Investigating the load transfer in carbon nanotube-reinforced nanocomposites
|關鍵字:||奈米複材;多尺度模擬;力量傳遞效益;剪力遲滯模型;奈米碳管;Nanocomposites;multi-simulation;load transfer efficiency;shear lag model;carbon nanotube|
In CNT nanocomposites, the efficiency of the load transfer from the matrix to the carbon nanotubes (CNTs) plays an important role in the mechanical response, since it can influence the efficacy of the nano-reinforcements. In multi-walled carbon nanotubes (MWCNTs), not only the outer, but also the inner graphene layers may be responsible for supporting the load. The loading capacity of the inner layers may therefore also influence the overall performance of the nanocomposites. This study aims to investigate the load transfer efficiency and stress distribution in CNT nanocomposites from the surrounding matrix to the CNTs, using shear lag model analysis and multi-scale simulation methods. Both single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) were considered in the investigation. A cylindrical representative volume element (RVE) containing the CNTs and matrix phases was employed in the shear lag analysis; using this, a characterization was made of the axial stress distribution and the load transfer efficiency in the CNTs. To investigate the atomistic interactions between the adjacent layers, the effect of the interlayer interactions on the stress transfer efficiency in the interior layers of DWCNTs (in the nanocomposites) was considered. CNTs have nanoscale dimensions, but in composites the matrix is often regarded as a bulk material; the load transfer efficiency within DWCNTs was therefore investigated using a multi-scale simulation scheme. The multiscale simulation consisted of two steps. First, the atomistic interactions between the adjacent graphite layers in DWCNTs were characterized using a molecular dynamic (MD) simulation, from which a cylindrical equivalent continuum solid of DWCNTs with embedded spring elements was proposed to describe the interactions between neighboring graphene layers. Two kinds of interatomistic properties—van der Waals (vdW) interactions, and artificially built covalent bonds—were considered in the equivalent DWNT solid. The equivalent solid was subsequently implemented as reinforcement in a micromechanical model of CNT nanocomposites, to allow an evaluation of the load transfer efficiency to be made. The effects of the number of layers, the atomistic interactions between the graphite layers, and the aspect ratio of the CNTs on the load transfer efficiency were investigated. The results indicated that SWCNTs exhibited a superior load transfer efficiency compared with MWCNTs, for the same CNT volume fraction in the nanocomposites. This was attributed to the fact that in MWCNTs, the load carrying capabilities reduce as the number of graphitic layers increases. Moreover, it was revealed that the inferior load transfer efficiency properties of the MWCNTs were not improved, even when covalent bonds were constructed between the graphite layers.
|Appears in Collections:||Thesis|