Browsing by Author "Gregory Buckner, Committee Member"

Now showing 1 - 12 of 12

Assessment of Stresses on Induction Motors Due to Momentary Service Interruptions
(2007-08-08) Cavaroc, John Peter Jr; Mesut Baran, Committee Chair; Arthur Kelley, Committee Co-Chair; Edward Grant, Committee Member; Gregory Buckner, Committee Member
This dissertation presents an assessment of the worst case stresses produced in an induction motor when the motor is allowed to ride through a power supply voltage disturbance. Results from laboratory experiments and computer simulations are shown. The experimental results are obtained from tests conducted on three squirrel cage induction motors, sized 10 hp, 50 hp, and 75 hp. Each motor is tested with three different load inertias, various motor loadings, and numerous interruption durations. The computer simulation results are obtained using a non-linear motor-load model, whose parameters are derived from a non-linear least squares parameter estimation technique. Experimental data acquired in the lab is used for the parameter estimation data and for the validation data. Deficiencies in the standard motor-load model are presented and addressed. Good agreement between the experimental data and the non-linear motor-load model data is achieved. Results show significant current and torque transients, but caused no significant damage to the motors or loads used for testing.
BATMAV: A Biologically-Inspired Micro Air Vehicle for Flapping Flight - Design and Fabrication of Skeleton Structure and Wing Membrane.
(2008-01-03) Place, Thomas Jefferson; Stefan Seelecke, Committee Chair; Gregory Buckner, Committee Member; Ashok Gopalarathnam, Committee Member
Development of a Thermo-Magneto-Mechanical Free-Energy Model for the Ferromagnetic Shape-Memory Material NiMnGa
(2008-08-05) Morrison, Phillip; Gregory Buckner, Committee Member; Stefan Seelecke, Committee Chair; M. K. Ramasubramanian, Committee Member
Fault Detection/Isolation and Fault Tolerant Control for Hypersonic Vehicle.
(2010-05-14) Cai, Xuejing; Fen Wu, Committee Chair; Branda Nowell, Committee Member; Paul Ro, Committee Member; Gregory Buckner, Committee Member; Fuh-Gwo Yuan, Committee Member
Ignition of a Liquid Fuel Jet by an Electrical Discharge Propagating along the Jet.
(2010-11-19) Gray, Parker; Alexei Saveliev, Committee Chair; Tiegang Fang, Committee Member; Gregory Buckner, Committee Member
Investigating the Significance of "One-to-many" Mappings in Multiobjective Optimization.
(2010-11-03) Simov, Peter; Scott Ferguson, Committee Chair; Robert Nagel, Committee Chair; Andre Mazzoleni, Committee Member; Gregory Buckner, Committee Member
LPV H∞ Control for the Longitudinal Dynamics of a Flexible Air-Breathing Hypersonic Vehicle.
(2010-11-02) Hughes, Hunter; Fen Wu, Committee Chair; Lawrence Silverberg, Committee Member; Jules Silverman, Committee Member; Gregory Buckner, Committee Member; Paul Ro, Committee Member
Microforming and Ultrasonic Forming
(2007-08-18) Bunget, Cristina Janeta; Gregory Buckner, Committee Member; Stefan Seelecke, Committee Member; Gracious Ngaile, Committee Chair
Modeling and Finite Element Analysis of Smart Materials
(2006-08-22) Li, Qifu; Ralph Smith, Committee Member; Stefan Seelecke, Committee Chair; Clement Kleinstreuer, Committee Member; Gregory Buckner, Committee Member
This dissertation consists of two parts, the modeling of piezoceramic (PZT) actuators and the finite element implementation of a shape memory alloy (SMA) model and the subsequent thermo-mechanically coupled multifield analysis of several devices, such as tensile wire and cantilever beam actuators. Both models are based on similar free energy expressions and allow for a unified treatment of a number of active materials. PZT actuators have been widely used in positioning applications due to their high bandwidth, high resolution, compact and light weight characteristics. However PZT materials also exhibit some inherent undesirable nonlinear effects like hysteresis, creep and frequency dependent response. To improve the performance of PZT actuators, these effects need to be taken into account. In this dissertation, based on a free energy model for perfect single crystal PZT materials and motivated by its extension to homogenized model for polycrystalline materials, a parameterization method is developed to model the hysteresis behaviors of polycrystalline PZT materials. In the parameterization method, the effective barrier is assumed to be a function of the phase fraction. Major loop effective barriers are identified from experimental polarization-electric field diagrams as functions of the phase fraction. Minor loops are constructed by major loops using a linear mapping method and a bookkeeping algorithm. A robust algorithm, which preserves the simple structure and efficiency of the original perfect single crystal model, is implemented to simulate the rate dependent minor loop behavior of the PZT materials and compared to experimental data. Shape memory alloys (SMAs) represent another type of smart materials that have been extensively used in many engineering applications due to their unique material properties, and new devices like SMA microactuators are constantly being developed. To facilitate these new development, an efficient computational tool like the finite element method has to be used in order to simulate the highly nonlinear, load-history and temperature dependent responses of SMA materials. In this dissertation, a 1-D free energy SMA model is implemented into the finite element software package FEMLAB using its general PDE form by treating the evolution equations of phase fractions as degenerated PDEs coupled with the mechanical equilibrium equation and the heat transfer equation. First, without including the latent heat effect and neglecting the heat transfer equation, simulations are conducted for SMA bars to demonstrate that the model can predict the low temperature quasiplastic and high temperature superelastic behaviors as well as shape memory effect. The finite element implementation is then expanded by including the nonlinear transient heat transfer equation with the phase transformation induced latent heat as a coupling term. In contrast to the so-called staggered iteration approach, where the individual fields are solved for in a decoupled way within an iteration, FEMLAB allows for a fully coupled solution. This approach generally provides for a robust and efficient solution even in the case of strong coupling between the fields. A number of different applications are then studied for the first time using such a coupled multi-field approach. The particular focus is on the effects of inhomogeneous fields and the strong coupling between thermal and mechanical fields. Tensile simulations of an SMA wire under different thermal boundary conditions with different loading rates are conducted to demonstrate the inhomogeneity and rate effects of the system responses. By including the Joule heating, the performance of an SMA wire actuator under different thermal boundary conditions is studied. The 1-D free energy model is also implemented into FEMLAB to study the inhomogeneous SMA beam bending problems by using the Euler-Bernoulli beam bending theory. The SMA beam bending problem is modeled as a system of first order PDEs and boundary conditions are implemented as Dirichlet boundary conditions. Detailed analysis is presented for inhomogeneous bending behavior of an SMA cantilever beam under constant temperatures and thermo-mechanical loading, respectively. The rate-dependent responses of an SMA cantilever beam due to strong thermo-mechanical coupling are also studied. Finally, using traditional incremental finite element method, the 1-D free energy model is also implemented into the finite element program ANSYS using its BEAM188 element and the user defined material subroutine USERMAT, which also serves as a validation tool for the FEMLAB implementation. Convergence behavior is studied systematically.
