Keywords: steel, plates, perforation, layered targets, experimental tests, LS-DYNA.

In this study, presenting work in progress, the ballistic perforation resistance of double-layered steel plates impacted by blunt and ogival projectiles has been investigated both experimentally and numerically. A main objective is to investigate if double-layered targets can be used to design safer, more cost-effective and more lightweight ballistic protection systems (see also [1,2,3]). In the tests, 12 mm thick (monolithic or layered) targets of Weldox 700E steel plates were impacted by 20 mm diameter, 197 g mass ogival and blunt projectiles fired from a gas-gun at sub-ordnance velocity, and by 7.62 mm diameter, 10 g mass APM2 bullets fired from a rifle at ordnance velocity. The ballistic limit of the different target combinations was obtained in all tests. The impact tests were then analysed using the explicit solver of the non-linear finite element code LS-DYNA. In the numerical simulations, the target plates were modelled using a slightly modified version of the Johnson-Cook constitutive relation [4], while various erosion-based fracture criteria were used to simulate failure (as described in [1,2,4,5]).

It has been found that in the sub-ordnance velocity regime the effect of double-layering is considerable. When impacted by ogival projectiles a drop in capacity of about 10% is obtained, while an increase in capacity of 50% is obtained when impacted by blunt projectiles. Based on simulations it has further been shown that if the 2x6 mm double-layered Weldox 700E target is replaced by a 4 mm Weldox 700E plate and a 8 mm Armox 560T plate, the increase in perforation resistance is additionally increased (while keeping the thickness and the mass of the target constant). In the ordnance velocity regime some of the layering effect disappears, and the perforation process is fully controlled by cavity expansion with hardly any global deformation. Under such impact conditions the capacity is similar between double-layered plates in contact and monolithic targets when impacted by ogival projectiles, while a small positive effect of layering is seen in numerical simulations using blunt projectiles. However, it remains to prove some of these findings experimentally. Nevertheless, it seems safe to state that double-layered plates in contact is an equally good or better configuration than monolithic plates for ballistic protection, giving a distinct increase in the overall perforation resistance of a target.

1

Dey S., Børvik T., Teng X., Wierzbicki T., Hopperstad O.S., "On the ballistic resistance of double-layered steel plates: An experimental and numerical investigation", International Journal of Solids and Structures, 44, 6701-6723, 2007. doi:10.1016/j.ijsolstr.2007.03.005

2

Teng X., Dey S., Børvik T., Wierzbicki T., "Protection performance of double-layered metal shields against projectile impact", Journal of Mechanics of Materials and Structures, 2, 1309-1330, 2007.

3

Børvik T., Dey S., Clausen A.H., "Perforation resistance of five different high-strength steel plates subjected to small-arms projectiles", Submitted for publication, 2008. doi:10.1016/j.ijimpeng.2008.12.003

4

Børvik T., Hopperstad O.S., Berstad T., Langseth M., "A computational model of viscoplasticity and ductile damage for impact and penetration", European Journal of Mechanics - A/Solids, 20(5), 685-712, 2001. doi:10.1016/S0997-7538(01)01157-3

5

Dey S., Børvik T., Hopperstad O.S., Langseth M., "On the influence of fracture criterion in projectile impact of steel plates", Computational Materials Science, 38, 176-191, 2006. doi:10.1016/j.commatsci.2006.02.003

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