Showing papers on "Acoustic emission published in 1991"
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
TL;DR: In this article, a moment tensor inversion based on P wave amplitude is employed to determine six independent tensor components, and a unified decomposition of eigenvalues into a double-couple (DC) part, a compensated linear vector dipole (CLVD) part and an isotropic part is proposed.
Abstract: An application of a moment tensor analysis to acoustic emission (AE) is studied to elucidate crack types and orientations of AE sources. In the analysis, simplified treatment is desirable, because hundreds of AE records are obtained from just one experiment and thus sophisticated treatment is realistically cumbersome. Consequently, a moment tensor inversion based on P wave amplitude is employed to determine six independent tensor components. Selecting only P wave portion from the full-space Green's function of homogeneous and isotropic material, a computer code named SiGMA (simplified Green's functions for the moment tensor analysis) is developed for the AE inversion analysis. To classify crack type and to determine crack orientation from moment tensor components, a unified decomposition of eigenvalues into a double-couple (DC) part, a compensated linear vector dipole (CLVD) part, and an isotropic part is proposed. The aim of the decomposition is to determine the proportion of shear contribution (DC) and tensile contribution (CLVD + isotropic) on AE sources and to classify cracks into a crack type of the dominant motion. Crack orientations determined from eigenvectors are presented as crack-opening vectors for tensile cracks and fault motion vectors for shear cracks, instead of stereonets. The SiGMA inversion and the unified decomposition are applied to synthetic data and AE waveforms detected during an in situ hydrofracturing test. To check the accuracy of the procedure, numerical experiments are performed on the synthetic waveforms, including cases with 10% random noise added. Results show reasonable agreement with assumed crack configurations. Although the maximum error is approximately 10% with respect to the ratios, the differences on crack orientations are less than 7°. AE waveforms detected by eight accelerometers deployed during the hydrofracturing test are analyzed. Crack types and orientations determined are in reasonable agreement with a predicted failure plane from borehole TV observation. The results suggest that tensile cracks are generated first at weak seams and then shear cracks follow on the opened joints.
248 citations
TL;DR: In this paper, plate theory is applied to the analysis of composite laminates and plate waves are used for understanding acoustic emission (AE) phenomena, and the fundamental extensional and flexural modes are observed.
Abstract: Plate theory is more easily applied to the analysis of composite laminates than exact three‐dimensional elasticity theory. Under conditions such that plate theory is applicable, it is suggested that plate waves are useful for understanding acoustic emission (AE) phenomena. To test this idea, pencil leads were broken on aluminum plates and composite plates, and the resulting waves were detected with a broadband ultrasonic transducer. Both the fundamental extensional and flexural modes were observed. Their characteristics are described and the implications for AE source location are discussed as well. Several transducers, commonly used for acoustic emission measurements, are compared with regard to their ability to reproduce the characteristic shapes of plate waves. Their different responses show why similar test specimens and test conditions can yield disparate results.
244 citations
TL;DR: In this paper, an alternative method to first threshold crossing for acoustic emission (AE) source location is presented for wave propagation in dispersive media, the accuracy of source location can be improved by locating corresponding phase points on the transducer outputs to determine the difference in arrival times.
Abstract: In this paper an alternative method to first threshold crossing for acoustic emission (AE) source location is presented. For wave propagation in dispersive media, the accuracy of source location can be improved by locating corresponding phase points on the transducer outputs to determine the difference in arrival times. The phase point location was done by cross‐correlating the transducer outputs with a single frequency cosine wave modulated by a Gaussian pulse. Experiments were performed using a lead break as the AE source on the surface of an aluminum plate. Due to the plate geometry and source orientation, the wave produced was highly dispersive. Although this wave was unsuitable for first threshold crossing techniques, the time differences needed for triangulation could be determined using the cross‐correlation technique.
200 citations
TL;DR: In this paper, an acoustic emission (AE) is used to estimate the location, size, orientation, and fracture mode of individual microcracks in concrete beams under four point loading.
