Failure and Penetration Response of Borosilicate Glass During Short-Rod Impact

The failure characterization of brittle materials like glass is of fundamental importance in describing the penetration resistance against impact of projectiles. A critical question is whether this failure front remains ``steady'' after the driving stress is removed. That is, does failure propagate similar to a wave propagating without a driving force, or is it failure kinetics-based with a slow down or a halt after the stress is removed? A test series with short gold rods (D = 1 mm, L/D 5 - 11) impacting borosilicate glass (D = 21mm, L = 60 mm) was carried out to investigate this fundamental question. For the experiments the reverse ballistic method was used and the impact and penetration process was observed simultaneously with five flash X-rays and a 16-picture high-speed optical camera. Very high measurement accuracy was established to ensure reliable results. Impact velocities from 1 km/s to 2 km/s were investigated. Results show that the failure front induced by rod impact and penetration does arrest (come to a standstill) after the rod is totally eroded inside the glass.