Study On Static And Dynamic Mechanical Properties Of Damaged Sandstone Under Different Cyclic Static Loads

Due to the current social demand for underground coal resources is steadily increasing,the response research of deep rock under mining has become one of the key research topics.In order to study the mechanical properties and energy evolution of deep underground sandstone under dynamic loading conditions,this paper firstly obtains sandstone specimens with different damage degrees by cyclic loading and unloading tests under different cyclic upper limits of mortar specimens.Three different definitions of sandstone damage are established from the perspectives of mechanical parameters,energy dissipation and ultrasonic wave velocity,and then the sand damage is analyzed The damage degree of rock specimen is different under different upper limit stress.Then,SHPB device was used to carry out dynamic iMPact test on sandstone specimens with different damage degrees.In order to study the performance of strain rate effect,the iMPact pressure was set to 0.3MPa,0.4MPa,0.5MPa and 0.6MPa respectively to analyze the mechanical properties and energy dissipation characteristics of damaged sandstone under dynamic iMPact load.The results show that:(1)The analysis of the peak stress,peak strain and elastic modulus of sandstone specimen in cyclic loading and unloading test shows that the internal damage of the specimen develops with the increase of the upper limit stress,and its rising rate reaches the peak point when the upper limit stress is between 24 MPa and 36 MPa.(2)The rate mutation point of elastic energy and dissipation energy ratio of sandstone specimens represents the failure of overall crushing and loss of bearing capacity.With the increase of upper limit stress,elastic deformation energy decreases,absorption energy is transformed into dissipative energy,and damage is accumulated steadily.(3)The three damage definition methods can reflect the evolution law of sandstone under cyclic loading and unloading.The damage variable is positively correlated with the upper limit stress,and the damage variable defined by acoustic wave velocity can better reflect the change of the overall damage degree of sandstone.(4)In the iMPact test,both the dynamic peak stress and the dynamic peak strain show obvious strain rate effect.With the increase of the damage degree,the slope of the stress-strain rate fitting line decreases,and the slope of the strain strain rate fitting line increases.When the upper limit stress reaches 60%of the peak strength,the strain rate effect of the stress declines.(5)Incident energy,reflected energy,transmitted energy and dissipated energy are positively correlated with strain rate.Incident energy is only correlated with strain rate,and does not change with the change of damage degree.At the same time,with the aggravation of damage degree,the proportion of reflected energy increases,the proportion of transmitted energy decreases,and the proportion of dissipated energy increases slightly in the later period.When the damage factor reaches 0.635,it reaches the critical damage value When the damage factor is lower than 0.635,the proportion of transmitted energy is the highest,while the proportion of dissipated energy is always the lowest.Figure[45]table[16]reference[115]...