Effect of projectile nose shape,impact velocity and target thickness on the deformation behavior of layered plates

The present study is based on the experimental and numerical investigations of deformation behavior of layered aluminum plates of different thicknesses under the impact of flat, ogive and hemispherical nosed steel projectiles. Thin-layered plates arranged in various combinations were normally impacted at different velocities with the help of a pneumatic gun. Ballistic limit velocity and the residual velocity of the projectiles for each layered combination were obtained experimentally as well as from the finite element code, and these were compared with those of the single plates of equivalent thicknesses. For two layers, the residual velocity was comparable to that of the single plate, however, when the number of layers was increased the velocity drop was found to be higher in the case of the single plate. Ogive nosed projectile was found to be the most efficient penetrator of the layered target. Hemispherical nosed projectile required maximum energy for perforation. Deformation profiles of the target plates in the layered combinations were measured, and it was found that hemispherical nosed projectile caused highest plastic deformation of target plates. Numerical simulation of the problem was carried out using finite element code ABAQUS. Explicit solution technique of the code was used to analyze the perforation phenomenon. Results of the finite element analysis were compared with experiments and a good agreement between the two was found.     

Ballistic Limit of Single and Layered Aluminium Plates

Abstract: This paper presents an experimental and finite‐element investigation of ballistic limit of thin single and layered aluminium target plates. Blunt‐, ogive‐ and hemispherical‐nosed steel projectiles of 19 mm diameter were impacted on single and layered aluminium target plates of thicknesses 0.5, 0.71, 1.0, 1.5, 2.0, 2.5 and 3 mm with the help of a pressure gun to obtain the ballistic limit in each case. The ballistic limit of target plate was found to be considerably affected by the projectile nose shape. Thin monolithic target plates as well as layered in‐contact plates offered lowest ballistic resistance against the impact of ogive‐nosed projectiles. Thicker monolithic plates on the other hand, offered lowest resistance against the impact of blunt‐nosed projectiles. The ballistic resistance of the layered targets decreased with increase in the number of layers for constant overall target thickness. Axi‐symmetric numerical simulations were performed with ABAQUS/Explicit to compare the numerical predictions with experiments. 3D numerical simulations were also performed for single plate of 1.0 mm thickness and two layered plate of 0.5 mm thickness impacted by blunt‐, ogive‐ and hemispherical‐nosed projectiles. Good agreement was found between the numerical simulations and experiments. 3D numerical simulations accurately predicted the failure mode of target plates.     

Numerical simulations of impact behaviour of thin steel plates subjected to cylindrical,conical and hemispherical non-deformable projectiles

In this paper, a numerical study of normal perforation of thin steel plates impacted by different projectile shapes is reported. The numerical simulations of this problem have been performed using a finite element code, ABAQUS-Explicit with a fixed and an adaptive mesh for the plate. To define the thermoviscoplastic behaviour of the material constituting the plate, the Johnson–Cook model has been used. This homogeneous behaviour has been coupled with the Johnson–Cook fracture criterion to predict completely the perforation process. Three kinds of projectile shape (blunt, conical and hemispherical) have been simulated with a large range of impact velocities from 190 to 600 m/s. The analysis considers the influence of adiabatic shear bands, plastic work and the gradient of temperature generated in the plate. The numerical results predict correctly the behaviour projectile-plate in agreement with experimental data published by other authors.     

Protection effectiveness of an oblique plate against a long rod

Protection effectiveness of an oblique metallic plate against a long rod projectile has been evaluated through a three-dimensional dynamic finite element computer program. The parameters considered in the simulations are the impact velocity, oblique plate thickness, gap distance between oblique plate and witness block, and obliquity. It was found that protection performance of an oblique plate was maximized in case that the ratio of line-of-sight (LOS) plate thickness to projectile diameter is around 2.0. This result may be used as a guide for the design of obliquely spaced armour structures against long rod projectiles.     

The effect of target strength on the perforation of steel plates using three different projectile nose shapes

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 ogival-nosed 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.     

