Showing papers on "Acoustic emission published in 1976"
TL;DR: In this article, a general method of calculating the location of defects in two dimensions from the arrival times at the sensors is presented. But the ACEMAN system, which uses this method can derive the resolution properties of a sensor array in about 7.5 min.
Abstract: Sensors on the surface of a material under stress can detect acoustic emissions from a defect within the material. The difference in time of detection of an emission from the defect at different sensors gives a way of finding where it is. This paper shows a general method of calculating the location of defects in two dimensions from the arrival times at the sensors. The ACEMAN system, which uses this method can derive the resolution properties of a sensor array in about 7.5 min.
260 citations
TL;DR: In this paper, the propagation of Love and Rayleigh waves in elastic bodies whose boundaries support surface stresses was studied and the behavior was shown to be sensitive to the relative values of the residual stress, elastic moduli, and density of the surface.
Abstract: A study is made of the propagation of Love and Rayleigh waves in elastic bodies whose boundaries support surface stresses, such as crystals cleaved in vacuo or bodies upon which are deposited extremely thin films. The surfaces of such bodies are herein modelled as two-dimensional elastic continua that adhere without slipping to their substrates and in which is located residual stress. The corresponding boundary condition gives rise to behaviour which is contrasted with that occurring in the absence of surface stress. The results are also related to previous studies of surface waves in thin strata superposed on elastic half-spaces, from which the present theory differs by taking into account residual stress. The behaviour is shown to be sensitive to the relative values of the residual stress, elastic moduli, and density of the surface. Attention is drawn to the relevance of the study to those signal-processing devices which utilize surface waves in thin films.
90 citations
TL;DR: In this article, the authors investigated the acoustic emission during tensile tests for several types of aluminium alloys and found that the mean square amplitude of the continuous emission is proportional to strain rate and sample length.
Abstract: The acoustic emission during tensile tests is investigated for several types of aluminium alloys. It is found that the mean square amplitude of the continuous emission is proportional to strain rate and sample length. It is assumed that the continuous emission is generated by dislocation loops, which are created continuously at Frank-Read sources. According to this model the mean square amplitude of the continuous emission U2 is proportional to the total length of the mobile dislocations L and the size of the loops l: ∼LI. Information about l was taken from Kuhlmann and Wilsdorf's observations of slip lines at the surface of deformed aluminium single crystals.
83 citations
TL;DR: In this article, the authors employed iterative methods to obtain the variations of propagation velocity with strain and found that while the individual contributions of the initial stresses, changes in elastic constants, and changes in density with strain can be considerable, their combined effect in some materials may be reduced by mutual cancellation.
Abstract: Variations of elastic constants and density with strain and the introduction of stresses can significantly affect the propagation velocity of surface acoustic waves Digital computation using iterative methods is employed to obtain the variations of propagation velocity with strain It is found that while the individual contributions of the initial stresses, changes in elastic constants, and changes in density with strain can be considerable, their combined effect in some materials may be reduced by mutual cancellation Computed results for YX quartz YZ LiNbO3 are compared with experimentally measured values
68 citations
TL;DR: In this article, a study has been made of the use of acoustic emission techniques to monitor failure processes within carbon-fibre-reinforced plastics and to establish some of the limitations of the technique.
Abstract: A study has been made of the use of acoustic emission techniques to monitor failure processes within carbon-fibre-reinforced plastics and to establish some of the limitations of the technique. The type of signal to be expected from a resonant transducer of the type most widely used is discussed, and simulation studies confirm this analysis. Bundles of different types of fibres have been broken in order to investigate the type of emission obtained when fibres fracture. Sources of extraneous emission arising from the grips and from shear damage at notch tips have also been studied.
43 citations
TL;DR: In this paper, the authors investigated the dependence of acoustic emission power and spectra for deformation of aluminum alloys over a wide frequency range of 100 kHz to 4 MHz, and found that acoustic emissions were proportional to the first power of the plastic strain rate times the gauge length of the specimen.
