Effect of projectile nose shape on ballistic resistance of interstitial-free steel sheets

In this paper an experimental and numerical work is reported concerning the process of perforation of thin steel plates using different projectile nose shapes. The main goal is to analyze how the projectile shape may change the ballistic properties of materials. A wide range of impact velocities from 35 to 180 m/s has been covered during the tests. All the projectiles were 13 mm in diameter and the targets were 1 mm thick, as such the projectile can be regarded as rigid and the target sheets were of interstitial-free (IF) steel. The mass ratio (projectile mass/steel sheet mass) and the ratio between the span of the steel sheet and the diameter of the projectile were kept constant, equal to 0.38 and 3.85 respectively. To define the thermoviscoplastic behavior of the target material, the Rusinek-Klepaczko (RK) constitutive model [1] was used. The complete identification of the material constants was done based on a rigorous material characterization. Numerical simulations of some experimental tests were carried out using a non-linear finite element code ABAQUS/Explicit. It was found that the numerical models are able to describe the physical mechanisms in the perforation process with a good accuracy.The National Centre of Research and Development under the grant WND-DEM-1-203/00

Modelling of thermo-viscoplastic behaviour of DH-36 and Weldox 460-E structural steels at wide ranges of strain rates and temperatures, comparison of constitutive relations for impact problems

In this paper, the thermo-viscoplastic behaviour of DH-36 and Weldox-460-E steels is analyzed at wide ranges of strain rates and temperatures. These materials are commonly used for naval applications. Thus, they may be subjected to a wide range of exploitation temperatures and at the same time to high strain rates due to accidental impact or explosion. The thermo-viscoplastic behaviour of these materials has been modeled by application of RK (Rusinek-Klepaczko) constitutive relation. The predictions obtained using RK constitutive relation have been compared with JC (Johnson-Cook) and PB (Physical Base) constitutive relations with use of the experimental results reported in the works of Nemat-Nasser and Guo [Nemat-Nasser, S., Guo, W.G., 2003. Thermomechanical response of DH-36 structural steel over a wide range of strain rates and temperatures. Mech. Mat. 35, 1023-1047] and Borvik et al. [Borvik, T., Hopperstad, O.S., Berstad, T., Langseth, M., 2001. A computational model of viscoplasticity and ductile damage for impact and penetration. Eur. J. Solid. Mech. A. 20, 685-712]. For both metals, a satisfactory agreement is reported between the experimental results and the analytical predictions using RK model at wide ranges of strain rates and temperatures (10-3 s-1 to 104 s-1, and 77 K to about 1000 K). Especially for high strain rate level, the predictions of RK model are notably more precise than those predictions obtained using PB and JC models. This proof converts RK model in suitable for modeling impact problems. Finally, numerical simulations of perforation process of DH-36 and Weldox 460-E steel plates impacted by conical non-deformable projectiles have been carried out using RK and JC models. Numerical results using FE simulations have revealed substantial influence of the constitutive relation concerning the ballistic limit, residual velocity and failure time predictions for the same initial and boundary conditions.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project UC3M/DPI 3395) and to the Ministerio de Educatión y Ciencia de España (Project DPI/2005 06769)Publicad

Estudio experimental y numérico del comportamiento de láminas de acero sometidas a impacto de media y alta velocidad

