In recent years the design of pedestrian bridges has become more slender. As a result the bridges has lower natural frequencies and are more prone to excessive vibrations when subjected to dynamic loads induced by pedestrians. Akademiska Hus are building such a bridge at Nya Karolinska Solna where the bridge will span over Solnavägenconnecting the hospital building, U2, and the research facility BioMedicum. Due to practical reasons, it is not possible to connect one of the bridge ends mechanicallyto the building which increases the risk for lateral modes in the sensitivefrequency range of 0-2.5 Hz. The increased risk of lateral modes of vibrations within the sensitive frequency range as well uncertainties when determining the dynamic response led to this thesis. This thesis covers a frequency analysis of the previously mention bridge and an evaluation of the dynamic response under pedestrian loading by implementation of several design guidelines. A literature review was conducted with the aim of giving a deeper knowledge of human induced vibrations and the relevant guidelines for modelling of pedestrian loading. Furthermore, a parametric study was conducted for parameters which might be prone to uncertainties in data. The investigated parameters were the Young’s modulus for concrete and the surrounding fill materialas well as the stiffness of the connection to BioMedicum. The parametric study yielded a frequency range of 2.20-2.93 Hz for the first lateral mode and 5.96-6.67 Hz for the first vertical mode of vibration. By including nonstructural mass the lower limit for the frequencies were lowered to 2.05 and 5.59 Hzin the first lateral and vertical mode respectively. The parametric study also showed that the largest impact on the natural frequencies were obtained by manipulating the parameters for the supports, both for BioMedicum and the substructure. The implementation of the guidelines resulted in a lateral acceleration between 0.05 and0.599 m/s2. No evaluation was conducted for the dynamic response in the vertical direction due to a natural frequency of 5.59 Hz, which is higher than the evaluation criteria stated in Eurocode 0. The results showed that the design of the Skyway bridge is dynamically sound with regard to pedestrian loading and no remedial actions are necessary.

Bridge edge beam system is an increasing concern in Sweden. Because it is the mostvisible part of the structure which is subjected to harsh weather. The edge beamcontributes to the stiffness of overhang slab and helps to distribute the concentratedload. The design of edge beam is not only affected by the structural members, but it isalso affected by non-structural members.The aim of the thesis is to investigate the influence of edge beam on the structuralbehavior of reinforced concrete overhang slab. A three-dimensional (3D) non-linearfinite element model is developed by using the commercial software ABAQUS version6.1.14. The load displacement curves and failure modes were observed. The bendingmoment and shear capacity of the cantilever slab is studied.The validated model from non-linear analysis of reinforced concrete slab gives morestiffer result and leads to the high value of load capacity when comparing with theexperimental test. The presence of the edge beam in the overhang slab of length 2.4 mslightly increases the load capacity and shows ductile behavior due to the self-weightof the edge beam. The non-linear FE-analysis of overhang slab of length 10 m leads tomuch higher load capacity and gives stiffer response as compare to the overhang slabof 2.4 m. The presence of the edge beam in the overhang slab of length 10 m giveshigher load capacity and shows stiffer response when comparing with the overhangslab of length 10 m. This might be due to the self-weight of the edge beam and theoverhang slab is restrained at the right side of the slab.

