Enhancement of wear and ballistic resistance of armour grade AA7075 aluminium alloy using friction stir processing

Industrial applications of aluminium and its alloys are restricted because of their poor tribological properties. Thermal spraying, laser surfacing, electron beam welding are the most widely used techniques to alter the surface morphology of base metal. Preliminary studies reveal that the coating and layering of aluminium alloys with ceramic particles enhance the ballistic resistance. Furthermore, among aluminium alloys,7075 aluminium alloy exhibits high strength which can be compared to that of steels and has profound applications in the designing of lightweight fortification structures and integrated protection systems. Having limitations such as poor bond integrity, formation of detrimental phases and interfacial reaction between reinforcement and substrate using fusion route to deposit hard particles paves the way to adopt friction stir processing for fabricating surface composites using different sizes of boron carbide particles as reinforcement on armour grade 7075 aluminium alloy as matrix in the present investigation. Wear and ballistic tests were carried out to assess the performance of friction stir processed AA7075 alloy. Significant improvement in wear resistance of friction stir processed surface composites is attributed to the change in wear mechanism from abrasion to adhesion. It has also been observed that the surface metal matrix composites have shown better ballistic resistance compared to the substrate AA7075 alloy. Addition of solid lubricant Mo S2 has reduced the depth of penetration of the projectile to half that of base metal AA7075 alloy. For the first time, the friction stir processing technique was successfully used to improve the wear and ballistic resistances of armour grade high strength AA7075 alloy.     

Influence of Al2O3 particles on the microstructure and mechanical properties of copper surface composites fabricated by friction stir processing

The influence of three factors, such as volume percentage of reinforcement particles (i.e. Al₂O₃), tool tilt angle and concave angle of shoulder, on the mechanical properties of Cu–Al₂O₃ surface composites fabricated via friction stir processing was studied. Taguchi method was used to optimize these factors for maximizing the mechanical properties of surface composites. The fabricated surface composites were examined by optical microscope for dispersion of reinforcement particles. It was found that Al₂O₃ particles are uniformly dispersed in the stir zone. The tensile properties of the surface composites increased with the increase in the volume percentage of the Al₂O₃ reinforcement particles. This is due to the addition of the reinforcement particles which increases the temperature of recrystallization by pinning the grain boundaries of the copper matrix and blocking the movement of the dislocations. The observed mechanical properties are correlated with microstructure and fracture features.     

Investigating the surface integrity of aluminium based composites machined by EDM

In the present work, the surface characteristics of Electrical Discharge Machined (EDM) Al (6351)SiC and Al (6351)SiCB₄C composites are investigated. The composites are prepared by employing the conventional stir casting technique, as it can produce better particle dispersion in the matrix. The detailed experimental study is performed on the composites by varying current (I), duty factor (τ), pulse on time (T_on), and the gap voltage (V) in order to analyze the Heat Affected Zone (HAZ) formed in the sub surface and the average crater diameter formed on the machined surface of the composites as an output function. The formation of recast layers, presence of bubbles and the surface texture of the composites at various machining conditions are observed. The results show that the increased Metal Removal Rate (MRR) increases the depth of HAZ and the average crater diameter on the machined area. Further, the addition of B₄C particles to the composite produces more surface defect than the AlSiC composite.     

Tuning the reactivity of Al–Ni by fine coating of halogen-containing energetic composites

In this paper, various core-shell structured Al–Ni@ECs composites have been prepared by a spray-drying technique. The involved ECs refer to the energetic composites (ECs) of ammonium perchlorate/nitrocellulose (AP/NC, NA) and polyvinylidene fluoride/hexanitrohexaazaisowurtzitane (PVDF/CL-20, PC). Two Al–Ni mixtures were prepared at atomic ratios of 1:1 and 1:3 and named as Al/Ni and Al/3Ni, respectively. The thermal reactivity and combustion behaviors of Al–Ni@ECs composites have been comprehensively investigated. Results showed that the reactivity and combustion performance of Al–Ni could be enhanced by introducing both NA and PC energetic composites. Among which the Al/Ni@NA composite exhibited higher reactivity and improved combustion performance. The measured flame propagation rate (v = 20.6 mm/s), average combustion wave temperature (T_max = 1567.0 °C) and maximum temperature rise rate (γ_t = 1633.6 °C/s) of Al/Ni@NA are higher than that of the Al/Ni (v = 15.8 mm/s, T_max = 858.0 °C, and γ_t = 143.5 °C/s). The enhancement in combustion properties could be due to presence of the acidic gaseous products from ECs, which could etch the Al₂O₃ shell on the surface of Al particles, and make the inner active Al to be easier transported, so that an intimate and faster intermetallic reaction between Al and Ni would be realized. Furthermore, the morphologies and chemical compositions of the condensed combustion products (CCPs) of Al–Ni@ECs composites were found to be different depending on the types of ECs. The compositions of CCPs are dominated with the Al–Ni intermetallics, combining with a trace amount of Al₅O₆N and Al₂O₃.     

