#### 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.