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URI permanente para esta colecciónhttps://hdl.handle.net/10953/245

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Comportamiento a fractura de yeso con adición de fibras poliméricas
(2019-04) Suárez-Guerra, Fernando; Felipe-Sesé, Luis; Díaz, Francisco A.; Gálvez-Ruíz, Jaime Carlos; García-Alberti, Marcos
El yeso es un material de construcción ampliamente utilizado como revestimiento interior en edificios por su bajo coste, manejabilidad y propiedades de habitabilidad (aislamiento acústico y térmico, aspecto estético, etc.). La industria del yeso ha ido buscando nuevos usos, fruto de lo cual, entre otros, han surgido los paneles sándwich de yeso laminado o las placas de yeso reforzado con fibras de celulosa, que mejoran considerablemente sus propiedades mecánicas. Por otro lado, el uso de fibras poliméricas ha dado recientemente interesantes resultados en hormigón, proporcionando buenas propiedades dúctiles a las mezclas y dotándolas de una importante capacidad resistente frente a esfuerzos de tracción. En el presente estudio se analiza el comportamiento a fractura de mezclas de yeso con adiciones de distintos tipos de fibras poliméricas, en particular microfibras de polipropileno y macrofibras de poliolefina. Para ello se realizaron ensayos de flexión en tres puntos con probetas prismáticas entalladas. Además, el uso de un sistema de correlación digital de imágenes (DIC) permite medir la evolución de la apertura de la fisura (CMOD) y, lo que es más innovador e importante para evaluar su comportamiento, obtener mapas completos de deformaciones que ayuden a entender cómo contribuyen los distintos tipos de fibras a la disipación de energía durante la propagación del daño.
Numerical modelling of fracture in polyolefin fibre reinforced concrete specimens under mixed-model loading (I+II)
(2019-06) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Enfedaque, Alejandro; García-Alberti, Marcos
In the last decades, many researchers have focused their work on studying the behaviour of fibre-reinforced concrete (FRC). The appearance of specific recommendations in several Standards has boosted their usage and the interest in this technology. Apart from the traditional steel fibres, new materials are now studied as fibre-type reinforcement in structural concrete. This is the case of polyolefin, a polymer that has proved to be a suitable alternative that overcomes some of the drawbacks of steel, namely those related to corrosion processes, and keeps a good ductile behaviour providing structural strength to concrete against tensile stresses. Modelling fracture of FRC elements has also proved to be successful using trilinear softening functions, not only with polyolefin fibres, but also with steel and glass fibres. Nevertheless, these numerical models have been used to contrast only notched specimens under three-point bending symmetric loading. In this contribution, trilinear softening functions are used to model fracture in specimens in which crack initiates under a combination of modes I and II. Fracture is modelled by means of an embedded crack formulation based on the strong discontinuity approach. Two sets of experimental data are compared, one with specimens of the same size with different proportions of fibres and another one where, keeping the fibre proportion constant, the specimens are scaled up in order to analyse the size effect. In both sets of experimental results, the Load-CMOD diagrams fit reasonably well using trilinear softening functions, predicting with correction the maximum load and the shape of the diagram due to the influence of the fibres.
Predictive approach of the size effect of PFRC simulated by using a softening function
(2022-05) Gálvez-Ruíz, Jaime Carlos; Suárez-Guerra, Fernando; Enfedaque, Alejandro; García-Alberti, Marcos
The size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using only diagram cannot capture the material behaviour on elements with different sizes due to dependence of the orientation factor of the fibres with the size of the specimen. In previous works, the use of a trilinear softening diagram proved to be very convenient for reproducing fracture of polyolefin-fibre-reinforced concrete elements, but only if it is previously adapted for each specimen size. In this work, a predictive methodology is used to reproduce fracture of polyolefin-fibre-reinforced concrete specimens of different sizes under three-point bending. Fracture is reproduced by means of a well-known embedded cohesive model, with a trilinear softening function that is defined specifically for each specimen size. The fundamental points of these softening functions are defined a priori by using empirical expressions proposed in past works, based on an extensive experimental background. Therefore, the numerical results are obtained in a predictive manner and then compared with a previous experimental campaign in which PFRC notched specimens of different sizes were tested with a three-point bending test setup, showing that this approach properly captures the size effect, although some values of the fundamental points in the trilinear diagram could be defined more accurately.
