Long-rod Projectiles Research Articles

Penetration Behavior of Concrete Targets Subjected to Tungsten-Alloy Long-Rod Projectile Impact

Penetration Behavior of Concrete Targets Subjected to Tungsten-Alloy Long-Rod Projectile Impact

Effects of Annealing Temperatures on Mechanical Behavior and Penetration Characteristics of FeNiCoCr High-Entropy Alloys

In this paper, the mechanical properties, penetration characteristics, and deformation behaviors of FeNiCoCr high-entropy alloys (HEAs) annealed at different temperatures were investigated. The quasi-static and dynamic compression tests were conducted by a universal testing machine and Split Hopkinson Pressure Bar (SHPB) system, respectively. Furthermore, the penetration experiments of long rod projectiles (LRPs) of FeNiCoCr HEAs into semi-infinite steel targets launched by a small caliber ballistic gun with velocities ranging from 650 m/s to 1500 m/s were carried out, in comparison with that of steel LRPs. The microstructures of recovered projectiles were observed by the X-ray diffraction, optical microscope, and transmission electron microscope, which were used to further analyze the deformation behaviors of FeNiCoCr HEAs. The results showed that FeNiCoCr HEAs owned a single face-centered cubic structure. Annealing twins and grain refinement were detected, affecting the yield strength of the alloys. The strength of the alloy annealed at 600 °C was the highest and then decreased with the increasing annealing temperature. At higher strain rates, special adiabatic shear characteristics occurred in the alloys, while twins dominated the whole deformation process of the projectiles. Compared to other annealed alloys, the alloy annealed at 600 °C performed the best penetration performance. While the impact velocity had significant effects on the penetration performance of the alloy annealed at 1000 °C, the penetration performance of the alloy annealed at 850 °C on steel targets was almost the same as that of the steel LRPs.

A study on the effectiveness of explosive reactive armour against the penetration of long-rod projectiles

The effect of explosive reactive armour (ERA) on the penetration of a long-rod projectile is investigated using computational techniques. This area of research is especially relevant to main battle tanks as a large portion of them utilise ERA which is effective against both kinetic and chemical munitions. The ERA package consists of steel flyer plates sandwiched between an explosive layer that detonates on projectile impact. The influence of the stand-off distance and detonation delay and variation of the angle of impact is assessed to determine the overall effectiveness of the ERA package. The analysis presented in this study allows for a better understanding of impact dynamics and can be used in the development and optimisation of ERA as well as projectiles designed to defeat it.

Study on energy release characteristics and penetration effects to concrete targets of Hf-based amorphous alloys

In this paper, the energy release characteristics and penetration effects of Hf-based amorphous alloys subjected to high velocity impact were investigated. The quasi-sealed test chamber system was used to record the impact energy release process of Hf-based amorphous alloy fragments shotted by 14.5 mm ballistic gun at elevated impact velocities. The reaction behaviors were observed by the high-speed camera and measured by the history curves of the impact reaction pressure using a piezoresistive pressure sensor. The penetration experiments of jacketed long rod projectiles (LRPs) of Hf-based amorphous alloys launching into concrete targets were carried out by 30 mm ballistic gun with velocities about 1400 m/s, where the experiments with inert steel jacketed LRPs were taken as a contrast. The video frames from the impact events were recorded by the high-speed camera. The results demonstrated that obviously shock-induced chemical reactions took place in Hf-based amorphous alloy fragments during the impact process, where the impact velocity played a significant role. Compared with the traditional steel jacketed LRPs, both the penetration depth and the crater of Hf-based amorphous alloy jacketed LRPs to concrete targets were significantly increased, which indicated that Hf-based amorphous alloy could be used to increase the damage effects of warheads.

Experimental and Numerical Study on a Non-Explosive Reactive Armour with the Rubber Interlayer Applied against Kinetic-Energy Penetrators-The 'Bulging Effect' Analysis.

The study concerns a protection system applied against kinetic-energy penetrators (KEPs) composed of steel plates sandwiching a rubber layer. Laminated steel-elastomer armours represent non-explosive reactive (NERA) armours that take advantage of a so-called ‘bulging effect’ to mitigate KEP projectiles. Upon an impact, the side steel plates deform together with the deforming rubber interlayer. Their sudden deformation (bulging) in opposite directions disturbs long and slender KEP projectiles, causing their fragmentation. The presented discussion is based on the experimental investigation, confirming that the long-rod projectiles tend to fracture into several pieces due to the armour perforation. A numerical simulation accompanies the ballistic test providing an insight into the threat/target interactions. The presented experimental–numerical study explains the principles of the analysed protection mechanism and proves the efficiency of the materials composition making up the laminated non-reactive protection system.

