conducted hydraulic fracturing (HF) experiments on 170 mm cubic granite specimens with a 20 mm diameter central hole to investigate how fluid viscosity affects HF process and crack properties. In experiments using supercritical carbon dioxide (SC-CO2), liquid carbon dioxide (L-CO2), water, and viscous oil with viscosity of 0.051–336.6 mPa · s, we compared the results for breakdown pressure, the distribution and fracturing mechanism of acoustic emission (AE), and the microstructure of induced cracks revealed by using an acrylic resin containing a fluorescent compound. Fracturing with low-viscosity fluid induced three-dimensionally sinuous cracks with many secondary branches, which seem to be desirable pathways for enhanced geothermal system (EGS), shale gas recovery and other processes.
TL;DR: In this article, the authors investigate the damage evolution and acoustic emission (AE) characteristics during failure process of anisotropic shale, the MTS 815 rock mechanics test system and the PAC AE test system were employed to perform Brazilian tests on shale samples, which revealed the effect of different layer inclination angles between the loading direction and the bedding plane.
TL;DR: In this paper, an acoustic emission (AE) based technique for low speed bearing fault diagnosis is presented, which starts with a heterodyne frequency reduction approach that samples AE signals at a rate comparable to vibration centered methodologies and then, the sampled AE signal is time synchronously resampled to account for possible fluctuations in shaft speed and bearing slippage.
TL;DR: In this paper, a robust condition monitoring system (CMS) and a novel signal processing method were used to detect and locate cracks on the surface of wind turbine blades using acoustic emission signals generated by breaking a pencil lead in the blade surface.
Abstract: The renewable energy industry is undergoing continuous improvement and development worldwide, wind energy being one of the most relevant renewable energies. This industry requires high levels of reliability, availability, maintainability and safety (RAMS) for wind turbines. The blades are critical components in wind turbines. The objective of this research work is focused on the fault detection and diagnosis (FDD) of the wind turbine blades. The FDD approach is composed of a robust condition monitoring system (CMS) and a novel signal processing method. CMS collects and analyses the data from different non-destructive tests based on acoustic emission. The acoustic emission signals are collected applying macro-fiber composite (MFC) sensors to detect and locate cracks on the surface of the blades. Three MFC sensors are set in a section of a wind turbine blade. The acoustic emission signals are generated by breaking a pencil lead in the blade surface. This method is used to simulate the acoustic emission due to a breakdown of the composite fibers. The breakdown generates a set of mechanical waves that are collected by the MFC sensors. A graphical method is employed to obtain a system of non-linear equations that will be used for locating the emission source. This work demonstrates that a fiber breakage in the wind turbine blade can be detected and located by using only three low cost sensors. It allows the detection of potential failures at an early stages, and it can also reduce corrective maintenance tasks and downtimes and increase the RAMS of the wind turbine.
TL;DR: In this article, the authors investigated the feasibility of in-service monitoring of the structural health of wind turbine blades by acoustic emission (AE) monitoring, which was performed over periods which totalled 21 days, during which AE monitoring was performed with a 4 sensor array.
TL;DR: In this article, an experimental campaign was carried out in a test bed to investigate the sensitivity of Acoustic Emission (AE) monitoring to water leaks, and the analysis permitted the identification of a clear correlation between three monitored parameters (namely total hits, cumulative counts and cumulative amplitude) and the characteristics of the examined leaks.
Abstract: The implementation of effective strategies to manage leaks represents an essential goal for all utilities involved with drinking water supply in order to reduce water losses affecting urban distribution networks. This study concerns the early detection of leaks occurring in small-diameter customers’ connections to water supply networks. An experimental campaign was carried out in a test bed to investigate the sensitivity of Acoustic Emission (AE) monitoring to water leaks. Damages were artificially induced on a polyethylene pipe (length 28 m, outer diameter 32 mm) at different distances from an AE transducer. Measurements were performed in both unburied and buried pipe conditions. The analysis permitted the identification of a clear correlation between three monitored parameters (namely total Hits, Cumulative Counts and Cumulative Amplitude) and the characteristics of the examined leaks.
TL;DR: In this paper, acoustic emission (AE) parameters are analyzed for five levels of damage, which are formation of hair line crack, visible crack in UHPC overlay, yielding of main bars and finally crushing of composite beams.
TL;DR: In this article, displacement-controlled diametral compression tests for the characterization of the cracking pattern according to acoustic emission parameters, three-dimensional localization of the AE sources and petrographic analysis were conducted.
TL;DR: In this paper, the authors proposed a framework based on the Hilbert-Huang Transform for the evaluation of material damages that facilitates the systematic employment of both established and promising analysis criteria, and provides unsupervised tools to achieve an accurate classification of the fracture type, the discrimination between longitudinal (P-) and traversal (S-) waves related to an acoustic emission event.
TL;DR: In this paper, a feasibility study of using smart aggregates (SAs), which are a type of embedded piezoceramic transducers, as embedded acoustic emission sensors for the health monitoring of concrete structures was conducted.
Abstract: Acoustic emission (AE) is a nondestructive evaluation technique that is capable of monitoring the damage evolution of concrete structures in real time. Conventionally, AE sensors are surface mounted on the host structures, however, the AE signals attenuate quickly due to the high attenuation properties of concrete structures. This study conducts a feasibility study of using smart aggregates (SAs), which are a type of embedded piezoceramic transducers, as embedded AE sensors for the health monitoring of concrete structures. A plain concrete beam with two surface mounted AE sensors and two embedded SAs was fabricated in laboratory and loaded under a designed three-point-bending test. The performance of embedded SAs were compared with the traditional surface mounted AE sensors in their ability to detect and evaluate the damage to the concrete structure. The results verified the feasibility of using smart aggregates as embedded AE sensors for monitoring structural damage in concrete. Potentially, the low cost smart aggregates could function as embedded AE sensors, providing great sensitivity and high reliability in applications for the structural health monitoring of concrete structures.
TL;DR: Among the failure modes of composite materials, delamination is the most striking one as mentioned in this paper, which may result in the reduction of stiffness and long-term performance of composite composite materials.
Abstract: Among the failure modes of composite materials, delamination is the most striking one. It may result in the reduction of stiffness and long-term performance of composite materials. The initiation s...
TL;DR: In this article, two extruded magnesium alloys, AZ31 and ZE10, were pre-compressed and subsequently subjected to tensile loading and the acoustic emission (AE) technique was concurrently applied to determine the activity of particular deformation mechanisms.
TL;DR: In this paper, the authors determined the crack tip position during propagation of mode I delamination and also evaluated interlaminar fracture toughness (GIC) in glass/epoxy composite specimens.
Abstract: The main objective of this study is to determine the crack tip position during propagation of mode I delamination and also to evaluate interlaminar fracture toughness (GIC) in glass/epoxy composite specimens. The crack tip location was identified using two methods: a) localization of the AE signal source and b) the cumulative AE energy. Interlaminar fracture toughness of the specimens was also determined using the ASTM standard methods and the AE-based methods. The AE-based methods results were in a close agreement with the results of ASTM standard. It was found that the novel AE-based methods are more applicable than conventional methods for characterization of the delamination.