Due to traumatic brain injury (TBI), numerous studies have focused on comprehensively determining the mechanical properties of the brain. This study examined the strain rate dependence of porcine brain under compression, and the microstructural damage was quantified using a confocal microscope and graphical user interface (GUI). The selected strain rates were 0.10 s-1, 0.025 s-1, and 0.00625 s-1 while the strain levels targeted for confocal imaging were 15%, 30%, and 40%. This study also characterized the stress-state dependence at a strain rate and strain level of 0.10 s-1 and 40%, respectively, under compression, tension, and shear. Strain rate dependency data exhibited viscoelastic behavior, and the analysis parameters correlated with increasing strain rate and strain level. Stress-state dependency data demonstrated distinct nonlinear behavior, and disparities were observed in the analysis parameters between different testing modes. Finite element procedures can implement this supplementary data for devising more realistic models.

Studien hade till syfte att adaptera och validera den multidimensionella stressenkäten Dundee Stress State Questionnaire (DSSQ) som mäter stress utifrån 12 skalor som sammanfaller kring tre högre dimensioner: uppgiftsfokus, ångest och oro. DSSQ adapteras från originalspråket, engelska, till svenska. Tillämpbarheten för den svenska versionen av DSSQ undersöks genom att studera enkätens reliabilitet och validitet samt genom att tillämpa enkäten i två olika kontext, där två olika typer av uppgifter genomförs, ett arbetsminnestest och en polisstudentövning. Sammantaget visade resultatet att den svenska adaptionen av DSSQ har en hög reliabilitet. Dock gick det inte att bekräfta att den svenska adaptionen av DSSQ bibehåller samma faktormodell som originalversionen av DSSQ. Den statistiska analysen visade att de förändringar som identifierats i deltagarnas sinnesstämning delvis stämmer överens med tidigare forskning. Slutsatsen är att fler deltagare behövs för att validera faktormodellen hos den svenska adaptionen av DSSQ och den svenska adaptionen av DSSQ anses vara tillämpar i forskning då den visar på god reliabilitet. / The purpose of this study was to adapt and validate the Dundee Stress State Questionnaire (DSSQ), which measures stress based on 12 scales that cohere around three higher order dimensions: task engagement, distress and worry. DSSQ is adapted from its original language, English, to Swedish. The applicability of the Swedish version of DSSQ is tested by studying the questionnaire's reliability and validity, and by applying the survey in two different contexts, where two different tasks are performed, a work memory task and a police student exam task. Overall, the result showed that the Swedish adaptation of DSSQ has high reliability. However, it was not possible to confirm that the Swedish adaptation of DSSQ maintained the same factor model as the original DSSQ has. The statistical analysis showed the changes identified in the participants' moods partly in lines with previous research. The conclusion is that more participants are needed to validate the factor model for the Swedish adaptation of DSSQ and since the Swedish adaptation of DSSQ shows good reliability, it can be applied in research.

O estudo em laboratório do desempenho mecânico de solos artificialmente cimentados está normalmente vinculado à simulação do comportamento de geomateriais naturalmente formados em campo. Por outro lado, o estudo desses novos materiais pode ser também ferramenta útil na previsão do comportamento de aterros de solos artificialmente melhorados. O comportamento de solos cimentados possui considerável influência da densidade e do estado de tensões a que estes materiais estão submetidos durante a fase que compreende a cimentação dessas partículas. Uma alternativa ao estudo da cimentação nestes solos, é a elaboração de um meio em que as amostras possam ser cimentadas sob um estado de tensões específico, e que ao mesmo tempo em que se promove uma redução do índice de vazios do respectivo material. Seguindo nessa analogia, o presente estudo visa apresentar resultados de ensaios triaxiais realizados em amostras de um solo artificialmente cimentado, curadas sob diferentes níveis de tensão e estado de tensões. São abordados os resultados do ponto de vista da rigidez e deformabilidade encontrados para o material. Os resultados demonstraram que a alteração dos estados de tensões de cura, bem como a magnitude das tensões confinantes durante a cura, apresentaram influência no comportamento tensão-deformação-dilatância das amostras artificialmente cimentadas. / The laboratory study of mechanical performance of artificially cemented soils is normally associated with the mechanical behaviour of geomaterials that were created in field. The behaviour of artificially cemented soils has substantial influence of density and the stress state that these materials have been submitted during the particles cementation. Thus, an alternative to the understanding of cement effects in these soils is the preparation of a similar environment where the specimens can be submitted the cementation while a specific stress state is applied, promoting the respective void ratio reduction. Following this approach, this study aims to show the results of triaxial tests carried out in an artificially cemented soil, which was cured at different stress states. The results have shown that the changing of stress state of curing, as well as the intensity of the confining stress during the cure, presented considerably influence in the stress-strain-dilatancy of the artificially cemented samples.

