Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 70-71). Also available via the Internet.

No description available.

The use of piezoelectric materials for actuation, and vibration suppression of thin beams, is the subject of study in this doctoral thesis. The initial focus is set on reducing beam vibrations with resistively shunted piezoelectric patches, where the converted electrical energy is dissipated by the resistor to give an additional damping. The amount of additional damping achieved depends on the value of shunted resistor, the dimensions of the piezoelectric, and its location on the substructure. Hence, the resistively shunted piezoelectric-beam was modelled to determine the optimal values, and to examine its dynamics. A multi-modal model was derived based on the Euler-Bernoulli beam theory, and a reduced non-dimensionalized transfer function was obtained from the multi-modal model. The presented model was derived from assumptions which aptly describe the dynamics of the resistively shunted piezoelectric-beam. The aptness of the presented model in representing the system, over the existing models, was evident from the comparison of the analytical predictions with the existing experimental data. With the model derived, the second part of the work deals with determining the value of resistance which would yield maximum amplitude attenuation (referred as the optimal resistance value). A method for obtaining the optimal resistance value from the analytical model, based on the presence of a fixed-point in the amplitude response, exists in the literature. But, this method cannot be used on the presented analytical model, as it includes the base-damping of the structure. Hence, a different approach was adopted to determine the optimal resistance from the analytical model. Analytical results were also validated with experimental results from a cantilever piezoelectric-beam. The amplitude plots of the first, second, and third modes of the piezoelectric-beam exhibited a softening e ect, indicating a non-linear behaviour of the piezoelectric patches. Hence, a non-linear constitutive equation was required to describe the behaviour of the piezoelectric patches. In the third part of the work, a two-step experimental procedure was devised to construct the non-linear constitutive equation of the piezoelectric actuators. In the first step, the piezoelectric patches were short circuited and a family of displacement curves were obtained for the first, second and third modes of the piezoelectric-beam by base excitation. The pro le of backbone curves from these plots were used to identify the type of non-linear terms required to describe the mechanical domain. In the second step, voltage excitation was used to obtain a similar set of displacement curves. A comparison of the profile of the backbone curves, of the displacement frequency response plot, from the voltage excited data with those from the base excited data, lead to the identification of the non-linear electromechanical coupling term. The constitutive equation, which accounts for the non-linear nature, of the piezoelectric actuator contains (apart from the linear terms) a quadratic strain term, a cubic strain term, and a term with the product of cubic strain and electric field.

The aim of the work described in this thesis is firstly to improve the collection of vibration energy for piezoelectric cantilever harvesters, by a mechanical technique, so that the devices can harvest energy over a wider bandwidth. Secondly to investigate a new circuit topology for achieving complex conjugate load matching to the piezoelectric harvester. The thesis has been divided into two parts - the mechanical approach and the electrical approach. For the mechanical approach, a novel multiresonant beam, comprising piezoelectric fiber composites on a clamped-clamped beam and side mounted cantilevers, was proposed. The side cantilevers are tuned by tip masses to be resonant at different frequencies. A Rayleigh-Ritz model was developed to predict the vibration response of the proposed model multiresonant beam. This model showed that the bandwidth of the multiresonant beam was increased over that of a single cantilever harvester. A multiresonant beam for energy harvesting was experimentally tested and compared with a single cantilever energy harvester. The transmissibility and voltage responses were investigated, the beam showed a wide frequency response between 14.5Hz and 31Hz, whereas the single cantilever only showed one resonant frequency. Therefore the multiresonant beam system is feasible for wide band energy harvesting. For the electrical approach, the task was to investigate complex conjugate impedance matching for the piezoelectric energy harvesters, so that the output impedance from the piezoelectric harvester can be reduced, and maximum energy extracted from the device with a possibility of frequency tuning. A new amplified inductor circuit was proposed to enable the capacitive output impedance of the piezoelectric device to be cancelled. Experimental and software simulations are provided to verify the theoretical predictions. A prototype amplified inductor circuit was simulated and tested. The results showed that a variable effective inductance was achieved. However the circuit is lossy due to imperfections within the system, and needs further work to eliminate these imperfections.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, September 2016 / The work in this dissertation presents the analysis of developing a novel means of flight trajectory alteration of a civil aircraft. Piezoelectric actuators have been advancing in the aerospace industry with uses in structural, vibrational and sensing applications. However, they have not been considered as a primary control method like an elevator, aileron and rudder. The analysis performed in this research involved developing an actuation model which is designed such that various changes in flight trajectory are brought about. The analysis began by building a base rigid aircraft model, where other analyses were appended to. The rigid aircraft model was developed using the aerodynamics of both Roskam (2001) and DATCOM. The DATCOM model was found to compensate for additional aircraft positions outside the flight envelope, whereas Roskam (2001) did not adequately provide the aerodynamics for when the aircraft would experience stall conditions, for example. The research then lead into developing the piezoelectric actuation model. This involved utilizing piezoelectric actuators on the wing of the aircraft, which was set to create vertical and twisting deformations, without altering the wing’s camber. Two novel methods of actuation are discussed. A wing - twist mode which consisted of three types of actuation, viz. linear twist, inverse linear twist, and linear twist symmetric. The second was the bending mode which altered the aircraft’s dihedral, and consisted of two types of actuation, viz. linear bending and linear bending symmetric. Effects of these two modes on the aerodynamics were depicted. Added to the overall model was the analysis of elastic aerodynamic effects. This was conducted by performing vibrational analysis on the individual components of the aircraft, viz. wing, horizontal tail and vertical tail. The results found that the elastic aerodynamic effects on the rigid model were significant only in lift. The rest were not significant because of the high frequency of the beams under consideration. Conclusively, the novel actuation methodology developed in this research yielded results demonstrating the viability of it being used above conventional methods such as elevator, rudder and ailerons. This was found by noting that various trajectory alterations were perceived without input from the conventional actuation methods. Increase in the rotational motions, as well as the translational motion was found, but did not cause any dynamic instabilities in the aircraft model. Thus, the actuation model was seen to operate well above the conventional methods, and situation specific uses were described for the actuation modes. These include uses in take-off and landing, cruise optimization and coordinated turns. / MT2017

