Dissertations / Theses on the topic 'Shape deformation'
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Piazolo, Sandra. "Shape fabric development during progressive deformation." [S.l. : s.n.], 2000. http://ArchiMeD.uni-mainz.de/pub/2001/0032/diss.pdf.
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Angelidis, Alexis, and n/a. "Shape modeling by swept space deformation." University of Otago. Department of Computer Science, 2006. http://adt.otago.ac.nz./public/adt-NZDU20060808.161349.
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In Computer Graphics, in the context of shape modeling on a computer, a common characteristic of popular techniques is the possibility for the artist to operate on a shape by modifying directly the shape�s mathematical description. But with the constant increase of computing power, it has become increasingly realistic and effective to insert interfaces between the artist and the mathematics describing the shape. While in the future, shape descriptions are likely to be replaced with new ones, this should not affect the development of new and existing shape interfaces. Space deformation is a family of techniques that permits describing an interface independently from the description. Our thesis is that while space deformation techniques are used for solving a wide range of problems in Computer Graphics, they are missing a framework for the specific task of interactive shape modeling. We propose such a framework called sweepers, together with a set of related techniques for shape modeling. In sweepers, we define simultaneous-tools deformation, volume-preserving deformation, topology-changing deformation and animated deformation. Our swept-fluid technique introduces the idea that a deformation can be described as a fluid. In fact, the sweepers framework is not restrained to shape modeling and is also used to define a new fluid animation technique. Since the motion of a fluid can be considered locally as rigid, we define a formalism for handling conveniently rigid transformations. To display shapes, we propose a mesh update algorithm, a point-based shape description and a discrete implicit surface, and we have performed preliminary tests with inverse-raytracing. Finally, our technique called spherical-springs can be used to attach a texture to our shapes.
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Mei, Lin. "Statistical analysis of shape and deformation." Thesis, Imperial College London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542932.
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Seaton, Alexander B. "Thermomechanical deformation of shape memory alloys." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/20317.
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NiTi is a shape memory alloy and can undergo crystallographically reversible martensitic transformation under applied loads resulting in recoverable of strains of the order of 5 %. The single crystal properties of shape memory alloys have been studied extensively in the past and a good understanding of the mechanical properties of the material in this form has been acquired. However, when used in practical applications shape memory alloys are used in their polycrystalline form. In a polycrystalline form the deformation behaviour may be quite different to that of a single crystal due to the constraints of surrounding grains and anisotropy of material properties. In the case of shape memory alloys these are anisotropic elastic and transformation properties. The main focus of the work in this thesis is the deformation behaviour of commercial rod samples of NiTi while under thermomechanical loads. The grain-orientation-specific internal strain development and phase faction evolution within particular grain orientations is evaluated during deformation by the in-situ neutron diffraction technique. The experimental results presented include stress-induced martensitic transformation, cooling through the martensitic transformation under a fixed stress, the generation of recovery stresses while heated under constraint, and studies of the detwinning of the B 19' martensite phase under compressive and tensile loading. In addition, the effect of ageing on mechanical properties of NiTi is investigated via the method. Changes in the load partitioning behaviour is noted for NiTi cooled under a fixed tensile stress of 200 MPa which compare well with modelling predictions in the literature. Large changes in the mechanical properties of NiTi as a results of ageing are ascribed to the presence of the R-phase due to the formation of precipitates during ageing. Evidence of detwinning of B 19' martensite in both tension and compression is found, in contrast to other work in the literature.
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Ito, Hiroaki. "Shape fluctuation and deformation of biological soft interfaces." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215286.
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Fender, Amanda. "Shape and deformation measurement using multicore optical fibres." Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2058.
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This thesis investigates the use of a novel optical fibre sensor (OFS) for structural monitoring in remote or inaccessible areas. OFSs are desirable for this application because they are intrinsically safe, add little weight and are free from electrical interference. Fibre Bragg gratings (FBGs) in particular are attractive since they act as optical strain gauges, converting fibre strain to a wavelength-encoded signal. This project uses FBGs written into three or four cores of a novel four-core fibre at the same point along the fibre length. This configuration allows the local curv~ture of the fibre to be obtained by measuring the strain difference between cores ·at an applied bend. The multicore fibre (MCF) eliminates any temperature sensitivity and strain transfer issues ofthe sensor. Dynamic curvature measurement was achieved by interrogating each of the MCF cores with an arrayed waveguide grating (AWG). This was demonstrated at interrogation speeds >11 kHz for a stainless steel cantilever vibrating at -30 Hz to achieve a curvature resolution of 0.09 m-I. Quasi-static tests found a curvature resolution of 0.02 m-I. This dynamic curvature measurement technique was applied to create an accelerometer from a cantilever formed from a short length ofMCF vibrating at frequencies up to 3 kHz. The accuracy of the acceleration measurement was better than 5 % at frequencies below 300 Hz. A commercial interrogator based on a tunable laser technique was used for several quasi-static applications. The curvature of a 240.8 mm diameter aluminium and Perspex cylinder was found to be resolved by the MCF sensor to 0.01 m-I. Four MCF FBGs were spliced together to form a multiplexed array in order to investigate shape measurement using several curvature measurements. The array was attached to a 33 cm long deformable Perspex rod and the MCF FBGs were found to measure curvatures that matched very closely with values predicted by a mathematical model. This was demonstrated for both horizontal and vertical deformations. Finally, an MCF FBG sensor was embedded in a short strip of compliant material (Sylgard) in order to create a sensor that could easily be wrapped around a small test object without the need for permanent bonding. This was used to measure the change in radius of a 2 cm diameter sample as it was compressed. This was found to be capable of measuring a radius change of< 30 Jlm.
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Perez, Daniel Eduardo. "Shield Design for Maximum Deformation in Shape-Shifting Surfaces." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4561.
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This research presents the initial studies and results on shield design for Shape-Shifting Surfaces (SSSs) seeking maximum compression and maximum expansion of a unit-cell. Shape-Shifting Surfaces (SSSs) are multilayered surfaces that are able to change shape while maintaining their integrity as physical barriers. SSSs are composed of polygonal unit-cells, which can change side lengths and corner angles. These changes are made possible by each side and corner consisting of at least two different shields, or layers of material. As the layers undergo relative motion, the unit-cell changes shape. In order for the SSS to retain its effectiveness as a barrier, no gaps can open between different layers. Also, the layers cannot protrude past the boundaries of the unit-cell. Based on these requirements, using equilateral triangle unit-cells and triangular shields, a design space exploration was performed to determine the maximum deformation range of a unit-cell. It was found that the triangular shield that offered maximum expansion and compression ratio is a right triangle with one angle of 37.5 degrees and its adjacent side equal to 61% of the side of the unit-cell. The key contribution of this paper is a first algorithm for systematic SSS shield design. Possible applications for SSSs include protection, by creating body-armor systems; reconfigurable antennas able to broadcast through different frequencies; recreational uses, and biomedical applications.
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Rajagopalan, Sudhir. "INSTRUMENTED NANOINDENTATION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3283.
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Near equi-atomic nickel titanium (NiTi) shape memory alloys (SMAs) are a class of materials characterized by their unique deformation behavior. In these alloys, deformation mechanisms such as mechanical twinning and stress induced phase transformation between a high symmetry phase (austenite) and a low symmetry phase (martensite) additionally occur and influence mechanical behavior and thus their functionality. Consequently, applications of SMAs usually call for precise phase transformation temperatures, which depend on the thermomechanical history and the composition of the alloy. Instrumented indentation, inherently a mechanical characterization technique for small sampling volumes, offers a cost effective means of empirically testing SMAs in the form of centimeter scaled buttons prior to large-scale production. Additionally, it is an effective probe for intricate SMA geometries (e.g., in medical stents, valves etc.), not immediately amenable to conventional mechanical testing. The objective of this work was to study the deformation behavior of NiTi SMAs using instrumented indentation. This involved devising compliance calibration techniques to account for instrument deformation and designing spherical diamond indenters. Substantial quantitative information related to the deformation behavior of the shape memory and superelastic NiTi was obtained for the first time, as opposed to existing qualitative indentation studies. For the case of shape memory NiTi, the elastic modulus of the B19' martensite prior to twinning was determined using spherical indentation to be about 101 GPa, which was comparable to the value from neutron diffraction and was substantially higher than typical values reported from extensometry (68 GPa in this case). Twinning at low stresses was observed from neutron diffraction measurements and was attributed to reducing the elastic modulus estimated by extensometry. The onset of predominantly elastic deformation of the twinned martensite was identified from the nanoindentation response and the elastic modulus of the twinned martensite was estimated to be about 17 GPa. Finite element modeling was used to validate the measurements. For the case of the superelastic NiTi, the elastic modulus of the parent austenite was estimated to be about 62 GPa. The onset of large-scale stress induced martensite transformation and its subsequent elastic deformation were identified from the nanoindentation response. The effect of cycling on the mechanical behavior of the NiTi specimen was studied by repeatedly indenting at the same location. An increase in the elastic modulus value for the austenite and a decrease in the associated hysteresis and residual depth after the initial few cycles followed by stabilization were observed. As for the case of shape memory NiTi, finite element modeling was used to validate the measurements. This work has initiated a methodology for the quantitative evaluation of shape memory and superelastic NiTi alloys with instrumented spherical indentation. The aforementioned results have immediate implications for optimizing thermomechanical processing parameters in prototype button melts and for the mechanical characterization of intricate SMA geometries (e.g., in medical stents, valves etc.) This work was made possible by grants from NASA (NAG3-2751) and NSF (CAREER DMR-0239512) to UCF.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
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Feng, Ping. "Deformation instability and morphology in shape memory alloy under stress /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20FENG.
