Subcritical Fracturing of Sandstone Characterized by the Acoustic Emission Energy

Excerpt

Subcritical fracture growth in rock may be attributable to several competing mechanisms, including cyclic loading. Experimental investigations (Tao and Mo 1990; Bagde and Petroš 2005; Xiao et al. 2010) have demonstrated the progressive weakening of rock due to cyclic loading. Among the techniques employed to interpret the extension of subcritical fractures under cyclic loading, the Paris law (Paris et al. 1961; Paris and Erdogan 1963) is probably the most popular method. The Paris law (\({\text{d}}a/{\text{d}}N=C{\left( {\Delta {K_{\text{I}}}} \right)^m}\)) was initially proposed for metals, and it was justified by the accumulation of damage in the form of material yield at the fracture tip (Weertman 1966; Rice 1967). However, there are the prominent characteristics of rock fractures at the generation of massive microcracks within the rock fracture process zone (FPZ) (Labuz et al. 1987; Anderson 2005). In addition, subcritical fracturing may occur during the application of various unconventional techniques, such as stimulation by liquid nitrogen (Zhao et al. 2017) and supercritical CO₂ (Zhou et al. 2018), to extract different types of energy (Wu et al. 2017). Thus, understanding the subcritical fracturing process in rocks remains a challenging and crucial task (Lu et al. 2017; Zhou et al. 2017). …