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Tesi sul tema "Mechanial behavior"
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1
Shen, Jianghua. "Mechanical behavior and deformation mechanism in light metals at different strain rates". Thesis, The University of North Carolina at Charlotte, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3711867.
Testo completoAbstract (sommario):
Developing light metals that have desirable mechanical properties is always the object of the endeavor of materials scientists. Magnesium (Mg), one of the lightest metals, had been used widely in military and other applications. Yet, its relatively poor formability, as well as its relatively low absolute strength, in comparison with other metals such as aluminum and steels, caused the use of Mg to be discontinued after World War II. Owing to the subsequent energy crisis of the seventies, recently, interest in Mg development has been rekindled in the materials community. The main focus of research has been quite straight-forward: increasing the strength and formability such that Mg and its alloys may replace aluminum alloys and steels to become yet another choice for structural materials. This dissertation work is mainly focused on fundamental issues related to Mg and its alloys. More specifically, it investigates the mechanical behavior of different Mg-based materials and the corresponding underlying deformation mechanisms. In this context, we examine the factors that affect the microstructure and mechanical properties of pure Mg, binary Mg-alloy (with addition of yttrium), more complex Mg-based alloys with and without the addition of lanthanum, and finally Mg-based metal matrix composites (MMCs) reinforced with ex-situ ceramic particles. More specifically, the effects of the following factors on the mechanical properties of Mg-based materials will be investigated: addition of rare earths (yttrium and lanthanum), in-situ/ex-situ formed particles, particle size or volume fraction and materials processing, effect of thermal-mechanical treatment (severe plastic deformation and warm extrusion), and so on and so forth.
A few interesting results have been found from this dissertation work: (i) although rare earths may improve the room temperature ductility of well-annealed Mg, the addition of yttrium results in ultrafine and un-recrystallized grains in the Mg-Y alloy subjected to equal channel angular pressing (ECAP); (ii) the reverse volume fraction effect arises as the volume fraction of nano-sized ex-situ formed reinforcements is beyond 10%; (iii) nano-particles are more effective in strengthening Mg than micro-particles when the volume fraction is below 10%; (iv) complete dynamic recovery and/or recrystallization is required to accomplish the moderate ductility in Mg, together with a strong matrix-particle bonding if it is a Mg-based composite; and (v) localized shear failure is observed in all Mg samples, recrystallized completely, which is attributed to the reduced strain hardening rate as a result of the exhaustion of twinning and/or dislocation multiplication.
2
Henry, Quentin. "Apport de l’expérimentation aux petites échelles spatiales et temporelles sur l’étude du comportement mécanique des céramiques à microstructure contrôlée soumises à des sollicitations dynamiques". Electronic Thesis or Diss., Paris, ENSAM, 2024. http://www.theses.fr/2024ENAME052.
Testo completoAbstract (sommario):
Dans le cadre de l'allègement des structures de blindage mécanique, les céramiques se distinguent comme des matériaux de choix en raison de leur grande résistance à la compression, tout en étant plus légères que les métaux conventionnellement utilisés. Certains modèles micromécaniques suggèrent que l'augmentation apparente des propriétés mécaniques des matériaux fragiles sous des sollicitations dynamiques résulte de l'interaction entre la vitesse de chargement et la vitesse de propagation des fissures dans une structure hétérogène. Cependant, cette hypothèse n'a pas encore été confirmée par des preuves expérimentales textit{in situ}. Une approche empirique a été proposée pour vérifier cette hypothèse et montrer l’influence de la microstructure des céramiques sur la sensibilité de leur réponse mécanique à la vitesse de déformation. Cette approche expérimentale doit considérer l’ensemble des effets dynamiques, notamment ceux liés à la propagation rapide des fissures. Une stratégie expérimentale a été élaborée pour mettre en évidence les mécanismes physiques induits par une sollicitation dynamique au sein d'une microstructure contrôlée.Pour maîtriser la microstructure, des pores ont été introduits dans une matrice d’alumine avec un contrôle précis de leur quantité, taille et morphologie. Il a été observé que les propriétés mécaniques diminuent à mesure que le taux de porosité augmente. À densité constante, les pores de grande taille sont particulièrement préjudiciables vis-à-vis des propriétés mécaniques.L'augmentation de la vitesse de déformation conduit à une augmentation des propriétés mécaniques apparentes. En employant des techniques conventionnelles de laboratoire sous des régimes dynamiques, et en les combinant à une analyse des fragments, il a été possible d’identifier le début de la zone transitoire où la contrainte à rupture des céramiques poreuses commence à augmenter. La compétition entre la propagation rapide des fissures et la cinétique de chargement décrite dans les modèles micromécaniques se reflète par la diminution plus importante de la taille des fragments des céramiques poreuses. L'ajout de pores entraîne une hausse de la densité des défauts critiques, ce qui facilite l'amorçage de fissures supplémentaires sous des contraintes dynamiques.L'analyse réalisée sous source synchrotron à l'ESRF a permis de suivre avec précision la cinétique de fissuration des céramiques ainsi que la réponse de la structure sous des sollicitations dynamiques. Les résultats obtenus, notamment la vitesse de propagation des fissures et les différents chemins de fissuration, offrent des références précieuses pour valider les approches numériques de modélisation de la rupture des matériaux fragiles. La propagation rapide des fissures génère des effets d'inertie, estimés par une approche numérique directe. Les résultats soulignent l'importance d'utiliser une telle méthode pour estimer l'énergie de rupture, sans quoi les effets dynamiques risquent d’être largement surestimés, compromettant ainsi l’intégrité des structuresCeramics stand out as materials of choice for lightening mechanical armor structures, thanks to their high compressive strength, while being lighter than conventionally used metals. Some micromechanical models suggest that the apparent increase in mechanical properties of brittle materials under dynamic loading results from the interaction between loading velocity and crack propagation velocity in a heterogeneous structure. However, no textit{in situ} experimental evidence has yet validated this hypothesis. An empirical approach has been proposed to verify this hypothesis and show the influence of ceramic microstructure on the sensitivity of their mechanical response to strain rate. This experimental approach must take account of all dynamic effects, particularly those linked to rapid crack propagation. The method envisaged for this thesis will put into perspective the effect of microstructure on the fragmentation process of ceramics at different strain rates.To control the microstructure, pores were introduced into an alumina matrix with precise control over their quantity, size and morphology. It was observed that mechanical properties decreased with increasing pore size. At constant density, large pores are particularly critical in terms of mechanical properties. An increase in strain rate leads to an increase in apparent mechanical properties. This sensitivity is even more pronounced in porous ceramics. The competition between rapid crack propagation and loading rates described in micromechanical models is reflected in the decrease in fragment size, which is more pronounced in porous ceramics. The introduction of pores leads to an increase in the density of critical defects, favoring the initiation of more cracks under dynamic loading. The analysis carried out under synchrotron source at ESRF enabled us to accurately track the fracture kinetics of the ceramics, as well as the response of the structure under dynamic loading. The results obtained, in particular the crack propagation velocity and the different fracture paths, provide valuable references for validating numerical approaches to modeling the fracture of brittle materials. This rapid crack propagation generates inertia effects, estimated by a direct numerical approach. The results underline the importance of using such a method to estimate fracture energy, otherwise dynamic effects could be greatly overestimated, compromising structural integrity
3
Rasmussen, Nathan Oliver. "Compliant ortho-planar spring behavior under complex loads". BYU ScholarsArchive, 2005. https://scholarsarchive.byu.edu/etd/664.
