The role of acoustic emission in the study of rock
01 Dec 1993-Vol. 30, Iss: 7
TL;DR: A review of the successes and limitations of acoustic emission (AE) studies as applied to the fracture process in rock with emphasis on our ability to predict rock failure is presented in this paper, where application of laboratory AE studies to larger scale problems related to the understanding of earthquake processes is also discussed.
Abstract: The development of faults and shear fracture systems over a broad range of temperature and pressure and for a variety of rock types involves the growth and interaction of microcracks. Acoustic emission (AE), which is produced by rapid microcrack growth, is a ubiquitous phenomenon associated with brittle fracture and has provided a wealth of information regarding the failure process in rock. This paper reviews the successes and limitations of AE studies as applied to the fracture process in rock with emphasis on our ability to predict rock failure. Application of laboratory AE studies to larger scale problems related to the understanding of earthquake processes is also discussed. In this context, laboratory studies can be divided into the following categories. 1) Simple counting of the number of AE events prior to sample failure shows a correlation between AE rate and inelastic strain rate. Additional sorting of events by amplitude has shown that AE events obey the power law frequency-magnitude relation observed for earthquakes. These cumulative event count techniques are being used in conjunction with damage mechanics models to determine how damage accumulates during loading and to predict failure. 2) A second area of research involves the location of hypocenters of AE source events. This technique requires precise arrival time data of AE signals recorded over an array of sensors that are essentially a miniature seismic net. Analysis of the spatial and temporal variation of event hypocenters has improved our understanding of the progression of microcrack growth and clustering leading to rock failure. Recently, fracture nucleation and growth have been studied under conditions of quasi-static fault propagation by controlling stress to maintain constant AE rate. 3) A third area of study involves the analysis of full waveform data as recorded at receiver sites. One aspect of this research has been to determine fault plane solutions of AE source events from first motion data. These studies show that in addition to pure tensile and double couple events, a significant number of more complex event types occur in the period leading to fault nucleation. 4) P and S wave velocities (including spatial variations) and attenuation have been obtained by artificially generating acoustic pulses which are modified during passage through the sample. (A) This paper was presented at the 34th U.S. Symposium on rock mechanics, 27-30 June 1993, University of Wisconsin-Madison. For the covering abstract see IRRD 863389.
Citations
More filters
TL;DR: In this paper, a numerical model for rock is proposed in which the rock is represented by a dense packing of non-uniform-sized circular or spherical particles that are bonded together at their contact points and whose mechanical behavior is simulated by the distinct element method using the two-and three-dimensional discontinuum programs PFC2D and PFC3D.
3,470 citations
Cites background from "The role of acoustic emission in th..."
...Acoustic-emission (AE) based observations of rock [6] record the acoustic signals that are generated spontaneously from this microcracking, thereby providing information about the size, location and deformation mechanisms of the acoustic events as well as properties of the medium through which the acoustic...
[...]
TL;DR: In this article, the authors investigated the inelastic and failure behavior of six sandstones with porosities ranging from 15% to 35% and used a broad range of effective pressures to investigate the transition in failure mode from brittle faulting to cataclastic flow.
Abstract: Triaxial compression experiments were conducted to investigate the inelastic and failure behavior of six sandstones with porosities ranging from 15% to 35%. A broad range of effective pressures was used so that the transition in failure mode from brittle faulting to cataclastic flow could be observed. In the brittle faulting regime, shear-induced dilation initiates in the prepeak stage at a stress level C' which increases with effective mean stress. Under elevated effective pressures, a sample fails by cataclastic flow. Strain hardening and shear-enhanced compaction initiates at a stress level C* which decreases with increasing effective mean stress. The critical stresses C' and C* were marked by surges in acoustic emission. In the stress space, C* maps out an approximately elliptical yield envelope, in accordance with the critical state and cap models. Using plasticity theory, the flow rule associated with this yield envelope was used to predict porosity changes which are comparable to experimental data. In the brittle faulting regime the associated flow rule predicts dilatancy to increase with decreasing effective pressure in qualitative agreement with the experimental observations. The data were also compared with prediction of a nonassociative model on the onset of shear localization. Experimental data suggest that a quantitative measure of brittleness is provided by the grain crushing pressure (which decreases with increasing porosity and grain size). Geologic data on tectonic faulting in siliciclastic formations (of different porosity and grain size) are consistent with the laboratory observations.
