This thesis presents a study on two types of X-ray diffraction methodologies applied to the characterization of amorphous materials. The purpose of this study was to assess the feasibility of measuring the diffractive spectrum of amorphous materials by Energy-Dispersive X-ray Diffraction (EDXRD) utilizing Cadmium Zinc Telluride detectors. The total scattering intensity (coherent plus incoherent scatter) spectra precisely measured by high-energy Wide-Angle X-ray Scattering (WAXS) were compared to the EDXRD spectra to determine the level of agreement between the two techniques. The EDXRD spectra were constructed by applying a spectra fusing technique which combined the EDXRD spectra collected at different scattering angles rendering a continuous total scattering spectrum. The spectra fusing technique extended the momentum transfer range of the observed scattered spectrum beyond the limitations of the X-ray source and CZT detection efficiencies. Agreement between the WAXS and fused EDXRD spectra was achieved. In addition, this thesis presents the atomic pair correlation functions and coordination numbers of the first coordination shell for four hydrogen peroxide solutions of varying mass concentrations using Empirical Potential Structural Refinement (EPSR). The results are compared to the state-of-the art ad initio quantum mechanical charge field molecular dynamics (QMCF MD) model of the hydrogen peroxide in solution to support the model's predictions on why hydrogen peroxide is stable in water. The EPSR results using the coherent scattering intensity calculated from the WAXS data set predicts a hydration shell of 6.4 molecules of water surrounding hydrogen peroxide. The results also indicate that hydrogen peroxide is more likely to behave as a proton donor than acceptor. These findings are in agreement with QMCF MD model of aqueous hydrogen peroxide. / Physics

Es wurde die Optimierungssoftware SPC-Opt entwickelt, mit welcher sich Aufgaben aus den Bereichen der Formoptimierung sowie der Material- und Formidentifikation bearbeiten lassen. Zur Lösung von Identifikationsproblemen steht eine robuste Implementierung des Levenberg-Marquardt-Fletcher-Verfahrens zur Verfügung. Ergänzt wird dieses durch Line-Search- und Trust-Region-Verfahren, welche sich besonders für Aufgaben der Formoptimierung eignen. Es wurden effiziente Algorithmen zur Approximation der Hesse-Matrix sowie verschiedene Verfahren zur Startparametervariation integriert. Das Programm verfügt über Schnittstellen zur Nutzung von ABAQUS, ANSYS, MSC.MARC, eigenen FEM-Programmen sowie LUA-Skripten. Für Formoptimierungen können geometrische Konturen durch NURBS approximiert und deren Kontrollpunkte als Formparameter genutzt werden. Die Aktualisierung der FEM-Netze entsprechend der Formparameteränderung erfolgt durch ein analytisches Verfahren. Der zweite Schwerpunkt der Arbeit bezieht sich auf die Weiterentwicklung bestehender Verfahren zur Materialparameteridentifikation im Bereich der Gummiwerkstoffe. Hierbei wurde das Konzept der Anpassung anhand bauteilnaher Probekörper entwickelt. Dabei wurde am Beispiel einer Fahrwerksbuchse ein Probekörper entworfen, welcher dem originalen Bauteil zwar ähnlich sieht, jedoch eine deutlich einfachere Geometrie hat. Durch diesen konnte das Verhalten des Bauteils gut approximiert und sichergestellt werden, dass die im Rahmen der Parameteridentifikation durchgeführten FEM-Simulationen sicher konvergieren. Zudem wurden die Nutzerschnittstellen des inelastischen Morph-Stoffgesetz für MSC.MARC und ABAQUS weiterentwickelt, sodass diese nunmehr auch im industriellen Umfeld nutzbar sind. Es konnte nachgewiesen werden, dass die Verwendung bauteilnah identifizierter Parameter zu einer erheblich besseren Abbildung des Materialverhaltens führt als die Verwendung anhand von Standardprobekörpern identifizierter Parameter. Weiterhin zeigte sich, dass vor allem der Einsatz eines Stoffgesetzes mit der Möglichkeit zur Abbildung des charakteristischen Verhaltens von Elastomeren unbedingt erforderlich ist. / Within the scope of this work the optimization software SPC-Opt has been developed to successfully process tasks in the fields of shape optimization and parameter identification. The software includes a robust Levenberg-Marquardt-Fletcher algorithm, several line search and trust region algorithms as well as efficient methods for the approximation of the Hessian matrix. Additionally, procedures for the variation of initial parameters (Design Of Experiments) were implemented. The software includes interfaces to ABAQUS, ANSYS, MSC.MARC, in-house FEM programs and LUA scripts. Within shape optimization problems, geometric shapes are approximated by NURBS and the related control points are employed as design variables. For the update of the FE mesh during the variation of the design variables, a special analytical algorithm is used to preserve the mesh topology. Another focus is related to the further development of existing material parameter identification procedures for rubber materials. Therefor, the concept of component-oriented specimens was developed. Using the example of a bushing, a specimen was designed, which is similar to the original component but has a much simpler geometry. According to this, the behavior of the original component is approximated and the stability of necessary FE simulations is ensured. Additionally, the utilized Model of Rubber Phenomenology (MORPH) is improved in view of the industrial use. It is shown that the identification of material parameters using component-oriented specimens leads to a much better approximation of the original component behaviour than using standard specimens. Additionally, it is shown that the use of a material law which can consider characteritic properties of elastomers, is absolutely necessary.

