Measurement of Thickness of Wall-Thinned Plate using Acoustic Wavenumber Spectroscopy and Spatial Local Wavenumber Filtering

Abstract

The surface of a structure can generate cracks or wall-thinning, due to corrosion. This can eventually lead to the fracture of the structure, which can trigger enormous fatality and property loss. Thereby, a laser imaging technology on such structures as thin plate structure, or piping which thickness is relatively thin in comparison to the area, has been steadily studied for the past 10 years. The most typical among the laser imaging technology is the pulse laser imaging. By using the same, a new technology for inspecting and imaging a desired area within a relatively short period of time was developed, so as to scan various structures including the thin-plate structure and piping. However, this method builds images by measuring waves reflected from defects, and have a time delay of a few milliseconds at each scanning point. Moreover, complexity of the systems is so high due to additional components such as laser focusing parts. This paper proposes laser imaging method with increased scanning speed based on excitation and measurement of standing waves in structures. Wavenumber of standing waves changes at sections with geometrical discontinuity such as thickness. It is shown that defects in a structure can be visualized by generating standing waves with single frequency and scanning the waves at each point by the laser scanning system suggested in this work. The proposed technique is validated by a wall-thinned plate that has a linear thickness variation