Dissertations / Theses on the topic 'Interphase analysi'

This thesis is devoted to the characterization and detailed understanding of the base compositional patterns and the distribution of genes in the chromosomes of the chicken genome. Vertebrate chromosomes are organized into isochores, very long DNA segments (»300 kb) that are compositionally fairly homogenous, and characterized by different GC levels.

A research group at University of Skövde has developed an interphase element for implementation in the commercial FE-software Abaqus. The element is using the Tvergaard & Hutchinson cohesive law and is implemented in Abaqus Explicit version 6.7 using the VUEL subroutine. This bachelor degree project is referring to evaluate the interphase element and also highlight problems with the element.

The behavior of the interphase element is evaluated in mode I using Double Cantilever Beam (DCB)-specimens and in mode II using End Notch Flexure (ENF)-specimens. The results from the simulations are compared and validated to an analytical solution.

FE-simulations performed with the interphase element show very good agreement with theory when using DCB- or ENF-specimens. The only exception is when an ENF-specimen has distorted elements.

When using explicit finite element software the critical time step is of great importance for the results of the analyses. If a too long time step is used, the simulation will fail to complete or complete with errors. A feasible equation for predicting the critical time step for the interphase element has been developed by the research group and the reliability of this equation is evaluated.

The result from simulations shows an excellent agreement with the equation when the interphase element governs the critical time step. However when the adherends governs the critical time step the equation gives a time step that is too large. A modification of this equation is suggested.

This work addresses the morphology of the wood/ Phenol-Formaldehyde (PF) adhesive interphase using yellow-poplar. In this case, morphology refers to the scale or dimension of adhesive penetration into wood. The objective is to develop methods for revealing ever smaller levels of wood/resin morphology. Dynamic techniques that are commonly utilized in polymer blend studies are investigated as potential methods for probing the wood/ adhesive interphase morphology. These are Dynamic Mechanical Analysis (DMA) and solid state NMR using CP/MAS. PF resin molecular weight is manipulated to promote or inhibit resin penetration in wood, using a very low or a very high molecular weight PF resin. With DMA, the influence of PF resin on wood softening is investigated. It is first demonstrated that the cooperativity analysis according to the Ngai coupling model of relaxation successfully applies to the in-situ lignin glass transition of yellow-poplar and spruce woods. No significant difference in intermolecular coupling is detected between the two woods. It is then demonstrated that combining simple DMA measurements with the cooperativity analysis yields ample sensitivity to the interphase morphology. From simple DMA temperature scans, a low molecular weight PF (PF-Low) does not influence lignin glass transition temperature. However, the Ngai coupling model of relaxation indicates that intermolecular coupling is enhanced with the low molecular weight PF. This behavior is ascribed to the low molecular weight PF penetrating lignin on a nanometer scale and polymerizing in-situ. On the other hand, a high molecular weight resin with a broad distribution of olecular weights (PF-High) lowers lignin glass transition temperature dramatically. This plasticizing effect is ascribed to a small fraction of the PF resin being low enough in molecular weight to penetrate lignin on a nanoscale, but being too dispersed for forming a crosslinked network. With CP/MAS NMR, intermolecular cross-polarization experiments are found unsuitable to probe the angstrom scale morphology of the wood adhesive interphase. However, observing the influence of the PF resins on the spin lattice relaxation time in the rotating frame, HT1r, and the cross-polarization time (TCH) is useful for probing the interphase morphology. None of the resins significantly affects the cross-polarization time, suggesting that angstrom scale penetration does not occur with a low nor a high molecular weight PF resin. However, the low molecular weight PF substantially modifies wood polymer HT1r, indicating that the nanometer scale environment of wood polymers is altered. On the other hand, the high molecular weight PF resin has no effect on wood HT1r. On average, the high molecular weight PF does not penetrate wood on a nanometer scale. Interestingly, the low molecular weight PF resin disrupts the spin coupling that is typical among wood components. Spin coupling between wood components is insensitive to the high molecular weight PF. Finally, it is noteworthy that the two PF resins have significantly different T1r 's in-situ. The low molecular weight resin T1r lies within the range of wood relaxations, suggesting some degree of spin coupling. On the other hand, the T1r of the high molecular weight PF appears outside the range of wood relaxations. Spin coupling between the high molecular weight resin and wood components is therefore inefficient. The CP/MAS NMR and DMA studies converge to identify nanometer scale penetration of the low molecular weight PF in wood. On the other hand, the high molecular weight PF resin forms separate domains from wood, although a very small fraction of the PF-High is able to penetrate wood polymers on a nanoscale.
Ph. D.

When bonded joints are subjected to harsh environmental conditions, the interphase, the three-dimensional region surrounding the adhesive/substrate interface, becomes critically important. Frequently, failure occurs in this region after adhesively bonded systems are subjected to elevated temperature oxidative aging. In a previous study, this was found to be the case with a polyimide adhesive bonded to chromic acid anodized (CAA) Ti-6Al-4V. The objective of the current research has been twofold: 1) to investigate the effect of thermal aging on the interphase region of polyimide/titanium adhesive joints, and 2) to evaluate the method used in the current study for durability characterization of other adhesive/substrate systems. The method used in this research has been to characterize the effect of elevated temperature aging on the following systems: 1) Notched coating adhesion (NCA) specimens and 2) bulk samples of dispersed substrate particles in an adhesive matrix. The NCA test has the advantages of an accelerated aging geometry and a mode mix that leads to failure through the interphase, the region of interest. The bulk samples have the advantage of an increased interphase volume and allow for the application of bulk analysis techniques to the interphase, a region that is traditionally limited to surface analysis techniques. The adhesive systems studied consisted of one of two polyimide adhesives, LaRC⠢ PETI-5 or Cytec Fiberite⠢ FM-5, bonded to CAA Ti-6Al-4V. The model filled system consisted of a PETI-5 matrix with amorphous titanium dioxide filler. Through the use of the NCA test, it was determined that bonded specimens made with FM-5 lose approximately 50% of their original fracture energy when aged in air at 177°C for 30 days. This aging temperature is well below the glass transition temperature of the adhesive, 250°C. At the same time, the failure location moves from the anodized oxide layer to the adhesive that is directly adjacent to the substrate surface, the interphase region. Through surface analysis of this region, it is determined that the adhesive penetrates the pores of the CAA surface to a depth of 70 to 100 nm, promoting adhesion at the interface. With aging, the adhesive in the interphase region appears to be weakening, although analysis of the bulk adhesive after aging shows little change. This indicates that adhesive degradation is enhanced in the interphase compared to the bulk. Analysis of the model filled system gave similar information. Specimens containing titanium dioxide filler had glass transition temperatures that were approximately 20°C lower than the neat polyimide samples. In addition, the filled samples contained a significant portion of low molecular weight extractable material that was not present in the neat specimens. The tan delta spectra from dynamic mechanical thermal analysis of the filled specimens exhibited a shoulder on the high-temperature side of the glass transition peak. This shoulder is attributed to the glass transition of the interphase, a distinct phase of the polyimide which is constrained by adsorption onto the filler particle surfaces. As a function of aging time at 177° or 204°C, the shoulder decreases substantially in magnitude, which may relate to loss of adhesive strength between the polyimide and the filler particles. From this research, it has been illustrated that information relating to the durability of adhesively bonded systems is gained using an interfacially debonding adhesive test and a model system of substrate particles dispersed in an adhesive matrix
Ph. D.

Les composites SiC/SiC à interphase pyrocarbone (PyC) sont des candidats prometteurs en tant que matériau de gainage du combustible et de structure des réacteurs à neutrons rapides, constituant une alternative aux alliages métalliques. Leur comportement sous irradiation neutronique et leur caractère réfractaire sont de sérieux atouts en milieu irradiant. Néanmoins, les fibres et la matrice en carbure de silicium (SiC) sont, individuellement, des céramiques fragiles. L’intégrité des structures ne peut donc être assurée que si le composite acquiert une tolérance aux déformations. Cette tolérance n’est possible que grâce à la présence d’une interphase de pyrocarbone, entre la matrice et les fibres, assurant le rôle de déviateur de fissures. La capacité des composites SiC/SiC à résister à l’endommagement est dictée par le couplage fibre/matrice (F/M). L’intensité de ce couplage peut être influencée par de nombreux paramètres, tels que la rugosité et la physicochimie de surface du renfort. Les travaux faisant l’objet de cette thèse ont mis en évidence une couche de carbone en surface des fibres par microscopie électronique en transmission à haute résolution (METHR) et via des analyses physicochimiques de surface. Les caractéristiques de cette couche de carbone varient avec le procédé de fabrication des fibres. Son impact sur le couplage F/M a été appréhendé par l’observation des mécanismes locaux d’endommagement. La décohésion fibre/matrice a été étudiée en analysant par METHR les régions interfaciales des composites SiC/SiC ayant subi un essai mécanique. La compréhension de l’origine de cette couche de surface de fibres a permis de mieux connaitre les mécanismes locaux d’interaction. Ces mécanismes dépendent de la structure du carbone de surface des fibres dont découle le mode d’adhésion entre ce carbone de surface et l’interphase de pyrocarbone. Un traitement de surface sur un type de fibres a alors été développé, suggérant une légère amélioration du comportement mécanique des composites SiC/SiC élaborés à partir de ces renforts fibreux
SiC/SiC composites including the third generation SiC fibers with pyrocarbon interphase (PyC) are promising candidates to improve the safety of nuclear reactors, especially for core materials such as cladding and to replace metallic alloys for these applications. Their intrinsic refractory properties, their neutron transparency and their microstructural stability when irradiated or exposed to high temperatures make them attractive for nuclear applications. However SiC fibers and SiC matrix are brittle ceramics. The integrity of the structures can be fulfilled only if the composite is damage tolerant and can acquire a pseudo-ductile mechanical behavior. An interphase is deposited between the fibers and the matrix to provide this damage tolerance of SiC/SiC composites.The ability of SiC/SiC composites to sustain damage is dictated by the fiber/matrix (F/M) coupling mode. The intensity of this coupling can be related to many parameters such as the roughness and the chemistry of the surface of the reinforcement. A carbon layer on the fiberssurface was highlighted by High Resolution Transmission Electronic Microscopy (HRTEM) and by physico-chemical analyses. The characteristics of this carbon layer vary with the fabrication process of the fibers. The impact of this carbon layer on the F/M coupling was investigated by the observation of the local damage mechanisms. To elucidate the local bonding modes governing the damage mechanisms at the F/M interface of these SiC/SiC composites, macroscopic mechanical tests have been coupled with observations of structural modifications occurring in the interface region after loading. Understanding the origin of this carbon layer allowed elucidating the local interaction mechanisms according to these studied materials. These mechanisms depend on the carbon structure of the SiC fibers surface which in turn governs the adhesion between this carbon and the PyC interphase. Thanks to this study, a surface treatment on fibers was developed to optimize the mechanical behavior of SiC/SiC composites, whatever the fibrous reinforcement chosen

