Showing papers on "Acoustic emission published in 1975"
TL;DR: In this article, a new technique is described which gives a quantitative assessment of the damage that occurs during the loading of materials, based upon the behaviour of an ideal material in which energy is dissipated by two processes.
Abstract: Synopsis A new technique is described which gives a quantitative assessment of the damage that occurs during the loading of materials. The technique is based upon the behaviour of an ideal material in which energy is dissipated by two processes. The first is taken to correspond to damage and energy is dissipated only during the first loading over a given strain range. The second process is analogous to damping and energy is dissipated whenever straining occurs. It is shown that, in many respects, concrete behaves similarly to the ideal material. Acoustic emission measurements show, over a wide strain range, that concrete is damaged only during the first loading. The assessment of energy dissipated in damage correlates well with the change in initial elastic modulus which is used as another indicator of structural degradation. Measurements indicate that the process offracture in concrete in uniaxial compression is continuous and begins at very low applied strains. No evidence to support the existence of ‘c...
110 citations
TL;DR: In this paper, acoustic emission detection has been used to study the damage occurring in unidirectional carbon-fibre-reinforced plastics (CFRP) during cyclic loading and stress relaxation at high stress levels.
Abstract: Acoustic emission detection has been used to study the damage occurring in unidirectional carbon-fibre-reinforced plastics (CFRP) during cyclic loading and stress relaxation at high stress levels. The results suggest that true fatigue processes do not occur in CFRP and that the damage sustained during cycling is of the same kind as that which occurs in ordinary tensile loading. As a result either of many reversals of load or of holding a sample at constant load, the rate of emission of stress waves associated with fibre fractures diminishes with time until the sample becomes silent. A sample in this state is relatively safe from further damage, and a procedure of proof testing based upon this result is suggested.
62 citations
Patent•
13 May 1975TL;DR: The electromechanical acoustic emission detector of as mentioned in this paper consists of a plurality of sensor elements secured in an areal array on a base plate, and the spacing and arrangement of the sensor elements are such that the transducer is "tuned" to acoustic emission waves that travel along the surface of the vessel to which the transducers are attached.
Abstract: The electromechanical acoustic emission detector of this invention comprises a plurality of sensor elements secured in an areal array on a base plate. The spacing and arrangement of the sensor elements are such that the transducer is "tuned" to acoustic emission waves that travel along the surface of the vessel to which the transducer is attached. Because of the non-linear character of the array the transducer detects waves arriving from different directions with substantially equal sensitivity.
35 citations
TL;DR: In this article, an acoustic emission technique for measuring the failure time in thermal shock experiments is described, which offers a unique opportunity to measure the heat-transfer coefficient of the test system and hence, to obtain a fully quantitative measure of the peak surface stress generated during the test.
Abstract: An acoustic emission technique for measuring the failure time in thermal shock experiments is described. The technique offers a unique opportunity to measure the heat-transfer coefficient of the test system and hence, to obtain a fully quantitative measure of the peak surface stress generated during the test. Measurements on soda-lime glass have demonstrated that rapid thermal fracture in the material occurs when the surface stress attains a critical value equal to the propagation stress for the most deleterious surface flaw. The effects of slow crack growth on the failure time are also investigated and correlated with recently developed theory.
32 citations
TL;DR: In this article, a method for the quantitative measurements of the acoustic emission is worked out and its performance is analyzed with regard to the transducer loss and the ultrasonic attenuation in the specimen.
Abstract: A method for the quantitative measurements of the acoustic emission is worked out. Its performance is analyzed with regard to the transducer loss and the ultrasonic attenuation in the specimen. This method is actually applied to the tension tests of pure aluminium specimens. The power spectrum of the acoustic emission is obtained over a wide range of 100 kHz to 4 MHz. The total power attains a peak of 5 pW at the beginning of the plastic deformation and decreases to 0.3 pW with the increase of the deformation. The autocorrelation function for the acoustic emission is given as a monotonically decreasing function. This result reveals that the elastic energy of the acoustic emission is radiated not oscillatorily but in the form of random pulses. Mean value of the pulse widths is estimated to change from 0.6 to 0.2 μsec in the early stages of the deformation. This change is shown to be attributable to the increase of the density of dislocations in the material.Subject Classification: 35.10.
28 citations
TL;DR: In this article, a means for quickly and easily determining the broadband frequency content of acoustic bursts as short as 20 μs in duration has been developed using a video tape recorder and a standard spectrum analyzer.
