The major Hot-Mix Asphalt (HMA) input for mechanistic-empirical (M-E) flexible pavement design is the dynamic complex modulus obtained from either the uniaxial or triaxial compressive dynamic modulus test. Furthermore, as part of the performance-based mix design process, the triaxial dynamic modulus has been selected to predict rutting and fatigue cracking, and the Indirect Tension (IDT) creep compliance test to predict low-temperature thermal cracking. The creep compliance and dynamic modulus are measured responses (viscoelastic functions) of viscoelastic materials under transient and cyclic loading, respectively. Under the assumptions of linearity, linear viscoelastic functions are equivalent. Moreover, these properties should be the same whether they are obtained from a uniaxial compressive or IDT test. For this dissertation, we tested the applicability of linear viscoelastic (LVE) theory to HMA mixes and determined whether HMA need to be modeled as a bimodular material to analyze IDT creep compliance test results. The need to model HMA as a bimodular material is a result of a number of studies that suggest that HMA tensile and compressive properties are different. A testing program was developed to experimentally measure the uniaxial compression, and IDT creep compliance, and the uniaxial compression dynamic modulus for different HMA mixes. The uniaxial compressive creep compliance and dynamic modulus master curves are constructed and the shift factors obtained from each test are compared. Interconversion between the creep compliance and dynamic modulus experimental results confirm the applicability of LVE theory for the HMA mixes investigated. Based on the applicability of LVE theory, a methodology to determine HMA LVE properties from the combined creep compliance and dynamic modulus test results was developed. As a practical application that is relevant to the M-E flexible pavement design procedure, LVE theory was used and compared to proposed approximate methods to perform the conversion of testing frequency to loading time. Specifically, dynamic modulus results were converted to relaxation modulus, creep compliance, and resilient modulus. Finally, the HMA IDT creep compliance test results at low and intermediate temperature (<20oC) were successfully analyzed using a HMA bimodular material model based on the Ambartsumyan model. The difference between the compressive modulus and the modulus calculated from the IDT test using Hondros' stress distribution is calculated. In addition, a method to determine the compressive-to-tensile modulus ratio using uniaxial compressive and IDT test results is illustrated for one of the tested HMA mixes. / Ph. D.

Les travaux effectués durant cette thèse portent sur l’étude du comportement mécanique dynamique de solutions amortissantes passives utilisées pour la réduction des niveaux vibratoires et la stabilisation des systèmes optroniques embarqués au sein de l’entreprise Thales LAS France. Ces solutions intègrent des matériaux élastomères au fort pouvoir dissipatif dont le comportement doit être parfaitement maîtrisé pour un bon dimensionnement de l’isolation vibratoire, et ce malgré leur dépendance à la température et à la fréquence. L’objectif général est d’améliorer la connaissance du comportement de ces matériaux, leur caractérisation, leur prise en compte dans les simulations numériques afin d’améliorer les pratiques employées dans les bureaux d’études qui conçoivent les structures accueillant ces systèmes.Dans ce cadre, les travaux présentés portent tout d’abord sur la caractérisation, la modélisation et l’identification du comportement viscoélastique des élastomères employés dans des amortisseurs de Thales LAS France. Un modèle de type Maxwell généralisé (GMM) est utilisé pour décrire ce comportement, et est introduit dans un modèle éléments finis de l’amortisseur afin d’obtenir une représentation physique satisfaisante de son comportement mécanique dynamique. Le problème est réécrit sous la forme d’une représentation d’état originale qui est associée à une stratégie de réduction de modèle pour réduire les temps de calcul. Différentes simulations sont alors réalisées pour illustrer le potentiel de l’approche proposée, analyse modale complexe, réponse fréquentielle et réponse temporelle. La température ayant une influence primordiale sur le comportement mécanique des élastomères, un modèle matériau thermomécanique spécifique est proposé en identifiant l’évolution en température de paramètres du GMM, et une analyse de robustesse portant sur la capacité de dissipation de l’amortisseur témoin en présence de méconnaissances sur cette variable est réalisée en se basant sur la théorie Info-Gap.L’analyse d’une campagne d’essais a permis de constater l’apparition d’un assouplissement de la structure sous de fortes sollicitations, laissant augurer la présence de non-linéarités. Un autre aspect abordé durant cette thèse porte ainsi sur la caractérisation, la modélisation et l’identification des phénomènes non-linéaires pouvant impacter le comportement dynamique de l’amortisseur. Deux sources ont été mises en évidence : une non-linéarité matérielle liée à la dépendance des caractéristiques mécaniques des élastomères au taux de déformation (effet Payne), et une non-linéarité de type contact liée à la présence de butées. Ces comportements ont été implémentés dans une représentation réduite de l’amortisseur afin d’expliquer les phénomènes non-linéaires observés expérimentalement au cours des campagnes de qualification du produit.Enfin, la dernière partie de ces travaux de thèse porte sur la conception d’un réseau d’absorbeurs à masses accordées (MTMD) afin de réduire le niveau vibratoire d’une pièce structurale supportant les systèmes optiques. Après une formulation du problème éléments finis, une procédure d’optimisation des paramètres du MTMD est mise en œuvre et une analyse de robustesse de la solution optimale en présence d’incertitudes sur la fréquence propre à contrôler est effectuée. Cette étude est menée pour différents jeux de paramètres et une méthode d’optimisation robuste est proposée en combinant la procédure d’optimisation et la théorie Info-Gap. Pour finir, une maquette du système étudié est réalisée ainsi qu’une version simplifiée de son MTMD associé afin de mettre à l’épreuve les règles d’accordage issues des études numériques grâce à une série d’essais vibratoires. / The work carried out during this thesis deals with