L’hydroformage de tube nécessite l’emploi d’outillage coûteux et la phase de mise au point utilise intensivement la simulation par éléments finis. Pour ces simulations, il est nécessaire de disposer de données matériaux adaptées dans le domaine plastique. Le comportement des matériaux utilisés en mise en forme dépend du mode de sollicitation. Ainsi, plusieurs essais de caractérisation tels que l’essai de traction et les essais de gonflement de flan et de tube sont traités dans ce travail.On s’intègre dans une démarche pragmatique afin d’offrir des méthodes simples pour une mise en œuvre dans un contexte industriel en limitant le nombre d’essai, une méthode expérimentale de caractérisation simple et une méthode d’analyse des résultats expérimentaux efficace. De plus, on se limite à des modèles matériaux disponibles dans tout type de code de calcul comme la loi d’écrouissage de Swift et le critère de plasticité de Hill 1948.Après une introduction des différents types d’hydroformage et des notions de bases du comportement plastique des matériaux, la mise en œuvre des essais est présentée. On retiendra qu’il existe plusieurs façons de post-traiter les résultats expérimentaux. La méthode classique a été choisie pour l’essai de traction, celle préconisée par Koç et al. est utilisée pour le gonflement de flan et enfin la méthode de Boudeau et Malécot a été adoptée pour le gonflement de tube.À partir des essais effectués sur un acier austénitique inoxydable de type AISI 304, plusieurs courbes d’écrouissages distinctes ont été obtenues. Des simulations numériques ont été menées afin de confronter ces lois de comportement sur la prédiction des profils des flans et des tubes déformés ainsi que sur les distributions d’épaisseur de ceux-ci. Enfin, le matériau ayant été considéré isotrope jusqu’à présent, on s’attache à l’influence de l’anisotropie du matériau dans le cadre de la mise en forme par hydroformage. Pour cela un plan complet est mené.Mots-clés : hydroformage, caractérisation de matériaux, tube, simulation E.F., expérimentation / Tube hydroforming requires the employment of expensive tooling and its industrial development makes an intensive use of finite element simulations. For these simulations, we need plastic material data. The material behavior, in forming, depends on the loading mode. Thus, several characterization tests such as uniaxial tensile test, the bulging test on sheet and tube, are investigated in this work.The works are conducted in the context of a pragmatic approach. The goal is to offer simple methods for implementation in an industrial setting based on a limited number of tests, a simple experimental method and an efficient method for post-processing experimental results. In addition, we limit ourselves to classical material models, available in any FE code, such as the Swift’s hardening law and the Hill 1948 plastic criterion.After the introduction of the different kind of hydroforming and the fundamentals on the plastic behavior of materials, the experimental tests are presented. There are many ways for post-processing the experimental results of these advanced testing methods. The conventional method is chosen for post-processing the experimental results obtained with the tensile test ; for the sheet bulging test, the method recommended by Koç et al. is used and the model proposed by Boudeau and Malécot’s is adopted for tube bulging test.The different tests are carried out on an austenitic stainless steel AISI 304 and, distinct hardening curves are obtained. Numerical simulations of the tests and a tube hydroforming operation are performed with the different hardening law. The FE results are compared; the comparisons are led on the resulting bulged sheet or tube and on the thickness distribution. Finally, the influence of the initial anisotropy in tube hydroforming is studied through a full Design Of Experiences.Keywords: hydroforming, material characterization, tube, F.E. simulation, experiment

