Examinando por Autor "Ossa, E.A."
Mostrando 1 - 10 de 10
Resultados por página
Opciones de ordenación
Ítem Análisis de falla de la mordaza plana de una prensa hidráulica(IMPRENTA UNIV ANTIOQUIA, 2008-01-01) Ossa, E.A.; Paniagua, M.A.; Ossa, E.A.; Paniagua, M.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaThis paper describes the analysis and investigation of the causes of the failure of an hydraulic press jaw face grip. Analysis of the fractured surfaces indicated the creation of cracks due to stress concentrators as a result of defective design. On the other hand, metallographic examination revealed the presence of aligned clusters of primary carbides that along with the stress concentrators induced the premature failure of the grip.Ítem Contributions of intermolecular bonding and lubrication to the mechanical behavior of a natural armor(ELSEVIER SCI LTD, 2020-01-01) Jiang, H.; Ghods, S.; Weller, E.; Waddell, S.; Ossa, E.A.; Yang, F.; Arola, D.; Jiang, H.; Ghods, S.; Weller, E.; Waddell, S.; Ossa, E.A.; Yang, F.; Arola, D.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaAmong many dermal armors, fish scales have become a source of inspiration in the pursuit of “next-generation” structural materials. Although fish scales function in a hydrated environment, the role of water and intermolecular hydrogen bonding to their unique structural behavior has not been elucidated. Water molecules reside within and adjacent to the interpeptide locations of the collagen fibrils of the elasmodine and provide lubrication to the protein molecules during deformation. We evaluated the contributions of this lubrication and the intermolecular bonding to the mechanical behavior of elasmodine scales from the Black Carp (Mylopharyngodon piceus). Scales were exposed to polar solvents, followed by axial loading to failure and the deformation mechanisms were characterized via optical mechanics. Displacement of intermolecular water molecules by liquid polar solvents caused significant (p = 0.05) increases in stiffness, strength and toughness of the scales. Removal of this lubrication decreased the capacity for non-linear deformation and toughness, which results from the increased resistance to fibril rotations and sliding caused by molecular friction. The intermolecular lubrication is a key component of the “protecto-flexibility” of scales and these natural armors as a system; it can serve as an important component of biomimetic-driven designs for flexible armor systems. Statement of Significance: The natural armor of fish has become a topic of substantial scientific interest. Hydration is important to these materials as water molecules reside within the interpeptide locations of the collagen fibrils of the elasmodine and provide lubrication to the protein molecules during deformation. We explored the opportunity for tuning the mechanical behavior of scales as a model for next-generation engineering materials by adjusting the extent of hydrogen bonding with polar solvents and the corresponding interpeptide molecular lubrication. Removal of this lubrication decreased the capacity for non-linear deformation and toughness due to an increase in resistance to fibril rotations and sliding as imparted by molecular friction. We show that intermolecular lubrication is a key component of the “protecto-flexibility” of natural armors and it is an essential element of biomimetic approaches to develop flexible armor systems. © 2020 Acta Materialia Inc.Ítem Effect of aging on the microstructure, hardness and chemical composition of dentin(PERGAMON-ELSEVIER SCIENCE LTD, 2015-12-01) Montoya, C.; Arango-Santander, S.; Peláez-Vargas, A.; Arola, D.; Ossa, E.A.; Montoya, C.; Arango-Santander, S.; Peláez-Vargas, A.; Arola, D.; Ossa, E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaObjective: Understanding the effects of biological aging on human tissues has been a topic of extensive research. With the increase in healthy seniors and quality of life that topic is becoming increasingly important. In this investigation the effects of aging on the microstructure, chemical composition and hardness of human coronal dentin was studied from a comparison of teeth within ``young'' and ``old'' age groups. Methods: The microstructure of dentin within three regions (i.e., inner, middle and outer) was analyzed using electron and optical microscopy. The mineral-to-collagen ratio in these three regions was estimated using Raman spectroscopy and the hardness was evaluated using microindentation. Results: Results showed that there were significant differences in tubule density, tubule diameter and peritubular cuff diameter with depth. Although there was no difference in tubule density and diameter of the tubules between the age groups, there was a significant difference in the occlusion ratio. A significant increase in hardness between young and old patients was found for middle and outer dentin. An increase in mineral-to-collagen ratio from inner to outer dentin was also found for both groups. In old patients, an increase in mineral content was found in outer coronal dentin as a consequence of tubule occlusion. Conclusions: An increase in occlusion ratio, hardness, and mineral content was found in the dentin of adult patients with age. This increase is most evident in the outer coronal dentin. (C) 2015 Elsevier Ltd. All rights reserved.Ítem 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 Failure analysis of a fastener system and its analytical prediction(2009-01-01) Ossa, E.A.; Paniagüa, M.A.; Ossa, E.A.; Paniagüa, M.