Análisis y modelización del golpe hidrodinámico en tanques integrados de combustible realizados en material compuesto

Actualmente, en la industria aeronáutica, uno de los principales análisis que se realizan durante la fase de diseño de una estructura de material compuesto es el estudio de la vulnerabilidad frente a impactos a alta velocidad. Particularmente, en el diseño de los tanques de combustible del ala de un avión se deben tener en cuenta los efectos del golpe hidrodinámico; este problema ha sido identificado como uno de los factores más importantes en la vulnerabilidad de una aeronave. El golpe hidrodinámico ocurre cuando un objeto altamente energético penetra a alta velocidad en una estructura con fluido en su interior transfiriendo parte de su energía cinética a través del fluido a la estructura. En la presente tesis doctoral se ha analizado el comportamiento de un tanque de material compuesto con fluido en su interior sometido a impactos de alta velocidad. Para ello se ha usado tanto una metodología experimental como numérica. En ambos casos se ha analizado la influencia de dos parámetros: la velocidad de impacto del proyectil y el porcentaje de llenado del tanque de material compuesto. Para la realización de los ensayos experimentales se ha usado un dispositivo neumático que acelera el proyectil a gran velocidad contra el tanque de combustible; el proceso de impacto se ha grabado mediante una cámara de alta velocidad, registrándose también tanto las deformaciones del tubo de material compuesto como las presiones en el interior del fluido. Los ensayos experimentales han servido para comprender los principales mecanismos que gobiernan el comportamiento del tanque de combustible frente al golpe hidrodinámico. Se ha observado que los mecanismos de fallo que aparecen en la estructura varían sensiblemente en función de los parámetros estudiados; es de destacar la importancia del porcentaje de llenado, parámetro que no había sido estudiado en profundidad para este tipo de tanques de combustible. En esta tesis, además, se ha desarrollado una metodología numérica para modelizar el fenómeno del golpe hidrodinámico. Esta metodología ha sido validada mediante los ensayos experimentales antes mencionados. Las simulaciones numéricas han sido realizadas empleando el código comercial de elementos nitos LS-DYNA v. R7. Para modelizar la interacción fluido estructura se han usado dos técnicas diferentes: la técnica Multimaterial Lagrangiana Euleriana Arbitraria (MM-ALE en sus siglas en inglés) y la técnica Smooth Particle Hydrodynamics (SPH). Para reproducir el comportamiento del material compuesto del que está hecho el tanque de combustible se ha usado un modelo que tiene en cuenta tanto el fallo intralaminar, implementado mediante una subrutina de usuario, como el fallo interlaminar, modelizado usando una interacción cohesiva. Atendiendo a la validación realizada, se ha comprobado que los modelos numéricos desarrollados muestran una adecuada correlación con respecto a la respuesta del tubo de material compuesto sometido al golpe hidrodinámico observada en los ensayos experimentales. Tanto el modelo que usa la técnica MM-ALE como el que emplea la técnica SPH son capaces de reproducir la transferencia de energía entre proyectil, fluido y estructura. En cuanto al modelo de material compuesto implementado, éste predice adecuadamente los fallos que se generan en el tanque para los distintos casos analizados.Nowadays, in the aeronautical industry, vulnerability against high-velocity impact loads has become one of the principal analyses performed for the design of composite structures. Particularly, in a wing fuel tank design, Hydrodymamic Ram (HRAM) effects have to be taken into account, because it has been identified as one of the important factors in aircraft vulnerability. Hydrodynamic Ram (HRAM) occurs when a high-energy object penetrates a fluid-filled container, transferring its momentum and kinetic energy through the fluid to the surrounding structure. In the present PhD Thesis it has been analyzed the behavior of a fluid filled composite fuel tank subjected to a high velocity impact. For this purpose, it has been used both an experimental and a numerical methodology. In both cases, it has been analyzed the influence of two parameters: projectile impact velocity and fluid filling level. In order to perform the experimental tests, it has been used a pneumatic launcher that accelerates the projectile to high velocity impacting against the composite fuel tank; the impact process has been recorded using a high-speed camera, registering also the strains in the composite fuel tank and the pressures inside the fluid. Experimental tests have been used to understand the principal mechanisms that govern the composite fuel tank response subjected to HRAM. It has been observed that the main failure mechanisms that appears in the structure vary noticeably as a function of the parameters analyzed, in particular the influence of fluid filled level; parameter that it has not been studied in depth previously for this type of fuel tank. In this PhD thesis, it has been also developed a numerical methodology for modelling the HRAM phenomenon. This methodology has been validated using the experimental tests. Numerical simulations have been carried out in the finite element commercial code LS-DYNA v.R7. Two numerical techniques have been used to model the fluid structure interaction, Multimaterial Arbitrary Lagrangian Eulerian (MM-ALE) and Smooth Particle Hydrodynamics (SPH). A material model accounting intralaminar failure, by means of a user subroutine, and the interlaminar failure, using a cohesive interaction has been employed to reproduce the composite material behavior. Considering the validation performed, it has been shown that the numerical models developed have a correct agreement with the experimental composite fuel tank response subjected to HRAM. Therefore, it can be said that both the numerical model that use MM-ALE technique and the model that employ SPH technique, are able to reproduce the energy transfer between projectile, fluid and structure. In addition, composite material model implemented predicts the failures appeared in composite fuel tank for the different studied parameters.Programa Oficial de Doctorado en Ingeniería Mecánica y de Organización IndustrialPresidente: Ramón Eulalio Zaera Polo.- Secretario: Ignacio Romero Olleros.- Vocal: David Ángel Cendón Franc

