Fracture Mechanisms of rock specimen under tensile stress and heat condition by micromechanics test

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Micromechanical tests, loading tests for 114 small granite specimens (about 5×7×1 mm), were carried out using a microscope under tensile stress and heat conditions. In this study, tensile loading tests were conducted at room temperature and at 50, 100 and 200°C. Factors influencing strength were considered. Furthermore, acoustic emissions (Aes) were monitored during loading. Finite element method(FEM) simulations, including those of thermal stress, were conducted.The following results were obtained :1. For the temperature at 50, 100 and 200°C, the tensile strength became lower than that at room temperature because of the influence of thermal stress. However, for specimens including pre-existing cracks vertical to the loading axis, results showed that the number of pre-existing cracks dominated the deterioration of strength more than the thermal stress condition.2. Results of FEM simulation with thermal conditions demonstrated that the stress concentration occurred at the complex area of the black mica boundary. This result confirms the laboratory tests.3. Many AE events were detected in specimens during the loading process. These AE events were generated not only from tensile cracking but also from shear sliding of cracks.The results obtained in this study demonstrate that the tensile fracture mechanism of granite specimen under heat condition must be considered separately for specimens with and without dominant pre-existing cracks vertical to the loading axis.In the former specimen, a pre-existing crack leads to rupture of the specimen with less influence of thermal stress. In the latter specimen, shear sliding might have developed along the cracks parallel to the loading axis before rupture. At that moment, an AE was generated with shear sliding of cracks. Moreover, this shear sliding can occur at a structurally complex area.