The many advances of nano technology extensively revolutionize mechanics. A tremendous need is growing to further bridge the gap between the classical mechanics and the nano scale for many applications at different engineering fields. For instance, the themes of interdisciplinary and multidisciplinary topics are getting more and more attention especially when the coherency is needed in diagnosing and treating terminal diseases or overcoming environmental threats. The fact that how mechanical, biomedical and electrical engineering can contribute to diagnosing and treating a tumor per se is both interesting and unveiling the necessity of further investments in these fields. This dissertation presents three different investigations in the area of nano mechanics and nano materials spanning from computational bioengineering to making mechanically more versatile composites. The first part of this dissertation presents a numerical approach to study the effects of the carbon nano tubes (CNTs) on the human body in general and their absorbability into the lipid cell membranes in particular. Single wall carbon nano tubes (SWCNTs) are the elaborate examples of nano materials that departed from mere mechanical applications to the biomedical applications such as drug delivery vehicles. Recently, experimental biology provided detailed insights of the SWCNTs interaction with live organs. However, due to the instrumental and technical limitations, there are still numerous concerns yet to be addressed. In such situation, utilizing numerical simulation is a viable alternative to the experimental practices. From this perspective, this dissertation reports a molecular dynamics (MD) study to provide better insights on the effect of the carbon nano tubes chiralities and aspect ratios on their interaction with a lipid bilayer membrane as well as their reciprocal effects with surface functionalizing. Single walled carbon nano tubes can be utilized to diffuse selectively on the targeted cell via surface functionalizing. Many experimental attempts have smeared polyethylene glycol (PEG) as a biocompatible surfactant to carbon nano tubes. The simulation results indicated that SWCNTs have different time-evolving mechanisms to internalize within the lipid membrane. These mechanisms comprise both penetration and endocytosis. Also, this study revealed effects of length and chirality and surface functionalizing on the penetrability of different nano tubes. The second part of the dissertation introduces a novel in situ method for qualitative and quantitative measurements of the negative stiffness of a single crystal utilizing nano mechanical characterization; nano indentation. The concept of negative stiffness was first introduced by metastable structures and later by materials with negative stiffness when embedded in a stiffer (positive stiffness) matrix. However, this is the first time a direct quantitative method is developed to measure the exact value of the negative stiffness for triglycine sulfate (TGS) crystals. With the advancements in the precise measuring devices and sensors, instrumented nano indentation became a reliable tool for measuring submicron properties of variety of materials ranging from single phase humongous materials to nano composites with heterogeneous microstructures. The developed approach in this chapter of the dissertation outlines how some modifications of the standard nano indentation tests can be utilized to measure the negative stiffness of a ferroelectric material at its Curie temperature. Finally, the last two chapters outline the possible improvements in the mechanical properties of conventional carbon fiber composites by introducing 1D nano fillers to them. Particularly, their viscoelastic and viscoplastic behavior are studied extensively and different modeling techniques are utilized. Conventional structural materials are being replaced with the fiber-reinforced plastics (FRPs) in many different applications such as civil structures or aerospace and car industries. This is mainly due to their high strength to weight ratio and relatively easy fabrication methods. However, these composites did not reach their full potential due to durability limitations. The majorities of these limitations stem from the polymeric matrix or the interface between the matrix and fibers where poor adhesion fails to carry the desired mechanical loadings. Among such failures are the time-induced deformations or delayed failures that can cause fatal disasters if not taken care of properly. Many methodologies are offered so far to improve the FRPs' resistance to this category of time-induced deformations and delayed failures. Several researchers tried to modify the chemical formulation of polymers coming up with stiffer and less viscous matrices. Others tried to modify the adhesion of the fibers to the matrix by adding different chemically functional groups onto the fibers' surface. A third approach tried to modify the fiber to matrix adhesion and at the same time improve the viscous properties of the matrix itself. This can be achieved by growing 1D nano fillers on the fibers so that one side is bonded to the fiber and the other side embedded in the matrix enhancing the matrix with less viscous deformability. It is shown that resistance to creep deformation and stress relaxation of laminated composites improved considerably in the presence of the nano fillers such as multiwall carbon nano tubes (MWCNTs) and zinc oxide nano wires (ZnO- NWs). The constitutive behaviors of these hybrid composites were investigated further through the use of the time temperatures superposition (TTS) principle for the linear viscoelastic behavior and utilizing phenomenological models for the viscoplastic behavior. / Ph. D.

