Macro-Fiber Composites (MFCs) are a piezoelectric material typically employed in applications ranging from vibration damping to actuation to structural health monitoring. These composites have flown in space but only with thermal protection and for a short duration. They have not been significantly tested under thermally cyclic conditions similar to those they would experience in Low-Earth Orbit (LEO) without shielding. Research has shown that the performance of MFCs varies when the MFC undergoes a thermal cycle. This paper outlines an autonomous experiment that will be able to run impedance measurements and actuate MFCs, further testing their performance in a space environment where thermal cycles are common. This will be installed on a CubeSat and flown to LEO where it will collect data and downlink it back for study. Details of the layout of the experiments and electronic systems being used on the CubeSat for the payload are presented alongside future steps that need to be taken to ensure a successful flight.
Research presented in this paper focuses on the experimental and theoretical analysis of a compact, nonlinear, broadband
energy harvesting device. Cantilevered structure zigzag beams have been shown to have natural frequencies orders of
magnitudes lower than traditional cantilever beam geometries of the same size. Literature has also demonstrated that a
cantilever beam harvester design combined with a magnetic field introduces nonlinearities in the response which can
increase bandwidth of the device. Current energy harvester designs are relatively large in size, are most efficient at high
frequencies, or only useful for narrowband linear operation. The proposed research introduces a zigzag geometry beam
used in conjunction with a magnetic field to create a compact device capable of low frequency broadband energy
harvesting. Experimental results are shown comparing both the linear and nonlinear energy harvesting capabilities of the
zigzag structures. Experimental results are the focus of this paper, however, analytical expressions for the fundamental
mode shape, natural frequency, and electromechanical coupling are presented for the linear lumped parameter system. A
physics based magnetic force model for the nonlinear system is also proposed.
KEYWORDS: Structural health monitoring, Microsoft Foundation Class Library, Damage detection, Composites, Thermal effects, Temperature metrology, Detection and tracking algorithms, Nondestructive evaluation, Ferroelectric materials, Epoxies
This work focuses on investigating the effects of thermal cycles in the impedance-based damage detection performance of Macro-Fiber Composites (MFC). A host structure with an MFC bonded to its surface is submitted to a 90 minutes temperature cycle that varies from -20°C to 65° C. After each cycle the electrical impedance of the test sample is measured with and without the presence of a representative damage (an added mass). The results indicate that the thermal cycling affects the smart device by changing its impedance profile, a phenomenon that should be taken into account in damage detection algorithms.
KEYWORDS: Structural health monitoring, Sensors, Acoustics, Digital signal processing, Ferroelectric materials, Prototyping, Signal processing, Signal generators, Discrete wavelet transforms, Aluminum
Structural damage for spacecraft is mainly due to impacts such as collision of meteorites or space debris. We present a
structural health monitoring (SHM) system for space applications, named Adverse Event Detection (AED), which
integrates an acoustic sensor, an impedance-based SHM system, and a Lamb wave SHM system. With these three
health-monitoring methods in place, we can determine the presence, location, and severity of damage. An acoustic
sensor continuously monitors acoustic events, while the impedance-based and Lamb wave SHM systems are in sleep
mode. If an acoustic sensor detects an impact, it activates the impedance-based SHM. The impedance-based system
determines if the impact incurred damage. When damage is detected, it activates the Lamb wave SHM system to
determine the severity and location of the damage. Further, since an acoustic sensor dissipates much less power than the
two SHM systems and the two systems are activated only when there is an acoustic event, our system reduces overall
power dissipation significantly. Our prototype system demonstrates the feasibility of the proposed concept.
We present a prototype human assistant system for space crew assessment and mission management. Our system is based on case episodes from American and Russian space missions and analog environments such as polar stations and undersea habitats. The general domain of small groups in isolated and confined environments represents a near ideal application area for case-based reasoning (CBR) -- there are few reliable rules to follow, and most domain knowledge is in the form of cases. We define the problem domain and outline a unique knowledge representation system driven by conflict and communication triggers. The prototype system is able to represent, index, and retrieve case studies of human performance. We index by social, behavioral, and environmental factors. We present the problem domain, our current implementation, our research approach for an operational system, and prototype performance and results.
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