Promyelocytic leukaemia nuclear bodies (PML NBs) are found within the nucleus of mammalian cells. Numbering between 10 and 30 per nucleus, they are an obvious feature of the nuclear landscape, yet their functions have still to be unambiguously defined. In the mammalian nucleus, compartmentalization of functions is apparent, as reflected in the wide-range of other nuclear compartments that can be identified. Quantification of relationships between PML NBs and other nuclear functional compartments is essential for a complete understanding of PML NB function. Initially, PML size, number, distance relationships, and spatial organisation in relation to each other, and the nuclear boundary and centroid, under the spatial point pattern theory hypothesis of Complete Spatial Randomness (CSR), were investigated in both normal and SV40 transformed MRC5 and WI38 human foetal lung fibroblasts. This was also completed in normal MRC5 cells treated with heat shock, and interferon β (both of which alter PML NB morphometrics), and also serum starvation. PML NBs appeared to locate according to CSR with respect to each other, and inter – PML distances were dependent upon median PML NB number per nucleus. PML NBs did not tend to associate with the nuclear centroid, and were repelled from the nuclear boundary in all cell lines and conditions. The distance and spatial organisation relationships between PML NBs and eleven different nuclear compartments were also compared and contrasted in the cell lines and conditions mentioned previously. PML NBs were shown to share strong distance and spatial organisation relationships with the 11S immunoproteasome regulator, SC35 domains, and transcriptional compartments in normal asynchronous nuclei, and with telomeres in transformed cells, highlighting likely functions for the bodies. Lastly, the three dimensional spatial preference of functional compartments in the nucleus was determined using an aggregate map, which provided a novel means to visualise the nuclear location of functional compartments in relation to each other, and under different cellular conditions. Spatial preference fell into four categories: 1) diffuse, 2) annular, 3) core, and 4) polar. Nucleoli and RNA polymerase maintained their spatial preference across cell lines and conditions, whereas other compartments showed altered spatial preferences. Interestingly, viral transformation led to global disorganisation of the nucleus, where most compartments (including PML NBs) reverted to a diffuse spatial preference.

Lithium Ion Batteries (LIBs) are important in today's society, powering cars and mobile devices. LIBs consist of a negative anode commonly made of graphite, and a positive cathode commonly made from transition metal oxides. Between these electrodes are separators and organic solvent based electrolyte. Due to the high potential of LIBs the electrolyte is reduced at the anode. The electrolyte reduction results in the formation of a layer called the Solid Electrolyte Interphase (SEI), which prohibits the further breakdown of the electrolyte. Despite being researched for over50 years, the composition formation of the SEI is still poorly understood. The aim of this project is to develop strategies for efficient identification and classification of various active and intermediate components in the SEI, to, in turn, gain an understanding of the reactions taking place, which will help find routes to stabilize and tailor the composition of the SEI layer for long-term stability and optimal battery performance. For a model gold/li-ion battery electrolyte system, Raman spectra will be obtained using Surface Enhanced Raman Spectroscopy (SERS) in a spectroelectrochemical application where the voltage of the working gold electrode is swept from high to low potentials. Spectra of common components of the SEI as well as similar compounds will be simulated using Density Functional Theory (DFT). The DFT data is also used to calculate the spontaneity of reactions speculated to form the SEI. The simulated data will be validated by comparing it to experimental spectra from pure substances. The spectroelectrochemical SERS results show a clear formation of Li-carbonate at the SERS substrate, as well as the decomposition of the electrolyte into other species, according to the simulated data. It is however shown that there are several issues when modelling spectra, that makes it harder to correlate the simulated spectra with the spectroelectrochemical spectra. These issues include limited knowledge of the structure of the compounds thought to form on the anode surface, and incorrect choices in simulational parameters. To solve these issues, more work is needed in these areas, and the spectroelectrochemical methods used in this thesis needs to be combined with other experimental methods to narrow down the amount of compounds to be modelled. More work is also needed to avoid impurities in the electrolyte. Impurities leads to a thick inorganic layer which prohibits the observation of species in the organic layer.

Cette thèse se concentre sur la caractérisation ultrasonore de l’interphase os-implant. Cette région est une zone de transition où a lieu le processus d’ostéointégration (i.e. le processus de guérison du tissu entourant l’implant). Donc, cette interphase a un rôle crucial dans l’ancrage à long-terme de l’implant, puisqu’elle dépend de la quantité ainsi que la qualité du tissu osseux environnant. Ensuite, en plus d’être un milieu complexe en remodelage continu, l’os néoformé présente une nature multi échelle et qui évolue dans le temps. Toutes ces motivations rendent la caractérisation de l’interphase os-implant critique et difficile. Dans ce contexte, les méthodes ultrasonores sont largement utilisées aujourd’hui dans le domaine clinique pour leur capacité de donner des informations sur les propriétés biomécaniques du tissu osseux. Compte tenu de ces éléments, dans le but de caractériser les propriétés mécaniques et microstructurales de l’interphase os-implant à travers des méthodes ultrasonores, il est important de développer et valider des modèles mécaniques ainsi que de méthodes de traitement du signal. A cause de la complexité du problème, afin de décrire avec précision le tissu environnant à l’implant, il est d’abord essentiel une modélisation fiable du tissu osseux. Pour cela, on étudie l’interaction entre une onde ultrasonore et le tissu osseux, en considérant aussi les effets dues à la microstructure. Pour ce faire, un modèle continu généralisé a été utilisé. Dans ce contexte, un test de transmission/réflexion réalisé sur un échantillon poroélastique immergé dans un fluide a renforcé la fiabilité du modèle. Les champs de pression réfléchi et transmis sont influencés par les paramètres de la microstructure. De plus, les résultats issus de l’analyse de dispersion sont en accord avec ceux observés dans les expériences pour les échantillons poroélastiques. Après, le problème a été compliqué en considérant une interphase qui se situe entre l’os et l’implant. Ainsi, on peut gérer la complexité ajoutée par la présence du tissu néoformé. Comme on l’a déjà mentionné, une difficulté additionnelle est représentée par le fait que l’interphase est un milieu hétérogène, un mélange de phases solides et fluides dont les propriétés évoluent avec le temps. Donc, afin de modéliser l’interaction des ondes ultrasonores avec une interphase, on a considéré dans le modèle une couche très fine avec des propriétés élastiques et inertielles. En partant de ça, on a étudié les effets des propriétés de réflexion d’une transition entre un milieu homogène et un milieu microstructuré. De même, il a aussi été étudié la caractérisation du milieu via des techniques avances de traitement du signal. En particulier, la réponse dynamique due à l’excitation ultrasonore du système os-implant a été analysée à travers une approche multifractale. Une première analyse basée sur les coefficients des ondelettes a montré une signature multifractale pour les signaux dérivants des simulations et aussi des expériences. Ensuite, une étude de sensibilité a aussi montré que la variation des paramètres tels que la fréquence centrale et la densité de l’os trabéculaire ne contribue pas à un changement dans la réponse. L’originalité réside dans le fait qu’il s’agit d’un des premiers efforts d’exploiter l’approche multifractale dans la propagation ultrasonore dans un milieu hétérogène
This thesis focus on the ultrasonic characterization of bone-implant interphase. This region is a transition zone where the osteointegration process (i.e. the healing process of the tissues surrounding the implant) takes place. Thus, this interphase is of crucial importance in the long-term anchorage of the implant, since it depends on the quantity and quality of the surrounding bone tissue. However, other than being a complex medium in constant remodeling, the newly formed bone presents a multiscale and time evolving nature. All these reasons make the characterization of the bone-implant interphase critical and difficult. In this context, ultrasound methods are nowadays widely used in the clinic field because of their ability to give information about the biomechanical properties of bone tissue. On this basis, with the aim of characterizing the mechanical and microstructural properties of the bone-implant interphase by ultrasound methods, it is important to develop and validate mechanical models and signal processing methods. Due to the complexity of the problem, in order to precisely describe the bone tissue surrounding the implant, first an accurate modelling of bone tissue is essential. Thus, the interaction between an ultrasonic wave and bone tissue has been investigated by also taking into account the effects dues to the microstructure. To do this, a generalized continuum modelling has been used. In this context, a transmission/reflection test performed on a poroelastic sample dipped in a fluid enhanced the reliability of the model. The reflected and transmitted pressure fields result to be affected by the microstructure parameters and the results coming from the dispersion analysis are in agreement with those observed in experiments for poroelastic specimens. Then, the problem has been complicated by considering the interphase taking place between the bone and the implant. In this way, we could handle the complexity added by the presence of the newly formed tissue. As already said, the fact that this interphase is a heterogeneous medium, a mixture of both solid and fluid phases whose properties evolve with time is an additional difficulty. Thus, in order to model the interaction of ultrasonic waves with this interphase, a thin layer with elastic and inertial properties has been considered in the model. The effects on the reflection properties of a transition between a homogeneous and a microstructured continuum have been investigated.Therefore, the characterization of the medium also via advanced signal processing techniques is investigated. In particular, the dynamic response due to the ultrasonic excitation of the bone-implant system is analyzed through the multifractal approach. A first analysis based on the wavelet coefficients pointed out a multifractal signature for the signals from both simulations and experiences. Then, a sensitivity study has also shown that the variation of parameters such as central frequency and trabecular bone density does not lead to a change in the response. The originality lies in the fact that it is one of the early efforts to exploit the multifractal approach in the ultrasonic propagation inside a heterogeneous medium

