Date of Award

2016-01-01

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Advisor(s)

Yirong Lin

Abstract

Continuous monitoring of high pressure and high temperature in energy system applications has been a developing research area in today’s energy sector. Multifunctional materials have the potential to provide real-time monitoring of structures where temperature and pressure sensing is critical to its performance and efficiency. In this study, multifunctional materials are studied by embedding piezoelectric materials with two ongoing technologies, woven fabric composites and additive manufacturing (AM). The AM technology allows the flexibility of embedding a sensor within the structure, all while not compromising the mechanical performance requirements. The “smart parts” are fabricated modifying the standard additive manufacturing process, using Electron Beam Melting and Selective Laser Melting, into a two stage fabrication in which a piezoelectric material is embedded in specific locations. Two case studies of “smart parts” are modeled, fabricated and analyzed in different conditions where the piezoelectric and pyroelectric response for pressure and temperature sensing are recorded. The design and performance of “smart parts” are compared to ideal conditions modeled in ABAQUS. The structural composition of smart parts showed a transition zone in the microstructure, indicating a change in mechanical behavior due to the “stop-and- go” process. Tensile results in cylindrical samples fabricated using “stop-and-go” process failed by brittle fracture near the interface where the second fabrication starts. However, the evaluation showed a voltage response that reached up to 6 V for the smart cylinders, and it generated 0.25 pA from the pyroelectric response on the smart tube. The smart parts demonstrate reliable methodologies that can be implemented as sensing components using the dielectric and pyroelectric response as temperature sensing mechanism, as well as piezoelectric response as pressure sensing mechanism. On the other side, the reinforcement with piezoelectric particles of woven fabric composites is achieved by a modified autoclave molding fabrication. The composites are fabricated with different weight percentages of PZT from 0% to 20%. These structures are analyzed in their mechanical integrity by three-point bend experiments which show a decrease in strength from 400 MPa to 250 MPa. The dispersion of particles verified the accumulation of epoxy in the depressions resulted from the intersection of the yarn and warp threads in these types of composites and was also confirmed by a dispersion index. The electrical characterization shows a piezoelectric response up to 1.5 V, and current generation from cyclic heating and cooling up to 0.74 μC/m 2 nA.

Language

en

Provenance

Received from ProQuest

File Size

113 pages

File Format

application/pdf

Rights Holder

Ricardo Martinez Hernandez

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