Date of Award

2003

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Senthil S. Vel

Second Committee Member

Donald A. Grant

Third Committee Member

Richard C. Hill

Abstract

Structural vibration suppression and health-monitoring have been the focus of intense research over the past decade, and piezoelectric actuators and sensors are particularly well suited to serve in this application. The first part is an analytical investigation into the cylindrical bending vibrations of piezoelectric composite plates. The second part is a fully experimental investigation into various vibration based structural health-monitoring techniques for bolted composites. The analytical solution consists of Fourier basis functions that satisfy the equations of motion and charge equation. The accuracy of the mechanical displacements, electric potential, and stresses are dependent on the number of terms in the series solution. The solution is validated by comparing the natural frequencies with published results for a simply supported piezoelectric plate. Studies were conducted to establish the convergence of the analytical solution. The analytical natural frequencies, electric potential, displacements and stresses compared well with the finite element method for cantilever piezoelectric composite plates. The bolted joint is one of the most common mechanical components in engineering structures. A common mode of failure for bolted joints is self-loosening. The objective of the second part of the thesis is to investigate different vibration based structural health monitoring schemes to actively interrogate a square composite plate to detect loose bolts in composite structures. The plate was excited using a piezoelectric actuator and piezoelectric shear accelerometers and dynamic strain sensors were used to characterize the system dynamics. The investigation began with the sensitivity of the fundamental frequency to changes in the bolt clamping force around the perimeter of the plate. Attempts were also made to quantify damage from changes in the transfer functions. The method of transmittance functions was employed extensively, and it was successful in detecting damage but proved to be unreliable in determining the damage location.

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