With increasing applications of composite materials, their health monitoring is of growing importance in engineering practice. Damage development in composite materials is more complex than for metallic materials, because in composite materials (a) multiple damage modes are simultaneously in play, and (b) individual 'damage events' that occur throughout a component's service life may neither noticeably affect its performance, nor suggest future failure. Therefore, informed health monitoring of composite components must include monitoring and analysis of their health state throughout their service life.
A crucial aspect of the health monitoring process of composites is the development of tools to help with this goal of understanding the health state of composites throughout their life. This knowledge can lead to timely anticipation of future failure in composite components, and advance the state of current technology. One, timely maintenance can be planned in advance. Two, each component's service life can be determined based on its individual health information, rather than empirical statistics of previously failed components. This dissertation develops such tools and methods.
Composite specimens of multiple ply-layups are subjected to tensile loading schemes until failure. Pencil Lead Breaks (PLBs) are used to simulate Acoustic Emission sources and generate acoustic waves that are acquired by installed piezoelectric sensors. A numerical method to estimate the arrival of wave modes from ultrasonic signals is presented. Methods are also presented that utilize PLB signals to indicate approaching failure of specimens under monotonic as well as cyclic loading. These processes have been developed prioritizing simplicity and ease-of-execution, to be adapted for practical deployment. / Ph. D. / Composites are modern engineering materials comprising strong load-bearing elements (such as carbon fibers) embedded in a binding polymer matrix (such as epoxy). Material properties in composite materials are directional in nature, and composite plies can be combined in layers to create components with specified engineering properties. Composites are therefore increasingly being used in diverse engineering applications.
Composite materials, however, are relatively complex in their damage development and failure. Unlike in metallic materials, damage in composites can progress via several different mechanisms. Further, numerous small damage events may occur throughout the service life of a composite component, which neither noticeably affect performance, nor forewarn of impending failure. Therefore, it is of crucial importance to develop tools and methods that improve the health analysis and anticipation of future failure in composites.
This dissertation develops such methods and tools. Composite specimens with several different ply sequences are experimentally subjected to tensile loading schemes until failure. Pencil Lead Breaks (PLBs) are used to simulate Acoustic Emission stress waves throughout each experiment, and these ultrasonic waves are acquired for further data analysis using installed piezoelectric sensors. A numerical method is developed that automatically estimates the arrival times of two fundamental wave modes in sets of acquired acoustic ultrasonic signals. Methods are also developed that utilize PLB signals to anticipate future failure of composite specimens under two different loading regimes.
The contributions herein prioritize simplicity and easy execution, to be adapted for practical deployment, and are applicable for a wide variety of fiber-reinforced composites.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/78766 |
| Date | 29 August 2017 |
| Creators | Gupta, Arnab |
| Contributors | Engineering Science and Mechanics, Duke, John C. Jr., Case, Scott W., Dowling, Norman E., Patil, Mayuresh J., Paul, Mark R. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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