Tension Fracture by Sub-critical Crack Growth

A macroscopic tension fracture of rock is analyzed as a result of the sub-critical crack growth in it, and a numerical procedure for the failure prediction is presented and discussed, basing upon the critical pressure-crack elongation curve (pc—a curve) for the pure mode I crack propagation (KII = 0, KI = KIC) in the homogenized joint model, which is accurately evaluated by means of the Stress Compensation-Displacement Discontinuity Method (SC-DDM). The crack elongation rate (da/dt) is formulated by the empirical equation of the form of da/dt ∝ KIn, where n: the sub-critical crack growth index. Computing the applied stress-crack elongation curves (p—a curves), the rate-dependent failure of rock in the tension test is concretely analyzed along with the time-dependent failure of rock in the creep test. The significant correlation between these experiments is discussed by comparing the non-linear stress-strain curves of the tension test to the non-linear time-strain curves of the creep test. It is clarified that the non-linearity is deeply associated with the sub-critical crack growth.