Thesis (M.S.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 27, 2009) Includes bibliographical references (p. 72-74).

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town,1999 / Smart structures technology featuring a network of sensors and actuators, real-time control capabilities, computational capabilities and host material will have tremendous impact upon the design, development and manufacture of the next generation of products in diverse industries. The idea of applying smart materials to mechanical and structural systems has been studied by researchers in various disciplines. Among the promising materials with adaptable properties such as piezoelectric polymers and ceramics, shape memory alloys, electrorheological fluids and optical fibers, piezoelectric materials can be used both as sensors and actuators because of their high direct and converse piezoelectric effects. The advantage of incorporating these special types of material into the structure is that the sensing and actuating mechanism becomes part of the structure by sensing and actuating strains directly. This advantage is especially apparent for structures that are deployed in aerospace and civil engineering. Active control systems that rely on piezoelectric materials are effective in controlling the vibrations of structural elements such as beams, plates and shells. The beam as a fundamental structural element is widely used in all construction. The purpose of the present project is to derive a set of approximate governing equations of smart composite beams. The approximate analytical solution for laminated beams with piezoelectric laminae and its control effect will be also presented. According to the review of the related literature, active vibration control analysis of smart beams subjected to an impulsive loading and a periodic excitation are simulated numerically and tested experimentally.

A dual approach integrating structural tailoring and adaptive materials technology and designed to control the dynamic response of cantilever beams subjected to external excitations is addressed. The cantilevered structure is modeled as a thin-walled beam of arbitrary cross-section and incorporates a number of non-classical effects such as transverse shear, warping restraint, anisotropy of constituent materials and heterogeneity of the construction. Whereas structural tailoring uses the anisotropy properties of advanced composite materials, adaptive materials technology exploits the actuating/sensing capabilities of piezoelectric materials bonded or embedded into the host structure. Various control laws relating the piezoelectrically-induced bending moment with combined kinematical variables characterizing the response at given points of the structure are implemented and their effects on the closed-loop frequencies and dynamic response to external excitations are investigated. The combination of structural tailoring and control by means of adaptive materials proves very effective in damping out vibration. In addition, the influence of a number of non-classical effects characterizing the structural model on the open and closed-loop dynamic responses have been considered and their roles assessed. / Ph. D.

General unsymmetric laminates exhibit large natural curvatures at room temperature. Additionally, inherent to most unsymmetric laminates is the presence of two stable configurations. Multiple configurations and stability issues arise because of the geometric nonlinearities associated with the large curvatures. The laminate can be changed from one stable configuration to the other by a simple snap-through action. This situation offers the opportunity to use shape memory alloys (SMA) attached to the laminate to generate the snap-through forces and change the shape of the laminate on command. Presented is a model which can predict SMA-induced deformations in general unsymmetric laminates and, particularly, the occurrence of the snap through. First, a methodology is developed to predict the deformations of flat general unsymmetric epoxy-matrix composite laminates as they are cooled from their elevated cure temperature. Approximations to the strain fields are used in the expression for the total potential energy, and the Rayleigh-Ritz approach is used to study equilibrium. To further study the laminate deformations, finite-element analyses are performed. Experimental results are presented which confirm the predictions of the developed theory and the finite-element analyses regarding the existence of multiple solutions and the magnitude of the deformations. Results are compared with those of several other investigators. Next, the deformation behavior of general unsymmetric laminates subjected to applied forces is studied. The principle of virtual work is used to derive the equilibrium equations relating the laminate deformations to the applied forces. By solving the equilibrium equations as a function of the force level, relations between the laminate deformations and the applied force are derived, and the force level at which the laminate changes shape is determined. Finally, an existing SMA constitutive model is implemented into the developed theory to predict the deformations of simple structures to SMA-induced forces. Experiments on a narrow aluminium plate with an externally attached SMA actuator are conducted. The experimental results show good agreement with the predictions from the developed theory. Next, the deformation behavior of general unsymmetric laminates subjected to SMA actuators is predicted using the developed theory. Experiments using SMA actuators to generate the snap through of nsymmetric laminates are conducted. Good correlation with the developed theory is obtained. / Ph. D.

