On the Influence of Fracture Criterion on Perforation of High-Strength Steel Plates Subjected to Armour Piercing Projectile / Wpływ Kryterium Pekania Materiału Na Perforacje Płyt Ze Stali Pancernej Pociskiem Przeciwpancernym (original) (raw)
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Modeling and Simulation of Perforation of Steel Plates by Blunt Projectiles
Due to the lack of the classical local continuum formulation to produce physically meaningful and numerically converging results within large deformation and strain localization computations, a thermodynamically motivated micro-damage formulation is proposed for highrate and temperature dependent materials. This model uses a combined viscosity and nonlocal gradient localization limiters in order to regularize the dynamic strain localization problems. The enhanced nonlocal gradient-dependent theory formulates a constitutive framework on the continuum level that is used to bridge the gap between the micromechanical theories and the classical (local) continuum theories. They are successful in explaining the size effects encountered at the micron scale and in preserving the well-posedeness of the initial boundary value problem governing the solution of material instability triggering strain localization. Moreover, viscosity (rate dependency) allows the spatial difference operator in the governing equations to retain its hyperbolicity and the initial boundary value problem is well-posed. This is due to the incorporation of either explicit (via nonlocal theory) or implicit (via viscosity) intrinsic material length scale parameter in the constitutive description. Model capabilities are preliminarily illustrated for the dynamic localization of inelastic flow in adiabatic shear bands and the perforation of Weldox 460E steel plates with different thicknesses by deformable blunt projectiles at various impact speeds. The simulated shear band results well illustrated the potential of the proposed model in dealing with the well-known mesh sensitivity problem. Consequently the introduced implicit and explicit length scale measures are able to predict size effects in localization failures.
2006
Due to the lack of the classical local continuum formulation to produce physically meaningful and numerically converging results within large deformation and strain localization computations, a thermodynamically motivated micro-damage formulation is proposed for highrate and temperature dependent materials. This model uses a combined viscosity and nonlocal gradient localization limiters in order to regularize the dynamic strain localization problems. The enhanced nonlocal gradient-dependent theory formulates a constitutive framework on the continuum level that is used to bridge the gap between the micromechanical theories and the classical (local) continuum theories. They are successful in explaining the size effects encountered at the micron scale and in preserving the well-posedeness of the initial boundary value problem governing the solution of material instability triggering strain localization. Moreover, viscosity (rate dependency) allows the spatial difference operator in the governing equations to retain its hyperbolicity and the initial boundary value problem is well-posed. This is due to the incorporation of either explicit (via nonlocal theory) or implicit (via viscosity) intrinsic material length scale parameter in the constitutive description. Model capabilities are preliminarily illustrated for the dynamic localization of inelastic flow in adiabatic shear bands and the perforation of Weldox 460E steel plates with different thicknesses by deformable blunt projectiles at various impact speeds. The simulated shear band results well illustrated the potential of the proposed model in dealing with the well-known mesh sensitivity problem. Consequently the introduced implicit and explicit length scale measures are able to predict size effects in localization failures.
International Journal of Impact Engineering, 2004
The effect of target strength on the perforation of steel plates is studied. Three structural steels are considered: Weldox 460 E, Weldox 700 E and Weldox 900 E. The effects of strain hardening, strain rate hardening, temperature softening and stress triaxiality on material strength and ductility are determined for these steel alloys by conducting three types of tensile tests: quasi-static tests with smooth and notched specimens, quasi-static tests at elevated temperatures and dynamic tests over a wide range of strain rates. The test data are used to determine material constants for the three different steels in a slightly modified version of the Johnson-Cook constitutive equation and fracture criterion. Using these three steel alloys, perforation tests are carried out on 12 mm-thick plates with blunt-, conical-and ogivalnosed projectiles. A compressed gas gun was used to launch projectiles within the velocity range from 150 to 350 m/s. The initial and residual velocities of the projectile were measured, while the perforation process was captured using a digital high-speed camera system. Based on the test data the ballistic limit velocity was obtained for the three steels for the different nose shapes. The experimental results indicate that for perforation with blunt projectiles the ballistic limit velocity decreases for increasing strength, while the opposite trend is found in tests with conical and ogival projectiles. The tests on Weldox 700 E and Weldox 900 E targets with conical-nosed projectiles resulted in shattering of the projectile nose tip during penetration. Finally, numerical simulations of some of the experimental tests are carried out using the non-linear finite element code LS-DYNA. It is found that the numerical code is able to describe the physical mechanisms in the perforation events with good accuracy. However, the experimental trend of a decrease in ballistic limit with an increase in target strength for blunt projectiles is not obtained with the numerical models used in this study.
