Acoustic Emission Investigation Research Articles

Investigation of mechanical properties and acoustic emission of travertine: A case study in Jiuzhaigou, Southwestern China

Investigation of mechanical properties and acoustic emission of travertine: A case study in Jiuzhaigou, Southwestern China

Acoustic emission and DSC investigations of anomalous stress-stain curves and burst like shape recovery of Ni49Fe18Ga27Co6 shape memory single crystals

Simultaneous acoustic emission, AE, and DSC measurements under compression along [110]A direction were carried out on Ni49Fe18Ga27Co6 shape memory single crystals. The compression resulted in anomalous stress-strain loops with stress drops/jumps on it, reflecting a sudden formation/dissolution of a more stable (detwinned) martensite structural modification than the thermally induced (twinned) one. The final detwinned martensite, obtained below a certain temperature, was stable even after downloading: during heating it showed a burst-like recovery at about 35K higher transformation temperature than that of the thermally induced one, with an audible click. It was obtained that the number of acoustic events showed strong asymmetry: e.g. for stress induced transformations the number of hits for uploading was larger. Simultaneous measurements of stress-time curves and AE versus time revealed that in the nucleation/dissolution processes in both (up and down) directions, as an intermediate step, the twinned martensite was first formed and resulted in additional AE events. This was interpreted by the easy as well as difficult nucleation of the twinned and detwinned martensites, respectively. The stress drops on the uploading stress-strain curve were attributed to subsequent nucleation of the detwinned martensite from the twinned modification and were followed by a sharp decrease of the AE activity. This indicated that the formation of detwinned martensite is a sudden, fast process and can take place without significant elastic energy storage. This was also in agreement with the fact that during burst like thermal recovery the width of the transition was very small (Af≅ As). Similarly, during downloading the stress jumps were interpreted as sudden dissolutions of the detwinned phase by retwinning and at all stress jumps there were local maxima on the AE activity curve.

Investigation of Acoustic Emissions and Friction Behavior in a Two-phase Flow with Different Sand Content

Investigation of Acoustic Emissions and Friction Behavior in a Two-phase Flow with Different Sand Content

Adaptive Approach to Time-Frequency Analysis of AE Signals of Rocks

The paper describes a new adaptive approach to the investigation of acoustic emission of rocks, the anomalies of which may serve as short-term precursors of strong earthquakes. The basis of the approach is complex methods for monitoring acoustic emission and for analysis of its time-frequency content. Piezoceramic hydrophones and vector receivers, installed at the bottom of natural and artificial water bodies, as well as in boreholes with water, are used as acoustic emission sensors. To perform a time-frequency analysis of geoacoustic signals, we use a sparse approximation based on the developed Adaptive Matching Pursuit algorithm. The application of this algorithm in the analysis makes it possible to adapt to the concrete characteristics of each geoacoustic pulse. Results of the application of the developed approach for the investigation of acoustic emission anomalies, occurring before earthquakes, are presented. We analyzed the earthquakes, that occurred from 2011 to 2016 in the seismically active region of the Kamchatka peninsula, which is a part of the circum-Pacific orogenic belt also known as the "Ring of Fire". It was discovered that geoacoustic pulse frequency content changes before a seismic event and returns to the initial state after an earthquake. That allows us to make a conclusion on the transformation of acoustic emission source scales before earthquakes. The obtained results may be useful for the development of the systems for environmental monitoring and detection of earthquake occurrences.

Investigation of Acoustic Emission of Cracks in Rails under Loading Close to Operational

The paper is devoted to the study of the possibility of detecting cracks in railway rails by the acoustic emission (AE) method. An experimental study of AE signals under cyclic compression loading of rail fragments, which simulates the rail operating load, has been carried out. Fragments of rails without defects, as well as fragments containing pre-grown fatigue cracks, were studied. It was found that AE signals generated by a rail with a crack have higher activity compared to signals from defect-free specimens. It is shown that the AE signals during the loading of defect-free specimens have a short duration and low amplitude and may be caused by the deformation of non-metallic inclusions. The crack presence leads to an increase in the AE hits rate and changes the nature of the distribution of the AE hits amplitudes. It is shown that the crack location has no effect on the reliability of its detection by the AE method. Criteria of crack detection by AE testing are offered as a result of this study.