Les ondes acoustiques et électromagnétiques offrent des méthodes de caractérisation des matériaux très peu invasives. Souvent utilisées à l'aide de capteurs indépendants, l'approche développée ici est de proposer un résonateur multimodal acoustique et électromagnétique. Afin de répondre à une grande variété d'applications, le choix de l'élément actif piézo-électrique s'est porté sur un disque de quartz de coupe AT. L'étude s'articule autour des étapes aboutissant in fine à un capteur magnéto acoustique on-chip à excitation sans contact.L'étude théorique d'un capteur magnéto-acoustique à excitation inductive est tout d'abord réalisée pour un capteur chargé par un fluide visqueux. Ce capteur est constitué de trois éléments : une sonde radiofréquence (RF), un résonateur RF à fort facteur de qualité et le quartz sur lequel ont été déposées deux électrodes en anneau. Cette étude montre comment déduire la viscosité complexe du matériau étudié à partir de l'impédance électrique du système complet. Les mesures effectuées sur des mélanges étalons montrent une très bonne correspondance avec les résultats théoriques.L'intégration du résonateur RF sur l'élément piézo-électrique s'effectuant via des électrodes circulaires, une étude préliminaire est menée sur les ondes acoustiques pouvant être générées sur le quartz et leur interaction avec les électrodes. Les mesures de vibration par vibrométrie laser montrent que des ondes de Lamb sont générées dans une large gamme de fréquence (de 100 kHz à 20 MHz). L'analyse de la réponse impulsionnelle spatiale par transformée de Gabor 3D localise la source de ces ondes sur le bord des électrodes. Par ailleurs, l'étude du disque au fondamental montre une grande non-linéarité mécanique du quartz.Le modèle de résonateur RF plan multi-tour puis son intégration sur le disque de quartz du capteur magnéto-acoustique on-chip sont ensuite étudiés. Les résultats expérimentaux par mesure d'impédance et vibrométrie laser valident le modèle. La gamme de fréquence sélectionnée (entre 5 et 20 MHz) permet d'envisager des mesures micro-rhéologiques. / Acoustic and electromagnetic waves are key probing candidates for characterizing their propagation media with minimum perturbation. Often used with independent sensors based on specialized transducing materials, the approach developed here provides an on-ship multimodal sensor using the same sensing material for probing the acoustic and electromagnetic properties of the material. To meet a wide range of applications, the choice of the active piezoelectric element is carried out on an AT cut quartz. The study focuses on the steps leading in fine to an on-chip magneto-acoustic sensor with a contactless excitation.The theoretical study of a magneto-acoustic sensor inductively excited and loaded by a viscous fluid is first carried out. This sensor consists of three elements: a radio frequency (RF) sensor, a high quality factor RF resonator and a quartz on which two ring electrodes have been deposited. The complex viscosity of the studied material is derived from the electrical impedance of the complete system. The measurements carried on etalon viscoelastic materials show a good agreement with the theoretical results.The integration of the RF resonator on the piezoelectric element being via circular electrodes, a preliminary study is performed for determining the acoustic waves that can be generated in the quartz and their interaction with the electrodes. The laser vibrometry measurements indicate that Lamb waves are generated in a wide frequency range, from 100 kHz to 20 MHz. The analysis of the spatial pulse response of the sensor surface by 3D Gabor transform locates the source of these waves on the edge of the electrodes. Furthermore, the study of the disk at it fundamental frequency points out the high nonlinear mechanical behavior of the quartz.The plane RF multi-turn resonator and its integration on the quartz disk of the magneto-acoustic on-chip sensor are then studied. The experimental results of impedance and laser vibrometry measurements validate the proposed theoretical model. The selected frequency range (between 5 and 20 MHz) allows one to consider micro rheological measurements.