Testo completoAbstract (sommario):
This thesis presents research on the feasibility of applying compliant-ortho-planar springs (COPS) to rotational applications. The primary motivation of this research is the application of COPS to a continuously variable transmission (CVT). The design space limitations, loading conditions, stresses, stress concentrations, and limitations of current design tools, such as pseudo-rigid-body models (PRBM) for COPS, are discussed. A new 3D PRBM is presented along with a discussion on the possible applications of such to a rotating COPS. Stress stiffening and lateral stability are two major phenomena occurring in a rotating COPS. Both phenomena are a direct result of the inertial loads a COPS would be subjected to in a rotational environment. The results show how stress stiffening and lateral buckling in the legs are influenced by design parameters. Conclusions and recommendations for further research are recommended.
4
Minnaar, Karel. "Comparison and analysis of dynamic shear failure behavior of structural metals". Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/16340.
Testo completo
5
Ortiz, Ryan C. "Mechanical Behavior of Grouted Sands". UKnowledge, 2015. http://uknowledge.uky.edu/ce_etds/26.
Testo completoAbstract (sommario):
Grouting techniques have been in used for many years, but several new grout materials have surfaced in recent decades that have re-defined the boundaries of the limitations of grouting programs. Typically these applications are used for seepage control in earthen impoundments, but strength of these earthen impoundments should be considered where there is potential for movement in the grouted soil mass. This study investigated initial conditions that could affect grout application effectiveness. The initial conditions in question were soil grain size and in situ moisture content. Two grouts were used, ultrafine and acrylate, and variations in pure grout properties were studied. An apparatus was developed so that a uniform grout could penetrate the pore spaces of a soil specimen. The rate of penetration of the grout into the soil was studied. The unconfined compressive strength of the resulting grouted soil was then analyzed.
In testing neat ultrafine grout, it was shown that increased water-to-cement ratios had negative effects on the stability of the grout. Increasing the water-to-cement ratio from 0.5 to 2.5 resulted in a decrease in strength by a factor of 100. An inhibitor chemical was used to increase the time for reaction in the acrylate grout. During the chemical reaction, the curing temperature and gel times were monitored. A grout mix was selected for the acrylate grout that achieved appropriate gel times. In general, this study found that the grout penetrations rates into the soil increased as the initial moisture was increased from dry conditions to a gravimetric moisture content of nine percent. In each study, increased initial moisture decreased the grouted soil strength, with decreases in strength exceeding 50 percent. Empirical relationships were realized when compared to the initial matric suction of the soil. This suggests initial matric suction may be a useful initial condition for estimating increases in soil strength upon implementation of a grouting program for both the acrylate and ultrafine grouts.
6
Tonyan, Timothy Donald. "Mechanical behavior of cementitious foams". Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13422.
Testo completo
7
Kearney, Cathal (Cathal John). "Mechanical behavior of ultrastructural biocomposites". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38269.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaves 154-163).
For numerous centuries nature has successfully developed biocomposite materials with detailed multiscale architectures to provide a material stiffness, strength and toughness. One such example is nacre, which is found in the shells of many mollusks, and consists of an inorganic phase of aragonite tablets 5-8jim in planar dimension and 0.5-1gm in thickness direction and an organic phase of biomacromolecules. High resolution microscopy imaging was employed to investigate the microscale features of seashell nacre to reveal the nucleation points within tablets, the sector boundaries and an overlap between tablets of neighboring layers of [approx.] 20 %. Aragonite, the mineral constituting the inorganic phase of nacre, is a calcium carbonate mineral that is ubiquitous in many natural systems, including both living organisms and geological structures. Resistance to yield is an important factor in the ability of aragonite to provide both strength and toughness to numerous biological materials. Conversely, plastic deformation of aragonite is a governing factor in the formation and flow of large scale geological structures. The technique of nanoindentation combined with in-situ tapping mode atomic force microscopy imaging was used to show the anisotropic nanoscale plastic behavior of single crystal aragonite for indentations into three mutually orthogonal planes.
(cont.) Force vs. indentation depth curves for nanoindentation coaxial to the orthorhombic crystal c-axis exhibited distinct load plateaus, ranging between 275-375gN for the Berkovich indenter and 400-500 [mu]N for the cono-spherical indenter, indicative of dislocation nucleation events. Atomic force microscopy imaging of residual impressions made by a cono-spherical indenter showed four pileup lobes; residual impressions made by the Berkovich indenter showed protruding slip bands in pileups occurring adjacent to only one or two of the Berkovich indenter planes. Anisotropic elastic simulations were used to capture the low load response of single crystal aragonite, with the elastic simulations for the (001) plane matching the experimental data up until the onset of plasticity. Numerical simulations based on a crystal plasticity model were used to interrogate and identify the kinematic mechanisms of plastic slip leading to the experimentally observed plastic anisotropy. In particular, in addition to the previously reported slip systems of the {100}<001> family, the family of {110}<001> slip systems is found to play a key role in the plastic response of aragonite.
by Cathal Kearney.
S.M.
8
Wallach, Jeremy C. (Jeremy Cole) 1975. "Mechanical behavior of truss materials". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88895.
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Page, Steven M. "Investigation into the Behavior of Bolted Joints". Wright State University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=wright1163527930.
Testo completo
10
Chia, Julian Yan Hon. "A micromechanics-based continuum damage mechanics approach to the mechanical behaviour of brittle matrix composites". Thesis, University of Glasgow, 2002. http://theses.gla.ac.uk/2856/.
Testo completoAbstract (sommario):
The thesis describes the development of a new continuum damage mechanics (hereafter, CDM) model for the deformation and failure of brittle matrix composites reinforced with continuous fibres. The CDM model is valid over sizes scales large compared to the spacing of the fibres and the dimensions of the damage. The composite is allowed to sustain damage in the form of matrix micro-cracking, shear delamination, tensile delamination and fibre failure. The constitutive equations are developed by decomposing the composite compliance into terms attributable to the fibre and matrix, and modelling the competing failure modes by intersecting failure surfaces based on maximum stress theory. The fibres are treated as being weakly bonded to the matrix so that the fibres only transmit axial loads, and fail in tension. The matrix is modelled as isotropic linear elastic and is treated as transversely-isotropic after damage has initiated. The effect of multiple matrix cracking on the stiffness was determined from experimental data, while failure was modelled by a rapid decay in the load bearing capacity. Although the model is motivated largely to proportional loading, matrix unloading and damage closure has been modelled by damage elasticity. During compression, the matrix stiffness is identical to the undamaged state with the exception that the fibres are assumed not to transmit compressive loads. The model was implemented computationally through a FORTRAN subroutine interfaced with the ABAQUS/Standard finite element solver. The CDM model was validated by comparing experimental and computational results of test specimens with unidirectional and balanced 0°-90° woven fibres of a brittle matrix composite, fabricated from polyester fibres in a polyester matrix. This composite system exhibits low elastic mismatch between fibres and matrix, and has similar non-dimensionalised stress-strain response to a SiC/SiC composite proposed for the exhaust diffuser unit of the Rolls-Royce EJ200 aero-engine.
