The main objective of the thesis is to assess the damage resistance and damage tolerance of the non-conventional dispersed laminates and compare the response with the conventional ones. However, part of the effort is spent on understanding the delamination behavior in multidirectional laminates. In the first part of the thesis, the delamination in multidirectional laminates is studied. The objective is to design a proper stacking sequence, capable of avoiding intralaminar damage (crack jumping), to enable the fracture toughness characterization under pure mode I. The result of this study shows that the higher the crack arm bending stiffness, the lower the tendency to crack jumping. This phenomenon is also studied experimentally and the same conclusion is drawn. / El principal objectiu de la tesi és valorar la resistència al dany i la tolerància al dany dels laminats no-convencionals dispersos i comparar la seva resposta amb la dels laminats convencionals. No obstant, part de l'atenció es dedica a comprendre el comportament de la delaminació en laminats multidireccionals. En la primera part de la tesi, s'analitza la delaminació en laminats multidireccionals. L'objectiu és dissenyar una seqüència d'apilament apropiada per evitar el dany intralaminar (migració de la delaminació) i permetre la caracterització de la tenacitat a la fractura en model. Els resultats d'aquests estudi mostren que a major rigidesa a flexió dels braços de l'esquerda, menor és la tendència a la migració de l'esquerda. Aquest aspecte també s'ha analitzat experimentalment, obtenint les mateixes conclusions.

The dynamical underpinnings of complex computation and information transmission within the brain, while of great interest to the neuroscience community at large, remain poorly understood. One of the striking manifestations of neuronal population activity is that of rhythmic oscillations in the local field potential. It is thought that distinct patterns of these oscillations such as cross-frequency coupling within a given spatial location and coherence between disparate brain regions may represent neuronal computation and communication, respectively. Here we show such dynamics within a human temporal neocortical in vitro model. In specific, we show theta-gamma cross frequency coupling in deep and superficial layers, phase coherence between layers at theta frequencies, and a measure of communication (phase dependent power correlations) between layers at theta frequency. Additionally, we show a novel correlation between communication across layers and cross frequency coupling within layers, demonstrating a dynamic link between local computation and intralaminar communication.

Cette thèse résulte d’une collaboration entre le Pr Ayadi de l’Institut National Polytechnique de Lorraine et le Pr Varna de l’Université Technologique de Luleå. Depuis 2005, le Professeur Varna a développé une méthode originale qui permet d’obtenir l’ensemble des constantes thermoélastiques d’un stratifié endommagé à partir de deux paramètres : l’ouverture moyenne et le glissement moyen des lèvres des fissures, normalisés par rapport à la contrainte appliquée. Dans cette thèse, nous analysons le potentiel de l’interférométrie de speckle pour obtenir la mesure de ces deux grandeurs. Plus généralement, nous montrons l’utilité de la mesure du champ de déplacement pour caractériser le développement de l’endommagement dans les stratifiés. Le premier chapitre décrit l’endommagement qui peut affecter les matériaux composites stratifiés. L’objectif est de mettre en évidence les points particuliers pour lesquels la mesure du champ de déplacement pourrait apporter des informations originales. Dans le deuxième chapitre, le principe de l’interférométrie de speckle est exposé. Nous avons particulièrement insisté sur les raisons qui nous on conduit à choisir cette technique pour réaliser cette étude. Dans le troisième chapitre, nous présentons une étude expérimentale du potentiel de l’interférométrie de speckle pour caractériser les différentes formes d’endommagement qui peuvent apparaître dans un stratifié verre/époxyde . Enfin, dans le dernier chapitre, nous analysons expérimentalement le développement de l’endommagement dans un stratifié carbone/époxyde / This work results from a collaboration between Pr Ayadi (Institut Polytechnique de Lorraine) and Pr Varna (Technical University of Luleå). Since 2005, Pr Varna has developed an original method that allows for the determination of all the thermoelastic constants of a damaged laminate. The stiffness reduction is governed by two parameters: the average value of the opening and the average value of the sliding of the crack surfaces. These values are normalized with respect to the applied loading. In this work, the potential of speckle interferometry is analysed to obtain these two parameters. More generally, we show the usefulness of displacement field measurements to characterize damage development in laminates. The first chapter is dedicated to the damage that occurs in laminates. The main objective is to highlight the points for which displacement field measurements could bring interesting information. In the second chapter, the principle of speckle interferometry is described. The choice of this technique for the considered application is discussed and justified. In the third chapter, an experimental study of the potential of speckle interferometry is proposed to characterize the damage forms that occur in a glass/epoxy laminate. In the last chapter, the development of damage is experimentally analysed in a carbon/epoxy laminate

