Rock fracture toughness study using cracked chevron notched Brazilian disc specimen under pure modes I and II loading – A statistical approach

• Mode I and mode II fracture tests were conducted on a white marble using CCNBD specimen.
• KIIc was noticeably higher than KIc due to negative T-stress that exists in mode II CCNBD samples.
• Weibull statistical distributions of rock fracture toughness results were obtained.
• The GMTS criterion was able to predict well both the direction and the onset of mode II fracture data.
• Mode II fracture probability curves were predicted in terms of mode I Weibull statistical data.

Fracture toughness of a white marble is studied experimentally using several cracked chevron notched Brazilian disc (CCNBD) specimens under pure mode I and pure mode II loading. Even in the presence of natural scatters in the test data, it was observed that the average mode II fracture toughness KIIc was considerably larger than that of mode I fracture toughness KIc such that the mean fracture toughness ratio (KIIc/KIc) was about 2. Using the generalized maximum tangential stress theory, the obtained mode II test results were estimated in terms of mode I fracture toughness data. The enhanced KIIc value in the CCNBD specimen could be related to the influence of very large negative T-stress value that exists in the mode II CCNBD specimens. The statistical analyses of test data were performed successfully to predict the Weibull parameters of mode II results in terms of mode I Weibull parameters.