11
Reuse, Rolando. "Thermomechanical behavior of monolithic Sn-Ag-Cu solder and copper fiber reinforced solders". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FReuse.pdf.
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Oswal, Mitesh. "Analyzing the Corrosion Behavior and Evaluating the Mechanical Integrity of Biodegradable Magnesium Implants". University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1311692279.
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Humphrey, Jay Dowell. "Mechanical behavior of excised visceral pleura". Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/19973.
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14
VILLARROEL, FLAVIA MARA GUZMAN. "PHYSICAL SIMULATION OF WELLBORE MECHANICAL BEHAVIOR". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15178@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROFUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
Um dos maiores desafios para a produção de hidrocarbonetos em reservatórios de arenitos pouco consolidados é o controle da produção de areia. Os mecanismos envolvidos nesse fenômeno são complexos e isto é resultado de uma grande variedade de fatores, como por exemplo, a magnitude das tensões in situ, a resistência mecânica da formação e as operações de desenvolvimento do poço. Este problema pode ser resolvido ou amenizado até níveis aceitáveis através de estratégias de completação específicas, como instalação de telas ranhuradas ou do gravel pack, desde que haja uma previsão do potencial de produção de areia da formação. Apesar do grande número de modelos numéricos desenvolvidos para prever este comportamento, a consistência dos mesmos pode ser questionada, uma vez que podem ser observadas diferenças entre as predições e os dados de campo. Para validar esses modelos, são necessários dados confiáveis, que podem ser obtidos através de ensaios de laboratório. Os objetivos do trabalho foram determinados considerando esses pontos, além da questão do uso em larga escala do gravel pack como técnica de controle da produção de areia nos campos brasileiros. São eles: (i) investigar o comportamento de um sistema de contenção de areia instalado em uma formação com potencial de produção de areia, (ii) verificar a influência do aumento de tensão efetiva na produção de areia e entender como a carga é transmitida para o sistema e (iii) validar um modelo numérico desenvolvido para o estudo de campo. Para ensaios, realizados em uma célula poliaxial sob condições controladas, utilizaram-se blocos de grandes dimensões. Foram analisados 5 casos representativos, sendo cada um deles simulado 4 vezes. O primeiro caso consiste na verificação da formação de um breakout em poço aberto, sem a utilização de nenhum sistema de contenção de areia. Os outros quatro casos são reproduções do sistema gravel-tela, com diferentes configurações. Os resultados foram satisfatórios e de acordo com eles, é possível identificar uma tendência de comportamento para cada cenário: gravel com distribuição uniforme no anular e diâmetro de partícula utilizada no gravel. A verificação de um modelo numérico, desenvolvido na Petrobrás, foi feita a partir destes resultados e mostrou uma boa aproximação de resultados de laboratório.
A major problem during hydrocarbon production from poorly consolidated sandstone in the influx of sand, or sand production. This problem is complex and can occur as a result of a large variety of reasons, like magnitude of the in situ stresses, formation strength, and wellbore-development operations. If the potential for sand production could be predicted, then the problem may be solved or reduced to an accepteble level by proper completion strategy, such as the use of stand alone screens or gravel pack. Although a large number of numerical models for sand production prediction hava been developes, the consistency of the models could be questioned, due to the differences between the predictions and field observations. To improve and validate these models, reliable data are necessary. This study has been developed based on these concerns, and also, considering the massive use of the gravel-pacck as sand control technique on Brazilian fields. The objective were (i) investigation of the gravel-pack system behavior, (ii) varifacation of the increase on effective stress on sand production and (iii) validation a numerical model developed for field sand production prediction. The large-scale tests were carried out on a poliaxial cell. It was selectes 5 representative cases, and they were developed on an artificial well, under controlled conditions. On the first one, it was observed a breakout formation on an openhole. On the other 4 cases, it was simulated the gravel pack, submitted to different conditions, each of them reproduced 4 times. The numerical model was developed by Petrobras/Roncador field engineers, using a commercial numericak modeling program. Results were satisfactory. According to them, is possible to identify a behavior tendency for each condition: the influence of the gravel uniform distribution on the annulus and the influence of gravel diameter. The numerical model showed a very good approach to the laboratory results.
15
Lokas, Rami (Rami Farouk) 1975. "Mechanical behavior of four brittle polymers". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89284.
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Zhang, Chao. "Mechanical behavior of tubular composite structures". University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1627489300935781.
Testo completo
17
Woodmansee, Michael W. "Thermal cycling and rate-dependent stress relaxation behavior of solders". Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/17301.
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18
Rasmussen, Nathan Oliver. "Behavior of compliant ortho-planar springs under complex loads /". Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd1023.pdf.
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Aryaei, Ashkan. "Mechanical Properties of Bio-nanocomposites and Cellular Behavior under Mechanical Stimulation". University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1398361357.
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20
Saeed-Akbari, Alireza [Verfasser]. "Mechanism Maps, Mechanical Properties, and Flow Behavior in High-Manganese TRIP/TWIP and TWIP Steels / Alireza Saeed-Akbari". Aachen : Shaker, 2011. http://d-nb.info/107408795X/34.
Testo completo
21
Wazne, Abdallah. "Non-linear mechanical behavior of strongly heterogeneous media by the mechanics of generalized continuous media and homogenization methods". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0153.
Testo completoAbstract (sommario):
L'objectif de cette thèse est d'étudier de manière exhaustive le comportement non linéaire des matériaux en treillis périodiques constitués de poutres de Timoshenko, en tenant compte des énergies de cisaillement, d'extension et de flexion, ainsi que de leurs interactions. Pour atteindre cet objectif, nous avons développé un ensemble complet de fonctions de forme non linéaires et dérivé les équations dynamiques non linéaires pour divers réseaux architecturés. Nous nous sommes concentrés sur l'intégration de la matrice de rigidité non linéaire et sur l'étude de l'impact de l'énergie non linéaire totale (y compris les modes de cisaillement, d'extension et de flexion) sur la réponse dynamique des matériaux architecturés. En outre, nous avons effectué une analyse comparative de la propagation des ondes dans différents matériaux architecturés, en tenant compte de l'influence de l'énergie non linéaire et de la contribution de chaque mode (extension, flexion et cisaillement) aux relations de dispersion. En outre, nous avons effectué des calculs d'homogénéisation dynamique discrète pour différents matériaux architecturés non linéaires et réalisé des analyses de propagation des ondes en tenant compte de l'effet des termes de second gradient à la fois en 1D et en 2DThe objective of this thesis is to comprehensively investigate the nonlinear behavior of periodic lattice materials made of Timoshenko beams, by considering shear, extension, and bending energies, as well as their interactions. To achieve this objective, we have developed a complete set of nonlinear shape functions and derived the nonlinear dynamical equations for various architected networks. Our focus has been on incorporating the nonlinear stiffness matrix and studying the impact of the full nonlinear energy (including shear, extension, and bending modes) on the dynamical response of architected materials. Furthermore, we have conducted a comparative analysis of wave propagation in different architected materials, considering the influence of nonlinear energy and the contribution of each mode (extension, flexion, and shear) to the dispersion relations. Additionally, we have performed discrete dynamical homogenization computations for different nonlinear architected materials and carried out wave propagation analyses taking into consideration the effect of second gradient terms in both 1D and 2D
22
Kao, Alexander Peter. "Spatial mechanical behaviour of skin". Thesis, Queen Mary, University of London, 2016. http://qmro.qmul.ac.uk/xmlui/handle/123456789/23192.
