Multifunctional design has evolved over the past decade, moving away from discrete unifunctional subsystems with clearly defined boundaries, to produce systems design and materials design methods that blend performance in new and innovative ways. This presentation looks at the development of multifunctional design from a systems and a materials perspecitve. A classification of multifunctional desings is presented, in terms of the decreasing scales at which the boundaries of subsystems, components and material are blurred. Guidelines for identifying multifunctional opportunities at the system and material scale are also discussed.
In multifunctional material design, two or more functions performed by distinct system components or materials are incorporated into a single component or material system to improve system performance. The aim of this paper is to present a framework for the design of structure-battery (power) multifunctional composite materials for unmanned air vehicle (UAV) applications. The design methodology is based on optimization of composite material performance indices and the use of material design selection charts introduced by Ashby and coworkers in a series of papers for homogeneous and two-phase composite materials. Performance indices are derived for prismatic structure-battery composites under various loading conditions. The development of simple design tools in the form of spreadsheet templates is also discussed. Finally, results based on the above-mentioned framework and actual material properties will be presented for structure-battery circular and square struts.
This paper presents multifunctional structure-plus-power developments being pursued under DARPA sponsorship with the focus on structure-battery components for unmanned air vehicles (UAV). New design strategies, analysis methods, performance indices, and prototypes for multifunctional structure-battery materials are described along with the development of two UAV prototypes with structure-battery implementation.
Finite element analysis was performed on the preliminary design of a multilayered composite panel for acoustic suppression. The panel design features a circuit board, alumina and circuit board base layer structure. An square array of 64 piezoelectric actuators is mounted on this base. These actuators are divided into 16 groups of four actuators by 16 alumina cap plates. A thin kapton layer is placed over the cap layer. The final top layer and the area between actuators are a polymer filler material. Unit cell analysis of the design was performed to evaluate the effectiveness of the embedded actuators in producing surface deformations, the stresses generated in the actuator during actuation and the role of a thin glue layer, between the actuator and alumina cap plate, in mitigating high stresses. The results show that the cap plates become curved during deformation. This deformation is transmitted through the top polymer layer to the surface. This suggests that the effect of this surface profile on acoustic fields generated by the actuator array motion should be understood. Stresses in the actuator are found to be high without the glue layer, compared to known critical fracture stress values. Inclusion of the glue layer significantly reduced the stresses and is therefore an important consideration in the design.
In this paper we are concerned with Smart Materials that contain many actuators and sensors along with digital signal processing electronics that allow for the implementation of a control algorithm. Smart Materials have been proposed for the active control of sound from a vibrating structure. Here we investigate the design of structural control systems for these Smart Structures for noise suppression. First we model the radiated acoustic waves in terms of the velocity of the surface of the structure. Then we formulate an optimal control problem as a linear system that has a transmission zero in the path between the disturbance force and the shape that radiates best.
The displacement performance of individual actuators is well documented. In a multiple actuator composite plate, the individual addressing of actuators, or small groupings of actuators, will result in a global displacement profile which may or may not be similar to the displacement predicted based on the performance of a single actuator. The purpose of this computational study is to determine the displacement performance of a composite plate which includes multiple ceramic actuators. Stresses and displacements resulting from the application to individual actuators of a electrical field of 0.2 MV/m are determined. Differences in displacement performance based on base plate material, support conditions and location in the array are determined.
KEYWORDS: Actuators, Sensors, Control systems, Control systems design, Finite element methods, Bridges, Wheatstone bridges, Resistance, Feedback control, Systems modeling
While the phenomenon of shifts in the poles of flexible structures caused by local stiffening due to bonded piezoceramic actuators is well documentated, shifts in the zeros associated with the distorted mode shapes due to localized stiffening has yet to be investigated. The finite element method in conjunction with state space models was used to derive transfer functions for both collocated and noncollocated sensor/actuator pairs. Models that considered the mode shape distortions compared favorably with experimental measurements. With the numerical models validated by experiments, state variable feedback control gains were determined using linear quadratic regulator design for noncollocated and collocated sensor/actuator pairs for the cases of classical mode shapes and distorted mode shapes. It is demonstrated that lack of consideration of distorted mode shapes can lead to a loss of performance of the control systems.
Dose gradients in large mirror substrates due to unequal exposure to the natural space radiation environment have been calculated for two circular orbits: 1200 km altitude/98 deg inclination and 3700 km/30 deg. Dose gradients were translated to density-change profiles based on experimentally determined density changes as a function of dose for fused silica and the low-CTE glass ceramic, Zerodur-M. Finite element analysis of deformation due to the radiation-induced density gradient was performed for a 4 meter by 0.5 cm disk representing a mirror faceplate. Displacements of nearly 2500 micrometers at the outer edge were calculated for a Zerodur faceplate after 10 yr at 3700 km/30 deg. Silica, which is much less sensitive, deformed by only a few angstroms. Reinforcement with a backing having the equivalent stiffness of 5 cm of SiC resulted in a 10-fold decrease in the calculated deformation.
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