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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Numerical modeling of mechanical properties of UAM-processed reinforced aluminum hat sections for automotive applications
Structural lightweighting is a key initiative in the automotive sector due to regulatory, customer, and powertrain demands. This research focuses on reinforcing aluminum sheet metal in strategic locations using ultrasonic additive manufacturing (UAM), as guided through an iterative optimization and simulation process. Among the three models used, the most successful is the multistep model (MSM) which simulates the forming of tailored blanks and the unloading processes to accurately map the hardening and the residual stress in hat and reinforcement sections. The MSM shows that approximately 65% of the mass can be saved by replacing a large gauged sheet metal hat section with a discretely reinforced hat section. Further increases in specific energy absorption (SEA) and additional mass savings can be expected when utilizing higher specific strength and specific stiffness materials for reinforcement such as titanium alloys, composites, or ceramic materials, all of which have been demonstrated with UAM.
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- Award ID(s):
- 1738723
- NSF-PAR ID:
- 10327744
- Date Published:
- Journal Name:
- International journal of material forming
- Volume:
- 14
- Issue:
- 2021
- ISSN:
- 1960-6206
- Page Range / eLocation ID:
- 917–928
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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