Showing papers on "Acoustic emission published in 1978"
TL;DR: In this paper, the authors used the acoustic emission technique to monitor fatigue crack growth, and attributed the peak load emissions to both crack extension and deformation and fracture events occurring within the crack tip plastic zone, and these emissions have been correlated with the energy released during crack growth.
240 citations
TL;DR: Partial discharges in transformers cause high frequency (ultrasonic) pressure pulses to propagate through the insulating media, similar in character to stress waves propagated in solids during crack formation (acoustic emission) as discussed by the authors.
Abstract: Partial discharges in transformers cause high frequency (ultrasonic) pressure pulses to propagate through the insulating media. These are similar in character to stress waves propagated in solids during crack formation (acoustic emission). The techniques involved in the detection of acoustic emission (AE) are shown to be well suited to the detection of emissions from partial discharges.
85 citations
TL;DR: A review of the current acoustic emission literature relating to fiber reinforced composite materials is presented in this paper, where the authors present summary tables which assist m the prompt delineation of the achievements in this research area.
Abstract: A review of the current acoustic emission literature relating to fiber reinforced composite materials is presented. Summary tables which assist m the prompt delineation of the achievements in this research area are developed. Because of the qualitative character of much of the current literature, suggestions to develop quantitative AE standards are strongly recommended
80 citations
01 Jan 1978
TL;DR: In this paper, the displacement of an arbitrary point on an infinite plate due to a point source force function is computed using a Fourier inversion technique, which yields exact formulas similar to those developed for seismological "ray" theories.
Abstract: Acoustic Emission (AE) signals are notorious for their complexity and irreproducibility. Because AE source characteristics are virtually unknown and because the detected AE signals are colored by the propagation media, the sensor response and the instrumentation set tings, interpretations of test results such as spectral analysis or correlation studies are mostly qualitative and sometimes controversial; theories either are empirically derived or cannot be verified by experiments . In this paper, we sketch an approach to the AE signal analysis problem. We first report the development of a theory which allows the computation of the displacement as a function of time at an arbitrary ·point on an infinite plate due to an arbitrary point source force function . The theory is based on a new Fourier inversion technique which yields exact formulas similar to those developed for seismological "ray" theories. We then report experimental results obtained on a 2. 52 em thick aluminum plate using a reproducible step function stress release pulse as a simulated AE signal and a wide band displacement capacitive transducer as a sensor. The measurements are in quantitative agreement with the predictions of theory. We also discuss applications wherein the simulated signal, capacitive transducer and plate theory are used for AE source signature analysis, and sensor calibration problems.
75 citations
44 citations
TL;DR: In this article, a capacitance transducer for use as a calibrated detector of energetic acoustic emission events is described, which is displacement-sensitive with a wide frequency response, and typically has a rise-time of 20 ns.
Abstract: The authors describe a capacitance transducer for use as a calibrated detector of energetic acoustic emission events It is displacement-sensitive with a wide frequency response, and typically has a rise-time of 20 ns The electrical output of the transducer has been calibrated as a function of displacement, and the device has been tested in a broad-band acoustic emission system It is envisaged that the transducer could either be used to measure emission transients directly, or act as a reference against which conventional piezoelectric transducers could be compared
43 citations
TL;DR: An analytical solution to the electric and acoustic fields generated by a surface charge source is obtained in this paper, where four types of acoustic waves can propagate along the surface of a general anisotropic medium.
Abstract: An analytical solution to the electric and acoustic fields generated by a surface charge source is obtained. As a result it is shown that four types of acoustic waves can propagate along the surface of a general anisotropic medium. Numerical examples are given for ST-cut quartz and rotated Y-cut X-propagating lithium niobate.
34 citations
TL;DR: It is demonstrated that the localization capability of the complete system can be efficiently improved by the inclusion of demodulation or deconvolution in signal processing.
34 citations
TL;DR: In this article, a broad-band approach to the detection of acoustic emission in which a capacitance transducer has been used to record the transient elastic waves generated by crack growth processes as surface displacements is described.
Abstract: Describes a new broad-band approach to the detection of acoustic emission in which a capacitance transducer has been used to record the transient elastic waves generated by crack growth processes as surface displacements. A unique specimen geometry, the 'Yobell' has been developed to reduce interference from internal reflections of the ultrasonic pulse, so that the measured surface displacements can be compared with those calculated for a source buried below the surface of the half-space. A static source model has been used to relate the rise-time and amplitude of transients to the time-scales and magnitudes of incremental crack growth.
