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Chapitre d'ouvrage
Nonlinear Frequency-Mixing Photoacoustic Characterisation of a Crack
Abstract : A one and two dimensional imaging of a crack by a novel nonlinear frequency-mixing photoacoustic method is presented. Acoustic waves are initiated by a pair of laser beams intensity-modulated at two different frequencies. The first laser beam, intensity modulated at a low frequency fL , generates a thermoelastic wave which modulates the local crack rigidity up to complete closing/opening of the crack, corresponding to crack breathing. The second laser beam, intensity modulated at much higher frequency fH , generates an acoustic wave incident on the breathing crack. The detection of acoustic waves at mixed frequencies fH±nfL ( n=1,2,… ), absent in the excitation frequency spectrum, provides detection of the crack, which can be achieved all-optically. The theory attributes the generation of the frequency-mixed spectral components to the modulation of the acoustic waves reflected/transmitted by the time-varying nonlinear rigidity of the crack. The crack rigidity is modified due to stationary and oscillating components from the laser-induced thermoelastic stresses. The amplitudes of the spectral sidelobes are non-monotonous functions of the increasing thermoelastic loading. Fitting such experimental evolutions with theoretical ones leads to estimating various local parameters of the crack, including its width and rigidity.
https://hal-univ-lemans.archives-ouvertes.fr/hal-02536848
Contributeur : Vitali Goussev <>
Soumis le : mercredi 8 avril 2020 - 13:34:51
Dernière modification le : jeudi 2 septembre 2021 - 16:00:33
Contributeur : Vitali Goussev <>
Soumis le : mercredi 8 avril 2020 - 13:34:51
Dernière modification le : jeudi 2 septembre 2021 - 16:00:33