Real-time structural integrity monitoring is a concept that is becoming a reality in the engineering community. It will soon be possible for a structure to warn the user when its own structural integrity has been altered. A qualitative impedance-based health monitoring technique, which can be implemented for real-time damage evaluation of complex structures, is investigated. The basic principle of the technique is to monitor the structure's mechanical impedance which will be changed with the presence of damage. The mechanical impedance variations are monitored by measuring the electrical impedance of a bonded piezoelectric actuator/sensor (PZT). This mechanical-electrical impedance relation is due to the electro-mechanical coupling property of piezoelectric materials. This health monitoring technique can be easily adapted to existing structures, since only a small non-intrusive PZT patch is needed. This impedance-based method operates at high frequencies (generally above 100kHz), which enables it to detect incipient type damage in a localized region. The localized sensing region offers the advantage of not being affected by nonnal operating conditions or by changing boundary conditions. In this thesis, a complete theoretical background on the impedance-based technique is derived. Then, the technique is applied successfully to a variety of case studies; such as composite patch repair, aircraft structures, precision parts, and civil infrastructure. By simplifying the impedance measurement interpretation through a simple scalar damage metric, the real-time implementation of the impedance-based technique has been proven feasible. / Master of Science

Smart structures are relevant and significant because of their relevance to phenomena such as hazard mitigation, structural health monitoring and energy saving. Electrical resistance could potentially serve as an indicator of structural well-being or damage in the structure. To this end, the development of a microprocessor-based automated resistance measurement system with customized GUI is desired. In this research, a nodal electrical resistance acquisition circuit (NERAC) system was designed. The system hardware interfaces to a laptop, which houses a customized GUI developed using DAQFactory software. Resistance/impedance was measured using DC/AC methods with four-point probes technique, on three substrates. Baseline reading before damage was noted and compared with the resistance measured after damage. The device was calibrated and validated on three different substrates. Resistance measurements were taken from PVDF samples, composite panels and smart concrete. Results conformed to previous work done on these substrates, validating the effective working of the NERAC device.

As estruturas aeronáuticas estão sujeitas a diversas solicitações, devido principalmente às interações com o escoamento aerodinâmico, que podem causar distúrbios e vibrações, comprometendo seu desempenho. Diversas pesquisas vêm sendo realizadas para solucionar estes problemas. Dentre elas está o uso de atuadores e sensores piezelétricos integrados na estrutura, que juntamente com um sistema de controle passa a ser denominada estrutura inteligente, a qual promove o controle ativo de vibrações garantindo um aumento no desempenho. O objetivo deste trabalho é obter parâmetros ótimos de um controlador não convencional baseado na lógica difusa para controle de vibrações em uma viga com atuadores e sensores piezelétricos. A viga e elementos piezelétricos são modelados pelo método de elementos finitos utilizando o princípio variacional eletromecânico. O sistema de controle difuso, o qual está se tornando amplamente utilizado principalmente devido à sua capacidade de representar sistemas não lineares e complexos, é baseado nos modelos difusos de Mamdani e Takagi-Sugeno-Kang. A otimização é feita através de algoritmo genético que é um processo de procura probabilística baseado nas leis de seleção natural influenciadas pelas teorias de Charles Darwin. São otimizados os valores dos ganhos de controle, bem como os suportes dos conjuntos difusos da base de conhecimento. São feitas comparações com o controlador difuso obtido por processo de ajuste manual. / Aeronautical structures are subject to a variety of loads, due mainly to the iteration with the aerodynamic flow that can present disturbances, compromising their performance. Various researches have been carried out to solve these problems. Among them, the use of piezoelectric actuators and sensors integrated to the structure, jointly with a control system, the so-called smart structure technology, has been seen with good potentiaI. A smart structure promotes active vibration control, guaranteeing a performance increase. The objective of this work is to obtain optimal control parameters of a non-conventional vibration controller based on the fuzzy logic. A smart beam with piezoelectric actuators and sensors, that has been modeled by the finite element method, has been used to controI. The fuzzy control, which is becoming broadly utilized, mainly due to its capacity to represent complex and non-linear systems, is based in Mamdani and Takagi-Sugeno-Kang fuzzy models. The optimization scheme is based on genetic algorithms, a methodology inspired on the natural selection laws influenced by the Darwin\'s theories. Gains values and membership functions are optimized. Comparisons with the fuzzy controller achieved by trial and error parameters tuning are presented.