Stress corrosion, SC, in some cases gives rise to stress corrosion cracking, SCC, which differs from purely stress intensity driven cracks in many aspects. They initiate and grow under the influence of an aggressive environment in a stressed substrate. They grow at low load and may branch. The phenomenon of SCC is very complex, both the initiation phase and crack extension itself of SCC is seemingly associated with arbitrariness due to the many unknown factors controlling the process. Such factors could be concentration of species in the environment, stress, stress concentration, electrical conditions, mass transport, and so on.In the present thesis, chemically assisted crack initiation and growth is studied with special focus on the initiation and branching of cracks. Polycarbonate plates are used as substrates subjected to an acetone environment. Experimental procedures for examining initiation and branching in polycarbonate are presented. An optical microscope is employed to study the substrate.The attack at initiation is quantified from pits found on the surface, and pits that act as origin for cracks is identified and the distribution is analysed. A growth criterion for surface cracks is formulated from the observations, and it is used to numerically simulate crack growth. The cracks are seen to coalesce, and this phenomenon is studied in detail. Branching sites of cracks growing in the bulk of polycarbonate are inspected at the sample surface. It is found that the total width of the crack branches are approximately the same as the width of the original crack. Also, angles of the branches are studied. Further, for comparison the crack growth in the bulk is simulated using a moving boundary problem based algorithm and similar behaviour of crack branching is found. / <p>Both papers in thesis as manuscript, paper II with title "Branching cracks in a layered material - Dissolution driven crack growth in polycarbonate"</p>

<p>Cellular structural mechanics play a key role in homeostasis by transducing mechanical signals to regulate gene expression and by providing adaptive structural stability for the cell. The alteration of nuclear mechanics in various laminopathies and in natural aging can damage these key functions. Arterial endothelial cells appear to be especially vulnerable due to the importance of shear force mechanotransduction to structure and gene regulation as is made evident by the prominent role of atherosclerosis in Hutchinson-Gilford progeria syndrome (HGPS) and in natural aging. Computational models of cellular mechanics may provide a useful tool for exploring the structural hypothesis of laminopathy at the intracellular level. This thesis explores this topic by introducing the biological background of cellular mechanics and lamin proteins in arterial endothelial cells, investigating disease states related to aberrant lamin proteins, and exploring computational models of the cell structure. It then presents a finite element model designed specifically for investigation of nuclear shear forces in arterial endothelial cells. Model results demonstrate that changes in nuclear material properties consistent with those observed in progerin-expressing cells may result in substantial increases in stress concentrations on the nuclear membrane. This supports the hypothesis that progerin disrupts homeostatic regulation of gene expression in response to hemodynamic shear by altering the mechanical properties of the nucleus.</p>

<p dir="ltr">Fretting wear occurs when two contacting bodies under load are subjected to small amplitude oscillatory motion. Depending on the applied normal load, displacement amplitude, coefficient of friction and resulting shear force, two types of fretting wear regimes exist – (i) partial slip and (ii) gross slip. At displacement amplitudes higher than gross slip condition, sliding wear regime prevails. Fretting wear becomes dominant in machine components subject to vibrations such as bearings, dovetail joints, etc. whereas sliding wear is observed in brakes, piston-ring applications, etc. The work in this dissertation primarily focuses on characterizing the material response of various machine components subjected to fretting and sliding wear regimes.</p><p dir="ltr">At first, the friction and fretting wear behavior of inlet ring and spring clip components used in land-based gas turbines was investigated at elevated (<a href="" target="_blank">500°C</a>) temperature. In order to achieve this objective, a novel high-temperature fretting wear apparatus was designed and developed to simulate the conditions existing in a gas turbine. The test apparatus was used to investigate fretting wear of atmospheric plasma sprayed (APS) Cr₃C₂-NiCr (25% wt.), high-velocity oxy-fuel (HVOF) sprayed Cr₃C₂-NiCr (25% wt.), HVOF sprayed T-800 and APS sprayed PS400 coated inlet rings against HVOF-sprayed Cr₃C₂-NiCr (25% wt.) coated spring clip. The PS400 coated inlet rings demonstrated a significant reduction in friction and wear. A finite element (FE) framework was also developed to simulate fretting wear in HVOF-sprayed Cr₃C₂-NiCr composite cermet coating. The material microstructure was modelled using Voronoi tessellations with a log-normal distribution of grain size. Moreover, the individual material phases in the coating were randomly assigned to resemble the microstructure from an actual SEM micrograph. A damage mechanics based cohesive zone model with grain deletion algorithm was used to simulate debonding of the ceramic carbide phase from the matrix and resulting degradation from repeated fretting cycles. The specific wear rate obtained from the model for the existing material microstructure was benchmarked against experiments. Novel material microstructures were also modeled and demonstrated to show less scatter in wear rate.