Le comportement mécanique du verre silico-sodo-calcique soumis à un contact ponctuel peut être amélioré par trempe. Les effets de trempe se manifestent par des gradients de propriétés sur le comportement du verre rendant la modélisation plus complexe. Ce travail a porté sur la modélisation et la simulation des verres non trempés et trempés soumis aux essais de nano-indentation et de nano-rayage. Les outils de simulation par éléments finis ont été développé et validés sur le verre métallique, choisi en raison de son comportement plastique connu. En comparant avec les données expérimentales, nous avons observé que les paramètres du matériau et les conditions expérimentales pouvaient donner la même réponse sur la courbe force-déplacement et l'empreinte. L’identification des propriétés du matériau doit être basée sur des comparaisons avec des simulations considérant la géométrie réelle de l'indenteur, la souplesse de la machine et le tilt de surface de l'échantillon. Les stratégies développées permettent de faire des identifications sur le comportement du verre silico-sodo-calcique. Dans la famille du verre silicaté, le verre silico-sodo-calcique a un comportement plastique semblable au verre de silice qui est affecté non seulement par le mécanisme de cisaillement mais aussi par la densification. Il est essentiel donc d'étudier le comportement densification/cisaillement du verre de silice car il est largement discuté dans la littérature. La comparaison des résultats de simulation par plusieurs modèles avec les courbes force-déplacement et les images d'empreinte a montré que la modélisation de la densification, en prenant en compte l'écrouissage et la modification des modules élastiques, est suffisante pour décrire le comportement des verres silicatés. Enfin, les connaissances sur les simulations des essais à chargement ponctuel et la modélisation du comportement du verre ont guidé une étude sur les effets du gradient de propriétés dans les verres trempées thermiquement et chimiquement. / The mechanical behavior of soda-lime-silica glass subjected to contact damage can be improved by tempering. The effects of tempering created tailor properties and the glass behavior more complicated. Therefore, this work studied the modeling and simulation of non-tempered and tempered glasses subjected to the nano-indentation and nano-scratch tests. The finite element simulation tools have been primarily validated and the metallic glass was chosen for the studies because of its known plastic behavior. By comparing with the experimental data, we have observed that the parameters of material model and the experimental conditions could give the same response on load displacement curve and imprint. The evaluation of material properties must be based on the comparisons with fully modeled simulation considering the real geometry of the indenter, the compliance of the instrument and the tilting of the sample surface. The developed strategies allow identification of soda-lime-silica glass behavior. Similar to that of silica glass, the plastic behavior of soda-lime-silica glass is not only affected by the shear mechanism but also the densification. Hence, it is essential to study the shear/densification behavior of silica glass as it is widely discussed in the literature. The comparison of simulation results by several models with the load displacement data and the images of imprint showed that the modeling of densification by taking into account the hardening and the change in elastic moduli is sufficient for describing the behavior of silicate glasses. Finally, the knowledge about the simulation of the contact loading tests and the modeling of glass behavior guided a study on the coupling of tailored properties effects in the thermally and chemically tempered glasses.

In this paper, the numerical simulation for nano-indentation is performed to measure time-dependent behavior of polymeric films. The possibility to extract the relaxed shear modulus of the polymer is evaluated using a rigid ball indenter. The viscoelastic behavior of the polymer was represented by the standard model. The effects of Poisson’s ratio are also discussed. / Singapore-MIT Alliance (SMA)

