Le travail de thèse présenté dans ce manuscrit est consacré au développement d’une nouvelle méthode de contrôle de la qualité d’un assemblage boulonné. Cette méthode utilise les courbes couple de serrage/angle de rotation de l’écrou obtenues lors d’un serrage et, plus précisément, les différents changements de pentes qui l’affectent. L’idée principale est d’utiliser ces changements de pentes pour découper la courbe en différents segments, correspondant chacun à un événement qu’il est alors possible d’identifier. Ces événements sont tout d’abord constitués d’une phase de freinage de l’écrou, suivie d’un « plateau », d’une éventuelle phase de réduction des jeux et enfin, d’un dernier segment linéaire traduisant le serrage. Afin de valider cette méthode, deux modèles, l’un analytique et l’autre de calcul par la méthode des éléments finis, ont été développés afin de créer une base de référence. Le modèle analytique est issu de la littérature tandis que le modèle éléments finis apporte une originalité car il simule la rotation de l’écrou mais également son freinage à travers une déformation préliminaire. Ces modèles sont ensuite validés lors d’une première campagne d’essais qui débute par le serrage d’échantillons de référence sans défaut. Puis des défauts sont introduits (jeux, bavures, copeaux…) afin d’évaluer les capacités de détection de la méthode. Des limitations sont alors découvertes, entraînant une modification des moyens de mesure. Un premier prototype est donc réalisé en instrumentant une visseuse pour pouvoir mesurer le couple de réaction (celui qui maintient la vis) en plus du couple de serrage. Cet ajout permet alors d’identifier des défauts qui restaient masqués. Finalement, un second prototype est conçu et réalisé, permettant de contrôler directement le serrage et ainsi de mettre en place de nouvelles stratégies pour le serrage prenant en compte les résultats obtenus lors des différentes campagnes d’essais. / The subject of the thesis presented in this manuscript is the development of a new method to control the quality of a bolted assembly. This method uses the tightening torque-turn angle of the nut curves, gathered during the tightening and, more precisely, the changes of slope that affects it. The main idea is to use these changes to divide the curve into segments, each corresponding to an event that it is then possible to identify. These events are: a nut locking phase, followed by a constant torque area, a possible gap reduction phase and finally, a last linear part corresponding to the actual tightening. To validate this method two models, one analytical and the other using the finite element method, have been developed to create a baseline. The analytical model is derived from the literature as the finite element model provides originality because it simulates the rotation of the nut but also the locking through a preliminary deformation. These models are then validated in a first test campaign, which begins with the tightening of reference sample without defects. Then, defects are introduced (gaps, burrs, chips...) in order to evaluate the method detection capabilities. Limitations are discovered leading to a modification of the measures means. A first prototype is designed by instrumenting a screwdriver to be able to measure the reaction torque (the one that holds the screw) in addition to the tightening torque. This addition improves the method by detecting hidden defects. Finally a second prototype was designed and built, with full control of the tightening and thus develop new strategies for tightening, taking into account the results obtained during the various test campaigns.

Myocardial infarction (i.e., a heart attack) is the most common heart disease in the United States. Mitral valve regurgitation, or the backflow of blood into the atrium from the left ventricle, is one of the complications associated with myocardial infarction. In this dissertation, a validated model of a sheep heart that has suffered myocardial infarction has been employed to study mitral valve regurgitation. The model was rebuilt with the knowledge of geometrical changes captured with MRI technique and is assigned with anisotropic, inhomogeneous, nearly incompressible and highly non-linear material properties. Patch augmentation was performed on its anterior leaflet, using a simplified approach, and its posterior leaflet, using a more realistic approach. In this finite element simulation, we virtually installed an elliptical patch within the central portion of the posterior leaflet. To the best of the author’s knowledge, this type of simulation has not been performed previously. In another simulation, the effect of patch within the anterior leaflet was simulated. The results from the two different surgical simulations show that patch implantation helps the free edges of the leaflets come close to one another, which leads to improved coaptation. Additionally, the changes in chordal force distributions are also reported. Finally, this study answers a few questions regarding mitral valve patch augmentation surgeries and emphasizes the importance of further investigations on the influence of patch positioning and material properties on key outcomes. The ultimate goal is to use the proposed techniques to assess human models that are patient-specific.

