After providing a technical introduction to the fracture toughness of rock, this paper describes
in detail two methods for measuring proposed by the isrm commission on testing
methods.'fracture toughness' is a critical value of stress intensity, above which catastrophic
crack growth is assumed to occur; its values for rock have several practical applications. The
two proposed methods for determining the fracture toughness of rock material both use core
specimens. The first method uses a'chevron bend'specimen with a notch cut perpendicular …