the study of the dynamic mechanical behavior of passive damping solutions used for the reduction of vibration levels and the stabilization of embedded optronic systems within Thales LAS France company. These solutions integrate elastomer materials with high dissipative power, whose behavior must be perfectly controlled for a good mechanical dimensioning of vibration isolation, despite their dependence on temperature and frequency. The general objective is to improve the knowledge of these material behavior, the characterization techniques, and the method taking into account this behavior in the numerical simulations in order to improve the practices used in the engineering department that design the structures hosting these systems.In this context, the work presented first focuses on the characterization, the modeling and the identification of the viscoelastic behavior of elastomers used in Thales LAS France damping devices. A Generalized Maxwell Model (GMM) is used to describe this behavior, and is introduced into a finite element model of the damper to obtain a satisfactory physical representation of its dynamic mechanical behavior. The problem is rewritten as an original state space representation that is associated with a model reduction strategy to reduce computation times. Various simulations are moreover performed to illustrate the potential of the proposed approach, such as complex modal analysis, frequency response and temporal response. Since temperature has a major influence on the mechanical behavior of elastomers, a specific thermomechanical material model is proposed by identifying the temperature evolution of GMM parameters, and a robustness analysis on the dissipation ability of the damper in the presence of a lack-of-knowledge on this variable is carried out based on the Info-Gap theory.Experimental test results showed the appearance of a softening of the structure under heavy load, suggesting the presence of non-linearities. Another aspect of this thesis deals with the characterization, the modeling and the identification of non-linear phenomena that can impact the dynamic behavior of the damper. Two sources have been highlighted: a material non-linearity related to the dependence of the mechanical characteristics of the elastomers to the rate of deformation (Payne effect), and a contact non-linearity related to the presence of mechanical stops. These behaviors were implemented in a reduced representation of the damper to explain the nonlinear phenomena observed experimentally during the damping device qualification campaigns.Finally, the last part of this thesis deals with the design of a network of tuned mass absorbers (MTMD) in order to reduce the vibratory level of a structural part supporting optical systems. After a formulation of the finite element problem, a procedure for optimizing the parameters of the MTMD is implemented and a robustness analysis of the optimal solution in the presence of uncertainties on the specific eigenfrequency to be controlled is performed. This study is carried out for different sets of parameters and a robust design optimization method is proposed by combining the optimization procedure and the Info-Gap theory. Finally, a model of the studied system is realized as well as a simplified version of its associated MTMD in order to test the tuning rules resulting from numerical studies thanks to a series of experimental tests.

Cancer progression is accompanied with alterations in the cell biomechanical phenotype, including changes in cell structure, morphology, and responses to microenvironmental stress. These alterations result in an increased deformability of transformed cells and reduced resistance to mechanical stimuli, enabling motility and invasion. Therefore, single cell biomechanical properties could be served as a powerful label-free biomarker for effective characterization and early detection of single cancer cells. Advances and innovations in microsystems and nanotechnology have facilitated interrogation of the biomechanical properties of single cells to predict their tumorigenicity, metastatic potential, and health state. This dissertation utilized Atomic Force Microscopy (AFM) for the cell biomechanical phenotyping for cancer diagnosis and early detection, efficacy screening of potential chemotherapeutic agents, and also cancer stem-like/tumor initiating cells (CSC/TICs) characterization as the critical topics received intensive attention in the search for effective cancer treatment. Our findings demonstrated the capability of exogenous sphingosine to revert the aberrant biomechanics of aggressive cells and showed a unique, mechanically homogeneous, and extremely soft characteristic of CSC/TICs, suitable for their targeted isolation. To make full use of cell biomechanical cues, this dissertation also considered the application of nonlinear viscoelastic models such as Fractional Zener and Generalized Maxwell models for the naturally complex, heterogeneous, and nonlinear structure of living cells. The emerging need for a high-throughput clinically relevant alternative for evaluating biomechanics of individual cells led us to the development of a microfluidic system. Therefore, a high-throughput, label-free, automated microfluidic chip was developed to investigate the biophysical (biomechanical-bioelectrical) markers of normal and malignant cells. Most importantly, this dissertation also explored the biomechanical response of cells upon a dynamic loading instead of a typical transient stress. Notably, metastatic and non-metastatic cells subjected to a pulsed stress regimen exerted by AFM exhibited distinct biomechanical responses. While non-metastatic cells showed an increase in their resistance against deformation and resulted in strain-stiffening behavior, metastatic cells responded by losing their resistance and yielded slight strain-softening. Ultimately, a second generation microfluidic chip called an iterative mechanical characteristics (iMECH) analyzer consisting of a series of constriction channels for simulating the dynamic stress paradigm was developed which could reproduce the same stiffening/softening trends of non-metastatic and metastatic cells, respectively. Therefore, for the first time, the use of dynamic loading paradigm to evaluate cell biomechanical responses was used as a new signature to predict malignancy or normalcy at a single-cell level with a high (~95%) confidence level. / Ph. D.