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.     

Hypervelocity penetration of tungsten alloy rods into ceramic tiles: experiments and 2-D simulations

A series of terminal ballistics experiments and 2-D simulations, with small scale tungsten alloy penetrators, was performed in order to quantify the ballistic efficiency of confined ceramic tiles. The data includes both depth of penetration (DOP), into thick steel backing and X-ray shadowgraphs during the penetration process. Impact velocities ranged between 1.25 to 3.0 km/s. The size of the tiles varied in order to check their performance as a function of thickness and lateral dimensions. We found that the differential ballistic efficiency of alumina tiles is practically independent on impact velocity and tile thickness, within the ranges of velocity and thicknesses, investigated here. A detailed simulation study, using the Eulerian processor of the PISCES 2-D ELK code, was performed in order to better understand the interaction between long-rods and ceramic tiles, and particularly, to adjust a proper failure criterion to the tiles. We found that a simple version of the Johnson-Holmquist model, with a single parameter, is fairly adequate to account for most of the data. These include: lateral confinement, tile thickness and impact velocity influence on the penetration depth. We used the code to further investigate the influence of lateral dimensions on tile performance.     

Impact resistance and fragmentation behaviour of glassceramics

Impact tests were carried out on five glassceramics tiles. The ballistic resistance was evaluated by the depth of penetration of the projectile into the backing. The fragmentation behaviour of the glassceramics showed that the glassceramics compared with with alumina and displayed some advantages over it.     

Computational modeling of the penetration response of a high-purity ceramic

This paper describes computational modeling of the penetration response of a high-purity ceramic, namely the AD-99.5 alumina. This material is the most widely investigated ceramic, and extensive materials testing and ballistic data are available. The model development is based on constitutive relationships inferred from bar impact and plate impact data. The model is then incorporated into the EPIC Lagrangian finite element code. A novel element removal scheme for ceramics is presented, and the code is then used to investigate the penetration response of AD-99.5 alumina in the depth of penetration and semi-infinite configurations. The computations are found to be in excellent agreement with the experimental results. The interface defeat problem is also investigated numerically, and the results are used to suggest an explanation for interface defeat.     

On the drop-weight testing of alumina/aluminum laminated composites

Laminated composites with ceramic front layers and metallic or composite backing layers have gained attractiveness as lightweight armours, as they exhibit the same ballistic performance with lower areal densities as compared to steels. Drop-weight testing (DWT) has potential for evaluating the low velocity impact behaviour of materials. This testing gives significant ideas and information about failure mechanisms and behaviour of materials under low velocity impact. In this study, DWT of alumina/aluminum laminated composites was done in order to investigate the effects of lamination type, density with respect to area and mechanical property of backing material on the low velocity ballistic performance of these composites. The experimental results showed that the laminated composite with ceramic front layer and aged-aluminum alloy as backing layer was the most effective among different investigated specimens against low velocity impact loads.     

Penetration of semi-infinite AD995 alumina targets by tungsten long rod penetrators from 1.5 to 3.5 km/s

The performance of confined AD995 Alumina against L/D 20 tungsten long rod penetrators was characterized through reverse ballistic testing. The semi-infinite ceramic target was cylindrical with a diameter approximately 30 times the rod diameter. The target configuration included a titanium confinement tube and a thick, aluminum coverplate. The impact conditions ranged from 1.5 to 3.5 km/s with three or four tests performed at each of six nominal impact velocities. Multiple radiographs obtained during the penetration process allowed measurement of the penetration velocity into the ceramic and the consumption velocity, or erosion rate, of the penetrator. The final depth of penetration was also measured.

Primary penetration approaches 75% of the hydrodynamic limit. Secondary penetration is very small, even at 3.5 km/s. The effective R_t value decreased from 90 kbar to 70 kbar with increasing impact velocity over the range of velocities tested.

In tests in which the ratio of target diameter to penetrator diameter was reduced to 15, R_t, dropped by 30% to 50%. When a steel coverplate was used, total interface defeat occurred at 1.5 km/s.     

Comparative analysis of oblique impact on ceramic composite systems

An experimental programme is presented which investigated the performance of oblique, ceramic/metal, bilayer composite armours. The ceramics, alumina and silicon carbide, were backed by either Rolled Homogeneous Armour steel (RHA) or 7000 series aluminium. Using a model scale tungsten penetrator at two velocities (representing current and future ordnance threats) the effect of configuration on ballistic limit or depth of penetration (DOP) areal densities was determined. Areal densities of the DOP targets decreased with increasing ceramic thickness, achieving a minimum at zero residual penetration in the backing. The bilayer targets, loaded at the ballistic limit needed a larger areal density to defeat the penetrator. This areal density also decreased with ceramic thickness but showed a minimum with respect to ceramic thickness, as a result of reduced support by the thinner metallic backing. At 1450ms⁻¹ the most efficient system was found to be a SiC/Al, which demonstrated a 25% weight saving over the monolithic aluminium reference target. The Al-alloy backing performs better than RHA, and SiC better than Al₂O₃.     