Response of simulated propellant and explosives to projectile impact—III. Experimental and numerical results of warhead penetration and fragmentation

This paper is the third of a series concerned with the effects of projectile impact on a simulated explosive or propellant, called Propergol. Experiments were conducted to study the fragmentation and perforation response of disks of this material when subjected to impact by blunt and cylindro-conical strikers. Similar tests were conducted on layered targets of Propergol and steel, and also for a simulated warhead that was struck by armor-piercing projectiles. Data were obtained by velocity measurement, high-speed photography and post-mortem target examination including collected fragments.

A fragmentation oriented penetration code, AUTODYN(frag) was developed from the interfacing of a two-dimensional commercial finite difference code, AUTODYN, with a fragmentation subroutine, BFRACT, developed by other investigators. This program was utilized to study the microfracture and fragmentation processes in both monolithic and composite Propergol plates during their penetration by projectiles. In addition, numerical evaluations of the effects of simulated warhead penetration by armor-piercing bullets were conducted using the publicly available finite-element code DYNA2D.

The numerical results were compared with corresponding experimental data and also with the predictions of an analytical representation of the phenomenon, described in the second paper of the series. Reasonable agreement was obtained in the domain where the hypotheses concerning the structure of the analysis and of the computations were applicable.     

Ballistic resistance of double-layered armor plates

In this paper, the ballistic resistance of double-layered steel shields against projectile impact at the sub-ordnance velocity is evaluated using finite element simulations. Four types of projectiles of different weight and nose shapes are considered, while armor shields consist of two layers of different materials. In a previous study of the same authors, it was shown that a double-layered shield of the same metal was able to improve the ballistic limit by 7.0–25.0% under impact by a flat-nose projectile, compared to a monolithic plate of the same weight. Under impact by a conical-nose projectile, a double-layered shield is almost as capable as a monolithic plate. The present paper extends the analysis to double-layered shields with various metallic material combinations. The study reveals that the best configuration is the upper layer of high ductility and low strength material and the lower layer of low ductility and high strength material. This configuration results in some 25% gain in the ballistic limit under moderate detrimental impact. This research helps clarify the long standing issue of the ballistic resistance of the multi-layered armor configuration.     

A combined experimental and numerical approach to study ballistic impact response of S2-glass fiber/toughened epoxy composite beams

A combined experimental and 3D dynamic nonlinear finite element (FE) approach was adopted to study damage in composite beams subject to ballistic impact using a high-speed gas gun. The time-histories of dynamic strains induced during impact were recorded using strain gages mounted on the front of the composite beam specimen. During ballistic impact tests, the impact velocity was also measured. The commercially available 3D dynamic nonlinear FE code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model, was then used to simulate the experimental results. In addition, LS-DYNA with the Chang–Chang linear-orthotropic damage model was also used for comparison. Good agreement between experimental and FE results was found from the comparisons of dynamic strain and damage patterns. Once the proposed nonlinear-orthotropic damage model was verified by experimental results, further FE simulations were conducted to predict the ballistic limit velocity (V₅₀) using either the number of damaged layer approach or a numerically established relation between the projectile impact velocity versus residual velocity or energy similar to the classical Lambert–Jonas equation for metals.     

Experimental impact study using an explosive driven projectile accelerator and numerical simulation

This paper presents a projectile impact experiment using a compact accelerator driven directly by explosives, and a numerical simulation of the impact. The compact projectile accelerator has been developed to evaluate the perforation resistance of structural materials. Projectile shooting tests were conducted and the relationship between the explosive weight and the injected projectile velocity was obtained. A series of impact tests on the targets, with varying projectile velocity, was examined using the developed accelerator. The projectile was made of SNCM (nickel–chromium–molybdenum special steel of the Japanese Industrial Standard) and the targets were aluminum 5052S alloy plates. The projectile track and the impact process on the targets were observed with a SHIMAZU HPV-1 high-speed video camera and the velocity of the projectile and interactive behavior were evaluated. A numerical simulation study was conducted using the parallel version of the non-linear finite element code of LS-DYNA to follow the impact experiments and determine the ballistic limit of the projectile for the targets.     