Thin unsymmetric carbon fiber reinforced polymeric(CFRP) composite laminates are examined for use of morphing structures using piezoelectric actuation. During fabrication, unsymmetric laminates are able to deform to more than one post-cure room temperature shape. Thin cross-ply laminates will deform to a cylindrical post-cure room temperature shape while thicker non-cross-ply laminates will deform to a saddle shape. Predictions of the deformed post-cure shape will be made by modeling the cure process using analytical and numerical. These models will then serve as expectations for experimental tests. Modeling the fabrication process allowed for characterizing important data such as residual stresses from the cure process, room temperature shapes, and bi-stability of the CFRP composite laminates all of which are needed to accurately model morphing structures. Cross-ply laminates will deform to a symmetric cylindrical shape, cylindrical shape I, after the cure process. Non cross-ply laminates will deform to a non-uniform saddle shape after the cure process. These post-cure room temperature deformation shapes can be used as morphing structures by applying a force large enough to create ”snap” through to the other cylindrical shape, cylindrical shape II. A piezoelectric actuator, bonded to the deformed room temperature shapes, is used to generate this ”snap through force”. Experimental verification was done by fabricating the CFRP composite laminates and comparing the post cure room temperature shapes to the analytical and numerical fabrication models. For morphing structures, experimental verification was done by actuating the piezoelectric actuator and comparing the deformation of cylindrical shape II to analytical and numerical piezoelectric models.

No description available.

The research presented herein aims to develop a bio-inspired swimming system for an autonomous underwater vehicle using Macro-Fiber Composite (MFC) actuators. The swimming system draws inspiration from the motion of carangiform fish, which limit their body motion while rapidly oscillating their caudal tail fin. The foundation for the bio-inspired swimming system is built upon a composite cantilever beam with MFC actuators in bimorph configuration. The MFC actuators excite the composite beam near its fundamental natural frequency to produce thrust as the vibration transfers momentum to the surrounding fluid. An analytical model that incorporates Euler-Bernoulli beam theory, linear piezoelectricity, and fluid mechanics is developed to predict the thrust generated by the beam vibration. Experimental testing is performed to verify aspects of, as well as recommend corrections to, the analytical model. A prototype carangiform swimmer is developed that employs a passive caudal tail fin to alter the vibratory motion of the system from a beam vibration mode to one more resembling carangiform swimming. This device is subjected to experimental testing to determine the swim speeds it is able to achieve. A maximum velocity of 90mm/s was observed when the system is excited at 900V. However, better performance may be achieved by increasing the excitation voltage. / Master of Science

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Lead zirconate titanate (PZT), in the form of both bulk and thin films, is used in most piezoelectric applications due to its high piezoelectric response coefficients. Strontium-doped lead zirconate titanate (PSZT) has shown improved piezoelectric response characteristics in bulk form. This work investigates the deposition and characterisation of PSZT in the form of thin films, and reports on results from the estimation of the piezoelectric response of these thin films using two new techniques. The influence of RF magnetron sputter deposition parameters on the composition and orientation of PSZT thin films has been studied. Investigation of the consequence of varying the oxygen partial pressure during deposition on thin film stoichiometry, the influence of the choice of metal-coated silicon substrates on thin film orientation, and the effect of post-deposition cooling rate have been used to identify optimal deposition conditions. The existence of a modified unit cell resulting from these deposition parameters has been verified, and the resulting lattice parameters were estimated. Extensive materials characterisation (using microscopy, diffraction, and spectroscopy) of the PSZT thin films deposited on gold and platinum coated silicon substrates is reported. The limited techniques available for quantitative estimation of d33 for piezoelectric thin films initiated an investigation into alternative possibilities, as a consequence of which two new techniques for piezoelectric coefficient estimation, under the inverse piezoelectric effect, have been developed. One technique capitalises on the measurement accuracy of the nanoindenter in following thin film displacement, while the other uses a standard atomic force microscope in contact imaging mode to estimate d33. The development, scope, and limitations of both techniques are discussed. The techniques developed have been used to estimate the piezoelectric response of PSZT thin films. Depending on the thin film deposition parameters and the analysis frequency, values of piezoelectric response higher than any measured for thin films on silicon have been estimated. PSZT thin films deposited on gold-coated silicon at low deposition temperatures resulted in d33 values up to 892 pm/V. The study of the piezoelectric response in the millihertz frequency regime resulted in colossal values (ranging in tens of thousands of pm/V) for PSZT thin films deposited at high temperatures on platinum-coated silicon. This was hypothesised to be a result of enhanced ferroelastic domain switching. This hypothesis was verified by reducing the clamping on domains by synthesising island-structured PSZT films and obtaining an increased piezoelectric response.