Influence of carbon fiber topographical roughness in epoxy based composite interfaces

The interface between carbon fiber and polymer matrix is a critical aspect of ultimate mechanical performance in carbon fiber reinforced composites. Molecular dynamics simulations have been instrumental in elucidating molecular-level details of the fiber-matrix interface, and have informed surface treatments that enhance interfacial shear strength. Almost all prior simulation efforts used few-layer graphite as a carbon fiber surrogate, and hence have yet to predict realistic mechanical response under shear load conditions for realistic pristine fiber-matrix interfaces. Here, atomistic carbon fiber surface models that feature intrinsic topographical complexity are interfaced with a typical epoxy resin to capture the influence of surface roughness at the composite interface. Both the lengthscale and character of carbon fiber surface roughness is found to affect the structuring of the liquid precursor epoxy, leading to changes in the cured network. Substrate displacement simulations of rough composites yield physically reasonable values of interfacial shear stress compared with previously published data for functionalized composite interfaces, providing a benchmark for future simulation work. The results suggest that treatments such as oxidation and functionalization may be impacted by the presence of intrinsic carbon fiber surface roughness, and should be accounted for in future simulations.