Determination of acousto-ultrasonic wave propagation in an isotropic aluminium Al6082-T6 plate

Abstract

Abstract The ability to guarantee reliable and damage-tolerant operation of structures is critical to their safe operation. Various non-destructive evaluation (NDE) techniques, such as ultrasonics, acoustic emission, thermography, acousto-ultrasonics (AU), among others could potentially provide a means of inspecting cracks, defects and damage responses in structures. The main aim of this study is to look into the physical problem of AU wave propagation through an isotropic plate and its analytical validation, using wave dispersion concept. The experimental investigation was conducted on aluminium Al6082-T6 alloy plate specimen. Wave propagation speed on top and bottom surfaces of the plate was investigated. The variation of the wave speed and attenuation with frequency were identified. From the results obtained experimentally, the wave dispersion was verified analytically. Interestingly, Lamb waves were discovered to be the dominating AU waves. The wave was appreciably non-dispersive in the frequency extent from 150 kHz to 1 MHz and the attenuation coefficient was increased with the frequency. This finding provides a significant breakthrough to the implementation of acousto- ultrasonics in the non- destructive testing applications, such as accessing the damage in composite structures, including wind turbine blades. AU has an active sensing mechanism, providing an edge over acoustic emission (AE) method which is a passive mode of damage sensing and detection, as external loading is needed for the damage sensing.