FIG 2 - uploaded by Avinoam Rabinovitch
Content may be subject to copyright.
Microscope photograph of a thin section of chalk; the real width of the picture is 1.2 mm. Large white spots are plankton skeletons ͑ calcite ͒ ; black spots are pores ͑ the one shown by arrow is 84 ␮ m in diameter ͒ and partly iron oxide; gray structure is micrite, or cryptocrystals ͑ very fine grains of carbonate, less than 10 ␮ m ͒ ; small white spots are microsparite, fine to medium size grains ͑ about 10–50 ␮ m ͒ of calcite. 

Microscope photograph of a thin section of chalk; the real width of the picture is 1.2 mm. Large white spots are plankton skeletons ͑ calcite ͒ ; black spots are pores ͑ the one shown by arrow is 84 ␮ m in diameter ͒ and partly iron oxide; gray structure is micrite, or cryptocrystals ͑ very fine grains of carbonate, less than 10 ␮ m ͒ ; small white spots are microsparite, fine to medium size grains ͑ about 10–50 ␮ m ͒ of calcite. 

Source publication
Article
Full-text available
In this article we consider the rise and fall time (which were earlier shown experimentally to be the same) of electromagnetic radiation (EMR) from propagating cracks. This feature is shown theoretically to be inversely proportional to the pulse frequency ω and to the fourth degree of the absolute temperature. It is shown experimentally that in gla...

Context in source publication

Context 1
... v R is the Rayleigh velocity. All aspects of this model except ␶ were experimentally confirmed. 9–12,17 In this article ␶ is considered in detail. A triaxial load frame TerraTeck stiff press model FX-S- 33090, axial pressure up to 450 MPa, confining pressure up to 70 MPa, stiffness 5 ϫ 10 9 N/m), combined with a closed- loop servocontrol, was used for the measurement. The servocontrol ͑ linearity 0.05% ͒ was used to maintain a constant axial piston displacement rate. The load was measured by a sensitive load cell LC-222M ͑ maximum capacity 220 kN, linearity 0.5% full scale ͒ . A cantilever set, consisting of axial and lateral detectors, was used to measure the sample strains in three orthogonal directions parallel to the principal stresses. A magnetic one-loop antenna with a diameter of 3 cm ͑ EHFP-30 Near Field Probe set, Electro-Metrics Penril Corporation ͒ was used for the EMR detection. The signals were amplified by means of a low-noise microsignal amplifier ͑ Mitek Corporation Ltd., frequency range 10 kHz-500 MHz, gain 60 Ϯ 0.5 dB, noise level 1.4 Ϯ 0.1 dB across the entire frequency band ͒ and transferred to a Tecktronix TDS 420 digital storage oscilloscope. The latter was connected to an IBM PC by means of a general purpose interface bus, so the signals were stored on the computer hard disk for further processing. The antenna was placed 2 cm away from the center of the loaded sample, its normal pointing perpendicu- lar to the cylinder axis. The EMR was monitored with an overall sensitivity of 1 ␮ V. To reduce the background noise level, the following means were employed: ͑ 1 ͒ the measurements were carried out in a thick-wall steel pressure vessel; ͑ 2 ͒ special radio frequency filters were used; ͑ 3 ͒ the amplifier power supply was independent of the industrial net; ͑ 4 ͒ the antenna was connected to the oscilloscope via the amplifier by means of special double-screen cables ͑ Alpha wire Corporation Ltd. ͒ . The samples had a cylindrical shape, with standard length of 100 mm and standard diameter of 53 mm. The experiments were carried out on: 1. chalk samples taken from the Horsha Foundation in the Beer Sheva syncline 18 ͑ all samples were cut from the same layer with the same orientation within the rock ͒ , 2. Eilat granite, 10 3. soda-lime glass and 4. glass ceramics. Also included in the analysis are some of the results obtained in our drilling experiments of glass and granite. 20 The distribution of pore radii was experimentally measured in a thin cut of chalk ͑ 20 ϫ 30 mm area, 30 ␮ m thickness ͒ . It was examined under a microscope with an enlarge- ment of 100. The cut was placed on a table that was moved by means of a computer program Automatic Point Meter ͑ steps 300 ␮ m in the ‘‘horizontal’’ direction and 600 ␮ m in the ‘‘vertical’’ direction ͒ so that different pieces of the cut were sequentially seen, and at each measuring instance the radius of the pore situated at the same point of the image was measured. Thus, as a result of a large number of measurements, pore-radii distribution was obtained. The measurement was carried out by means of a micrometer with accuracy of 5 ␮ m, which is actually a ‘‘ruler’’ of 1 mm divided by 100 equal parts, 10 ␮ m each. A photograph of the cut, where pores can clearly be seen, is shown in Fig. 2. We assume that EMR is originated by surface atomic ͑ ionic ͒ vibrations 21 caused by bonds rupture, similar to Rayleigh waves or surface optical phonons. It has been shown elsewhere 22 that surface waves decay as a result of interaction with bulk phonons. We therefore consider ␶ to be the relaxation time of such a surface ͑ Rayleigh-like ͒ wave, which interacts with a bulk phonon, leading to the creation of another bulk phonon ͑ a three-phonon process ͒ , and use Eq. ͑ 13 ͒ of King and Sheard 23 to characterize the process. The rate of occurrence of the process per unit time, or its transition probability, is given by the golden rule formula 24 P if ϭ 2 ␲ / ប ͉ ͗ f ͉ H 3 ͉ i ͘ ͉ 2 ␦ ( E f Ϫ E i ), where the initial and the final states are ͉ i ͘ ϭ ͉ n R , n b 1 , n b 2 ͘ , ͉ f ͘ ϭ ͉ n R Ϫ 1, n b 1 Ϫ 1, n b 2 ϩ 1 ͘ , where H is the time dependent anharmonic part of the crys- tal Hamiltonian, n R , n b 1 and n b 2 are the numbers of surface phonons, and initial and final bulk phonons, respectively. E i and E f are the initial and the final energies of the three- phonon system, so that E f Ϫ E i ϭ ប ( ␻ b 2 Ϫ ␻ R Ϫ ␻ b 1 ), where the ␻ - s denote the related frequencies. The relaxation time is obtained from the golden rule formula ͑ 1/ ␶ being proportional to the transition probability ͒ using the explicit expres- sion for H 3 ͓ Eq. ͑ 6.47 ͒ in Srivastava 22 ͔ , the displacement field due to the surface modes written in second quantized notation ͓ Eq. ͑ 8.26 ͒ op. cit. 22 ͔ , and integrating over the states of the initial and final bulk phonons b 1 and b 2; one obtains ͓ Eq. ͑ 8.36 ͒ op. cit. 22 ...

Citations

... Also it is vulnerable to the high-frequency interference from mechanical and electrical equipment [20]. However, low-frequency electromagnetic wave can propagate a longer distance (around 3.5 km), with a small attenuation [21], and will be less affected by mining equipment. So, it is very important to study the characteristics of low-frequency EMR from coal under dynamic loading, to develop monitoring and early warning technology for coal and rock mines. ...
Article
Full-text available
Dynamic loads provided by the SHPB test system were applied to coal specimens, and the TEM signals that emerged during coal rupture were recorded by the TMVT system. Experiments on coal-mass blasting rupture in excavating workface were also carried out, and the emerged TEM signal was analyzed. The results indicate that the low-frequency TEM signals were detected close to the coal specimens under high strain dynamic load applied by the SHPB, initially rising sharply and dropping rapidly, followed by a small tailing turbulence. And the field test results obtained during coal blasting process coincided with the results from the SHPB tests. Furthermore, its initial part shaped like a pulse cluster had a more pronounced tail and lasted even longer. And the generation mechanism of the low-frequency TEM effect was analyzed. It suggests that the low-frequency TEM effect of coal during dynamic rupture is contributed by the fractoemission mechanism and the resonance or waveguide effects. Because its wavelength is longer than the higher ones, the low-frequency TEM has a good anti-interference performance. That can expand the scope and performance of the coal-rock dynamic disaster electromagnetic monitoring technique.
... The part of air-filled pores depends on the rock porosity. Assuming that the porosity of the tunnel granite is at most 5% (Rabinovitch et al., 2003), then a maximal volume of 0.465 m 3 is the maximal air-filled volume within the 9.3 m 3 granite bulk torus that contributes an additional gamma quantity of 0.465 of the net integral activity DC Rn Bq/ m 3 in the tunnel space. This radon activity within the pores of the 30 cm layer of wall rock is part of the radon temporal anomaly that migrated from the rock bulk and reached equilibrium within the tunnel internal air. ...
... According to Fig. 4 the corresponding crack velocity v cr is 2209 m/s (calculated for c s = 3330 m/s). Now, it was shown [19] that τ is a function of the pulse frequency ω and for glass can be obtained from ...
Article
Our model of electromagnetic radiation (EMR) emanated from fracture implies that EMR amplitude is proportional to crack velocity. Soda lime glass samples were tested under uniaxial tension. Comparison of crack velocity observed by Wallner line analysis and the peak amplitude of EMR signals registered during the test, showed very good correlation, validating this proportionality.
... This slope is KA 1 /t 2 . In our experiments as well as in our theory Rabinovitch et al., 2003), t 1 Z t 2 . All the parameters A 0 , T 0 , u and t (Fig. 2) can be calculated by a least squares fit (Rabinovitch et al., 1998) to the experimental results. ...