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Blanco, Fausto Richetti. "A technique for interactive shape deformation on non-structured objects." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/11176.
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Este trabalho apresenta uma técnica para deformação interativa de objetos 3D não estruturados que combina o uso de sketches em 2D e manipulação interativa de curvas. Através de sketches no plano de imagem, o usuário cria curvas paramétricas a serem usadas como manipulares para modificar a malha do objeto. Um conjunto de linhas desenhadas sobre a projeção do modelo pode ser combinado para criar um esqueleto composto de curvas paramétricas, as quais podem ser interativamente manipuladas, deformando assim a superfície associada a elas. Deformações livres são feitas movendo-se interativamente os pontos de controle das curvas. Alguns outros efeitos interessantes, como torção e escalamento, são obtidos operando-se diretamente sobre o campo de sistemas de coordenadas criado ao longo da curva. Um algoritmo para evitar inter-penetrações na malha durante uma sessão de modelagem com a técnica proposta também é apresentado. Esse algoritmo é executado a taxas interativas assim como toda a técnica apresentada neste trabalho. A técnica proposta lida naturalmente com translações e grandes rotações, assim como superfícies não orientáveis, não variedades e malhas compostas de múltiplos componentes. Em todos os casos, a deformação preserva os detalhes locais consistentemente. O uso de curvas esqueleto permite implementar a técnica utilizando uma interface bem intuitiva, e provê ao usuário um controle preciso sobre a deformação. Restrições sobre o esqueleto e deformações sem inter-penetrações são facilmente conseguidos. É demonstrada grande qualidade em torções e dobras nas malhas e os resultados mostram que a técnica apresentada é consideravelmente mais rápida que as abordagens anteriores, obtendo resultados similares. Dado seu relativo baixo custo computacional, esta abordagem pode lidar com malhas compostas por centenas de milhares de vértices a taxas interativas.This work presents a technique for interactive shape deformation of unstructured 3D models, based on 2D sketches and interactive curve manipulation in 3D. A set of lines sketched on the image plane over the projection of the model can be combined to create a skeleton composed by parametric curves, which can be interactively manipulated, thus deforming the associated surfaces. Free-form deformations are performed by interactively moving around the curves’ control points. Some other interesting effects, such as twisting and scaling, are obtained by operating directly over a frame field defined on the curve. An algorithm for mesh local self-intersection avoidance during model deformation is also presented. This algorithm is executed at interactive rates as is the whole technique presented in this work. The presented technique naturally handles both translations and large rotations, as well as non-orientable and non-manifold surfaces, and meshes comprised of multiple components. In all cases, the deformation preserves local features. The use of skeleton curves allows the technique to be implemented using a very intuitive interface, and giving the user fine control over the deformation. Skeleton constraints and local self-intersection avoidance are easily achieved. High-quality results on twisting and bending meshes are also demonstrated, and the results show that the presented technique is considerably faster than previous approaches for achieving similar results. Given its relatively low computational cost, this approach can handle meshes composed by hundreds of thousand vertices at interactive rates.
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Nguyen, Tran. "Optical measurement of shape and deformation fields on challenging surfaces." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10551.
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A multiple-sensor optical shape measurement system (SMS) based on the principle of white-light fringe projection has been developed and commercialised by Loughborough University and Phase Vision Ltd for over 10 years. The use of the temporal phase unwrapping technique allows precise and dense shape measurements of complex surfaces; and the photogrammetry-based calibration technique offers the ability to calibrate multiple sensors simultaneously in order to achieve 360° measurement coverage. Nevertheless, to enhance the applicability of the SMS in industrial environments, further developments are needed (i) to improve the calibration speed for quicker deployment, (ii) to broaden the application range from shape measurement to deformation field measurement, and (iii) to tackle practically-challenging surfaces of which specular components may disrupt the acquired data and result in spurious measurements. The calibration process typically requires manual positioning of an artefact (i.e., reference object) at many locations within the view of the sensors. This is not only timeconsuming but also complicated for an operator with average knowledge of metrology. This thesis introduces an automated artefact positioning system which enables automatic and optimised distribution of the artefacts, automatic prediction of their whereabouts to increase the artefact detection speed and robustness, and thereby greater overall calibration performance. This thesis also describes a novel technique that integrates the digital image correlation (DIC) technique into the present fringe projection SMS for the purpose of simultaneous shape and deformation field measurement. This combined technique offers three key advantages: (a) the ability to deal with geometrical discontinuities which are commonly present on mechanical surfaces and currently challenging to most deformation measurement methods, (b) the ability to measure 3D displacement fields with a basic single-camera single-projector SMS with no additional hardware components, and (c) the simple implementation on a multiple-sensor hardware platform to achieve complete coverage of large-scale and complex samples, with the resulting displacement fields automatically lying in a single global coordinate system. A displacement measurement accuracy of ≃ 1/12,000 of the measurement volume, which is comparable to that of an industry-standard DIC system, has been achieved. The applications of this novel technique to several structural tests of aircraft wing panels on-site at the research centre of Airbus UK in Filton are also presented. Mechanical components with shiny surface finish and complex geometry may introduce another challenge to present fringe projection techniques. In certain circumstances, multiple reflections of the projected fringes on an object surface may cause ambiguity in the phase estimation process and result in incorrect coordinate measurements. This thesis presents a new technique which adopts a Fourier domain ranging (FDR) method to correctly identifying multiple phase signals and enables unambiguous triangulation for a measured coordinate. Experiments of the new FDR technique on various types of surfaces have shown promising results as compared to the traditional phase unwrapping techniques.
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Neophytou, Alexandros. "Data driven models of human shape, pose and garment deformation." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/808505/.
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This thesis addresses the problem of modeling human shape in three dimensions. Specifically, this thesis is focused on modeling body shape variation across multiple individuals, pose induced shape deformations and garment deformations that are influenced both by body shape and pose. A methodology for constructing data driven models of human body and garment deformation is provided. Additionally, an application for online fashion retailing is presented. Abstract Firstly, a quantitative and qualitative evaluation, is introduced, of surface representations used in recent statistical models of human shape and pose. It is shown that the Euclidean representation generates a more compact human shape model compared to other representations. A small number of model parameters indicates better convergence in a human body estimation framework. In contrast, a high number of model parameters increases the risk of the optimization getting trapped in a local optimum. Based on these insights a system for human body shape estimation and classification for on-line fashion applications is presented. Given a single image of a subject and the subject's height and weight the proposed framework is able to estimate the 3D human body shape using a learnt statistical model. Results demonstrate that a single image holds sufficient information for accurate shape classification. This technology has been exploited as part of a collaborative project with fashion designers to develop a mobile app to classify body shape for clothing recommendation in online fashion retail. Abstract Next, Shape and Pose Space Deformation (SPSD) is presented, a technique for modeling subject specific pose induced deformations. By exploiting examples of different people in multiple poses, plausible animations of novel subjects can be synthesized by interpolating and extrapolating in a joint shape and pose parameter space. The results show that greater detail is achieved by incorporating subject specific pose deformations as opposed to a subject independent pose model. Finally, SPSD is extended to a three layered data-driven model of human shape, pose and garment deformation. Each layer represents the deformation of a template mesh and can be controlled independently and intuitively. The garment deformation layer is trained on sequences of dressed actors and relies on a novel technique for human shape and posture estimation under clothing.
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Shao, Wei. "Identifying the shape collapse problem in large deformation image registration." Thesis, University of Iowa, 2016. https://ir.uiowa.edu/etd/2276.
