A study of a thin-walled curved rectangular box beam under torsion and out-of-plane bending is documented in this thesis. A new one-dimensional theory that takes into account warping and distortion in the beam cross-sections is the main focus. Existing available theories for thin-walled curved beams lack rigorous theoretical development, and most have ignored the effects of warping and distortion. A higher order theory including two additional degrees of freedom corresponding to warping and distortion was derived. The conventional three degrees of freedom model was compared with the new five degrees of freedom model. The variation of beam thickness to control and decrease the high distortion variable is investigated.

The use of timber in building structures is steadily increasing. cross laminated timber (CLT) is an engineered wood product made of an uneven number of layers of lamellas glued at an angle of 90 degrees to each other. This gives CLT high stiffness and strength to bending in all directions, and capability of taking load both in-plane and out-of-plane. Due to the large size of CLT elements, they allow for quick assembly of strong structures. Due to both economic and environmental reasons it is important for producers of CLT to optimize the use of the wood material by using the timber with higher stiffness and strength where it is most needed. This thesis is about evaluating the bending and shear stiffness of CLT elements, when used as plates, depending on the quality of wood used in the different layers. Four-point bending tests are carried out on elements of different compositions and a parametrized finite element model is created. Thus, the model is validated on the basis of experimental tests to evaluate the influence of different quality of different layers. The measured dynamic MoE proved to have good potential to be used as the longitudinal bending stiffness in an FE-model, with a deviation from the experimental tests of less than 1%. There is a strong correlation between the bending stiffness and bending strength of the plates. The effective rolling shear modulus in pine was calculated to be around 170 MPa for pine of dimension 40 x 195 mm2 . Grading the boards into two different classes used for different layers proved to increase the MoE of the plates by 11-17% for 3- and 5-layer CLT.

Master’s thesis fully fashioned within the frame of engineer study M-STM Manufacturing Technology and Management in Industry put literary study of bending technology. In the work is concept manufacture sidewall car for Fiat Ducato Valnik. Compare different technologies of manufacture press breaking, welding and casting. For the choose technology contains selection material, calculation parameters for project machinery and tools including of techno economic valorization.

No description available.

This thesis has taken place at ABB High Voltage Cables in Karlskrona and focuses on their reinforcement process (AR50) which reinforces the cable by application of reinforcement wires. The research is strictly limited to only the short period during the application of the wire on the cable and investigates stress differences in one reinforcing wire depending on cable - and wire dimensions as well as brake forces used in the production. The study follows a model - and theory development research process combined with a testing process to obtain the results. The study aims is to increase and expand ABB's knowledge about the reinforcing process that is used to strengthen and protect ABB’s all different high voltage cables together with a computational calculation model. The model is developed in the FEA (Finite Element Analysis) program ABAQUS through a dynamic explicit model. An explanation of how the calculation model has been built and the parameters used are described in this report. These parts then contribute to the outcome of the study which provides a sense that the brake force used in AR50’s reinforcement process does not need to be controlled with a high precision so long as it is large enough to hold the reinforcement wire stretched upon the application. The study also shows that different cable - and wire dimensions does not affect the stress levels somewhat significantly by reinforcing the process and that the nipple used in reinforcement process to press down the reinforcing wire on the cable is the main source that determines how the stress distribution looks like on the reinforcement wire. / Detta examensarbete har tagit plats på ABB High Voltage Cables i Karlskrona och fokuserar på deras armeringsprocess (AR50) som förstärker kabeln genom påläggning av armeringstrådar. Arbetet är starkt begränsat till enbart den korta perioden för själva påläggningen av tråden och undersöker spänningsskillnader i en armeringstråd beroende på olika kabel – och tråddimensioner samt bromskrafter som används i produktionen. Studien följer en modell – och teoriutvecklande forskningsprocess kombinerat med ett utprövande resultatbildande. Studiens syfte är att tillsammans med en beräkningsmodell öka och fördjupa ABBs kunskaper kring armeringstråden som idag används för att stärka och skydda ABBs alla olika högspänningskablar. Beräkningsmodellen tas fram i FEA (Finita Element Analys) prorammet ABAQUS genom en dynamisk explicit modell. En förklaring till hur beräkningsmodellen har byggts upp och vilka parametrar som används beskrivs i rapporten. Dessa delar bidrar sedan till resultatet i studien som ger en bild av att bromskraften som används i AR50s armeringsprocessen inte behöver kontrolleras med en hög precision så länge den är tillräckligt stor för att hålla armeringstråden sträckt vid påläggningen. Studien visar också att olika kabel – och tråddimensioner inte påverkar spänningsnivåerna något markant vid armeringsprocessen och att nippeln som används i armeringsprocesen för att trycka ner armeringstråden mot kabeln bestämmer hur spänningsbilden ser ut. / <p>This thesis is kept confidential</p>

