The unique features of flexoelectric and dielectric effects are investigated, and exploited for a variety of functions, in a wide range of helicoidal liquid crystal systems, including non-chiral, cholesteric and blue phases. Electrooptic techniques are developed to measure flexoelectric parameters in non-chiral and cholesteric liquid crystals using twisted nematic and Grandjean geometries respectively. A crystal rotation method, and using a lock-in amplifier, is used to enable the measurement of a very small e/K of 0.011 C/N^-1m^-1. Enhancement in chiral-flexoelectric switching is demonstrated theoretically in liquid crystals with negative dielectric anisotropy and in systems in which the pitch is constrained to be other than the natural pitch. A methodological framework for inducing stable Uniform Lying Helix alignment is developed based on weak homeotropic alignment conditions and a method to bias the helicoidal axis orientation; a series of approaches within this framework are demonstrated, including nano-grooved interfaces, periodic boundaries conditions, in-plane fields, and mould-templated micro-channels. The latter approach is potentially commercially viable for sub-millisecond electrooptic technology. The contribution to a cholesteric material's effective dielectric permittivity of flexoelectric polarization is formulated, and an ability to switch a cholesteric between Grandjean and lying-helix configurations based on the dispersion in the flexoelectric polarization and resultant relaxation in dielectric properties is demonstrated. The flexoelectric contribution to dielectric permittivity is exploited to enable switching in bistable reflective displays and alignment of the Uniform Lying Helix. The existence of a flexoelectric contribution to Kerr switching in blue phases is demonstrated, and a semi-empirical model for the effect is developed. The effect is the first known example of a non-polar flexoelectrooptic effect. Independent flexoelectric and dielectric contributions to Kerr switching in blue phases are measured experimentally by measuring the induced birefringence as a function of driving frequency in flexoelectric- and dielectric-dominated wide-temperature-range blue phase materials.

The unique thermo-mechanical behavior of Shape Memory Alloys (SMAs), such as their ability to recover the original shape upon heating or being able to tolerate large deformations without undergoing plastic transformations, makes them a good choice for actuators. This work studies their application in the aerospace and defense industries where SMA components can serve as release mechanisms for gates of enclosures that have to be deployed remotely. This work provides a novel approach in evaluating the stress and heat induced change of phase in a SMA, in terms of the transformation strain tensor. In particular, the FEA tool ANSYS has been used to perform a 2-D analysis of a Cu-Al-Zn-Mn SMA specimen undergoing a nontraditional loading path in two steps with stress and heating loads. In the first load step, tensile displacement is applied, followed by the second load step in which the specimen is heated while the end displacements are held constant. A number of geometric configurations are examined under the two step loading path. Strain results are used to calculate transformation strain which provides a quantitative measure of phase at a material point; when transformation strain is zero, the material point is either twinned martensite, or austenite depending on the temperature. Transformation strain value of unity corresponds to detwinned martensite. A value between zero and one indicates mixed phase. In this study, through two step loading in conjunction with transformation strain calculations, a method for mapping transient non-uniform distribution of phases in an SMA is introduced. Ability to obtain drastically different phase distributions under same loading path by modifying the geometry is demonstrated. The failure behavior of SMAs can be designed such that the load level the crack initiates and the path it propagates can be customized.

In this thesis, new methods for shear strength are proposed and backed up through extensive experimentation, ABAQUS models and data analysis of Titanium welds of three different alloys. The results are compared with those obtained by using the procedure outlined by AWS B4 for calculating Shear Strength in the transverse and longitudinal directions; this equation is widely used by the American Welding Society (AWS) and all those in search of more efficient designs involving welding. It is a well-documented issue that the equation provided by AWS yields a large discrepancy between the values for shear strength of longitudinal and transverse welds.