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This thesis examines and identifies the problems of shape collapse in large deformation image registration. Shape collapse occurs in image registration when a region in the moving image is transformed into a set of near zero volume in the target image space. Shape collapse may occur when the moving image has a structure that is either missing or does not sufficiently overlap the corresponding structure in the target image. We state that shape collapse is a problem in image registration because it may lead to the following consequences: (1) Incorrect pointwise correspondence between different coordinate systems; (2) Incorrect automatic image segmentation; (3) Loss of functional signal. The above three disadvantages of registration with shape collapse are illustrated in detail using several examples with both real and phantom data. Shape collapse problem is common in image registration algorithms with large degrees of freedom such as many diffeomorphic image registration algorithms. This thesis proposes a shape collapse measurement algorithm to detect the regions of shape collapse after image registration in pairwise and group-wise registrations. We further compute the shape collapse for a whole population of pairwise transformations such as occurs when registering many images to a common atlas coordinate system. Experiments are presented using the SyN diffeomorphic image registration algorithm and diffeomorphic demons algorithm. We show that shape collapse exists in both of the two large deformation registration methods. We demonstrate how changing the input parameters to the SyN registration algorithm can mitigate the collapse image registration artifacts.
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Daieff, Marine. "Deformation and shape of flexible, microscale helices in viscous flows." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC189/document.
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Les interactions fluide-structure sont d'un grand intérêt en ingénierie et pour des applications industrielles et médicales. Comprendre les interactions entre des particules aux formes complexes et des écoulements peut mener à de nouveaux projets pour l'administration ciblée de médicaments, pour des micro capteurs de débit et à une meilleure compréhension du comportement des micro-organismes. Dans cette thèse, nous étudions l'interaction fluide-structure de particules chirales de taille microscopique à bas nombres de Reynolds. Les particules sont rigides et confinées dans une géométrie 2D ou flexibles avec une forme hélicoïdale. Combiner des techniques de microfabrication, comme des méthodes d'assemblage multi-échelles et la microfluidique, permet d'avoir un excellent contrôle à la fois sur les propriétés géométriques et mécaniques des fibres et aussi sur les caractéristiques de l'écoulement comme ses propriétés Newtoniennes et non Newtoniennes, sa vitesse et sa géométrie. Dans un premier temps, nous avons étudié des fibres rigides, 2D et asymétriques, i.e. des fibres en L. Les confinements latéral et transversal ont été étudiés tout comme la forme de la fibre. Lorsque la particule est transportée dans un écoulement visqueux, elle tourne jusqu'à atteindre une orientation d'équilibre. Dans cette orientation particulière, la fibre se décale vers les murs latéraux du canal. Une étude complète des trajectoires de la fibre a été réalisée et des comparaisons avec des particules symétriques ont été faites. Ce sujet de recherche pourrait aider à concevoir des dispositifs pour trier des particules à des fins médicales. Dans un second temps, nous avons étudié des fibres hélicoïdales flexibles de taille micrométrique. La dynamique de formation de l'hélice a été analysée. Les hélices se forment à partir de rubans droits 2D qui, de façon spontanée, s'enroulent quand ils sont libérés dans l'eau. La forme hélicoïdale est obtenue seulement quelques minutes après la libération des rubans mais l'hélice continue à rétrécir pendant plusieurs heures jusqu'à ce qu'elle atteigne une courbure préférentielle. Deux temps caractéristiques sont identifiés dans cette dynamique de formation. Un modèle a été développé pour comprendre le complexe équilibre entre les forces élastiques, de tension de surface et visqueuses aux temps courts. Après avoir analysé plusieurs hypothèses, comme l'impact d'une couche sacrificielle, une possible modification du module du matériau et la présence de fluage, l'évolution du rayon de l'hélice aux temps longs s'explique probablement par du fluage. La dynamique d'extension et de relaxation de la fibre flexible a aussi été étudiée dans des fluides Newtonien et non Newtonien. L'étude dans des solutions de polymères est pertinente et intéressante car la taille des micro hélices est comparable à celle des flagelles des micro-organismes et à celle de chaînes de polymères de grande masse moléculaire. Il s'agit donc d'un problème mutli-échelles complexe car la viscosité locale au niveau du ruban pourrait être différente de la viscosité globale de l'écoulementFluid-structure interactions are of wide interest in engineering, industrial and medical applications. Understanding the interactions between complex shaped particles and flows might lead to new designs for targeted delivery, microflow sensors and to a better understanding of the behavior of microorganisms. In this thesis, we study the fluid-structure interaction of microscale chiral particles at low Reynolds numbers. The particles are rigid and confined in a 2D geometry or flexible with a helical shape. The combination of microfabrication techniques, such as multiscale assembly methods and microfluidics, enables to have a perfect control on both the geometrical and mechanical properties of the fibers and the flow features such as Newtonian or non Newtonian properties, the flow velocity and the flow geometry. First we studied asymmetric 2D rigid fibers, i.e. L-shaped fibers. Both lateral and transversal confinements have been investigated, as well as the shape of the fiber. When the particle is transported in viscous flows, it rotates until reaching an equilibrium orientation. In this specific orientation, the fiber drifts towards the lateral walls of the channel. A full investigation on the trajectories of the fiber has been performed and comparisons with symmetric particles have been done. Such research may help design devices to sort particles for medical purposes. Secondly we studied flexible microscale helical fibers. The dynamics of the helix formation has been investigated. The helices are formed from straight 2D ribbons, which spontaneously coil when released in water. The helical shape is reached only several minutes after the release but the helix keeps shrinking during several hours until reaching a preferred curvature. Two different timescales are identified in this formation dynamics. A model has been developed to understand the complex balance between elastic, surface tension and viscous forces at short times. After investigating several assumptions such as the impact of a sacrificial layer, a possible change in the modulus of the material and a creep behavior, the evolution of the radius at long times is most likely explained by creep. The extension and relaxation dynamics of the flexible fiber has also been studied in Newtonian and non Newtonian fluids. The study in polymer solutions is relevant and interesting because the size of the microhelix is comparable to the flagella of microorganisms and to the chains of high molecular weight polymers. Complex multiscale problems are then involved as the local viscosity at the scale of the ribbon might differ from the global viscosity at the scale of the flow
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Xu, Ying. "A new constrained shape deformation operator with applications in footwear design /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?IELM%202008%20XU.
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Nordén, Kristina. "Surface and Inner Deformation during Shape Rolling of High Speed Steels." Licentiate thesis, KTH, Materials Science and Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4460.
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Shape rolling is a common manufacturing process used to produce long products i.e. bars and wire. One of the problems that might occur during rolling is defect formation leading to rejection of the finished product. This work is a step towards a better understanding of the evolution of some of these defects.
The evolution and reduction of cracks during shape rolling is studied in this thesis. To accomplish this, artificial longitudinal cracks are machined along bars of high speed steel. The cracks are positioned at different sites evenly distributed along the periphery in intervals of 45°. Some of the cracks are left open and some are filled with carbon or stainless steel welds. FE simulations are performed using the commercial code MSC.Marc and the results from the simulations are compared with experimental ones. Generally, simulations predict less reduction than observed experimentally. For most positions, the cracks tend to reduce most effectively followed by carbon steel welds and stainless steel welds.
To evaluate the inner deformation of a cross section during shape rolling in an oval-round-oval-round series, sample bars of M2 high speed steel are prepared with grids made up by stainless steel wires. After collecting samples after each pass, they are X-rayed to create an image of the grid. The deformation of the wires can favorably be described by FE simulations of a bar originally rotated 10° when entering the first pass. The results suggest that the simulations describe the deformation during shape rolling well.
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Nordén, Kristina. "Surface and inner deformation during shape rolling of high speed steels /." Stockholm : Materialvetenskap Materials Science and Engineering, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4460.
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Nardoni, Chiara. "Mesh deformation strategies in shape optimization. Application to forensic facial reconstruction." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066248/document.
