Statistics Of Acoustic Emission Research Articles

Mechanical anisotropy associated with beddings in shale under Brazilian test conditions: Insights from acoustic emission statistics

A comprehensive understanding of shale’s bedding anisotropy is crucial for shale-related engineering activities, such as hydraulic fracturing, drilling and underground excavation. In this study, seven Brazilian tests were conducted on shale samples at different bedding orientations with respect to the loading direction (0°, 45° and 90°) and the disc end face (0°, 45° and 90°). An acoustic emission (AE) system was employed to capture the evolution of damage and the temporal-spatial distribution of microcracks under splitting-tensile stress. The results show that the Brazilian tensile strength decreases with increasing bedding inclination with respect to the disc end face, while it increases with the angle between bedding and loading directions. Increasing the bedding inclination with respect to the end face facilitates the reduction in b value and enhances the shale’s resistance to microcrack growth during the loading process. Misalignment between the bedding orientation and the end face suppresses the growth of mixed tensile-shear microcracks, while reducing the bedding angle relative to the loading direction is beneficial for creating mixed tensile-shear and tensile cracks. The observed microscopic failure characteristics are attributed to the competing effects of bedding activation and breakage of shale matrix at different bedding inclinations. The temporal-spatial distribution of microcracks, characterized by AE statistics including the correlation dimension and spatial correlation length, illustrates that the fractal evolution of microcracks is independent of bedding anisotropy, whereas the spatial distribution shows a stronger correlation. The evolution features of correlation dimension and spatial correlation length could be potentially used as precursors for shale splitting failure. These findings may be useful for predicting rock mass instability and analyzing the causes of catastrophic rupture.

Influence of the Structure of a Gouge-Filled Fault on the Parameters of Acoustic Emission

Presented are the results of laboratory experiments on investigating manifestations of acoustic emission (AE) of a gouge-filled fault during stick-slip. The laboratory experiments were held at the slider-model setup, when a granite block slides along a rough granite base under normal and shear loads. In the course of experiments we altered the structure of the two-component filler of the fault and focused on variations of the AE parameters. The kinematic parameters of fault slip events in all the realizations remained approximately the same. The eff ect of gouge structure on the statistics of AE has been revealed. An alteration of proportion of quartz sand / glass beads in the filler of the fault was accompanied by an alteration of the b-value of frequency-energy distribution from 0.53 to 0.85, and the p-value of Omori law from 1.00 to 2.06. Also, it has been demonstrated that the nucleation of a slip event is accompanied by an alteration of the mechanism of AE generation – at the initial stage the 'tensile crack' signals prevailed, while at the final stage – the 'shear crack' signals did. The alteration of AE genesis manifested vividly in a corresponding alteration of the emitted waveforms for all the realizations.

Experimental Evidence of Accelerated Seismic Release without Critical Failure in Acoustic Emissions of Compressed Nanoporous Materials.

The total energy of acoustic emission (AE) events in externally stressed materials diverges when approaching macroscopic failure. Numerical and conceptual models explain this accelerated seismic release (ASR) as the approach to a critical point that coincides with ultimate failure. Here, we report ASR during soft uniaxial compression of three silica-based (SiO_{2}) nanoporous materials. Instead of a singular critical point, the distribution of AE energies is stationary, and variations in the activity rate are sufficient to explain the presence of multiple periods of ASR leading to distinct brittle failure events. We propose that critical failure is suppressed in the AE statistics by mechanisms of transient hardening. Some of the critical exponents estimated from the experiments are compatible with mean field models, while others are still open to interpretation in terms of the solution of frictional and fracture avalanche models.

Acoustic emission during different-type inter-block movements

The article reports the lab experimentation on seismic/acoustic emission during different-type inter-block movements of rock mass. The fact that co-seismic displacement under induced earthquakes occurs along the existing interfaces is the basis for relatively simple tests on a slip-model plant. Using different materials as fracture fillers allowed modeling entire range of probable deformation modes. The deformation modes are conditionally grouped as creep or steady-state slip, unsteady-state slip and regular discontinuous slip or stick-slip. The authors show that statistics of acoustic emission during slip is described using the Gutenberg–Richter law. The strongest “representative” events under shearing occur quasiregularly, with probability much higher than follows from G–R law. The functional relation is found between the acoustic emission energy and the shear velocity.

