Tesis sobre el tema "Nanoindentation"
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Ziegenhain, Dr Gerolf. "Atomistische Simulation von Nanoindentation". Kaiserslautern Dr. Gerolf Ziegenhain c/o TU Kaiserslautern, 2009. http://gerolf.ziegenhain.com.
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Tang, Bin. "Nanoindentation of viscoelastic materials". Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B3655408X.
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Wheeler, Jeffrey M. "Nanoindentation under dynamic conditions". Thesis, University of Cambridge, 2009. https://www.repository.cam.ac.uk/handle/1810/218320.
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Nanoindentation has emerged as a leading technique for the investigation of mechanical properties on small volumes of material. Extensive progress has been made in the last 20 years in refining the nstrumentation of nanoindentation systems and in analysis of the resulting data. Recent development has enabled investigation of materials under several dynamic conditions. The palladium-hydrogen system has a large miscibility gap, where the palladium lattice rapidly expands to form a hydrogen-rich β phase upon hydrogenation. Nanoindentation was used to investigate the mechanical effects of these transformations on foils of palladium. Study of palladium foils, which had been cycled through hydrogenation and dehydrogenation, allowed the extent of the transformed region to be determined. Unstable palladium foils, which had been hydrogenated and were subject to dynamic hydrogen loss, displayed significant hardening in the regions which were not expected to have transformed. The reason for this remains unclear. Impact indentation, where the indenter encounters the sample at relatively high speeds, can be used to probe the strain rate dependence of materials. By combining impact indentation and elevated temperature indentation, the strain rate dependence of the superelasticity of nickel-titanium was probed over a range of temperatures. Similar trends in elastic energy ratios with temperature were observed with the largest elastic proportions occurring at the Austenite finish transformation temperature. Multiple impact and scratch indentation are two modes of indentation which are thought to approximate erosive and abrasive wear mechanisms, respectively. These were utilised to investigate the wear resistance of several novel coatings formed by plasma electrolytic oxidation (PEO) of Ti-6Al4-V. Multiple impact indentation results appear to subjectively rank the erosive wear performance of both ductile and brittle materials. Comparison of normalised performance of coating systems on aluminium in abrasive wear to scratch hardness showed similar degrees of resistance.
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Feng, Gang y 封剛. "Creep effects in nanoindentation". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31224350.
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Tang, Bin y 唐斌. "Nanoindentation of viscoelastic materials". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B3655408X.
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Pfetzing, Janine. "Nanoindentation von NiTi-Formgedächtnislegierungen". Aachen Shaker, 2009. http://d-nb.info/995887918/04.
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Feng, Gang. "Creep effects in nanoindentation". Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23273288.
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McGee, Edward. "Multiscale modelling of nanoindentation". Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/35387.
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The process of nanoindentation causes physical phenomena not only at the nano-scale, but at multiple length scales up to the macroscopic. This thesis investigates multiscale modelling of nanoindentation that links atomistic scale molecular dynamics (MD) to a finite element (FE) model in order to extend the length scales that can be modelled. Existing multiscale models are investigated and the relevant advantages and disadvantages of each are discussed. New coupling techniques are developed in both 2D and 3D, which are applied to nanoindentation test simulations to verify the models. A new force attribution 3D multiscale model is applied to some studies of nanoindentation of Au and Fe. The results are compared to those obtained through experiment and to atomistic only models to investigate the effect of the embedding continuum region. These studies show that by extending the length scales, long range effects of nanoindentation can be modelled in the far field by continuum mechanics giving results that are in closer agreement with the experiment. The new coupling method has wide application and a study of laser ablation of Au has been carried out to show that the multiscale modelling technique can be used to improve the description of this phenomenon also.
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Christopher, David. "Molecular dynamics modelling of nanoindentation". Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/6924.
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This thesis presents an atomic-scale study of nanoindentation, with carbon materials and both bcc and fcc metals as test specimens. Classical molecular dynamics (MD) simulations using Newtonian mechanics and many-body potentials, are employed to investigate the elastic-plastic deformation behaviour of the work materials during nanometresized indentations. In a preliminary model, the indenter is represented solely by a non-deformable interface with pyramidal and axisymmetric geometries. An atomistic description of a blunted 90° pyramidal indenter is also used to study deformation of the tip, adhesive tip-substrate interactions and atom transfer, together with damage after adhesive rupture and mechanisms of tip-induced structural transformations and surface nanotopograpghy. To alleviate finite-size effects and to facilitate the simulation of over one million atoms, a parallel MD code using the MPI paradigm has also been developed to run on multiple processor machines. The work materials show a diverse range of deformation behaviour, ranging from purely elastic deformation with graphite, to appreciable plastic deformation with metals. Some qualitative comparisons are made to experiment, but available computer power constrains feasible indentation depths to an order of magnitude smaller than experiment, and over indentation times several orders of magnitude smaller. The simulations give a good description of nanoindentation and support many of the experimental features.
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McCann, Martha Mary. "Nanoindentation of Gold Single Crystals". Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/27170.
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Nanoindentation is an increasingly used tool to investigate the mechanical properties of very small volumes of material. Gold single crystals were chosen as a model system for surface modification studies, because of the electrochemical advantages and the simple structure of the material. Experiments on these samples displayed a spectrum of residual deformation, with measured hardness values on the same surface differing by over a factor of two. The yield point also exhibited considerable variation, but the depth of penetration was independent of this elasticâ plastic transition. The onset of plastic deformation in these tests is observed at stress levels on the order of the theoretical yield strength. There are a limited number of defects in a single crystal specimen of gold, especially on the length scale required to influence nearly every indentation experiment. A test matrix was designed to change the concentrations of possible defects in a sample (dislocations, vacancies, and structural features), by altering some of the surface preparation parameters. The results of these experiments were extremely consistent. Observed trends within the matrix, combined with the observations of reduced hardness and earlier plasticity when compared to the preliminary testing, indicate a decline in the structural continuity of the sample. This is surprising considering the extensive material removal and thermal history of some of these surfaces. There is no indication of a cause for the dramatic inconsistencies in mechanical properties observed in preliminary testing, but a consistent surface enables the study of intentional modifications. Changes in contact area that were undetectable in preliminary results now demonstrate predictable shifts in hardness values. The deposition of a single monolayer of gold oxide raised the average load at yield by a factor of three and increased the hardness by over 26%. Attributing this change to the oxide is corroborated by the reduction of hardness when the oxide is stripped. Similar behavior is observed when a lead monolayer is deposited and tested ex-situ. It is surprising that layers <0.5 nm in thickness would have such a dramatic influence on indentation tests at least 35 nm deep. This indicates that no surface layer can be ignored at this scale. These experiments demonstrate that there is still much to be learned about nanoscale deformation mechanisms.Ph. D.