La nécessité de pouvoir visualiser et manipuler des nano-échantillons de matériaux minéraux ou biologiques, tout en menant des expériences quantitatives de traction, compression, flexion et cisaillement, a mené au développement d’un dispositif de nano manipulation pouvant évoluer dans un microscope électronique à balayage en transmission environnemental.Un tel dispositif permettra donc de mesurer les différentes forces mises en jeu et de visualiser l’interface d’intérêt durant les différentes manipulations réalisées dans des conditions environnementales contrôlées (pression partielle de gaz de 10-8 à 2500 Pa, milieu liquide). Ce travail de thèse a permis le développement opérationnel d’un nanomanipulateur à 9 degrés de liberté (Nanomanipulateur 9D). Une fois construit, nous avons réalisé un logiciel de contrôle et d’acquisition des paramètres de positions et de déplacements. Nous avons développé et étalonné des nano-supports et nano-outils peu onéreux permettant la mesure de forces de l’ordre du nanonewton. Il s’agit de micro-aiguilles de verre préparées par la méthode de fusion étirage de baguettes de verre ordinaire ou borosilicaté au chalumeau. Ces micro-aiguilles ont été recouvertes d’une fine couche de métal (4 nm d’or pour nos essais) par pulvérisation cathodique afin de les rendre conductrices et réduire les effets de charges.Enfin, afin d’illustrer une partie des capacités de nano-caractérisation quantitative offertes par le nanomanipulateur, installé dans le MEBE, et d’évaluer ses limitations, nous avons réalisé une série de mesures quantitatives de flexion, d’adhérence et de frottement statique et dynamique sur différents types de nanoparticules dérivées du carbone. Les nanoparticules étudiées sont le noir de carbone partiellement fluoré (NCF), le graphite exfolié, les nano-disques et nano-cônes de carbone amorphe (CND-A et CNC-A), les nano-disques et nano-cônes de carbone graphitisé (CND-G et CNC).Les différentes mesures sur des nanoparticules dérivées de carbone :•On a effectué des mesures de raideurs d’un nano disque poly nano cristallin de carbone (CND-A). Une partie du nano-disque sélectionné est fixée sur une micro-aiguille, et l’autre partie est déformée élastiquement. La raideur angulaire en torsion mesurée est de l’ordre de 0,041 ± 0,009 µN*µm/°.• Dans les essais d’adhérence sur des contacts or/noir de carbone fluoré et or/graphite fluoré, on a noté une décroissance significative des forces et des énergies d’adhérence en fonction de la succession chronologique des essais. Cette décroissance peut être attribuée au transfert, par délamination, d’une fraction croissante de matériaux de la surface des nanoparticules sur la surface dorée des micro-aiguilles.•Des expériences de tribologie à l’échelle nanométrique ont été réalisées afin de mesurer quantitativement les coefficients de frottement statique et dynamique pour des contacts or/carbone établis entre l’extrémité libre d’une micro-aiguille dorée et la surface de différentes nanoparticules (graphite exfolié, CND-A et CND-G) et des contacts carbone/carbone établis entre les surfaces de deux nanoparticules. On a mesuré les coefficients de frottement dynamique sur des contacts or/CND-A (µD ≤ 0,05) et pour des contacts CND-A/CND-A (0.02 ≤ µD ≤0.2). Les résultats obtenus dans le cas des coefficients de frottement statiques sont de quelques ordres de grandeur supérieurs à ceux attendus. Ces différences ont été attribuées à un phénomène de « soudure » du contact dû au faisceau d’électrons.Pour chacune de ces expériences une analyse précise et minutieuse des images réalisées au MEB nous a permis d’extraire des données permettant de quantifier les phénomènes étudiés. / The need to be able to visualize and manipulate nano-samples of mineral or biological materials, while conducting quantitative tensile, compression, bending and shearing experiments, led to the development of a nano-manipulation device that can evolve in an electron microscope. scanning in environmental transmission.Such a device will therefore make it possible to measure the various forces involved and to visualize the interface of interest during the various manipulations performed under controlled environmental conditions (gas partial pressure of 10-8 to 2500 Pa, liquid medium).For each of these experiments a precise and meticulous analysis of the images realized with the SEM allowed us to extract data making it possible to quantify the phenomena studied.