Baseline-free damage imaging technique for Lamb wave based structural health monitoring systems

In Lamb wave based structural health monitoring (SHM) systems, damage scatter signals are usually used for damage identification. Such scatters are obtained by subtracting the current signal from a baseline. However, changes in the environmental condition, particularly temperature, make false scatters in the damage scatter signal. This affects the overall efficiently of the system. To overcome this obstacle, this study proposes a baseline-free damage identification technique. A dual-PZT actuation scheme is applied to generate a comparatively pure A0 mode. A wave velocity determination procedure is then developed to actively determine the velocity of the generated A0 mode in the presence of unmeasured temperature changes. Using a damage scatter separation process, the damage scatter wave is separated from other waves appear in the current signal. Finally, a damage diagnostic image is constructed to illustrate the most probable location of damage. The experimental validation of the developed technique is conducted on two aluminum plates one carrying an L shape crack and the other carrying a hole, subjected to temperatures changes. The experimental results demonstrate the effectiveness of the developed technique for damage identification in the presence of unmeasured temperature. During the proposed procedure no baseline data is used. This bright advantage, qualify the presented technique for practical SHM systems.