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Morasch, Kevin R. "Nanoindentation induced thin film fracture". Online access for everyone, 2005. http://www.dissertations.wsu.edu/Thesis/Spring2005/k%5Fmorasch%5F042605.pdf.
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Nibur, Kevin Andrew. "Nanoindentation slip steps and hydrogen embritlement". Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Summer2005/k%5Fnibur%5F071305.pdf.
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Li, Han. "The nanoindentation size effects of creep". Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B30696380.
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Haque, Feza. "Nanoindentation of polymer and protein films". Thesis, Queen Mary, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510875.
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Li, Han y 李晗. "The nanoindentation size effects of creep". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B30696380.
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Selby, Alastair Phillip. "Nanoindentation of soft contact lens materials". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/nanoindentation-of-soft-contact-lens-materials(502085d8-3325-4ea8-926c-ad75b15a557d).html.
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The launch of silicone hydrogel contact lenses has led to a rise in the incidence of mechanically-related clinical complications, which is thought to be due to the increased stiffness of these materials compared to conventional hydrogel lens materials. The mechanical characteristics of hydrogel contact lenses have traditionally been investigated using tensile testing which investigated the bulk material characteristics. This thesis presents a study intended to establish a repeatable method for local mechanical measurement of hydrogel contact lenses using nanoindentation. Hydrogel materials in phosphate buffered saline were indented using a Hysitron Triboindenter mounted on a Veeco Explorer AFM using Triboscope software (version 3.5a) with a specially constructed wet cell. A model hydrogel (poly(HEMA-MMA)) was used to validate the methodology and investigate a the effect of controlled change in specimen thickness. A range of commercially available hydrogel contact lenses were then characterised (including conventional and silicone hydrogel lenses) using the same method. Two different analytical techniques were employed to determine the mechanical properties data; elastic analysis and a time-dependent viscoelastic analytical technique.A strong influence of specimen thickness on apparent mechanical properties was seen with the elastic analysis and an empirical relationship was derived to correct for this which was found to be appropriate for all contact lens specimens studied and reported in the thesis. The viscoelastic analysis results were more complex and exhibited a less clear influence of specimen thickness. However, as this is a very simple approximation as contact lenses are suspected to be poroelastic rather than viscoelastic this work could not be fully resolved in the scope of this thesis. For all contact lenses analysed, nanoindentation produced data similar to that found with conventional tensile testing, however, there was evidence for a slight dependence of elastic properties across the lens that does not correlate with sample thickness. This thesis shows the development of a way of accounting for the variation of thickness of a range of contact lenses, and demonstrated that traditional analysis is accurate enough to determine local differences in modulus across contact lenses. The viscoelastic analysis may be more appropriate for hydrogels, however, it produced irregularities that will require further work to fully resolve.
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Pfetzing, Janine [Verfasser]. "Nanoindentation von NiTi-Formgedächtnislegierungen / Janine Pfetzing". Aachen : Shaker, 2009. http://d-nb.info/1159832773/34.
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Johnson, Lars. "Nanoindentation in situ a Transmission Electron Microscope". Thesis, Linköping University, Department of Physics, Chemistry and Biology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8333.
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The technique of Nanoindentation in situ Transmission Electron Microscope has been implemented on a Philips CM20. Indentations have been performed on Si and Sapphire (α-Al2O3) cut from wafers; Cr/Sc multilayers and Ti3SiC2 thin films. Different sample geometries and preparation methods have been evaluated. Both conventional ion and Focused Ion Beam milling were used, with different ways of protecting the sample during milling. Observations were made of bending and fracture of samples, dislocation nucleation and dislocation movement. Basal slip was observed upon unloading in Sapphire. Dislocation movement constricted along the basal planes were observed in Ti3SiC2. Post indentation electron microscopy revealed kink formation in Ti3SiC2 and layer rotation and slip across layers in Cr/Sc multilayer stacks. Limitations of the technique are presented and discussed.
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Breuils, Jacques. "Caractérisation par nanoindentation de surfaces métalliques fonctionnalisées". Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAD044.
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Les travaux de thèse se sont attachés à développer des outils permettant :(i) d'estimer par nanoindentation le niveau de contraintes résiduelles locales de type biaxial introduit dans un alliage d'aluminium 2050-T8. Nous proposons une méthode d'estimation qui couple des essais expérimentaux de nanoindentation, l'observation des empreintes résiduelles et une analyse numérique de l'effet de contraintes résiduelles élastiques biaxiales sur la géométrie des empreintes résiduelles d'indentation. et (ii) de déterminer par nanoindentation le comportement mécanique d'un film d'oxyde ultra-mince, d'épaisseur variant entre 15 et 20nm, formé sur un acier inoxydable biphasé de type Duplex. Nous avons développé une méthode de caractérisation de films ultra-minces qui couple la réalisation et l'analyse d'essais expérimentaux à l'aide d'indenteurs dont le défaut de pointe est déterminé, et la reproduction de ces essais en simulation numérique 3D à l'aide des géométries réelles des indenteursWorks performed during this thesis were dedicated to development of tools allowing:(i) To estimate using nanoindentation tests the level of biaxial residual stresses introduced within a 2050-T8 aluminium alloy. We propose an estimation method that couples experimental nanoindentation tests, residual imprints observation and numerical evaluation of the impact of elastic biaxial residual stresses on the geometries of residual indentation imprints. And (ii) the determination by nanoindentation of the mechanical behavior of an ultra-thin oxide film, between 15 to 20nm thickness, formed on a dual phased Duplex stainless steel. We developed a characterization method that couples analysis of experimental nanoindentation tests using several indenters with known tip defects, and reproduction of these tests in 3D finite element simulations using the true indenters' geometries
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Scholz, Torben. "Charakterisierung von Bariumtitanat mittels Nanoindentation und Rasterkraftmikroskopie". Göttingen Sierke, 2006. http://d-nb.info/986402141/04.
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Tang, Allen. "Nanoindentation of peri-implant bone and dentin". Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2648.
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Advances in the field of medicine have extended the average human life expectancy worldwide. As a result an increasing number of people will suffer from problems associated with their mineralized tissues and will require orthopedic and dental implants to restore their quality of life. Ideally, implants should have mechanical and structural properties compatible with the original mineralized tissue, and should also promote faster and stronger implant fixation. An improved understanding of the properties of mineralized tissues can help with the improvements of implants. This thesis focuses on improving the understanding of two aspects related to mineralized tissues and implant systems: the mechanical properties of peri-implant bone, and the mechanical, composition and structural properties of dentin and jawbone.
