Methodologies for Designing and Developing New Concepts in Vertical Transportation

Escalator and moving walkway are multibody systems with a design of more than a century. Developed methodology allows studying and improving any subsystem of both systems. In addition, new concepts can be developed and tested without the necessity and cost of a real construction. CITEF (Railway Technologies Research Centre) has been modelling escalators for more than four years. Several complex and innovative models has been developed to characterize static, kinematic and dynamic escalator behaviour. The high number of mechanical elements that are part of escalators complicate modelling task. In this way, methodologies and tools have been developed in order to automate these task and saving computational and time costs. Developed methodologies have been validated with the results of comparing real measurements and simulated outputs from a dynamic model.

Antiguo Poblado de Algarrobito ubicado en el Valle del Elqui Chile, y su Patrón Urbano Bioclimático

La importancia de conocer bien el entorno para un proyecto arquitectónico es que podemos adaptarlo a nuestras necesidades fisiológicas de Confort Térmico. Podemos decir entonces que el edificio juega un papel fundamental como técnica de control de nuestro entorno. El edificio nos debería entregar un entorno controlado para que nos sintamos bien térmicamente, considerando además, que la arquitectura por sí misma puede lograr dicho confort la mayor parte de las veces. De no ser así, los usuarios tienden a colocar elementos mecánicos, para generar frío o calor artificialmente. Es fundamental entonces que nuestros edificios, tengan una correcta interacción con los recursos naturales del lugar para lograr dicho confort térmico. Pero lograr el Confort Térmico en todos los edificios de una ciudad como unidad, no logrará que la ciudad entera sea confortable térmicamente, ya que las complejas interacciones hacen que la problemática se deba enfrentar como algo sistémico. Esto quiere decir, que para que una ciudad o un conjunto logren la Confortabilidad Térmica deseada por sus habitantes debiera haber sido planificada conforme a variables urbanas que interactúen con el medio natural en forma eficiente. Con la observación de ciertos conjuntos habitacionales antiguos en el interior del Valle del Elqui, Chile y de sus relaciones entre variables urbanas y naturales, queda de manifiesto ciertas características que conllevan a pensar que existió una planificación ambiental en éstos que llevaron a lograr un conjunto con características bioclimáticas. Las evidencias de la existencia en primer lugar de un patrón urbanístico en dichos conjuntos habitacionales antiguos, hacen pensar que dicho patrón se trataría de un patrón bioclimático rural planificado, lo que hace que exista un gran interés por el estudio de estos conjuntos. Hasta ahora, en Chile, los pocos estudios de Confort Térmico que existen, están orientados a edificaciones aisladas, al Confort térmico interior de la edificación en el ámbito urbano, y en nada a Patrones Bioclimáticos de Conjuntos Habitacionales en una situación de ruralidad como a la referida en esta investigación. Además, los estudios referidos al clima urbano, difieren a los del clima rural, por lo que se necesitan mayores estudios aún para comprender mejor la problemática. Es por esto, que la mayoría de los casos mencionados en este estudio son contextualizados al ámbito urbano por carecer de otros estudios rurales. Es en este sentido que esta investigación cobra real importancia y pretende establecer la relación existente entre las variables morfológicas rurales y los recursos naturales del lugar y que generan un confort térmico ideal para sus habitantes, al mismo tiempo, se analiza la existencia de un Patrón Bioclimático en un poblado denominado Algarrobito ubicado en la cuenca del Valle del Elqui, Chile. Es en este sentido que el propósito principal de este trabajo es determinar la real existencia de un Patrón Bioclimático que relacione la morfología rural y edificada de los antiguos poblados pertenecientes a la cuenca del Valle de Elqui Chile con el microclima del lugar. La metodología empleada se basa en realizar primeramente el estudio del microclima del lugar a través de las Cartas Bioclimáticas. Para ello se obtuvo información de datos climatológicos de las estaciones meteorológicas ubicadas en la cuenca del Valle de Elqui, principalmente las más cercanas al lugar de estudio. Mediante una revisión exhaustiva de la información arquitectónica, así como de una labor de reconocimiento en terreno realizada en el poblado seleccionado y de la aplicación del Climograma local, se identificaron las diferentes zonas bioclimáticas del poblado antiguo y potenciales áreas de estudio