Acoustic emission investigation of coal gangue cementitious composites under effects on fiber type

A material known as coal gangue cementitious composite (CGCC), which is made of coal gangue, cement, and additives among other things, is frequently used in the field of coal backfilling mining to regulate the stability of surrounding rock and protect the environment. Due to the strict criteria for high performance of CGCC under the unique operating conditions in mining, it has been widely discussed to increase CGCC performance by adding fibers. In the absence of relevant basic research, fiber insertion results in significant differences in microstructure and mechanical failure behavior between materials and standard CGCC. The CGCCs with CF and SF were subjected to a uniaxial compression acoustic emission test in this study, and the samples' mechanical deformation characteristics and acoustic emission parameters were measured during the loading procedure. To compare and contrast CGCCs made of various fiber types, mechanical properties, fracture evolution laws, and acoustic emission characteristics are used. According to the findings, addition of fibers and the increase of curing age have a positive effect on improving the mechanical properties, and rate of maximum compressive strength was 25.0%. According to the analysis of AE parameter method, the existence of fibers has a positive impact on the on the ability to resist tensile failure of CGCC, leading to the transformation of structural damage from tensile crack to shear crack. Furthermore, as curing age increases, the development of shear cracks in the sample deepens, resulting in an increase in the proportion of AF:RA< 1 of up to 4.97 %. This paper proposes new ideas for promoting the development of environmentally friendly composite materials and realizing the multi-functional use of CGCCs.

Investigation of passive acoustic emissions during powder mixing in a V-blender

Powder mixing is a complex process and a critical step in production across various industries. Passive acoustic emissions provide a promising potential for inline powder mixing monitoring. Vibrations from these emissions were measured during rotations of a V-blender using glass beads as a model solid as well as starch granules. Vibration profiles were correlated to specific phases of particle motion within the revolving V-shells. The phase, labeled Feature #1b, associated with particle collisions of the V-shell lid with attached accelerometer provided the largest measured vibration amplitudes and most reliable and relevant information on particle movement. After wavelet filtering to remove large-scale vibrations of the V-shell, the optimal information extraction method was identified as the average of the 50 highest amplitudes within the Feature #1b phase. An example illustrating the mixing of two size ranges of granules shows the potential of this monitoring method for pharmaceutical powder mixing in V-blenders. • Passive acoustic emissions are measured by a sensor on the lid of a V-blender. • Passive acoustic emissions from collisions reflect particle size and flow. • The largest emission amplitudes occur from collisions with the V-blender lids. • The 50 largest emissions amplitudes allow a mixing profile to be estimated.

Denouement of the Energy-Amplitude and Size-Amplitude Enigma for Acoustic-Emission Investigations of Materials.

There are many systems producing crackling noise (avalanches) in materials. Temporal shapes of avalanches, U(t) (U is the detected voltage signal, t is the time), have self-similar behaviour and the normalized U(t) function (e.g., dividing both the values of U and t by S1/2, where S is the avalanche area), averaged for fixed S, should be the same, independently of the type of materials or avalanche mechanisms. However, there are experimental evidences that the temporal shapes of avalanches do not scale completely in a universal way. The self-similarity also leads to universal power-law-scaling relations, e.g., between the energy, E, and the peak amplitude, Am, or between S and Am. There are well-known enigmas, where the above exponents in acoustic emission measurements are rather close to 2 and 1, respectively, instead of and , obtained from the mean field theory, MFT. We show, using a theoretically predicted averaged function for the fixed avalanche area, (where a and b are non-universal, material-dependent constants), that the scaling exponents can be different from the MFT values. Normalizing U by Am and t by tm (the time belonging to the Am: rise time), we obtain (the MFT values can be obtained only if φ would be zero). Here, φ is expected to be material-independent and to be the same for the same mechanism. Using experimental results on martensitic transformations in two different shape-memory single-crystals, φ = 0.8 ± 0.1 was obtained (φ is the same for both alloys). Thus, dividing U by Am as well as t by (~tm) leads to the same common, normalized temporal shape for different, fixed values of S. This normalization can also be used in general for other experimental results (not only for acoustic emission), which provide information about jerky noises in materials.