Studies have shown that local delivery of alendronate, an anti-osteoporosis drug, enhances new bone formation; however, the effects of the drug on the elastic modulus of new formed bone are unknown. In this study, nanoindentation was used to evaluate and compare the elastic modulus of peri-implant bone with and without the presence of alendronate. To better understand the properties of dentin and jawbone, nanoindentation and qualitative backscattered electron imaging were used to measure their elastic modulus, mineral content and volume fraction, and regression analyses were used to establish correlation between the properties.
In this thesis, mineralized tissue samples were collected from an animal study. To study the effects of alendronate on the elastic modulus of peri-implant bone, porous tantalum implants with three different coating treatments were used: non-coated (Ta), calcium phosphate coated (Ta-CaP), alendronate-immobilized-calcium-phosphate coated (Ta-CaP-ALN). The calcium phosphate coatings, with or without alendronate, increased the elastic modulus of peri-implant Ingrown Bone by approximately 22% (3GPa). The addition of alendronate did not significantly increase the elastic modulus of peri-implant.
For the study of dentin and jawbone, regression analyses showed that the elastic modulus of dentin is strongly dependent on the porosity and to a lesser extent on the calcium content. The elastic modulus of jawbone and dentin were compared and the elasticmodulus of jawbone was generally higher than that of dentin while the mineral content was lower.
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Stewart, Alistair. "Dynamic nanoindentation of various polymer nano-composites". Thesis, University of Ulster, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.593883.
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There is a strong rationale for replacing traditional carbon fibre and glass fibre composites with nano-composites as smaller size and higher aspect ratio reinforcement can lead to improved mechanical properties, via improved load transfer from reinforcement to polymer matrix but also increased dissipation of mechanical energy within the material, an advantage for maximising toughness and fatigue resistance. This project focuses on using dynamic nanoindentation to characterise polymer nano-composites made with graphene and carbon nanotubes (CNT), namely, CNT-polymethylmethacrylate (PMMA) composites, CNT-polydymethylsiloxane (PDMS) and graphene-polyamide composites. Melt-processed PMMA nano-composites studied by optical microscopy show a gradual increase in aggregate size for the functionaLized CNT/PMMA composites, the results for the nonfu nctionalised CNT/PMMA composite showing a poorer dispersion of CNT. Thermogravimetric analysis (TGA) also indicates that the functionalized-CNT are better dispersed into the polymer. These results are consistent with those obtained by nanoindentation and Rockwell hardness testing; higher storage modulus, lower loss tangent and higher HR value for the composites made with functionalized-CNT, sign of a better interfacial load transfer. The addition of solvent, the use of tip sonication as well as the e NT aspect ratio were all found to have an influence on the CNT dispersion within in-situ cured CNTIPDMS nano-composites. TGA showed a lowering of the degradation temperature upon CNT addition, indicative of CNT inhibiting the cure process, in accordance with recently reported results. Nanoindentation resu lts indicate that the specimen made with the better dispersed CNT exhibit the larger storage modu lus. Generally, these stiffness values increase at low CNT content and then decrease, possibly because of the effect that CNT have upon the PDMS cross-linking. In these nanocomposites, the loss tangent is large, dominated by the elastomeric matrix and not sensitive to the interfacial energy dissipation. Finally. in situ-polymerised graphene-polyamide nano-composites were investigated. TGA showed that the graphene was oxidised in these composites. Optical microscopy indicates that the fine-dispersion of the reinforcement disappear at higher graphene content. Nanoindentation showed that the storage modulus peaked at low graphene content and then decreased at higher percentages, while tested at a larger scale (mm\ the mechanical properties of these composites only saturates with graphene content. This result may be due to the processing of the high graphene content specimen, made by solvent evaporation, during which aggregates may reform, as observed by optical microscopy. Overall, this investigation has shown that dynamic nanoindentation is a valuable tool for studying the dispersion of reinforcement in polymer nanocomposites.
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Alsayegh, Rajab. "Vision-augmented molecular dynamics simulation of nanoindentation". Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/13660.
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This thesis has contributed to the literature by providing a pathway to simplify the process of carrying out molecular dynamics simulation. As a part of the investigation, a user-friendly vision-augmented technique was developed to set up and carry out atomistic simulations using hand-gestures. The system is novel in its concept as it enables the user to directly manipulate the atomic structures on the screen, in 3D space using hand gestures, allowing the exploration and visualisation of molecular interactions at different relative conformations. The hand gestures are used to pick and place atoms on the screen allowing thereby the ease of preparing and carrying out molecular dynamics simulations in a more intuitive way. The end result is that users with limited expertise in developing molecular structures can now do so easily and intuitively by the use of body gestures to interact with the simulator to study the system in question. The proposed system was tested by performing parallel molecular dynamics simulations to study (i) crystal anisotropy of a diamond cubic substrate (crystalline silicon) using nanoindentation with a long-range (Screened bond order) Tersoff potential and (ii) crystal anisotropy of a body centre cubic metal (tantalum) using nanoindentation with an Embedded Atomic Method (EAM) type potential. The MD data was post-processed to reveal size effects observed in anisotropy of both these materials, namely, silicon and tantalum. The value of hardness and elastic modulus obtained from the MD data was found in accordance with what has been discovered previously by experiments, thereby validating the simulations. Based on this, it is anticipated that the proposed system will open up new horizons to the current methods on how an MD simulation is designed and executed.
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Mason, Jeremy K. (Jeremy Kyle). "Statistical physics of dislocation nucleation by nanoindentation". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32914.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Page 82 blank.
Includes bibliographical references (page 79-81).
Current understanding of the onset of plasticity during nanoindentation of crystalline materials involves homogenous dislocation nucleation in the crystal underneath the indenter. Through the use of cutting-edge nanoindentation techniques, this study examines the initiation of plastic deformation in single crystal oriented platinum samples. Variations in the temperature and loading rate during indentation reveal temporal and thermal dependencies, and support the stochastic and thermally-activated nature of the initial plastic event. These dependencies of dislocation nucleation are precisely quantified by developing analysis methods based on statistical thermodynamics, and are used to evaluate the probability of various atomistic mechanisms. The results of this procedure implicate a critical activation event occurring in a single atomic volume, with an activation enthalpy of a fraction of an electron volt. These findings strongly indicate that the initiation of plasticity begins with a heterogeneous dislocation nucleation event, in conflict with the current belief, and significantly advance understanding of the onset of plastic deformation during nanoindentation.
by Jeremy K. Mason.
S.B.
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Gathier, Benjamin. "Multiscale strength homogenization : application to shale nanoindentation". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43049.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references (p. 236-246).