Abstract: An acoustic emission (AE) is a localized rapid release of strain energy in a stressed material. Quantitative acoustic emission measurements techniques have recently been developed to estimate the location, size, orientation, and fracture mode of individual microcracks. Quantitative AE techniques were applied to a laboratory study of plain concrete beams under four point loading. Center-notched and off-center-notched beams were loaded in order to produce, respectively, mode I and mixed mode failure. Using AE seismic moment tensor representation, microcracking was characterized as mode I, mode II, or mixed mode. The mode of microcracking was compared to the mode of the visible crack. Most microcrack planes were in a direction normal to the tensile stress for a mode I macrocrack (center-notched), whereas microcrack planes were relatively uniformly distributed for a mixed-mode macrocrack (off-center notched). A large number of mixed-mode microcracks were observed even for the center-notched beam indicating that fracture mechanisms of microcracks may differ from the main macromechanical crack. It is shown that AE measurements can provide a potentially powerful tool in assessing damage.
109 citations
TL;DR: In this article, the measurement and subsequent analysis of acoustic emission signals from lubricated sliding contacts is concerned with the measurement of the time-dependent nature of the acoustic signal, which is able to detect the presence of wear-reducing additives and the predominant wear process occurring.
108 citations
TL;DR: In this article, a three dimensional acoustic emission technique is applied to observe the phase of the fracture process zone of concrete which is created ahead of the crack tip and significantly influences the tension softening behaviour of concrete.
104 citations
TL;DR: In this paper, the authors used a point-like transducer to detect plate-wave acoustic emission in cross-ply laminate graphite/epoxy coupons by tensile loading.
101 citations
TL;DR: The kinetic and micromechanical behavior of hydrogen-assisted cracking (HAC) was evaluated on Fe-3 wt pct Si single crystals with {001} and {00l} orientations.
Abstract: The kinetic and micromechanical behavior of hydrogen-assisted cracking (HAC) was evaluated on Fe-3 wt pct Si single crystals with {001} and {00l} orientations. This was accomplished by sustained load tests in gaseous hydrogen under various temperatures and in humid air at ambient temperature. Severe plastic deformation was observed to accompany the hydrogenassisted sustained load slow crack growth. The crack growth proceeded by a tunneling behavior in both orientations, indicating that plane strain conditions promoted the kinetic process. Microscopically, the crack propagated discontinuously with a 1-μm size instability along (1l0) directions, as revealed by fractographic and acoustic emission (AE) results. The crack growth rate was found to exhibit a plateau region with regard to the applied stress intensity. In this stage II regime, the growth rate increased with temperature in the lower temperature Arrhenius rate regime, with an apparent activation energy of 25 kJ/mol. After reaching its maximum at about 100 °C, the growth rate dropped down rapidly, and no slow crack growth was observed above 160 °C. The experimental observations were analyzed to show that the kinetics of HAC were controlled by hydrogen availability rather than by plasticity. Based on this, a transient kinetic model was applied to fit the data. The present interpretation of the crack tip stress field and the HAC nucleation site strongly implies that long-range diffusion of hydrogen over distances ranging from one to several microns is required. The kinetic aspects of this study are presented here with the underlying micromechanics being considered in terms of a decohesion mechanism
68 citations
TL;DR: In this paper, acoustic emission measurements were used to locate the sources of fracture of a single high-strength fiber embedded in an epoxy matrix which is loaded in tension. But the results were limited to small-diameter glass and graphite fibres.
Abstract: The application of acoustic emission (AE) measurements to locate the sources of fracture of a single high-strength fibre embedded in an epoxy matrix which is loaded in tension is described. From the micromechanical model and the fragment length distribution, interfacial shear strength values were calculated. The technique is demonstrated for small-diameter glass and graphite fibres as well as for fibres which exhibit fibrillar fracture, such as Kevlar and PBZT. Good agreement is found between the mean fragment length values obtained by optical and AE measurements for glass and graphite fibres. Values obtained for interfacial shear strength by the AE technique are comparable with those obtained using other techniques.
