Characteristics of energy evolution during total stress-strain in rocks under uniaxial compression

To study the energy evolution of rocks under uniaxial compression, uniaxial compression and uniaxial step loading and unloading tests were performed on granite, sandstone, and coal, and the stress-strain curves under different conditions were obtained. The total energy density, elastic energy density and dissipation energy density for the whole process of rock specimens under different conditions were obtained by using the integral and formula. The energy evolution characteristics of rock specimens before and after the peak were analyzed, and the relationship between elastic energy density and total energy density under uniaxial compression were investigated. The results show that the outer envelope of the uniaxial step loading and unloading stress-strain curves have the same trend as the uniaxial compression curves, and the overall deviation exists to a certain extent, and the greater the density of the rock, the smaller the deviation is. The elastic energy density and total energy density of the rock specimens satisfy the linear energy storage law under uniaxial compression and uniaxial step loading and unloading. The energy storage limit of uniaxial compression and uniaxial step loading and unloading, which are almost equal, is obtained by using the linear energy storage law, and the greater the strength of the rock is, the greater the energy storage limit is.