Shales are one of the most encountered materials in sedimentary basins. Because of their highly heterogeneous nature, their strength prediction for oil and gas exploitation engineering has long time been an enigma. In this thesis, we propose a two-scale non-linear procedure for the homogenization of their yield design strength properties, based on the Linear Comparison Composite Theory. At Level 0, the intrinsic friction of shales is captured via a cohesive-frictional strength criterion for the clay particles (Drucker-Prager). Level I is composed of a porous clay phase and Level II incorporates silt and quartz grains. Homogenization yields either an elliptical or an hyperbolc strength criterion, depending on the packing density of the porous clay phase. These criteria are employed in an original reverse algorithm of indentation hardness to develop hardness-packing density scaling relations that allow a separation of constituent properties and volume fraction and morphology parameters, including interface conditions between the porous clay matrix and the (rigid) silt inclusions. The application of this algorithm to 11 shale samples from the GeoGenome project data base allows us to identify: (i) an invariant value of the solid hardness of clay particles, which is independent of clay mineralogy, porosity, etc.; and (ii) shale independent scaling relations of the cohesion and of the friction coefficient with the mean clay packing density, which provides some evidence that the elementary building block of shale is a clay polycrystal. The use of these scaling relations in the Level II-homogenization provides a first-order model for the prediction of the macroscopic strength properties of shale, based on only two parameters that delineate shale's macroscopic diversity: clay packing density and silt inclusion volume fraction.
by Benjamin Gathier.
S.M.
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Molina, Aldareguia Jon Mikel. "Processing and nanoindentation behaviour of nitride multilayers". Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620432.
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Gibbons, Melissa Marie. "Computational mechanics of nanoindentation of viral capsids". Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1709825191&sid=4&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Clausner, André. "Bewertung von Verfahren zur Fließspannungsbestimmung in der Nanoindentation". Doctoral thesis, Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-124038.
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Die Nanoindentation ist ein inzwischen etabliertes Verfahren zur Bestimmung der Materialkennwerte Härte und Elastizitätsmodul in kleinen Größendimensionen. Eine zusätzliche Bestimmung der Fließspannung aus solchen Nanoindentationsexperimenten würde deren Einsatzmöglichkeiten deutlich erweitern und zum Beispiel für die Bauteilauslegung kleiner Strukturen, Schichtcharakterisierung und die Beschaffung von Simulationseingangsdaten einen großen Fortschritt bedeuten. Diese Gründe machen das Thema zu einem aktuellen Forschungsgegenstand. In der vorliegenden Arbeit steht deswegen die Bewertung von Fließspannungsbestimmungsverfahren für Massivmaterialien in der Nanoindentation mittels einer Kombination aus Finite-Elemente-Simulationen und umfangreichen Experimentaldaten im Zentrum. Im Speziellen wird dabei das Konzept des effektiv geformten Indenters mit dem erweiterten Hertzschen Ansatz und dessen Anwendung zur Fließspannungsbestimmung aus Eindringversuchen mit selbstähnlichen Berkovichpyramiden betrachtet.
Zur Bearbeitung dieser Aufgabenstellung wurden unter anderem drei Referenzverfahren zur Fließspannungsbestimmung (die Expanding cavity-Modelle, das Loading partial unloading-Verfahren und Minidruckversuche) ausführlich charakterisiert. Damit konnten dann im Weiteren belastbare Referenzfließspannungen für die umfangreiche Experimentaldatenbasis zur Verfügung gestellt werden. Außerdem wurden die untersuchten Materialien auf den Einfluss der Größenabhängigkeit der Fließspannungen, den Indentation size effect, hin untersucht. Dabei wurden die vorliegenden physikalischen Vorgänge in den Proben beschrieben, dahingehende Unterschiede bei den betrachteten Referenzverfahren charakterisiert und den Fließspannungswerten die Fließzonendimensionen zugeordnet. Mit den damit zur Verfügung stehenden Informationen konnte das Konzept des effektiv geformten Indenters in seiner Anwendung zur Fließspannungsbestimmung grundlegend bewertet werden. Alle Untersuchungen wurden dabei stets parallel mit Hilfe von Simulations- und Experimentaldaten durchgeführt, um tiefere Einblicke in die zu Grunde liegende Mechanik der Fließprozesse zu gewinnen.
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Chalasani, Praveen K. "Nanoindentation of Layered Materials with a Nonhomogeneous Interface". Scholar Commons, 2006. http://scholarcommons.usf.edu/etd/3902.
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Indentation is used as a technique for mechanical characterization of materials for a long time. In the last few decades, new techniques of mechanical characterization at micro and nano level using indentation have been developed. Mechanical character-ization of thin films has become an important area of research because of their crucial role in modern technological applications. Theoretical and computational models of indentation are less time consuming,cost effective, and flexible. Many researchers have investigated mechanical properties of thin films using theoretical and computational models. In this study, an indentation model for a thin layer-substrate geometry with the possibility of nonhomogeneous or homogeneous interface of finite thickness between layer and substrate has been developed. The layer and substrate can be nonhomogeneous or homogeneous. Three types of indenters are modeled: 1) Uniform pressure indenter 2) Flat indenter 3) Smooth indenter. Contact depth, maximum interfacial normal stress and maximum interfacial shear stress play an important role in design and mechanical characterization of thin films using indentation and the effect of modeling the interface as homogeneous and nonhomogeneous on these parameters is studied. A sensitivity analysis is also conducted to find the effect of indentation area, substrate to layer Young's modulus ratio, layer to interface thickness ratio on contact depth and critical interfacial stresses.
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Kavalur, Aditya Vijay. "Nanoindentation of Crystalline Materials Using a Multiscale Methodology". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1592133016715324.
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Moharrami, Noushin. "Extracting reliable mechanical properties using the nanoindentation technique". Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2738.
