Dissertations / Theses on the topic 'Thermal Arrest Memory Effect'

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xix, 156 p.; also includes graphics (some col.). Includes bibliographical references (p. 152-156).

Shape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of this work is to develop an SMA based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulk head arrangement for NASA. The design of the thermal conduction switch is based on a biased, two-way SMA actuator and utilizes a commercially available NiTi alloy as the SMA element to demonstrate the feasibility of this concept. This work describes the design from concept to implementation, addressing methodologies and issues encountered, including: a finite element based thermal analysis, various thermo-mechanical processes carried out on the NiTi SMA elements, and fabrication and testing of a prototype switch. Furthermore, recommendations for improvements and extension to NASA's requirements are presented. Such a switch has potential application in variable thermal sinks to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. The SMA thermal conduction switch offers the following advantages over the currently used gas gap and liquid gap thermal switches in the cryogenic range: (i) integrates both sensor and actuator elements thereby reducing the overall complexity, (ii) exhibits superior thermal isolation in the open state, and (iii) possesses high heat transfer ratios between the open and closed states. This work was supported by a grant from NASA Kennedy Space Center (NAG10-323) with William U. Notardonato as Technical Officer.
M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering

Le projet de cette thèse est d'évaluer les propriétés multicaloriques, et notamment magnétocaloriques et élastocaloriques éventuellement couplées entre elles des alliages d'Heusler de type Ni-Mn-X (X= In, Co-In,...). C'est une recherche amont pouvant rapidement conduire à la recherche de développement de nouveaux dispositifs de refroidissement ou de nouvelles fonctionnalités d'où l'intérêt porté par certains acteurs du monde socio-économique. D'un point de vue fondamental, il s'agissait d'étudier la transformation structurale et magnétique qui se produit en température entre la phase cubique à haute température dite « austénite » et la phase basse température dite « martensite ». L'application d'un champ magnétique ou d'une contrainte uniaxiale déplace les températures de transformation respectivement vers les basses températures ou les hautes températures et permet également d'induire la transformation d'une phase vers l'autre. Les propriétés multicaloriques résultent de la variation d'entropie conséquente à l'application des champs mentionnés ci-dessus d'autant plus importante qu'elle se produit proche de la température de transformation.Un effort soutenu a été porté sur la détermination de la structure martensitique qui reste à ce jour non consensuelle au travers des résultats de la littérature. Or la martensite est responsable des propriétés à mémoire de forme et une connaissance de la structure a permis d'éclairer la transformation martensitique à la base des propriétés élastocaloriques.L'originalité de l'étude reposait à la fois dans l'étude des propriétés élastocaloriques, moins étudiées que les propriétés magnétocaloriques, et sur une combinaison d'approches théoriques et expérimentales. En effet, les études de diffractions neutroniques ont permis de mieux comprendre la structure cristallographique des phases. Elles ont été couplées avec des mesures expérimentales visant à déterminer les variations d'entropie. Ces mesures expérimentales reposaient également sur la mise en place de systèmes de mesure versatiles combinant généralement l'application d'une contrainte uniaxiale, un balayage en température (77K – 400K), des mesures fines en température ou en transport et l'application éventuelle d'un champ magnétique. Cette versatilité expérimentale mise en œuvre a permis d'appréhender dans sa globalité l'effet élastocalorique des alliages ferromagnétiques à mémoire de forme
This manuscript is devoted to the study of the multicaloric properties, and in particular magnetocaloric and elastocaloric properties possibly coupled between them, of Ni-Mn-X type Heusler alloys (X= In, Co-In,...). This preliminary research can quickly lead to the development of new cooling devices or new functionalities, hence the interest shown by certain players in the socio-economic world. To achieve this, we studied the structural and magnetic transformation that occurs in temperature between the high-temperature cubic phase known as « austenite » and the low-temperature phase known as « martensite ». The application of a magnetic field or a uniaxial strain shifts the transformation temperatures respectively towards low temperatures or high temperatures and also makes it possible to induce the transformation from one phase to the other. The multicaloric properties result from the near-transformation-temperature-entropy-variation due to the application of those external perturbations.A particular effort has been made to determine the non-consensual martensitic structure. However, martensite is responsible for shape memory properties and a knowledge of the structure led to the understanding of the martensitic transformation at the basis of elastocaloric properties.The originality of the study wad both on the study of elastocaloric properties and on a combination of theoretical and experimental approaches. Indeed, neutron diffraction studies have led to a better understanding of the crystallographic structures. They were coupled with experimental measurements to determine the entropy variations. Those measurements were based on the implementation of versatile measurement systems generally combining the application of uniaxial strains, temperature scanning (77K - 400K), fine temperature or transport measurements and the possible application of a magnetic field. This experimental versatility has made it possible to fully understand the elastocaloric effect of shape memory ferromagnetic alloys