TL;DR: In this article, it was shown that the acoustic source profile, and thus the convective velocity, is peaked about 200 km deeper than what is expected from standard mixing length theory.
Abstract: Recently Libbrecht and Jefferies et al. have reported regular peaks in the solar oscillation power spectrum extending well above 5.3 mHz, the maximum frequency of trapped acoustic modes. Kumar et al. argued that these peaks are primarily due to the interference of traveling waves which are excited due to acoustic emission from turbulent convection. In contrast with the standing wave P-mode frequencies below 5.3 mHz, the positions of the high-frequency interference peaks (HIPs) are dependent on the location of the source of the acoustic oscillations. In the present work, Kumar et al.'s argument is strengthened, and more importantly, use is made of the above dependence to determine the acoustic source strength as a function of depth. It is found that the acoustic source profile, and thus the convective velocity, is peaked about 200 km deeper than what is expected from standard mixing length theory.
TL;DR: In this article, the authors proposed a simple model to generate a damped sinusoidal pulse for every bubble formed, as calculated from the bubble size distribution, where the range from the receiver to the breaker is known, and the only unknown parameters are the initial fractional amplitude of the bubble oscillation, and L, the dipole moment arm.
Abstract: The sound produced from a single bubble, oscillating at its breathing mode frequency, and the bubble size distribution are used to model the sound produced by breaking waves The data of Medwin and Daniel [J Acoust Soc Am 88, 408–412 (1990)] is used to evaluate the performance of the model The model generates a damped sinusoidal pulse for every bubble formed, as calculated from the bubble size distribution If the range from the receiver to the breaker is known then the only unknown parameters are e, the initial fractional amplitude of the bubble oscillation, and L, the dipole moment arm It is found that if the product e×L is independent of the bubble radius the model reproduces the shape and magnitude of their measured sound spectrum accurately The success of this simple model implies that the inverse problem (calculation of the bubble size distribution from the sound power spectrum) may be solved without the need to explicitly identify individual bubble pulses in the acoustic time series
TL;DR: In this paper, an advanced acoustic emission (AE) analysis procedure is proposed to determine crack locations, crack types and crack orientations from AE relative amplitudes of the first motions.
Abstract: Elastic waves emitted by microfracturing are called acoustic emission (AE). Recently AE techniques have been extensively applied to concrete engineering as a non–destructive testing (NDT) method. A key aspect of AE is that the nucleation of internal cracks is directly detected by a surface observation. In conventional AE techniques, such AE parameters as event count (activity), amplitude, energy and spectra are correlated with the failure process of materials. Thus, AE characteristics are utilized for NDT. The AE source (crack) is also located by employing a multichannel (more than 5) AE detecting and recording system. In this Paper an advanced AE analysis procedure is proposed. In addition to crack locations, crack types and crack orientations are determined from AE relative amplitudes of the first motions. The procedure classifies cracks into tensile cracks and shear cracks. Based on information of the crack type, the crack orientation is determined; this is the direction of crack opening in the case of...
TL;DR: In this article, the authors studied the dependence of the acoustic emission signal energy on orthogonal machining variables such as cutting velocity, uncut chip thickness and the chip-tool contact length.
TL;DR: In this paper, changes in wear rate and acoustic emission activity were measured across the mild-severe wear transition in the sliding of metals and determined the usefulness of acoustic emission measurements for the study of wear.
TL;DR: In this paper, a composite synthetic resin-ceramic piezoelectric element is used to detect acoustic emission from an acoustic-emission sensor, which has a plurality of substantially mutually parallel columnar ceramic bodies.
Abstract: An acoustic-emission sensor includes a composite synthetic resin-ceramic piezoelectric element which has a plurality of substantially mutually parallel columnar ceramic piezoelectric bodies. The columnar ceramic piezoelectric bodies are polarized in a longitudinal direction and are disposed in a synthetic-resin matrix. Since only longitudinal waves can be detected from among acoustic-emission waves, an intensity and variation in intensity can be detected accurately.