The dynamical underpinnings of complex computation and information transmission within the brain, while of great interest to the neuroscience community at large, remain poorly understood. One of the striking manifestations of neuronal population activity is that of rhythmic oscillations in the local field potential. It is thought that distinct patterns of these oscillations such as cross-frequency coupling within a given spatial location and coherence between disparate brain regions may represent neuronal computation and communication, respectively. Here we show such dynamics within a human temporal neocortical in vitro model. In specific, we show theta-gamma cross frequency coupling in deep and superficial layers, phase coherence between layers at theta frequencies, and a measure of communication (phase dependent power correlations) between layers at theta frequency. Additionally, we show a novel correlation between communication across layers and cross frequency coupling within layers, demonstrating a dynamic link between local computation and intralaminar communication.

Validerat; 20140915 (global_studentproject_submitter)

Les composites stratifiés de plis unidirectionnels en carbone/époxy sont fortement utilisés pour alléger les structures aéronautiques tout en conservant de bonnes propriétés structurales. Toutefois, les avantages de ce type de matériau ne sont pas encore pleinement exploités de par le manque de confiance accordée aux modèles de prévision de l’endommagement, dont notamment ceux concernant le délaminage. C’est pourquoi l’objectif de cette thèse était de développer une stratégie de modélisation du délaminage adaptée aux structures composites stratifiées. Cette stratégie s’est appuyée sur le développement d’un modèle de zone cohésive prenant en compte les ingrédients nécessaires à la bonne description de l’amorçage et de la propagation de la fissure : (i) un critère d’amorçage avec un renforcement en compression/cisaillement hors-plan, (ii) une loi de propagation décrivant l’évolution de la ténacité en fonction de la mixité de mode et (iii) la prise en compte du couplage inter/intralaminaire. Pour identifier ce nouveau modèle, une procédure d’identification efficace, s’appuyant sur un essai de traction sur plaque rainurée, a été mise en place. Cette procédure d’identification a permis de démontrer que la ténacité semble indépendante (i) de l’orientation des plis adjacents à l’interface et (ii) de l’empilement étudié. De même, pour décrire l’évolution de la ténacité, une nouvelle loi de propagation adaptée au matériau carbone/époxy a été proposée. Pour finir, la stratégie de modélisation, complétée par une stratégie de calcul, a été appliquée sur différents cas structuraux pour mettre en avant ses apports et ses premières limites. / The carbon/epoxy laminated composites of unidirectional plies are strongly used in order to reduce the weight of aeronautical structures while at the same time proposing good structural properties. However, the advantages of this kind of material are not fully exploited due to the lack of confidence in damage models, like ones concerning delamination. Then, the purpose of this work was the development of a strategy to model delamination in laminated composite structures. This strategy was based on the development of a cohesive zone model taking into account the ingredients necessary to the well description of the onset of delamination and the crack growth: (i) an onset criterion with an out-of-plan compression/shearing reinforcement, (ii) a propagation law describing the evolution of the fracture toughness as a function of mixed mode ratio and (iii) the inter/intralaminar coupling. To identify this new model, an efficient identification procedure, basing on a tensile test on notched specimen, has been proposed. This identification procedure has demonstrated that the fracture toughness seems to be independent of (i) the orientation of plies closed to the interface and (ii) the stacking sequence. Furthermore, to describe the evolution of the fracture toughness, a new propagation law adapted to carbon/epoxy material has been proposed. Finally, the strategy to model delamination, completed by a calculation strategy, has been applied on several structural cases to prove its contributions and its first limitations.