O estudo em laboratório do desempenho mecânico de solos artificialmente cimentados está normalmente vinculado à simulação do comportamento de geomateriais naturalmente formados em campo. Por outro lado, o estudo desses novos materiais pode ser também ferramenta útil na previsão do comportamento de aterros de solos artificialmente melhorados. O comportamento de solos cimentados possui considerável influência da densidade e do estado de tensões a que estes materiais estão submetidos durante a fase que compreende a cimentação dessas partículas. Uma alternativa ao estudo da cimentação nestes solos, é a elaboração de um meio em que as amostras possam ser cimentadas sob um estado de tensões específico, e que ao mesmo tempo em que se promove uma redução do índice de vazios do respectivo material. Seguindo nessa analogia, o presente estudo visa apresentar resultados de ensaios triaxiais realizados em amostras de um solo artificialmente cimentado, curadas sob diferentes níveis de tensão e estado de tensões. São abordados os resultados do ponto de vista da rigidez e deformabilidade encontrados para o material. Os resultados demonstraram que a alteração dos estados de tensões de cura, bem como a magnitude das tensões confinantes durante a cura, apresentaram influência no comportamento tensão-deformação-dilatância das amostras artificialmente cimentadas. / The laboratory study of mechanical performance of artificially cemented soils is normally associated with the mechanical behaviour of geomaterials that were created in field. The behaviour of artificially cemented soils has substantial influence of density and the stress state that these materials have been submitted during the particles cementation. Thus, an alternative to the understanding of cement effects in these soils is the preparation of a similar environment where the specimens can be submitted the cementation while a specific stress state is applied, promoting the respective void ratio reduction. Following this approach, this study aims to show the results of triaxial tests carried out in an artificially cemented soil, which was cured at different stress states. The results have shown that the changing of stress state of curing, as well as the intensity of the confining stress during the cure, presented considerably influence in the stress-strain-dilatancy of the artificially cemented samples.

O estudo em laboratório do desempenho mecânico de solos artificialmente cimentados está normalmente vinculado à simulação do comportamento de geomateriais naturalmente formados em campo. Por outro lado, o estudo desses novos materiais pode ser também ferramenta útil na previsão do comportamento de aterros de solos artificialmente melhorados. O comportamento de solos cimentados possui considerável influência da densidade e do estado de tensões a que estes materiais estão submetidos durante a fase que compreende a cimentação dessas partículas. Uma alternativa ao estudo da cimentação nestes solos, é a elaboração de um meio em que as amostras possam ser cimentadas sob um estado de tensões específico, e que ao mesmo tempo em que se promove uma redução do índice de vazios do respectivo material. Seguindo nessa analogia, o presente estudo visa apresentar resultados de ensaios triaxiais realizados em amostras de um solo artificialmente cimentado, curadas sob diferentes níveis de tensão e estado de tensões. São abordados os resultados do ponto de vista da rigidez e deformabilidade encontrados para o material. Os resultados demonstraram que a alteração dos estados de tensões de cura, bem como a magnitude das tensões confinantes durante a cura, apresentaram influência no comportamento tensão-deformação-dilatância das amostras artificialmente cimentadas. / The laboratory study of mechanical performance of artificially cemented soils is normally associated with the mechanical behaviour of geomaterials that were created in field. The behaviour of artificially cemented soils has substantial influence of density and the stress state that these materials have been submitted during the particles cementation. Thus, an alternative to the understanding of cement effects in these soils is the preparation of a similar environment where the specimens can be submitted the cementation while a specific stress state is applied, promoting the respective void ratio reduction. Following this approach, this study aims to show the results of triaxial tests carried out in an artificially cemented soil, which was cured at different stress states. The results have shown that the changing of stress state of curing, as well as the intensity of the confining stress during the cure, presented considerably influence in the stress-strain-dilatancy of the artificially cemented samples.

