Dissertations / Theses on the topic 'Soft Material Mechanics'
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Jin, Lihua. "Mechanical Instabilities of Soft Materials: Creases, Wrinkles, Folds, and Ridges." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13064983.
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Subject to a sufficiently large compression, materials may undergo mechanical instabilities of various types. When the material is homogeneous, creases set in. When the material is a bilayer consisting of a stiff thin film on a thick compliant substrate, wrinkles set in. Creases are localized self-contact regions with large strain deviating from the smooth state, while wrinkles are undulations finite in space with infinitesimal strain deviating from the smooth state. After the formation of wrinkles, if the compression further increases, wrinkles double their period and form localized folds. If the substrate is subject to a sufficiently large pre-tension, wrinkles transit to ridges. This thesis explores different types of mechanical instabilities: creases, wrinkles, folds, and ridges.
We start with studying creases in different materials. Soft tissues growing under constraint often form creases. We adopt the model of growth that factors the deformation gradient into a growth tensor and an elastic deformation tensor, and show that the critical conditions for the onset of creases take a remarkably simple form. We then perform simulations to explore creases in strain-stiffening materials. For a solid that stiffens steeply at large strains, as the compression increases, the surface is initially smooth, then forms creases, and finally becomes smooth again. For a solid that stiffens steeply at small strains, creases never form for all levels of compression. In order to better control the formation and disappearance of creases, we design a soft elastic bilayer with same moduli of the film and substrate but the substrate pre-compressed, and show that the bilayer can snap between the flat and creased states reproducibly with tunable hysteresis in a large strain range. We also show that an interface between two soft materials can form creases under compression.
We then investigate the critical conditions for the onset of wrinkles and creases in bilayers with arbitrary thicknesses and moduli of the two layers, and show several new types of bifurcation behavior when the film and substrate have comparable moduli and thicknesses. We study the effect of substrate pre-stretch on post-wrinkling bifurcations, and show that pre-tension stabilizes wrinkles while pre-compression destabilizes wrinkles. When the pre-compression is sufficiently large, `chaotic' morphologies emerge. When the pre-tension is sufficiently large, we realize ridge localizations and networks under an equi-biaxial compression, and study the mechanics of ridge formation and propagation.Engineering and Applied Sciences
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Zhang, Li Ying Grace. "Fatigue and integrity of hard ceramics and coatings using the soft impressor technique." Thesis, University of Hull, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363272.
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Hockings, Nicholas. "Material and mechanical emulation of the human hand." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720651.
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The hands and feet account for half of the complexity of the musculoskeletal system, while the skin of the hand is specialised with many important structures. Much of the subtlety of the mechanism of the hand lies in the soft tissues, and the tactile and proprioceptive sensitivity depends on the large number of mechanoreceptors embedded in specific structures of the soft tissues. This thesis investigates synthetic materials and manufacturing techniques to enable building robots that reproduce the biomechanics and tactile sensitivity of vertebrates – histomimetic robotics. The material and mechanical anatomy of the hand is reviewed, highlighting difficulty of numerical measurement in soft-tissue anatomy, and the predictive nature of descriptive anatomical knowledge. The biomechanical mechanisms of the hand and their support of sensorimotor control are presented. A palate of materials and layup techniques are identified for emulating ligaments, joint surfaces, tendon networks, sheaths, soft matrices, and dermal structures. A method for thermoplastically drawing fine elastic fibres, with liquid metal amalgam cores, for connecting embedded sensors is demonstrated. The performance requirements of skeletal muscles are identified. Two classes of muscle-like bulk MEMS electrostatic actuators are shown theoretically to be capable of meeting these requirements. Means to manufacture them, and their additional application as mechanoreceptors are described. A novel machine perception algorithm is outlined as a solution to the problem of measuring soft tissue anatomy, CAD/CAE/CNC for layup of histomimetic robots, and sensory perception by such robots. The results of the work support the view that histomimetic robotics is a viable approach, and identify a number of areas for further investigation including: polymer modification by graft-polymerisation, automated layup tools, and machine perception.
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Huang, Shan. "Nano-chemo-mechanics of advanced materials for hydrogen storage and lithium battery applications." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42710.
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Chemo-mechanics studies the material behavior and phenomena at the interface of mechanics and chemistry. Material failures due to coupled chemo-mechanical effects are serious roadblocks in the development of renewable energy technologies. Among the sources of renewable energies for the mass market, hydrogen and lithium-ion battery are promising candidates due to their high efficiency and easiness of conversion into other types of energy. However, hydrogen will degrade material mechanical properties and lithium insertion can cause electrode failures in battery owing to their high mobilities and strong chemo-mechanical coupling effects. These problems seriously prevent the large-scale applications of these renewable energy sources. In this thesis, the atomistic and continuum modeling are performed to study the chemical-mechanical failures. The objective is to understand the hydrogen embrittlement of grain boundary engineered metals and the lithium insertion-induced fracture in alloy electrodes for lithium-ion batteries.
Hydrogen in metallic containment systems such as high-pressure vessels and pipelines causes the degradation of their mechanical properties that can result in sudden catastrophic fracture. A wide range of hydrogen embrittlement phenomena was attributed to the loss of cohesion of interfaces (between grains, inclusion and matrix, or phases) due to interstitially dissolved hydrogen. Our modeling and simulation of hydrogen embrittlement will address the question of why susceptibility to hydrogen embrittlement in metallic materials can be markedly reduced by grain boundary engineering. Implications of our results for efficient hydrogen storage and transport at high pressures are discussed.
Silicon is one of the most promising anode materials for Li-ion batteries (LIB) because of the highest known theoretical charge capacity. However, Si anodes often suffer from pulverization and capacity fading. This is caused by the large volume changes of Si (~300%) upon Li insertion/extraction close to the theoretical charging/discharging limit. In particular, large incompatible deformation between areas of different Li contents tends to initiate fracture, leading to electro-chemical-mechanical failures of Si electrodes. In order to understand the chemo-mechanical mechanisms, we begin with the study of basic fracture modes in pure silicon, and then study the diffusion induced deformation and fracture in lithiated Si. Results have implications for increasing battery capacity and reliability.
To improve mechanical stability of LIB anode, failure mechanisms of silicon and coated tin-oxide nanowires have been studied at continuum level. It's shown that anisotropic diffusivity and anisotropic deformation play vital roles in lithiation process. Our predictions of fracture initiation and evolution are verified by in situ experiment observations. Due to the mechanical confinement of the coating layers, our study demonstrates that it is possible to simultaneously control the electrochemical reaction rate and the mechanical strain of the electrode materials through carbon or aluminum coating, which opens new avenues of designing better lithium ion batteries.
This thesis addresses the nano-chemo-mechanical failure problems in two green energy-carrier systems toward improving the performance of Li-ion battery anode and hydrogen storage system. It provides an atomistic and continuum modeling framework for the study of chemo-mechanics of advanced materials such as nano-structured metals and alloys. The results help understand the chemical effects of impurities on the mechanical properties of host materials with different metallic and covalent bonding characteristics.
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Kramer, Rebecca Krone. "Soft Active Materials for Actuation, Sensing, and Electronics." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10368.
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Future generations of robots, electronics, and assistive medical devices will include systems that are soft and elastically deformable, allowing them to adapt their morphology in unstructured environments. This will require soft active materials for actuation, circuitry, and sensing of deformation and contact pressure. The emerging field of soft robotics utilizes these soft active materials to mimic the inherent compliance of natural soft-bodied systems. As the elasticity of robot components increases, the challenges for functionality revert to basic questions of fabrication, materials, and design - whereas such aspects are far more developed for traditional rigid-bodied systems. This thesis will highlight preliminary materials and designs that address the need for soft actuators and sensors, as well as emerging fabrication techniques for manufacturing stretchable circuits and devices based on liquid-embedded elastomers.Engineering and Applied Sciences
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Lin, Gaojian. "Instability driven reconfigurable soft materials: mechanics and functionality." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/508542.
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Mechanical EngineeringPh.D.
Mechanical instability, a deformation mode involving abrupt switching between two distinct equilibrium structural configurations, has historically been viewed as a failure mechanism in engineering and materials science. Since the pioneering work in harnessing spontaneous buckling for surface micro-patterning in 1998, tremendous research interest has focused to utilize, rather than avoid, buckling instability in soft materials at small scale for achieving unique properties and multifunctionality. The benefit of small-scale bucking instability in soft materials and structures lies in the reversible dynamic tunability of the buckled structural or surface configuration in response to different external stimuli, which enables the coupling of structural or surface reconfiguration with dynamically tunable properties, such as mechanical, optical, wetting, and electrical properties. In this dissertation, I explore the fundamental mechanics and functionality of surface-based buckling and hierarchical wrinkling on substrates in multifunctional opto-electronic devices and smart windows. I will first explore the benefits of classical plate buckling in soft materials. The challenge lies in the intrinsic indeterminate characteristics of buckling in terms of its buckling orientation, which could lead to geometric frustration and random global structures. To address this challenge, I introduce cuts-based geometrical imperfection to guide the deterministic buckling in arrays of parallel active polymeric plates on rigid substrates. After introducing patterned cuts, the originally random phase-shifted buckling transits to a prescribed buckling with controllable phases. The design principle for cut-directed deterministic buckling in plates is revealed through both mechanics model and finite element simulation. By harnessing cut-directed buckling for controllable contacts and interactions in buckled parallel plates, I demonstrate the array of parallel plates as a multifunctional platform for selectively steering the electronic and optical pathways on demand, as well as the potential application in design of mechanical logic gates. I then explore the hierarchical wrinkling of thin films on soft substrates via sequential wrinkling for design of a potential multifunctional smart window with combined structural color and water droplet transport control. The self-similar hierarchical wrinkles with both nanoscale and microscale features are generated on a pre-strained poly(dimethylsiloxane) (PDMS) elastomer through sequential strain release and multi-step oxygen plasma treatment. I exploit the criteria for generating self-similar hierarchical wrinkles through both simplified theoretical model and experiments. I show that the hierarchically wrinkled elastomer displays both opaqueness and iridescent structural color. I further show its ability in control of water droplet transport on demand through mechanical stretching and release. I further extend the study of self-similar hierarchical wrinkling to the dynamic wetting behavior of multiscale self-similar hierarchical wrinkled surfaces on PDMS substrates through combined plasma and ultraviolet ozone (UVO) treatment. The generated surface structure shows an independently controlled dual-scale roughness with level-1 small-wavelength wrinkles resting on level-2 large-wavelength wrinkles, as well as accompanying orthogonal cracks. By tuning the geometry of hierarchical wrinkles, I explore the small degree of wetting anisotropy in hierarchical wrinkled surfaces, defined as the contact angle difference between the parallel and perpendicular directions to the wrinkle grooves through both experimental characterization (confocal fluorescence imaging) and theoretical analyses. I find that the measured larger apparent contact angle than the theoretically predicted Wenzel contact angle is attributed to the three-phase contact line pinning effect of both wrinkles and cracks, which generates energetic barriers during the contact line motion. I reveal that the observed small degree of wetting anisotropy in the hierarchical wrinkled surfaces arises from the competition between orthogonal wrinkles and cracks in the contact line pinning.
Temple University--Theses
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Liu, Qihan. "Mechanics and Physics of Soft Materials." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493423.
