The Mechanical Property Of Diamond-like Nanomaterials And Its Application In Improving The Performance Of Cement-based Materials

The diamond-like nanomaterials with diamond cubic crystal structure have unique properties such as large specific surface area,high strength,high temperature resistance and so on,which are different from macroscopic materials.They can be used in the strengthening and toughening of composites to improve the physical and mechanical properties of composites.A multi-scale analysis model of diamond-like nanomaterials was established by using nano-mechanics to study the structural and mechanical properties of Si and SiO₂ nanomaterials.Then,the Si and SiO₂ nanomaterials were used in cement composites modification,and the toughening mechanism was studied by nanoindentation test.The main research contents are as follows:Based on the analysis of microstructure characteristics of Si and SiO₂nanomaterials,the high order Cauchy-Born rule is used to calculate the atomic bond length,the Tersoff-Brenner potential function is used to describe the role between atoms,the multi-scale constitutive model of diamond-like nanomaterials is established based on the energy minimization of basic structures,and the calculation program is written,and the structural and mechanical properties of Si and SiO₂ nanomaterials are systematically studied.The results show that:The results show that the elastic modulus of SCS varies with the crystal directions,anisotropy,but the value are very close in the directions[112]and[110].For the components in the plane and normal to the plane,both shear modulus and Poisson's ratio vary with direction for Si?110?plane and where they are the constant value for Si?111?plane.The value of shear modulus and poisson's ratio,in the crystal plane component for Si?111?,are greater than that normal to the plane component.The bending rigidity values change with the different of the bending direction in the crystal plane,except in the Si?111?plane where it has a constant value.With water reducing agent in cement-based materials as dispersant,cement composites were prepared by fully dispersing Si and SiO₂ nanomaterials into cement matrix.The nano-cement composite was made into a standard nano-indentation pattern,and the nano-indentation instrument was used to test the indentation of the sample.By analyzing the distribution law of hardness and elastic modulus of the array measuring points on the surface of the sample,the modification mechanism of the micro-mechanical properties of the cement matrix was studied.The experimental study concluded are as follows:the nanoSiO₂ and nanoSi enhance the macroscopic mechanical properties and durability of cement-based compoeite materials by increasing the content of HD C-S-H gels in the matrix.Besides,the modification effect of nanoSiO₂ and nanoSi to the cement-based materials is higher in the early than the later age.The results of indentation for nanoSiO₂ and nanoSi with different contents show that exists an optimal contents.With different age,the results show the age only caused the change of C-S-H gel packing density.