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Cette thèse est consacrée à la conception, au développement et à l'analyse de méthodes de déformation de maillage pour la modélisation, le traitement et la comparaison de forme -telles que l'appariement et la reconstruction de surface- ainsi qu’à la conception d'une méthode numérique robuste pour la reconstruction faciale. La reconstruction faciale tridimensionnelle consiste à estimer un visage numérique à partir de la seule donnée de son crâne sec. Il s'agit d'un défi en médecine légale et en anthropologie. La contribution majeure de cette thèse est la conception d'une nouvelle méthode pour l'appariement de forme, en s'appuyant sur des techniques d'optimisation de forme. Sous la seule hypothèse que les deux formes ont la même topologie, la transformation cherchée s'obtient comme une suite de déplacements élastiques, solutions d'un problème de minimisation d’énergie basée sur une fonction distance signée.Nous proposons également une méthode de drapage permettant la génération d'un modèle de surface fermée à partir d'un maillage source. La méthode repose sur une technique d’évolution de maillage utilisant les équations de l'élasticité linéaire. Un maillage modèle est itérativement déformé pour générer une séquence de formes qui s’approche de plus en plus de la triangulation source. Dans la deuxième partie de ce manuscrit, nous nous intéressons au développement d’une méthode automatique de reconstruction faciale numérique. En s’appuyant sur des techniques de déformation continue telles que le ‘morphing' et le ’warping’, l'approche proposée est intégrée par des connaissances anthropologiques et mécaniquesThis thesis is devoted to the conception, the development and the analysis of mesh deformation strategies for shape modeling, processing and comparison -as shape matching and surface reconstruction- and, in a rather independent concern, for devising a robust computational method for facial reconstruction. Facial reconstruction is about the estimation of a facial shape from the sole datum of the underlying skull and is a challenging problem in anthropology and forensic science. The main contribution of the thesis is the design of a novel method for shape matching, borrowing techniques from the shape optimization context. Under the sole assumption that the two shapes share the same topology, the desired mapping is achieved as a sequence of elastic displacements by minimizing an energy functional based on a signed distance function. Several numerical examples are presented to show the efficiency of the method.Also, a novel method for generating a closed surface mesh model of an initially non-closed source mesh model is developed. The method relies on an original PDE-based mesh evolution technique. A template shape is iteratively deformed, producing a sequence of shapes that get 'closer and closer' to the source triangulation.The second part of the manuscript deals with the development of a landmark-free, fully automated method for digital facial reconstruction. Based on techniques of continuous deformation as 'morphing' and 'warping', the proposed approach is integrated with anthropological assumptions and mechanical models
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ROUSSEAU, Yannick, Igor MEN'SHOV, and Yoshiaki NAKAMURA. "Morphing-Based Shape Optimization in Computational Fluid Dynamics." 日本航空宇宙学会, 2007. http://hdl.handle.net/2237/13876.
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He, Yongjun. "Non-local model for deformation patterns in NiTi microtubing /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20HE.
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Raji, Abdulganiy Olayinka. "Discrete element modelling of the deformation of bulk agricultural particulates." Thesis, University of Newcastle Upon Tyne, 1999. http://hdl.handle.net/10443/871.
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The Discrete Element Method (DEM) has been applied to numerical modelling of the bulk compression of low modulus particulates. An existing DE code for modelling the contact mechanics of high modulus particles using a linear elastic contact law was modified to incorporate non-linear viscoelastic contact, real containing walls and particle deformation. The new model was validated against experimental data from the literature and physical experiments using synthetic spherical particles, apple and rapeseed. It was then used to predict particle deformation, optimum padding thickness in a handling line and bulk compression parameters during oilseed expression. The application of DEM has previously been limited to systems of hard particles of high compressive and shear modulii with relatively low failure strain. Material interactions have therefore commonly been modelled using linear contact law. For high modulus particles, particle shape change resulting from deformation is a not a significant factor. Most agricultural particulates however deform substantially before failure and their interaction is better represented with non-linear hysteretic viscoelastic contact relationship. Deformation of geometrically shaped particles in DEM is usually treated as "virtual" deformation, which means that particles are allowed to overlap rather than deform due to contact force. Change to particle shape has not previously been possible other than in the case of particles modelled as 2-D polygons or where each particle is also modelled concurrently with an FE mesh. In this work a new approach has been developed which incorporates a non-linear deformation dependent contact damping relationship and a shape change while maintaining sufficient geometrical symmetry to allow the problem to be handled by the same DE algorithms as used for true spheres. The method was validated with available experimental results on impact behaviour of rubber and the variations with different damping coefficients were simulated for a selected fruit. A fruit handling process dependent on the impact process was then simulated to obtain data required in the design of a fruit processing line. Changes in shape of spherical synthetic rubber particles and rapeseeds under compression were predicted and validated with physical experiments. Images were taken and analysed using image processing techniques with 1: 1 scaling. The method on shape change entails a number of simplifying assumptions such as uniform stress distribution and homogeneous material properties and uniform material distribution when deformed, which are not observed in real agricultural materials and will tend to overestimate the true contact area between particles. In reality for fruits and vegetables, material redistribution is a complex process involving a combination of compaction and movement. However with the new method a better approximation of bed voidage (which standard DEM approaches underestimate) and stress were obtained in the compression of a synthetic material. This is a significant improvement on existing methods particularly with respect to stress distribution within a bulk particulate system comprising deforming elements where the size and orientation of contact surface between particles has a strong influence on the bulk modulus. The new model was used for prediction of mechanical oil expression in four oilseed beds. Similar patterns in the variation of the characteristic parameters were obtained as observed in existing experimental data. The data could not be matched exactly as the quantity and arrangement of seeds in the initial seedbeds were not the same as those used in the experimental work. However the DE model gave approximate oil point data for seedbeds with the same physical properties and initial conditions as in the experiment. This suggests that the new model may be a useful tool in the study of mechanical seed-oil expression and other agricultural particulate compression processes.
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RATHOD, CHANDRASEN. "DIFFRACTION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS AND SELECTED ENGINEERING COMPONENTS." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2892.
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Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
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Wang, Liu Sheng. "Shape and deformation measurement of 3D surface using phase stepping speckle interferometry." Thesis, Nottingham Trent University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386409.
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Ji, Wei. "Spatial Partitioning and Functional Shape Matched Deformation Algorithm for Interactive Haptic Modeling." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1226364059.
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Kulkarni, Ajay V. "Effect of ausforming via severe plastic deformation on shape memory behavior of NiTi." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/3246.
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In this study, Thermomechanical properties of Ti-50.8 and 50.7 at% Ni alloy severely deformed using Equal Channel Angular Extrusion (ECAE) are investigated. The aim of this study is to reveal the effects of severe plastic deformation on shape memory, pseudelasticity, interplay between plastic deformation via dislocation slip and twinning, and forward and reverse martensitic transformation. The samples are processed at room temperature, i.e. slightly above the austenite finish temperature, and at 450 °C, i.e. well-above the austenite finish temperature. Transformation temperatures, microstructural evolution, and thermomechanical properties of ECAE processed samples are studied before and after low temperature annealing heat treatment and compared with conventional cold drawn and precipitation hardened material. The unique findings are: 1) the observation of a mixture of heavily deformed B2 (austenite) and B19 (martensite) phases in the samples processed at room temperature although martensite stabilization was expected, 2) the observation of highly organized, twin-related nanograins in B2 phase of the samples deformed at room temperature which was attributed to B2 to B19' via SIM, and B19' to B2 via SPD (SIM: Stress Induced Martensitic transformation, SPD: Severe Plastic Deformation) transformation sequence, 3) simultaneous observation of B2 austenite and strain induced B19 martensite in the samples deformed at 450 °C, and 4) perfect pseudoelasticity, small pseudoelastic stress hysteresis and excellent cyclic response with no irrecoverable strain up to 1000 cycles for ECAE at 450 °C processed sample. Strain induced martensite in NiTi alloys was reported for the first time. The formation of well-organized twin-related nanograins via severe plastic deformation opens a new opportunity for twinning induced grain boundary engineering in NiTi alloys which significantly improves the matrix strength and the cyclic response against degradation of shape memory and pseudoelasticity.
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Hong, Sung Min. "Shape Modeling of Plant Leaves with Unstructured Meshes." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1182.
Full textAbstract:
The plant leaf is one of the most challenging natural objects to be realistically depicted by computer graphics due to its complex morphological and optical characteristics. Although many studies have been done on plant modeling, previous research on leaf modeling required for close-up realistic plant images is very rare. In this thesis, a novel method for modeling of the leaf shape based on the leaf venation is presented. As the first step of the method, the leaf domain is defined by the enclosure of the leaf boundary. Second, the leaf venation is interactively modeled as a hierarchical skeleton based on the actual leaf image. Third, the leaf domain is triangulated with the skeleton as constraints. The skeleton is articulated with nodes on the skeleton. Fourth, the skeleton is interactively transformed to a specific shape. A user can manipulate the skeleton using two methods which are complementary to each other: one controls individual joints on the skeleton while the other controls the skeleton through an intermediate spline curve. Finally, the leaf blade shape is deformed to conform to the skeleton by interpolation. An interactive modeler was developed to help a user to model a leaf shape interactively and several leaves were modeled by the interactive modeler. The ray-traced rendering images demonstrate that the proposed method is effective in the leaf shape modeling.
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Valencia, Angel. "3D Shape Deformation Measurement and Dynamic Representation for Non-Rigid Objects under Manipulation." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40718.