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Materials where thermal energy is comparable to the interaction energy between molecules are called soft materials. Soft materials are everywhere in our life: food, rubber, polymer diaper, our own body, etc. The thermal fluctuation endows soft materials with fundamentally different behavior comparing to hard materials like metals and ceramics. This dissertation studies three aspects of the mechanics and physics of soft materials, as is reviewed below.
First, soft materials are generally swellable and viscous. The combination of diffusion and viscous flow gives rise to a length scale we called poroviscous length. The emergence of a length scale results in size dependent relaxation. We show that the coupling between diffusion and viscous flow explains the Brownian motion in supercooled liquids, where the classical result of Stokes-Einstein relation generally fails. The concurrent diffusion and viscous flow cannot be described by the classical hydrodynamics, where all the material transport is lumped into velocity field. We formulated a continuum theory to modify the classical hydrodynamics. In particular, the new theory predicts a new bulk viscosity that could exist in incompressible material. We generalize this idea of bulk viscosity to binary systems and study the mixing of materials that is limited by local structural rearrangement instead of diffusion. This model develops formulation of non-equilibrium thermodynamics by removing the common assumption of local equilibrium.
Second, capillarity has strong influence on the morphology of soft materials. The competition between capillarity and elasticity gives rise to the elastocapillary length, which is defined as surface tension over the shear modulus. We show that elastocapillary effect explains the complex nucleation of crease, a widely observed surface instability in soft elastic materials. We also explore the possible competition between capillarity and osmosis in gels, which defines the osmocapillary length, the surface tension divided by osmotic pressure. We show that at small enough length scale or for a gel that is nearly fully swollen, surface tension can pull liquid solvent out from the gel phase, a phenomenon we termed osmocapillary phase separation.
Third, soft materials are nearly incompressible. The incompressibility and softness makes elastomers ideal for the design of seals. Although the failure of seals has been studies for decades, existing studies mainly focus on the damage and degradation of materials. Here we study the leak of a seal due to elastic deformation without any damage. We call such a failure mode the elastic leak. We point out that elastic leak is involved in any leak event no matter whether material is damaged or not. We also show that the reversible nature of the elastic leak enable seal series to achieve higher sealing capability.Engineering and Applied Sciences - Engineering Sciences
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Perera, M. Mario. "Dynamic Soft Materials with Controllable Mechanical Properties." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595847753887897.
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Salahshoor, Pirsoltan Hossein. "Nanoscale structure and mechanical properties of a Soft Material." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-theses/924.
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"Recently, hydrogel have found to be promising biomaterials since their porous structure and hydrophilicity enables them to absorb a large amount of water. In this study the role of water on the mechanical properties of hydrogel are studied using ab-initio molecular dynamics (MD) and coarse-grained simulations. Condensed-Phased Optimized Molecular Potential (COMPASS) and MARTINI force fields are used in the all-atom atomistic models and coarse-grained simulations, respectively. The crosslinking process is modeled using a novel approach by cyclic NPT and NVT simulations starting from a high temperature, cooling down to a lower temperature to model the curing process. Radial distribution functions for different water contents (20%, 40%, 60% and 80%) have shown the crosslinks atoms are more hydrophilic than the other atoms. Diffusion coefficients are quantified in different water contents and the effect of crosslinking density on the water diffusion is studied. Elasticity parameters are computed by constant strain energy minimization in mechanical deformation simulations. It is shown that an increase in the water content results in a decrease in the elastic. Finally, continuum hyper elastic model of contact lens is studied for three different loading scenarios using Finite Element Model. "
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Bhattacharjee, Tirthankar. "Cohesive Zone Modeling of Tearing in Soft Materials." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313765176.
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Geri, Michela. "Dynamics and rheology of soft phase-change materials." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/121885.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 325-353).
Many industrial processes involve multicomponent or composite materials in which one component can undergo a phase transition leading to the appearance of a solid phase dispersed in a liquid-like continuous phase. Examples of soft phase-change materials can be found in a variety of applications from food products (e.g., organogels, casein gels and gelatin), pharmaceutical products (e.g., tissue mimicking phantoms and encapsulating agents), cosmetics (e.g., foundations and lipsticks), and in the oil and gas industry, where formation of paraffin waxes and clathrate hydrates represent major issues for upstream production and flow assurance.
Historically, phase-changing materials have been exploited for their unique thermal properties in energy storage applications, however soft solids and complex fluids that undergo phase transformation have broader impact in industrial and biomedical applications because of the dramatic changes in mechanical properties that result from the conditions across the phase transition. Typically, these soft phase-change materials are part of the broader class of elasto-visco-plastic materials, showing both viscoelasticity at small deformations and plasticity at large deformations. However, their material properties are greatly influenced by the specific processing conditions during formation, such as temperature and applied deformation, leading to a thermo-rheological complexity that still poses major challenges for their experimental and theoretical characterization.
In this Thesis, we develop novel experimental protocols and theoretical frameworks to characterize and describe the complex rheological behavior of soft phase-changing materials, under both linear and non-linear deformations. We focus mainly on two types of materials that are of major importance in the oil and gas industry: paraffin gels, as model waxy crude oils, and clathrate hydrate suspensions. In the limit of small deformations, we are usually interested in measuring the frequency response of the material as it evolves, or mutates, over time. Current state-of-the-art techniques have major limitations in providing both time- and frequency-resolution primarily due to the type of input signals used. To overcome this, we develop a robust excitation signal that allows us to perform time-resolved mechanical spectroscopy of fast mutating systems. Inspired by the biosonar signals of bats and dolphins, we introduce a joint frequency- and amplitude- modulated chirp signal.
Combining experiments and numerical simulations, we show that there exists an optimized range of amplitude modulation that minimizes the estimation error while reducing the total acquisition time by almost two orders of magnitude. With this new technique, which we call the Optimally Windowed Chirp (or OWCh), we then explore the phase transition during gelation of a series of mutating, phase-changing materials, including casein gels, gelatin and paraffin gels. To address large, non-linear deformations, we start from a thorough investigation of the steady state and transient response of paraffin gels under shear. We develop a robust protocol that enables us to systematically extract the main rheological features including the thermokinematic memory (i.e. the effect of thermal and shear history on the rheological behavior of the gel) and thixotropy (i.e. the time-dependent behavior under constant applied deformation).
We show that these features can be understood in terms of microstructural rearrangements of the underlying solid particle network, which can be quantified through differential scanning calorimetry, birefringence imaging and rheometry. Based on this understanding, we present a constitutive framework that captures all of the different features while respecting thermodynamic and objectivity constraints. We also investigate mechanical instabilities that may arise during rheological measurements. Combining ultrasonic image velocimetry and rheometry, we show that both shear banding and slip can take place during steady shear below a critical value of the shear rate. However, the thixotropic nature of these materials precludes the banding instability from growing in the sheared region of the gap, ensuring that the measured stress response corresponds to the real bulk behavior. Finally, we study the visco-plastic response of clathrate hydrate suspensions.
To do so, we develop a novel method to robustly control their formation, which so far has been a major issue in experimental studies due to uncontrolled nucleation and growth of hydrate crystals. Our method, based on the use of "frozen emulsions", decreases the induction time by orders of magnitude while guaranteeing that all the water droplets initially frozen into ice particles are converted into hydrate particles. Rheological measurements for different water volume fractions and shear rates reveal that the macroscopic rheological response is again governed by rearrangements of the microstructure; however, due to the very strong interparticle forces (which are the result of a continuous sintering process) the microstructure evolves towards a fully connected network that behaves as a porous solid structure.
Incorporating this limit into our theoretical model, we show that the framework developed for softer interparticle interaction can also capture the macroscopic plastic response of hydrate suspensions. The results from this Thesis have the potential to impact many industrial processes that involve soft phase-change materials, such as flow assurance and oil extraction, thermal energy storage, gas transport and storage, and other processes where the dynamics of gelation are used to control the rheological properties of the ultimate product.
by Michela Geri.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Tegeler, Lisa Jan. "Mechanics and materials issues in processing and flexibility of soft contact lenses." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38071.
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McNally, Lisa M. "Mechanical and biological properties of novel denture soft lining materials." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520186.
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Kim, Yoonho S. M. Massachusetts Institute of Technology. "Printing ferromagnetic domains in soft materials : mechanism, modeling, and applications." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118709.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-63).
Soft materials capable of transforming between three-dimensional (3D) shapes have applications in areas as diverse as flexible electronics, soft robotics, and biomedicine. This thesis introduces a method of printing ferromagnetic domains in soft materials that yield fast transformation between complex 3D shapes via magnetic actuation. This approach is based on direct ink writing of an elastomer composite containing hard ferromagnetic microparticles. By applying a magnetic field to the dispensing nozzle while printing, we make the particles reoriented along the applied field direction to impart patterned magnetic polarity to printed filaments. This method allows us to design ferromagnetic domains in 3D-printed soft materials encoded with complex programmed shapes. A mathematical model based on a continuum mechanics framework is developed to predict such complex transformation of printed structures under the applied magnetic fields. For this computational model, a constitutive law is developed to describe the behavior of soft materials incorporating hard ferromagnetic microparticles under applied magnetic fields. The capability to quantitatively predict the shape changes enables designing a set of previously inaccessible modes of transformation such as remotely controlled 3D auxetic behaviors in an extremely fast and fully reversible manner via magnetic actuation. The actuation speed and power density of the printed soft materials with programmed ferromagnetic domains are orders of magnitude greater than existing 3D-printed active materials. Diverse functions derived from the fast and complex shape changes such as reconfigurable soft electronics, interaction with quickly moving objects, rolling-based locomotion and delivery of drug pills, and a horizontal leap of a 3D auxetic structure.
by Yoonho Kim.
S.M.
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Liang, Heyi. "Rational Design of Soft Materials through Chemical Architectures." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1573085345744325.
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Pisani, R. "Footwear and soft ground interaction." Thesis, University of Salford, 2002. http://usir.salford.ac.uk/2170/.
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The aim of the research reported in this thesis was to improve the understanding of footwear and soft ground interaction and, in particular, its mathematical modelling. The work was undertaken for the Military Footwear Section of the MOD's Defence Clothing and Textiles Agency (DCTA) who funded the research in conjunction with the Engineering and Physical Sciences Research Council (EPSERC). Although research has been carried out on the interaction of footwear on firm surfaces, minimal work has previously been carried out on softer surfaces often encountered in combat situations and little effort has been applied to its mathematical modelling. The research programme included the development of mathematical models using soil mechanics theory, and experimental work using a soft-ground slip-rig. The prototype soft-ground footwear slip-rig that has been developed is a manually operated device based on simple mechanical mechanisms using weights and pulleys. The rig enables the measurement of traction and sinkage for different soil types, sole materials and tread geometry, at various angles of heel contact and applied vertical load. All experimental work has been carried out with the use of scaled up cleats to obtain measurable results. An investigation into three dimensional end effects has determined at what cleat length the problem becomes two dimensional. The experimental results have shown the effects of cleat geometry on total cleat traction for sand, and in particular the geometric characteristics that promote and reduce traction. These results have been analysed using Taguchi's Analysis of Variance technique. Traction distribution experiments have determined the proportion of traction obtained from different cleat areas. Soil mechanics theory, and in particular Coulomb's retaining wall theory, has been applied in the theoretical modelling of footwear and soft ground interaction. A two dimensional total traction model has been developed using MATLAB software and experimental and theoretical results have been compared. The traction versus cleat geometry trends for both the experimental and theoretical results were in good agreement.
