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.

Examinar

Mostrando 1 - 20 de 136

Análisis de la deformación de rotura en el ensayo de tracción en probetas cilíndricas de acero perlítico
(2011-04) Suárez Guerra, Fernando; Cendón, David A.; Atienza, José Miguel; Gálvez, Jaime C.; Elices, Manuel
El 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.
Influence of coiling in stress relaxation of prestressing steel wires
(2011-06) Elices, Manuel; Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón, David A.; Atienza, José Miguel
The 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.
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 A.; Gálvez, Jaime C.; Atienza, José Miguel; Elices, Manuel
La 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.
A fracture model for pearlitic steel bars using a cohesive model
(2012-09) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón, David A.; Atienza, José Miguel; Elices, Manuel
The 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.
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, Jaime C.; Atienza, José Miguel; Cendón, David A.; Elices, Manuel
Las 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.
Experimental validation of a fracture model for pearlitic steel bars based on the cohesive zone model
(2013-06) Suárez Guerra, Fernando; Gálvez, Jaime C.; Atienza, José Miguel; Cendón, David A.; Elices, Manuel
This 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.
The sustainable manufacturing concept, evolution and opportunities within Industry 4.0: A literature review
(SAGE, 2014-05) Antonio Sartal; Roberto Bellas; Alberto García Collado; Ana Mejías
On strain localization under bending
(2014-07) Jirásek, Milan; Suárez Guerra, Fernando
The aim of the present contribution is to assess the localization properties of nonlocal damage models under bending. To permit a partially analytical treatment and to display the fundamental properties of various formulations, the idealized case of uniform bending is considered. This means that the beam has a constant cross section and is subjected to a uniformly distributed bending moment and zero normal force. The beam is assumed to be very long, and boundary effects that might be introduced by the supports at the end sections are eliminated by imposing periodic boundary conditions on the fluctuating part of the response, which is superimposed on the solution that corresponds to uniform curvature. The average curvature serves as a loading parameter that is monotonically increased.
Damage evolution in pearlitic steel specimens under tension by means of X-ray computed tomography
(2015-06) Suárez Guerra, Fernando; Gálvez, Jaime C.; Atienza, José Miguel; Cendón, David A.; Elices, Manuel; Sket, Federico; Molina-Aldareguia, Jon
In 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.
Study on Nonlocal Damage Localisation Under Pure Bending
(2015-07) Suárez Guerra, Fernando; Jirásek, Milan
This contribution is focused on studying the localisation properties of nonlocal damage models under bending. In order to allow an easy interpretation of the results, the uniform bending case is studied. Therefore, a beam with a constant cross section subjected to pure bending is analysed.
Development of Vertical Wind Turbines via FDM Prototypes
(ELSEVIER, 2015-12-25) Guerrero-Villar, Francisca; Torres-Jiménez, Eloísa; Dorado-Vicente, Rubén; Jiménez-González, Jose Ignacio
In the present work, we propose to design and manufacture a specific Vertical Axis Wind Turbine (VAWT) prototype in order to evaluate its performance when some geometrical parameters are modified. The key idea is to take advantage of additive manufacturing flexibility to print the main components in an easy way and at low cost. Prototype size (scale 1:250, with respect to a 2 MW wind turbine) is small enough to be tested in a 40 cm x 40 cm wind tunnel. We use a Fused Deposition Modeling (FDM) machine to print the prototype, which is previously designed via CAD software. Different tests have been performed to determine an adequate printing configuration, mainly regarding how layer height influences roughness and printing time. Main dimensions, roughness and weight of the printed pieces were measured and finally, parts of highest quality were used to assemble a working prototype. The methodology presented in this paper shows it is possible to manufacture a wind turbine prototype with the following characteristics: flexibility to modify the design throughout the course of the investigation, low cost and low time needed to obtain the components with enough quality.
Análisis del método de Borino para formulaciones no locales en modelos de elementos finitos
(2016-04) Suárez Guerra, Fernando
A diferencia de lo que ocurre con los modelos usuales de elementos finitos, en los modelos no locales el comportamiento del material en un punto de integración no depende únicamente del estado del material en ese punto sino de un valor promediado utilizando otros puntos de integración que lo rodean. Esto disminuye notablemente la dependencia del tamaño de malla de los modelos. Cuando el punto de integración en cuestión se encuentra cerca de un borde del cuerpo han de adoptarse estrategias que permitan corregir el valor no local obtenido por la fórmula estándar. Además de algunas que dependen de la cercanía al borde y otras que lo hacen del estado de tensiones de dicho punto, existe un método propuesto por Borino que añade al valor obtenido por la fórmula estándar un cierto valor que depende del local. En algunos estudios realizados con modelos no locales se han observado resultados que presentan ciertas irregularidades cuando se emplea el método propuesto por Borino. En esta contribución se estudian los motivos que provocan estas irregularidades y por qué otras formulaciones proporcionan modelos más estables sin irregularidades en los resultados.
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, Jaime C.; Cendón , David A.; Atienza, José M.
Construction 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.
Study of the last part of the stress-deformation curve of construction steels with distinct fracture patterns
(Elsevier, 2016-10) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón , David A.; Atienza, José M.
The 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.
Analysis of the damage evolution in steel specimens under tension by means of XRTC
(2017-03) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón, David A.; Atienza, José Miguel; Sket, Federico; Molina-Aldareguia, Jon
When 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.
Controlled formation of bubbles in a planar co-flow configuration