Problem of the reference height of the projectile trajectory as a reduced meteo-ballistic weighting factor

This paper deals with the issue of preparation of the aiming angles with the use of tabular firing tables and needed determination of the ballistic elements μ_B (ballistic wind w_B, w_xB, w_ZB, ballistic (virtual) temperature τ_B, ballistic density ρ_B) from the standardized met messages. The weighting factors are used for the calculation of ballistic elements μ_B that are incorporated into the trajectory calculations characteristics of weapon and ammunition. Two different methodologies practically used in the praxis are analysed and compared. For the comparison of the two methodologies the reference height of trajectory determined from the weighting factor functions is employed. On the basis of the analyses conducted, the potential for further increase in accuracy of these aiming angles preparation methods is pointed out.     

An investigation on anti-impact and penetration performance of basalt fiber composites with different weave and lay-up modes

The woven basalt fiber composites (WBFC) and the unidirectional [0°/90°/45°/-45°]_s basalt fiber composites (UBFC) were prepared by hot-pressing. Three-point bending test, low velocity impact test, and ballistic test were performed to the prepared composites. After the tests, the specimens were recovered and analyzed for micromorphology. Three-point bending tests show that both the bending strength and stiffness of the WBFC surpass those of the UBFC. Low velocity impact test results show that the low velocity impact resistance to hemispherical impactor of the UBFC is higher than that of the WBFC, but the low velocity impact resistance to sharp impactor of the UBFC is lower than that of the WBFC. For the ballistic test, it can be found that the ballistic property of the UBFC is higher than that of the WBFC. After the tests, microscopic analysis of the specimens was applied, and their failure mechanism was discussed. The main failure modes of the UBFC are delamination and fibers breakage under the above loading conditions while the main failure mode of the WBFC is fibers breakage. Although delamination damage can be found in the WBFC under the above loading conditions, the degree of delamination is far less than that of the UBFC.     

Effect of silicon carbide and wire-mesh reinforcements in dissimilar grade aluminium explosive clad composites

Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight, superior corrosion resistance and higher specific properties. These composites reduce the weight of the aircraft, improve the fuel efficiency and enhance the maintenance duration. This study proposes the development of dissimilar grade aluminium (aluminium 1100-aluminium 5052) composites with different reinforcement’s viz., stainless steel wire-mesh, silicon carbide (SiC) powders and SiC powder interspersed wire-mesh, by explosive cladding technique. Wire-mesh enhances the friction and restricts the movement of flyer plate to craft a defect free clad, while SiC particles form a band on the interface. Highest strength is obtained when SiC powder interspersed wire mesh is employed as reinforcement. The dissimilar aluminium explosive clad with SiC particle reinforcement results in lower strength, which is higher than that of the weaker parent alloy and that of the conventional dissimilar aluminium explosive clads without any reinforcement.     

Statistical variability and fragility assessment of ballistic perforation of steel plates for 7.62 mm AP ammunition

The paper describes field test results of 7.62 × 51 mm M61 AP (armour piercing) ammunition fired into mild steel targets at an outdoor range. The targets varied from 10 mm to 32 mm in thickness. The tests recorded penetration depth, probability of perforation (i.e., complete penetration), muzzle and impact velocities, bullet mass, and plate yield strength and hardness. The measured penetration depth exhibited a variability of approximately ±12%. The paper then compared ballistic test results with predictive models of steel penetration depth and thickness to prevent perforation. Statistical parameters were derived for muzzle and impact velocity, bullet mass, plate thickness, plate hardness, and model error. A Monte-Carlo probabilistic analysis was then developed to estimate the probability of plate perforation of 7.62 mm M61 AP ammunition for a range of impact velocities, and for mild steels, and High Hardness Armour (HHA) plates. This perforation fragility analysis considered the random variability of impact velocity, bullet mass, plate thickness, plate hardness, and model error. Such a probabilistic analysis allows for reliability-based design, where, for example, the plate thickness with 95% reliability (i.e. only 1 in 20 shots will penetrate the wall) can be estimated knowing the probabilistic distribution of perforation. Hence, it was found that the plate thickness to ensure a low 5% probability of perforation needs to be 11–15% thicker than required to have a 50/50 chance of perforation for mild steel plates. Plates would need to be 20–30% thicker if probability of perforation is reduced to zero.     