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Fiorenza, Roberta Maria. "Mechanism of Formation of Soft Particles in Biodiesel Fuel Blends." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-275685.
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The large environmental impact related to the use of fossil fuel has driven the shift toward renewable sourced alternatives. Fossil diesel can be nowadays replaced by biodiesel, obtained from vegetable oils and fats, mostly used as biodiesel blends. However, some drawbacks are related to the use of this bio-fuel, among which the formation of deposit in injectors and filters causing a reduction of engine performances or engine failure. This thesis project focuses on the analysis of the mechanism of formation of soft particles in biodiesel deposits. These particles are constituted mostly of carboxylic metal soaps, and were found in biodiesel engines after using aged biofuel with contaminants, such as engine oil. The role of short chain fatty acids (SCFAs) has been investigated, together with the use of three different calcium sources, to analyse the formation mechanism of calcium soaps. Artificial ageing of B10 and B100 test fuels was performed, and in some cases an inert gas was bubbled to remove the formed SCFAs. Calcium sources, namely calcium oxide, calcium carbonate and engine oil, were added to investigatethe formation of soft particles. Ion chromatography, pH measurements, NMR spectroscopy and oxidation stability tests have been performed on the liquid test fuel to verify the presence and effect of SCFAs, while FTIR spectroscopy and GC/MS analyses were used to verify the presence of calcium soaps in the deposit and in solution. In contrast to the expectation, it was found that the presence of SCFAs in the fuel not is fundamental for the formation of carboxylic soap. Moreover, the different calcium sources result in different amounts and textures of metal soaps in deposits and in solution.Den stora miljöpåverkan relaterad till användningen av fossilt bränsle har drivit övergången till förnybara alternativ. Fossil diesel kan numera ersättas av biodiesel, härledd av vegetabiliska oljor och fetter, oftast används som biodieselblandningar. Vissa nackdelar är emellertid relaterade till användningen av detta biobränsle, bland annat bildandet av avlagring i injektorer och filter som orsakar en minskning av motorprestanda eller motorfel. Detta projekt fokuserar på analysen av mekanismen för bildning av mjuka partiklar i biodieselavlagring. Dessa partiklar består huvudsakligen av karboxylmetall tvålar och hittades i biodieselmotorer efter användning av åldrad biobränsle med föroreningar, såsom motorolja. Rollen för kortkedjiga fettsyror (SCFA) har undersökts, tillsammans med användning av tre olika kalciumkomponenter, för att analysera bildningsmekanismen för kalciumtvålar. Experimentellt åldring av testbränslen B10 och B100 på labbet utfördes, och i vissa fall bubblades en inert gas för att avlägsna de bildade SCFA. Kalcium komponenter, nämligen kalciumoxid, kalciumkarbonat och motorolja, tillsattes för att undersöka bildningen av mjuka partiklar. Jonkromatografi, pH-mätningar, NMR- spektroskopi och oxidations stabilitetstester har utförts på det flytande testbränslet för att verifiera närvaron och effekten av SCFA, medan FTIR-spektroskopi och GC/MS-analyser användes för att verifiera närvaron av kalciumtvålar i sedimentet och i lösning. I motsats till förväntningarna visades det att närvaron av SCFA i bränslet inte är grundläggande för bildandet av karboxyltvål. Dessutom resulterar de olika kalciumkomponenterna i olika mängder och strukturer av metalltvålar i sediment och i lösning.
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Ying, Min. "A Soft-Body Interconnect For Self-Reconfigurable Modular Robots." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-theses/234.
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Disaster support and recovery generally involve highly irregular and dangerous environments. Modular robots are a salient solution to support search and rescue efforts but are still limited to do their reliance on a rigid structure design. To enhance flexibility and resilience to damage, a soft-body interconnection mechanism for self-reconfigurable modular robotic systems has been developed. The soft-body interconnection mechanism utilizes elastomeric polymers instead of a rigid body. Hence, it is capable of deforming under extreme loads without damage. This thesis presents the work completed towards the realization of a soft-body interconnection mechanism. The functional requirements of the soft-body mechanism were broken down into two separate modules for extension and capture. An initial simulation demonstrated the inability of using a simulated model made of hypo-elastic materials as a basis for design. Hence, an iterative design process was used to develop an initial extension and capture soft-body mechanisms that conformed to the desired performance parameters. An empirical study which varied multiple structural parameters was then completed with the initial extension and capture soft-body mechanisms as a basis for the modified designs. The data from the study was correlated with measured performance data with resulted in diagrams useful for the optimal design of soft-body extension and capture mechanisms. The use of the diagrams for design was demonstrated in the design and development of a soft-body interconnection mechanism for an in-house designed small hard shell modular robot system.
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Butcher, Annabel Louise. "Deformation and fracture of soft materials for cartilage tissue engineering." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277890.
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Damaged cartilage can cause severe pain and restricted mobility, with few long term treatments available. The developing field of tissue engineering offers an alternative to the currently used full joint replacement. Restoring damaged cartilage through tissue engineering would enable an active lifestyle to be recovered and retained, without restrictions to joint mobility. This is increasingly important as the prevalence of osteoarthritis rises. Tissue engineering requires biomaterial scaffolds that mimic the function of the tissue while cells develop, and so the scaffold must provide the appropriate biological, chemical and mechanical stimuli. In this work, methods were developed to enable the design of scaffolds that mimic the microstructure and mechanical properties of articular cartilage. Electrospinning was investigated as a method to mimic the nanoscale collagen fibres within cartilage extracellular matrix. A parametric study was conducted to determine how changes to a gelatin solution affect the mechanical properties of the non-woven fibrous mesh. The solution properties had a clear impact on the morphology of the fibres, but the effect on the mesh mechanical properties was convoluted. The results demonstrated the need for greater understanding of the 3D morphology of electrospun meshes, to establish how these may be altered in order to design scaffolds with desirable mechanical properties. The fracture mechanics of soft materials are complex, and are generally overlooked when designing tissue engineering scaffolds. The complexities have led to a lack of standardised testing, making comparisons between studies impractical. In this work, fracture testing methods were compared, using a viscoelastic polymer to mimic some of the complexities of soft tissue mechanics. Mode III trouser tear tests and mode I pure shear tests were found to provide reliable measurements. Due to the ease of testing small samples, trouser tear testing was concluded to be the most advantageous for determining the fracture resistance of soft tissue engineering scaffolds. Finally, electrospun meshes were combined with hydrogels to create biomimetic scaffolds, which were characterised using tensile and trouser tear fracture tests. Fibre-reinforcement was shown to enhance the mechanical properties of a weak hydrogel, but diminished those of a strong, tough polyacrylamide (PAAm)-alginate hydrogel. The PAAm-alginate hydrogel exhibited mechanical properties close to those of natural articular cartilage, but without the microstructure that would enhance its suitability for use as a cartilage tissue engineering scaffold. An alternative method for reinforcing PAAm-alginate was proposed, which shows promise for producing a biocompatible scaffold that mimics both the mechanics and the microstructure of articular cartilage. Ultimately, this thesis aimed to improve the design of biomimetic scaffolds for cartilage tissue engineering, and advance mechanical characterisation techniques within this field.
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Gaballa, Mohamed Abdelrhman Ahmed. "Nonlinear multiphasic mechanics of soft tissue using finite element methods." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184837.
Full textAbstract:
The purpose of the research was to develop a quantitative method which could be used to obtain a clearer understanding of the time-dependent fluid filteration and load-deformation behavior of soft, porous, fluid filled materials (e.g. biological tissues, soil). The focus of the study was on the development of a finite strain theory for multiphasic media and associated computer models capable of predicting the mechanical stresses and the fluid transport processes in porous structures (e.g. across the large blood vessels walls). The finite element (FE) formulation of the nonlinear governing equations of motion was the method of solution for a poroelastic (PE) media. This theory and the FE formulations included the anisotropic, nonlinear material; geometric nonlinearity; compressibility and incompressibility conditions; static and dynamic analysis; and the effect of chemical potential difference across the boundaries (known as swelling effect in biological tissues). The theory takes into account the presence and motion of free water within the biological tissue as the structure undergoes finite straining. Since it is well known that biological tissues are capable of undergoing large deformations, the linear theories are unsatisfactory in describing the mechanical response of these tissues. However, some linear analyses are done in this work to help understand the more involved nonlinear behavior. The PE view allows a quantitative prediction of the mechanical response and specifically the pore pressure fluid flow which may be related to the transport of the macromolecules and other solutes in the biological tissues. A special mechanical analysis was performed on a representative arterial walls in order to investigate the effects of nonlinearity on the fluid flow across the walls. Based on a finite strain poroelastic theory developed in this work; axisymmetric, plane strain FE models were developed to study the quasi-static behavior of large arteries. The accuracy of the FE models was verified by comparison with analytical solutions wherever is possible. These numerical models were used to evaluate variables and parameters, that are difficult or may be impossible to measure experimentally. For instance, pore pressure distribution within the tissue, relative fluid flow; deformation of the wall; and stress distribution across the wall were obtained using the poroelastic FE models. The effect of hypertension on the mechanical response of the arterial wall was studied using the nonlinear finite element models. This study demonstrated that the finite element models are powerful tools for the study of the mechanics of complicated structures such as biological tissue. It is also shown that the nonlinear multiphasic theory, developed in this thesis, is valid for describing the mechanical response of biological tissue structures under mechanical loadings.
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Bufi, Nathalie. "Identification of soft tissue material constants using tailored finite element model based regressions." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104874.
Full textAbstract:
Efficient and reliable tools are needed to accurately characterize the mechan- ical properties of soft tissue. A knowledge of Young's modulus and Poisson's ratio is essential to model mechanical behavior and quantify stresses and strain within soft tissues. The goal of this study was to investigate indirect methods for the identification of soft tissue material parameters from experimental data for irregular sample shapes and compositions. The approach was to solve an overdetermined inverse problem. Three-dimensional finite element simulations were performed, assuming a homogeneous isotropic linear elastic material. Simulation results were compared to measured surface strains obtained from Digital image correlation techniques. Material parameters were identified using an iterative approach, through the minimization of the mean square difference between simulated and measured strain data. The feasibility of this method was investigated using uniaxial tension tests of porcine vocal fold tissue samples. The identified material constants were compared with vo- cal fold data reported in the literature. This method may be generalized to other types of soft tissues.Le développement d'outils efficaces pour la caractérisation des propriétés mécaniques des tissus mous est nécessaire. La connaissance du module d'Young et du coefficient de Poisson est essentielle à la modélisation du comportement mécanique et à l'estimation des champs de contraintes et de déplacements. L'objectif de cette étude est de mettre en oeuvre une méthode indirecte permet- tant d'identifier les constantes de matériau de tissus mous à partir de données expérimentales, pour des échantillons de forme et de composition variables. L'approche retenue est la résolution d'un problème inverse sur-déterminé. Des simulations par éléments finis en trois dimensions ont été réalisées, modélisant un corps homogène de matériau élastique linéaire isotrope. Les résultats de ces simulations ont été confrontés au champ de déplacement mesuré sur la surface d'échantillons en tension simple, par des techniques de corrélation d'image. Les constantes du matériau sont identifiés lorsque la différence entre le champ de déplacement mesuré et calculé atteint un minimum. La faisabilité de cette méthode a été vérifiée dans le cas de tests de tension simple sur des cordes vocales de porc. Les paramètres identifiés ont été comparés à des données publiées dans la littérature. Cette méthode peut être développée et appliquée à une grande variété de tissus mous.
