Estudio experimental y numérico del comportamiento de tanques integrados de combustible frente a impacto de alta velocidad

Los impactos a alta velocidad sobre tanques de combustible están considerados como amenazas de gran importancia en relación con la vulnerabilidad de las aeronaves, ya que dichos tanques ocupan una gran parte de las alas, y éstas representan la mayor superficie expuesta de todos los elementos estructurales susceptibles de recibir cualquier tipo de impacto. En esta Tesis Doctoral se ha estudiado el comportamiento de tanques de aluminio, conteniendo fluido, frente a impacto de alta velocidad. Se ha analizado, tanto por medio de una metodología experimental como numérica, la influencia de dos factores sobre la respuesta estructural del tanque: la velocidad de impacto y la fracción de llenado del tanque. Para la realización de los ensayos experimentales se ha empleado un sistema neumático de impulsión, a través del cual se han lanzado proyectiles a distintas velocidades, y una cámara de alta velocidad capaz de filmar el proceso de penetración del proyectil en el fluido. Las simulaciones numéricas se han realizado mediante un código comercial de elementos finitos, empleando dos técnicas diferentes (ALE y SPH) para evaluar la capacidad predictiva de cada una de ellas en este tipo de problemas de impacto. Mediante el análisis de los resultados se ha conseguido una mayor comprensión del fenómeno de Golpe Hidrodinámico, que puede contribuir a su atenuación en futuros diseños de tanques de combustible. En este sentido, el desarrollo y validación del modelo de simulación empleado permitirá facilitar el diseño y reducir el número de ensayos experimentales._______________________________________________________High speed impacts on fluid-filled tanks are considered as one of the most important threats in aircraft vulnerability, since the fuel tanks represent the largest exposed area of all the vulnerable components. In this Ph.D. Thesis the behavior of fluid-filled aluminium tanks subjected to high-velocity impact has been studied. An experimental and numerical methodology has been employed to analyze the influence of two different factors on the tank structural behavior: impact velocity and volume fraction. To perform the experimental tests, a pneumatic boost system, to launch projectiles at different velocities, and a high-speed camera, which is capable of record the penetration process of the projectile into de fluid, have been used. The numerical simulations have been carried on by means of a finite element commercial code, applying two different approaches (ALE and SPH) to evaluate its predictive capacity in this kind of impact problems. The results analysis have allowed a better understanding of the Hydrodynamic Ram phenomenon, which could contribute to attenuate it on future fuel tanks designs. On this way, the development and validation of the simulation model used will make the design process easier and reduce the number of experimental tests

Experimental characterization framework for SLA additive manufacturing materials

This article belongs to the Special Issue Mechanical Performance of Polymeric Parts Obtained by Additive Manufacturing.Additive manufacturing (AM) is driving a change in the industry not only regarding prototyping but due to the ease of including printed parts in final designs. Engineers and designers can go deeper into optimization and improvements of their designs without drawbacks of long manufacturing times. However, some drawbacks such as the limited available materials or uncertainty about mechanical properties and anisotropic behavior of 3D printed parts prevent use in large-scale production. To gain knowledge and confidence about printed materials it is necessary to know how they behave under different stress states and strain-rate regimes, and how some of the printing parameters may affect them. The present work proposes an experimental methodology framework to study and characterize materials printed by stereolithography (SLA) to clarify certain aspects that must be taken into account to broaden the use of this kind of material. To this end, tensile and compression tests at different strain rates were carried out. To study the influence of certain printing parameters on the printed material behavior, samples with different printing angles (θ = [0–90]) and different printing resolution (layer height of 50 and 100 µm) were tested. In addition, the effects of curing time and temperature were also studied. The testing specimens were manufactured in the non-professional SLA machine Form 2 from Formlabs® using resin called Durable. Nevertheless, the proposed experimental methodology could be extended to any other resin.Ministerio de Asuntos Económicos y Transformación Digital, Gobierno de España grant number DPI2017-85073-R, and Vicerrectorado de Política Científica UC3M (Projects 2013/00413/003 and 2014/00006/003)