6 pages, 14 figures.-- Contributed to: "XXV Encuentro del Grupo Español de Fractura" (Sigüenza, Spain, Mar 5-7, 2008).[EN] In the present work it is experimentally and numerically analyzed the mechanical response of steel sheets subjected to medium and high impact velocity (40 m/s – 300 m/s). The experimental device developed, based on the Hopkinson bar technique, has allowed to evaluate the influence of friction in the fracture mechanics of the steel sheets. The material behaviour has been modelled using the Rusinek-Klepaczko constitutive relation which has been implemented into the FE code ABAQUS/Explicit via user subroutine. The validation of the results obtained from the numerical simulations has been made in terms of failure time, force-time history, ballistic limit and failure mode. The numerical simulations consider the influence of the projectile shape in the failure mode and particularly the petalling process apparition. The use of 3D simulation technique has permitted to reproduce accurately the asymmetry of this kind of processes.[ES] En este trabajo se ha analizado experimental y numéricamente la respuesta mecánica de láminas de acero de bajo contenido en carbono (mild steel ES) sometidas a impacto de media y alta velocidad (40 m/s-300 m/s). El dispositivo experimental desarrollado, basado en la técnica de la barra Hopkinson, ha permitido constatar la influencia de la fricción en los mecanismos de fallo del componente. El comportamiento del material se ha modelizado mediante la ecuación constitutiva de Rusinek-Klepaczko, implementada a tal efecto en el código de elementos finitos ABAQUS/Explicit. La validación de los resultados numéricos con los datos de los ensayos experimentales realizados se ha llevado a cabo en términos de tiempo de fractura, evolución fuerza-tiempo, límite balístico y modo de fallo. Las simulaciones numéricas consideran la influencia de la forma del proyectil en el modo de fallo y en particular en la aparición del fenómeno de "petalling". La utilización de simulaciones 3D ha permitido reproducir con precisión la asimetría característica de este tipo de procesos.Los investigadores de la Universidad Carlos III de Madrid desean agradecer al Ministerio de Educación (proyecto DPI2005-06769) y a la Comunidad Autónoma de Madrid (proyecto CCG06-UC3M/DPI-0796) por el soporte económico que ha permitido la realización de este proyecto. Los investigadores de la Universidad Paul Verlaine de Metz (LPMM) desean agradecer el soporte financiero recibido del CNRS-France.Publicad

Influence of conical projectile diameter on perpendicular impact oh thin steel plate

A numerical study of conical projectiles for perpendicular impact on a thin steel plate is reported. The target material considered, Weldox 460 E steel, is frequently used for this kind of application and several results of experiments are available in the international literature to verify numerical simulations. The Johnson-Cook constitutive relation coupled with the Johnson-Cook failure criterion have been applied to analyse penetration of the target and also the failure process. The analysis has been focussed on the influence of the projectile diameter on the perforation process, assuming the same projectile mass. The aim was to preserve the same initial kinetic energy and identical nose angle. The goal is to estimate the ballistic limit, the residual velocity, the plastic work, and the temperature levels produced during the penetration process. The analysis has shown a linear increase of the ballistic limit with the projectile diameter.Publicad

Mecanismos de fallo en placas de acero sometidas a impacto de proyectiles cilíndricos, cónicos y hemisféricos

6 pages, 14 figures.-- Contributed to: "XXV Encuentro del Grupo Español de Fractura" (Sigüenza, Spain, Mar 5-7, 2008).[EN] In this work a numerical study is presented of the behaviour of Weldox 460 E steel plates of 12 mm thickness subjected to perpendicular impact of rigid projectiles of different nose shapes: cylindrical, hemispherical and conical. The numerical simulations have been carried out using the FE commercial code ABAQUS/Explicit. The validation of the numerical results using experimental results available in the international literature has been done considering failure time, ballistic limit and the energy absorbed by the plate. In order to evaluate the influence of the thermoviscoplastic material behaviour on the results obtained, two different constitutive relations have been compared: Johnson-Cook and Rusinek-Klepaczko.[ES] En este trabajo se presenta un análisis numérico del comportamiento de placas de acero Weldox 460 E de 12 mm de espesor sometidas al impacto normal de proyectiles rígidos de diferentes geometrías: cilíndrica, hemisférica y cónica. Las simulaciones numéricas se han llevado a cabo utilizando el código comercial de elementos finitos ABAQUS/Explicit. La validación de los resultados numéricos con los datos experimentales disponibles en la bibliografía se ha realizado considerando el tiempo de fractura, el límite balístico y la energía absorbida por la placa. Para evaluar la influencia de la definición del comportamiento termoviscoplástico del material en los resultados obtenidos, se han empleado dos ecuaciones constitutivas: Johnson-Cook y Rusinek-Klepaczko.Los investigadores de la Universidad Carlos III de Madrid desean agradecer al Ministerio de Educación (proyecto DPI2005-06769) y a la Comunidad Autónoma de Madrid (proyecto CCG06-UC3M/DPI-0796) el soporte económico que ha permitido la realización de este trabajo. Los investigadores de la Universidad Paul Verlaine de Metz (LPMM) desean agradecer el soporte financiero recibido del CNRS-France.Publicad