One of the principal energy absorbing structural components that influences the crashworthiness of a vehicle is the side-rail, which is also commonly referred to as an s-rail due to its shape that is reminiscent of an “s”. To improve the crashworthiness of a vehicle, in the wake of significant environmental pressures requiring vehicle light-weighting, the parameters that govern the crash response of the s-rail and the implications of light-weight material substitution need to be better understood. In this work, the main parameters that govern the crash response of an s-rail and the variables that influence them were identified and assessed through a combined experimental and numerical modelling programme. In particular, the as-formed properties of aluminium alloy s-rails, due to the tube bending and hydroforming fabrication route were examined. Tube bending, hydroforming and crash experiments were conducted to examine and assess the effects of initial tube thickness, strength, geometry, bend severity, work hardening, thickness changes and residual stresses on the crash response of the s-rail. The forming process variables, springback, thickness, strains, and force and energy response measured in the experiments were used to validate the finite element models developed herein. The validated numerical models of tube bending, hydroforming and crash provided additional insight and also allowed further investigation of the parameters governing the crash response of s-rails. The relevant parameters governing the crash response of s-rails were isolated and the basis for a set of design guidelines, in terms of maximizing energy absorption or minimizing mass, was established. The overall size is the most influential design parameter affecting the energy absorption capability of the s-rail, followed by the initial thickness, material strength, cross-sectional geometry, bend severity and hydroforming process employed, and finally boost in bending. The most significant conclusion made based on this research is that the effects of forming history must be considered to accurately predict the crash response of the s-rail. There are additional conclusions with respect to the tube bending and hydroforming processes, as well as s-rail crash response, that will contribute to improving the design of s-rails for better crashworthiness of vehicles.

Since single nanopores were firstly proposed as a potential rapid and low-cost tool for DNA sequencing in 1990s (PNAS, 1996, 93, 13770), extensive studies on both biological and synthetic nanopores and nanochannels have been reported. Nanochannel based stochastic sensing at single molecular level has been widely reported through the detection of transient ionic current changes induced by geometry blockage due to analytes translocation. Novel properties, including ion current rectification (ICR), memristive and memcapacitive behaviors were reported. These fundamental properties of nanochannels arise from the nanoscale dimensions and enables applications not only in single molecule sensing, but also in drug delivery, electrochemical energy conversion, concentration enrichment and separation, nanoprecipitation, nanoelectronics etc. Electrostatic interactions at nanometer-scale between the fixed surface charges and mobile charges in solution play major roles in those applications due to high surface to volume ratio. However, the knowledge of surface charge density (SCD) at nanometer scale is inaccessible within nanoconfinement and often extrapolated from bulk planar values. The determination of SCD at nanometer scale is urgently needed for the interpretation of aforementioned phenomena. This dissertation mainly focuses on the determination of SCD confined at a nanoscale device with known geometry via combined electroanalytical measurements and theoretical simulation. The measured currents through charged nanodevices are different for potentials with the same amplitude but opposite polarities, which deviates away from linear Ohm's behavior, known as ICR. Through theoretical simulation of experiments by solving Poisson and Nernst-Planck equations, the SCD within nanoconfinement is directly quantified for the first time. An exponential gradient SCD is introduced on the interior surface of a conical nanopre based on the gradient distribution of applied electric field. The physical origin is proposed based on the facilitated deprotonation of surface functional groups by the applied electric field. The two parameters that describe the non-uniform SCD distribution: maximum SCD and distribution length are determined by fitting high- and low-conductivity current respectively. The model is validated and applied successfully for quantification and prediction of mass transport behavior in different electrolyte solutions. Furthermore, because the surface charge distribution, the transport behaviors are intrinsicaly heterogeneous at nanometer scale, the concept is extended to noninvasively determine the surface modification efficacy of individual nanopore devices. Preliminary results of single molecule sensing based on streptavidin-iminobiotin are included. The pH dependent binding affinity of streptavidin-iminobiotin binding is confirmed by different current change signals ("steps" and "spikes") observed at different pHs. Qualitative concentration and potential dependence have been established. The chemically modified nanopores are demonstrated to be reusable through regenerating binding surface.

