Topological imaging of structures, like plane wings or pipes containing dangerous fluids, needs efficient computation of acoustic fields when these structures are healthy. By a semi-analytical approach, i.e. we know the exact solution in the perpendicular/radial direction after integral transformations with respect to time (Laplace transform) and to the other directions (Fourier transform/series), we are able to efficiently compute the 3D wave propagation in multilayer plates [Mora et al., Ultrasonics, 2016] or pipes [yet unpublished, PhD in progress], which can be immersed or embedded. The limitation is that the geometry must be invariant with respect to the latter other directions.

The evaluation of damage at an early stage of fracture is relevant in many industrial applications such as aeronautics or nuclear plants. Ultrasonic methods based on linear wave scattering are ecient for detecting defects and for characterizing material elasticity, but are less sensitive to micro-cracks or closed cracks. In this context, nonlinear acoustics constitutes a good alternative for detection and evaluation of these defects, taking advantages of the nonlinear behavior of contact dynamics induced by an acoustic wave if its amplitude activates suciently nonlinear contact behavior. In order to exploit nonlinear effects (harmonic generation, DC-effect, nonlinear wave mixing…) it is essential to understand the complex interactions between waves and contact interfaces. To do that, the association of different models (analytical and numerical FE models) including specific algorithm for contact treatment and experiments are achieved. Interactions between bulk waves and contact interfaces [Meziane et. al. JASA 2011, Blanloeuil et. al., JASA, 2014], closed cracks [Blanloeuil et. al., Wave Motion, 2014] are intensively investigated in order to develop methodology based on nonlinear acoustics to quantitatively evaluate contact interface properties [Saidoun et. al., submitted in Wave Motion in 2019].