Numerical analysis of CFRP fluid-filled tubes subjected to high-velocity impact

In recent years, vulnerability against high-velocity impact loads has become an increasingly critical issue in the design of composite aerospace structures. The effects of Hydrodynamic Ram (HRAM), a phenomenon that occurs when a high-energy object penetrates a fluid-filled container, are of particular concern in the design of wing fuel tanks for aircraft because it has been identified as one of the important factors in aircraft vulnerability. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure. In the present paper, the commercial finite-element code ABAQUS/Explicit has been used to simulate an HRAM event due to the impact of a steel spherical projectile into a water-filled woven CFRP square tube. In order to simulate the fluid-structure interaction, the Coupled Eulerian Lagrangian (CEL) approach is used. Experimental tests which indicate the pressure at different points of the fluid, strains of the walls and cavity evolution for different impact velocities are compared with the numerical results in order to assess the validity and accuracy of CEL technique in reproducing such a complex phenomenon. Also, several numerical impacts at different initial projectile velocities are performed to study its influence in the HRAM phenomenon.This research was done with the fianancial support of the Spanish Ministry of Education under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694. The authors would like also to acknowledge the Center for the Development of Industrial Technology (CDTI) of Spain and to the company AERNNOVA Aerospace for the financial support for this research. We wish to express sincere gratitude to Mr. S. Puerta for his valuable help during the experimental testing

Analysis of high velocity impacts of steel cylinders on thin carbon/epoxy woven laminates

In this work a numerical model was developed to predict the behavior of thin woven laminates under high velocity impacts. The material model, implemented in a user subroutine to be used with a commercial FE code, takes into account different failure mechanisms. The inter-lamina failure prediction is achieved by means of the use of cohesive elements. Finally, in order to validate the model, experimental tests were accomplished in a wide range of velocities from 100 to 400 m/s. Residual velocity of the projectile and damaged area of the laminates are compared with the numerical results. Once the model is validated, a further investigation has been made in order to analyze the influence of projectile slenderness on the laminate response.This research was done with the ¯nancial support of the Spanish Ministry of Education under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694

On the influence of filling level in CFRP aircraft fuel tank subjected to high velocity impacts

In this work, the process of impact that takes place in a partially filled tank is analyzed, performing a numerical simulation, in order to understand the response of the composite laminated structure. The commercial finite-element code LS-DYNA v.R7 has been used to simulate an Hydrodynamic RAM event created by a steel spherical projectile impacting a partially water-filled woven CFRP square tube using two different approaches (MM-ALE and SPH). The intralaminar and interlaminar damage have been taken into account implementing an user subroutine and by means of a cohesive interaction, respectively. Once the numerical model is validated using available experimental data, the effect of the filling level in the failure of the tank is analyzed in detail taking advantage of the information provided by the numerical model. (C) 2013 Elsevier Ltd. All rights reserved.This research was done with the financial support of the Spanish Ministry of Education under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694

Experimental analysis of normal and oblique high velocity impacts on carbon/epoxy tape laminates

In this work, the effect of high velocity impacts on carbon/epoxy tape quasi-isotropic laminates is studied. Experimental test were carried out at two different impact angles and in a wide range of velocities (from 80 to 490 m/s). Both parameters, the residual velocity and the damaged area, are used to evaluate the effect of the kinetic energy of the projectile on the laminate response. In addition it has been proposed a simplified analytical model which allows to identify the different energy absorbtion mechanisms and predict the residual velocity of the projectile. Finally the energy absorbed by the laminate during the impact is studied.This research was done with the financial support of the Spanish Ministry of Ed- ucation under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694

