Examinando por Materia "Microstructure"
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Ítem Designed for resistance to puncture: The dynamic response of fish scales(ELSEVIER SCIENCE BV, 2019-01-01) Ghods S.; Murcia S.; Ossa E.A.; Arola D.; Ghods S.; Murcia S.; Ossa E.A.; Arola D.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaNatural dermal armors are serving as a source of inspiration in the pursuit of “next-generation” structural materials. Although the dynamic strain response of these materials is arguably the most relevant to their performance as armors, limited work has been performed in this area. Here, uniaxial tension and transverse puncture tests were performed on specimens obtained from the scales of Asian carp over strain rates spanning seven decades, from 10-4 to 103 s-1. The importance of anatomical variations was explored by comparing the performance of scales from the head, middle and tail regions. In both loading orientations, the scales exhibited a significant increase in the resistance to failure with loading rate. The rate sensitivity was substantially higher for transverse loading than for in-plane tension, with average strain rate sensitivity exponents for measures of the toughness of 0.35 and 0.08, respectively. Spatial variations in the properties were largest in the puncture responses, and scales from the head region exhibited the greatest resistance to puncture overall. The results suggest that the layered microstructure of fish scales is most effective at resisting puncture, rather than in-plane tension, and its effectiveness increases with rate of loading. X-ray microCT showed that delamination of plies in the internal elasmodine and stretching of the fibrils were key mechanisms of energy dissipation in response to puncture loading. Understanding contributions from the microstructure to this behavior could guide the development of flexible engineered laminates for penetration resistance and other related applications. © 2018 Elsevier LtdÍtem Differences in the microstructure and fatigue properties of dentine between residents of North and South America.(PERGAMON-ELSEVIER SCIENCE LTD, 2014-10-01) Ivancik J; Naranjo M; Correa S; Ossa A; Tay FR; Pashley DH; Arola D; Universidad EAFIT. Departamento de Ingeniería Mecánica; Bioingeniería GIB (CES – EAFIT)UNLABELLED: Spatial variations in the microstructure of dentine contribute to its mechanical behaviour. OBJECTIVE: The objective of this investigation was to compare the microstructure and fatigue behaviour of dentine from donors of two different countries. METHODS: Caries-free third molars were obtained from dental practices in Colombia, South America and the US to assemble two age-matched samples. The microstructure of the coronal dentine was evaluated at three characteristic depths (i.e. deep, middle and superficial dentine) using scanning electron microscopy and image processing techniques. The mechanical behaviour of dentine in these three regions was evaluated by the fatigue crack growth resistance. Cyclic crack growth was achieved in-plane with the dentine tubules and the fatigue crack growth behaviour was characterized in terms of the stress intensity threshold and the Paris Law parameters. RESULTS: There was no difference in the tubule density between the dentine of patients from the two countries. However, there were significant differences (pÍtem Differences in the microstructure and fatigue properties of dentine between residents of North and South America.(PERGAMON-ELSEVIER SCIENCE LTD, 2014-10-01) Ivancik J; Naranjo M; Correa S; Ossa A; Tay FR; Pashley DH; Arola D; Universidad EAFIT. Departamento de Ingeniería de Diseño; Ingeniería de Diseño (GRID)UNLABELLED: Spatial variations in the microstructure of dentine contribute to its mechanical behaviour. OBJECTIVE: The objective of this investigation was to compare the microstructure and fatigue behaviour of dentine from donors of two different countries. METHODS: Caries-free third molars were obtained from dental practices in Colombia, South America and the US to assemble two age-matched samples. The microstructure of the coronal dentine was evaluated at three characteristic depths (i.e. deep, middle and superficial dentine) using scanning electron microscopy and image processing techniques. The mechanical behaviour of dentine in these three regions was evaluated by the fatigue crack growth resistance. Cyclic crack growth was achieved in-plane with the dentine tubules and the fatigue crack growth behaviour was characterized in terms of the stress intensity threshold and the Paris Law parameters. RESULTS: There was no difference in the tubule density between the dentine of patients from the two countries. However, there were significant differences (pÍtem Differences in the microstructure and fatigue properties of dentine between residents of North and South America.