Lors du fonctionnement des packages électroniques, ceux ci sont exposés à diverses sollicitations d'ordres thermiques et mécaniques. De même, la combinaison de ces sources de contraintes constitue l'origine de la quasi majorité des défaillances des packages électroniques. Pour s'assurer de la bonne résistance des packages électroniques, les fabricants pratiquent des tests de fiabilité et des analyses de défaillance avant toute commercialisation. Toutefois, les essais expérimentaux, lors de la phase de conception et de l'élaboration des prototypes, s'avèrent contraignants en termes de temps et de ressources matérielles. En revanche, la simulation numérique à l'aide de la méthode des éléments finis constitue une option alternative en termes de temps et de ressources. Les objectifs dévolus aux travaux de recherche visent à élaborer quatre modèles éléments finis en 3D, validés/calibrés par des essais expérimentaux, intégrant les recommandations JEDEC (1) en vue de : - Procéder à la caractérisation thermique et thermomécanique des packages électroniques ; - Et prédire la durée de vie en fatigue thermique des joints de brasures et ce, en lieu et place de la caractérisation expérimentale normalisée. Or, la mise en œuvre des modèles éléments finis présente certains inconvénients liés aux incertitudes au niveau de la géométrie, des propriétés matériaux, les conditions aux limites ou les charges. Ceux ci ont une influence sur le comportement thermique et thermomécanique des systèmes électroniques. D'où la nécessité de formuler le problème en termes probabilistes et ce, dans le but de mener une étude de fiabilité et d’optimisation des packages électroniques. Pour remédier au temps de calcul énorme généré par les méthodes d’analyse de fiabilité classiques, nous avons développé des méthodologies spécifiques à cette problématique, via des méthodes d’approximation basées sur le krigeage avancé,qui nous ont permis de bâtir un modèle de substitution, qui rallie efficacité et précision. Par conséquent, une analyse de fiabilité a été menée avec exactitude et dans un temps extrêmement court, via les méthodes de simulation Monte Carlo et FORM/SORM, couplées avec le modèle de krigeage avancé. Ensuite, l’analyse de fiabilité a été associée dans le processus d’optimisation, en vue d’améliorer la performance et la fiabilité de la conception structurelle des packages électroniques. A la fin, nous avons procédé à l’applicabilité des dites méthodologies d’analyse de fiabilité aux quatre modèles éléments finis ainsi développés. Il résulte que les analyses de fiabilité menées se sont avérées très utiles pour prédire les effets des incertitudes liées aux propriétés matériaux. De même, l’analyse d’optimisation de fiabilité ainsi réalisée nous a permis d’améliorer la performance et la fiabilité de la conception structurelle des packages électroniques. (1) JEDEC (Joint Electron Device Engineering Council) est un organisme de normalisation des semi-conducteurs. / During operation, electronic packages are exposed to various thermal and mechanical solicitations. These solicitations combined are the source for most of electronic package failures. To ensure electronic packages robustness, manufacturers perform reliability testing and failure analysis prior to any commercialization. However, experimental tests, during design phase and prototypes development, are known to be constraining in terms of time and material resources. This research aims to develop four finite element models in 3D, validated/calibrated by experimental tests, integrating JEDEC recommendations to : - Perform electronic packages thermal and thermomechanical characterization ; - Predict the thermal fatigue life of solder joints in place of the standardized experimental characterization.However, implementation of the finite element model has some disadvantages related to uncertainties at the geometry, material properties, boundary conditions or loads. These uncertainties influence thermal and electronic systems thermomechanical behavior. Hence the need to formulate the problem in probabilistic terms, in order to conduct a reliability study and a electronic packages reliability based design optimization.To remedy the enormous computation time generated by classical reliability analysis methods, we developed methodologies specific to this problem, using approximation methods based on advanced kriging, which allowed us to build a substitution model, combining efficiency and precision. Therefore reliability analysis can be performed accurately and in a very short time with Monte Carlo simulation (MCS) and FORM / SORM methods coupled with the advanced model of kriging. Reliability analysis was associated in the optimization process, to improve the performance and electronic packages structural design reliability. In the end, we applied the reliability analysis methodologies to the four finite element models developed. As a result, reliability analysis proved to be very useful in predicting uncertainties effects related to material properties. Similarly, reliability optimization analysis performed out has enabled us to improve the electronic packages structural design performance and reliability. In the end, we applied the reliability analysis methodologies to the four finite element models developed. As a result, reliability analysis proved to be very useful in predicting uncertainties effects related to material properties. Similarly, reliability optimization analysis performed out has enabled us to improve the electronic packages structural design performance and reliability.