Experimental and numerical study on the perforation process of mild steel sheets subjected to perpendicular impact by hemispherical projectiles

23 pages, 28 figures."This paper is dedicated to our friend, Professor Janusz Roman Klepaczko who passed away on August 15, 2008, for his pioneer contribution in the area of dynamic behavior of materials".In this paper a study is presented on the experimental and numerical analysis of the failure process of mild steel sheets subjected to normal impact by hemispherical projectiles. The experiments have been performed using a direct impact technique based on Hopkinson tube as a force measurement device. The tests covered a wide range of impact velocities. Both lubricated and dry conditions between specimen and projectile have been applied. Different failure modes for each case were found. For lubricated conditions a petalling was observed, whereas for dry conditions a radial neck along with a hole enlargement reduces the formation of petalling. The perforation process has been simulated by the application of 3D analysis using ABAQUS/Explicit FE code. The material behavior of the circular specimen was approximated by three different constitutive relations. The main task was to study the influence of the material definition on the response of the sheet specimen with special attention to the failure mode.The researchers of the University Carlos III of Madrid are indebted to the Spanish Ministry of Education (project DPI2005-06769), and to the Region of Madrid (project CCG06-UC3M/DPI-0796) for the financial support that allowed to perform a part of the numerical simulations. The researchers from the Metz University (Laboratory of Physics and Mechanics of Materials) acknowledgement some support by CNRS – France.Publicad

3D meso-scale modelling of concrete material in spall tests

Tensile strength is one of the key factors of concrete material that need be accurately defined in analysis of concrete structures subjected to high-speed impact loads. Dynamic tensile strength of concrete material is usually obtained by conducting laboratory tests such as direct tensile test, Brazilian splitting test and spall test. Concrete is a heterogeneous material with different components, but is conventionally assumed to be homogeneous, i.e., cement mortar only, in most previous experimental or numerical studies. The aggregates in concrete material are usually neglected owing to testing limitation and numerical simplification. It has been well acknowledged that neglecting coarse aggregates might not necessarily give accurate concrete dynamic material properties. In the present study, a 3D meso-scale model of concrete specimen with consideration of cement mortar and aggregates is developed to simulate spall tests and investigate the behaviour of concrete material under high strain rate. The commercial software LS-DYNA is used to perform the numerical simulations of spall tests. The mesh size sensitivity is examined by conducting mesh convergence tests. The reliability of the numerical model in simulating the spall tests is verified by comparing the numerical results with the experimental data from the literature. The influence of coarse aggregates on the experimental test results is studied. The wave attenuation in concrete specimen is analysed, and empirical equations are proposed for quick assessment of the test data to determine the true dynamic tensile strength of concrete material. The contributions of aggregates to dynamic strength in spall tests are quantified for modifying the test results based on mortar material in the literature

