Sistemas de Gestión de la Calidad. Metodología para implementar proyectos de mejora continua para la reducción de los defectos de construcción en edificación de viviendas

La mejora continua debería estar presente siempre en las empresas, dispongan o no de sistemas de gestión. Sin embargo, su aplicación en el sector de la construcción es especialmente difícil debido a las características particulares del mismo. Por este motivo se plantea el objetivo principal de esta Tesis Doctoral: “Establecer una metodología de trabajo que permita a las empresas constructoras implantar proyectos de mejora continua para incrementar la calidad de las viviendas entregadas a los usuarios”. En la investigación llevada a cabo se han inspeccionado 818 viviendas, recogiendo un total de 82.550 incidencias, las cuales se han analizado aplicando cuatro de las siete herramientas estadísticas básicas de la mejora continua (Hoja de recogida de datos, Estratificación, Histograma y Diagrama de Pareto), concluyendo que los tres oficios que concentran el 80% de los defectos, en los que convendría actuar para reducir de manera significativa los fallos de construcción en la fase de pre-entrega, son: Carpintería de Madera, Revestimientos Cerámicos e Instalación de Electricidad. De entre estos tres oficios se ha seleccionado el de Revestimientos Cerámicos para poner en práctica un proyecto de mejora continua. Analizando los datos relativos a este oficio se elabora un listado de 25 defectos tipo en los que se pueden agrupar todas las incidencias detectadas. Aplicando de nuevo las cuatro herramientas básicas de la calidad se destacan los 10 defectos tipo con mayor impacto en volumen de incidencias y en coste de reparación, para focalizar los esfuerzos de mejora. Con esta información se elabora un documento de criterios técnicos para la ejecución de los Revestimientos Cerámicos que se implanta, en parte, en varias obras para tratar de reducir los defectos detectados en las viviendas antes de la entrega a sus propietarios, y se definen unos Índices de Calidad para medir los resultados. Se toman datos de nuevo a 6 y 20 meses desde la implantación del protocolo, se analizan y se calculan los resultados del proyecto de mejora, concluyendo que se está avanzando positivamente. En base a toda la información recogida a lo largo del proceso de la investigación y de la experiencia del proyecto de mejora implantado, se presenta una propuesta de metodología para implementar proyectos de mejora, así como la documentación recomendada para su puesta en práctica, además de la documentación técnica específica para la prevención de los defectos de construcción en Revestimientos Cerámicos incluyendo las fichas de control para la recepción de materiales, control de ejecución y control de recepción del revestimiento terminado. ABSTRACT Continuous improvement should always be a core value in firms of all kinds, whether or not they implement management systems. Nevertheless, its application in the construction sector seems especially difficult due to its inherent intricacies and complexity. The study of this phenomenon is the main aim of the hereby presented PhD dissertation "Establishment of a working methodology that allows construction (related) firms to carry out projects of continuous improvement in order to increase the quality of housing upon delivery to the client". In the present research 818 housing units have been inspected, collecting a total of 82550 incidence entries, which have been analyzed by means of 4 out of the 7 basic statistical tools of continuous improvement: Data collection sheets, stratification, histogram, and Pareto diagram. The data shows that the 3 main trades where special actions should be taken in order to significantly reduce construction defects are: carpentry, ceramic cladding, and electricity systems. These trades combined account for the 80% of the total defects detected during the inspections. Among the mentioned works, ceramic tiling is selected as a continuous improvement case study project. Analysing data relative to this specific trade, a list of 25 defect types is developed. These types gather all detected defects under this group. Further applying the four statistical tools referred to above, the 10 most significant events are highlighted as to clearly determine the improvement measures. These events have the most impact on both volume of defects and reparation costs. This information is then put together in a document of technical criteria for the correct execution of ceramic tiling that is implemented in various ongoing projects under construction as to minimize the defects prior to the final delivery to the client. Also, a series of Quality Index are defined as criteria for execution suitability. 6 to 20 months after the implementation of this control protocol, the same process is repeated with the purpose of comparing results. It is concluded that a positive evolution takes place. Based both on the information collected throughout the research process and the experience of the case study, the dissertation proposes a methodology to successfully implement improvement projects along with reference documentation and specific technical documents for the prevention of construction defects in ceramic tiling, including (i) material reception control sheets, (ii) an execution control sheet, and a sheet relative to the (iii) control of the finished cladding.

