Abstract:

In order to investigate the mechanical response of sandstone under cyclic stress from the energy perspective, the loading and unloading tests conducted along three cyclic paths which included an incremental step-by-step increase in initial peak stress at 10 MPa, an incremental step-by-step increase in initial peak stress at 80 MPa, and a constant peak stress maintained at 100 MPa. Subsequently, we analyzed the evolution characteristics of each energy component of sandstone based on the stress-strain curve and energy calculation results, taking into account the number of cycles and peak stress. The results show that as the number of cycles and peak stress increase, the hysteresis loop migrated to the direction of strain increase obviously only in the second cycle at the initial peak stress of 80 and 100 MPa. Different stress cycle paths make the unit volume dissipated energy shows different stage evolution characteristics. The energy values of sandstone change from a quadratic to a linear growth law as the peak stress increases in the hierarchical cyclic loading and unloading way, while in the constant amplitude cyclic loading and unloading way with the peak stress constant at 100 MPa, the unit volume energy and unit volume elastic energy of sandstone show an open downward quadratic decrease trend and the unit volume dissipative energy shows an exponential decrease trend. The effect of cyclic paths on the energy of sandstone in different stress ranges is quite different. In a comparison of the single and the hierarchical cyclic loading and unloading way, the energy difference is less than 10% when the peak stress is 80 MPa, while the energy difference is 22.74%-62.58% when the peak stress is 100 MPa.

Key words: cycle path, sandstone, peak stress, hysteresis loop, energy evolution, dissipation energy