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Dexterous robotic manipulation of non-rigid objects is a challenging problem but
necessary to explore as robots are increasingly interacting with more complex environments in which such objects are frequently present. In particular, common manipulation tasks such as molding clay to a target shape or picking fruits and vegetables for use in the kitchen, require a high-level understanding of the scene and objects. Commonly, the behavior of non-rigid objects is described by a model. Although, well-established modeling techniques are difficult to apply in robotic tasks since objects and their properties are unknown in such unstructured environments. This work proposes a sensing and modeling framework to measure the 3D shape deformation of non-rigid objects. Unlike traditional methods, this framework explores data-driven learning techniques focused on shape representation and deformation dynamics prediction using a graph-based approach. The proposal is validated experimentally, analyzing the performance of the representation model to capture the current state of the non-rigid object shape. In addition, the performance of the prediction model is analyzed in terms of its ability to produce future states of the non-rigid object shape
due to the manipulation actions of the robotic system. The results suggest that the representation model is able to produce graphs that closely capture the deformation behavior of the non-rigid object. Whereas, the prediction model produces visually plausible graphs when short-term predictions are required.
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Simon, Anish Abraham. "Shape memory response and microstructural evolution of a severe plastically deformed high temperature shape memory alloy (NiTiHf)." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/3139.
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NiTiHf alloys have attracted considerable attention as potential high temperature Shape Memory Alloy (SMA) but the instability in transformation temperatures and significant irrecoverable strain during thermal cycling under constant stress remains a major concern. The main reason for irrecoverable strain and change in transformation temperatures as a function of thermal cycling can be attributed to dislocation formation due to relatively large volume change during transformation from austenite to martensite. The formation of dislocations decreases the elastic stored energy, and during back transformation a reduced amount of strain is recovered. All these observations can be attributed to relatively soft lattice that cannot accommodate volume change by other means. We have used Equal Channel Angular Extrusion (ECAE), hot rolling and marforming to strengthen the 49.8Ni-42.2Ti-8Hf (in at. %) material and to introduce desired texture to overcome these problems in NiTiHf alloys. ECAE offers the advantage of preserving billet cross-section and the application of various routes, which give us the possibility to introduce various texture components and grain morphologies. ECAE was performed using a die of 90º tool angle and was performed at high temperatures from 500ºC up to 650ºC. All extrusions went well at these temperatures. Minor surface cracks were observed only in the material extruded at 500 °C, possibly due to the non-isothermal nature of the extrusion. It is believed that these surface cracks can be eliminated during isothermal extrusion at this temperature. This result of improved formability of NiTiHf alloy using ECAE is significant because an earlier review of the formability of NiTiHf using 50% rolling reduction concluded that the minimum temperature for rolling NiTi12%Hf alloy without cracks is 700°C. The strain level imposed during one 90° ECAE pass is equivalent to 69% rolling reduction. Subsequent to ECAE processing, a reduction in irrecoverable strain from 0.6% to 0.21% and an increase in transformation strain from 1.25% to 2.18% were observed at a load of 100 MPa as compared to the homogenized material. The present results show that the ECAE process permits the strengthening of the material by work hardening, grain size reduction, homogeneous distribution of fine precipitates, and the introduction of texture in the material. These four factors contribute in the increase of stability of the material. In this thesis I will be discussing the improvement of mechanical behavior and stability of the material achieved after various passes of ECAE.
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Nilsson, Bengt. "Interferometric 3-D Camera for Shape and Deformation Measurements using Ultra Short Laser Pulses." Doctoral thesis, KTH, Production Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3321.
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UEHARA, Takuya, Takato TAMAI, and Nobutada OHNO. "Molecular Dynamics Simulations of Shape-Memory Behavior Based on Martensite Transformation and Shear Deformation." The Japan Society of Mechanical Engineers, 2006. http://hdl.handle.net/2237/9014.
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Wang, Zhiyi S. M. Massachusetts Institute of Technology. "Computational framework for simulating the deformation and fracture response of oligocrystalline shape memory alloys." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120442.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 89-94).
Shape memory alloys (SMAs) are a class of metallic materials that can recover their original shapes when heated above a certain temperature. Unique features including the superelasticity and shape memory effect have made SMAs attractive materials for a variety of fields ranging from bioengineering to aerospace engineering. In polycrystalline forms, the desirable properties of SMAs have been significantly limited by severe premature intergranular fractures at grain boundaries. Chen et al. (2009) showed that the intergranular fracture in Cu-based SMAs can be mitigated in fine wire forms with bamboo-shaped oligocrystalline microstructure. Tensile tests conducted in the oligocrystalline systems show that large ductility limits approaching those of a single crystal can be achieved while avoiding the issues involved in single crystal processing. It is, thus, of great importance to investigate how the microstructure and grain boundary characteristics affect phase transformation of oSMAs and how to delay transformation-induced fractures. In this thesis, an anisotropic single-crystal constitutive model is developed to study the underlying mechanism of transformation-induced fracture in oSMAs from a numerical perspective at the microstructural level. The model is based on the micromechanical constitutive framework by Thamburaja and Anand (2001) and a robust explicit integration scheme is developed to update the constitutive law. In order to investigate the effects the grain boundary characteristics have on the martensitic phase transformation and transformation-induced fracture, finite element simulations are performed for modeling the stress-strain response and martensite-austenite phase transformation under uniaxial tension loading condition for oSMA wires with triple junction structures. A quantitative analysis of the simulation results is conducted at the microstructural level in each transformation system to interpret the initiation of transformation-induced fracture. The simulations provide insights on the mechanical response, energy absorption of oSMA wires, as well as shed light on the microstructural design objectives of oSMA to avoid or delay the intergranular fracture.
by Zhiyi Wang.
S.M.
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Giacalone, Giuliano. "A matter of shape : seeing the deformation of atomic nuclei at high-energy colliders." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP072.
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Les expériences conduites au collisionneurs de particules BNL RHIC et CERN LHC montrent que l'émission azimutale de hadrons vers l'état final des collisions relativistes noyau-noyau est fortement anisotrope. Cette observation est compatible avec un paradigme hydrodynamique, selon lequel les hadrons observés dans l'état final sont émis à l'issue de l'expansion d'un milieu fluidiforme créée dans la région d'interaction. Ce paradigme prédit notamment que l'anisotropie de l'émission des particules est sensible à la déformation de l'état fondamental des noyaux interagissants. A travers des comparaisons de haute précision entre les données des expériences et le modèle hydrodynamique, j'étudie les manifestations phénoménologiques de la déformation des noyaux atomiques dans les collisions ¹⁹⁷Au+¹⁹⁷Au, ²³⁸U+ ²³⁸U, et ¹²⁹Xe+¹²⁹Xe. Cette analyse mène à des résultats remarquables. Les données de RHIC me permettent de conclure que la géométrie du noyau ²³⁸U est bien celle d'un ellipsoïde, ainsi que d'établir, pour la première fois dans une expérience, que le noyau ¹⁹⁷Au est presque sphérique. Les données venant du LHC montrent que le noyau ¹²⁹Xe est aussi bien ellipsoïdal dans l'état fondamental, ce qui apparaît être en désaccord avec les modèles théoriques de structure nucléaire. J'introduis ensuite une méthode pour isoler les configurations de collision où l'orientation des noyaux déformés brise la symétrie azimutale du système d'une façon maximale. Cela me permet de définir une nouvelle catégorie d'observables très sensibles à la déformation des noyaux qu'on utilise, en ouvrent ainsi le chemin vers des études quantitatives de la structure des noyaux atomiques en physique des hautes énergiesCollider experiments conducted atthe BNL RHIC and at the CERN LHC show thatthe the emission of particles following the interactionof two nuclei at relativistic energy is highlyanisotropic in azimuthal angle. This observationis compatible with a hydrodynamic paradigm, accordingto which the final-state hadrons are emittedfollowing the expansion of a fluidlike systemcreated in the interaction region. Withinthis paradigm, anisotropy in the emission of particlesis enhanced whenever the colliding nucleihave deformed ground states. By meansof high-quality comparisons between the predictionsof hydrodynamic models and particle colliderdata, I study the phenomenological manifestationsof the quadrupole deformation of atomicnuclei in relativistic ¹⁹⁷Au+¹⁹⁷Au, ²³⁸U+²³⁸U,and ¹²⁹Xe+¹²⁹Xe collisions. This analysis demonstratesthat a deep understanding of the structureof the colliding ions is required for the interpretationof data in high-energy experiments. RHICdata confirms in particular the well-known factthat the geometry of ²³⁸U nuclei is that of a welldeformedellipsoid, while indicating that ¹⁹⁷Au nuclei are nearly spherical, a result which is atodds with the estimates of mean-field and empiricalnuclear models. LHC data brings instead evidenceof quadrupole deformation in the groundstate of ¹²⁹Xe nuclei, ascribable to the first visiblemanifestation of shape coexistence phenomena inhigh-energy nuclear experiments. I introduce asimple method to isolate collision configurationsthat maximally break azimuthal symmetry dueto the orientation of the deformed nuclei. Thisallows me to define observables with an unprecedentedsensitivity to the deformation of the collidingspecies, thus paving the way for quantitativestudies of nuclear structure at high energy
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Debora, Monego. "Effect of Surface Ligands on Colloidal Stability, Shape and Sedimentation of Apolar Nanoparticles." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23288.
