Author

Zhaoyun Ma

Date of Award

Fall 2020

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Lingyu Yu

Abstract

Structure components are designed with a certain service life and damage may occur, or they may come with manufacture defects. Such damage and defects may lead to structural failure if not detected in time. To ensure the structural safety and prevent catastrophic failure, effective inspection is critical for in-time maintenance. Nondestructive evaluation (NDE) and structural health monitoring (SHM) have been widely applied for damage inspection and evaluation in various industries due to their noninvasive nature. Lamb wave based NDE/SHM has become the most popular ultrasonic methods that has been proved effective in different engineering applications that can be used to detect not only surface damage but also those internal. Lamb waves are guided waves that propagate in plate-like structures and they can propagate long distance with low energy loss which makes large structure inspection possible. They are also sensitive to various damage/defects across the thickness such as crack in metallic structures and delamination or debonding in composite structures. Despite the intensive studies and application of Lamb wave based NDE/SHM, there are still some challenges that need to be addressed such as damage with complex profiles that is difficult to quantify; alternative excitation and sensing methods that can be applied remotely without the need to leave the transducers on the structure surface; and also the feasibility and effectiveness of the Lamb wave methodologies in real world applications.

This dissertation aims to address the aforementioned challenges. Two parts of research work have been conducted for this purpose: Part I focuses on the fundamental studies of Lamb waves and development of the system as well as the supplementary damage detection methodologies, while Part II focuses on applying the developed methods to various NDE/SHM applications from aerospace to nuclear structures. In Part I, the Lamb wave based wavefield analysis methods are first demonstrated. Based on that, an actuator network Lamb wave imaging method that can quantify complex damage with great details is developed. In addition, a fully noncontact/remote NDE system through laser excitation and sensing strategy is developed and evaluated on both metallic and composite structures towards more flexible real-world applications. In Part II, the developed Lamb wave based systems and methodologies are investigated and evaluated on various real-world applications in order to prove their efficacy and reliability, including inspection on typical damage/defects such as crack, wrinkle, and delamination in aerospace structures, and stress corrosion cracking and material degradation in nuclear structures.

This dissertation uniquely addressed the complex damage profile quantification issue with a high-resolution actuator network imaging method, developed a reliable and noncontact/remote laser based Lamb system accompanied with effective evaluation methods which enables more flexible field application, and systematically investigated the Lamb wave based NDE reliability and effectiveness on various real world applications which provided guidelines for typical damage and defects inspection in aerospace and nuclear structures. In the long run, this research work will facilitate the advancement of actuation and sensing strategies, development of evaluation methodologies, and the formation of standard guidelines towards more effective, rapid and flexible Lamb wave based NDE/SHM to ensure the structural safety.

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