Energy dissipation in thin metallic shells under projectile impact

• Behaviour of spherical shells against blunt and ogive nosed projectile impact.
• Energy absorption characteristics in different deformation modes.
• Failure mechanism through perforation and maximum crown deformation.
• Strain energy computation in radial, polar, elevation and shear direction.

The ballistic performance of hemispherical aluminium shells was studied and the energy absorption in different modes of deformation has been computed. The experiments were performed wherein blunt and ogive nosed steel projectiles of 19 mm diameter were fired on 0.7–1.5 mm thick 1100-H12 aluminum hemispherical shells of different effective spans. The mechanics of deformation and energy absorption capacity was found to be significantly influenced by the shell thickness and projectile nose shape. The ogive nosed projectile caused failure through perforation by petal formation. Against blunt nosed projectile, however, the shells underwent significant dishing and reverse bending and thus defeated the projectile by dissipating its energy in global plastic deformation. The experimental findings were reproduced numerically on ABAQUS/Explicit finite element code. The numerical results were further employed for the computation of plastic strain energy in stretching in polar, radial, elevation and shear directions of the shell in order to eventually extract the total energy absorbed in plastic deformation. For a given span diameter and thickness of shell, the energy dissipation was found maximum in shear stretching while it was minimum in polar stretching of the material.