Ce travail se situe à l’intersection des trois disciplines : méthodes numériques, techniques expérimentales et du machine learning, a pour but de proposer une famille de techniques d’identification par analyse inverse des lois de comportement en mécanique. Dans le domaine d’identification des matériaux, l’indentation instrumentée est particulièrement attractive, car elle permet de procéder à des essais non-destructifs sur l’échantillon ou sur une structure en service. L’essai d’indentation, similaire à un test de dureté, consiste à enfoncer la pointe de l’indenteur à une faible profondeur dans la matière tout en enregistrant le déplacement en fonction de la force appliquée. L’identification des propriétés élastoplastiques des matériaux est basée alors sur l’exploitation de la courbe force-déplacement (courbe P-h). Toutefois, le problème inverse est souvent mal posé et des problèmes d’unicité mènent à la notion de paires de "matériaux mystiques" produisant, dans des conditions d’essai donnés, des courbes P-h identiques, malgré des propriétés différentes. L’idée de notre travail est de compléter la procédure d’identification en faisant appel à des dispositifs expérimentaux récents, notamment à la microscopie laser, permettant de mesurer la carte 3D de l’empreinte résiduelle obtenue après le retrait de l’indenteur. Pour aborder la question de la richesse d’information de l’empreinte par rapport à la courbe P-h seule, nous proposons de construire, dans un espace affine réduit, la variété des formes d’empreinte admissibles au sens d’une loi de comportement et du modèle d’éléments finis de l’essai. La mesure de la dimension intrinsèque nous indique alors le nombre maximal de paramètres potentiellement identifiables. Cela nous permet de proposer et de valider numériquement des nouveaux procédés expérimentaux, plus représentatifs, à partir des données synthétiques, ainsi que des algorithmes d’identification associés. La prise en compte de l’erreur de modèle et de l’erreur de mesure, nous mène ensuite à proposer un ensemble d’algorithmes de projection d’empreintes expérimentales, réalisées en collaboration avec l’INSA de Rennes sur la variété synthétique. Nous abordons alors le problème d’identification des propriétés d’écrouissage de plusieurs matériaux de complexité croissante et départageons des "jumeaux mystiques" par des essais de multi-indentation, basés sur l’exploitation de l’empreinte seule ou en complément de la courbe P-h. / The thesis lies at the intersection of three disciplines : numerical methods, experimental techniques, and machine learning. The primary aim of this work is to develop a group of algorithms for characterization by inverse analysis of a material’s constitutive law. In the field of material characterization, indentation test is especially attractive since it is considered non-destructive, and may be performed even on a structure in service. The test, similar to a hardness test, consists in penetrating an indenter into the surface of the material. The force exerted on the indenter is recorded against the penetration depth over a series of time instants, leading to a force-displacement (P-h) curve, which is the most frequently used source of information for the identification of material properties. However, the inverse problem based solely on this curve tends to be ill-posed, leading to nonunique identification solution, i.e., the "mystical material pair", for whom the corresponding force-displacement curves are almost identical despite the very different material properties. The basic idea is then to complete the identification process with innovative experimental measurements, such as laser microscope, which allows measuring the 3D residual imprint after the withdrawal of the indenter. To address the advantage of this measurement over P-h curve, we propose to construct, within a reduced affine space, a manifold of shapes admissible to the postulated constitutive law, experimental and simulation setups, based on synthetic data. The intrinsic dimensionality of the manifold limits the number of identifiable parameters allowing to validate numerically experimental procedures. Considering both the model and measurement errors, we develop a series of local manifold learning algorithms to solve the inverse problem iteratively for experimental results obtained in cooperation with INSA de Rennes. This approach allows us to characterize diverse metallic materials of increasing complexity, based on actual experimental measurements. For example, for the Hollomon’s law, the mystical pair is alleviated in using a single imprint, while for the Voce law, a multi-depth experimental protocol is proposed to differentiate mystical siblings.

