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Mención Internacional en el título de doctor Composite materials are widely used nowadays to build structures and protections. Their good mechanical properties along with their light weight has lead to an increase in the use of these materials over the last decades. Specifically, Glass Fibre Reinforced Polymers (GFRP) plates are really resistant to corrosion and permeable to electromagnetic waves. Because of that, GFRP are suitable for naval and telecommunication applications. Although these structures may not be designed as protections they may be subjected to different kind of impacts during their service life. Since some elements can be critical, safety must be ensured and thus engineers need a deeper knowledge of the impact performance. That is why the development of analytical, theoretical and finite element models is a hot topic in order to predict critical design factors such as the ballistic limit. This doctoral thesis focuses on the modelling of the high-velocity impact phenomenon through different approaches in order to reproduce better the effects that take place during a high-velocity impact. First of all, a wide set of experiments have been carried out to obtain the data necessary for the models. Characterization tests have been carried out to know the mechanical properties needed for the models. Furthermore, ballistic impact tests have been performed on 9 mm thick specimens. In addition, non-destructive inspection tests have been carried out to evaluate the damaged area after impact. After that, two non-dimensional energy-based theoretical models are presented in order to predict the ballistic behaviour of woven GFRP plates. Some important nondimensional groups that are useful to analyze the behaviour and validity of the models appear naturally using this formulation. Hypotheses based on physical phenomena are also taken into account in the formulation. Then, a finite element model is developed by means of a new constitutive model and a continuum damage mechanics approach to predict the performance of GFRP plates under high-velocity impact. In addition, the failure modes of this model are formulated in such a way that allows to associate the energy dissipated by each of them to the energy absorption mechanisms defined in the theoretical models. Finally, some of the new hypotheses assumed in the theoretical models are validated with the finite element one. Furthermore, the energy absorption mechanisms are compared between both approaches to draw enlightening conclusions. Los materiales compuestos se utilizan ampliamente en la actualidad para construir estructuras y protecciones. Sus buenas propiedades mecánicas junto con su bajo peso específico han favorecido un incremento en el uso de estos materiales durante las últimas décadas. En concreto, los laminados reforzados con fibra de vidrio (GFRP en inglés) son muy resistentes a la corrosión y permeables a las ondas electromagnéticas. Por esta razón, los GFRP son indicados para aplicaciones navales y de telecomunicaciones. Aunque estas estructuras pueden no estar diseñadas como protecciones, son susceptibles de estar sometidas a diferentes tipos de impacto durante su vida útil. Dado que algunos elementos pueden ser críticos, se debe asegurar la seguridad y por lo tanto, los ingenieros necesitan un conocimiento más profundo del comportamiento frente a impacto. Es por ello que el desarrollo de modelos teóricos y de elementos finitos es una línea de investigación de interés que permite predecir factores de diseño críticos como el límite balístico. Esta tesis doctoral está enfocada en la modelización del fenómeno de impacto a alta velocidad a través de diferentes métodos para poder reproducir de la manera más fidedigna los efectos que tienen lugar durante un impacto a alta velocidad. Primero, se ha llevado a cabo un gran número de experimentos con el objetivo de obtener los datos necesarios para los modelos desarrollados. Se han realizado experimentos de caracterización mecánica para determinar las propiedades requeridas por los modelos. Además, se han llevado a cabo ensayos de impacto balístico en especímenes de 9 mm de espesor. Igualmente, se han realizado ensayos de inspección no destructiva (IND) para evaluar el área dañada del laminado después de impacto. Posteriormente, se presentan dos modelos teóricos no dimensionales basados en criterios energéticos para predecir el comportamiento balístico en laminados GFRP. Algunos grupos no dimensionales que son útiles para analizar el comportamiento y la validez de los modelos aparecen de forma natural al utilizar esta formulación. En la formulación se tienen en cuenta hipótesis basadas en fenómenos físicos. A continuación, se desarrolla un modelo de elementos finitos mediante un modelo constitutivo a través de un modelo de daño continuo para predecir el comportamiento de los laminados GFRP frente a impactos de alta velocidad. Además, los modos de fallo están formulados de tal forma que la energía disipada por cada uno de ellos se puede asociar a los mecanismos de absorción de energía definidos en los modelos teóricos. Por último, algunas de las nuevas hipótesis asumidas en los modelos teóricos se han validado con el modelo de elementos finitos. Los mecanismos de absorción de energía se comparan entre los modelos teóricos y el modelo de elementos finitos para extraer conclusiones esclarecedoras. Programa de Doctorado en Ingeniería Mecánica y de Organización Industrial Presidente: Federico París Carballo.- Secretario: Sonia Sánchez Sáez.- Vocal: Ana Paula Betencourt Martins Amaro