Impact of thick PMMA plates by long projectiles at low velocities. Part I: Effect of head’s shape

A hybrid experimental–numerical investigation of the penetration process in thick polymethylmethacrylate (PMMA) plates was carried out. The response of such plates to the impact of long hard steel projectiles having either blunt, hemispherical or ogive-head shapes was investigated experimentally in the range of velocities of 100 (m/s) < V₀ < 250 (m/s). The penetration process can be divided into 3 stages: entrance, propagation and backwards bouncing. The last two stages are associated with brittle fracture of the plates. The tests were modeled using 3D explicit finite element analyses. The numerical results provide insight regarding the variations of field variables such as stresses, velocities, resisting forces and energies. A good agreement regarding the trajectory of the projectile and the depths of penetration is obtained. The enhanced backwards bouncing phenomenon is explained, and it is shown that the average deceleration during the penetration process is constant. The resisting force to the penetration is higher for blunt projectiles. It is 10% lower for the hemispherical head and 50% lower for ogive-headed projectiles.     

Experimentation and modeling of inclined ballistic impact in thick polycarbonate plates

The penetration and perforation of a thick polycarbonate (PC) plate (one and 3 stacked) by an armor piercing 7.62 mm projectile is investigated experimentally and numerically. The characteristic structure of the projectile’s trajectory in the PC plates is studied. It is observed that the trajectory consist of a cavity and a circumferential cracked zone attached to it, which is fully embedded within a cylindrical plastic zone. The size of the plastic zone is approximately twice that of the cavity zone and can be clearly observed due to the change of the refractive properties of the material. Strong local recovery of the PC is shown as well.A 3D transient non-linear adiabatic finite element simulation is performed using the commercial software Abaqus 6.9-EF1. The numerical analyses include two combined failure criteria: “Ductile failure with damage evolution”, and tensile failure. The material properties are strain rate and temperature dependent. The numerical simulations are tested by comparing the numerical trajectory prediction to actual trajectories of inclined impacts of projectiles. It is found that the projectile perforates the plate at angles of inclinations of 30° and higher. The observed agreement between experiments and numerical modeling indicates that the combined effect of the two failure criteria (tensile vs. ductile failure) can reasonably well predict the projectile’s trajectory within a thick PC plate.The numerical analyses are further used to study the effect of the projectile impact velocity on the depth of penetration (DOP). It is found that the DOP scales slightly non-linear with the impact velocity. The core velocity during the penetration process is also slightly non-linear. The deceleration during penetration is almost a linear function of the penetration velocity and it is higher for higher penetration velocities.     

Analytical and numerical investigation of polyurea layered aluminium plates subjected to high velocity projectile impact

This paper discusses on the penetration of high velocity projectiles through aluminium–polyurea composite layered plate systems. An analytical model has been proposed to predict the residual velocity of aluminium–polyurea composite plates, and validated with both experimental and numerical investigations. Full metal jacket (FMJ) projectiles (5.56 mm × 45 mm), corresponding to NATO standard SS109, were fired at the aluminium–polyurea composite layered plate systems from a distance of 10.0 m at a fixed velocity of 945 m/s. Four different composite plate configurations were used with thicknesses varying from 16 to 34 mm. Each configuration consisted of six specimens. Residual velocities for each individual test were recorded. Numerical simulations of the penetration process have been performed using advanced finite element code LS-DYNA®. The well-established Johnson–Cook and Mooney–Rivlin material models were used to represent the stress–strain behaviour of aluminium and polyurea in the numerical analysis. The analytical and numerical models provided good approximations for the residual velocities measured during the experimental tests. Polyurea layers contributed positively towards the reduction of residual velocity of the projectile in composite plate systems. In addition, ballistic limit curves for different composite systems have been established based on the validated models. As the results showed that polyurea contributes positively towards the reduction of residual velocity of projectiles, the findings of this study can be effectively used for the similar applications in future armour industry.     