This thesis presents a study on solutions to high-speed analog-to-digital conversion in CMOS image sensors using time-interpolation methods. Data conversion is one of the few remaining speed bottlenecks in conventional 2D imagers. At the same time, as pixel dark current continues to improve, the resolution requirements on imaging data converters impose very high system-level design challenges. The focus of the presented investigations here is to shed light on methods in Time-to-Digital Converter interpolation of single-slope ADCs. By using high-factor time-interpolation, the resolution of single-slope converters can be increased without sacrificing conversion time or power. This work emphasizes on solutions for improvement of multiphase clock interpolation schemes, following an all-digital design paradigm. Presented is a digital calibration scheme which allows a complete elimination of analog clock generation blocks, such as PLL or DLL in Flash TDC-interpolated single-slope converters. To match the multiphase clocks in time-interpolated single-slope ADCs, the latter are generated by a conventional open-loop delay line. In order to correct the process voltage and temperature drift of the delay line, a digital backend calibration has been developed. It is also executed online, in-column, and at the end of each sample conversion. The introduced concept has been tested in silicon, and has showed promising results for its introduction in practical mass-production scenarios. Methods for reference voltage generation in single-slope ADCs have also been looked at. The origins of error and noise phenomenona, which occur during both the discrete and continuous-time conversion phases in a single-slope ADC have been mathematically formalized. A method for practical measurement of noise on the ramp reference voltage has also been presented. Multiphase clock interpolation schemes are difficult for implementation when high interpolation factors are used, due to their quadratic clock phase growth with resolution. To allow high interpolation factors a time-domain binary search concept with error calibration has been introduced. Although the study being conceptual, it shows promising results for highly efficient implementations, if a solution to stable column-level unit delays can be found. The latter is listed as a matter of future investigations.

Magneto-optical materials such as permalloy can be used to create artificial spin- ice (ASI) lattices with antiferromagnetic ordering. Magneto-optical materials used to create diffraction lattices are known to exhibit magnetic scattering at the half- order Bragg peak while in the ground state. The significant drawbacks of studying the magneto-optical generation of OAM using x-rays are cost, time, and access to proper equipment. In this work, it is shown that the possibility of studying OAM and magneto-optical materials in the spectrum of visible light at or around 2 eV is viable. Using spectroscopic ellipsometry it is possible to detect a change in the magnetization of thin permalloy films with thicknesses between 5 and 20 nm. Patterns consistent with OAM were found at 1.95 eV using a square lattice with a 4𝜋 radial phase shift in the antiferromagnetic ground state. Evidence of magnetic scattering at the half-order Bragg peak using 1.95 eV was also found.

In this study, the effect of ultrasonic treatment (UST) parameters such as amplitude, sonication time, and melt temperature on microstructure and microhardness of Al 6061 alloy is evaluated. The effect of UST on the dispersion of tungsten disulfide (WS2) and carbon nanotubes (CNT) as reinforcement particles in Al 6061 during casting is also studied. The cast Al 6061 with UST demonstrated 32% grain size reduction and 8% increase in the microhardness for optimum processing conditions. The cavitation process induced by UST is responsible for the refinement in microstructure and increase of hardness by enhancing the degassing and nucleation process. UST treated 6061 Al alloy demonstrated Hall-Petch relationship for all processing conditions. The UST process also aids in excellent dispersion of WS2 and CNT as reinforcement particles. UST treated WS2 and CNT reinforced Al 6061 composites displayed improved wear resistance as compared to samples without cavitation.

