Sliding of a diamond sphere on K9 glass under progressive load

Micro-scratch tests have been carried out on borosilicate K9 glass using a Rockwell C diamond indenter with a spherical tip radius 105 μm in order to study deformation/damage regimes and microcracking patterns of K9 glass with increasing normal load. The abrupt changes of test data together with optical microscopy observation can be used to determine three transition loads corresponding to initiation of sub-surface median crack, onset of surface ring crack, and lateral cracks reaching the surface, respectively. Based on linear elastic fracture mechanics, fracture toughness obtained from scratch test under a low driving speed and a suitable fitting range of nominal size is found to be 0.85 MPa•m1/2 for K9 glass, which is close to 0.82 MPa•m1/2 obtained from Vickers hardness technique, making micro-scratch a powerful means to assess fracture toughness of material, and opening new application of scratch test as a quantitative method.