Study On Energy Characteristics Of Sandstone Under Dynamic Cyclic Loading

In practical engineering,the main body and foundation of geotechnical engineering often encounter cyclic loading,and the essence of rock deformation and failure process is energy accumulation and dissipation.Therefore,it is of great significance to study the deformation and failure of rock under cyclic loading from the perspective of energy.In this paper,the cyclic loading tests of sandstone specimens under different stress amplitudes,confining pressures,loading frequencies,sizes and strain rates are carried out by using WDT-1500 multi-functional material testing machine.The experimental results are studied and analyzed.The main conclusions are as follows:(1)Based on the cyclic loading tests of sandstone samples under different stress amplitudes,the laws of sandstone energy evolution during loading and unloading are analyzed.The results show that the total energy and elastic energy increase while the dissipated energy decreases with the increase of the number of cycles.In addition,when the stress amplitude increases from 15MPa to 55MPa,the increments of energy,elastic energy and dissipated energy are 234.470/%,216.23%and 99.04%respectively.(2)The effects of confining pressure and loading frequency on energy characteristics of sandstone during deformation and failure are analyzed respectively.The results show that with the increase of confining pressure,the ability of energy accumulation and dissipation of sandstone specimens is improved,and the limit values of energy,dissipated energy and elastic energy are increased,and the cumulative total energy,cumulative elastic energy and cumulative dissipated energy of sandstone specimens are also increased.The cumulative total energy increases with the increase of frequency.When the frequency is 0.5Hz,1.0Hz,2.0Hz and 4.0Hz,the cumulative total energy increases by 293.80%,53.38%and 170.89%respectively.(3)Based on the cyclic loading tests of sandstone under different strain rates and sizes,the energy absorbed and dissipated by rock samples are calculated and analyzed.During cyclic loading,the energy and dissipation energy of sandstone samples are negatively correlated with aspect ratio and positively correlated with strain rate.In addition,the cumulative total energy and cumulative dissipated energy of sandstone samples increase with the increase of cumulative residual strain.(4)According to the evolution law of dissipated energy and cycle number in sandstone cyclic failure process,a dissipated energy model is established based on the law of entropy conservation and energy conservation.The model is non-linearly fitted by Origin software.The accuracy of the dissipated energy model is verified by comparing the experimental data with the fitting results.