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Loading effect of a metallic parabolic tip on S$_0$ and A$_0$ lamb waves

Abstract : The loading effect induced by the contact between a parabolic duralumin tip and a free glass plate is investigated using Lamb waves and an optical heterodyne interferometric probe. The instrument detects 1MHz impulse symmetric S₀ and antisymmetric A₀ Lamb wave trains launched in 1-mm-thick B270-type glass. Strain-optic modeling is carried out to explain optical measurement through the transparent medium and the loading effect of the tip. Three-wave optical interference modeling is also developed to explain the presence of fringes of equal thickness in C-scans of both modes propagating in a plate that has a 1.1-mrad wedge. Results show that through-glass probing inverts by a factor of -3.1 the signal that is normally returned by the interferometer at a free-air surface for the S₀ Lamb mode. Fringes of equal thickness reveal the spatial extension of the mechanical loading. Through-glass probing on A₀ produces about the same signal as in a free-air measurement configuration. This mode appears to be more appropriate for the evaluation of the loading effect of the tip. For this parabolic tip, we observe an A₀ attenuation of about 50% in the contact area.
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Submitted on : Wednesday, April 25, 2018 - 3:27:03 PM
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J-P Nikolovski. Loading effect of a metallic parabolic tip on S$_0$ and A$_0$ lamb waves. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Institute of Electrical and Electronics Engineers, 2013, 60, pp.208-217. ⟨10.1109/TUFFC.2013.2552⟩. ⟨cea-01778312⟩



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