Energy partitioning in ballistic impact fragmentation of titanium boride

The study focuses on setting up a laboratory-scale ballistic testing apparatus in order to investigate the mechanisms through which the ballistic energy of a projectile is dissipated by a nearly monolithic nanostructured ceramic (titanium boride or TiB) and to determine the partitioning of the ballistic energy. From the past research in our group, it has been found that nanostructured TiB possesses attractive mechanical properties such as high hardness and high elastic modulus which makes it a potential candidate for armor applications. The ballistic testing system consisted of a chamber made from compressed rubber pads with a backing plate made of steel or aluminum (on which the target sample was attached) and a rifle mounted on a rest pad at the other end. To validate the testing system, mild steel plates of three thicknesses were impacted with bullets having velocities in the range of 700 to 830 m/s. The velocities were controlled by varying the amount of gunpowder load in the bullets. Complete penetration was observed in the thin plates (with thickness 9.5 mm) whereas the penetration was partial in the 15.9 and the 19.1 mm thick plates. Two batches of nine TiB plates with thicknesses varying between 5 mm to 18 mm were hot pressed and impacted by bullets having velocities in the range of 725 to 750 m/s. Aluminum backing plates were glued to the TiB plates to help in calculating the energy absorbed by the ceramic. The thinner TiB plates had a larger proportion of finer iv fragments compared to the thicker plates. The calculated energy of fragmentation for the TiB plates was found to be negligible with respect to the bullet kinetic energy. The energy spent in backing plate deformation was calculated by adding the energies for bending and tensile stretching of the plate. It was found that for the thinnest TiB plate (5 mm), the percentage of the bullet energy that went into backing plate deformation was close to 50 % whereas for plates thicker than 12 mm, it was between 5-10 %. The energy absorption of the TiB plates increased with the plate thickness but beyond a certain thickness (15 mm), the increase was not significant. The kinetic energy of the fragments, erosion of the bullet, sound, heat, and light appear to be additional mechanisms of energy dissipation.