Dans ce travail, la caractérisation mécanique de l’interphase entre les zones amorphes et cristallines dans le polyéthylène a été abordée. La caractérisation élastique est effectuée en appliquant deux approches micromécaniques à partir des données de la simulation moléculaire pour la zone interlamellaire. Ces approches micromécaniques sont d’une part le modèle étendu d’inclusion composite, et d’autre part la méthode de double inclusion. Les résultats des deux approches s’accordent parfaitement. Il a été mis en évidence que le tenseur de rigidité de l’interphase n’est pas défini positif, l’interphase est donc mécaniquement instable. La comparaison avec les résultats expérimentaux valide la méthodologie proposée. Pour la caractérisation hyperélastique, l’algorithme hybride proposé consiste à appliquer la loi de comportement d’un milieu continu isotrope, compressible et hyperélastique aux résultats de la simulation de la dynamique moléculaire d’un élément unitaire de polyéthylène. La notion d’optimisation d’un ensemble de fonctions coûts non négatives est l’idée clé de cette partie. Les paramètres hyperélastiques identifiés sont en bon accord avec ceux qui ont été estimés expérimentalement. L’évolution des frontières de l’interphase avec la déformation est le second résultat de cette analyse. La fin du travail est dédiée à la simulation numérique de la grande déformation viscoplastique d’un agrégat de polyéthylène. Le modèle de Gent adopté pour la contrainte de rappel, le tenseur de projection proposé pour l’approche modifiée de Taylor, et l’optimisation multiniveau font parties des contributions apportées
Elastic characterization of the interphase layer in polyethylene is implemented by applying the relationships of two micromechanical approaches, “Extended Composite Inclusion Model” and “Double-Inclusion Method”, to the Monte Carlo molecular simulation data for the interlamellar domain. The results of the two approaches match perfectly. The interphase stiffness lacks the common feature of positive definiteness, which indicates its mechanical instability. Comparison with experimental results endorses the proposed methodology. For the hyperelastic characterization of the interlamellar domain and the interphase layer, the proposed hybrid algorithm consists in applying the constitutive equations of an isotropic, compressible, hyperelastic continuum to the molecular dynamics simulation results of a polyethylene stack. Evolution of the interphase boundaries are introduced as auxiliary variables and the notion of minimizing a set of nonnegative objective functions is employed for parameter identification. The identified hyperelastic parameters for the interlamellar domain arein good agreement with the ones that have been estimated experimentally. Finally, the large, viscoplastic deformation of an aggregate of polyethylene is reexamined. The Gent model adopted for the back stress of the noncrystalline phase, correcting the projection tensor for the modified Taylor approach, and the idea of multilevel optimization are among the contributions made

Polytäne Riesenchromosomen von Drosophila melanogaster bieten ein ideales Modellsystem für die Untersuchung der Mechanismen zur strukturellen Bildung chromosomaler Domänen. Über Manipulation und Rekonstruktion des chromosomalen Bandenmusters polytäner Chromosomen können artifiziell kondensierte als auch dekondensierte Domänen etabliert werden. Diese Eigenschaft habe ich in meiner Arbeit genutzt für die Etablierung eines experimentellen Systems zur Analyse der strukturellen Vorraussetzungen zur Bildung offener Chromatindomänen. Dafür wurde eine transgene kondensierte Chromatindomäne ektopisch innerhalb offenen Chromatins generiert. Diese kondensierte „Modellbande“ bietet einen definierten genetischen Hintergrund für die gezielte Insertion von DNA-Sequenzen unter Ausschluss variabler Positionseffekte und ermöglicht dadurch eine vergleichende Analyse dieser Sequenzen auf ihr Vermögen offenes Chromatin zu bilden. Zu diesem Zweck wurde über Sequenz-spezifische Rekombination die 61C7/8 Interbandensequenz gezielt in die „Modellbande“ eingefügt. Die zytogenetische Untersuchung dieser Insertion zeigt, dass infolge der Insertion offenes Chromatin gebildet wird, was in einer Aufsplittung der kondensierten „Modellbande“ resultiert. Molekulare Analysen weisen darauf hin, dass auch die epigenetischen Charakteristika wie z.B. die Rekrutierung typischer Proteine oder transkriptionelle Eigenschaften zur endogenen Domäne immitiert werden. Über Deletionsanalysen konnte von mir die essentielle DNA-Sequenz zur Bildung offenen Chromatins auf ein ~490bp großes Fragment im proximalen Bereich der 61C7/8 Sequenz kartiert werden. Dieses Fragment überlappt mit Bindungsstellen spezifischer Proteine, welche dafür bekannt sind eine Rolle in der chromosomalen Domänenbildung zu spielen wie z.B. das Chromatin-Protein Chriz, die Histon-Kinase Jil1 oder das Insulator-Protein CP190. Desweiteren überlappt es mit einer Promoterregion, welche zwischen den Genen Rev1 und Med30 lokalisiert ist.
Polytene chromosomes of Drosophila melanogaster provides an ideal model-system for the analysis of the mechanisms needed for chromosomal domain formation. Condensed as well as decondensed chromosomal domains can be formed by manipulating and reconstructing the polytene banding pattern. This possibility i ha-ve used for the establishment of an experimental system to study the structural requirements for open chromatin formation. Therefor i have generated a condensed chromatin domain at ectopic positions. This condensed „model“ domain provides a defined genetic context for the targeted insertion of sequences of interest, excluding any variable position effects. This allows comarative analysis of different sequences in order to identify the structural requirements for open chromatin formation. For this purpose the 61C7/8 interband sequence was targetly integrated into the condensed „model“ domain by site-specific recombination. Thereby i could show that the 61C7/8 interband sequence maintains the capacity to form open chromatin cognizable by the splitting of the condensed „model“ domain. Furthermore the newly formed open chromatin domain also keeps epigenetic characteristica like transcriptional activity or the recruitment of typical proteins. By deletion analysis, i have mapped the essential region needed for open chromatin formation to a ~490bp fragment located in the proximal part of the 61C7/8 interband sequence. This fragment overlaps binding sites for characteristic proteins known to be involved in chromosomal domain formation like the chromatin protein Chriz, the histone kinase Jil1 or the insulator protein CP190. Furthermore the fragment overlaps a promoter region that locates between the Rev1 and Med30 genes.

Un composite époxy/fibre de verre élaboré à partir de matériaux simplifiés a été soumis en parallèle à du vieillissement artificiel (UV et thermohydrique) et à du vieillissement naturel (climat tropical humide). Une étude des matériaux (résine seule et composite) à travers un large panel de techniques de caractérisation physico-chimiques, mécaniques et de moyens d'observation (MEB, AFM) a permis d'identifier clairement la structure, la morphologie et les principales propriétés du réseau époxy-amine de l'état initial. Une caractérisation systématique des échantillons par couches de 20 microns d'épaisseur a permis, en particulier, d'identifier un gradient de structure et de propriétés dans les 200 premiers microns à la surface des plaques de résine et de composite. Ce gradient est attribué à l'évaporation du durcisseur amine lors de l'élaboration des matériaux. Dans les plaques de composites, le DMA ainsi que l'AFM ont permis de mettre en évidence une zone d'interphase autour des fibres pour laquelle le réseau époxy-amine présente des caractéristiques différentes de celles de la résine en masse.La même méthodologie a été adoptée pour suivre l'évolution de ces matériaux lors des vieillissements artificiels et naturels.Les études séparées des vieillissements UV et thermohydrique ont permis de mettre en évidence les altérations chimiques et physico-chimiques de la matrice seule d'une part, et des interphases fibres/matrice d'autre part. Le vieillissement photochimique se montre le plus dégradant pour la surface des plaques, alors que les effets du vieillissement thermohydrique sont principalement observés au niveau des interfaces fibres/matrice dans les composites. Dans les deux cas également, nous pouvons proposer des mécanismes simplifiés de dégradation de la résine époxy-amine.Enfin, les résultats de caractérisation après le vieillissement naturel nous permettent de faire des corrélations avec les vieillissements artificiels et de pointer les effets prépondérants des deux paramètres de vieillissement, ainsi que d'avancer un facteur d'accélération.