(PERGAMON-ELSEVIER SCIENCE LTD, 2014-10-01) Ivancik J; Naranjo M; Correa S; Ossa A; Tay FR; Pashley DH; Arola D; Ivancik J; Naranjo M; Correa S; Ossa A; Tay FR; Pashley DH; Arola D; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaUNLABELLED: Spatial variations in the microstructure of dentine contribute to its mechanical behaviour. OBJECTIVE: The objective of this investigation was to compare the microstructure and fatigue behaviour of dentine from donors of two different countries. METHODS: Caries-free third molars were obtained from dental practices in Colombia, South America and the US to assemble two age-matched samples. The microstructure of the coronal dentine was evaluated at three characteristic depths (i.e. deep, middle and superficial dentine) using scanning electron microscopy and image processing techniques. The mechanical behaviour of dentine in these three regions was evaluated by the fatigue crack growth resistance. Cyclic crack growth was achieved in-plane with the dentine tubules and the fatigue crack growth behaviour was characterized in terms of the stress intensity threshold and the Paris Law parameters. RESULTS: There was no difference in the tubule density between the dentine of patients from the two countries. However, there were significant differences (pÍtem Effect of chemical composition and microstructure on the mechanical behavior of fish scales from Megalops Atlanticus(ELSEVIER SCIENCE BV, 2016-03-01) Gil-Duran, S.; Arola, D.; Ossa, E.A.; Gil-Duran, S.; Arola, D.; Ossa, E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaThis paper presents an experimental study of the composition, microstructure and mechanical behavior of scales from the Megalops Atlanticus (Atlantic tarpon). The microstructure and composition were evaluated by Scanning Electron Microscopy (SEM) and RAMAN spectroscopy, respectively. The mechanical properties were evaluated in uniaxial tension as a function of position along the length of the fish (head, mid-length and tail). Results showed that the scales are composed of collagen and hydroxyapatite, and these constituents are distributed within three well-defined layers from the bottom to the top of the scale. The proportion of these layers with respect to the total scale thickness varies radially. The collagen fibers are arranged in plies with different orientations and with preferred orientation in the longitudinal direction of the fish. Results from the tensile tests showed that scales from Megalops Atlanticus exhibit variations in the elastic modulus as a function of body position. Additional testing performed with and without the highly mineralized top layers of the scale revealed that the mechanical behavior is anisotropic and that the highest strength was exhibited along the fish length. Furthermore, removing the top mineralized layers resulted in an increase in the tensile strength of the scale. © 2015 Elsevier Ltd.Ítem Envejecimiento termo-oxidativo de asfaltos(Universidad EAFIT, 2014) Gamarra Escamilla, AdrianaÍtem Influence of substrate temperature on the microstructure of TiN/TiC(Universidad EAFIT, 2011-12-01) Devia, D M; Mesa, Fernando; Arango, Pedro José; Universidad Tecnológica de Pereira; Universidad Tecnológica de Pereira; Universidad Nacional de Colombia, sede ManizalesÍtem Mechanical responses of plasma sprayed coatings from residual stress measurements and finite element analysis: Effect of the pore network architecture(Universidad de Tarapaca, 2011-01-01) Espinosa, C.C.P.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)This study aims a better understanding residual stress and stress field within composite plasma sprayed coatings submitted to strains. In order to reach out this objective, residual stress techniques can be implemented for measurements during elaboration of coatings and finite element analyses (FEA) can be conducted on domains resulting from the discretization of Scanning Electron Microscopy (SEM) high resolution pictures of coating structures. TiO 2-Cu and Al 2O 3-13TiO 2 plasma sprayed coatings were considered for demonstrative purposes regarding residual stress measurements and effect of the pore network architecture, respectively. Several operating parameters permitted to manufacture coatings exhibiting different magnitude of residual stress and several porous architectures, in terms of pore content, crack density and crack orientation. Residual stress determined from measurements of deflection during elaboration of TiO 2-Cu coatings allow to identify their nature while numerical simulations show the very significant influence of the network architecture on the stress field within the Al 2O 3-13TiO 2 coatings. Based on the same analyzed structures, other theoretical compositions were considered in the finite element analyses by modifying the intrinsic mechanical properties of the phases. For the considered cases, simulations show the poor influence of the nature of the secondary phase on the stress field within the coatings. Beside these results, the paper proposes a generic methodology and points out its advantages and limits, emphasizing in particular the importance of the representative elementary volume (REV).Ítem Study of APS and conventional sintering parameters for the manufacture of TiO2 targets for PAPVD(IOP PUBLISHING LTD, 2019-01-01) Jaramillo Raquejo D.; Palacio C.C.; Ageorges H.; Jaramillo Raquejo D.; Palacio C.C.; Ageorges H.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In surface science of functional oxides, titanium dioxide (TiO2) is one of the most investigated crystalline systems either in rutile or anatase phases. In this work commercial TiO2 powders are used to study the required process conditions to obtain TiO2 targets by Atmospheric Plasma Spray (APS) and conventional sintering, with suitable physical and chemical properties to be source material for Plasma Assisted Physical Vapor Deposition (PAPVD) for technological and medical applications. Two three factor Box Behnken experimental designs combined with surface modeling were employed to estimate the influence of spraying parameters (gun current, Ar/H2 ratio and standoff distance) and sintering parameters (heating rate, sintering temperature and holding time) within the targets microstructure (cracks and pores in cross section) and phases composition. The microstructure and composition of APS-deposited targets and sintered ones were characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The lowest defects percentages of the targets manufactured in this work were 0.41 ± 0.30 % for APS-deposited targets and 0.05 ± 0.04 % for the sintered ones using the optimal parameters suggested by the statistical model, which allowed confirming the advantages of sintering process and limitations of APS in terms of microstructural homogeneity, but also of the use of design of experiments in the modeling of systems of many variables when there is not diagnostic equipment of the processes available. © Published under licence by IOP Publishing Ltd.