Thesis (M.S.)--University of Toledo, 2007. / Typescript. "Submitted as partial fulfillment of the requirements for the Master of Science Degree in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 204-209.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

<p>In sheet metal forming processes, friction has decisive effects on the strain distribution in the deformed sheets and the quality of the final product due to the large surface/thickness ratio of the blank sheets. It is well known that friction in sheet forming operations is dependent on local contact conditions such as surface roughness, contact pressure and sliding velocity. Adding complexity to this frictional behavior, some rolled sheets have oriented surface roughness and show considerable frictional anisotropy. A constant friction model without consideration of these relevant phenomena is regarded as the reason why sheet metal forming simulations often fail to produce satisfying results despite the well developed material models. </p> <p>To develop a friction model which considers both of the varying conditions of local contact and the frictional anisotropy was the aim of this thesis. For this purpose, the analysis method of the friction test (draw-bend test) had to be examined for the capability to evaluate these parameters independently. Through careful study using finite element simulations, it was found that the conventional method has shortcomings in addressing pressure dependent friction due to the pressure non-uniformity existing in the test. Therefore, a new analysis method, which can evaluate pressure dependency of a friction coefficient, was developed. In the new method, contact pressure maps obtained from simulations were included in the analysis of test data.</p> <p>The new analysis method was applied to friction measurement of aluminum sheets with known anisotropic mill finish, and friction coefficients were obtained as functions of contact pressure, sliding velocity and sliding direction. In the obtained friction model, a friction coefficient is a continuous surface over the domain of contact pressure and sliding velocity. Lastly, the new friction model was implemented into a finite element code and the model was validated through circular cup drawing experiments and simulations. The comparisons showed good agreements in the aspects of punch force, cup size and failure location. Thus, the newly developed model can accurately predict the effects of anisotropic friction in sheet metal forming processes. </p> / Thesis / Doctor of Philosophy (PhD)

Nanostructured systems composed of two or more technologically important materials are useful for device applications and intriguing for the new fundamental physics they may display. Magnetism at the nanoscale is dominated by size and surface effects which combined with other media lead to new spin dynamics and interfacial coupling phenomena. These new properties may prove to be useful for optimizing sensors and devices, increasing storage density for magnetic media, as well as for biomedical applications such as drug delivery, MRI contrast enhancement, and hyperthermia treatment for cancer. In this project we have examined the surface and interface magnetism of composite nanoparticles and multilayer thin films by using conventional DC magnetization and AC susceptibility as well as transverse susceptibility, a method for directly probing the magnetic anisotropy of materials. Au and Fe3O4 synthesized together into three different nanoparticle configurations and ranging in size for 60 nm down to 9nm are used to study how the size, shape, and interfaces affect the most fundamental properties of magnetism in the Au-Fe3O4 system. The findings have revealed ways in which the magnetic properties can be enhanced by tuning these parameters. We have shown that by changing the configurations of the Au and Fe3O4 particles, exotic behavior can be observed such as a large increase in anisotropy field (H[subscript]K ranging from 435 Oe to 1650 Oe) and the presence of exchange bias. Multilayer thin films have been studied as well which combine the important classes of ferromagnetic and ferroelectric materials. In one case, barium hexaferrite/barium strontium titanate thin films, the anisotropic behavior of the ferromagnet is shown to change due to the introduction of the secondary material. In the other example, CrO2/Cr2O3 bilayers, exchange coupling is observed as Cr2O3 is an antiferromagnet as well as a ferroelectric. This coupling is manifest as a uniaxial anisotropy rather than the unidirectional anisotropy associated with exchange biased bilayers. Not only will such multifunctional structures will be useful for technological applications, but the materials properties and configurations can be chosen and tuned to further enhance the desired functional properties.