Abstract: Strain‐rate dependence of acoustic‐emission power and spectra for deformation of aluminum alloys is investigated over a wide frequency range of 100 kHz to 4 MHz. In case of Al‐Cu‐Mg alloy (2024) and pure aluminum (1100), it is found that acoustic‐emission power is proportional to the first power of the plastic strain rate times the gauge length of the specimen. Normalized acoustic‐emission power spectra show no significant change at a given strain depending on the strain rate, though they vary with the strain in early stages of deformation. In case of Al‐Mg alloy (5056), repeated bursts of acoustic emission are recorded accompanied by repeated discontinuous yielding. The mode of inhomogeneous deformation and the pattern of acoustic emission vary with the strain rate.
36 citations
TL;DR: In this paper, a method for absolute calibration of acoustic emission transducers using a reciprocity technique in a Rayleigh-wave sound field was developed. But it was applied to practical transducers, and their sensitivity was obtained over a frequency range of 100 kHz to 1 MHz.
Abstract: A new method is developed for absolute calibration of acoustic‐emission transducers using a reciprocity technique in a Rayleigh‐wave sound field. It is applied to practical transducers, and their sensitivity is obtained over a frequency range of 100 kHz to 1 MHz. The result is compared with frequency spectrum of an actual acoustic emission signal from a large structure detected by an identical transducer. It is shown that practical characteristics of transducers can be estimated with ease and repeatability in an acoustical environment similar to that of structures such as pressure vessel walls.Subject Classification: [43]40.42; [43]85.40.
35 citations
TL;DR: In this article, a detailed study of the motion of bubbles in a focused 1 MHz acoustic field established in water is made by audio-visual observations, including cine-photography, by measuring acoustic emission, and by studying the acoustic impedance changes due to bubble activity.
33 citations
TL;DR: In this article, the authors investigated the acoustic emission response of granular soils, cohesive soils, and field monitoring, and concluded that the acoustic response is directly related to soil deformation and can be used in lieu of same in both laboratory and field situations.
Abstract: The study is subdivided into three phases: granular soils, cohesive soils, and field monitoring; the present paper addresses itself to the first phase of the overall project. Acoustic emissions are internally generated sounds that occur when a soil sample is stressed and subsequently deforms. The major conclusion of this research is that the acoustic emission response is directly related to this deformation and can be used in lieu of same in both laboratory and field situations. Other significant results as related to granular soils are the following: (1)Acoustic emission wave velocities are from 400fps-800fps (120m/s-240m/s); (2)acoustic emission frequencies range from 500 Hz - 8 kHz; (3)acoustic emission attenuation is strongly dependent on frequency and can be as high as 300dB/ft (10 dB/cm) at 16 kHz; (4)angular particles produce more emissions than rounded ones; (5)well-graded soils emit more acoustic emissions than poorly graded soils; and (6)particle size is not significant in the acoustic emission response.
31 citations
TL;DR: In this article, the excitation and spectral calibration of acoustic emission systems using a helium gas jet was shown to produce system independent acoustic emission spectral information, which can be conveniently used for specimen or structural response mapping.
Abstract: The excitation and spectral calibration of acoustic emission systems using a helium gas jet is shown to produce system independent acoustic emission spectral information. The calibration source makes no mechanical contact with the specimen or structure under investigation and can be conveniently used for specimen or structural response mapping.
31 citations
TL;DR: In this article, tensile tests were used to study the acoustic emission from several 7075-T6 aluminum plates and it was shown that the burst-type emission resulted from the brittle fracture of large primary inclusions in the microstructure.
Abstract: Tensile tests were used to study the acoustic emission from several 7075-T6 aluminum plates. Specimens from one plate produced a large burst-type emission in addition to the continuous emission. Metallographic and fracture surface studies indicated that the burst-type emission resulted from the brittle fracture of large (20 to 60 μm) primary inclusions in the microstructure.
TL;DR: In this paper, the application of acoustic emission (AE) for investigating flaw formation and propagation in grp pressure tubes and evaluating the fracture behaviour of notched bend specimens in flexural and fatigue experiments is described.