en el conjunto. Esta actividad incluyó un estudio preliminar de la energía solar local, vientos, humedad, temperaturas y su interacción con el conjunto, permitiendo una primera aproximación a la problemática del espacio exterior y las viviendas. Esto permitió en base a las condicionantes del lugar, la arquitectura vernácula y los materiales descubrir un Patrón en el antiguo conjunto que permitía entregar confortabilidad térmica a sus habitantes y darse cuenta también, que el nuevo conjunto emplazado en el sector no seguía ese patrón con las disfuncionalidades que ello llevaba. Con esto quedó demostrado en primer lugar la existencia de un Patrón Bioclimático rural, los beneficios del patrón, la importancia de éste como causante de Confortabilidad Térmica del conjunto, y por ende de mejor eficiencia energética, así como también, que el nuevo conjunto no sigue para nada este Patrón, pero que existe también la posibilidad de rectificación y por supuesto, que los nuevos desarrollos residenciales del Valle del Elqui, puedan planificarse en base al patrón bioclimático descubierto. ABSTRACT Knowing the environment of an architectonic proyect is really important for adjusting it to our physiological needs of Thermal Comfort. So we can say that the building plays a key role as a technique of control of our environment. The building should give us a controlled environment to make us feel good thermally, and it usually can reach pleasurable temperatures by itself. If it isn't like that, people cooled or heated the ambience with mechanical elements. So a correct interaction between the buildings and natural resources is important to reach a thermal comfort. But achieving Thermal Comfort in all the buildings of a city as a unit will not achieve the whole city is thermally comfortable, because the complex interactions cause the problem needs to be solved as something systemic. This means that for a city or a set reach the Thermal Comfortability desired by its inhabitants, it should have been planned according to the urban variables that interact with the natural environment efficiently. Observing some old housing complexes in Elqui Valley, Chile, and the relationships between their natural and urban variables, some features lead to think that the environmental planning in these led to achieve a set with bioclimatic features. First, the evidences about the existence of an urban pattern in those old housing complexes, make thinking that the pattern would be a planned urban pattern, which generates interest in its study. In Chile, there have been few studies about Thermal Comfort, oriented to isolated buildings and indoor thermal comfort, but Bioclimatic Urban Patterns haven't been studied at all. In this sense, this investigation acquires a real importance and pretends to establish the relationship between urban variables and natural resources of the place that generates a good thermal comfort for its habitants. At the same time, the existence of a Bioclimatic Urban Pattern in Algarrobito, located in Elqui Valley basin, Chile, is analized. It is in this sense that the main purpose of this work is to determine the real existence of a Bioclimatic Urban Pattern, that links the urban and constructive form of the old villages of it with its microclimate. The methodology used is based on performing first the study of the microclimate of the place through the Bioclimatic Cards. To do this, weather stations, located in Elqui valley, near the place that was studied, were used to obtain information of climatological data. The different bioclimatic zones to the old town and potential areas of study in the set were identified, through an exhaustive review of the architectural information, a field reconnaissance work performed on the selected town and the application of the Local Climograph. This activity included a preliminary study of the local solar energy, the winds, the moisture, the temperatures, and their interaction with the set, allowing a first aproximation to troubles of outer space and housing. This allowed, based on the conditions of the place, vernacular architecture and materials, discovering an urban pattern in the old set, which allowed to give thermal comfort to its inhabitants and realize that the new set of the place did not follow this pattern, with the dysfunctions that it carried. These points demonstrated, in first place, the existence of a Bioclimatic Urban Pattern, the benefits of it, the importance of it as a cause of Thermal Comfortability, and therefore a better efficiency of energy, also that the new set doesn’t follow this Pattern at all, but that the posibility of rectification exists and, of course, that the new residencial development in Elqui Valley can be planned based on bioclimatic pattern discovered.