Testo completoAbstract (sommario):
Skin is a complex biological composite system that serves as the outermost barrier to the environment and is mechanically robust. Understanding the mechanical properties of skin is important to improve and compare current in vitro experiments to the physiological conditions as the mechanical properties have a crucial role in determining cell behaviour. The mechanical behaviour of skin at the cellular level is expected to be dominated by the collagen fibre network within the dermis, which displays an anisotropic mechanical response to macroscopic loading. However, the three dimensional mechanical properties of skin at the nanoscale are not well understood. The aim of this work is to examine the mechanical properties of skin at the nanoscale in three dimensions and explore the links between the nanoscale and the macroscopic behaviour. Multiple sample preparation techniques are employed to expose the different layers of skin for mechanical testing and the elastic modulus of skin is evaluated by using atomic force microscopy (AFM) nanoindentation. The effect of freezing skin to cryogenic temperatures on the mechanical properties is evaluated and found to have no impact on the mechanical response of skin, indicating that the composition and structure of skin are robust enough to withstand the cryosectioning sample preparation methods used to expose the transverse layers of skin. AFM indentation was used to evaluate the elastic modulus of the dermis depending on the orientation of the sample and found to have an isotropic mechanical response. This result is opposite to anisotropy observed in macroscopic skin due to small scale mechanical testing ignoring collagen fibril orientation during strain. The variations in the elastic modulus of skin are also evaluated by AFM indentation at high spatial resolution to construct a composite model of the mechanical behaviour of skin at the nanoscale to predict the macroscopic response. The AFM nanoindentation technique was extended to evaluate the mechanical properties of a cell derived matrix deposited on an electrospun nanofibre scaffold, where the results indicate increasing the nanofibre diameter produces a cell derived matrix with an increased elastic modulus for more effective scaffolds. This work highlights the use of AFM mechanical testing to evaluate the nanoscale mechanical behaviour of skin, treated as a composite biological system, and determine the influence of the length scale and sample orientation on the observed mechanical response.
23
Jackman, Henrik. "Mechanical behaviour of carbon nanostructures". Doctoral thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32041.
Testo completoAbstract (sommario):
Abstract Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in future nanoelectromechanical systems and for many other applications. The extraordinary properties are however only attained by perfectly crystalline CNTs and quickly deteriorate when defects are introduced to the structure. The growth technique affects the crystallinity where in general CNTs grown by arc-discharge are close to perfectly crystalline, while CVD-grown CNTs have large defect densities. Mechanical deformation also affects these properties, even without introducing defects. When CNTs are bent they behave similarly to drinking straws, i.e. they buckle or ripple and their bending stiffness drops abruptly. In this thesis, the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers (VACNFs) has been studied by performing force measurements inside electron microscopes. Cantilevered CNTs, and VACNFs, were bent using a force sensor, yielding force-deflection curves while their structure was imaged simultaneously. We have found that CNTs grown by arc-discharge have a high enough crystallinity to possess a Young’s modulus close to the ideal value of 1 TPa. CVD-grown CNTs possess a Young’s modulus that is about one order of magnitude smaller, due to their large defect density. The VACNFs are yet another order of magnitude softer as a result of their cup-stacked internal structure. We also found that a high defect density will increase the critical strain for the rippling onset and the relative post-rippling stiffness. Multi-walled CNTs with a small inner diameter are less prone to ripple and have a larger relative post-rippling stiffness. Our findings show large variations in the onset of rippling and the bending stiffness before and after rippling. These variations open up possibilities of tailoring the mechanical properties for specific applications.Baksidetext Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in nanoelectromechanical systems (NEMS), and many other applications. In this thesis the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers has been studied by performing force measurements inside electron microscopes. We have found that the mechanical behaviour is very sensitive to the defect density and the internal structure of the CNTs. The extraordinary properties are only attained by defect free CNTs and quickly deteriorate if defects are introduced to the structure. Mechanical deformations also alter these properties. Single-walled CNTs behave similarly to drinking straws when bent, i.e. they buckle, while the inner tubes of multi-walled CNTs prevent buckling. Instead a more distributed rippling pattern is created for multi-walled CNTs. Both these deformation behaviours will cause an abrupt drop in the bending stiffness, which is detrimental for many applications. The findings in this work will have implications for the design of future NEMS.
Artikel 2 Image formation mechanisms tidigare som manuskript, nu publicerad: urn:nbn:se:kau:diva-16425 (MÅ 150924)
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Radhakrishnan, Harish. "Mechanical behavior of a carbon nanotube turf". Online access for everyone, 2006. http://www.dissertations.wsu.edu/Thesis/Fall2006/h_radhakrishnan_092206.pdf.
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Ramamoorthy, Thiagarajan. "Mechanical behavior of membranes in electrostatic pecipitators". Ohio : Ohio University, 2005. http://www.ohiolink.edu/etd/view.cgi?ohiou1125868299.
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Wellner, Patrick. "Thermo-mechanical behavior of NiAl thin films". Stuttgart : Max-Planck-Inst. für Metallforschung, 2003. http://deposit.d-nb.de/cgi-bin/dokserv?idn=970713428.
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Tan, Xin. "Hydro-mechanical coupled behavior of brittle rocks". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-131492.
Testo completoAbstract (sommario):
‘Coupled process’ implies that one process affects the initiation and progress of the others and vice versa. The deformation and damage behaviors of rock under loading process change the fluid flow field within it, and lead to altering in permeable characteristics; on the other side inner fluid flow leads to altering in pore pressure and effective stress of rock matrix and flow by influencing stress strain behavior of rock. Therefore, responses of rock to natural or man-made perturbations cannot be predicted with confidence by considering each process independently. As far as hydro-mechanical behavior of rock is concerned, the researchers have always been making efforts to develop the model which can represent the permeable characteristics as well as stress-strain behaviors during the entire damage process.
A brittle low porous granite was chosen as the study object in this thesis, the aim is to establish a corresponding constitutive law including the relation between permeability evolution and mechanical deformation as well as the rock failure behavior under hydro-mechanical coupled conditions based on own hydro-mechanical coupled lab tests. The main research works of this thesis are as follows:
1. The fluid flow and mechanical theoretical models have been reviewed and the theoretical methods to solve hydro-mechanical coupled problems of porous medium such as flow equations, elasto-plastic constitutive law, and Biot coupled control equations have been summarized.
2. A series of laboratory tests have been conducted on the granite from Erzgebirge–Vogtland region within the Saxothuringian segment of Central Europe, including: permeability measurements, ultrasonic wave speed measurements, Brazilian tests, uniaxial and triaxial compression tests. A hydro-mechanical coupled testing system has been designed and used to conduct drained, undrained triaxial compression tests and permeability evolution measurements during complete loading process. A set of physical and mechanical parameters were obtained.
3. Based on analyzing the complete stress-strain curves obtained from triaxial compression tests and Hoek-Brown failure criterion, a modified elemental elasto-plastic constitutive law was developed which can represent strength degradation and volume dilation considering the influence of confining pressure.
