Abstract Linear Fracture mechanics defines the fracture toughness as an intrinsic material parameter describing the ability of the material to resist to crack propagation. To investigate the effect of the testing method and of the geometry of the samples on fracture toughness determination, a series of tests under different loading conditions was conducted on an oolitic limestone. The tests were performed together with digital image correlation (DIC) analysis and finite elements numerical simulations. The test methods chosen are two types of Brazilian disc tests with a central notch (CCBD and CCNBD), the SCB and ASCB tests. The experimental results show that the obtained values for the mode I fracture toughness KIC vary between 0.62 and 0.68 MPa.m¼ which corroborates with the DIC analysis. The mode II/mixed fracture toughness KIC varies between 0.58 and 0.70MPa.m¼ and KIIC varies between 0.70 and 0.82MPa.m¼, for the mixed mode (ASCB, CCBD and CCNBD).
1. Introduction Linear fracture mechanics theory defines the fracture toughness as an intrinsic material parameter describing the ability of the material containing a crack to resist to its propagation (Irwin 1957). Despite the efficiency of this theory, measuring the fracture toughness from laboratory experiments is associated with large uncertainties related to rock intrinsic variability, and also to the characteristics of the testing methods and to the geometry of the samples. Several authors have explored the fracture toughness of rocks comparing values obtained from different testing configurations and made contradictory conclusions. Some authors found that results depend on the testing method and on the sample geometry (e.g. Aliha et al., 2012, Khan & Al-Shayea, 2000, Liu & Chao, 2003 and Chao et al., 2001) whereas others found that it does not (e.g. Donovan & Karfakis, 2004). Moreover, asymmetry and anisotropy lead to additional difficulties in the laboratory tests. The objective of this work is to get deeper insight in the influence of the testing methods on rock fracture toughness evaluation.