To enable fast and reliable processors, advances must be made in the interconnections on the printed circuit board and in the interconnections from the chip to the printed circuit board. Processing techniques have been demonstrated to fabricate a copper-clad encapsulated air dielectric layer to enable low loss off-chip electrical signal lines using sacrificial polymers and the three dimensional patterning capabilities of imprint lithography. The inclusion of an air gap can eliminate the dielectric loss allowing the signal to propagate over longer lengths. Additionally, the low dielectric constant of air lowers the loss contributions from the conductor and increases the signal propagation velocity reducing delay. The metal shielding could minimize the crosstalk noise and radiation losses that are significant at high frequencies. The three dimensional patterning capabilities of imprint lithography fabricated curved structures and rounded terminations which can reduce reflections at discontinuities. Furthermore, imprint lithography also created planarized surfaces which simplified the buildup process. Since imprint lithography, only uses temperature and pressure to make a pattern it is an inexpensive and simple process advancement. The metal-clad encapsulated air dielectric structures were fabricated in a comparable number of registration steps to traditional transmission lines. Implementation of all copper chip to substrate interconnects would provide high conductivity electrical connections, resistance to electromigration while avoiding formation of brittle intermetallics. High aspect ratio polymer molds for copper electroplating interconnects could enable improved integrated circuit electrical performance. The properties of a new aqueous base develop, negative-tone photosensitive polynorbornene polymer have been characterized to develop mechanically compliant all copper connections between the chip and printed circuit board. High aspect ratio features of 7:1 (height:width) were produced in 70 ìm thick films in a single coat with straight side-wall profiles and high fidelity. The polymer films studied had a contrast of 11.6 and a low absorption coefficient. To evaluate the polymer's suitability to microelectronics applications, epoxy cross-linking reactions were studied as a function of processing condition through Fourier transform infrared spectroscopy, nano-indentation, and dielectric measurements. The fully cross-linked films had an elastic modulus of 2.9 GPa and hardness of 0.18 GPa which can improve the mechanical compliance of the copper interconnections. A photo-imprint lithography process was developed to improve the photo-patterning of the polynorbornene polymer for high aspect ratio hollow structures. A shallow photo-imprint stamp was developed to physically displace material in the polymer core. Since the imprint stamp displaces material in the area of the feature, the effective film thickness is reduced compared to the bulk film. The reduction in film height reduced the effects of scattering in the core and also facilitated transport of developer within the core. The photo-imprint lithography process resulted in high aspect ratio hollow core pillars that exceeded optical resolution capabilities for comparable feature sizes.

Les verres métalliques sont des matériaux récents (≈ 50 ans), obtenus par refroidissement rapide d'un alliage en fusion. La structure amorphe de ces matériaux leur confère des propriétés particulières : une très grande résistance mécanique (limite à la rupture de l'ordre de 1,7 GPa pour des alliages base Zr), une déformation élastique de l'ordre de 2% mais pas ou peu de ductilité. Les compositions pouvant être élaborées à l'état amorphe, et, sous forme massive, sont en nombre limité. Le travail présenté dans ce manuscrit démontre la possibilité de consolider par frittage SPS (Spark Plasma Sintering), des poudres amorphes obtenues par atomisation (Фmoy.≈70 μm), tout en conservant majoritairement le caractère amorphe. L'optimisation de ce protocole, avec la composition Zr57Cu20Al10Ni8Ti5, a permis de retrouver le même comportement mécanique qu'un verre massif monolithe. Une cristallisation partielle du matériau se produit cependant aux points de contact des particules, mais pourrait être réduite en poursuivant le modèle de frittage esquissé dans ce manuscrit. Aux vues de ces résultats, la conception de nouvelles compositions, et leur élaboration sous forme de rubans, ont été menées. La caractérisation par nano-indentation permet d'estimer de manière fiable les propriétés mécaniques de ces alliages. Enfin, une nouvelle méthode d'évaluation du volume d'activation, qui est le volume élémentaire cisaillé initiant la déformation plastique, est présentée. Il s'agit de l'analyse statistique d'essais de pseudo-fluage en nano-indentation, réalisés à température ambiante. En conclusion, ce travail propose de nouvelles perspectives d'élaboration de verre métalliques sous forme massive dans une gamme de composition bien plus large

The study of asphalt chemo-mechanics requires a basic understanding of the physical properties and chemical composition of asphalt and how these properties are linked to changes in performance induced by chemical modifications. This work uniquely implements the framework of chemo-mechanics by investigating two types of chemical modification processes, natural (oxidative aging) and synthetic (chemical doping) as they relate not only to macro-scale properties of asphalt binder but also to the asphalt microstructure and nanorheology. Furthermore, this study demonstrates the application of atomic force microscopy (AFM) imaging and the extraction of nano-scale engineering properties, i.e. elastic modulus, relaxation modulus, and surface energy, as a method to predict performance related to the fatigue characteristics of asphalt binders by modeling intrinsic material flaws present amongst phase interfaces. It was revealed that oxidative aging induces substantial microstructural changes in asphalt, including variations in phase structure, phase properties, and phase distribution. It has also been shown that certain asphalt chemical parameters have a consistent and measureable effect on the asphalt microstructure that is observed with AFM. In fact, particular phases that emerged via chemical doping revealed a surprising correlation between oxidative aging and the saturates chemical parameter of asphalt in terms of how they explicitly impact durability and performance of asphalt. By implementing a crack initiation model – which requires measureable microstructural characteristics as an input parameter – it was found that microstructural flaws (depending on the extremity) can have a more profound impact on asphalt performance than the properties of the material located between the flaws. It was also discovered by comparing the findings to performance data in the Strategic Highway Research Program’s (SHRP’s) Materials Reference Library (MRL), that the crack initiation model predicts very similar performance as the SHRP’s distress resistance indicators. Overall, this body of work yields improved input values for asphalt prediction models and serves as the basis for ongoing studies in the areas of asphalt chemical mapping, modeling of nano-damage, and nano-modification using AFM.