805 citations
TL;DR: An overview of the results obtained with lattice models of the fracture, highlighting the relations with statistical physics theories and more conventional fracture mechanics approaches is presented.
Abstract: Disorder and long-range interactions are two of the key components that make material failure an interesting playfield for the application of statistical mechanics. The cornerstone in this respect has been lattice models of the fracture in which a network of elastic beams, bonds, or electrical fuses with random failure thresholds are subject to an increasing external load. These models describe on a qualitative level the failure processes of real, brittle, or quasi-brittle materials. This has been particularly important in solving the classical engineering problems of material strength: the size dependence of maximum stress and its sample-to-sample statistical fluctuations. At the same time, lattice models pose many new fundamental questions in statistical physics, such as the relation between fracture and phase transitions. Experimental results point out to the existence of an intriguing crackling noise in the acoustic emission and of self-affine fractals in the crack surface morphology. Recent advances ...
464 citations
TL;DR: A review of the available experimental evidence for brittle creep in crustal rocks, and various models developed to explain the observations can be found in this paper, where three main classes of brittle creep model have been proposed to explain these observations: phenomenological, statistical, and micromechanical.
463 citations
Cites background or methods from "The role of acoustic emission in th..."
...When the experimental arrangement allows an array of multiple AE transducers (typically 8e32) to be positioned around the sample, it is also possible to determine the spatio-temporal distribution of AE hypocentres during deformation (e.g., Lockner, 1993a,b)....
[...]
...A similar approach was followed by Lockner (1998), who extended his earlier work (Lockner, 1993a,b) to incorporate macroscopic fracture at a threshold axial inelastic strain....
[...]
TL;DR: In this article, the authors analyzed the acoustic emission and the mechanical behavior of granite samples during triaxial compression tests and found that the size of AE events displays power law distributions, conforming to the Gutenberg-Richter law observed for earthquakes.
Abstract: The acoustic emission (AE) and the mechanical behavior of granite samples during triaxial compression tests have been analyzed. The size of AE events displays power law distributions, conforming to the Gutenberg-Richter law observed for earthquakes, which is characterized by the b value. As the confining pressure increases, the macroscopic behavior becomes more ductile. For all different stages of the rock mechanical behavior (linear, nonlinear prepeak, nonlinear postpeak, shearing), there is a systematic decrease of the b value with increasing confining pressure. A numerical model based on progressive elastic damage and the finite element method allows simulations of the main experimental observations on AE and of a wide range of macroscopic behaviors from brittleness to ductility. The model reproduces a decrease in the b value that appears to be related to the type of macroscopic behavior (brittle-ductile) rather than to the confining pressure. Both experimental and numerical results suggest a relationship between the b value and the brittle-ductile transition. Moreover, these results are consistent with recent earthquake observations and give new insight into the behavior of the Earth's crust.
337 citations
References
More filters
Book•
24 Sep 1993TL;DR: In this article, the authors present a unified continuum, microstructural and atomistic treatment of modern day fracture mechanics from a materials perspective, focusing on the basic elements of bonding and microstructure that govern the intrinsic toughness of ceramics.
Abstract: This is an advanced text for higher degree materials science students and researchers concerned with the strength of highly brittle covalent–ionic solids, principally ceramics. It is a reconstructed and greatly expanded edition of a book first published in 1975. The book presents a unified continuum, microstructural and atomistic treatment of modern day fracture mechanics from a materials perspective. Particular attention is directed to the basic elements of bonding and microstructure that govern the intrinsic toughness of ceramics. These elements hold the key to the future of ceramics as high-technology materials - to make brittle solids strong, we must first understand what makes them weak. The underlying theme of the book is the fundamental Griffith energy-balance concept of crack propagation. The early chapters develop fracture mechanics from the traditional continuum perspective, with attention to linear and nonlinear crack-tip fields, equilibrium and non-equilibrium crack states. It then describes the atomic structure of sharp cracks, the topical subject of crack-microstructure interactions in ceramics, with special focus on the concepts of crack-tip shielding and crack-resistance curves, and finally deals with indentation fracture, flaws, and structural reliability.
