1. Αποθετήριο Παραδοτέων Υποτρόφων Δράσεων ΕΣΠΑ Τριτοβάθμιας Εκπαίδευσης 2017-2023
2. Όλο το Αποθετήριο
3. Μεταδιδακτορικοί ερευνητές

Τύπος:	Κείμενο εργασίας
Τίτλος:	Thermal control through multifunctional and atructures and materials
Εναλλακτικός τίτλος:	Θερμοκρασιακός έλεγχος με τη χρήση πολυλειτουργικών και προσαρμοστικών δομών και υλικών
Συγγραφέας:	[EL] Αθανασόπουλος, Νικόλαος[EN] Athanasopoulos, Nikolaos
Ημερομηνία:	18/08/2018
Περίληψη:	In materials engineering and science, urgent needs to be fulfilled are the development of low-weight structures, the integration of different functionalities and sensing abilities, as well as the energy efficiency and financial feasibility in different applications. In this research activity, we present the development of responsive multilayer anisotropic materials capable of transforming their shape under temperature stimulus. The proposed responsive materials were used for the fabrication of more complex smart surfaces with variable and programmable effective thermo-optical properties for the passive thermal control of a body. Furthermore, optimized ultralight smart surfaces for the thermal management in Space applications were thoroughly studied. The calculated and measured variable effective thermo-optical properties were used for the redesign of the thermal control strategy of a certain nano-satellite. We investigated theoretically and experimentally the major parameters and the performance of the proposed low-cost smart surfaces. In nature, extremely complex movements can be realized through the materials’ self-shaping and self-folding capabilities in response to a stimulus. The nonliving tissues of various plants are designed to undergo predetermined shape transformations through their anisotropic fibrous structure. The geometry of these materials can be transformed under humidity or temperature stimulus or both, whereas their initial and final shapes can be determined by the geometry, the homogeneous or nonhomogeneous nature of the materials’ structure, as well as the anisotropic nature of the different layers. Apart from the well-known SMAs and shape-memory polymers (SMPs), three dimensional (3D) printed hydrogel architectures have been developed. Various parameters control the shape transformation of the material, such as the filament size, orientation, and interfilament spacing. A 2D geometry alters its shape to assume a 3D complex geometry in response to a stimulus. Moreover, by observing the manner in which plants and animals control their temperature and their geometrical characteristics, we may deduce that nature is a specialist in purely mechanistic thermal management strategies. Nature addresses thermal management issues—prevention of overheating and damages—through an efficient holistic and mechanistic design approach. While the extremely heavy mechanical systems and complex MEMs use hinges, actuators in order to develop simple movements, in nature extremely complex movements can be realized through the materials’ self-shaping & self-folding capabilities in response to a stimulus. The view factor and the material that is exposed to the environment are regulated in nature for prevention from overheating. In this study we present the development of low-cost anisotropic multilayer films that largely deform when a temperature change occurs; this behaviour is attributed to the mismatch in the coefficient of thermal expansion between the film layers and to the anisotropic structure of the layers that causes the transformation of the material. The proposed responsive multilayer anisotropic materials/films are able to passively react under temperature stimuli by transforming from 2D to 3D complex shapes. The deformation of the developed multilayer anisotropic materials is reversible and repeatable. Owing to their large deformation, one of the most important parameters that affect their integrity is their performance under thermal fatigue conditions. Moreover, two different fabrication processes for the development of 3D complex responsive materials, where the 3D geometry was formed at room temperature (initial shape) and then transformed to a 2D geometry as the temperature increased. The proposed responsive multilayer anisotropic materials were able to passively react under temperature stimuli by transforming their geometry from 3D shapes to 2D shapes. This approach bypasses the use of complex tools to form the geometry of the structure in 3D space. The developed materials and methodologies were used for the design and fabrication of smart surfaces that are capable to alter drastically their effective thermo-optical properties and control passively the temperature of a body. We prove that smart patterned surfaces consisting of smaller structures may be designed to respond uniquely through combinatorial design strategies. When the unit cells are in the closed position, the effective emissivity is small. As the temperature increases, the unit cells open and the effective emissivity increases owing to the internal highemissivity coating, thus creating a variable behaviour as a function of temperature. We studied theoretically and we proved experimentally that we can design the entire emissivity function of a patterned surface through the combination of the orientation and the colour sequences of its motifs. Ultimately, the handling of the effective thermo-optical properties of a surface through a material that interacts with the radiative heat flux and temperature will lead to the development of advanced materials and structures for optimized thermal applications in satellites and other energy systems. Satellites exchange heat with other bodies via thermal radiation, and they control their temperature within the allowable limits using passive and active thermal control systems (TCS). Owing to the variable heat inputs, different strategies, devices, and materials are necessary for the thermal control. The smart surfaces are able to manipulate thermal radiation passively, without the use of controllers, sensors, and power supplies. We developed and studied optimized ultra-light smart surfaces with variable emissivity for Space applications with high Δε in small ΔT. Moreover, we conducted low-cost and out-of-vacuum thermal fatigue tests to measure the shape-shift of the unit cells—which can be caused by the thermal degradation of the material properties. We proved theoretically and experimentally, that it is possible to design the entire emissivity and absorptivity behaviour of the smart surface as a function of temperature, and to significantly alter their values (Δε ≈ 0.7 to 0.8) using a trilayer material. A certain nano-satellite was selected in order to redesign its thermal control using the emissivity and absorptivity curves of the proposed smart surfaces.
Γλώσσα:	Αγγλικά
Τόπος δημοσίευσης:	Patras, Greece
Σελίδες:	121
Θεματική κατηγορία:	[EL] Αεροδιαστημική μηχανική[EN] Aerospace Engineering [EL] Μηχανολογία[EN] Mechanics [EL] Μηχανική Υλικών[EN] Materials Engineering [EL] Εφαρμοσμένη φυσική[EN] Applied Physics
Λέξεις-κλειδιά:	smart materials; biomimetics; bioinspired materials; active materials; responsive materials; thermal radiation; satellites; additve manufacturing; thermal control; thermal protection; large deformation; thermal fatigue; emissivity
Κάτοχος πνευματικών δικαιωμάτων:	Copyright 2018 by Nikolaos Athanasopoulos
Όροι και προϋποθέσεις δικαιωμάτων:	All rights are reserved by Nikolaos Athanasopoulos, and content may not be reproduced, disseminated, published in any form or by any means, except with the prior written permission of the Author. According the official contract (2016-050-0503-8297, MIS 5001552), only the State Scholarships Foundation (IKY) has the permission to disseminate the content of the research activity without the permission of the author. Some parts of the manuscript have been published prior in full or partial form in the following international research journals and conferences. Copyright 2018 by Nikolaos Athanasopoulos https://creativecommons.org/licenses/by-nc-nd/4.0/
Σημειώσεις:	“ECTOTHERM” Thermal control through multifunctional and atructures and materials This research was conducted through the scholarships program of the State Scholarships Foundation (IKY) and is co-financed by the European Social Fund(ESF) and the Greek national funds through the action entitled “Reinforcement of Postdoctoral Researchers” of the National Strategic Reference Framework (NSRF), 2014–2020.
Εμφανίζεται στις συλλογές:	Μεταδιδακτορικοί ερευνητές