The size effect in the thermo-mechanical behavior of polymeric materials is a critically important phenomenon and has been the subject of many researches in past decades. For example, polystyrene (PS), a widely used polymeric material, is brittle at the bulk state. When the dimensions decreases to the nanoscale, such as PS in nanofibers, their ductility becomes orders higher than their bulk state. In recent years a number of diverse applications, such as scaffolds in tissue engineering, drug delivery devices, as well as soft robotics, are designed by utilizing the unique properties of polymers at nanoscale. However, the inside mechanism of the size dependency in polymeric materials are still not clear yet. In this dissertation, systematic computational and experimental studies are made in order to understand the origins of the size effect for one- and two-dimensional polymeric materials. This framework is also expanded to investigate the size-dependent multi-physics response of functional polymeric materials (shape memory polymers) which are actuated by high-intensity focused ultrasound (HIFU). Our computational studies are based on molecular dynamic (MD) simulations at the atomistic scale, and experimentally-validated finite element models at the bulk level. From bottom-up direction, molecular dynamics can reveal the mechanisms of the size effect in polymers at molecular level, and help predict properties of the bulk materials. In this research, MD simulations are performed to track the origins of the size-effect in the mechanical properties of PE and PS nanofibers. In addition, the size-dependent thermal response of functional polymeric films is also studied at the atomistic scale by utilizing molecular dynamics simulations to predict the thermal properties and actuation mechanisms in these materials when subjected to HIFU fields. From top-down direction, experiments and finite element analysis, are also conducted in this research. An experimentally-validated finite element framework is built to study the mechanical response of shape memory polymers (SMPs) triggered by HIFU. As an external trail towards application fields, a SMP composite with enhanced shape memory ability and also a two-way SMP are synthesized. A smart gripper and also a self-rolling structure are designed by using these SMPs, which approves that these SMPs are good components in designing soft robotics. Finally, The influence of evaporation during fiber forming process is investigated by molecular dynamics simulation. It is found that the formation of the microstructure of polymeric fibers at nanoscale depends on the balance of stretching force and evaporation rate when the fiber is forming. / Doctor of Philosophy / Thermomechanical properties of a thin fiber, a thin film and a cube made of a polymer are significantly different. Although, based on the extensive research that has been performed in recent years our understanding of this size-dependency is advanced to a great degree in the past decades, there are still many unanswered basic questions that can only be addressed by performing computational and experimental investigation at different length scales, from atomistic up to bulk level in polymers. In this research we target exploring some unknown aspects of the size dependency in the thermomechanical properties of polymers by investigating their deformation mechanisms at different length scales. As the first step, we will investigate the mechanical properties of polymeric fibers. For these fibers, the mechanical properties are strongly connected to the fiber's diameter. The prevailing hypothesis is that this size dependency is closely related to the thickness of the surface layer of the nanofibers. Our results show some unknown origins behind the size dependency of the mechanical properties in polyethylene (PE) and polystyrene (PS) nanofibers, which originate from the deformation mechanisms at the atomistic scale. In addition, not just the mechanical properties, the thermal properties and response of functional polymers subjected to an external stimulation are also related to their size. For example, the thermal conductivity of a fiber, a sheet and a cube may be significantly different. Our study shows the thermal responses of different polymers triggered by ultrasound are also different. The size and the type of the polymers will both have influence on the final temperature in the polymeric materials, when the polymeric materials are heated by same ultrasound source. We also have applied our computational and experimental frameworks to investigate this phenomenon. In addition, we also used a new shape memory polymer composite and a two-way shape memory polymer on designing soft robotics-like structures. Overall this research indicates that both mechanical response and thermal responses of polymers are highly related to their dimension. Taking advantage of these unique size effects, and by tailoring this property, diverse devices can be made for being used in a broad range of applications.

