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Nonlinear effects of micro-cracks on acoustic surface and wedge waves

: Rjelka, Marek; Pupyrev, Pavel D.; Köhler, Bernd; Mayer, Andreas P.


Low temperature physics 44 (2018), No.7, pp.946-953
ISSN: 1063-777X
ISSN: 1090-6517
Deutsche Forschungsgemeinschaft DFG
MA 1074/11
Journal Article
Fraunhofer IKTS ()

Micro-cracks give rise to non-analytic behavior of the stress-strain relation. For the case of a homogeneous spatial distribution of aligned flat micro-cracks, the influence of this property of the stress-strain relation on harmonic generation is analyzed for Rayleigh waves and for acoustic wedge waves with the help of a simple micromechanical model adopted from the literature. For the efficiencies of harmonic generation of these guided waves, explicit expressions are derived in terms of the corresponding linear wave fields. The initial growth rates of the second harmonic, i.e., the acoustic nonlinearity parameter, has been evaluated numerically for steel as matrix material. The growth rate of the second harmonic of Rayleigh waves has also been determined for microcrack distributions with random orientation, using a model expression for the strain energy in terms of strain invariants known in a geophysical context.