Deformation and failure mechanism of flat-nosed TC4 titanium alloy projectile penetrating steel target at different velocities

• Penetration behavior of flat-nosed TC4 alloy projectiles impacting Q235 steel targets at various velocities. • Adiabatic shear bands evolution of the projectiles from a mushroom-like nose to a sharp one. • Critical threshold of 840–860 m/s for the projectile nose transition from simulation results. The dynamic behavior of flat-nosed Ti-6Al-4V (TC4) alloy projectiles penetrating Q235 steel targets under three velocities (800 m/s, 983 m/s, and 1167 m/s) was studied experimentally and numerically, emphasizing the evolution of adiabatic shear bands of the projectile. The experimental results showed that the projectile at 800 m/s failed to penetrate the target. For this projectile nose, severe plastic deformation occurred; the shape was changed to mushroom-like; abundant adiabatic shear bands accompanied by defects of micro voids and cracks were found. The projectile at 983 m/s tended to sharpen the nose by material spalling, which was caused by the development of defects. It led to a reduced number of shear bands after penetration. This self-sharpening trend was more obvious for the projectile at 1167 m/s, and shear bands nearly disappeared after penetration. The two projectiles with sharp noses penetrated the targets, generating a perforated tunnel with ductile reaming. Good consistency was achieved between the experimental and numerical results. Further simulation results revealed a critical threshold of 840–860 m/s for the nose transition and showed a similar transformation of nose shape after increasing the target thickness.