| Nano-indentation test can reveal the mesoscopic influence mechanism of macro-mechanical properties of rocks,and also indirectly obtain the macro-mechanical parameters of rocks.Granite,limestone and mudstone are three typical common rocks with great strength differences,which are highly representative.Therefore,it is of great theoretical significance and potential engineering application value to carry out research on the influence of nanomechanical properties and defects of these three rocks on nanoindentation properties.Scholars have studied a lot on the mechanical properties of these three kinds of rock,and formed relatively mature theories.However,with the development of rock mechanics and the deepening study of related issues of rock engineering,it is found that some phenomena in practical engineering are closely related to the microscopic mechanism of rock materials,such as the water disintegration characteristics of rock.Scholars have studied the failure characteristics of rock microstructure through microscopic experiments,and combined with the results of macroscopic mechanics,the corresponding problems have been studied and analyzed,and a wealth of research results have been given.However,these methods either qualitatively analyze the microscopic mechanism of the macroscopic mechanical properties of rocks,or indirectly give the macroscopic and microscopic relations of rocks through microscopic tests and introducing parameters such as fractal parameters.Nanoindentation test can directly measure the micromechanical parameters and reveal the micromechanical influence mechanism of the macroscopic mechanical properties of rock.It can also indirectly obtain the macroscopic mechanical parameters of rock,providing a new method for the study of the macroscopic mechanical properties of rock.In this paper,limestone in a certain area of Shaanxi Province,granitic gneiss in the northern Qinling Tunnel section of the Hanjiwei Project and red-bed mudstone in Yunnan region are selected as the research objects.The micromechanical properties of the three types of rocks are studied by nano-indentation test,and the variation rule is obtained:(1)The elastic deformation of the red mudstone sample is the largest.Granite-gneiss hardness is relatively large,the rock strength is strong,toughness is poor,brittleness is large;The hardness of limestone and red mudstone is relatively small,so the rock strength is weak,the toughness is good,and the brittleness is small.(2)The variation law of the nano-level load-displacement curves of the three types of rock samples is basically the same in each stage.In the load retaining stage,the displacement change of granitic gneiss is the least,that is,the creep variable is the least,followed by limestone,and the creep variable of red mudstone is the largest.The microstructure morphology of the three types of rock samples was obtained by SEM scanning.The conclusions are as follows:the size of indentation morphology on the surface of granitic gneiss,limestone and red mudstone decreases successively.From the microscopic point of view,granitic gneiss is mineral particles bonded together by ionic bonds.Limestone is formed when large mineral grains are cemented by small ones.Red mudstone is formed by mineral particles cemented by clay minerals.Based on ABAQUS software,the process of nanoindentation test was simulated by numerical simulation method,and the influence of defects on the characteristics of nanoindentation test was studied.The results are that the strain concentration will occur near the defect when the defect is relatively large;The location of the defect has an effect on the test.In the test process,try to avoid dots around the defects to avoid test errors. |