One of the most critical issues for Polymer Matrix Composites (PMCs) in naval applications is the structural performance of composites at high temperature such as that experienced in a fire. A three-dimensional model including the effect of orthotropic viscoelasticity and decomposition is developed to predict the thermo-mechanical behavior and compressive failure of polymer matrix composites (PMCs) subjected to heat and compressive load. An overlaid element technique is proposed for incorporating the model into commercial finite element software ABAQUS. The technique is employed with the user subroutines to provide practicing engineers a convenient tool to perform analysis and design studies on composite materials subjected to combined fire exposure and mechanical loading. The resulting code is verified and validated by comparing its results with other numerical results and experimentally measured data from the one-sided heating of composites at small (coupon) scale and intermediate scale. The good agreement obtained indicates the capability of the model to predict material behavior for different composite material systems with different fiber stacking sequences, different sample sizes, and different combined thermo-mechanical loadings. In addition, an experimental technique utilizing Vacuum Assisted Resin Transfer Molding (VARTM) is developed to manufacture PMCs with a hypodermic needle inserted for internal pressure measurement. One-sided heating tests are conducted on the glass/vinyl ester composites to measure the pressure at different locations through thickness during the decomposition process. The model is employed to simulate the heating process and predict the internal pressure due to the matrix decomposition. Both predicted and measured results indicate that the range of the internal pressure peak in the designed test is around 1.1-1.3 atmosphere pressure. / Ph. D.

Cette étude est consacrée à la modélisation du comportement thermo-mécanique des argiles raides saturées et au développement d'un algorithme d'intégration efficace de contrainte correspondant. Le comportement mécanique de l'argile de Boom naturelle dans des conditions isothermes a été caractérisé. Le modèle Cam Clay modifié (MCC) a été ensuite appliquée pour simuler le comportement de l'argile de Boom naturel. Il a été constaté que le MCC donne des prédictions de mauvaise qualité pour le comportement de l'argile de Boom naturel. Ainsi, un modèle Cam Clay (ACC-2) adapté a été développé en introduisant une nouvelle surface de charge et un nouveau potentiel plastique ainsi que d'un mécanisme plastique de Deux surfaces. Ce modèle permet la description satisfaisante des caractéristiques principales du comportement mécanique de l'argile de Boom naturelle. De plus, les équations de ce modèle peuvent être formulées mathématiquement comme dans un modèle élasto-plastique classique. L'algorithme d'intégration de contrainte classique peut donc être appliqué. Les effets thermiques ont été examinés par l'évaluation de la pertinence de trois lois thermomécaniques avancées (Cui et al, 2000; Abuel-Naga et al, 2007; Laloui et François, 2008; 2009). Il apparaît que tous les trois modèles peuvent décrire les caractéristiques principales du comportement thermo-mécanique des argiles saturées. Cependant, chaque modèle a ses limites ou des points peu clairs du point de vue théorique. L'algorithme d'intégration de contrainte du modèle thermo-mécanique de Cui et al. (2000) au point de contrainte a également été développé spécifiquement en utilisant une méthode adaptive du pas de temps. Le temps de calcul nécessaire pour obtenir une précision donnée est ainsi largement réduit pour des chemins de chargements thermiques et mécaniques. Un modèle thermo-mécanique à Deux surfaces (modèle TEAM) a été développé en se basant sur le mécanisme plastique de Deux surfaces. Le modèle proposé a étendu le modèle de Cui et al. (2000) à une formulation de Deux surfaces considérant le couplage entre les déformations plastiques des chemins de chargements thermiques et mécaniques. La simulation des essais drainés montre que ce modèle peut décrire les caractéristiques principales thermo-mécaniques de l'argile de Boom naturelle le long de différents chemins de chargements. Le modèle TEAM a finalement été étendu à des conditions non drainées. Après la clarification du concept des contraintes effectives et la définition d'une condition de déformation volumique, le processus d'échauffement non drainé est analysé. La validité des équations thermo-hydro-mécaniques de ce modèle a été examinée en se basant sur des résultats d'essais typiques / This study is devoted to the thermo-mechanical constitutive modeling for saturated stiff clays and the development of a corresponding efficient stress integration algorithm. The mechanical behavior of natural Boom Clay in isothermal conditions was first characterized. The Modified Cam Clay model (MCC) was then applied to simulate the natural Boom Clay behavior. It has been found that the MCC gives poor-quality predictions of the natural Boom Clay behavior. Thereby, an adapted Cam Clay model (ACC-2) was developed by introducing a new yield surface and a new plastic potential as well as a Two-surface plastic mechanism. This model allows satisfactory prediction of the main features of the mechanical behavior of natural Boom Clay. Moreover, the constitutive equations of this model can be formulated mathematically as in a classic elasto-plastic