4. The mechanism of HM-coupled behavior according to the Biot theory of elastic porous medium is summarized. A trilinear evolution rule for Biot’s coefficient based on the laboratory observations was deduced to eliminate the error in predicting rock strength caused by constant Biot’s coefficient.
5. The permeability evolution of low porous rock during the failure process was described based on literature data and own measurements, a general rule for the permeability evolution was developed for the laboratory scale, a strong linear relation between permeability and volumetrical strain was observed and a linear function was extracted to predict permeability evolution during loading process based on own measurements.
6. By combining modified constitutive law, the trilinear Biot’s coefficient evolution model and the linear relationship between permeability and volumetrical strain, a fully hydro-mechanical coupled numerical simulation scheme was developed and implemented in FLAC3D. A series of numerical simulations of triaxial compression test considering the hydro-mechanical coupling were performed with FLAC3D. And a good agreement was found between the numerical simulation results and the laboratory measurements under 20 MPa confining pressure and 10 MPa fluid pressure, the feasibility of this fully hydro-mechanical coupled model was proven.
28
Miller, James Thomas Ph D. Massachusetts Institute of Technology. "Mechanical behavior of elastic rods under constraint". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/88280.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 213-223).
We present the results of an experimental investigation of the mechanics of thin elastic rods under a variety of loading conditions. Four scenarios are explored, with increasing complexity: i) the shape of a naturally curved rod suspended under self-weight, ii) the buckling and post-buckling behavior of a rod compressed inside a cylindrical constraint, iii) the mechanical instabilities arising when a rod is progressively injected into a horizontal cylinder, and iv) strategies for mitigation of these instabilities by dynamic excitation of the constraint. First, we consider the role of natural curvature in determining the shape of a hanging elastic rod suspended under its own weight. We categorize three distinct configurations: planar hooks, localized helices, and global helices. Experimental results are contrasted with simulations and theory and the phase diagram of the system is rationalized. Secondly, in what we call the classic case experiment, we study the buckling and post-buckling behavior of a rod compressed inside a cylindrical constraint. Under imposed displacement, the initially straight rod buckles into a sinusoidal mode and eventually undergoes a secondary instability into a helical configuration. The critical buckling loads are quantified and found to depend strongly on the aspect ratio of the rod to pipe diameter. Thirdly, we inject a thin elastic rod into a horizontal cylinder under imposed velocity in the real case experiment. Friction between the rod and constraining pipe causes an increasing axial load with continued injection. Consecutive buckling transitions lead to straight, sinusoidal, and helical configurations in a spatially heterogeneous distribution. We quantify critical lengths and loads for the onset of the helical instability. The geometric parameters of the system strongly affect the buckling and post-buckling behavior. Finally, we explore active strategies for delaying the onset of helical buckling in the real case. Distributed vertical vibration is applied to the cylindrical constraint, which destabilizes frictional contacts between the rod and pipe. Injection speed, peak acceleration of vibration, and vibration frequency are all found to affect the postponement of helical initiation. The process is rationalized and design
by James T. Miller.
Ph. D.
29
Pearce, Jonathan P. (Jonathan Patrick) 1978. "Qualitative behavior prediction for simple mechanical systems". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86692.
Testo completoAbstract (sommario):
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (p. 55-56).
by Jonathan P. Pearce.
M.Eng.
30
Baxter, Diane Yamane. "Mechanical Behavior of Soil-Bentonite Cutoff Walls". Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/27079.
Testo completoAbstract (sommario):
A soil-bentonite cutoff wall is a type of subsurface vertical barrier constructed by back-filling a trench with a mixture of soil, bentonite, and water. Although soil-bentonite cutoff walls are common, their mechanical behavior is not well understood. Current design procedures do not consider the final stress state of the consolidated soil-bentonite backfill or deformations in adjacent ground. The final stress state in the completed wall is important because it influences the hydraulic conductivity of the cutoff (Barrier 1995), the cutoff's susceptibility to hydraulic fracture, and the magnitude of deformations adjacent to the cutoff wall. Deformations adjacent to the cutoff wall can be significant and can cause damage to adjacent structures. The objectives of this research are to 1) add to the current body of knowledge of the properties of soil-bentonite mixtures, 2) evaluate constitutive models and select a model to represent soil-bentonite, 3) model a soil-bentonite cutoff wall using finite elements, and 4) investigate the influence of several factors on the deformations in adjacent ground.
These objectives were met by first summarizing information from the literature on soil-bentonite properties and then performing a laboratory testing program on different soil-bentonite mixtures. Five constitutive models were evaluated to determine how well they match the data from the laboratory testing program. A model referred to as the RS model was chosen to best represent soil-bentonite, and provided a good match of the soil-bentonite behavior. The RS model, which is a special case of a more complicated existing model, is a non-associative Modified Cam Clay type model that has parameters to change the yield surface and plastic potential surface into ellipses of varying shapes. The RS model was implemented into the finite element program SAGE.
A finite element model was developed using SAGE to simulate all stages of construction of a soil-bentonite cutoff wall including excavation of a trench under bentonite-water slurry, replacement of the bentonite-water slurry with soil-bentonite backfill, and consolidation of the soil-bentonite backfill. The model was calibrated with a well-documented case history, and predicted deformations in adjacent ground were close to measured deformations. Evaluation of the model indicates that there is good confidence in the prediction of deformations in adjacent ground, but there is lower confidence in the predicted stresses in the consolidated soil-bentonite and settlement of the backfill in the trench. A parametric study was then performed using the finite element model assuming sand sites of varying density and OCR. Deformations in adjacent ground were calculated for various soil conditions, soil-bentonite properties, and trench configurations. A correlation was found between maximum calculated settlement in adjacent ground and factor of safety against trenchPh. D.
31
Ramamoorthy, Thiagarajan. "Mechanical Behavior of Membranes in Electrostatic Precipitators". Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1125868299.
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Seki, Yasuaki. "Structure and mechanical behavior of bird beaks". Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3355486.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed June 18, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 199-215).
33
Évora, Victor Manuel Fortes. "Fabrication and dynamic mechanical behavior of nanocomposites /". View online ; access limited to URI, 2004. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3135902.
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Dehghanghadikolaei, Amir. "Enhance its Corrosion Behavior of Additively Manufactured NiTi by Micro-Arc Oxidation Coating". University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1525475381922659.
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Alsup, Jeremy S. "Mimicking the Mechanical Behavior of Advancing Disc Degeneration Through Needle Injections". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3569.
