Abstract
Scratch-induced cracking is a serious problem for the use of glass products. At the scratch process, both median (vertical to the glass surface) and lateral (horizontal to the glass surface) cracks are formed. In this study, morphology of the scratch-induced cracks in a commercial soda-lime-silica glass was investigated by the scanning electron microscopy for the specimen broken across the scratch groove. Scratch test was carried out using a Knoop indenter in water and in dehydrated heptane. When scratch speed was 70 x 10-6 ms-1, length of both vertical and horizontal cracks was proportional to the normal load at scratching, and environmental dependence was not observed. When scratch speed was increased with the constant normal load of 200g, length of both cracks was decreased. In the case of horizontal crack, no environmental effect was observed. On the other hand, length of the vertical crack scratched in water was much longer than that in heptane. At very high scratch speed as high as 1000 x 10-6 ms-1, no vertical crack was formed in the heptane. These differences between horizontal and vertical cracks should be due to the differences of crack initiation position and the influence of subcritical crack growth to these cracks.
Highlights
Scratch-induced crack formation in glass is important for grinding process in glass-related industry and for degradation of strength in practical use
We found that the composition dependence of crack initiation load at scratching process [scratch resistance (SR)] is different from that at indentation process [crack resistance (CR)]
One is the median crack, which is almost normal to the glass surface, and the other is the lateral crack, which is almost parallel to the glass surface
Summary
Scratch-induced crack formation in glass is important for grinding process in glass-related industry and for degradation of strength in practical use. We are focusing the crack initiation load and studied its composition dependence for borosilicate, aluminosilicate, and some commercial glasses together with the environmental effect (Yoshida et al, 2001, 2004, 2005). Morphology of cracks formed by scribing process was investigated by SEM observation of the cross section of scratched specimens. The crack introduced before the scratch test was used as the origin of this bending fracture, and the scratched surface of the specimen suffered a compressive stress at the breaking process. All of the experiments were carried out 20 times for one condition
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