Ballistic impact testing of acrylic and alumina thin-films

High velocity projectiles cause damage to critical structures in space. Many of them travel at speeds of a few km/s to several hundered km/s. Such projectiles can punch through aircraft. In addition, bullets from modern weapons might reach 2.5 km/s. Spherical projectiles are tested against Poly-Methyl-Metha-Acrylate (PMMA) glasses and single-crystal corundum alumina (?-Al2O3). PMMA is created from two configurations: random and oriented. The penetration velocity (V50) of PMMA is found to be 400 m/s and that of alumina to be 4.5 km/s, 9 times higher than that of PMMA. PMMA thin films, where the chains are oriented along impact direction, heats up to 2628 K, which is less than 5450 K in random films at 5 km/s. Peak temperatures of up to 1615 K are reached in ?-Al2O3. The specific penetration energy (Ep) of PMMA is 0.322 MJ/kg at 400 m/s. In comparison, alumina shows higher specific penetration energies (Ep) of 16.5 MJ/kg and reduces the projectile velocity from 4.5 km/s to a residual velocity (Vr) of 576 m/s. This study indicates that PMMA sandwiched between two layers of alumina can be produced, with a thickness that can be calculated using specific penetration energies (Ep) from the projectile radius, to stop most projectiles effectively.