Abstract
No unified criterion exists for the transition threshold of rock mechanical characteristics. We combine rock stress‐strain curves to propose an increment ratio of axial pressure based on uniaxial compression tests on granite at high temperature. The behavior of the increment ratio of strain, elastic modulus, Poisson’s ratio, and energy with axial pressure is analyzed, and the following conclusions are drawn. (1) High temperatures aggravate rock deterioration, reduce failure strength, and enhance ductility characteristics. (2) Under loading, the compression‐to‐elasticity and elasticity‐to‐plasticity transition thresholds for rock occur, respectively, at 20%–35% and 75%–80% stress levels at temperatures of 25–800°C. (3) The source data for calculating rock deformation parameters or unloading points for unloading tests can be selected over the stress level range of 35%–75%.
Highlights
(2) When the stress-strain curve is used to solve for deformation parameters, the data interval selection varies from user to user and is often chosen on the premise of conforming to objective facts. (3) ere is no uniform standard for selecting the unloading point in an uniaxial or triaxial unloading test
We combine high-temperature uniaxial compression tests on granite with the concept of an increment ratio of axial pressure. e following conclusions are drawn: (1) With increasing temperature, granite transitions from brittle to ductile failure
(2) Based on the analysis of the increment ratio of granite parameters to axial pressure, it is considered that the transition thresholds of compaction to elasticity and elasticity to plasticity are 20%–35% and 75%–80% stress level, respectively
Summary
Rock mechanics tests have gathered significant attention worldwide. e tests include uniaxial and triaxial, singlestress and complex-stress paths, dry and saturated environments, freeze-thaw and high-temperature conditions, cracks and pore pressure, and natural and prefabricated samples, as well as auxiliary methods (e.g., acoustic emission, electromagnetic or infrared radiation, and computed tomography scanning) and have provided important results [1,2,3,4,5,6]. E tests include uniaxial and triaxial, singlestress and complex-stress paths, dry and saturated environments, freeze-thaw and high-temperature conditions, cracks and pore pressure, and natural and prefabricated samples, as well as auxiliary methods (e.g., acoustic emission, electromagnetic or infrared radiation, and computed tomography scanning) and have provided important results [1,2,3,4,5,6]. (1) In the stress-strain curve, the transition zone or conversion threshold in the compaction-to-elastic and elastic-to-plastic stages is not quantified and the selection is inevitably affected by subjective factors. We further study the mechanical properties of rock after high temperature under different stress conditions. Materials and Methods e granite samples used in the tests were collected from a mine in Weifang, Shandong, China, with an average density of 2.612 g/cm at room temperature. e samples were processed into standard cylindrical specimens of Φ50 mm × H100 mm (error ± 0.5 mm) following the International Society of Rock Mechanics (ISRM) standards, as shown in Figure 1. e tests were performed using an MTS815.02 electrohydraulic servo material test system (Figure 2)
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