Les problématiques de corrosion restent un sujet d'étude majeur lorsqu'il s'agit d'améliorer les propriétés des alliages pour structures aéronautiques. Dans le cadre de ce travail, le comportement en corrosion d'un alliage AW2050 de type Al-Cu-Li-X est étudié. L'analyse du couplage entre les microstructures caractéristiques de cet alliage et l'environnement agressif constitue un point central de l'étude. Le travail réalisé a permis d'identifier les facteurs de premier ordre parmi les paramètres métallurgiques et les paramètres chimiques relatifs à l'électrolyte sur le comportement en corrosion de l'alliage AW2050. Ensuite, l'impact de l'application de contraintes monotones et cycliques sur le comportement en corrosion du matériau a été étudié. Les principaux résultats montrent que la microstructure de l'alliage a un effet prépondérant sur le comportement en corrosion du matériau par rapport aux sollicitations mécaniques et aux conditions d'exposition au milieu agressif, même si des couplages existent entre microstructure, chargement mécanique et environnement. L'étude réalisée a permis de générer des avancées significatives dans la compréhension des mécanismes de corrosion, de corrosion sous contrainte et de fatigue corrosion de l'alliage AW2050. / Corrosion issues still are a major subject of study to improve alloys properties for aircraft structures. In the framework of this work, the corrosion behavior of an Al-Cu-Li-X AW2050 alloy is studied. This study is focussed on the coupling between the microstructures of the alloy and the aggressive environment. The present work allowed to determine, among metallurgical parameters and chemical parameters related to the electrolyte, the factors of the first order on the corrosion behavior of AW2050 alloy. Afterwards, the impact of monotonic and cyclic stresses on the material corrosion behavior was studied. The main results show that the alloy microstructure has a prevailing effect on its corrosion behavior compared to mechanical stresses and exposure conditions to the aggressive media, even though, coupling exist between microstructure, mechanical stresses and environment. The study led to significant advances in the understanding of the following mechanisms: corrosion, stress corrosion cracking and fatigue-corrosion of an alloy AW2050.

<p>Predmet&nbsp; istraživanja&nbsp; u&nbsp; ovom&nbsp; radu&nbsp; je&nbsp; eksperimentalno&nbsp; &ndash;&nbsp; teorijsko&nbsp; modelska analiza ponašanja centrično pritisnutih stubova spregnutog&nbsp; preseka.&nbsp; Modeli&nbsp; su&nbsp; formirani&nbsp; od&nbsp; AB&nbsp; stubova&nbsp; kvadratnog&nbsp; poprečnog&nbsp; preseka&nbsp; ojačanih&nbsp; na&nbsp; tri&nbsp; načina.&nbsp; U&nbsp; prvom&nbsp; slučaju&nbsp; upotrebljene su čelične cevi.&nbsp; AB stubovi su postavljeni unutar&nbsp; cevi dok je međuprostor popunjavan&nbsp; etonskim mešavinama tri različita&nbsp; kvaliteta.&nbsp; Druga&nbsp; metoda&nbsp; ojačavanja&nbsp; obuhvatala&nbsp; je&nbsp; izradu&nbsp; omotača&nbsp; od&nbsp; betona&nbsp; i&nbsp; čeličnih&nbsp; ugaonika&nbsp; međusobno&nbsp; mestimično&nbsp; spojenih&nbsp; veznim limovima čime je&nbsp; formiran &quot;kavez&quot; oko AB stuba. Razmak&nbsp; veznih&nbsp; limova&nbsp; variran&nbsp; je&nbsp; u&nbsp; dva&nbsp; slučaja.&nbsp; Treća&nbsp; metoda&nbsp; ojačavanja&nbsp; obuhvatala&nbsp; je&nbsp; pritezanje&nbsp; poprečno&nbsp; postavljenih&nbsp; visokovrednih&nbsp; zavrtnjeva. Variran je broj zavrtnjeva, odnosno njihov međusobni&nbsp; razmak.&nbsp; Numerička&nbsp; analiza&nbsp; ponašanja&nbsp; stubova&nbsp; izvršena&nbsp; je&nbsp; MKE&nbsp; metodom.&nbsp; Izvršeno&nbsp; je&nbsp; poređenje&nbsp; rezultata&nbsp; računskog&nbsp; modela&nbsp; i&nbsp; rezultata eksperimentalnog ispitivanja i dat je predlog za&nbsp; proračun nosivosti preseka/modela za sve analizirane uzorke.