Study On Red Sandstone's The Characteristics Of Infrasonic Wave And The Display Of Damage Under Cyclic Loading And Unloading

In order to study the characteristics of low-frequency signals during the damage and failure of rock materials,the red sandstone was subjected to uniaxial compression and cyclic loading and unloading infrasonic wave experiments.The variation characteristics of the mechanical parameters were first studied,and then the characteristics of infrasonic wave and parameters in the cyclic loading and unloading process of red sandstone were analyzed as well as being compared with the characteristics of infrasonic signals under uniaxial compression.In addition,studying and analysis the characteristics of damage evolution of rock based on the dissipative energy method and the infrasound method were made.The main conclusions follows:(1)Analyze the mechanical parameters of red sandstone.With the increase of the number of cycles,the elastic strain and the total strain increase linearly,The plastic strain decreased significantly and then slowly increased.The proportion of elastic strain may decrease at the high stage while the other cycles increase with the increase of the number of cycles;the proportion of the plastic strain is contrary to that of elastic strain and greater in the first cycle.Modulus of the loading deformation increases with the increase of the number of cycles,and decreases at the high stress stage;while modulus of the unloading deformation generally shows a slowly rising trend.(2)The analysis of the infrasonic wave characteristics of red sandstone shows that the higher infrasonic amplitude,ringing count rate and energy rate under cyclic loading and unloading are more likely to appear at or near the upper stress limit of each cycle.At the low stress stage,infrasonic amplitude,ringing count rate and energy ratio of infrasound are relatively low and stable;cumulative ringing counts and energy increments are relatively few,and infrasonic activity is weak;with the increase of stress,infrasound signals has significant changes,and infrasound activity enhances.At the high stress stage,the characteristics of the infrasound signal change in a most significant way,infrasonic amplitude,ringing count rate and energy rate all arrive at the maximum,and the increment of cumulative ringing counts and cumulative energy shows the largest.The characteristics are irrelevant to the loading path,but the strength of the stress.Before reaching the stress peak,the infrasound activity is relatively mild,but more obvious under cyclic loading and unloading,though with a large of number of infrasound signals.(3)Based on the dissipative energy method of the rock damage characterization,the damage variation and the cumulative damage variation increase with the increase of the number of cycles,and the curve presents an "overhang" shape.At the low stress stage,the damage is less;with the increase of stress,the damage increases;when the stress reaches the high stage,the cumulative damage variation reaches the maximum in the fifth cycle,with the largest damage increment.(4)Based on the infrasonic ringing count and infrasonic energy charaterizing the rock damage,the damage can be produced both at the loading and unloading stage;the cumulative damage variation increases with the increase of the cycle,and the curve shows an upwardly curved nonlinear growth pattern.At the low stress stage,the damage is less;with the increase of the stress,the damage increases significantly;at the high stress stage,the damage increases rapidly.(5)Rock damage can be well characterized on the basis of dissipative energy method and infrasonic wave method.The growth of rock damage is monotonous and irreversible under external loading.The characterization of damage based on the infrasonic wave method can characterize the damage either at the loading stage or at the unloading stage.However,based on the dissipative energy method,only the damage of each cycle can be characterized.