Revisiting the method to obtain the mechanical properties of hydrided fuel cladding in the hoop direction

The method reported in the literature to calculate the stress–strain curve of nuclear fuel cladding from ring tensile test is revisited in this paper and a new alternative is presented. In the former method, two universal curves are introduced under the assumption of small strain. In this paper it is shown that these curves are not universal, but material-dependent if geometric nonlinearity is taken into account. The new method is valid beyond small strains, takes geometric nonlinearity into consideration and does not need universal curves. The stress–strain curves in the hoop direction are determined by combining numerical calculations with experimental results in a convergent loop. To this end, ring tensile tests were performed in unirradiated hydrogen-charged samples. The agreement among the simulations and the experimental results is excellent for the range of concentrations tested (up to 2000 wppm hydrogen). The calculated stress–strain curves show that the mechanical properties do not depend strongly on the hydrogen concentration, and that no noticeable strain hardening occurs. However, ductility decreases with the hydrogen concentration, especially beyond 500 wppm hydrogen. The fractographic results indicate that as-received samples fail in a ductile fashion, whereas quasicleavage is bserved in the hydrogen-charged samples.

Residual strain scanning of alumina-based ceramic composites by neutron diffraction

The objective of this work is to non-destructively determine the residual stress profile in the bulk of two characteristic types of alumina-based composites, with the aim of improving their durability and structural integrity.

Crack mechanical failure in ceramic materials under ion irradiation: case of lithium niobate crystal

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.

Determination of the hoop fracture properties of unirradiated hydrogen-charged nuclear fuel cladding from ring compression tests

In this work, a new methodology is devised to obtain the fracture properties of nuclear fuel cladding in the hoop direction. The proposed method combines ring compression tests and a finite element method that includes a damage model based on cohesive crack theory, applied to unirradiated hydrogen-charged ZIRLOTM nuclear fuel cladding. Samples with hydrogen concentrations from 0 to 2000 ppm were tested at 20 �C. Agreement between the finite element simulations and the experimental results is excellent in all cases. The parameters of the cohesive crack model are obtained from the simulations, with the fracture energy and fracture toughness being calculated in turn. The evolution of fracture toughness in the hoop direction with the hydrogen concentration (up to 2000 ppm) is reported for the first time for ZIRLOTM cladding. Additionally, the fracture micromechanisms are examined as a function of the hydrogen concentration. In the as-received samples, the micromechanism is the nucleation, growth and coalescence of voids, whereas in the samples with 2000 ppm, a combination of cuasicleavage and plastic deformation, along with secondary microcracking is observed.

New designs of the ceramic bricks of horizontal hexagonal hollow

This article is intended to state that Technical Drawing is a multiple tool of expression and communication essential to develop inquiry processes, the scientifically basis and comprehension of drawings and technological designs that can be manufactured. We demonstrate graphically and analytically that spatial vision and graphic thinking allow us to identify graphically real life problems, develop proposals of solutions to be analysed from different points of view, plan and develop the project, provide information needed to make decisions on objects and technological processes. From the knowledge of Technical Drawing and CAD tools we have developed graphic analyses to improve and optimize our proposed modification of the geometry of the rectangular cells of conventional bricks by hexagonal cells, which is protected by a Spanish patent owned by the Polytechnic University of Madrid. This new internal geometry of the bricks will improve the efficiency and the acoustic damping of walls built with the ceramic bricks of horizontal hollow, maintaining the same size of the conventional bricks, without increasing costs either in the manufacture and the sale. A single brick will achieve the width equivalent to more than FOUR conventional bricks.