Testo completoAbstract (sommario):
Objective - To investigate the effects of injected protease solution on the mechanical advancement of disc degeneration, and to establish test protocol for future pre-clinical validation of spinal arthroplasty devices. The hypothesis that injection of a protease into a cadaveric lumbar disc will mimic advanced degeneration mechanics was the subject of this study. Summary of Background Information - Spinal disc degeneration is a universal condition that progresses in adults due to aging, disease, or injury. Stages of disc degeneration have been categorized in cadaver specimens, with each degeneration level exhibiting characteristic changes in flexibility parameters. Spinal disc tissue can be compromised through introduction of proteolytic enzymes into the collagenous fibers of the annulus fibrosus. Methods - 18 motion segments from 8 human lumbar spines were subjected to flexibility testing. Each specimen was either injected with 0.600 mL of trypsin solution in the annulus fibrosus, 0.600 mL of phosphate-buffed saline, or a fluid-less needle-stick. Motion testing followed with rotations applied in all three major spinal motions. Test sections were transected mid-disc after testing to characterize initial degeneration severity, and acquired motion data was analyzed to show flexibility traits over time. Results - Trypsin, saline, and control injections all caused changes in motion from pre-injection baselines. Saline injections were slightly more effective at mimicking the mechanics of higher grades of degeneration with more fidelity than trypsin injections. All motion parameters were altered by the study treatments, with hysteresis and neutral zone parameters experiencing changes similar to that seen in natural degeneration with greater fidelity. Lateral Bending motion showed the greatest magnitude response to injections, with Flexion-Extension tests showing the smallest change. Discussion - Unexpectedly, fluid-less control injections caused changes to hysteresis and neutral zone parameters, suggesting an alteration to viscoelastic properties due to simple needle puncture. Fluid injections (Trypsin and Saline) caused an immediate transient post-injection change to biomechanics that dissipated over time, except in Axial Rotation. Saline injections provided the highest fidelity in mimicking the motion of more advanced stages of degeneration.
36
Eskner, Mats. "Mechanical Behaviour of Gas Turbine Coatings". Doctoral thesis, KTH, Materials Science and Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3776.
Testo completoAbstract (sommario):
Coatings are frequently applied on gas turbine components inorder to restrict surface degradation such as corrosion andoxidation of the structural material or to thermally insulatethe structural material against the hot environment, therebyincreasing the efficiency of the turbine. However, in order toobtain accurate lifetime expectancies and performance of thecoatings system it is necessary to have a reliableunderstanding of the mechanical properties and failuremechanisms of the coatings.
In this thesis, mechanical and fracture behaviour have beenstudied for a NiAl coating applied by a pack cementationprocess, an air-plasma sprayed NiCoCrAlY bondcoat, a vacuumplasma-sprayed NiCrAlY bondcoat and an air plasma-sprayed ZrO2+ 6-8 % Y2O3topcoat. The mechanical tests were carried out ata temperature interval between room temperature and 860oC.Small punch tests and spherical indentation were the testmethods applied for this purpose, in which existing bending andindentation theory were adopted for interpretation of the testresults. Efforts were made to validate the test methods toensure their relevance for coating property measurements. Itwas found that the combination of these two methods givescapability to predict the temperature dependence of severalrelevant mechanical properties of gas turbine coatings, forexample the hardness, elastic modulus, yield strength, fracturestrength, flow stress-strain behaviour and ductility.Furthermore, the plasma-sprayed coatings were tested in bothas-coated and heat-treated condition, which revealedsignificant difference in properties. Microstructuralexamination of the bondcoats showed that oxidation with loss ofaluminium plays an important role in the coating degradationand for the property changes in the coatings.
Keywords:small punch test, miniaturised disc bendingtests, spherical indentation, coatings, NiAl, APS-NiCoCrAlY,VPS-NiCrAlY, mechanical properties
37
Dingle, Matthew, e mikewood@deakin edu au. "Elastic behaviour in mechanical draw presses". Deakin University. School of Engineering and Technology, 2001. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20051017.150247.
Testo completoAbstract (sommario):
This thesis explores the elastic behaviour of the mechanical double action press and draw die system commonly used to draw sheet metal components in the automotive industry. High process variability in production and excessive time spent in die try-out are significant problems in automotive stamping. It has previously been suggested that the elastic behaviour of the system may contribute to these problems. However, the mechanical principles that cause the press system to affect the forming process have not been documented in detail. Due to a poor understanding of these problems in industry, the elasticity of the press and tools is currently not considered during the die design. The aim of this work was to explore the physical principles of press system elasticity and determine the extent to which it contributes to problems in try-out and production. On the basis of this analysis methods were developed for controlling or accounting for problems during the design process.
The application of frictional restraining force to the edges of the blank during forming depends on the distribution and magnitude of the clamping force between the binders surfaces of the draw die. This is an important control parameter for the deep drawing process. It has been demonstrated in this work that the elasticity of the press and draw die can affect clamping force in two ways. The response of the press system, to the forces produced in the press during forming, causes the magnitude of clamping force to change during the stroke. This was demonstrated using measured data from a production press. A simple linear elastic model of the press system was developed to illustrate a definite link between the measured force variation and the elasticity of the press and tools. The simple model was extended into a finite element model of the complete press system, which was used to control a forming simulation. It was demonstrated that stiffness variation within the system could influence the final strains in a drawn part. At the conclusion of this investigation a method is proposed for assessing the sensitivity of a part to clamping force variation in the press during die design. A means of reducing variation in the press through the addition of a simple linear spring element is also discussed.
The second part of the work assessed the influence of tool structure on the distribution of frictional restraining forces to the blank. A forming simulation showed that tool stiffness affects the distribution of clamping pressure between the binders. This was also shown to affect the final strains in a drawn part. However, the most significant influence on restraining force was the tendency of the blank to increase in thickness between the binders during forming. Using a finite element approximation of the try-out process it was shown that the structure of the tool would also contribute to the problems currently experienced in try-out where uneven contact pressure distributions are addressed by manually adjusting the tool surfaces.
Finally a generalised approach to designing draw die structures was developed. Simple analysis methods were combined with finite element based topology optimisation techniques to develop a set of basic design guidelines. The aim of the guidelines was to produce a structure with uniform stiffness response to a pressure applied at the binder surface.
The work concludes with a recommendation for introducing the methods developed in this thesis into the standard production process.
38
Bhuiyan, M. A. S. "The mechanical behaviour of stabilised soils". Thesis, University of Newcastle Upon Tyne, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382836.
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Miroshnychenko, Dmytro. "Mechanical behaviour of PVC : model evaluation". Thesis, Loughborough University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250881.
Testo completo
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Williams, Jonathan Mark. "Mechanical behaviour of flexible polyurethane foams". Thesis, University of Leicester, 1995. http://hdl.handle.net/2381/34725.
Testo completoAbstract (sommario):
Dunlop Suspensions and Components manufacture microvon, a flexible polyurethane foam, which is used extensively in the automotive industry as spring aids for car suspension systems. The material is used because of its desirable non-linear elastic stress/stain characteristics, its quick recovery behaviour, and because it tends to produce little lateral expansion during compression. The design of such spring aid components, however, remains something of a black art, since the behaviour of the material is not fully understood. Complications arise because the mechanical properties of the material are controlled by a large number of physical, chemical and processing effects. The aim of the research has been to gain further understanding of the material, and its response under load, in order to be able to predict the compressive behaviour of the material. This has been achieved by combining microstructural observations of the deforming material with information obtained from detailed mechanical tests. There have been many attempts by researchers to describe the behaviour of cellular materials. This has been done in a variety of ways, and approaches have included developing complicated strain energy functions or utilising simple models based on repeating cell units. However, a number of difficulties are encountered when applying these material models to microvon. The microstructural observations and mechanical tests undertaken in this research have led to the development of new material models for cellular materials. Two types of model have been developed; a physical model and a series of phenomenological models. The physical model is a bi-linear relationship between stress, strain and density, in which the mechanisms of deformation are described. The phenomenological models have been developed using curve- fitting, to accurately predict the axial stress/strain and lateral/axial strain behaviour of microvon over a wide range of strain, density, temperature and strain rate.