Round robin using the depth of penetration test method on an armour grade alumina

The depth of penetration (DOP) method is a well-known ballistic test method for characterisation and ranking of ceramic armour materials. The ceramic tile is bonded to a backing material of semi-infinite thickness, and the penetration depth of the projectile gives a measure of the performance of the ceramic. There is, however, an inherent variability in the results from this test method. In this work, the accuracy and the variability of the DOP method has been investigated in a round robin exercise. Six ballistic test centres took part in the exercise. A test protocol was developed, in which the threat type (projectile and impact conditions) and a procedure on how to prepare the targets were specified. The targets consisted of alumina tiles of two different thicknesses that were bonded to polycarbonate backing cubes. Two different 7.62 mm armour piercing projectiles were employed; one with a hard steel core and one with a tungsten carbide core. The projectiles and the other materials all came from single material batches in order to avoid batch-to-batch variations in material properties. These materials were distributed between the ballistic test centres. The test results of the different ballistic test facilities were collected and compared. There was not a lot of variation between the average DOP values obtained at each laboratory, but the variation in penetration depth between shots was high. The consequence of this variation may be less confidence in the test results, and a statistical method was used to evaluate the required number of tests that are sufficient to obtain an average result with high confidence. In most cases, the required number of tests is much higher than what is practically feasible. This work was conducted as part of the European Defence Agency-project CERAMBALL.     

Performance study of jute-epoxy composites/sandwiches under normal ballistic impact

This study is undertaken to explore the use of natural fiber Jute-epoxy (JE), Jute-epoxy-rubber (JRE) sandwich composite for ballistic energy absorption. Energy absorbed and residual velocities for these composites are evaluated analytically and through Finite Element Analysis (FEA). FE analysis of JE plates is carried out for different thicknesses (3, 5, 10 and 15 mm). JE plates and JRE sandwiches having the same thickness (15 mm) are fabricated and tested to measure residual velocity and energy absorbed. The analytical results are found to agree well with the results of FE analysis with a maximum error of 9%. The study on JE composite plate reveals that thickness influences the energy absorption. Experimental and FE analysis study showed that JRE sandwiches have better energy absorption than JE plates. Energy absorption of a JRE sandwich is about 71% greater than JE plates. Damages obtained from FEA and testing are in good agreement. SEM analysis confirms composites failed by fiber rupture and fragmentation.     

穿甲子弹偏心入射陶瓷/钢复合靶板试验

设计并进行了7.62mm穿甲子弹侵彻陶瓷/低碳钢复合靶板的弹道试验,得到了极限速度及陶瓷锥底部半径等数据。分析了锥底半径与入射速度、面板及背板厚度的关系,着重分析了偏心入射时靶板的抗弹机理。结果表明:陶瓷锥可分为破碎区和粉碎区,粉碎区半径约为面板厚度与弹丸半径之和;当弹着点距离陶瓷面板边缘大于5mm时,靶板的抗弹性能变化不大,而弹着点位于距陶瓷面板边缘小于5mm的板边区时,抗弹性能明显降低,靶板的有效防护面积应扣除板边区。     

Investigation of the mechanical and ballistic properties of hybrid carbon/ aramid woven laminates