</p> / <p>The topic of research in this dissertation is experimental-theoretical&nbsp; model&nbsp; analysis&nbsp; of&nbsp; behavior&nbsp; of&nbsp; axially&nbsp; compressed&nbsp; composite&nbsp; section&nbsp; columns.&nbsp; Models&nbsp; are&nbsp; formed&nbsp; from&nbsp; RC&nbsp; squared&nbsp; cross&nbsp; section columns strengthened in three ways. In first case steel pipes&nbsp; were&nbsp; used.&nbsp; RC&nbsp; columns&nbsp; were&nbsp; placed&nbsp; inside&nbsp; the&nbsp; pipe&nbsp; while&nbsp; free&nbsp; space&nbsp; was&nbsp; filled&nbsp; with&nbsp; three&nbsp; different&nbsp; quality&nbsp; concrete.&nbsp; Second&nbsp; method&nbsp; of&nbsp; strengthening&nbsp; included&nbsp; making&nbsp; of&nbsp; concrete&nbsp; jacket&nbsp; and&nbsp; using&nbsp; steel&nbsp; angles&nbsp; connected&nbsp; to&nbsp; each&nbsp; other&nbsp; by&nbsp; connecting&nbsp; plates&nbsp; forming steel&nbsp; cage around RC column. Space between connecting&nbsp; plates&nbsp; were&nbsp; varied&nbsp; in&nbsp; two&nbsp; cases.&nbsp; Third&nbsp; method&nbsp; of&nbsp; strengthening&nbsp; included tightening of the cross placed prestressed bolts. Number&nbsp; of&nbsp; bolts&nbsp; and&nbsp; their&nbsp; spaces&nbsp; were&nbsp; varied.&nbsp; Numerical&nbsp; analysis&nbsp; of&nbsp; the&nbsp; behavior of columns was carried by FEM method. Comparison of&nbsp; the&nbsp; numerical&nbsp; and&nbsp; experimental&nbsp; results&nbsp; was&nbsp; conducted&nbsp; and&nbsp; numerical&nbsp; model&nbsp; for&nbsp; calculating&nbsp; cross&nbsp; section/member&nbsp; capacity&nbsp; was proposed for all analyzed specimens.</p>

Military personnel often experience mild traumatic brain injury (mTBI) from exposure to improvised explosive devices (IEDs). Soldiers typically endure blast trauma from the IED pressure wave as well as blunt trauma from ensuing head impacts. Researchers have not reached a consensus on whether the biomechanical response from blunt or blast trauma plays a more dominant role in mTBI because the specific biomechanical sources of injury are often undetermined. Consequently, the goal of this dissertation was to conduct three separate studies in order to characterize the mechanical behavior of the brain after exposure to mTBI conditions. For Study 1, mild blunt and blast trauma were induced in Sprague-Dawley rats using a custom-built device. In-house diffusion tensor imaging (DTI) software was used to make 3-D reconstructions of white matter fiber tracts before and after injury (1, 4, and 7 days). Axonal integrity was characterized by examining the fiber count, fiber length, and fractional anisotropy (FA). In-house image analysis software also quantified the microstructural variations in Hematoxylin and Eosin (H&E) stained brain sections, where significant differences in parameters such as the area fraction (AF) and nearest neighbor distance (NND) correlated to voids that formed after water diffused extracellularly from axons. Study 2 employed a computational approach involving the development of a finite element (FE) model for the rat head followed by the simulation of blunt and blast trauma, respectively. FE parameters such as von Mises stress, pressure, and maximum principal strain were analyzed at various locations including the skull, cerebral cortex, corpus callosum, and hypothalamus to compare injury cases. Study 3 involved interruption mechanical testing of porcine brain, a suitable animal surrogate of human brain. Compression, tension, and shear experiments were performed at a strain rate of 0.1 s-1 to examine the differential mechanical response. Microstructural changes in H&E stained brain sections were analyzed with in-house image analysis software to quantify differences among stress states at strains of 0.15, 0.30, and 0.40. Studies 1 and 2 confirmed that the brain behaves differently in response to blunt and blast trauma, respectively, while Study 3 further demonstrated the stress state dependent behavior of brain tissue.