Doctor of Philosophy / Department of Chemistry / Takashi Ito / This dissertation describes single-molecule tracking (SMT) measurements for the quantitative characterization of one-dimensional (1D) nanostructures in 200 nm-thick surfactant-templated mesoporous silica (STMS) and cylinder-forming polystyrene-poly(ethylene oxide) diblock copolymer (CF-PS-b-PEO) films with a μm-scale thickness. SMT is advantageous for the characterization of nanomaterials over conventional methods because it permits the simultaneous and quantitative assessment of the nanoscale and microscale morphologies, and mass-transport properties of the materials with a high nanometer-scale resolution under ambient conditions. It offers a unique means for the assessment and evaluation of the μm-scale nanostructure alignment in polymer films induced by vertical spin-coating (for STMS films), directional solution flow and solvent-vapor penetration (SVP) methods (both for CF-PS-b-PEO films), highly crucial for many potential technological applications using the materials. Through this work, we have identified suitable sample preparation conditions (e.g. solvent, temperature or solution flow rate) for obtaining highly-ordered mesoporous and microdomain structures over a long-range (> 5 μm). For the quantitative assessment of the 1D SMT data, orthogonal regression analysis was employed, providing assessment of the in-plane orientation and size of individual nanostructures with nanometer-scale precision. The analysis of the 1D trajectory data allowed the radius (ca. 11 nm) of cylindrical PEO microdomains to be estimated, yielding results consistent with the AFM results (ca. 14 nm). The distribution of the trajectory angles offered the estimation of the average orientation and order of the nanostructures in domains/grains for a μm-wide region of the polymer films, revealing the higher efficiency of SVP in the nanostructure alignment as compared to the spin coating and solution flow approaches. Systematic SMT measurements across the film depth and along lateral mm-scale distances afforded valuable insights into the shear- and solvent-evaporation-based alignment mechanisms induced by solution flow and SVP/spin coating approaches, respectively. Fluorescence recovery after photobleaching (FRAP) measurements in a SVP-aligned CF-PS-b-PEO film permitted the longer-range mass-transport properties to be probed, reflecting the effective continuity of the aligned cylindrical nanostructures over > 100 μm in length. In this dissertation, FRAP and more importantly SMT methods have provided a unique and useful means for the in-depth characterization of morphology and mass-transport characteristics in thin polymer films under ambient conditions, in confined spaces, and with a nanometer-scale resolution.

Doctor of Philosophy / Department of Chemistry / Daniel A. Higgins / This dissertation describes single-molecule tracking (SMT) studies for the quantitative characterization of one-dimensional (1D) nanostructures in surfactant-templated mesoporous silica monoliths prepared within microfluidic channels. Single molecule diffusion of fluorescent probe molecules within the cylindrical mesopores reflects microscopic morphologies and mass-transport properties of the materials with high temporal and spatial resolution. The pore organization and materials order are initially investigated as a function of sol aging prior to loading into the microfluidic channels. Mesopores in these materials are templated by Cetyltrimethylammonium bromide (CTAB). Wide-field fluorescence videos depict 1D motion of the dyes within the individual mesopores. Orthogonal regression analysis of these motions provides a measure of the mesopore orientation. Channels filled prior to gelation of the sol produce monoliths incorporating large monodomains with highly aligned mesopores. In contrast, channels filled close to or after gelation yield monoliths with misaligned pores that are also more disordered. Two-dimensional (2D) small angle X-ray scattering (SAXS) experiments support the results obtained by SMT. These studies help to identify conditions under which highly aligned mesoporous monoliths can be obtained and also demonstrate the utility of SMT for characterization of mesopore order. The non-ionic surfactant Pluronic F127 is also utilized as the structural-directing agent. The diffusive motions of PDI dyes that are uncharged, cationic and anionic are explored by SMT and fluorescence correlation spectroscopy (FCS). The SMT studies for the uncharged dye show development of 1D diffusion along the flow direction while charged dyes exhibit predominant isotropic diffusion, with each of these behaviors becoming more prevalent as a function of aging time after filling of the microfluidic channels. SMT studies from silica-free F127 gels suggest that partitioning plays a important role in governing the diffusion behavior of the PDI dyes within the surfactant-filled mesopores. FCS results exhibit similar mean diffusion coefficients for all three dyes that suggest these dyes diffuse through similar sample regions. These studies demonstrate that the silica pore walls in the mesoporous silica monoliths remain permeable after gelation and that partitioning of solute species to different regions within the pores plays an important role in restricting the dimensionality of their diffusive motion

abstract: There is a concerted effort in developing robust systems health monitoring/management (SHM) technology as a means to reduce the life cycle costs, improve availability, extend life and minimize downtime of various platforms including aerospace and civil infrastructure. The implementation of a robust SHM system requires a collaborative effort in a variety of areas such as sensor development, damage detection and localization, physics based models, and prognosis models for residual useful life (RUL) estimation. Damage localization and prediction is further complicated by geometric, material, loading, and environmental variabilities. Therefore, it is essential to develop robust SHM methodologies by taking into account such uncertainties. In this research, damage localization and RUL estimation of two different physical systems are addressed: (i) fatigue crack propagation in metallic materials under complex multiaxial loading and (ii) temporal scour prediction near bridge piers. With little modifications, the methodologies developed can be applied to other systems. Current practice in fatigue life prediction is based on either physics based modeling or data-driven methods, and is limited to predicting RUL for simple geometries under uniaxial loading conditions. In this research, crack initiation and propagation behavior under uniaxial and complex biaxial fatigue loading is addressed. The crack propagation behavior is studied by performing extensive material characterization and fatigue testing under in-plane biaxial loading, both in-phase and out-of-phase, with different biaxiality ratios. A hybrid prognosis model, which combines machine learning with physics based modeling, is developed to account for the uncertainties in crack propagation and fatigue life prediction due to variabilities in material microstructural characteristics, crack localization information and environmental changes. The methodology iteratively combines localization information with hybrid prognosis models using sequential Bayesian techniques. The results show significant improvements in the localization and prediction accuracy under varying temperature. For civil infrastructure, especially bridges, pier scour is a major failure mechanism. Currently available techniques are developed from a design perspective and provide highly conservative scour estimates. In this research, a fully probabilistic scour prediction methodology is developed using machine learning to accurately predict scour in real-time under varying flow conditions. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2016