</p><p dir="ltr">Following, a three-dimensional (3D) continuum damage mechanics (CDM) FE model was developed to investigate the effects of fretting wear on rolling contact fatigue (RCF) of bearing steels. In order to determine the fretting scar geometry, a 3D arbitrary Lagrangian-Eulerian (ALE) adaptive mesh (AM) FE model was developed to simulate fretting wear between two elastic bodies for different initially pristine fretting pressures (0.5, 0.75 and 1 GPa) and friction coefficients (0.15, 0.175 and 0.25) resulting in stick zone to contact width ratios, c/a = 0.35, 0.55 and 0.75. The resulting wear profiles were subjected to various initially pristine RCF pressures (1, 2.2 and 3.4 GPa). The pressure profiles for RCF were determined by moving the contact over the fretted wear profiles in 21 steps. These pressure profiles were then used in the CDM-FE model to predict the RCF life of fretted surfaces. The results indicate that increased fretting pressure leads to more wear on the surface, thereby reducing RCF life. As the RCF pressure increases (P_RCF ≥ 2.2 GPa), the effect of fretting on RCF life decreases for all fretting pressures and c/a values, indicating that life is primarily governed by the RCF pressure. The results from CDM-FE model were used to develop a life equation for evaluating the L₁₀ life of fretted M-50 bearing steel for the range of tested conditions.</p><p dir="ltr">Lastly, the sliding wear characteristics of pitch and poly-acrylonitrile based carbon-carbon (C/C) composites were investigated in air and nitrogen environment by designing and developing a disc brake test rig. It was found that the temperature of the disc, the surrounding environment, the supplied energy flux as well as the type of composite play a critical role in determining whether C/C composites operate in normal wear or dusting wear regime. Further analysis of wear mechanisms revealed interface and matrix cracking with fiber breakage from tests in air environment, whereas in nitrogen environment, particulate and layered debris played a prominent role.</p>

The use of Fibre Reinforced Polymer (FRP) composite materials in structural applications has increased in the past decades in high­performance sectors, such as in the automotive and aeronautic industries, for weight reduction purposes. However, FRP composite materials can offer more significant innovation potential. The application of CNTs in conjunction with composite material can allow the creation of multifunctional materials, relying on FRP for the structural side and CNT for the sensing ability. In this master thesis, the embedment of a Vertical Aligned Carbon Nanotube (VACNT) layer into the interlaminar region of Carbon Fibre (CF) laminates to provide polyvalent sensing ability to the material was investigated. In order to obtain accurate results, the sensor had to be isolated from the rest of the laminate. For this reason, the main problem to be solved in this project was the electrical isolation on the CNT layer and its contacts from the layers of CF laminate. This study aims to find a suitable isolation technique in order to apply the CNT sensor technology, developed in previous studies, into CF laminate. Although thought for aerospace applications, these sensors could be applied to different structural components in various fields. / Användningen av fiberförstärkta polymerer (FRP)-­kompositmaterial i strukturella applikationer har ökat under de senaste decennierna i högpresterande sektorer, såsom i fordons­ och flygindustrin, för viktminskningsändamål. FRP-­kompositmaterial kan dock erbjuda mer betydande innovationspotential. Användningen av CNTs i kombination med kompositmaterial kan möjliggöra skapandet av multifunktionella material, beroende på FRP för den strukturella sidan och CNT för avkänningsförmågan. I denna masteruppsats undersöktes inbäddningen av ett Vertical Aligned Carbon Nanotube (VACNT) lager i den interlaminära regionen av Carbon Fiber (CF) laminat för att ge polyvalent avkänningsförmåga till materialet. För att få exakta resultat måste sensorn isoleras från resten av laminatet. Av denna anledning var huvudproblemet som skulle lösas i detta projekt den elektriska isoleringen på CNT-­lagret och dess kontakter från lagren av CF­-laminat. Denna studie syftar till att hitta en lämplig isoleringsteknik för att tillämpa CNT­sensorteknologin, utvecklad i tidigare studier, i CF-­laminat. Även om de är tänkta för flygtillämpningar, kan dessa sensorer appliceras på olika strukturella komponenter inom olika områden.

