Intelligent materials are those that exhibit coupling between their electromagnetic response and their thermomechanical response. This coupling allows smart materials to react mechanically (e.g., an induced displacement) to applied electrical or magnetic fields (for instance). These materials find many important applications in sensors, actuators, and transducers.
Recently interest has arisen in the development of smart composites that are formed via the combination of two or more phases, one or more of which is a smart material. To design with and utilize smart composites, designers need theories that predict the coupled smart behavior of these materials from the electromagnetothermoelastic properties of the individual phases. The micromechanics model known as the generalized method of cells (GMC) has recently been extended to provide this important capability (ref. 1). This coupled electromagnetothermoelastic theory has recently been incorporated within NASA Glenn Research Center's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) (ref.2). This software package is user friendly and has many additional features that render it useful as a design and analysis tool for composite materials in general, and with its new capabilities, for smart composites as well.
MAC/GMC prediction compared with experimental results for the
"effective piezoelectric modulus" d*33 = e*3k S*k3,
where Sij are the effective compliance components, of a continuous-fiber PZT-7A/epoxy composite.
Long description
The results shown here were generated to demonstrate and validate the capabilities of the enhanced MAC/GMC code. The preceding figure compares MAC/GMC predictions with experimental results (ref.3) for a PZT-7A/epoxy composite. The simple 2-by-2 GMC repeating unit cell depicted in the figure was employed for the analysis. Clearly, the agreement is good, indicating MAC/GMC's ability to predict the effective piezoelectric properties of smart composites. The next figure highlights MAC/GMC's simulated loading capabilities along with its ability to examine more refined unit cell geometries. The simulated loading is in the form of an applied electric field component, E 3, while all other quantities besides D 3 are held fixed at zero. Results show the amount of mechanical strain that is induced as the electric field is applied. Because of the refined unit cell geometry employed in the simulation, and the fact that the GMC theory provides predictions for the microscale fields within composite materials, the local fields shown in the final figure can be generated. The contour plots shown represent the internal fields that arise at the end of the simulation, when the applied electric field, E 3, reaches 2.0 MV/N. It is important to note that although all global stress components on the composite are zero, MAC/GMC clearly shows that significant stresses arise internally in response to the applied electric field. This microscale capability inherent to GMC also allows the incorporation of submodels within MAC/GMC to represent local phenomena such as damage, interfacial debonding, and viscoplasticity.
MAC/GMC prediction for the mechanical response of 35-vol%
continuous-fiber BaTiO3/CoFe2O4 to the applied electric field loading, E33.
Long description
MAC/GMC prediction for the internal microfields within 35-vol% continuous-fiber
BaTiO3/CoFe2O4 at an applied electric
field load level of E33 = 2.0 MV/m. B3 = magnetic flux,
J2 = sqrt[(3/2)(SijSij)], where Sij = stress deviator components.
Long description
Glenn contact: Dr. Steven M. Arnold, 216-433-3334, Steven.M.Arnold@grc.nasa.gov
Authors: Dr. Brett A. Bednarcyk, Dr. Steven M. Arnold, and Prof. Jacob Aboudi
Headquarters program office: OAT
Programs/Projects: RAC
Last updated: June 2002
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