Wireless communications have been an indispensable aspect of everyday life, and there is an increasing consumer demand for accessing several wireless communication technologies from a single, compact, mobile device. System-on-package (SOP) technology is an advanced packaging technology that has been proven to realize the convergence of multiple functions into miniaturized, high-performance systems to meet this demand. With the advancements in the SOP technology, the miniaturization of the front-end module has been achieved using embedded passives in multilayer packages. However, the integration of the antenna directly on the module package is still the barrier to achieve a fully-integrated, high-performance RF SOP system. The main reason for this missing link is that integrating the antenna on the package requires miniaturizing the antenna, which is a difficult task. The focus of this dissertation is to design high-performance antennas along with developing techniques for miniaturization and system-on-package (SOP) integration of these antennas to achieve fully-integrated SOP systems using advanced multilayer organic substrates and thin-film magneto-dielectric materials. The targeted spectrum for the antenna designs are 2.4/5 GHz WLAN/WiMAX and 60 GHz WPAN bands. Several novel antenna designs and configurations to integrate the antenna on the package along with the module are discussed in this dissertation. The advanced polymers used in this research are Liquid Crystalline Polymer (LCP), RXP, and thin-film magneto-dielectrics.

The current clinical management of abdominal aortic aneurysm (AAA) disease is based on measuring the aneurysm maximum diameter to decide when timely intervention can be recommended to a patient. However, other parameters may also play a role in causing or predisposing the AAA to either an early or delayed rupture relative to its size. Therefore, patient-specific assessment of rupture risk based on physical principles such as individualized biomechanics can be conducive to the development of a vascular tool with translational potential. To that end, the present doctoral research materialized into a framework for image based patient-specific vascular biomechanics assessment. A robust generalized approach is described herein for image-based volume mesh generation of complex multidomain bifurcated vascular trees with the capability of incorporating regionally varying wall thickness. The developed framework is assessed for geometrical accuracy, mesh quality, and optimal computational performance. The relative influence of the shape and the constitutive wall material property on the AAA wall mechanics was explored. This study resulted in statistically insignificant differences in peak wall stress among 28 AAA geometries of similar maximum diameter (in the 50 – 55 mm range) when modeled with five different hyperelastic isotropic constitutive equations. Relative influence of regionally varying vs. uniform wall thickness distribution on the AAA wall mechanics was also assessed to find statistically significant differences in spatial maxima of wall stresses, strains, and strain energy densities among the same 28 AAA geometries modeled with patient-specific non-uniform wall thickness and two uniform wall thickness assumptions. Finally, the feasibility of estimating in vivo wall strains from individual clinical images was evaluated. Such study resulted in a framework for in vivo 3D strain distributions based on ECG gated, unenhanced, dynamic magnetic resonance images acquired for 20 phases in the cardiac cycle. Future efforts should be focused on further development of the framework for in vivo estimation of regionally varying hyperelastic, anisotropic constitutive material models with active mechanics components and the integration of such framework with an open source finite element solver with the goal of increasing the translational potential of these tools for individualized prediction of AAA rupture risk in the clinic.

