Abstract
Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in plates and laminated structures, such as airframe skins, storage tanks and pressure vessels. Their propagation properties in these media depend on the vibrational frequency as well as on the thickness and material properties of the structure. Structural flaws such as disbonds, corrosion and fatigue cracks represent changes in effective thickness and local material properties, and therefore measurement of variations in Lamb wave propagation can be employed to assess the integrity of these structures. In this study, the local phase velocimetry based on the spatio-temporal gradient analysis is derived theoretically. The proposed method has an ability to characterize the phase velocity of the Lamb-wave propagation through the linearity among the 4-dimensional vector which is composed by following components: (1)a vertical (z-directional) displacement, (2)its vertical particle velocity, (3)x-directional and (4)y-directional out-of-plane strains. In this study, the computational process of the local velocimetry is discussed and their physical meanings are investigated through numerical and acoustical experiments.
