SCRATCH TEST OF SODA-LIME GLASS

A series of single point scratch tests have been performed on soda-lim e glass slides using spherical and conical diamond indenters. The coni cal indenters had different apex angles, 2 theta. The force ratio (hor izontal to normal) is independent of normal load or driving speed, but increases linearly with cot theta, indicating a plowing mechanism in which the scratch hardness (normal load divided by one half of the ver tically projected contact area) is equal to the plowing stress (horizo ntal force divided by the horizontally projected contact area). As the driving speed increases, the width of the scratch decreases so both t he scratch hardness and the plowing stress increase proportionally whi le the crack density decreases. For spherical indenters, the friction appears to be caused by adhesion rather than plowing. In a liquid envi ronment (water) the horizontal force increases and stick-slip appears. The rate of crack formation seems to follow first order kinetics in w hich the probability of cracking within an interacting distance is pro portional to the fraction of the uncracked portion of the scratch. The damage mechanism changes from deformation to cracking with the increa se of scratch depth. (C) 1998 Acta Metallurgica Inc. Published by Else vier Science Ltd. All rights reserved.