abstract: A hybrid molecular dynamics (MD) simulation framework is developed to emulate mechanochemical reaction of mechanophores in epoxy-based nanocomposites. Two different force fields, a classical force field and a bond order based force field are hybridized to mimic the experimental processes from specimen preparation to mechanical loading test. Ultra-violet photodimerization for mechanophore synthesis and epoxy curing for thermoset polymer generation are successfully simulated by developing a numerical covalent bond generation method using the classical force field within the framework. Mechanical loading tests to activate mechanophores are also virtually conducted by deforming the volume of a simulation unit cell. The unit cell deformation leads to covalent bond elongation and subsequent bond breakage, which is captured using the bond order based force field. The outcome of the virtual loading test is used for local work analysis, which enables a quantitative study of mechanophore activation. Through the local work analysis, the onset and evolution of mechanophore activation indicating damage initiation and propagation are estimated; ultimately, the mechanophore sensitivity to external stress is evaluated. The virtual loading tests also provide accurate estimations of mechanical properties such as elastic, shear, bulk modulus, yield strain/strength, and Poisson’s ratio of the system. Experimental studies are performed in conjunction with the simulation work to validate the hybrid MD simulation framework. Less than 2% error in estimations of glass transition temperature (Tg) is observed with experimentally measured Tgs by use of differential scanning calorimetry. Virtual loading tests successfully reproduce the stress-strain curve capturing the effect of mechanophore inclusion on mechanical properties of epoxy polymer; comparable changes in Young’s modulus and yield strength are observed in experiments and simulations. Early damage signal detection, which is identified in experiments by observing increased intensity before the yield strain, is captured in simulations by showing that the critical strain representing the onset of the mechanophore activation occurs before the estimated yield strain. It is anticipated that the experimentally validated hybrid MD framework presented in this dissertation will provide a low-cost alternative to additional experiments that are required for optimizing material design parameters to improve damage sensing capability and mechanical properties. In addition to the study of mechanochemical reaction analysis, an atomistic model of interphase in carbon fiber reinforced composites is developed. Physical entanglement between semi-crystalline carbon fiber surface and polymer matrix is captured by introducing voids in multiple graphene layers, which allow polymer matrix to intertwine with graphene layers. The hybrid MD framework is used with some modifications to estimate interphase properties that include the effect of the physical entanglement. The results are compared with existing carbon fiber surface models that assume that carbon fiber has a crystalline structure and hence are unable to capture the physical entanglement. Results indicate that the current model shows larger stress gradients across the material interphase. These large stress gradients increase the viscoplasticity and damage effects at the interphase. The results are important for improved prediction of the nonlinear response and damage evolution in composite materials. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017

