Progressive failure of brittle rocks with non‐isometric flaws: Insights from acousto‐optic‐mechanical (AOM) data

Abstract

Uniaxial compression tests combined with nondestructive testing techniques are performed to explore the roles of non‐isometric flaws in crack developments in brittle rocks. The acoustic emission (AE) rate‐process theory is adopted to analyze fracture‐related AE event rate characteristics. The full‐field optical method is applied to detect cracking modes. Experimental results show that AE activity is quite active when the matrix microcracking is dominant, while after each macrocracking event, AE activity becomes inactive because of the stress release. Multiphysical data for each tested flaw configuration faithfully confirm the rupture progressivity. The larger the flaw length ratio, the lower the peak stress (also peak axial strain and elastic modulus), as well as the more progressive the cracking process. Moreover, ultimate failure is triggered by the shear fracturing from the relatively long flaw. The short flaw is conditionally involved in ultimate failure when the stress buildup effect dominates. Finally, the fracture mechanism of brittle rocks with non‐isometric flaws is revealed.

Experimental study on fracture behaviour of three‐flawed sandstone specimens after high‐temperature treatments

“…Compared with the low-strength rock-like specimen comprising barite, sand, plaster and water by Wong et al 68 and the low-strength gypsum specimen by Xu and Li, 61 a direct shear crack coalescence was not observed in the present study, indicating that the crack coalescence behaviour was affected by the rock type. The present ultimate failure modes of the preflawed sandstone after thermal treatment were similar to those in Yang et al 14 and Zhang et al, 69 who tested another two types of brittle sandstone specimens containing three parallel flaws without thermal treatment. Specifically, the flaw angles were fixed at 30 or 45 , which were relatively low.…”

“…Specifically, the flaw angles were fixed at 30 or 45 , which were relatively low. 14,67,69 However, crack coalescence types III and VI were not discovered at the relatively low angles without thermal treatment, but they occurred at the relatively high flaw angles after thermal treatments. Hence, the present experimental results of three-flawed specimens provided some insights into the crack coalescence behaviour of fractured rocks.…”

Transfer and dissipation of strain energy in surrounding rock of deep roadway considering strain softening and dilatancy

“…The opening or slipping of these fractures in the plastic zone will dissipate a considerable amount of strain energy, 44 which is consistent with the conclusions in Sections 2.3 and 3.3 that the strain energy is dissipated in the plastic zone. Strain softening is closely associated with the microcrack growth in the surrounding rock, as well as the upscaling fracturing 45‐48 . These fractures are not uniformly distributed in the plastic zone, indicating that the strain softening of the surrounding rock is discontinuous, verifying the conclusion in Section 3.3.…”

Forecasting Catastrophic Rupture in Brittle Rocks Using Precursory AE Time Series

“…Pre‐existing flaw, an analogy to in situ discontinuities such as joints, faults, and fissures in natural rocks, is capable of inducing mechanically the formation of catastrophic rupture (Amitrano et al, 2005; Hall et al, 2006; Raynaud & Vasseur, 2014; Vasseur et al, 2015; Zhang et al, 2019; Zhou et al, 2018, 2019; Zhou et al, 2020). In the present study, a “through‐thickness” pre‐existing flaw of 10 mm in length and 1 mm in width, with a changing flaw inclination angle (denoted by α in Figure 1a), is designed at the midlength of the specimen.…”