Perforation of honeycomb sandwich plates by projectiles

Abstract

An analytical solution for the ballistic limit of a honeycomb plate subjected to normal impact by blunt and spherical projectiles is presented. The solution involves a three-stage, perforation process that results in complete perforation of the sandwich. Stages 1–3 describe perforation of the top facesheet, honeycomb core, and bottom facesheet, respectively. Residual velocities in Stages 1 and 2 are found from energy balances between each stage. The plastic work dissipated in deformation and fracture at each stage is approximated from the solution of the previous stage. Shear forces are transmitted in the bond between facesheets and honeycomb core. The predicted ballistic limits are found to be within 5% of the measured ballistic limits for sandwich plates perforated by the blunt and spherical projectiles. The lateral extent and deformation of the damaged facesheets are also found to be within 34 and 51% of limited test results, respectively. It has also been found that most of the work is dissipated in perforation of the bottom facesheet during impact. The work to perforate the bottom facesheet by the blunt and spherical projectiles accounts for 63–85 and 55% of the initial kinetic energy, respectively. Therefore, the perforation resistance of the bottom facesheet, rather than the top facesheet or honeycomb core, would be an important parameter in determining the perforation resistance of the entire sandwich panel.