CETTE THÈSE INTRODUIT UNE CLASSE DES TRANSFORMÉS MULTI­ ÉCHELLES BIDIMENSIONNELLES ADAPTÉES AUX CONTOURS. CELLES-CI SONT DIFFÉ­RENTES DES TRANSFORMÉES EN ONDELETTES BIDIMENSIONNELLES, CAR ELLES SONT BASÉES SUR DES OPÉRATEURS NONLINÉAIRES DEPENDENTS DES DONNÉES. CES OPÉRATEURS SONT INSPIRÉS DES OPÉRATEURS D'INTERPOLATION ENO INTRODUITS PAR HARTEN ET OSHER DANS LE CONTEXTE DE LA SIMULATION NUMÉRIQUES DES ONDES DE CHOC. LE BUT EST D'INCLURE DANS LA TRANSFORMÉE UN TRAITEMENT SPECIFIC DES CONTOURS QUI, EN TENANT COMPTE DE LEURS RÉGULARITÉ GEOMETRIQUE, PERMETTRAS D'OBTENIR DES REPRÉSENTATIONS PLUS CREUSES ET DONC DES MEILLEU­RES PROPRIÉTÉS D'APPROXIMATIONS. D'UN POINT DE VUE THÉORIQUE ON S'INTERESSE À LA CONSERVATION DES MÊME PROPRIÉTÉS DE CONCENTRATION POUR LES ESPACES FONCTIONNELS CLASSIQUES (BESOV ET $BV$), ET ON S'INTERROGE AUSSI SUR LA STABILITÉ DE CES DÉ­COMPOSITIONS. CE PROBLÈME EST LOIN D'ÊTRE AUSSI SIMPLE QUE DANS LE CAS DES REPRÉ­SENTATIONS LINÉAIRES. NOUS ABORDONS DANS CETTE THÈSE CHACUNE DE CES DIFFICULTÉS, ET NOUS Y APPORTONS DES ÉLÉMENTS DE RÉPONSE, AINSI QUE DES TESTS NUMÉRIQUES VISANT À ÉVALUER CONCRÈTEMENT LES PERFORMANCES DES MÉTHODES PROPOSÉES.

Le présent travail étudie la caractérisation expérimentale et la modélisation de l'anisotropie induite par effet Mullins, i.e., la perte de raideur après les premiers cycles de chargement, très souvent observée dans les matériaux de type élastomère. Après une description des caractéristiques mécaniques du matériau silicone utilisé dans notre étude, des essais expérimentaux originaux sont développés pour créer des historiques de chargement complexes. D'une part, des successions d'essais de traction uniaxiale classiques sont réalisées, avec changement de directions de chargement. D'autre part, des états hétérogènes de contrainte et déformation obtenus lors d'essais de gonflement de membrane circulaire ont été complètement caractérisés grâce à des mesures de champs cinématiques réalisées par la méthode de corrélations d'images 3D ; les chargements effectués sont alors de type traction biaxiale-traction simple. Les paramètres clés pour la modélisation de l'effet Mullins ont ainsi pu être mis en évidence, avec notamment ses parts isotrope et anisotrope. Un modèle a ainsi été développé à partir d'une théorie de double réseau prenant en compte des critères expérimentalement motivés. Une version adaptée à une implantation simple dans un code de calculs éléments finis est finalement développée pour la réalisation de calculs de structures. / The present work studies the experimental characterization and modeling of the anisotropy induced by Mullins effect, i.e., the loss of stiffness in the first loading cycles, often observed in rubber-like materials. After a description of the mechanical characteristics of the particular silicone material used in our study, experimental tests are developed to create original and complex loading histories. First, successions of conventional uniaxial tensile tests are performed with changing directions of loading. Second, the state of heterogeneous stress and strain obtained in circular membrane swelling tests was completely characterized by means of kinematic field measurements made by the 3D image correlation method, and the loadings are then biaxial tension followed by uniaxial traction. The key parameters for modeling the Mullins effect were able to be identified, including its isotropic and anisotropic parts. A model was thus developed based on the double-network theory taking into account the experimentally motivated criteria. A suitable version with simple implementation in a finite element computer code was finally developed to allow the calculation of a structural part.

La recherche de défauts dans les matériaux est un sujet complexe et important, en particulier lorsque la sécurité est en jeu comme dans le domaine aéronautique. Cette thèse s’inscrit dans cette problématique et s’organise en deux parties. La première partie est dédié à la détection des défaut dans les composites carbones par trois nouvelles méthodes radiofréquences permettant de détecter, en particulier, les impacts sur les peaux des composites carbones. La deuxième partie est consacrée à la détection des infiltrations d’eau dans les composites alvéolaires par une méthode multiphysique couplant une onde hydraulique non linéaire et une détection par un RADAR CW. / Detecting default inside material is a complex and important topic, particularly when the safety is at riske like for instance in the aeronautic field. This phd thesis is divided in two parts. In a first part, mainly we will present three new RF methods allowing to detect, for example, impact damages on carbon composite skins. In a second part we will present a new method aimed to detect water ingress in cellular composite. This new method is based on the interaction of a nonb-linear water wawe with a RADAR

