Structural hierarchy and mechanical properties of rocks. Part II. Structural hierarchy, size effect and strength

The concept of the structural hierarchy of rock opens a new way to the interpretation of size effect. Analysis based on this concept shows that the size effect can be attributed to the existence of a structural hierarchy of rock. It is demonstrated that the strain rate sensitivity of rock strength can be considered as a result of competition between the coexisting thermoactivation and macroviscous mechanisms, which dominate at different strain rate values. Comparison with experimental data shows that the suggested model describes very well the strain rate sensitivity of rock strength in a wide range of strain rates. The influence of dynamic loading on the size of a rock fragment is in that more shear strain energy can be accumulated prior to fracture due to strength increase induced by high strain rate, stress state change and plastic strain accumulation. The proposed relation qualitatively describes the fragmentation law.