The potential of Rayleigh wave spectroscopy for the in-depth reconstruction of elastic properties of multilayers for materials with a continuous profile of elastic properties is explored. Two models to calculate the surface acoustic wave (SAW) dispersion spectrum from the profile of the elastic parameters are elaborated and compared. It is found that the relevant elastic parameters for Rayleigh wave dispersion in multilayers are the “effective” Rayleigh velocities, i.e., the Rayleigh velocities calculated for virtually semi-infinite layers. For the solution of the inverse problem, a neural network and a singular value decomposition model are proposed and tested on simulated SAW spectra. The reconstruction techniques are applied to reconstruct the elastic depth profile of shot-peened steel samples from laser-generated and laser-detected SAW data.

International audienceThe present paper reports the results of a blind round robin test dedicated to the measurement of the retained austenite content of different TRIP assisted multiphase steels. Various surface and volume techniques, i.e. light microscopy, X-ray diffraction, electron backscattered diffraction (EBSD), magnetic saturation, thermal diffusivity and laser ultrasonics, were used by different partners. The compiled results show a quite large variability of the estimated retained austenite content, particularly for well established techniques, such as X-ray diffraction (XRD) and magnetisation. On the other hand, emerging techniques like EBSD, thermal diffusivity and laser ultrasonics warrant further investigations

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