Evaluation of the reliability of commercial concentrator triple-junction solar cells by means of accelerated life tests (ALT)

A temperature accelerated life test on commercial concentrator lattice-matched GaInP/GaInAs/Ge triple-junction solar cells has been carried out. The solar cells have been tested at three different temperatures: 119, 126 and 164 °C and the nominal photo-current condition (820 X) has been emulated by injecting current in darkness. All the solar cells have presented catastrophic failures. The failure distributions at the three tested temperatures have been fitted to an Arrhenius-Weibull model. An Arrhenius activation energy of 1.58 eV was determined from the fit. The main reliability functions and parameters (reliability function, instantaneous failure rate, mean time to failure, warranty time) of these solar cells at the nominal working temperature (80 °C) have been obtained. The warranty time obtained for a failure population of 5 % has been 69 years. Thus, a long-term warranty could be offered for these particular solar cells working at 820 X, 8 hours per day at 80 °C.

Characterisation of the operation & maintenance phase in PV rural electrification programmes

Con 1.300 millones de personas en el mundo sin acceso a la electricidad (la mayoría en entornos rurales de países empobrecidos), la energía solar fotovoltaica constituye una solución viable técnica y económicamente para electrificar las zonas más remotas del planeta donde las redes eléctricas convencionales no llegan. Casi todos los países en el mundo han desarrollado algún tipo de programa de electrificación fotovoltaica rural durante los últimos 40 años, principalmente los países más pobres, donde a través de diferentes modelos de financiación, se han instalado millones de sistemas solares domiciliarios (pequeños sistemas fotovoltaicos para uso doméstico). Durante este largo período, se han ido superando muchas barreras, como la mejora de la calidad de los sistemas fotovoltaicos, la reducción de costes, la optimización del diseño y del dimensionado de los sistemas, la disponibilidad financiera para implantar programas de electrificación rural, etc. Gracias a esto, la electrificación rural descentralizada ha experimentado recientemente un salto de escala caracterizada por la implantación de grandes programas con miles de sistemas solares domiciliarios e integrando largos períodos de mantenimiento. Muchos de estos grandes programas se están llevando a cabo con limitado éxito, ya que generalmente parten de supuestos e hipótesis poco contrastadas con la realidad, comprometiendo así un retorno económico que permita el desarrollo de esta actividad a largo plazo. En este escenario surge un nuevo reto: el de cómo garantizar la sostenibilidad de los grandes programas de electrificación rural fotovoltaica. Se argumenta que la principal causa de esta falta de rentabilidad es el imprevisto alto coste de la fase de operación y mantenimiento. Cuestiones clave tales como la estructura de costes de operación y mantenimiento o la fiabilidad de los componentes del sistema fotovoltaico no están bien caracterizados hoy en día. Esta situación limita la capacidad de diseñar estructuras de mantenimiento capaces de asegurar la sostenibilidad y la rentabilidad del servicio de operación y mantenimiento en estos programas. Esta tesis doctoral tiene como objetivo responder a estas cuestiones. Se ha realizado varios estudios sobre la base de un gran programa de electrificación rural fotovoltaica real llevado a cabo en Marruecos con más de 13.000 sistemas solares domiciliarios instalados. Sobre la base de este programa se ha hecho una evaluación en profundidad de la fiabilidad de los sistemas solares a partir de los datos de mantenimiento recogidos durante 5 años con más de 80.000 inputs. Los resultados han permitido establecer las funciones de fiabilidad de los equipos tal y como se comportan en condiciones reales de operación, las tasas de fallos y los tiempos medios hasta el fallo para los principales componentes del sistema, siendo este el primer caso de divulgación de resultados de este tipo en el campo de la electrificación rural fotovoltaica. Los dos principales componentes del sistema solar domiciliario, la batería y el módulo fotovoltaico, han sido analizados en campo a través de una muestra de 41 sistemas trabajando en condiciones reales pertenecientes al programa solar marroquí. Por un lado se ha estudiado la degradación de la capacidad de las baterías y por otro la degradación de potencia de los módulos fotovoltaicos. En el caso de las baterías, los resultados nos han permitido caracterizar