Prediction of Mode I Fracture Toughness of Shale Specimens by Different Fracture Theories Considering Size Effect

Abstract In this study, mode I fracture tests on cracked straight-through Brazilian disc (CSTBD) and notched semi-circular bend (NSCB) shale specimens with different sizes were conducted to investigate the difference between maximum tangential stress criterion size effect law (SEL) model in predicting apparent toughness ( K a ) of shale. addition, effects specimen geometry selection prediction inherent Ic also studied. The results show that increases increase size, predicted by process zone length determined further improved (FIMTS) is smallest. For NSCB specimen, FIMTS are closest tested toughness. However, SEL applied poor. effective establishment requires high accuracy for test data, especially configuration large variation dimensionless intensity factor Y *) normalized crack ? ).