This work focuses on the thermomechanical characterization and constitutive model calibration of shape memory polymers (SMPs). These polymers have the ability to recover seemingly permanent large deformations under the appropriate thermomechanical load path. In this work, a contribution is made to both existing experimental and modeling efforts. First, an experimental investigation is conducted which subjects SMPs to a thermomechanical load path that includes varying the value of applied deformations and temperature rates. Specifically, SMPs are deformed to tensile extensions of 10% to 100% at temperature rates varying from 1 degree C /min to 5 degree C/min, and the complete shape recovery profile is captured. The results from this experimental investigation show that the SMP in question can recover approximately 95% of the value of the applied deformation, independent of the temperature rate during the test. The data obtained in the experimental investigation are then used to calibrate, in one-dimension, two constitutive models which have been developed to describe and predict the material response of SMPs. The models include a model in terms of general deformation gradients, thus making it capable of handling large deformations. In addition, the data are used to calibrate a linearized version of the constitutive model for small deformations. The material properties required for calibrating the constitutive models are derived from portions of the experimental results, and the model is then used to predict the shape memory effect for an SMP undergoing various levels of deformation. The model predictions are shown to match well with the experimental data.

Titanium-nickel is a unique class of material known as Shape Memory Alloy (SMA). A thermoelastic martensitic phase transformation is responsible for its extraordinary properties such as shape memory effect and superelasticity. The near equiatomic Ti-Ni alloys are the commercially most exploited SMAs because of the unique combination of these properties and superior ductility, strength, fatigue resistance and corrosion resistance. The properties of Ti-Ni SMAs are very sensitive to composition and the processing parameters. The properties of Ti-Ni SMAs can be modified to a great extent by choice of composition, mechanical working and heat treatment. Thermo-mechanical treatments are required to strengthen the matrix and improve the shape memory characteristics. Plastic deformation and subsequent annealing is the common way to improve shape memory properties. In the present study, Ti- 50 at% Ni wire specimens are produced and used for the investigation of the effect of different heat treatment and cold working processes on shape memory characteristics. To investigate the thermomechanical behavior of differently processed wire specimens, a fully computerized servo hydraulic thermomechanical testing machine was designed and constructed. Testing machine was capable to perform different types of tests that are selected by the user. It can both heat and cool the specimen automatically according to the testing sequence by applying DC current directly through the SMA wire or by sending liquid nitrogen into the cooling chamber. Temperature is measured by a K-type thermocouple directly mounted on the wire specimen with a glass tape. Force that is applied to the specimen is produced by hydraulic power unit with a double action cyclinder and it is controlled by a controller which takes the feedback from the loadcell and LVDT (Linear Variable Distance Transducer). During performig thermomechanical-tests all the data of loadcell, LVDT and thermocouple are collected by a data acqusition system integrated with a host computer that operates the program XPC Target. Ti-Ni alloy with equiatomic composition is prepared in vacum induction furnace. Specimen cast in the form of rod was then hot swaged. Subsequent to swaging, cold wire drawing, intermediate annealing at 500 &amp / #61616 / C and water quenching was applied to obtain SMA wire with a diameter of 1.52 mm. Ti-Ni wires produced were subjected to four different processes. All the samples were initially solution heat treated at 925 &amp / #61616 / C for 30 minutes prior to water quenching. Some of the samples were further treated by an intermediate anneal at 500 &amp / #61616 / C. To see the effect of cold working / prior to intermediate annealing, 20 % or 40 % cold work was applied to another group of specimens. To study the shape memory characteristics of specimens subjected to the above mentioned processes, four types of test, namely constant stress free recovery test, constant strain free recovery test, constant stress constrained recovery test and constant strain constrained recovery test, were designed and applied cyclically. The tests have shown that the stress plateau observed in the first cycle of the tests disappear upon cycling and the shape memory characteristics improve and stabilize with cycling. Once trained by cycling, fractional free recovery was observed to reach to 100 % and recovery stress to reach 120% of the applied stress if shape recovery is prevented.

