An approach towards a baseline-free technique for damage detection utilising advances in 3D laser vibrometry

Lamb wave based detection techniques have received a lot of attention over the past twenty years. Many of these techniques utilise a baseline data subtraction method to evaluate the presence of mechanical damage in plate and shell components. In this subtraction method, the baseline signal previously recorded for a defect-free structure is compared or subtracted with the signal during damage inspections. A significant difference between these signals, which depends on the particular application, is treated as the presence of critical damage. However, the accuracy of this method can be significantly compromised by various changes in Lamb wave propagation characteristics, which can be associated with temperature variations, degradation of material, PZT and adhesive properties. In the proposed technique, 3D Laser Vibrometery (3D LV), in conjunction with explicit FE modelling of guided waves, are utilised to compensate all variations and degradation effects, and to produce the baseline signal for the current conditions. The paper describes a virtual implementation of this technique for a simple beam structure and 1D wave propagation. Future work will be directed to implement this technology to 2D and 3D structures as well as to practically important situations.