Interaction of Lamb mode (Ao) with structural discontinuity and generation of “Turning modes” in a T-joint

In the present work, the interaction of the fundamental anti-symmetric guided Lamb mode (Ao) with a structural discontinuity in a composite structure was studied through Finite Element numerical simulations and experiments. The structural component selected for this study was a T-joint section made from glass/epoxy material. This co-cured composite structure is made-up of an upper shell (skin) and a spar as the sub-components. It was observed that when Ao mode interacts with the junction (structural discontinuity) of these sub-components, a mode-converted So mode is generated. Experiments were conducted using air-coupled ultrasound to validate the numerical simulations. The back-propagating “Turning modes”, which propagate from the thin region to the spar web and vice versa, were also numerically simulated and experimentally verified.

Research highlights
► Interaction of Ao mode with structural discontinuity in a T-joint was studied.
► During the interaction, mode conversion and propagation of Turning modes were observed.
► Amplitude ratios, power transmission and reflection coefficients of Lamb modes were estimated.
► Turning modes and mode conversion phenomenon in NDE/SHM applications were envisaged.