Simulación por elementos finitos de los primeros instantes de la extrusión de vainas de combustible para centrales nucleares

Se simularon los primeros instantes del proceso de extrusión de vainas de ZRY-4, utilizando el código de Elementos Finitos VELPEF, y un modelo para el material de tipo viscoelástico seudoplástico. Se estudiaron los campos de tensiones, presiones y velocidades, presiones en la matriz, el mandril, el contenedor y el pistón, la influencia en las anteriores de la fricción, la geometría y la temperatura.ZRY-4 cladding estrusion first moments were simulated, by VELPEF finite elements code, and a viscoelastic pseudoplastic model for the material. Stress, strain, presure and velocity fields, pressure on the die, mandrel, container and piston were studied, as weii as the influence of friction, geometry and temperature on the former.Peer Reviewe

Simulación por elementos finitos de los primeros instantes de la extrusión de vainas de combustible para centrales nucleares

Se simularon los primeros instantes del proceso de extrusión de vainas de ZRY-4, utilizando el código de Elementos Finitos VELPEF, y un modelo para el material de tipo viscoelástico seudoplástico. Se estudiaron los campos de tensiones, presiones y velocidades, presiones en la matriz, el mandril, el contenedor y el pistón, la influencia en las anteriores de la fricción, la geometría y la temperatura.ZRY-4 cladding estrusion first moments were simulated, by VELPEF finite elements code, and a viscoelastic pseudoplastic model for the material. Stress, strain, presure and velocity fields, pressure on the die, mandrel, container and piston were studied, as weii as the influence of friction, geometry and temperature on the former.Peer Reviewe

Computational modelling of the FSSW joining for the analysis of the welding process

En el presente trabajo se estudia el proceso de friction stir spot welding de planchuelas de aleación de aluminio AA6082 utilizando dos métodos de cálculo sucesivos. En una primera etapa se modela la inserción del perno en el material a soldar como un problema unidimensional axisimétrico no estacionario.De este caso se extrae el campo de temperaturas que es utilizado como campo de condiciones térmicas iniciales al momento de modelar el proceso de permanencia en el paso siguiente. Esta segunda etapa del proceso se realiza mediante un modelo bidimensional axisimétrico considerando al material constitutivamenteviscoplástico y, consecuentemente, resolviendo un problema de flujo de Stokes con viscosidades no lineales. Como resultados de este caso se obtienen los campos de velocidades, temperaturas y tensiones para todo el continuo. Las estimaciones realizadas se comparan con resultados experimentales de soldaduras de punto por fricción agitación.In this work, the friction stir spot welding process of AA6082 aluminium allow slabs is studied by means of two different methods of calculation. Firstly, the pin insertion is modelled as an axisymmetric one dimensional non stationary problem. The resulting temperatures field is used in the second phase of calculus as initial thermal conditions at the moment of modelling the following tool dwelling process. This second phase the welding process is modelled using an axysimmetric continuum, assuming a viscoplastic material, therefore solving a Stokes’ flow problem with non linear viscosity. The velocity, temperatures and stress fields are obtained for the whole domain. The obtained results are compared to experimental results in friction stir spot weldments.Fil: Carr, Gustavo Eduardo. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santiago, Diego A.. Universidad Nacional de Mar del Plata; ArgentinaFil: Urquiza, Santiago Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Lombera, Guillermo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata; Argentin

Sensitivity analysis and parameter estimation of heat transfer and material flow models in Friction Stir Welding

Although numerical models of heat transfer and material flow have contributed to understand the underlying mechanisms of friction stir welding (FSW), there are certain input model parameters that can not be easily determined. Thus, the model predictions do not always agree with experimental results. In this work, sensitivity analysis and parameter estimation were applied to test heat transfer and material flow models. A forward-difference approximation was used to compute the sensitivity of the solution with respect to the unknown model parameters. The Levenberg-Marquardt (LM) method was applied to solve the nonlinear parameter estimation problem. The numerical models were developed by the finite element method (FEM). The way in which the unknown model parameters independently affect the results and the importance of the location of reference points that take part in the objective function were determined.Fil: Pereyra, Sebastián. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata; ArgentinaFil: Lombera, Guillermo Alfredo. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata; ArgentinaFil: Urquiza, Santiago. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Frontini, Gloria Lia. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata; Argentin

Prediction of weld line location for injection molded thermoplastic components

Weld lines in polymeric injection molded parts occur wherever two or more melt fronts meet. They cause reduced mechanical properties and visual defects due to the poor intermolecular entanglement, molecular orientation induced by the fountain flow and the stress concentration effect of surface V-notch. A challenge related to these defects is that they are hard to detect and monitor because they’re usually not visible to the naked eye. Through this paper a numerical model for mold filling simulations has been developed aiming to predict the location of this defect and the initial meeting angle between the colliding flow fronts. A hybrid interface tracking technique was implemented in conjunction with a fix topology pseudo-quadratic mesh. Navier-Stokes equations were reduced to Hele-Shaw equations for thin plates. For validating purposes polypropylene plates injection moldings with weld lines were produced using a two-gated mold in a laboratory scale injector machine. Location of the defect was measure using an optical polariscope and then contrasted with simulation results. In order to establish the differences between 3D and Hele-Shaw models, predictions of weld line location were compared with the results provided by commercial injection molding simulation package Moldex3D.Publicado en: Mecánica Computacional vol. XXXV, no. 6Facultad de Ingenierí

