Departamento de Ingeniería Mecánica y Minera
URI permanente para esta comunidadhttps://hdl.handle.net/10953/41
En esta Comunidad se recogen los documentos generados por el Departamento de Ingeniería Mecánica y Minera y que cumplen los requisitos de Copyright para su difusión en acceso abierto.
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Examinando Departamento de Ingeniería Mecánica y Minera por Autor "Atienza, José Miguel"
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Ítem A fracture model for pearlitic steel bars using a cohesive model(2012-09) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José Miguel; Elices, ManuelThe fracture of ductile materials, such as metals, is usually explained with the theory of nucleation, growth and coalescence of microvoids. Based on this theory, many numerical models have been developed, with a special mention to Gurson-type models. These models simulate mathematically the physical growth of microvoids, leading to a progressive development of the internal damage that takes place during a tensile test. In these models, the damage starts to develop in very early stages of the test.Ítem Análisis de la deformación de rotura en el ensayo de tracción en probetas cilíndricas de acero perlítico(2011-04) Suárez-Guerra, Fernando; Cendón, David Ángel; Atienza, José Miguel; Gálvez-Ruíz, Jaime Carlos; Elices, ManuelEl ensayo de tracción permite obtener la curva tensión-deformación hasta el instante de carga máxima, sin embargo, a partir de ese momento el análisis de las tensiones y de las deformaciones resulta complicado. Conocer el comportamiento del material a partir del instante de carga máxima resulta fundamental para diseñar estrategias que mejoren la seguridad estructural. Este trabajo presenta los resultados de una campaña experimental de ensayos de tracción sobre acero perlítico en la que se han estudiado sus deformaciones de rotura así como sus superficies de fractura, todo ello en probetas cilíndricas con diferentes diámetros. Esta campaña ha sido acompañada de simulaciones numéricas con el fin de analizar el comportamiento del material en el interior de la sección. Adicionalmente, se han analizado las superficies de fractura de las probetas y se ha observado una relación no proporcional entre el tamaño de las probetas y el tamaño de la zona interna atribuida al crecimiento de poros. Esta relación no proporcional sugiere que dicha zona actuaría como un concentrador de tensiones, de forma similar a una fisura, y estaría afectado por el efecto de la triaxialidad de las tensiones en la zona de rotura.Ítem Analysis of the damage evolution in steel specimens under tension by means of XRTC(2017-03) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José Miguel; Sket, Federico; Molina-Aldareguia, JonWhen a steel specimen is tested under tension, damage usually develops evenly all along the specimen, finally necking and leading to the typical cup-cone fracture surface. Nevertheless, some steels present an unusual fracture pattern consisting on a plane fracture surface with a dark region in the centre of the fracture zone. In this contribution, the authors analyse the evolution of the internal damage by using X-ray computed tomography (XRCT) on 3mm-diametre specimens of two steels. The specimens are tested in subsequent loading steps, after each of which it is unloaded and analysed with XRCT. This procedure helps to identify the evolution of damage developed inside each specimen at predefined strain levels. XRCT reveals a very high initial porosity in the material with the cup-cone fracture pattern and a very low initial porosity in the other. In the latter, fracture is triggered by a concentrated internal damage that can be seen as an internal notch which produces a stress concentration that leads to the eventual failure.Ítem Damage evolution in pearlitic steel specimens under tension by means of X-ray computed tomography(2015-06) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Atienza, José Miguel; Cendón, David Ángel; Elices, Manuel; Sket, Federico; Molina-Aldareguia, JonIn this contribution, the authors analyse the evolution of the internal damage by using X-ray computed tomography on a 3mm-diametre specimen. The specimen is tested in consecutive loading steps, after each of which it is unloaded and analysed with a X-ray tomograph. This procedure helps to identify the evolution of damage developed inside the specimen at predefined strain levels. Finally, these results are compared with the numerical results provided by the GTN model.