Simulation Study On Mechanical Properties Of CNTs/HA Composite Material For Bone Repair

With the continuous improvement of living standards,people pay more attention to their health problems.Compared with cancer and cardiovascular diseases,bone defects are not highly dangerous,but they can easily lead to limb dysfunction or even paralysis,which will seriously reduce the survival quality of patients.In recent years,with the development of medical technology and the emergence of new biomedical materials,bioactive ceramics are gradually becoming the main alternative implants for bone transplantation because of superior biomedical properties.Carbon nanotubes reinforced hydroxyapatite composite,as a new types of bone repair material,has received extensive attention in biomedicine and materials science.Representative volume element(RVE)is a concept on meso-level,and its function is to reflect the macroscopically effective properties of the material with the average properties of the meso-structure.In this paper,CNTs/HA composite is the research object.By establishing a RVE model of CNTs/HA composite,the macroscopic material parameters of the material are solved using the finite element method.Firstly,the modeling method of CNTs/HA composite RVE model is studied,the random sequential adsorption(RSA)algorithm is improved to build the RVE model with periodic structure,and the efficiency of the improved algorithm is increased by more than 10 times.On the basis,the correct form of transformation matrix from the model space to the assembly space is deduced,and the modeling of the RVE geometric model is realized by the secondary development of Solid Works using VBA method.VBA is a development method using VB as interface language.Subsequently,the finite element modeling and analysis process of the CNTs/HA composite RVE model is introduced.For the RVE finite element model of the CNTs/HA composite,since it is impossible to divide complete periodic mesh,the general periodic boundary conditions are chosen.Based on the finite element theory,the mathematical form of the general periodic boundary conditions is re-derived,which makes up for the deficiencies in the original literature.Based on the direct homogenization theory,the corresponding finite element numerical integration format is derived to solve the equivalent elastic modulus and equivalent poisson’s ratio.The calculation results of the finite element model and the Halpin-Tsai classical theory are in good agreement,which shows the effectiveness of the finite element modeling and analysis method.Finally,the correlation of the equivalent modulus and equivalent poisson’s ratio of CNTs/HA composite with the volume fraction and aspect ratio of CNTs is calculated and analyzed.It is concluded that the equivalent modulus and equivalent poisson’s ratio have a linear negative correlation with the volume fraction of CNTs,but have nothing to do with the aspect ratio of CNTs.The reason why the equivalent modulus of CNTs/HA decreases with the increase of CNTs volume fraction is that the transverse elastic modulus of CNTs is too small,which makes the overall elastic property of CNTs weaker than that of HA.In addition,the transverse modulus of CNTs plays a major role in the equivalent modulus of CNTs/HA composite in the random distribution state.This phenomenon has a certain reference significance for reducing the stress shielding effect of artificial orthopaedic implants.At the same time,the difference between the isotropic fiber model and the transversely isotropic fiber model is compared.The results show that the isotropic fiber model will lead to higher calculation results of equivalent modulus,and the error can not be ignored,whitch shows that it is incorrect to convert CNTs to isotropic fibers.