Damage size characterization algorithm for active structural health monitoring using the A0 mode of Lamb waves

In this study, a damage size characterization algorithm has been developed to continuously obtain the extent of damage, which is vital for further investigations into the remaining life or residual strength of damaged structures. This technique uses an active PZT network with pulse-echo and pitch-catch configurations. In order to facilitate the identification of scattered wave components, a dual-PZT actuation scheme was applied to generate a comparatively pure A(0) mode with an enhanced energy. The damage size characterization algorithm starts by identifying the damage location. To this end, relying on temporal information of the scattered signal, a diagnostic image was constructed to highlight the most probable location of damage. Then, as wave scattering occurs from the edges of damage sites, for each sensing path the most probable location of the wave scattering source was estimated and considered as one point on the damage boundary. As a result, the location of some points on the damage boundary are estimated. Since, in practice, the captured signals are usually polluted with noise, a data processing scheme was used to separate points correctly located on the damage boundary from those related to noise. Finally, a convex hull of selected points gives the approximate shape and size of the damage. The approach was validated by defining the location, size and shape of corrosion at its earliest stage of existence. Corrosion severity was also evaluated by obtaining reflection and transmission coefficients, subject to corrosion with different depths. The obtained experimental results demonstrated the potential of the algorithm in providing detailed information about the damage, such as its location, size, shape and severity.