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Understanding how nanoparticles interact with one another and their surroundings is critical to controlling their colloidal stability and assembly behaviour, and surface ligands play a vital role in determining the inter-particle forces both during and after synthesis. How- ever, our ability to predict the effect of these molecules on how nanoparticles behave in solution is currently poor. This thesis presents a theoretical study of the effect of surface ligands on the colloidal stability, sedimentation and shape deformation of apolar nanoparticles. In particular, inspired by recent experimental results, we develop models of Au and CdSe nanoparticles coated with apolar ligands in apolar solvents and use molecular dynamics simulations to study the conformational and energetic state of the ligand shell and to characterise the interaction between nanoparticles in solution. This work is divided in two parts. In Part I, we characterise and explain the effect of surface ligands on the colloidal stability of apolar nanoparticles. We show that agglomeration in solution can be induced either by the van der Waals attraction between the cores or the attractive interaction between ordered ligand shells, depending on the particle size. We find that in the shell-dominated case, stability depends strongly on the difference in free energy between the ordered and disordered states of the ligands, being affected by even small changes in ligand and solvent structure. In Part II, we show that ligands can strongly affect other properties of nanoparticles in solution, which we do by studying the sedimentation and shape deformation of apolar CdSe nanoparticles. Overall, our results provide a microscopic description of the forces induced by surface ligands and explain why classical colloid theories often fail to explain the colloidal stability of apolar nanoparticles.
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Zhang, Baozhuo. "Synchrotron Radiation X-Ray Diffraction of Nickel-Titanium Shape Memory Alloy Wires During Mechanical Deformation." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc848138/.
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Shape memory alloys (SMAs) are a new generation material which exhibits unique nonlinear deformations due to a phase transformation which allows it to return to its original shape after removal of stress or a change in temperature. It shows a shape memory effect (martensitic condition) and pseudoelasticity (austenitic condition) properties depends on various heat treatment conditions. The reason for these properties depends on phase transformation through temperature changes or applied stress. Many technological applications of austenite SMAs involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity, but are limited due to poor fatigue life. In this thesis, I investigated two important mechanical feature to fatigue behavior in pseudoelastic NiTi SMA wires using high energy synchrotron radiation X-ray diffraction (SR-XRD). The first of these involved simple bending and the second of these involved relaxation during compression loading. Differential scanning calorimetry (DSC) was performed to identify the phase transformation temperatures. Scanning electron microscopy (SEM) images were collected for the initial condition of the NiTi SMA wires and during simple bending, SEM revealed that micro-cracks in compression regions of the wire propagate with increasing bend angle, while tensile regions tend to not exhibit crack propagation. SR-XRD patterns were analyzed to study the phase transformation and investigate micromechanical properties. By observing the various diffraction peaks such as the austenite (200) and the martensite (100), (110), and (101) planes, intensities and residual strain values exhibit strong anisotropy depending upon whether the sample is in compression or tension during simple bending. This research provides insight into two specific mechanical features in pseudoelastic NiTi SMA wires.
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Benafan, Othmane. "Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5123.
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The unique ability of shape memory alloys (SMAs) to remember and recover their original shape after large deformation offers vast potential for their integration in advanced engineering applications. SMAs can generate recoverable shape changes of several percent strain even when opposed by large stresses owing to reversible deformation mechanisms such as twinning and stress-induced martensite. For the most part, these alloys have been largely used in the biomedical industry but with limited application in other fields. This limitation arises from the complexities of prevailing microstructural mechanisms that lead to dimensional instabilities during repeated thermomechanical cycling. Most of these mechanisms are still not fully understood, and for the most part unexplored. The objective of this work was to investigate these deformation and transformation mechanisms that operate within the low temperature martensite and high temperature austenite phases, and changes between these two states during thermomechanical cycling. This was accomplished by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The primary focus was to investigate the thermomechanical response of a polycrystalline Ni49.9Ti50.1 (in at.%) shape memory alloy under uniaxial deformation conditions. Starting with the deformation of the cubic austenitic phase, the microstructural mechanisms responsible for the macroscopic inelastic strains during isothermal loading were investigated over a broad range of conditions. Stress-induced martensite, retained martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were captured and compared to the bulk macroscopic response of the alloy. This isothermal deformation was found to be a quick and efficient method for creating a strong and stable two-way shape memory effect. The evolution of inelastic strains with thermomechanical cycling of the same NiTi alloy, as it relates to the alloy stability, was also studied. The role of pre-loading the material in the austenite phase versus the martensite phase as a function of the active deformation modes (deformation processes as revealed in this work) were investigated from a macroscopic and microstructural perspective. The unique contribution from this work was the optimization of the transformation properties (e.g., actuation strain) as a function of deformation levels and pre-loading temperatures. Finally, the process used to set actuators, referred to as shape setting, was investigated while examining the bulk polycrystalline NiTi and the microstructure simultaneously through in situ neutron diffraction at stress and temperature. Knowledge gained from the binary NiTi study was extended to the investigation of a ternary Ni-rich Ni50.3Ti29.7Hf20 (in at.%) for use in high-temperature, high-force actuator applications. This alloy exhibited excellent dimensional stability and high work output that were attributed to a coherent, nanometer size precipitate phase that resulted from an aging treatment. Finally, work was initiated as part of this dissertation to develop sample environment equipment with multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory. The developed capability will immediately aid in making rapid multiaxial measurements on shape memory alloys wherein the texture, strain and phase fraction evolution are followed with changes in temperature and stress. This work was supported by funding from the NASA Fundamental Aeronautics Program, Supersonics Project including (Grant No. NNX08AB51A). This work has also benefited from the use of the Lujan Neutron Scattering Center at LANSCE, which is funded by the Office of Basic Energy Sciences DOE. LANL is operated by Los Alamos National Security LLC under DOE Contract No. DE-AC52-06NA25396.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
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Hradil, Jiří. "Adaptive parameterization for Aerodynamic Shape Optimization in Aeronautical Applications." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-234267.
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Cílem mé disertační práce je analyzovat a vyvinout parametrizační metodu pro 2D a 3D tvarové optimalizace v kontextu průmyslového aerodynamického návrhu letounu založeném na CFD simulacích. Aerodynamická tvarová optimalizace je efektivní nástroj, který si klade za cíl snížení nákladů na návrh letounů. Nástroj založený na automatickém hledání optimálního tvaru. Klíčovou částí úspěšného optimalizačního procesu je použití vhodné parametrizační metody, metody schopné garantovat možnost dosažení optimálního tvaru. Parametrizační metody obecně používané v oblasti aerodynamické tvarové optimalizace momentálně nejsou připravený na komplikované průmyslové aplikace vyskytující se u moderních dopravních letounů, které mají šípová zalomená křídla s winglety a motorovými gondolami, přechodové prvky spojující např. trup s křídlem atd.. Existuje tedy potřeba nalezení obecné parametrizační metody, která bude aplikovatelná na širokou škálu různých geometrických tvarů. Free-Form Deformation (FFD[1]) parametrizace může, vzhledem ke svým schopnostem při zacházení s geometrií, být odpovědí na tuto potřebu. Adaptivní parametrizace by se měla být schopna automaticky přizpůsobit danému tvaru tak, aby byly její kontrolní body vhodně rozmístěny. Což umožní dostatečnou kontrolu deformací objektu, která zaručí možnost vytvoření optimálního tvaru objektu a splnění geometrických omezení. Primární aplikací takové parametrizační metody je deformace tvaru objektu. Dalším navrhovaným cílem je modifikace FFD parametrizační metody pro současné deformace tvaru objektu a CFD výpočetní sítě, umožnující velké deformace objektu při zachování kvality výpočetní sítě.
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Yu, Hao. "Modeling of High Strain Rate Compression of Austenitic Shape Memory Alloys." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062835/.