la curva de degradación en capacidad llegando a obtener una propuesta de nueva definición del umbral de vida útil de las baterías en electrificación rural. También sobre la base del programa solar de Marruecos se ha llevado a cabo un estudio de caracterización de los costes reales de operación y mantenimiento a partir de la base de datos de contabilidad del programa registrados durante 5 años. Los resultados del estudio han permitido definir cuáles son costes que más incidencia tienen en el coste global. Se han obtenido los costes unitarios por sistema instalado y se han calculado los montantes de las cuotas de mantenimiento de los usuarios para garantizar la rentabilidad de la operación y mantenimiento. Finalmente, se propone un modelo de optimización matemática para diseñar estructuras de mantenimiento basado en los resultados de los estudios anteriores. La herramienta, elaborada mediante programación lineal entera mixta, se ha aplicado al programa marroquí con el fin de validar el modelo propuesto. ABSTRACT With 1,300 million people worldwide deprived of access to electricity (mostly in rural environments), photovoltaic solar energy has proven to be a cost‐effective solution and the only hope for electrifying the most remote inhabitants of the planet, where conventional electric grids do not reach because they are unaffordable. Almost all countries in the world have had some kind of rural photovoltaic electrification programme during the past 40 years, mainly the poorer countries, where through different organizational models, millions of solar home systems (small photovoltaic systems for domestic use) have been installed. During this long period, many barriers have been overcome, such as quality enhancement, cost reduction, the optimization of designing and sizing, financial availability, etc. Thanks to this, decentralized rural electrification has recently experienced a change of scale characterized by new programmes with thousands of solar home systems and long maintenance periods. Many of these large programmes are being developed with limited success, as they have generally been based on assumptions that do not correspond to reality, compromising the economic return that allows long term activity. In this scenario a new challenge emerges, which approaches the sustainability of large programmes. It is argued that the main cause of unprofitability is the unexpected high cost of the operation and maintenance of the solar systems. In fact, the lack of a paradigm in decentralized rural services has led to many private companies to carry out decentralized electrification programmes blindly. Issues such as the operation and maintenance cost structure or the reliability of the solar home system components have still not been characterized. This situation does not allow optimized maintenance structure to be designed to assure the sustainability and profitability of the operation and maintenance service. This PhD thesis aims to respond to these needs. Several studies have been carried out based on a real and large photovoltaic rural electrification programme carried out in Morocco with more than 13,000 solar home systems. An in‐depth reliability assessment has been made from a 5‐year maintenance database with more than 80,000 maintenance inputs. The results have allowed us to establish the real reliability functions, the failure rate and the main time to failure of the main components of the system, reporting these findings for the first time in the field of rural electrification. Both in‐field experiments on the capacity degradation of batteries and power degradation of photovoltaic modules have been carried out. During the experiments both samples of batteries and modules were operating under real conditions integrated into the solar home systems of the Moroccan programme. In the case of the batteries, the results have enabled us to obtain a proposal of definition of death of batteries in rural electrification. A cost assessment of the Moroccan experience based on a 5‐year accounting database has been carried out to characterize the cost structure of the programme. The results have allowed the major costs of the photovoltaic electrification to be defined. The overall cost ratio per installed system has been calculated together with the necessary fees that users would have to pay to make the operation and maintenance affordable. Finally, a mathematical optimization model has been proposed to design maintenance structures based on the previous study results. The tool has been applied to the Moroccan programme with the aim of validating the model.

