Mode-II fatigue response of AS4/8552 carbon /epoxy composite laminates interleaved by electrospun nanofibers

Abstract The advantages of applying electrospun nylon 6,6 as a toughening agent in epoxy-based composite laminates have been considered already under quasi-static mode-I and mode-II fracture loads. In the present study, the fatigue behavior of unidirectional carbon/epoxy laminates interleaved by nylon 6,6 is investigated under mode-II loading. To this aim, a 50-μm nylon 6,6 nanofibrous mat was put between mid-layers of a carbon/epoxy laminate, and then quasi-static and cyclic loadings were applied on End Notched Flexure (ENF) samples to investigate the onset of delamination growth and crack propagation rate (da/dN) under different ratios of GIIin/GIIC. The results showed that the mode-II fracture toughness increased about 161% under quasi-static loading tests. Additionally, the fatigue test results proved that the crack propagation was 14–27 times slower in the modified sample (with the same GIImax) because of the bridging between composite layers caused by nanofibers. Different fractography techniques including optical microscopy, microscopic 3D surface scanning device, and scanning electron microscopy (SEM) were also used to explore further the toughening mechanism.