Energy-damage analysis of rock brittleness incorporating complete stress-strain behavior and effects of confining pressure and lithology

As a critical mechanical characteristic of rock, brittleness significantly influences fracture modes and damage evolution processes. Accurate quantitative evaluation of brittleness is essential for ensuring the stability of various engineering applications. Based on the pre-peak and post-peak stages of the rock stress-strain curve, this study constructed a brittleness index BI*. The index quantifies the ability of rock to resist plastic deformation during the pre-peak crack growth stage and evaluates the intensity of strength drop during the post-peak softening stage. Another index, BII, was established based on the degree of pre-peak elastic energy accumulation and the instability characteristics of post-peak dissipated energy. This index reflects the essential properties of rock failure by revealing the energy evolution mechanism. Furthermore, by defining a damage variable from the energy dissipation over the entire deformation process, an index B D was introduced to evaluate brittleness from the perspective of internal damage development. Triaxial compression and cyclic loading tests were conducted on rocks of different lithologies to evaluate the new index. The influences of confining pressure and lithology on rock brittleness were analyzed, along with the sensitivity analysis of various brittleness index parameters. The results indicated that the proposed brittleness indices accurately distinguish the brittleness differences among various lithologies and show effective consistency with the failure modes of specimens under different confining pressures. Meanwhile, different brittleness indices were affected by confining pressure and lithology to different degrees. The post-peak softening stage of rock played a particularly significant role in brittleness analysis. A brittleness classification system under different confining pressures and lithologies was established. The research results contribute to the enhancement and refinement of the rock brittleness evaluation system.