Date of Award

2016

Document Type

Open Access Thesis

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Victor Giurgiutiu

Abstract

There has been an increasing demand for Nondestructive Testing (NDT) and Structural Health Monitoring (SHM) techniques to continuously monitor during all processes of a structure to prevent catastrophic failure and reduce maintenance costs. NDT and SHM are inspection processes which form part of the quality assurance/quality control (QA/QC) scheme. Among NDT and SHM methods, ultrasonic and guided wave techniques are the most commonly and widely used in industry. Ultrasonic methods provide the advantage of accurately locating and dimensioning defects within structures. Most of these structures consist of welded joints because welding is an economical and efficient method for obtaining a permanent joint. However, austenitic stainless steels, especially the welding process zone, exhibit heterogeneous and anisotropic behavior which has a decisive influence on the ultrasonic beam making the interpretation of ultrasonic inspection results notoriously difficult. NDT and SHM methods aim to detect possible defects and characterize them (location and dimensions) so that their severity can be assessed, and the mechanical integrity of the welded components guaranteed.

Experimental investigations confirm the challenges and significant shortcomings in the inspection of future industrial components where such microstructures are desirable for their mechanical properties.

First, the methods of fabricating artificial weld defects are investigated. Because of the great variety of possible types of cracks and causes for their formation, the problem of safeguarding against crack formation in welding operations is a highly complex one. The experimental set-up is fabricated to meet these challenges.

Austenitic stainless steel welds are inspected with X-ray radiography (RT) and advanced ultrasonic NDT such as phased array ultrasonic testing (PAUT).

Second, guided wave propagation in elastic structures is discussed. High frequency guided waves within thick structures and along weld geometries are discussed. Furthermore, the interaction of weld guided waves with defects is examined through Pitch-Catch and Scanning Laser Doppler Vibrometer (SLDV) methods. The thesis finishes with a comparison between NDT and SHM followed by a summary, conclusions, and suggestions for future work.

Rights

© 2016, Saad Mohammed

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