Abstract: A means for quickly and easily determining the broadband frequency content of acoustic bursts as short as 20 μs in duration has been developed using a video tape recorder and a standard spectrum analyzer. It is shown by examples from several tests on laboratory specimens and on large structures that the frequency content of an acoustic burst is related to the mechanism which produced it and is not affected substantially by the specimen size or by mode conversion due to multiple reflections in the structure. The frequency content of the burst can be changed in two ways, however: by the frequency-dependent attenuation of the propagation medium and in the cases where the medium is dispersive. Results of measurements on the effect of these factors in a variety of structures are given. Although acoustic emissions from many materials tend to be "white noise," several examples of acoustic emissions and exwaneous background noise bursts having distinctive frequency spectra are given which suggest possibilities for discriminating true acoustic emission signals from background noise on the basis of frequency content alone.
27 citations
TL;DR: In this article, the authors describe a data acquisition system to determine the frequency spectrum between 500 KHz and 3 MHz of the initial acoustic emission of a low-carbon steel, using the transfer function of a piezoelectric transducer.
Abstract: The authors describe a data acquisition system to determine the frequency spectrum between 500 KHz and 3 MHz of the initial acoustic emission. They measured the transfer function of the piezoelectric transducer and of the specimen for their results using a computer. They present an application of this device to the study of the emission of a low-carbon steel.
26 citations
TL;DR: In this article, an acoustic emission technique has been used to study the dislocation processes occurring at various strain levels during deformation of polycrystalline Fe -3% Si samples.
26 citations
TL;DR: In this article, a basic model for macro-crack propagation in polycrystalline ceramics is developed, based on experimental acoustic emission amplitude studies, which has implications concerning the role of the micro-structure on the crack propagation resistance of ceramic materials.
24 citations
TL;DR: In this article, the results of experiments on adhesively bonded aluminium-alloy lap joints where stress, far less than needed to break the joint, causes acoustic emission were presented.
Abstract: The author presents the results of experiments on adhesively bonded aluminium-alloy lap joints where stress, far less than needed to break the joint, causes acoustic emission. The lap shear strength of those joints bonded with Redux 775 proved to be related to the cummulative acoustic emission energy per unit volume of the adhesive layer for different thicknesses of adhesive. What evidence there is for those joints bonded with the more ductile BSL 308 points to a similar relationship. The results demonstrate that acoustic-emission energy monitoring has potential as a non-destructive test of bond strength and merits further examination to establish the true relationship between bond strength and the total acoustic-emission energy released in the fracture of various structural adhesive systems.
TL;DR: In this article, an analysis is presented which shows how acoustic emission caused by microcracking is expected to vary during an elastically reversible load cycle, and a measure of the severity of the residual stress that results from irreversibility can be determined from measured acoustic emission.
Abstract: An analysis is presented which shows how acoustic emission caused by microcracking is expected to vary during an elastically reversible load cycle. The acoustic emission rate during unloading can be predicted directly from the acoustic emission rates observed during the loading and holding periods of a test cycle. Any discrepancy between the measured and predicted rates during unloading indicates irreversible behavior. A measure of the severity of the residual stress that results from irreversibility can be determined from the measured acoustic emission.
TL;DR: The application of acoustic emission to industrial ndt is hindered by a lack of exact knowledge of the significance of parameters such as total count, to characterize the emissions, and any novel parameters which can be derived, must be critically re-examined for their relation to metallurgical, mechanical and geometrical characteristics of structures if progress is to be achieved.
Abstract: The application of acoustic emission to industrial ndt is hindered by a lack of exact knowledge of the significance of parameters such as total count, to characterize the emissions. These parameters, and any novel parameters which can be derived, must be critically re-examined for their relation to metallurgical, mechanical and geometrical characteristics of structures if progress is to be achieved. The author describes experimental and theoretical work to this end on emissions from plastic deformation and fracture of various test pieces. The author concludes from his findings that the problems of noise and transducer sensitivity seem to be surmountable.
TL;DR: In this article, acoustic emission techniques were used to detect the onset of slow crack growth and to obtain a relation between COD and AE characteristics in the COD test, which can also be regarded as a critical value of fracture characteristics.
Patent•
TL;DR: In this paper, the sensitivity of a transducer was determined using a reciprocity calibration technique, and the output responses from the transducers were compared to the reverberant sound field.
Abstract: A method of calibrating acoustic emission transducers. The sensitivity of a standard transducer is first determined utilizing a reciprocity calibration technique, and the standard transducer and the acoustic emission transducer are then connected to a bounded acoustic medium. Random acoustic white noise is transmitted into the acoustic medium thereby establishing a multi-mode reverberant sound field, and the output responses from the standard transducer and the acoustic emission transducer to the reverberant sound field are obtained and compared to determine the sensitivity of the acoustic emission transducer.
