Discussion: Strength-to-fracture scaling in scratching

• We perform an analytical derivation of Bazant’s Size Effect Law for quasi-brittle materials in the case of scratch tests.
• The Size Effect Law parameters strongly depend on the blade width.
• Fracture processes are predominant for large enough blade widths.
• The Size Effect Law provide an alternative means to assess the fracture toughness from scratch tests.

In their paper, Lin and Zhou (2013) add a new dimension to the scratch test analysis, challenging the applicability of Linear Elastic Fracture Mechanics to scratch tests. The question raised is how to integrate the three-dimensionality of scratch tests into the energetic Size Effect Law (SEL) formulated by Bažant for quasi-brittle materials. We show that Lin and Zhou’s analysis, although relevant is incomplete, as it neglects the blade width, which is critical for the fracture property assessment. In return, if the blade width is properly taken into account, the SEL here proposed is a formidable means to ascertain the fracture toughness from scratching.