Analytic and computational micromechanics techniques based on the composite cylinders method and the finite element method, respectively, have been used to determine the effective coefficient of thermal expansion (CTE) of carbon nanotube-epoxy nanocomposites containing aligned nanotubes. Both techniques have been used in a parametric study of the influence of interphase stiffness and interphase CTE on the effective CTE of the nanocomposites.  For both the axial and transverse CTE of aligned nanotube nanocomposites with and without interphase regions, the computational and analytic micromechanics techniques were shown to give similar results.  The Mori-Tanka method has been used to account for the effect of randomly oriented fibers.   Analytic and computational micromechanics techniques have also been used to assess the effects of clustering and clustering with interphase on the effective CTE components.  Clustering is observed to have a minimal impact on the effective axial CTE of the nanocomposite and a 3-10%.  However, there is a combined effect with clustering and one of the interphase layers.
Master of Science

Une translocation équilibrée résulte d'un échange de fragments entre deux chromosomes non homologues, sans perte ni gain de matériel génétique. La ségrégation méiotique des chromosomes de sujets porteurs de translocations est analysée par hybridation in situ en fluorescence (FISH) multicouleur sur noyaux spermatiques interphasiques. Elle a d'abord été étudiée dans 27 000 spermatozoïdes provenant de deux frères porteurs d'une translocation réciproque t(6 ;11) (q14 ;p14). Trois sondes centromériques, spécifiques des chromosomes 6, 11 et 1 ont été hybridées simultanément afin de détecter tous les fragments centriques de la translocation ainsi que la ploïdie de chaque cellule. Chez ces deux sujets, les fréquences respectives des modes de ségrégation alterne/adjacent1, adjacent2, 3:1 et 4:0 sont de 70% (estimation par défaut), 9%, 3% et 0. 06%. Un sujet porteur d'une translocation t(2 ;14) (p23. 1 ;q31) a aussi fait l'objet d'une analyse de ségrégation par FISH en deux-couleurs sur 4 610 spermatozoïdes. Une sonde centromérique spécifique du chromosome 2 et une sonde clonée dans un YAC (yeast artificial chromosome), spécifique du fragment centrique du chromosome 14, ont été co-hybridées. Les fréquences respectives des ségrégations alterne/adjacent 1, adjacent2, et 3:1 sont de 80% (estimation par défaut), 5. 2%, et 5. 8%. De même, la ségrégation méiotique des chromosomes 14 et 21 a été étudiée grâce a deux sondes de YAC spécifiques des bras longs de ces chromosomes. Ces deux sondes ont été co-hybridées sur 1 116 spermatozoïdes d'un sujet oligoasthénospermique porteur d'une translocation robertsonienne t(14q ;21q). Plus des deux tiers des spermatozoïdes analysés résultent d'une ségrégation alterne, et 12% sont déséquilibrés selon le mode adjacent. L’analyse des ségrégations des chromosomes X, Y et 1 par FISH en trois couleurs sur les spermatozoïdes des quatre sujets porteurs de translocations n'a pas mis en évidence d'effet interchromosomique majeur. Cependant une légère augmentation des taux de disomies 1 a été observée.

Cette thèse est essentiellement consacrée à la caractérisation et à l’analyse des propriétés mécaniques de matériaux composites constitués d’un renfort taffetas verre et d’une résine acrylate (Elium®). Avant l’apparition de la résine Elium® sur le marché en 2013, les polymères acrylates n’étaient pas utilisés dans l’industrie des composites fibres longues. Dans le volet expérimental de la thèse, nous nous intéressons principalement à l’influence de l’ensimage (traitement de surface appliqué aux fibres pour favoriser l’adhésion de la matrice) sur le comportement mécanique de nos composites. En complément de différents essais mécaniques macroscopiques « classiques » (traction, flexion etc.), nous avons utilisé des techniques d’analyse locales fines (mesures de champ cinématique, microtomographie X, Microscopie Électronique à Balayage, nanoindentation…) qui nous ont permis de caractériser et d’étudier certains mécanismes locaux de déformation et d’endommagement. L’influence de l’ensimage sur les propriétés en fatigue a été mise en évidence grâce à des mesures d’autoéchauffement pour lesquelles nous avons développé un traitement original des données. A l’issue de nos investigations, nous avons pu quantifier le bénéfice qui résulte de l’utilisation d’un ensimage spécifiquement conçu pour favoriser l’adhésion d’un polymère acrylate sur des fibres de verre. Dans le volet « simulation numérique » de la thèse, nous avons modélisé le comportement mécanique de nos composites taffetas verre/matrice acrylate grâce au solveur spectral CraFT (Composite response and Fourier Transforms). Le détail des champs de contrainte et de déformation a été obtenu à l’échelle de la mésostructure et révèle une structuration périodique induite par la présence du renfort tissé. Une analyse quantitative a permis de vérifier que les champs de déformation qui ont été obtenus grâce au solveur CraFT sont en très bon accord avec des mesures réalisées par corrélation d’images. A partir du champ de contrainte, nous avons mis en évidence les régions de la mésostructure qui subissent les plus fortes sollicitations mécaniques. En visualisant par microtomographie X la structure interne d’éprouvettes précédemment déformées, nous avons pu établir le lien entre la localisation de l’endommagement au sein de la mésostructure et les régions de concentration de contrainte que la simulation numérique avait mises en évidence
This thesis is devoted to the characterization and the analysis of the mechanical properties of composite materials made of a plain weave glass fiber reinforcement and an acrylic resin (Elium®). Before the commercialization of the Elium resin in 2013, acrylics polymers were not used in the composite industry. In the experimental part of this thesis, we mainly focused on the sizing effect (surface treatment of the fibers to enhance the bonding between the matrix and the fibers) on the mechanical behavior of our composites. The characterizations were carried out through classical macroscopic mechanical tests (tensile, bending, shearing…) but using metrological tools for local analysis (full-field strain measurements, X ray micro-tomography, Scanning Electron Microscopy, Nano-indentation etc.). We were able to study strain and damage phenomena at local scales. Fatigue properties of the sizing were highlighted by heat build-up experiments. To analyze these measurements, an original data treatment has been developed which makes clear the benefit of an acrylic sizing in order to enhance the bonding between glass fibers and our acrylic matrix. In the theoretical part of this thesis, we studied the mechanical behaviour of our glass fiber plain weave/acrylic resin composite through a numerical simulation based on the CraFT spectral solver (Composite response and Fourier Transforms). Local stress and strain fields were obtained at the mesoscopic scale. The strain field analysis shows a periodic structure induced by the presence of the plain weave reinforcement. By a quantitative study, a good agreement between the numerical strain field obtained by CraFT and the 3D-DIC experimental strain measurements was found. The numerical stress field analysis reveals regions were a high local stress occurs. Comparing with X ray micro-tomography observationsof the internal structure of previously loaded composite sampleswe noticed that the damages occurring inside the mesostructure are totally correlated with the local stress concentration revealed by CraFT numerical simulations

The exceptional properties of carbon nanomaterials make them ideal reinforcements for polymers. However, the main challenges in utilizing their unique properties are their tendency to form agglomerates, their non-controlled orientation, non-homogeneous distribution and finally the change in their shape/size due to processing. All the above are the result of the nanomaterial/polymer interfacial interactions which dictate the overall performance of the composites including the mechanical properties. The aforementioned uncertainties are the reason for the deviation observed between the experimentally determined properties and the theoretically expected ones. The focus of this study is to understand the reinforcing efficiency of carbon nanomaterials in polymers through finite element modeling that captures the effect of the interfacial interactions on the tensile modulus of polymer nanocomposites (PNCs). The novelty of this work is that the probability distribution functions of nanomaterials dispersion, distribution, orientation and waviness, determined through image analysis by extracting 3-D information from 2-D scanning electron micrographs, are incorporated into the finite element model allowing thus for fundamental understanding of how the nanostructure parameters affect the tensile modulus of the PNCs. The nanocomposites are made using melt mixing followed by either injections molding or melt spinning of fibers. Polypropylene (PP) is used as the polymer and carbon nanotubes (CNT) or exfoliated graphite nanoplatelets (xGnP) are used as nanoreinforcements. The presence of interphase, confirmed and characterized in terms of stiffness and width using atomic force microscopy, is also accounted for in the model. The dispersion and distribution of CNT within the polymer is experimentally altered by using a surfactant and by forcing the molten material to flow through a narrow orifice (melt spinning) that promotes alignment of CNT and even of the polymer chains along the flow/drawing direction. The effect of nanomaterials' geometry on the mechanical behavior of PNCs is also studied by comparing the properties of CNT/PP to those of xGnP/PP composites. Finally the reinforcing efficiency of CNT is determined independently of the viscoelastic behavior of the polymer by conducting tensile testing at temperatures below the glass transition temperature of PP. The finite element model with the incorporated image analysis subroutine has sufficient resolution to distinguish among the different cases (dispersion, distribution, geometry and alignment of nanomaterials) and the predicted tensile modulus is in agreement with the experimentally determined one. In conclusion, this study provides a tool, that integrates finite element modeling and thorough experiments that enables design of polymer nanocomposites with engineered mechanical properties.

Thesis (M.S.)--University of Cincinnati, 2008.
Advisor: James Boerio. Title from electronic thesis title page (viewed Feb.16, 2009). Includes abstract. Keywords: AFM; FTIR spectroscopy; atomic force microscopy; interphase; adhesive analysis; interferogram. Includes bibliographical references.

