Effect of target bending in normal impact of a flat-ended cylindrical projectile near the ballistic limit

Abstract

The current work is concerned with the normal impact of flat-nosed cylindrical projectiles striking at a velocity in the vicinity of the ballistic limit on metallic targets. The ratio of target thickness to striker diameter ranges from ¼ to ½. The resulting penetration model extends existing theories to include the extensive deformation of the target resulting from the bending effect. The dynamic and static stress-strain relations of 2024-0 aluminum are obtained by means of the split-Hopkinson bar technique and an Instron machine, respectively. A series of tests with 0.8 mm diameter pre-drilled holes in each target is conducted to assess the relative effects of bending and shear on the plate deformation. A total of 20 shots are executed to examine the phenomenon of the plate response under impact loading. The 12.7 mm diameter hard-steel projectiles are fired with a pneumatic gun against 3.18, 4.76, and 6.35 mm aluminum targets at a velocity of up to 182 m s−1. A dynamic plastic bending theory is proposed that will be superposed on the previously developed one-dimensional phenomenological penetration model of Liss et at. (Int. J. Impact Engng 1, 321–324 (1983)), to permit a more accurate prediction of target response. This phenomenological model is numerically analyzed and compared with the experimental findings and the two-dimensional Lagrangian computational codes Dyna2d and Autodyn using a Cray X/MP-48 and PC-AT, respectively. Excellent correspondence with data is obtained for the projectile exit velocity when a higher impact speed is employed. The final deformation field computed from the model is not limited to a narrow zone and shows good correlation with the experimental data, especially for thinner targets.