Fusion energy has been said to be the solution to all the world’s energy problems. The International Thermonuclear Experimental Reactor (ITER) is the flagship project to demonstrate the feasibility of fusion energy. The Central Solenoid (CS), an important component of the reactor, is needed to induce plasma current, initiate, ramp-up, ramp-down, and sustain plasma in a very controlled manner. In order to achieve this, the CS coil packs must be manufactured under controlled conditions. The CS conductor is an advanced cable-in-conduit Nb3Sn superconductor. The CS cable will be made in long continuous sections but with thousands of meter of cable needed, splices will have to be made in the field during construction of the ITER reactor. With the ends of the CS cable being exposed to the environment for an unspecified amount of time, concern has been expressed about the effect of the cable exposure on the quality of the splice. As a result an experimental program was devised to replicate and expedite the environmental damage the cable may see while in the field. The CS cable samples were exposed to 100% humidity at 60, 80, and 100oC for periods ranging from one week to four weeks. Once the samples were soaked for a period of time they were then sintered as would be done in the field. After sintering the mechanical tests were done to determine the load required to push the sintered strands out of the copper sleeve. Initial results obtained with samples having the sleeve thickness of 1.25mm (0.05in) were inconclusive due to the presence of a fold in the copper sleeve formed during the compaction of the sleeve around the cable. To prevent the fold formation, another set of samples were prepared with thicker copper sleeve of 5mm (0.20in). Results from these samples yielded data that was more conclusive and showed a possible correlation between aging temperature and sintering strength. The experimental data suggests that the thin oxide layer formed during the elevated temperature soak at 100% humidity may even be beneficial to the sinter quality.

This thesis recounts the experimental study of the dynamic response of polycarbonate blast resistant glazing systems to explosive loading through the use of triaxial load cells, pressure sensors, and a laser displacement gauge. This instrumentation captured the response of the glazing systems to blast loading over three phases of testing. The first phase of testing characterizes the load distribution around the perimeter and the second phase examines the repeatability of the results. The final phase of testing pushes the samples to failure. The results are then compared to HazL, a commonly used blast resistant glazing system analysis software tool. The experimental data is also compared to data available characterizing the response of laminated glass.