31 citations
TL;DR: In this paper, the authors investigated the acoustic emission generated during the tensile deformation of pure iron and found that the acoustic emissions occurred predominantly in two regions, the early part of the elastic portion of the test and the second region was at, or near, plastic yield.
30 citations
TL;DR: In this article, a detailed study is made of the distribution of the two characteristic parameters of the beat patterns appearing in the acoustic signals emitted by rotating beds of nominal 0.6 cm glass spheres within each harmonic mode.
01 Jan 1978
TL;DR: In this paper, the stress wave factor was measured with simple contact probes requiring only one-side access to a part, which is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus measure material properties in directions assumed by actual loads.
Abstract: Details of the method used to measure the stress wave factor are described. Frequency spectra of the stress waves are analyzed in order to clarify the nature of the wave phenomena involved. The stress wave factor was measured with simple contact probes requiring only one-side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus measure material properties in directions assumed by actual loads. The technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite/polyimide composite panels, and results obtained are compared with through transmission immersion ultrasonic scans.
TL;DR: In this article, a mathematical method is developed which allows the location of sources on a spherical surface by using a system of coordinates which is easily applied to an industrial vessel, where the radius of the sphere is inceased to infinity.
Abstract: Using the differences in time of arrival from an acoustic emission source to several sensors, the position of the source may be calculated. A mathematical method is developed which allows the location of sources on a spherical surface by using a system of coordinates which is easily applied to an industrial vessel. If the radius of the sphere is inceased to infinity, the formulae can be used for the location of sources on a plane surface. A brief discussion of the results is given, keeping in mind the industrial aspect of the technique.
TL;DR: In this paper, the authors proposed optical transducers to provide accurate, quantitative, highly localized information; they do not disturb the waves being measured and are not limited by frequency response.
Abstract: The usual sensor for acoustic emission is the piezoelectric transducer. Although this transducer is readily available, reasonably inexpensive, and very sensitive to ultrasonic transients, it has several serious drawbacks as a transducer: It distorts the signals being measured, it exhibits resonances, it has limited bandwidth, it responds differently to surface acoustic waves and bulk waves (because of its large sensitive area), and its calibration is a matter of considerable uncertainty. Essentially, it is a qualitative transducer. Furthermore, it cannot measure local effects within a millimeter of an emission source, where the mechanisms causing the ultrasonic transient are presumably most clearly distinguishable. Optical transducers, on the other hand, have the great advantage of providing accurate, quantitative, highly localized information; they do not disturb the waves being measured and are not limited by frequency response.
TL;DR: In this paper, it is shown that the process is strain rate-insensitive in the presence of the first source alone, and rate-dependent when both are involved, and that the slower the strain rate, the longer the time available for crack development and the stronger the AE activity.
TL;DR: In this article, the breakdown of the ceramic electrolyte beta-alumina during the transport of sodium ions has been investigated using an acoustic emission probe, and the results indicate that the ceramic undergoes a mechanical deterioration which depends on current density, and that the final stage of breakdown is subcritical crack growth.
Abstract: The breakdown of the ceramic electrolyte beta-alumina during the transport of sodium ions has been investigated using an acoustic emission probe. A characteristic feature associated with the onset of electronic conduction through the electrolyte is the presence of sodium metal filaments penetrating the ceramic. The results of this preliminary investigation indicate that the ceramic undergoes a mechanical deterioration which depends on current density, and that the final stage of breakdown is subcritical crack growth.
TL;DR: A vibrator is held in contact with a structure undergoing testing, such asn airplane wing Vibrations are distributed through the structure and structural defects such as fissures will respond by emitting an acoustic signal The acoustic signal may occur over a wide frequency range.
Abstract: A vibrator is held in contact with a structure undergoing testing, such asn airplane wing Vibrations are distributed through the structure and structural defects such as fissures will respond by emitting an acoustic signal The acoustic signal may occur over a wide frequency range A pick-up having a crystal transducer also makes contact with the surface of the structure to detect acoustic emissions The crystal has a wide band response capable of detecting structural defect acoustic emissions The pick-up has electrical leads connected thereto so that the acoustic emissions are converted to electrical signals which may be recorded or viewed on an oscilloscope Movement of the pick-up across the surface of the structure will help determine the location of the structural defect
TL;DR: In this article, the amplitude of the transmitted and reflected waves and the jump of the acceleration of the shock were explicitly determined, and the reflexion of plane acoustic waves through a longitudinal shock wave in elastic isotropic solids was investigated.
Abstract: Transmission and reflexion of plane acoustic waves through a longitudinal shock wave in elastic isotropic solids are investigated. As a result, the amplitude of the transmitted and reflected waves and the jump of the acceleration of the shock are explicitly determined.
