Date of Award

2017-01-01

Degree Name

Doctor of Philosophy

Department

Electrical Engineering

Advisor(s)

Virgilio Gonzalez

Abstract

Fiber-Bragg Gratings (FBG) for Structural Health Monitoring (SHM) have been studied extensively as they offer electrically passive operation, electromagnetic interference (EMI) immunity, high sensitivity and multiplexing as compared to conventional electric strain sensors. FBG sensors written within polarization maintaining (PM) optical fiber offer ad- ditional dimensions of strain measurement, greatly reducing the number of sensors needed to properly monitor a structure. This reduction however, adds complexity to the dis- crimination of the sensorâ??s optical response to its corresponding applied strains. This Dissertation defines the set of algorithms needed to measure planar strain using PM-FBGs exclusively. It defines the minimum number of sensors needed to reconstruct the full state of strain, ε and the maximum number of strain tensor components a single PM-FBG is capable of measuring. Two experiments were performed under the same test specifications; a single PM-FBG and 2 multiplexed PM-FBGs in a rosette pattern adhered to a test spec- imen subject to uniaxial tension. The far field strain was measured at the location of the sensor using only the optical response and PM-FBG axes orientation with respect to the specimen axes. Strains at the surface of the specimen were measured using Digital Image Correlation (DIC) analysis and an electronic extensometer. The PM-FBG measurements where then compared to the DIC/extensometer data for validation. The comparison of the strains εxx, εyy, and εxy resulted in a high correlation, averaging .97 between the strain mea- surement techniques. The PM-FBG measured specimen surface strains with low percent error values (approximately 20%). PM-FBG sensitivity is greatly affected by the sensorâ??s material properties and installation or embedding techniques. The algorithm for measuring a full state of planar strain at a point presented in this Dissertation and is validated though experimental analysis. It can be applied to multiple or single PM-FBG systems with low error and high correlation to actual strains on the surface of a specimen. It is the first step in practical implementation of PM-FBGs for Structural Health Monitoring.

Language

en

Provenance

Received from ProQuest

File Size

78 pages

File Format

application/pdf

Rights Holder

Joel Quintana

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