Le lithium métal représente le candidat optimal comme électrode négative dans les batteries au lithium, de par sa capacité théorique élevée (3860 mAh.g-1) et son faible potentiel (-3,04 V ESH). En revanche, l'inconvénient majeur de cette technologie est la formation de dendrites qui peut provoquer des emballements thermiques et des courts-circuits internes. Ces dernières sont également responsables de la durée de vie limitée des cellules lithium métal. La maîtrise de l’électrodépôt du lithium est nécessaire pour le développement de cette technologie haute densité d’énergie et demande une compréhension approfondie de ces phénomènes dendritiques.L’objectif de ce travail est de corréler données expérimentales et modèle afin de comprendre la formation et la croissance des dendrites. Le modèle permet de théoriser les conditions dans lesquelles la croissance des dendrites est facilitée ou évitée, et comment les propriétés des composants de la cellule et la nature de la surface d'électrode peuvent l'affecter, pour suggérer des solutions permettant de réduire les dendrites. D'autre part, la partie expérimentale a pour but de définir un cadre de techniques permettant de déterminer des paramètres fiables à utiliser dans le modèle, et de valider ses tendances.Le modèle continu proposé montre que l’interphase électrode/électrolyte (‘SEI’ pour Solid Electrolyte Interphase) est fondamentale pour évaluer la formation de dendrites et leur croissance, tandis que la définition d’une densité de courant limite n'est pas une condition suffisante pour éviter les dendrites. Cette prise en compte de la SEI dans le modèle permet d’étudier l'influence de ses propriétés mécaniques et électrochimiques sur la croissance dendritique. A partir de la géométrie de surface initiale et des propriétés électrochimiques et mécaniques des composants, le modèle est capable de prédire les conditions qui favorisent la croissance dendritique et de distinguer différentes morphologies de surface. Des dendrites arborescentes (tree-like), moussues (mossy-like) et whiskers sont obtenues selon la densité de courant appliquée. De plus, l'ajout de la mécanique de la SEI permet au modèle de faire la distinction entre la croissance induite par la pointe (tip-induced) et celle induite par la racine (root-induced). À partir des résultats du modèle, une SEI avec une faible résistivité, un coefficient de diffusion élevé et une vitesse de réaction rapide réduit la croissance des dendrites, tandis que la résistance mécanique de la SEI est une arme à double tranchant puisqu’une résistance élevée peut à la fois limiter l'expansion incontrôlée de l’électrode de lithium, mais également stimuler la croissance en cas de fractures.Enfin, les propriétés électrochimiques et mécaniques de la SEI formée dans un électrolyte liquide sont déterminées par spectroscopie d'impédance électrochimique (SIE) et microscopie à force atomique (AFM). L’évolution des spectres d'impédance en fonction du temps permet de caractériser l'évolution de la SEI et de déterminer ses propriétés (épaisseur, coefficient de diffusion et résistivité). D'autre part, l’AFM est utilisée dans le mode spectroscopie de force, à partir duquel il est possible de déterminer des valeurs locales du module de Young de la SEI. La spectrométrie photoélectronique X (XPS), capable d'identifier les composants chimiques à la surface des électrodes, permet de valider les résultats de l’AFM. Enfin, les tendances prédites par le modèle sont validées grâce à la mise au point d’une nouvelle configuration de cellule lithium métal, adaptée à une étude operando de l’électrodépôt du lithium métal par microscopie optique.Ce travail représente une étude complète de la formation et croissance des dendrites dans les accumulateurs au lithium métal. Tandis que seuls les électrolytes liquides sont considérés ici, la méthodologie pourrait tout à fait être étendue aux électrolytes solides et aux revêtements artificiels à la suite de ce travail
Lithium metal represents the optimal candidate for the negative electrode in lithium batteries, due to its high theoretical capacity (3860 mAh.g-1) and low potential (-3.04 V SHE). On the other hand, the major drawback of this technology is the formation of dendrites, which can cause thermal runaway and internal short-circuits, and are responsible for the limited lifetime of the cells. A dendrite-free lithium deposition is needed to improve this high energy density technology, thus, a deeper understanding of the phenomena and parameters that influence dendrite growth and formation is necessary.The goal of this work is the correlation between experiments and modelling, to understand the formation and the growth of dendrites. The output of the model allows one to theorize in which conditions dendrites growth is boosted or avoided, and how the properties of the cell components and the design of the electrode surface can affect it, to suggest solutions to reduce dendrites. On the other hand, the experimental work has the purpose to define a framework of techniques to find reliable parameters to be used in the model, and to validate the trends of the model.The proposed continuum model shows that the Solid Electrolyte Interphase (SEI) is fundamental to assess dendrites formation and growth, while the definition of a limiting current density is not a sufficient condition to avoid dendrites. Thanks to the introduction of the SEI concept and properties, the proposed model studies the influence of its mechanical and electrochemical properties on the dendritic growth. Starting from the initial surface geometry and the electrochemical and mechanical properties of the cell components, the model is able to predict the conditions that favours dendritic growth and to distinguish different surface morphologies. Tree-like, mossy-like and whisker dendrites are obtained, depending on the applied current density. Moreover, the addition of the mechanics of the SEI allows the model to distinguish between tip-induced growth and root-induced growth. From the model results, it can be concluded that a SEI with low resistivity, high diffusion coefficient and fast reaction rate can reduce dendrite growth, while the mechanical resistance of the SEI is a double-edge sword because it can limit the uncontrolled expansion of the lithium electrode but also boost the root-growth in case of fractures.Electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) techniques are used to find electrochemical and mechanical properties of the SEI formed in liquid electrolytes. By following electrochemical impedance response over time, it is possible to observe SEI evolution and determine mean values for its thickness, its diffusion coefficient and its conductivity. On the other hand, the AFM technique is used in the force spectroscopy mode, from which it is possible to determine local values of the SEI Young’s modulus. X-ray photoelectron spectroscopy (XPS) technique, which is able to identify the chemical components on the electrode surface, helps to validate the results of AFM. Finally, the trends predicted by the model are validated with a novel cell configuration suitable for an operando optical microscopy study of lithium metal stripping/plating.This work represents a comprehensive study on dendrites formation and growth in lithium metal batteries. While it considers only liquid electrolytes so far, as a perspective, it could easily be expanded to solid electrolytes and artificial coatings

Le procédé de coextrusion permet de combiner à l’état fondu plusieurs couches de polymères dans une même structure. La compatibilisation des différentes couches est généralement réalisée à l’aide de liants qui réagissent in-situ. Bien que la compatibilisation puisse permettre de réduire ou même supprimer les instabilités macroscopiques d’écoulement, un nouveau défaut qualifié de « granité » peut apparaitre. Très peu de travaux de la littérature traitent les mécanismes gouvernant ce type de défaut. Les phénomènes mis en jeu sont particulièrement complexes puisqu’ils impliquent de façon couplée des phénomènes hydrodynamiques via l’écoulement, la rhéologie des différentes couches et des phénomènes physico-chimiques via la diffusion et la réaction chimique aux interfaces polymère/polymère. Ce mémoire s’articule autour d’une étude multi-échelle du rôle des copolymères aux interfaces sur la stabilité des écoulements stratifiés. L’étude a été réalisée à la fois sur des systèmes non-réactifs et réactifs constitués d’une couche barrière, le polyamide 6 (PA6) ou le poly(éthylène-co-alcool vinylique) (EVOH), avec un polypropylène (PP) ou un polypropylène greffé anhydride maléique (PP-g-AM). Le défaut de « granité » a été mis en évidence en coextrusion. Les paramètres procédé et matériaux influençant son apparition ont été identifiés. Il a pu être différencié des défauts et des instabilités interfaciales généralement rencontrées en coextrusion. Le phénomène de compatibilisation a également été étudié via les caractérisations morphologiques (MET, MEB, AFM) et physico-chimiques (XPS) aux interfaces. Le comportement rhéologique en cisaillement et élongation en viscoélasticité linéaire et non linéaire s’est révélé très sensible à l’effet la présence de copolymères aux interfaces et à leur architecture moléculaire. Cette étude a permis de déterminer les propriétés intrinsèques de l’interface/interphase en fonction du copolymère formé entre le liant et le PA6 ou l’EVOH. Elles ont pu être corrélées aux défauts macroscopiques observés dans les films multicouches coextrudés. La stabilité de ces écoulements stratifiés résulte d’un couplage de phénomènes qui se produisent à différentes échelles : nano (réaction de copolymérisation), micro (interphase) et macro (écoulement dans le procédé)
Several polymers can be combined in one multilayer structure by reactive coextrusion. Tie-layers are often used to compatibilize the adjacent layers and may reduce or suppress the interfacial instabilities and the defects in the multilayer coextrusion flow. However, an additional defect defined as the “grainy” defect can be observed. In the best of our knowledge, no study in literature has been devoted to understand its origin. The phenomena are quite complex due to the coupling of the effects of flow and the physico-chemical mechanisms at the interface. The aim of this work is to understand the relations between the instabilities and the defects encountered in multilayer coextruded films and the role of the copolymer formed in-situ between tie and barrier layers. Polyamide 6 (PA6) and ethylene-vinyl alcohol copolymer (EVOH) were used as the barrier layers sandwiched in a polypropylene (PP) with or without a polypropylene grafted maleic anhydride (PP-g-MA) as a tie-layer. The effect of the process parameters and the structure of the polymers on the generation of the “grainy” defect was assessed in correlation with the rheological and the physicochemical properties of the layers. These experiments have shown that this defect appeared mainly in the compatibilized EVOH system and could be distinguished from the usual coextrusion instabilities. The interfacial properties between tie and barrier layers were investigated. The characterization of the interfacial morphology by TEM and AFM highlighted an irregular and rough interface between PP-g-MA and EVOH while a flat interface was observed with PA6 and PP-g-MA. Step shear and startup elongation rheology was shown to be sensitive to the copolymer at the polymer/polymer interface. The study of the interfacial properties highlighted that the copolymer architecture significantly impacts the interfacial roughness and the rheology of the multilayer stuctures. Hence, relations between the relaxation process, the interfacial morphology and the copolymer architecture were established in correlation with the generation of the macroscopic grainy defect in coextrusion