A ce jour il n'est toujours pas possible de prédire avec exactitude le phénomène d'érosion par cavitation. La raison principale est qu'il est difficile de caractériser l'agressivité de l'écoulement. Cette thèse propose d'utiliser une méthode inverse pour estimer l'agressivité de l'écoulement à partir de l'observation des cratères (pits) imprimées sur la surface dans les premiers instants de l'érosion de cavitation. Trois matériaux ont été testés dans la veine d'écoulement PREVERO disponible au LEGI de Grenoble dans les mêmes conditions expérimentales. La géométrie des pits laissés sur la surface est précisément mesurée à l'aide d'une méthode systématique permettant de s'affranchir de l'effet de rugosité. Supposant que chaque pit a été généré par une bulle unique dont le champ de pression est assimilé à une forme Gaussienne, des calculs par éléments finis permettent d'estimer le chargement qui a créé l'empreinte résiduelle. On montre que la distribution des chargements suit une loi universelle indépendante du matériau testé; le matériau le plus tendre (alliage d'aluminium) mesurant les plus faibles impacts tandis que le matériau le plus résistant (Acier inoxydable) donne accès aux plus grandes pressions d'impact. On en conclu que le matériau peut être utilisé comme capteur de pression mesurant le niveau d'agressivité de l'écoulement. La méthode inverse repose sur une caractérisation mécanique des matériaux prenant en compte la sensibilité de la contrainte à la vitesse de déformation. On montre que les essais de nanoindentation sont mieux adaptés que les essais de compression pour déterminer les paramètres de la loi de comportement, notamment pour l'alliage d'aluminium pour lequel la microstructure est très hétérogène. Des essais de compression à haute vitesse par barres de Hopkinson complètent la loi de comportement en donnant la sensibilité à la vitesse de déformation. Des simulations prenant en compte la dynamique du chargement montrent que des impacts de fort amplitude mais appliqués sur un temps court ne laissent pas d'empreinte résiduelle si la fréquence est plus élevée que la fréquence naturelle du matériau assimilé à un oscillateur amorti. Un mécanisme d'accumulation dynamique de la déformation plastique pouvant conduire à la rupture par fatigue est proposé. Finalement, la courbe de perte de masse est simulée en appliquant aléatoirement sur un maillage 3D, la population d'impacts estimée par la méthode inverse. / Numerical prediction of cavitation erosion requires the knowledge of flow aggressiveness, both of which have been challenging issues till-date. This thesis proposes to use an inverse method to estimate the aggressiveness of the flow from the observation of the pits printed on the surface in the first moments of the cavitation erosion. Three materials were tested in the same experimental conditions in the cavitation tunnel PREVERO available LEGI Grenoble. The geometry of the pits left on the surface is precisely measured using a systematic method to overcome the roughness effect. Assuming that each pit was generated by a single bubble collapse whose pressure field is treated as a Gaussian shape, finite element calculations are run for estimating the load that created each residual imprint. It is shown that the load distribution falls on a master curve independent of the tested material; the softer material (aluminum alloy) measuring the lowest impacts while the most resistant material (duplex stainless steel) provides access to the largest impact pressures. It is concluded that the material can be used as a pressure sensor measuring the level of aggressiveness of the flow. The inverse method is based on a material characterization taking into account strain rate effects. It is shown that nanoindentation tests are more suitable than compression tests to determine the parameters of the behavior law, particularly for the aluminum alloy for which the microstructure is very heterogeneous. High-speed compression tests with split Hopkinson pressure bars complement the constitutive law giving the sensitivity to the strain rate. Simulations considering the dynamic loading show that impacts of strong amplitude but applied in a short time do not leave any residual pit if the frequency is higher than the natural frequency of the material treated as a damped oscillator. A dynamic mechanism of plastic strain accumulation that could eventually lead to fatigue failure is proposed. Finally, the mass loss curve of cavitation erosion is simulated by applying randomly on a 3D mesh, the impact force population estimated by the inverse method.