Spalling uniaxial strength of Al2O3 at high strain rates

In this article research into the uniaxial tensile strength of Al2O3 monolithic ceramic is presented. The experimental procedure of the spalling of long bars is investigated from different approaches. This method is used to obtain the tensile strength at high strain rates under uniaxial conditions. Different methodologies proposed by several authors are used to obtain the tensile strength. The hypotheses needed for the experimental set-up are also checked, and the requirements of the set-up and the variables are also studied by means of numerical simulations. The research shows that the shape of the projectile is crucial to achieve successfully tests results. An experimental campaign has been carried out including high speed video and a digital image correlation system to obtain the tensile strength of alumina. Finally, a comparison of the test results provided by three different methods proposed by different authors is presented. The tensile strength obtained from the three such methods on the same specimens provides contrasting results. Mean values vary from one method to another but the trends are similar for two of the methods. The third method gives less scatter, though the mean values obtained are lower and do not follow the same trend as the other methods for the different specimens

Impact tension of sheet metals - Effect of initial specimen length

It is well known that a specimen for impact testing of materials must be optimized concerning its dimensions. The main reason is to reduce strain gradients due to the effects of elastic-plastic wave propagation. On the other hand, when Split Hopkinson Bar (SHB) is applied for tension test, the net displacement of the specimen ends is very limited, usually from 2.0 to 3.0 mm. Thus, to reach maximum strain 0.5 the specimen length must be reduced to dimensions from 4.0 mm to 6.0 mm. Consequently small diameter, or lateral dimensions in case of flat specimen, must be applied to assure one-dimensional deformation. Such small lengths substantially perturb the real material behavior to be determined. So the main motivation of this study was to perform a systematic analysis, numerical and analytical, to find differences in behavior of short and long specimens loaded in impact tension. The FE code Abaqus/Explicit has been used to simulate several specimen lengths from 10 mm to 40 mm, and several velocities from 10 m/s to 100 m/s

Comportement viscoplastique des tôles en traction et cisaillement. Analyse de la vitesse d'impact critique

Les processus de technologie moderne utilisés pour la production de pièces métalliques ou pour la fabrication de tôles sont continuellement améliorés. Un domaine de développement consiste à réduire les temps de production qui induisent des vitesses de déformation élevées durant les processus d'emboutissage. Ensuite, il faut assurer la résistance aux chocs des structures. Celles-ci devront être fabriquées avec des matériaux dont les propriétés mécaniques seront bien connues ; par exemple, les pièces mises en œuvre en construction automobile devront présenter une bonne résistance aux crashs et aux chocs. Les vitesses de déformation locales au cours de l'écrasement d'une structure métallique à profil tubulaire peuvent atteindre des vitesses de déformation de l'ordre de 5 x 102 s-1. Dans ce domaine de vitesse de déformation, le comportement du matériau et surtout la résistance aux déformations plastiques peuvent changer considérablement.Ces besoins industriels nous ont poussés à développer des techniques expérimentales dites "dynamiques" où les vitesses de déformation maximales peuvent atteindre 103 s-1. Au cours de ces essais, le chargement de l'échantillon se fait par la propagation d'ondes élastiques. On observe également une transition de régime isotherme-adiabatique en raison de la courte durée du chargement. Un autre phénomène inconnu pour un grand nombre de personne apparaît : il s'agit de la vitesse d'impact critique (VIC). Cette vitesse peut être définie comme une propriété physique intrinsèque au matériau comme le sont également le module d'Young et le coefficient de Poisson. Une fois que cette vitesse est atteinte, un processus d'instabilité plastique apparaît induisant une rupture fragile du matériau au niveau du point d'impact.Le couplage de techniques expérimentales traditionnelles avec les techniques dites dynamiques permet de couvrir un large spectre de vitesse de déformation variant entre [math] en double cisaillement. En traction, la vitesse de déformation obtenue avec cette nouvelle technique varie dans l'intervalle [math].L'ensemble de ces résultats nous a permis de proposer une nouvelle loi de comportement thermoviscoplastique en grande déformation. L'avantage considérable que présente cette loi est le nombre minimum de paramètres à identifier et la possibilité de l'introduire aisément dans un code de calcul par éléments finis. Un exemple d'application est l'analyse de la traction directe