TL;DR: In this article, the authors measured the radius of the contraction zone on the side of the specimen and load-load point displacement during fracture of single edge notched specimens containing fatigue cracks of different lengths.
TL;DR: In this paper, the authors described the acoustic emission from a crazing polyvinyltoluene in a tensile and bending experiment, which most likely correspond to the initiation and growth of crazes.
Abstract: The acoustic emission from a crazing polyvinyltoluene in a tensile and bending experiment is described Acoustic emission appears as a series of bursts which most likely correspond to the initiation and growth of crazes The emission intensity is characterised by acoustic activity (pulse rate) measured by the ring-down technique The average activity increases with strain During repeated loading the acoustic activity shows a measurable intensity and significant rise only beyond the maximum strain of the former runs This is equivalent to Kaiser's effect in metals Acoustic emission during the creep experiment occurs in three characteristic periods They are characterized as the relaxation, fatigue, and breakdown periods Visual observations indicate that the relaxation period corresponds to the initiation, and the fatigue period to the growth of crazes In the breakdown period a macroscopic crack develops and the sample fails
TL;DR: In this article, it was shown that the internal friction in the high amplitude range is due to breakaway of dislocations from pinning points and by the generation of Frank-Read loops which results in plastic strain.
TL;DR: In this article, the use of acoustic emission techniques for studying fatigue and fracture in unidirectional plane samples of carbon fiber reinforced plastic has been investigated, and experiments have been carried out on a single-dimensional plane.
Abstract: Following earlier work on the use of acoustic emission techniques for studying fatigue and fracture in unidirectional plane samples of carbon fibre reinforced plastic, experiments have been...
Patent•
13 May 1976
TL;DR: In this article, the authors proposed a method to generate a simulated acoustic emission signal and simultaneously introduce the signal into a test article by using elastic energy within the test article itself to simulate the stress pulse generated by a flaw in the material.
Abstract: This device generates a simulated acoustic emission signal and simultaneously introduces the signal into a test article. The device provides a means for positioning precision brittle tubes or rods against the test article in a controlled fashion. A simulated signal, a stress pulse, is introduced into the test article at a point source when sufficient force is applied to break the tubes or rod against the test article. The stress pulse is generated by the rapid release of elastic energy within the test article itself therefore it very closely simulates the acoustic emission signal generated by a flaw in the material.
TL;DR: In this paper, an experimental comparison of the stress waves generated by three sources of simulated acoustic emission events: a piezoelectric generator, an electric spark, and a pulsed laser is presented.
Abstract: The paper describes an experimental comparison of the stress waves generated by three sources of simulated acoustic emission events: a piezoelectric generator, an electric spark, and a pulsed laser. The stress waves produced by the electric spark indicate that the stress generating mechanism is the thermally excited pressure pulse in the air surrounding the spark. Each of the sources is shown to be capable of producing stress waves of less than 1-..mu..s duration, but the piezoelectric generator appears to be the most advantageous technique.
Patent•
13 Jul 1976
TL;DR: In this article, a method and apparatus for the excitation and spectral calibration of acoustic emission systems in which a helium or other gas jet is used as a calibration source which makes no mechanical contact with the specimen or structure under examination is presented.
Abstract: A method and apparatus for the excitation and spectral calibration of acoustic emission systems in which a helium or other gas jet is used as a calibration source which makes no mechanical contact with the specimen or structure under examination. The gas jet which simulates an acoustic emission event, is sprayed on a reference material which is acoustically coupled to either an acoustic emission transducer or to a transducer having a flat frequency response up to 1 MHz. The transducer spectra are measured in decibels and subtracted from each other thereby obtaining a "transducer calibration". The "calibrated" transducers are then coupled to a specimen under test, the gas jet is applied and a "gas jet system spectrum" is measured. The spectrum of acoustic emission activity is then measured and corrected by subtracting, in decibels, the "gas jet system spectrum", thereby obtaining system independent acoustic emission spectral information which can be used to compare results in other systems.