Key factors that influence the design of paved and unpaved roads are the strength and stiffness of the pavement layers. Among other factors, the strength of pavements depends on the thickness and quality of the aggregates used in the pavement base layer. In India and many other countries, there is a high demand for good quality aggregates and the availability of aggregate resources is limited. There is a need for the development of sustainable construction methods which can handle aggregate requirements with least available resources and provide good performance. Hence it is imperative to strive for alternatives to achieve improved quality of pavements using supplementary potential materials and methods. The strength of pavement increases with increase in the thickness of the base which has a direct implication on construction cost whereas decreasing the thickness of the base makes it weak which results in low load bearing capacity especially for unpaved roads. The use of different types of geosynthetics like geocell and geogrid are a potential and reliable solution for the lack of availability of aggregates and studies are conducted in this direction. To better understand the performance of any geosynthetically reinforced base layers, it is essential to characterize the pavement material by studying the behavior of these materials under static as well as repeated loading. For unpaved roads, the base layer, made of granular aggregates plays a crucial role in the reduction of permanent deformation of the pavements. The resilient modulus (Mr) of these materials is a key parameter for predicting the structural response of pavements and for characterizing materials in pavement design and evaluation. Usually, during the design of flexible pavements, pavement materials are treated as homogeneous and isotropic. The use of rollers in the field during pavement construction leads to a higher compaction of material in the vertical direction which introduces stress-induced anisotropy in the base material. The effect of stress-induced anisotropy on the properties of the granular material is studied and discussed in the first part of the research by conducting repeated load triaxial tests. Isotropic consolidated and anisotropically consolidated samples were prepared to investigate the behavior of base materials under stress induced anisotropic conditions. An additional axial load was applied on the isotropically consolidated sample to create anisotropically consolidated sample. The axial loading was provided such that the stress ratio (σ1/σ3), during anisotropic consolidation was kept constant for all the tests at different confining pressures. The effect of repeated loading on the permanent deformation and the resilient modulus for both isotropically and anisotropically consolidated samples, at different confining pressure and loading conditions, are discussed. The behavior of both anisotropically and isotropically consolidated samples has been explained using the record of the excess pore pressures generated during the experiments. The experimental studies show that the permanent strains measured in the vertical direction of the anisotropically consolidated samples are less compared to the results obtained for isotropically consolidated samples. The resilient moduli of the anisotropically consolidated samples were also observed to be higher than that of the isotropically consolidated sample. The study conducted on the pore pressure of both the samples explains better performance of the anisotropically consolidated samples. The studies showed that the isotropically consolidated samples showed higher pore pressures compared to the anisotropically consolidated specimens. Another factor which influences the resilient modulus of the pavement materials is the geosynthetic reinforcement. Geocell and geogrid reinforced triaxial samples were prepared to study the effect of reinforcement in the resilient modulus of the base materials. From the literature, it can be seen that most of the research in the triaxial testing equipment were carried out in the non-destructive range of confining pressure and deviatoric stress. Several studies have been conducted by the researchers to visualize the pavement response in the elastic range. However, the studies in the plastic creep range and incremental collapse range were highly limited. In the current study, testing is carried out on the triaxial samples for two different stress ranges. In the first sections, loading was applied in the elastic and elastic shakedown range as per AASTHO T-307. For various loading sequences, a comparative analysis has been done for the resilient modulus of the geogrid and geocell. In the next section, the loading was applied on the sample in the plastic shakedown range and incremental collapse range. The results of the permanent strains and resilient modulus of the sections are compared with the corresponding results of the unreinforced section. In the plastic shakedown and incremental collapse range also the permanent strains of reinforced samples were less than those observed in the unreinforced section. The performance of geosynthetically reinforced pavement layers can be better understood by studying the samples prepared under realistic field conditions. In the case of triaxial experiments the sample size is very less compared to the field conditions and the effect of other pavement layers on the performance of the base layers cannot be studied on triaxial samples. Samples were prepared in the laboratory by modeling the pavement sections in a cuboidal tank, in which different pavement layers are laid one over the other, and a static loading or repeated loading is applied to overcome the bottleneck of small sample size in the triaxial setup. The experiments were conducted on the unreinforced section; geocell reinforced section and geogrid reinforced section placed above strong and weak subgrade. The results of the study are examined regarding the resilient deformation, permanent deformation, pressure distribution and strain measurements for different thicknesses of base layers under repeated loading. The initial parts of the study present the results of experiments and analysis of the results to understand the behavior of geocell reinforced granular base during repeated loading. In this study, an attempt is made to understand the various factors which influence the behavior of geocell reinforced granular base under repeated loading by conducting plate load tests. The loads applied on the pavements are much higher than the standard axle loading used for the design of pavements. High pressure was applied on all the test sections