Research on size effect of fracture toughness of sandstone using the center-cracked circular disc samples.

• The length of fracture process zone is determined by finite element analysis. • The size effect of fracture toughness test value is analyzed. • The reason of size effect of fracture toughness test value is revealed. • The crack growth paths and failure characteristics of samples are discussed. In order to investigate the size effect and reason of rock fracture toughness, the split loading test was carried out in the GCTS rock mechanics testing machine using the center-cracked circular disc (CCCD) samples with diameters of 50 mm, 100 mm, 150 mm and 205 mm, respectively. The lengths of fracture process zone (l FPZ) were determined by the maximum normal stress criterion. The size effect of the l FPZ , fracture toughness test value (K Ic), and fracture energy (G f) were analyzed. The influence of the l FPZ on the size effect of the K Ic was revealed. The crack growth paths and failure characteristics of the samples were discussed. The results show that the l FPZ and the K Ic increase linearly with the sample size, and there is obvious size effect within the range of the test. The K Ic and the l FPZ do not always increase linearly with the size in a larger size range, but gradually stabilize by extrapolation analysis. The l FPZ increases with the size, which means the release of stored energy increases with the size corresponding to the size effect of the G f , and in turn leads to the size effect of the K Ic. It is helpful to deeply understand the cause of the size effect reason of rock fracture toughness. [ABSTRACT FROM AUTHOR]