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The principal aim of this research is the design of a more compliant horseshoe which allows the natural expansion and compression of the horse hoof. Three different simulations have been carried out in by using Finite Element Method in order to know the behaviour of the horse hoof when is analysed under the same load conditions. First the hoof will be studied without any horseshoe to obtain the produced displacement by the hoof expansion. Once the displacement of the barefoot hoof is known, an assembly, in which a sample stiff horseshoe is attached to the hoof by nails, will be performed to obtain both the hoof displacement as the horseshoe one. Finally, after three different researches about the current horseshoes, different possible alternative materials and most commons attachment methods, a more flexible horseshoe will be created and analysed. The results obtained in the three simulations will be compared and commented.

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This thesis investigates two a posteriori error estimators, based on gradient recovery, aiming to fill the gap of the error estimations for the Generalized FEM (GFEM) and, mainly, its modified versions called Corrected XFEM (C-XFEM) and Stable GFEM (SGFEM). In order to reach this purpose, firstly, brief reviews regarding the GFEM and its modified versions are presented, where the main advantages attributed to each numerical method are highlighted. Then, some important concepts related to the error study are presented. Furthermore, some contributions involving a posteriori error estimations for the GFEM are shortly described. Afterwards, the two error estimators hereby proposed are addressed focusing on linear elastic fracture mechanics problems. The first estimator was originally proposed for the C-XFEM and is hereby extended to the SGFEM framework. The second one is based on a splitting of the recovered stress field into two distinct parts: singular and smooth. The singular part is computed with the help of the J integral, whereas the smooth one is calculated from a combination between the Superconvergent Patch Recovery (SPR) and Singular Value Decomposition (SVD) techniques. Finally, various numerical examples are selected to assess the robustness of the error estimators considering different enrichment types, versions of the GFEM, solicitant modes and element types. Relevant aspects such as effectivity indexes, error distribution and convergence rates are used for describing the error estimators. The main contributions of this thesis are: the development of two efficient a posteriori error estimators for the GFEM and its modified versions; a comparison between the GFEM and its modified versions; the identification of the positive features of each error estimator and a detailed study concerning the blending element issues. / Esta tese investiga dois estimadores de erro a posteriori, baseados na recuperação do gradiente, visando preencher o hiato das estimativas de erro para o Generalized FEM (GFEM) e, sobretudo, suas versões modificadas denominadas Corrected XFEM (C-XFEM) e Stable GFEM (SGFEM). De modo a alcançar este objetivo, primeiramente, breves revisões a respeito do GFEM e suas versões modificadas são apresentadas, onde as principais vantagens atribuídas a cada método são destacadas. Em seguida, alguns importantes conceitos relacionados ao estudo do erro são apresentados. Além disso, algumas contribuições envolvendo estimativas de erro a posteriori para o GFEM são brevemente descritas. Posteriormente, os dois estimadores de erro propostos neste trabalho são abordados focando em problemas da mecânica da fratura elástico linear. O primeiro estimador foi originalmente proposto para o C-XFEM e por este meio é estendido para o âmbito do SGFEM. O segundo é baseado em uma divisão do campo de tensões recuperadas em duas partes distintas: singular e suave. A parte singular é calculada com o auxílio da integral J, enquanto que a suave é calculada a partir da combinação entre as técnicas Superconvergent Patch Recovery (SPR) e Singular Value Decomposition (SVD). Finalmente, vários exemplos numéricos são selecionados para avaliar a robustez dos estimadores de erro considerando diferentes tipos de enriquecimento, versões do GFEM, modos solicitantes e tipos de elemento. Aspectos relevantes tais como índices de efetividade, distribuição do erro e taxas de convergência são usados para descrever os estimadores de erro. As principais contribuições desta tese são: o desenvolvimento de dois eficientes estimadores de erro a posteriori para o GFEM e suas versões modificadas; uma comparação entre o GFEM e suas versões modificadas; a identificação das características positivas de cada estimador de erro e um estudo detalhado sobre a questão dos elementos de mistura.

