Scratch test of soda-lime glass

A series of single point scratch tests have been performed on soda-lime glass slides using spherical and conical diamond indenters. The conical indenters had different apex angles, 2θ. The force ratio (horizontal to normal) is independent of normal load or driving speed, but increases linearly with cot θ, indicating a plowing mechanism in which the scratch hardness (normal load divided by one half of the vertically projected contact area) is equal to the plowing stress (horizontal force divided by the horizontally projected contact area). As the driving speed increases, the width of the scratch decreases so both the scratch hardness and the plowing stress increase proportionally while the crack density decreases. For spherical indenters, the friction appears to be caused by adhesion rather than plowing. In a liquid environment (water) the horizontal force increases and stick–slip appears. The rate of crack formation seems to follow first order kinetics in which the probability of cracking within an interacting distance is proportional to the fraction of the uncracked portion of the scratch. The damage mechanism changes from deformation to cracking with the increase of scratch depth.