Ballistic behavior of high hardness perforated armor plates against 7.62 mm armor piercing projectile

In this paper, some of the important defeating mechanisms of the high hardness perforated plates against 7.62 × 54 armor piercing ammunition were investigated. The experimental and numerical results identified three defeating mechanisms effective on perforated armor plates which are the asymmetric forces deviates the bullet from its incident trajectory, the bullet core fracture and the bullet core nose erosion. The initial tests were performed on the monolithic armor plates of 9 and 20 mm thickness to verify the fidelity of the simulation and material model parameters. The stochastic nature of the ballistic tests on perforated armor plates was analyzed based on the bullet impact zone with respect to holes. Various scenarios including without and with bullet failure models were further investigated to determine the mechanisms of the bullet failure. The agreement between numerical and experimental results had significantly increased with including the bullet failure criterion and the bullet nose erosion threshold into the simulation. As shown in results, good agreement between Ls-Dyna simulations and experimental data was achieved and the defeating mechanism of perforated plates was clearly demonstrated.     

Effect of buttering and hardfacing on ballistic performance of shielded metal arc welded armour steel joints

Quenched and tempered (Q & T) steel closely confirming to AISI 4340 is well known for its superior ballistic performance and hence used in the fabrication of armour vehicles. These steels are traditionally welded by austenitic stainless steel (ASS) fillers to prevent hydrogen induced cracking. Due to weld thermal cycles and under matching fillers, the armour steel joints show poor ballistic performance compared to the base metal. Attempts were made to deposit hardfaced interlayer between ASS weld metals. Though this method yielded marginal improvements in ballistic performance, cracks were observed in between base metal and hardfaced layers. In this investigation an attempt has been made to eliminate these cracks by depositing a soft buttering layer using ASS consumable in between base metal and hardfaced layer. This paper reveals the effect of buttering and hardfacing on ballistic performance of shielded metal arc welded armour steel joints.     

Influence of surface coating on ballistic performance of aluminum plates subjected to high velocity impact loads

Ballistic response of single or multi-layered metal armor systems subjected to high velocity impact loads was investigated in many experimental, theoretical and numerical studies. In this study, influences of plasma spray surface coating on high velocity impact resistance of AA 6061 T651 aluminum plates were analyzed experimentally. Two different types of surface coating were applied to plates using plasma spray. Using 9.00 mm Parabellum bullets, ballistic performance of both uncoated and coated plates was tested. After the impact tests, penetration depth including plate bending on the front face and bulging on the rear face of the target plate was measured. The improvement on the ballistic resistance of the coated plates was clearly observed. The increase in non-perforating projectile velocity and the decrease in penetration depth were both experienced.     

Ballistic resistance of high hardness armor steels against 7.62 mm armor piercing ammunition

Although advanced lightweight composite based armors are available, high hardness steels in military vehicles are often used to provide ballistic protection at a relatively low cost and is an interesting material due to its widespread usage in vehicle structure. In this study, ballistic limit of 500 HB armor steel was determined against 7.62 mm 54R B32 API hardened steel core ammunition. Lagrange and smoothed particle hydrodynamics (SPH) simulations were carried out using 3D model of bullet and high hardness armor target. Perforation tests on 9 and 20 mm thickness armor were performed to validate simulation methodology. Also material tests were performed for armor steel and ammunition hardened steel core to develop Johnson–Cook constitutive relations for both strength and failure models. Finally, results from 3D numerical simulations with detailed models of bullet and target were compared with experiments. The study indicates that the ballistic limit can be quantitatively well predicted independent of chosen simulation methodology, but qualitatively some differences are seen during perforation and fragmentation. As shown in results, good agreement between Ls-Dyna simulations and experimental data was achieved by Lagrange formulation with the full bullet model.     

On the comparison of the ballistic response of coated aluminum plates

This study presents the output of an experimental study conducted to determine the effect of two types of plasma spray surface coatings on the ballistic resistance of three specific aluminum alloys. Utilizing the plasma spray technique, aluminum alloys 2024-T351, 6061-T651 and 7075-T651 were coated with Co–Mo–Cr and ZrO₂ and the ballistic performance of both uncoated and coated plates against high velocity impact by 9.00 mm Parabellum bullets was examined. Improvement on the ballistic resistance of the plates was clearly seen in the coated ones. It was observed from the tests that Co–Mo–Cr coating is more efficient against penetration and bulging for AA6061-T651 and AA2024-T351 plates while ZrO₂ coating is slightly superior to Co–Mo–Cr coating for AA7075-T651 plates.     

