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smart structures and materials 1995: smart structures and Integrated Systems

作者： Ben-Zeev, Oren Chopra, Inderjit Univ. of Maryland/Coll. Park Coll. Park MD USA

ISBN: (纸本)0819417920

The continued development of a Froude-Scale helicopter rotor model featuring a trailing-edge flap driven by piezoceramic bimorph actuators for active vibration suppression is discussed. Block force and stroke of the current actuators are evaluated using two theories and compared with experimental results. Dynamic performance of the actuator as well as the actuator-flap assembly are examined. Earlier hover tests have shown severe degradation in flap deflections with increasing rotor speed, and flap deflections were too small to be effectively utilized for significant vibration control. To investigate the causes of the performance degradation, new blades are constructed and tested in-vacuo to isolate the effects of centrifugal loading on the actuator-flap system. A beam model of the piezo bimorph including propeller moment effects is formulated to better illustrate the physical mechanisms affecting the system in a rotating environment. The cause of the reduced deflections is traced to frictional forces created at the junction where the flap is supported during rotation of the blades. The use of a thrust bearing was found to alleviate this problem and subsequent tests on a hover stand showed a dramatic increase in flap detection at high excitation frequencies.

关键词： Helicopter rotors

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Nonlinear analysis of composite strength loss due to embedded ductile metal coated optical fiber sensors

Nonlinear analysis of composite strength loss due to embedde...

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smart structures and materials 1995: mathematics and control in smart structures

作者： Sirkis, James S. Grande, R. Univ. of Maryland/Coll. Park Coll. Park MD USA

ISBN: (纸本)0819417912

The great many advantages to using composite materials in structural applications are often overshadowed by the fact that composites possess relatively low impact resistance and the fact that the damage from impacts is often at a location that makes detection difficult and costly. An inexpensive and reliable method of detecting location and severity of damage in composites would be of great benefit. Embedded optical fibers have previously been used to detect damage using an optical fiber fracture concept, where the optical fiber is intended to fracture at the load that causes damage to the composite host, which in turn prevents light from being transmitted through the fiber. Untreated optical fibers have been embedded in composites subject to loading for this purpose, and the strengths of the optical fibers were found to be such that only severe damage could be detected. To tailor the sensitivity of the fiber, an etching technique was developed to predispose optical fibers to break at a known load. Ductile metallic coated fibers have been suggested as a potential alternative to fiber breakage-type damage sensors, where permanent deformation in the coating is used as a metric of thermal or mechanical overloads. One possible advantage offered by this configuration over etched fibers is that the information includes more than just binary (go or no go) data. The actual magnitude of the event may be recoverable from the residual strain data. If the metal coated optical fiber sensor concept proves feasible for damage detection, then the mechanical and physical attributes that are desirable in a coating must be determined. Sirkis and Dasgupta used non-linear analytical techniques to investigate behavior of a metal coated fiber (not embedded) subjected to axial tension and uniform thermal loading, and found that the concept was feasible. Chang and Sirkis then tested this type of sensor in uniaxial tension and by embedding them in graphite/epoxy plates subjected to impact lo

关键词： structures (built objects)

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Preisach modeling and compensation for smart material hysteresis

Preisach modeling and compensation for smart material hyster...

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Active materials and smart structures

作者： Hughes, Declan C. Wen, John T. Rensselaer Polytechnic Inst. Troy NY USA

ISBN: (纸本)0819417750

Many of the smart materials being investigated (e.g., Shape Memory Alloys (SMAs), piezoceramics, and magnetostrictives) exhibit significant hysteresis effects, especially when driven with large control signals. In this paper the similarity between the microscopic domain kinematics that generate static hysteresis effects, or ferromagnetics, piezoceramics and SMAs is noted. The Preisach independent domain hysteresis model, and its derivatives, have been shown to be a comprehensive class of hysteresis operator that captures the major features of ferromagnetic hysteresis, and hence it is proposed here as a suitable model for piezoceramic and SMA hysteresis also. This basic Preisach model is used to model piezoceramic sheet actuators bonded to a flexible aluminum beam, and a Nitinol SMA wire muscle that applies a bending force to the end of the beam. A numerical inverse Preisach hysteresis series compensator is also proposed and applied in a real time experiment thereby reducing the apparent nonlinear hysteresis effects for the piezoceramic actuator quasi-static case.

关键词： Intelligent materials

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Optimization of unsymmetric actuators for maximum panel deflection control

Optimization of unsymmetric actuators for maximum panel defl...

