Enhanced damage tolerance and fracture toughness of lightweight carbon-Kevlar fiber hybrid laminate

Low damage tolerance and residual strength are the main drawbacks of carbon fiber composite laminates that limit their application in many lightweight structures. This study demonstrates the exceptional damage tolerance and high fracture toughness of carbon-Kevlar hybrid laminate, where Kevlar plies are placed between two carbon fiber face sheets. Flexural strength after damage and mode I translaminar fracture toughness of carbon and Kevlar and the hybrid laminates were evaluated using three-point bending and single-edge notched bending tests, respectively. The damage mechanisms in the three configurations were investigated using micro-computed tomography and correlated with their mechanical responses. The results showed that the hybrid laminate could sustain 70% of the laminate strength after fiber damage occurs and can sustain the same strength for large strains, unlike carbon and Kevlar fiber laminates, where they both lose their mechanical integrity after fiber breakage. Moreover, this laminate showed 200% and 170% larger specific absorbed energy than carbon and Kevlar laminates, respectively. The improvement can be justified by the propagation of fiber breakage at three different positions in the Kevlar core and the delamination at the carbon-Kevlar interface that allowed larger energy dissipation during fracture. Additionally, it showed 21% and 42.7% larger absolute and specific fracture toughness, respectively, than the carbon fiber laminate.