41
Tahir, Muhammed. "Quantum behaviour in nano-mechanical systems". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/5676.
Testo completoAbstract (sommario):
The emerging field of nano-electro-mechanical systems (NEMS), in which the single mode of a nanomechanical oscillator plays the role of an active device, is receiving much attention due to its technological importance. The characteristic component that gives the name to these devices is an oscillator of nanometer size coupled to the electrons on the dot that transfer electrons one-by-one between a source and a drain lead. From a fundamental point of view, it is important to understand the interplay between the electronic transport and the nanomechanical motion of the oscillator quantum mechanically. This thesis contains the description and analysis of the dynamics of a nanomechanical oscillator coupled to a resonant tunnel junction (RTJ) and its realization as a shuttle device. The models we consider describe both the mechanical and electrical degrees of freedom quantum mechanically; Firstly, a RTJ coupled to a nanomechanical oscillator. Secondly, we report a first complete quantum mechanical analysis of a charge shuttle. We introduce a new non-perturbative quantum mechanical description for the strong interaction of both the electrical and the mechanical object, which is beyond the existing experiments. We describe a nonequilibrium Green’s function formalism: a well suited technique to treat this kind of far from equilibrium systems, which can deal with very small to very large applied bias. The numerical implementation of these models are discussed in detail, and the transient and the steady state behavior of the system is also considered here for the quantum dynamics of the oscillator as a function of time. This will provide useful insight for the design of experiments aimed at studying the quantum behavior of an oscillator.
42
Webb, Carolyn H. "Mechanical traction behaviour of artificial turf". Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/25672.
Testo completoAbstract (sommario):
Artificial surfaces are increasingly more common in a number of sports including football, rugby and hockey. Each specific sport has mechanical properties designed to suit the requirements of the sport which can be achieved through appropriate selection of surface specification, as well as the appropriate selection of footwear. In player-surface interactions, traction is a key system property that needs to be measured for comfort, performance and any potential injury risk. Many of the current industry tests used to measure traction are simplistic and have limitations when used in tests. The aim of the thesis was to make a contribution to knowledge with regard to the mobilisation of traction and apply this to the understanding of shoe-surface interactions. This was achieved by completing a number of objectives. These included reviewing current knowledge of player-surface interaction behaviour in relation to traction and obtaining relevant human boundary conditions for biofidelic mechanical test development. The mechanisms of traction were then investigated and the variables in the mobilisation of traction identified. The traction forces developed were quantified with appropriate measurement systems. Mechanical test equipment was then developed along with protocols to replicate the translational and rotational lower limb behaviour during sport specific behaviour. This included the standard FIFA rotational device being modified to include two sensors which record continuous data throughout a trial to allow for more than a peak torque value to be analysed. In addition, a piece of equipment to measure translational traction was developed and constructed to support the rotational traction device and help to understand the mobilisation of traction. The device pulled a tray containing a surface sample, with a shoe/plate placed on the sample. The horizontal force was measured, as well as the amount of stud penetration into the surface. It was also necessary to characterise the state of the surface and the effects that any changes may have on the traction that is mobilised. Testing completed involved repeated testing on both the rotational and translational to allow for comparison. Changes in the surface properties were made such as the number of fibres in a set area and the rubber infill density as well as shoe properties such as stud spacing, stud type and number of studs. In the results, the initial stiffness response of the surface was often focussed on as it was stated that this may be a better indicator of the mechanisms involved in the traction mobilised by subjects, compared to peak torque. This is due to actual foot rotation measured in subject testing being observed to be much smaller than the rotation/distance required to produce the peak force. The larger angles/displacements were also considered to help inform the mechanisms of traction. The final objective was to refine the mechanisms based on the experimental design. This all adds to the contribution of knowledge regarding the mobilisation of traction. A key outcome from the thesis is the effect the surface and shoe properties have on traction, therefore it is essential to state the specification when reporting results otherwise comparisons are not able to be made. The mechanism of traction has not previously been fully understood, with this thesis beginning to understand the details of how the change in surface or shoe properties affect how the surface reacts during shoe-surface interactions.
43
Nguyen, Tuan Minh. "MODELING OF THERMO-MECHANICAL BEHAVIOR OF NITINOL ACTUATOR FOR SMART NEEDLE APPLICATION". Master's thesis, Temple University Libraries, 2012. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/192929.
Testo completoAbstract (sommario):
Mechanical EngineeringM.S.M.E.
A large and increasing number of cancer interventions, including both diagnosis and therapy, involve precise placement of needles, which is extremely difficult. This challenge is due to lack of proper actuation of the needle (i.e., actuated from the proximal end, which is far away from the needle tip). To overcome this challenge, we propose to bend the needle using a smart actuator that applies bending forces on the needle body; thereby, improving the navigation of the needle. The smart actuator is designed with shape memory alloy (SMA) wires, namely Nitinol, due to their unique properties such as super-elasticity, shape memory effect, and biocompatibility. For accurate steering of the smart needle, there is a need to understand Nitinol thermo-mechanical behaviors. Various existing SMA constitutive models were investigated and compared. Since SMA is used as an actuator in this project, only one dimensional constitutive models are considered. Two distinct models with different phase transformation kinetic approaches were chosen. The first model was proposed by Terriault and Brailovski (J. Intell. Mat. Systems Structures, 2011) using a modified one dimensional Likhachev formulation. The second model was developed by Brinson (J. Intell. Mat. Systems Structures , 1993). Since all SMA constitutive models are empirically based, several important materials' constants such as Phase Transformation Temperatures are needed. The four Transformation Temperatures are: Martensite start (Ms), Martensite finish (Mf), Austenite start (As), Austenite finish (Af). Differential Scanning Calorimetry (DSC) was used to obtain these constants. These temperatures are also influenced by stress, defined by the Clausius-Clayperon coefficients. The coefficients were obtained by measuring Nitinol temperature and displacement response under various constant stress conditions. In order to study its actuation behavior, Nitinol wires under constant strain configuration and resistance heating were tested for their force response. The thermo-mechanical responses were then compared with numerical simulations. While Terriault and Brailovski resistance heating formulation agrees strongly with temperature responses, the model cannot be used to simulate the actuator mechanical responses. Brinson model simulations of the force responses were found to agree well with experimental results. In conclusion, Terriault and Brailovski resistance heating formulation should be coupled with Brinson model to accurately simulate Nitinol actuation behavior for the smart needle.
Temple University--Theses
44
DeArdo, Ian A. "Mechanical behavior of IF 409 ferritic stainless steel". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0025/MQ50600.pdf.
Testo completo
45
Tyber, Jeffrey Alan. "Mechanical behavior of materials for reconstructive bioengineering applications". Diss., Connect to online resource, 2005. http://wwwlib.umi.com/cr/colorado/fullcit?p1430186.
Testo completo
46
Conley, Jill Anne. "Hygro-thermo-mechanical behavior of fiber optic apparatus". Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17308.
Testo completo
47
Blasbalg, David A. "The dynamic behavior of two-phase mechanical seals". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/17795.