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Shape memory alloys (SMAs) exhibit the ability to absorb large dynamic loads and, therefore, are excellent candidates for structural components where impact loading is expected. Compared to the large amount of research on the shape memory effect and/or pseudoelasticity of polycrystalline SMAs under quasi-static loading conditions, studies on dynamic loading are limited. Experimental research shows an apparent difference between the quasi-static and high strain rate deformation of SMAs. Research reveals that the martensitic phase transformation is strain rate sensitive. The mechanism for the martensitic phase transformation in SMAs during high strain rate deformation is still unclear. Many of the existing high strain rate models assume that the latent heat generated during deformation contributes to the change in the stress-strain behavior during dynamic loading, which is insufficient to explain the large stress observed during phase transformation under high strain rate deformation. Meanwhile, the relationship between the phase front velocity and strain rate has been studied. In this dissertation, a new resistance to phase transformation during high strain rate deformation is discussed and the relationship between the driving force for phase transformation and phase front velocity is established. With consideration of the newly defined resistance to phase transformation, a new model for phase transformation of SMAs during high strain rate deformation is presented and validated based on experimental results from an austenitic NiTi SMA. Stress, strain, and martensitic volume fraction distribution during high strain rate deformation are simulated using finite element analysis software ABAQUS/standard. For the first time, this dissertation presents a theoretical study of the microscopic band structure during high strain rate compressive deformation. The microscopic transformation band is generated by the phase front and leads to minor fluctuations in sample deformation. The strain rate effect on phase transformation is studied using the model. Both the starting stress for transformation and the slope of the stress-strain curve during phase transformation increase with increasing strain rate.
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Donoghue, Jack. "Hybrid additive manufacture and deformation processing for large scale near-net shape manufacture of titanium aerospace components." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/hybrid-additive-manufacture-and-deformation-processing-for-large-scale-nearnet-shape-manufacture-of-titanium-aerospace-components(5bb9e7db-824e-46e2-a832-c2780e15d6b8).html.
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The titanium alloy Ti-6Al-4V has been favoured by the aerospace industry for the past several decades due to its good combination of specific mechanical properties, alongside corrosion and fatigue resistance. Titanium alloys are naturally suited to the near net shape processing technique of Additive Manufacture (AM) due to both the inherent high cost of the raw materials, and the difficulties associated with machining the alloys. Unfortunately, the combination of Ti-6Al-4V with AM has been found to lead to undesirable microstructures with respect to large columnar prior β grains being found to grow potentially across the entire height of builds. This microstructure has been shown to lead to property anisotropy and poor fatigue resistance. However, it has recently been found that the integration of an additional process step that lightly deforms the deposited material between added layers leads to the refinement of this undesirable microstructure. This work characterises the effect that two different deformation processing techniques have on two different additive manufacturing processes; the effect of peening on a laser-powder AM technique, and the effect of rolling on an electric arc-wire AM technique. In both cases far more randomly textured prior β grains were found with an average grain size of > 100 µm rather than mm long columnar grains with a common growth direction formed in the non-deformed builds. The refined β microstructure was found to lead to a reduction in texture of the room temperature alpha phase. The low stains involved (>10%) indicated that the refined grain structures did not form by traditional recrystallisation mechanisms. In-situ EBSD measurements at temperatures spanning the alpha → β phase transformation have been used to observe the growth of new β orientations from crystallographic twins in the deformed microstructure that may explain the origin of the refined grains. New β orientations were observed to grow from twinned alpha colonies and from between alpha laths, where the new β is found to grow sharing a twinning relationship with the residual β. Simulation of both of the individual processing steps under laboratory conditions has been found to successfully replicate the refinement observed in process. Orientation analysis suggests that twinning of the residual β could lead to the texture observed in the refined grains. It is therefore suggested that the refined grains are formed from β twinned regions in the deformed material growing under the alpha → β phase transformation, as the material is heated by the next added layer during AM.
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Veelo, Bastiaan Niels. "Variations of Shape in Industrial Geometric Models." Doctoral thesis, Norwegian University of Science and Technology, Department of Product Design, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-240.
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This thesis presents an approach to free-form surface manipulations, which conceptually improves an existing CAD system that constructs surfaces by smoothly interpolating a network of intersecting curves. There are no regularity requirements on the network, which already yields superior modelling capabilities compared to systems that are based on industry-standard NURBS surfaces.
Originally, the shape of such a surface can be modified only locally by manipulating a curve in the network. In this process there is an inherent danger that the curve is being pulled away from intersections that it has with other curves. When this happens, the network is invalidated as a surface representation, and many curves may have to be adjusted to restore network consistency and surface quality. This thesis contributes a method that solves these problems by propagating changes that are made in one curve to curves in its vicinity. How and to what extent curves react to changes is controlled by two parameters that can be varied along the curve that is being manipulated. Any curve may be constrained in one or more degrees of freedom. The integrity of the curve network is implicitly conserved, as well as the geometric continuity of the surface.
The result is a tool for the modification of curve-interpolating surfaces, which can easily be applied to large areas on models with any level of detail. This allows designers to concentrate on the creative process, rather than on planning chains of actions. They can explore different design variations, optimise shapes further, and generally be more productive.
Dette doktorgradsarbeidet presenterer en fremgangsmåte for formgivning og modifisering av datamaskinbaserte, skulpturerte flater. Metoden forbedrer et eksisterende system for data-assistert konstruksjon (DAK) som bygger dobbeltkrummede flater ved å interpolere et nettverk av skjærende kurver. Nettverket trenger ikke være regelmessig, noe som allerede gir bedre modelleringsmuligheter sammenliknet med systemer som er basert på standard NURBS flater.
En slik flate kan opprinnelig bare endres lokalt ved å dra i en kurve. I denne prosessen er det fare for at kurven blir dratt fra skjæringspunkter den har med andre kurver. Hvis dette skjer, representerer ikke nettverket en flate lenger, og mange kurver må justeres for å få tilbake integriteten i nettverket og kvaliteten i formen. Denne avhandlingen bidrar med en metode som løser disse problemene ved å spre endringer som blir gjort i en kurve til andre kurver i nærheten. Hvordan og i hvilken utstrekning kurvene reagerer på endringen styres av to parametre som kan varieres langs kurven som blir endret. Enhver kurve kan låses i en eller flere frihetsgrader. Integriteten til nettverket samt glattheten i formen blir bevart automatisk.
Resultatet er et redskap for modifikasjon av kurve-interpolerende flater som med letthet kan brukes på større områder av modeller med hvilken som helst grad av detalj. Dette gir designere muligheten til å konsentrere seg om det kreative, istedenfor å planlegge handlingsrekker. De kan utforske forskjellige designvariasjoner, optimalisere former ytterligere, og i det hele tatt være mer produktive.
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Blenkinsopp, Robert. "A method for measuring human foot shape during running stance." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/16907.
Full textAbstract:
Knowledge of the three dimensional shape of the human foot is important in the design of shoes to facilitate correct fit. Currently only the static shape of the foot is considered despite the fact that the foot undergoes changes in its shape, particularly in athletic pursuits, due to associated movements and loadings. Attempts, presented in research, have been made to measure dynamic foot shape. However, to date, measurements have been limited in detail as well as restricted to walking gait, as a result of the method. The work of this thesis aimed to develop a methodology that would be capable of measuring the three dimensional shape of the human foot during the stance phase of gait, in locomotion speeds associated with running.
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Rose, Kelly Kathleen. "Identification of Fold Hinge Migration in Natural Deformation: A New Technique Using Grain Shape Fabric Analysis." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/43205.
Full textAbstract:
Partitioning of finite strains in different domains within the limb and hinge regions of a fold can be used to understand the deformation processes operative during fold formation. Samples taken from the limb and hinge regions of a gently plunging, asymmetric, tight, mesoscale fold in the Erwin formation of the Blue Ridge in North Carolina were analyzed to determine the deformation mechanisms and strains associated with the folding event. Rf/phi grain shape fabric analysis was conducted for each sample and used to calculate the orientation and magnitude of the final grain shape fabric ellipsoids. Flexural folding and passive-shear folding models predict that the highest finite strains will be recorded in the hinge of a fold. The highest grain shape magnitudes recorded in the North Carolina fold, however, lie along the overturned fold limb.
The final geometry of many folds indicates that hinge plane migration processes are active during compressive deformation events. Numeric, conceptual, and analogue based studies have demonstrated the migration of fold hinges during deformation. However, documentation of these processes in field based studies is rare and limited to techniques that are frequently site specific. Methods proven successful in natural studies include the analysis of superposed folding; the migration of earlier hinge-related features such as fractures, cleavage planes, and boudinaged bedding planes; and the kinematic analysis of syntectonic pressure shadows. The magnitude and orientation of the grain shape ellipsoids calculated for the North Carolina fold indicate that rocks in the overturned limb were once located in the hinge of the fold. Subsequent noncoaxial deformation processes operative during folding resulted in the migration of the hinge to its present orientation and position. This relationship indicates that it is possible to use strain/shape fabric analysis as a test for hinge migration in folds, and that this technique may be more generally applicable in natural settings than previously proposed tests.Master of Science
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Casalena, Lee. "Multimodal Nanoscale Characterization of Transformation and Deformation Mechanisms in Several Nickel Titanium Based Shape Memory Alloys." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1499568013015563.