Hydroxyapatite (HA) has received wide attention in orthopedics, due to its biocompatibility and osseointegration ability. Despite these advantages, the brittle nature and low fracture toughness of HA often results in rapid wear and premature fracture of implant. Hence, there is a need to improve the fracture toughness and wear resistance of HA without compromising its biocompatibility. The aim of the current research is to explore the potential of nanotubes as reinforcement to HA for orthopedic implants. HA- 4 wt.% carbon nanotube (CNT) composites and coatings are synthesized by spark plasma sintering and plasma spraying respectively, and investigated for their mechanical, tribological and biological behavior. CNT reinforcement improves the fracture toughness (>90%) and wear resistance (>66%) of HA for coating and free standing composites. CNTs have demonstrated a positive influence on the proliferation, differentiation and matrix mineralization activities of osteoblasts, during in-vitro biocompatibility studies. In-vivo exposure of HA-CNT coated titanium implant in animal model (rat) shows excellent histocompatibility and neobone integration on the implant surface. The improved osseointegration due to presence of CNTs in HA is quantified by the adhesion strength measurement of single osteoblast using nano-scratch technique. Considering the ongoing debate about cytotoxicity of CNTs in the literature, the present study also suggests boron nitride nanotube (BNNT) as an alternative reinforcement. BNNT with the similar elastic modulus and strength as CNT, were added to HA. The resulting composite having 4 wt.% BNNTs improved the fracture toughness (~85%) and wear resistance (~75%) of HA in the similar range as HA-CNT composites. BNNTs were found to be non-cytotoxic for osteoblasts and macrophages. In-vitro evaluation shows positive role of BNNT in osteoblast proliferation and viability. Apatite formability of BNNT surface in ~4 days establishes its osseointegration ability.

It has been found that commercially pure (CP) Titanium (Ti) undergoes substantial amount of deformation twinning during plastic forming in a wide range of temperatures and strain rates giving CP-Ti good ductility and allowing up to 90% thickness reduction by cold rolling. Aluminium (Al) rich ! Ti-alloys lack this superior ductility but exhibit therefore up to five times higher yield strength, which was connected experimentally to reduced activity of deformation twinning with addition of Al to Ti. Ultimately this is also valid in the ! phase of two-phase alloys such as Ti6Al4V and thought to be key to the reduced ductility in Al rich alloys. It is to date unclear if ordering of Al in the Ti matrix, a change in the stacking fault energy (SFE) with alloying or a transition of the cellular dislocation structures in CP-Ti to planar slip patterns at high Al contents reduces twin activity. The focus of this dissertation project is therefore the transition of microstructural details and the deformation structures in the ! phase with increasing Al concentration. For simplified investigations binary Ti-Al alloys containing 3.5, 7, 10 and 13at.% Al have been created with comparable grain morphology and texture within this study. For a better understanding of the role of Al also binary Ti-Sn (Tin) alloys (1 & 3.4at.% Sn) and Ti-Zr (Zirconium) alloys (3.6 & 10at.%) as well as an Oxygen (O) rich Ti-10at.%Al and the industrial compositions of Ti6Al4V were produced on the same route and investigated by the same methods. This alloy range allows evaluation of the effects of the c/a ratio, ordering phenomena and the SFE on the twin activity. The knowledge was finally transferred to industrially forged CP-Ti and Ti5Al2.5Sn. TEM and neutron diffraction confirmed the onset of Ti3Al formation from Al concentrations above 7at.% (4wt%), but no ordering of Zr or Sn atoms was found after solution treatments. The evolution of lattice strain and lattice reorientation due to twinning with increasing compressive strain was captured by in-situ experiments under neutron diffraction at Engin-X, ISIS. Post-mortem EBSD micro and macro texture mappings revealed that the twin fraction in Al reduces above a critical concentration of 7at.% (4wt%), which was enhanced with increasing ordering towards Ti3Al. Sn and Zr addition showed no significant effect on the overall twin fraction, but increased twin numbers with facilitated nucleation and impeded twin growth, which may be related to the SFE. Increasing slip planarity and a transition from prismatic slip towards basal slip with addition of Al was found with means of Digital image correlation (DIC). DIC also revealed intense prismatic slip in grains undergoing !"!! tension twinning and virtually barely any strain accumulation within a twin below 9% plastic strain, rationalised by much increased nanohardness in the twin in comparison to the parent. Nanoindentation also revealed that alloying with Al reduces the crystal anisotropy. Finally it is believed that ordering and the closely related transition of slip patterns lead to the reduction in twin activity, while c/a ratio, crystal anisotropy and SFE seem less important.

