Study on microcrack growth-based dynamic compressive mechanical properties in brittle rocks

The dynamic microcrack growth has a great influence on the macroscopic dynamic mechanical properties of brittle rocks under dynamic compressive loadings. However, the relationships between dynamic microcrack growth and macroscopic dynamic mechanical properties are rarely studied. Based on the microcrack growth-induced stress-strain constitutive relationship, the relationship between quasi-static and dynamic fracture toughness, the relationship between crack velocity and strain rate, the relationship between strain rate and dynamic fracture toughness, a micromechanics-based stress-strain constitutive model is proposed. Furthermore, the relationship between crack velocity and strain rate is derived by the time derivative of equation describing the relationship between crack length and axial strain. The relationship between strain rate and dynamic fracture toughness is obtained by coupling the suggested relationship between crack velocity and strain rate, and the crack velocity and fracture toughness. Effects of strain rate on stress-strain relation and dynamic compressive strength are studied. The reasonability of the proposed dynamic constitutive model is verified by the experimental results. Sensitivities of initial damage, confining pressure, parameters m, e0 and R on stress-strain relation, dynamic compressive strength and dynamic elastic modulus are discussed. These studies will provide a certain theoretical help for analyzing the stability of brittle surrounding rocks in deep undergrounding engineering.