Crack mechanical failure in lithium niobate crystal under ion irradiation; novel simulation by extended finite elements

Swift heavy ion irradiation (ions with mass heavier than 15 and energy exceeding MeV/amu) transfer their energy mainly to the electronic system with small momentum transfer per collision. Therefore, they produce linear regions (columnar nano-tracks) around the straight ion trajectory, with marked modifications with respect to the virgin material, e.g., phase transition, amorphization, compaction, changes in physical or chemical properties. In the case of crystalline materials the most distinctive feature of swift heavy ion irradiation is the production of amorphous tracks embedded in the crystal. Lithium niobate is a relevant optical material that presents birefringence due to its anysotropic trigonal structure. The amorphous phase is certainly isotropic. In addition, its refractive index exhibits high contrast with those of the crystalline phase. This allows one to fabricate waveguides by swift ion irradiation with important technological relevance. From the mechanical point of view, the inclusion of an amorphous nano-track (with a density 15% lower than that of the crystal) leads to the generation of important stress/strain fields around the track. Eventually these fields are the origin of crack formation with fatal consequences for the integrity of the samples and the viability of the method for nano-track formation. For certain crystal cuts (X and Y), these fields are clearly anisotropic due to the crystal anisotropy. We have used finite element methods to calculate the stress/strain fields that appear around the ion-generated amorphous nano-tracks for a variety of ion energies and doses. A very remarkable feature for X cut-samples is that the maximum shear stress appears on preferential planes that form +/-45º with respect to the crystallographic planes. This leads to the generation of oriented surface cracks when the dose increases. The growth of the cracks along the anisotropic crystal has been studied by means of novel extended finite element methods, which include cracks as discontinuities. In this way we can study how the length and depth of a crack evolves as function of the ion dose. In this work we will show how the simulations compare with experiments and their application in materials modification by ion irradiation.

Numerical analysis of mixe-mode fracture of brickwork masonry with embedded discontinuity elements

One of the common pathologies of brickwork masonry structural elements and walls is the cracking associated with the differential settlements and/or excessive deflections of the slabs along the life of the structure. The scarce capacity of the masonry in order to accompany the structural elements that surround it, such as floors, beams or foundations, in their movements makes the brickwork masonry to be an element that frequently presents this kind of problem. This problem is a fracture problem, where the wall is cracked under mixed mode fracture: tensile and shear stresses combination, under static loading. Consequently, it is necessary to advance in the simulation and prediction of brickwork masonry mechanical behaviour under tensile and shear loading. The quasi-brittle behaviour of the brickwork masonry can be studied using the cohesive crack model whose application to other quasibrittle materials like concrete has traditionally provided very satisfactory results.

Dynamic analysis using finite elements to calculate the critical wear section of the contact wire in suburban railway overhead conductor rails

The purpose of this study is to determine the critical wear levels of the contact wire of the catenary on metropolitan lines. The study has focussed on the zones of contact wire where localised wear is produced, normally associated with the appearance of electric arcs. To this end, a finite element model has been developed to study the dynamics of pantograph-catenary interaction. The model includes a zone of localised wear and a singularity in the contact wire in order to simulate the worst case scenario from the point of view of stresses. In order to consider the different stages in the wire wear process, different depths and widths of the localised wear zone were defined. The results of the dynamic simulations performed for each stage of wear let the area of the minimum resistant section of the contact wire be determined for which stresses are greater than the allowable stress. The maximum tensile stress reached in the contact wire shows a clear sensitivity to the size of the local wear zone, defined by its width and depth. In this way, if the wear measurements taken with an overhead line recording vehicle are analysed, it will be possible to calculate the potential breakage risk of the wire. A strong dependence of the tensile forces of the contact wire has also been observed. These results will allow priorities to be set for replacing the most critical sections of wire, thereby making maintenance much more efficient. The results obtained show that the wire replacement criteria currently borne in mind have turned out to be appropriate, although in some wear scenarios these criteria could be adjusted even more, and so prolong the life cycle of the contact wire.

