Multiscale Modeling of Multifunctional Carbon Nanotube Reinforced Polymer Composites

Download or read book Multiscale Modeling of Multifunctional Carbon Nanotube Reinforced Polymer Composites written by AHMED ROWAEY Rowaey Abdelazeam ALIAN and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, novel multiscale modeling techniques have been successfully developed to study multifunctional nanocomposite polymeric materials. Interfacial, mechanical, electrical, and piezoresistive properties of carbon nanotube (CNT)-reinforced polymer composites were investigated using molecular dynamics (MD), micromechanics, and coupled electromechanical modeling techniques. Additionally, scanning electron microscopy was used to determine the morphology and dispersion state of a typical CNT-epoxy composite. Based on these measurements, realistic nanocomposite structures were modeled using representative volume elements (RVEs) reinforced by CNTs with different aspect ratios, curvatures, orientations, alignment angles, and bundle sizes. At the nanoscale level, the interfacial shear strength was determined via pull-out MD simulations. Additionally, the stiffness constants of a pure polymer, pristine and defective CNTs, and an effective fiber consisting of a CNT and a surrounding layer of polymeric chains were determined using the constant-strain energy minimization method. The obtained atomistic mechanical properties of the composite constituents were then scaled up using Mori-Tanaka micromechanical scheme. Monte Carlo simulations were conducted to determine the percolation and electrical conductivity of RVEs containing randomly dispersed CNTs. An advanced search algorithm was developed to identify percolating CNT networks and transform them into an equivalent electrical circuit formed from intrinsic and tunneling resistances. A solver based on the modified nodal analysis technique was then developed to calculate the effective conductivity of the RVE. Finally, the electrical model was coupled with a three-dimensional finite element model of the RVE to determine the coupled electromechanical behavior of the composite under tensile, compressive, and shear loads from the resistance-strain relationship. The outcome of the developed modeling approach revealed that: the elastic modulus of a nanocomposite reinforced with well-dispersed straight CNTs was found to increase almost linearly with the increase of their volume fraction and double at CNT volume fraction of 5.0 %; the combined effect of CNT waviness and agglomeration results in a significant reduction in the bulk properties of the nanocomposite; CNTs with grain boundaries perpendicular to the tube axis experience 60% reduction in its mechanical strength; and the nanocomposite gauge factor can reach up to 3.95 and is sensitive to loading direction and CNT concentration.