TL;DR: In this paper, acoustic emissions during high temperature frictional sliding in faulted granite were detected with a piezoelectric transducer placed outside the furnace and pressure vessel.
Abstract: Acoustic emissions during high temperature frictional sliding in faulted granite were detected with a piezoelectric transducer placed outside the furnace and pressure vessel. Suitable choice of materials allowed the transmission of signals sufficiently large for measurement and analysis. Acoustic emissions were also monitored during the fracture runs at room temperature and could be compared with earlier studies. As observed previously, the emission rate increased dramatically prior to failure and the Ishimoto-Iida relationship between emission amplitude, A, and number of emissions, N(A), of amplitude, A, i. e., log N(A) = K′ − (b + 1) log A, was followed. The constant, b, was typically about 1.4, higher than the value of 1 or less indicated by previous experimental and theoretical studies.
TL;DR: Fracture-mechanics studies of chemically vapor-deposited ZnSe show that this material has a low fracture toughness and is susceptible to water-dependent slow crack growth as mentioned in this paper.
Abstract: Fracture-mechanics studies of chemically vapor-deposited ZnSe show that this material has a low fracture toughness and is susceptible to water-(moisture-) dependent slow crack growth. Investigations of biaxial flexural strength indicate that fracture (in this configuration) is controlled primarily by surface flaws and that macrofracture mechanics adequately describe the propagation of typical preexisting flaws in this ZnSe. Crack growth can be detected consistently by the acoustic emission technique; fracture in air is preceded by precursor events which occur up to 2 s prior to catastrophic propagation. Failure diagrams generated from the slow-crack-growth parameters show that the lifetime requirements of the laser window can be achieved by overload proof-testing to a proof ratio of 1.35 when the proper proof-test precautions are implemented.
TL;DR: In this article, the authors observed that the intensity of acoustic emission generated during martensite formation decreased markedly as the carbon content of the steel decreased, becoming nearly undetectable in a maraging steel.
Abstract: Acoustic emission was monitored during phase transformations that occur during cooling in a wide variety of steels. Acoustic emission was generated during the formation of martensite but not during the formation of ferrite, bainite, or pearlite. This observation is consistent with the rapid, diffusionless, shear-like nature of martensite formation and the slow, diffusion-controlled growth of ferrite, bainite, or pearlite. The martensite start temperatures, and the temperature range of martensite formation determined by acoustic emission were in good agreement with those determined by metallographic or dilatometric methods. The intensity of acoustic emission generated during martensite formation decreased markedly as the carbon content of the steel decreased, becoming nearly undetectable in a maraging steel. This decrease in intensity correlates with a morphological change from large plate-shaped martensite units to smaller lath-shaped martensite units as the carbon content of the steel is decreased.
TL;DR: In this paper, a series of simulated acoustic emission experiments in thin plates and bars were conducted to assess the effects of structural geometry on the detection of emission, and it was shown that the structure introduces peaks in the received signal spectra corresponding to thickness resonances that may be estimated from Lamb wave theory.
Abstract: A series of simulated acoustic emission experiments in thin plates and bars conducted to assess the effects of structural geometry on the detection of emission is described. It is shown that the structure introduces peaks in the received signal spectra corresponding to thickness resonances that may be estimated from Lamb wave theory. Spectra of acoustic emission signals from a thin−walled pressure vessel show a peak at the frequency corresponding to the lowest symmetric plate mode. It is concluded that a significant portion of the energy detected by a surface contact transducer on a thin−walled structure is concentrated at these resonances and should be accounted for in choosing a detection system.Subject Classification: 35.10, 35.80.
TL;DR: In this article, a high-strength 4340 steel fracture-toughness specimen was heat treated to give a ductile-rupture type of slow crack growth under rising load.
Abstract: A high-strength 4340 steel fracture-toughness specimen was heat treated to give a ductile-rupture type of slow crack growth under rising load. For evaluation of the step-wise growth process, the specimen was instrumented with acoustic stress wave emission (SWE) detection equipment. The resulting crack area swept out by the advancing crack was correlated to the magnitude and number of the acoustic emission pulses. A crack growth model was developed which accounts for the direct relationship between crack area swept out and the sum of the individual SWE amplitudes, and for the experimentally observed bimodal distribution of the SWE amplitudes. The model postulates that slow crack growth takes place in a step-wise mechanism. This involves a repeated two-step process where the first step is the formation of a multitude of individual thumbnail cracks and the second step is the simultaneous interconnection of these thumbnail cracks to form a new continuous crack front.
