Energy evolution principle of fracture propagation of marble with different unloading stress paths

With the aim to explore the principles of real-time evolution of energy in the fracture propagation, the loading and unloading tests were carried out including the marble specimens with different stress paths for the analysis of evolution principles of axial energy and actual absorbed energy as the strain changes. The results show that the axial energy rises nonlinearly as the strain increases with the complex stress paths. The rate of rise remains low at the initial stage, and the rate will turn to an abrupt inflection point and tend to be stabilized when the rate grows gradually to the critical damage point. With different stress paths, the curves of axial energy-strain and gross energy-strain have abrupt inflection points of rate, and the point of the axial energy appears at the critical damage of corresponding stress-strain curves while the point of the gross energy appears at the corresponding peak. The change of confining pressure fails to change the axial energy of the specimen with different stress paths. However, with different confining pressures, the gross energy-strain curve of loading axial pressure and unloading confining pressure present different forms. The rate of the unloading confining pressure does not change the curve form of axial energy and gross energy, and it can only alter the changing rates of the curves at different stages. With different stress paths, the increase of confining stress comes with the increase of the gap between axial energy and gross energy while the effect on unloading rate is just on the contrary. © 2016, Central South University Press. All right reserved.