High cycle fatigue of ARMCO iron severely deformed by ECAP

The high-cycle fatigue behavior of ARMCO iron severely deformed by Equal Channel Angular Pressing (ECAP) at room temperature through route Bc until 8 passes, with an average grain size of ~365 nm, was studied and compared with the same material in the annealed state with an average grain size of ~72 µm. The fatigue limit of the 8 passes ECAPed sample increased with respect to the annealed material by more than 250% rising from 274 MPa to 717 MPa. Striations and dimpled relief were observed on the fracture surfaces of the fatigued ultrafine and coarse grain fatigue samples. The microstructure was characterized by Electron Backscattered Diffraction (EBSD) before and after the fatigue tests and it was observed in both samples an increment in the fraction of Low Angle Grain Boundaries (LAGB) at high number of cycles to failure. A texture analysis for the materials after the fatigue failure was done. This study shown a preferential orientation towards the ¿ fiber for both conditions.Peer ReviewedPostprint (author's final draft

Innovación tecnológica en el proceso de producción de alimentos en la fábrica “la Matagalpa”, municipio de Matagalpa, año 2013

El presente trabajo expone un estudio realizado en la fábrica “La Matagalpa” sobre el proceso de producción de alimentos “Encurtidos a base de vegetales” con el objetivo de conocer las etapas de su producción, para determinar las principales dificultades que se encuentran en el proceso y proponer técnicas de innovación que ayuden a la empresa a mejorar su proceso. Este trabajo se enfoca en el estudio del proceso de producción que realizan en la empresa, teniendo como fundamentos para nuestro estudio, la calidad y productividad de la empresa, para esto es necesario identificar los elementos del sistema, las normas de higiene, la capacidad y disposición de los operarios en las gestiones a realizar dentro del proceso productivo. Actualmente la empresa cuenta con procesos manuales y cuenta con ayuda de pequeñas maquinarias para la elaboración de los distintos procesos, las instalaciones de la empresa podrían mejorar para brindar una mejor condición e higiene laboral, sin embargo el producto cumple con los requerimientos higiénicos exigidos. La empresa, a pesar de contar con cierto material, equipo y conocimientos necesarios para la producción de encurtidos, aún no ha adquirido una nueva cultura de calidad, productividad e innovación contínua en lo que se elabora, ente esto surgen aspectos que obstaculizan la calidad, la productividad y el éxito de la empresa. Entre estos el más influyente, la indisposición de sus directivos en la inversión, para generarles nuevos conocimientos a sus operarios a través de capacitaciones y la falta de actitud de los operarios hacia la mejora contínua. Existen distintos factores que puede afectar todo el proceso productivo, por ello se recomienda tomar en cuenta los distintos aspectos mencionados en la guía de recomendaciones los cuales están basados en las dificultades encontradas en la empresa y podría ser de ayuda para búsqueda de la calidad, productividad y el éxito de la empres

Supervisión de microseguros en Colombia

El supervisor financiero en Colombia, debe velar por el respeto de los derechos de los consumidores financieros por parte de las entidades captadoras de dinero. Dado el aumento de los microseguros en Colombia , la Superintendencia Financiera de Colombia con el ánimo de proteger los intereses del consumidor de esta clase de seguros, debe verificar que estos productos sean diseñados bajo criterios técnicos, financieros y jurídicos estables, brindando una real y oportuna cobertura a la población menos favorecida, por lo cual debe evaluar que estas primas de seguros que pagan los asegurados, signifiquen un verdadero respaldo y no una forma de captación de dineros por parte de las compañías de seguros, no ofreciendo ninguna contraprestación

Characterization of a hypoeutectic Al alloy obtained by selective laser melting

In this investigation, a hypoeutectic AlSi11Cu alloy was printed. This alloy was obtained in powder form with an average particle size of 40 µm. Bars 20 mm in diameter and 100 mm in length were printed with the building direction parallel to the bars' longitudinal direction. The microstructural characterization demonstrated an Al matrix surrounded by a Si network forming a coral-like pattern. The microstructure of the alloy showed a heterogeneous behavior with a mixture of columnar and equiaxed grains. Likewise, the texture indicated that the columnar grains were preferentially oriented towards the building direction, while the equiaxed followed a texture dominated by the cube component. On the other hand, the as-printed material strength showed higher values than those obtained in the same alloy using conventional processes such as casting. In addition, strength and ductility differences were found in the printed material, depending on the measurement direction. The highest values were obtained in the radial direction (565 MPa maximum strength and 4.8% elongation to failure). The lowest values corresponded to the transverse direction (508 MPa maximum strength and 3.2 elongation to failure), which corroborate the material anisotropy.Peer ReviewedPostprint (published version

On the microstructure and texture of Cu-Cr-Zr alloy after severe plastic deformation by ECAP

Samples of a commercial Cu-1Cr-0.1Zr (wt.%) alloy were subjected to severe plastic deformation at room temperature using equal-channel angular pressing (ECAP) up to 16 passes via route Bc. The microstructure and texture of the processed samples were analyzed through electron backscatter diffraction (EBSD). Most of the grains were more or less inclined in the direction of shearing (45° from the extrusion direction) and substantially refined. The deformation structure evolved from elongated grains to a duplex equiaxed-elongated microstructure upon straining. The fraction of high angle boundaries gradually increased with the number of passes up to 70%. The texture after ECAP was mainly of ECAP shear type whose components shifted slightly from their ideal positions. A net strengthening and stabilization of the B/View the MathML sourcecomponents were observed.Peer ReviewedPostprint (author's final draft