One of the principal energy absorbing structural components that influences the crashworthiness of a vehicle is the side-rail, which is also commonly referred to as an s-rail due to its shape that is reminiscent of an “s”. To improve the crashworthiness of a vehicle, in the wake of significant environmental pressures requiring vehicle light-weighting, the parameters that govern the crash response of the s-rail and the implications of light-weight material substitution need to be better understood. In this work, the main parameters that govern the crash response of an s-rail and the variables that influence them were identified and assessed through a combined experimental and numerical modelling programme. In particular, the as-formed properties of aluminium alloy s-rails, due to the tube bending and hydroforming fabrication route were examined. Tube bending, hydroforming and crash experiments were conducted to examine and assess the effects of initial tube thickness, strength, geometry, bend severity, work hardening, thickness changes and residual stresses on the crash response of the s-rail. The forming process variables, springback, thickness, strains, and force and energy response measured in the experiments were used to validate the finite element models developed herein. The validated numerical models of tube bending, hydroforming and crash provided additional insight and also allowed further investigation of the parameters governing the crash response of s-rails. The relevant parameters governing the crash response of s-rails were isolated and the basis for a set of design guidelines, in terms of maximizing energy absorption or minimizing mass, was established. The overall size is the most influential design parameter affecting the energy absorption capability of the s-rail, followed by the initial thickness, material strength, cross-sectional geometry, bend severity and hydroforming process employed, and finally boost in bending. The most significant conclusion made based on this research is that the effects of forming history must be considered to accurately predict the crash response of the s-rail. There are additional conclusions with respect to the tube bending and hydroforming processes, as well as s-rail crash response, that will contribute to improving the design of s-rails for better crashworthiness of vehicles.

Brazing, as a type of joining process, is widely used in manufacturing industries to join individual components of a structure. Structural reliability of a brazed assembly is strongly dependent on the joint mechanical properties. In the present work, mechanical reliability of low carbon steel brazed joints with copper filler metal is investigated and a methodology for failure analysis of brazed joints using the cohesive zone model (CZM) is presented. Mechanical reliability of the brazed joints is characterized by strength and toughness. Uniaxial and biaxial strengths of the joints are evaluated experimentally and estimated by finite element method using the ABAQUS software. Microstructural analysis of the joint fracture surfaces reveals different failure mechanisms of dimple rupture and dendritic failure. Resistance of the brazed joints against crack propagation, evaluated by the single-parameter fracture toughness criterion, shows dependency on the specimen geometry and loading configuration. Fracture of the brazed joints and the subsequent ductile tearing process are investigated using a two-parameter CZM. The characterizing model parameters of the cohesive strength and cohesive energy are identified by a four-point bend fracture test accompanied with corresponding FE simulation. Using the characterized CZM, the joint fracture behavior under tensile loading is well estimated. Predictability of the developed cohesive zone FE model for fracture analysis of brazed joints independent of geometry and loading configuration is validated. The developed cohesive zone FE model is extended to fatigue crack growth analysis in brazed joints. A cyclic damage evolution law is implemented into the cohesive zone constitutive model to irreversibly account for the joint stiffness degradation over the number of cycles. Fatigue failure behavior of the brazed joints is characterized by performing fully reversed strain controlled cyclic tests. The damage law parameters are calibrated based on the analytical solutions and the experimental fatigue crack growth data. The characterized irreversible CZM shows applicability to fatigue crack growth life prediction of brazed joints.

