Ballistic limit for oblique impact of thin sandwich panels and spaced plates

Abstract

Ballistic perforations of monolithic steel sheets, two-layered sheets and lightweight sandwich panels were investigated both experimentally and numerically. The experiments were performed using a short cylindrical projectile with either a flat or hemispherical nose that struck the target plate at an angle of obliquity. A total of 170 tests were performed at angles of obliquity 0–45°. The results suggest that during perforation by a flat-nosed projectile, layered plates cause more energy loss than monolithic plates of the same material and total thickness. There was no significant difference in the measured ballistic limit speed between monolithic plates and layered plates during oblique impact perforation by a hemispherical-nosed projectile. To develop understanding of the process of fracture development and perforation of a thin stainless-steel sheet resulting from oblique impact by a hard, flat-nosed projectile, numerical simulations by ABAQUS/Explicit finite element code were compared against the experimental fracture patterns, residual velocities and ballistic limits of perforated plates. Effects of projectile length-to-diameter ratio and spacing between layered plates struck by flat-nosed projectiles were investigated. For projectiles of equal mass, a longer projectile (larger ratio of length to diameter, L/ D>2) results in a drastic decrease in the ballistic limit speed for a double-layered plate. For thin, layered plates, the ballistic limit speed is affected significantly by the spacing between layers.