TL;DR: In this article, acoustic emission measurements have been made in conjunction with fracture toughness tests on nine steels of yield strengths from 247 −1606 MNm−2, and the significance of the results has been assessed in terms of the application of acoustic emission to provide 100% coverage during the periodic inspection of pressure vessels.
TL;DR: In this article, it was shown that the emission of a single elastic stress wave could be correlated to a load drop, ΔP, occuring during crack growth, and this load drop could be interpreted via a theoretical compliance analysis in terms of area swept out by the advancing crack.
01 Feb 1975
TL;DR: In this article, a combination of acoustic emission and linear fracture mechanics can be used to estimate the stress intensity factor K at a growing crack, and therefore provide predictive information regarding structural failure.
Abstract: The combination of acoustic emission and linear fracture mechanics can provide quantitative information regarding failure. This report has shown that, for certain situations, acoustic emission techniques can be used to accurately estimate the stress intensity factor K at a growing crack, and therefore provide predictive information regarding structural failure. The importance of locating defects in large complicated structures, such as bridges and power plant pressure vessels, was also stressed, and a multiple-channel computer system was described for accomplishing this function. The ability to locate a growing defect, coupled with the ability to quantify the growth rates with fixed sensors (no scanning required) places acoustic emission in the forefront of new techniques for the prevention of structural failures.
TL;DR: In this article, a radiation condition for time-harmonic elastic waves in a homogeneous, isotropic, perfectly elastic medium is presented based upon certain physical considerations pertaining to the elastodynamic radiation generated by a source of finite extent.
Abstract: In the present paper, a radiation condition for time-harmonic elastic waves in a homogeneous, isotropic, perfectly elastic medium is presented. It is based upon certain physical considerations pertaining to the elastodynamic radiation generated by a source of finite extent. In it, the particle displacement on and the traction across a spherical surface around the source occur. Separate conditions are imposed on the radial and the angular parts of these quantities. It is shown that the resulting far-field radiation characteristics for the particle displacement are in accordance with the properties that could be expected from the physical considerations we have started with.
TL;DR: In this paper, the acoustic emission count rates for tensile loading of unidirectional boron-epoxy and aluminum sheets reinforced with unIDirectional BORON-EPoxy are presented.
Abstract: Acoustic-emission (AE) count rates are presented for tensile loading of unidirectional boron-epoxy and for aluminum sheets reinforced with unidirectional boron-epoxy. It is shown that different prepreg materials have different characteristic AE patterns. Results from composite-reinforced metal specimens show that early failures are accompanied by a sharp increase in AE count rate at the knee of the bilinear stress-strain diagram. It is further shown that the count rates are a function of specimen fabrication and that higher total counts do not necessarily correspond to early failures.
TL;DR: In this paper, the relationship between acoustic emission and crack size was investigated using a power series of applied stress model, and the first-order approximation is consistent with that of a macroscopic fracture mechanics consideration on the emission related to the plastic zone size.
Abstract: Acoustic emission from a crack vicinity in a uniformly stressed solid is correlated with the crack size based on a continuous theory of dislocations. It is assumed that the total number of acoustic emissions is directly proportional to the total number of nonuniformly distributed moving dislocations in the plastic zone near the crack. The resultant equation of the relationship between acoustic emission and crack size can be expanded into a power series of applied stress. The first‐order approximation is consistent with that of a macroscopic fracture mechanics consideration on the emission related to the plastic zone size. The theoretical calculation is verified with experimental results obtained from a flawed carbon steel vessel by a multichannel acoustic emission monitoring system and agrees reasonably well with the experimental data. Further calculations by utilizing the theory and by analyzing available experimental data of acoustic emissions from center‐surface‐flaw specimens and wedge opening load specimens of various crack sizes also show agreement between the theory and the experimental data.
TL;DR: In this paper, a series of tests were carried out to determine the scatter in acoustic emission data gathered during stress rupture and fatigue testing of a simple fiber-reinforced epoxy composite.
Abstract: A series of tests was carried out to determine the scatter in acoustic emission data gathered during stress rupture and fatigue testing of a simple fiber-reinforced epoxy composite. Single-end organic fiber-epoxy strands were monitored for acoustic emission during tension tests to failure, stress rupture tests, and dynamic fatigue tests. During the stress rupture and fatigue tests, the plots of summation of acoustic emission counts versus time were found to resemble metal creep curves in that primary, secondary, and tertiary regions could be distinguished. Because of a significant amount of scatter, only a limited correlation can be made between the slope of the summation of acoustic emission in the steady-state region and the specimen life during stress rupture and fatigue testing. In addition, flawed specimens were easily sorted out during the tension tests. These results indicate that acoustic emission data gathered during composite fatigue and stress rupture testing might be useful for life prediction.