Abstract

In this work, the effect of storage, annealing and chemical strengthening on indentation radial cracks of a sodalime glass is presented. During the storage of an indented glass with a Vickers indenter, the induced radial cracks propagate under the combined effect of the residual stresses and the environmental humidity (stress corrosion). The cracks length achieves a threshold of stability after 6 to 24 h. The threshold level and the necessary time to reach it depend both on crack dimensions (length and aperture) which are directly related to the indentation load. The annealing glass treatment leads to a crack healing phenomenon caused by viscous flow. A maximal healing effect corresponding to 20% crack length decrease is reached after annealing at 620°C during 90 min. The strength value of this healed state corresponds to that of a non indented glass (90 MPa). The probable causes of this strengthening are the crack shortening and the indentation residual stresses relaxation demonstrated by photoelasticimetry measurements. The chemical treatment (ion exchange by KNO₃ salt melt) generates residual compressive stresses on the glass surface as shown by photoelsticimetry investigations.

Key words: Glass, indentation, cracks, annealing, ion exchange, residual stress.