Experimental and numerical analysis of reinforced concrete elements subjected to blast loading

El hormigón es uno de los materiales de construcción más empleados en la actualidad debido a sus buenas prestaciones mecánicas, moldeabilidad y economía de obtención, entre otras ventajas. Es bien sabido que tiene una buena resistencia a compresión y una baja resistencia a tracción, por lo que se arma con barras de acero para formar el hormigón armado, material que se ha convertido por méritos propios en la solución constructiva más importante de nuestra época. A pesar de ser un material profusamente utilizado, hay aspectos del comportamiento del hormigón que todavía no son completamente conocidos, como es el caso de su respuesta ante los efectos de una explosión. Este es un campo de especial relevancia, debido a que los eventos, tanto intencionados como accidentales, en los que una estructura se ve sometida a una explosión son, por desgracia, relativamente frecuentes. La solicitación de una estructura ante una explosión se produce por el impacto sobre la misma de la onda de presión generada en la detonación. La aplicación de esta carga sobre la estructura es muy rápida y de muy corta duración. Este tipo de acciones se denominan cargas impulsivas, y pueden ser hasta cuatro órdenes de magnitud más rápidas que las cargas dinámicas impuestas por un terremoto. En consecuencia, no es de extrañar que sus efectos sobre las estructuras y sus materiales sean muy distintos que las que producen las cargas habitualmente consideradas en ingeniería. En la presente tesis doctoral se profundiza en el conocimiento del comportamiento material del hormigón sometido a explosiones. Para ello, es crucial contar con resultados experimentales de estructuras de hormigón sometidas a explosiones. Este tipo de resultados es difícil de encontrar en la literatura científica, ya que estos ensayos han sido tradicionalmente llevados a cabo en el ámbito militar y los resultados obtenidos no son de dominio público. Por otra parte, en las campañas experimentales con explosiones llevadas a cabo por instituciones civiles el elevado coste de acceso a explosivos y a campos de prueba adecuados no permite la realización de ensayos con un elevado número de muestras. Por este motivo, la dispersión experimental no es habitualmente controlada. Sin embargo, en elementos de hormigón armado sometidos a explosiones, la dispersión experimental es muy acusada, en primer lugar, por la propia heterogeneidad del hormigón, y en segundo, por la dificultad inherente a la realización de ensayos con explosiones, por motivos tales como dificultades en las condiciones de contorno, variabilidad del explosivo, o incluso cambios en las condiciones atmosféricas. Para paliar estos inconvenientes, en esta tesis doctoral se ha diseñado un novedoso dispositivo que permite ensayar hasta cuatro losas de hormigón bajo la misma detonación, lo que además de proporcionar un número de muestras estadísticamente representativo, supone un importante ahorro de costes. Con este dispositivo se han ensayado 28 losas de hormigón, tanto armadas como en masa, de dos dosificaciones distintas. Pero además de contar con datos experimentales, también es importante disponer de herramientas de cálculo para el análisis y diseño de estructuras sometidas a explosiones. Aunque existen diversos métodos analíticos, hoy por hoy las técnicas de simulación numérica suponen la alternativa más avanzada y versátil para el cálculo de elementos estructurales sometidos a cargas impulsivas. Sin embargo, para obtener resultados fiables es crucial contar con modelos constitutivos de material que tengan en cuenta los parámetros que gobiernan el comportamiento para el caso de carga en estudio. En este sentido, cabe destacar que la mayoría de los modelos constitutivos desarrollados para el hormigón a altas velocidades de deformación proceden del ámbito balístico, donde dominan las grandes tensiones de compresión en el entorno local de la zona afectada por el impacto. En el caso de los elementos de hormigón sometidos a explosiones, las tensiones de compresión son mucho más moderadas, siendo las tensiones de tracción generalmente las causantes de la rotura del material. En esta tesis doctoral se analiza la validez de algunos de los modelos disponibles, confirmando que los parámetros que gobiernan el fallo de las losas de hormigón armado ante explosiones son la resistencia a tracción y su ablandamiento tras rotura. En base a los resultados anteriores se ha desarrollado un modelo constitutivo para el hormigón ante altas velocidades de deformación, que sólo tiene en cuenta la rotura por tracción. Este modelo parte del de fisura cohesiva embebida con discontinuidad fuerte, desarrollado por Planas y Sancho, que ha demostrado su capacidad en la predicción de la rotura a tracción de elementos de hormigón en masa. El modelo ha sido modificado para su implementación en el programa comercial de integración explícita LS-DYNA, utilizando elementos finitos hexaédricos e incorporando la dependencia de la velocidad de deformación para permitir su utilización en el ámbito dinámico. El modelo es estrictamente local y no requiere de remallado ni conocer previamente la