Experimental investigation of mode I rock fracture toughness

Abstract

Mode I fracture toughness (KIC) is one of the most important parameters in rock fracture mechanics. KIC is an intrinsic material property that represents the ability of a material containing a pre-existing defect to resist tensile failure. The International Society for Rock Mechanics (ISRM) has proposed four suggested methods for determining KIC. However, these methods present some drawbacks. The main objective of this thesis is to develop a simple testing approach, called pseudo-compact tension (pCT) test, to measure KIC in rocks using cylindrical single edge-notched specimens loaded in pure tension. The study is based on the results of a large set of fracture toughness experiments performed with different rock types, sample sizes, and a range of notch length ratios. The KIC values derived with the pCT test are compared with those obtained with one of the suggested methods of the ISRM, the semi-circular bend (SCB) test. Some selected pCT and SCB tests were also complemented with the concurrent monitoring of the acoustic emission (AE) activity. With the obtained data, we compare and analyse both testing methods, the effects of specimen size, notch length and lithology, the mechanical evolution along the experiments and the significance of different AE parameters.