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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Metal-matrix composites embedded with piezoelectric PVDF sensors using ultrasonic additive manufacturing
Metal-matrix composites with active components have been investigated as a way to functionalize metals. As opposed to surface-mounted approaches, smart materials embedded in metals can be effectively shielded against the environment while providing in-situ sensing, health monitoring, actuation, or energy harvesting functions. Typical manufacturing approaches can be problematic, however, in that they may physically damage the smart material or degrade its electromechanical properties. For instance, non-resin-based embedment procedures such as powder metallurgy involve isostatic compression and diffusion bonding, leading to high process temperatures and breakdown of the electromechanical properties of the active component to be embedded. This paper presents the development and characterization of an aluminum-matrix composite embedded with piezoelectric polyvinylidene fluoride (PVDF) sensors using ultrasonic additive manufacturing (UAM). UAM incorporates the principles of solid-state, ultrasonic metal welding and subtractive processes to fabricate metal-matrices with seamlessly embedded smart materials and without thermal loading. As implemented in this study, the UAM process uses as-received, commercial Al 6061 tape foilstock and TE Connectivity PVDF film. In order to increase the mechanical coupling between the sensor and the metal-matrix without the aid of adhesives, the PVDF sensor is embedded with an empirically optimized pre-compression defined by the tape foils welded above the sensor. The specimen is characterized by tensile (d31 mode), bending (d31 mode), and compression tests (d33 mode) to evaluate its functional performance. Within the investigated load range, the specimen exhibits open-circuit sensitivities of 4.6 mV/N under uniaxial tension and 9.7 mV/N under compressive impulse tests with better than 95% linearity and frequency bandwidth of several kilohertz. The technology presented in this study could be applied for load and tactile sensing, impact detection and localization, thermal measurements, energy harvesting, and non-destructive testing applications.
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- Award ID(s):
- 1738723
- PAR ID:
- 10228087
- Editor(s):
- Meyendorf, Norbert G.; Farhangdoust, Saman
- Date Published:
- Journal Name:
- NDE 4.0 and Smart Structures for Industry, Smart Cities, Communication, and Energy
- Page Range / eLocation ID:
- 8
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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Abstract Additive manufacturing (AM) of complex three‐dimensional (3D) metal oxides at the micro‐ and nanoscales has attracted considerable attention in recent years. State‐of‐the‐art techniques that use slurry‐based or organic–inorganic photoresins are often hampered by challenges in resin preparation and synthesis, and/or by the limited resolution of patterned features. A facile process for fabricating 3D‐architected metal oxides via the use of an aqueous metal‐ion‐containing photoresin is presented. The efficacy of this process, which is termed photopolymer complex synthesis, is demonstrated by creating nanoarchitected zinc oxide (ZnO) architectures with feature sizes of 250 nm, by first patterning a zinc‐ion‐containing aqueous photoresin using two‐photon lithography and subsequently calcining them at 500 ºC. Transmission electron microscopy (TEM) analysis reveals their microstructure to be nanocrystalline ZnO with grain sizes of 5.1 ± 1.6 nm. In situ compression experiments conducted in a scanning electron microscope show an emergent electromechanical response: a 200 nm mechanical compression of an architected ZnO structure results in a voltage drop of 0.52 mV. This photopolymer complex synthesis provides a pathway to easily create arbitrarily shaped 3D metal oxides that could enable previously impossible devices and smart materials.
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Purpose Ultrasonic additive manufacturing (UAM) is a solid-state joining technology used for three-dimensional printing of metal foilstock. The electrical power input to the ultrasonic welder is a key driver of part quality in UAM, but under the same process parameters, it can vary widely for different build geometries and material combinations because of mechanical compliance in the system. This study aims to model the relationship between UAM weld power and system compliance considering the workpiece (geometry and materials) and the fixture on which the build is fabricated. Design/methodology/approach Linear elastic finite element modeling and experimental modal analysis are used to characterize the system’s mechanical compliance, and linear system dynamics theory is used to understand the relationship between weld power and compliance. In-situ measurements of the weld power are presented for various build stiffnesses to compare model predictions with experiments. Findings Weld power in UAM is found to be largely determined by the mechanical compliance of the build and insensitive to foil material strength. Originality/value This is the first research paper to develop a predictive model relating UAM weld power and the mechanical compliance of the build over a range of foil combinations. This model is used to develop a tool to determine the process settings required to achieve a consistent weld power in builds with different stiffnesses.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1117/12.2581845