trayectoria de la fisura. Este modelo constitutivo ha sido utilizado para simular dos campañas experimentales, probando la hipótesis de que el fallo de elementos de hormigón ante explosiones está gobernado por el comportamiento a tracción, siendo de especial relevancia el ablandamiento del hormigón. Concrete is nowadays one of the most widely used building materials because of its good mechanical properties, moldability and production economy, among other advantages. As it is known, it has high compressive and low tensile strengths and for this reason it is reinforced with steel bars to form reinforced concrete, a material that has become the most important constructive solution of our time. Despite being such a widely used material, there are some aspects of concrete performance that are not yet fully understood, as it is the case of its response to the effects of an explosion. This is a topic of particular relevance because the events, both intentional and accidental, in which a structure is subjected to an explosion are, unfortunately, relatively common. The loading of a structure due to an explosive event occurs due to the impact of the pressure shock wave generated in the detonation. The application of this load on the structure is very fast and of very short duration. Such actions are called impulsive loads, and can be up to four orders of magnitude faster than the dynamic loads imposed by an earthquake. Consequently, it is not surprising that their effects on structures and materials are very different than those that cause the loads usually considered in engineering. This thesis broadens the knowledge about the material behavior of concrete subjected to explosions. To that end, it is crucial to have experimental results of concrete structures subjected to explosions. These types of results are difficult to find in the scientific literature, as these tests have traditionally been carried out by armies of different countries and the results obtained are classified. Moreover, in experimental campaigns with explosives conducted by civil institutions the high cost of accessing explosives and the lack of proper test fields does not allow for the testing of a large number of samples. For this reason, the experimental scatter is usually not controlled. However, in reinforced concrete elements subjected to explosions the experimental dispersion is very pronounced. First, due to the heterogeneity of concrete, and secondly, because of the difficulty inherent to testing with explosions, for reasons such as difficulties in the boundary conditions, variability of the explosive, or even atmospheric changes. To overcome these drawbacks, in this thesis we have designed a novel device that allows for testing up to four concrete slabs under the same detonation, which apart from providing a statistically representative number of samples, represents a significant saving in costs. A number of 28 slabs were tested using this device. The slabs were both reinforced and plain concrete, and two different concrete mixes were used. Besides having experimental data, it is also important to have computational tools for the analysis and design of structures subjected to explosions. Despite the existence of several analytical methods, numerical simulation techniques nowadays represent the most advanced and versatile alternative for the assessment of structural elements subjected to impulsive loading. However, to obtain reliable results it is crucial to have material constitutive models that take into account the parameters that govern the behavior for the load case under study. In this regard it is noteworthy that most of the developed constitutive models for concrete at high strain rates arise from the ballistic field, dominated by large compressive stresses in the local environment of the area affected by the impact. In the case of concrete elements subjected to an explosion, the compressive stresses are much more moderate, while tensile stresses usually cause material failure. This thesis discusses the validity of some of the available models, confirming that the parameters governing the failure of reinforced concrete slabs subjected to blast are the tensile strength and softening behaviour after failure. Based on these results we have developed a constitutive model for concrete at high strain rates, which only takes into account the ultimate tensile strength. This model is based on the embedded Cohesive Crack Model with Strong Discontinuity Approach developed by Planas and Sancho, which has proved its ability in predicting the tensile fracture of plain concrete elements. The model has been modified for its implementation in the commercial explicit integration program LS-DYNA, using hexahedral finite elements and incorporating the dependence of the strain rate, to allow for its use in dynamic domain. The model is strictly local and does not require remeshing nor prior knowledge of the crack path. This constitutive model has been used to simulate two experimental campaigns, confirming the hypothesis that the failure of concrete elements subjected to explosions is governed by their tensile response, being of particular relevance the softening behavior of concrete.

