FRRA - Artículos en Revistas

Permanent URI for this collectionhttp://48.217.138.120/handle/20.500.12272/3553

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    Análisis de homogeneidad en piezocerámicos libres de plomo de Ba0.85Ca0.15Zr0.1Ti0.9O3 y Ba0.85Ca0.15Hf0.1Ti0.9O3 por Tomografía de Rayos X
    (2022) Di Loreto, Ariel O.; Frattini, Agustín; Machado, Rodrigo; Peralta, Matías; Díaz, Felipe; Stachiotti, Marcelo
    En este trabajo se presentan ensayos no destructivos utilizando la técnica de tomografía de rayos X (TRX) para determinar la homogeneidad y distribución de defectos en piezocerámicos libres de plomo de composición Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT). Para realizar un estudio comparativo se analiza también la composición Ba0.85Ca0.15Hf0.1Ti0.9O3 (BCHT). Las pastillas cerámicas fueron preparadas por el método convencional de reacción de estado sólido, calcinando a 1250 ºC y sinterizando a dos temperaturas distintas: 1400 ºC y 1500 ºC. La TRX detectó la presencia de defectos o inclusiones con dimensiones de 50 a 300 m. El porcentaje de defectos no supera el 3% en la cerámica de BCZT sinterizada a 1500 ºC y es inferior a 0,5% en muestra sinterizada a 1400 ºC. El porcentaje de inclusiones en BCHT es más del doble que en BCZT. Dado el tamaño de las mismas y analizando la densidad relativa de las pastillas, estas imperfecciones no son asignadas a porosidad remanente sino a inhomogeneidades del material que presentan distinta absorción a los rayos X. Una comparación con fotografías SEM, junto al análisis de esfericidad de las inclusiones, permite identificar estos defectos como regiones amorfas remanentes en el interior del material.
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    High-quality nodule analysis in spheroidal graphite cast iron using X-ray micro-computed tomography.
    (2022) Díaz, Felipe; Peralta, Matías; Toledo, J.C,; Fernandino, D. O.
    This work is a continuation of the studies presented in a recent paper by the authors, where a methodology to obtain different nodule quality categories in spheroidal graphite cast iron, was proposed. In this study, an exhaustive analysis of the highest-quality graphite nodules was performed. The experimental methodology involves X-ray micro-computed tomography analysis and digital image post-processing of the high-quality graphite nodule population. Furthermore, different subpopulations were selected, following a nodular size criterion. The procedure involves the evaluation and comparison of the sphericity and compactness distributions and the distances between neighbouring nodules by using ad-hoc image processing software. The results reveal the complementary nature of the sphericity and compactness parameters, which allow classifying, with great accuracy, different nodular quality categories of spheroidal graphite cast iron. Additionally, new viewpoints about the nodular morphology study and the distribution of quality nodules in the metallic matrix were provided, which could be extended to other heterogeneous materials.
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    Tomografía computada de rayos X aplicada a estudios de porosidad en fundiciones de aluminio
    (2023-09) Felcaro, Martín; Díaz, Felipe; Peralta, Matías
    La tomografía computada de rayos X es una compleja técnica no-destructiva que, a partir de la generación de una imagen 3D del sólido evaluado, brinda información digital muy precisa tanto de las heterogeneidades como de la geometría de dicho sólido. A modo de ejemplo, este trabajo presenta, empleando esta técnica, una metodología para analizar la porosidad cercana a la zona de fractura en una muestra de fundición de Al-Si, solicitada a flexión de 3 puntos. Un total de 1106 poros fueron examinados en 6 regiones de interés, 2 de las cuales contienen a las superficies de fractura. El software utilizado en el pos-procesamiento de las imágenes obtenidas posibilitó el diseño de una estrategia para analizar y comparar la porosidad en dichas regiones (tanto simétricas como adyacentes), lo cual a su vez permitió evaluar la correlación entre la porosidad y el plano de fractura. Los resultados obtenidos muestran que la mayoría de los poros examinados tienen valores medios de compacidad (rango de 0,3-0,6). Por otra parte, las regiones de interés que contienen a las superficies de fractura muestran marcadas asimetrías en cuanto al conteo general de poros, y también, en cuanto al conteo de poros de diámetro pequeño. Finalmente, a partir de las imágenes 3D de dichas zonas de interés, es posible advertir que la fractura inicia y se desarrolla en un plano de transición entre una zona de elevada porosidad y otra de menor densidad, siendo dicho plano, necesariamente, aquel cuyo momento de inercia es mínimo.
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    Emisiones de GEI en lagunas de tratamiento de efluentes en dos sistemas lecheros: comunicación.
    (2021-11-17) Gere, J.; Panigatti, María C.; Ceron Cucchi, M.; Charlon, V.; Taverna, M.; Griffa, C.; Boglione, Rosana; Schierano, María C.; Pepino, R.; Fonseca, J. M.; Tieri, M. P.
