Experimental Research On Nano-indentation Of Granite Gneiss Physical And Mechanical Parameters

Nano-indentation test,as a commonly used test method in materials science,has been used for the surface mechanical parameter test of thin film materials,metal materials,crystal materials,etc.for nearly 30 years.It has high accuracy,simple operation,Damage and other advantages.This article introduces it to the mechanical parameter testing of granite gneiss in the Qinling area,which makes up for the difficulty of sampling in traditional uniaxial or triaxial compression tests in some areas,and solves the problem of difficult to reuse the samples in destructive tests.The acquisition of macro-mechanical parameters of rock materials provides new ideas.In order to obtain the elastic modulus and Poisson’s ratio of the macro-mechanical parameters of rocks,the following work is performed in this paper:First,use a bridge cutting machine,angle grinder,sandpaper,polishing machine and other equipment to obtain granite gneiss samples that meet the test requirements.Put the samples in an ultrasonic cleaner and use absolute ethanol to clean them.Dry at 50 ° C for testing.Second,place the sample on the nanoindenter operating platform,observe its surface with a microscope,and calibrate the target area to perform a lattice indentation test.One cycle of loading and unloading test is used to determine the specific loading and unloading parameters and study the specific The fracture toughness of mineral components,ten cycles of loading and unloading tests were used to study the relationship between the elastic modulus and hardness of each mineral with the depth of the indentation.Then,the samples were analyzed by X-ray diffraction to analyze the mineral composition and proportion in the rock samples,and the SEM scanning electron microscope test was used to observe the detailed maps of the indentations on the surface of each mineral and analyze the crack development law.Then,four commonly used homogenization analysis methods are compared and analyzed,and the secondary homogenization method is finally selected to homogenize the sample,and the macro mechanical parameters of the sample are obtained.Finally,several samples of the same granite gneiss block were core-drawn,and uniaxial and triaxial compression tests were performed to obtain the macroscopic mechanical parameters of the rock.The results were compared with the results of the nanoindentation test homogenization.The feasibility of the proposed method for obtaining rock mechanical parameters.Through the above work,the following conclusions are obtained:(1)The nano-indentation test has high requirements for the surface flatness of the sample,and the fineness of the sample treatment has a greater impact on the test result.(2)The magnitude of the maximum load has little effect on the mechanical parameters of the sample,and the incorrect selection of the holding time and loading and unloading rate will cause the Nose phenomenon.Therefore,the holding time of quartz and feldspar is selected to be 50 s and the loading rate is 20 gf / s,mica holding time 70 s,loading rate 10 gf / s.(3)The average fracture toughness of the three minerals is: quartz> feldspar> mica,and the fracture dispersion of quartz fracture toughness is the smallest and mica is the largest.The fracture toughness of the three minerals is not significantly changed by changes in their mechanical parameters.(4)The mechanical properties of quartz are good.Compared with feldspar and mica,the elastic modulus and hardness are the largest,and mica is the softest.Its mechanical parameter values are the smallest and the dispersion is large.The reason may be related to the pore structure in mica.There is a positive correlation between the elastic modulus and the hardness,and the linear regression relationship is good;the regression relationship between the elastic modulus and the hardness of the mica is not obvious,and the data is highly discrete.(5)The elastic modulus and hardness of quartz decrease with the increase of the indentation depth,but its mechanical parameter values are basically stable after the indentation depth exceeds500nm;the mechanical parameter values of feldspar decrease rapidly with the increase of the indentation depth,and then The growth is basically stable after the indentation depth exceeds1200nm: the mechanical parameter values of the mica increase with the increase of the indentation depth,and the dispersion is very large.(6)The macro-mechanical parameters of granite gneiss were estimated by the secondary homogenization method.Compared with the uniaxial or triaxial compression test results,it was found that the deviation rate was only 14.9%.It proves that the research method proposed in this paper is feasible.