Research On Nano-Indentation Test Of Find Macroscopic Properties Of Granular Materials

With the development of research methods,the research on the mechanical properties of soil has gradually shifted from macro to micro.At present,the study of soil material’s micro-scale has become an important topic.The study of micro-scale mechanical properties of materials has also attracted much attention not only in soil materials,but also in other material fields.In this context,Nano-indentation technology developed has become an important means for people to study the micro-mechanical properties of materials.Therefore,it has become a general trend to apply Nano-indentation technology to the study of micro-scale mechanical properties of soil materials,which is of great significance to the study of micro-scale mechanical properties of soil materials.However,the traditional Nano-indentation technology theory is applicable to the continuous materials at the corresponding test scale,but not directly applied to the discontinuous materials.In other words,it needs to be analyzed and corrected.Accordingly,an ideal composite material which has clear mechanical transfer mechanism after compression is needed to correct the theory of applying Nano-indentation technology to soil material.Therefore,in this paper,glass beads which have the same particle size are mixed with cementitious materials as the material framework.Then,an ideal composite composed of particles and cementitious materials is made through special arrangement.The mechanical transmission mechanism is clear,the strength is stable,and it is easy to analyze.During the experiment,load-displacement curve of the pressing head acting on the continuous material and the discontinuous material was obtained by changing the relative position of the indentation.On the basis of analyzing the characteristics of loading stage and unloading stage of load-displacement curve and combining with the traditional theory of Nano-indentation technology,we can draw a conclusion that there are essential differences of pressing head acting on skeleton particles and cementing materials lies in the different loading functions related to the profile of pressing head.Based on the two-dimensional model of composites proposed above,the loading function of Nanoindentation applied to idealized composites is derived.According to different loading models when the head ACTS on the framework particles and cements and the definition of material hardness and the calculation of elastic modulus in the theory of Nanometer testing technology,the elastic modulus and hardness of idealized composite materials are derived and calculated respectively.Finally,two important factors influencing the strength of local structure of idealized composites are cementation and particle arrangement.The results show:(1)When the head ACTS on the center of the skeleton particle and cementation,the P-h curve is different in the loading stage.This is mainly because when h is less than 1000nm,the indentation results are only affected by the single-phase material,skeleton particles.The pressing head is a conical pressing head,and its contour function USES the contour function corresponding to the conical pressing head.When h is over than 1000nm,there is an interaction between the two-phase materials,and the head can be abstracted as a cylindrical flat-bottomed head.The contour function of the head uses the corresponding contour function of the flat-bottomed head.(2)By analyzing the characteristics of loading stage of load-displacement curve when indentation is applied to different positions and combining with the two-dimensional stress section of the idealized composite material,several loading functions of the Nano-indentation technology applied to the idealized composite material are proposed.(3)The fitting loading function was obtained by fitting the part of data on the unloading curve of the load-displacement curve.After comparison,it was found that the fitting loading function obtained by the fitting of the experimental data was consistent with the loading function derived from the theory above.According to the loading model of different working conditions and the definition of material hardness and the calculation of elastic modulus in the theory of Nanometer testing technology,the elastic modulus and hardness of idealized composite materials are derived and calculated respectively.(4)The cementing strength of the composite material consists of the cementing strength itself and the cementing strength of the cementing material and the skeleton particles.And the local structural strength of the composite material decreases successively when EAV synthetic resin gels,polyethylene glycol 3000 and polyethylene wax are used.The arrangement of matrix particles has a certain influence on the local structural strength of the idealized composite material,which is shown that the structural strength of the composite material is higher when the matrix particles are loosely arranged than when the matrix particles are closely arranged.