Experimental and Numerical Study of the Influence of Prefabricated Crack Width on the Fracture Toughness of NSCB Specimens

The accuracy measurement of rock fracture toughness is one of the basic tasks of rock fracture mechanics. In order to study the influence of the width of the prefabricated crack on the fracture toughness of rock, the failure process of notched semi-circular bend (NSCB) specimens with four sizes and five different width of the prefabricated crack was studied by experimental and numerical methods. The influence of the width of the prefabricated crack on the peak load, crack initiation position, dimensionless stress intensity factor and fracture toughness is analyzed and discussed. The results show that the peak load and fracture toughness of NSCB increase with the increase of the width of the prefabricated crack, and the smaller the specimen size is, the larger the increase is. When the width of the prefabricated crack is less than 1.3 mm, the crack initiates at the dichotomy of the prefabricated crack tip; when the width of the prefabricated crack is greater than or equal to 1.3 mm, the crack initiates near the corner of the prefabricated crack tip. If NSCB specimen is adopted to determine the fracture toughness of limestone, it is recommended that the width of prefabricated crack should be less than 1.3 mm. The conclusions provide a reference for the fabrication of NSCB specimens and the accurate measurement of limestone fracture toughness.