A new development cracked chevron notched direct tension method for determining the mode I fracture toughness of rocks

Abstract A new development has been proposed to measure the tensile fracture toughness (KIc) of rocks. An innovative configuration of chevron notch was applied acting as a cracked chevron notched direct tension (CCNDT) method to determine the mode I fracture toughness, which also could be suggested as a direct method to specify the tensile fracture toughness. In this method, the initial crack is generally created in the form of a chevron notch by a simple rotary saw, and afterward, the crack is subjected to the direct tensile load. Using the chevron notch in the desired specimen is mainly due to the advantages of the sub-critical crack growth in brittle materials. In the present study, a new expression is proposed to calculate the fracture toughness of CCNDT specimens. Various finite element analyses are performed using different chevron crack geometries to obtain the minimum dimensionless stress intensity factor of the CCNDT specimen. The analytical approach based on Bluhm's slice synthesis method is also implemented for evaluating the minimum dimensionless stress intensity factor of the CCNDT specimens. Furthermore, several experiments are carried out on Hornfels rock using CCNDT and ASTM standard fracture toughness; single-edge notched bend (SENB) tests to verify the proposed CCNDT method. The geometrical parameters of the CCNDT specimens are also provided to meet the plane strain fracturing condition.