

Lamb Wave Interaction with a T-Joint
Abstract
An experiment was conducted to improve understanding of Lamb waves interacting with a T-joint on a plate fabricated from T-6061 aluminum for the purposes of structural health monitoring (SHM). The shape of the test article, similar to the orthogonality symbol (â”´), geometrically represents the complexity of many rib-like aircraft components. A small piezoceramic sensor, placed on the horizontal section of the structure, was used to generate Lamb waves at frequencies ranging from 100 to 300 kHz. A three-dimensional (3D) scanning laser Doppler vibrometer (LDV) system was used to measure the elastic wave interaction providing both in- and out-of-plane velocities. The scan grid, consisting of approximately 25,000 points at 1 mm spacing covered the front and back of the horizontal and vertical sections. The goal of this research was to measure how the wave's response to rapid changes in material thickness. Results clearly show the waves dividing into separate components as they travelled through the remaining sections of the structure and lower amplitude wave components reflecting back towards the sensor. A composite scan was also created by combining data from the top and bottom horizontal face of the structure to evaluate the symmetric and antisymmetric behavior of Lamb waves. Results shed light on the usefulness of Lamb wave investigative techniques in geometrically complex structures.