Experimental study on fatigue properties and acoustic emission characteristics of salt rock under variable cyclic rate effect
In order to investigate the impact of variations in gas injection and extraction rates on the fatigue mechanical properties and fine-scale mechanism of the surrounding rock in compressed air energy storage salt caverns(CAES).Four groups of variable cyclic rate fatigue tests on salt rock were conducted using acoustic emission monitoring(loading and unloading rates are consistent),with varying upper limit stress and stress routes.The correlations of residual strain,cyclic acoustic emission cumulative ring counts(AE counts)and peak frequency with cyclic rate were analyzed.The results showed that:(1)Cyclic residual strain and cumulative AE counts have an obvious rate correlation(obvious power law relationship with the cyclic rate,εri=mv-b+ε1,NAE-i=m'vi-b),and a positive correlation has been observed between stress level and stress factor(coefficient terms of power functions m,m').The rate dependence of creep plasticity is positively correlated with stress level(power function exponential term b),while the rate dependence of cyclic cumulative AE counts is opposite(power function exponential term b'decreases).The rate correlation parameters(b,b')are all able to predict the onset of the accelerated damage stage differently in advance of the cyclic residual strain.(2)Accelerated rise of cyclic cumulative AE counts occurs at the transition point between phases Ⅰand Ⅱ of the cyclic residual strain development trend.This corresponds to 2.382％,3.464％and 4.297％cumulative residual strains in tests of 19,23,27 MPa upper limit stress,respectively.(3)The proportion of low-frequency signals reduces with increasing cyclic rate,while high-frequency signals rise with lowering cyclic rate.Mid-frequency signals only increase with increasing stress level.(4)Fast and slow cycling operate as hardening and softening,respectively,with the softening effect resulting in lower fracture initiation stresses and stronger plastic deformability(and vice versa for hardening)in the latter cycle.This mechanism can be linked to increased small-scale crack sprouting and expansion during slow cycling,as well as the full release of internal stress during slow unloading.This work provides valuable insights into the control of gas injection and extraction frequency in CAES salt caverns,as well as the analysis of damage progression.
rock mechanicscompressed air energy storagesalt rockfatigue testacoustic emission
万方数据
维普