Article
Full-text available
This study introduces several innovations in the experimental study of fracture. (1) A new method of simulating fringe cracks; this is accomplished by the application of uniaxial compression on cylinders that contain out-of-plane pre-cuts along their walls. Previous investigators combined independent operations of mode III to mode I, whereas in the present experiment, a single remote compression was transformed into mixed modes I and III by local stress rotation along the pre-cuts. An enlargement of inter pre-cut angle causes an increase of sample strength. (2) Contrary to previous experiments and many field exposures in sediments that exhibit transitions from parent fractures to fringes, the present study simulates a reverse transition, from fringes to parent fractures (to tensile longitudinal (axial) splits). Thus, a change occurs from local mixed modes I and III to local single mode I. The new results may be applied to the interpretation of secondary fractures and fringes in naturally fractured granites. (3) Monitoring of the electromagnetic radiation (EMR) that was induced by the fractured samples enabled us to determine in real time, the sequence of events and the fracture velocities along the various failure stages. Strings of high-frequency EMR pulses (with a frequency of several MHz) were measured during the fringe formation, indicating small widths of en échelon cracks, while the subsequent longitudinal splitting initiated lengthy EMR pulses of lower frequency (some tens of kHz) indicating much wider cracks (which indeed were measured).
... Here A 0 is the maximum amplitude of the pulse, t 0 is its onset time and T is the time to reach the maximum value of the amplitude; ω is the pulse frequency, τ 1 and τ 2 are the rise and the fall times respectively. It has been shown [16] that the rise and fall times of the same pulse are equal, τ 1 = τ 2 = τ . The model implies that the time elapsed from the pulse onset to its maximum, which is denoted by T = T − t 0 , is proportional to the crack length L [10], ...
Article
Full-text available
As shown at the Laboratory of Rock Mechanics, electromagnetic radiation (EMR) emitted by propagating fractures provides relatively accurate information on the dimensions of the cracks emitting it. In this paper we demonstrate that this method (i.e.?EMR analysis) can also be advantageously used for obtaining the exact time sequence of double or triple pulses when they appear simultaneously and, hence, the sequence of the relevant cracks. The method is first used to analyse the time sequence of a triple fracture during failure and for a double fracture in relaxation of a glass ceramic sample. The analysis is in good agreement with the actual fractography of the sample. A similar procedure applied to fracture of chalk enabled us to show that most large fractures are, in fact, double, and to find the specific time sequences involved.
Article
As a form of energy dissipation, electromagnetic radiation (EMR) is gradually becoming a mainstream method prediction method for damage monitoring of coal and rock. To better improve the prediction accuracy of EMR, it is crucial to investigate time‐frequency characteristics of EMR and the influence of coal and rock properties on EMR that occurs in the fracture process. In this paper, the deformation and fracture process of raw coal, shaped coal, and cement specimens under compression are observed, and time‐frequency evolution characteristics of EMR below ultralow frequency (ULF) under different loading stages are evaluated. Then, the inherent reasons of time‐frequency evolution of EMR reflecting the damage performance are analyzed. Meanwhile, the effect of loading condition and composition and structure of materials on EMR is discussed. Results show that there is obvious EMR below ULF in the deformation and fracture process of coal and rock materials, and the combined denoising method of ensemble empirical mode decomposition (EEMD) and wavelet is suitable for extraction of EMR. Besides, the amplitude is approximately inversely proportional to frequency of electromagnetic signals, and the relationship between pulse count of EMR and damage is related to the homogeneity of coal and rock materials. Moreover, the time‐frequency characteristic parameter of EMR, such as amplitude, pulse count, and frequency spectrum, can indirectly reflect the damage evolution process of coal and rock. These results can provide a theoretical basis for remote monitoring of coal and rock dynamic disaster using EMR below ULF.
Article
Full-text available
This technical note portrays that one of the main reasons for the lack of progress in the application of the Fracture induced ElectroMagnetic Radiation (FEMR) method for the stress field assessment in underground conditions is the lack of a single measurement methodology/protocol. Three FEMR parameters (frequency range, intensity/sensitivity and activity) are analyzed in relation to micro-crack dimensions and rock elastic properties. Two seismic acoustic parameters (seismic moment and b-factor) are considered from the perspective of FEMR application in underground. It is proposed that the combined use of intensity, activity, b-factor and calculated seismic moment FEMR, together with the proposed FEMR instrument sensitivity and frequency range, be entered into the future FEMR measurement protocol as mandatory parameters for the FEMR instruments design for the successful assessment of the stress state in the vicinity of mine workings.