This master thesis deals with the performance of existing reinforced concrete bridges strengthened with externally bonded carbon fibre reinforced polymers (CFRP). One of the main aims of this work is to understand the functionality of such an external strengthening method applied to a concave surface in a heavy concrete structure such as a bridge. Another important goal is to investigate the bond behavior of this method. To accomplish the aforementioned aims a case study bridge is chosen to be examined. The Essinge bridge located in the central Stockholm, is the selected bridge in which this report will focus on. Externally strengthening an existing bridge is a method used to both preserve as well as improve the existing structure. Some examples justifying the need to use such a technique are: the degradation of materials or changes in the bearing capacity of the structure which might be the result of increased traffic loads. In the case of Essinge bridge, the structure is strengthened with externally bonded CFRP sheets after the extension of the bridge which led to changes in the statical mode of action of the structure. An additional reason which makes this case interesting to study is the ’’concave’’ surface on which the CFRP sheets are applied to. To study the Essinge bridge in detail, both a numerical analysis and a three-dimensional finite element model is used. All the numerical simulations are performed in the Abaqus software. It is important to mention that for the majority of the simulations a two-axle vehicle load of 300kN (per axle) is applied to the structure. Moreover, a quality assurance of the FE model is carried out to verify the functionality of the model. Some of the results coming from these analyses can be compared with measurements from the monitoring system placed on the bridge. Moreover, other simulation results could be compared with results coming from a test loading performed on the bridge on May 2021. From this comparison, a satisfactory agreement could be found in the peak values of normal strain in concrete and CFRP. Due to time limitations, only linear static analyses are performed. Consequently, in order to capture the non-linearity of the concrete, the Extended Finite Element Method (XFEM) available in Abaqus is used to model a possible crack in the concrete. More specifically, the crack is placed in the concrete part of the deck plate where the maximum value of normal stress is obtained. The bond behavior between the concrete and the CFRP sheets is modelled in two different ways. The first way represents a ’’perfect’’ bond between these two materials meanwhile the second one is based on the so-called Cohesive Zone Method (CZM). The fundamental difference between these two methods is that when using the CZM, a possible failure mode in the bond layer can be captured. Moreover, the input data and parameters defined in the CZM have a detrimental role in the obtained results. It can be noted that the results of the case study bridge cannot be generalized. On the other hand, a better understanding about the external strengthening method implemented on the example of Essinge bridge is obtained. By using the CZM, a vehicle load which could initiate damage in the bond layer could be found. / Detta examensarbete handlar om prestandan för befintliga betongarmerade broar som är externt förstärkta med kolfiberväv. Ett av huvudsyftena med detta arbete är att förstå hur en sådan förstärkningsmetod fungerar när den är applicerad på ett konkavt underlag av en tung betongkonstruktion, såsom en bro. Ett annat viktigt mål är att undersöka beteendet av bindningsskiktet som finns mellan betongen och kolfiberväven. För att uppnå de ovannämnda målen, undersöks en fallstudie bro. Bron över Pampaslänken, som ligger i centrala Stockholm, är den utvalda bron som denna rapport kommer att fokusera på. Att förstärka en befintlig bro externt är en metod som använts för att både bibehålla och förbättra den existerande strukturen. Några exempel som motiverar behovet av att använda en sådan metod är nedbrytning av material eller förändringar i konstruktionens bärförmåga som kan vara ett resultat av ökade trafikbelastningar. När det gäller bron över Pampaslänken, applicerades den externa förstärkningen efter breddningen av bron, vilket ledde till förändringar i strukturens statiska verkningssätt. En ytterligare anledning som gör detta fall intressant att studera är den konkava ytan för vilken förstärkningsmetoden används. För att studera bron över Pampaslänken i detalj, används både en numerisk analys samt en tredimensionell finit elementmodell. Alla numeriska simuleringar är utförda i programvaran Abaqus. Det är viktigt att nämna att för de flesta av simuleringarna appliceras en tvåaxlig fordonslast på 300kN (per axel) på konstruktionen. Dessutom genomförs en kvalitetssäkring av FE-modellen för att verifiera modellens funktionalitet. Några av resultaten från dessa analyser kan jämföras med mätningar från systemet med trådtöjningsgivarna som är placerade på bron. Andra simuleringsresultat kan jämföras med resultat som kommer från en provbelastning som utfördes på bron under maj 2021. Från denna jämförelse kan en överenskommelse hittas i de maximala töjningsvärdena i både betongen och kolfiberväven. På grund av tidsbegränsningar utförs endast linjära elastiska analyser. För att kunna fånga betongens olinjära beteende används den så kallade utvidgade finita elementmetoden (XFEM) som finns i Abaqus, för att modellera in en eventuell spricka i betongen. Mer specifikt placeras sprickan på den delen av farbaneplattan där de maximala normalspänningarna erhålls. Bindningsskiktet som finns mellan betongen och kolfibervävarna modelleras på två olika sätt. I det första sättet skapas ett ’’perfekt’’ band/skikt mellan dessa två material medan i det andra baseras modelleringen på den så kallade Cohesive Zone Method (CZM). Den grundläggande skillnaden mellan dessa två metoder är att när man använder CZM kan ett eventuellt vidhäftningsbrott fångas upp i bindningsskiktet. Dessutom har indata samt olika parametrar som är definierade i CZM, en stor påverkan på de erhållna resultaten. Det kan konstateras att resultaten från fallstudiebron inte kan generaliseras. Däremot har man fått en bättre förståelse för den externa förstärkningsmetoden som implementerats i bron över Pampaslänken. Genom att använda CZM hittas en fordonlast som kan orsaka skador i bindningsskiktet.