An inverse optimization strategy to determine single crystal mechanical behavior from polycrystal tests: Application to AZ31 Mg alloy

An inverse optimization strategy was developed to determine the single crystal properties from experimental results of the mechanical behavior of polycrystals. The polycrystal behavior was obtained by means of the finite element simulation of a representative volume element of the microstructure in which the dominant slip and twinning systems were included in the constitutive equation of each grain. The inverse problem was solved by means of the Levenberg-Marquardt method, which provided an excellent fit to the experimental results. The iterative optimization process followed a hierarchical scheme in which simple representative volume elements were initially used, followed by more realistic ones to reach the final optimum solution, leading to important reductions in computer time. The new strategy was applied to identify the initial and saturation critical resolved shear stresses and the hardening modulus of the active slip systems and extension twinning in a textured AZ31 Mg alloy. The results were in general agreement with the data in the literature but also showed some differences. They were partially explained because of the higher accuracy of the new optimization strategy but it was also shown that the number of independent experimental stress-strain curves used as input is critical to reach an accurate solution to the inverse optimization problem. It was concluded that at least three independent stress-strain curves are necessary to determine the single crystal behavior from polycrystal tests in the case of highly textured Mg alloys.

Mechanical behaviour of laminated functionally graded fibre-reinforced self-compacting cementitious composites

