Non-destructive testing of plates based on the visualisation of Lamb waves by double-pulsed TV holography

We describe a new technique, currently under development, intended to detect the presence of flaws such as cracks and holes in thin-walled mechanical components. This technique combines ultrasonics with optics, both at a low power density, that allows to perform the tests in the non-destructive range. Lamb waves, a kind of surface acoustic waves that propagate in thin plates, are generated to explore metallic samples while double-pulsed TV holography, a whole-field interferometric technique, is used to detect them. This scheme provides maps of the instantaneous surface displacements produced by the waves, where the effects of the flaws can be visualised by contrast against the smooth propagation of the wavefront in defect free plates. Images with reasonable resolution can be achieved almost in real-time. Several examples of detection of typical flaws in plates using the proposed method complete this work.