Date of Award

1-1-2011

Document Type

Campus Access Thesis

Department

Mechanical Engineering

First Advisor

Victor Giurgiutiu

Abstract

The field of structural health monitoring (SHM) is a fast-growing field that is extending into many industries. SHM uses a set of sensing elements permanently attached to or embedded in the structure in order to effectively monitor its structural integrity, detect and quantify damage that develops during the entirety of its life. Effective SHM will not only increase the safety of structures, it will also limit the amount of manual, error prone inspections that currently dominate the field. Over the past several decades, much work has been done in developing SHM methods.

Composite materials are at the leading edge of material selection for many types of structures, offering a high strength to weight ratio resulting in a better performance. As the use of composite materials becomes more prevalent, especially in human-rated structures, the need to have an accurate measure of the damage present in the material is important. Due to their intrinsic anisotropic and heterogeneous properties, SHM for composite structures face a lot of challenges.

This thesis is focused on studying the state of the art methods for damage detection and health monitoring on composites, as well as developing a novel active sensing method which utilizes the embeddable low-profile piezoelectric wafer active sensors (PWAS). PWAS utilize the piezoelectric principle to convert electric energy to mechanical energy or mechanical energy back to electrical energy. This type of sensor can be readily mounted on the existing structures or embedded into them during the manufacturing process without degrading the structural performance. Though the damage detection capabilities of PWAS have been proven effectively for metallic structures by other researchers, but a limited amount of work has been done on composites. This thesis explores the damage detection capabilities of the PWAS on composites using wave propagation as well as electromechanical impedance spectroscopy methods. The damage studied includes both material level damage and structural level damage. The self-diagnosis capability of the sensor has also been developed in this study.

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