Analysis of Ice Impact Process at High Velocity

In this work the high velocity impact of ice spheres is analysed. An experimental methodology has been developed in order to launch, at high velocity, ice spheres of different diameters against a load cell to measure the force induced during the impact. An analysis of the influence of the ice mass on the impact force is accomplished using the contact force which was calculated by means of an inverse problem technique. Finally a study of the impact phenomenon has been performed using the videos obtained with a high speed camera.This research was done with the financial support of the Spanish Ministry of Education under Project reference DPI2013-41094-R

Experimental analysis of ice sphere impacts on unidirectional carbon/epoxy laminates

This work analyses the behaviour of carbon/epoxy unidirectional laminates subjected to high velocity impacts of ice spheres. To this end, ice projec- tiles were launched against composite laminates in a wide range of velocities (50 -250 m/s). Two different ice diameters (40 and 50 mm) and two laminate thicknesses (4 and 6 mm) were considered. The internal damage was measured using both destructive and non-destructive techniques, which allow an accurate quanti cation of the delaminated area. Finally the in uence of the different parameters considered on the damage of the laminate is analysed by means of a dimensionless variable.This research was done with the financial support of the Spanish Ministry of Economy and Competitiveness under Project reference DPI2013-41094-R

High-velocity ice impact damage quantification in composite laminates using a frequency domain-based correlation approach

This paper investigates the feasibility of using a novel domain-based correlation approach derived from the complex frequency domain assurance criterion (CFDAC) for the detection and quantification of impact damage in composite laminates. The CFDAC is essentially a complex-valued two-dimensional indicator of the covariance between two sets of frequency response functions for each pair of spectral lines corresponding to vibration-response of pristine and damage states. The study focuses on damage induced by high-velocity ice impacts on carbon fiber laminated plates. The experimental results demonstrate that the proposed methodology correctly identifies the level of induced damage via a user-independent scalar damage indicator. Therefore, this approach has potential use as a damage indicator, which could be adapted as a structural assessment non-destructive method. This research aims to contribute to the further development of functional, autonomous, and reliable structural health monitoring systems for composite structures based on spectral-domain indices.This research was done with the financial support of the Spanish Ministry of Economy and Competitiveness through the projects IPT-2011-1765-920000 and DPI2013-41094-R. The authors are very grateful to Joan Fernández for constructive suggestions

Model updating of uncertain parameters of carbon/epoxy composite plates using digital image correlation for full-field vibration measurement

Model updating is usually based on the contrast between the modal characteristics predicted by the models and those experimentally identified. Traditional experimental methods are based on the use of contacting sensors, but more recently other techniques as 3D Digital Image Correlation (DIC) have also been used successfully. In this paper the results obtained by applying these alternative techniques are compared, to obtain physically-sound models of carbon/epoxy composite plates. Primarily a roving hammer exciting the plates at evenly distributed degrees of freedom (DoF), and a mono-axial accelerometer attached to a single DoF reference point, have been used for modal identification. Alternatively, high speed cameras were applied to measure full-field vibrations of the plates. 3D DIC allowed obtaining a lower number of natural frequencies but much smoother mode shapes and similar results for model updating. The experimental setup has been benchmarked using two different sets of plates varying thickness and ply stacking.This research was done with the financial support of the Spanish Ministry of Economy and Competitiveness under Project reference DPI2013-41094-R, and the Vicerrectorado de Política Científica UC3M (Projects 2014/00006/002 and 2013/00413/003)

Experimental study of the impactor mass effect on the low velocity impact of carbon/epoxy woven laminates

In this work, the analysis of the impactor mass effect on the behaviour of carbon/epoxy woven laminates under low velocity impact is carried out. To this end experimental test were performed by means of a drop weigh tower in a range of energies varying from 10 to 110 J, and using three different impactor masses. Two different laminate thicknesses were considered in order to take into account its possible influence. An analysis of the impact tests is performed using the Composite Structure Impact Performance Assessment Program, in order to observe the influence of impactor mass. Once impacted, the laminates were inspected by means of a C-Scan (to quantify the delamination extension) and a phased array ultrasonic system (to analyse the failure through the thickness); this non-destructive analysis will determine the influence of the impactor mass on the laminate failure. (C) 2015 Elsevier Ltd. All rights reserved.This research was done with the financial support of the Spanish Ministry of Economy and Competitiveness under Project reference DPI2013 41094 R