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Proceedings Paper

Response of a structural health monitoring fastener to fatigue crack growth and loads in metallic joints
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Paper Abstract

Fatigue cracks initiating at fastener hole locations in metallic structure are among the most common form of airframe damage. Current methods for inspecting airframes for these cracks are manual, whereby inspectors rely on nondestructive inspection equipment or hand-held probes to scan over areas to be monitored. Use of this equipment often demands disassembly of the airframe to search appropriate hole locations for cracks, which elevates the complexity and cost of maintenance inspections. In this study an Additive, Interleaved, Multi-layer Electromagnetic (AIME) sensor was developed and integrated with the shank of a fastener to form a Structural Health Monitoring Fastener, a new technology targeted at insitu detection of fastener hole cracks. The major advantages of the Structural Health Monitoring (SHM) Fastener over other SHM technologies are its installation, which does not require joint layer disassembly, its capability to detect inner layer cracks in a multi-layer joint, and its capability to operate in a continuous monitoring mode. The AIME sensor design, SHM Fastener, and complete SHM system are presented along with experimental results from a series of single-layer and bolted double lap-joint aluminum specimens to validate the capability of these sensors to monitor metallic joints for fastener hole cracks and loads. Fatigue cracks were successfully tracked to over 0.7 inches from the fastener hole in these tests. Sensor output obtained from single-layer fatigue specimens was compared with analytical predictions for fatigue crack growth versus cycle number showing a good correlation in trend between sensor output and predicted crack size.

Paper Details

Date Published: 30 March 2009
PDF: 11 pages
Proc. SPIE 7292, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2009, 72921K (30 March 2009); doi: 10.1117/12.816017
Show Author Affiliations
Alexi S. Rakow, Stanford Univ. (United States)
Fu-Kuo Chang, Stanford Univ. (United States)

Published in SPIE Proceedings Vol. 7292:
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2009
Masayoshi Tomizuka, Editor(s)

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