Ballistic impact behavior of commercially pure titanium with gradient nanostructure against projectiles with different nose shapes

With the continuous development of lightweight armor, there is an increasing demand for titanium and its alloys with enhanced mechanical properties and ballistic performance. The introducing of gradient nanostructure (GNS) offers a promising approach to enhance comprehensive mechanical properties and ballistic performance of titanium and its alloys. In the present research, GNS commercially pure titanium (CP Ti) was prepared using explosion hardening (EH) technique. Both experimental tests and numerical simulations were conducted to investigate ballistic performance of GNS CP Ti. Projectiles with different head shapes were used to perforate GNS CP Ti targets at different velocities, and ballistic curves were fitted. The microstructure of the projectile holes in the recovered targets was characterized by optical microscopy to analyze the failure modes. The experiment results show that the introducing of GNS effectively increases the ballistic limit velocity of CP Ti. After the introducing of GNS, the ballistic limit velocity of CP Ti increased by 5.8 %, 7.5 %, and 12 % under impact against ogival-nosed, hemisphere-nosed, and blunt-nosed projectiles, respectively. Microstructural analysis of the projectile holes indicates that the deformation of targets against blunt-nosed projectile is less than that against ogival-nosed projectile. Targets against ogival-nosed projectile absorbs more energy, resulting in a higher ballistic limit velocity than that against blunt-nosed projectile. A finite element model of GNS CP Ti was established using a layered modeling approach, and the simulation results were in good agreement with experimental findings. The enhanced mechanisms of ballistic performance of GNS CP Ti were revealed through both experiments and simulations. The target of GNS CP Ti can absorb more energy than untreated CP Ti under penetration. The GNS produced by EH treatment can not only improve the shear resistance of the target plate, but also redistribute the stress distribution in the target plate. Therefore, the GNS CP Ti target plate under blunt nosed shaped projectile has the strongest enhancement effect of ballistic performance.