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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 1 (1980), S. 215-224 
    ISSN: 1573-4862
    Keywords: Acoustic emission ; slip ; microcracking ; deformations ; displacement field ; elastic waves ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The theory of elastic wave emission (i.e., acoustic emission; AE) from damage processes such as slip and microcracking is discussed. Analogous developments in the literature on earth-quake seismology and dynamic dislocation theory are noted and utilized. A general representation of the displacement field of an AE event is given in terms of the double-couple response to a distribution of “moment density tensor” in the source region. Results are specialized to a point source model and to a general far-field analysis of outgoing elastic waves, and conditions for validity of such representations and their low-frequency specializations are noted. Emitted wave fields are compared for tensile opening and slip events, and procedures which might enable the approximate determination of the size or area increase of tensile microcracks are discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4862
    Keywords: Acoustic emission ; envelope strength ; energy calibration ; elastic strength energy ; martensitic transformations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An approximate method for the quantitative characterization of acoustic emission sources whose signals are recorded with traditional instrumentation has been developed to evaluate the emission from a Fe-Ni alloy undergoing martensitic transformations. The calibration principle is based upon using pseudo sources of known elastic strain energy to produce a calibration curve relating a parameter of the acoustic emission signal measured (envelope strength) to the strain energy of the source. The curve can then be used to determine the strain energy of naturally occurring sources during martensitic transformations.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4862
    Keywords: Acoustic emission ; AE source location ; single-fiber-composite ; fragmentation ; interfacial shear strength ; fiber/matrix interface ; size effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In the single-fiber-composite (SFC) test, a fiber imbedded in a matrix is loaded in tension, resulting in a fragmentation of the fiber. In the conventional version of this test, the final fiber fragmentation length distribution is used with a micro-mechanical model to determine the average fiber/matrix interfacial shear stress. In the enhanced version of this test, one also determines the applied stress at each fiber fracture, and from this, one can evaluate the strength of the fiber at short gage lengths. In our measurement system, we utilize an acoustic emission (AE) technique to detect the fiber fractures and to locate the fiber breaks and so determine both the fiber failure stresses as well as the fiber fragmentation lengths while the test is in progress. Critical to the success of this test is a broadband AE system that utilizes point-like AE sensors, procedures for evaluatingin situ, the wavespeed of the first wave arrival and signal processing techniques for determining the arrival time of this signal as precisely as possible for a broad range of wave shapes. Here we describe the application of such an enhanced SFC test procedure to investigate the failure of a Nicalon™ fiber in an epoxy matrix.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-4862
    Keywords: Acoustic emission ; energy analysis ; composite materials ; strength ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A new technique which uses the output of a true RMS voltmeter to measure the acoustic emission energy output of a transducer is presented. To demonstrate its use in a typical case, this procedure is used to measure acoustic emission energy during tensile tests on [0°/±30°/90°]s glass-epoxy laminate uniaxial and 10° off-axis tensile coupons. The test results were compared with numerical predictions of laminate response and acoustic emission energy. The experiments indicate that acoustic emission energy can be used to indicate the onset of ply and interlaminar failure.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-4862
    Keywords: Acoustic emission ; microcracking ; fracture mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A three-dimensional quantitative acoustic emission (AE) analysis of microcracking in unreinforced mortar beams was conducted. In order to facilitate the analysis of the large amounts of data generated by an AE test, a simplified method for the inversion of AE signals was developed. By applying the theoretical Green's function for an infinite space, the multichannel deconvolution normally required of AE data inversion reduces to a nonlinear curve-fitting problem. Using this procedure, microcracking in a mortar specimen was evaluated using a seismic moment tensor representation. Source-time functions for the microcracks were also recovered. The locations of the AE events were calculated, and damage localization was observed. The moment tensor analysis showed the dominant mode of microfracture to be mode II, with a limited number classified as mixed mode. A microstructural mechanism for this behavior is presented.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 16 (1997), S. 175-186 
    ISSN: 1573-4862
    Keywords: Acoustic emission ; mixed-mode crackings ; elastic waves ; displacement field ; displacement discontinuity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An analytical expression for the relationship between acoustic emission (AE) surface motion and displacement discontinuity of a finite crack extending in mixed mode was investigated based on an analogy to earthquake problems in seismology and crackings in fracture mechanics. The displacement field in an infinite body was expressed in terms displacement discontinuity for a growing plane crack with arbitrary shape and orientation. The complete field response, including far-field, near-field, and intermediate-field motion has been studied. The displacement field in an infinite body was converted into the normal surface motion at the sensor site at the boundary of a half-space through local modification, considering the first reflection and mode conversion of the incident P and S waves at the traction-free boundary. The surface motion obtained is valid for finite crack propagation, while an algebraic equation for microcracking is given as a special case for illustration. Using these results, we will be able to analyze the fracture mode and relative location and orientation of sensor and crack plane according to the waveform obtained.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 6 (1987), S. 159-166 
    ISSN: 1573-4862
    Keywords: Acoustic emission ; finite element ; finite difference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Two computer programs which solve the partial differential equations for sound propagation numerically are applied to the study of problems in acoustic emission. The programs use finite difference and finite element techniques to calculate sound fields due to distributions of sources in complex geometries in two dimensions. The potential to handle more complex geometries and to model more realistic sources is the main advantage of these numerical calculations over the analytic calculations. The main disadvantage of the numerical techniques is the cost of obtaining results since a large main frame computer or supercomputer is required. Both numerical methods are found to agree well with analytic calculations using Green's functions. The finite difference method agrees very well with the analytic calculations but, in its current implementation, is much slower and contains more numerical noise compared to the finite element method. The finite element method has the additional advantage of being capable of handling more complex geometries than the finite difference method.
    Type of Medium: Electronic Resource
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