The effect of mineralogy and grain size on stress damage thresholds of granite and diorite

The deformation and failure properties of the loaded rocks are divided into different stages based on cracks' formation and growth. The different damage stress thresholds separate these stages. Considering the damage stress thresholds as a material property, geological properties of rocks can affect the damage stress thresholds. In this research, damage stress thresholds were identified for granite and diorite in the uniaxial compressive loading test with the help of the Acoustic Emission test (AE). Then fluorescence thin sections were prepared from the samples loaded to each damage stress threshold to investigate the effect of the mineralogy and the grain size. The results show that strong minerals increase the stress damage thresholds level due to the high cracking resistance. Furthermore, by decreasing the mean grain size, a better interlocking between the grains is created, and the number of grain boundaries increases. Therefore, the applied force has a higher surface to distribute. Consequently, minerals are less affected by the applied force; their crack density reduces, and crack initiation stress threshold increases.