abstract: Damage detection in heterogeneous material systems is a complex problem and requires an in-depth understanding of the material characteristics and response under varying load and environmental conditions. A significant amount of research has been conducted in this field to enhance the fidelity of damage assessment methodologies, using a wide range of sensors and detection techniques, for both metallic materials and composites. However, detecting damage at the microscale is not possible with commercially available sensors. A probable way to approach this problem is through accurate and efficient multiscale modeling techniques, which are capable of tracking damage initiation at the microscale and propagation across the length scales. The output from these models will provide an improved understanding of damage initiation; the knowledge can be used in conjunction with information from physical sensors to improve the size of detectable damage. In this research, effort has been dedicated to develop multiscale modeling approaches and associated damage criteria for the estimation of damage evolution across the relevant length scales. Important issues such as length and time scales, anisotropy and variability in material properties at the microscale, and response under mechanical and thermal loading are addressed. Two different material systems have been studied: metallic material and a novel stress-sensitive epoxy polymer. For metallic material (Al 2024-T351), the methodology initiates at the microscale where extensive material characterization is conducted to capture the microstructural variability. A statistical volume element (SVE) model is constructed to represent the material properties. Geometric and crystallographic features including grain orientation, misorientation, size, shape, principal axis direction and aspect ratio are captured. This SVE model provides a computationally efficient alternative to traditional techniques using representative volume element (RVE) models while maintaining statistical accuracy. A physics based multiscale damage criterion is developed to simulate the fatigue crack initiation. The crack growth rate and probable directions are estimated simultaneously. Mechanically sensitive materials that exhibit specific chemical reactions upon external loading are currently being investigated for self-sensing applications. The "smart" polymer modeled in this research consists of epoxy resin, hardener, and a stress-sensitive material called mechanophore The mechanophore activation is based on covalent bond-breaking induced by external stimuli; this feature can be used for material-level damage detections. In this work Tris-(Cinnamoyl oxymethyl)-Ethane (TCE) is used as the cyclobutane-based mechanophore (stress-sensitive) material in the polymer matrix. The TCE embedded polymers have shown promising results in early damage detection through mechanically induced fluorescence. A spring-bead based network model, which bridges nanoscale information to higher length scales, has been developed to model this material system. The material is partitioned into discrete mass beads which are linked using linear springs at the microscale. A series of MD simulations were performed to define the spring stiffness in the statistical network model. By integrating multiple spring-bead models a network model has been developed to represent the material properties at the mesoscale. The model captures the statistical distribution of crosslinking degree of the polymer to represent the heterogeneous material properties at the microscale. The developed multiscale methodology is computationally efficient and provides a possible means to bridge multiple length scales (from 10 nm in MD simulation to 10 mm in FE model) without significant loss of accuracy. Parametric studies have been conducted to investigate the influence of the crosslinking degree on the material behavior. The developed methodology has been used to evaluate damage evolution in the self-sensing polymer. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2014

Additive manufacturing (AM) is a general name used for manufacturing methods which have the capabilities of producing components directly from 3D computeraided design (CAD) data by adding material layer-by-layer until a final componentis achieved. Included here are powder bed technologies, laminated object manufacturing and deposition technologies. The latter technology is used in this study. Laser Metal Powder Deposition (LMPD) is an AM method which builds components by fusing metallic powder together with a metallic substrate, using a laser as energy source. The powder is supplied to the melt-pool, which is created by the laser, through a powder nozzle which can be lateral or coaxial. Both the powder nozzle and laser are mounted on a guiding system, normally a computer numerical control (CNC) machine or a robot. LMPD has lately gained attentionas a manufacturing method which can add features to semi-finished components or as a repair method. LMPD introduce a low heat input compared to conventional arc welding methods and is therefore well suited in, for instance, repair of sensitive parts where too much heating compromises the integrity of the part. The main part of this study has been focused on correlating the main process parameters to effects found in the material which in this project is the superalloy Alloy 718. It has been found that the most influential process parameters are the laser power, scanning speed, powder feeding rate and powder standoff distance.These process parameters have a significant effect on the temperature history ofthe material which, among others, affects the grain structure, phase transformation, and cracking susceptibility of the material. To further understand the effects found in the material, temperature measurements has been conducted using a temperature measurement method developed and evaluated in this project. This method utilizes a thin stainless steel sheet to shield the thermocouple from the laser light. This has proved to reduce the influence of the laser energy absorbed by the thermocouples.