TL;DR: In this paper, the spatial distribution of newly developed microcracks, which are the sources of acoustic emissions and scatterers of elastic wave, can be influenced by the grain of the rock.
TL;DR: In this paper, the relationship of fracture process zone to tension softening behavior of concrete has been studied using an acoustic emission (AE) source location technique and a simulation of tensionsoftening behavior in double cantilever beam specimens.
TL;DR: In this article, it was shown that individual fiber breaks, to the last fiber in the bundle, can be detected using acoustic emission (AE) and the single-fibre strength distribution was deduced.
Abstract: In tensile tests on lubricated bundles of a few hundred parallel E-glass fibres it is shown that individual fibre breaks, to the last fibre in the bundle, can be detected using acoustic emission (AE). By this means the single-fibre strength distribution is deduced. Relationships are obtained between some AE signal parameters and the fibre fracture stress which are consistent with theoretical expectations. Studies are made of the distribution of fibre break locations, the occurrences of multiple (stimulated) fibre breaks and the attenuation of the AE signals.
TL;DR: In this paper, the relationships between several AE paramaters and AE original sources were investigated, and fracture mechanisms of CFRP are discussed in terms of observations of fracture surfaces and internal damage of the laminates by a SEM and a scanning acoustic microscope (SAM), respectively.
Abstract: Although the AE method provides useful information on the operating fracture processes of materials, a synthesized evaluation of AE signals using several AE parameters is necessary for composite materials because AE signals arise from various fracture processes. In this paper, the relationships between several AE paramaters and AE original sources were investigated, and fracture mechanisms of CFRP are discussed in terms of observations of fracture surfaces and internal damage of the laminates by a SEM and a scanning acoustic microscope (SAM), respectively. Synthesized AE signal wave analyses including the distributions of AE amplitude, AE event duration, and counts/duration (corresponding to frequency), give us useful and powerful information to analyze the complicated fracture mechanisms of composite materials. The fracture in tensile tests and cyclic tensile tests of unidirectionally reinforced carbon/epoxy composites goes through fiber/matrix interface debond and fiber breaking.
08 Dec 1991
TL;DR: In this paper, a series of experiments has been performed to determine if acoustic emission (AE) monitoring can be used to detect termite infestations in wood, and results obtained with a computer-controlled measuring system indicate that termite activities in the wood generate a significant amount of AE which has frequency components extending to above 100 kHz.
Abstract: A series of experiments has been performed to determine if acoustic emission (AE) monitoring can be used to detect termite infestations in wood. Results obtained with a computer-controlled measuring system indicate that termite activities in the wood generate a significant amount of AE which has frequency components extending to above 100 kHz. These emissions can be easily detected by commercially available AE sensors (50 kHz resonant sensors were used in these measurements). Spectral analysis of noise signals (including some deliberately generated) indicate that nearly all noise signals have most of their energy below 20 kHz. Thus, it appears feasible to separate termite-generated signals from noise signals by filtering. The ultrasonic propagation characteristics of wood, especially the large and frequency dependent propagation losses, have a significant impact on the detection process. However by working below 100 kHz, termite-generated signals could be detected at least 2 m away from the site of the infestation, as long as the sensor was on the same piece of wood. A practical hand-held, battery-powered detection system has been designed, fabricated, and tested successfully in the laboratory. >
01 Jan 1991
TL;DR: In this paper, the authors reported that there was a certain relation between the indentation hardness of rock and the AE parameters, such as accumulated number of events, peak RMS and integrated RMS.