to simulate these higher loading conditions in the field. The optimum width and height of the geocell to be provided, to get maximum reduction in permanent deformation is studied in detail. The effect of resilient deformation of reinforced and unreinforced base layers is quantified by calculating the resilient modulus of these layers. The studies showed that the geocell reinforcement was effective in reducing the permanent and resilient deformations of base layer when compared to the unreinforced samples. The resilient modulus calculated was higher for the reinforced sample with half of the thickness of the unreinforced sample. The effect of reinforcement in the stress distribution within the base layer is also studied by measuring the pressures at different depths of the base layer. The results showed that the pressure getting transferred to the subgrade level was much lower in the case of geocell reinforced base layer. The ultimate aim of any pavement design method is to reduce the distress in the subgrade level and thus leading to increased life of pavements. Pressures at the subgrade level for reinforced and unreinforced sections are studied in detail, the main parameter under study being the stress distribution angle, to investigate the distress in the subgrade level. It was observed that the geocell reinforced sample showed higher stress distribution angle when compared to its unreinforced counterpart. Another important factor that has to be studied is the strains at the subgrade level since it is the governing factor of causing rutting in the pavements. From the experiments conducted in the study, it was shown that the reinforcement is very effective in reducing the strains at the top of subgrades. The implications of the current study are brought out in terms of improved pavement performance as the carbon emission reductions. It is important to analyze the performance of reinforced section under realistic field conditions. To do that experiment were conducted on reinforced and unreinforced base layers placed on top of weak subgrade material. The study showed that the reinforcements are effective in reducing the deformations under weak subgrade conditions also but not as effective as it was under strong subgrade case. The experimental results were then validated with the two-dimensional mechanistic-empirical model for geocell reinforced unpaved roads for predicting the performance of pavements under a significant number of cycles. The modified permanent deformation model which incorporates the triaxial test results and strains measured directly from the base sections were used to model and validate. Plate load experiments were also conducted on base layers reinforced with geogrid to understand the behavior of these reinforced samples under repeated loading. Several factors like the width of the geogrid to be provided and the depth of placing the geogrid in the base layer were studied in detail to achieve maximum reduction in deformations. Permanent and resilient deformation studies were carried out for both reinforced and unreinforced sections of varying thicknesses, and a comparison was made to understand the effect of reinforcement. The geogrid reinforcement could effectively reduce the permanent and resilient deformations when compared to the unreinforced sections. A study was also carried out on the resilient modulus, which explained the better performance of the geogrid reinforced samples by showing higher resilient modulus for reinforced samples than the unreinforced specimens. The performance of the geogrid reinforced base layers was further verified by studying the pressure distribution at the subgrade level and by calculating the stress distribution angle corresponding to the reinforced and unreinforced samples. The strains at the subgrade level were also studied and compared with the unreinforced sample which showed a better performance of geogrid reinforced samples. The results from the strain gauges fixed in the geogrid were further used to model and validate the permanent deformation model. Experiments were conducted on geogrid-reinforced base layer placed above weak subgrade conditions. The results showed that the reinforcement was effective in reducing the deformations under weak subgrade conditions also. Apart from conducting the laboratory studies, experimental results were numerically modeled to accurately back-calculate the resilient moduli of the layers used in the study. 3D numerical modeling of the unreinforced and honeycomb shaped geocell reinforced layers were carried out using finite element package of ANSYS. The subgrade layer, geocell material, and infill material were modeled with different material models to match the real case scenario. The modeling was done for both static and repeated load conditions. The material properties were changed in a systematic fashion until the vertical deformations of the loading plate matched with the corresponding values measured during the experiment. The experimental study indicates that the geocell reinforcement distributes the load in the lateral direction to a relatively shallow depth when compared to the unreinforced section. Numerical modeling further strengthened the results of the experimental studies since the modeling results were in sync with the experimental data.

A compositionally graded Ti-xCr (10≤x≤30 wt%) alloy has been fabricated using Laser Engineered Net Shaping (LENSTM) to study the microstructural phase evolution along a compositional gradient in both as-deposited and heat treated conditions (1000°C followed by furnace cooling or air cooling). The alloys were characterized by SEM BSE imaging, XRD, EBSD, TEM and micro-hardness measurements to determine processing-structure-property relations. For the as-deposited alloy, α-Ti, β-Ti, and TiCr2 (C15 Laves) phases exist in varying phase fractions, which were influential in determining hardness values. With the furnace cooled alloy, there was more homogeneous nucleation of α phase throughout the sample with a larger phase fraction of TiCr2 resulting in increased hardness values. When compared to the air cooled alloy, there was absence of wide scale nucleation of α phase and formation of ω phase within the β phase due to the quicker cooling from elevated temperature. At lower concentrations of Cr, the kinetics resulted in a diffusionless phase transformation of ω phase with increased hardness and a lower phase fraction of TiCr2. In contrast at higher Cr concentrations, α phase separation reaction occurs where the β phase is spinodally decomposed to Cr solute-lean β1 and solute-rich β2 resulting in reduced hardness.

No description available.