Examinando por Materia "Indentation"

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    Comparative studies of the feed gas composition effects on the characteristics of DLC films deposited by magnetron sputtering
    (ELSEVIER SCIENCE SA, 2004-07-01) Libardi, J.; Grigorov, K.; Massi, M.; Otani, C.; Ravagnani, S.P.; Maciel, H.S.; Guerino, M.; Ocampo, J.M.J.; Libardi, J.; Grigorov, K.; Massi, M.; Otani, C.; Ravagnani, S.P.; Maciel, H.S.; Guerino, M.; Ocampo, J.M.J.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)
    Mixtures of acetylene/argon and methane/argon with different volume percents of hydrocarbon were used as the precursor gas to grow DLC films, keeping constant the other process parameters. The substrates used were p-type (100) silicon wafers. The films were characterized by Raman spectroscopy, nanoindentation, atomic force microscopy (AFM) and by a profilometer. In order to grow DLC films with special properties that could make this material an alternative candidate for applications in micro-electromechanical systems (MEMS) production, a comparative analysis focused on the influence of the hydrocarbon precursor gas mixture on the mechanical and chemical properties of the DLC films is reported. © 2004 Elsevier B.V. All rights reserved.
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    Hardness of thermal sprayed coatings: Relevance of the scale of measurement
    (ELSEVIER SCIENCE SA, 2015-04-25) Chicot, D.; Ageorges, H.; Voda, M.; Louis, G.; Ben Dhia, M.A.; Palacio, C.C.; Kossman, S.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    The coatings obtained by thermal spraying can present a large variety of geometrical parameters (thickness, roughness...), of microstructures (constituents, nature of phases...), of mechanical properties (hardness, elastic modulus...) and of morphological defects (cracks, pores...) depending on the spraying conditions. In order to determine the mechanical properties of the coating, one of the most relevant techniques is probably the instrumented indentation test. Nowadays this technique is very attractive since it allows the determination of numerous parameters. Moreover, recent developments allow the use of a phenomenological approach and modeling at different scales of measurement, from nano (even ultra-nano) to macro scale, i.e. from few milligrams to several kilograms of loading. However, the information, which can be extracted at the different regimes of loading can be the same or lead to different values of the mechanical properties, which can be complementary or contradictory depending on the nature of the coating and the preparation of the sample. For example, roughness, porosity and cracks present in the coating will affect the mechanical characterization since the indentation data analysis is based on how a rigid indenter penetrates into the material. So, an important question arises: Should the influence of these defects to be taken into account, or neglected, for the mechanical characterization? The present work proposes different methodologies for determining the hardness of coated materials by considering or not the influence of both the porosity and roughness of the surface. In the first part, results of microindentation experiments performed on the rough surface of alumina coatings are compared to those obtained on a polished cross-section. Although the surface of the cross-section is irregular even after caution polishing, the hardness can be measured. A decrease of about 30% of the hardness number on the cross-section is observed. The second part is related to the microstructured yttria-stabilized zirconia analysis. A methodology based on the indentation size effect analysis is presented to avoid the influence of roughness and the defects, which can be crossed by the indenter during the indentation. This methodology allows the hardness determination of the coating exempt of defects. In the last part, a statistical analysis using nanoindentation data resulting from the continuous stiffness measurement mode applied to nanostructured yttria-stabilized zirconia shows that, even if the hardness number varies to a great extent according to the applied load and the location of the indent, the hardness can be represented by means of a unique hardness number independent of the sense of the hardness variation during the indenter displacement. (C) 2014 Elsevier B.V. All rights reserved.
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    Indentación esférica en asfaltos envejecidos
    (Universidad EAFIT, 2022) D paola Puche, Plinio; Vidal Valencia, Julián
    Permanent deformation is one of the most frequent failures produced in the asphalt pavement, mainly in heavy and low-speed traffic lanes. Predicting this type of defect is made difficult by the high complexity of asphalt, since it is a thermoplastic material that exhibits linear viscoelastic behavior at low loads and nonlinear viscoelastic behavior at high loads. Its behavior also varies due to oxidative aging, produced by environmental effects throughout its useful life, which makes its prediction more complicated. The tests used for its analysis are highly expensive and often require a large number of destructive laboratory tests, which sometimes fail to reproduce the same environmental and support conditions of the tracks. In this work, it is proposed to use the spherical indentation method, for asphalts aged by the mechanical agitation test at high revolutions, which are economic tests that use easily accessible equipment for any pavement laboratory, such as the manual penetrometer (previously established for spherical indentation calculations) and a conventional double helix mechanical stirrer (used in the oxidative aging process). This method was used in a conventional asphalt AC 60-70, aged in times of 30 min, 1 hour, 1.5 hours, 2 hours, 2.5 hours and 3 hours, in order to determine the variation of its properties as it increases. the effect of aging.
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    Inverse-FEM Characterization of a Brain Tissue Phantom to Simulate Compression and Indentation
    (Universidad EAFIT, 2012-12-01) Mesa-Múnera, Elizabeth; Ramírez–Salazar, Juan F; Boulanger, Pierre; W Branch, John; Universidad Nacional de Colombia; Universidad Nacional de Colombia; University of Alberta; Universidad Nacional de Colombia
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    Spherical indentation behavior of asphalt mixtures
    (ASCE-AMER SOC CIVIL ENGINEERS, 2007-01-01) Ossa, E.A.; Collop, A.C.; Ossa, E.A.; Collop, A.C.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de Ingeniería
    The spherical indentation response of a dense bitumen macadam asphalt mixture with two different volume fractions of bitumen binder is investigated both experimentally and via an analytical model. The model for the indentation of bitumen developed by Ossa et al. in 2005, was used to study the spherical indentation behavior of the mixtures with good agreement when compared to experimental results. An extensive experimental study of the monotonic and recovery spherical indentation behavior is reported for a range of temperatures. In line with the predictions of the model, the monotonic indentation response of the mixtures exhibits a power-law dependence on the indentation force. The model is also successful in capturing the indentation recovery behavior of the mixtures. A comparison of the material parameters obtained from uniaxial compression and indentation tests showed that indentation tests can be used in an easy and reliable way to obtain the fundamental asphalt parameters. Further, parameters found from indentation tests implicitly account for the confining conditions generated by the aggregate particles below the indenter. © 2007 ASCE.