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Krishnan, Vinu Bala. "Low temperature NiTiFe shape memory alloys actuator engineering and investigation of deformation mechanisms using in situ neutron diffraction at Los Alamos National Laboratory /." Orlando, Fla. : University of Central Florida, 2007. http://purl.fcla.edu/fcla/etd/CFE0001934.
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Krishnan, Vinu. "LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS: ACTUATOR ENGINEERING AND INVESTIGATION OF DEFORMATION MECHANISMS USING IN SITU NEUTR." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3373.
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Shape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable fatigue response. Overall, this work is an investigation of selected science and engineering aspects of low temperature NiTiFe shape memory alloys. The scientific study was performed using in situ neutron diffraction measurements at the newly developed low temperature loading capability on the Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory and encompasses three aspects of the behavior of Ni46.8Ti50Fe3.2 at 92 K (the lowest steady state temperature attainable with the capability). First, in order to study deformation mechanisms in the R-phase in NiTiFe, measurements were performed at a constant temperature of 92 K under external loading. Second, with the objective of examining NiTiFe in one-time, high-stroke, actuator applications (such as in safety valves), a NiTiFe sample was strained to approximately 5% (the R-phase was transformed to B19' phase in the process) at 92 K and subsequently heated to full strain recovery under a load. Third, with the objective of examining NiTiFe in cyclic, low-stroke, actuator applications (such as in cryogenic thermal switches), a NiTiFe sample was strained to 1% at 92 K and subsequently heated to full strain recovery under load. Neutron diffraction spectra were recorded at selected time and stress intervals during these experiments. The spectra were subsequently used to obtain quantitative information related to the phase-specific strain, texture and phase fraction evolution using the Rietveld technique. The mechanical characterization of NiTiFe alloys using the cryogenic capability at SMARTS provided considerable insight into the mechanisms of phase transformation and twinning at cryogenic temperatures. Both mechanisms contribute to shape memory and pseudoelasticity phenomena. Three phases (R, B19' and B33 phases) were found to coexist at 92 K in the unloaded condition (nominal holding stress of 8 MPa). For the first time the elastic modulus of R-phase was reported from neutron diffraction experiments. Furthermore, for the first time a base-centered orthorhombic (B33) martensitic phase was identified experimentally in a NiTi-based shape memory alloy. The orthorhombic B33 phase has been theoretically predicted in NiTi from density function theory (DFT) calculations but hitherto has never been observed experimentally. The orthorhombic B33 phase was observed while observing shifting of a peak (identified to be B33) between the R and B19' peaks in the diffraction spectra collected during loading. Given the existing ambiguity in the published literature as to whether the trigonal R-phase belongs to the P3 or P space groups, Rietveld analyses were separately carried out incorporating the symmetries associated with both space groups and the impact of this choice evaluated. The constrained recovery of the B19' phase to the R-phase recorded approximately 4% strain recovery between 150 K and 170 K, with half of that recovery occurring between 160 K and 162 K. Additionally, the aforementioned research methodology developed for Ni46.8Ti50Fe3.2 shape memory alloys was applied to experiments performed on a new high temperature Ni29.5Ti50.5Pd20 shape memory alloys. The engineering aspect focused on the development of (i) a NiTiFe based thermal conduction switch that minimized the heat gradient across the shape memory actuator element, (ii) a NiTiFe based thermal conduction switch that incorporated the actuator element in the form of helical springs, and (iii) a NiTi based release mechanism. Patents are being filed for all the three shape memory actuators developed as a part of this work. This work was supported by grants from SRI, NASA (NAG3-2751) and NSF (CAREER DMR-0239512) to UCF. Additionally, this work benefited from the use of the Lujan Center at the Los Alamos Neutron Science Center, funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr PhD
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Mahoi, Salie. "Influence of shape of solid explosives on the deformation of circular steel plates : experimental and numerical investigations." Doctoral thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/5514.
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Gervais, Olivier. "Effects of Long-Term Selection for Non-Destructive Deformation in White Leghorns." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217200.
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Lundgren, Paulina, and Husein Mohammed Harbe. "Model correlation of an articulated hauler frame." Thesis, Linnaeus University, School of Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-6376.
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This master thesis has been carried out on behalf of Volvo Construction Equipment. A front frame of an
articulated hauler should be analysed according to the Finite Element Method and vibration tests should be
made. The results from the experimental tests should be correlated with the analytical test results here using
MAC-values. These values will show if the FE-model represents the physical structure correctly.
Visualisations are made on both the experimental and analytical results to get a better understanding about the
eigenmodes of the frame.
The final results showed that the FE-model was not a match to the physical structure which the experimental
tests were made on. It should be noted that the final result only states the present situation. The CAD-model had
not been completed when this thesis was performed and therefore some deviation occurred in the results. Some
actions are needed in order to reach a better result and they are stated in this report. When they are made, the
results can be improved by following the work that has been done in this master thesis.
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AZEGAMI, Hideyuki, Takahiro IWAI, 秀幸 畔上, and 孝広 岩井. "大変形を考慮した接触する弾性体の形状同定." 一般社団法人日本機械学会, 2008. http://hdl.handle.net/2237/21119.
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Zhang, Xiaoliu. "MRI-based active shape model of the human proximal femur using fiducial and secondary landmarks and its validation." Thesis, University of Iowa, 2018. https://ir.uiowa.edu/etd/6349.
Full textAbstract:
Osteoporosis, associated with reduced bone mineral density and structural degeneration, greatly increases the risk of fragility fracture. Magnetic resonance imaging (MRI) has been applied to central skeletal sites including the proximal femur due to its non-ionizing radiation. A major challenge of volumetric bone imaging of the hip is the selection of regions of interest (ROIs) for computation of regional bone measurements. To address this issue, an MRI-based active shape model (ASM) of the human proximal femur is applied to automatically generate ROIs. The challenge in developing the ASM for a complex three-dimensional (3-D) shape lies in determining a large number of anatomically consistent landmarks for a set of training shapes. This thesis proposes a new method of generating the proximal femur ASM, where two types of landmarks, namely fiducial and secondary landmarks, are used. The method consists of—(1) segmentation of the proximal femur bone volume, (2) smoothing the bone surface, (3) drawing fiducial landmark lines on training shapes, (4) drawing secondary landmarks on a reference shape, (5) landmark mesh generation on the reference shape using both fiducial and secondary landmarks, (6) generation of secondary landmarks on other training shapes using the correspondence of fiducial landmarks and an elastic deformation of the landmark mesh, (7) computation of the active shape model. A proximal femur ASM has been developed using hip MR scans of 45 post-menopausal women. The results of secondary landmark generation were visually satisfactory, and no topology violation or notable geometric distortion artifacts were observed. Performance of the method was examined in terms of shape representation errors in a leave-one-out test. The mean and standard deviation of leave-one-out shape representation errors were 0.34mm and 0.09mm respectively. The experimental results suggest that the framework of fiducial and secondary landmarks allows reliable computation of statistical shape models for complex 3-D anatomic structures.
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Srivastava, Vikas. "A large-deformation thermo-mechanically coupled elastic-viscoplastic theory for amorphous polymers : modeling of micro-scale forming and the shape memory phenomenon." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57787.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 185-193).
Amorphous polymers are important engineering materials; however, their nonlinear, strongly temperature- and rate-dependent elastic-viscoplastic behavior is still not very well understood, and is modeled by existing constitutive theories with varying degrees of success. There is no generally agreed upon theory to model the large-deformation, thermo-mechanically coupled response of these materials in a temperature range which spans their glass transition temperature. Such a theory is crucial for the development of a numerical capability for the simulation and design of important polymer processing operations, and also for predicting the relationship between processing methods and the subsequent mechanical properties of polymeric products. We have developed a large-deformation thermo-mechanically coupled elastic-viscoplastic theory for thermoplastic amorphous polymers and shape memory polymers which spans their glass transition temperature. The theory has been specialized to represent the major features of the thermo-mechanical response of three technologically important thermoplastic amorphous polymers - a cyclo-olefin polymer (Zeonex-690R), polycarbonate, poly(methyl methacrylate) and a representative thermoset shape memory polymer - in a temperature range from room temperature to approximately 40 C above the glass transition temperature of each material, in a strain-rate range of ~ 10-4 to 101 s-1, and compressive true strains exceeding 100%. Our theory has been implemented in the finite element program ABAQUS. In order to validate the predictive capability of our constitutive theory, we have performed a variety of macro- and micro-scale validation experiments involving complex inhomogeneous deformations and thermal processing cycles. By comparing some key features, such as the experimentally-measured deformed shapes and the load-displacement curves from various validation experiments against corresponding results from numerical simulations, we show that our theory is capable of reasonably accurately reproducing the results obtained in the validation experiments.
by Vikas Srivastava.
Ph.D.