SMART STRUCTURES

AND MATERIALS

Smart materials and adaptive structures refer to those types of materials and structural systems that can either actuate or sense motion or displacement and can then change their behavior according to specific design constraints. Most of our studies have focused on coupled-field materials such as piezoelectric solids or magnetostrictive elements. These materials have coupled-field behavior through their constitutive laws, and possess a number of interesting physical features and computational challenges, especially when applied to unusual materials such as wood.

Our efforts to date have been directed toward obtaining exact and more robust approximate models for laminated adaptive media. Of primary interest is the through-thickness behavior of the elastic, electric, and magnetic fields under static and free vibration behavior. Our exact solutions must satisfy the equations of motion, Gauss's law, and Gauss's law for magnetics along with the boundary conditions on the laminae edges and surfaces and the interface conditions between layers. Our approximate models are based on discrete-layer beam, plate, and shell models that solve the weak form of these governing equations and the boundary conditions in an integral sense.

Past and current sponsors of this work include NASA-Lewis Research Center and the United States Department of Agriculture. Our research team includes Professor Dimitris Saravanos (University of Patras, Greece), Dr. Ernian Pan (Unmiversity of Akron), Mr. Fernando Ramirez (CSU), and Professor Paul Heyliger (CSU).

The above laminate is a typical adaptive composite, possessing outer layers of the piezoelectric barium titanate and an inner core of the magnetostrictive cobalt ferrite. The composite responds to both electric and magnetic field through a product property quantified by the constitutive laws of the two constituent materials in the composite. With its specific color scheme and unique coupled properties, this material is known as a ``Raminate''.
Electric displacement and magnetic flux are two of the secondary variables (along with elastic stress) that allow us to quantify the behavior of this class of composite. In this figure, the through-thickness component of the magnetic flux vector is shown for a 2-layer hybrid laminate under applied surface magnetic potential. The top layer is not magnetostrictive, and hence has a very simple linear behavior through the thickness. The lower layer of cobalt ferrite has a much stronger nonlinear response behavior. Shown here is the exact solution comapred with a discrete-layer model using a varying number of mathematical layers to describe the laminate fields.