Closure and Repropagation of Healed Cracks in Silicate Glass

Abstract
Cracks in soda‐lime‐silica and vitreous silica glass close against a finite load at humidities between 0.01 % and 100%. The force associated with crack closure (0.15 J/m2) can be predicted by a model which involves hydrogen‐bonded linkages of surface‐adsorbed water molecules. The fracture energy to reopen healed cracks in vitreous silica is also in the range of hydrogen‐bonding interactions. In the driest environments used, healed cracks in soda‐lime‐silica glass required 1.7 ± 0.2 J/m2 to reopen. This bonding energy can be attributed to the formation of either cationic bridges or siloxane bonds between fracture surfaces. Since crack healing was observed to be independent of the number of cycles, a cationic bridging model is favored to explain healing effects at room temperature.

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