On the penetration of high strength steel rods into semi-infinite aluminium alloy targets

•A theoretical model has been developed for the long rod penetration problem where penetrator dynamic strength is greater than target static resistance (i.e., Yp>S).•Based on the physical consideration, the hydrodynamic velocity is defined as an impact velocity at which a stable mushrooming head is formed.•The newly developed model have been found to be in good agreement with the test data for the penetration of semi-infinite 6061-T651 targets by 4340 steel rods in the velocities ranging from 0.5 to 3.0 km/s.•The newly developed model have been found to be better than the existing analytical and numerical models.

Three modes of penetration were observed experimentally in the literature for the penetration of semi-infinite aluminium alloy targets struck normally by high strength steel rods with hemispherical ends and they are, depending upon initial impact velocity, penetration by a rigid penetrator, penetration by a deformable penetrator and penetration by an erosive penetrator. A theoretical study is presented herein to describe these three modes of penetration within a unified framework and the critical conditions for the transition among the three modes are determined by means of two critical velocities, namely, the rigid body velocity (VR) and the hydrodynamic velocity (VH). The rigid body velocity is defined as the impact velocity at which the resultant target resistance force is equal to the dynamic strength of the penetrator times the cross-sectional area of the shank and the hydrodynamic velocity as an impact velocity at which a stable mushrooming head is formed on the basis of physical consideration. Furthermore, the secondary penetration by debris tube is also considered. It transpires that the present model predictions are in better agreement with the experimental data for the penetration of 4340 steel rods into 6061-T6511 aluminium alloy targets at impact velocities between 0.5 km/s and 3.0 km/s as compared to the existing analytical and numerical models.