Hydraulic fracturing is an indispensable technique for developing unconventional resources such as shale gas and tight oil. When hydraulic fractures interact with pre-existing natural fractures, it can result in a complex fracture network. The interaction depends on in-situ stresses, rock and natural fracture mechanical properties, approach angle and hydraulic fracture treatment parameters. Most simulation studies treat natural fractures as frictional interfaces with cohesive properties. However, from core observation, partially cemented and fully cemented natural fractures are widely present and it is not clear whether they would fit the common description. In this study, semi-circular bending test is utilized to examine the propagation paths and strength of samples with pre-existing cemented fractures. Synthetic hydrostone samples are used to represent the rock and different inclusion slices with different mechanical properties are used to mimic cemented natural fractures. In a series of experiments, we assess the influence of the fracture approach angle, inclusion strength, and inclusion thickness on fracture propagation. Current results show that fractures tend to cross the inclusion when the approach angle is high and divert into the inclusion when the approach angle is low. The crossing surface is not a clean cut, but often has a jog distance. The thickness of the inclusion does not change the crossing/diverting behavior for orthogonal approaching samples, however it does change the jog distance along the interface. Preliminary simulation results using finite element software, ABAQUS, are presented better to analyze the experimental observations. The assessments of fracture interaction in this study are in good agreement with previous work and theories. / text

As the world’s population increases, the demand for energy also grows. The strain on our limited resources of fossil fuels is unsustainable in the long term. An alternative, renewable method of energy generation must be implemented. Solar energy has good potential as an environmentally sound, unlimited energy source, but solar devices are not yet able to efficiently store energy for later use. A device has been proposed which uses direct sunlight to split water into hydrogen and oxygen. The hydrogen can then be harvested and stored as fuel, solving the question of how to effectively store energy generated during times of peak sunlight for use when sunlight levels are low. The prototype device incorporates arrays of doped silicon microwires which function as light absorbers and current-carriers, driving the chemical reactions that evolve hydrogen from water. This work aims to quantify and characterize the reduction in microwire resistivity that is achievable through application of silicon’s piezoresistive properties. Silicon displays a change in electrical resistance as a function of applied mechanical strain. This electromechanical effect has been studied extensively in bulk and top-down (etched) microstructures, but studies on microstructures grown bottom-up have been limited. A simple method is presented for piezoresistive characterization of individual, released, bottom-up silicon microwires. It is shown that these n-type microwires display a consistent negative piezoresistive response which increases in magnitude with increasing doping concentration. It was found that harnessing the piezoresistive response of moderately-doped (∼10^17 cm^−3) n-type wires allowed for a maximum observed reduction in resistivity of 49%, which translated to a 1% reduction in overall system resistance of a prototype unit cell of the artificial photosynthesis device, if all other components therein remained unchanged. / February 2015

No description available.