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smart structures and materials 1995: smart structures and Integrated Systems

作者： Leeks, Tamara J. Weisshaar, Terrence A. Purdue Univ. West Lafayette IN USA

ISBN: (纸本)0819417920

Bending a thin flat panel on an aerodynamic surface using piezoelectric actuators has been proposed to control phenomena such as flutter, sing divergence and transonic drag. Such smart material applications are not feasible unless actuators can produce larger panel bending deflections than are presently predicted. The objective of this study is to maximize bending deflection of a flat, rectangular panel by attaching a thin piezoelectric actuators to one side of the panel. Two optimization cases are considered: (a) the rectangular actuator is mounted in the center of the panel surface and has area and thickness as design variables;(b) the rectangular actuator is composed of two stacked layers, each having an independent design thickness and area. Studies are presented for different panel aspect ratios for simply supported and clamped (fixed) boundary conditions, and for aluminum and steel host panels. The results show that, for a simply supported aluminum panel with an aspect ratio of 1.5, the best single thickness PZT actuator has a thickness of 0.634 of the host panel and covers 64.7% of the panel. For the two layer stacked actuator, one PZT layer has a thickness ratio of 0.391 and covers 70.6% of the panel, while the other layer has a thickness ratio of 0.313 and covers only 35.7% of the panel. Both of these configurations create nearly identical panel center deflections, but the two layer design weighs slightly less. This study also indicates that formal optimization is a necessary tool for actuator design and that shaped actuators can save weight.

关键词： Actuators

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Review of embedded particle tagging methods for nondestructive evaluation (NDE) of composite materials and structures

Review of embedded particle tagging methods for nondestructi...

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smart structures and materials 1995: smart Sensing, Processing, and Instrumentation

作者： Zhou, Su-Wei Chaudhry, Zaffir A. Rogers, Craig A. Quattrone, Robert Virginia Polytechnic Inst. and State Univ. Blacksburg VA USA

ISBN: (纸本)0819417939

Acceptance of advanced composites in both retrofit applications and new construction necessitates quality control (QC)/quality assurance (QA) and in-service monitoring techniques to ensure the performance and serviceability of the composites. A technology that enhances the inspectability of the advanced composites is the particle tagging method. The concept of particle tagging involves embedding micron-sized particles into materials, such as composites, or adhesive layers to make them an integral part of the host material. When interrogated by suitable instrumentation, the embedded particle sensors interact with their host material and generate certain types of measurable signatures. The signatures can be correlated with the material and structural conditions, such as internal stress states, voids, inclusions, state-of-cure, and delaminations. This paper presents a technology assessment of the current and emerging state-of-the- art tagging methods. The objective of this review is to provide a framework for further understanding the physics and mechanisms involved in using the tagging method for in-field nondestructive evaluation (NDE) of composite materials. Information concerning the development of this technique has been obtained from patents, publications, databases within Newman Library at Virginia Polytechnic Institute and State University (Virginia Tech), and previous work and in-progress research at the Center for Intelligent Material Systems and structures (CIMSS) at Virginia Tech. This paper includes a historic review of tagging techniques, a description of the tagging systems used for in-situ NDE of composites, and experimental results to date. The current and potential applications of this technique are also addressed. The analysis presented in this paper will assist in further efforts to develop the tagging approach that may be used as a new NDE technique for quality assurance of advanced composites.

关键词： Composite materials

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Precision position-control of piezoelectric actuators using charge feedback

Precision position-control of piezoelectric actuators using ...

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smart structures and materials 1995: smart materials

作者： Main, John A. Garcia, Ephrahim Newton, David V. Vanderbilt Univ. Nashville TN USA

ISBN: (纸本)0819417904

The issue of precision position control is critical if piezoelectric actuator technology is to be applied in increasingly demanding applications. In one particular application, the NASA NAOMI project, piezoelectric actuators have been proposed as the pointing and focusing elements for thousands of small mirror-lenslets because of their fast response time and load-carrying ability. In this application the positions of these actuators must be precisely controlled both statically and dynamically to the nanometer level. This requirement necessitates a careful study of the concept and design of the driving electronics of the system. This paper is focused on finding an appropriate method for driving piezoelectric stack actuators for ultraprecision position and motion control. In this paper the theoretical basis of the electrical control of piezoelectric stack actuators is derived using the fundamental physical laws governing dielectrics and piezoceramics. It is shown that the relationships used for voltage control of piezoelectric actuators result from an approximation of the constitutive equations. An exact input/output relationship for piezoelectric actuators is derived and shows that displacement relies fundamentally on charge, not voltage. Experimental verification was obtained to illustrate the differences between driving piezoactuators with voltage control and charge control.

关键词： Position control

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Comparison of a new rapid convergent adaptive control algorithm to least mean square on an active noise control system

Comparison of a new rapid convergent adaptive control algori...