Ítem Distinct Fracture Patterns in Construction Steels for Reinforced Concrete under Quasistatic Loading— A Review(MDPI, 2018-03) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José MiguelSteel is one of the most widely used materials in construction. Nucleation growth and coalescence theory is usually employed to explain the fracture process in ductile materials, such as many metals. The typical cup–cone fracture pattern has been extensively studied in the past, giving rise to numerical models able to reproduce this pattern. Nevertheless, some steels, such as the eutectoid steel used for manufacturing prestressing wires, does not show this specific shape but a flat surface with a dark region in the centre of the fracture area. Recent studies have deepened the knowledge on these distinct fracture patterns, shedding light on some aspects that help to understand how damage begins and propagates in each case. The numerical modelling of both fracture patterns have also been discussed and reproduced with different approaches. This work reviews the main recent advances in the knowledge on this subject, particularly focusing on the experimental work carried out by the authors.Ítem Experimental validation of a fracture model for pearlitic steel bars based on the cohesive zone model(2013-06) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Atienza, José Miguel; Cendón, David Ángel; Elices, ManuelThis work presents the experimental validation of a fracture model for steel specimens in a tensile test, based on a cohesive behaviour and taking into account the effect of stress triaxiality. Experimental tests have been carried out on cylindrical specimens of three different diameters: 3, 6 and 9mm. These tests have been reproduced numerically using the aforementioned cohesive element. Results from the numerical simulations have been compared with the experimental results, showing good agreement with them.Ítem Fracture of eutectoid steel bars under tensile loading: Experimental results and numerical simulation Author links open overlay panel(Elsevier, 2016-06) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José MiguelConstruction steel bars tested under tension usually show a cup-cone fracture pattern. Nevertheless, some steels, such as the eutectoid one used for manufacturing prestressing steel wires, show a different pattern: a flat fracture surface with a dark region inside. This paper presents experimental work performed to identify the fracture mechanisms that trigger this particular flat fracture pattern and numerical simulations where it is reproduced numerically. The experimental tests are carried out on cylindrical specimens of three diameters, 3, 6 and 9 mm, subjected to tension. In order to analyse the fracture mechanism, numerical simulations are performed by using the finite element method and the cohesive zone approach. To that end, a cohesive interface element with mechanical properties that depend on the stress triaxiality is presented and assessed. This approach provides reasonably good agreement with the experimental results. In addition, when compared with other popular models such as the GTN model, it presents certain advantages since it requires a smaller number of parameters to be defined.Ítem Influence of coiling in stress relaxation of prestressing steel wires(2011-06) Elices, Manuel; Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José MiguelThe possible deleterious effects of coiling and long-time storage of coiled wires on the stress relaxation behaviour of prestressing steel wires has been checked by means of experimental work and a simple analytical model. The results show that if the requirements of Standards are fulfilled (minimum coiling diameters) these effects can be neglected. However, some other factors like previous residual stresses, long-time storage or storage at high temperatures, can trigger or emphasise this damage to the material. In the authors’ opinion it is recommendable to control the final curvature of the wires after uncoiling prior to prestressing, as required in some Standards.Ítem Simulación de la rotura de barras de acero perlítico sometidas a tracción mediante un modelo de fisura cohesiva. Validación experimental(2013-04) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Atienza, José Miguel; Cendón, David Ángel; Elices, ManuelLas probetas cilíndricas fabricadas con materiales metálicos de elevada ductilidad, como el aluminio o el cobre, sometidas a tracción suelen presentar una rotura comúnmente denominada rotura en copa y cono, debido a su geometría. Este tipo de rotura se reproduce numéricamente con éxito mediante el modelo de Gurson-Tvergaard-Needleman, cuya formulación matemática se basa en el fenómeno físico de nucleación, crecimiento y coalescencia de microhuecos. A diferencia de dichos materiales, las barras de acero perlítico, material con una ductilidad apreciable, presentan un frente de rotura plano que no puede simularse correctamente con los modelos antes mencionados, apareciendo una región interior de daño que, en principio, también puede atribuirse a un fenómeno de nucleación y crecimiento de microhuecos, mientras que en el exterior aparece una zona cuya micrografía permite asociar su rotura a un mecanismo de clivaje. En trabajos anteriores los autores han presentado un elemento de intercara cohesivo dependiente de la triaxialidad de tensiones que, incorporado a un código de elementos finitos, permite reproducir de forma razonable el daño que se desarrolla en la región interior mencionada. En este trabajo se presentan los resultados de una campaña experimental que permite validar el modelo desarrollado. Para ello, se ensayan probetas de diferentes diámetros y se comparan los resultados con los obtenidos numéricamente, empleando tres bases extensométricas diferentes en cada uno de los diámetros. Los resultados numéricos se ajustan razonablemente bien a los obtenidos experimentalmente.