A Micromechanics-Based Model of Direct Tensile Fracture in Brittle Rocks under Confining Pressure

A novel micromechanics-based model in brittle rocks is presented during the confined tensile fracture. This model is formulated by using the stress intensity factor of crack under distinct loading modes in the fracture mechanics theory. The confined tensile fracture mechanisms with and without initial crack friction are established. The development process from the confined tensile fracture without initial crack friction to that with initial crack friction is studied. The stress–strain constitutive relationship describing the transformation mechanism from the unloading of axial stress at a compressive state to the loading of axial stress at a tensile state is also studied during the confined tensile fracture. The tension–compression transformation mechanism codetermined by the friction of the initial crack, the angle of initial crack inclination, and the confining pressure is proven. With the decrease of the angle of initial crack inclination or the increase of the confining pressure, the confined tensile fracture constitutive model tends to be dominated by the tensile fracture mechanism with initial crack friction. The confined tensile fracture of brittle rocks tends to happen at the larger angle of initial crack inclination. The reasonableness of the presented model is checked by contrasting the experimental data. Effects of the friction, density, inclination angle and size of the initial crack, and the confining pressure on the tensile relation curve of strain and stress, the tensile relation curve of crack length and stress, the tensile elastic modulus, the tensile stress of crack initiation, and the tensile strength are discussed.