Fatigue Mechanical Properties of Salt Rocks Under High Stress Plateaus: The Interaction Between Creep and Fatigue

To meet the requirements of the United Nations Framework Convention on Climate Change, i.e., the Paris Agreement, countries around the world have developed carbon-peaking and carbon-neutral action programs. The use of renewable energy sources is an effective means of meeting this requirement. Compressed air energy storage using salt caverns is an effective way to enhance the efficiency of renewable energy use. To investigate the damage pattern of salt cavern surrounding rocks subjected to cyclic injection and extraction loads during the operation of compressed air energy storage plants, using a MTS815 rock mechanics test system, a series of creep-fatigue mechanics tests on salt rock were carried out, and the effects on the fatigue damage of salt rock were investigated by setting different high stress plateau times and stress levels. (1) The development pattern of the corresponding creep-fatigue stress-strain curve is similar to that of ordinary fatigue, which is also divided into three stages: comb-dense-comb. The cyclic load has a positive effect on creep, but there is a threshold value of plateau time, and the creep deformation is minimal at a plateau time of 15 min. (2) The residual strain before the plateau in A cycle is greater than that after the plateau in B cycle, which is different from the traditional fatigue test, and the difference between the residual strain before and after the plateau is positively correlated with the plateau time. (3) The fatigue life of the salt rock specimens decreases and their creep life increases as the high stress plateau time increases. (4) The effect of the high stress plateau starts to appear under lower stress conditions, and the residual strain difference before and after the plateau increases with increasing stress level. (5) The different responses of the internal structure of the salt rock to fatigue and creep lead to the interaction between creep and fatigue.

Automated summary

The study found that the cyclic load has a positive effect on creep of salt rock, but there is a threshold value of plateau time, and minimal creep deformation is observed at a plateau time of 15 min. The residual strain before the plateau in A cycle is greater than that after the plateau in B cycle, and the difference between the residual strain before and after the plateau is positively correlated with the plateau time. The fatigue life of the salt rock specimens decreases, and their creep life increases as the high stress plateau time increases.