886219 Suggested methods for determining the fracture toughness of rock : ISRM Commission on Testing Methods Int J Rock Mock Min SciV25, N2, April 1988, P71–96

Abstract

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 to the core axis. The specimen rests on two support rollers, and a compressive load is applied to press apart the notch sides, causing transverse splitting of the specimen by crack growth in the unnotched part of the notched cross section during the test. The second method uses a 'short rod' specimen with a notch cut parallel to the core axis. A tensile load is applied to the specimen to pull apart the notch side, causing lengthwise splitting of the specimen by crack growth in the unnotched part of the notched cross section during the test. The use of two methods is justified by the frequent occurrence of anisotropy in rock material; both methods offer two test levels, the first of which can be made with portable equipment, and the second of which is complicated and laboratory oriented. For each method, details are given of scope, specimen description, apparatus, procedure, calculations, validity, and requirements for reports of results.