Shape memory polymers (SMPs) are a relatively new class of active materials that can store a temporary shape and return to the original configuration upon application of a stimulus such as temperature. This shape changing ability has led to increased interest in their use for biomedical and aerospace applications. A major challenge, however, in the advancement of these applications is the ability to accurately predict the material behavior for complex geometries and boundary conditions. This work addresses this challenge by developing an experimentally calibrated and validated constitutive model that is implemented as a user material subroutine in Abaqus ? a commercially available finite element software package. The model is formulated in terms of finite deformations and assumes the SMP behaves as a thermoelastic material, for which the response is modeled using a compressible neo-Hookean constitutive equation. An internal state variable, the glassy volume fraction, is introduced to account for the phase transformation and associated stored deformation upon cooling from the rubbery phase to the glassy phase and subsequently recovered upon heating. The numerical implementation is performed such that a system of equations is solved using a Newton-Raphson method to find the updated stress in the material. The conductive heat transfer is incorporated through solving Fourier's law simultaneously with the constitutive equations. To calibrate and validate the model parameters, thermomechanical experiments are performed on an amorphous, thermosetting polyurethane shape memory polymer. Strains of 10-25% are applied and both free recovery (zero load) and constrained displacement recovery boundary conditions are considered for each value of applied strain. Using the uniaxial experimental data, the model is then calibrated and compared to the 1-D experimental results. The validated finite element analysis tool is then used to model biomedical devices, including cardiovascular tubes and thrombectomy devices, fabricated from shape memory polymers. The effects of heat transfer and complex thermal boundary conditions are evaluated using coupled thermal-displacement analysis, for which the thermal material properties were experimentally calibrated.

L’objectif de cette thèse est de développer des matériaux polymérisés par rayonnement ultra-violet possédant une bonne balance des propriétés thermomécaniques entre résistance à la température, rigidité (strength) et résistance à l’impact. Une direction vers cet objectif est l’utilisation de résines (meth)acrylate modifiées avec des thiols polyfonctionnels. Cependant, les thiol-ene en général sont sujets à un problème de polymérisation prématurée incontrôlée même à l’abri de la lumière. Ce problème doit être traité puisque celui-ci conditionne le succès des thiol-ene dans le domaine des photopolymères. La première partie de cette thèse concerne l’élaboration de résine (meth)acrylate modifiée par l’incorporation d’un polythiol, le pentaerythritol tetrakismercaptopropionate (PETMP), à différents ratio. Les propriétés thermomécaniques et photochimiques de ces résines sont à l’étude. La seconde partie traite du problème de polymérisation prématurée incontrôlée des thiol-ene. Une étude de stabilité thermique aboutissant à des résultats très encourageant est proposée. Finalement, la dernière partie porte sur la caractérisation des réseaux photo-réticulés par pyrolyse-GC/MS. La compréhension de la constitution des réseaux tridimensionnels devraient apportés des avancées dans l’élaboration de nouveaux matériaux. Une nouvelle méthode de caractérisation utilisant la pyrolyse-GC/MS directe à multi-étapes est développée. Enfin, des résultats sur l’application de la méthode sur des matériaux à base de (meth)acrylate difonctionnel photopolymérisés ainsi qu’une tentative de caractérisation de matériaux à base de polythiol/(meth)acrylates photopolymérisés sont reportés puis discutés. / This thesis fall within an approach aiming to develop UV-processed materials having a good thermo-mechanical properties balance between strength, temperature resistance and impact resistance. A direction toward this objective is the use of photocurable (meth)acrylate resins modified with polyfunctional thiols. Indeed, thiol-ene chemistry is known to have poor sensitivity toward oxygen inhibition, to improve the dimensional stability and toughness properties of photocured materials. However, thiol-ene resins are subjected to premature uncontrolled dark polymerization, an issue that has to be solved for their success in the photopolymers area. The first part of this work is focused on the thermo-mechanical and the photopolymerization properties investigation of a pentaerythritol tetrakismercaptopropionate (PETMP) modified (meth)acrylate based resin by looking at different ratio of polythiol/(meth)acrylate. The second part is dedicated to the understanding of the thermal instability of such systems and to the solving of this issue. Finally, a special interest is brought to the characterization of photopolymeric networks by pyrolysis-GC/MS. The lake of deep understanding and view about how the cured networks are really constituted due to the difficulty to analyze insoluble cured polymers, prevents improvements in the formulation of high performance materials. Further information on cured networks constitution could bring useful information for the elaboration of new materials. A new characterization method based on direct multi-step pyrolysis-GC/MS is developed and an attempt on the characterization of polythiol (meth)acrylate material by Py-GC/MS is reported and discussed.