Subcritical Growth of Indentation Median Cracks in Soda‐Lime‐Silica Glass

The influence of load and dwell time on the subcritical growth of indentation cracks was investigated. The behavior of soda‐lime‐silica glass in both active and inert environments was considered. Vickers indentations were obtained.using loads ranging from 1.96 to 39.2 N and the dwell time.at maximum load was varied between 5 s and 30 min. Indented samples were broken and the fracture surfaces.observed using optical microscopy. Anomalous crack shapes were obtained in air and water for long dwell times, particularly at higher indentation loads. The cracks were markedly circular in shape and substantially deeper than conventional median/radial indentation cracks, evidencing a time‐dependent growth. Comparison of the measured crack depth with a theoretical analysis demonstrated that the appearance of the “circular” cracks was related to the subcritical growth of median cracks.