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 projectiles. A critical question is whether this failure front remains 'steady' after the driving stress is removed. A test series with short gold rods (D = 1 mm, L/D≅5-11) impacting borosilicate glass at ∼1 to 2 km/s was carried out to investigate this question. The reverse ballistic method was used for the experiments, and the impact and penetration process was observed simultaneously with five flash X-rays and a 16-frame high-speed optical camera. Very high measurement accuracy was established to ensure reliable results. Results show that the failure front induced by rod impact and penetration does arrest (ceases to propagate) after the rod is totally eroded inside the glass. The impact of a second rod after a short time delay reinitiates the failure front at about the same speed