Mechanical Behavior of Twisted Bilayer Graphene and Titanium Nanocomposites

Abstract

This study investigates the mechanical behavior of twisted bilayer graphene (TBLG) and its reinforced titanium matrix nanocomposites (TBLG-RT) through molecular dynamics (MD) simulations. Young's modulus and shear modulus of TBLG are systematically calculated for the first time, across twist angles from 0° to 30° with 1° increments. Our results demonstrate that while Young's modulus exhibits minimal angular fluctuations, tensile strength displays anisotropic behavior: decreasing in the zigzag direction yet increasing in the armchair direction with larger twist angles. Furthermore, the shear moduli show negligible angular dependence across the studied range. A critical finding is that TBLG manifests transversely isotropic material properties at a critical twist angle of approximately 29°∼30°. Consequently, TBLG with a 29.96° twist configuration is selected for titanium reinforcement in uniaxial tensile and shear simulations. and the TBLG with twist angles of 6.01° and 12.90° are used to verify the angle independence of TBLG-RT. The MD simulations reveal that even minimal TBLG volume fractions induce substantial mechanical property enhancements compared to pure titanium. However, significant discrepancies emerge between conventional micromechanical models (Rule of Mixtures and Halpin-Tsai) and MD-derived results at higher reinforcement fractions. To address this divergence, we propose modified versions of these models calibrated against MD simulation data, enabling more accurate predictions of TBLG-RT composite performance. Furthermore, the modified micromechanical models establish a computational framework for tailoring graphene-reinforced composites across length scales, bridging quantum-scale MD insights with macroscopic engineering applications.