Modelización de contactos termoelastohidrodinámicos

La mejora en la eficiencia energética y la reducción de la tasa de fallos en los contactos lubricados son aspectos que resultan de gran interés en numerosos sectores de la industria, y plantean en estos momentos nuevas dificultades operativas y retos para un futuro próximo. Los avances tecnológicos han incrementado las exigencias técnicas que se requieren a los aceites para cumplir su función al extender sus variables operativas a un mayor espectro de aplicaciones, tanto de condiciones de funcionamiento como a la gran variedad de nuevos materiales constitutivos de los engranajes en los que se tiene que utilizar. Por ello, actualmente se está incentivado el desarrollo de nuevos procedimientos que permitan comprender el comportamiento de este tipo de contactos lubricados, con el fin de lograr mejoras técnicas en su diseño y la correcta selección del aceite. En esta Tesis Doctoral se presenta una metodología de cálculo numérico que permite simular el comportamiento de contactos elastohidrodinámicos (EHD) puntuales, como puede ser el caso de un rodamiento. La resolución de este problema presenta diversas complejidades matemáticas y exige el desarrollo de un elaborado procedimiento de cálculo basado en técnicas multinivel. Para hacer del procedimiento una herramienta válida en un gran número de condiciones de funcionamiento y tipos de lubricantes, se ha tenido en cuenta en el cálculo la posible aparición de comportamientos no-Newtonianos del lubricante y fenómenos de generación y disipación de calor, provocados por el movimiento relativo del fluido y las superficies en contacto. Para la validación del procedimiento, se han contrastado los resultados numéricos obtenidos con nuestro método, con los resultados numéricos y experimentales publicados por otros autores y con valores experimentales propios medidos en un equipo de ensayo de contacto puntual tipo MTM. El desarrollo de este programa ha dotado a la División de Ingeniería de Máquinas de una herramienta que ha permitido, y sobre todo va permitir, evaluar la importancia de cada uno de los parámetros reológicos en los diferentes problemas que va a tener que abordar, evaluación que hasta el momento se realizaba con métodos aproximados que describen la fenomenología con mucha menos precisión. A la hora de emplear nuestro procedimiento numérico para simular situaciones reales, nos hemos encontrado con el obstáculo de que es muy complicado encontrar, en la bibliografía y bases de datos, los parámetros que caracterizan el comportamiento reológico del lubricante en las condiciones de presión, temperatura y grado de cizallamiento habituales en las que se trabaja en este tipo de contactos, y las pocas medidas que existen para estas condiciones de funcionamiento son poco fiables. Por ello como complemento al objetivo principal de esta Tesis hemos desarrollado una metodología para caracterizar los lubricantes en estas condiciones extremas. Dicha metodología está basada en la buena descripción que hace nuestro programa del coeficiente de fricción, lo que nos ha permitido obtener los parámetros reológicos del III lubricante a partir de las medidas experimentales del coeficiente de fricción generado en un equipo MTM lubricado con el lubricante que se desea caracterizar. Madrid, Octubre de 2012 IV Improving energy efficiency and reducing the failure rate in lubricated contacts are issues that are of great interest in many sectors of industry, and right now posed operational difficulties and new challenges for the near future. Technological advances have increased the technical demands required to oils to fulfil its role by extending its operational variables to a wider range of applications, both operating conditions and to the wide variety of new materials which constitute the gear in which must be used. For this reason, has being encouraged currently to develop new procedures to understand the behaviour of this type of lubricated contacts, in order to achieve improvements in design techniques and the correct oil selection. In this Thesis we present a numerical methodology to simulate the puntual elastohydrodynamic contact behaviour (EHD), such as a roller bearing. The resolution of this problem presents various mathematical complexities and requires the development of an elaborate calculation procedure based on multilevel techniques. To make the procedure a valid tool in a wide range of operating conditions and types of lubricants, has been taken into account in calculating the possible occurrence of non-Newtonian behaviour of the lubricant and phenomena of generation and dissipation of heat, caused by the fluid relative motion and contacting surfaces. For the validation of the method, we have compared the numerical results obtained with our method with numerical and experimental results published by other authors also with own experimental values measured on point-contact test equipment MTM. The development of this program has provided the Machines Engineering Division of a tool that has allowed, and especially will allow to evaluate the importance of each of the rheological parameters on the various problems that will have to be addressed, evaluation performed hitherto described methods that phenomenology approximated with much less accuracy. When using our numerical procedure to simulate real situations we have encountered the obstacle that is very difficult to find, in the literature and database, parameters characterizing the rheological behaviour of the lubricant in the usual conditions of pressure, temperature and shear rate in which you work in this type of contact, and the few measures that exist for these operating conditions are unreliable. Thus in addition to the main objective of this thesis, we have developed a methodology to characterize the lubricants in these extreme conditions. This methodology is based on the good description, which makes our program, of the coefficient of friction, that allowed us to obtain the lubricant rheological parameters from experimental measurements of the friction coefficient generated on lubricated MTM equipment with the lubricant to be characterized.