Predicting the fragmentation onset velocity for different metallic projectiles using numerical simulations

For cubes and spheres under high velocity impact there exists for each system of projectile and target, a threshold velocity that is just sufficient to shatter the projectile. This velocity, usually above 2km/s for metallic projectiles, is known as the fragmentation onset velocity. To determine the fragmentation onset velocity experimentally, a number of experiments in which the impact velocity of the projectile is varied in a controlled manner needs to be conducted [1]. In the work described in this paper, the numerical analysis code AUTODYN was used to simulate the impact of stainless steel and tantalum projectiles onto transparent targets in an attempt to simulate the onset of fragmentation. Using the meshfree SPH method for discretizing the spatial domain of the projectile and a simple failure model that allows the critical spall stress of the material to vary with the local material and loading conditions, encouraging results were obtained, with the fragmentation onset velocity for both projectile/target configurations being reasonably well predicted. In addition, further experiments conducted at TNO-PML, to determine the fragmentation onset velocity for tungsten projectiles, will be reported.     

Deformation and fracture of a long-rod projectile induced by an oblique moving plate: Experimental tests

The influence of projectile length to diameter ratio (15, 30 and 45), plate thickness (0.5, 1 and 2 projectile diameters), projectile velocity (1500, 2000 and 2500 m/s) and plate velocity (−300 to 300 m/s) on the interaction between long-rod tungsten projectiles and oblique steel plates (obliquity 60°) was studied experimentally in small-scale reverse impact tests. The residual projectiles and their motions were characterised in terms of changes in length, velocity, angular momentum, linear momentum and kinetic energy. The parameters found to have the largest influence on the disturbance of the projectile were the plate velocity, in particular its direction, and the thickness of the plate. In the ranges studied, the influence of length to diameter ratio and of projectile velocity were found to be less important.     

Penetration of 6061-T6511 aluminum targets by ogive-nosed VAR 4340 steel projectiles at oblique angles: experiments and simulations

In this paper we present the results from a combined experimental, analytical, and computational penetration program. First, we conducted a series of depth-of-penetration experiments using 0.021 kg, 7.11 mm diameter, 71.12 mm long, vacuum-arc-remelted 4340 ogive-nose steel projectiles. These projectiles were launched with striking velocities between 0.5 and 1.3 km/s using a 20 mm powder gun into 254 mm diameter, 6061-T6511 aluminum targets with angles of obliquity of 15°, 30°, and 45°. Next, we employed the initial conditions obtained from the experiments with a new technique that we have developed to calculate permanent projectile deformation without erosion. With this technique we use an explicit, transient dynamic, finite element code to model the projectile and an analytical forcing function derived from the dynamic expansion of a spherical cavity (which accounts for compressibility, strain hardening, strain-rate sensitivity, and a finite boundary) to represent the target. Results from the simulations show the final projectile positions are in good agreement with the positions obtained from post-test radiographs.     

风致飞掷物冲击建筑浮法玻璃试验和数值模拟

通过试验和有限元数值模拟的方法研究风致飞掷物对建筑浮法玻璃的冲击破坏效应。首先进行钢球冲击浮法玻璃面板的破坏试验,然后基于LS-DYNA建立与试验对应的飞掷物冲击浮法玻璃有限元模型,并通过对比试验和数值模拟的结果验证有限元模型的可靠性。最后基于验证后的有限元模型,以板状飞掷物为代表,研究风致飞掷物的冲击位置、冲击姿态和外形等特性对其冲击效应的影响。结果表明,建筑浮法玻璃在风灾中非常容易受到飞掷物的冲击而破坏。采用JH-2作为浮法玻璃的本构模型并以SIGP1=75 MPa作为失效准则,能够较准确地模拟浮法玻璃在冲击荷载下的破坏特性。板状飞掷物的冲击位置对其冲击效应影响不大,但其冲击姿态和边厚比对冲击效应有较大的影响。     

低速大质量球头弹冲击下薄板穿甲破坏机理数值分析

为探讨薄板穿甲破坏机理,采用动态非线性有限元,结合弹道冲击试验,分析了薄板在低速大质量球头弹体冲击下的穿甲破坏过程及其变形机理,薄板的变形吸能规律及破坏模式,并将有限元分析结果与实验结果进行了比较,有限元分析结果与实验结果吻合良好.结果表明:薄板穿甲破坏过程大致可分为三个阶段,即隆起变形阶段,碟形变形阶段和弹体贯穿阶段.其中薄板的隆起变形主要由剪力和弯矩引起的;隆起变形结束后,碟形变形区膜力逐渐增大,超过动态屈服极限,并随冲击速度的减小而增大,到弹道极限附近成为最主要的广义应力;低速冲击下碟型变形是靶板主要的变形吸能方式.大质量低速球头弹冲击下薄板的穿甲破坏模式可归纳为三种:隆起-碟形变形,隆起-碟形变形-贯穿破坏和隆起-贯穿破坏.     