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Extracting the mechanical properties of thin films and small volumes of bulk materials through the use of nanoindentation is a well established technique but getting good data from all types of test sample is not always easy. Factors such as surface roughness and oxidation, density/porosity of the material, adhesion/detachment of a thin film, pile-up/sink-in, the presence of the substrate, as well as grain size and its distribution have a significant effect on the observed mechanical properties (e.g. Young’s modulus and hardness). Considerable differences between predicted and observed performance can be seen depending on the material tested and how it has been prepared. This thesis concerns developing test protocols to get good nanoindentation data and reliable measurements of the properties for a range of material types (chiefly metals and ceramics). Firstly, this work highlights the effect of crystallographic anisotropy, grain size, shape and orientation on the mechanical response of metallic thin films such as copper used for semiconductor metallisation. Results obtained on highly polished semiconductor materials were compared with those from engineering surfaces with much higher roughness which show increased scatter in results across the complete range of contact scales. Further studies were carried out on hard coatings and bulk materials such as titanium carbide, zirconium nitride and tungsten. The scatter in data obtained at low tests loads is dominated by anisotropy and grain size effects but disappears at higher loads. For soft materials such as copper, the appearance of pile-up was shown to be significant when compared with harder materials which tend to sink-in. Secondly, to assess the effect of creep (time-dependent behaviour) and also grain boundary effects on the measured mechanical properties, soft materials with a range of grain sizes have been examined. Different indentation control cycles (load and displacement control, single indent and multicycling tests) have been investigated to determine what is most suitable with displacement control being essential in most cases. To study the effect of the density/porosity of the sample and its surface roughness on mechanical properties, the work was carried out on porous coatings of tin, copper and copper-tin alloy coatings with a low density. To further understand the behaviour of porous materials and their mechanical properties, finite element analysis was also used to compare the experimental results with a numerical model. The size, shape and location of porosity with respect to the indenter is critical in determining the mechanical properties of a porous material obtained from nanoindentation analysis. Finally, fully processed engineering surfaces were investigated at the component scale to compare with idealised flat plate samples. Titanium-based and cobalt-chrome alloys in the form of femoral heads and stems for replacement hips have been used to assess the effect of in service oxidation on mechanical properties. These have been studied to look at the effects of sample fixturing and support and surface contact in worn and virgin regions of the sample surface. The extent of oxidation and the mechanical properties of the oxide produced are critical in dictating performance.
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Barnoush, Afrooz. "Hydrogen embrittlement, revisited by in situ electrochemical nanoindentation". Aachen Shaker, 2007. http://d-nb.info/992479851/04.
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Gheewala, Ismail. "Multiscale modelling of nanoindentation of multi-layered systems". Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/34987.
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This thesis presents molecular dynamics simulations of nanoindentation and nanoscratching simulations on a number of oxide. materials. In particular, the oxides studied are used as thin films in optical coatings. These films provide a variety of different functionalities, including reducing infra-red transmission through the glass to lower the heating and cooling costs for buildings. Simulations are performed initially on magnesium oxide, which is studied as a test material due to the simple structure. Simulations are then performed on the rutile and anatase polymorphs of titanium dioxide, which are used in the anti-reflective and self-cleaning part of the coatings, respectively. Finally, simulations are performed into zinc oxide and a silver layer sandwiched between two zinc oxide layers. This multi-layered stack represents the typical structure of the energy saving part of the coatings. Mechanical properties of the thin films have been calculated and compared with experiment. Generally, there is a good level of agreement between the modelling and the experiments. Deformation mechanisms in the different systems have been identified so as to help understand the failure mechanisms in these coatings.
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De, Bono Damaso M. "Inverse analysis and microstructure effects in nanoindentation testing". Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/841572/.
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Inverse analysis of nanoindentation data has attracted increasing interest in industry due to its ability to estimate the bulk tensile properties of materials and potentially offers an alternative technique to conventional characterisation methods. Inverse analysis of nanoindentation data is particularly valuable in applications where conventional techniques are not suitable due to either the scale of characterisation (very small regions) or because the testing is expensive and time consuming. Despite using best practices to minimise sources of error in the experimental data, given the scale of the indentations, the heterogeneity of material microstructure can create significant variability in the data, ultimately affecting the reliability of the inverse analysis solution. This thesis proposes and discusses pragmatic approaches to mitigate the effects of material heterogeneity on the accuracy of the inverse problem solution as well as of nanoindentation data in general. The work has involved finite element analysis modelling, nanoindentation and tensile testing. One mitigation approach consisted in the implementation and verification of a new ‘multi-objective’ function inverse analysis methodology where the bias of selecting only one experimental nanoindentation curve as representative of the homogenised response of the material is overcome. The new approach uses all the experimental curves generated from a grid of nanoindentations and employs a weighted averaging procedure. This methodology was applied to S355 steel samples through recording nanoindentation and tensile test data. Despite the variation present in the experimental nanoindentation load-depth curves, this being in the order of 13%, the ‘multi-objective’ function approach was found to estimate the tensile parameters with an error margin as low as 3-6% compared to an error margin of 9-20% for the conventional method. A framework of activities was also undertaken to monitor the variation of the measured nanoindentation properties (e.g. hardness) as function of the indentation depth, in relation to the average grain size of the material. Commercial purity aluminium 1050 samples (with varying average grain sizes) and S355 steel were employed as test materials. These results in addition to those from other materials were used to construct a look-up plot of the hardness COV values as function of the normalised nanoindentation depths (normalised with respect to the average grain diameter). The plot is based on upper and lower bound curves and intends to provide guidance on the selection of the nanoindentation testing parameters to minimise the variability of the indentation response.
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Cuadrado, Lafoz Núria. "Micromechanical characterization of small volumes by means of nanoindentation". Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/130025.
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Mechanical characterization of micro-volume systems, as thin films or micro-sized phases embedded in multiphase materials, has attracted special interest in the last decades since different micromechanical techniques have been developed to characterize microdevices and materials at the micro
and nano scale and it has become apparent that mechanical properties may depend on the analysis scale. An example is the way a crack grows in a bulk material that is likely to be different from crack propagation in a micro-volume where crack and microstructural dimensions are comparable. Consequently, there is a need of a detailed knowledge of material properties at micro and nano scale to design materials with advanced mechanical properties. In this way, micro and nanoscale science and technology enables to improve new materials and applications at macroscopic scale through a sound
micromechanical design. The accuracy of test methodologies will depend on the size scale in which specific mechanical properties are studied. Micro scale is usually defined as the length scale in the range of 1-1000 microns, whereas nanoscale is usually defined as smaller than a one tenth of a micrometer in at least one dimension, although this term is sometimes also used for materials of larger dimension but smaller than one micrometer. Efforts to characterize the mechanical response of small volumes have led to the development of a variety of test methodologies, as uniaxial micro testing machines, micro beam cantilever deflection or nanoindentation devices. Challenges of testing at the micro scale include micro specimen preparation and handling, the application of small forces, and stress and strain measurement. Nanoindentation appears as the easiest way to study local behaviour on thin films or micro-sized phases, since no special sample preparation is required and tests can be performed quickly and inexpensively. Nanoindentation tests consist in the application of a controlled load on the specimen surface through the direct contact with a sharp diamond indenter and recording the evolution of the load versus the penetration depth of the indenter.
The use in engineering of thin films, advanced coatings and materials with small tailored microstructures has led to the analysis of mechanical properties of very small volumes in which size effects might be important. Efforts to design and model the reliability of small-scale devices are directly dependent on the availability of accurate and reliable measurements of relevant mechanical properties at small scales.
