Strength criterion for crystalline rocks considering grain size effect and tensile-compressive strength ratio

The macroscopic mechanical properties of rocks are significantly influenced by their microstructure. As a material bonded by mineral grains, the grain morphology of crystalline rock is the primary factor influencing the strength. However, most strength criteria neglect the strength variations caused by different grain characteristics in rocks. Furthermore, the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity. To address these shortcomings, a piecewise strength criterion that considers the grain size effect has been proposed. A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane, to accurately reproduce the low tensile-compressive strength ratio. Based on the analysis of experimental data, both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion. The corresponding finite element algorithm has been implemented. The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.