Relationship between residual stresses and mechanical behavior in ceramic composites

En este trabajo, materiales de tipo alúmina/Y-TZP (ZrO2 tetragonal, estabilizada con 3 mol. % Y2O3), como sistema cerámico popular por sus mejoradas propiedades mecánicas en comparación con las cerámicas de alúmina puras, han sido estudiados en términos de propiedades mecánicas y tensiones residuales. El novedoso método de colado en cinta, consistente en el apilamiento de cintas de cerámica verde a temperatura ambiente y el uso de bajas presiones, se ha escogido para la presente investigación con el fin de poder aprovechar al máximo el futuro desarrollo de materiales laminados de alúmina-óxido de circonio. Se han determinado las propiedades de los materiales obtenidos por este nuevo método de procesamiento comparándolas con las de los materiales obtenidos por “slip casting”, con el fin de analizar si el método propuesto afecta a la microestructura y, por tanto, a las propiedades mecánicas y tensiones residuales propias de estos materiales. Para analizar la idoneidad del proceso de fabricación, utilizado para evitar la presencia de discontinuidades en las intercaras entre las láminas así como otros fenómenos que puedan interferir con las propiedades mecánicas, se estudiaron materiales cerámicos con la misma composición en cintas. Por otra parte también se analizó el efecto de la adición de óxido de circonio sobre la aparición de tensiónes residuales en cerámicas Al2O3/Y-TZP, teniendo en cuenta su notable influencia sobre las propiedades microestructurales y mecánicas de los materiales, así como el requisito de co-sinterización de capas con diferentes materiales compuestos en materiales laminados. La caracterización del material incluye la determinación de la densidad, el análisis de la microestructura, la obtención de las propiedades mecánicas (módulo de elasticidad, dureza, resistencia a la flexión y tenacidad de fractura) así como de las tensiones residuales. En combinación con otros métodos de medida tradicionales, la nanoindentación también se empleó como una técnica adicional para la medida del módulo de elasticidad y de la dureza. Por otro lado, diferentes técnicas de difracción con neutrones, tanto las basadas en longitud de onda constante (CW) como en tiempo de vuelo (TOF), han sido empleadas para la medición fiable de la deformación residual a través del grosor en muestras a granel. Las tensiones residuales fueron determinadas con elevada precisión, aplicando además métodos de análisis apropiados, como por ejemplo el refinamiento de Rietveld. Las diferentes fases en cerámicas sinterizadas, especialmente las de zirconia, se examinaron con detalle mediante el análisis de Rietveld, teniendo en cuenta el complicado polimorfismo del Óxido de Zirconio (ZrO2) así como las posibles transformaciones de fase durante el proceso de fabricación. Los efectos del contenido de Y-TZP en combinación con el nuevo método de procesamiento sobre la microestructura, el rendimiento mecánico y las tensiones residuales de los materiales estudiados (Al2O3/Y-TZP) se resumen en el presente trabajo. Finalmente, los mecanismos de endurecimiento, especialmente los relacionados con las tensiones residuales, son igualmente discutidos. In present work, Alumina/Y-TZP (tetragonal ZrO2 stabilized with 3 mol% Y2O3) materials, as an popular ceramic system with improved mechanical properties compared with the pure alumina ceramics, have been studied in terms of mechanical properties and residual stresses. The novel tape casting method, which involved the stacking of green ceramics tapes at room temperature and using low pressures, is selected for manufacturing and investigation, in order to take full advantage of the future development of alumina-zirconia laminated materials. Features of materials obtained by the new processing method are determined and compared with those of materials obtained by conventional slip casting in a plaster mold, in order to study whether the proposed method of processing affects microstructure and thereby the mechanical properties and residual stresses characteristics of materials. To analyse the adequacy of the manufacturing process used to avoid the presence of discontinuities at the interfaces between the sheets and other phenomena that interfere with the mechanical properties, ceramic materials with the same composition in tapes were investigated. Moreover, the effect of addition of zirconia on residual stress development of Al2O3/Y-TZP ceramics were taken into investigations, considering its significantly influence on the microstructure and mechanical properties of materials as well as the requirement of co-sintering of layers with different composites in laminated materials. The characterization includes density, microstructure, mechanical properties (elastic modulus, hardness, flexure strength and fracture toughness) and residual stresses. Except of the traditional measurement methods, nanoindentation technique was also used as an additional measurement of the elastic modulus and hardness. Neutron diffraction, both the constant-wavelength (CW) and time-of-flight (TOF) neutron diffraction techniques, has been used for reliable through-thickness residual strain measurement in bulk samples. Residual stresses were precisely determined combined with appropriate analysis methods, e.g. the Rietveld refinement. The phase compositions in sintered ceramics especially the ones of zirconia were accurately examined by Rietveld analysis, considering the complex polymorph of ZrO2 and the possible phase transformation during manufacturing process. Effects of Y-TZP content and the new processing method on the microstructure, mechanical performance and residual stresses were finally summarized in present studied Al2O3/Y-TZP materials. The toughening mechanisms, especially the residual stresses related toughening, were theoretically discussed.

