Prediction of interfacial shear strength of CNT overwrapped carbon fibers using molecular dynamics and Fourier series decomposition of surface asperities

This paper aims to develop a novel approach to determining the fiber/ matrix interfacial shear strength (IFSS) due to both carbon fiber rough-ness and the presence of carbon nanotubes (CNTs) in the matrix of a polymer composite in the form of a fiber overwrap. Under an atomic force microscope (AFM), the carbon fiber surface exhibits multi-scale asperities extending from a nanometer to several microns, likely caused by shrinkage during the graphitization process. Therefore, a Fourier series decomposition of the surface asperity data is performed to model these asperities present at various wavelengths on the fiber resulting in an amplitude and wavelength corresponding to each Fourier series term, effectively capturing the surface roughness over the entire spectrum of wavelengths. Furthermore, Molecular Dynamics (MD) simulations were performed to determine the interfacial shear strength of any subcomponent asperity of a specific amplitude and wavelength. Using MD data, governing equations were developed to compute the length-scale-averaged shear strength for a carbon fiber with any given surface asperities from the interfacial shear force for each of these subcomponent wavelengths. The results show that the presence of CNTs enhanced the IFSS by about 19% overall for a given surface asperity profile compared with the case without CNTs. [GRAPHICS]