model. Thus, the classic stress integration algorithm can be applied. The thermal effects were considered by assessing the performance of some advanced thermo-mechanical models (Cui et al., 2000; Abuel-Naga et al., 2007; Laloui and François, 2008; 2009). It appears that all the three models can capture the main features of the thermo-mechanical behavior of saturated clays. However, each constitutive model has its own limitations or unclear points from the theoretical point of view. The stress integration algorithm of the thermo-mechanical model proposed by Cui et al. (2000) at the stress point level was also developed using a specifically designed adaptive time-stepping scheme. The computation time required to achieve a given accuracy is largely reduced with the adaptive sub-stepping considered for both mechanical and thermal loadings. A Two-surface thermo-mechanical model (TEAM model) was developed based on the Two-surface plastic mechanism. The proposed model extends the model of Cui et al. (2000) to a Two-surface formulation, considering the plastic strain coupling between the thermal and the mechanical loading paths. The simulation of drained tests shows that this model can capture the main thermo-mechanical features of natural Boom Clay along different loading paths. The TEAM model was finally extended to undrained conditions. After setting up an appropriate effective stress principle and defining a volumetric strain condition, the undrained heating process was analyzed. The validity of the thermo-hydro-mechanical constitutive equations was examined based on the data from typical tests

Vascular networks are required to support the formation and function of three-dimensional tissues. Biodegradable scaffolds are being considered in order to promote vascularization where natural regeneration of lost or destroyed vascular networks fails. Particularly; composite materials are expected to fulfill the complex demands of a patient's body to support wound healing. Microbial biopolyesters are being regarded as such second and third generation biomaterials. Methylobacterium extorquens is one of several microorganisms that should be considered for the production of advanced polyhydroxyalkanoates (PHAs). M. extorquens displays a distinct advantage in that it is able to utilize methanol as an inexpensive substrate for growth and biopolyester production. The design of functionalized PHAs, which would be made of both saturated short-chain-length (scl, C [less than or equal to] 5) and unsaturated medium-chain-length (mcl, 6 [less than or equal to] C [less than or equal to] 14) monomeric units, aimed at combining desirable material properties of inert scl/mcl-PHAs with those of functionalized mcl-PHAs. By independently inserting the phaC1 or the phaC2 gene from Pseudomonas fluorescens GK13, recombinant M. extorquens strains were obtained which were capable of producing PHAs containing C-C double bonds. A fermentation process was developed to obtain gram quantities of biopolyesters employing the recombinant M. extorquens ATCC 55366 strain which harbored the phaC2 gene of P. fluorescens GK13, the better one of the two strains at incorporating unsaturated monomeric units. The PHAs produced were found in a blend of scl-PHAs and functionalized scl/mcl-PHAs (4 [less than or equal to] C [less than or equal to] 6), which were the products of the native and of the recombinant PHA synthase, respectively. Thermo-mechanical analysis confirmed that the functionalized scl/mcl-PHAs exhibited the desirable material properties expected. This project contributed to current research on polyhydroxyalkanoates at different levels. The terminal double bonds of the functionalized scl/mcl-PHAs are amenable to chemical modifications and could be transformed into reactive functional groups for covalently linking other biomacromolecules. It is anticipated that these biopolyesters will be utilized as tissue engineering materials in the future, due to their functionality and thermo-mechanical properties.

A study on shape memory alloy materials as vibration dampers is reported. An important component is the strain rate-dependent and temperature-dependent constitutive behavior of shape memory alloy, which can significantly change its energy dissipation capacity under cyclic loading. The constitutive model used accounts for the thermo-mechanical strain rate-dependent behavior and phase transformation. With increasing structural flexibility, the hysteretic loop size of shape memory alloy dampers increases due to increasing strain rates, thus further decreasing the response of the structure to cyclic excitation. The structure examined is a beam, and its behavior with shape memory alloy dampers is compared to the same beam with conventional dampers. Parametric studies reveal the superior performance of the shape memory alloy over the conventional dampers even at the resonance frequency of the beam-damper system. An important behavior of the shape memory alloy dampers is discovered, in that they absorb energy from the fundamental and higher vibration modes. In contrast, the conventional dampers transfer energy to higher modes. For the same beam control, the stiffness requirement for the shape memory alloy dampers is significantly less than that of the conventional dampers. Response quantities of interest show improved performance of the shape memory alloy over the conventional dampers under varying excitation intensity, frequency, temperature, and strain rate.

