Impact characteristics of stiffened plates penetrated by sub-ordnance velocity projectiles

A series of experiments are carried out to explore the impact characteristics of stiffened plates struck by the sub-ordnance velocity projectiles. Considering the relative position of impact point to the nearest stiffeners on target, six kinds of representative target plates with different stiffened styles are specially designed. Altogether sixteen target plates, respectively without, single- and cross-stiffened are tested and compared. Two kinds of projectiles, one with spherical nose and the other with truncated oval nose, are fired using a 25 mm refitted cannon. The initial velocities of projectiles range from 244 to 430 m/s. Experimental results show that the penetration process is greatly dependent on the nose shapes of projectiles. The tumbling of truncated oval-nosed projectiles is very prominent, which results in the great uncertainty of deformation and failure mode of target plates. While the spherical-nosed projectiles keep much more stable, plugging and ductile hole enlargement are the most distinct failure modes. In the end, some empirical formulas aimed at blunt-nosed projectiles are proposed, which could be helpful for the design of the protection structures.