(Elsevier, 2017-03-01) Ruiz-Rus, Javier; Bolaños Jimenez, Rocio; Gutiérrez-Montes, Cándido; Sevilla, Alejandro; Martínez-Bazán, Carlos
We present a new method that allows to control the bubble size and formation frequency in a planar air-water co-flow configuration by modulating the Water velocity at the nozzle exit. The forcing process has been experimentally characterized determining the amplitude of the water velocity fluctuations from measurements of the pressure variations in the water stream. The effect of the forcing on the bubbling process has been described by analyzing the pressute signals in the air stream in combinatiOn with visualizations performed with a high-speed camera. We show that, when the forcing amplitude is sufficiently large, the bubbles can be generated at a rate different from the natural bubbling frequency, f(n), which depends on the water-to-air velocity ratio, Lambda u(n)/u(q), and the Weber number, We rho(w)u(n)(2)H(0)/sigma, where H(0) is the half-thickness of the air stream at the exit slit, rho(w), the water density and a the surface tension coefficient. Consequently, when the forcing is effective, monodisperse bubbles, of sizes smaller than those generated without stimulation, are produced at the prescribed frequency, f(f) > f(n). The effect of the forcing process on the bubble size is also characterized by measuring the resulting intact length, l, i.e. the length of the air stem that remains attached to the injector when a bubble is released. In addition, the physics behind the forcing procedure is explained as a purely kinematic mechanism that is added to the effect of the pressure evolution inside the air stream that would take place in the unforced case. Finally, the downstream position of the maximum perturbation amplitude has been determined by a one-dimensional model, exhibiting a good agreement with both experiments and numerical simulations performed with OpenFOAM.
Distinct Fracture Patterns in Construction Steels for Reinforced Concrete under Quasistatic Loading— A Review
(MDPI, 2018-03) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón , David A.; Atienza , José M.
Steel 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.
Modelo de fractura en modo mixto (I y II) para materiales cementicios
(2018-03) Suárez Guerra, Fernando; Cendón, David A.; Gálvez, Jaime C.
Durante las pasadas décadas se ha dedicado un gran esfuerzo a la simulación de la fractura de materiales cuasifrágiles, como el hormigón. Muchos de los modelos propuestos se basan en el concepto de fisura cohesiva, habitualmente formulados en base a un comportamiento de rotura en modo predominantemente I, con un papel muy débil de las tensiones de cortante (modos II y III). En esta contribución se propone un modelo de material para simular la rotura en materiales de base cemento sometidos a estados de carga mixtos que combinan los modos de rotura I y II. La formulación propuesta se basa en el modelo de fisura cohesiva, extendida al caso de rotura en modo mixto, con un modo II significativo. El modelo se inspira en trabajos anteriores de Gálvez et al., pero, frente a ellos, aquí la rotura se formula a nivel de material, es decir, a nivel de los puntos de integración en un análisis con elementos finitos. A diferencia de trabajos anteriores, en los que la rotura se modelizaba mediante elementos intercara, el modelo propuesto es capaz de reproducir el camino de rotura sin información previa sobre el mismo.
On the localisation of damage under pure bending using a nonlocal approach
(Elsevier, 2018-06) Suárez Guerra, Fernando
To reproduce the behaviour of quasibrittle materials mathematically, constitutive laws with softening are needed, which often leads to development of damage localisation bands. If a standard local formulation is used, this approach leads to a pathological mesh dependence, which can be eliminated by making use of alternative nonlocal formulations. The aim of this paper is to assess the localisation properties of damage models under pure bending using different nonlocal formulations; to permit a partially analytical treatment, the idealised case of pure bending is studied. Under these conditions, the localisation process starts at the tensile face of the beam, which belongs to the boundary of the domain on which the problem is solved. Consequently, localisation patterns are affected by the boundary treatment as well as other parameters, such as the characteristic length that defines the area contributing to the nonlocal averaging. This paper presents an analytical study of the onset of localisation of different nonlocal formulations for a beam under pure bending. In addition to it, the subsequent evolution of the localised solution is explored by numerical simulations, analysing the localisation bands spacing, the dissipated energy profile along the fracture plane and the Moment-curvature diagrams, with curvature being a parameter that represents the rotation that drives the loading process (ϕ stands for the relative rotation angle of the cross section and L for the beam length). An analysis of damage localisation on longer beams where damage localises in several areas is also carried out and, finally, the damage localisation due to shrinkage is studied as a more realistic example of the problem addressed here.
Macro Photography as an Alternative to the Stereoscopic Microscope in the Standard Test Method for Microscopical Characterisation of the Air-Void System in Hardened Concrete: Equipment and Methodology
(MDPI, 2018-08) Suárez Guerra, Fernando; Conchillo, José J.; Gálvez, Jaime C.; Casati, María J.
The determination of the parameters that characterize the air-void system in hardened concrete elements becomes crucial for structures under freezing and thawing cycles. The ASTM C457 standard describes some procedures to accomplish this task, but they are not easy to apply, require specialised equipment, such as a stereoscopic microscope, and result in highly tedious tasks to be performed. This paper describes an alternative procedure to the modified point-count method that is described in the Standard that makes use of macro photography. This alternative procedure uses macro-photographic images that can be obtained with a quite standard photo camera and it is successfully applied to a large set of samples and presents some advantages over the traditional method, since the required equipment is less expensive and provides a more comfortable and less tedious procedure for the operator.

RUJA: Repositorio Institucional de Producción Científica

Examinar

Examinando Departamento de Ingeniería Mecánica y Minera por Fecha