The development of a new technology for the manufacturing of adaptive structures on the basis of thin monolithic peizoceramic wafers is an important goal of the German industrial project 'Adaptronik'. Partners from automotive-, space-, medical-, engineering- and optical industry participate in this project to enable new adaptive solutions for their applications. Due to the extreme brittleness of the piezoceramic material the manufacturing of these structures is still very demanding. Very often cracks in the piezoceramic material make the structure useless. This problem becomes serious when large scale structures with many actuators and sensor are considered. To come to more reliable results the use of encapsulated piezoceramic actuators and sensor came into focus. With respect to the great variety of different requirements given by the industrial partners the use of standardized solutions was not feasible. The goal was to develop new elements with improved performance parameters that can easily be adapted to different applications. Due to a modular concept, the developed multifunctional elements can be designed to meet a great variety of different structures was developed. A first step to adapt this technology to prototype structures has been done by the development of special encapsulated patches for an adaptive lightweight satellite mirror.
Future scientific space missions based on interferometric optical and infrared astronomical instruments are currently under development in the United States as well as in Europe. These instruments require optical path length accuracy in the order of a few nanometers across structural dimensions of several meters. This puts extreme demands on static and dynamic structural stability. It is expected that actively controlled, adaptive structures will increasingly have to be used for these satellite applications to overcome the limits of passive structural accuracy. Based on the evaluation of different piezo-active concepts presented two years ago analysis and design of an adaptive lightweight satellite mirror primarily made of carbon-fiber reinforced plastic with embedded piezoceramic actuators for shape control is being described. Simulation of global mirror performance takes different wavefront-sensors and controls for several cases of loading into account. In addition extensive finite-element optimization of various structural details has been performed. Local material properties of sub-assemblies or geometry effects at the edges of the structure are investigated with respect to their impact on mirror performance. One important result of the analysis was the lay-out of actuator arrays consisting of specifically designed and custom made piezoceramic actuators. Prototype manufacturing and testing of active sub-components is described in detail. The results obtained served as a basis for a final update of finite-element models. The paper concludes with an outline on manufacturing, testing, and space qualification of the prototype demonstrator of an actively controllable lightweight satellite mirror currently under way. The research work presented in this paper is part of the German industrial research project 'ADAPTRONIK'.
Up to now all mirrors verified and flown in interferometric optical and IR astronomic instruments on space missions documented in the literature have been passive systems. Preliminary investigations have shown that requirements of future systems like a significant reduction in mass while maintaining optical quality or an increase of optical quality at constant mass, as well as realization of mirrors with several meters in diameter while meeting all requirements for modern satellite systems can only be achieved by active shape control of the optical surface.
Structural fin or wing vibrations are observed on high performance aircraft when flying at high angles of attach. The severity of the so-called buffeting vibration depends on the aircraft configuration and aerodynamic optimization of the configuration. The vibrations are caused by flow fluctuations resulting from flow separation at wings or from bursting of wing leading edge and front fuselage vortices. The resulting dynamic loads with maneuver loads lead to increased material fatigue and may require an augmented effort in aircraft maintenance.
One of the most innovative concepts for active fin-buffet alleviation in vertical tail aircraft is the use of piezoelectric patch actuators distributed across the tail surface to actively induce a counter-strain into the structure. This concept involves the development of a novel material compound structure consisting of a fiber-composite aircraft skin, a ceramic patch actuator and the bonding layer between both components. This actively controllable structure has to provide enough authority to dampen the fin- buffet vibrations. It also has to function reliably during long-term aircraft operation under severe mechanical and environmental load conditions.
Introduction of new technologies to aerospace applications necessarily requires methods of non-destructive testing suitable to evaluate structural integrity. This important task also occurred when it was decided to develop and manufacture a large Fin-Box-Demonstrator equivalent to a fighter aircraft tail equipped with surface bonded piezoceramic actuators between DaimlerChrysler Aerospace - Military Aircraft Division and DaimlerChrysler Research and Technology. The objective of this project is to prove that structural vibrations of a fighter aircraft tail fin due to buffeting can be damped actively by means of surface bonded piezoceramic actuators.
Up to now experimental and theoretical research on active structures for aerospace applications has put the focus mainly on surface bonded actuators. Simultaneously peizoceramics became the major type of actuating device being investigated for smart structures.In this context various techniques of insulating, bonding and operating these actuators have been developed. However, especially with regard to actuators only a few investigations have dealt with embedding of these components into the load bearing structure so far. With increasing shares of fiber- reinforced plastics applied in aerospace products the option of integrating the actuation capability into the components should be reconsidered during the design process. This paper deals with different aspects related to the integration of piezoceramic actuators into fiber reinforced aerospace structures. An outline of the basic possibilities of either bonding an actuator to the structure's surface or embedding it into the composite is given while the emphasis is put on different aspects related to the latter technology. Subsequently recent efforts at Daimler-Benz Aerospace Dornier concerning aircraft components with surface bonded actuators are presented. Design considerations regarding embedded piezoceramic actuators are discussed. Finally some techniques of non-destructive testing applicable to structures with surface bonded as well as embedded piezoelectric actuators are described.
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