Modeling of Armour-piercing Projectile Perforation of Thick Aluminium Plates
2014
This study investigates the perforation process of armour-piercing projectiles on commercially available high-strength aluminium. A LS-DYNA model is developed with thick target plates of aluminium alloy 7075-T651 and an incoming 7.62 mm armour-piercing projectile with an impact velocity of 850 m/s. A numerical formulation combining classic Lagrangian finite elements with an adaptive mesh algorithm is utilized to overcome large deformation challenges and more accurately predict failure mechanisms. Both aluminium target and projectile have been modelled as deformable with a modified version of the Johnson-Cook strain-rate and temperature dependent plasticity model, based on input parameters from literature. Main model results include projectile residual velocity after target perforation and prediction of target failure mechanism. The model results are validated against experimental results from live ballistic tests and a sensitivity study is carried out to identify influential materia...
On the influence of constitutive relation in projectile impact of steel plates
International Journal of Impact Engineering, 2007
In this paper the influence of constitutive relation has been studied in numerical simulations of the perforation of 12-mm thick Weldox 460 E steel plates impacted by blunt-nosed projectiles in the sub-ordinance velocity regime. A modified version of the well-known and much used constitutive relation proposed by Johnson-Cook and both the bcc-and hcpversion of the Zerilli-Armstrong constitutive relation were combined with the Johnson-Cook fracture criterion. These models were implemented as user-defined material models in the non-linear finite element code LS-DYNA. Identification procedures have been proposed, and the different models were calibrated and validated for the target material using available experimental data obtained from tensile tests where the effects of strain rate, temperature and stress triaxiality were taken into account. Perforation tests carried out in a compressed gas gun on 12-mm-thick circular Weldox 460 E steel plates were then used as base in a validation study of plate perforation using LS-DYNA and the proposed constitutive relations. The numerical study indicated that the physical mechanisms during perforation can be qualitatively well predicted by all constitutive relations, but quantitatively more severe differences appear. The reasons for this are discussed in some detail. It was concluded that for practical applications, the Johnson-Cook constitutive relation and fracture criterion seems to be a good choice for this particular problem and excellent agreement with the experimental results of projectile impact on steel plates were obtained under the conditions investigated.
Coupled numerical-experimental study of an armour perforation by the armour-piercing projectiles
Computational Methods and Experimental Measurements XV, 2011
This paper concerns an analysis of target penetration by a selected armourpiercing (AP) projectile: 7.62x54R with steel core. Numerical and experimental research was carried out. The aim of this work was a comparison of the results obtained in real conditions of ballistic test and computer simulation. In this study, two three-dimensional targets and the core of the projectile were built. The structure of the projectile is complex, but steel core plays the main role in the perforation process. Then the numerical model of the projectile was reduced to describe only steel core dynamics. The 3D Element Free Galerkin method is applied to solve the problem under consideration. The algorithm implemented in the Ls-Dyna code was used. Space discretization of the analyzed problem was prepared by means of the HyperWorks Software (HyperMesh module). The total amount of the elements reaches 500 000 in this model. The Johnson-Cook constitutive model is applied to describe the behaviour of the metallic parts: steel layers and the projectile's core. The experimental results were obtained using a high speed video-camera. The target penetrations by the projectile were recorded. The processing of the data obtained from a high speed camera was carried out by means of the TEMA Software. In this paper, a good correlation between the numerical and experimental results was obtained. A lot of interesting mechanical effects observed during the experiment were analyzed.
