Energy Evolution and Nonlinear Breakage Constitutive Model of Granite Influenced by Non-uniformity of Crystal Combinations Under Cyclic Loading

Energy evolution and nonlinear breakage mechanical properties of brittle rock are closely related to the non-uniformity of crystal combinations, which need deeply been evaluated to date, providing a reasonable basis for the investigation of rock engineering stability. Micro- and macro-scale experiments of 5 types of granite were conducted. Different types of granites exhibit distinct characteristics in fracture development, failure combination patterns, energy evolution, and theoretical models. The micro-deformation of granite is manifested by the distribution of strong deformation fracture zone and the heterogeneity of microstructure. The plastic deformation of granite specimen is not obvious during the breakage process. The Helmholtz free energy of granite sample system under load is nonlinearly separated. Based on the analytical solution of the nonlinear separation parameters and breakage evolution, granite mechanical model is deduced. This model is well matched with the experiment and reflects the nonlinear mechanical properties of granite. The study reveals intriguing findings. One type of granite fails; it undergoes fragmentation into small splash rocks, accompanied by a violent release of energy. Another type of granite fails, there is no occurrence of violent splash rocks, causing partial breakage in the form of rock powder. Both types of granite specimens exhibit strange phenomena in the theoretical curves at the moment of macroscopic fracture, where the peak value is almost infinitely large, but the experimental values before the peak stress are well matched with the theoretical values. Elastic energy storage rate of brittle fracture granite specimens decreases significantly at about 90% of the peak strength. While granite sample with singular phenomena on the constitutive curve, the critical rate growth points before the singular point are about 95% of the peak stress. This phenomenon can be used as a critical warning value before granite breakage. It may provide a theoretical basis for rock to be widely used in engineering practice.