Modelling seed germination in forest tree species through survival analysis. The Pinus pinea L. case study

The direct application of existing models for seed germination may often be inadequate in the context of ecology and forestry germination experiments. This is because basic model assumptions are violated and variables available to forest managers are rarely used. In this paper, we present a method which addresses the aforementioned shortcomings. The approach is illustrated through a case study of Pinus pinea L. Our findings will also shed light on the role of germination in the general failure of natural regeneration in managed forests of this species. The presented technique consists of a mixed regression model based on survival analysis. Climate and stand covariates were tested. Data for fitting the model were gathered from a 5-year germination experiment in a mature, managed P. pinea stand in the Northern Plateau of Spain in which two different stand densities can be found. The model predictions proved to be unbiased and highly accurate when compared with the training data. Germination in P. pinea was controlled through thermal variables at stand level. At microsite level, low densities negatively affected the probability of germination. A time-lag in the response was also detected. Overall, the proposed technique provides a reliable alternative to germination modelling in ecology/forestry studies by using accessible/ suitable variables. The P. pinea case study highlights the importance of producing unbiased predictions. In this species, the occurrence and timing of germination suggest a very different regeneration strategy from that understood by forest managers until now, which may explain the high failure rate of natural regeneration in managed stands. In addition, these findings provide valuable information for the management of P. pinea under climate-change conditions.

Study about the Problem of Dropping of Subjects by Students During an Academinc Year at the University.

In university studies, it is not unusual for students to drop some of the subjects they have enrolled in for the academic year. They start by not attending lectures, sometimes due to neglect or carelessness, or because they find the subject too difficult, this means that they lose the continuity in the topics that the professor follows. If they try to attend again they discover that they hardly understand anything and become discouraged and so decide to give up attending lectures and study on their own. However some fail to turn up to do their final exams and the failure rate of those who actually do the exams is high. The problem is that this is not only the case with one specific subject, but it is often the same with many subjects. The result is that students arent’s productive enough, wasting time and also prolonging their years of study which entails a great cost for families. Degree courses structured to be conducted and completed in three academic courses, it may in fact take up to an average of six or more academic courses. In this paper, we have studied this problem, which apart from the waste of money and time, produces frustration in the student, who finds that he has not been able to achieve what he had proposed at the beginning of the course. It is quite common, to find students who do not even pass nor 50% of the subjects they had enrolled in for the academic year. If this happens repeatedly to a student, it can be the point when he considers dropping out altogether. This is also a concern for the universities, especially in the early courses. In our experience as professors, we have found that students, who attend lectures regularly and follow the explanations, approach the final exams with confidence and rarely fail the subject. In this proposal we present some techniques and methods carried out to solve in possible, the problem of lack of attendance to lectures. This involves "rewarding students for their assistance and participation in lectures". Rewarding assistance with a "prize" that counts for the final mark on the subject and involving more participation in the development of lectures. We believe that we have to teach students to use the lectures as part of their learning in a non-passive way. We consider the professor's work as fundamental in terms of how to convey the usefulness of these topics explained and the applications that they will have for their professional life in the future. In this way the student see for himself the use and importance of what he is learning. When his participation is required, he will feel more involved and confident participating in the educational system. Finally we present statistical results of studies carried out on different degrees and on different subjects over two consecutive years. In the first year we assessed only the final exams without considering the students attendance, or participation. In the second year, we have applied the techniques and methods proposed here. In addition we have compared the two ways of assessing subjects.

A friendly online C compiler to improve programming skills based on student self-assessment

This paper presents an online C compiler designed so that students can program their practical assignments in Programming courses. What is really innovative is the self-assessment of the exercises based on black-box tests and train students’ skill to test software. Moreover, this tool lets instructors, not only proposing and classifying practical exercises, but also evaluating automatically the efforts dedicated and the results obtained by the students. The system has been applied to the 1st-year students at the Industrial Engineering specialization at the Universidad Politecnica de Madrid. Results show that the students obtained better academic performance, reducing the failure rate in the practical exam considerably with respect to previous years, in addition that an anonymous survey proved that students are satisfied with the system because they get instant feedback about their programs.