As estruturas aeronáuticas estão sujeitas a diversas solicitações, devido principalmente às interações com o escoamento aerodinâmico, que podem causar distúrbios e vibrações, comprometendo seu desempenho. Diversas pesquisas vêm sendo realizadas para solucionar estes problemas. Dentre elas está o uso de atuadores e sensores piezelétricos integrados na estrutura, que juntamente com um sistema de controle passa a ser denominada estrutura inteligente, a qual promove o controle ativo de vibrações garantindo um aumento no desempenho. O objetivo deste trabalho é obter parâmetros ótimos de um controlador não convencional baseado na lógica difusa para controle de vibrações em uma viga com atuadores e sensores piezelétricos. A viga e elementos piezelétricos são modelados pelo método de elementos finitos utilizando o princípio variacional eletromecânico. O sistema de controle difuso, o qual está se tornando amplamente utilizado principalmente devido à sua capacidade de representar sistemas não lineares e complexos, é baseado nos modelos difusos de Mamdani e Takagi-Sugeno-Kang. A otimização é feita através de algoritmo genético que é um processo de procura probabilística baseado nas leis de seleção natural influenciadas pelas teorias de Charles Darwin. São otimizados os valores dos ganhos de controle, bem como os suportes dos conjuntos difusos da base de conhecimento. São feitas comparações com o controlador difuso obtido por processo de ajuste manual. / Aeronautical structures are subject to a variety of loads, due mainly to the iteration with the aerodynamic flow that can present disturbances, compromising their performance. Various researches have been carried out to solve these problems. Among them, the use of piezoelectric actuators and sensors integrated to the structure, jointly with a control system, the so-called smart structure technology, has been seen with good potentiaI. A smart structure promotes active vibration control, guaranteeing a performance increase. The objective of this work is to obtain optimal control parameters of a non-conventional vibration controller based on the fuzzy logic. A smart beam with piezoelectric actuators and sensors, that has been modeled by the finite element method, has been used to controI. The fuzzy control, which is becoming broadly utilized, mainly due to its capacity to represent complex and non-linear systems, is based in Mamdani and Takagi-Sugeno-Kang fuzzy models. The optimization scheme is based on genetic algorithms, a methodology inspired on the natural selection laws influenced by the Darwin\'s theories. Gains values and membership functions are optimized. Comparisons with the fuzzy controller achieved by trial and error parameters tuning are presented.

This research presents the initial studies and results on shield design for Shape-Shifting Surfaces (SSSs) seeking maximum compression and maximum expansion of a unit-cell. Shape-Shifting Surfaces (SSSs) are multilayered surfaces that are able to change shape while maintaining their integrity as physical barriers. SSSs are composed of polygonal unit-cells, which can change side lengths and corner angles. These changes are made possible by each side and corner consisting of at least two different shields, or layers of material. As the layers undergo relative motion, the unit-cell changes shape. In order for the SSS to retain its effectiveness as a barrier, no gaps can open between different layers. Also, the layers cannot protrude past the boundaries of the unit-cell. Based on these requirements, using equilateral triangle unit-cells and triangular shields, a design space exploration was performed to determine the maximum deformation range of a unit-cell. It was found that the triangular shield that offered maximum expansion and compression ratio is a right triangle with one angle of 37.5 degrees and its adjacent side equal to 61% of the side of the unit-cell. The key contribution of this paper is a first algorithm for systematic SSS shield design. Possible applications for SSSs include protection, by creating body-armor systems; reconfigurable antennas able to broadcast through different frequencies; recreational uses, and biomedical applications.

Bibliography: leaves 188-203. / xxii, 203 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / In this thesis insect vision principles are applied to the main mechanism for motion detection. Advanced VLSI technologies are employed for designing smart micro-sensors in which the imager and processor are integrated into one monolithic device. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1996