Mechanical properties and damage characterization of cracked granite after cyclic temperature action

To study investigates the mechanical properties and damage characteristics of granite under the influence of cyclic temperature and crack inclination, uniaxial compression tests were conducted on granite with prefabricated cracks at cyclic temperatures of 30 °C, 50 °C, 70 °C, 100 °C, and 130 °C. The mechanical properties and damage characteristics of the granite were analyzed using characteristic stress, acoustic emission parameters, damage variables, fractal dimensions, and SEM. The results indicate that: (1) At the same cyclic temperature, the granite with a 45 ° prefabricated crack exhibits the lowest peak stress, elastic modulus, and σci/σm, resulting in a significant reduction in the specimen's load-bearing capacity. At the same crack inclination, the granite at 70 °C shows the highest peak stress, elastic modulus, σ _cc /σ _m , and σ _ci/ σ _m , with a noticeable reduction in internal microcracks. (2) At the same cyclic temperature, the b-value drop point of acoustic emissions in the 45 ° prefabricated crack specimen occurs earlier, indicating the earlier formation of the main crack inside the specimen. At the same crack inclination, the cumulative ring count and total energy of acoustic emissions are the lowest at 70 °C, indicating the least thermal damage to the specimen. (3) At the same cyclic temperature, the damage in the 45 ° prefabricated crack granite specimen develops more rapidly, with the damage variable reaching above 0.8 at the damage stress point, and the fluctuation in fractal dimension is minimal, indicating strong orderliness in the development of internal microcracks. At the same crack inclination, the fractal dimension of the granite specimen significantly increases at 70 °C, and the dispersion of damage proportion increases significantly after 70 °C. (4) At a cyclic temperature of 70 °C, the changes in cracks and pores in the granite uniaxial compression specimen are evident, with relatively mild damage; the final failure modes of specimens under various cyclic temperatures and crack inclinations differ significantly, transitioning from tensile-shear failure to shear failure and tensile failure as the crack inclination increases. The research results can provide theoretical references for understanding the mesoscopic damage and failure mechanisms of granite under different cyclic temperatures and crack inclinations.