3,550 citations
TL;DR: In this paper, the frequency-magnitude relation of microfracture deformation was studied and the dependence of the parameter b on rock type, stress, and confining pressure was found to depend primarily on stress.
Abstract: During the deformation of rock in laboratory experiments, small cracking events, i.e., microfractures, occur which radiate elastic waves in a manner similar to earthquakes. These radiations were detected during uniaxial and triaxial compression tests and their frequency-magnitude relation studied. They were found to obey the Gutenberg and Richter relation log N = a + b M
Where N is the number of events which occurred of magnitude M , and a and b constants. The dependence of the parameter b on rock type, stress, and confining pressure was studied. It was found to depend primarily on stress, in a characteristic way. The frequency-magnitude relation for events which accompanied frictional sliding and deformation of a ductile rock was found to have a much higher b value than that observed in brittle rock. The Gutenberg and Richter formulation of the frequency-magnitude relation was derived from a statistical model of rock and crustal deformation. This analysis demonstrates the basis of similarity between rock deformation experiments in the laboratory and deformation of the crust.
1,415 citations
"The role of acoustic emission in th..." refers background in this paper
...In addition to a correlation between AE rate and strain rate, numerous studies have noted a power law frequency-magnitude relation for AE events [26, 33-39]....
[...]
...Laboratory studies of AE events consistently show a decrease in b with increasing stress during deformation of intact samples [23, 33, 35, 37]....
[...]
TL;DR: In this article, the authors proposed a state-variable constitutive formulation for the rate of earthquake production resulting from an applied stressing history, which was implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties.
Abstract: Seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress- ing history control the timing of earthquakes. The model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate- and state- dependent fault properties. This yields a general state-variable constitutive formulation for rate of earthquake production resulting from an applied stressing history. To illustrate and test the model some characteristics of seismicity following a stress step have been explored. It is proposed that various features of earthquake clustering arise from sensi- tivity of nucleation times to the stress changes induced by prior earthquakes. The model gives the characteristic Omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate. Earthquake data appear to support a model prediction that aftershock duration, defined as the time for rates to return to the back- ground seismicity rate, is proportional to mainshock recurrence time. Observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen- dence of stress changes of the first event of the pair and stress-sensitive time-dependent nucleation. Applications of the constitutive formulation are not restricted to the simple stress step models investigated here. It may be applied to stressing histories of arbitrary complexity. The apparent success at modeling clustering phenomena suggests the possibil- ity of using the formulation to estimate short- to intermediate-term earthquake probabil- ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress.
1,338 citations
"The role of acoustic emission in th..." refers background in this paper
...A similar approach, in which relaxation phenomena are restricted to pre-existing faults, has recently been developed [32]....
[...]
TL;DR: In this article, the failure process in a brittle granite sample can be stabilized by controlling axial stress to maintain a constant rate of acoustic emission, and the post-failure stress curve can be followed quasi-statically, extending to hours the fault growth process.
Abstract: The failure process in a brittle granite sample can be stabilized by controlling axial stress to maintain a constant rate of acoustic emission. As a result, the post-failure stress curve can be followed quasi-statically, extending to hours the fault growth process which normally would occur violently in a fraction of a second. Using a procedure originally developed to locate earthquakes, acoustic emission arrival-time data are inverted to obtain three-dimensional locations of microseisms. These locations provide a detailed view of fracture nucleation and growth.
870 citations
"The role of acoustic emission in th..." refers background in this paper
...[23, 42] developed a feed-back control system in which axial stress was continuously adjusted to maintain constant AE rate....
[...]
...The proportionality depends on such factors as system sensitivity, crack type and attenuation and has been observed to change in a single experiment [23, 28]....
[...]
...Laboratory studies of AE events consistently show a decrease in b with increasing stress during deformation of intact samples [23, 33, 35, 37]....
[...]
...Even so, since good correlations have been reported between inelastic strain rate and AE rate [19-23], monitoring AE with a single transducer can be useful in describing damage accumulation rate during a deformation test [24]....
[...]
TL;DR: In this article, it was shown that there is an infinity of generalized dimensions for strange attractors, related to the order-q Renyi entropies, and that these dimensions are monotonically decreasing with q.
861 citations
"The role of acoustic emission in th..." refers background in this paper
...were D is a kind of fractal dimension called the correlation exponent [96]....
[...]