A matrix pencil approach to the existence of compactly supported reconstruction functions in average sampling

The aim of this work is to solve a question raised for average sampling in shift-invariant spaces by using the well-known matrix pencil theory. In many common situations in sampling theory, the available data are samples of some convolution operator acting on the function itself: this leads to the problem of average sampling, also known as generalized sampling. In this paper we deal with the existence of a sampling formula involving these samples and having reconstruction functions with compact support. Thus, low computational complexity is involved and truncation errors are avoided. In practice, it is accomplished by means of a FIR filter bank. An answer is given in the light of the generalized sampling theory by using the oversampling technique: more samples than strictly necessary are used. The original problem reduces to finding a polynomial left inverse of a polynomial matrix intimately related to the sampling problem which, for a suitable choice of the sampling period, becomes a matrix pencil. This matrix pencil approach allows us to obtain a practical method for computing the compactly supported reconstruction functions for the important case where the oversampling rate is minimum. Moreover, the optimality of the obtained solution is established.

Statistical Calculation of the Main Reliability Functions of GaAs Concentrator III-V Solar Cells

This paper presents some of the results of a method to determine the main reliability functions of concentrator solar cells. High concentrator GaAs single junction solar cells have been tested in an Accelerated Life Test. The method can be directly applied to multi-junction solar cells. The main conclusions of this test carried out show that these solar cells are robust devices with a very low probability of failure caused by degradation during their operation life (more than 30 years). The evaluation of the probability operation function (i.e. the reliability function R(t)) is obtained for two nominal operation conditions of these cells, namely simulated concentration ratios of 700 and 1050 suns. Preliminary determination of the Mean Time to Failure indicates a value much higher than the intended operation life time of the concentrator cells.

Effect of the temperature, strain rate and microstructure on flow and fracture characteristics of Ti-45Al-2Nb-2Mn+0.8vol.% TiB2 XD alloy

A series of quasi-static and dynamic tensile tests at varying temperatures were carried out to determine the mechanical behaviour of Ti-45Al-2Nb-2Mn+0.8vol.% TiB2 XD as-HIPed alloy. The temperature for the tests ranged from room temperature to 850  ∘C. The effect of the temperature on the ultimate tensile strength, as expected, was almost negligible within the selected temperature range. Nevertheless, the plastic flow suffered some softening because of the temperature. This alloy presents a relatively low ductility; thus, a low tensile strain to failure. The dynamic tests were performed in a Split Hopkinson Tension Bar, showing an increase of the ultimate tensile strength due to the strain rate hardening effect. Johnson-Cook constitutive relation was used to model the plastic flow. A post-testing microstructural of the specimens revealed an inhomogeneous structure, consisting of lamellar α2 + γ structure and γ phase equiaxed grains in the centre, and a fully lamellar structure on the rest. The assessment of the duplex-fully lamellar area ratio showed a clear relationship between the microstructure and the fracture behaviour.

Overal reaction rate and stoichiometry for thermal decomposition of hydrazine

An asymptotic analysîs of the Eberstein-Glassman kinetic mechanlsm for the thermal décomposition of hydrazine is carried out. It is shown that at températures near 800°K and near 1000°K,and for hydrazine molar fractions of the order of unity, 10-2 the entire kinetics reduces to a single, overall reaction. Characteristic times for the chemical relaxation of ail active, intermediate species produced in the décomposition, and for the overall reaction, are obtained. Explicit expressions for the overall reaction rate and stoichiometry are given as functions of température, total molar concentration (or pressure)and hydrazine molar fraction. Approximate, patched expressions can then be obtained for values of température and hydrazine molar fraction between 750 and 1000°K, and 1 and 10-3 respectively.

Meromorphic continuation of functions and arbitrary distribution of interpolation points

We characterize the region of meromorphic continuation of an analytic function ff in terms of the geometric rate of convergence on a compact set of sequences of multi-point rational interpolants of ff. The rational approximants have a bounded number of poles and the distribution of interpolation points is arbitrary.

Seismic hazards of the Iberian Peninsula - evaluation with Kernel functions

The seismic hazard of the Iberian Peninsula is analysed using a nonparametric methodology based on statistical kernel functions; the activity rate is derived from the catalogue data, both its spatial dependence (without a seismogenetic zonation) and its magnitude dependence (without using Gutenberg–Richter's law). The catalogue is that of the Instituto Geográfico Nacional, supplemented with other catalogues around the periphery; the quantification of events has been homogenised and spatially or temporally interrelated events have been suppressed to assume a Poisson process. The activity rate is determined by the kernel function, the bandwidth and the effective periods. The resulting rate is compared with that produced using Gutenberg–Richter statistics and a zoned approach. Three attenuation laws have been employed, one for deep sources and two for shallower events, depending on whether their magnitude was above or below 5. The results are presented as seismic hazard maps for different spectral frequencies and for return periods of 475 and 2475 yr, which allows constructing uniform hazard spectra.

