Difference of cracking behavior due to Vickers indentation between physically and chemically tempered glasses

Crack formation phenomena for the thermally and chemically tempered commercial soda-lime float glasses were investigated by using an indentation method. Since crack formation generally can be related with stress around an indent, the crack initiation load and the residual stress generated around the indent were measured using Vickers indentation method and a birefringence imaging system, respectively. In the case of thermally tempered glass, the crack initiation load became higher than on the original glass, whereas in the case of chemically tempered glass, the load became higher than on the original glass only when the surface stress was higher than a critical stress. The size of the residual stress field normalized by the indent size was smaller in the thermally tempered glass and larger in the chemically tempered glass than that in the original glass. The cracking resistance of both tempered glasses can be related to the residual stresses generated in the glass.