Predicting the Enhancement in the Compressive Strength of Carbon Fiber Reinforced Polymer Composites by Overwrapping Multiwalled Carbon Nanotubes using a Multiscale Approach

摘要

The high tensile strength of polymer matrix composites (PMC) is derived primarily from the high strength of the carbon fibers embedded in the polymer matrix. Fibers typically have high strength in tension. However, their compressive strength is generally much lower due to the fact that under compression, the fibers tend to fail through micro-buckling (or kinking) well before compressive fracture occurs. One approach to improve properties of the fiber/matrix interface in a PMC is the so-called "fuzzy fiber" concept, where carbon nanotubes (CNT) are grown directly on the carbon fiber through CVD. But, this often leads to degradation of in-plane fiber properties due to the high processing temperatures. In this work, we consider multi-walled CNT sheets (MWNTS) wrapped around carbon fiber at room temperature to improve fiber/matrix interfacial properties which, in turn, influences compressive strength of the composite. To investigate the effect of the wrapping of CNT sheet on composite strength, an atomistic model of a representative volume element (RVE) was developed to study the interface region between the epoxy (Epon-862), carbon fiber and the scrolled MWNT sheets. Molecular Dynamics (MD) simulations were performed on this model using the LAMMPS software to study its behavior under shear deformation. After proper equilibration, a uniform shear strain was imposed on the MD model with appropriate boundary conditions at room temperature. The compressive strength of the unidirectional composite was computed using a novel hierarchical multi-scale model comprising of the rule of mixtures at the microscale, and the modified Argon's formula for composites at the macroscale. Model predictions were benchmarked through comparison with experimental data for different volume fractions of MWNT sheet.