Mechanical behavior and deformation micromechanisms of polypropylene nonwoven fabrics as a function of temperature and strain rate

The mechanical behavior and the deformation and failure micromechanisms of a thermally-bonded polypropylene nonwoven fabric were studied as a function of temperature and strain rate. Mechanical tests were carried out from 248 K (below the glass transition temperature) up to 383 K at strain rates in the range ≈10−3 s−1 to 10−1 s−1. In addition, individual fibers extracted from the nonwoven fabric were tested under the same conditions. Micromechanisms of deformation and failure at the fiber level were ascertained by means of mechanical tests within the scanning electron microscope while the strain distribution at the macroscopic level upon loading was determined by means of digital image correlation. It was found that the nonwoven behavior was mainly controlled by the properties of the fibers and of the interfiber bonds. Fiber properties determined the nonlinear behavior before the peak load while the interfiber bonds controlled the localization of damage after the peak load. The influence of these properties on the strength, ductility and energy absorbed during deformation is discussed from the experimental observations.

Seismic hazard of the Iberian Peninsula: evaluation with Kernel functions

The seismic hazard of the Iberian Peninsula is analysed using a nonparametric methodology based on statistical kernel functions; the activity rate is derived from the catalogue data, both its spatial dependence (without a seismogenic zonation) and its magnitude dependence (without using Gutenberg–Richter's relationship). The catalogue is that of the Instituto Geográfico Nacional, supplemented with other catalogues around the periphery; the quantification of events has been homogenised and spatially or temporally interrelated events have been suppressed to assume a Poisson process. The activity rate is determined by the kernel function, the bandwidth and the effective periods. The resulting rate is compared with that produced using Gutenberg–Richter statistics and a zoned approach. Three attenuation relationships have been employed, one for deep sources and two for shallower events, depending on whether their magnitude was above or below 5. The results are presented as seismic hazard maps for different spectral frequencies and for return periods of 475 and 2475 yr, which allows constructing uniform hazard spectra

Multiscale modeling of the plastic behaviour in single crystal tungsten: from atomistic to crystal plasticity simulations