In designing structural or machine components an important step is the identification of the main micromechanical damage mechanisms. It is particularly interesting to determine the first fracture step, i.e., the crack nucleation in order to optimize the material resistance to crack nucleation. Stable brittle
fracture takes place easily by the contact of a hard indenter on a brittle surface; this methodology is known as indentation fracture. Indentation fracture yields valuable information on the fundamental processes of brittle fracture in covalent-ionic solids, and detail on subsidiary deformation processes in the contact region; it provides ‘controlled flaws’ for systematically evaluating fracture properties, and it serves as a simple microprobe for determining material fracture parameters, toughness, crack-growth exponent, etc. For materials that exhibit R-curves behaviour, it affords a much needed bridge between the short-crack domain of microstructural flaws and the long-crack domain of traditional toughness testing; mainly in the study of the first regimes of crack propagation. The great appeal of the indentation methodology is its versatility, control and simplicity, requiring only access to routine hardness testing apparatus. In order to study the mechanical behaviour of small-volumes and micro-sized phases, nanoindentation has become a suitable technique for the mechanical characterization of small-volumes and micrometer – sized phases, in terms of hardness (H), elastic modulus (E) and fracture toughness (Kc). While H and E can be routinely measured by nanoindentation from the load – displacement curves, the evaluation of Kc of hard micro-sized phases can in principle be measured from the length of the cracks at the corners of the indentation. This method of evaluation of Kc is known as Indentation Microfracture (IM) and it was proposed in the 1970s for Vickers indentation cracks in bulk materials. However, the design of new materials leads to ever smaller microstructures, hence lower loads and sharper indenters has to be used in order to concentrate the deformation and fracture only in the very small volume of phases of interest. Mechanical characterization of small volumes, has recently received much attention, and many
works have focused on the determination of Kc by nanoindentation following the IM method. Nanoindentation allows using low loads needed for accurate micromechanical characterization with high spatial resolution. However, the use of a different kind of tip geometry and load range in nanoindentation
technique raises some questions about the applicability of the existent fracture toughness equations which were developed in the past mainly for Vickers tips and for loads typically more than two orders of magnitude higher. Therefore, for a better knowledge of the micromechanical behaviour of brittle
materials, this work is directed to the study of indentation microfracture applied to small volumes, focussing on the understanding of the fracture behaviour of brittle materials in terms of indenter tip geometry, applied load and crack morphology generated. On the other hand, since it is of a scientific and technological interest to understand the mechanical response of micro-volume systems, the feasibility of extending the IM developed for brittle bulk materials to engineering systems formed by micro-sized hard phases in multiphase materials or thin films will be also studied.
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Keung, Lok Hang. "Experimental investigation of size effect in nanoindentation on epoxy /". View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?MECH%202006%20KEUNG.
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Ziegenhain, Gerolf [Verfasser]. "Atomistische Simulation von Nanoindentation / Dr. Gerolf Ziegenhain. TU Kaiserslautern". Kaiserslautern : Dr. Gerolf Ziegenhain c/o TU Kaiserslautern, 2009. http://gerolf.ziegenhain.com.
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Davies, Michael I. "High temperature nanoindentation characterisation of P91 and P92 steel". Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13233/.
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Modern demands in power generation call for higher efficiencies from every area of the power plant. One aspect of this is a drive to increase plant operating temperatures placing higher demand on structural materials. P91 and P92 are two steels commonly used in steam pipes. In order to accurately predict the service lifetime of components, mechanical properties at operating temperatures are critical. In particular properties of material around weld fusion joints are of interest as it is in these regions where failures occur. Conventional techniques such as Vicker’s hardness testing and uniaxial tensile testing are used to characterise the mechanical properties and creep behaviour of bulk materials. These techniques are often used to determine the properties of P91 and P92 parent and weld materials, the limitation of these techniques is that they require large volumes of material. They are therefore unable to determine differences in properties through the heat affected zone of the parent material which is typically only a few millimetres across. Nanoindentation is a technique which offers a potential solution to this problem. It was developed in order to examine the properties of thin films and small material volumes. In recent years several approaches have been developed to perform nanoindentation experiments at elevated temperature. These approaches have been examined in order to establish which provides the best thermal stability for high temperature nanoindentation measurements. This technique has then been used to perform high temperature nanoindentation experiments to determine the mechanical properties and creep behaviour of P91 and P92 steel. The correlation between nanoindentation measurements on bulk materials and those obtained using conventional methods is examined. In particular the significance of creep stress exponents calculated from nanoindentation dwell data is discussed. Nanoindentation is then used to characterise the heat affected zone of a weld, giving clear indications of the effects of microstructural differences on the material properties.
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Rajagopalan, Sudhir. "INSTRUMENTED NANOINDENTATION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS". Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3283.
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Near equi-atomic nickel titanium (NiTi) shape memory alloys (SMAs) are a class of materials characterized by their unique deformation behavior. In these alloys, deformation mechanisms such as mechanical twinning and stress induced phase transformation between a high symmetry phase (austenite) and a low symmetry phase (martensite) additionally occur and influence mechanical behavior and thus their functionality. Consequently, applications of SMAs usually call for precise phase transformation temperatures, which depend on the thermomechanical history and the composition of the alloy. Instrumented indentation, inherently a mechanical characterization technique for small sampling volumes, offers a cost effective means of empirically testing SMAs in the form of centimeter scaled buttons prior to large-scale production. Additionally, it is an effective probe for intricate SMA geometries (e.g., in medical stents, valves etc.), not immediately amenable to conventional mechanical testing. The objective of this work was to study the deformation behavior of NiTi SMAs using instrumented indentation. This involved devising compliance calibration techniques to account for instrument deformation and designing spherical diamond indenters. Substantial quantitative information related to the deformation behavior of the shape memory and superelastic NiTi was obtained for the first time, as opposed to existing qualitative indentation studies. For the case of shape memory NiTi, the elastic modulus of the B19' martensite prior to twinning was determined using spherical indentation to be about 101 GPa, which was comparable to the value from neutron diffraction and was substantially higher than typical values reported from extensometry (68 GPa in this case). Twinning at low stresses was observed from neutron diffraction measurements and was attributed to reducing the elastic modulus estimated by extensometry. The onset of predominantly elastic deformation of the twinned martensite was identified from the nanoindentation response and the elastic modulus of the twinned martensite was estimated to be about 17 GPa. Finite element modeling was used to validate the measurements. For the case of the superelastic NiTi, the elastic modulus of the parent austenite was estimated to be about 62 GPa. The onset of large-scale stress induced martensite transformation and its subsequent elastic deformation were identified from the nanoindentation response. The effect of cycling on the mechanical behavior of the NiTi specimen was studied by repeatedly indenting at the same location. An increase in the elastic modulus value for the austenite and a decrease in the associated hysteresis and residual depth after the initial few cycles followed by stabilization were observed. As for the case of shape memory NiTi, finite element modeling was used to validate the measurements. This work has initiated a methodology for the quantitative evaluation of shape memory and superelastic NiTi alloys with instrumented spherical indentation. The aforementioned results have immediate implications for optimizing thermomechanical processing parameters in prototype button melts and for the mechanical characterization of intricate SMA geometries (e.g., in medical stents, valves etc.) This work was made possible by grants from NASA (NAG3-2751) and NSF (CAREER DMR-0239512) to UCF.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
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Vachhani, Shraddha J. "Stored energy maps in deformed metals using spherical nanoindentation". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51813.
