Guided Wave Tomography for Corrosion Monitoring in Planar Structures

International audienceGuided wave tomography offers a quantitative and very robust way of monitoring corrosion in planar structures. We explore here different tomography algorithms and compare their performances to reconstruct an extended area of corrosion (represented by a continuous thickness reduction) in an aluminum plate. These studies are performed on both experimental and simulated data. Simple tomography algorithms, such as SART, are based on a straight ray propagation assumption and requires the determination of the time of flight between all the couples of the sensor's distribution around the monitored area. However, in practice, refraction caused by the defect must be taken into account which is done by allowing a curvature of the rays (bent-ray algorithm). A recent algorithm, called HARBUT, can deal with the diffraction phenomena, but requires not only the time of flight but the whole signal between the different couples of transducers. The range of validity of these imaging algorithms (e.g. with respect to Born approximation) are explored using simulations performed with a spectral finite element formulation offered within CIVA simulation platform developed at CEA. Practical recommendations are given on the inspection intervals, based on the expected corrosion increasing rate, in order to maximize the quality of the reconstruction. Tomographic reconstructions based on experimental results are also presented