01 Jan 1978
TL;DR: In this article, the sources of acoustic emission that are prevalent in brittle solids are examined, especially microcrack sources and sources that accompany macrocrack extension, and emission amplitude distributions are derived using crack opening displacement solutions pertinent to each source type, and assuming an extreme value size distribution of precursors consistent both with the functional form of typical emission amplitude distribution and with defect size observations.
Abstract: The sources of acoustic emission that are prevalent in brittle solids are examined, especially microcrack sources and sources that accompany macrocrack extension. The emission amplitude distributions are derived using crack opening displacement solutions pertinent to each source type, and assuming an extreme value size distribution of precursors consistent both with the functional form of typical emission amplitude distributions and with defect size observations. Acoustic emission event rates are derived from the stress and time dependence of crack growth. Stress history effects are afforded particular emphasis. Finally, some applications of acoustic emission that emerge from the analysis of the source characteristics are briefly evaluated.
TL;DR: In this article, the acoustic emission power and energy accompanying the deformation of Al-4%Cu have been systematically studied as a function of ageing time at 170±5°C.
Abstract: The acoustic emission power and energy accompanying the deformation of Al-4%Cu have been systematically studied as a function of ageing time at 170±5°C. The emission shows a strong dependence upon microstructure, a large peak in energy being observed after ageing for 1 to 2 h; this corresponded to a microstructure containing GP zones. A shear localization mechanism has been postulated to account for the ageing peak, in which pile-ups of dislocations are released during the cutting of GP(I) zones.
TL;DR: In this article, two qualitatively different simulated acoustic emissions have been studied in some detail, theoretically and experimentally, to explore the possibility that the frequency spectrum of an acoustic emission burst may be a partial signature, identifying the source.
Abstract: It has been suggested that the frequency spectrum of an acoustic emission burst may be a partial ’’signature,’’ identifying the source. To explore this possibility we have studied in some detail, theoretically and experimentally, two qualitatively different simulated acoustic emissions. The first is the fracture of small (20–40 μm) silicon carbide grains on a steel slab. The second is the impact of a small elastic sphere of various materials on the same slab. Our primary objective has been to test our understanding of the medium response, and, consequently, the extent to which we can determine the source spectrum from the observed spectrum.
TL;DR: In this article, an acoustic contact fuze that is responsive to highfrequency actic emission stress waves and distinguishes between such waves caused by impacts and signals caused by the operating environment is presented.
Abstract: An acoustic emission contact fuze that is responsive to high-frequency actic emission stress waves and distinguishes between such waves caused by impacts and signals caused by the operating environment.
01 Jul 1978
TL;DR: In this article, an acoustic emission (AE) method is used to measure the burning rate of solid propellant strands, which has a precision of 0.5% and excellent burning rate correlation with both subscale and large rocket motors.
Abstract: An acoustic emission (AE) method is being used to measure the burning rate of solid propellant strands. This method has a precision of 0.5% and excellent burning rate correlation with both subscale and large rocket motors. The AE procedure burns the sample under water and measures the burning rate from the acoustic output. The acoustic signal provides a continuous readout during testing, which allows complete data analysis rather than the start-stop clockwires used by the conventional method. The AE method helps eliminate such problems as inhibiting the sample, pressure increase and temperature rise, during testing.
TL;DR: In this paper, the authors analyzed the behavior of graphite under small bending and tension stresses (observed frequency range 0,1-0,3 MHz) and showed that the acoustic emission rate is higher during the first loading than during the following load cycles where emission can only be observed when the stress level exceeds the preceding one.
01 Jan 1978
TL;DR: Hsu et al. as mentioned in this paper reported experimental results of a computer-based test system consisting of a large plate and a capacitive transducer, which can be characterized by solving the Toplitz matrix directly.
Abstract: Acoustic emission signals carry potentially useful information about the criticality of deformation source mechanisms in materials, but signal processing techniques such as threshold counting, RMS voltage recording, peak detection, and spectral analysis often failed to extract such information unambiguously. The difficulty lies in the determination of the transfer characteristics of the structure and the sensor. We report experimental results of a computer‐based test system consisting of a large plate and a capacitive transducer [N. N. Hsu, J. A. Simmons, and S. C. Hardy, Materials Evaluations 35(10), 100–106 (1977)]. The transient wave propagation behavior of the plate and the transfer function of the capacitive transducer are known. Consequently, unknown sources can be characterized by solving the Toplitz matrix directly. Explicit force‐time functions of simulated signals such as breaking glass capillaries, breaking pencil leads, dropping steel balls, electrical arcs, and pulsed piezoelectric transducer...