The focus of this work is on the modeling and simulation of shock wave propagation in reactive metal powder mixtures. Reactive metal systems are non-explosive, solid-state materials that release chemical energy when subjected to sufficiently strong stimuli. Shock loading experiments have demonstrated that ultra-fast chemical reactions can be achieved in certain micron-sized metal powder mixtures. However, the mechanisms of rapid mixing that drive these chemical reactions are currently unclear. The goal of this research is to gain an understanding of the shock-induced deformation that enables these ultra-fast reactions. The problem is approached using direct numerical simulation. In this work, a finite element (FE) model is developed to simulate shock wave propagation in discrete particle mixtures. This provides explicit particle-level resolution of the thermal and mechanical fields that develop in the shock wave. The Ni/Al powder system has been selected for study. To facilitate mesoscale FE simulation, a new dislocation-based constitutive model has been developed to address the viscoplastic deformation of fcc metals at very high strain rates. Six distinct initial configurations of the Ni/Al powder system have been simulated to quantify the effects of powder configuration (e.g., particle size, phase morphology, and constituent volume fractions) on deformation in the shock wave. Results relevant to the degree of shock-induced mixing in the Ni/Al powders are presented, including specific analysis of the thermodynamic state and microstructure of the Ni/Al interfaces that develop during wave propagation. Finally, it is shown that velocity fluctuations at the Ni/Al interfaces (which arise due to material heterogeneity) may serve to fragment the particles down to the nanoscale, and thus provide an explanation of ultra-fast chemical reactions in these material systems.

Conventional solder balls used in microelectronic packaging suffer from thermo- mechanical damage due to difference in coefficient of thermal expansion between the die and the substrate or the substrate and the board. Compliant interconnects are replacements for solder balls which accommodate this differential displacement by mechanically decoupling the die from the substrate or the substrate from the board and aim to improve overall reliability and life of the microelectronic component. Research is being conducted to develop compliant interconnect structures which offer good mechanical compliance without adversely affecting electrical performance, thus obtaining good thermo-mechanical reliability. However, little information is available regarding the behavior of compliant interconnects under shock and impact loads. The objective of this thesis is to study the response of a proposed multi-path compliant interconnect structure when subjected to shock and impact loading. As part of this work, scaled-up substrate-compliant interconnect-die assemblies will be fabricated through stereolithography techniques. These scaled-up prototypes will be subjected to experimental drop testing. Accelerometers will be placed on the board, and strain gauges will be attached to the board and the die at various locations. The samples will be dropped from different heights to different shock levels in the components, according to Joint Electron Devices Engineering Council (JEDEC) standards. In parallel to such experiments with compliant interconnects, similar experiments with scaled-up solder bump interconnects will also be conducted. The strain and acceleration response of the compliant interconnect assemblies will be compared against the results from solder bump interconnects. Simulations will also be carried out to mimic the experimental conditions and to gain a better understanding of the overall response of the compliant interconnects under shock and impact loading. The findings from this study will be helpful for improving the reliability of compliant interconnects under dynamic mechanical loading.

Brazing, as a type of joining process, is widely used in manufacturing industries to join individual components of a structure. Structural reliability of a brazed assembly is strongly dependent on the joint mechanical properties. In the present work, mechanical reliability of low carbon steel brazed joints with copper filler metal is investigated and a methodology for failure analysis of brazed joints using the cohesive zone model (CZM) is presented. Mechanical reliability of the brazed joints is characterized by strength and toughness. Uniaxial and biaxial strengths of the joints are evaluated experimentally and estimated by finite element method using the ABAQUS software. Microstructural analysis of the joint fracture surfaces reveals different failure mechanisms of dimple rupture and dendritic failure. Resistance of the brazed joints against crack propagation, evaluated by the single-parameter fracture toughness criterion, shows dependency on the specimen geometry and loading configuration. Fracture of the brazed joints and the subsequent ductile tearing process are investigated using a two-parameter CZM. The characterizing model parameters of the cohesive strength and cohesive energy are identified by a four-point bend fracture test accompanied with corresponding FE simulation. Using the characterized CZM, the joint fracture behavior under tensile loading is well estimated. Predictability of the developed cohesive zone FE model for fracture analysis of brazed joints independent of geometry and loading configuration is validated. The developed cohesive zone FE model is extended to fatigue crack growth analysis in brazed joints. A cyclic damage evolution law is implemented into the cohesive zone constitutive model to irreversibly account for the joint stiffness degradation over the number of cycles. Fatigue failure behavior of the brazed joints is characterized by performing fully reversed strain controlled cyclic tests. The damage law parameters are calibrated based on the analytical solutions and the experimental fatigue crack growth data. The characterized irreversible CZM shows applicability to fatigue crack growth life prediction of brazed joints.