Ce travail de thèse porte sur la modélisation du procédé de sertissage de contacts électriques sur des câbles à destination d'applications aéronautiques et de la tenue à l'arrachement des contacts sertis. Le sertissage est un assemblage par déformation plastique du contact électrique (composant) sur un câble multibrin. Deux types de technologies de sertissage sont traités. La technologie cuivre, couramment utilisée chez les industriels, met en jeux un contact de cuivre et un câble de cuivre composé de 19 brins. La technologie aluminium, mise au point ces dernières années pour limiter le poids des aéronefs, est caractérisée par l'assemblage d'un câble de 7 brins avec un contact en cuivre au travers d'une liaison électrique et d'une liaison d'étanchéité. Dans un premier temps, la caractérisation des paramètres de loi de comportement élastoplastique des matériaux est faite. La détermination des moyens d'essais appropriés, directement impactée par la faible dimension (ordre millimétrique) de nos échantillons, est suivie d'une analyse détaillée des résultats. Le recours à l'analyse inverse d'essais non normalisés est privilégié. Les résultats des différentes analyses sont validés indépendamment du sertissage. Dans un second temps, les étapes de mise au point des simulations de sertissage sont abordées de façon précise. Pour ce type de modèles fortement multi domaines, l'étude de l'influence des interactions est conduite. La détermination des paramètres de profondeur de sertissage est développée pour chaque technologie. Les premiers résultats de simulation sont discutés pour réduire les temps de calculs. Finalement, le modèle numérique développé est utilisé pour simuler le sertissage de contacts et l'arrachement de contacts sertis dans différentes configurations. L'étude de paramètres géométriques (diamètre des brins, diamètres des contacts, pas de torsadage des câbles), rhéologiques (cuivre standard, ayant subi un recuit insuffisant ou trop important) ou mécaniques (sous-sertissage, sur-sertissage) est faite pour vérifier l'influence sur les efforts de sertissage et les mécanismes de rupture à l'arrachement. Cette étude complète a pour objectif de valider des domaines de validité du sertissage. Celles-ci permettront aux industriels de vérifier la validité d'un sertissage en temps réel, en les comparant aux courbes d'efforts expérimentales par l'intermédiaire d'une pince électronique / This thesis focuses on the modeling of the aeronautical electrical contact crimping process for aircraft applications and the crimped contact mechanical holding. Electrical crimping is a plastic deformation process of a contact (component) on a multi-strand wire. Two types of crimping technologies are studied. The copper technology, widely used in the industry, is characterized by the assembly of a copper contact and a 19 strands copper cable. The aluminum technology, which has been recently developed to reduce the aircraft weight, is characterized by the assembly of a copper contact with a 7 strands cable through two electrical and sealing crimpings. At first, the elastoplastic parameters characterizations of the materials constitutive laws are made. The appropriate testing facilities determination, directly impacted by the small size (millimeter order) of our samples, is followed by a detailed results analysis. The non-standard tests inverse analysis use is preferred. The whole analyzes results are validated, regardless of the process itself. In a second step, the crimping simulation development steps are accurately performed. For this highly multi-model fields type, the study of the interactions influence is conducted. Determining the crimping indentation depth parameters is developed for each technology. The first simulation results are discussed to reduce computation time. Finally, the developed numerical model is used to simulate the contacts crimping and the mechanical holding over various configurations. The geometrical (strands diameter, contact diameter, twisting thread cables), rheological (standard copper having been insufficiently or excessively annealed) or mechanical (under-crimping, over-crimping) parameters study are made to check their influences on the crimping forces and the failure mechanisms while pulling. This study aims to validate the crimping efficiency. The manufacturers could be able to check in real time the crimping validity by comparing the experimental crimping force curves to validity curves integrated in an electronic crimping tool.

Previously great attention has been given for the quality of the track super structure to improve the overall performance of the railway. Frequent research on the track supporting materials shows a good result which improves the existing overall performance. Good ride quality with high speed, minimum initial construction capital, long life service and low maintenance cost are the issue on the railway technology. Ballast is one of the determinant parts of the railway structure which has great influence on the performance of the railway track. The aim of this project is to assess the different aspects which affect the overall performance on the ballast structure, its material characterization, gradation, failure modes and modelling techniques. Quality based ballast material characteristics investigation and proper selection of ballast gradation with proper modelling methods will lead to an economical, minimum defect, minimum maintenance and replacement cost.

Hot Electron Nanoscopy and Spectroscopy (HENs) is a current-sensing AFM technique recently developed in our lab, which have proven a new kind of response on conduction at the nanometer scale, casting a new light for the comprehension of electronic states in nanomaterials. Direct imaging of DNA structure has long been investigated, with the development of HENs technology, more structural information about DNA could be revealed by simultaneous measurements of height, phase, Raman signal, and conductivity. With the aim of applying it for the first time on biological molecules, customized double-stranded DNA sequences, including thiol-modified oligonucleotides are designed to create preferential conductive paths through the basis as a benchmark system for the technique on biomolecules. This work aims to a final goal to characterize hot-electron current between gold tip and thiol modified DNA which ideally is covalently bonded to the gold surface and optimized for the application. In this work, high density of DNA absorbed by SERS active gold surface with atomic flat islands has been prepared for HENs application. The samples have been characterized by AFM, SKPM and Raman Spectroscopy, as non-destructive and controlled interactive image analysis. High-resolution images of DNA have been acquired, S-S and Au-S bonding of DNA anchored on SERS active gold substrate are also visible with Surface-enhanced Raman and Tip-enhanced Raman signals. A submolecular feature has also been found in both topographical and electrical results. Herein, we report the synthesis and characterization steps to obtain the optimized operation standard.