<div>Metallic uranium-10 weight percent zirconium (U-10wt.%Zr) nuclear fuels are classified as potential fuels for fast breeder reactors as they possess a high fissile density and have increased compatibility with sodium, a frequently used reactor coolant. Despite their advantages when exposed to neutron irradiation in reactors, the fuels are subject to damage cascades and microstructural alterations. Fuel constituent re-distribution, phase transformation, fuel swelling, and fuel cladding chemical interactions (FCCI) are a few of the major interdependent microstructural alterations that occur in these fuels at the onset of neutron irradiation. The primary objective of this research is to understand the above-mentioned microstructural alterations in different regions of a neutron irradiated U-10wt.%Zr fuel and HT9 cladding that has achieved a cross-sectional burnup of 5.7 atomic percent (at%.). Additionally, this study also aims to provide a relationship between the microstructural alterations and local mechanical property changes exhibited at different regions of the HT9 cladding as a consequence of neutron irradiation, FCCI, and fission product migration.</div><div>To achieve this goal, a coordinated group of experiments was performed on the neutron irradiated U-10wt.%Zr/HT9 (fuel/cladding) at the nanoscale, microscale, and mesoscale, respectively. The experimental techniques used for microstructural analysis included the following: (1) transmission electron microscopy of focused ion beam (FIB) lamellas for nanoscale assessments, (2) serial sectioning of FIB cuboids for microscale assessments, and (3) synchrotron micro-computed tomography of FIB obelisks for mesoscale assessment. Following the microstructural assessments, nano-indentation experiments were performed on the neutron irradiated HT9 cladding to determine the changes in mechanical properties as a function of distance from cladding edge to FCCI locality, and the changes in mechanical properties as a consequence of several microstructural alterations. Furthermore, the results produced from the various experiments in this study were compared and correlated to existing literature (both in-reactor and out-of-reactor experiments), and new theories to explain the reason for the observed changes were established. This research also revealed several novel observations such as probable radiation induced segregation in fuels, localized fuel swelling and porosity distribution at different regions in the fuel, crystal structure of phases present at different regions in the fuel and their influence on pore morphologies, and nano mechanical properties of a neutron irradiated HT9 cladding.</div>

<p>This Dissertation aims at establishing an integrated framework of multimodal experiments and multiphysics theory to extend the understanding of the mechanics in electrochemically active materials using organic mixed ionic-electronic conductors (OMIECs) as a model system. </p> <p>OMIECs allow the transport of both ions and electrons, which is accompanied by the (electronic, micro-) structural reorganization. The electronic structural change in OMIECs induces transforms in the electrical conductivity and optical absorbance. The change in molecular packing invites the size change and evolution of mechanical properties. The multiphysics processes render OMIECs a fascinating platform for understanding the multi-physics coupling and advancing organic electrochemical devices. </p> <p>Despite significant progress, there are urgent needs in the experimental techniques and the subsequent mechanical characterization, theoretical understanding of the multiphysics processes, and mechanics-informed design principles for high-performance devices. Specifically, (i) an accurate and straightforward experimental method is in need to better understand the mechanical behaviors and kinetics such as swelling and softening of OMIECs upon electrochemical redox reactions; (ii) a theoretical framework is missing that describes the rich coupled multiphysics processes such as large deformation, charge and mass transport, electrostatics, and phase evolution in OMIECs; (iii) the rational design of the materials and structures based on mechanics principles are required for mechanically reliable, high-performance organic electrochemical devices.</p> <p>In this Dissertation, the mechanics of OMIECs are studied systematically. The basics of OMIECs, knowledge gaps, and the outline are introduced in Chapter 1. The in-situ environmental nanoindentation apparatus and the associating characterization techniques are presented in Chapter 2. In Chapter 3, a theoretical mechanics model is presented that elucidates the interfacial mechanical degradation of thin-film electrodes and outlines the design principles for mechanically reliable electrodes. In Chapter 4, the electrochemical doping kinetics and its stress dependency on conductive polymers are studied via a designed moving front device. Chapter 5 presents a thermodynamically consistent continuum theory of two-phase OMIECs undergoing large deformation, charge and mass transport, electrostatics, and phase separation, which forms the theoretical foundation for such conductive polymer systems. The conclusion and perspectives on future work are presented in Chapter 6. </p>

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