Theoretical analysis for self-sharpening penetration of tungsten high-entropy alloy into steel target with elevated impact velocities

The “self-sharpening” effect has been observed experimentally in the penetration of tungsten high-entropy alloy (WHEA) into steel targets in previous study. From the microscopic observation of the residual WHEA long-rod projectile (LRP), the multiphase structure at micro-scale of WHEA is the key effects on self-sharpening penetration process. In order to describe the distinctive penetration behavior, the interaction between micro phases is introduced to modify the hydrodynamic penetration model. The yield strengths of WHEA phases are determined based on the solid solution strengthening methods. Combined with the elbow-streamline model, the self-sharpening mechanism is revealed in view of the multi-phase flow dynamics and the flow field in the deformation area of the LRP nose is characterized to depict the shear layer evolution and the shape of the LRP’s nose as well as the determination of the penetration channel. The self-sharpening coefficient considering the reduction of nose radius is proposed and introduced into the penetration model to calculate the depth of penetration and the penetration channel. Results show that the multi-phase interaction at the microscopic level contributes to the inhomogeneous distribution of the WHEA phases. The shear layer evolution separates part of the LRP material from the nose and makes the nose radius decrease more quickly. It is also the reason that WHEA LRPs have a pointed nose compared with the mushroom nose of WHA heavy alloy (WHA) LRPs. The calculated results agree well with the corresponding experimental data of WHA and WHEA LRPs penetrating into semi-infinite medium carbon steel targets with elevated impact velocities. The flow field in the projectile nose was established to describe the self-sharpening penetration process of the tungsten high-entropy alloy. Combined with the solid solution strengthening methods, the flow field of the projectile nose was structured based on the multi-phase flow. The nose radius before separation was set as $$r_\mathrm{b}$$ and after separation is $$r_\mathrm{a}$$ . The shear layer evolution separated part of the material from the nose and made the nose radius decrease more quickly.

Characteristics of interface defeat and penetration during the impact between a ceramic armor and a long-rod projectile

Interface defeat/dwell can effectively improve the anti-penetration performance of a ceramic armor at certain degree, which attracts the attention from researchers all over the world in recent years. Experiments on a ceramic armor subjected to the impact of a long-rod projectile (LRP) were carried out to investigate the characteristics of interface defeat and penetration during the impact in this paper. A theoretical model for the penetration process of a LRP into a ceramic target with semi-finite thickness at different impact velocities was established by considering interface defeat/dwell to study quantitatively the effect of interface defeat/dwell on the penetration. The theoretically calculated results on dwell/penetration transition velocity, dwell time, penetration velocity and depth of penetration agree well with the experimental data, which proves that the established theoretical model is accurate. The influences of the projectile and ceramic materials on the interface defeat/dwell and penetration were analyzed. Both the experimental results and the calculated results by the theoretical model show that the interaction between LRPs and ceramics transfers from interface defeat to penetration when the impact velocity increases. It also indicates that the established theoretical model can depict the interaction modes of ceramics and LRPs under different impact velocities. The yield stress and density of the projectile materials play a coupling role in the interaction between LRPs and ceramics when the interface defeat/dwell occurs. The higher the yield strength and density of the projectile materials, the shorter the dwell time and the higher the penetrating ability of the projectile. The higher the dynamical yield strength of the ceramics, the more markedly the interface defeat/dwell and the higher the anti-penetration ability of the ceramic armors. The established theoretical model in consideration of interface defeat/dwell can partially reveal the mechanism of the interface defeat, and it can provide a reference for the design of ceramic composite targets.

Equivalent protection factor of bi-layer ceramic metal structures

With increasing ballistic threat levels, there is ever more demand on developing ceramic armor designs with improved performance. This paper presents finite element simulations that investigate the performance of silicon carbide ceramic with steel 4340 backing material and titanium alloy, graphite as buffer layers when subjected to normal and oblique impacts by a tungsten alloy long rod projectile (LRP). Depth of penetration from experimental measurements is compared with simulations to confirm the validity of constitutive, failure model parameters. Titanium alloy cover plate and graphite interface weak layer laterally spread the impact shock away from the SiC tile and reduces the amplification of the stress accumulation at the front surface of the SiC tile. The dwelling time increases before it penetrates into ceramic armor. Further, using AUTODYN® numerical simulations detailed parametric study is carried out to identify the minimum areal density armor for a given ballistic limit velocity. The equivalent protection factor for the bi-layer armor is a simple function of the cosine of the angle of impact.