High-performance ballistic fibers, such as aramid fiber and ultra-high-molecular-weight polyethylene (UHMWPE), are commonly used in anti-ballistic structures due to their low density, high tensile strength and high specific modulus. However, their low modulus in the thickness direction and insufficient shear strength limits their application in certain ballistic structure. In contrast, carbon fiber reinforced epoxy resin matrix composites (CFRP) have the characteristics of high modulus in the thickness direction and high shear resistance. However, carbon fibers are rarely used and applied for protection purposes. A hybridization with aramid fiber reinforced epoxy resin matrix composites (AFRP) and CFRP has the potential to improve the stiffness and the ballistic property of the typical ballistic fiber composites. The hybrid effects on the flexural property and ballistic performance of the hybrid CFRP/AFRP laminates were investigated. Through conducting mechanical property tests and ballistic tests, two sets of reliable simulation parameters for AFRP and CFRP were established using LS-DYNA software, respectively. The experimental results suggested that by increasing the content of CFRP that the flexural properties of hybrid CFRP/AFRP laminates were enhanced. The ballistic tests’ results and the simulation illustrated that the specific energy absorption by the perforation method of CFRP achieved 77.7% of AFRP. When CFRP was on the striking face, the shear resistance of the laminates and the resistance force to the projectiles was promoted at the initial penetration stage. The proportion of fiber tensile failures in the AFRP layers was also enhanced with the addition of CFRP during the penetration process. These improvements resulted in the ballistic performance of hybrid CFRP/AFRP laminates was better than AFRP when the CFRP content was 20 wt% and 30 wt%.     

导弹突防后弹道机动调整策略强化学习

针对弹道导弹中段突防后飞行弹道与标准弹道产生较大偏离的弹道机动调整问题,建立了机动调整时机策略最优化模型。设计了机动调整逆序Q学习算法,采用Tile coding逼近器编码状态特征空间,并对其进行线性逼近。构建了Q学习算法与蒙特卡罗方法相结合的逆序更新策略机制,以对导弹机动调整最优时机进行训练。仿真测试分析结果表明,在给定场景参数下,通过10 000代强化学习算法训练得到的策略能够可靠地使用最少机动次数控制导弹突防后飞行弹道的调整决策,验证了方法的有效性。     

Influence of thickness and projectile shape on penetration resistance of the compliant composite

The present study deals with development of conceptual proof for jute rubber basedflexible composite block to completely arrest the projectile impacting the target at high velocity impact of 400 m/s through numerical simulation approach using finite element (FE) method. The proposed flexible composite blocks of repeating jute/rubber/jute (JRJ) units are modelled with varying thickness from 30 mm to 120 mm in increments of 30 mm and impacted by flat (F), ogival (O) and hemispherical (HS) shaped projectiles. All the considered projectiles are impacted with proposed flexible composite blocks of different thicknesses and the penetration behaviour of the projectile in each case is studied. The penetration depth of the projectile in case of partially penetrated cases are considered and the effect of thickness and projectile shape on percentage of penetration depth is statistically analyzed using Tagu-chi's design of experiments (DOE). Results reveal that the though proposedflexible composite block with thickness of 90 mm is just sufficient to arrest the complete penetration of the projectile, considering the safety issues, it is recommended to use theflexible composite with thickness of 120 mm. The nature of damage caused by the projectile in the flexible composite is also studied. Statistical studies show that thickness of the block plays a prominent role in determining the damage resistance of the flexible composite.     

添加SiC微粉对硅树脂先驱体转化3D Cf/Si-O-C材料性能的影响

以三维碳纤维织物和廉价的硅树脂为原料,采用先驱体转化工艺制备3D G/Si-O-C材料,考察了浸渍液中添加SiC填料对材料微观结构、力学性能和抗氧化性能影响.结果表明:添加适量的SiC填料有助于减少基体孔隙,改善界面结合,从而提高材料的力学性能;而SiC含量过高时,容易在材料内部形成闭孔,从而导致材料力学性能下降.当SiC微粉含量为18.2%时,材料具有最好的力学性能,弯曲强度和断裂韧度分别为421.3MPa和13.0 MPa·m1/2;而材料的抗氧化性能随着SiC微粉含量的增加而增加,当SiC微粉含量为25.0%时,材料的弯曲强度保留率最高,达到了89.5%.     

Shock-induced reaction behaviors of functionally graded reactive material

In this paper, the ballistic impact experiments, including impact test chamber and impact double-spaced plates, were conducted to study the reaction behaviors of a novel functionally graded reactive material (FGRM), which was composed of polytetrafluoroethylene/aluminum (PTFE/Al) and PTFE/Al/bismuth trioxide (Bi₂O₃). The experiments showed that the impact direction of the FGRM had a significant effect on the reaction. With the same impact velocity, when the first impact material was PTFE/Al/Bi₂O₃, compared with first impact material PTFE/Al, the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates. The theoretical model, which considered the shock wave generation and propagation, the effect of the shock wave on reaction efficiency, and penetration behaviors, was developed to analyze the reaction behaviors of the FGRM. The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials. The conclusion of this study provides significant information about the design and application of reactive materials.     