Cellulose is the most abundant biopolymer on Earth as it is found in every plant cell wall; therefore, it represents one of the most promising natural resources for the fabrication of sustainable materials. In plants, cellulose is mainly used for structural integrity, however, some species organise cellulose in helicoidal nano-architectures generating strong iridescent colours. Recent research has shown that cellulose nanocrystals, CNCs, isolated from natural fibres, can spontaneously self-assemble into architectures that resemble the one producing colouration in plants. Therefore, CNCs are an ideal candidate for the development of new photonic materials that can find use to substitute conventional pigments, which are often harmful to humans and to the environment. However, various obstacles still prevent a widespread use of cellulose-based photonic structures. For instance, while the CNC films can display a wide range of colours, a precise control of the optical appearance is still difficult to achieve. The intrinsic low thermal stability and brittleness of cellulose-based films strongly limit their use as photonic pigments at the industrial scale. Moreover, it is challenging to integrate them into composites to obtain further functionality while preserving their optical response. In this thesis, I present a series of research contributions that make progress towards addressing these challenges. First, I use an external magnetic field to tune the CNC films scattering response. Then, I demonstrate how it is possible to tailor the optical appearance and the mechanical properties of the films as well as to enhance their functionality, by combining CNCs with other polymers. Finally, I study the thermal properties of CNC films to improve the retention of the helicoidal arrangement at high temperatures and to explore the potential use of this material in industrial fabrication processes, such as hot-melt extrusion.

Thermally activated NiTi based Shape Memory Alloys (SMAs) are of tremendous practical interest as actuators in varied engineering applications owing to its characteristic Martensitic Phase Transformation (MPT). The MPT in thermally activated SMAs from a parent Austenite (A) to a product Martensite (M) structure, can be brought by a change in temperature or stress and is accompanied by reversible strain, typically between 5-8% whichis exploited in commercial applications. In practical applications, due to varied nature of thermomechanical loading, this phase transformation can be partial, incomplete, interrupted or discontinuous. While significant body of literature exists on phase evolution in kinetics, several aspects of kinetics still need focused study. Furthermore, this MPT is also accompanied by several effects like latent heat of transformation, changes in modulii, specific heat, thermal conductivity and electrical resistivity which gives rise to a coupled the thermal mechanical and electrical problem. A better experimental understanding of the kinetics of phase transformation and a modeling framework that can predict the response under realistic application scenarios would facilitate better design and efficient applications. With this motivation, this thesis attempts to highlight the SMA response in general and phase kinetics in particular and develop models with desired predictive capability.Different types of thermal cyclic loads are chosen to induce different types of partial or interrupted transformations. Arbitrary loads leading to partial or incomplete transformation in both forward and reverse loading directions is studied with series of experiments on wire form NiTi based SMAs. Type of loading that involves transformation interrupted or incomplete and the loading does not induce reverse transformation and the transformation resumes upon increased loading in subsequent cycles. As the transformation in such loading are arrested it is referred as Thermal Arrest Memory Effect (TAME). It is reported in the literature that TAME is associated only during the MA transformation, the present study brings out a case wherein the AM transformation also exhibits TAM. Experiment shows during TAME, the material remembers the loading condition at which the transformation was arrested. In contrast during the loading with partial loops a “memory” of the state corresponding to the maximum evolution of the product phase is present in the material. Furthermore, this study, shows that the memory is not perfect and transformation seem to resume at a loading level that is lesser than the previously applied load level. For a better understanding of the kinetics of phase transformation and a modeling framework that can predict the response under realistic application scenarios would facilitate better design and efficient applications. A relatively simple phenomenological model with memory parameter is proposed to capture the hysteretic response under arbitrary thermomechanical loading. Distance of a point on the load path, In the σ -T phase diagram is used as the memory parameter. To also incorporate the observed imperfection in memory and stabilization associated with it, another empirical material dependent parameter is introduced in the form of „stabilization parameter”. The proposed model with these two new parameters is shown to be able to capture the complex response of SMAs under arbitrary thermomechanical loading under 1-D loading. A 3-D SMA material model extended from the earlier developed 1-D model using the principles of generalized plasticity is formulated. This methodology is used to solve several case studies of practical relevance to highlight the capability of the proposed methodology to solve complex IBVPs. Numerical case studies have clearly highlighted that the proposed model can capture realistic SMA response under combined electro-thermo-mechanical loading. Furthermore, effect of conditions like crimping of wires, multi-axial state of stress and geometric complexities like notches on the phase inhomogeneity is clearly illustrated. The present work may be extended to assess the role of such phase inhomogeneities on the functional and mechanical fatigue of SMAs under arbitrary cyclic loading.