Hypervelocity penetration of concrete targets with long-rod steel projectiles: experimental and theoretical analysis

Hypervelocity penetration experiments were performed on semi-infinite concrete targets with 7 mm-diameter 40CrNiMo steel long-rod projectiles at impact velocities ranging from 2117 m/s to 3086 m/s by using a two-stage combustion light-gas gun. After the experiments, the crater dimensions and penetration depth were carefully measured, also the residual projectiles were recovered. The depth of penetration was found to be greater than the hydrodynamic limit penetration depth. Numerical simulation was conducted to analyze the penetration process, and combined with the experimental results, it was obtained that the head of the long-rod projectile eroded and deformed into a hemisphere during hypervelocity penetration. According to the experimental and numerical simulation results, the penetration model of long-rod projectiles penetrating concrete targets at hypervelocity was constructed based on the Alekseevskii-Tate model. The penetration model was compared with the experimental depths of penetration, showing that the model had good applicability.

A Comparative Study on the Ballistic Performance and Failure Mechanisms of High-Nitrogen Steel and RHA Steel Against Tungsten Heavy Alloy Penetrators

Traditionally, medium-carbon, low-alloy steels with tempered martensitic microstructures are widely used in structural armor applications. There have been continuous attempts to develop alternative structural armor materials that can provide further weight reduction of armored vehicles. In this context, high-nitrogen steel (HNS) plates with austenitic microstructures were studied against a full-scale tungsten heavy alloy penetrator (500 mm in length and 25 mm in diameter), and the results were compared with those of rolled homogeneous armor steels with tempered martensitic microstructures. The ballistic trials on HNS and RHA steel plates were carried out against a WHA penetrator at velocities of 1630 ± 20 m/s (at a 0° angle of attack and a distance of 100 m) to determine the depth of penetration. HNS exhibited higher ballistic performance (i.e., a lower normalized depth of penetration) against WHA long-rod projectiles than RHA steel. The ballistic results were analyzed with the help of the initial mechanical properties and operating failure mechanisms. The better ballistic performance of HNS against tungsten heavy alloy can be primarily attributed to its higher dynamic flow stress. Post-ballistic hardness measurements on crater cross sections indicated that a higher volume of material was involved in energy dissipation in the HNS target than in the RHA steel target. Microstructural analysis showed that adiabatic shear band-induced cracking played an important role in the failure of both steel targets.

Hypervelocity Impact Cratering on Semi-Infinite Concrete Targets of Projectiles with Different Length to Diameter Ratios

Impact cratering experiments were performed on semi-infinite concrete targets with 7 mm-diameter 40CrNiMo steel long-rod projectiles at impact velocities ranging from 2117 m/s to 3086 m/s by using a two-stage combustion light-gas gun. After the impact experiments, the crater diameter and depth as well as the crater volume were carefully measured. The concrete fragments were collected from the target chamber and the fragment mass was measured. The size of the crater (including the volume, diameter, and depth) and the fragment mass increased with increasing impact velocities, while the fragment distributions at different impact velocities were almost the same. Scaling laws for the crater volume impacted by the rod-shaped projectile were discussed and an empirical formula of crater volume was determined by the experimental data from the literature. Through the verification of the present experimental results, the predictive ability of the empirical formula proved to be reliable. Scaling laws for the size distribution of concrete fragments were also discussed. The normalized fragment mass distribution was proportional to the impact velocity raised to the power 1.5.

Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets. However, the mechanism of impact flash remains unclear. A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun. The impact flash spectra for 6061 aluminum at 1.3–3.2 km/s collision speeds were recorded with a high-speed camera, a photoelectric sensor, and a time-resolved spectrometer. The intensity of the impact flash exhibited a pulse characteristic with time. The intensity (I) increased with impact velocity (V0) according to I∝V0n , where n = 4.41 for V0 > 2 km/s. However, for V0 < 2 km/s, n = 2.21, and the intense flash duration is an order of magnitude less than that of higher V0. When V0 > 2 km/s, a continuous spectrum (thermal radiation background) was observed and increased in intensity with V0. However, for V0 < 2 km/s, only atomic line spectra were detected. There was no aluminum spectral lines for V0 < 2 km/s, which indicated that it had not been vaporized. The initial intense flash was emission from excited and ionized ambient gases near the impact surface, and had little relationship with shock temperature rise, indicating a new mechanism of impact flash.