Wrinkles represent a pathway towards the spontaneous generation of ordered surface microstructure for applications in numerous fields. Examples of highly complex ordered wrinkle structures abound in Nature, but the ability to harness this potential for advanced material applications remains limited. This work focuses on understanding the relationship between the patterns on a wrinkled surface and the experimental conditions under which they form. Because wrinkles form in response to applied stresses, particular attention is given to the nature of the stresses in a wrinkling surface. The fundamental insight gained was then utilized to account for observed wrinkle formation phenomena within more complex geometric and kinetic settings. In order to carefully control and measure the applied stresses on a wrinkling film, a swelling-based system was developed using poly(dimethylsiloxane) (PDMS), surface-oxidized with a UV-ozone treatment. The swelling of the oxidized surface upon exposure to an ethanol vapor atmosphere was characterized using beam-bending experiments, allowing quantitative measurements of the applied stress. The wrinkle morphologies were characterized as a function of the overstress, defined as the ratio of the applied swelling stress to the critical buckling stress of the material. A transition in the dominant morphology of the wrinkled surfaces from dimple patterns to ridge patterns was observed at an overstress value of ~2. The pattern dependence of wrinkles on the ratio of the principal stresses was examined by fabricating samples with a gradient prestress. When swollen, these samples exhibited a smooth morphological transition from non-equibiaxial to equibiaxial patterns, with prestrains as low as 2.5% exhibiting non-equibiaxial characteristics. This transition was seen both in samples with low and high overstresses. To explore the impact of these stress states in more complex geometries, wrinkling hemispherical surfaces with radii of curvature ranging from 50-1000 μm were fabricated using the same material system. Upon wrinkling, the hemispheres formed complex hierarchical assemblies reminiscent of naturally occurring structures. The curvature of a surface exhibited a correlation with its critical buckling stress, independent of other factors. This enables the surface curvature to be used as an independent control over the dimple-to-ridge transition which occurs as a function of overstress. As in the flat buckling surfaces, this transition was shown to occur at an overstress value of ~2. Surface curvature was also shown to improve the observed hexagonal ordering of the dimple arrays, resulting in the formation of regular "golf ball" structures. Geometric effects in finite flat plates were also examined. Using circular masks during the oxidation process, plates with radii ranging from 0.4-8.6 mm were created. Upon wrinkling, a dimple-to-ridge transition was observed with increasing plate size, with the morphological switch occurring at a radius of ~2 mm. This observed transition was not found to be due to the inherent mechanics of plates of different sizes, but instead to a reduction in the oxide conversion due to shadowing or stagnation caused by the masking process, which lowered the applied overstress. The shape of the finite plate was found to have little impact on the resulting wrinkle morphologies. Kinetic aspects of wrinkling were qualitatively characterized by observing the wrinkling process over the course of swelling. Wrinkling was observed to frontally propagate across the surface, and the ordering of the patterns which developed showed a qualitative correlation with the degree of uniformity in the advancing wrinkle front. Swelling with different solvents was found to lead to the formation of different patterns, based on the swelling kinetics of the UVO-treated PDMS upon exposure to each solvent.