    La generación de metano (CH4) a partir de los sistemas de efluentes en tambos es una fuente importante de emisiones de GEIs (gases de efecto invernadero) y poco cuantificada (Leytem et al., 2017). Según Vander-Zaag et al. (2010) las tendencias de flujo de CH4 de los purines en lagunas consisten en 2 componentes principales: los flujos de referencia debidos a la difusión y las explosiones intermitentes debidos al flujo de burbujas. Además, las características fisicoquímicas de la laguna - sólidos totales (ST), demanda química de oxígeno (DQO) y sólidos volátiles (SV) - están altamente correlacionadas con las emisiones. El objetivo del presente trabajo fue determinar la emisión de GEI en 2 sistemas de tratamiento de efluentes. Si bien el diseño experimental contempla el monitoreo anual, para considerar los flujos estacionales, se presentan de manera preliminar los primeros resultados correspondientes al verano 2021.
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    Study of Residual Stress Relaxation Mechanics Using a Micro-indent Method
    (2016-12-05) Díaz, F.V; Mammana, C. A.; Guidobono, A. P. M.
    The aim of this study is to show the feasibility and accuracy of a micro-indent method to comprehensively evaluate the relaxation mechanics of residual stress in specimens of rolled aluminium alloy. This micro-indent method was adapted to implement four annealing treatments. The residual displacements were measured using a high-accuracy measuring machine, which enables to decrease the absolute error down to ±300 nm. This study presents an innovative data analysis using Mohr's circles, which allowed to study all directions of the inplane residual stress for different relaxation times. The results revealed that the relaxation process finishes when the residual stress relief is completed in some preferential directions and then, a brief stress recovery phase begins.
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    Evaluation of Residual Stresses Induced by Face Milling Using a Method of Micro-indents
    (2017-02-17) Díaz, F.V; Mammana, C. A.; Guidobono, A. P. M.
    The aim of this study is to determine and evaluate residual stresses induced by face milling in different zones, which are associated with asymmetries in orientation of cutting edge. In this study, a micro-indent method is used to determine these stresses, which were induced in samples of AA 7075-T6 aluminum alloy. The residual displacements were measured, with high accuracy, using a universal measuring machine. This study includes a thorough data analysis using Mohr's circles, which enabled to assess the stress states in all in-plane directions. The results obtained in samples subjected to different combinations of process parameters showed the introduction of compressive normal components for all directions of each zone evaluated. From the high sensitivity of the microindent method used, it was possible to detect smaller differences generated between the levels reaching the stress components in the cutting zones evaluated. Furthermore, these differences were similar for all evaluated directions when the highest feed rate was selected. This significant fact, finally, would reveal equivalent differences between asymmetrical zones, regarding the combination of local plastic deformation and heat reaching the milled surface, for all in-plane directions.
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    Analysis of Residual Stresses in High Speed Milled Aluminum Alloys
    (2017-03-15) Vottero, S.; Díaz, F.V.; Mammana, C.A; Guidobono, A. P. M.
    The purpose of this study is to evaluate, from high speed machining tests, the behavior of the residual stresses induced in samples of AA 6082-T6 and AA 7075-T6 aluminum alloys. This study includes an exhaustive analysis of residual stress anisotropy from diameters of Mohr's circles. The combination of process parameters was modified in order to evaluate the stress changes introduced in different zones of the surfaces generated. A method of micro-indents, which includes the adaptation of a universal measuring machine, was used to determine, with high accuracy, the normal components of residual stress in several directions. The obtained results reveal that although, in the alloy 7075-T6, the normal components are lower, in the alloy 6082-T6, these normal components tend to be grouped into smaller intervals and also, to show a more homogeneous directional behavior when the cutting conditions are more severe.
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    Determination and Analysis of Residual Stresses Induced by High Speed Milling Using a Micro-indent Method
    (2018-06-15) Vottero, S.; Mammana, C. A.; Guidobono, A. P. M.
    Abstract: The purpose of this work is to determine and analyze residual stress normal components and anisotropy degrees introduced by high-speed milling in specimens of AA 6082-T6 and AA 7075-T6 aluminum alloys. At each machined sample, the climb and conventional cutting zones were evaluated and compared. This paper includes a comprehensive study of thermal and mechanical effects associated with the residual stress introduction. For normal components determination, an optimized micro-indent method was used. Each measurement sequence from this approach was performed using a high accuracy measuring machine and classified according to thermal deviations measured. The residual displacements were determined with an absolute error down to ±300 nm. The normal components analysis allowed to infer the strong influence of the rolling process previous to high-speed milling and besides, the stress levels associated with thermal effects (higher in AA 7075-T6). Finally, the lower residual stress anisotropy degrees in both materials observed in the conventional cutting zone would indicate more homogenous local plastic stretching in this region for all planar directions.