Made available in DSpace on 2014-12-17T15:37:15Z (GMT). No. of bitstreams: 1 AlaneMS_DISSERT1red.pdf: 4031089 bytes, checksum: da896508e54d2cd0138d081ad42b95de (MD5) Previous issue date: 2013-03-27 / Funda??o de Apoio ? Pesquisa do Estado do Rio Grande do Norte / The midline/intralaminar nuclei form a remarkable group of nuclei of the medial and dorsal thalamus. The midline nuclei, in rats, comprises the paratenial nuclei (PT), paraventricular (PV), intermediodorsal (IMD), reuniens (Re) and rhomboid (Rh). The intralaminar nuclei comprises the central medial (CM), paracentral (PC), central lateral (CL) and parafascicular (PF). Such nuclei have dense serotonergic innervation originating from the brainstem, especially from the so-called ascending activation system. These nuclei, in turn, send projections to various cortical and subcortical areas, specifically to limbic areas, which suggests the important role of this neurotransmitter in the limbic circuitry. The aim of this study was to characterize the distribution pattern and morphology of serotonin fibers in the nuclei of the midline and intralaminar thalamic of rocky cavy (Kerodon rupestris), a tipical rodent from brazilizan northeast. To reach this aim we used four rock cavies adults. Following the transcardially perfusion with paraformaldehyde and brain microtomy steps was performed immunohistochemistry for serotonin (5-HT), Nissl technique and subsequent achievement and image analysis to characterize the cytoarchitecture of these nuclei and the serotonergic fibers visualized. An analysis was made of Relative Optical Density (ROD) to semi-quantify the concentration of serotonin fibers in the areas of interest. Thus, we observed a cytoarchitectonic arrangement of these nuclei similar to that found in rats. In case of fibers distribution, those immunoreactive to 5-HT were presented in a higher concentration according as ROD in the midline nuclei relative to intralaminar; Re being the core which has a higher pixel value followed by the PV , Rh, IMD and PT. In intralaminar CL showed higher pixels, followed by nuclei CM, PC and PF. The serotonergic fibers were classified as number of varicosities and axon diameter, therefore find three types of fibers distributed through this nuclear complex: fibers rugous, granular and semi-granular. In PV fibers predominated rugous; in PT fibers predominated granular; IMD, CL and PF fibers were represented by semi-granular and Re, Rh, PC and CM fibers showed granular and semi-granular. Morphological characterization of serotonergic fibers and differences in density between the nuclei may suggest different patterns of synaptic organization of this neurotransmitter beyond confirming his large repertoire functional / O complexo nuclear da linha m?dia/intralaminar forma um not?vel grupo de n?cleos da parte medial e dorsal do t?lamo. Os n?cleos da linha m?dia, em ratos, s?o compreendidos pelos n?cleos paratenial (PT), paraventricular (PV), intermediodorsal (IMD), reuniens (Re) e romb?ide (Rh). J? os intralaminares compreendem os n?cleos central medial (CM), paracentral (PC), central lateral (CL) e parafascicular (PF). Tais n?cleos apresentam densa inerva??o seroton?rgica oriunda do tronco encef?lico, a partir, principalmente, do denominado sistema de ativa??o ascendente. Esses n?cleos, por sua vez, emitem proje??es para diversas ?reas corticais e subcorticais, mais especificamente para ?reas l?mbicas, o que prop?e o importante papel desse neurotransmissor na circuitaria l?mbica. O objetivo desse trabalho foi caracterizar o padr?o de distribui??o e morfologia das fibras de seroton?rgicas nos n?cleos da linha m?dia e intralaminares do t?lamo do moc? (Kerodon rupestris), um roedor t?pico da regi?o Nordeste. Para isso, foram utilizados 4 moc?s adultos jovens. Ap?s etapas de perfus?o e microtomia, foi realizada imunoistoqu?mica para serotonina (5-HT), t?cnica de Nissl e posterior coleta e an?lise de imagens a fim de caracterizar a citoarquitetura desses n?cleos, bem como as fibras de 5-HT neles visualizadas. Foi realizada ainda uma an?lise de Densidade ?ptica Relativa (DOR) para semiquantificar a concentra??o de fibras de 5-HT nas ?reas de interesse. Sendo assim, observamos uma distribui??o citoarquitet?nica desses n?cleos semelhante ao observado em ratos. Em se tratando da distribui??o de fibras, aquelas imunorreativas a 5-HT apresentaram-se em maior concentra??o, conforme a DOR, nos n?cleos da linha m?dia em rela??o aos intralaminares, sendo o Re o n?cleo que apresenta maior valor de pixels, seguido do PV, Rh, IMD e PT. Nos intralaminares o CL apresentou maior valor de pixels, seguido dos n?cleos CM, PC e PF. As fibras seroton?rgicas foram classificadas conforme n?mero de varicosidades, bem como di?metro axonal. Assim, encontramos tr?s tipos de fibras distribu?das atrav?s desse complexo nuclear: fibras rugosas, granulares e semi-granulares. No PV predominaram fibras rugosas; PT predominaram fibras granulares; IMD, CL e PF foram representados por fibras semi-granulares e Re, Rh, PC e CM apresentaram fibras granulares e semi-granulares. A caracteriza??o morfol?gica das fibras seroton?rgicas encontradas e as diferen?as de densidades entre os n?cleos permite sugerir diferentes padr?es de organiza??o sin?ptica deste neurotransmissor al?m de confirmar seu grande repert?rio funcional