Chip-package interaction (CPI) has become a critical reliability issue for flip-chip packaging of Cu/low-k chip with organic substrate. The thermo-mechanical deformation and stress develop inside the package during assembly and subsequent reliability tests due to the mismatch of the coefficients of thermal expansion (CTEs) between the chip and the substrate. The thermal residual stress causes many mechanical reliability issues in the solder joints and the underfill layer between die and substrate, such as solder fatigue failure and underfill delamination. Moreover, the thermo-mechanical deformation of the package can be directly coupled into the Cu/low-k interconnect, inducing large local stresses to drive interfacial crack formation and propagation. The thermo-mechanical reliability risk is further aggravated with the implementation of ultra low-k dielectric for better electrical performance and the mandatory change from Pb-containing solders to Pb-free solders for environmental safety. These CPI-induced reliability issues in flip-chip packaging of Cu/low-k chips are investigated in this dissertation at both chip level and package level using high-resolution Moiré interferometry and Finite Element Analysis (FEA). Firstly, the thermo-mechanical deformation in flip-chip packages is analyzed using high-resolution Moiré interferometry. The effect of underfill properties on package warpage is studied and followed by a strategy study of proper underfill selection to improve solder fatigue life time and reduce the risk of interfacial delamination in underfill and low-k interconnects under CPI. The chip-package interaction is found to maximize at the die attach step during assembly and becomes most detrimental to low-k chip reliability because of the high thermal load generated by the solder reflow process before underfilling. A three-dimensional (3D) multilevel sub-modeling method combined with modified virtual crack closure (MVCC) technique is employed to investigate the CPI-induced interfacial delamination in Cu/low-k interconnects. It is first focused on the effects of dielectrics and solder materials on low-k interconnect reliability and then extended to the scaling effect where the reduction of the interconnect dimension is accompanied with an increased number of metal levels and the implementation of ultralow-k porous dielectrics. Recent studies on CPI-induced crack propagation in the low-k interconnect and the use of crack-stop structures to improve the chip reliability are also discussed. Finally, 3D integration (3DI) with through silicon vias (TSV) has been proposed as the latest solution to increase the device density without down-scaling. The thermo-mechanical reliability issues facing 3DI are analyzed. Three failure modes are proposed and studied. Design optimization of 3D interconnects to reduce the thermal residual stress and the risks of fracture and delamination are discussed. / text

Ce travail de thèse a porté sur la simulation numérique du comportement thermique et mécanique d'un combustible nucléaire à particules. Il s'agit d'un composite réfractaire constitué d'une matrice de graphite comportant 45 % en fraction volumique de particules sphériquesd'UO2 revêtues de deux couches de pyrocarbone. L'objectif était de développer une modélisationmulti-échelles de ce composite afin d'estimer son comportement moyen, ainsi que les hétérogé-néités des champs mécaniques au sein des constituants. Nous avons modélisé la microstructuredu combustible et généré des échantillons numériques en 3D. Pour cela, des outils de générationde distributions aléatoires de sphères, de maillage et de caractérisation microstructurale, tellela covariance, ont été développés dans le code de calcul Cast3M. Une centaine d'échantillonsnumériques de différentes tailles ont été réalisés. Le comportement thermo-élastique du combustiblea été caractérisé à partir de ces échantillons, à l'aide de calculs de microstructures paréléments finis. Nous avons étudié l'influence de divers paramètres de la modélisation, dont lesconditions aux limites. Nous proposons une méthode pour s'affranchir des effets des conditionsaux limites sur les résultats, appelée méthode d'érosion. Elle s'appuie sur l'analyse des résultatssur un érodé du volume élémentaire. Nous avons alors déterminé les propriétés effectives ducomposite (modules d'élasticité, conductivité thermique, dilatation thermique), ainsi que lesdistributions des champs mécaniques locaux au sein de la matrice. Enfin, nous avons proposéun modèle de changement d'échelles permettant d'obtenir, non seulement les valeurs moyennesdes variables mécaniques dans chaque phase, mais également leurs variances et covariances pourtout chargement macroscopique imposé. Cette approche statistique de changement d'échellespermet ainsi d'estimer la distribution des grandeurs mécaniques au sein de chaque phase ducomposite. / The aim of this work was to perform numerical simulations of the thermal and mechanical behavior of a particle-based nuclear fuel. This is a refractory composite material made of UO2spherical particles which are coated with two layers of pyrocarbon and embedded in a graphitematrix at a high volume fraction (45 %). The objective was to develop a multi-scale modelingof this composite material which can estimate its mean behavior as well as the heterogeneity ofthe local mechanical variables. The first part of this work was dedicated to the modeling of themicrostructure in 3D. To do this, we developed tools to generate random distributions of spheres,meshes and to characterize the morphology of the microstructure towards the finite elementcode Cast3M. A hundred of numerical samples of the composite were created. The secondpart was devoted to the characterization of the thermo-elastic behavior by the finite elementmodeling of the samples. We studied the influence of different modeling parameters, one of themis the boundary conditions. We proposed a method to vanish the boundary conditions effectsfrom the computed solution by analyzing it on an internal sub-volume of the sample obtained byerosion. Then, we determined the effective properties (elastic moduli, thermal conductivity andthermal expansion) and the stress distribution within the matrix. Finally, in the third part weproposed a multi-scale modeling to determine the mean values and the variance and covarianceof the local mechanical variables for any macroscopic load. This statistical approach have beenused to estimate the intra-phase distribution of these variables in the composite material.