Ítem Simulación del proceso de rotura por tracción de alambres de acero perlítico con un modelo de fisura cohesiva(2012-04) Suárez-Guerra, Fernando; Cendón, David Ángel; Gálvez-Ruíz, Jaime Carlos; Atienza, José Miguel; Elices, ManuelLa fractura de metales dúctiles como el acero suele explicarse a partir de la hipótesis de nucleación, crecimiento y coalescencia de microhuecos. A partir de esta teoría, se han desarrollado diversos modelos numéricos, entre los que el modelo de Gurson y sus variantes son los más extendidos. Dichos modelos reproducen matemáticamente el fenómeno físico de crecimiento de huecos resultando en un desarrollo progresivo del daño en el interior del material durante un ensayo de tracción. En estos modelos, el daño comienza a desarrollarse en fases muy tempranas del ensayo, incluso anteriores a la carga máxima. Ensayos realizados por los autores parecen indicar, sin embargo, que en el caso de barras de acero eutéctico empleado en la fabricación de alambres de pretensado, el daño originado en el interior del material como consecuencia del crecimiento de microhuecos sólo es apreciable en un estado muy avanzado del ensayo, momentos antes de producirse la rotura. Además, desde hace décadas se conoce que la triaxialidad de tensiones tiene una fuerte influencia sobre la rotura de los materiales. En este trabajo se presenta un modelo de rotura para elementos de acero sometidos a tracción, basado en un comportamiento cohesivo del material y que contempla el valor de la triaxialidad de tensiones, diferente en cada punto de la sección crítica de rotura.Ítem Study of the last part of the stress-deformation curve of construction steels with distinct fracture patterns(Elsevier, 2016-10) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José MiguelThe principal mechanical characteristics of construction steels are obtained by tensile testing. Nevertheless, the standards neglect the behaviour of steel beyond the maximum load point and do not define parameters related to the part of the stress-deformation curve that lies between the maximum load point and failure. The necking process that begins when the maximum load is reached makes it somewhat difficult to study the material behaviour beyond that point. However, the ductility of steel is highly affected by this last part of the load-deformation curve. For such a reason, and especially since structural safety is directly related to ductility, a deeper knowledge of this may help in designing safer structures. In this paper, this part of the load-deformation curve is analysed in two construction steels that exhibit distinct fracture patterns: one shows the typical cup-cone fracture surface, while the other shows a flat fracture surface with a dark region inside. An experimental campaign has been carried out with cylindrical specimens of contrasting diameters: 3 mm, 6 mm and 9 mm for each material. The use of a digital image correlation system is shown to be extremely useful in studying the behaviour of steel beyond the maximum load point, with an innovative procedure for identifying the growth of the internal damage that leads to failure in a specimen being developed.Ítem The Evolution of Internal Damage Identified by Means of X-ray Computed Tomography in Two Steels and the Ensuing Relation with Gurson’s Numerical Modelling(MDPI, 2019-03) Suárez-Guerra, Fernando; Sket, Federico; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José Miguel; Molina-Aldareguia, JonThis paper analyzes the evolution of the internal damage in two types of steel that show different fracture behaviors, with one of them being the initial material used for manufacturing prestressing steel wires, and the other one being a standard steel used in reinforced concrete structures. The first of them shows a flat fracture surface perpendicular to the loading direction while the second one shows the typical cup-cone surface. 3 mm-diameter cylindrical specimens are tested with a tensile test carried out in several loading steps and, after each of them, unloaded and analyzed with X-ray tomography, which allows detection of internal damage throughout the tensile test. In the steel used for reinforcement, damage is developed progressively in the whole specimen, as predicted by Gurson-type models, while in the steel used for manufacturing prestressing steel-wire, damage is developed only in the very last part of the test. In addition to the experimental study, a numerical analysis is carried out by means of the finite element method by using a Gurson model to reproduce the material behavior.