Experimental and theoretical study on steel long-rod projectile penetration into concrete targets with elevated impact velocities

To have a better understanding of behaviors of projectiles and concrete targets during impacts at different velocities, experiments and analysis of medium carbon steel long-rod projectiles impact on concrete targets have been carried out in this paper. The impact mechanics of projectiles and concrete targets has been investigated for impact velocities in range of 500 m/s to 1700 m/s covering three penetration regimes. Based on the observation of the residual projectiles and penetration depths, a deforming model has been proposed to investigate the deformable process of projectiles. Furthermore, deforming penetration model was established based on a rigid penetration model and the projectile deformation parameters, which was validated by the experimental results. The applicability of existing eroding penetration models penetration into concrete were validated and discussed based on the experimental results. At last, the eroding penetration model was further justified and improved by taking the deforming penetration regime into consideration. Influence of projectile and target strength on penetration process were investigated based on the theoretical model. Results show that the crater diameter and depth are linearly proportional to the impact velocity, while the volume of the crater and the initial impact kinetic energy of the projectile have a linear relationship. The calculated diameters of residual projectiles and Depth of Penetration (DOP) with a board range of impact velocities are in good agreement with experimental results. It is noted that the strength of projectiles and concrete targets have significantly influences on DOPs and critical velocities.

Study on transition from dwell/interface defeat to penetration of long-rod projectile impacting silicon carbide

Dwell/interface defeat phenomenon plays a pivotal rule in enhancing the protective ability of ceramic armor. In this study, the transition from dwell to penetration was studied experimentally and numerically, focusing on the dwell time, penetration and damage evolution in ceramic. A series of depth of penetration experiments were conducted of silicon carbide impacted by tungsten–iron–nickel (93%W–Fe–Ni) conical long-rod projectile (LRP) between 900 and 1400 m/s. The transition from interface defeat to extended dwell to penetration of ceramics was observed experimentally. Data analysis suggested that instead of a sharp transition velocity above which dwell phenomenon stopped, dwells with a phase of gradual decreasing time over a range of velocities were observed in experimental work. This observation was then studied by using numerical simulation software AUTODYN with two material models, Johnson–Cook for LRP and witness target, while Johnson–Holmquist for ceramic. The results of numerical simulation agreed well with the corresponding experimental data. Significant influences of nose shape of LRP, projectile material, ratio of each layer of target structure and thickness of back plate on transition from dwell to penetration were investigated numerically. It is shown that dwell/penetration transition predominantly depends on the damage accumulation in ceramic and the performance of back plate. In addition, mass erosion of LRP, rather than the decrease of velocity, functions vitally in affecting the transition when different projectile materials are taken into consideration.

Interface defeat studies of long-rod projectile impacting on ceramic targets

Abstract The interface defeat phenomenon always occurs when a long-rod projectile impacting on the ceramic target with certain velocity, i.e., the projectile is forced to flow radially on the surface of ceramic plates for a period of time without significant penetration. Interface defeat has a direct effect upon the ballistic performance of the armor piercing projectile, which is studied numerically and theoretically at present. Firstly, by modeling the projectiles and ceramic targets with the SPH (Smoothed Particle Hydrodynamics) particles and Lagrange finite elements, the systematic numerical simulations on interface defeat are performed with the commercial finite element program AUTODYN. Three different responses, i.e., complete interface defeat, dwell and direct penetration, are reproduced in different types of ceramic targets (bare, buffered, radially confined and oblique). Furthermore, by adopting the validated numerical algorithms, constitutive models and the corresponding material parameters, the influences of projectile (material, diameter, nose shape), constitutive models of ceramic (JH-1 and JH-2 models), buffer and cover plate (thickness, constraints, material), as well as the prestress acted on the target (radial and hydrostatic) on the interface defeat (transition velocity and dwell time) are systematically investigated. Finally, based on the energy conservation approach and taking the strain rate effect of ceramic material into account, a modified model for predicting the upper limit of transition velocity is proposed and validated. The present work and derived conclusions can provide helpful reference for the design and optimization of both the long-rod projectile and ceramic armor.

Interface defeat of ceramic armor

Interface Defeat, which can effectively defeat the long-rod projectile (LRP), is a specific phenomenon of ceramic armor. Studies on this area have been conducted for the last three decades both at home and abroad proving that delaying dwell time or increasing interface defeat/penetration transition velocity can defeat projectile and enhance the ballistic performance of ceramic armor. Related researches on the experimental techniques, theoretical models and numerical simulations of interface defeat are introduced, including the study of interface defeat at the micro and macro scale, a method for the design of the ceramic composite armor, etc. According to the insufficient work of interface defeat, some suggestions are proposed in this paper.