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Microstructure changes that occur during the deformation and heat treatments involved in wrought processing of metals are of central importance in achieving the desired properties or performance characteristics in the finished products. However, thorough understanding of the evolution of microstructure during thermo-mechanical processing of metallic materials is largely hampered by lack of methods for characterizing reliably their local (anisotropic) properties at the sub-micron length scales. Recently, remarkable advances in nanoindentation data analysis techniques have been made which now make it possible to obtain quantitative information about the local mechanical properties of constituent individual grains in polycrystalline metallic samples. In this work, a novel approach that combines mechanical property information obtained from spherical nanoindentation with the complementary structure information measured locally at the indentation site, using Electron Backscattered Diffraction (EBSD), is used to systematically investigate the local structure-property relationships in fcc metals. This work is focused on obtaining insights into the changes in local stored energies of polycrystalline metallic samples as a function of their crystal orientation at increasing deformation levels. Furthermore, using the same approach, the evolution of mechanical properties in the grain boundary regions in these samples is studied in order to better understand the role of such interfaces during deformation and recrystallization processes. The findings provide valuable information regarding development of stored energy gradients in polycrystalline materials during macroscopic deformation.
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GutieÌrrez, Berasategui R. Eva. "Determining the properties of thin-coated systems by nanoindentation". Thesis, University of Newcastle Upon Tyne, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399329.
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Rastegar, Tohid Reza. "Nanoindentation of metallic materials : time-dependent and crystallographic effects". Thesis, University of Newcastle Upon Tyne, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445580.
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Lim, Yong Yee. "Nanoindentation hardness studies of metallic surfaces and thin films". Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268686.
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ALMEIDA, CLARA MUNIZ DA SILVA DE. "CHARACTERIZATION OF MECHANICAL DEFECTS PRODUCED BY NANOINDENTATION IN INP". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=13442@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONesta tese foi estudado o mecanismo de deformação mecânica de semicondutores III-V, em especial do InP, através da criação de defeitos utilizando um microscópio de força atômica e o indentador Triboscope. A liberdade de torção da ponta do AFM dificulta o controle e a reprodutibilidade dos experimentos de nanoindentação, por outro lado, através desta liberdade da técnica foi possível medir a pressão necessária para a criação das primeiras discordâncias no cristal. Foi realizado um estudo da deformação mecânica do óxido nativo presente na superfície do InP(100) e do GaAs(001) através de indentações utilizando o nanoindentador. Impressões plásticas residuais atribuídas à camada de óxido nativo foram observadas na superfície dos semicondutores. O processo de deformação plástica do InP foi estudado a partir de nanoindentações utilizando uma ponta Berkovich e uma ponta conosférica. O processo de deformação do InP com a ponta Berkovich apresenta descontinuidades para indentações realizadas com altas forças que são associadas a sucessivos escorregamentos de planos {111} seguidos de travamento das discordâncias. A distribuição de pressão na região indentada para a ponta conosférica é isotrópica, permitindo uma melhor visualização da transição elástico/plástico da deformação do material. Para essa ponta a deformação plástica do InP é iniciada com um evento catastrófico, que aparece nas curvas de indentação como uma descontinuidade. Foram observadas características ao redor das indentações, indicando o aparecimento de discordâncias na superfície do cristal. Microscopia eletrônica de transmissão foi utilizada para a observação das seções transversais das indentações que apresentaram alta densidade de discordâncias formadas pelos planos {111} escorregados.
In this thesis, the mechanical deformation mechanism of semiconductors III-V was studied, especially for InP. Defects were produced by indentations using an atomic force microscope and a Triboscope nanoindenter. The AFM tip torsion during indentation difficult the control and the reproducibility of AFM nanoindentation experiments. Nevertheless, the tip torsion allowed the measurement of the materials Yield stress. A study of the mechanical deformation mechanism of the native oxide that is presented in the surface of InP (100) and GaAs (100) was done. The residual plastic impressions attributed to native oxides were observed on the semiconductors surface. The plastic deformation process of the InP was studied in nanoindentation experiments using a Berkovich and a conosferical tip. The InP deformation mechanism observed with a Berkovich tip presents discontinuities for indentations performed at high loads, that are associated with successive slip of {111} planes along the <110> directions. The pressure distribution on the indented region, applied by the conosferical tip, is isotropic allowing a better visualization of the elastic/plastic transition in a material deformation process. The plastic deformation of InP using this tip is initialized with a catastrophic event, that appears in the indentation curves as a discontinuity. Small cracks were observed around the indentations using both tips, suggesting that some dislocations loops ends on the InP surface. Bigger cracks were observed in indentations with the conosferical tip and they were attributed to material fracture produced by the locking of dislocations near the surface. Transmission electron microscopy was done in the nanoindentation cross section showing a high density of defects created by the slip of the {111} planes.
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Delafargue, A. (Antoine) 1981. "Material invariant properties of shales : nanoindentation and microporoelastic analysis". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28625.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2005.Includes bibliographical references (p. 228-236).
Shales compose the major part of sedimentary rocks and cover most of hydrocarbon bearing reservoirs. Shale materials are probably one of the most complex natural composites, and their mechanical properties are still an enigma that has deceived many decoding attempts from experimental and theoretical sides. Advanced experimental techniques, such as nanoindentation, and theoretical microporomechanics make it possible today to break such a heterogeneous material down to a scale where physical chemistry meets mechanics, to extract intrinsic material properties that do not change from one material to another, and to upscale the intrinsic material behavior from the submicroscale to the macroscale of engineering application. This thesis identifies material invariant properties of shales by investigating the elastic properties of shales at multiple scales. We combine new experimental data of shale microstructure and mechanical properties, with nanoindentation analysis and microporomechanics. This leads to the development of a novel multiscale upscaling model for shale poroelasticity. The proposed model relies on a few quantities that can be easily obtained from mineralogy and porosity data. This model is calibrated and validated, and its domain of application and limitations are discussed. The strong predictive capabilities of the model are particularly important for the Oil and Gas Industry, which can apply our predictive model of shale elasticity for geophysics and exploitation engineering applications.
by A. Delafargue.