The relation between ballastic efficiency and compressive strength of ceramic tiles

Ballistic tests with armor piercing projectiles on different ceramic tiles are presented. The tests were conducted using the thick-backing configuration, which is a new experimental technique to evaluate ballistic efficiencies of ceramic tiles. The residual penetration of the projectile into a thick metallic backing plate, which supports the ceramic tile, is measured. It is shown that the ballistic efficiencies of the different tiles increase monotonically with their normalized effective strength. This strength parameter is defined as the average of the static and dynamic compressive strengths divided by the density of the ceramic. A simple analysis is presented which accounts for the linear dependence of the ballistic efficiency on the normalized effective strength.     

The design of mosaic armour: The influence of tile size on ballistic performance

Silicon carbide square tiles of different areal geometries and manufactured via two different processing routes have been bonded to polycarbonate layers to evaluate their ballistic performance. Four ceramic tile sizes were tested: 85 mm, 60 mm, 50 mm and 33 mm. In each case the residual depth-of-penetration into a polycarbonate semi-infinite backing was recorded. To elucidate the penetration and failure mechanisms, a computational model using the JH-1 ceramic model [Holmquist TJ, Johnson GR. Response of silicon carbide to high velocity impact. J Appl Phys 2002;91:5858–66] of the projectile used in the experimental study penetrating into a silicon carbide-faced polycarbonate was implemented in the hydrocode AUTODYN-2D. This paper shows that there is a critical dimension of tile that should be used in a silicon carbide-based ceramic-faced mosaic armour system design to ensure optimum system performance when each tile is struck centrally.     

Ballistic impact performance of an armor material consisting of alumina and dual phase steel layers

Utilization of a ceramic front layer provides an improvement in the ballistic efficiency of monolithic metallic materials. In the current paper, the ballistic behavior of laminated composite having alumina front and dual phase steel backing layers was studied using 7.62 mm armor piercing (AP) projectiles under normal impact. The variables used were martensite content of the backing layer and the areal density of the composite. Experimental results showed that utilization of a 6 mm thick alumina front layer which was bonded to dual phase steel enhanced the ballistic resistance of the dual phase steel remarkably.     

Quantitative analysis of the microstructural homogeneity of zirconia-toughened alumina composites

The Voronoi diagram approach was applied to quantify the level of microstructural homogeneity of ceramic ZTA samples. From SEM pictures of polished cross-sections of ZTA samples a point pattern representing the distribution of the zirconia phase in the composite was generated. This point pattern was converted into a Voronoi diagram. The level of microstructural homogeneity was quantified by statistical analysis of the relevant properties (area, perimeter and number of faces) of the Voronoi polygons. A dimensionless parameter defining the level of microstructural homogeneity was calculated from the different sets of statistical data. The calculated parameters indicated significant differences in homogeneity between the ZTA samples. These differences were in qualitative agreement with previously published wear rates of the same ZTA composites. This illustrates the relevance of microstructural homogeneity for wear performance.     

Modelling of the adhesive layer in mixed ceramic/metal armours subjected to impact

The effect of the adhesive layer, used to bond ceramic tiles to a metallic plate, on the ballistic behaviour of ceramic/metal mixed armours is analysed mathematically and experimentally. Two types of adhesives, polyurethane (soft adhesive) and rubber-modified epoxy resin (rigid adhesive), and different thicknesses, are considered in the study. Numerical simulations were made of low calibre projectiles impacting on alumina tiles backed by an aluminium plate, using a commercial finite difference code. Full-scale tests were carried out to check the influence of the adhesive. An engineering model was also developed to provide a preliminary design tool taking account of the influence of the adhesive.     

Impact response of layered steel–alumina targets

The efficacy of a ceramic in protecting against penetration by high velocity projectiles depends not only on its hardness but also on its resistance to flow after comminution. Here we investigate experimentally the response of a model armor system comprising an alumina tile and two steel face sheets subject to impact by steel spherical projectiles. Complementary experiments are performed on the face sheet materials and the ceramic alone in order to gain insights into the inelastic responses of the constituent materials. A parallel numerical modeling study is performed of the system response with emphasis on the shape of the back face following impact. To this end, we employ the ceramic deformation model developed by Deshpande and Evans and modified here to account for dilatational softening following full comminution. Comparisons between model predictions and experimental measurements demonstrate the important role of granular flow. Preliminary parametric studies further suggest that additional effort is required to understand the transition in mechanical response of a ceramic as it transforms from a monolithic solid to a densely-packed granulated medium.     

