Abstract
Elastic parameters and the subcritical crack growth of different bedding angle slate specimens were studied using uniaxial compression testing and the double torsion constant displacement load relaxation method using SANS and MTS Insight machines. To study the relations of the mode-I stress intensity factor K I versus the subcritical crack growth velocity V , the fracture toughness K I C , the stagnation speed, and the threshold values, the double torsion constant displacement load relaxation method was carried out. The related rules between the bedding angles (β) and the uniaxial compressive strength, fracture toughness, and threshold values were investigated. Experimental results show that the uniaxial compression, the fracture toughness, and the threshold value curves move to the bottom then increase with the increase of the β angle. In addition, its fracture toughness is minimal when the β angle of the slates is 45°, and crack initiation and crack propagation are generated under load, which can lead to the failure of the slate. lg K I - lg V relations of transversely isotropic slates measured by this method are in accordance with linear rules, which is in good agreement with the Charles theory. The range of K 0 / K I C for these different bedding angle slates is from 0.511 to 0.789. The test results would provide the basis for studying seepage and time-dependency of rock engineering stability.
Highlights
Rocks are mineral aggregates after a long geological process; rocks of layered structure can be simplified into a transversely isotropic body, whose physical and mechanical properties in parallel to the bedding plane are different from those in perpendicular to the bedding plane
Transverse isotropy is a special case of anisotropy; these studies have a great significance on helping us have a better understanding of the permeability and mechanical properties of transversely isotropic rocks
According to the fracture mechanics and stress corrosion theory [10, 11], when a crack tip stress intensity factor KI exceeds its fracture toughness KIC, the crack will quickly expand; when the stress intensity factor is less than its fracture toughness, the crack growth will process at the speed of stress corrosion subcritical crack growth
Summary
Rocks are mineral aggregates after a long geological process; rocks of layered structure can be simplified into a transversely isotropic body, whose physical and mechanical properties in parallel to the bedding plane are different from those in perpendicular to the bedding plane. The stability analysis of the layered rock is complicated by the isotropic characteristics of the bedding surface and the coupling effect of the seepage field and stress field [1]. Transverse isotropy is a special case of anisotropy; these studies have a great significance on helping us have a better understanding of the permeability and mechanical properties of transversely isotropic rocks. The study shows that the crack in certain circumstances propagates until the material fractures with a collective effect of tensile stress and corrosion medium, which is called stress corrosion [12]. The mode-I stress intensity factor KI at the crack tip is regarded as a parameter to control the crack growth. The stress corrosion lower limit is K0; when the stress intensity factor is less than
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