El hormigón autocompactante (HAC) es una nueva tipología de hormigón o material compuesto base cemento que se caracteriza por ser capaz de fluir en el interior del encofrado o molde, llenándolo de forma natural, pasando entre las barras de armadura y consolidándose únicamente bajo la acción de su peso propio, sin ayuda de medios de compactación externos, y sin que se produzca segregación de sus componentes. Debido a sus propiedades frescas (capacidad de relleno, capacidad de paso, y resistencia a la segregación), el HAC contribuye de forma significativa a mejorar la calidad de las estructuras así como a abrir nuevos campos de aplicación del hormigón. Por otra parte, la utilidad del hormigón reforzado con fibras de acero (HRFA) es hoy en día incuestionable debido a la mejora significativa de sus propiedades mecánicas tales como resistencia a tracción, tenacidad, resistencia al impacto o su capacidad para absorber energía. Comparado con el HRFA, el hormigón autocompactante reforzado con fibras de acero (HACRFA) presenta como ventaja una mayor fluidez y cohesión ofreciendo, además de unas buenas propiedades mecánicas, importantes ventajas en relación con su puesta en obra. El objetivo global de esta tesis doctoral es el desarrollo de nuevas soluciones estructurales utilizando materiales compuestos base cemento autocompactantes reforzados con fibras de acero. La tesis presenta una nueva forma de resolver el problema basándose en el concepto de los materiales gradiente funcionales (MGF) o materiales con función gradiente (MFG) con el fin de distribuir de forma eficiente las fibras en la sección estructural. Para ello, parte del HAC se sustituye por HACRFA formando capas que presentan una transición gradual entre las mismas con el fin de obtener secciones robustas y exentas de tensiones entre capas con el fin de aplicar el concepto “MGF-laminados” a elementos estructurales tales como vigas, columnas, losas, etc. El proceso incluye asimismo el propio método de fabricación que, basado en la tecnología HAC, permite el desarrollo de interfases delgadas y robustas entre capas (1-3 mm) gracias a las propiedades reológicas del material. Para alcanzar dichos objetivos se ha llevado a cabo un amplio programa experimental cuyas etapas principales son las siguientes: • Definir y desarrollar un método de diseño que permita caracterizar de forma adecuada las propiedades mecánicas de la “interfase”. Esta primera fase experimental incluye: o las consideraciones generales del propio método de fabricación basado en el concepto de fabricación de materiales gradiente funcionales denominado “reología y gravedad”, o las consideraciones específicas del método de caracterización, o la caracterización de la “interfase”. • Estudiar el comportamiento mecánico sobre elementos estructurales, utilizando distintas configuraciones de MGF-laminado frente a acciones tanto estáticas como dinámicas con el fin de comprobar la viabilidad del material para ser usado en elementos estructurales tales como vigas, placas, pilares, etc. Los resultados indican la viabilidad de la metodología de fabricación adoptada, así como, las ventajas tanto estructurales como en reducción de costes de las soluciones laminadas propuestas. Es importante destacar la mejora en términos de resistencia a flexión, compresión o impacto del hormigón autocompactante gradiente funcional en comparación con soluciones de HACRFA monolíticos inclusos con un volumen neto de fibras (Vf) doble o superior. Self-compacting concrete (SCC) is an important advance in the concrete technology in the last decades. It is a new type of high performance concrete with the ability of flowing under its own weight and without the need of vibrations. Due to its specific fresh or rheological properties, such as filling ability, passing ability and segregation resistance, SCC may contribute to a significant improvement of the quality of concrete structures and open up new field for the application of concrete. On the other hand, the usefulness of steel fibre-reinforced concrete (SFRC) in civil engineering applications is unquestionable. SFRC can improve significantly the hardened mechanical properties such as tensile strength, impact resistance, toughness and energy absorption capacity. Compared to SFRC, self-compacting steel fibre-reinforced concrete (SCSFRC) is a relatively new type of concrete with high flowability and good cohesiveness. SCSFRC offers very attractive economical and technical benefits thanks to SCC rheological properties, which can be further extended, when combined with SFRC for improving their mechanical characteristics. However, for the different concrete structural elements, a single concrete mix is selected without an attempt to adapt the diverse fibre-reinforced concretes to the stress-strain sectional properly. This thesis focused on the development of high performance cement-based structural composites made of SCC with and without steel fibres, and their applications for enhanced mechanical properties in front of different types of load and pattern configurations. It presents a new direction for tackling the mechanical problem. The approach adopted is based on the concept of functionally graded cementitious composite (FGCC) where part of the plain SCC is strategically replaced by SCSFRC in order to obtain laminated functionally graded self-compacting cementitious composites, laminated-FGSCC, in single structural elements as beams, columns, slabs, etc. The approach also involves a most suitable casting method, which uses SCC technology to eliminate the potential sharp interlayer while easily forming a robust and regular reproducible graded interlayer of 1-3 mm by controlling the rheology of the mixes and using gravity at the same time to encourage the use of the powerful concept for designing more performance suitable and cost-efficient structural systems. To reach the challenging aim, a wide experimental programme has been carried out involving two main steps: • The definition and development of a novel methodology designed for the characterization of the main parameter associated to the interface- or laminated-FGSCC solutions: the graded interlayer. Work of this first part includes: o the design considerations of the innovative (in the field of concrete) production method based on “rheology and gravity” for producing FG-SCSFRC or as named in the thesis FGSCC, casting process and elements, o the design of a specific testing methodology, o the characterization of the interface-FGSCC by using the so designed testing methodology. • The characterization of the different medium size FGSCC samples under different static and dynamic loads patterns for exploring their possibilities to be used for structural elements as beams, columns, slabs, etc. The results revealed the efficiency of the manufacturing methodology, which allow creating robust structural sections, as well as the feasibility and cost effectiveness of the proposed FGSCC solutions for different structural uses. It is noticeable to say the improvement in terms of flexural, compressive or impact loads’ responses of the different FGSCC in front of equal strength class SCSFRC bulk elements with at least the double of overall net fibre volume fraction (Vf).

The effects of tantalum addition on the microtexture and mechanical behaviour of tungsten for ITER applications

Tungsten (W) and its alloys are very promising materials for producing plasma-facing components (PFCs) in the fusion power reactors of the near future, even as a structural part in them. However, whereas the properties of pure tungsten are suitable for a PFC, its structural applications are still limited due to its low toughness, ductile to brittle transition temperature and recrystallization behaviour. Therefore, many efforts have been made to improve its performance by alloying tungsten with other elements. Hence, in this investigation, the thermo-mechanical performance of two new tungsten-tantalum materials has been evaluated. Materials with We5wt.%Ta and We15wt.%Ta were processed by mechanical alloying (MA) and later consolidation by hot isostatic pressing (HIP), with distinct settings for each composition. Thus, it was possible to determine the relationship between the microstructure and the addition of Ta with the macroscopic mechanical properties. These were measured by means of hardness, flexural strength and fracture toughness, in the temperature range of 300e1473 K. The microstructure and the fracture surfaces features of the tested materials were analysed by Field Emission Scanning Electron Microscopy (FESEM).