Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Mechanical Engineering

First Advisor

Victor Giurgiutiu

Abstract

The goal of this research is to develop the scientific and engineering basis for piezoelectric wafer active sensors (PWAS) in structural health monitoring (SHM). PWAS are studied in both theoretical and practical aspects. The research focuses on three areas: (I) modeling of PWAS power and energy transduction; (II) PWAS installation and durability study; (III) novel miniaturized PWAS approaches for SHM.

In part I, the dissertation presents a systematic investigation of power and energy transduction of PWAS. The PWAS transmitter model, receiver model, and pitch-catch model are developed. Frequency response functions are developed for voltage, current, complex power, active power, etc. The power and energy transduction with PWAS attached to a structure are investigated and the following aspects are discussed: (i) the electrical power of transmitter and receiver; (ii) the mechanical power of transmitter and receiver; (iii) wave power and energy in structures. A parametric study with respect to PWAS size, PWAS impedance, and external electrical load was performed to provide a PWAS design tool for PWAS actuating, sensing and power harvesting applications. In addition, the analytical PWAS modeling is compared with coupled-field finite element results.

In part II, the dissertation presents an experimental study in which issues of PWAS fabrication, installation, and testing were investigated. The installation procedure of PWAS on metallic structures was examined statistically using design of experiments method (DOE) with pre-manufactured piezoelectric wafers adhesively bonded to the structural surface. The durability and survivability of PWAS on metallic structures under various exposures (temperature cycling, freeze-thaw, outdoor environment, operational fluids, large strains, fatigue load cycling) were tested thoroughly. Both installation DOE study and durability tests showed that the bonding layer is the weak link that may lead in-service failure due to loss of contact with the structural substrate.

In part III, the dissertation explores several novel PWAS configurations that may overcome the shortcomings of conventional PWAS. The study of novel PWAS configurations includes: composite PWAS, PVDF PWAS, and nano-PWAS. Methods for in-situ fabrications of composite and PVDF PWAS on curved and/or complicated structural surfaces were explored. A novel nano-PWAS concept was also investigated. The nano-PWAS requires much less power and can be fabricated directly on the structure. In collaboration with University of Texas at San Antonio, University of Texas Arlington, Army Research Laboratory, several deposition methods, materials, and substrates were investigated for thin-film nano-PWAS fabrication. As a result, nano-scale BTO thin films with enhanced piezoelectric properties were developed on Ni and Ti substrates.

The dissertation ends with conclusions and suggestions for future work.

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