Structural health monitoring (SHM) is a rapidly growing field focused on detecting damage in complex systems before catastrophic failure occurs. Advanced sensor technologies are necessary to fully harness SHM in applications involving harsh or remote environments, life-critical systems, mass-production vehicles, robotic systems, and others. Fiber Bragg Grating (FBG) sensors are attractive for in-situ health monitoring due to their resistance to electromagnetic noise, ability to be multiplexed, and accurate real-time operation. Ultrasonic additive manufacturing (UAM) has been demonstrated for solid-state fabrication of 3D structures with embedded FBG sensors. In this paper, UAM-embedded FBG sensors are investigated with a focus on SHM applications. FBG sensors embedded in an aluminum matrix 3 mm from the initiation site are shown to resolve a minimum crack length of 0.286 ± 0.033 mm and track crack growth until near failure. Accurate crack detection is also demonstrated from FBGs placed 6 mm and 9 mm from the crack initiation site. Regular acrylate-coated FBG sensors are shown to repeatably work at temperatures up to 300 ∘ C once embedded with the UAM process.
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HIGH TEMPERATURE CHARACTERIZATION OF FIBER BRAGG GRATING SENSORS EMBEDDED INTO METALLIC STRUCTURES THROUGH ULTRASONIC ADDITIVE MANUFACTURING
Embedded fiber Bragg grating (FBG) sensors are attractive
for in-situ structural monitoring, especially in fiber reinforced
composites. Their implementation in metallic structures is hindered
by the thermal limit of the protective coating, typically a
polymer material. The purpose of this study is to demonstrate
the embedding of FBG sensors into metals with the ultimate objective
of using FBG sensors for structural health monitoring of
metallic structures. To that end, ultrasonic additive manufacturing
(UAM) is utilized. UAM is a solid-state manufacturing
process based on ultrasonic metal welding that allows for layered
addition of metallic foils without melting. Embedding FBGs
through UAM is shown to result in total cross-sectional encapsulation
of the sensors within the metal matrix, which encourages
uniform strain transfer. Since the UAM process takes place at essentially
room temperature, the industry standard acrylate protective
coating can be used rather than requiring a new coating
applied to the FBGs prior to embedment. Measurements presented
in this paper show that UAM-embedded FBG sensors accurately
track strain at temperatures higher than 400 C. The
data reveals the conditions under which detrimental wavelength
hopping takes place due to non-uniformity of the load transferred
to the FBG. Further, optical cross-sectioning of the test specimens
shows inhibition of the thermal degradation of the protective
coating. It is hypothesized that the lack of an atmosphere
around the fully-encapsulated FBGs makes it possible to operate
the sensors at temperatures well above what has been possible
until now. Embedded FBGs were shown to retain their coatings
when subjected to a thermal loading that would result in over 50
percent degradation (by volume and mass) in atmospherically
exposed fiber.
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- Award ID(s):
- 1738723
- NSF-PAR ID:
- 10060497
- Date Published:
- Journal Name:
- Proceedings of the ASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems
- Volume:
- SMASIS2017
- Issue:
- 3840
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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