碩士
國立中山大學
材料與光電科學學系研究所
103
In this study, three kinds of resistive switching mechanism: Forming、Reset、Set process in Resistance Random Access Memory(RRAM) will be discussion. And measure by Agilent B1530 fast IV measurement instrument, it makes the time resolution in 10 ns, providing instantaneous observation. The first three part, RRAM was connected in transistor drain, the transistor acts as current controller in order to prevent huge current passing through RRAM causing it hard breakdown result it couldn’t operate normally. As the Forming process compliance current is more larger, it’s High Resistance State(HRS) will distribute from high to low and fitting the I-V curve, the electron transported in HRS by different way. In the Reset process, by controlling different of triangle pulse Raising time to modulate the Heating time before starting Reset. When the Heating time is more longer, the HRS will gradually increasing and stop at a saturation value. The HRS has different because of the heat activing the different of number oxygen(active O2-),the final saturation value is causing by the maximum voltage. Reset input larger power rate, the HRS will larger, too. In Set process, hafnium oxide was served as RRAM active layer, deposited by Atomic Layer Deposition (ALD) with a thickness of 10nm, Applying a triangle pulse, causing RRAM set to the Low Resistance State (LRS).And calculating the charge quantity during set process in different switching time. It could divide into two switching processes.Besides, the I-V curve fitting shows there are two step of Schottky emission conduction mechanism. The second Schottky emission was special and it was caused by the oxygen ion accumulation.

碩士
國立交通大學
電子工程系所
98
In this thesis, we used metal-oxide-metal (MOM) structure of nickel (Ni), non-stoichiometric hafnium oxide (HfOx), and titanium nitride (TiN) to demonstrate RRAM characteristics. Voltage-induced resistance switching is repeatedly observed in the Ni/HfOx/TiN device with average resistance ratio greater than 100. The HfOx film which is annealed in Ar ambient exhibits large current operation. It is probably due to crystallization of HfOx film by X-Ray Diffraction (XRD) result. In order to reduce power dissipation, HfOx is oxygen annealed and we use filamentary model to explain the measured data. Measurement result shows that all operation current and power are smaller about 10 times than the sample which is not annealed in O2 ambient. Operation voltage is not elevated noticeably and endurance is slightly improved after oxygen annealing process. Besides, data retention and non-destructive readout are tested in this thesis. Our study shows that the annealed Ni/HfOx/TiN RRAM is a promising candidate for low power nonvolatile memory applications.