Interest in superelastic (and shape memory) materials continues to rise, and there is a strong incentive to develop techniques for monitoring of their superelastic characteristics. This is conventionally done via uniaxial testing, but there are many advantages to having a capability for obtaining these characteristics (in the form of parameter values in a constitutive law) via indentation testing. Specimens can then be small, require minimal preparation and be obtainable from components in service. Interrogation of small volumes also allows mapping of properties over a surface. On the other hand, the tested volume must be large enough for its response to be representative of behaviour. Precisely the same arguments apply to more "mainstream" mechanical properties, such as yielding and work hardening characteristics. Indeed, there has been considerable progress in that area recently, using FEM simulation to predict indentation outcomes, evaluating the "goodness of fit" for particular sets of parameter values and converging on a best-fit combination. A similar approach can be used to obtain superelastic parameters, but little work has been done hitherto on sensitivities, uniqueness characteristics or optimal methodologies and the procedures are complicated by limitations to the constitutive laws in current use. The current work presents a comprehensive examination of the issues involved, using experimental (uniaxial and indentation) data for a NiTi Shape Memory Alloy. It was found that it is possible to obtain the superelastic parameter values using a single indenter shape (spherical). Information is also presented on sensitivities and the probable reliability of such parameters obtained in this way for an unknown material.

The aim of this thesis was to understand how a non-Newtonian fluid like chocolate fluidises under vibration. The problem was approached both experimentally and computationally, employing the finite element method as implemented in oomph-lib. In order to model a non-Newtonian fluid its constitutive behaviour has to be known. For this purpose, rheological measurements on tempered chocolate were performed. The chocolate was modelled using generalised Newtonian models for the viscosity and it was found that the Sisko model provided the best fit to the data. The generalised Newtonian Navier-Stokes equations were implemented within oomph-lib and their validation against analytical solutions yielded excellent agreement. Both the experiments and the computations for a sessile drop of chocolate, which is vibrated vertically, spreading on a layer of the same fluid yielded qualitatively similar results. The parameter which controls the spreading is the acceleration arising from the vibration. The drop rests on the layer and does not spread under gravity and small accelerations. However, as the acceleration increases and exceeds a threshold the drop starts to spread out. For a constant amplitude vibration, the spreading rate increases with increasing frequency and for large frequencies approaches a theoretical spreading law which corresponds to viscous dominated spreading of a Newtonian drop.

Airframes operating in the hypersonic regime are subjected to complex structural and thermal loads. Structural loads are a result of aggressive high G maneuvers, rapid vehicle acceleration and deceleration, and dynamic pressure, while thermal loads are a result of aerodynamic heating. For such airframes, structural members are typically constructed from steel, titanium and nickel alloys. However, with most materials, rapid elevations in temperature lead to undesirable changes in material properties. In particular, reductions in strength and stiffness are observed, along with an increase in thermal conductivity, specific heat and thermal expansion. Thus, hypersonic airframes are typically designed with external insulation, active cooling or a thermal protection system (TPS) added to the structure to protect the underling material from the effects of temperature. Such thermal protection may consist of adhesively bonded, pinned, and bolted thermal protection layers over exterior panels. These types of attachments create abrupt changes in thermal expansion and stiffness that make the structure susceptible to cracking and debonding as well as adding mass to the airframe. One of the promising materials concepts for extreme environments that was introduced in the past is the so-called Spatially Tailored Advanced Thermal Structures (STATS). The concept of STATS is rooted in functionally graded materials (FGMs), in which a directional variation of material properties exists. These materials are essentially composites and consist of two or more phases of distinct materials in which the volume fractions of each phase continuously change in space. Here, the graded material will serve a dual-purpose role as both the structural/skin member and thermal management with the goal of reducing the weight of the structure while maintaining structural soundness. This is achieved through the ability to tailor material properties to create a desired or enhanced thermomechanical response through spatial variation (e.g. grading). The objective of this study is to present a computational framework for modeling and evaluating the thermomechanical response of STATS and FGMs for highly maneuverable hypersonic (Mach > 5) airframes. To meet the objective of this study, four key steps have been defined to study the thermomechanical response of such materials in extreme environments. They involve: (1) modeling of graded microstructures; (2) validation of analytical and numerical modeling techniques for graded microstructures; (3) determination of effective properties of variable composition composites; (4) parametric studies to evaluate the performance of FGMs for use in the hypersonic operating environment; (5) optimization of the material spatial grading in hypersonic panels aiming to improve the thermomechanical performance. Modeling of graded microstructures, representing particulate reinforced FGMs, has been accomplished using power law distribution functions to specify the spatial variation of the constituents. Artificial microstructures consisting of disks and spheres have been generated using developed algorithms. These algorithms allow for the creation of dense packing fractions up to 0.61 and 0.91 for 2D and 3D geometry, respectively. Effective properties of FGMs are obtained using micromechanics models and finite element analysis of representative volume elements (RVEs). Two approaches have been adopted and compared to determine the proper RVE for materials with graded microstructures. In the first approach, RVEs are generated by considering regions that have a uniform to slow variation in material composition (i.e., constant volume fraction), resulting in statistically homogenous piecewise RVEs of the graded microstructure neglecting interactions from neighboring cells. In the second approach, continuous RVEs are generated by considering the entire FGM. Here it is presumed that modeling of the complete variation in a microstructure may influence the surrounding layers due to the interactions of varying material composition, particularly when there is a steep variation in material composition along the grading direction. To determine these effects of interlayer interactions, FGM microstructures were generated using three different types of material grading functions, linear, quadratic and square root, providing uniform, gradual and steep variations, respectively. Two- and three-dimensional finite element analysis was performed to determine the effective temperature-dependent material properties of the composite over a wide temperature range. The outcome of the computational analysis show that the similar effective properties are obtained by each of the modeling approaches. Furthermore, the obtained computational results for effective elastic, thermal, and thermal expansion properties are consistent with the known analytical bounds. Resulting effective temperature-dependent material properties were used to evaluate the time-dependent thermostructural response and effectiveness of FGM structural panels. Structural panels are subjected to time- and spatial-dependent thermal and mechanical loads resulting from hypersonic flight over a representative trajectory. Mechanical loads are the by-product of aggressive maneuvering at high air speeds and angles of attack. Thermal loads as a result of aerodynamic heating are applied to the material systems as laminar, turbulent and transitional heat flux on the outer surface. Laminar and turbulent uniform heat fluxes are used to evaluate the effectiveness of FGM panels graded in the through-thickness direction only. Transitional heat fluxes are used to evaluate the effectiveness of FGMs graded in two principal directions, e.g., through-thickness and the surface parallel to flow. The computational results indicate that when subjected to uniform surface heat flux, the graded material system can eliminate through-thickness temperature gradients that are otherwise present in traditional thermal protection systems. Furthermore, two-dimensional graded material systems can also eliminate through-thickness temperature gradients and significantly reduce in-plane surface temperature gradients when subjected to non-uniform surface aerodynamic heating.