Thesis advisor: Udayan Mohanty / In chapter one, two simple models are used to estimate the electrostatic contributions to the stiffness of short DNA fragments. The first model views DNA as two strands that are appropriately parameterized and are wrapped helically around a straight cylinder radius equal to the radius of the DNA molecule. The potential energy of the DNA due to phosphate-phosphate electrostatic interactions is evaluated assuming that the charges interact through Debye-Hückle potentials. This potential energy is compared with the potential energy as computed using our second model in which DNA is viewed as two helical strands wrapping around a curved tube whose cross-section is a disk of radius equal to the radius of the DNA. The results are compared with counterion condensation models and experimental data (Guo et al. J. Phys. Chem. B, 2008, 112, 16163-16169). In chapter two, the fidelity of translation selection begins with the base pairing of codon-anticodon complex between the mRNA and tRNAs. Binding of cognate and near-cognate tRNAs induces 30S subunit of the ribosome to wrap around the ternary complex, EF-Tu(GTP)aa-tRNA. We have proposed that large thermal fluctuations play a crucial role in the selection process. The binding energies of over a dozen unique site-bound magnesium structural motifs are investigated and provide insights into the nature of interaction of divalent metal ions with the ribosome (Guo et al. Proc. Nat. Acad. Sci. 2011, 108, 3947-3951). In chapter three, we use extensive molecular dynamics simulations to study a series of stapled alpha helical peptides over a range of temperatures in solution. The peptides are found to exhibit substantial variations in predicted helicities that are in good agreement with the experimental value. In addition, we find significant variation in local structural flexibility of the peptides with the position of the linker, which appears to be more closely related to the observed differences in activity than the absolute alpha helical stability (Guo et al. Chem. Biol. Drug. Des. 2010, 75, 348-359.). In chapter four, the alpha helical conformation and structural stability of single and double stapled all-hydrocarbon cross-linked p53 peptides in solution and when bound to MDM2 is investigated. We determined the effects of the peptide sequence, the stereochemistry of the cross-linker, the conformation of the double bond in the alkene bridge, the length of the bridge, on the relative stability of the alpha helix structure. The conformation population distribution indicates a fully helical state and several partially folded states. The distribution of dihedral pairs of the stapled peptides in the bound state indicates a significant population around the alpha helical region. Sequences over which the linker spans tend to have the highest helical occupancy. Significant helical content is observed for a double stapled p53 peptide at 575 K. The probability to form native contacts is increased when the stapled peptides are bound to MDM2. The distribution of the end-to-end distance of the peptides is bimodal. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Em projetos de alvenaria estrutural é indispensável à verificação de elementos submetidos à flexão simples, como vigas, vergas, reservatórios e muros de arrimos. Neste trabalho foram analisados oito grupos de vigas, compostos por três exemplares cada um, diferenciando seu comprimento, altura, tipo da unidade (blocos de concreto e blocos cerâmicos) e taxa de armadura. Os traços de graute e argamassa foram mantidos. As vigas e as armaduras longitudinais foram instrumentadas para obtenção dos deslocamentos e deformações. A finalidade do trabalho foi realizar uma comparação dos resultados obtidos através de ensaios experimentais com os dimensionamentos propostos pelas normas ABNT NBR 15812-1:2010 e NBR 15961-1:2011. Foi possível observar que o dimensionamento proposto pelas normas é conservador, pois limita o comportamento à flexão das vigas em cargas baixas quando comparados com experimentais. Já com a retirada dos coeficientes de segurança pode ocorrer, em alguns casos, que a carga teórica prevista seja maior que a dos resultados experimentais. A formulação adaptada da NBR 6118:2007 para obter valores de deslocamentos apresentou uma boa correlação para as vigas de uma fiada. Já para as vigas de duas fiadas observou-se uma pior correlação entre valores teóricos e experimentais, sendo os deslocamentos teóricos menores que os valores medidos experimentalmente. / In structural masonry projects is essential to verify elements subjected to simple bending, such as beams, lintels, water tanks and retaining walls. In this study, an experimental parametric analysis was conducted. Eight groups of beams composed by three specimens were tested and the parameters varied were: length, height, unit type (concrete blocks and ceramic blocks) and reinforcement ratio. The proportion of grout and the mortar were fixed. The beams and longitudinal bars were instrumented to obtain the displacements and strains. The purpose of this study was to compare the results obtained through experimental analysis with the proposed methods presented on ABNT NBR 15812-1:2010 and NBR 15961-1:2011. In the comparison was observed that the proposed design method is conservative, due to the limit load obtained by the code prescriptions was lower than the experimental results. In some cases, the theoretical load results were greater than experimental results when the safety factors were removed. The adapted formulation of the NBR 6118:2007, to obtain displacement values, showed a good correlation to the beams of one row. Regarding to beams with two rows, the correlation between experimental and theoretical values was not suitable, the theoretical displacements presented smaller than the values measured in the tests.