Geometry,mechanical properties and mounting of perforated plates for ballistic application

In this paper, the ballistic resistance of perforated plates made of different types of steel, mounting and geometry was investigated. Different types of steel in various heat treatment conditions were tested. Target mounting was also varied: rigid, oblique and hanging. Furthermore, four different perforated plate geometries were tested: two plate thicknesses and two hole diameters. Their behaviour was tested using impact from firing 12.7 mm M-8 API ammunition at eleven perforated plate samples. These samples were placed by means of a steel frame over a 13 mm RHA plate, at two distances. Damaged area on targets was correlated to ballistic resistance of the whole armour to find the optimal perforated plate. It was found that perforated plates, in optimized case offer a frequent fracture of the penetrating core in up to five parts. This debris is unable to penetrate the basic plate, offering mass effectiveness of the whole armour model of 1.76 and the mass effectiveness of the perforated plate of 5.91.     

Experimental and numerical investigation on the deformation and failure behavior in the Taylor test

The present paper presents an experimental and numerical study concerning the deformation and failure behavior in the Taylor impact test. Projectiles manufactured from a commercial high strength and super-hard aluminum alloy 7A04-T6 with a nominal diameter of 12.6 mm and a length of 50.8 mm were fired against a hardened tool steel plate by a one- and two-stage compressed gas gun within the velocity range of 175–370 m/s. Three different deformation and failure modes were observed from the test: mushrooming, shear cracking and fragmentation. Individual velocity ranges and the transitions between the deformation/failure modes are identified by both experiments and numerical simulations. Slightly modified Johnson–Cook models of strength and accumulative damage failure are employed in 3D numerical simulations to describe material behavior of the striking cylinders. Good agreement between the numerical simulations and the experimental results was found. Detailed computational results of each scenario are offered to understand the deformation and failure mechanisms.     

Optimization of a fender structure for the crashworthiness design

Ship fenders often take large crash loads during berthing. This paper presents a crashworthiness design of a regular ship fender structure with varying geometric dimensions. In the optimization, specific energy absorption (SEA) and maximum crushing force (Pm) are set as two objectives and the thickness of the outer skin, the thickness of the frames, the thickness of the longitudinally reinforced stiffener and the height of the fender are selected as four design variables. Nonlinear finite element analysis is first carried out to capture the crash responses of 196 samples. Afterwards, parametric studies are performed to investigate the influences of different variables on the design objectives. A back-propagation neural network is then constructed as the surrogate model to formulate the mapping between the variables and the objectives. When the network is validated, a multi-objective genetic algorithm is applied to obtain the Pareto optimal solutions. The optimum set is defined as the solution with the maximum SEA to Pm ratio. The independent design variables of the optimum set are tested and verified using sensitivity analysis technique.     

Deformed microstructure evolution in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s

Deformed microstructure in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s⁻¹ were investigated through optical microscope, scanning electron microscope and transmission electron microscope. The results show that four deformed zones around the crater can be classified based on the different deformed microstructure, including ultrafine grain zone, ultrafine grain and deformation twin zone, high and low density deformation twin zones. The dislocation slipping, deformation twins and ultrafine grains are the dominant components in the four deformed zones, and the evolution of deformed microstructure is speculated based on the deformed microstructure observed in four zones. Slipping and twinning play a critical role for the formation of the dynamic recrystallized grains, and twinning-induced rotational dynamic recrystallization mechanism is thought to be the main mechanism for the formation of ultrafine grains. The microhardness and dynamic compressive strength in different deformed zones were measured, and the high microhardness and yield strength in ultrafine grain zone should be attributed to the strain hardening and grain refining.     

Effect of joint design on ballistic performance of quenched and tempered steel welded joints

A study was carried out to evaluate the effect of joint design on ballistic performance of armour grade quenched and tempered steel welded joints. Equal double Vee and unequal double Vee joint configuration were considered in this study. Targets were fabricated using 4 mm thick tungsten carbide hardfaced middle layer; above and below which austenitic stainless steel layers were deposited on both sides of the hardfaced interlayer in both joint configurations. Shielded metal arc welding process was used to deposit for all layers. The fabricated targets were evaluated for its ballistic performance and the results were compared in terms of depth of penetration on weld metal. From the ballistic test results, it was observed that both the targets successfully stopped the bullet penetration at weld center line. Of the two targets, the target made with unequal double Vee joint configuration offered maximum resistance to the bullet penetration at weld metal location without any bulge at the rear side. The higher volume of austenitic stainless steel front layer and the presence of hardfaced interlayer after some depth of soft austenitic stainless steel front layer is the primary reason for the superior ballistic performance of this joint.     