Simulation of fracture on PFRC specimens subjected to high temperature using a cohesive model
(2022-05) Suárez-Guerra, Fernando; Enfedaque, Alejandro; García-Alberti, Marcos; Gálvez-Ruíz, Jaime Carlos
Concrete has been traditionally reinforced with steel rebars that confer good tensile properties to this material. Nevertheless, concrete can also be reinforced with fibres, which have been traditionally made of steel, although in the last years new types of fibres have appeared, such as polypropylene fibres, glass fibres or polyolefin fibres. Their use widens the range of application of fibre-reinforced concrete (FRC) and has experienced an significant boost by national and international standards, which now include guidelines for their use in structures. More specifically, textured polyolefin macro-fibres have proved to provide very good tensile properties in concrete. The use of these fibres has significant advantages when compared with traditional steel fibres, since they reduce the tear and wear of devices involved in their production, avoid corrosion problems in concrete and have no influence on magnetic fields, which can be very important in some situations. Concrete properties, both in fresh and hardened states, have been extensively studied in the last years, proving to be a promising alternative to steel fibres. Fracture of FRC, and more specifically of PFRC, has been successfully reproduced using the finite element analysis by means of an embedded cohesive model with a trilinear softening function. On another note, concrete has a good behaviour when subjected to high temperatures and fire, especially when it is compared with other traditional construction materials, such as wood or steel. Nevertheless, concrete reinforcement is usually made of materials that are critically sensitive to these events and the behaviour of the composite material must be assessed to meet the requirements described in the structural standards. With regard to polyolefin-fibre reinforced concrete (PFRC), a recent study has analysed how the fracture properties of this material degrade when subjected to high-temperatures, ranging from 20oC to 200oC. As temperature increases, fibres modify their geometry and their mechanical properties, which leads to a reduction of their effectiveness. In this work, the fracture behaviour of PFRC specimens subjected to high temperatures is reproduced by using an embedded cohesive model that uses a trilinear softening function. The specific trilinear softening diagram that provides a good numerical simulation of fracture is obtained for each temperature increment. This helps to understand how the trilinear diagram must be adapted when PFRC is subjected to high temperatures and will allow the use of this model to a wider range of situations.
Simulation of mixed-mode fracture (I-II) on PFRC specimens with various fibre proportions using an embedded cohesive crack model
(IOP Science, 2019-09) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Enfedaque , Alejandro; García-Alberti, Marcos
The study of fibre-reinforced concrete (FRC) has become of increasing interest in the last decades. Although it is not a new technology, it has experienced a remarkable progress with the appearance of some recommendations in the standards. More specifically, the use of polyolefin fibres has proved to increase the tensile strength of concrete without the problems usually found with steel fibres, especially those related to corrosion. This type of fibres have been studied in depth and its fracture behaviour has been successfully simulated in the past by means of an embedded crack model using a trilinear softening function. Nevertheless, these simulations have been always focused on cases where fracture took place under pure mode I conditions, namely using the classical three-point bending test on notched specimens. In this study, such embedded crack model is used to reproduce the fracture behaviour on notched specimens subjected to a modified three-point bending test that induces fracture under a combination of modes I and II. Three PFRC mixes are analysed, all of them with the same proportions of concrete components but different proportions of polyolefin fibres. The experimental and numerical diagrams properly agree and allow identifying how the increasing proportion of fibres can be reflected in the trilinear softening function that numerically drives the damage evolution.

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Examinando DIMM-Comunicaciones a Congresos, Conferencias... por Autor "García-Alberti, Marcos"