Mesostructure Change Of Granite Under Ultrasonic Vibration

At present,the destruction means of hard rock materials are limited,and conventional technical means have the problems of unsatisfactory effect and high cost on such materials.Therefore,it is of great practical significance to study the new hard rock crushing methods and destruction mechanism.Vibration can effectively reduce the rock strength,improve the efficiency of fractured rocks.Especially when the vibration frequency applied by the outside is close to the natural frequency of the rock the internal crack of the rock is generated rapidly,and the rock is more easily destroyed,which can greatly improve the service life of the broken tools,reduce drilling costs,with low energy consumption,high grinding efficiency,save the economic cost,etc.Granite is a typical hard rock material,are often intrusive facies to batholith,wall rock,rock bed is widely distributed in the form of the upper continental crust.It contains important resources such as metal deposits and geothermal energy.Its main components are feldspar,quartz and other silicate minerals and secondary minerals such as mica and amphibolite.It has experienced the effects of magma condensation diagenesis,extremely high formation pressure and low temperature gradient,and various tectonic evolution geological processes during the long geological evolution.It leads to the heterogeneity of its mesostructure and mechanical properties.Therefore,this paper will use the electron microscopy method to observe the surface of granite samples with different ultrasonic vibration loading time,and study the meso-fracture evolution and morphological characteristics of the samples.The image of the electron microscope scanning test was processed by MATLAB to obtain the actual mesostructure of the rock.In this paper,the mesostructural changes and crack evolution characteristics of granite under ultrasonic vibration are studied in depth,and the existing micromechanical models and simulation methods of granite are studied and optimized.Based on the fact that the microstructure development of granite conforms to the ultrasonic vibration test,the prediction of the macroscopicequivalent mechanical properties of granite under the action of ultrasonic vibration will be realized in this paper.The paper takes medium-grained plagioclase granite as the research object.Start from the theoretical analysis,numerical simulation and physical experiment are combined to study the mesostructure changes of granite under the ultrasonic vibration.The main research contents are as follows:(1)Theoretical results show that on the microscopic scale,the crack propagation process is essentially the process of atomic bond rupture in mineral crystals under the action of external force.The crack initiation is mainly affected by the maximum response displacement of granite under ultrasonic vibration;on the microscopic scale When the crack propagates to the vicinity of the crystal boundary,the direction of crack propagation is affected by the degree of crystal mismatch on both sides of the boundary.The greater the degree of mismatch,the more the crack tends to extend along the boundary of the mineral crystal.On the macroscopic scale,the high frequency vibration close to the natural frequency of the rock is applied.The response displacement of the rock increases and the rock crushing efficiency increases.(2)The numerical simulation results show that the internal cracks of the granite numerical model are mainly tensile micro-cracks,and the shear micro-cracks appear only a small amount when the micro-cracks penetrate into macroscopic cracks.The tensile failure is the main failure mode of the numerical model;the micro-crack azimuth It mainly concentrates on the positive direction of ultrasonic vibration loading,in which the intergranular crack first appears and concentrates on the vibration loading direction.The transgranular crack is accompanied by the macroscopic crack,and its azimuth is mainly concentrated in the ultrasonic vibration loading direction and the macro crack direction.(3)The experimental results show that under the action of ultrasonic vibration,the occurrence of microcracks inside the granite,the expansion of the joints into macroscopic cracks eventually lead to the macroscopic failure of the granitesamples,accompanied by the shedding of the debris;during the macroscopic crack propagation process,the interior of the granite is mainly Quartz damage is dominant,the fracture particle size is small,feldspar minerals are mainly destroyed along the cleavage direction,and the fracture particle size is large;the microcracks are composed of intergranular cracks and transgranular cracks,and many feldspars and quartz crystals are nearby.Mica minerals have little effect on the development of microcracks,and almost no damage occurs.The analysis of electron micrographs using digital image processing technology shows that the microcrack area on the surface of granite samples increases with the loading of vibration time,especially The most obvious when the microcracks expand into macroscopic cracks.The crack azimuth and length obey the positive distribution characteristics.