An experimental study on the ballistic impact behavior of some metallic armour materials against 7.62 mm deformable projectile

The investigation describes and analyses the ballistic impact behavior of a high strength armour steel and Al-7017 alloy under 7.62 mm deformable projectiles at a velocity of 830 ± 10 m/s at normal angle of attack. The high strength armour steel is subjected to two different heat treatments to see the effect of different mechanical properties on the ballistic behavior. The ballistic result of the Al-7017 alloy is compared with that of the steel. Some observations relating to the adiabatic shear bands formation have also been presented. Experimental results showed that among the investigated materials, the best ballistic performance was attained with the armour steel at 910 °C austenitisation followed by 200 °C tempering condition.     

On the behavior of nitrogen in a low-Ni high-Mn super duplex stainless steel

The present work describes an investigation on a new series of low-Ni high-Mn super duplex stainless steels (DSSs) 25Cr–2Ni–3Mo–10Mn–xN with nitrogen concentrations varying in the range between 0.37 and 0.50 wt.%. It was observed that these alloys have a ferrite–austenite structure. Under the same heat-treatment conditions, the austenite shows a marked upward tendency with an increase in N content. Nitrogen delays the precipitation of σ phase. The increase in nitrogen enhances the yield strength (YS), ultimate tensile strength (UTS) and ductility as well as the pitting corrosion potential of the materials. The pitting corrosion occurs in the austenite phases in the case of low N content (0.37 wt.%), but in the case of high N content (0.50 wt.%) it happens in the ferrite phases.     

Synergistic investigation into the marine parameters’ effect on the corrosion rate of AISI 316 stainless steel

In this paper, the corrosion rate of the austenitic stainless steel AISI 316, under the synergistic effect of environmental factors, has been assessed via potentiodynamic polarization scan. Salinity, velocity, pH and temperature are the factors that induce effects on the corrosion rate of the considered metal. Quantitative analysis is applied using the full two-level factorial experimental design method. This analysis calculates the contribution value of each parameter in changing the quantity of average corrosion rate in both individual and synergistic cases. In addition, qualitative analysis has been used to predict the variation direction. These two analyses show the important role of the synergistic action that changes the variation direction of corrosion rate and the contribution percentage of each parameter in varying the value of corrosion rate. Applying both quantitative and qualitative analyses can show the magnitude and quality of each parameter’s effect, which is remarkably valuable in marine application designs.     

On the mechanical behavior at sharp indentation of materials with compressive residual stresses

The correlation between residual stresses and the global properties, i.e. hardness and size of the contact area, given by a sharp indentation test have been studied quite frequently in recent years. The investigations presented have been based on experimental, theoretical and numerical methods and as a result, the basic features of the problem are now well understood. Furthermore, in this context quantitative relations, for the determination of residual stresses using sharp indentation, have been presented. Such relations have proven to be reliable in case of predominantly tensile residual stresses while the accuracy of predictions is much worse at compressive stress states. It is therefore the aim of the present study to investigate this matter in some detail and to present possible mechanisms for the difference in indentation behavior between tension and compression. Accordingly, the results are essentially qualitative but necessary and detailed investigations needed for a quantitative understanding are suggested. The present analysis is based on theoretical and numerical methods and in the latter case, the finite element method (FEM) is relied upon. Classical Mises elastoplastic material behavior is assumed throughout the investigation.     

Effect of mean stress on fatigue properties of 1800 MPa-class spring steels

Fatigue tests were conducted for 1800 MPa-class spring steels at various stress ratios. For comparison, similar fatigue tests were conducted for conventional steels whose tensile strength was lower than 1200 MPa. The spring steels exhibited fish-eye fractures, and the origins of these fractures were oxide, TiN and the matrix itself. In contrast, the conventional steels never exhibited fish-eye fractures. The fatigue strength of these steels decreased monotonously as the stress ratio increased, when the fatigue strength was evaluated in terms of stress amplitude. However, the fatigue strength degradation was less than that expected from a modified-Goodman line, and the best fit line was obtained by connecting the fatigue limit at zero mean stress to true fracture strength instead of tensile strength. This research also reviewed application of a power low to the stress ratio effect evaluation. In these results, the difference between the spring and conventional steels was negligible.     

Wire fence as applique armour

In this paper, the behaviour of wire fence was investigated for potential as applique armour. The wire fence used was made from commercial high-strength patented wire and the supporting frames were made of mild steel L-profiles. Both patented wire and L-profiles are of-the-shelf materials. The fence was tested by firing 12.7 mm M8 API ammunition at four applique armour models: two of these models use a parallel wire arrangement, with one mounted at a 90° angle from the incoming projectile and the other at 70°; and two of these models use a zig-zag wire arrangement, one mounted at a firm 90° angle and the other is left in a hanging arrangement. Fence damage was correlated with RHA basic plate damage, on both the face and back. Wire fence has considerable potential as an improvised applique armour, except if the projectile impacts near the center of the wire or near the center between two wires. The latter case was successfully overcome by placing the armour model at an angle and by using a zig-zag wire arrangement. The lowest basic RHA plate damage level was found using the hanging armour model. However, from the point of view of ease of attachment, the most convenient was found to be the armour model with the zig-zag wire arrangement fixed at 90° angle from the incoming projectile. SEM fracto graphy revealed that the fracture surface was predominantly ductile, with dimples filled with debris from the incendiary effect of the projectile.     

