Experimental and numerical study on the ballistic resistance of 6061-T651 aluminum alloy thin plates struck by different nose shapes of projectiles

The aim of the present paper is to study the effect of shapes of projectile nose on the ballistic resistance of 6061-T651 aluminum alloy thin plates, and to evaluate the effect of Lode angle dependent fracture criterion when predicting the ballistic resistance of 6061-T651 aluminum alloy thin plates struck by projectiles with different nose shapes through finite element (FE) simulations. To this end, the ballistic impact tests are firstly conducted using different nose shapes of projectiles. Ballistic limit velocities (BLVs) of different projectile-plate pairs considered are calculated by using initial versus residual velocity data obtained from the experiments. It can be found that the BLV of spherical projectile is the highest, followed by ogival-, blunt- and hemispherical-nosed projectiles. Subsequently, a 3D FE model corresponding to the test is built by ABAQUS/Explicit software and then they are adopted to predict the ballistic resistance of the plate. In these simulations modified Johnson-Cook (MJC) strength model accompanied with either the Lode angle independent and slightly modified Johnson-Cook (MJC) fracture criterion or the Lode angle dependent and modified Mohr-Coulomb (MMC) fracture criterion are adopted to describe plate material properties. Finally, the predicted ballistic resistance of the plates is compared with those observed in the experiments. The numerical predictions of the plate struck by different nose shapes of projectiles show that the BLV predicted by Lode angle dependent MMC fracture criterion is more accurate for spherical and ogival-nosed projectile, while the BLV predicted by Lode angle independent MJC fracture criterion is more accurate for blunt- and hemispherical-nosed projectile. In addition, the results show that the Lode angle's effect is related to the curvature radius of the nose shape of projectile, i.e., the Lode angle's effect decreases with the increase of the curvature radius.