Analysis and modelization of lightweight structures subjected to impact

Mechanics of Advanced Materials research group (Department of Continuum Mechanics and Structural Analysis) of the University Carlos III of Madrid (Spain) offers their experience in the analysis and modelization of high and low velocity impact behaviour of composite structures. Their research focuses on both numerical analysis and non-standard experimental methodologies)

An analytical model for high velocity impacts on thin CFRPs woven laminated plates

15 pages, 12 figures.-- MSC2000 codes: Primary: 74R15; Secondary: 74M20, 74E30, 74K20, 74-05.Zbl#: Zbl 1178.74147An analytical model to study the impact process of a spherical projectile penetrating at high velocity into a carbon/epoxy plain woven laminate is developed in this work. The model is based on an energy balance, where the kinetic energy of the projectile is absorbed by the laminate by three different mechanisms: laminate crushing, linear momentum transfer and tensile fiber failure. A non-homogeneous differential equation is obtained. A subsequent simplification using regular perturbation analysis gives a closed-form solution that allows the approximative calculation of the residual velocity and hence the ballistic limit. The model is validated with the results of experimental tests in which the residual velocity is measured by means of high speed cameras.The authors are indebted to the Comisión Interministerial de Ciencia y Tecnología of Spain for the financial support of this work (Project MAT98-0273).Publicad

The effect of low temperatures on the intermediate and high velocity impact response of CFRPs

8 pages, 13 figures.The influence of low temperature on the damage produced on CFRPs by intermediate and high velocity impacts is analyzed. Spherical projectiles were launched against different carbon fiber/epoxy laminates (tape and woven). Experimental tests were done at temperatures ranging from 25 to −150 °C. The extension of the damage was measured by C-Scan. Results show a clear dependence of damage on temperature, impact velocity and the type of the laminate.The authors are indebted to the Comisión Interministerial de Ciencia y Tecnología of Spain for financial support of this work (Project MAT98-0273). They also thank EADSCASA for assistance in C-Scan measurements.Publicad

Prediction of the behaviour of CFRPs against high-velocity impact of solids employing an artificial neural network methodology

8 pages, 9 figures.A new methodology based on artificial neural networks has been developed to study the high velocity oblique impact of spheres into CFRP laminates. One multilayer perceptron (MLP) is employed to predict the occurrence of perforation of the laminate and a second MLP predicts the residual velocity, the obliquity of trajectory of the sphere after perforation and the damage extension in the laminate. In order to train and test the networks, multiple impact cases have been generated by finite-element numerical simulation covering different impact angles and impact velocities of the sphere for a given system sphere/laminate.Publicad

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

Experimental and numerical analysis of normal and oblique ballistic impacts on thin carbon/epoxy woven laminates

14 pages, 17 figures.A finite element numerical model for carbon/epoxy woven laminates has been used to predict residual velocity and damaged area when subjected to high impact velocities. Experiments using a gas gun were conducted to investigate the impact process and to validate the model, measuring the two variables previously indicated. A morphology analysis was also made to investigate the different breakage mechanisms that appear during the penetration process. The influence of the impact velocity and obliquity has been studied using the numerical tool, in a wide range of impact velocities and considering two impact angles, 0° and 45°.The authors are indebted to the Comisión Interministerial de Ciencia y Tecnología of Spain for the financial support of this work (Project MAT98-0273).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

High energy impact on woven laminates

6 pages, 5 figures.-- Issue title: "EURODYMAT 2003 - 7th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading" (Porto, Portugal, Sep 8-10, 2003).The influence of high velocity impacts on CFRPs was studied by launching Spherical steel masses, at velocities from 60 m/s to 550 m/s, against carbon fiber/epoxy woven laminates. The extension of the damage induced in the laminate was measured by C-Scan. Finite element numerical simulation of the impact test used a failure model based on the Chang-Chang model. A comparison was made of the damaged areas resulting from non-destructive inspection of the specimens and those predicted by numerical simulation. To conclue the analysis, an analytical model developed by Cantwell-Morton was used to calculate the residual velocity of the projectile after perforation. The residual velocities predicted by numerical and by analytical models, were also compared.The authors are indebted to the Comisión Interministerial de Ciencia y Tecnologia of Spain for financial support of this work (Project MAT98-0273). They also thank EADS-CASA for assistance in C-Scan measurements.Publicad