Cette thèse vise à étudier le comportement multiéchelle (nano-, micro- et macroscopique) des composites, basé sur une étude fine utilisant les techniques les plus modernes pour comprendre les interfaces et les quantifier. Deux séries de renforts sur une échelle micrométrique, des fibres de carbone (CF) et des matériaux à base de graphène ont été utilisées ici. Pour améliorer l'interaction entre les nanorenforts et la matrice polymère, deux voies principales ont été utilisées dans cette thèse : l'oxydation des renforts et la greffe de nanotubes de carbone sur leur surface.L'étude en elle-même a été menée à une échelle microscopique pour étudier la résistance interfaciale entre une fibre de carbone (CF) et la matrice époxy, avec des essais de traction effectués in situ dans la chambre d'un microscope à double colonne MEB-FIB (microscope électronique à balayage couplé à un faisceau d'ions focalisé). Le faisceau d'ions a été utilisé pour découper une éprouvette de traction du composite contenant à la fois de l'époxy et de la CF. Le champ de tractiona été appliqué via le nanomanipulateur et l'essai a été observé via les deux colonnes ionique et électronique (sous deux angles de vue différents) et a permis d'estimer le champ de déformation, et donc la résistance interfaciale au moment de la rupture. Une expérience similaire a été menée sur un composite où les renforts sont des nanoplaquettes de graphène.Enfin, l'étude en microscopie électronique en transmission de la région de l'interface entre l'époxy et les renforts a révélé la présence d'une interphase et a permis de mesurer son épaisseur et donner une indication de sa nature. À cette fin, une analyse EELS (spectroscopie par pertes d'énergie des électrons) a été effectuée, permettant de mesurer la densité de l'échantillon très localement (taille de sonde de l'ordre du dixième de nanomètre) en travers ou parallèlement à l'interface. Un scénario sur les modes de liaison chimique entre les deux milieux en fonction du traitement de surface utilisé permet d'expliquer la nature des interphases observées
This thesis aims to investigate the multiscale (nano-, micro-, and macro-scopic) behavior of the composites based on a fine investigation using the most modern techniques, to understand the interfaces and to quantify them. Two series of reinforcements on a micrometer scale, carbon fibers (CFs) and graphene-based materials, were studied here. To improve the interactions between these nanofillers and the surrounding polymer matrix, two major routes were used in this thesis: the oxidation of the fillers and the grafting of carbon nanotubes on their surface.The study itself was conducted on a microscopic scale on the interfacial strength between CFs and the epoxy matrix, with tensile tests carried out in-situ in the chamber of a double-column FIB-SEM microscope (scanning electron microscope coupled to a focused ion beam). The ion beam was used to mill a thin bond-shaped tensile specimen of composite containing both an epoxy and a CF part. Thetensile stress field was applied using the nanomanipulator and the test was observed both via the ionic and the electronic columns (with two different angles of view) to estimate the strain field, hence the interfacial strength when the failure is observed. A similar experiment was led on a composite with GNPs.Finally, the transmission electron microscopy (TEM) study of the interface region between the epoxy and the graphene-based nanofillers revealed the existence of an interphase and allowed to measure its thickness and give an indication of its nature. For this purpose, an EELS (electron energy-loss spectroscopy) analysis was carried out, making it possible to measure the density of the sample very locally (probe size of the order of a tenth of a nanometer) across or parallelly to an interface. A scenario on the chemical bonding modes between the two media as a function of the surface treatment used makes it possible to explain the nature of the observed interphases

Nanocomposites represent a new class of materials which, thanks to the outstanding functional and mechanical properties are endowed with, is earning more and more interest from the scientific community and the industry. As a matter of facts, results available in the literature indicate the possibility to obtain exceptional performance increments even at low nanofiller volume fraction. To effectively exploit the huge potential of nanocomposites it is of primary concern that with the experimental analysis, abundantly developed in the literature among the rest, comes an adequate modeling activity. Of course, the creation of models, either analytical or numerical, is a milestone for the comprehension and prediction of the mechanical behavior of this kind of materials and their successive application in engineering design. One of the most critical issues in modeling macro-mechanical properties of nanostructured materials is their hierarachical structure which spans from nano to macro length-scales. A good model should take into account the characteristic phenomena of each length-scale and bridge their effects from the “smaller” scale to the macroscale. As a consequence, a different way of thinking from traditional approaches is needed and a completely new class of models is required. In this work an extensive review on the main approaches available in the literature for mechanical properties modeling of polymeric-based nanocomposites is proposed. The importance of a multiscale approach either hierarchical or concurrent is discussed and a classification of the models based on the scale level used to address the model (micro-, nano and molecular) is introduced as well. Then, a comprehensive study on interfacial effects on nanoparticle debonding is presented. The analysis is developed within the frame of Finite Fracture Mechanics and Surface Elasticity. It accounts, contemporaneously, for the emergence of an interphase zone around the nanoparticle and for surface stresses on the nanoparticle periphery. Afterwards, a unique multiscale analytical procedure useful to evaluate the overall fracture toughness of a polymer/nanoparticle nanocomposite is proposed. The models developed for each damaging mechanism are introduced, highlighting the most important parameters. All models are finally integrated and comparison is carried out between the predicted nanocomposite fracture toughness and some experimental data taken from the literature. In the second part of the work, the experimental investigations carried out by the author are described and discussed. The effects of nanomodification by nanoclays on polymers and composite laminates in terms of quasi-static and cyclic fracture properties are investigated. In case of nanomodified polymers, it is found that nanomodification significantly enhances the fracture behaviour of the system either in quasi-static or cyclic regime and for different loading modes. In the case of nanomodified laminates, due to the nanofiller morphology, the behaviour of clay-modified laminates is still almost comparable to that of the base laminates.
I nanocompositi, ottenuti mediante modificazione di resine polimeriche con cariche di dimensioni nanometriche, rappresentano una classe di materiali che sta riscuotendo un notevole interesse da parte della comunità scientifica e del mondo industriale. Combinando infatti, in maniera opportuna, rinforzi su scala nanometrica con polimeri tradizionali è possibile ottenere dei nuovi materiali dalle eccezionali proprietà fisiche e di resistenza. I risultati finora disponibili in letteratura indicano la possibilità di ottenere incrementi prestazionali molto elevati già con frazioni di nanocarica limitate, dell’ordine di qualche percento. Al fine di poter sfruttare l’enorme potenziale di questo tipo di materiali è necessario che l’attività sperimentale sia accompagnata da un’adeguata attività di modellazione, così da mettere a punto dei modelli comportamentali capaci di prevedere le proprietà meccaniche del nanocomposito, includendo la struttura gerarchica e la peculiarità dei meccanismi di rinforzo. In questo lavoro viene proposta una panoramica e un’analisi critica delle principali metodologie di modellazione finora disponibili in letteratura, con riferimento alle proprietà meccaniche e in particolare alla tenacità a frattura. Per ciascun modello analizzato vengono descritti gli aspetti maggiormente significativi, le ipotesi di base e le conseguenze che tali ipotesi hanno sul risultato finale. Viene delineata l'importanza di un approccio multi-scala, gerarchico o concorrente, alla modellazione e viene introdotta una classificazione dei principali approcci basata sulla scala di lunghezza investigata per affrontare il problema (micro-, nano- e molecolare). Successivamente, viene presentato uno studio approfondito degli effetti interfacciali sul meccanismo di debonding di nanoparticelle. L'analisi è stata condotta nell'ambito della teoria della Finite Fracture Mechanics e della Surface Elasticity. Vengono tenuti in considerazione, contemporaneamente, gli effetti di un'interfase che circonda la nanoparticella e di tensioni superficiali agenti all'interfaccia con la matrice. L'analisi del meccanismo di debonding rappresenta la base di una procedura multiscala per il calcolo della tenacità a frattura di nanocompositi particellari. L'approccio proposto in questo lavoro unisce i modelli di danneggiamento sviluppati dall'autore. Vengono discussi il funzionamento del modello e l'influenza dei principali parametri e le previsioni sono confrontate con risultati sperimentali provenienti da letteratura. Nella seconda parte del lavoro vengono presentati e discussi i risultati delle campagne sperimentali condotte dall'autore con particolare enfasi agli effetti della nanomodificazione sul comportamento a frattura, quasi-statico e ciclico, sia di polimeri nanomodificati che di laminati nanomodificati con nanoclay. Nel caso di polimeri nanomodificati, viene mostrato come l'aggiunta di nanorinforzi comporti un miglioramento significativo del comportamento a frattura del sistema sia in regime quasi-statico che ciclico e per diversi modi di sollecitazione. Nel caso di laminati nanomodificati, a causa della morfologia del nanofiller, il comportamento a frattura è risultato ancora confrontabile a quello dei laminati base.

Cette étude porte sur le développement de modèles et de méthodes numériques pour prédire les propriétés électriques et mécaniques des nanocomposites polymères/graphènes.Dans une première partie, un modèle nonlinéaire de conduction électrique prenant en compte l’effet tunnel est introduit pour déterminer la conductivité effective de ces nanocomposites au travers d’une procédure d’homogénéisation numérique. Celle-ci, basée sur une formulation éléments finis a mis en évidence l’influence des paramètres microstructuraux sur la conductivité effective au travers d’une étude statistique.Ensuite, un modèle atomistique de l’interface polymère/graphène a été proposé pour valuer les propriétés de l'interface et de l'interphase. Les champs de contrainte et de déplacement ont été identifiés par une extension de la procédure d'Hardy-Murdoch à partir des simulations de mécanique moléculaire. À l'aide de ces champs, un modèle élastique continue avec des interfaces imparfaites a été identifié et comparé aux résultats des simulations de mécanique moléculaire. Finalement, le modèle atomistique a permis d’identifier un modèle de zone cohésive nonlinéaire pour modéliser la décohésion à l’interface polymère/graphène. Une procédure d’homogénéisation numérique par la méthode des éléments finis a été introduite pour estimer les propriétés mécaniques effectives dans le cadre des transformations finies. Les microstructures déformées ont été utilisées dans le modèle électrocinétique pour déterminer l’impact de la décohésion interfaciale sur la conductivité effective
This work contributes to developing numerical methodologies for predicting the electrical and mechanical properties of graphene/polymer nanocomposites, which can provide a better view for the design of new materials.First, a nonlinear electrical conduction model taking into account the tunneling effect is introduced to determine the effective conductivity of the graphene/polymer nanocomposites through a numerical homogenization procedure. The influences of barrier height and microstructural parameters on the conductivity were demonstrated.Then, to characterize the properties of interphases and interfaces, we employed the Murdoch-Hardy procedure combined with the molecular dynamics method to study the mechanical properties of the graphene/polymer nanocomposites. The stiffness tensor components of the interphase, interface andnbulk polymer region are identified. Based on these fields, a continuous elastic model with imperfect interface has been identified and compared with the results of molecular dynamics simulations.Finally, the atomistic model was used to identify a nonlinear cohesive zone model to simulate the decohesion at the interface of polymer and graphene. A numerical homogenization procedure by finite element method was introduced to estimate the effective mechanical properties in the framework of the finite strains. The proposed mechanical modeling is finally extended to the finite strain problem to predict the evolution of percolation threshold under tension within the proposed electrical model