Ítem Temperature effects on the fracture resistance of scales from Cyprinus carpio(ELSEVIER SCI LTD, 2015-03-01) Murcia S; McConville M; Li G; Ossa A; Arola D; Murcia S; McConville M; Li G; Ossa A; Arola D; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaIn this investigation the fracture resistance of scales from Cyprinus carpio was evaluated as a function of environmental temperature. Tear specimens were prepared from scales obtained from three characteristic regions (i.e. head, mid-length and tail) of multiple fish. The fracture resistance was characterized in Mode III loading and over temperatures ranging from 150 degrees C to 21 degrees C. Results showed that there was a significant reduction in tear resistance with decreasing temperature and the lowest resistance to fracture was obtained at 150 degrees C. There was a significant difference in the relative tear toughness between scales from the three locations at ambient conditions (21 degrees C), but not below freezing. Scales obtained near the head exhibited the largest resistance to fracture (energy 150 25 kJ m(-2)) overall. The fracture resistance was found to be primarily dependent on the thickness of the external mineralized layer and the number of external elasmodine plies, indicating that both the anatomical position and the corresponding microstructure are important to the mechanical behavior of elasmoid fish scales. These variables may be exploited in the design of bioinspired armors and should be considered in future studies concerning the mechanical behavior of these interesting natural materials. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.Ítem Thermo-oxidative aging of bitumen(Taylor and Francis Ltd., 2018-07-03) Gamarra, A.; Ossa, E.A.; Gamarra, A.; Ossa, E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaThermo-oxidative bitumen ageing has been commonly recognised as the main cause of asphalt cracking. The effect of thermo-oxidative ageing level on bitumen has been studied in this work by means of a simple and effective mechanical stirring process. Physical characteristics of the material as Softening Point, Penetration and Viscosity were measured to samples with different ageing conditions. Chemical changes in the material were evaluated by means of SARA fractioning to measure the effect of ageing on the fundamental components of bitumen, and Infrared Spectroscopy in order to study the changes found on the oxidation-related compounds of the material. Microstructural changes on the material were evaluated using atomic force microscopy (AFM) finding that the ageing process on bitumen increases the number and size of the phases related to asphaltenes and resins, and decreases the amount of phases related to aromatics. The changes in chemical and physical characteristics of bitumen were found to be strongly dependent on the carbonyl formation. An extension to a previously proposed oxidation kinetics model was used to predict the fast rate (transient) and constant rate (steady-state) oxidation behaviour of bitumen and its relation to physical properties. The thermo-oxidative changes suffered by bitumen are associated with increasing hardening of the material, making it susceptible to cracking when in contact with aggregate as thin films in flexible pavements. © 2016 Informa UK Limited, trading as Taylor & Francis Group.Ítem Validation d’une approche numérique permettant la simulation du comportement des tôles d’épaisseur submillimétrique(Universidad EAFIT, 2008) Echeverri Restrepo, Sebastián; Bonnet, Nicolás; Lipinski, Pawel; Tidu, AlbertLes micropièces sont des pièces ou des structures qui ont des dimensions dans le domaine submillimétrique et sont très utilisées dans les dispositifs électroniques et micromécaniques -- Lors de leur fabrication il faut tenir compte d’un certain nombre de particularités dans leur comportement liés au changement d’échelle, appelés effets de taille -- Le premier objectif de ce travail de master est de valider une approche numérique proposée dans le cadre de la thèse de doctorat de BONNET [1] en faisant des mesures expérimentales pour comparer les résultats -- Le deuxième objectif consiste en avancer l’implémentation d’une autre approche numérique dans le code d’éléments finis ABAQUS® pour simuler un comportement plastique -- Dans un premier temps, une campagne d’essais expérimentaux a été menée pour obtenir des éprouvettes avec une épaisseur submillimétrique et une taille de grains moyenne de quelques millimètres -- Ceci, pour être sûr que les effets de taille seraient présentés -- Dans un deuxième temps, des essais expérimentaux en traction sont réalisés sur les éprouvettes préparées -- Sur ces éprouvettes sollicitées, des mesures de l’évolution des orientations cristallographiques et de la topographie sont faites -- Parallèlement, une modélisation numérique d’un essai de traction est mise en œuvre en utilisant la routine implémentée par BONNET [1] -- Finalement, les résultats obtenus avec les méthodes expérimentales et numériques sont comparés et analysés pour parvenir à un premier ensemble de conclusions