Mechanical behaviour of Zn–Fe alloy coated mild steel

Zinc alloy coatings containing various amounts of Fe were deposited by electrodeposition technique on a mild steel substrate. The concentration of Fe in the produced alloy coatings ranged from 0 to 14 wt.%, whereas the thickness of the coatings was about 50 μm. Structural and metallurgical characterization of the produced coatings was performed with the aid of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. This study aims in investigating the mechanical behaviour of Zn–Fe coated mild steel specimens, as no research investigation concerning the tensile behaviour of Zn alloy coated ferrous alloys has been reported in the past. The experimental results indicated that the ultimate tensile strength of the Zn–Fe coated mild steel was lower than the bare mild steel. In addition, the ductility of the Zn–Fe coated mild steel was found to decrease significantly with increasing Fe content in the coating.     

Tensile behavior of dissimilar friction stir welded joints of aluminium alloys

The heat treatable aluminium alloy AA2024 is used extensively in the aircraft industry because of its high strength to weight ratio and good ductility. The non-heat treatable aluminium alloy AA5083 possesses medium strength and high ductility and used typically in structural applications, marine, and automotive industries. When compared to fusion welding processes, friction stir welding (FSW) process is an emerging solid state joining process which is best suitable for joining these alloys. The friction stir welding parameters such as tool pin profile, tool rotational speed, welding speed, and tool axial force influence the mechanical properties of the FS welded joints significantly. Dissimilar FS welded joints are fabricated using five different tool pin profiles. Central composite design with four parameters, five levels, and 31 runs is used to conduct the experiments and response surface method (RSM) is employed to develop the model. Mathematical regression models are developed to predict the ultimate tensile strength (UTS) and tensile elongation (TE) of the dissimilar friction stir welded joints of aluminium alloys 2024-T6 and 5083-H321, and they are validated. The effects of the above process parameters and tool pin profile on tensile strength and tensile elongation of dissimilar friction stir welded joints are analysed in detail. Joints fabricated using Tapered Hexagon tool pin profile have the highest tensile strength and tensile elongation, whereas the Straight Cylinder tool pin profile have the lowest tensile strength and tensile elongation. The results are useful to have a better understanding of the effects of process parameters, to fabricate the joints with desired tensile properties, and to automate the FS welding process.     

Microstructure and properties of austenitic stainless steel reinforced with in situ TiC particulate

Austenitic stainless steel reinforced with 5 vol.% TiC particulate was in situ synthesized by in situ reaction during melting process successfully and its microstructure, mechanical properties as well as oxidation behavior were investigated. Microstructure observations revealed that in situ TiC particulates with an average size of 2–10 μm distributed uniformly in the matrix and the interface boundaries between TiC particulates and austenite matrix were clean without any impurities and contaminations. Addition of TiC particulates refined the grain structure of austenitic matrix, but did not cause formation of any new phases in microstructure. Beneficial effects of TiC addition to austenitic stainless steel on both mechanical properties and oxidation resistance were found. Both at ambient and elevated temperature, tensile strengths of the steel with TiC addition were notably higher than those of its matrix alloy, however, a decrease in ductility also appeared, as exhibited by other particulate reinforced alloys. Besides tensile strengths, creep resistance of austenitic stainless steel was also significantly increased by TiC addition at elevated temperature of 923 K. Oxidation test at 1073 K revealed that TiC addition to austenitic stainless steel raised the oxidation resistance of the steel remarkably.     

Finite element analysis of the effect of welding heat input and layer number on residual stress in repair welds for a stainless steel clad plate

Stainless steel clad plate is widely used in petroleum, chemical and medicine industries due to its good corrosion resistance and high strength. But cracks are often formed in clad layer during the manufacture or service, which are often repaired by repair welding. In order to ensure the structure integrity, the effects of residual stress need to be considered. The objective of this paper is to estimate the residual stress and deformation in the repair weld of a stainless steel clad plate by finite element method. The effects of heat input and welding layer number on residual stresses and deformation have been studied. The results show that large residual stresses have been generated in the repair weld. The heat input and layer number have great effects on residual stress distribution. With the heat input and welding layer number increasing, the residual stresses are decreased. Using multiple-layer welding and higher heat input can be useful to decrease the residual stress, which provides a reference for optimizing the repair welding technology of this stainless steel clad plate.