Mechanical properties and failure characteristics of granite with non-through cracks under thermal cycling.

Abstract

Thermal cycling and pre-existing cracks significantly influence the mechanical response and damage evolution of granite in high-temperature rock engineering. To clarify their coupled effects, granite specimens with different prefabricated crack inclination angles (0°, 45°, and 90°) were subjected to different temperature conditions (30-130 °C) and thermal cycle numbers (1-5 cycles), followed by uniaxial compression tests. Characteristic stresses, AE (AE) parameters, AE b-value evolution, fractal dimensions, macroscopic failure patterns, and SEM observations were jointly analyzed to reveal the damage mechanism.The results show that the mechanical and AE responses of cracked granite exhibit clear nonlinear dependence on temperature, thermal cycle number, and crack inclination. Under the same crack inclination, the peak stress, crack initiation stress ratio, AE counts, and cumulative AE energy vary non-monotonically with temperature, and 70 °C appears to be a critical transition temperature for AE activity and damage evolution. Increasing the number of thermal cycles promotes damage accumulation, enhances AE activity, and advances the abrupt drop point of the AE b-value, indicating earlier dominance of large-scale crack propagation and main crack formation. The prefabricated crack inclination further controls the crack propagation path and failure pattern. In particular, 45° cracks are more likely to guide inclined crack coalescence and tensile-shear failure under intensified thermal cycling, whereas 90° cracks tend to maintain tensile-dominated failure. SEM observations and box-counting fractal analysis further confirm that thermal cycling promotes the development of pores and microcracks, especially at 50 °C, 100 °C, and 130 °C. These findings provide a multi-scale understanding of the coupled thermal-mechanical damage mechanism of cracked granite and may support stability evaluation of rock masses subjected to repeated thermal disturbance.