Failure criteria with unilateral conditions for simulation of plate perforation
European Journal of Mechanics - A/Solids, 2011
Finite element analysis of plate perforation is performed using a thermoelasticethermoviscoplastic constitutive model and two uncoupled damage criteria with unilateral conditions. The first criterion is based on continuum damage mechanics, while the second is the CockcrofteLatham criterion. Fracture is assumed to occur at a critical damage, and crack propagation is modelled with element erosion. The identification of the material parameters is based on inverse modelling of a uniaxial tension test. The constitutive model and damage criteria are applied in explicit finite element analysis of the perforation of a 12 mm thick steel plate struck by a blunt projectile in the sub-ordinance velocity regime. The results show the importance of the unilateral conditions in obtaining accurate prediction of the adiabatic shear banding process. The two fracture criteria have comparable dependence on the stress triaxiality and the Lode parameter when the microcrack-closure parameter is set to zero in the criterion based on continuum damage mechanics, and give similar failure mode and ballistic limit in the plate perforation problem.
Experimental and numerical study on fragmentation of steel projectiles
2012
A previous experimental study on penetration and perforation of circular Weldox 460E target plates with varying thicknesses struck by blunt-nose projectiles revealed that fragmentation of the projectile occurred if the target thickness or impact velocity exceeded a certain value. Thus, numerical simulations that do not account for fragmentation during impact can underestimate the perforation resistance of protective structures. Previous numerical studies have focused primarily on the target plate behaviour. This study considers the behaviour of the projectile and its possible fragmentation during impact. Hardened steel projectiles were launched at varying velocities in a series of Taylor tests. The impact events were captured using a high-speed camera. Fractography of the fragmented projectiles showed that there are several fracture mechanisms present during the fragmentation process. Tensile tests of the projectile material revealed that the hardened material has considerable variations in yield stress and fracture stress and strain. In the finite element model, the stress-strain behaviour from tensile tests was used to model the projectile material with solid elements and the modified Johnson-Cook constitutive relation. Numerical simulations incorporating the variations in material properties are capable of reproducing the experimental fracture patterns, albeit the predicted fragmentation velocities are too low.
International Journal of Impact Engineering, 2009
Thin plates of high-strength steel are frequently being used both in civil and military ballistic protection systems. The choice of alloy is then a function of application, ballistic performance, weight and price. In this study the perforation resistance of five different high-strength steels has been determined and compared against each other. The considered alloys are Weldox 500E, Weldox 700E, Hardox 400, Domex Protect 500 and Armox 560T. The yield stress for Armox 560T is about three times the yield stress for Weldox 500E, while the opposite yields for the ductility. To certify the perforation resistance of the various targets, two different ballistic protection classes according to the European norm EN1063 have been considered. These are BR6 (7.62 mm Ball ammunition) and BR7 (7.62 mm AP ammunition), where the impact velocity of the bullet is about 830 m/s in both. Perforation tests have been carried out using adjusted ammunition to determine the ballistic limit of the various steels. In the tests, a target thickness of 6 mm and 6 þ 6 ¼ 12 mm was used for protection class BR6 and BR7, respectively. A material test programme was conducted for all steels to calibrate a modified Johnson-Cook constitutive relation and the Cockcroft-Latham fracture criterion, while material data for the bullets mainly were taken from the literature. Finally, results from 2D non-linear FE simulations with detailed models of the bullets are presented and the different findings are compared against each other. As will be shown, good agreement between the FE simulations and experimental data for the AP bullets is in general obtained, while it was difficult to get reliable FE results using the Lagrangian formulation of LS-DYNA for the soft core Ball bullet.
Journal of Pressure Vessel Technology, 2008
This article studies the perforation of mild steel square and rectangular plates struck normally by cylindrical projectiles having blunt, hemispherical, and conical impact faces. Experimental results are obtained in a drop hammer rig for the perforation of 4 mm and 8 mm thick plates struck by relatively heavy projectiles weighing between 11.9 kg and 200 kg and traveling at an initial velocity up to about 13 m / s. The plates were struck at the center and at several positions near the fully clamped supports. The effect of the aspect ratio on the perforation energies of rectangular plates is examined, and comparisons are made with the perforation behavior of fully clamped circular plates. The predictions of several empirical equations are compared with the corresponding experimental values of the perforation energies. Simple design equations are also presented for predicting the maximum permanent transverse displacements of square plates prior to any cracking or perforation.