Security and defence of mobile systems under impact

The Group “Dynamics and Fracture of Structural Elements” offers its experience in Solid Mechanics analysis for the study of the impact protection of vehicles, aircrafts and persons. The Group activities have a strong research component, in which numerical simulation tools as well as sophisticated experimental techniques are employed. This technological offer could be of interest to automobile companies (impact and collision security), aeronautical companies (impact of external body on fuselage, attack, and fragments o ice) and defence companies (special armours for mobile systems and persons).Contrato Programa de Comercialización e Internacionalización. Sistema Regional de Investigación Científica e Innovación Tecnológica. (Comunidad de Madrid; Universidad Carlos III de Madrid

Finite element simulation of steel ring fragmentation under radial expansion

24 pages, 25 figures.This paper presents a numerical analysis of the expansion of a mild steel ring with of 50 mm diameter, 1 mm thickness and a cross section of 1 mm2. A hardening relation which takes into account strain, strain rate and temperature is proposed to define precisely the thermoviscoplastic behaviour of the material considered in the study. As a second step, an algorithm to integrate the thermoviscoplastic constitutive equations, including the hardening law, is implemented in the commercial finite element code ABAQUS/Explicit via a user subroutine. Finally, this tool is used to simulate the problem of a ring expanding radially in a broad range of strain rates, covering both low and high initial velocities (from 1 to 370 m/s). The aim is to analyse the effect of loading velocity on the number of fragments resulting from the multiple failure of the ring and also the influence of the hardening behaviour of the material on the number of fragments and on the failure mode of the ring, considering different values of the plastic strain hardening exponent n0. A simple failure criterion was used, based on a critical value of the equivalent strain which depends on the hardening exponent. The numerical predictions, in perfect agreement with the experimental observations, are compared with several analytical or numerical models used to solve the same problem in other materials such as aluminium, steel or copper.Publicad

Modelling the fracture processes in the ballistic impact on ceramic armours

6 pages, 6 figures.-- Issue title: "EURODYMAT 1997 - 5th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading".-- Published in: Colloque C3, Supplement au Journal de Physique III d'août 1997.[EN] This work examines the essential physical processes in the perforation of metal backed ceramic armours which include projectile erosion, fracture of the ceramic tile and ductile deformation of the metal backing plate. The impact of projectiles onto alumina and aluminium nitride ceramic materials is studied experimentally and numerically. Observations were performed using an X-ray shadowgraph technique to obtain accurate data of the penetration process at different times. From the examination of computer simulations and corresponding impact experiments a simple analytical model is developed by assuming some hypotheses simplifying the actual mechanisms of the penetration process. Material description is simplified by using simple equations and a few material parameters easily obtained experimentally, such as the elastic modulus, the compressive and tensile strength and the rupture strain.[FR] Ce travail examine les procès physiques essentiels qui concernent la perforation des blindages céramique/métal en incluant dans un modèle analytique l'érosion du projectile, la fracture de la céramique et la déformation plastique de la plaque métallique. L'impact de projectiles sur des plaques d'oxide d'aluminium et de nitrure d'aluminium est étudié expérimentale et numériquement. Pour obtenir les donnés expérimentales un appareil photographique à rayons X a été utilisé, permettant observer avec précision le procès de pénétration. À partir de l'analyse des simulations numériques et des données expérimentales un modèle analytique a été développé en assumant une grande simplification des mécanismes de perforation. Le comportement mécanique des matériaux est simplifié en faisant appel à des équations constitutives simples avec quelques paramètres facilement accessibles expérimentalement comme le module d'élasticité, la résistance à compression et la déformation maximale.The authors are indebted to the Research & Development Department of Empresa Nacional Santa Bárbara (Spain) for the performance of the ballistic tests and the obtention of the X-ray shadowgraphs. This work is a part of the EUCLID RTP 3.2 project, supported by the Ministries of Defence of Spain, Denmark, Holland and Italy. The above project is being developed with the collaboration of several companies and research centres of the aforementioned countries.Publicad

Using an analytical model of simulation in the design of light-weight armours

9 pages, 13 figures.This paper presents a model for the simulation of the impact of projectiles of high kinetic energy on lightweight ceramic/metal armours. The work was financed jointly by the Defence Ministries of Spain, Italy, Holland and Denmark as part of a project among nations for the development of tools for the design of this type of armour. The model consists of a series of differential equations incorporating the most essential phenomena of the impact process, formulated after a close study of a series of real fire tests. It features a nucleus of calculation into which the equations may in time be integrated, and may also include a user interface. This practical, preliminary design tool's efficacy is amply confirmed by test results.The authors are indebted to the Research & Development Department of Empresa Nacional Santa Bárbara (Spain) for the performance of the ballistic tests and the X-ray shadowgraphs. This work is part of the EUCLID RTP 3.2 project, supported by the Ministries of Defence of Spain, Denmark, Holland and Italy. The above project has been developed with the collaboration of several companies and research centres of the aforementioned countries.Publicad

Análisis del comportamiento frente a impacto de elementos de estructuras aeronáuticas y aeroespaciales

El grupo de “Dinámica y Fractura de Elementos Estructurales” ofrece su experiencia en el análisis de problemas de mecánica de sólidos para estudiar el comportamiento de elementos estructurales sometidos a cargas de impacto. Para ello el grupo dispone de herramientas de simulación y equipamiento experimental específico para sus actividades de investigación. Sus actividades pueden resultar atractivas a empresas aeronáuticas que precisen de técnicas de análisis no convencionales

Analysis of the behaviour of aircraft and aerospace structural elements under impact

The Group “Dynamics and Fracture of Structural Elements” offers its experience in Solid Mechanics analysis for the study of the behaviour of structural elements subjected to impact loads. The Group activities have a strong research component, in which numerical simulation tools as well as sophisticated experimental techniques are employed. These activities could be of interest to aeronautical companies that require non standard analysis

Seguridad y defensa de sistemas móviles sometidos a cargas de impacto

El grupo "Dinámica y Fractura de Elementos Estructurales" ofrece su experiencia en el análisis de problemas de mecánica de sólidos para estudiar la protección frente impacto de vehículos, aeronaves y personas. Para ello dispone de herramientas de simulación y equipamiento experimental específico y sus actividades tienen una alta componente de investigación. Su oferta tecnológica resulta atractiva para empresas del sector automóvil (seguridad frente a impacto y choques), aeronáutico (impactos debidos a accidente, ataque, fragmentos o hielo) y defensa (blindajes especiales para vehículos y protección personal ligera)

Role of porosity in controlling the mechanical and impact behaviours of cement-based materials

14 pages, 12 figures.This work deals with the influence of porosity on the tensile, the compressive and the impact behaviours of two fine cementitious mortars—one with silica fume and one without. The addition of silica fume is shown to change the pore size distribution. The mix without silica fume is characterized by porosity at the scale of the grains of fine sand (approximately 100 μm), while silica fume addition results in a more porous matrix with pore sizes of millimetre-length size. The mortar with silica fume shows a higher quasi-static compressive and flexural strength whereas the mix without silica fume is observed to be less compressible (by irreversible reduction of volume) under heavy confinement pressure (quasi-oedometric tests) and shows better ballistic performance. A numerical simulation of the impact tests employing the Krieg, Swenson and Taylor model, which accounts for both deviatoric and volumetric inelastic behaviour of the material, was undertaken using the data from quasi-oedometric tests. These calculations follow the experimental results and confirm the influence of the macroscopic porosity on the impact performance of cement-based materials.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour l’Armement (DGA/France) for the mobility grant provided to Dr. Forquin

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 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