Les matériaux composites constitués de fibres de carbone et de résine époxy présentent des propriétés spécifiques remarquables qui les destinent à une utilisation à grande échelle dans de nombreux domaines où des gains de masse sont recherchés, comme le transport. Les réservoirs d’hydrogène de type IV présents dans les véhicules automobiles en sont un exemple. Dans le cadre de la sécurité des biens et des personnes, le risque incendie doit alors être considéré : lorsqu’un réservoir d’hydrogène subit une agression thermique telle qu’un feu, son enveloppe en matériau composite est sujette à décomposition thermique qui, couplée aux transferts de chaleur et à l’endommagement dû au chargement mécanique, peut conduire à l’explosion de la structure. Pour prédire numériquement le comportement des réservoirs dans des situations de charges couplées, thermiques et mécaniques, un modèle construit sur la prise en compte des phénomènes ayant une conséquence majeure sur le comportement du matériau a été développé. Il intègre, dans un cadre thermodynamique, la microfissuration matricielle, la rupture des fibres et des interfaces fibres/matrice ainsi que le délaminage et représente les effets de la température sur les propriétés mécaniques. A cet endommagement mécanique est adjoint la décomposition thermique due aux températures élevées (>350°C). Elle induit des changements de structure du matériau due à la gazéification de la résine époxy, une modification des paramètres thermiques (ce qui a une influence sur les transferts de chaleur) et une perte des propriétés mécaniques.A l’échelle de l’éprouvette, des calculs sont menés afin de déterminer les paramètres des différents sous-modèles. Cela comporte les critères d’initiation et les lois d’évolution des endommagements, les paramètres réactionnels pour la décomposition thermique et les paramètres thermiques (masse volumique, capacité thermique et conductivité) pour chaque état de décomposition. Une méthode est proposée pour fixer les paramètres clés du couplage thermomécanique, à savoir l’influence de la décomposition thermique sur le comportement mécanique. Des calculs entièrement couplés sont également réalisés afin de déterminer le poids de chaque phénomène (température, décomposition thermique et endommagement mécanique) sur la rupture finale du matériau en condition d’exposition au feu.A l’échelle du réservoir hyperbare, des prédictions de pressions d’éclatement, en situation d’incendie et à température ambiante, sont menées. A température ambiante, le rôle de chaque processus d’endommagement dans la pression ultime est évalué afin de déterminer leur nécessité dans la modélisation. Dans des conditions d’incendie, le temps à éclatement est évalué lorsque le réservoir est soumis à différentes pressions internes. Le modèle est capable de prédire correctement la transition entre un mode d’éclatement à haute pression et un mode de fuite par le corps à plus faible pression, dû à la fusion du liner avant que le niveau de contraintes soit critique dans la coque composite et conduise à l’éclatement. Cette approche, mise en place à l’échelle du réservoir, permet donc d’établir la succession des événements menant à son éclatement (ordre et plis d’apparition des endommagements, champ de température dans l’épaisseur l’enveloppe composite, temps à explosion). / Composite materials made of carbon fibres and epoxy resin have remarkable specific properties that make them suitable for large-scale use in many areas where mass savings are required, such as transport. An example is the type IV hydrogen tank in motor vehicles. In the context of the safety of persons, the fire risk must then be considered: when a hydrogen tank undergoes thermal aggression such as a fire, its composite shell is subject to thermal decomposition which, coupled with heat transfers and damage due to mechanical loading, can lead to burst of the structure. To numerically predict the behaviour of tanks subjected to coupled load (thermal and mechanical), a model based on the phenomena having a major impact on the behaviour of the material has been developed. It involves, in a thermodynamic framework, matrix microcracking, fibre failure and fibre/matrix interfaces decohesion as well as delamination and represents the effects of temperature on mechanical properties. To this mechanical damage is added the thermal decomposition due to high temperatures (>350°C). It induces structural changes in the material due to the gasification of the epoxy resin, a change in thermal parameters (which has an influence on heat transfers) and a loss of mechanical properties.At the specimen scale, calculations are carried out to determine the parameters of the different sub-models. This includes initiation criteria and damage evolution laws, reaction parameters for thermal decomposition and thermal parameters (density, thermal capacity and conductivity) for each decomposition state. A method is proposed to