Time-Frequency Characteristics of Acoustic Emission Signals on Water-Bearing Sandstone Specimen Subjected to Conventional Uniaxial Compression

This paper presents an experimental investigation of acoustic emission (AE) time-frequency characteristics of a water-bearing sandstone specimen in a conventional uniaxial compression test. The main achievements are as follows: (1) The violent fluctuation of AE time domain parameters indicates that the water-bearing sandstone specimen is about to be destroyed. This characteristic provides a theoretical basis for predicting the failure of water-bearing rock in engineering practice. (2) In the elastic phase, the AE b value is the lowest but has a sudden increase after falling into the steady crack propagation phase. In the unsteady crack propagation phase, the AE b value is further increased. This characteristic is of great indicative value for predicting the failure of the water-bearing sandstone specimen. (3) The difference of dominant frequency among the three key points is very small, indicating that the crack initiation and propagation of the water-bearing sandstone specimen has a certain stability in the damage and failure process. But, the two-dimensional frequency spectrum structure of AE waveform signals shows that the closer to failure, the more the number of the frequency spectrum structure peaks. (4) The energy of AE signals is mainly concentrated in the first three frequency bands. The closer to failure, the more the energy proportion of the first three frequency bands is reduced; conversely, the energy proportion of the latter five frequency bands is increased, which leads to more complexity of the failure modes of the water-bearing sandstone specimen.

Laboratory-Scale Insight into Fractal Dimension Indicators for Seismic Hazard Assessment Associated with Rock Failures

Investigation of acoustic emission (AE) characteristics during laboratory tests of coal samples can provide useful guidance on the recognition of microseismicity (MS) precursors for seismic hazards in underground coal mining. In this study, a methodology, involving fractal dimension indices and a fuzzy comprehensive evaluation model, was developed and demonstrated using AE monitoring data in a uniaxial loading test of coal samples, which allows for a better and quantitative recognition of AE/MS precursors to seismic hazards associated with rock failures. In this methodology, the fractal dimension indices include six information dimension indices as well as three previously used capacity dimension indices. The assessment results were initially characterised as probabilities belonging to each of four risk levels (none, weak, moderate, and strong), and then output as a comprehensive result corresponding to one of these four risk levels. The results indicated that this developed methodology was able to recognise the AE precursors for rock failures.

The influence of AlSi10Mg recycled powder on corrosion-resistance behaviour of additively manufactured components: mechanical aspects and acoustic emission investigation

The effects of using recycled AlSi10Mg aluminium alloy powders on the mechanical properties and the corrosion-resistance behaviour of the components manufactured via selective laser melting (SLM) were analysed. The microstructural results show that the utilisation of recycled powder causes coarsening of interdendritic Si-network, especially along the melt pool boundaries of the SLM specimens. The corrosion resistance of the samples was evaluated by means of neutral salt spray (NSS) tests for 1000 h and mass loss measurements. The corrosion behaviour, in terms of surface roughness, density and porosity, however, remains almost the same between the samples produced by virgin and recycled powder. In addition to this, a passive NDE tool has been used to investigate and study the impact of powders on the corrosion performance of the alloy: Acoustic Emission (AE) technique. SEM observations allowed to highlight the morphological differences in the surface of the test specimens induced by the exposure condition. Thus, it was possible to correlate the AE results to corrosion mechanisms activated on the surfaces of the test specimen. A good correlation between the corrosion-resistance behaviour and the AE test results were obtained. Finally, the mechanical properties before and at the end of the accelerated corrosion were evaluated according to the yield strength, tensile strength, and elongation at breakage. The results showed comparable mechanical properties for the samples produced using both virgin and recycled powders. Besides, no notable influence of the exposure to corrosive environment on the mechanical performance was observed.

