Development of an ISRM Suggested Method for Determining Mode I Static Fracture Toughness

Abstract

A number of standard methods have been proposed to determine the Mode I fracture toughness of rock. They include those based on short rod (SR) specimen, chevron bend (CB) specimen and cracked chevron-notched Brazilian disk (CCNBD) specimen. The semi-circular bend (SCB) specimen has been widely used for fracture toughness determination of geomaterials owing to inherent favourable properties such as its simplicity, minimal requirement of machining and the convenience of testing that can be accomplished by applying 3-point compressive loading using a common laboratory load frame. Use of more than one type of specimen is regarded as appropriate when it is required to measure the fracture toughness of anisotropic materials in different material directions of a rock sample. The objective of this paper is to provide details of the process of development of ISRM Suggested Method for Mode I static fracture toughness determination of rock and other geomaterials using SCB specimen, which was recently approved by ISRM. The details of the development process including the stress intensity factor calibration using the finite element method, improvement of the suggested experimental method including the steps taken to minimise errors, and suggestions to improve the accuracy of results are given.