determine the key parameters of thermomechanical coupling, namely the influence of thermal decomposition on mechanical behaviour. Fully coupled calculations are also performed to determine the weight of each phenomenon (temperature, thermal decomposition and mechanical damage) on the final failure of the material under fire exposure conditions.At the hyperbaric tank scale, burst pressure predictions, in a fire situation and at room temperature, are carried out. At room temperature, the role of each damage process in the ultimate pressure is evaluated to determine their relative weight in the modelling. Under fire conditions, the time to burst is evaluated when the tank is subjected to different internal pressures. The model is able to correctly predict the transition from a burst mode at high pressure to leak mode at lower pressure due to melting of the liner before the stress level is critical in the composite shell and leads to burst. This approach, implemented at the scale of the tank, therefore makes it possible to establish the sequence of events leading to burst (plies in which damage occurs, temperature field in the composite wall, burst time).

Fundamental thermodynamic investigations have been carried out regarding the phase equilibria of La0.8Sr0.2MnO3±δ (LSM), a cathode of a solid oxide fuel cell (SOFC), utilizing the CALculation of PHAse Diagram (CALPHAD) approach. The assessed thermodynamic databases developed for LSM perovskite in contact with YSZ fluorite and the other species have been discussed. The application of computational thermodynamics to the cathode is comprehensively explained in detail, including the defect chemistry analysis as well as the quantitative Brouwer diagrams, electronic conductivity, cathode/electrolyte interface stability, thermomechanical properties of the cathode and the impact of gas impurities, such as CO2 as well as humidity, on the phase stability of the cathode. The quantitative Brouwer diagrams for LSM at different temperatures are developed and the detailed analysis of the Mn3+ charge disproportionation behavior and the electronic conductivity in the temperature range of 1000-1200°C revealed a good agreement with the available experimental observations. The effects of temperature, CO2 partial pressure, O2 partial pressure, humidity level and the cathode composition on the formation of secondary phases have been investigated and correlated with the available experimental results found in the literature. It has been indicated that the CO2 exposure does not change the electronic/ionic carriers’ concentration in the perovskite phase. The observed electrical conductivity drop is predicted to occur due to the formation of secondary phases such as LaZr2O7, SrZrO3, SrCO3 and Mn oxides at the LSM/YSZ interface, resulting in the blocking of the electron/ion transfer paths. For the thermo-mechanical properties of LSM, a new weight loss Mechanism for (La0.8Sr0.2)0.98MnO3±δ using the La-Sr-Mn-O thermodynamic database is modeled with respect to the compound energy formalism model. This newly proposed mechanism comprehensively explains the defect formation as a result of volume/weight change during the thermal cycles. According to the proposed mechanism the impact of cation vacancies regarding the volume change of cathode was explained.

During the flight of missiles, depending on the flight conditions, rotation of missiles around its centerline can cause instabilities. To override this issue, missile generally is designed in 2 sections. In the missile, the rear tail section and the front section are to rotate freely by means of bearings. Tail section on which bearings are mounted is designed according to thermal loads due to flow of hot gasses through the nozzle and mechanical loads due to inertial load, interference fit and thread preload which appear during flight of missile. The purpose of this thesis is to determine the most suitable structural parameters according to the flight conditions of missile. The geometrical and load parameters which have effect on the results were determined. Finite element model is formed by using FEA software. After that, transient nonlinear thermo-mechanical analyses are performed and the most effective parameter on VM (Von-Mises) stress and force is determined. DOE (Design of Experiments) method was used to determine the most suitable values for the structural parameters. Totally 27 different configurations are studied to achieve to the most suitable values for variable set. It is observed that VM stress and force results for all configurations are within the &plusmn / %5 ranges. So this means parameters don&rsquo / t affect the systems response very much. By taking manufacturing processes into consideration, configuration with the highest bearing inner/outer ring interference is taken. From the comparison of the results, the most suitable configuration is obtained after checking forces and VM stress on the bearings.