Publication: Análisis y simulación de impactos de hielo sobre laminados carbono/epoxi
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2013-03
Defense date
2013-05-17
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Abstract
El diseño y la optimización de componentes estructurales aeronáuticos constituyen un campo de gran importancia en la ingeniería debido a los elevados requerimientos de seguridad y fiabilidad que se exigen a las aeronaves. Durante su vida útil, estas estructuras están sometidas a diversos tipos de solicitación y, en particular, pueden recibir impactos de fragmentos de diferentes materiales. En la búsqueda de nuevas soluciones estructurales, el uso de los materiales compuestos (laminados en la mayoría de los casos) se está extendiendo en la aeronáutica civil a las estructuras primarias incrementándose el riesgo de impacto en estos materiales. Se ha demostrado la baja resistencia frente a impacto cuando este ocurre en la dirección perpendicular al plano del laminado, y por esta razón es necesario investigar su comportamiento frente a impacto. Esta tesis doctoral se centra en el estudio de los materiales compuestos frente a impacto de hielo. Con este objetivo, se ha realizado un análisis desde el punto de vista experimental y num érico, de laminados unidireccionales de fibras de carbono en matriz epoxi sometidos a impacto de esferas de hielo. Para llevar a cabo el estudio experimental se han realizado ensayos empleando un sistema neumático capaz de impulsar los proyectiles de hielo a la velocidad deseada. En primer lugar se han realizado ensayos impactando los proyectiles de hielo contra una célula de carga para medir la fuerza inducida en el impacto. En segundo lugar, se han impactado los laminados de carbono/epoxi para estudiar el comportamiento de estos frente al impacto. El análisis de los resultados obtenidos de los ensayos experimentales ha permitido estudiar la fuerza ejercida por el impacto de los proyectiles esféricos de hielo, así como la influencia sobre ésta de la velocidad de impacto y de la masa de proyectil. Además, se ha podido analizar el comportamiento de los laminados sometidos a impacto de hielo determinando la influencia de diferentes variables en el daño producido por el impacto: espesor del laminado, energía de impacto y diámetro del proyectil. Para complementar el estudio, se ha evaluado la capacidad predictiva de modelos de elementos finitos en este tipo de problemas de impacto. Para ello se ha propuesto e implementado, en un código comercial, un modelo de comportamiento mecánico para el hielo y se ha empleado un modelo simplificado para los laminados de carbono/epoxi. Los modelos anteriormente citados han sido validados empleando los resultados experimentales. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Design and optimization of aeronautic structural components represent fields of great importance in engineering due to the high requirements, both security and reliability, that aircrafts are demanded. During its service life, these structures are subjected to very different kinds of loads and, in particular, they can be impacted by various material's debris. As a result of the searching of new structural solutions, the usage of composites has been spread to primary structures in civil aeronautics. Due to its low resistance against impact when it occurs in the normal direction to the plane of the laminate, it is necessary to investigate its impact behavior. This Ph.D. thesis focuses on the study of composite materials under ice impact. With this purpose, an experimental and numerical analysis of sphere ice impact on unidirectional carbon fibers laminate in epoxy matrix has been made. To accomplish the experimental study, tests were carried out using a pneumatic system capable of propelling the ice projectiles at the desired speed. Firstly tests were made impacting ice projectiles against a load cell to measure the force induced by impact. Secondly, the carbon/epoxy laminates were impacted, in order to study their behavior against ice impact. The analysis of the experimental results of the experimental tests has allowed studying the impact force induced by the spherical ice projectiles, determinig the influence of the impact velocity and mass of the projectile in the force. Furthermore, it has been possible to analyze the behavior of laminates subjected to ice impact determining the influence on the laminates damage of different variables: laminate thickness, impact energy and projectile diameter. As a complement to this study, the predictions of finite element models were evaluated for this type of impact problems. To this end, a constitutive model for the ice has been proposed and implemented in a commercial finite element code, and a simplified model combining material behavior and cohesive interaction has been used for the composite laminates. Aforementioned models has been validated using the experimental results.
Design and optimization of aeronautic structural components represent fields of great importance in engineering due to the high requirements, both security and reliability, that aircrafts are demanded. During its service life, these structures are subjected to very different kinds of loads and, in particular, they can be impacted by various material's debris. As a result of the searching of new structural solutions, the usage of composites has been spread to primary structures in civil aeronautics. Due to its low resistance against impact when it occurs in the normal direction to the plane of the laminate, it is necessary to investigate its impact behavior. This Ph.D. thesis focuses on the study of composite materials under ice impact. With this purpose, an experimental and numerical analysis of sphere ice impact on unidirectional carbon fibers laminate in epoxy matrix has been made. To accomplish the experimental study, tests were carried out using a pneumatic system capable of propelling the ice projectiles at the desired speed. Firstly tests were made impacting ice projectiles against a load cell to measure the force induced by impact. Secondly, the carbon/epoxy laminates were impacted, in order to study their behavior against ice impact. The analysis of the experimental results of the experimental tests has allowed studying the impact force induced by the spherical ice projectiles, determinig the influence of the impact velocity and mass of the projectile in the force. Furthermore, it has been possible to analyze the behavior of laminates subjected to ice impact determining the influence on the laminates damage of different variables: laminate thickness, impact energy and projectile diameter. As a complement to this study, the predictions of finite element models were evaluated for this type of impact problems. To this end, a constitutive model for the ice has been proposed and implemented in a commercial finite element code, and a simplified model combining material behavior and cohesive interaction has been used for the composite laminates. Aforementioned models has been validated using the experimental results.
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Keywords
Ensayo de materiales, Materiales compuestos, Resistencia frente a impacto, Laminados carbono/epoxi, Método de elementos finitos, Industria aeronáutica