scholarly journals Micromechanisms of brittle fracture: Acoustic emissions and electron channeling analyses

1990 ◽  
Author(s):  
W.W. Gerberich
Keyword(s):  
Brittle Fracture ◽  
Acoustic Emissions ◽  
Electron Channeling

scholarly journals Acoustic Emission in Snow at Constant Rates of Deformation

1973 ◽  
Vol 12 (64) ◽  
pp. 144-146 ◽  
Author(s):  
W. F. St. Lawrence ◽  
T. E. Lang ◽  
R.L. Brown ◽  
C. C. Bradley
Keyword(s):  
Acoustic Emission ◽  
Brittle Fracture ◽  
Uniaxial Compression ◽  
Laboratory Experiments ◽  
Acoustic Emissions ◽  
Snow Sample ◽  
Frequency Range ◽  
Snow Samples

AbstractAcoustic emissions in the audio spectrum are reported from observations of laboratory experiments conducted on snow samples in uniaxial compression. A number of tests show the pattern of acoustic emissions to be a function of the rate of deformation. Over the frequency range 20 to 7 000 Hz acoustic emissions are associated with rates of deformation corresponding to brittle fracture of the snow sample. Though probably present, no acoustic emissions were detected from samples deforming plastically.

Acoustic Emission From a Brief Crack Propagation Event

1979 ◽  
Vol 46 (1) ◽  
pp. 107-112 ◽  
Author(s):  
J. D. Achenbach ◽  
J. G. Harris
Keyword(s):  
Acoustic Emission ◽  
Brittle Fracture ◽  
Crack Propagation ◽  
Acoustic Emissions ◽  
Elastic Solid ◽  
Propagation Speed ◽  
Crack Edge ◽  
Arbitrary Distribution ◽  
Canonical Solution ◽  
Phase Functions

Acoustic emissions produced by elementary processes of deformation and fracture at a crack edge are investigated on the basis of elastodynamic ray theory. To obtain a two-dimensional canonical solution we analyze wavefront motions generated by an arbitrary distribution of climbing edge dislocations emanating from the tip of a semi-infinite crack in an unbounded linearly elastic solid. These wavefront results are expressed in terms of emission coefficients which govern the variation with angle, and phase functions which govern the intensity of the wavefront signals. Explicit expressions for the emission coefficients are presented. The coefficients have been plotted versus the angle of observation, for various values of the crack propagation speed. The phase functions are in the form of integrals over the emanating dislocation distributions. Specific dislocation distributions correspond to brittle fracture and plastic yielding at the crack tip, respectively. Acoustic emission is most intense for brittle fracture, when the particle velocities experience wavefront jumps which are proportional to the stress-intensity factors prior to fracture. An appropriate adjustment of the canonical solution accounts for curvature of a crack edge. Such effects as focussing, finite duration of the propagation event, and finite dimensions of the crack are briefly discussed. As a specific example, the first signals generated by brittle Mode I propagation of an elliptical crack are calculated.

scholarly journals Acoustic Emission in Snow at Constant Rates of Deformation

1973 ◽  
Vol 12 (64) ◽  
pp. 144-146 ◽  
Author(s):  
W. F. St. Lawrence ◽  
T. E. Lang ◽  
R.L. Brown ◽  
C. C. Bradley
Keyword(s):  
Acoustic Emission ◽  
Brittle Fracture ◽  
Uniaxial Compression ◽  
Laboratory Experiments ◽  
Acoustic Emissions ◽  
Snow Sample ◽  
Frequency Range ◽  
Snow Samples

Abstract Acoustic emissions in the audio spectrum are reported from observations of laboratory experiments conducted on snow samples in uniaxial compression. A number of tests show the pattern of acoustic emissions to be a function of the rate of deformation. Over the frequency range 20 to 7 000 Hz acoustic emissions are associated with rates of deformation corresponding to brittle fracture of the snow sample. Though probably present, no acoustic emissions were detected from samples deforming plastically.

Electron Channeling Patterns

1977 ◽  
Vol 35 ◽  
pp. 12-13
Author(s):  
David C. Joy
Keyword(s):  
Electron Diffraction ◽  
Incidence Angle ◽  
Photographic Plate ◽  
Diffraction Effect ◽  
Angle Of Incidence ◽  
Bulk Single Crystal ◽  
Time Resolved ◽  
Electron Channeling ◽  
Spatially Resolved ◽  
Large Bulk

Electron channeling patterns (ECP) were first found by Coates (1967) while observing a large bulk, single crystal of silicon in a scanning electron microscope. The geometric pattern visible was shown to be produced as a result of the changes in the angle of incidence, between the beam and the specimen surface normal, which occur when the sample is examined at low magnification (Booker, Shaw, Whelan and Hirsch 1967).A conventional electron diffraction pattern consists of an angularly resolved intensity distribution in space which may be directly viewed on a fluorescent screen or recorded on a photographic plate. An ECP, on the other hand, is produced as the result of changes in the signal collected by a suitable electron detector as the incidence angle is varied. If an integrating detector is used, or if the beam traverses the surface at a fixed angle, then no channeling contrast will be observed. The ECP is thus a time resolved electron diffraction effect. It can therefore be related to spatially resolved diffraction phenomena by an application of the concepts of reciprocity (Cowley 1969).

Oto Acoustic Emissions (OAE): the shape-similarity of pure-tone audiogram and OAE-gram

1999 ◽  
Vol 24 (4) ◽  
pp. 377-383
Author(s):  
G. A. van zanten ◽  
A. van de sande ◽  
M. P. brocaar
Keyword(s):  
Pure Tone ◽  
Acoustic Emissions ◽  
Shape Similarity ◽  
Pure Tone Audiogram
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