Prediction of weld line location for injection molded thermoplastic components

Weld lines in polymeric injection molded parts occur wherever two or more melt fronts meet. They cause reduced mechanical properties and visual defects due to the poor intermolecular entanglement, molecular orientation induced by the fountain flow and the stress concentration effect of surface V-notch. A challenge related to these defects is that they are hard to detect and monitor because they’re usually not visible to the naked eye. Through this paper a numerical model for mold filling simulations has been developed aiming to predict the location of this defect and the initial meeting angle between the colliding flow fronts. A hybrid interface tracking technique was implemented in conjunction with a fix topology pseudo-quadratic mesh. Navier-Stokes equations were reduced to Hele-Shaw equations for thin plates. For validating purposes polypropylene plates injection moldings with weld lines were produced using a two-gated mold in a laboratory scale injector machine. Location of the defect was measure using an optical polariscope and then contrasted with simulation results. In order to establish the differences between 3D and Hele-Shaw models, predictions of weld line location were compared with the results provided by commercial injection molding simulation package Moldex3D.Publicado en: Mecánica Computacional vol. XXXV, no. 6Facultad de Ingenierí

FEM modelling of the three stages of friction stir spot welding

A three-dimensional modelling of the Friction Stir Spot Welding process was carried out by means of a two-dimensional continuum with symmetry of revolution around the tool axis. The model included the plunging, dwelling and withdrawal stages of two (Formula presented.) mm thick AA6061 alloy plates joining process. A highly viscous flow model was adopted, as well as the hypothesis of full stick contact between tool and material. The model was solved by means of the Finite Element Method (FEM) and Arbitrary Lagrangian Eulerian (ALE) techniques in an axisymmetric domain with mesh tracking and algorithms to account for contact and free flow. Numerical results were compared to experimental data found in literature. The maximum temperature for the pin front face was found within less than (Formula presented.) % of the experimental value. The velocity field were found close to those reported in literature and the final shape of the weld flash was similar to its experimental counterpart.Fil: Carr, Gustavo Eduardo. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Biocca, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lombera, Guillermo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Urquiza, Santiago Adrian. Universidad Nacional de Mar del Plata; Argentin

La inmersión infantil en la cultura del consumo. La fidelidad a la marca

The present work analyses how advertising works, from a critical perspective. Advertising is used not only as a tool for selling products but also as a platform that fosters certain lifestyles and ways of thinking – in short, as a vehicle for ideological concepts. The arguments presented in the work are based on research carried out in the Spanish city of Ceuta, located in North Africa, amongst boys, girls and adolescents, using different questionnaires to study issues of brand recognition and slogan recall. A core theme of the work is how childhood and adolescence are used in advertising, which is linked to the aim of creating brand loyalty. Boys and girls of just five years old already recognise and recall a large number of brands, albeit fewer slogans; they live in a visual society that is dominated by images. What is more, this is a society in which it is important to advertisers to create homogeneous groups, with similar tastes. The media via which advertising is conveyed are many and diverse, but it is television that stands out in particular, thanks to its omnipresence in every-day life. It is important, therefore, to continue researching these issues and, as a priority, to provide education within schools on the advertising strategies employed, so that young people are made aware of the different ways in which they are being manipulated.En este artículo se analiza desde una perspectiva crítica el funcionamiento de la publicidad, herramienta desde la que se pretende no sólo vender un producto, sino que también es usada como plataforma a través de la cual se fomentan estilos de vida y formas de pensamiento, en definitiva, se transmite una concepción ideológica. Los argumentos son apoyados por investigaciones realizadas en la ciudad de Ceuta con niños, niñas y adolescentes, utilizándose diferentes cuestionarios para estudiar aspectos como el reconocimiento de marcas o eslóganes.A lo largo del trabajo se señala la utilización que se hace en publicidad de los menores, interés que está relacionado con la pretensión de crear la “fidelidad a la marca”. Niños y niñas de tan sólo cinco años de edad reconocen un gran número de marcas, siendo menor el de eslóganes; sociedad visual en la que domina la imagen. Pero, además, en la que es de gran importancia la construcción de un grupo homogéneo de personas, con gustos semejantes. Para conseguir todo esto se utilizan diversos medios de transmisión, pero entre todos ellos destaca la televisión ya que está en casa desde que nacemos. Es necesario seguir investigando sobre estos asuntos y que estos trabajos lleven a hacer ver la necesidad de la enseñanza del funcionamiento de la publicidad en los centros escolares, con el fin de dar al individuo herramientas que les puedan ayudar a poner al descubierto las diferentes formas de manipulación de las que está siendo objeto

Estimation of stresses in arterial tissue: from residual stresses to material parameters