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Kalcioglu, Zeynep Ilke. "Mechanical behavior of tissue simulants and soft tissues under extreme loading conditions." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79558.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 157-168).
Recent developments in computer-integrated surgery and in tissue-engineered constructs necessitate advances in experimental and analytical techniques in characterizing properties of mechanically compliant materials such as gels and soft tissues, particularly for small sample volumes. One goal of such developments is to quantitatively predict and mimic tissue deformation due to high rate impact events typical of industrial accidents and ballistic insults. This aim requires advances in mechanical characterization to establish tools and design principles for tissue simulant materials that can recapitulate the mechanical responses of hydrated soft tissues under dynamic contact-loading conditions. Given this motivation, this thesis studies the mechanical properties of compliant synthetic materials developed for tissue scaffold applications and of soft tissues, via modifying an established contact based technique for accurate, small scale characterization under fully hydrated conditions, and addresses some of the challenges in the implementation of this method. Two different engineered material systems composed of physically associating block copolymer gels, and chemically crosslinked networks including a solvent are presented as potential tissue simulants for ballistic applications, and compared directly to soft tissues from murine heart and liver. In addition to conventional quasistatic and dynamic bulk mechanical techniques that study macroscale elastic and viscoelastic properties, new methodologies are developed to study the small scale mechanical response of the aforementioned material systems to concentrated impact loading. The resistance to penetration and the energy dissipative constants are quantified in order to compare the deformation of soft tissues and mechanically optimized simulants, and to identify the underlying mechanisms by which the mechanical response of these tissue simulant candidates are modulated. Finally, given that soft tissues are biphasic in nature, atomic force microscopy enabled load relaxation experiments are utilized to develop approaches to distinguish between poroelastic and viscoelastic regimes, and to study how the anisotropy of the tissue structure affects elastic and transport properties, in order to inform the future design of tissue simulant gels that would mimic soft tissue response.
by Zeynep Ilke Kalcioglu.
Ph.D.
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Shan, Sicong. "Planar Soft Functional Periodic Structures Exploiting Instabilities and Large Deformation." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:23845411.
Full textAbstract:
Soft materials can significantly change their shape and volume when subjected to various stimuli.
Materials with deliberately designed periodic microstructure have long been proved to be characterized by properties that may exceed those of the corresponding bulk material. Though traditionally
avoided as modes of failure, mechanical instabilities have recently been exploited to design systems
with novel and tunable functionalities. Interestingly, the studies I conducted during my PhD show
that the combination of soft materials, periodic structures, mechanical instabilities and large deformation give us the opportunity to design materials and structures with enhanced functionality.
In this thesis, I present a systematic study on the response of planar sof୴ functional materials
which use their large deformation and geometric rearrangements to dramatically change their properties. In particular, I used a combination of experiments and numerical simulations to investigate
the effect of important parameters, such as pore shape, hole arrangement and loading conditions. With the fundamental understanding I gained, I developed a novel class of planar soft periodic
materials with enhanced material functionalities such as tunable phononic band-gap, spontaneous
symmetry breaking, chirality amplification and energy trapping. Remarkably, since the continuous
2D soft and porous structures I studied take advantage of reversible and scale-independent mechanisms, the proposed designs can be applied over a wide range of length scales.
The studies presented here show that by mastering the interplay between the microstructure of
soft periodic structures and their large deformation behavior, novel materials with enhanced funcEngineering and Applied Sciences - Engineering Sciences
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Mosier, Aaron P. "Microfluidic-assisted atomic force microscopy for the mechanical characterization of soft biological materials." Thesis, State University of New York at Albany, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3566554.
Full textAbstract:
Viable methods for bacterial biofilm remediation require a fundamental understanding of biofilm mechanical properties and their dependence on dynamic environmental conditions. Mechanical test data, quantifying elasticity or adhesion, may be used to perform physical modeling of biofilm behavior, thus enabling the development of novel remediation strategies. To achieve real-time, dynamic measurements of these properties, a novel analysis platform consisting of a microfluidic flowcell device has been designed and fabricated for in situ analysis using atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). The flowcell consists of microfluidic channels for biofilm establishment that are then converted into an open architecture, laminar flow channel for AFM measurement in a liquid environment. Computational fluid dynamics (CFD) was used to profile fluid conditions within the device during biofilm establishment. The validity of the AFM nanoindentation measurement mechanism was confirmed in the context of the system through the elastic characterization of several non-living reference materials. Force-mode AFM was used to measure the elastic properties of mature Pseudomonas aeruginosa PAO1 biofilms and observe a dynamic response to a chemical antagonist. Elastic moduli ranging from 0.58 to 2.61 kPa were determined for the mature biofilm, which fall within the range of moduli previously reported by optical, rheometric, and microindentation techniques. A modified version of the flowcell was employed to perform similar elastic characterization of mouse submandibular glands (SMGs), demonstrating the adaptability of the system to perform ex situ analyses of a broader set of biological materials. These results demonstrate the validity of the microfluidic flowcell system as an effective platform for future investigations of the mechanical and morphological response of biofilms and other soft biomaterials to dynamic environmental conditions.
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Meem, Asma Ul Hosna. "On the Mechanics and Dynamics of Soft UV-cured Materials with Extreme Stretchability for DLP Additive Manufacturing." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1628358191573142.
Full text
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Owino, Vivianne. "Structural Analysis of Soft-Hard Material Interface in an Ant Neck Joint." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376947061.
Full text
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Wang, Zhixin. "Polydimethylsiloxane Mechanical Properties Measured by Macroscopic Compression and Nanoindentation Techniques." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3402.
Full textAbstract:
In this thesis, the relationship between the elastic modulus of PDMS and the base/agent ratio (the amount of crosslinking) is studied. Reliable macroscopic compression test instrument was developed. Preload method was applied for the nanoindentation flat punch test to develop full contact.
In chapter 2, an easy instrument setup for macroscopic compression test is described. A series of PDMS samples with different base/agent ratios were tested using the macroscopic compression method. The relationship between PDMS elastic modulus and its base/agent ratio was established.
In chapter 3, PDMS nanoindentation DMA tests provide stable data with different test control models. The storage modulus collected using nanoindenting DMA tests is comparable with elastic modulus collected in PDMS compression test in chapter 2. Nanoindentation experiments with flat punch were also done to test the elastic modulus of PDMS network 5:1. The adhesion force tests with different nanoindentation tips, which are Berkovich tip, conical tip and cube corner tip, show that PDMS's adhesion force is related to the sample's base/agent ratio, the nanoindentating depth and the tip's geometrical shape.
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Nguyen, Van Tang. "Nanostructured soft-hard magnetic materials with controlled architecture." Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1007.
Full textAbstract:
Parmi les aimants sans terres raresactuellement étudiés, τ-MnAl ferromagnétique est uncandidat à haut potentiel, car il possède despropriétés magnétiques intrinsèques prometteuses.Dans cette thèse, Mn(Fe)AlC a été synthétisé parbroyage mécanique. Les effets du carbone sur lamicrostructure et les propriétés magnétiques ont étéétudiés. Les résultats montrent qu’une pureté élevéede τ-MnAl(C) pouvait être obtenue avec un dopage à2% en atomes de carbone, montrant clairement l’effetstabilisant du carbone. L’alliage Mn54.2Al43.8C2possède les meilleures propriétés magnétiques :aimantation à 2T M2T = 414 kAm-1, aimantationrémanente Mr = 237 kAm-1, coercivité HC = 229 kAm-1et |BH|max = 11,2 kJm-3. HC augmente inversementproportionnellement avec la taille des cristallites de laphase τ et proportionnellement à la teneur en C. Descalculs ab initio confirment l’effet stabilisant etindiquent les positions interstitielles préférentielles ducarbone dans la maille quadratique de la phase τ-MnAl.Les alliages Mn51-xFexAl47C2 (x = 0,25, 0,5, 1, 2, 4, 6)ont également été synthétisés par broyagemécanique, montrant une pureté élevée de la phaseτ jusqu'à un taux de substitution de 2% du Mn par duFe. L'ajout de Fe dans MnAl(C) réduit l'aimantationet TC, mais augmente légèrement la valeur de HC. Laspectrométrie 57Fe Mössbauer à 300K a été utiliséepour sonder l'environnement local dans ε-, τ-, β- etγ2-MnFeAl(C). γ2-, ε- et β-MnFeAl(C) présentent unestructure hyperfine quadripolaire alors que τ-Mn50.5Fe0.5Al47C2 montre une structutr hyperfinemagnétique assez complexe. Une expérience despectrométrie Mössbauer effectuée à bassetempérature (10K) et sous champ magnétique (8T)montre un ordre ferromagnétique local non colinéairedes moments magnétiques de Fer par rapport à ladirection du champ appliqué. Le champ hyperfin del’alliage MnFeAl calculé par Wien2k confirme lespropriétés magnétiques et les résultats despectrométrie MössbauerAmong currently investigated rare-earth-free magnets, ferromagnetic τ-MnAl is a highly potential candidate as having promising intrinsic magnetic properties. In my thesis, Mn(Fe)AlC was synthesized by mechanical alloying method. Effects of carbon on microstructure and magnetic properties were systematically investigated. It was found that high purity of τ-MnAl(C) could be obtained at 2 at.% C doping, showing clearly stabilizing effect of carbon. Mn54.2Al43.8C2 has the best magnetic properties: magnetization at 2T M2T = 414 kAm-1, remanent magnetization Mr = 237 kAm-1, coercivity HC = 229 kAm-1, and |BH|max = 11.2 kJm-3. HC increased inversely with the crystallite size of τ phase and proportionally with C content. Moreover, first principle calculation showed both stabilizing effect and preferable interstitial positions of carbon in tetragonal τ-MnAl. Mn51-xFexAl47C2 (x= 0.25, 0.5, 1, 2, 4, 6) alloys were also synthesized by mechanical alloying method, showing high purity of τ phase up to 2 at.% Fe doping. Adding of Fe on MnAl(C) reduced both magnetization and TC but likely increased slightly HC. 57Fe Mössbauer spectrometry at 300K was used to probe local enviroment in ε-, τ-, β-, and γ2-MnFeAl(C). In which, γ2-, ε-, and β-MnFeAl(C) exhibited a quadrupolar structure while τ -Mn50.5Fe0.5Al47C2 spectrum showed a rather complex magnetic hyperfine splitting. The interaction between Fe and Mn examined by in-field Mössbauer measurement at 10 K and 8 T showed a non-collinear magnetic structure between Fe and Mn with different canting angles at different sites. Hyperfine field of MnFeAl alloy calculated by Win2k supported both magetic properties and Mossbauer results
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Van, der Westhuizen Artho Otto. "Impact response of a continuous fibre reinforced thermoplastic from a soft bodied projectile." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80095.