A Multi-Channel Power Controller for Actuation and Control of Shape Memory Alloy Actuators.
(2010-07-29) Hangekar, Rohan; Stefan Seelecke, Committee Chair; Gregory Buckner, Committee Member; Paul Ro, Committee Member
Probabilistic Damage Size Estimation for Structural Health Management.
(2010-10-22) Li, Gang; Fuh-Gwo Yuan, Committee Chair; Kara Peters, Committee Member; Gregory Buckner, Committee Member; Murthy Guddati, Committee Member
Processing and Characterization of Functionally Graded Hydroxyapatite Coatings for Biomedical Implants
(2010-08-07) Bai, Xiao; William L. Roberts, Committee Member; Michael Rigsbee, Committee Member; Afsaneh Rabiei, Committee Chair; Gregory Buckner, Committee Member
Hydroxyapatite [Ca10(PO4)6(OH)2, HA] has been widely applied as a coating on various biomedical bone/dental implants to improve biocompatibility and bioactivity. It has been observed that primary reasons leading to implantation failure of commercial HA coated implants processed by plasma spraying are the poor mechanical properties of coatings and infections accompanied by implantation. It has been also reported an ideal coating should be able to stimulate new bone growth at the initial stage of implantation and stay stable both mechanically and chemically thereafter. This research has investigated a functionally graded hydroxyapatite (FGHA) coating that is capable of improving the stability of implants, facilitating recovery, and preventing infections after implantation. A series of FGHA coatings with incorporated Ag 0 ~ 13.53 wt. % has been deposited onto Ti substrate using ion beam assisted deposition (IBAD) with in-situ heat treatment. The compositional, microstructural, mechanical, and biological properties of coatings have been analyzed via various tests. The relationship among processing parameters, coating properties and biological behaviors has been established and the processing parameters for processing FGHA coatings with/without incorporated Ag have been optimized. Microstructure observations of coating cross section via transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) for set temperature coatings deposited at 450 oC ~ 750 oC reveals that in-situ substrate temperature is the primary factor controlling the crystallinity of the coatings. The microstructure observation of cross section via TEM / STEM for both FGHA coatings with / without incorporated Ag has shown that coatings are dense and have a gradually decreased crystallinity from substrate/coating interface to top surface. In particular, the interface has an atomically intermixed structure; the region near the interface has a columnar grain structure whereas the region near coating top surface is mostly amorphous. TEM / STEM observation of FGHA coating with incorporated Ag has also demonstrated that the metallic silver particles in size of 10 ~ 50 nm distribute at the coating cross section throughout the coating thickness. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis have shown that coatings consist of HA and various calcium phosphate compounds. The pull off tests have shown that the average adhesion strength of FGHA coatings (both with and without Ag) to substrate are in the range of 83.44 Â± 5.71 ~ 89.36 Â± 5.13 MPa. Further optical observation of pull off area of coating shows that no coating delamination is observed and epoxy failure is dominant, indicating a well-boned interface and a strong coating itself. It has been concluded that the high adhesion strength of coating to substrate is attributed to the atomic intermixed interface and dense structure of coating, which is resulted from the increased mobility of coating atoms at high substrate temperature under bombardment of assisted ion beam. Culture tests have shown a distinct increase in osteoblast cell attachment to FGHA surface after 24 hours culture test when compared to blank Ti controls. Both calcium and silver release tests of Ag-doped FGHA coatings have shown the release rate is high at the initial stage and it steadily decreases, which is the expected performance of FGHA coatings. Antibacterial test using S. aureus has revealed that Ag doped FGHA coatings show an inhibitory effect when compared to coating without Ag and blank Ti. In particular, with higher amounts of Ag in coatings, the inhibition of S. aureus is stronger. Cytotoxicity test indicates that the FGHA coating with the highest amounts of Ag shows a negative effect on the osteoblast response.