碩士
國立交通大學
電機學院微電子奈米科技產業專班
98
In recent years, nonvolatile memory research of person more and more, among them in order to resistive random access memory (RRAM) have attracted a large attention, including simple structure, low power consumption, high operation speed, low operation voltage, long retention time, high endurance, non-destruvtive readout, and small cell size. Accordingly, RRAM has been proposed to be one candidate of next generation nonvolatile memory. In this thesis, the HfO2 resistive switching device offers a promising potential for high density and low power memory application with the ease of processing integration. First, we would introduce fundamental Current-Voltage characters of the bistable resistive switching behavior. The Pd and Pd/Al was doped top electrical with different treatment by sputtering method, and discussion treatment effect. Finally, we would decline the conduction mechanism of the device and discuss the influence of treatment. We would choose is operation of low-voltage as development component later.

碩士
國立臺灣大學
材料科學(工程)研究所
84
In this work,six CuAlBe shape memory alloys with different chemical compositions around eutectoid and a Zr content Cu-11.87 wt%Al-0.594wt%Be-0.949wt%Zr alloy were aged at 260、350 ℃ and 400℃.In order to study the effects of Be and Al on the various pro- perties of the alloys,the transformation temperatuers of the aged alloys were estimated by resistance method;the microstructures of the alloys were observed by SEM and TEM;the shape memory recovery of the alloys were examined by bending test and MTS tensile test. There are various precipetates such as.alpha.,.alpha.1-plate, .gamma.2(Al4Cu9), coherent precipitates,and eutectoid phases in the grain boundary were ob served during isothermal aging of the alloys. These precipitates with different effects on retarding martensitic transformation result in much large variation in the transformation temperature of the alloys after thermal cycling . The Cu-11.91Al-0.54Be alloy aged at 260℃*600hr shows the largest effect mation temperatures,the Ms of the alloy increases 66.5℃ after 100cycles.For the alloys aged at 350℃ and 400℃,the change of Ms much smaller than at 260℃ because the discontinous precip- itates at grain boundary are dominate. For the alloys with the .alpha.1-plate precipitates,the more Be content,the larger varia- tion in the thermal cycle transformation temperature after aging. To study the pseudo- elasticity and the effects on the mecha- nical properties of the refined alloys,adding Zr to refine the grain size of the alloys and using 1% and 3% strain cycle by dy- namical tensile test.The alloys show excellent superelasticity and short fatigue life.For the alloys aged at 260℃ and 3% strain cycle, the strain recovery lower than 100% .But for the alloys aged at 260℃ for 200hr and 1% strain cycle,the best strain re- covery,100% ,could be reached.The refined alloys show very good superelasticity and long fatigue life.

碩士
國立臺灣大學
材料科學與工程學研究所
88
In this work, two kinds of Cu-Al-Mn shape memory alloys with different chemical compositions (Cu-8wt%Al-10wt%Mn, Cu-8wt%Al-9wt%Mn) were melted by VAR. After homogenized and hot rolled, the specimens were heat-treated by direct-quench or step-quench into oil-bath at 100℃, 150℃and 200℃. Then they were investigated by electrical resistance measurement, hardness test and shape memory recovery test to get their characteristics. Further studies were also conducted by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and X-ray diffraction (XRD) in order to get the different phase structures of the alloys. Besides, thermal cycling experiments were used to study the effect of thermal cycling on the Shape Memory Alloy. The results shows that whether under direct-quench or step-quench treatments, both martensites in the two alloys are M18R type, and the extent of monoclinicity is greatly influenced by alloy-type and methods of heat treatment. In Cu-8Al-10Mn alloy, the 150℃ step-quenched specimen has the relatively greatest ordering; while in Cu-8Al-9Mn alloys, it is the direct-quenched one gets the first place. Moreover, when the step-quenched specimen proceeds cycling tests, the hysteretic loop area will get smaller with increasing cycling numbers, which means the shape recovery ability has a decreasing tendency. However, it doesn’t go this way under direct-quench treatment and shape recovery test shows that direct-quenched specimen has better shape memory effect.