Full textAbstract:
Thesis (MScEng)--Stellenbosch University, 2013.AFRIKAANSE OPSOMMING: Saamgestelde materiale het baie gewilde materiale in die lugvaart- en motor industrië geword as gevolg van die gewigsbesparende voordele wat dit inhou. Kostes en ander verwerkingsprobleme het tradisioneel die wydverspreide gebruik van spesifiek termoplasties-versterkte vesels in hierdie areas verhinder. Baie van die vervaardigingsprobleme (spesifiek lang siklusse) is aangespreek met die aanvang van termoplastiese matriks materiaal soos Polyphenolien Sulfied (PPS). Hierdie materiaal voldoen ook aan die lugvaart-industrie se brand-, rook- en giftigheidstandaarde. Termoplastiese saamgestelde materiale kan byvoorbeeld gevind word op komponente in vliegtuie se binneruimtes en ook die voorste rand van die vlerke. Hierdie komponente is hoogs vatbaar vir impakskade. Die hoë sterkte en styfheid tot gewig verhoudings van saamgestelde materiale laat toe vir dun materiaal dwarssnitte. Komponente is dus kwesbaar vir uit-vlakkige impak beladings. Saamgestelde materiale kan ook intern deur hierdie beladings beskadig word en kan nie met die blote oog waargeneem kan word nie. Dit is dus nodig om die skade weens hierdie beladings tydens normale gebruik akkuraat te voorspel. Verder sal dit nuttig wees om die struktuur se gedrag te bepaal in toepassings waar byvoorbeeld passasier veiligheid krities is, soos op vliegtuig ruglenings tydens noodlandings. In hierdie studie is die potensiële vervaardigingsvoordele van termoplastiese saamgestelde materiale gedemonstreer. Daarbenewens is 'n uit-vlakkige impak deur 'n sagte liggaam herbou in 'n laboratorium omgewing. Die primêre doelwit van hierdie studie was om die impak numeries te modelleer. Vervaardigingsvoordele van `n vesel versterkte termoplastiese laminaat is gedemonstreer deur die vervaardiging van 'n konkawe, agt laag laminaat uit 'n vooraf gekonsolideerde geweefde doek. Die totale verwerkingstyd van die plat laminaat na 'n konkawe laminaat was minder as vyf minute. 'n Eenvoudige plat laminaat en 'n konkawe laminaat is onderwerp aan 'n lae snelheid impak deur 'n sagte projektiel. Die impak is gemodelleer deur die evaluering van drie modelleringsmetodes vir die saamgestelde paneel. Die evalueringskriteria het o.a. ingesluit of laminaat se volle gedrag suksesvol gemodelleer kon word met behulp van slegs 2D dop elemente. Die reaksie van die saamgestelde paneel en gepaardgaande faling is met wisselende vlakke van sukses deur die drie geëvalueerde modelle voorspel. Die faling van tussen-laminêre bindings (verwys na as delaminasie) kon nie deur enige van die modelle voorspel word nie. Twee van die modelle het egter in-vlak faling met redelike akkuraatheid voorspel.
ENGLISH ABSTRACT: Due to weight saving advantages composite materials have become a highly popular material in the aerospace and automotive industries. Traditionally processing difficulties and costs have been a barrier to widespread composite material use in these industries. With the advent of thermoplastic matrix materials such as Polyphenoline Sulphide (PPS) the processing difficulties (especially long cycle times) experienced with traditional thermosetting resins can be addressed while maintaining aerospace Fire-Smoke and Toxicity (FST) approval. Thermoplastic composites can for example be found on aircraft interior components and leading edges of the wings. These areas are highly susceptible to impact damage. The high strength- and stiffness to weight ratios of composites allows for thin material cross sections. This leaves the components vulnerable to out-of-plane impact loads. Composite materials may also be damaged internally by these loads, leaving the damage undetectable through visual inspections. It may therefore be necessary to predict the amount of damage a component would sustain during normal operation. Additionally, it would be useful to predict structural response of these materials in applications where passenger safety is crucial, such as aircraft seat backrests during emergency landings. In this study the potential processing benefits of thermoplastic composite materials were demonstrated. Additionally an out-of-plane impact from a soft bodied projectile was reconstructed in a laboratory environment. The primary objective was to numerically model the impact event. Processing benefits of thermoplastics were demonstrated by producing a single curvature eight layered laminate from a pre-consolidated woven sheet. The total processing time from flat panel to a single curvature panel was below five minutes. A simple flat laminate and a single curvature laminate were subjected to a low velocity drop weight impact load from a soft bodied projectile. These impact events were modelled by evaluating three modelling methods for the composite panel structural response and damage evolution. Part of the evaluation criteria included whether laminate failure could be modelled successfully using only 2D shell elements. The response of the composite panel and accompanying failure were predicted with varying levels of success by the three evaluated models. The failure of interlaminar bonds (referred to as delamination) could not be predicted by either model. However two of the models predicted in-plane failure with reasonable accuracy.
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Bruton, Jared Thomas. "Packing Sheet Materials Into Cylinders and Prisms Using Origami-based Approaches." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5998.
Full textAbstract:
Packing sheet materials into cylinders and prisms using Origami-based approaches (Soft Origami or traditional Origami) is of interest in fields where sheet materials need folded into cylinders or prisms. Fully-dense packing has application in fields where a sheet material is to be folded with minimal gaps into a cylinder or prism. Partially-dense packing is applicable to fields where gaps are required between packed surfaces or where hollow volumes are to be filled, such as in fluid filter design. Soft Origami is explored as a method for folding soft-sheet materials into fully-dense cylinders. Two fold patterns, the "flasher'' and the "inverted-cone fold,'' are explored for packing soft-sheet materials into cylindricals. An application to driver's side automobile airbags is successfully performed, and deployment tests are completed to compare the influence of packing method and origami pattern on deployment performance. In total, two origami patterns and six packing methods are examined for folding soft-sheet materials into fully-dense cylindrical prisms, and it is shown that modifying the packing method impacts deployment performance. A special case of the Miura-ori, the ninety-degree case, is briefly explored as a traditional Origami method for packing arbitrary-shaped sheet materials into fully-dense arbitrary prisms. Examples are shown and it is concluded that this pattern can be used to configure a large number of fully-dense packed prisms with configurable characteristics.Finally, patterns that fold into partially-dense cylindrical prisms are examined using traditional Origami approaches and their efficiency compared. Efficiency is defined as the ratio of the surface area of a pattern compared to an idealized high-surface-area model. Patterns include traditional (non-Origami-based) fluid filter patterns (the Basic Pleat and M-pleat) and cylindrical Origami patterns (the Accordion and Kresling). An offset crease method is used to modify the Accordion and Kresling Origami patterns so the comparison is objective. Results are presented that determine which individual pattern variations have the highest efficiency at different outside-to-inside diameter ratios. Ranges over which each pattern is most efficient are presented. It is concluded that based purely on geometry, the M-pleat provides the highest overall efficiency, but depending on other factors each pattern is viable for different purposes.
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Fincan, Mustafa. "Assessing Viscoelastic Properties of Polydimethylsiloxane (PDMS) Using Loading and Unloading of the Macroscopic Compression Test." Scholar Commons, 2015. https://scholarcommons.usf.edu/etd/5480.
Full textAbstract:
Polydimethylsiloxane (PDMS) mechanical properties were measured using custom-built compression test device. PDMS elastic modulus can be varied with the elastomer base to the curing agent ratio, i.e. by changing the cross-linking density. PDMS samples with different crosslink density in terms of their elastic modulus were measured. In this project the PDMS samples with the base/curing agent ratio ranging from 5:1 to 20:1 were tested. The elastic modulus varied with the amount of the crosslinker, and ranged from 0.8 MPa to 4.44 MPa. The compression device was modified by adding digital displacement gauges to measure the lateral strain of the sample, which allowed obtaining the true stress-strain data. Since the unloading behavior was different than the loading behavior of the viscoelastic PDMS, it was utilized to asses viscoelastic properties of the polymer. The thesis describes a simple method for measuring mechanical properties of soft polymeric materials.
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Petekkaya, Ali Tolga. "In Vivo Indenter Experiments On Soft Biological Tissues For Identification Of Material Models And Corresponding Parameters." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610071/index.pdf.
Full textAbstract:
Soft biological tissues, being live and due to their physiological structures,
display considerably complex mechanical behaviors. For a better understanding
and use in various applications, first study to be carried out is the tests made
particularly as in vivo. An indenter test device developed for this purpose in the
METU, Department of Mechanical Engineering, Biomechanics Laboratory is
operational.
In this study, in order to carry out precise and dependable tests, initially, various
tests and improvements were conducted on the device and the software
controlling the device. At the end of this study, displacement and load
measurement accuracies and precisions were improved. Better algorithms for
filtering the noisy data were prepared. Some test protocols within the software
were improved and new protocols were annexed. To be able to conduct more
dependable tests a new connection system was attached to the device. In order to
study the anisotropic behavior of soft tissues ellipsoid tips were designed and
produced.
In the second phase of the study, tests on medial forearm were carried out. In
these tests, hysteresis, relaxation and creep behaviors displaying the viscoelastic
v
properties of the soft biological tissues were observed. In addition to viscoelastic
behaviors, preconditioning (Mullin’
s) effect and anisotropic response were examined. By using the results of the relaxation and creep tests, parameters of the Prony series capable of modelling these data were determined. With this study, some important conclusions regarding the soft biological tissues were drawn and thus the behaviors of the soft biological tissues were better understood. Besides, the difficulties inherent to in-vivo tests were recognized and actions to reduce these difficulties were explained. Finally, clean experimental data, to be used in the computer simulations, were obtained.
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Pelegrini, Leandro. "Influência do tempo de moagem por mecâno-síntese nas propriedades da liga magnética Fe-3%Si-0,75%P aplicada em núcleos de máquinas elétricas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/72911.
Full textAbstract:
O presente trabalho objetiva o estudo, obtenção e caracterização da liga magnética macia Fe-Si-P produzida por metalurgia do pó convencional visando à futura aplicação em núcleos de máquinas elétricas, atualmente fabricados por estampagem de chapas. Escolheu-se com base em testes prévios a liga Fe-3%Si-0,75%P. Para a obtenção da liga, foi utilizada a rota de mecâno-síntese com diferentes tempos de moagem: 1 h, 3 h e 9 h, além do material sem moagem para comparação. Na sequência compactaram-se uniaxialmente a frio os corpos de prova a 600 MPa seguido de sinterização a 1150 ºC em atmosfera de gás argônio. A análise da influência do tempo de moagem nas propriedades físicas, mecânicas, magnéticas e elétricas no material sinterizado foi a meta central deste trabalho. A caracterização das propriedades físicas mostrou uma redução da densidade aparente do pó moído, um aumento da distribuição do tamanho de partícula e redução do mesmo com o aumento do tempo de moagem. No que se refere às propriedades magnéticas, evidenciou-se que o material moído durante 3h apresentou os melhores resultados de indução de saturação (1,15 T), apesar do aumento na coercitividade já previsto devido ao processo de mecâno-síntese. Além disso, a difração de raios-X detectou a formação da liga através da solução sólida dos elementos P e Si na matriz ferrita. A análise metalográfica revelou a diminuição do tamanho de grãos com o aumento do tempo de moagem. Por fim, realizou-se a simulação do protótipo para análise do desempenho do material visando à aplicação futura. Esta, realizada pelo método de elementos finitos em um núcleo de um gerador síncrono com ímãs permanentes de NdFeB resultou em uma densidade de fluxo (1,95T) para o material com 3h de moagem e um torque de apenas 13% inferior se comparado ao gerador convencional produzido com núcleos de chapas de aço elétrico.The present work aims to study, obtaining and characterization of Fe-Si-P soft magnetic alloy produced by conventional powder metallurgy intended for the future application in electrical machines cores, currently manufactured by sheet metal forming. The alloy Fe-3%Si-0,75%P was chosen based on previous tests. To obtain the alloy was used mechanical alloying route with different milling times: 1 h, 3 h and 9 h, and the material without milling for comparison. In the sequence, the specimens were uniaxially cold compacted at 600 MPa followed by sintering at 1150 ° C in an atmosphere of argon. The analysis of the influence of milling time on the physical, mechanical, magnetic and electric properties of the sintered material was the central goal of this work. The physical properties characterization showed a reduction in the bulk apparent density of the milled powder, an increase in particle size distribution and reduction thereof with increasing milling time. As regards magnetic properties, it was observed that the milled material for 3 hours showed the best results of saturation induction (1.15 T), despite the increase in the coercivity as expected due to the inherent mechanical alloying process. Furthermore, the X-ray diffraction detected the alloy formation through the solid solution of P and Si elements in the ferrite matrix. The metallographic analysis showed the decrease in grain size with increasing milling time. Finally, were performed a simulation prototype for analysis of material performance in order to future implement. This, held by finite element method on a synchronous generator core with NdFeB permanent magnets, resulting in a flux density (1.95 T) for the material with 3h of milling and a torque of only 13% lower compared to conventional generator produced with cores of electric steel sheet.