En règle générale, les études de sûreté-criticité concernant les combustibles usés stockés, transportés ou retraités sont très conservatives et considèrent ce combustible comme neuf donc le plus réactif possible. Le « Crédit Burn-up » (CBU) est la prise en compte de l’antiréactivité du combustible irradié par rapport au combustible neuf. Une méthodologie CBU rigoureuse, développée par le CEA en collaboration avec AREVA-NC a récemment été validée et réévaluée pour les combustibles REP-UOx. Cependant, 22 réacteurs sur les 58 que compte la France utilisent également du combustible MOx. De plus en plus d’assemblages MOx irradiés doivent donc être entreposés et transportés, ce qui conduit les industriels à s’intéresser à la prise en compte du CBU pour ces applications, dans le but de pouvoir gagner des marges en terme de dimensionnement des installations. Des publications récentes et les travaux du Groupe de Travail Français sur le CBU ont souligné l’importance de la prise en compte des 15 produits de fission stables et non volatiles les plus absorbants qui sont à l’origine de la moitié de l’antiréactivité totale apportée dans les combustibles REP-MOx. C’est pourquoi, dans le but de garantir la sous-criticité de la configuration étudiée suivant les dispositions règlementaires relatives à la sûreté des installations, les biais de calcul affectant leur bilan-matière et leur effet individuel en réactivité doivent également être pris en considération dans les études de sûreté-criticité s’appuyant sur des calculs de criticité. Dans ce contexte, une revue bibliographique exhaustive a permis d’identifier les particularités des combustibles REP-MOx et une démarche rigoureuse a été suivie afin de proposer une méthodologie CBU adaptée à ces combustibles validée et physiquement représentative, permettant de prendre en compte les produits de fission et permettant d’évaluer les biais liés au bilan-matière et à l’antiréactivité des isotopes considérés. Cette démarche s’est articulée autour des études suivantes : • détermination de facteurs correctifs isotopiques permettant de garantir le conservatisme du calcul de criticité sur la base de la qualification du formulaire d’évolution DARWIN-2.3 pour les applications REP-MOx et d’une analyse des données nucléaires des produits de fission métalliques afin de déterminer l’impact des incertitudes associées sur le calcul de leur bilan matière ; • évaluation de l’antiréactivité individuelle des produits de fission sur la base des résultats d’interprétation des expériences d’oscillation des programmes CBU et MAESTRO, réalisés dans le réacteur expérimental MINERVE à Cadarache, avec le formulaire dédié PIMS développé au SPRC/LEPh avec mise à jour des schémas de calcul pour la criticité ; • élaboration de matrices de covariances réalistes associées à la capture de deux des principaux produits de fission du CBU REP-MOx : 149Sm et le 103Rh associées à l’évaluation JEFF-3.1.1 ; • détermination des biais et incertitudes « a posteriori » dus aux données nucléaires des actinides et produits de fission considérés pour deux applications industrielles (piscine d’entreposage et château de transport) par une étude de transposition réalisée avec l’outil RIB, développé au SPRC/LECy, qui a bénéficié à cette occasion de développements spécifiques et de mises à jour des données utilisées (importation des données de covariance issues de la bibliothèque COMAC V0 associée à JEFF-3.1.1 pour les isotopes 235,238U, 238,239,240,241,242Pu, 241Am et 155Gd et prise en compte des corrélations inter-réactions pour un même isotope). • évaluation de la méthodologie proposée pour deux applications industrielles (piscine d’entreposage et château de transport), démonstration de son intérêt et de sa robustesse. / Considering spent fuel management (storage, transport and reprocessing), the approach using « fresh fuel assump-tion » in criticality-safety studies results in a significant conservatism in the calculated value of the system reactivity.The concept of Burnup Credit (BUC) consists in considering the reduction of the spent fuel reactivity due to its burnup.A careful BUC methodology, developed by CEA in association with AREVA-NC was recently validated and writtenup for PWR-UOx fuels. However, 22 of 58 french reactors use MOx fuel, so more and more irradiated MOx fuelshave to be stored and transported. As a result, why industrial partners are interested in this concept is because takinginto account this BUC concept would enable for example a load increase in several fuel cycle devices. Recent publi-cations and discussions within the French BUC Working Group highlight the current interest of the BUC concept inPWR-MOx spent fuel industrial applications. In this case of PWR-MOx fuel, studies show in particular that the 15FPs selected thanks to their properties (absorbing, stable, non-gaseous) are responsible for more than a half of the totalreactivity credit and 80% of the FPs credit. That is why, in order to get a conservative and physically realistic valueof the application keff and meet the Upper Safety Limit constraint, calculation biases on these 15 FPs inventory andindividual reactivity worth should be considered in a criticality-safety approach. All of this work is supported by the use of the CEA reference calculation tools : the deterministic code APOLLO-2.8and the probabilistic code TRIPOLI-4 used by the CRISTAL V2 criticality-safety package, the DARWIN-2.3 packagefor fuel cycle applications, the JEFF-3.1.1 nuclear data library and the Integral Experiment Methodology based on thestatistical adjustment method of the nuclear data and the integral experiment representativity.The feedback on the nuclear data of the oscillation programmes BUC and MAESTRO allows to halve the prioruncertainties linked to 149Sm and 103Rh capture cross sections. The application of the developed methodology,benefiting from the CEA dedicated experimental programmes quality and better physically justified to twoapplications, representative of fuel storage and transport, shows that the introduced conservatisms represents40 % of the total Burnup Credit. On top of that, the two configurations results comparison shows that theevaluated BUC is independent from the considered application and proves the calculation route robustness.

A new method for pre-impregnating nickel coated carbon fiber with a thermoplastic polymer to make towpreg, similar to a recently developed coating-line by João P. Nunes et al and a new electrically conductive thermoplastic are developed. A melted bath was used to help mitigate health concerns and waste for dispersion of nickel coated carbon fibers (NCF) in low density polyethylene (LDPE). This towpreg was then mixed with more LDPE or a mixture of LDPE and nickel nanostrands (NiNS) to a desired filler volume fraction to test the electrical conductivity of the composite. Some of these mixtures were then injection molded and tested again for conductivity as well as tensile and impact strength and compared to each other and the non-injection molded samples. It was found that mixing NiNS into the polymer in addition to NCF created a more conductive part than with NCF alone, in a couple orders of magnitude. Also, the shorter the NCF were, the greater the contribution of the NiNS to the electrical properties of the NCF filled material. The tensile strength was increased by adding the NCF and NiNS, while the impact strength (toughness) decreased.