Corrosion Resistance Behaviour of recycled AlSi10Mg alloy: Surface Morphology and Acoustic Emission Investigation

The corrosion resistance behaviour of recycled AlSi10Mg alloy prepared using Selective Laser Melting (SLM) process is investigated. The specimens are exposed to salt solution attack (5% NaCl) atomized in uniform droplets, inside a controlled Salt Spray Test (SST) chamber for 1000 h. The surface morphology of the specimens exposed to different predefined exposure times (0 h, 6 h, 48 h, 168 h, 480 h and 1000 h) are investigated under Scanning Electron Microscope (SEM). The SEM micrographs shows the salient features of the corrosion attack such as the formation both of pits and corrosion products on samples surface in different exposure times in the SST chamber. Similarly, the Acoustic Emission (AE) signals generated during the corrosion process are recorded for the different exposure times. The AE waveforms are studied using advanced waveform processing techniques. The waveforms, in their time-frequency domain, provide detailed information on the characteristic features of the acoustic source. The different AE sources have been characterized from the time-frequency analysis of the waveforms.

Evolution of Natural Joints' Mesoscopic Failure Modes under Shear Tests: Acoustic Emission Investigation

Natural joints play an important role in the stability performance of rock engineering. To deeply understand the shear mechanism of natural joints (i.e., tensile fracture or shear fracture), direct shear experiments and acoustic emission (AE) monitoring were carried out for different kinds of joints under five levels of normal stress. By disposing the AE signals during a joint's shear process as AE samples databases, an optimal criterion to identify the tensile fracture and shear fracture modes was established based on the AE parameters, and this method was applied to reveal the shear damage of natural joints under the shear process. The results showed that the shear failure regions of natural joints were localized and inhomogeneous on a joint's surface, and the mesoscopic shear fracture and tensile fracture appeared along all the shearing process of the joint. The moment and the type of failure mode changed with the increase of the normal stress, but the main type of fracture did not change in each period during the whole shearing process, which provided a new way for disaster warning of shear damage.

Modification of Coal Samples with Bursting Liability Subjected to Microwave Irradiation

This paper introduces the innovative technique to release the bursting liability of coal seam via microwave irradiation. To verify the feasibility of this environment-friendly technique, a series of laboratory tests incorporating acoustic emission (AE) investigation were carried out. Test results indicated that both the uniaxial compressive strength (UCS) and bursting energy index of raw and water-soaked coal samples were significantly reduced. In particular, the bursting liability was reduced by one level when the values of UCS were compared, the evidence of which is the variation of wave velocities of tested coal samples. It can also be found from the events and hits in the complete stress-strain curve and the cumulative curve of acoustic emission that the elastic modulus of the raw and water-soaked coal samples subjected to microwave irradiation decreased by 58.42% and 29.63%, respectively. This facilitates the entry into the stage of stable crack propagation more quickly, the growth rate and size of the cracks were slower and more uniform, and there were no smaller coal fragments ejecting during the failure process of the coal samples. Meanwhile, the proportion of high-energy events released in coal samples experienced a decline after the treatment of the microwave. Moreover, microwave heating principally promoted the initiation and expansion of microcracks in coal samples under the influence of microwave power of 1 kW and a heating time of 120s, which may cause the overall damage of large fractures to break into multiple small and medium cracks. Based on the experimental results, the conceptual process of using microwave in weakening the bursting liability of coal seam was then proposed, which will be the meaningful reference for microwave-assisted oil recovery and coal bed methane production.