Caracterización de la cerámica para su empleo como material de enfriamiento evaporativo en la envolvente de los edificios = Ceramic characterization towards its application as evaporative cooling material in building envelopes

El presente trabajo de investigación determina las características de la cerámica que más eficientemente se comporta a evaporación y a enfriamiento. Con el objeto de ser empleado como material integrado en la envolvente de los edificios para reducir su carga de refrigeración. La cerámica es un buen material para ser empleado para la refrigeración por evaporación. Es un sólido poroso inerte que, tras ser sometido a cocción a temperaturas por encima de los 900ºC, resulta uno de los materiales que mejor se comportan como contenedor de agua en su red capilar para, posteriormente, ir liberándola por evaporación al mismo tiempo que se enfría su superficie. La metodología general de investigación, se divide en tres etapas: Búsqueda y análisis del estado de la técnica y de la investigación. Estudio teórico de la eficacia del enfriamiento evaporativo como estrategia de enfriamiento pasivo en la arquitectura. Etapa experimental, desarrollada en tres fases: una primera de definición de los parámetros determinantes del Enfriamiento Evaporativo en piezas cerámicas, una segunda de selección cerámica y diseño de ensayos experimentales y una tercera de caracterización de la cerámica bajo criterios de evaporación y de enfriamiento. El recorrido por el estado de la cuestión ha identificado las aplicaciones tecnológicas y las investigaciones científicas que emplean el Enfriamiento Evaporativo con piezas cerámicas como técnica de enfriamiento. Como resultado se ha obtenido una tabla de clasificación de sistemas de enfriamiento evaporativo y se ha constatado que el conjunto de las aplicaciones están centradas en el diseño de piezas o sistemas pero que, sin embargo, no existe una definición de las características de la cerámica para su empleo como material de enfriamiento por evaporación. El estudio teórico de la eficacia del empleo del enfriamiento evaporativo como estrategia de enfriamiento pasivo en la arquitectura se ha realizado mediante cálculos de porcentaje de ampliación de horas en confort con empleo de técnicas de enfriamiento evaporativo directo e indirecto (EED y EEI). Como resultado se obtienen unos mapas para el ámbito español de potencial de aplicación del EED y EEI. Los resultados permiten afirmar que mediante EE se puede llegar a confort en prácticamente la totalidad de las horas de los días más cálidos del año en muchas localidades. La metodología experimental se ha desarrollado en tres fases. En la fase inicial, se han definido los parámetros determinantes del enfriamiento evaporativo en un medio cerámico mediante ensayos experimentales de capacidad de evaporación y de caracterización. Se realizaron un total de 12 ensayos. Se determinó que el material cerámico tiene una gran influencia en la capacidad de evaporación y enfriamiento en las piezas cerámicas, apoyando la hipótesis inicial y la necesidad de caracterizar el material. La primera fase empírica se centró en la selección cerámica y el diseño de los ensayos experimentales de comportamiento hídrico. Se seleccionaron muestras de 5 tipos de cerámica. Se realizaron 4 tipos de ensayos de caracterización y 6 tipos de ensayos experimentales de comportamiento hídrico (total 123 muestras ensayadas). Los resultados obtenidos son de dos tipos, por un lado, se determinó cuál es el tipo de cerámica que más eficientemente se comporta a EE y, por otro, se rediseñaron los ensayos de la última fase experimental. Para la segunda fase experimental se seleccionaron cerámicas de fabricación manual abarcando el mayor número de localidades del ámbito español. Se realizaron ensayos de caracterización de 7 tipos y ensayos de comportamiento hídrico de 5 tipos (total 197 muestras ensayadas). Los resultados de caracterización han permitido aportar unos rangos de las características de la cerámica que más eficientemente se comporta en los ensayos de comportamiento hídrico. Al final de la investigación se ha caracterizado el material cerámico aportando características acerca de su porosidad, capacidad de absorción, color, rugosidad y mineralogía. Así como datos de referencia de su comportamiento hídrico. Además se ha desarrollado una metodología de ensayo específica que permite evaluar la capacidad de enfriamiento eficiente de una pieza cerámica. ABSTRACT The purpose of this research is to determine the characteristics of ceramic materials having the most efficient performance in terms of evaporation and cooling, so that they can be integrated in building envelopes to reduce cooling loads. Ceramics are suitable materials for cooling through passive evaporation. After being fired at temperatures over 900 °C (1,652 °F), the capillary network of this inert porous medium turns to be excellent to retain water, which is progressively liberated by evaporation while the material surface gets colder. Research methodology has involved the following steps: Search and analysis on the state of the art in technology and research. Theoretical study on the efficiency of evaporation as passive cooling strategies in buildings. Experimental stage developed in three phases, namely: definition of parameters determining evaporative cooling in ceramic elements; ceramic selection and design of experimental tests; characterization of ceramic materials under evaporation and cooling criteria. Search and analysis on the state of the art in this field have been useful to identify technology applications and scientific research where ceramics are employed for evaporative cooling. The resulting table shows that applications are wholly focused on the design of pieces and systems. Nonetheless, there is lack of definition of material characteristics in this scope. The theoretical study on efficiency of the passive strategy applied to buildings has been realized by calculation of the percentage increase in comfort hours through direct/indirect evaporative cooling techniques (DEC/IEC). The mapping of their potential application in Spain clearly shows that comfort conditions can be reached in almost all the hours of the hottest days in many towns. In the initial phase of the experimental stage, parameters determining evaporative cooling in ceramic media have been defined. For this purpose, characterization tests and evaporation and cooling rates experiments have been carried out; the number of samples tested amounted to 12. It has been concluded that material characteristics have great influence on these rates, which supports the initial hypothesis and the need for their characterization. The first empirical phase has focused on ceramic selection and design of water behaviour experimental methods. The samples covered five different kinds of ceramic materials. Four different characterization tests and six different water behaviour experiments were carried out; the number of samples tested amounted to 123. The experimental testing procedures served to determine the most efficient types of ceramic materials in terms of evaporative cooling efficiency and, at the same time, made it necessary to change the original designed experimental test for the last phase. In the second phase, a number of varied hand-made ceramic tiles have been selected. Seven different characterization tests and five different water behaviour tests were carried out; the number of samples amounted to 197. The results of characterization served to establish a range of features in ceramic materials according to their efficiency in water behaviour experiments. Finally, ceramic materials have been characterized according to porosity, water absorption, colour, surface roughness and mineralogy. Also, reference data regarding water behaviour have been included. Moreover, an innovative and specific experimental test to evaluate cooling efficiency of ceramic tiles has been developed.

