Single fiber push-out characterization of interfacial properties of hierarchical CNT-carbon fiber composites prepared by electrophoretic deposition

Electrophoretic deposition (EPD) of carbon nanotubes (CNTs) on carbon fibers has been implemented as a continuous process on laboratory-scale. The interfacial adhesion and fracture toughness of the carbon fibers in an epoxy composite is assessed by a modified single-fiber push-out test. A detailed energy analysis yields the different energy contributions in the push-out process. A comparison between CNT-deposited, as received and oxidized carbon fibers (passing through the EPD process without CNT) indicates that interfacial adhesion and fracture toughness are not affected by the different fiber treatments. Interfacial friction after fiber debonding, however, is significantly changed. This is confirmed by finite element simulation which has to include friction for reproducing the essential features of the load–displacement plots from fiber push-out. Scanning electron micrographs indicate little interaction between CNT and carbon fibers, but point to changes in surface roughness of CNT-deposited and oxidized fibers after push-out. Therefore, the cyclic loading–unloading fiber push-out test seems well suited to investigate the micromechanical behavior of carbon fiber composites and to discriminate and quantify the different energy contributions to the total load–displacement curves.