Abstract
To study the energy dissipation characteristics and damage evolution law of sandstone under cyclic loading, uniaxial cyclic loading tests are conducted on sandstone specimens under different frequencies with an MTS-815 rock testing machine. Furthermore, the characteristics of elastic modulus and energy evolution law during cyclic loading and unloading are explored. The results show that the loading and unloading moduli increase with the loading frequency. Under higher frequencies, the deformation resistance of the specimen is stronger, the elastic energy stored in a single cycle of loading is larger, the released energy is less, and it is less likely for the specimen to be damaged. At the beginning of loading, the energy dissipation ratio K decreases slowly with increasing loading cycles, and it then remains stable. When the specimen is close to failure, an inflection point of K appears, and K increases rapidly. Furthermore, the evolution equation of the damage variable is derived according to the strength characteristics and energy evolution law in the process of cyclic loading, and the reasons for the failure of sandstone specimens are explained from the perspectives of energy and fatigue damage.
Highlights
To study the energy dissipation characteristics and damage evolution law of sandstone under cyclic loading, uniaxial cyclic loading tests are conducted on sandstone specimens under different frequencies with an MTS-815 rock testing machine
The evolution equation of the damage variable is derived according to the strength characteristics and energy evolution law in the process of cyclic loading, and the reasons for the failure of sandstone specimens are explained from the perspectives of energy and fatigue damage
Some scholars [11,12,13,14,15] studied the behavior of energy dissipation and release in the process of rock deformation and failure under uniaxial compression and revealed the evolution of volume energy, elastic energy, and dissipated energy during rock mass failure; subsequently, they obtained the characteristics of energy accumulation and dissipation before and after the peak compressive force
Summary
Erefore, uniaxial compression tests were performed on group 1 to obtain the uniaxial compressive strength of the specimens, which is used as the basis for selecting the reasonable upper limit value of stress σmax. E secant method was used to calculate the loading and unloading moduli: Eli. Here, σmax and σmin are the upper limit and lower limit of stress, respectively, MPa; εmi is the maximum strain of a cycle; εli and εui are the strains at the beginning and end of a cycle, respectively. Loaded from σmin to σmax, the released elastic energy density Uei is the area between the unloading curve and the strain axis, which can be approximately expressed as the area of graph AEDF. E zone between the loading and unloading stress-strain curves represents the dissipated energy density Udi , which causes irreversible plastic deformation and internal damage.
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