Book
Full-text available
Kachchh is a pericratonic rift basin in western India, which is currently experiencing basin inversion. The basin is known for its recent recurrent earthquake episodes. The Kachchh mainland Fault (KMF) and the South Wagad Fault (SWF) are two E-W trending major faults of eastern Kachchh. The Bachau-Samakhiali basin is an intra-basinal half-graben in between the KMF and the SWF. The fact that the Anjar earthquake (Mw 6.0, 1956) and the Bhuj earthquake (Mw 7.7, 2001) epicenters are located at close vicinity around the Bachau-Samakhiali basin signifies that the basin is tectonically very active. The KMF and the SWF are topographically expressed as fault related anticlines along them. The anticline along the KMF (Northern Hill Range) verges opposite to that along the SWF. The study makes an attempt to understand the tectono-geomorphic setting and evolution of this earthquake prone region, by analyzing field structures, stress and strain measurements and sandbox analogue modelling in order to lay the foundation for the long term seismic hazard zonation.This study presents an application of the geogenic Electromagnetic Radiation (EMR) technique for deciphering the directions of principal horizontal stress in the eastern Kachchh. The major horizontal principal stress based on the EMR study shows an azimuth of N60°E  10o. The study also deals with the first application of electromagnetic radiation emissions to identify active fracture planes in sandstones that could become potential active faults later. This study is based on linear profiling at six different places across the KMF and the SWF. Anomalously high EMR emissions are observed in the eastern part of the KMF, indicating active surface deformation. Magnetic fabric analysis by Anisotropy of Magnetic Susceptibility (AMS) method divides the study area in two distinct zones related to shape parameter and bedding-magnetic foliation angular relationship. The western part of the KMF and eastern part of the SWF show depositional fabric characterized by parallelism between bedding and magnetic foliation expressed by AMS oblate fabrics, while the eastern part of the KMF, and the western part of the SWF show layer parallel shortening (LPS) fabric characterized by oblique to high-angular relationships between bedding and magnetic foliation, with prolate susceptibility fabrics. Two different kinds of fault dynamics is thus dominant along the strike of the KMF and the SWF. The present work deals with the sand box analogue model experiments to study the evolution of the anticlines along the KMF and the SWF. The study revels that the anticlines were formed by hanging wall accommodation above rigid thrust ramps. The rigid thrust ramps are the pre-existing normal fault planes which formed due to regional extension prior to the basin inversion. The study also shows that the eastern KMF is characterized by more strike-slip component of thrusting. Moreover the rigid ramp along the eastern KMF and the western SWF is not continuous rather segmented in enechelon pattern. Finally accumulating all the results together an evolutionary model of the Bachau-Samakhiali basin is proposed. The dominant strike-slip in the eastern KMF and western SWF along with over all oblique compression produced active transpression in the Bachau-Samakhiali basin responsible for the enhanced seismicity in the basin. Keywords: Kachchh, Bhuj, Earthquake, Fault, Electromagnetic Radiation, Anisotropy of Magnetic Susceptibility, Analogue Modelling, Transpression.
Chapter
Originating from the field of geophysics science, electromagnetic emission analysis is a nondestructive measurement technique to monitor crack formation and propagation. Similar to acoustic emission analysis, the electromagnetic emission method is capable of providing real-time information on microscopic failure mechanisms on a qualitative basis. In both cases the reliability of quantitative information still hinges on the lack of a detailed understanding of the correlation between the source mechanism and the measured signal. Therefore, electromagnetic emission analysis is currently considered a method under development and is mostly limited to applications in materials research and has not yet been used for structural health monitoring applications. In this chapter the principle of operation of electromagnetic emission is presented first. Subsequent to that, aspects of the source mechanism, the detection systems and some applications of the method used as in situ technique are introduced. Due to the novelty of the method, some applications are demonstrated to monitor failure of reference materials such as polymers and carbon fibers to elucidate basic relationships between failure mechanisms and the EME phenomenon. At the end of the chapter the established approaches are than extended to applications monitoring failure of fiber reinforced composites.
Article
The paper describes the mechanism of electromagnetic emission generation in active landslides and measuring techniques. Special attention is given to electromagnetic emission fields. The author proposes an original system for measuring both continuous and pulsed magnetic emission of landslides. For such measurements boreholes must be drilled in the landslide. It is essential that the tubing constituting the borehole's lining be made of a material which does not attenuate magnetic fields. Besides its primary function, i.e. the registration of landslide magnetic field activity, the system can be used for the structural inhomogeneity of rock strata examination subjected to considerable stresses. The results of examinations of active and inactive landslide in Poland are presented. The post-extraction cave in the SMZ Jelsava Mine in Jelsava, Slovakia, is presented too. © 2015, National Institute of Telecommunications. All rights reserved.