Comparison Between Impact and Hertzian Indentation on Glass
As a preliminary study of impact phenomena in ceramic materials, experiments have been conducted on glass with small steel ball indenters. Both dynamic impact experiments as well as quasi-static Hertzian indentations were performed. We show that different damage mechanisms act in the glass in the two different cases. The impact experiments have been performed with a small calibre gas gun with velocities up to 225 m/s. Comparison between impact and quasi-static experiments show that the theories that relate a maximum impact load to an impact velocity overestimate the impact load. Hertz theory can be used only as long as the target responds with tensile stress damage, that is the low velocity region. Hertzian indentations show excellent agreement with theory where the predicted contact zone radii are in very good agreement with the measured ones. The radius of the largest ring crack formed in the experiments is approximately 1.25 times the theoretical contact zone radius.
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