01 Jan 1976
01 May 1976
TL;DR: In this article, an analytical model is developed to determine the velocity of surface acoustic waves in strained media, and it is shown that the SAW propagation may depend significantly on the velocity change with strain.
Abstract: An analytical model is developed to determine the velocity of surface acoustic waves in strained media. It is shown that, in addition to the variations in path length, the SAW propagation may depend significantly on the velocity change with strain.
TL;DR: In this article, the degree of development of microcracks in bone tissue subject to longitudinal extension is estimated for the first time by the acoustic-emission method, and three characteristic regions of deformation are established.
Abstract: A review of papers relating to the rupture of bone tissue subjected to various forms of stress is presented. The degree of development of microcracks in bone tissue subject to longitudinal extension is estimated for the first time by the acoustic-emission method. Three characteristic regions of deformation are established. The rupture process (ɛ11/ɛ11*>0.94) takes part with a practically constant acoustic emission intensity of 210 pulses/sec.
TL;DR: In this paper, the output voltage of a propagating surface elastic wave on a piezoelectric ceramic plate is described as a function of external tensile stress, and the convolution output increases with the cumulative load.
Abstract: Experimental results on the output voltage via a propagating surface elastic wave and the convolution output of two oppositely propagating surface elastic waves on a piezoelectric ceramic plate are described as a function of external tensile stress. The convolution output increases with the cummulative load, while the output voltage via the surface elastic wave decreases. The variation of the output voltage is considered to be due to the change in nonlinearity that arises from the external load.
TL;DR: In this paper, results are reported of acoustic emission measurements made during mechanical deformation of indium single crystals, and a correspondence exists between the duration of the acoustic signal and the volume of twinned material as determined by cinematographic observation of the generation of acoustic emissions.
Abstract: With the increased use of acoustic emission as a nondestructive testing tool, it has become extremely important to document and to understand the emissions characteristic of various modes of deformation and fracture. In the present work, results are reported of acoustic emission measurements made during mechanical deformation of indium single crystals. Although the metal indium is of little structural importance, it develops well‐delineated twins with associated acoustic emissions, and therefore affords an excellent medium with which to develop techniques and to generate interpretations which can be applied to structurally important materials. By recording the acoustic emission signals on a video‐tape recorder it was possible to play them back as often as desired and to observe them in slow and stop motion. The experimental results show that a correspondence exists between the duration of the acoustic signal and the volume of twinned material as determined by cinematographic observation of the generation ...
01 Apr 1976
TL;DR: In this paper, three possible methods of acoustic emission energy analysis are examined: digital processing, signal length processing and electronic processing, and each method is discussed and the three are compared.
Abstract: Three possible methods of acoustic emission energy analysis are examined. These are digital processing, signal length processing and electronic processing. Each method is discussed and the three are compared. This comparison indicates that electronic processing is the method of choice. Experimental studies of energy analysis versus ring-down count analysis are used to illustrate where energy analysis should be superior to ring-down count analysis and where both methods will give approximately the same results.
Patent•
09 Oct 1976
TL;DR: In this article, the output from the AE (Acoustic emission) sensor is conducted and controlled by an output from a dummy sensor, and noise from outside the system is removed when measuring AE.
Abstract: PURPOSE:The output from the AE(Acoustic Emission) sensor is conducted and controlled by an output from a dummy sensor, and noise from outside the system is removed when measuring AE.
TL;DR: In this article, acoustic emission source location techniques were successfully used on a production-size aircraft wing fatigue test article to monitor crack growths in the range from 0.25 mm to 1.6 mm per load cycle.
Abstract: Acoustic emission source location techniques were successfully used on a production-size aircraft wing fatigue test article to monitor crack growths in the range from 0.25 mm to 1.6 mm per load cycle. The AE data showed good correlation with the crack length data. Analyses of these correlations show that AE monitoring has the potential for being used to determine crack length over this range of crack growth rates. The fatigue test article was constructed of 7075-T6511 aluminum alloy. The test period lasted 14 days and the results demonstrated that AE has application to aircraft structures.