In the past decades a considerable amount of literature has been published addressing the study of the mechanical behavior of arterial walls. In these works, researchers have developed constitutive models and characterized the typical ranges for the values of material parameters of vascular tissues. Moreover, the existence of residual stresses in configurations free of loads was revealed, and its impact in the general stress state of the tissue was quantified. Currently, ex-vivo experiments such as inflation-extension tests and biaxial stress tests are extensively used for the estimation of the constitutive parameters in arterial wall probes. Also, destructive experiments involving radial cutting of specimens and the separation of arterial layers are used to identify layer-specific residual deformations (and stresses). For the latter scenario, material parameters are assumed to be known. In this context, a technique for the simultaneous characterization of residual deformations and material parameters in the arterial wall is proposed. This approach is based on data tipically obtained from inflation-extension tests, assuming that the material configuration and the radial displacement of the vessel is known for different load conditions given by fixed axial stretch and internal pressure values. The characterization problem is tackled through the minimization of a cost functional that measures the mechanical disequilibrium of the known material configuration and the discrepancy between the predicted and observed displacement of the outer vessel boundary. To illustrate the feasibility of the proposed methodology a manufactured-solution example is presented.Publicado en: Mecánica Computacional vol. XXXV, no. 9.Facultad de Ingenierí

Adaptability to climate change in forestry species : drought effects on growth and wood anatomy of ponderosa pines growing at different competition levels

More stressful conditions are expected due to climatic change in several regions, including Patagonia, South-America. In this region, there are no studies about the impact of severe drought events on growth and wood characteristics of the most planted forestry species, Pinus ponderosa (Doug. ex-Laws). The objective of this study was to quantify the effect of a severe drought event on annual stem growth and functional wood anatomy of pines growing at different plantation densities aiming to understand how management practices can help to increase their adaptability to climate change. Growth magnitude and period, specific hydraulic conductivity, and anatomical traits (early- and latewood proportion, lumen diameter, cell-wall thickness, tracheid length and bordered pit dimensions) were measured in the ring 2008-2009, which was formed during drought conditions. This drought event decreased annual stem growth by 30-38% and 58-65% respect to previous mean growth, in open vs. closed stand trees, respectively, indicating a higher sensitivity of the latter, which is opposite to reports from the same species growing in managed native forests in USA. Some wood anatomical variables did differ in more water stressed trees (lower cell wall thickness of early wood cells and higher proportion of small-lumen cells in latewood), which in turn did not affect wood function (hydraulic conductivity and resistance to implosion). Other anatomical variables (tracheid length, pit dimensions, early- and latewood proportion, lumen diameter of early wood cells) did not differ between tree sizes and plantation density. The results suggest that severe drought affects differentially the amount but not the function and quality of formed wood in ponderosa pine growing at different competition levelsLos pronósticos de cambio climático indican condiciones de mayores niveles de estrés ambiental para muchas regiones del mundo, incluyendo la Patagonia, Sudamérica. En esta región no existen antecedentes acerca del impacto de eventos de sequía severa sobre el crecimiento y la anatomía funcional de la madera de Pinus ponderosa (Doug. ex-Laws), la especie forestal más plantada. El objetivo de este estudio fue cuantificar el efecto de un evento de este tipo sobre el crecimiento anual en diámetro y la anatomía de la madera de pinos creciendo a densidades de plantación bien diferenciadas, con la intención de entender cómo las prácticas de manejo pueden ayudar a incrementar la adaptabilidad al cambio climático. Se midieron las siguientes variables en el anillo de crecimiento 2008-2009: magnitud y período de crecimiento, conductividad hidráulica específica, proporción de madera temprana y tardía, y morfometría de los elementos de conducción: diámetro de lúmen, grosor de pared y longitud de traqueidas, y dimensiones de las punteaduras entre traqueidas. Este evento de sequía redujo la magnitud del crecimiento en un 30-38% y un 58-65% con respecto a los años previos en árboles creciendo en baja y alta competencia intraespecífica, respectivamente. Esto indica una mayor sensibilidad de los segundos, mientras se había encontrado una tendencia opuesta en bosques nativos de esta especie gestionados en EEUU. Se observaron diferencias en algunas variables anatómicas de los árboles más estresados (menor grosor de pared en traqueidas del leño temprano y células con lúmenes más pequeños en el leño tardío), que sin embargo no tuvieron un efecto en la función de la madera (conductividad hidráulica y resistencia a la implosión). Otras variables anatómicas no difirieron entre ambas densidades de plantación ni tamaño de árboles analizados (largo de traqueidas, dimensiones de punteaduras, proporción de madera temprana y tardía, diámetro de lúmenes de madera temprana). Los resultados sugieren que los eventos de sequía extrema afectan diferencialmente la cantidad pero no la función y calidad de la madera formada en pino ponderosa creciendo bajo distintos niveles de competenciaFil: Fernandez, Marí­a Elena. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Gyenge, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: De Urquiza, Maria Mercedes. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Varela, Santiago Agustin. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; Argentin