Formula for calculating the critical stress intensity factor in rock fracture toughness tests using cracked chevron notched Brazilian disc (CCNBD) specimens

摘要

In 1995 the International Society for Rock Mechanics (ISRM) presented a suggested method (1; see also 3–6) for determining mode I fracture toughness of rock using cracked chevron notched Brazilian disc (CCNBD) specimens (Fig. 1). Recently, Iqbal and Mohanty [2] claimed that the equation proposed in Ref. [1] contains a typographical error. The present author has been engaged for over a decade in attempting to clarify and improve the ISRM formula [7–9]. The purpose of the present note is to show that the “corrected” equation proposed by Iqbal and Mohanty [2] had the effect of replacing the original slightly inaccurate formula given in Ref. [1] with a formula that cannot be correct, as it apparently violates obvious bounds.