Impact of small steel spheres on glass surfaces

Abstract

A high speed photographic study has been made as part of a detailed investigation of the impact of small steel spheres (∼ 800 and 1000 μm diameter) on to Pyrex and soda-lime glasses. The velocity of the spheres was varied from 20 to 300 m sec−1 and the fracturing process during the complete impact cycle was followed. Observations revealed substantial differences in the behaviour of the two glasses, particularly at higher velocities; Pyrex behaved as though indented by a sphere, whereas soda lime glass behaved as though indented with a pointed indenter. As with quasi-static pointed indentations, cracking was observed during the unloading cycle. It was also found that the angle of the Hertzian cone crack in Pyrex glass varied in a systematic manner with velocity. Rebound velocity, time of contact and extent of flattening of the steel spheres were also recorded. The relevance of these observations to impact erosion and strength degradation of brittle materials is pointed out.