Experimental study 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 and excessive structural damage. For the present work, water-filled CFRP square tubes were subjected to an impact of steel spherical projectiles (12.5 mm diameter) at impact velocities of 600–900 m/s. The CFRP tubes were filled to different volumes to examine how volume might influence the tank behavior. The composite test boxes were instrumented with six strain gauges and two pressure transducers, and the formation process of the cavity was recorded using a high-speed camera. The damage produced in the tubes was then analyzed, and differences were found according to the testing conditions. This work presents the results of these tests.The authors would like 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.Publicad

Numerical modelling of the hydrodynamic ram phenomenon

12 pages, 16 figures.Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-kinetic energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. This is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. In the present paper, the commercial finite-element code LS-DYNA has been used to simulate an HRAM event created by a steel spherical projectile impacting a water-filled aluminium square tube. Two different formulations (ALE and SPH) are employed to reproduce the event. Experimental tests which indicate the pressure at different points of the fluid, displacement 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 both ALE and SPH techniques in reproducing such a complex phenomenon.Publicad

Experimental analysis of fluid-filled aluminium tubes subjected to high-velocity impact

11 pages, 20 figures.Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure increasing the risk of catastrophic failure and excessive structural damage. It is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. For the present work, water-filled aluminium square tubes (6063-T5) were subjected to impact by steel spherical projectiles (12.5 mm diameter) at impact velocities of 600–900 m/s. The aluminium tubes were filled at different volumes to study how an air layer inside the tank might influence the impact behaviour. The test boxes were instrumented with five strain gauges and two pressure transducers. The formation process of the cavity was recorded with a high-speed camera. This work presents the results of these tests.This research was done with the financial support of the Spanish Ministry of Education under Project reference DPI2005-06769, and of the University Carlos III of Madrid and Comunidad Autónoma de Madrid under project reference CCG07-UC3M/DPI-3395.Publicad

Numerical Analysis of the Hydrodynamic Ram Phenomenon in Aircraft Fuel Tanks

Hydrodynamic ram (H RAM) is a phenomenon that occurs when a high-energetic object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage on adjacent components. It is 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. To study the aforementioned phenomenon, water-filled aluminum tubes (to different volume percentages) were subjected to impact of spherical projectiles. This work is focused on the analysis of energies, momenta, and pressure contours obtained by means of a previously developed and validated numerical model to achieve a better understanding of the fluid/structure interaction problem that takes place during the HRAM phenomenon.This research was done with the financial support of the Spanish Ministry of Science and Innovation under Project references DPI/2008-06408 and DPI/2010-15123, and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694Publicad

Experimental analysis at different loading rates of 3D printed polymeric auxetic structure based on cylindrical elements

This work proposes the experimental study of an auxetic polymeric structure manufactured by 3D printing (SLA). The structure is composed by a re-entrant unit cell based on cylindrical elements not previously studied. The effect of the number and size/scale of the unit cells used in the specimens, subjected to both static and dynamic loads, has been analysed. The results show how the studied variables affect the behaviour of the structure in terms of stress and strain and that the dimensions of the cylindrical elements, as well as the contact between them, could help to modify the stiffness structure as required. The tests performed have allowed to understand the sequence of physical phenomena that appears at different strain rates and how they affect the response of the structure. The results obtained may contribute to the knowledge of both polymeric auxetic structures and the use of additive manufacturing methods for such structures.This research was funded by Ministerio de Asuntos Económicos y Transformación Digital, Gobierno de España grant number DPI2017-85073-R, and Vicerrectorado de Política Científica UC3M (Projects 2013/00413/003 and 2014/00006/003)

Analytical modelling of high velocity impacts of cylindrical projectiles on carbon/epoxy laminates

8 pages, 15 figures.-- Special Issue: JNC 15 - 15èmes Journées Nationales sur les Composites (Marseille, France, Jun 6-8, 2007).In this work an analytical model has been developed in order to predict the residual velocity of a cylindrical steel projectile, after impacting into a woven carbon/epoxy thin laminate. The model is based in an energy balance, in which the kinetic projectile energy is absorbed by the laminate through three different mechanisms: linear momentum transfer, fiber failure and laminate crushing. This last mechanism needs the quantification of the through-thickness compressive strength, which has been evaluated by means of quasi-static punch tests. Finally, high velocity impact tests have been accomplished in a wide range of velocities, to validate the model.This research was done with the financial support of the University Carlos III of Madrid and of the Comunidad Autónoma de Madrid under Projects CCG08-UC3M/MAT-4464 and CCG08-UC3M/DPI-4348.Publicad

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 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