Quantitative acoustic emission investigation on the crack evolution in concrete prisms by frequency analysis based on wavelet packet transform

To gain an insight into the evolution of micro-cracks in concrete materials, a quantitative acoustic emission investigation on the damage process of concrete prisms subjected to three-point bending loading was performed. Each of the monitored acoustic emission signals was processed by a two-level wavelet packet decomposition into four different frequency bands (AA2, DA2, AD2, and DD2), and the energy coefficients R1, R2, R3, and R4 that parameterize their characteristic frequency bands were calculated. By analyzing variations in energy coefficients of the lowest frequency band (AA2), R1, and the energy coefficients of the highest frequency band (DD2), R4, the whole damage process was divided into three stages: crack initiation, crack growth, and crack coalescence. An inverse relationship between the frequency of the acoustic emission signal emitted by the propagating crack and the crack size in concrete materials was acquired based on the damage theory of brittle materials and the strain energy release theory. The statistical analysis results of the experimental data indicated that the average of R1 increased in turn, and the average of R4 correspondingly decreased in turn from Stage 1 to Stage 3. It revealed that the frequencies of acoustic emission signals decreased gradually with the evolution of the damage of concrete prisms, which is in a good agreement with the theoretical analysis result.

Acoustic Emission Investigation on Crack Propagation Mode of Sandstone During Brazil Splitting Process

In the present work, the Brazilian tests for six sandstone samples were carried out. The acoustic emission (AE) method was applied to analyze the characteristics of the crack propagating mode and further to classify the cracking mode during the whole sandstone lump Brazilian splitting process. The study results showed that the AE event produced during the whole loading process, and different loading stages demonstrate different AE features. The amplitude of AE signals was increasing along with the loading stress, and there is a period of quiet time before the failure of the sample. It also concluded that more than 99% of the whole cracking signals are classified as tensile mode, and there are precious few shear cracks that occurred during the Brazilian test; the central frequency of the occurrence of the tensile crack is 138.58 kHz.

Acoustic Emission Investigation on an Electronically Controlled Two-Stroke Low-Speed Marine Diesel Engine: in Axial and Vertical Directions

An experimental method in a real-working condition was conducted to collect acoustic emission (AE) signals emitted from cylinders of a large two-stroke low-speed marine diesel engine. Measurements were performed in an axial direction of the cylinder in medium-frequency (20–80 kHz) and high-frequency (100–900 kHz) ranges and in a vertical direction only in the medium-frequency range under two engine operating modes. The collected AE signals were analyzed in crank angle and crank angle–frequency domains. kurtosis and root mean square (RMS) parameters were employed to identify engine operating modes based on the obtained AE signals as well as investigate their characteristics. A fast Fourier transform (FFT) algorithm was also utilized to discover the frequency range of the AE signals. The results showed that only the AE signals generated by combustion processes, friction and wear, and exhaust valve opening (EVO) were partially detected. However, the AE signal radiated by the friction phenomenon was not apparent in the high-frequency range. Also, the combustion process had a strong influence on the remaining AE’s sources, especially in the axial direction of the medium-frequency range. Furthermore, the measurements should be implemented for the AE signals due to friction and wear in the medium and low frequencies; meanwhile, the combustion should be investigated in the frequency range of 200–300 kHz

Simultaneous lithospheric-atmospheric signals of acoustic emission at “Karymshina” site in Kamchatka

We present the results of complex lithospheric-atmospheric investigations of acoustic emission in a seismically active region (Kamchatka peninsula). A laser strainmeter-interferometer, a geophone, a wide-band acoustic system and a microbarometer, installed at Karymshina site (IKIR FEB RAS), are used in the monitoring. Rock deformation, acoustic emission in the near-surface rocks and in the atmosphere by the ground surface are under the consideration. Moreover, we suggest a method to detect acoustic signals recorded simultaneously in the near-surface rocks and in the atmosphere by the ground surface. The method consists in filtration of acoustic signals from the sensors at different frequency sub-ranges from fractions to the first hundreds of hertz followed by detection and accumulation of on 1-second interval. We analyze the data from September 2016 to December 2020. Examples of records of simultaneous acoustic signals in rocks and in the atmosphere are illustrated. The investigation is topical for the construction of a model of lithosphere-atmosphere interaction in a seismically active region.