Experiments and 2-D simulations of high velocity penetrations into ceramic tiles

This paper investigates the interaction of long-rod penetrators with thick ceramic tiles, sandwiched between steel plates, through several model experiments and 2-D simulations. Experimental data from low velocity penetrations have been used to calibrate the relevant properties of the ceramic specimens. The influence of increasing impact velocity on tile performance was then investigated through data and simulations of shaped charge jets penetrating the ceramic. We found that the ballistic efficiency of the ceramic tile is lower against high velocity (5 km/s) long-rods, in contrast with the common thesis that their improved performance against shaped charge jets is the result of their enhanced strength. On the other hand, our simulations clearly show that, for high strength ceramics, there is a radial motion of metal and ceramic debris towards the penetration axis. This effect is, probably, the main reason for the considerable improvement in the performance of ceramic tiles against shaped charge jets.     

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.     

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.     

Zirconia-toughened alumina (ZTA) ceramics

In the previous decade, a considerable amount of work has been done on the alumina-zirconia ceramic composite system with a particular emphasis on improving the mechanical properties utilizing the recognized toughening mechanisms. Zirconia-toughened aluminas (ZTA) can be regarded as a new generation of toughened ceramics; for example, a toughness of >12 MPa m^0.5 has been obtained, compared with 3 MPa m^0.5 for commercial alumina ceramics. The fracture strength of ZTA is also greatly in excess of that for alumina. The mechanical properties of ZTA are critically dependent on their microstructures, which can be designed in terms of specific applications and controlled by means of powder preparation and densification processes. This review also includes details of the possible future development of ZTA; these are expected to involve the development and measurement of the mechanical properties for high-temperature engineering applications.     

The response of layered aluminum nitride targets subjected to hypervelocity impact

This work presents both experimental and computational ballistic results of layered Aluminum Nitride (AlN) targets. An L/D = 6 tungsten penetrator is used to impact AlN targets at a nominal impact velocity of 2100m/s. The primary objective of this work is to determine the ballistic performance of layered ceramic targets to hypervelocity impact. Various layering configurations are investigated including separating the AlN ceramic layers by thin, low impedance, polymethyl methacrylate (PMMA). PMMA thicknesses of 1 mm, 0.5 mm and 0 mm are used. The number of AlN ceramic layers is also investigated. Target configurations of two, four, six, and twelve layers are considered. All targets consist of 76.2 mm of AlN. The experiments show that target resistance decreases when PMMA is added. Target resistance is also reduced when more layers are used. A secondary objective of this work is to evaluate the ballistic effect of reducing the lateral dimension of the ceramic tile (reduction in self-confinement). The experiments show reduced target resistance when the lateral tile size is decreased. Computations of selected experiments are presented to provide insight into the behavior of the AlN targets. The computations capture the effect of layering, PMMA separation and lateral tile size and provide insight into the behavior of the ceramic when used in these types of configurations.     

Modeling prestressed ceramic and its effect on ballistic performance

This article presents computed results for the responses of ceramic targets, with and without prestress, subjected to projectile impact. Also presented is a computational technique to include prestress. Thin and thick ceramic target configurations are used to understand the effect prestressing has on ballistic performance. For both targets two prestress levels (small and large), and two prestress states (radial and hydrostatic) are investigated. The small prestress is similar in magnitude to values obtained experimentally and the large prestress is approximately the maximum prestress the confinement can produce (determined computationally). The targets are subjected to projectile impact and the resulting ballistic responses are evaluated. In all cases prestressing the ceramic enhanced the ballistic performance, although the effect of the different prestress conditions on the ballistic response was not always obvious.     

仿生柔性防护装具的设计及防弹性能测试

依据仿生学原理,借鉴硬骨鱼鳞的微观结构及叠加模式,设计并制备了6套仿生柔性防护装具。使用了两种复合鳞片,分别为SiC陶瓷-超高分子量聚乙烯(UHMWPE)复合防护鳞片和Al₂O₃陶瓷-UHMWPE复合防护鳞片。对柔性防护装具进行侵彻测试,分析了复合鳞片类型、覆盖角度和子弹侵彻位置对柔性鳞片防护装具防弹性能的影响。结果表明,新型柔性鳞片状防护装具均能成功抵挡速度为(445±10) m/s的手枪弹(铅芯)侵彻,垫层材料的凹陷深度为5~20 mm。SiC-UHMWPE复合鳞片防护装具的防弹性能显著优于Al₂O₃-UHMWPE复合鳞片防护装具。此外,柔性防护装具的防弹性能均随着鳞片覆盖率的增加而提高。本研究成果为新型柔性防护装具的设计提供理论依据和科学指导。