No description available.

<p>Norrborns Industri AB in Bollnäs manufactures truck trailers with the brand Parator. One of their trailers is Parator LX 10-20. The trailer is designed to transport hooklift containers with the option to tip loose goods such as gravel, asphalt and seed. The container is mounted on a frame which is placed on the chassis. To reduce weight a redesign of the trailer is needed. The purpose of this study was to develop a concept that makes the frame lighter and easier to manufacture while maintaining safety and rigidity. The thesis also discusses factors to consider when designing with high-strength steel.</p><p> </p><p>The optimization was based on existing 2D drawings of the frame. Analysis of the structure served as a basis for the optimization. First, a 3D model was created from the drawings. Then, the frame was analyzed with selected loads and boundary conditions. Initially simple models were used to develop concepts. From these, two concepts were selected and one of them was thoroughly analyzed.</p><p> </p><p>The optimization resulted in a concept design weight of 732 kg, which is 179 kg less compared to the current frame at 911 kg.</p> / <p>Norrborns Industri AB i Bollnäs tillverkar lastbilssläp som säljs under varumärket Parator. Ett av deras släp är Parator LX 10-20 som är en lastväxlarvagn avsedd för att transportera olika lastbärare, t ex grusflak och containrar, som behöver kunna tippas. Lastbäraren sitter monterad på en tippram som i sin tur sitter på ett släpchassi. En omkonstruktion av detta släp önskas för att minska vikten. Syftet med examensarbetet var att ta fram förslag som gör tippramen lättare samt enklare att tillverka med bibehållen säkerhet och vridstyvhet. Examensarbetet tar även upp faktorer att tänka på vid konstruktion med höghållfast stål.</p><p> </p><p>Optimeringen utgick från befintliga 2D-ritningar på ramen. Först skapades en 3D-modell från ritningarna. Sedan analyserades ramen utifrån valda laster och randvillkor. Analyserna av den nuvarande konstruktionen låg sedan till grund för optimeringen. Till en början användes enklare modeller för att ta fram koncept. Därefter modellerades två valda koncept varpå ett av dem har analyserats mer genomgående.</p><p> </p><p>Arbetet resulterade i ett koncept som vägde 732 kg. Det är 179 kg lättare än den nuvarande konstruktionen på 911 kg.</p>

No description available.