S.M.
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Venkovic, Nicolas. "Nanoindentation relaxation study and micromechanics of Cement-Based Materials". Master's thesis, Université Laval, 2016. http://hdl.handle.net/20.500.11794/27066.
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Ce travail évalue le comportement mécanique des matériaux cimentaires à différentes échelles de distance. Premièrement, les propriétés mécaniques du béton produit avec un bioplastifiant à base de microorganismes efficaces (EM) sont etudiées par nanoindentation statistique, et comparées aux propriétés mécaniques du béton produit avec un superplastifiant ordinaire (SP). Il est trouvé que l’ajout de bioplastifiant à base de produit EM améliore la résistance des C–S–H en augmentant la cohésion et la friction des nanograins solides. L’analyse statistique des résultats d’indentation suggère que le bioplastifiant à base de produit EM inhibe la précipitation des C–S–H avec une plus grande fraction volumique solide. Deuxièmement, un modèle multi-échelles à base micromécanique est dérivé pour le comportement poroélastique de la pâte de ciment au jeune age. L’approche proposée permet d’obtenir les propriétés poroélastiques requises pour la modélisation du comportoment mécanique partiellement saturé des pâtes de ciment viellissantes. Il est montré que ce modèle prédit le seuil de percolation et le module de Young non drainé de façon conforme aux données expérimentales. Un metamodèle stochastique est construit sur la base du chaos polynomial pour propager l’incertitude des paramètres du modèle à travers plusieurs échelles de distance. Une analyse de sensibilité est conduite par post-traitement du metamodèle pour des pâtes de ciment avec ratios d’eau sur ciment entre 0.35 et 0.70. Il est trouvé que l’incertitude sous-jacente des propriétés poroélastiques équivalentes est principalement due à l’énergie d’activation des aluminates de calcium au jeune age et, plus tard, au module élastique des silicates de calcium hydratés de basse densité.This work assesses the mechanical behavior of cement-based materials through different length scales. First, the mechanical properties of concrete produced with effective microorganisms (EM)-based bioplasticizer are investigated by means of statistical nanoindentation, and compared to the nanomechanical properties of concrete produced with ordinary superplasticizer (SP). It is found that the addition of EM-based bioplasticizer improves the strength of C–S–H by enhancing the cohesion and friction of solid nanograins. The statistical analysis of indentation results also suggests that EM-based bioplasticizer inhibits the precipitation of C–S–H of higher density. Second, a multiscale micromechanics-based model is derived for the poroelastic behavior of cement paste at early age. The proposed approach provides poroelastic properties required to model the behavior of partially saturated aging cement pastes. It is shown that the model predicts the percolation threshold and undrained elastic modulus in good agreement with experimental data. A stochastic metamodel is constructed using polynomial chaos expansions to propagate the uncertainty of the model parameters through different length scales. A sensitivity analysis is conducted by post-treatment of the meta-model for water-to-cement ratios between 0.35 and 0.70. It is found that the underlying uncertainty of the effective poroelastic proporties is mostly due to the apparent activation energy of calcium aluminate at early age and, later on, to the elastic modulus of low density calcium-silicate-hydrate.
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Guduguntla, Varun. "Effects of Thermostats in Molecular Dynamics Simulations of Nanoindentation". University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1573573614853041.
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Hemmasizadeh, Ali. "Characterization of Heterogeneous Material Properties of Aorta Using Nanoindentation". Diss., Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/240046.
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Mechanical EngineeringPh.D.
Arterial mechanical properties have received increasing attention in the past few decades due to their vast effect on predicting cardiovascular diseases and injuries. The heterogeneity of thoracic aortic tissue was characterized in terms of viscoelastic material properties and correlations were obtained between these properties and tissue morphology. Additionally, the effect of material preservation on the material properties was determined. Changes in the mechanical properties of porcine thoracic aorta wall in the radial direction were characterized using a quasi-linear viscoelastic modeling of nanoindentaiton tests. Two layers of equal thickness were mechanically distinguishable in descending aorta based on the radial variations in the instantaneous Young's modulus E and reduced relaxation function G(t). Overall, comparison of E and Ginf of the outer half (70.27±2.47 kPa and 0.35±0.01) versus the inner half (60.32±1.65 kPa and 0.33±0.01) revealed that the outer half was stiffer and showed less relaxation. The results were used to explain local mechanisms of deformation, force transmission, tear propagation and failure in arteries. A multimodal and multidisciplinary approach was adopted to characterize the transmural morphological properties of aorta. The utilized methods included histology and multi-photon microscopy for describing the wall micro-architecture in the circumferential-radial plane, and Fourier-Transform infrared imaging spectroscopy for determining structural protein, and total protein content. The distributions of these quantified properties across the wall thickness of the porcine descending thoracic aorta were characterized and their relationship with the mechanical properties was determined. It was revealed that there is an increasing trend in mechanical stiffness, Elastic lamella Density (ELD), Structural Protein (SPR), Total Protein (TPR), and Elastin and Collagen Circumferential Percentage (ECP and CCP) from inner layers toward the outer ones. Finally two larger regions with equal thickness (inner and outer halves) were determined based on cluster analysis results of ELD which were in agreement with the cluster analysis of instantaneous Young's modulus. Changes to the local viscoelastic properties of fresh porcine thoracic aorta wall due to three common storage temperatures (+4 oC, -20 oC and -80 oC) within 24 hours, 48 hours, 1 week and 3 weeks were characterized. The changes to both elastic and relaxation behaviors were investigated considering the multilayer, heterogeneous nature of the aortic wall. For +4 oC storage samples, the average instantaneous Young's modulus (E) decreased while their permanent average relaxation amplitude (Ginf) increased and after 48 hours these changes became significant (10%, 13% for E, Ginf respectively). Generally, in freezer storage, E increased and Ginf showed no significant change. In prolonged preservation (> 1 week), the results of +20 oC storage showed significant increase in E (20% after 3 weeks) while this increase for -80 oC was not significant, making it a better choice for tissue cold storage applications. Results from this dissertation present a substantial step toward the anatomical characterization of the aortic wall building blocks and establishing a foundation for understanding the role of microstructural components on the functionality of blood vessels. A better understanding of these relationships would provide novel therapeutic targets and strategies for the prevention of human vascular disease.
Temple University--Theses
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Du, Ke. "Noval nanoindentation-based techniques of MEMS and microfluidics applications". [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002778.
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Cakiroglu, Dilek. "An exploratory investigation of viscoelastic nanoindentation on polyvinyl acetate". Click HERE to connect, 2009. http://digital.library.okstate.edu/etd/Cakiroglu_okstate_0664M_10174.pdf.
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