This paper presents a numerical investigation into the behaviour of headed shear stud in composite beams with profiled metal decking. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS to study the behaviour of through-deck welded shear stud in the composite slabs with trapezoidal deck ribs oriented perpendicular to the beam. Both static and dynamic procedures were investigated using Drucker Prager model and Concrete Damaged Plasticity model respectively. In the dynamic procedure using ABAQUS/Explicit, the push test specimens were loaded slowly to eliminate significant inertia effects to obtain a static solution. The capacity of shear connector, load-slip behaviour and failure modes were predicted and validated against experimental results. The delamination of the profiled decking from concrete slab was captured in the numerical analysis which was observed in the experiments. ABAQUS/Explicit was found to be particularly suitable for modelling post-failure behaviour and the contact interaction between profiled decking and concrete slabs. It is concluded that this model represents the true behaviour of the headed shear stud in composite beams with profiled decking in terms of the shear connection capacity, load-slip behaviour and failure modes.

Ce travail s'inscrit dans le domaine des cellules solaires organiques et se focalise sur le dimensionnement et design de la cellule. Nous avons cherché à établir la relation entre la forme d'une cellule solaire et sa dissipation thermique dans les électrodes, plus spécifiquement l'électrode inférieure transparente, car les matériaux utilisés pour la réaliser ont souvent une conductivité très faible par rapport à celle des électrodes métalliques. D'autre part nous présentons un modèle actif capable de simuler le comportement de la couche active selon différentes conditions d'éclairage (illumination partielle et défauts localisés) et pour différents régimes de fonctionnement (injection, polarisation). Dans le cadre du projet PHASME en partenariat avec Disasolar et l'INES, on a posé les bases pour le développement d'un logiciel de conception capable de réaliser un module solaire multicolore à partir d'un substrat de forme géométrique quelconque. On a identifié deux types d'algorithme. Une solution A (dite matricielle), pour laquelle on effectue le remplissage de la surface active du module avec des cellules identiques, relie entre elles ces cellules en sous-groupes pour créer le potentiel de fonctionnement souhaité. Une méthode B (dite non-matricielle) consiste à partager la surface du module en sous-modules de surface quelconque adaptée aux zones de couleur. Ces sous-modules sont ensuite découpés en groupement en série cellules du même type (couleur, performance, matériaux de couche active), mais dont la forme s'adapte exactement au remplissage du sous-module. Ces cellules doivent nécessairement avoir la même surface, afin de produire le même courant pour éviter les pertes dans le groupement en série. / This work concerns organic solar cells and it focuses on several aspects of the design of the device that are related to the sizing. The core of this study highlights the relation between the shape of an organic solar cell and the thermal dissipation inside the electrodes. The main contribution to this power loss comes from the transparent back electrode, since its conductivity is typically lower than those of the top electrode. In parallel we developed a non-linear model for the active layer in order to simulate the behavior of the solar cells in several particular illumination cases (such as spotlights, shadows and defects in the active layer) and different working regime. In the framework of PHASME project, a grant in collaboration with Disasolar and CEA-INES, we developed another piece of software closer to the CAD domain which the main function was to create a photovoltaic polychrome module starting from a substrate with given shape and size. We found two strategies. One consists in filling by the same solar cell shape and size the entire substrate and then in finding a suitable grouping in order to have the correct working point outside the device (matrix approach). The other one (non-matrix approach) consists in adapting the shape of the device to a given colored region, each individual cell keeping the same surface extension, which allows them to be connected in series since they all generate the same amount of current.