Testo completo
48
DeArdo, Ian A. "Mechanical behavior of IF 409 ferritic stainless steel". Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21287.
Testo completoAbstract (sommario):
IF 409 stainless steel is a common industrial steel grade used in automotive exhaust systems. It combines a high formability with the corrosion resistance associated with stainless steels. Two particular grades of IF 409 were used in these experiments: a titanium stabilized and a titanium-niobium stabilized. The current work explores the mechanical behavior Of this grade with emphasis on the occurrence of dynamic recrystallization. Hot torsion tests were performed over a range of temperatures and strains to determine the behavior. The tests were analyzed using the flow curves, optical microscopy and texture measurements. The optical micrographs indicated that dynamic recrystallization was occurring. The texture results confirmed that the titanium stabilized steel dynamically recrystallized around 1000°C and the titanium-niobium grade recrystallized around 1200°C. In addition, the effects of strain and temperature were quantified. The results allow the feasibility of dynamic recrystallization in industrial applications to be determined.
49
Nguyen, Van-Tri. "Thermal and thermo-mechanical behavior of energy piles". Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1160/document.
Testo completoAbstract (sommario):
Le comportement thermique et thermo-mécanique des pieux énergétiques est étudié par plusieurs approches : mesures au laboratoire sur des éprouvettes de sol, modélisation physique en modèle réduit, expérimentations sur pieu en vraie grandeur, et calculs numériques/analytiques. D’abord, la conductivité thermique d’un loess à l’état non saturé est mesurée en fonction de la teneur en eau et de la succion. Les résultats montrent une relation univoque entre la conductivité thermique et la teneur en eau pendant un cycle d’humidification/séchage alors qu’une boucle d’hystérésis est observée pour la relation entre la conductivité thermique et la succion. Deuxièmement, des essais thermiques sont réalisés sur un pieu énergétique expérimental en vraie grandeur pour étudier le transfert thermique à l’échelle réelle. Troisièmement, une solution analytique est proposée pour simuler la conduction thermique d’un pieu énergétique vers le sol environnant pendant un chauffage. Les tâches mentionnées ci-dessus concernant le comportant thermique sont ensuite complétées par des études sur le comportement thermo-mécanique des pieux énergétiques. D’un côté, des expérimentations sont réalisées sur un modèle réduit de pieu installé dans un sable sec ou dans une argile saturée. Trente cycles thermiques, représentant trente cycles annuels, sont appliqués au pieu sous différentes charges axiales en tête. Les résultats montrent un tassement irréversible avec les cycles thermiques ; ce tassement est plus important sous une charge axiale plus grande. De plus, le tassement est plus marqué pendant les premiers cycles thermiques et devient négligeable pour les cycles suivants. De l’autre côté, les travaux expérimentaux sur le modèle réduit de pieu sont complétés par les calculs numériques utilisant la méthode des éléments finis. Cette approche est d’abord validée avec les résultats obtenus sur le pieu modèle avant d’être utilisée pour prédire les résultats des expérimentations en vraie grandeurThe thermal and thermo-mechanical behavior of energy piles is investigated by various approaches: laboratory measurement on small soil samples, physical modeling on small-scale pile, experiments on real-scale pile, and analytical/numerical calculations. First, the thermal conductivity of unsaturated loess is measured simultaneously with moisture content and suction. The results show a unique relationship between thermal conductivity and moisture content during a wetting/drying cycle while a clear hysteresis loop can be observed on the relationship between thermal conductivity and suction. Second, thermal tests are performed on a full-scale experimental energy pile to observe heat transfer at the real scale. Third, an analytical solution is proposed to simulate conductive heat transfer from an energy pile to the surrounding soil during heating. The above-mentioned tasks related to the thermal behavior are then completed by studies on the thermo-mechanical behavior of energy piles. On one hand, experiments are performed on a small-scale pile installed either in dry sand or in saturated clay. Thirty thermal cycles, representing thirty annual cycles, are applied to the pile under various constant pile head loads. The results show irreversible pile head settlement with thermal cycles; the settlement is higher at higher pile head load. In addition, the irreversible thermal settlement is the most significant during the first cycles; it becomes negligible at high number of cycles. On the other hand, the experimental work with small-scale pile is completed with numerical calculations by using the finite element method. This approach is first validated with the results on small-scale pile prior to be used to predict the results of full-scale experiments
50
JARAMILLO, NATALIA ANDREA DURÁN. "MECHANICAL BEHAVIOR OF SOILS REINFORCED WITH TIRES RUBBER". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=27554@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
O volume de pneus inservíveis continua aumentando a cada ano, se tornando um tema de grande preocupação para a sociedade. Motivados por esta problemática ambiental, o presente estudo experimental propõe utilizar a borracha de pneu triturada como reforço de solos, em duas diferentes granulometrias (chips e fibras), como material alternativo para o reforço de dois tipos de solos (areia e solo argiloso). Com este fim realizaram-se ensaios mecânicos, tais como ensaios de compactação proctor standard, ensaios triaxiais do tipo consolidado e isotropicamente drenado e ensaios de adensamento unidimensional, para avaliar os efeitos da granulometria da borracha de pneu, triturada em chips e fibras (com os tamanhos médios de 4,6 mm e 2 mm, respectivamente) e do teor de borracha de pneu (5, 10 por cento e 15 por cento em relação à massa de solo seco), no comportamento mecânico de misturas de areia-borracha e de misturas solo argiloso-borracha. Os resultados mostraram que tanto os chips como as fibras de pneu de borracha contribuem no aumento dos parâmetros de resistência ao cisalhamento de ambos os solos e aumentam a energia de deformação absorvida durante o cisalhamento. Ao analisar a resposta obtida em ambos os solos, se evidencia que, tanto para a argila quanto para a areia, foi mais efetivo o reforço com 10 por cento de fibras de borracha de pneu. Todos os compósitos estudados possuem características de resistência que poderiam cumprir as exigências de determinadas obras geotécnicas (aterros sobre solos moles, reforço de taludes, solo de base de fundações superficiais), portanto o uso da borracha de pneu como reforço de solos contribuiria com o menor consumo de material natural e redução dos custos de transporte e volume de material mobilizado.
The volume of discarded tires continues to increase each year, becoming a major topic of concern for society. Motivated by this environmental issue, this experimental study proposes using tire chips and tire buffings as an alternative material to improve the shear strength of two types of soil (sand and clayey soil). Because of this, standard Proctor compaction tests, consolidated-drained triaxial tests and compressibility tests were performed to assess the influence of tire rubber particle size, (with average sizes of 4.6 mm and 2 mm, respectively) and tire rubber content (5, 10 percent and 15 percent by dry weight of soil) into the mechanical behavior of sand and clayey soil. The tests results showed that both, chips and buffings contribute increasing the shear strength parameters of both the soil and increase the strain energy absorbed during the shear phase. By analyzing, the mechanical response both for clayey soil and for sand was found that the best shear strength improvement was obtained at 10 percent of tire buffings. All the composites showed resistance characteristics that would ensure the requirements for many geotechnical applications (embankments over soft soils, slope reinforcement and surface foundations), so the use of waste tires as a reinforcement material would help solve problems associated with natural resources and reducing transportation costs and earthmoving.