On the Opposite Effect Fluid Loading has on the Velocity of Dilatational Waves in Thin Plates and Rods

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Longitudinal guided wave propagation in thin plates and rods is of great practical importance. Such guided modes are commonly used to evaluate the material properties of thin foils and plates, metal wires, optical fibers, and reinforcement filaments used in epoxy, metal, and ceramic matrix composites. The feasibility of using such longitudinal guided waves to evaluate the interface properties between the fiber and the surrounding solid matrix was investigated by both theoretical and experimental means [1,2]. Another interesting application is when an imbedded fiber is used to monitor the properties of the surrounding material during polymerization [3]. In this case, the fiber properties are known and the interface conditions are assumed to be perfect. Any change in the velocity or the attenuation of the guided mode in the fiber can be attributed to the surrounding material that changes from a viscous fluid to an elastic solid during the curing process. Guided modes producing mainly tangential displacement can be readily used to measure fluid viscosity. From this point of view, torsional modes are the best [4, 5], but they are more difficult to generate and detect than extentional modes [6]. Nagy and Kent recently utilized the fundamental symmetric mode in thin wires and fibers to assess their Poisson’s ratio through measuring the leaky attenuation of these modes in such structures [7].