Date of Award

8-9-2014

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Victor Giurgiutiu

Abstract

Structural health monitoring (SHM) is crucial for monitoring structures performance, detecting the initiation of flaws and damages, and predicting structural life span. The dissertation emphasizes on developing analytical and numerical models for ultrasonics transduction between piezoelectric wafer active sensors (PWAS), and metallic and composite structures.

The first objective of this research is studying the power and energy transduction between PWAS and structure for the aim of optimizing guided waves mode tuning and PWAS electromechanical (E/M) impedance for power-efficient SHM systems. Analytical models for power and energy were developed based on exact Lamb wave solution with application on multimodal Lamb wave situations that exist at high excitation frequencies and/or relatively thick structures. Experimental validation was conducted using Scanning Laser Doppler Vibrometer. The second objective of this work focuses on shear horizontal (SH) PWAS which are poled in the thickness-shear direction (d35 mode). Analytical and finite element predictive models of the E/M impedance of the free and bonded SH-PWAS were developed. Next, the wave propagation method has been considered for isotropic materials. Finally, the power and energy of SH waves were analytically modeled and a MATLAB graphical user interface (GUI) was developed for determining the phase and group velocities, modeshapes, and the energy of SH waves.

The third objective focuses on guided wave propagation in composites. The transfer matrix method (TMM) has been used to calculate dispersion curves of guided waves in composites. TMM suffers numerical instability at high frequency-thickness values, especially in multilayered composites. A method of using stiffness matrix method was investigated to overcome instability. A procedure of using combined stiffness transfer matrix method (STMM) was presented and coded in MATLAB. This was followed by a comparative study between commonly used methods for the calculation of ultrasonic guided waves in composites, e.g. global matrix method (GMM), semi–analytical finite element (SAFE).

The last part of this dissertation addresses three SHM applications: (1) using the SH-PWAS for case studies on composites, (2) testing of SHM industrial system for damage detection in an aluminum aerospace-like structure panel, and (3) measuring dispersion wave propagation speeds in a variable stiffness CFRP plate.

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