La projection thermique cold spray consiste en l'envol de poudres à haute vitesse sur une cible : le substrat. Leur adhérence et leur accumulation mène à des revêtements plus ou moins denses, utilisés dans le domaine automobile, biomédical, etc. La première étape de construction du dépôt passe par un contact entre la poudre et le substrat. Il est admis que la liaison créée est mécanique et, si la nature des matériaux le permet, métallurgique. Cette étude permet de statuer sur ces deux composantes. Pour cela, deux systèmes privilégiant l'une ou l'autre, sont choisis. L'ancrage mécanique est vu au travers de la métallisation de polymère avec l'emploi d'aluminium projeté sur polyamide 6,6. La liaison métallurgique est abordée avec l'emploi de titane sur un substrat plus rigide en TA6V. Avant d'étudier les mécanismes de liaison, une étape d'élaboration des dépôts est réalisée balayant de nombreux paramètres « procédé » et différentes propriétés des matériaux (température, granulométrie). Des outils sont déployés pour connaître les conditions d'impact : la vitesse de particule par DPV2000, la température du substrat par thermographie infra-rouge et la température des particules par voie numérique. L'ancrage mécanique dans le polymère est décrit grâce à l'étude de l'impact de particules élémentaires ainsi que de la rugosité d'interface 2D (coupes micrographiques) et 3D (laminographie X). Le gradient de porosité est également quantifié. La liaison métallurgique est étudiée par MET. Au préalable, la simulation numérique par éléments finis est employée pour retracer la phénoménologie de l'impact ainsi que quantifier les déformations et les températures locales atteintes à l'interface. La morphologie simulée des particules à l'impact est comparée à celles observées dans des conditions réelles de projection. Enfin, l'adhérence des différents dépôts est évaluée par essai « plot collé » et les faciès de rupture observés. L'influence de la morphologie de surface est étudiée avec des prétraitements de sablage et de structuration laser. / Cold Spray consists in the high-speed spray of powder particles onto a target; namely the substrate. Their adhesion and accumulation leads to a more or less dense coating to be used in the automotive, the biomedical… areas. The first stage of coating results from a powder to substrate contact. Bonding is due to mechanical anchoring and, depending on the involved materials, to metallurgical interaction. This study helps to rule on these two components. For this, two systems, which promote either mechanical or metallurgical mechanism separately, are selected. Mechanical anchoring is studied through polymer metallization using of aluminum for spraying onto polyamide 6,6. Metallurgical bonding is studied using titanium onto Ti-6Al-4V. Before studying the bonding mechanisms, the spraying process is investigated using many process parameters and materials properties (temperature, particle size…). Advanced tools are employed to determine impact conditions; i.e. particle velocity by DPV2000, substrate temperature by infrared thermography and particle temperature by numerical calculation. Mechanical anchoring onto the polymer is described through the analysis of elementary particle impacts and through 2D (micrograph sections) and 3D (laminography) study of interface roughness. The porosity gradient is also quantified. Metallurgical bonding is studied by TEM. Before that, a finite element simulation is used to go into the phenomenology of the impact and to quantify the local deformation and temperature at the interface. The simulated particle morphology is compared to those observed in real spraying conditions. Lastly, deposit adhesion is assessed by pull-off testing and the fractured surface is observed. The influence of the substrate surface morphology is exhibited using sand-blasting and laser structuring pretreatments.