En una planta de fusión, los materiales en contacto con el plasma así como los materiales de primera pared experimentan condiciones particularmente hostiles al estar expuestos a altos flujos de partículas, neutrones y grandes cargas térmicas. Como consecuencia de estas diferentes y complejas condiciones de trabajo, el estudio, desarrollo y diseño de estos materiales es uno de los más importantes retos que ha surgido en los últimos años para la comunidad científica en el campo de los materiales y la energía. Debido a su baja tasa de erosión, alta resistencia al sputtering, alta conductividad térmica, muy alto punto de fusión y baja retención de tritio, el tungsteno (wolframio) es un importante candidato como material de primera pared y como posible material estructural avanzado en fusión por confinamiento magnético e inercial. Sin embargo, el tiempo de vida del tungsteno viene controlado por diversos factores como son su respuesta termo-mecánica en la superficie, la posibilidad de fusión y el fallo por acumulación de helio. Es por ello que el tiempo de vida limitado por la respuesta mecánica del tungsteno (W), y en particular su fragilidad, sean dos importantes aspectos que tienes que ser investigados. El comportamiento plástico en materiales refractarios con estructura cristalina cúbica centrada en las caras (bcc) como el tungsteno está gobernado por las dislocaciones de tipo tornillo a escala atómica y por conjuntos e interacciones de dislocaciones a escalas más grandes. El modelado de este complejo comportamiento requiere la aplicación de métodos capaces de resolver de forma rigurosa cada una de las escalas. El trabajo que se presenta en esta tesis propone un modelado multiescala que es capaz de dar respuestas ingenieriles a las solicitudes técnicas del tungsteno, y que a su vez está apoyado por la rigurosa física subyacente a extensas simulaciones atomísticas. En primer lugar, las propiedades estáticas y dinámicas de las dislocaciones de tipo tornillo en cinco potenciales interatómicos de tungsteno son comparadas, determinando cuáles de ellos garantizan una mayor fidelidad física y eficiencia computacional. Las grandes tasas de deformación asociadas a las técnicas de dinámica molecular hacen que las funciones de movilidad de las dislocaciones obtenidas no puedan ser utilizadas en los siguientes pasos del modelado multiescala. En este trabajo, proponemos dos métodos alternativos para obtener las funciones de movilidad de las dislocaciones: un modelo Monte Cario cinético y expresiones analíticas. El conjunto de parámetros necesarios para formular el modelo de Monte Cario cinético y la ley de movilidad analítica son calculados atomísticamente. Estos parámetros incluyen, pero no se limitan a: la determinación de las entalpias y energías de formación de las parejas de escalones que forman las dislocaciones, la parametrización de los efectos de no Schmid característicos en materiales bcc,etc. Conociendo la ley de movilidad de las dislocaciones en función del esfuerzo aplicado y la temperatura, se introduce esta relación como ecuación de flujo dentro de un modelo de plasticidad cristalina. La predicción del modelo sobre la dependencia del límite de fluencia con la temperatura es validada experimentalmente con ensayos uniaxiales en tungsteno monocristalino. A continuación, se calcula el límite de fluencia al aplicar ensayos uniaxiales de tensión para un conjunto de orientaciones cristalográticas dentro del triángulo estándar variando la tasa de deformación y la temperatura de los ensayos. Finalmente, y con el objetivo de ser capaces de predecir una respuesta más dúctil del tungsteno para una variedad de estados de carga, se realizan ensayos biaxiales de tensión sobre algunas de las orientaciones cristalográficas ya estudiadas en función de la temperatura.-------------------------------------------------------------------------ABSTRACT ----------------------------------------------------------Tungsten and tungsten alloys are being considered as leading candidates for structural and functional materials in future fusion energy devices. The most attractive properties of tungsten for the design of magnetic and inertial fusion energy reactors are its high melting point, high thermal conductivity, low sputtering yield and low longterm disposal radioactive footprint. However, tungsten also presents a very low fracture toughness, mostly associated with inter-granular failure and bulk plasticity, that limits its applications. As a result of these various and complex conditions of work, the study, development and design of these materials is one of the most important challenges that have emerged in recent years to the scientific community in the field of materials for energy applications. The plastic behavior of body-centered cubic (bcc) refractory metals like tungsten is governed by the kink-pair mediated thermally activated motion of h¿ (\1 11)i screw dislocations on the atomistic scale and by ensembles and interactions of dislocations at larger scales. Modeling this complex behavior requires the application of methods capable of resolving rigorously each relevant scale. The work presented in this thesis proposes a multiscale model approach that gives engineering-level responses to the technical specifications required for the use of tungsten in fusion energy reactors, and it is also supported by the rigorous underlying physics of extensive atomistic simulations. First, the static and dynamic properties of screw dislocations in five interatomic potentials for tungsten are compared, determining which of these ensure greater physical fidelity and computational efficiency. The large strain rates associated with molecular dynamics techniques make the dislocation mobility functions obtained not suitable to be used in the next steps of the multiscale model. Therefore, it is necessary to employ mobility laws obtained from a different method. In this work, we suggest two alternative methods to get the dislocation mobility functions: a kinetic Monte Carlo model and analytical expressions. The set of parameters needed to formulate the kinetic Monte Carlo model and the analytical mobility law are calculated atomistically. These parameters include, but are not limited to: enthalpy and energy barriers of kink-pairs as a function of the stress, width of the kink-pairs, non-Schmid effects ( both twinning-antitwinning asymmetry and non-glide stresses), etc. The function relating dislocation velocity with applied stress and temperature is used as the main source of constitutive information into a dislocation-based crystal plasticity framework. We validate the dependence of the yield strength with the temperature predicted by the model against existing experimental data of tensile tests in singlecrystal tungsten, with excellent agreement between the simulations and the measured data. We then extend the model to a number of crystallographic orientations uniformly distributed in the standard triangle and study the effects of temperature and strain rate. Finally, we perform biaxial tensile tests and provide the yield surface as a function of the temperature for some of the crystallographic orientations explored in the uniaxial tensile tests.