Study On Rock Failure Rate By Ultrasonic Vibration

In recent years,the exploration depth of mineral resources is increasing,and there are more and more hard rock strata.The scholars of every country will solve the basic problems of hard rock drilling in the acoustic vibration of rock.Ultrasonic vibrating rock is loved by all countries because of its small required axial force,large volume broken,portable equipment and helping reduce drilling cost and other advantages.Ultrasonic vibrating rock use the ultrasonic vibrating rock device to apply the magnified mechanical amplitude to the rock along the drill pipe and drill bit.When the natural frequency of the rock and the mechanical vibration frequency applied to the rock are equal,the resonance occurs,so that the rock samples are destroyed,and ultimately to achieve the purpose of ultrasonic vibration of rock.However,due to the particularity of its own materials,including unpredictable damagesof joints,cracks,holes and so on,the rock becomes the most complicated material in the natural material used for artificial use.With the prolongation of the time of ultrasonic vibration,the pore expansion of the rock is expanded,and a large number of irregular and multi-sized pores are developed in the interior,which affect the physical and mechanical properties of the rock.Therefore,this paper uses the methods of theoretical analysis,finite element numerical simulation and experiment to explore the law of damage to granite pore structure and strength with prolonged ultrasonic vibration.At present,a large number of tests have been done on ultrasonic vibrating rock,but the study of the effect of ultrasonic vibration time on the rock is almost blank.Hence,the study of vibrating time of ultrasonic vibration has important reference significance to further improve the effect of ultrasonic cutting.This paper studies the law of rock descending under different vibration time and the law of rock damage(pore size,how many change laws),and provides the theoretical guidance for the application of ultrasonic vibrator to hard rock drilling,deep exploration and development of ultrasonic vibration rock drilling rig.Based on the fatigue damage,damage mechanics and Griffith theory of rock,the influence of ultrasonic vibration time on the damage of rock is studied,and the mechanism of rock damage under ultrasonic vibration is obtained: Ultrasonicvibration increases with the vibration time and there is a minimum threshold time for fatigue lithotripsy.Only when the ultrasonic vibration time is greater than the minimum threshold time,the loading energy causes the microcracks in the granite to crack into the middle crack,and the ultrasonic vibration energy leads to the accumulation of granite internal damage and the microcracks of the granite.The finite element of ANSYS is used to simulate the influence of ultrasonic vibration time on the damage law of rock.A reasonable model of heterogeneous rock is established,and the damage degree of the granite is obtained with the time of prolonged ultrasonic vibration,and the ultrasonic vibration time threshold(the time threshold for the simulation analysis is between 15 and 20 minutes)is obtained by simulation,which will further improve the ultrasonic vibration of rock to provide theoretical guidance for the test.The effects of ultrasonic vibration time on the damage of crushed rock are studied by using NMR and uniaxial compressive strength tests.The results are reached as follows: 1.Under the action of ultrasonic frequency,the failure law of brittle materials is studied at different time.The decrease in strength and the change of porosity are the basis for quantitative analysis of the failure mode of rock mass structure.2.Under the ultrasonic frequency vibration,the nonuniform rock samples contain defects from microscopic to macroscopic dimensions.In the whole process from the original state to the final failure,the crack propagation confluence of small cracks gradually develops into large-size cracks in the increasing number of cases.Ultrasonic vibrating rock generally undergoes four stages: The first stage(0-10minutes): under the action of fatigue,the initial damage within the rock develops and the effect of vibration on the internal cracks of the rock is mainly concentrated in the shallow part of the rock.The second stage(15-20 minutes): the microcracks crack and the initial damage begins to intensify.The rock is subjected to the damage accumulation stage.At this time,the ultrasonic vibration energy is used for microcrack cracking,and the crack enters the critical value of crack cracking under low stress.The third stage(20-25 minutes): the crack is in the stage of steady development,and the extension of time can promote the improvement of the crushingefficiency of the rock under the ultrasonic vibration.However,the increment of the crack is smooth and the crack is cracked at the steady speed.The fourth stage(25-30minutes): when the rock enters the rapid accumulation stage of the damage,the crack propagation speed of the rock is accelerated,the internal large cracks converge and the rate of decrease in the strength of the rock is greatly increased,which results in rock damage and destruction leading to rock fracture.