L'état de contrainte initial est l'état de contrainte dans le sous-sol avant toute intervention humaine. Sa connaissance est essentielle pour atteindre des objectifs aussi bien scientifiques (compréhension de la tectonique des plaques) que préventifs (étude et prédiction des séismes) ou industriels (compréhension de la mécanique des réservoirs pétroliers pour leur exploitation). Dans cette thèse, nous présentons une méthode permettant d'estimer l'état de contrainte initial en trois dimensions, à partir de données éparses. Cette méthode repose sur une approche inverse dans laquelle la méthode des éléments finis est utilisée pour résoudre le problème mécanique élastique. Les paramètres de modèles sont les conditions de Neumann décrites par des fonctions linéaires par morceaux. Les données sont des mesures partielles de l'état de contrainte en quelques points du domaine d'étude. Une optimisation d'ensemble est utilisée pour résoudre le problème inverse. La méthode est testée sur un cas synthétique où la solution de référence dans tout le domaine est supposée connue. Sur cet exemple, la méthode présentée est capable de retrouver un état de contrainte en accord avec les mesures, et cohérent avec l'état de contrainte de référence dans tout le domaine. La méthode est ensuite enrichie par des critères mécaniques qui contraignent l'état de contrainte dans les zones où les données sont absentes. La méthode est ensuite appliquée sur un cas réel: le bassin de Neuquèn en Argentine, sur lequel des données de puits sont disponibles. La confrontation de la méthode avec un cas d'étude permet de déterminer quelles en sont les limites. L'impact des failles sur l'état de contrainte et les différentes façons de les modéliser sont discutés. En effet, la prise en compte de ces structures complexes est problématique dans les calculs induits par les méthodes inverses puisqu'elles introduisent des non linéarités rendant le temps de calcul trop important. Nous investiguons alors la possibilité de les modéliser uniquement par des propriétés élastiques. Enfin, nous consacrons un chapitre sur l'environnement logiciel intégratif que nous avons développé pour la réalisation des calculs mécaniques. Cet environnement est composé de RINGMesh, une bibliothèque proposant une structure de données pour les modèles géologiques et de RINGMecha, permettant la réalisation de calculs mécaniques sur ces modèles. RINGMecha interface plusieurs simulateurs, chacun ayant ses spécificités, de manière totalement transparente pour l'utilisateur. RINGMecha a été utilisé pour la réalisation de tous les calculs présentés dans cette thèse et a été pensé pour pouvoir être étendu à d'autres problèmes, avec d'autres simulateurs / Initial stress state is the stress state before any human activity. Its knowledge is essential when dealing with scientific (understanding of plate tectonics), preventive (earthquake prediction) and industrial (understanding reservoirs before their exploitation) purposes. We present a method to estimate the initial stress state in a 3D domain from sparse data. This method relies on an inverse approach which uses the finite elements method to solve the elastic mechanical problem. The model parameters are Neumann conditions, which are defined as piecewise linear functions. The data parameters are stress state observations, such as intensity and orientation at a few points. An ensemble optimization method is used to solve the inverse problem. The method is tested on a synthetic case where the reference solution is known. On this example, the method succeeds in retrieving the stress state at data points as well as in the whole domain. The method is enriched with a mechanical criterion which imposes mechanical constraints in the domain under study. The method is then applied to a real case: the Neuquèn basin in Argentina where borehole stress data is available. This application reveals some of the limits of the presented method. Then, the effect of faults on the stress state is investigated. Different modeling strategies are presented: the objective is to reduce the computing cost, which can be very high when dealing with such complex structures. We propose to model them using only elastic properties. Finally, we present the integrative software which were developed to run mechanical simulations. RINGMesh handles the structural model data structure and RINGMecha runs the mechanical simulations on the model. RINGMecha is interfaced with several simulators. Each of them can be called separately, depending on the problem to be solved. The interface of RINGMecha with third party simulators is done in a user friendly manner. RINGMecha was used for all the computations presented in this thesis. It was built in order to be extended to other problems, with other simulators