ÍtemMicrostructure and mechanical properties of fish scales from MegalopsAtlanticus(IEEE, 2013-01-01) Gil, S.; Ossa, E. A.; Gil, S.; Ossa, E. A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaThis work studies the microstructure and mechanical properties of fish scales from Tarpon fish (MegalopsAtlanticus) with cycloid scales. Mechanical properties of the scales were evaluated in uniaxial tension from three different positions along the length of the fish (head, mid-length and tail), similarly it was evaluated the effects of dehydration of the material in the mechanical properties, demonstrating an increased stiffness as a function of dehydrationas also reported Garrano et al. for CyprinusCarpio . Microstructural analysis revealed that the scaleis composed by different layers associated with collagen to form a plywood like structure and a top layer associated with hydroxyapatite, as it has just been reported by several authors to different fish species [2, 3, 4]. This combination of collagen and hydroxyapatitelayers allows the fish scaleto have a high penetration resistance . Microstructural analysis also reveals that the scale have a rugged circular concentric pattern on top to provide advantages associated with hydrodynamic, unlike the inner part of the scale that is in contact with the dermis which presents a smooth surface. Thus all these microstructural and mechanical characteristics are used by fish as drag reduction system, mobility and increase protection against predators, which are desirable features in engineering applications through the design of bioinspired materials. ÍtemNatural flexible armor as an inspirationfor body armor design(Soc. for the Advancement of Material and Process Engineering, 2015-05-21) Alexander Ossa, E.; Alexander Ossa, E.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaAnimals have developed different strategies to protect themselves from environmental and predatory threats. One of these strategies concerns with the development of natural flexible dermal armor, usually consisting of rigid and highly mineralized units (e. g. scales or osteoderms) attached by flexible collagen fibers. These kinds of arrangements have been proven to achieve high flexibility without significant reduction in strength in comparison to monolithic structures. These are in fact features extremely valued by body armor users. This work studies the mechanical characteristics of scales and osteoderms of different animals (including mammals, reptiles and fishes), in order to compare them with other characteristics of the animal itself (like length and mobility) and characteristics of their predators like geometry and composition of their teeth and strength of bite. This comparison extends our knowledge and open new ways of understanding on how to design body armor materials and structures looking into improvements on flexibility and mobility. Copyright 2015. Used by the Society of the Advancement of Material and Process Engineering with permission. ÍtemFailure 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. ÍtemMorphological and mechanical characteristics of rigid polyurethane foams(2009-01-01) Restrepo-Zapata, N.C.; Ossa H., E.A.; Mejia, F.C.; Restrepo-Zapata, N.C.; Ossa H., E.A.; Mejia, F.C.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaCellular materials are formed by solid cells in a gaseous core. They exhibit good strength to mass ratio and they are used as insulators and as a core in sandwich composite manufacture. This work describes an extensive study on the structure and physical-mechanical properties of rigid polyurethane (PU) foams. The effect of composition and processing conditions on the mechanical properties were studied. Morphology, specific strength and density were evaluated to determine the optimal levels of processing for a required application. Foam morphology was characterized using stereoscopy and optical microscopy. A basic mechanical property as compression strength was measured in the plateau zone.