Penetration of limestone targets by ogive-nosed VAR 4340 steel projectiles at oblique angles: experiments and simulations

In this paper, we document the results of a combined experimental, analytical, and computational research program that investigates the penetration of steel projectiles into limestone targets at oblique angles. We first conducted a series of depth-of-penetration experiments using 20.0 g, 7.11-mm-diameter, 71.12-mm-long, vacuum-arc-remelted (VAR) 4340 ogive-nose steel projectiles. These projectiles were launched with striking velocities between 0.4 and 1.3 km/s using a 20-mm powder gun into 0.5 m square limestone target faces with angles of obliquity of 15° and 30°. Next, we employed the initial conditions obtained from the experiments with a technique that we have developed to calculate permanent projectile deformation without erosion. With this technique we use an explicit, transient dynamic, finite element code to model the projectile and an analytical forcing function based on the dynamic expansion of a spherical cavity to represent the target. Due to angle of obliquity we developed a new free surface effect model based on the solution of a dynamically expanding spherical cavity in a finite sphere of incompressible Mohr–Coulomb target material to account for the difference in target resistance acting on the top and bottom sides of the projectile. Results from the simulations show the final projectile positions are in good agreement with the positions obtained from post-test castings of the projectile trajectories.     

Quasi-brittle fracture during structural impact of AA7075-T651 aluminium plates

The stress–strain behaviour of the aluminium alloy 7075 in T651 temper is characterized by tension and compression tests. The material was delivered as rolled plates of thickness 20 mm. Quasi-static tension tests are carried out in three in-plane directions to characterize the plastic anisotropy of the material, while the quasi-static compression tests are done in the through-thickness direction. Dynamic tensile tests are performed in a split Hopkinson tension bar to evaluate the strain-rate sensitivity of the material. Notched tensile tests are conducted to study the influence of stress triaxiality on the ductility of the material. Based on the material tests, a thermoelastic–thermoviscoplastic constitutive model and a ductile fracture criterion are determined for AA7075-T651. Plate impact tests using 20 mm diameter, 197 g mass hardened steel projectiles with blunt and ogival nose shapes are carried out in a compressed gas-gun to reveal the alloy's resistance to ballistic impact, and both the ballistic limit velocities and the initial versus residual velocity curves are obtained. It is found that the alloy is rather brittle during impact, and severe fragmentation and delamination of the target in the impact zone are detected. All impact tests are analysed using the explicit solver of the non-linear finite element code LS-DYNA. Simulations are run with both axisymmetric and solid elements. The failure modes are seen to be reasonably well captured in the simulations, while some deviations occur between the numerical and experimental ballistic limit velocities. The latter is ascribed to the observed fragmentation and delamination of the target which are difficult to model accurately in the finite element simulations.     

Impact of conical tungsten projectiles on flat silicon carbide targets: Transition from interface defeat to penetration

Normal impact of conical tungsten projectiles on flat silicon carbide targets was studied experimentally and numerically for half apex angles 5° and 5–15°, respectively, and comparisons were made with cylindrical projectiles. A 30 mm powder gun and two 150 kV and four 450 kV X-ray flashes were used in the impact tests. The numerical simulations were run with the Autodyn code in two steps. In the first, the surface loads were determined for different impact velocities under assumed condition of interface defeat. In the second, these surface loads were applied to the targets in order to obtain critical states of damage and failure related to the transition between interface defeat and penetration, and the corresponding critical velocities. In the impact tests, interface defeat occurred below a transition velocity, which was significantly lower for the conical than for the cylindrical projectiles. Above the transition velocity, the initial penetration of conical projectiles differed markedly from that usually observed for cylindrical projectiles. It occurred along a cone-shaped surface crack, qualitatively corresponding to surface failure observed in the simulations. The transition velocity for the conical projectile was found to be close to the critical velocity associated with this surface failure.