Development of composite materials has caused that innovative features and capabilities are being sought for their use in new technology applications. Catastrophic events, like high velocity impacts, are likely to appear in elds where composite materials are being lately applied. Lightweight headgear for modern military ground forces, structural shielding for a knew orbiter spacecraft, or blades intended for high-e ciency wind turbines, are just some examples. The dynamic response of composite materials has become an essential knowledge. New set of tools need to be developed in order to spread this knowledge and decrease design cost. As compared to experimental testing and numerical methods, analytical models stand out as the cheapest and fastest way to provide preliminary results that successfully assist early design stages. The main goal of this project relies on laying the basics for the development of a predesign tool on the implementation of this latter type of models. This tool will support the early design of composite material structural components likely subjected to impact situations. During the last three decades, a great number of analytical models have being developed intended to theoretically predict the behavior under impact of composite materials. The present work covers the basics ndings on the eld. Two models, based on the impact over carbon ber, and glass and polymer ber composites, are selected and thoroughly described in order to evaluate their applicability into a pre-design tool. Description of both models are provided with the needed background and theoretical foundations. In order to evaluate the applicability of analytical models, a simple requirements-based method is presented. It is based on three broad requirements: good predictions, broad applicability and event sensitivity. Both analytical models are evaluated against these requirements. Results of this evaluation show how the rst model (carbon ber model) reproduces one speci c case with accuracy. In spite of this good agreement, there is no possibility to reproduce further environments. This makes the model non optimal to be implemented into a design tool. The second model (glass and polymer ber model) appears to successfully meet the three established requirements. Finally, some guidelines in the development of future analytical models under the method here described, and some possible paths to be followed in the implementation of the pre-design tool, are presented. Ingeniería Industrial

The use of composite materials has grown considerably during recent years, most prominently in the aerospace and automobile industries, as well as in the civil and naval industries. Composite materials display outstanding specific strength and stiffness properties, and a broad capacity for customization. Both qualities have contributed to their application in industries sensitive to the weight of materials such as steel or other alloys. However, composites’ behavior is more difficult to predict due to multiple failure modes. Therefore, complex models and powerful software are normally required to design components made of composite materials, both during the creation of the model and in the results post-processing, adding time to the design process. It would be helpful to automate part of this process in order to speed up the pre-design step. The aim of this project is the development of a tool that will ease the design of composite stiffened panels, reducing the time required to create the model while also allowing fast modifications of a given design in order to maximize the design efficiency. The tool will be able to generate the mesh and geometry from a set of predefined parameters that defines a given panel, and it will compute the critical buckling load of the first five modes, along with the visualization of the deformed panel to ensure quick post-processing. In order to render this tool accessible, it will be implemented in a web environment (CADEC) using advanced features such as object-oriented programming, user authentication and databases. After implementing such a tool in CADEC, it was used to predict the buckling load of several real cases of stiffened panels. Since the results obtained with CADEC generally coincided with the experimental results analyzed, the tool and its results can be safely validated. Ingeniería Industrial

The use of composite materials has grown considerably during recent years, most prominently in the aerospace and automobile industries, as well as in the civil and naval industries. Composite materials display outstanding specific strength and stiffness properties, and a broad capacity for customization. Both qualities have contributed to their application in industries sensitive to the weight of materials such as steel or other alloys. However, composites’ behavior is more difficult to predict due to multiple failure modes. Therefore, complex models and powerful software are normally required to design components made of composite materials, both during the creation of the model and in the results post-processing, adding time to the design process. It would be helpful to automate part of this process in order to speed up the pre-design step. The aim of this project is the development of a tool that will ease the design of composite stiffened panels, reducing the time required to create the model while also allowing fast modifications of a given design in order to maximize the design efficiency. The tool will be able to generate the mesh and geometry from a set of predefined parameters that defines a given panel, and it will compute the critical buckling load of the first five modes, along with the visualization of the deformed panel to ensure quick post-processing. In order to render this tool accessible, it will be implemented in a web environment (CADEC) using advanced features such as object-oriented programming, user authentication and databases. After implementing such a tool in CADEC, it was used to predict the buckling load of several real cases of stiffened panels. Since the results obtained with CADEC generally coincided with the experimental results analyzed, the tool and its results can be safely validated. Ingeniería Industrial