Study On The Effect Of Ultrasonic Vibration Frequency On Granite Fracture Law

With the increase of the depth of mineral resources exploration,the drilling rate of complex strata and difficult drilling is increasing,and the proportion of hard rock strata is increasing.The existing drilling technology can not fully meet the needs of today's drilling operations.Especially in the drilling of hard rock strata,the conventional drilling method has the technical problem of short drilling life,low drilling efficiency and high drilling cost.Therefore,it is urgent to study the efficient rock technology to solve this problem,so as to improve the drilling efficiency and reduce the drilling cost.In view of the above drilling problem,this paper proposed the use of ultrasonic vibration method to help break the rock.The frequency of ultrasonic vibration is high,which can reach the natural frequency of hard rock.The rock will produce large amplitude under the resonance condition.At this time,the cracks inside the rock are easy to develop,expand and penetrate,resulting in a significant decrease in the difficulty of rock fracture.However,with the deterioration of rock mechanical properties,the natural frequency of the law of decline and its own natural frequency range has yet to be tested.Therefore,it is very meaningful to study the law of the hard vibration of the hard rock.By studying the breaking law of the rock,the natural frequency of the hard rock can be estimated on the one hand and the law of the change of the rock frequency can be determined on the other hand.Frequency loading range and loading method,which provides theoretical guidance and technical support for ultrasonic vibration assisted hard rock drilling..This paper takes granite as the research object.Based on the experimental study,combined with the theoretical analysis and numerical simulation analysis of the means to carry out the ultrasonic vibration frequency of hard rock breaking law research.The main contents and achievements of this thesis are as follows:(1)Based on the theory of fracture mechanics and the theory of resonant rock,the mechanism of rock breaking under ultrasonic vibration is analyzed theoretically.The ultrasonic vibration mechanics model was established to analyze the influence of ultrasonic vibration frequency on rock breaking.The results show that the vibrating load on the rock is more favorable for the crushing of the rock in the natural frequency range.The stronger the damping of the system,the stronger the vibration suppression effect.(2)ANSYS / WORKBENCH software was used to simulate the model.The effects of internal crack parameters on model modal frequency,harmonic response frequency,stress intensity factor and stress and strain are studied.It is found that the direction,size and quantity of the crack will cause the modal frequency of the rock particle model to decrease,and the peak value of rock stress and strain increases first and then decreases with the increase of vibration frequency,and the maximum value appears when the vibration frequency is 35 KHz.(3)Ultrasonic vibration test rig was developed,and the ultrasonic vibration test was carried out on the granite samples.The granite samples were subjected to nuclear magnetic resonance(NMR)and uniaxial compressive strength tests before and after the test.The changes of porosity,pore size distribution,T2 spectrum and uniaxial compressive strength of granite under different experimental conditions were observed,and the influence of ultrasonic vibration frequency on the mechanical properties of rock was analyzed.The results show that the NMR test results of the granite samples are consistent with the results of uniaxial compressive strength,and the degree of damage of the rock can be better reflected by the porosity.The natural frequency of the granite samples between 30 KHz and 35 KHz,but closer to 30 KHz.(4)Micro-drilling test bed was developed,select a frequency suitable ultrasonic transducer for ultrasonic vibration drilling pilot test.The difference between the ultrasonic vibration drilling method is compared with the conventional drilling method,and the influence of the drilling pressure on the ultrasonic vibration rotary drilling method is summarized.In the drilling experiment,it was found that the increase rate of drilling speed increased first and then decreased with the increase of drilling pressure,the increase ranges from 13.93% to 38.11%.