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Usu, Kerem. "Identification Of Soft Tissue Mechanical Material Model And Corresponding Parameters From In Vivo Experimental Data By Using Inverse Finite Element Method." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609885/index.pdf.
Full textAbstract:
The purpose of this thesis is to search for the best material model for soft biological tissues in general. Different sections of human body exhibit different responses like stress relaxation, creep, hysteresis and preconditioning to external loading conditions. These body sections can be assumed as viscoelastic, poroelastic or pseudoelastic. After making the choice of the material model from one of these for the current study, the finite element model and the material code to be used with this model have been created. The material code has also been tried on a simple finite element model before implementing to the real model to prove the fact that it is
working properly. Then, the constants in the code which simulates the in vivo experimental data that was obtained by indenting the elliptic indenter tip into the forearm, medial part as close as possible, have been derived by inverse finite element method. Consequently, the characteristic behaviors of the soft tissue could be simulated. Despite the big size of the finite element model and very long submission times (up to one day for preconditioning simulation), relaxation and creep behaviors could be simulated with the maximum normalized sum of square errors of 0.74 % and 0.43 %, respectively. The number of square errors for the hysteresis and preconditioning behaviors appeared as 2.56 % and 3.89 % which are also acceptable values. These values prove that these material models are well suited for the simulation of the behavior of soft biological tissues. By using different experimental data obtained from other sections of human body, simulation of the behavior of different soft tissues can be achieved by using these material models.
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Chang, Hong. "Hydraulic Fracturing in Particulate Materials." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4957.
Full textAbstract:
For more than five decades, hydraulic fracturing has been widely used to enhance oil and gas production. Hydraulic fracturing in solid materials (e.g., rock) has been studied extensively. The main goal of this thesis is a comprehensive study of the physical mechanisms of hydraulic fracturing in cohesionless sediments. For this purpose, experimental techniques are developed to quantify the initiation and propagation of hydraulic fractures in dry particulate materials. We have conducted a comprehensive experimental series by varying such controlling parameters as the properties of particulate materials and fracturing fluids, boundary conditions, initial stress states, and injection volumes and rates. In this work, we suggest principle fundamental mechanisms of hydraulic fracturing in particulate materials and determine relevant scaling relationships (e.g., the interplay between elastic and plastic processes).
The main conclusion of this work is that hydraulic fracturing in particulate materials is not only possible, but even probable if the fluid leak-off is minimized (e.g., high flow rate, high viscosity, low permeability). Another important conclusion of this work is that all parts of the particulate material are likely to be in compression. Also, the scale effect (within the range of the laboratory scales) appears to be relatively insignificant, that is, the observed features of fractures of different sizes are similar.
Based on the observed fracture geometries, and injection pressures we suggested three models of hydraulic fracturing in particulate materials. In the cavity expansion or ??e driving model, the fracturing fluid is viewed as a sheet pile (blade) that disjoints the host material, and the cavity expansion occurs at the fracture (blade) front. The shear banding model is also consistent with a compressive stress state everywhere in the particulate material and explains the commonly observed beveled fracture front. The model of induced cohesion is based on the fluid leak-off ahead of the fracture front. The induced cohesion may be caused by the tensile strain near the fracture tip (where the stress state is also compressive), which, in turn, induces the cavitation of the leaked-off fluid and hence capillary forces.
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Tanguy, Francois. "Debonding mechanisms of soft adhesives : toward adhesives with a gradient in viscoelasticity." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2014. http://tel.archives-ouvertes.fr/tel-01021169.
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During the debonding of a soft adhesive (as are Pressure Sensitive Adhesives or PSA), complex mechanisms enter in competition at the interface and in the bulk of the adhesive film. In order to optimize these adhesives, it is crucial to understand the transitions between the different debonding modes. We studied these transitions using model materials and carried out a quantitative analysis of debonding experiments with a new image analysis method. We also modeled the mechanical behavior of our materials under uniaxial deformation by using a 2-modes Phan-Thien and Tanner (PTT) viscoelastic model. These studies showed the strong heterogeneity of the debonding mechanisms where process at the interface and in the bulk are in competition. To obtain more efficient PSA, we optimized their properties by introducing a gradient in the viscoelastic properties of the film along their thickness. Bi-layer optimized systems showed interesting properties on surfaces with high or low adhesion. Finally, adhesives with a continuous gradient were realized and characterized by the diffusion of a cross-linker in a polymer film followed by an activation of the cross-linking reaction at a given time
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Kaminuza, Irénée. "Thermal and chemical analysis of carbonaceous materials: diesel soot and diesel fuel reactor deposits." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/16911.
Full textAbstract:
Methods for the characterisation of fuel-derived carbonaceous materials were assessed. These methods were applied to two such materials, viz. diesel soot and diesel fuel deposits. Diesel soot: Diesel soot, sampled from a commuter bus, was characterised using an array of analytical techniques. Physical and chemical characterisation of diesel soot was conducted with particular interest in the component of soot known as the soluble organic fraction (SOF). The SOF represents adsorbed chemical species and is traditionally obtained via Soxhlet extraction of soot using an organic solvent. Chemical speciation of the SOF was performed using GC-MS analysis. Five solvents (hexane, cyclohexane, toluene, methanol and acetone) were compared with dichloromethane, the most extensively used solvent for the extraction of soot with respect to their ability to extract a variety of species, including polyaromatic hydrocarbons (PAHs) and potential endocrine disrupting molecules, e.g. phthalates. Extraction results suggest that the SOF quantity depends significantly on the extraction solvent. For the soots analysed, SOF ranged between 1.0 and 4. 8 wt %, depending on the solvent used. Moreover, it was shown that polar solvents extracted a greater SOF than non- polar solvents. For PAH extraction the order of efficiency was acetone > methanol > > toluene > hexane > cyclohexane while for esters, including endocrine disrupting phthalates, the order in efficiency was methanol > dichloromethane >acetone > toluene > > hexane > cyclohexane > n-hexane. A suggestion is made that to maximise SOF, sequential extraction should be made. Thermogravimetric analysis revealed a discrepancy between VOF and SOF which was ascribed to the presence of sulfurous and sulfuric acid which were not extracted by the organic solvents investigated Fuel deposits: Fuel was degraded in three reaction vessels, viz. a continuous flow reactor, open glass flask s and closed metal reactors (bombs) in an attempt to synthesise carbonaceous deposits, analogous to those found in diesel injectors. The degradation of four diesel fuels, viz. an EN590 reference diesel, a commercial diesel and two B20 biodiesel blends (rapeseed and soybean methyl esters blended with EN590 diesel), was investigated in the thermo-oxidative temperature regime, i.e. below 300° C.
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Lefranc, Maxime. "Fracture properties of Soft Materials : From Linear Elastic Fracture to damage at the microscopic scale." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112028/document.
Full textAbstract:
Notre nouvelle approche expérimentale consiste à étudier la fissuration de matériaux mous, principalement des gels polymériques et colloidaux, qui ont des tailles microstructurales micrométriques. Cette augmentation de la taille microscopique va avoir pour conséquence d’augmenter la taille de la zone de process et va rendre son observation plus facile avec des moyens standard de microscopie (à transmission et confocale).Pour se faire, nous avons mis au point un nouveau dispositif expérimental pour étudier la propagation de fissures dans des matériaux mous. Cette expérience permet de faire croître une fissure de manière contrôlée dans un échantillon mou et d’inspecter la pointe de fissure à haute résolution pour des fissures se propageant entre 1 µm/s and 1cm/s. En travaillant avec des gels de polymère physiques, nous avons analyse la forme de fissure ainsi que les champs de déplacement proches pointe (en utilisant des techniques de corrélation d’image) à petites et grandes échelles et à différentes vitesses. Nous avons montré qu’il existait une séparation d’échelles spatiales entre les échelles où l’élasticité linéaire s’applique, les échelles auxquelles les non linéarités émergent et les échelles auxquelles la dissipation se produit. Cette dernière échelle n’a pas pu être investigué dans le cas de gels polymériques. De récentes expériences sur des gels colloïdaux, ayant une longueur micro-structurale plus grande que celle des gels polymers, montre que nous sommes capables de sonder en temps réel les échelles d’endommagement lors de la fissurationOur novel experimental approach consists in studying fracture mechanics of soft materials, mainly polymer and colloidal gels, which have microstructures with large typical length scales. This increase in the microscopic length scale will consequently increase the typical size of the process zone and make its observation easier with standard microscopy techniques (optical or confocal).To do so, we designed a novel experimental device to study crack propagation in such soft materials. This experiment enables us to grow a unique crack in a controlled way in a soft specimen and to look at the crack tip at high magnification for crack velocities between 1 µm/s and 1cm/s. Working on physical polymer gels, we analysed the crack shape and crack displacement fields (using Digital Image Correlation) at large and intermediate scales for various velocities. We realized there was a separation of scales between the scale at which LEFM applies, the scale at which elastic nonlinearities emerge and the scale at which dissipation occurs. This last scale could not be investigated with the polymer gel. Recent experiments on colloidal gels, which have a microscopic length scale bigger than the one of polymer gels, show that we are able to probe damage at the microstructural scale
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Manisha. "Evaluation of thermal stresses in planar solid oxide fuel cells as a function of thermo-mechanical properties of component materials." Texas A&M University, 2008. http://hdl.handle.net/1969.1/86039.
Full textAbstract:
Fuel cells are the direct energy conversion devices which convert the chemical energy of a
fuel to electrical energy with much greater efficiency than conventional devices. Solid Oxide
Fuel Cell (SOFC) is one of the various types of available fuel cells; wherein the major
components are made of inherently brittle ceramics. Planar SOFC have the advantages of
high power density and design flexibility over its counterpart tubular configuration.
However, structural integrity, mechanical reliability, and durability are of great concern for
commercial applications of these cells. The stress distribution in a cell is a function of
geometry of fuel cell, temperature distribution, external mechanical loading and a mismatch
of thermo-mechanical properties of the materials in contact. The mismatch of coefficient of
thermal expansion and elastic moduli of the materials in direct contact results in the
evolution of thermal stresses in the positive electrode/electrolyte/negative electrode (PEN)
assembly during manufacturing and operating conditions (repeated start up and shut down
steps) as well. It has long been realized and demonstrated that the durability and reliability of
SOFCs is not only determined by the degradation in electrochemical performance but also
by the ability of its component materials to withstand the thermal stresses.