Acoustic emission and CT investigation on fracture evolution of granite containing two flaws subjected to freeze–thaw and cyclic uniaxial increasing-amplitude loading conditions

The deterioration mechanism and fatigue fracturing evolution of granite with two pre-existing flaws experiencing freeze–thaw (F-T) treatment are investigated in this work. The flaws in the rock sample were prepared as a combination of a horizontal flaw with an upper inclined flaw above the horizontal flaw according to the joint characteristics in an open pit slope. In-situ acoustic emission monitoring combined with the post-test 3D computed tomography (CT) technique was employed to reveal the fracture evolution behaviors of rock treated with 0, 50, and 80 freeze–thaw cycles. Results show that the freeze–thaw damage impacts the frost heaving force, cyclic deformation, AE activates, crack coalescence pattern and fatigue life of the granite samples. The accumulative AE count/energy decreases with increasing number of freeze–thaw cycles, and the accumulated AE count/energy in a loading stage gradually grows faster. In addition, AE spectral frequency analysis reveals the impact of previous freeze–thaw damage on the formation of the crack scale, the sample is prone to producing large scale cracks under high freeze–thaw treatment. Moreover, 3D reconstructed CT images present an internal crack network pattern, and the most striking finding is that a simple crack network forms for a sample experiencing high F-T fatigue damage. It is suggested that deterioration of the rock bridge structure is strongly impacted by the accumulative freeze–thaw damage. The testing results are helpful to understand the influence of freeze–thaw and fatigue loading on the fracture evolution characteristics of rock in cold regions.

Experimental failure analysis and mechanical performance evaluation of fiber-metal sandwich laminates interleaved with polyamide-6,6 interlayers through the combined usage of acoustic emission, thermography and microscopy techniques

Fiber-metal laminates are hybrid sandwich composite structures made of thin metallic sheets and layers of fiber-reinforced plastics. In this study, for the first time, the effects of polyamide 66 nonwoven interlayers on the tensile, three-point bending, interlaminar shear strength, and low velocity impact responses of fiber-metal laminates are investigated by coupling acoustic emission, thermography, and microscopy techniques. The fiber-metal laminates are interleaved with polyamide 66 nonwoven fabrics at two different areal weight density, namely, 17 gsm (grams per square meter) and 50 gsm. The tensile, bending, interlaminar shear strength, and low velocity impact tests are carried out in accordance with the ASTM standards. During the tensile and flexural tests, acoustic emission data are collected to understand damage types occurring under various loading conditions and, in turn, clearly shed light on the performance of polyamide 66 for interfacial strengthening in fiber-metal laminates. The results of acoustic emission investigation are correlated with the optical and scanning electron microscope-based microscopic analysis. It is shown that the interlaminar shear strength of fiber-metal laminates can be increased significantly (about 42%) by using polyamide 66 nonwoven interlayers. The impacted fiber-metal laminate specimens are examined to determine damage area and length using the lock-in thermography method. It is found that the polyamide 66 interlayers decrease the debonded length and damaged area up to 39 and 32%, respectively. The tensile and flexural strength and modulus of the fiber-metal laminate are not significantly affected by the presence of polyamide 66 interlayers, except a negligible drop in the value of tensile and flexural strength by 6 and 4%, respectively. The polyamide 66 interlayers are proved to be very successful in enhancing plastic deformation ability of the matrix and bonding efficiency between aluminum and composite sections.