Author

Peter Osterc

Date of Award

5-2015

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Graduate Studies

Committee Chair

Dr. Daewon Kim

First Committee Member

Dr. Namilae Sirish

Second Committee Member

Dr. Jeff Brown

Abstract

In this study a guided wave phased array beamsteering approach is applied to composite laminates. Current beamsteering algorithms derived for isotropic materials assume omnidirectional wave propagation. Due to inherent anisotropy in composites, guided wave propagation varies with direction and wavefronts no longer have perfect circular shapes.

By examining slowness, velocity and wave curves, as well as amplitude variation with direction for a given composite laminate, the wavefront from a single source can be described as a function of the angle of propagation and distance from origin. Using this approach, a more general delay and sum beamforming algorithm for composite laminates is developed for any desired wave mode.

It is shown that anisotropic wave mode shapes can be effectively used for beamsteering in certain directions with a linear array and performance similar or even better than the isotropic case. However, the useful range of angles with a 1-D linear array for anisotropic wave modes is quite small and other directions exhibit undesired grating lobes and large sidelobes.

Results from the modified beamforming algorithm are also compared and validated with Finite Element Model simulations. Good agreement is shown between analytical predictions and finite element results.

Experimental validation is performed using an aluminum and composite plate and linear arrays of piezoelectric actuators for guided wave excitation. Successful beamforming is shown in the experimental study based on the algorithm predictions.

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