Role of superposition of dislocation avalanches in the statistics of acoustic emission during plastic deformation

Various dynamical systems with many degrees of freedom display avalanche dynamics, which is characterized by scale invariance reflected in power-law statistics. The superposition of avalanche processes in real systems driven at a finite velocity may influence the experimental determination of the underlying power law. The present paper reports results of an investigation of this effect using the example of acoustic emission (AE) accompanying plastic deformation of crystals. Indeed, recent studies of AE did not only prove that the dynamics of crystal defects obeys power-law statistics, but also led to a hypothesis of universality of the scaling law. We examine the sensitivity of the apparent statistics of AE to the parameters applied to individualize AE events. Two different alloys, MgZr and AlMg, both displaying strong AE but characterized by different plasticity mechanisms, are investigated. It is shown that the power-law indices display a good robustness in wide ranges of parameters even in the conditions leading to very strong superposition of AE events, although some deviations from the persistent values are also detected. The totality of the results confirms the scale-invariant character of deformation processes on the scale relevant to AE, but uncovers essential differences between the power-law exponents found for two kinds of alloys.

Check valve's fault detection with wavelet packet's kernel principal component analysis

High pressure piston diaphragm pump is the most important power source of the pipeline transportation.To solve the problem of on-line monitoring on the fault of internal piston,the authors put forward a detection method based on acoustic emission signal's wavelet packet frequency and Kernel Principal Component Analysis(KPCA).Firstly,the author adopted wavelet packet to deal with the acoustic emission data to get each frequency band energy value.Secondly,the authors used KPCA to decompose the energy in high dimensional space to find the feature model,and made use of statistics SPE and T2 in feature model to make detection on fault signal.Finally,the authors conducted experiments to verify the statistics of acoustic emission of GEHO diaphragm pump's check valve.In comparison with the PCA method,the proposed method can make on-line monitoring on fault of internal piston fast and accurate,so it has good application prospect on the domain of the high pressure piston diaphragm pump's non-destructive fault detection.

Identifying fault heterogeneity through mapping spatial anomalies in acoustic emission statistics

Seismicity clusters within fault zones can be connected to the structure, geometric complexity and size of asperities which perturb and intensify the stress field in their periphery. To gain further insight into fault mechanical processes, we study stick‐slip sequences in an analog, laboratory setting. Analysis of small scale fracture processes expressed by acoustic emissions (AEs) provide the possibility to investigate how microseismicity is linked to fault heterogeneities and the occurrence of dynamic slip events. The present work connects X‐ray computer tomography (CT) scans of faulted rock samples with spatial maps of b values (slope of the frequency‐magnitude distribution), seismic moments and event densities. Our current experimental setup facilitates the creation of a series of stick‐slips on one fault plane thus allowing us to document how individual stick‐slips can change the characteristics of AE event populations in connection to the evolution of the fault structure. We found that geometric asperities identified in CT scan images were connected to regions of low b values, increased event densities and moment release over multiple stick‐slip cycles. Our experiments underline several parallels between laboratory findings and studies of crustal seismicity, for example, that asperity regions in lab and field are connected to spatial b value anomalies. These regions appear to play an important role in controlling the nucleation spots of dynamic slip events and crustal earthquakes.

Statistics of acoustic emission in paper fracture: precursors and criticality

We present statistical analysis of acoustic emission (AE) data from tensile experiments onpaper sheets, for loading mode I, with samples broken under strain control. The results arebased on 100 experiments on unnotched samples and 70 samples with a long initial edgenotch. First, AE energy release and AE event rates are considered for both cases,to test for the presence of ‘critical points’ in fracture. For AE energy, no clearsignatures are found, whereas the main finding is that the event rate diverges whena sample-dependent ‘critical time’ of the maximum event rate is approached.This takes place after the maximum stress is reached. The results are comparedwith statistical fracture models of heterogeneous materials. We also discuss thedependence of the AE energy and event interval distributions on average event rates.

Acoustic emission from periodically perturbed systems: SOC and predictability

The statistics of acoustic emission (AE) from as diverse processes as volcanic activity (Stromboli, Italy) and martensitic transformations driven by thermal cycles, is shown to verify the paradigm of self-organized criticality. However, catastrophic event predictability both in laboratory (the onset of martensitic transformations) and in on-site applications (volcanic seisms and explosions) through the analysis of historical AE series, is not ruled out as long as the emitting samples are subjected to (quasi)periodic low-frequency/large-scale dynamics.