Manufacturing arbitrarily-shaped active waveguides with liquid crystal cladding

Many photonic devices are based on waveguides (WG) whose optical properties can be externally modified. These active WGs are usually obtained with electrooptic materials in either the propagating film (core) or the substrate (cladding). In the second case, the WG tunability is based on the interaction of the active material with the evanescent field of the propagating beam.Liquid crystals (LCs) are an excellent choice as electrooptic active materials since they feature high birefringence, low switching voltage, and relatively simple manufacturing. In this work, we have explored alternative ways to prepare WGs of arbitrary shapes avoiding photolithographic steps. To do this, we have employed a UV laser unit (Spectra Physics)attached to an xyzCNC system mounted on an optical bench. The laser power is 300mW, the spot size can be reduced slightly below 1 µm, and the electromechanicalpositioning is well below that number.Different photoresinshave been evaluated for curing time and uniformity; the results have been compared to equivalent WGs realized by standard photolithographic procedures. Best results have been obtained with several kinds of NOA adhesives (Norland Products Inc.) and SU8 (Microchem). NOA81 optical adhesive has been employed by several groups for the preparation ofmicrochannels [1] and microfluidic systems[2]. In our case, several NOAs having different refractive indices have been tested in order to optimize light coupling and guiding. The adhesive is spinnedonto a substrate, and a number of segmented WGs are written with the laser system. The laser power is attenuated 20 dB. Then the laser spot is swept a number of times (from 1 to 900) on every segment. It has been found that, for example, the optimum number of sweeps for NOA81 is 30-70 times (center of the figure) under these conditions. The WG dimensions obtained with this procedure are about 7 µm high and 12 µm wide.