In the present work, an attempt has been made to evaluate the thermal stresses as a function
of thermal and mechanical properties of the component materials assuming contribution
from other factors such as thermal gradient, mechanical loading and in-service loading
conditions is insignificant. Materials used in the present study include the state of art anode (Ni-YSZ), electrolyte(YSZ) and cathode materials(LM and LSM) of high temperature SOFC
and also the ones being suggested for intermediate temperature SOFC Ni-SCZ as an anode,
GDC and SCZ as electrolyte and LSCF as the cathode. Variation of thermo-mechanical
properties namely coefficient of thermal expansion, and elastic and shear moduli were
studied using thermo-mechanical analyzer and resonant ultrasound spectroscope respectively
in 25-900°C temperature range. A non-linear variation in elastic and shear moduli- indicative
of the structural changes in the studied temperature range was observed for most of the
above mentioned materials. Coefficient of thermal expansion (CTE) was also found to
increase non-linearly with temperature and sensitive to the phase transformations occurring
in the materials. Above a certain temperature (high temperature region- above 600°C), a
significant contribution from chemical expansion of the materials was also observed.
In order to determine thermal stress distribution in the positive electrode, electrolyte,
negative electrode (PEN) assembly, CTE and elastic and shear moduli of the component
materials were incorporated in finite element analysis at temperature of concern. For the
finite element analysis, anode supported configuration of PEN assembly (of 100mm x
100mm) was considered with 1mm thick anode, 10μm electrolyte and 30μm cathode. The
results have indicated that cathode and anode layer adjacent to cathode/electrolyte and
electrolyte/anode interface respectively are subjected to tensile stresses at the operating
temperature of HT-SOFC (900°C) and IT-SOFC (600°C). However, the magnitude of
stresses is much higher in the former case (500MPa tensile stress in cathode layer) when
compared with the stress level in IT-SOFC (178MPa tensile stress in cathode layer). These
high stresses might have been resulted from the higher CTE of cathode when compared with
the adjacent electrolyte. However, it is worth mentioning here that in the present work, we
have not considered any contribution from the residual stresses arising from fabrication and
the stress relaxation from softening of the glass sealant.
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Siéfert, Emmanuel. "Inflating to shape : from soft architectured elastomers to patterned fabric sheets." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS018.
Full textAbstract:
Dans cette thèse à l'interface entre élasticité et géométrie, nous nous attachons à développer, étudier et programmer des structures gonflables élancées qui changent de forme. Une première stratégie consiste à fabriquer des plaques d'élastomère incluant des réseaux de canaux. L’expansion de ces canaux mis sous pression se produit presque exclusivement perpendiculairement à leur direction principale. Le choix de l'orientation et de la densité locales du réseau de canaux permet de contrôler la direction et l'intensité de la pseudo-croissance de cette plaque homogénéisée. Sous pression, la métrique cible de ces objets devient en général incompatible avec l'état plan. La structure flambe alors spontanément pour adopter une forme qui minimise l’énergie élastique, ce qui revient à suivre la métrique imposée par gonflement dans le cas d’objets minces. Une deuxième technique consiste à thermocoller entre elles deux feuilles minces inextensibles selon un réseau de lignes qui définit des canaux gonflables. Le système élémentaire, constitué d'un seul tube formé de deux rubans sinueux joints le long de leurs bords, voit sa courbure amplifiée lors du gonflement. Nous mesurons, expliquons et exploitons cet effet surprenant qui résulte de la maximisation du volume contenu dans le tube sous la contrainte de l'inextensibilité de l'enveloppe. Nous étendons l'étude à des structures bidimensionnelles qui voient la distance entre deux lignes de couture parallèles se contracter lors du gonflement. Le contrôle de la déformation homogénéisée dans le plan permet de programmer le déploiement dans l'espace de surfaces complexes à partir de ces structures initialement planesIn this thesis at the interface between geometry and mechanics, we aim at developing, studying and programming slender morphing inflatables structures. A first strategy consists in manufacturing elastomeric plates embedding a network of channels, which expand, when inflated, mainly perpendicular to their local orientation, similarly to simple elastic tubes. Playing with both the orientation and density of channels, we control the direction and intensity of the in-plane homogenized ``growth", in general incompatible with a flat geometry. The structure spontaneously buckles and adopts a shape which minimizes its elastic energy. For very thin slender bodies, this reduces to follow the target metric induced by inflation. We then study the inflation of structures made of two superimposed inextensible thin sheets, sealed together along a specific line network. Starting with flat curved ribbons, we observe and rationalize the surprising overcurvature upon inflation by maximizing the inner volume given the inextensibility constraint. We finally extend our investigation to two-dimensional structures and control the in-plane contraction upon inflation, which occurs perpendicular to the seam?s direction. We program the morphing of such stiff inflatable structures and investigate their mechanics
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Chafetz, Jared Richard. "A Novel Fiber Jamming Theory and Experimental Verification." DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2102.
Full textAbstract:
This thesis developed a novel theory of fiber jamming and experimentally verified it. The theory relates the performance, which is the ratio between the stiff and soft states of a fiber jamming chamber, to three relative design parameters: the ratio of the wall thickness to the membrane inner diameter, the ratio of the fiber diameter to membrane inner diameter, and the number of fibers. These three parameters, when held constant across different chamber sizes, hold the performance constant. To test the theory, three different types of fiber jamming chambers were built in three different sizes. Each chamber was set up as a cantilever beam and deflected 10mm in both the un-jammed (soft) and jammed (stiff) states. When the three design parameters were held constant, the performance of the chamber was consistent within 10\%. In contrast, when the parameters were altered, there was a statistically significant $p < .0001$ and noticeable effect on chamber performance. These two results can be used in tandem to design miniaturized fiber jamming chambers. These results also have a direct application in soft robots designed for minimally invasive surgery.
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Kukatla, Harish C. "A Study of Strain Elastography Under a Normal Tensile Testing Condition." Youngstown State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1296334599.
Full text
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Darvish, Shadi. "Thermodynamic Investigation of La0.8Sr0.2MnO3±δ Cathode, including the Prediction of Defect Chemistry, Electrical Conductivity and Thermo-Mechanical Properties." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3653.
Full textAbstract:
Fundamental thermodynamic investigations have been carried out regarding the phase equilibria of La0.8Sr0.2MnO3±δ (LSM), a cathode of a solid oxide fuel cell (SOFC), utilizing the CALculation of PHAse Diagram (CALPHAD) approach. The assessed thermodynamic databases developed for LSM perovskite in contact with YSZ fluorite and the other species have been discussed. The application of computational thermodynamics to the cathode is comprehensively explained in detail, including the defect chemistry analysis as well as the quantitative Brouwer diagrams, electronic conductivity, cathode/electrolyte interface stability, thermomechanical properties of the cathode and the impact of gas impurities, such as CO2 as well as humidity, on the phase stability of the cathode. The quantitative Brouwer diagrams for LSM at different temperatures are developed and the detailed analysis of the Mn3+ charge disproportionation behavior and the electronic conductivity in the temperature range of 1000-1200°C revealed a good agreement with the available experimental observations. The effects of temperature, CO2 partial pressure, O2 partial pressure, humidity level and the cathode composition on the formation of secondary phases have been investigated and correlated with the available experimental results found in the literature. It has been indicated that the CO2 exposure does not change the electronic/ionic carriers’ concentration in the perovskite phase. The observed electrical conductivity drop is predicted to occur due to the formation of secondary phases such as LaZr2O7, SrZrO3, SrCO3 and Mn oxides at the LSM/YSZ interface, resulting in the blocking of the electron/ion transfer paths. For the thermo-mechanical properties of LSM, a new weight loss Mechanism for (La0.8Sr0.2)0.98MnO3±δ using the La-Sr-Mn-O thermodynamic database is modeled with respect to the compound energy formalism model. This newly proposed mechanism comprehensively explains the defect formation as a result of volume/weight change during the thermal cycles. According to the proposed mechanism the impact of cation vacancies regarding the volume change of cathode was explained.
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Stanciu, Cristina Daniela. "Matériaux magnétiques doux Fe-Si de hautes performances obtenus par mécanosynthèse." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY020/document.
