In this study, autonomous composites (AutoCom) are suggested by embedding multifunctional mechano-luminescenceoptoelectronic (MLO) composites into fiber reinforced polymer (FRP) structural composites. The AutoCom is designed for next generation unmanned aerial vehicles to enhance self-sustainability by benefiting from the self-powered strain sensing damage detection capability. The MLO composites generate direct current (DC) in response to mechanical stimuli, and the generated DC varies with magnitude of strain and strain rate. The DC-based strain sensing capability of MLO composites enables AutoCom to measure strain by itself without any external electrical source. The strain sensing data produced from the AutoCom can be potentially used to detect damage using vibration-based damage detection scheme. First, the MLO composites are fabricated by assembling two functional building blocks, such as mechanooptoelectronic (MO) poly(3-hexylthiophene) (P3HT)-based sensing thin films and mechano-luminescent (ML) copperdoped zinc sulfide (ZnS:Cu)-based elastomeric composites. The MLO composites’ self-powered strain sensing capability is validated by subjecting the MLO composites to cyclic tensile strains. Second, AutoCom specimen is fabricated and tested for validating its self-powered strain sensing capability using four-point bending test. Third, mechanical properties of the AutoCom are assessed through theoretical study by comparing to FRP composites without MLO embedment. Last, strain-based system identification methodology is proposed and used for performing system identification of FRP composites.
Aerospace structural systems are prone to structural damage during their use by vibration, impact, material degradation, and other factors. Due to the harsh environments in which aerospace structures operate, aerospace structures are susceptible to various types of damage and often their structural integrity is jeopardized unless damage onset is detected in timely manner. Yet, current state-of-the-art sensor technologies are still limited for structural health monitoring (SHM) of aerospace structures due to their high power consumption, need for large form factor design, and manageable integration into aerospace structures. This study proposes a design of multilayered self-powered strain sensor by coupling mechano-luminescent (ML) property of copper-doped zinc sulfide (ZnS:Cu) and mechano-optoelectronic (MO) property of poly(3-hexylthiophene) (P3HT). One functional layer of the self-powered strain sensor is ZnS:Cu-based elastomeric composites that emit light in response to mechanical deformation. Another functional layer is P3HT-based thin films that generate direct current (DC) under light illumination and DC magnitude changes with applied strain. First, ML light emission characteristics of ZnS:Cu-based composites are studied under cyclic tensile strain with two various maximum strain up to 10% and 15% at various loading frequencies from 5 Hz to 20 Hz. Second, piezo-optical properties of P3HT-based thin films are investigated by acquiring light absorption of the thin films at various strains from 0% to 2% tensile strain. Last, micro-mechanical properties of the P3HT-based thin films are characterized using nanoindentation.
This study aims to devise multifunctional composites using fracto-mechanoluminescent (FML) materials and photoactive sensing thin films for autonomous and self-powered impact damage detection. In previous studies, multifunctional photoactive thin films were suggested as a strain sensor that does not require any external electrical source. Instead, the photoactive thin films generated direct current (DC) (or photocurrent) under ambient light, whose magnitude varied linearly with applied strain. In this study, multifunctional FML materials-photoactive thin film composites will be devised for autonomously sensing high-speed compressive strains without supplying any external photonic or electrical energy. FML materials exhibit transformative properties that emit light when its crystalline structures are fractured. The developed photoactive strain sensing thin film will be integrated with the FML materials. Thus, it is envisioned that the FML materials will emit light, which will be supplied to the photoactive sensing thin films when the high-speed compressive loadings break FML materials’ crystalline structures. First, synthesized europium tetrakit(dibenzoylmethide) triethylammonium (EuD4TEA) crystals will be embedded in the elastomeric and transparent polydimethylsiloxane (PDMS) matrix to prepare test specimens. Second, the FML properties of the EuD4TEA-PDMS composites will be characterized at various compressive strains, which will be applied by Kolsky bar testing setup. Light emission from the EuD4TEA-PDMS test specimens will be recorded using a high-speed camera. Intensity of the light emissions will be quantified via image processing techniques by taking into account pixel profiles of the high-speed camera captured images (e.g., pixel values, counts of pixels, and RGB values) at various levels of compressive strains. Lastly, the autonomous high-speed compressive sensor modules will be fabricated by integrating the EuD4TEA-PDMS composites with the photoactive thin film sensor. Self-powered sensing capability will be validated by measuring DC at various compressive strains.
Structural systems deteriorate due to excessive deformation and corrosive environments. If damage is left undetected, they can propagate to cause sudden collapse. However, one of the main difficulties of monitoring damage progression is that, for example, excessive/plastic deformation and corrosion are drastically different physical processes. Strain is a mechanical phenomenon, whereas corrosion is a complex electrochemical process. The current strategy for structural health monitoring (SHM) is to use either different types of sensors or to employ system identification for quantifying overall changes to the structure. In this study, an alternative SHM paradigm is proposed in that a single, multifunctional material would be able to selectively sense different but simultaneously occurring structural damage. In particular, a photoactive and self-sensing thin film was developed for monitoring strain and corrosion. Another unique aspect was that the films were self-sensing and did not depend on external electrical energy for operations. First, the thin films were fabricated using photoactive poly(3-hexylthiophene) (P3HT) and other functional polymers using spin-coating and layerby- layer assembly. Second, the fabricated thin films were interrogated using an ultraviolet-visible (UV-Vis) spectrophotometer for quantifying their optical response to applied external stimuli, such as strain and exposure to pH buffer solutions. Lastly, the multifunctional thin films were tested and validated for strain and pH sensing. Interrogation of these separate responses was achieved by illuminating the thin films different wavelengths of light and then measuring the corresponding electrical current generated.
There is a dire need to develop novel robust and reliable sensing technologies for identifying the onset of structural
damage and for preventing sudden catastrophic structure failures. While numerous sensors (e.g., fiber optics, wireless
sensors, piezoelectrics, and remote sensing, among others) have been proposed for structural health monitoring, the
current generation of sensing systems suffer from some fundamental limitations such as discrete sensing and high energy
demand. In this study, a new paradigm for strain sensing and structural monitoring is proposed by developing a novel
optoelectronic nanocomposite that can generate strain-sensitive photocurrent. Unlike other common sensing transducers,
the proposed nanocomposite sensor is a self-sensing material, is conformable to structural surfaces, is of small form
factor, and does not require an external power source. First, regioregular poly(3-hexylthiophene) (P3HT) conductive
polymer (i.e., the main photoactive component of the nanocomposite) is synthesized in the laboratory and characterized
via nuclear magnetic resonance (NMR). Second, thin films comprising of P3HT and carbon nanotubes are fabricated via
spin coating. Upon specimen fabrication, the nanocomposite's photocurrent generation capabilities are investigated and
evaluated. Finally, thin film specimens are loaded in an electromechanical load frame, and the preliminary results show
that the magnitude of generated photocurrent varies in tandem with applied tensile strains.
Conference Committee Involvement (8)
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2025
17 March 2025 | Vancouver, Canada
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2024
25 March 2024 | Long Beach, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2023
13 March 2023 | Long Beach, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
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Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
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Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
27 April 2020 | Online Only, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
4 March 2019 | Denver, Colorado, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
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