Investigation on the ballistic behavior of Al2O3/Al2024 laminated composites
Introduction
Development of lightweight armor structures is very important with respect to saving energy and increasing mobility of the defense systems. Laminated composite armors containing a ceramic front layer and a metallic or composite backing layer offer a significant weight saving compared to steel for the same ballistic threat. In the composite armor, the ceramic plate breaks up and erodes the projectile. Meantime, the broken ceramic forms a conoid which distributes a force over a larger area and reduces the pressure on the backing plate. Then the metallic or composite backing plate absorbs the remaining kinetic energy of the projectile more easily and supports the ceramic fragments. In such composite armors, the ballistic performance depends on several physical and material parameters. These are the impact velocity of the projectile; the hardness, density and toughness of the ceramic tile; the rigidity and strength of the backup plates; the thicknesses of ceramic tiles, backup plate and interface layer. In laminated composite armor studies, alumina as a ceramic front layer and aluminum alloy as a backing layer have found a wide interest due to the fact that these materials are relatively cheap, light and available in comparison to other candidate materials.
In an earlier study, Wilkins (1978) studied the penetration and perforation characteristics of the alumina/aluminum composite target using 7.62 mm projectiles. He demonstrated the cone crack as the main damage mechanism for the composite target. And also some other researchers showed the cone crack formation in ceramics subjected to ballistic impact (Shockey et al., 1990a, Shockey et al., 1990b, Curran et al., 1993). Roeder and Sun (2001) investigated the effects of structural layering and thermal residual stresses on the impact resistance of alumina/aluminum laminated structures. They used the three-layered and nine-layered targets to be tested over an incident velocity range of 100–300 m/s. Roeder and Sun showed that thick layer laminates allowed less penetration than thin layer laminates for the same areal density. In a study by Zaera et al. (2000), both the numerical and experimental results pointed out that a thicker layer of adhesive caused a larger area affected by plastic deformation of the metallic plate in the composite armor consisting of alumina tile and aluminum plate. In another study, Hetherington (1992) investigated the optimization of two component composite armor containing alumina tile as a front plate and aluminum as a backing plate and made comparison between the theoretical results based on Florence model and experimental results. A good agreement was found between the theoretical and experimental results. Sadanandan and Hetherington (1997) studied the performance of alumina/aluminum and alumina/steel armors when subjected to oblique impact by 7.62 mm Armor Piercing (AP) and ball ammunition. They obtained that the ballistic limit velocity increased with obliquity. A very informative study was done by Sherman and Brandon using semi-infinite supported alumina tiles either by using drop weight test or armor-piercing tests with 7.62 mm projectiles (Sherman and Brandon, 1997). They determined the ballistic failure mechanisms for the samples by using these two test methods. Study on the effects of confinement on alumina tiles was conducted by Sherman and Ben-Shushan who investigated the quasi-static impact damage in confined ceramics tiles (Sherman and Ben-Shushan, 1998). Kaufmann et al. (2003) conducted depth of penetration tests on four different ceramics including alumina bonded to aluminum cylinders, against 12.7 mm projectiles. They concluded that alumina was outperformed by silicon carbide and boron carbide. In order to estimate trends in impact behavior of two component ceramic/metal composite armors, four analytical (Florence, 1969, Woodward, 1990, den Reijer, 1991, Zaera and Sanchez-Galvez, 1998) and four numerical modeling (Zaera et al., 2000, Lee and Yoo, 2001, Abrate, 2001, Espinosa et al., 1998) were proposed by different researchers.
The expected failure mechanisms for the ceramic faced armor are tensile radial crack formation, cone formation, crushing and pulverizing conoid structure at ceramic layer and petalling at backing layer (Wilkins, 1978, Sherman and Brandon, 1997). In the literature, the effect of different laminations and mechanical properties of the backing layer on the ballistic performance of the alumina/aluminum laminated composites are missing. In this study, the main objective was to investigate the effects of mechanical properties of aluminum backing material, adhesive type, laminating type on the ballistic performance of Al2O3/Al2024 (alumina/aluminum) laminated composite armors against 7.62 × 51 mm projectiles. Moreover, inspections of the fracture surfaces were examined using scanning electron microscope (SEM) to determine deformation mode.
Section snippets
Experimental procedure
Alumina and Al2024 alloy were chosen to be used as the front and backing layer, respectively. Alumina tiles having 50 mm × 50 mm in size with different thicknesses (4, 6, 8 and 10 mm) were used for the ceramic front layer. These ceramic tiles which were supplied from Kale Porselen A.Ş., had a purity of 99%. In order to bond layers, two different adhesives namely, commercially available epoxy and polyurethane adhesives were utilized. Al2024 alloy plates received as annealed (O) condition of which
Results
Table 3 gives the probability of perforation out of six shots concerning epoxy bonded sample groups. As explained below, polyurethane bonded samples showed very similar characteristics. The sample groups: R4, R7, R13 and R14 were completely penetrated and perforated by 7.62 mm AP projectile while R2, R3, R6, R9, R11 and R12 maintained the full protection against these projectiles. On the other hand, the sample groups, R1, R5, R8, R10 and R15 were successful partially under the impact of the
Discussion
The composite sample groups (R1, R2 and R3) using the Al2024-T6 showed higher ballistic resistance against 7.62 mm AP projectiles than those with Al2024-O (R4, R5 and R6). Just after the impact of the projectile to the target material, very high compressive waves occur and these waves reflect from the backing layer as tensile waves towards the interface and front layer. Then, the interaction of these waves causes the separation, fracture and fragmentation of the ceramic layer. In order to
Conclusions
The main conclusions for this study can be given as follows:
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Fig. 15 shows the comparison of the successful samples by taking their normalized weights into consideration. One can see that among these samples, R2 and R11 are the most suitable for the lightweight armor design since they provided ∼25% weight saving compared to others.
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Heat treated aluminum alloy (Al2024-T6) exhibited higher ballistic resistance on laminated composite than aluminum alloy (Al2024-O) as received condition due to the
Acknowledgements
This work was supported by the Research Fund of the Middle East Technical University, Project #BAP-2004-07-02-00-114 and State Planning Organization of Turkey, Project #BAP-08.04.DPT2002K120540/21.
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2022, Composites Part C: Open AccessCitation Excerpt :The dynamic stiffness of these materials affects the ceramic fragmentation and projectile erosion [36]. The use of high-tensile-strength materials in a multi-layered arrangement in our system provides resistance to the tensile stresses generated by the projectile impact [4,37]. A schematic representation of the laminate assembly is shown in Fig. 4a.