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smart structures and materials 1995: smart Sensing, Processing, and Instrumentation

作者： Koshigoe, Shozo Gordon, Alan Teagle, Allen Tsay, Ching-Hsu The Aerospace Corp. El Segundo CA USA

ISBN: (纸本)0819417939

In this paper, an efficient rapid convergent control algorithm will be developed and will be compared with other adaptive control algorithms using an experimental active noise control system. Other control algorithms are Widrow's finite impulse response adaptive control algorithm, and a modified Godard's algorithm. Comparisons of the random noise attenuation capability, transient and convergence performance, and computational requirements of each algorithm will be made as the order of the controller and relevant convergence parameters are varied. The system used for these experiments is a test bed of noise suppression technology for expendable launch vehicles. It consists of a flexible plate backed by a rigid cavity. Piezoelectric actuators are mounted on the plate and polyvinylidene fluoride is used both for microphones and pressure sensors within the cavity. The plate is bombarded with an amplified random noise signal, and the control system is used to suppress the noise inside the cavity generated by the outside sound source.

关键词： Acoustic noise

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Experiences with integral microelectronics on smart structures for space

Experiences with integral microelectronics on smart structur...

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smart structures and materials 1995: smart Electronics

作者： Nye, Ted Casteel, Scott Navarro, Sergio A. Kraml, Bob TRW Inc. Redondo Beach CA USA

ISBN: (纸本)0819417971

One feature of a smart structure implies that some computational and signal processing capability can be performed at a local level, perhaps integral to the controlled structure. This requires electronics with a minimal mechanical influence regarding structural stiffening, heat dissipation, weight, and electrical interface connectivity. The Advanced controls Technology Experiment II (ACTEX II) space-flight experiments implemented such a local control electronics scheme by utilizing composite smart members with integral processing electronics. These microelectronics, tested to MIL-STD-883B levels, were fabricated with conventional thick film on ceramic multichip module techniques. Kovar housings and aluminum-kapton multilayer insulation was used to protect against harsh space radiation and thermal environments. Development and acceptance testing showed the electronics design was extremely robust, operating in vacuum and at temperature range with minimal gain variations occurring just above room temperatures. Four electronics modules, used for the flight hardware configuration, were connected by a RS-485 2 Mbit per second serial data bus. The data bus was controlled by Actel field programmable gate arrays arranged in a single master, four slave configuration. An Intel 80C196KD microprocessor was chosen as the digital compensator in each controller. It was used to apply a series of selectable biquad filters, implemented via Delta Transforms. Instability in any compensator was expected to appear as large amplitude oscillations in the deployed structure. Thus, over-vibration detection circuitry with automatic output isolation was incorporated into the design. This was not used however, since during experiment integration and test, intentionally induced compensator instabilities resulted in benign mechanical oscillation symptoms. Not too surprisingly, it was determined that instabilities were most detectable by large temperature increases in the electronics, typically not

关键词： Microelectronics

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Dynamic response of structures constructed from smart materials

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smart materials and structures 1995年第1 A期4卷 A101-A106页

作者： Caughey, T.K. California Inst of Technology Pasadena United States

The Dynamic analysis of structures constructed of homogeneous smart materials is greatly simplified by the observation that the eigenfunctions of such structures are identical to those of the same structures constructed entirely of purely elastic materials. The dynamic analysis of such structures is thus reduced to the analysis of the temporal behaviour of the eigenmodes of the structure. The theory is illustrated for both continuous and discrete structures using the generalization of 'positive position feedback' to distributed control.

关键词： Dynamic response

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Spatial compensator design for active vibration damping with links to temporal compensator design

Spatial compensator design for active vibration damping with...

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smart structures and materials 1995: smart structures and Integrated Systems

作者： Meyer, John E. Burke, Shawn E. Failure Analysis Associates Inc. Menlo Park CA USA

ISBN: (纸本)0819417920

A technique for spatial compensator design is developed for the active vibration damping of interconnected flexible structures. Spatially gain weighted distributed transducers are utilized in order to `shape' the system's forward-loop transfer function, thereby increasing control effectiveness by increasing loop gain over a specified bandwidth. Colocated transducer locations and spatial distributions are chosen to shape the system's loop transfer function, making modal coefficients `large' within the control bandwidth, and `small' for higher frequency modes of vibration while remaining simple to implement in hardware. Temporal compensator design is linked to spatial compensator design by showing the dependency of the maximum velocity feedback gain on transducer modal coefficients. Closed-loop control experiments were performed in order to demonstrate the utility of the compensator design technique on a dynamically complex, interconnected structure: a 56' by 59' nine-bay aluminum grillage. A velocity feedback dissipative temporal compensator design was evaluated. For a band-limited transient disturbance exciting the first twelve modes of vibration (up to 40 Hz), the experiment showed a decrease in settling time from over 30 seconds to less than 8 seconds. For a band-limited stochastic input with a 2 - 22 Hz bandwidth, disturbance attenuation up to 8 dB was shown. In order to assess the model robustness of the compensator design, modifications were made to the experimental plant, changing plant natural frequencies up to 21.2%. Without changing the temporal compensator used in the previous tests, similar closed-loop vibration damping performance was observed, exhibiting significant compensator robustness to plant variations.

关键词： Vibration control

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