Indicadores relevantes para la toma de decisiones en el sistema de gestión integral de la Policía Nacional

La siguiente monografía pretende hacer una contextualización y exposición de motivos acerca de la alta dirección en la Policía Nacional y la toma de decisiones soportada en las herramientas tecnológicas con las que cuenta la institución. Adicionalmente es importante tener presente que dentro de este análisis se tratará de establecer si se encuentran vacíos, frente a los cuales se presentarán propuestas que integren un sistema no solo de control y evaluación inicial del proceso de gestión actual de la policía, sino además, de los planes de corrección o mejora que permitan ejercer control frente a la gestión inicial.The below monograph intends to contextualize and preamble about senior management in the National Police and supported decision making in technological tools to the institution. Additionally it is important to note that in this analysis will seek to establish if they are empty, against which proposals to integrate a system not only control and appraisal of current management process of the police, but also to be presented plans of correction or improvement a controlling versus initial management

Effect of heat treatments on the mechanical and microstructural behavior of a hypoeutectic Al alloy obtained by laser power bed fusion

Large gains in strength and ductility are of little significance if the material’s anisotropy is high. Therefore, improving the mechanical properties and reducing the anisotropy of Al alloys obtained by additive manufacturing is a topic of growing interest. This manuscript examines the effect of distinct heat treatments on the mechanical, anisotropic, and microstructural behavior of a hypoeutectic, almost eutectic, AlSi11Cu alloy obtained by laser powder bed fusion (L-PBF). The microstructural characterization revealed an Al matrix surrounded by a Si-rich network, forming a coral-like pattern with a heterogeneous combination of columnar and equiaxed grains. The texture indicated that the columnar grains were preferentially oriented towards the building direction with strong Cube and Goss components. Different strength-ductility ratios were obtained following the annealing and solution heat treatments at different temperatures (200 °C–550 °C) with a holding time of 1 h. In terms of grain size and dislocation density, no significant changes were found in the microstructure, suggesting that grain size and dislocation strengthening mechanisms are not highly affected by the heat treatments. In addition, the Si-enriched network remained interconnected until 300 °C. At higher temperatures, this interconnection was lost, giving rise to large Si particles depleting the Si content in solid solution in the Al matrix. Digital image correlation maps revealed that deformation fields were more homogeneous when the cellular structure disappeared. The visco-plastic self-consistent model showed that when applying the load at 30° in the building direction (BD), the largest tensile strength was generated, whereas the lowest strength was obtained when the load was parallel to the BD. Heat treatments for 1 h holding time were found to be efficient in reducing the Lankford coefficients dispersion, suggesting improvements in formability and reducing the alloy’s planar anisotropy. These results revealed that annealing up to 400 °C or higher temperatures followed by water quenching leads to good strength and ductility ratios while reducing anisotropy.Peer ReviewedPostprint (published version

Microstructural and mechanical study in the plastic zone of ARMCO iron processed by ECAP

Plastic deformation of ARMCO iron processed by ECAP up to a maximum equivalent strain of sixteen (i.e., 1, 4, 8, and 16 ECAP passes) following route Bc was investigated by analyzing its microstructure and the stress-strain curves obtained after tensile tests at different levels of deformation. Three values of deformation (two in the plastic region taking into account the modified Crussard-Jaoul analysis and one after failure) were considered. Fractions of LAGB and HAGB, grain size and grain aspect ratio were calculated and compared for the different ECAP passes and tensile deformation levels. The dislocation density evolution calculated by the Bergström model for both the tensile curves and the ECAP curve showed a higher increase in the amount of dislocations during the initial stages of deformation than at higher values of deformation due to higher probabilities of dislocations annihilation. The strain hardening exponents calculated via the Bergström model for each ECAP pass shows that there is a continuous decrease in the strain hardening capacity until the eighth pass where a small increase with a subsequent stabilization was found. The dislocation densities calculated by the Estrin model presented a good correlation with values reported in bibliography for iron especially with those calculated by X-ray diffraction. This latter model predicted well the strain hardening evolution for stages III, IV and V for ARMCO iron processed by ECAP, where the main increments in hardening for stages IV and V were coming from the cell interiors.Preprin

Dislocation study of ARMCO iron processed by ECAP

The aim of this work was to study the deformation behavior of an Armco iron after severe plastic deformation by equal channel angular pressing (ECAP). Particular attention was paid to predict the dislocation density by different approaches like the model proposed by Bergström. Experimental measures of dislocation density by different techniques are used in the discussion. Cylindrical samples of ARMCO iron (8mm of diameter, 60mm of length) were subjected to ECAP deformation using a die with an intersecting channel of F=90° and outer arc of curvature of ¿= 37° die. Samples were deformed for up to 16 ECAP passes following route Bc. The mechanical properties of the material were measured after each pass by tensile tests. The original grain size of the annealed iron (70 µm) was drastically reduced after ECAP reaching grain sizes close to 300nm after 16 passes.Peer ReviewedPostprint (author's final draft