Full textAbstract:
Les alliages Fe-Si sont connus pour combiner d’excellentes propriétés magnétiques avec de bonnes propriétés électriques (forte résistivité électrique). Dans ce contexte nous avons recherché à élaborer des matériaux à forte teneur en Si, souvent difficiles à obtenir et mettre en forme industriellement. Des alliages magnétiques doux de type Fe-Si avec une teneur élevée en Si (4,5%, 6,5%, 10% et 15% massique) ont été obtenus avec succès à l’état nanocristallin par broyage mécanique et recuit. La formation des alliages a été étudiée par diffraction X, spectroscopie Mössbauer et analyses thermomagnétiques. La stabilité thermique de la poudre a été analysée par DSC. Des mesures d’aimantation ont été réalisées pour caractériser les performances magnétiques. La durée de broyage nécessaire pour la formation de l’alliage a été déterminée pour chaque teneur en Si. Pour les faibles temps de broyage, le recuit conduit à la formation du composé Fe3Si. Après la formation de l’alliage par le broyage mécanique, l’effet du recuit est seulement de réduire les tensions internes du second ordre, induites dans la poudre par le broyage. L’addition de Si conduit à la diminution de la température de Curie de 770 °C pour le Fe pur, à 725 °C pour une teneur de 4,5% massique de Si et à 550 °C pour 15% massique de Si. Pour les temps faibles de broyage, l’écart entre l’aimantation de la poudre avant et après recuit est dû à la formation du composé Fe3Si pendant le recuit, lequel a une aimantation plus faible que la solution solide de Feα(Si). Pour les longs temps de broyage, le recuit à 400 °C pour 4 heures n’a pas d’effet sur la valeur de l’aimantation à saturation. En augmentant la teneur en Si, l’aimantation à saturation de l’alliage Fe-Si décroit.Les alliages Ni3Fe (aussi connus comme Permalloys) présentent de meilleures propriétés magnétiques, mais ils ont une résistivité inférieure à celles des Fe-Si. Une voie attractive semble la combinaison des propriétés des 2 classes de matériaux doux en formant un composite. Les alliages Fe-Si précédemment obtenus ont été utilisés pour l’élaboration des poudres composites de type Permalloy/Fe-Si par la mécanosynthèse. Le broyage mécanique conduit à la formation des particules composites avec un aspect stratifié. Quatre heures de broyage de l’alliage Fe-Si avec du Ni3Fe ne conduisent pas à la formation des nouvelles phases, mais la formation d’un alliage ternaire Ni-Fe-Si résulte d’un recuit ultérieur à 900 °C. L’aimantation à saturation du composite augmente avec la croissance de la teneur le d’alliage Fe-Si, mais le temps de broyage ne semble avoir aucun effet sur cela.Une étude préliminaire a été réalisée sur l’élaboration des compacts composites de type Ni3Fe/Fe-Si par frittage flash, dans le but de préserver l’état nanocristallin par de basses températures de frittage. L’influence de la température de frittage et de la durée de maintien sur la structure, et les propriétés physiques des compacts est discutée. Des températures allant jusqu'à 750 °C pour une durée de maintien minimale ou un palier de 2 minutes maximum à 700 °C ne conduisent pas à la diffusion des éléments des alliages. L'augmentation de la température ou de la durée de frittage conduit à des cristallites plus grandes, mais qui restent dans le domaine nano pour les températures étudiées. La densité des compactes augmente avec la température et le palier. En outre, la résistivité diminue en augmentant ces 2 paramètres. L'effet de la teneur en Fe-Si est de diminuer la densité et en même temps d'augmenter la résistivité des compacts. La perméabilité magnétique est réduite avec l'augmentation de la température et de la durée de frittage, ainsi que lors de la diminution du contenu de Ni3Fe. Une température élevée et un long temps de maintien à la température de frittage conduisent à l’augmentation des pertes magnétiques. Le champ coercitif est également influencé par les paramètres de frittage, via l'effet qu'ils ont sur la taille des cristallitesFe-Si alloys are known for combining excellent magnetic properties with good electric characteristics (high resistivity). In this context we sought to develop materials with a relatively high Si content, often difficult to obtain and shape industrially.In this thesis, soft magnetic Fe-Si alloys with high Si content (4.5, 6.5, 10 and 15 wt. %) were successfully obtained in nanocrystalline state by mechanical alloying and annealing. The formation of the alloy was studied by X-ray and neutron diffraction, Mossbauer spectroscopy and thermomagnetic analysis. DSC technique was used in order to study the powder’s thermal stability. Magnetisation measurements were also made in order to characterise their magnetic performances. The milling duration necessary for the formation of the alloy was determined for each Si content. For low milling times, annealing leads to the formation of the Fe3Si compound. Once the alloy is formed by mechanical milling, the effect of the annealing is only to reduce the second order stress induced in the powder by the milling process. Si addition leads to the decrease of the alloy’s Curie temperature from 770 °C for pure Fe to 725 °C for a 4.5 wt. % Si and down to 550 °C if the Si content increases to 15 wt. %. For low milling times, a gap between the magnetisation of the as-milled alloy and of the milled and subsequently annealed one is due to the formation of the Fe3Si compound during annealing which has a lower magnetisation than that of the αFe (Si) solid solution. For longer milling durations, annealing at 400 °C for 4 hours has no effect on the saturation magnetisation value. By increasing the Si content, the Fe-Si alloy’s saturation magnetisation decreases.Fe-Ni alloys whose composition is close to Ni3Fe (commonly known as Permalloys) have better magnetic properties, but a resistivity well inferior to that of Fe-Si alloys. Therefore, a combination of the properties of these 2 alloy classes of soft magnetic materials into a composite seems to be an attractive route. The previously obtained Fe-Si alloys were used for the preparation of Permalloy/Fe-Si composite powders by mechanical milling. Milling leads to the formation of composite powder particles with a stratified aspect. Milling of the Fe-Si and Ni3Fe alloys for 4 hours does not lead to the formation of new phases, but a subsequent annealing at 900 °C results in the formation of a Ni-Fe-Si alloy. Saturation magnetisation of the composite increases with increasing of the Fe-Si content, but milling duration seems to have no effect on it.A preliminary study was made on the elaboration of Ni3Fe/Fe-Si composite compacts obtained by spark plasma sintering, aiming to preserve the nanocrystalline state by lower sintering temperatures. The influence of the sintering temperature and temperature holding duration on the structure, density, resistivity and magnetic properties of the compacts is discussed. Temperatures of up to 750 °C for minimal holding duration or a maintain at the temperature of 700 °C for a duration of up to 2 minutes does not lead to a diffusion of the alloys’ elements. Increasing of the sintering temperature or duration leads to larger crystallite sizes, but they remain in the nano domain for the studied temperatures. The compacts’ density increases with temperature and sintering duration. Resistivity, on the other hand decreases when increasing the aforementioned parameters. The effect of the Fe-Si content is to decrease the density and at the same time increase the compacts’ resistivity. Magnetic permeability is reduced with increasing sintering temperature and duration, as well as when decreasing of the Ni3Fe content. High temperature and long maintaining duration leads to an increase of magnetic losses. Coercive field is also influenced by sintering parameters by the effect they have on the crystallite size
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Ramirez, Arias José Luis. "Development of an artificial muscle for a soft robotic hand prosthesis." Thesis, Paris 10, 2016. http://www.theses.fr/2016PA100190/document.
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Le thème central de cette thèse est la conception d’actionneurs doux à partir de matériaux intelligents et d’une prothèse de main robotique souple. Notre approche prends en compte les différents points qui peuvent influer sur le développement d’une stratégie d’actionnement ou d’un muscle artificiel : i) Les mécanismes et la fonctionnalité de la main humaine afin d’identifier les exigences fonctionnelles pour une prothèse de main robotique en matière de préhension. ii) L’analyse et l’amélioration des mécanismes de la main robotique pour intégrer un comportement souple dans la prothèse. iii) L’évaluation expérimentale de la prothèse de main robotique afin d’identifier les spécifications du système d’actionnement nécessaire au fonctionnement cinématique et dynamique du robot. iv) Le développement et la modélisation d’une stratégie d’actionnement utilisant des matériaux intelligents.Ces points sont abordés successivement dans les 4 chapitres de cette thèse1. Analyse du mouvement de la main humaine pour l’identification des exigences technologiques pour la prothèse de main robotique.2. Conception et modélisation de la prothèse de main robotique à comportement souple.3. Evaluation mécatronique de la prothèse de main.4. Conception d’un muscle artificiel basé sur des matériaux intelligentsIn the field of robotic hand prosthesis, the use of smart and soft materials is helpful in improving flexibility, usability, and adaptability of the robots, which simplify daily living activities of prosthesis users. However, regarding the smart materials for artificial muscles, technologies are considered to be far from implementation in anthropomorphic robotic hands. Therefore, the target of this thesis dissertation is to reduce the gap between smart material technologies and robotic hand prosthesis. Five central axes address the problem: i)identification of useful grasping gestures and reformulation of the robotic hand mechanism, ii) analysis of human muscle behavior to mimic human grasping capabilities, iii) modeling robot using the hybrid model DHKK-SRQ for the kinematics and the virtual works principle for dynamics, iv) definition of actuation requirements considering the synergy between prehension conditions and robot mechanism, and v) development of a smart material based actuation system.This topics are addressed in four chapters:1. Human hand movement analysis toward the hand prosthesis requirements2. Design and modeling of the soft robotic hand ProMain-I3. Mechatronic assessment of Prosthetic hand4. Development of an artificial muscle based on smart materials
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Czarnecki, Jarema S. "Engineered carbon-based scaffolds for hard and soft tissue repair, reconstruction or regeneration." University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1386953861.
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Villanova, Julie. "Détermination des contraintes résiduelles dans les matériaux céramiques pour SOFC : mesures multi-échelles et influence des cycles d'oxydo-réduction." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2010. http://tel.archives-ouvertes.fr/tel-00582358.
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Les piles à combustible Solid Oxide Fuel Cell sont des systèmes de production d'électricité. Une cellule élémentaire est un multicouche constitué de matériaux céramiques et de métal. Elles sont très sensibles aux contraintes mécaniques générées lors des cycles thermiques et d'oxydo-réduction, limitant leur durée de vie.Ce travail a porté sur la détermination expérimentale des contraintes résiduelles dans des cellules SOFC à anode support en fonction des sollicitations du système. Parallèlement à des mesures in-situ en température, une approche multi-échelles a été développée pour évaluer les hétérogénéités de contraintes dans l'électrolyte liées à la forte anisotropie élastique de la zircone yttriée qui le constitue. Différentes techniques ont été mise en œuvre afin de couvrir les 3 ordres de contraintes. Les mesures à l'échelle macroscopique ont été effectuées par diffraction de rayons X de laboratoire (méthode des sin²(Ψ)). La microdiffraction de rayonnement synchrotron en mode faisceau blanc et monochromatique a permis, après un important travail d'amélioration du protocole de mesure et d'analyse, de déterminer les tenseurs complets de contraintes et déformations grain à grain dans l'électrolyte. Les déformations intra-granulaires ont été évaluées par une technique d'EBSD.Les résultats obtenus ont permis d'analyser les mécanismes principaux qui régissent les évolutions de contraintes dans l'électrolyte. Des hétérogénéités de contraintes entre grains liées à leurs orientations cristallographiques ont été mises en évidence. Au-delà du problème des SOFC, les techniques mises en œuvre ouvrent la voie aux validations expérimentales des modèles mécaniques poly-cristallins.
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Davis, Andrew Scott. "Temperature Induced Deflection of Yttria Stabilized Zirconia Membranes." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338369600.
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SILVA, MAVIAEL J. da. "Desenvolvimento de selantes vitrocerâmicos para uso em SOFC pertencentes ao sistema BAS (BaO-Alsub(2)0sub(3)-SiOsub(2)) modificados com Bsub(2)Osub(3)." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23655.
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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-04-10T16:38:07Z
No. of bitstreams: 0Made available in DSpace on 2015-04-10T16:38:07Z (GMT). No. of bitstreams: 0
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Bohec, Pierre. "Étude du comportement hors-équilibre du cortex cellulaire." Phd thesis, Université Paris-Diderot - Paris VII, 2012. http://tel.archives-ouvertes.fr/tel-00870466.
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La cellule est capable, en consommant l'énergie issue de l'hydrolyse de l'ATP, d'exercer des forces qui prennent leurs origines dans des réactions biochimiques. Un élément important de la cellule est le cytosquelette, composé principalement de microtubules et de filaments d'actine, il en constitue l'architecture et lui donne l'essentiel de ses propriétés mécaniques. Il est composé de polymères réticulés et, du point de vue de la rhéologie, a un comportement viscoélastique. Au sein du cytosquelette, des processus tels que la polymérisation de l'actine ou des microtubules permettent d'exercer des forces. Des protéines, de la famille des moteurs moléculaires, ont pour rôle spécifique de convertir l'énergie stockée sous forme chimique en énergie mécanique. L'activité mécanique hors-équilibre de la cellule est donc directement reliée à ces forces d'origine biochimique. Dans ce travail, nous avons étudié la distribution statistique des forces d'origine biochimique s'exerçant sur une bille de taille micrométrique attachée au cortex d'actine par l'intermédiaire de récepteurs de l'adhésion cellulaire : les intégrines. L'étude des forces d'origine biologique est inséparable de la connaissance des forces d'origine thermique car à cette échelle microscopique la contribution des forces thermiques n'est pas négligeable. Les forces s'exerçant sur la sonde ont deux origines possibles : biologique ou thermique. Notre approche expérimentale est basée sur la combinaison de deux techniques de microrhéologie, active et passive, ce qui nous permet de calculer la fonction d'autocorrélation temporelle des forces exercées sur une sonde accrochée à l'actine corticale et de la comparer à la fonction d'autocorrélation des forces thermiques estimée via le théorème de fluctuation-dissipation. La différence entre ces deux spectres nous donne une idée de la contribution des forces d'origine biologique au mouvement de la bille et une mesure de l'écart du système à l'équilibre thermodynamique. Afin d'étudier plus en détail ce système de bille subissant des forces de la part de l'actine corticale, nous avons étudié l'effet de la variation de la densité de ligand recouvrant la bille. La question qui nous a animés tout au long de ce travail est l'origine de ces forces biologiques ou plus exactement la nature du composant du cytosquelette qui exerce ces forces athermiques. Dans un premier temps, nous avons étudié l'influence de la température sur ces forces biologiques. Nous avons ensuite étudié l'effet de la déplétion de l'ATP dans la cellule, de la dépolymérisation de l'actine et de l'inhibition des moteurs moléculaires de la famille des myosines.