Abstract: This paper reports rock indentation tests which indicated that there was a certain relation between the indentation hardness of rock and the AE parameters, such as accumulated number of events, peak RMS and integrated RMS. Among the above-mentioned AE parameters, the correlation of RMS of AE events with indentation hardness is pronounced and more than ever the integrated RMS is the best index to correlate with the indentation hardness of rock. It represents the sum of amplitudes of AE varied during all the indentation process and reflects the size of AE energy released in the time period of indentation. Indentation hardness corresponds well to peak RMS value for different rock types. The onset of significant AE activity appears at about 40% peak indentation load, and intense AE activity corresponding to fracture propagation and chipping initiates at about 80-90% of peak indentation load. The peak RMS and integrated RMS may be recommended as the indexes to express rock hardness and may be further employed to predict rock drillability using these indexes in association with penetration rate of drilling.
01 Nov 1991
TL;DR: In this paper, a ray-theory analysis of the solar p-modes was performed and it was shown that most of the emitted energy may come from rare localized events that are well separated from one another in space and time.
Abstract: The source exciting the solar p-modes is likely to be acoustic noise generated in the top part of the sun's convection zone. If so, then simple arguments suggest that most of the emitted energy may come from rare localized events that are well separated from one another in space and time. This note describes the acoustic emission that would be expected from such events, based on a ray-theory analysis. Most of the acoustic energy is found to emerge very close to the source, so that observations to identify emission events will require high spatial resolution.
TL;DR: In this paper, the viability of acoustic emission as a method of quantitative analysis was investigated and a sensor based on this principle was described, which is achieved through the use of the enzyme catalase immobilized on the surface of an acoustic transducer.
TL;DR: In this article, acoustic emission response has been used to detect the development of short intergranular stress corrosion cracks in laboratory samples of sensitized type 304 (UNS S30400) stainless steel (SS).
Abstract: Acoustic emission response has been used to detect the development of short intergranular stress corrosion cracks in laboratory samples of sensitized type 304 (UNS S30400) stainless steel (SS). Tests were conducted at 25°C in water containing either 15 ppm of Na2S2O3 or 100 ppm of NaCl. Cylindrical samples with piezoelectric detectors mounted on both ends and the corrosion cell confined to the gauge section were used. The dual detectors allowed discrimination between signals generated within the sample from those generated from the surroundings. It was found that intergranular stress corrosion cracks of 200 to 300 µm length by 100 to 200 µm depth could be reliably detected with this technique. Shallow 10-µm-deep longitudinal flaws were also detected in tests conducted in the 100 ppm NaCl environment.
01 Jan 1991
TL;DR: In this article, the Shadow Moire Interferometry for composites was used to identify the shear properties of the Lamina in the framework of plasticity and to detect the deformation of the laminates.
Abstract: General Lectures.- Identification of the Rigidities of Composite Systems by Mixed Numerical/Experimental Methods.- Measurement of Complex Moduli of Composite Materials and Discussion of some Results.- Moire Interferometry for Composites.- A Damage Approach for Composite Structures: Theory and Identification.- Contributions.- Identification.- Identification of Temperature Dependence for Orthotropic Material Moduli.- Experimental Identification of Complex Stiffnesses of Composite Materials by Ultrasonic Wave Propagation.- A Hybrid Method to Determine Material Parameters of Composites.- Non Determined Tests as a Way to Identify Wood Elastic Parameters: the Finite Element Approach.- Measurement of Laminate bending Elastic Parameters from Non-Uniform Strain Fields.- Identification of the Shear Properties of the Lamina in the Framework of Plasticity.- Parametric Identification of Mechanical Structures: General Aspects of the Methods used at the LMA.- Static and Dynamic Characterization.- Material Parameters in Anisotropic Plates.- Evaluation of Global Composite Laminate Stiffnesses by Structural Wave Propagation Experiments.- Dynamic Measurements of Elastic Properties of Filament-Wound Cylindrical Shells.- Torsion Response Analysis of T300/914 and T800/914 Unidirectional Specimens.