Partial penetration of annular grooved projectiles impacting ductile metal targets

Changing and optimizing the projectile nose shape is an important way to achieve specific ballistic performance. One special ballistic performance is the embedding effect, which can achieve a delayed high-explosive reaction on the target surface. This embedding effect includes a rebound phase that is significantly different from the traditional penetration process. To better study embedment behavior, this study proposed a novel nose shape called an annular grooved projectile and defined its interaction process with the ductile metal plate as partial penetration. Specifically, we conducted a series of low-velocity-ballistic tests in which these steel projectiles were used to strike 16-mm-thick target plates made with 2024-O aluminum alloy. We observed the dynamic evolution characteristics of this aluminum alloy near the impact craters and analyzed these characteristics by corresponding cross-sectional views and numerical simulations. The results indicated that the penetration resistance had a brief decrease that was influenced by its groove structure, but then it increased significantly-that is, the fluctuation of penetration resistance was affected by the irregular nose shape. Moreover, we visualized the distribution of the material in the groove and its inflow process through the rheology lines in microscopic tests and the highlighted mesh lines in simulations. The combination of these phenomena revealed the embed-ment mechanism of the annular grooved projectile and optimized the design of the groove shape to achieve a more firm embedment performance. The embedment was achieved primarily by the target material filled in the groove structure. Therefore, preventing the shear failure that occurred on the filling material was key to achieving this embedding effect.     

Determination of penetration depth at high velocity impact using finite element method and artificial neural network tools

Determination of ballistic performance of an armor solution is a complicated task and evolved significantly with the application of finite element methods(FEM) in this research field.The traditional armor design studies performed with FEM requires sophisticated procedures and intensive computational effort,therefore simpler and accurate numerical approaches are always worthwhile to decrease armor development time.This study aims to apply a hybrid method using FEM simulation and artificial neural network(ANN) analysis to approximate ballistic limit thickness for armor steels.To achieve this objective,a predictive model based on the artificial neural networks is developed to determine ballistic resistance of high hardness armor steels against 7.62 mm armor piercing ammunition.In this methodology,the FEM simulations are used to create training cases for Multilayer Perceptron(MLP) three layer networks.In order to validate FE simulation methodology,ballistic shot tests on 20 mm thickness target were performed according to standard Stanag 4569.Afterwards,the successfully trained ANN(s) is used to predict the ballistic limit thickness of 500 HB high hardness steel armor.Results show that even with limited number of data,FEM-ANN approach can be used to predict ballistic penetration depth with adequate accuracy.     

Kevlar fabric reinforced polybenzoxazine composites filled with silane treated microcrystalline cellulose in the interlayers: The next generation of multi-layered armor panels

The design of astonishing combinations of benzoxazine resins with various fillers is nowadays of great interest for high quality products, especially in ballistic armors. The objective of this study is to investigate a new hybrid material prepared as multi-layered composite plate by hand lay-up technique. Different composites were manufactured from Kevlar fabrics reinforced polybenzoxazine, which was filled with silane treated microcrystalline cellulose (MCC Si) at various amounts in the interlayers. The developed materials were tested for their flexural, dynamic mechanical and ballistic performance. The aim was to highlight the effect of adding different amounts of MCC Si on the behavior of the different plates. Compared to the baseline, the dynamic mechanical and bending tests revealed an obvious decrease of the glass transition of 21 °C and a notable increase in storage modulus and flexural strength of about 180 %and17%, respectively, upon adding 1% MMC Si as filler. Similarly, the ballistic test exhibited an enhancement in kinetic energy absorption for which the composite supplemented with 1% MCC Si had the maximal energy absorption of 166.60 J. These results indicated that the developed panels, with interesting mechanical and ballistic features, are suitable to be employed as raw materials to produce body armor.     

Ballistic impact properties of woven bamboo- woven E-glass- unsaturated polyester hybrid composites

In this study, a laminated woven bamboo/woven E glass/unsaturated polyester composite is developed to combat a ballistic impact from bullet under shooting test. The aim of this study is to understand the fundamental effects of the woven bamboo arrangement towards increasing ballistic resistance properties. The work focusses on the ballistic limit test known as NIJ V50, which qualifies materials to be registered for use in combat armor panels. The results show that the composites withstood 482.5 m/s ± 5 limit of bullet velocity, satisfying the NIJ test at level II. The findings give a strong sound basis decision to engineers whether or not green composites are qualified to replace synthetic composites in certain engineering applications.