Des nuances d’aciers à moyen carbone, microalliés au vanadium, ont été élaborées avec l’objectif d’obtenir de nouvelles microstructures, majoritairement constituées de ferrite aciculaire (FA). Le contrôle de la composition chimique (0.1-0.3 % V) et la vitesse de refroidissement (2.0 °Cs-1) conduit à des fractions de FA atteignant 80 %. Un paramètre empirique, le pouvoir ferritisant, P, a été introduit pour évaluer l’effet combiné de la composition chimique et de la vitesse de refroidissement sur la fraction de FA. Les caractérisations par MEB et MET montrent que la FA se développe à partir de la ferrite proeutectoïde recouvrant les inclusions de MnS. Une précipitation interphase de carbonitrures de vanadium, V(C,N), serait à l’origine d’un appauvrissement local en carbone de la matrice austénitique autour des aiguilles de FA, favorisant une germination autocatalytique. Le caractère fractal de la FA a été mis en évidence par des caractérisations morphologiques. Les dimensions fractales, D, et les longueurs de coupure ont été déterminées par la méthode de comptage de boîtes à partir d’images MEB. Des essais mécaniques isothermes-quasistatiques révèlent des propriétés mécaniques équivalentes à celles des microstructures bainitiques. Les courbes contrainte-déformation montrent un comportement mécanique de type Hollomon. Les structures de ces aciers présentent des taux de consolidation qui augmentent avec l’accroissement de la fraction de FA. Une corrélation entre les propriétés mécaniques et la dimension fractale a été établie. Ce lien s’exprime par des relations de type exponentiel : [delta]M = c exp [[alpha](D -2)] où M représente? les propriétés mécaniques (Re, Rm, etc.) et c? et ?[alpha] des constantes
Medium carbon vanadium microalloyed steels have been developed to obtain new microstructures, mainly formed of acicular ferrite (AF). Controlling the chemical composition and (0.1-0.3 % V) and the cooling rates (2.0 °Cs-1) lead to AF fractions up to 80 %. An empirical parameter, the ferritisant power, P, has been introduced to evaluate the combined effect of chemical composition and cooling conditions. Scanning (SEM) and transmission (TEM) electron microscopy investigations indicate that AF develops from proeutectoid ferrite enveloping MnS inclusions. An interphase precipitation of vanadium carbo-nitrides, V(C,N) has been identified. It is suggested that this precipitation is at the origin of carbon depletion in the austenitic matrix surrounding the AF plates. The formation of the AF is then enhanced by an autocatalytic effect. The fractal nature of AF has been determined by SEM and TEM characterisations. Fractal dimensions, D, and cut off lengths have been derived by the counting box method applied to SEM images. Mechanical tests conducted in isothermal and quasistatic conditions reveal that mechanical properties of AF are of the same grade of that of bainitic microstructures. Experimental strain-stress curves are described by the Hollomon law. The work hardening of the studied microstructures increases with the AF fraction. The mechanical properties have been linked to the fractal dimension by the following exponential relation : [delta]M = c exp [[alpha] (D -2)], where M represents the mechanical property (Re, Rm, etc.) and c and [alpha] are constants parameters

This dissertation focused on development and utilization of numerical and experimental approaches to improve the CFD modeling of fluidization flow of cohesive micron size particles. The specific objectives of this research were: (1) Developing a cluster prediction mechanism applicable to Two-Fluid Modeling (TFM) of gas-solid systems (2) Developing more accurate drag models for Two-Fluid Modeling (TFM) of gas-solid fluidization flow with the presence of cohesive interparticle forces (3) using the developed model to explore the improvement of accuracy of TFM in simulation of fluidization flow of cohesive powders (4) Understanding the causes and influential factor which led to improvements and quantification of improvements (5) Gathering data from a fast fluidization flow and use these data for benchmark validations. Simulation results with two developed cluster-aware drag models showed that cluster prediction could effectively influence the results in both the first and second cluster-aware models. It was proven that improvement of accuracy of TFM modeling using three versions of the first hybrid model was significant and the best improvements were obtained by using the smallest values of the switch parameter which led to capturing the smallest chances of cluster prediction. In the case of the second hybrid model, dependence of critical model parameter on only Reynolds number led to the fact that improvement of accuracy was significant only in dense section of the fluidized bed. This finding may suggest that a more sophisticated particle resolved DNS model, which can span wide range of solid volume fraction, can be used in the formulation of the cluster-aware drag model. The results of experiment suing high speed imaging indicated the presence of particle clusters in the fluidization flow of FCC inside the riser of FIU-CFB facility. In addition, pressure data was successfully captured along the fluidization column of the facility and used as benchmark validation data for the second hybrid model developed in the present dissertation. It was shown the second hybrid model could predict the pressure data in the dense section of the fluidization column with better accuracy.

碩士
國立臺南大學
綠色能源科技學系碩士班
106
In this study is employed a pseudo two-dimensional (P2D) lithium-ion ｂattery electro-chemical model to discuss the temperature variation of lithium-ion battery and solid electrolyte interphase (SEI) film had an impact on battery. In numerical analysis, this mode is composed of electrochemical model, heat transfer model and capacity fade mode. The results have good agreement with experimental battery (LiC6-LiMn5Ni3Co2) and the error is 2.24%. In the literature review, the literature refers three kind of models for using its formulas as the basis for the study. The study focus on the major factors of temperature rising and effect of SEI layer after charging cycles in different C-rate. Battery’s temperature rising is caused from the heat source. The heat source is assembled in reaction heat, reversible heat and ohmic heat that centralized generated between the electrode and the separator. After adding the capacity fade model, we discuss the battery effected the SEI film when adjust the C-rate and cycle number. When charging cycles get up to 500, the capacity drops to 82.9% of the initial value. As the C-rate rises, the rate of SEI film formation also increases and affects the battery temperature.

碩士
國立臺灣科技大學
應用科技研究所
105
In this study, benzimidazole as the main body of the structure to research different functional groups as the electrolyte solution of lithium salt. The results were tested by electrochemical quartz crystal microbalance to investigate benzimidazole lithium salt additives in different electrodes electrochemical reaction kinetics and the formation mechanism of Solid Electrolyte Interface (SEI). The chemical composition of solid electrolyte interface film was identified by nuclear magnetic resonance spectroscopy. The results showed the addition of benzimidazole lithium salt did affect the EC reduction potential, especially in LiBZ and LiMB, not only in the results of the gold electrode but also the results of the graphite electrode showed the effects of the early reduction reaction. The reaction of kinetics changed significantly as well. In addition, LiTFB contains (-CF3) substituents improved the electron density of LiTFB. In the previous research and in-situ EQCM proved that the LiTFB and carbonates would produce novel forms of solid electrolytes.