- A Computerized Test Setup for the Determination of the In-Plane and Out-of-Plane Shear Modulus in Orthotropic Specimens.- Some Experience from the Application of the Iosipescu Shear Test.- Constitutive Prediction for a Non-linear Orthotropic Media.- Creep and Relaxation of Coated Fabrics under Biaxial Loading.- Joints and Assemblies of Composite Material Structural Elements: Characterization of adhesives in bulk form and in composite structures.- Static and Dynamic Characterization of Composites using a Fourth Generation Programming Language on a Macintosh.- Impact Behaviour and Damage Characterization.- Use of the Shadow Moire Technique for the Investigation of the Impact Behaviour of Composite laminates.- Delamination Detection via Holographic Interferometry Techniques.- Dynamic Failure Processes in Fibre-Reinforced Composites.- Effect of Strain Rate on the Compressive Strength of Woven Glass-Reinforced/Epoxy Laminates.- Characterization of Highly Anisotropically Reinforced Solids in High Velocity Tension.- Micromechanics and Interfaces.- Determination of the Effective Mechanical Response of Polymer Matrix Composites via Microstructural Data.- A microstructural Method for Predicting the Damping of Lamina.- Theoretical and Experimental Study Technique of the Mechanical Properties of Fiber-Reinforced Laminates and of the Strain Features of Structural Elements.- Dynamic Properties of Layer Reinforced by Two Families of Fibres.- Micromechanical Modelling of Unidirectional Glassfiber Reinforced Polyester: Effect of Matrix Shrinkage.- Plastic Failure of Unidirectional Fibrous Composite Materials with Metal Matrix in Compression.- Analytical Model of Fibre Pull-Out Mechanism.- Nonlinear Viscoelastic Behavior of the Fibre-Matrix Interphase: Theory and Experiment.- Empirical Model Building and Surface Response Methodology Applied to Sclerometrical Investigation for Refractories Concrete.- Fracture and Fatigue Damage Mechanics.- Development of Fatigue Damage Mechanics for Application to the Design of Structural Composite Components.- Influence of Fibre Orientation on the Cracking and Fracture Energy in Brittle Matrix Composites.- Application of the Method of Caustics to Fibre-Reinforced Materials.- Modelling of Orthotropic Layered Structures Containing Cracks in the Interfaces.- A Criterion of Mixed Mode Delamination Propagation in Composite Material.- Fracture and Fatigue Damage in a CSM Composite.- Damage Modelling and Non-Destructive Testing.- Non linear Behaviour of Ceramic Matrix Composites.- Notched Strength and Damage Mechanism of Laminated Composites with Circular Holes.- Damage Modeling and Experimental Tools for 3D Composites.- Increasing Energy Absorption by 'Rope Effect' in Brittle Matrix Composites.- Specific Damping of a Carbon/Epoxy Laminate under Cyclic Loading.- The Application of automated Ultrasonic Inspection for Damage Detection and Evaluation in Composite Materials.- The Use of Vibrothermography for Monitoring Damage Evolution in Composite Materials.- Acoustic Emission Source Location in Anisotropic Plates.- List of Participants.- Index of Contributors.
TL;DR: In this paper, a neural network is used to calculate the location of the unknown source with the mathematical relationship deduced by the neural network, and then the times taken for each output signal, corresponding to acoustic emission events of unknown source location, to exceed two predetermined amplitudes from the datum are measured and are used for calculating the location.
Abstract: An apparatus for locating a source of acoustic emission in a material comprises four spaced transducers coupled to the material. Each transducer produces an output signal corresponding to a detected acoustic emission activity, and each output signal is amplified, rectified and enveloped before being supplied to a processor. Artificially induced acoustic emission events, of known location, are generated in the material. The processor measures the times taken for each output signal corresponding to artificially induced acoustic emission events, to exceed two predetermined amplitudes from a datum time. A neural network analyzes the measured times to exceed the predetermined amplitudes for the output signals corresponding to the artificially induced acoustic emission events and infers the mathematical relationship between values of time and location of acoustic emission event. The times taken for each output signal, corresponding to acoustic emission events of unknown source location, to exceed two predetermined amplitudes from the datum are measured and are used to calculate the location of the unknown source with the mathematical relationship deduced by the neural network.