Le traitement endovasculaire des anévrismes de l’aorte (Endovascular Aneurysm Repair ou EVAR) est une chirurgie mini-invasive qui consiste à faire glisser une endoprothèse par voie fémorale jusqu’au niveau de l’anévrisme afin de re-canaliser le flux sanguin. Les principales complications qui peuvent survenir sont les phénomènes de migration et d’endofuites (écoulement persistant de sang dans le sac anévrismal) de type Ia. Ces phénomènes apparaissent lorsque l’étanchéité n’est plus assurée entre l’extrémité proximale de l’endoprothèse et le vaisseau sanguin. Dans ce travail, des simulations paramétrées de déploiement complet d’un système de pose de stent ont été développées en utilisant la Méthode des Éléments Finis (FEM) afin d’étudier la stabilité du contact lors du largage d’une endoprothèse en nitinol dans un Anévrisme de l’Aorte Thoracique (AAT) réaliste. Les facteurs suivants associés à ces complications ont été étudiés : (1) la longueur de la zone de fixation proximale (PASL), (2) la valeur de surdimensionnement ou « oversizing » du stent (O %), (3) la valeur du coefficient de frottement entre le stent et l’aorte (µ) et (4) l’angulation du collet proximal. L’influence de la présence de calcifications sur le comportement biomécanique de l’endoprothèse lors de son déploiement dans les zones de fixation a également été analysée. Les résultats des simulations ont montré qu’une PASL supérieure à 18 mm est un facteur décisif pour éviter la migration de l’endoprothèse pour une angulation du collet de l’anévrisme de 60° et dans des conditions de contact glissant (µ=0,05). L’augmentation de la valeur de l’oversizing de 10 % à 20 % améliore la résistance de la fixation de la prothèse. En revanche, un oversizing supérieur à 25 % pour une angulation du collet de 60° entraine des déformations excentriques ainsi que la ruine du stent. D’autre part, aucune migration n’a été observée dans un modèle d’aorte idéalisé où l’angulation du collet était de 0°, la PASL de 18 mm et le coefficient de frottement µ de 0,05. Afin d’améliorer le contact et de prévenir l’apparition de phénomènes de migration et d’endofuite de type Ia chez des patients présentant une aorte tortueuse et calcifiée avec un anévrisme fortement angulé, un nouveau design de stent a été proposé, basé sur les résultats des simulations numériques effectuées. La principale difficulté était de trouver un compromis entre flexibilité et raideur. Les résultats des simulations réalisées avec ce nouveau stent ont montré une amélioration de la stabilité de contact, ce qui a pour effet de limiter l’apparition des phénomènes de migration et donc de réduire les complications liées à la procédure endovasculaire. / The main mechanical related problems of endovascular aneurysm repair are migration and endoleak type Ia. They occur when there is no effective seal between the proximal end of stent-graft and the vessel. In this work, we have developed parameterized-deployment simulations of a complete stenting system using finite element method (FEM) to investigate the contact stiffness of a nitinol stent in a realistic Thoracic Aortic Aneurysm (TAA). Therefore, the following factors associated with these complications have evaluated: (1) Proximal Attachment Site Length (PASL), (2) stent Oversizing value (O %), (3) different contact friction situations (stent/aorta) and (4) proximal neck angulation. The calcification impact on the biomechanical behaviour of the deployment at the attachment zone has also been investigated. The simulation results showed that PASL>18mm was a crucial factor to prevent migration at a neck angle of 60⁰and smoothest contact condition (μ=0.05). The increase in (O %) ranging from 10% to 20% improved the fixation strength; however, O % ≥ 25% at 60° caused eccentric deformation and stent collapse. No migration was reported in an idealized aorta model with a neck angle of 0⁰, PASL=18mm and μ=0.05. The numerical observations are used as a guide to optimize the stent design in such neck morphology to strengthen the contact and prevent migration or endoleak type Ia. The optimized stent results showed better contact stability to resist the migration. They also showed a good compromise of stent design requirements (flexibility and stiffness). Moreover, the new design can also prevent the risk of folding or collapse of stent struts by mitigating the energy of eccentric deformation caused by high angulation and oversizing.