Anisotropy of hydraulic properties of the subsurface geologic formations is an essential feature that has been established as a consequence of the different geologic processes that undergo during the longer geologic time scale. With respect to subsurface reservoirs, in many cases, anisotropy plays significant role in dictating the direction of flow that becomes no longer dependent only on driving forces like the pressure gradient and gravity but also on the principal directions of anisotropy. Therefore, there has been a great deal of motivation to consider anisotropy into the subsurface flow and transport models. In this dissertation, we present subsurface flow modeling in single and dual continuum anisotropic porous media, which include the single-phase groundwater flow coupled with the solute transport in anisotropic porous media, the two-phase flow with gravity effect in anisotropic porous media, and the natural gas flow in anisotropic shale reservoirs. We have employed the multipoint flux approximation (MPFA) method to handle anisotropy in the flow model. The MPFA method is designed to provide correct discretization of the flow equations for general orientation of the principal directions of the permeability tensor. The implementation of MPFA method is combined with the experimenting pressure field approach, a newly developed technique that enables the solution of the global problem breaks down into the solution of multitude of local problems. The numerical results of the study demonstrate the significant effects of anisotropy of the subsurface formations. For the single-phase groundwater flow coupled with the solute transport modeling in anisotropic porous media, the results shows the strong impact of anisotropy on the pressure field and the migration of the solute concentration. For the two-phase flow modeling with gravity effect in anisotropic porous media, it is observed that the buoyancy-driven flow, which emerges due to the density differences between the phases, migrates upwards and the anisotropy aligns the flow directions closer to the principal direction of anisotropy. Lastly, for the gas flow modeling in anisotropic shale reservoirs, we observe that anisotropy affects the pressure fields and the velocity fields of the matrix and fracture systems as well as the production rate and cumulative production. It is observed from the results that all of the anisotropic cases produce higher amount of gas compared to isotropic case during the same production time. Furthermore, we have also examined the performance of MPFA with respect to mixed finite element (MFE) method over the lowest-order Raviart-Thomas (RT0) space and the first-order Brezzi-Douglas-Marini (BDM1) space. From the comparison of the numerical results we observe that MPFA method show very good agreement with the BDM1 than RT0. In terms of numerical implementation, however, MPFA method is easier than BDM1 and it also offers explicit discrete fluxes that are advantageous. Combining MPFA with the experimenting pressure field approach will certainly adds another advantage of implementing MPFA method as compared with RT0 and BDM1. Moreover, the computational cost (CPU cost) of the three different methods are also discussed.

Les pertes fer dans une machine électrique sont d'importance capitale, une estimation approximative de ces pertes peu mener à des solutions non viable sur le plan thermique, c'est dans ce contexte qu'il est indispensable d'avoir les caractéristiques les plus précises des matériaux magnétiques utilisés, de plus avec l'engouement récent pour les machines électriques haute vitesse (donc haute fréquence), il est important de caractériser les matériaux à haute fréquence. Dans les travaux de cette thèse, un système de mesure haute fréquence (1 T - 10 kHz) en champ unidirectionnel a été mis en place et des modèles de pertes magnétiques hautes fréquences ont été étudiés et discutés. Les champs magnétiques circulant dans une machine électrique sont de type alternatifs dans une direction donnée ou des champs elliptiques et tournants. C'est dans ce contexte qu'une caractérisation et un modèle en champ tournant ont été proposés. Enfin, dans le cas où le stator d'une machine électrique est découpé d'un seul tenant, la direction de découpe par rapport àla direction de laminage change d'un pas dentaire à un autre, pour cela une étude sur l'anisotropie des matériaux FeSi non orientés a été menée. / Iron losses in electrical machine applications are of paramount importance, an approximate estimation of these losses can easily lead to a thermally unsustainable solution, in this context, it is essential to get exactly the magnetic characteristics of the magnetic materials used, moreover, with the recent interest for high speed electrical machines (high frequency), It is important to characterize magnetic materials at high frequency. In this work, a high frequency characterizing system (1 T - 10 kHz) under unidirectional field has been proposed and magnetic losses models has been studied and discussed. Magnetic fields in electrical machines could be alternative in one direction, elliptical or circular. In this context, a characterization under rotating field and a magnetic loss model has been proposed. Finally, when stator steel sheets are cut all in one piece, the cutting direction with regard to the rolling direction will change from one tooth pitch to another, for that a study of the FeSi non oriented anisotropy has been performed.

This paper presents a semianalytical method for the prediction of interlaminar stresses and displacements near the free edges and ply cracks in general angle-ply laminates subjected to biaxial extensions and/or in plane shear deformation. The method is based on a state space representation of the three-dimensional equations of elasticity. Numerical solutions are obtained by using layer refinement in the through thickness direction and Fourier series expansion in the other directions. By this approach, an angle-ply laminate may be composed of an arbitrary number of monoclinic layers and each layer may have different material property and thickness. This method guarantees continuous fields of all interlaminar stresses across interfaces between material layers. Numerical results are compared with those obtained from other methods. It is found that the theory provides a satisfactory approximation to the stress singularities near the free edges and ply cracks. Numerical solutions for antisymmetric laminates under extension and general laminates under shearing are new in the literature and can be used as benchmarks for validating new models.