Penetration of confined ceramics targets

We have investigated the penetration response of confined ceramic targets impacted by Tungsten long-rod projectiles in the so-called Lundberg test setup with the ceramic modelled using a mechanism-based constitutive model. The calculations accurately predict the three observed penetration regimes, viz. interface defeat, dwell followed by penetration and penetration with no/short dwell. More importantly, the calculations suggest that these regimes occur in both a ceramic target and a reference target where microcracking of the ceramic is artificially switched off. This is because penetration occurs by a spherical cavity expansion mechanism with the onset of continued penetration set by the attainment of either a critical size of a plastic or damage zone. The dwell time then correlates with the time required to establish this inelastic zone. The main influence of damage is to reduce the pressure required to setup this critical inelastic zone and thereby reduce the interface defeat velocity as well as increase the penetration rate for a given velocity above the interface defeat velocity. We further show that an increase in the downward force due to the backflow of the deforming impactor is not essential for a dwell regime to exist. The mechanism-based ceramic model includes three material length scales and we demonstrate that the penetration size effect reported in experiments is primarily associated with the length scale associated with rate dependent lattice plasticity and the critical size of the comminuted zone that is required to trigger granular flow. The material model is also used to probe the dependence of material properties such as strength and toughness on the penetration resistance. Two regimes of penetration, viz. a plasticity-dominated and a microcracking-dominated regime emerge from the calculations. These predictions suggest that increasing the strength rather than toughness of the Corbit-98 Alumina will have a greater beneficial influence on its penetration performance.

Criterion for interface defeat to penetration transition of long rod projectile impact on ceramic armor

In this paper, an analytical model for the prediction of damage evolution, through impact of long rod projectile (LRP), at interface defeat condition, against silicon carbide (SiC) target is developed. The model comprises four calculation parts, namely interface pressure distribution, stress state in the ceramic target, wing cracks micro-mechanical and macro-cone crack propagation. A micro-mechanical constitutive model with wing crack distribution is used for inelastic deformation of ceramic. Subsurface damage evolution in ceramic impacted by blunt and conical LRPs at different impact velocities and length scales are presented to depict the potential mechanisms involved in transition from interface defeat to penetration. The damage evolution results agree well with the available literature experimental measurements. The proposed possible criteria can be used to predict the interface defeat to penetration transition for blunt and conical LRPs.

Influence of Geometry and Hardness of the Backing Plate on Ballistic Performance of Bi-Layer Ceramic Armor

The high hardness and strength of technical ceramics is exploited to design ballistic armors and their low toughness, brittleness is overcome by joining them with a metallic or long fiber reinforced composite backing plate. The thickness of backing plate (BP) on the ballistic performance SiC ceramic armor is studied through finite element simulations based on AUTODYN®. In this work, depth of penetration (DOP) from experimental measurements is compared with simulations using explicit software AUTODYN® for 3D modelling. The ballistic performance of three layer armor (cover plate (CP), ceramic tile and backing plate (BP)) under normal and oblique (NATO 60°) for long rod projectile (LRP) with a conical tip is investigated. The LRP and CP have been modelled using smooth particle hydrodynamic (SPH) particles and rest of the component is modelled using lagrangian processor. The Johnson-Cook and Johnson-Holmquist (JH-2) constitutive models are used for metal and ceramic materials, respectively. It is found that thicker BP enhances SiC armor via supporting longer period and prevent any premature failure at the rear surface of ceramic. It is also noticed that high hardness (low ductile) BP improves the ballistic performance of ceramic armor through offsetting tension of ceramic.

On improving ballistic limit of bi-layer ceramic–metal armor

This paper investigates experimentally and numerically methods to enhance the ballistic performance of ceramic armor. Initially we demonstrate an experimental set-up to impose pre-stress to ceramic-metal bi-layer armor and study the depth of penetration to measure the ballistic efficiency as a function of pre-stress intensity validating our previous numerical studies on effect of pre-stress on the ballistic limit of ceramic armor (Int. Journal of Impact Engineering, 2015(84)159-170). Secondly, a module is designed and tested to achieve interface defeat in ceramic armor with multiple interface layers. Finally, influence of thickness of the steel cover plate (CP) on ballistic performance of SiC ceramic is studied through AUTODYN® finite element simulations for normal and oblique (NATO 60°) against long rod projectile (LRP) with a conical tip. The LRP and CP are modeled using smooth particle hydrodynamic (SPH) particles and rest of the component is modeled using Lagrangian domain. The numerical analyses of armor modules are compared via depth of penetration (DOP) and LRP residual length for varying cover plate thicknesses.