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaThis paper describes the failure analysis performed for a fastener system commonly used in civil construction. This system was manufactured using AISI-SAE 1045 steel and showed unusual sudden cracking while a preload was applied under normal working conditions. An exhaustive study aiming to find the cause or causes of this unusual cracking, including experimental work and analytical prediction, is the main objective of this work. Experimental techniques like fractography, metallographic inspection and spectrometry revealed defective manufacture and processing techniques of the elements. Furthermore, microstructural analysis revealed the presence of Widmanstatten ferrite which induces a fragile behaviour of the material. An analysis of the applied stresses on the fastener during preloading using a proposed analytical method demonstrated the presence of elevated loads that caused the initiation of cracks along the length of the fastener. This premature failure could be avoided if a proper heat treatment was applied to the fasteners. The analytical model, based on Lamé's theory, is considered an easy to use tool in order to predict the failure of similar fasteners and mechanical elements.Ítem Importance of tubule density to the fracture toughness of dentin(PERGAMON-ELSEVIER SCIENCE LTD, 2016-07-01) Montoya, C.; Arola, D.; Ossa, E.A.; Montoya, C.; Arola, D.; Ossa, E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaObjective: The fracture toughness of dentin is critical to the prevention of tooth fracture. Within the tooth crown, the mechanical properties of dentin are influenced by spatial variations in the density and diameter of the dentin tubules with distance from the pulp. There are also relevant changes to the microstructure of dentin with age. In this investigation the importance of tubule density to the fracture toughness of dentin was evaluated in ``young'' and ``old'' age groups. Methods: The variations in microstructure (density and diameter of tubules) from young and old donor teeth were studied by means of optical microscopy. Results: A reduction in the density and diameter of tubules was identified to occur with aging. An approach previously proposed to study the mechanical behavior of porous materials was used to model the fracture toughness of coronal dentin in terms of the tubule characteristics. Results were then compared with published results from previous studies. Conclusions: The model predictions were consistent with experimental results for the fracture toughness of dentin from young donor teeth, but overestimated the values that have been reported for ``old'' dentin. (C) 2016 Elsevier Ltd. All rights reserved.Ítem 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 IngenieríaThe 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.Ítem Suspension and landing gear failures(Elsevier Inc., 2015-01-01) Ossa, E.A.; Paniagua, M.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaFailure of landing gears in aircrafts represents approximately a 10% of the total of failures reported for the aerospace industry. This chapter discusses the main causes of these failures, their prevention, and a complete analysis of three cases of failure of this kind of components. On the other hand, failures of suspension systems in vehicles represent approximately a 13% of the total of failures for the automotive industry. In this industry, it is a common practice to replace failed parts without any further investigation of the root causes of failure, which can make the amount of failures to be underestimated. This chapter will discuss the main types and causes of failures of suspension systems. One case of failure of this kind of components will be analyzed and discussed in detail. © 2016 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 Time-dependent Mechanical Response at the Nanoscale(Elsevier B.V., 2020-01-01) Múnera, J.C.; Goswami, D.; Martinez, R.V.; Ossa, E.A.; Múnera, J.C.; Goswami, D.; Martinez, R.V.; Ossa, E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaModern nanofabrication processes on metals, polymers, and ceramics often require deforming these materials at strain rates ranging ~101 – 107 s–1. Therefore, there is a need to develop an appropriate methodology capable of measuring and predicting the effects of these deformation rates on the final mechanical response of the nanomaterial being processed. Here we report an experimental study of the indentation response of three materials with different nature and mechanical properties, but with known time-dependent mechanical responses. These materials allow validation of the findings under a wide variety of conditions. One metal (Pb), and two polymers (PMMA and PS), were indented at the sub-20 nm scale using commercial atomic force microscopy (AFM) probes. Based on our experimental findings, we also propose an analytical model for creeping solids in which their nanoscale mechanical behavior is completely described by two components: an elastic component (characterized by the Hertz contact model) and a time-dependent component (characterized by a power-law model). The proposed experimental protocol is easy to implement, and the analytical model can be extended to a large variety of materials. The ability to characterize the time-dependence of the mechanical response of different materials at the nanoscale will enable a better estimation of the effect of manufacturing processes on the properties and performance of nanomaterials. © 2020 Elsevier Ltd