Effects and Uses of Membrane Loads in Structural Dynamics - More than Frequency Shifts!

Professor George A. Lesieutre, Aerospace Engineering, Penn State University

The primary effects of in-plane loads on the linear dynamics of flexural structures (beams, plates, shells) are generally considered to be changes in the natural frequencies (and mode shapes) of the structures. This can be qualitatively understood by analogy with the behavior of a string in tension. Such behavior can be exploited in the development of, for example, tunable transducers. Other effects of these membrane loads, however, are not as widely appreciated. This talk will describe a couple of these effects and their potential uses in aerospace applications. For instance, such loads can change the damping observed in various modes of structural vibration. This effect can be considerable in applications such as pressurized aircraft fuselages or spinning rotor blades. An additional effect is specialized to piezoelectric structures - structures in which electrical and mechanical behavior are intimately coupled. In this case, membrane loads are found to influence the apparent strength of the system electromechanical coupling coefficient. In principle, these coupling coefficients can exceed those of the piezoelectric material, and even approach the ideal of perfect energy conversion! This effect of membrane loads has potential applications to actuators and sensors: for flight control of micro air vehicles, for active Gurney flaps on helicopter blades, and for energy-harvesting devices.