Numerical Simulation Of Local Electro-mechanical Response Of CNTs Filled Conductive Polymer Composites

The electro-mechanical response of conductive carbon-nanotube-polymer composites(CNT-CPCs)is vital when they are used as smart-sensing materials.Clarifying the variation mechanism of tunnel resistance between two CNTs under strain is of great significance for the quantitative design of piezoresistivity of such materials.Many existing researches have proposed three electro-mechanical response mechanisms of CPCs:1.the change of tunnel resistance between conductive fillers;2.the change of conductive network in the composite;3.the inherent piezoresistivity of fillers.For CNT-CPCs,the former two are main mechanisms.Among the existing approaches,numerical simulation and experiment are suitable for studying different conductive mechanisms.And numerical simulation method will be used in this paper to explore the interaction between CNT and matrix under deformation,and analyze its influence on the changing trend of CPCs’ equivalent resistance.The main work is as follows:1.Two three-dimensional models with hollow cylinders and solid cylinders,which represent CNTs,are constructed and put into a cuboid representative volume unit.Then mechanical simulations based on different Elastic modulus and Poisson’s ratios of the matrix are carried out in ANSYS software.2.Based on the tunnelling resistance theory,a set of software for automatically searching and adding tunnel elements are developed using APDL and C++language.Using our method,3D simulation of the local electro-mechanical response of CNTCPCs is realized,which simplifies the calculation process and improves the efficiency.3.Different tunnelling resistances before and after deformation are calculated with simulation results.Changes of tunnelling resistance,tunnelling distance,d,and tunnelling area,A,are compared.And key factors affecting the electro-mechanical responses of CNT-CPCs are analyzed.Simulation results show that the local electro-mechanical response between CNTs is sometimes monotonic and sometimes non-monotonic,which is related to the Elastic modulus and Poisson’s ratio of the matrix and the angle,θ,between tunnel resistance and strain.The main conclusions are as follows:1.Hollow CNTs may deform in the radial direction under strain,which leads to different local electro-mechanical responses of CNT-CPCs.The classical simulation scheme using solid model or one-dimensional beam model can not reflect this deformation,which leads to the calculation error and covers the non-monotonicity of part of the electro-mechanical response in some cases.2.The Elastic modulus ratio of CNT to the polymer matrix directly determines the radial deformation of CNTs under strain.The variation of CNTs’ curvature will lead to the change of the distance,d,and the tunnelling area,A,between CNTs which directly affect the tunnelling resistance.Influences of the change of d and A on tunnelling resistance are sometimes consistent and sometimes opposite.For the cases with smallθ,the local tunnelling resistance first increase and then decrease with the compression strain when the Elastic modulus of the matrix is high.On the contrary,the resistance decreases monotonously when the Elastic modulus of the matrix is low.3.When θ>0,the Poisson effect of the matrix will lead to the relative displacement between CNTs.And its effect is maximum when θ=90°.Poisson’s ratio and Elastic modulus of the matrix are important parameters that lead to the negative GF value of CNT-CPCs.The larger the Poisson’s ratio of the matrix is or the smaller its Elastic modulus is,the more obvious the trend of negative GF is.The different monotonous and non-monotonic local electro-mechanical response trends of CNT-CPCs and their influencing factors described in this paper play an important role in the accurate design and control of the piezoelectric properties of this kind of composites.