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Chapitre D'ouvrage Année : 2020

Nonlinear Frequency-Mixing Photoacoustic Characterisation of a Crack

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Résumé

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.
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Dates et versions

hal-02536848 , version 1 (08-04-2020)

Identifiants

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Sylvain Mezil, Nikolay Chigarev, Vincent Tournat, Vitali Goussev. Nonlinear Frequency-Mixing Photoacoustic Characterisation of a Crack. Measurement of Nonlinear Ultrasonic Characteristics, pp.235-281, 2020, ⟨10.1007/978-981-15-1461-6_6⟩. ⟨hal-02536848⟩
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