IWSHM 2017: Damage-scattered wave extraction in an integral stiffened isotropic plate: a baseline-subtraction-free approach

Ultrasonic guided waves enable long-distance inspection of structures for health monitoring purposes. However, this capability is diminished when applied to complex structures where damage-scattered waves are often buried by scattering from various structural components or boundaries in the time–space domain. Here, a baseline-subtraction-free inspection concept based on the Radon transform is proposed to identify and separate these scattered waves from those scattered by damage. The received time–space domain signals can be converted into the Radon domain, in which the scattered signals from structural components are suppressed into relatively small regions such that damage-scattered signals can be identified and extracted. In this study, a piezoelectric wafer and a linear scan via laser Doppler vibrometer were used to excite and acquire the Lamb wave signals in an aluminum plate with multiple stiffeners. Linear and inverse linear Radon transform algorithms were applied to the direct measurements. Currently, this method needs baseline measurements for comparison in the Radon domain, but avoids baseline subtraction. The results demonstrate the effectiveness of the Radon transform as an extraction tool for damage-scattered waves in a stiffened aluminum plate for a damage site in the bay area between two stiffeners and also suggest the possibility of generalizing this technique for application to a wide variety of complex, large-area structures.