Σκοπός της συγκεκριμένης εργασίας είναι η κατασκευή, η μοντελοποίηση και η μελέτη της φυσικής και μηχανικής συμπεριφοράς συνθέτων υλικών πολυμερικής μήτρας ενισχυμένης με νανοσωλήνες άνθρακα. Πρώτος στόχος της εργασίας είναι η μελέτη των φυσικών και μηχανικών ιδιοτήτων νανοσυνθέτων υλικών εποξικής ρητίνης ενισχυμένης με νανοσωλήνες άνθρακα. Για τη μελέτη αυτή πραγματοποιήθηκαν μια σειρά διαφορετικών πειραμάτων προκειμένου να προκύψουν αξιόπιστα συμπεράσματα. Το πρώτο και βασικότερο πρόβλημα που μελετά η συγκεκριμένη εργασία είναι η κατασκευή νανοσυνθέτων υλικών εποξικής ρητίνης ενισχυμένης με νανοσωλήνες άνθρακα με τρόπους που συνδυάζεται το χαμηλό κόστος εξοπλισμού και η μικρή διάρκεια προετοιμασίας για την κατασκευή. Η κατασκευή των νανοσυνθέτων έγινε με δύο βασικές μεθόδους, με μηχανική ανάδευση και με χρήση υπερήχων. Το κύριο πρόβλημα που έπρεπε να ξεπερασθεί ήταν η ομογενής διασπορά μέσα στη ρητίνη καθώς η τάση που έχουν οι νανοσωλήνες να σχηματίζουν συσσωματώματα επιδρά αρνητικά. Από τη βιβλιογραφική και πειραματική μελέτη που έγινε προκύπτει πως ο χρόνος ανάμιξης, η μέθοδος ανάμιξης και η μεθοδολογία κατασκευής παίζουν καθοριστικό ρόλο στην επίτευξη καλής διασποράς των νανοσωλήνων μέσα στη ρητίνη. Εδώ πρέπει να σημειωθεί πως ο τύπος της ρητίνης και ο τύπος των νανοσωλήνων ανατρέπουν τη βέλτιστη μέθοδο. Για παράδειγμα στη μία ρητίνη που χρησιμοποιήθηκε, βέλτιστος χρόνος ήταν τα 10 λεπτά ενώ στην άλλη ρητίνη, βέλτιστος χρόνος ήταν τα 20 λεπτά. Για το στατικό μηχανικό χαρακτηρισμό νανοσυνθέτων υλικών εποξικής ρητίνης ενισχυμένης με νανοσωλήνες άνθρακα πραγματοποιήθηκαν πειράματα κάμψης τριών σημείων. Για πληρότητα της εργασίας χρησιμοποιήθηκαν δύο τύποι εποξικών ρητινών. Και οι δύο τύποι ρητινών ενισχύθηκαν με νανοσωλήνες άνθρακα σε διάφορες περιεκτικότητες. Από τα συγκεκριμένα πειράματα προέκυψε ότι υπάρχει μία συγκεκριμένη περιεκτικότητα σε νανοσωλήνες στην οποία το νανοσύνθετο εμφανίζει βελτιωμένες μηχανικές ιδιότητες. Συγκεκριμένα, για τον πρώτο τύπο εποξικής ρητίνης βρέθηκε πως το ποσοστό αυτό είναι το 0.3% κ.β. με ποσοστιαία αύξηση 10.6% και 2.6% σε μέτρο ελαστικότητας και αντοχής σε κάμψη. Σε ποσοστό 3% κ.β., η αύξηση στο μέτρο ελαστικότητας ήταν 14.03% αλλά η αντοχή του ήταν πολύ μικρή. Για το δεύτερο τύπο εποξικής ρητίνης βρέθηκε ότι το ποσοστό αυτό είναι το 0.2% κ.β., με ποσοστιαία αύξηση στο μέτρο ελαστικότητας σε κάμψη 22.8% και στην αντοχή σε κάμψη 29.4%. Για τον πειραματικό χαρακτηρισμό της βισκοελαστικής συμπεριφοράς (Long term testing) των υλικών που κατασκευάσθηκαν πραγματοποιήθηκαν πειράματα εφελκυστικού ερπυσμού-επανάταξης, ενώ για τον έλεγχο της βραχυπρόθεσμης βισκοελαστικής συμπεριφοράς πραγματοποιήθηκαν πειράματα κάμψης τριών σημείων σε διαφορετικούς ρυθμούς παραμόρφωσης για τα οποία έγινε μοντελοποίηση με εφαρμογή των βισκοελαστικών προτύπων του στερεού των τεσσάρων και τριών παραμέτρων, αντίστοιχα. Εξίσου σημαντική ήταν και η μελέτη των υλικών σε μη ιδανικές συνθήκες, δηλαδή σε συνθήκες όπου μπορεί να βρεθούν τα υλικά αυτά όταν αποτελέσουν μέρος μιας πραγματικής μηχανολογικής κατασκευής. Για το σκοπό αυτό έγινε μελέτη της βλάβης που εμφανίζεται σε υλικά καθαρής ρητίνης αλλά και ενισχυμένης τόσο ύστερα από κυκλικό θερμικό σοκ όσο και μετά από απορρόφηση υγρασίας. Η μελέτη που έγινε χωρίζεται σε δύο μέρη, το πειραματικό και το θεωρητικό. Όσον αφορά το πειραματικό σκέλος έγινε μηχανικός χαρακτηρισμός των υλικών με στατικά πειράματα κάμψης τριών σημείων, ενώ όσον αφορά το θεωρητικό σκέλος έγινε εξήγηση των μηχανισμών που λαμβάνουν χώρα με αποτέλεσμα την πρόκληση βλάβης. Τα αποτελέσματα που προκύπτουν στην περίπτωση της θερμικής κόπωσης είναι ενθαρρυντικά. Συγκεκριμένα για το μέτρο ελαστικότητας σε περιεκτικότητα 0.2%, όπου έχει γίνει μια επιτυχημένη κατασκευή νανοσυνθέτου με αύξηση που ξεπερνάει το 22.5%, παρατηρείται ότι η σχετική αύξηση σε πέντε κύκλους θερμικής κόπωσης ξεπερνάει το 30% (30, 40, 50, 80 και 90) και μάλιστα φτάνει το 40.2% στους 80 κύκλους. Όσον αφορά την αντοχή, αντίστοιχα είναι τα συμπεράσματα. Φαίνεται πως τα νανοσύνθετα συνεχίζουν να υπερτερούν έναντι του παρθένου υλικού με πιο χαρακτηριστική περίπτωση την αύξηση που παρατηρείται στους 40 κύκλους θερμικής κόπωσης όπου φτάνει το 46.7%. Τα αποτελέσματα που προκύπτουν μετά από απορρόφηση υγρασίας δεν είναι ενθαρρυντικά καθότι τόσο στο 0.2%κ.β. όσο και στο 0.3%κ.β. η σχετική μείωση των ιδιοτήτων είναι ιδιαίτερα υψηλή. Για το δυναμικό χαρακτηρισμό των υλικών έγιναν πειράματα δυναμικής θέρμο-μηχανικής ανάλυσης μέσω των οποίων προσδιορίσθηκε η θερμοκρασία υαλώδους μετάβασης Tg και η ικανότητα απόσβέσης των νανοσυνθέτων. Από τα πειράματα προέκυψε πως τα νανοσύνθετα έχουν Tg μεγαλύτερη από αυτή του μητρικού υλικού και συγκεκριμένα 126°C έναντι 101°C. Επίσης, η ικανότητα απόσβεσης των νανοσυνθέτων φαίνεται να είναι αισθητά μικρότερη. Τα πειραματικά αποτελέσματα ενισχύθηκαν με θεωρητική μελέτη. Για το σκοπό αυτό έγινε εφαρμογή αναλυτικών μοντέλων και αριθμητική ανάλυση με τη μέθοδο των Πεπερασμένων Στοιχείων. Το πρώτο μοντέλο που χρησιμοποιήθηκε ήταν το μοντέλο της υβριδικής ενδιάμεσης φάσης που έχει αναπτυχθεί από τον καθηγητή Γ. Παπανικολάου και την ερευνητική του ομάδα. Το μοντέλο αυτό εισάγει την έννοια του συντελεστή πρόσφυσης και της ενδιάμεσης φάσης, ως μίας φάσης που ξεκινά αμέσως μετά τη διεπιφάνεια ίνας-μήτρας και καταλήγει στη μήτρα. Κατά το πάχος της ενδιάμεσης φάσης οι ελαστικές ιδιότητες. Η ενδιάμεση φάση συμπεριφέρεται βισκοελαστικά με αποτέλεσμα το πάχος της να μεταβάλλεται με το χρόνο. Η υβριδική ενδιάμεση φάση είναι πολύ σημαντική και πρέπει να λαμβάνεται υπόψη στο σχεδιασμό από τους μηχανικούς. Η άποψη αυτή ενισχύεται από την παρατήρηση που γίνεται στη συγκεκριμένη εργασία, ότι, δηλαδή, μπορεί να προκύψει ένα σύνθετο υλικό με πλήρως τροποποιημένη μήτρα. Στην περίπτωση αυτή, το σύνθετο σε μικροσκοπική κλίμακα εμφανίζει ιδιότητες ίνας και ιδιότητες ενδιάμεσης φάσης, αλλά όχι μήτρας. Τα μοντέλα, τόσο της υβριδικής ενδιάμεσης φάσης όσο και της βισκοελαστικής ενδιάμεσης φάσης χρησιμοποιήθηκαν στη μοντελοποίηση που έγινε με τη μέθοδο των Πεπερασμένων Στοιχείων. Συγκεκριμένα, έγινε μοντελοποίηση ενός αντιπροσωπευτικού στοιχείου όγκου που συνδέει τις μακροσκοπικές με τις μικροσκοπικές ιδιότητες και στη συνέχεια μελετήθηκε η εντατική κατάσταση που αναπτύσσεται στη διεπιφάνεια. Τα αποτελέσματα συγκρίθηκαν με αναλυτικά μοντέλα που μελετούν τη διεπιφάνεια.
Nanocomposites constitute a very special category of composite materials. Only a small amount of nano-inclusions is enough to achieve unique mechanical, electrical and other properties. Carbon nanotubes have gain the scientists’ interest the last ten years due their becoming a material with many prospects. After an extended research by Iijima, S. in 1991, carbon nanotubes became a new attractive material to Nanotechnology. Thorough investigations in polymer matrix composites reinforced with carbon nanotubes are being developed in an effort to explain their properties. The aim of the present master thesis is multiple. The first step was the experimental procedure which started with the static mechanical characterization of epoxy polymer matrices reinforced with Multi Walled Carbon Nanotubes in order to define the factors that, mainly, come up during the mixing process and contribute to the final mechanical properties, namely the bending modulus and the strength. High speed shearing and ultrasonication were the two main manufacturing techniques that were applied in order to disperse the nanotubes in different volume fractions. Neat epoxy and MWCNT’s-reinforced epoxy specimens were also tested with Dynamic Thermo Mechanical Analysis bending experiments, by which the glass transition temperature, Tg, and the damping response were defined. Furthermore, three point bending tests in different strain rates and creep-recovery tests were executed for the definition of the short-term and long-term viscoelastic response, respectively. Finally, the damage that occurs after thermal shock cycling and water absorption was examined thoroughly. More specifically, the elastic properties degradation, due to damage, of the neat epoxy and of the nanocomposites was compared. Next, using the hybrid interphase concept and the viscoelastic intrphase, a theoretical investigation of the fiber-matrix interphase region was executed in an effort to compute both analytically and numerically its effect on the interfacial stress and strain fields developed in the area close to CNT’s. Analytical models that give the distribution of the normal and shear stresses were applied and the results were compared with the numerical analysis. The Finite Element Method was used for the numerical analysis. Many simplifying assumptions were necessary for both analytical and numerical technique. Experimental findings combined with analytical and numerical results gave a better understanding on the structural and mechanical performance of epoxy resin-carbon nanotubes composites. The static mechanical characterization that is being presented shows that we can achieve better mechanical properties by using a quit simple and low cost mixing process, but it needs much better techniques to achieve high performance materials. Glass transition temperature, Tg, of the nanocomposite is clearly higher from that of the neat epoxy. On the other hand, the damping of the nanocomposite is much lower, especially in higher temperatures. Finally, the nanocomposites seem to have much better response after cyclic thermal shock in contrast with the effect of water absorption, that seem to degrade the properties. The theoretical investigation showed that the third phase formatted around the inclusion is responsible for the stress and strain field developed in the area close to the nanotube. The interphase is not simply a geometrical concept but it mainly a property dependent concept, the thickness of which vary in compliance with the adhesion coefficient and time. Nanocomposites are materials that need further investigation in order to achieve things that the human brain could never imagine a few decades before.