Conductivity-Based Nanocomposite Structural Health Monitoring via Electrical Impedance Tomography.

Nanocomposites have incredible potential when integrated as matrices in fiber-reinforced composites for transformative conductivity-based structural health monitoring (SHM). Key to this potential is the dependence of nanocomposite conductivity on well-connected nanofiller networks. Damage that severs the network or strain that affects the connectivity will manifest as a conductivity change. These damage or strain-induced conductivity changes can then be detected and spatially located by electrical impedance tomography (EIT). The nanofiller network therefore acts as an integrated sensor network giving unprecedented insight into the mechanical state of the structure. Despite the potential of combining nanocomposite matrices with EIT, important limitations exist. EIT, for example, requires large electrode arrays that are too unwieldy to be practically implemented on in-service structures. EIT also tends to be insensitive to small, highly localized conductivity losses as is expected from common modes fiber-reinforced composite damage such as matrix cracking and delamination. Furthermore, there are gaps in the fundamental understanding of nanocomposite conductivity. This thesis advances the state of the art by addressing the aforementioned limitations of EIT for conductivity-based SHM. This is done by insightfully leveraging the unique properties of nanocomposite conductivity to circumvent EIT's limitations. First, nanocomposite conductive properties are studied. This results in fundamental contributions to the understanding of nanocomposite piezoresistivity, the influence of nanofiller alignment on transverse percolation and conductivity, and conductivity evolution due to electrical loading. Next, the potential of EIT for conductivity-based health monitoring is studied and demonstrated for damage detection in carbon nanofiber (CNF)/epoxy and glass fiber/epoxy laminates manufactured with carbon black (CB) filler and for strain detection in CNF/polyurethane (PU). Lastly, the previously developed insights into nanocomposite conductive properties and damage detection via EIT are combined to greatly enhance EIT for SHM. This is done by first exploring how the sensitivity of EIT to delamination can be enhanced through nanofiller alignment and tailoring. A method of coupling the EIT image reconstruction process with known conductivity changes such as those induced by straining piezoresistive nanocomposites is developed and presented. This approach will tremendously bolster the image quality of EIT or, synonymously, significantly abate the number of electrodes required by EIT.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111613/1/ttallman_1.pd

Advances in Vibration Analysis Research

Vibrations are extremely important in all areas of human activities, for all sciences, technologies and industrial applications. Sometimes these Vibrations are useful but other times they are undesirable. In any case, understanding and analysis of vibrations are crucial. This book reports on the state of the art research and development findings on this very broad matter through 22 original and innovative research studies exhibiting various investigation directions. The present book is a result of contributions of experts from international scientific community working in different aspects of vibration analysis. The text is addressed not only to researchers, but also to professional engineers, students and other experts in a variety of disciplines, both academic and industrial seeking to gain a better understanding of what has been done in the field recently, and what kind of open problems are in this area

A multi-coil magnetostrictive actuator: design, analysis, and experiment

This dissertation investigates a new design for a magnetostrictive actuator that employs individually controlled coils distributed axially along the magnetostrictive rod. As a quantitative goal, the objective is to show that the multi-coil actuator can operate effectively at frequencies as high as 10,000 Hz with 900 N force and 50 microns of displacement. Conventional, single coil actuators with the same parameters for force and displacement develop significant attenuation in their response at frequencies above the first longitudinal vibration resonance at about 2750 Hz. The goal of the research is to investigate whether multiple coils can effectively increase the frequency range a least four times the range of conventional magnetostrictive actuators. This document derives a new mathematical model of the actuator that represents the spatial distributions of magnetic field and vibration, devises a control design that takes advantage of the multiple inputs to control the displacement of the actuator while consuming minimum electrical power, and describes a prototype multi-coil actuator and experimental system developed to test the idea. The simulations of the multi-coil actuator and control design demonstrate successful transient operation of the actuator over the targeted frequency range with feasible levels of input power and current. Experimental tests of the design, although limited by a computer sampling rate less than 10,000 Hz, are able to validate the predictions of the developed model of the actuator and reproduce the simulated control performance within the constraints of the experimental system.Ph.D.Committee Chair: Zinn, Ben T.; Committee Member: Book, Wayne; Committee Member: Glezer, Ari; Committee Member: Neumeier, Yedidia; Committee Member: Seitzman, Jerr

Design and Application of Electrical Machines

Electrical machines are one of the most important components of the industrial world. They are at the heart of the new industrial revolution, brought forth by the development of electromobility and renewable energy systems. Electric motors must meet the most stringent requirements of reliability, availability, and high efficiency in order, among other things, to match the useful lifetime of power electronics in complex system applications and compete in the market under ever-increasing pressure to deliver the highest performance criteria. Today, thanks to the application of highly efficient numerical algorithms running on high-performance computers, it is possible to design electric machines and very complex drive systems faster and at a lower cost. At the same time, progress in the field of material science and technology enables the development of increasingly complex motor designs and topologies. The purpose of this Special Issue is to contribute to this development of electric machines. The publication of this collection of scientific articles, dedicated to the topic of electric machine design and application, contributes to the dissemination of the above information among professionals dealing with electrical machines