Dynamic failure of steel under hypervelocity impact of polycarbonate up to 9 km/s

We performed hypervelocity impact experiments on SS400 steel with a polycarbonate projectile at velocities up to 9 km/s. Spall fracture damages were observed near a rear surface of the impacted target. The microstructure and microdamages were examined using optical microscopy and scanning electron microscopy. The α-ε phase transition region was observed near the crater. Cracks parallel to the impact direction were observed below the crater, and radial cracks grew from the α-ε phase interface at high velocity impact tests, especially above 6 km/s. Cleavage was the dominant mechanism for a spall fracture surface, and ductile fracture structures were also observed at the edge of spall plane. Geometric spall behaviors were well reproduced by numerical simulations using a hydrocode. These simulation results also showed that the cracks below the crater would be due to dynamic tensile stresses. The calculated results using the value of 13 GPa as the transition pressure showed that the duration necessary for the phase transition is about 150 ns for impact velocity of 8.8 km/s. © 2003 American Institute of Physics.