A baseline-free SH wave sparse array system for structural health monitoring

Abstract

Guided wave based inspection has been regarded as a promising technique in structural health monitoring (SHM) due to its large coverage area and is thus cost-effective. In the past two decades, Lamb wave based sparse array technologies had been extensively investigated while applications were limited by the inherent multi-mode and dispersion of Lamb waves. Moreover, the baseline-dependent characteristic of conventional sparse array system always has some problems during long-term monitoring because the baseline may change or is not available at all. In this work, we proposed a baseline-free sparse array system for SHM of isotropic plates based on the fundamental shear horizontal (SH0) wave, which is totally non-dispersive. Firstly, the working principle of the sparse array system was introduced. Then the signal processing method was presented. Finally, experiments were carried out to examine its capability in defect localization. Results indicated that the proposed system can detect both surface defects and through-thickness defects effectively at varied frequencies without baseline. Moreover, it has a high resolution and can detect a through-thickness hole as small as 4 mm in diameter (corresponding to 0.17λ where λ is the wavelength) with the location error of about 2.5% (12 mm). Besides, it can also detect multi defects simultaneously. The good performance of the proposed system was benefited from two points. One is the special transducer arrangement which made it possible to extract the scattered waves resulted by defects without baseline; the other is the employed single mode non-dispersive SH0 wave which can greatly decrease the difficulty in signal identification. The proposed baseline-free sparse array system is a promising solution to guided wave based SHM.