Friday, March 8 at 4:10pm
Packard Laboratory, 466
19 Memorial Dr W, Bethlehem, PA 18015
On the Edge: Stories of Stability Lost and Found in Structural Mechanics
Modern engineering structures frequently need to be lightweight; yet, also able to withstand harsh loading environments. These competing requirements can manifest in structures that operate on the edge of stability. Here, we will discuss recent efforts to model and test two such structures.
First, we will consider the peculiar history of fluttering hydrofoils. In the early days of fluid-structure interaction research, there was considerable debate as to whether it is possible for a structure to flutter underwater. A 1965 test demonstrated that flutter of a fully submerged sub-cavitating hydrofoil is indeed possible. However, the test article failed because of the instability, and no subsequent tests on fluttering hydrofoils have been reported. Efforts to model the 1965 test were met with limited success and there remains an unresolved question as to why classical aerodynamic models used with water as the fluid medium either considerably over-predict the flutter speed or fail to predict the flutter phenomenon altogether. With a series of new water tunnel tests and modeling efforts, we are attempting to resolve this long-standing question and uncover the key physical mechanisms responsible for underwater flutter.
Next, we will look at recent efforts involving the use of flexible piezoelectric materials to delay or avoid the onset of snap-through instability. Post-buckled and curved structures experience dramatic snap-through instabilities when external loads from mechanical, fluid, or thermal environments result in a loss of local stability and a jump to a remote stable equilibrium. Fatigue caused by snap-through is a concern in many engineered systems because of the large stress reversals involved. Here, we numerically and experimentally consider the use of piezoelectric materials to either increase critical snap-through loads or invoke stable transitions between remote equilibria in post-buckled beams. This nonlinear electromechanical system is modeled using elastica theory with new extensions to account for the influence of piezoelectric actuation on the structure. Experimental results demonstrate that critical snap-through loads can be altered by factors ranging from 0.4 to 2.0, and numerical results indicate that even larger changes to snap-through loads are physically realizable. Numerical and experimental studies also demonstrate how the use of piezoelectric actuation can stably transition a structure from one post-buckled configuration to another.
Ben Davis joined the faculty of the College of Engineering at the University of Georgia as an Assistant Professor in the fall of 2014. He leads the Dynamic Devices and Solutions Lab, home to the only high-speed water tunnel in the Southeast, and the only such facility dedicated to fluid-structure interaction research. Previously, he worked for six years at NASA as a propulsion structural dynamics and acoustics analyst at the Marshall Space Flight Center. His professional and research expertise span the areas of structural vibration, acoustics, acoustic-structure interaction, nonlinear dynamics, fluid-structure interaction, and elastic stability. He holds a B.S.E. from Duke University, an M.S. from Georgia Tech, and a Ph.D. from Duke University, all in Mechanical Engineering.