Numerical Simulation Study On Granite Nanoindentation Test And Mechanical Parameter Upgrade

Nanoindentation test has outstanding advantages in the study of material micromechanical properties,and is widely used in metal surface mechanical properties,ceramic materials,polymer materials and other fields.The advantages of nanoindentation test are high test accuracy,simple test operation,small sample volume,minimal damage to the sample,and the same sample can be repeated.This has obvious advantages for many difficult,rare and expensive materials.In the field of geotechnical engineering,the nanoindentation test can obtain the physical and mechanical properties of the elastic modulus and hardness of rocks,providing new ideas for the testing and research of the physical and mechanical properties of rocks.In this paper,the following work was carried out based on nanoindentation technology:In this paper,the mechanical properties of granite were obtained by nanoindentation tests on its fine mineralogy.The finite element simulation of the nanoindentation test on quartz,feldspar,mica was carried out to reproduce the test process.The problem is systematically analyzed by a combination of theoretical derivation and finite element simulation for the effect of the radius of curvature of the indenter tip on the actual nanoindentation test.For granite nanoindentation test scale is at the nanoscale,the mechanical parameters measured by the test are the mechanical properties of rock minerals(quartz,feldspar,mica),which are at the fine scale and cannot directly reflect the macroscopic mechanical properties of granite.To address this problem,a numerical model of granite composed of mineral grains(quartz,feldspar,mica)is established,and the prediction of its macroscopic mechanical properties is achieved by calculating the mechanical properties of the granite model.The main insights and conclusions obtained from the above research work are as follows:(1)The finite element simulation of nanoindentation test was carried out for quartz,feldspar and mica minerals.Comparing the load-displacement curves obtained from the test and simulation,the results show that they are in good agreement,which verifies the accuracy and feasibility of nanoindentation finite element simulation of rock minerals.(2)Finite element simulation provides dynamic change information that is difficult to display and observe by actual experiments and theoretical formula calculations.By combining the means of experiments and numerical simulations,it can provide and display more complete and comprehensive information for the study,making the study more intuitive and in-depth.(3)The tip of an indenter can develop a radius of curvature during long-term use,which can affect the test results.In this paper,seven indenter tips with different tip radii were established and their effects on the hardness test results of quartz,feldspar and mica minerals were investigated under different indentation depth conditions.The finite element calculation results show that the measured rock mineral hardness is high when the tip radius of the indenter exists.The test error is positively correlated with the indenter tip radius and negatively correlated with the indentation depth.The results are consistent with the theoretical analysis considering the tip radius of the indenter,and the problem is systematically investigated in this paper by theoretical analysis and quantitative verification of finite elements.When the indenter is pressed into a depth of 350nm or more,even if the tip radius of the indenter is 150nm,the resulting test error will be reduced to within 5%,i.e.,when the tip radius of the indenter is large,the accuracy of the test results can be improved by increasing the indentation depth.(4)The finite element means provides the visualization of the strain field information of the material under test.Comparing the verification of three materials under test with different tip radii of indenter pressed into quartz,feldspar and mica,it can be seen that the strain of the material under test is concentrated under the action of the indenter with small tip radius.The results show that even extremely small changes in the indenter can affect the test results and the test accuracy in nanoscale tests.(5)A macroscopic granite model composed of fine mineral grains is established,and the mineral grains are assigned with fine mechanical parameters(quartz,feldspar,mica)obtained from nanoindentation tests;each mineral grain is randomly distributed in the model according to its actual proportion of the granite(obtained from X-ray diffraction tests)through a script file;the elastic modulus of the granite model is calculated quickly and efficiently by using Esay PBC plug-in.By calculating the elastic modulus of the granite model,a transition bridge between the fine and macroscopic mechanical parameters of granite is established.The calculation results of the numerical calculation method of this paper and the traditional homogenization theory method are compared by three arithmetic cases,which validate the feasibility of the numerical calculation method of this paper and provide a new method for upgrading the scale of mechanical parameters of granite nanoindentation test.