Effect of nanofiller alignment on the mode-I cohesive parameters of CNF-doped GFRP composites

Fiber reinforced polymer (FRP) composites with enhanced interlaminar fracture properties are crucial for many structural applications. Use of through-thickness nanofillers and their alignment are proven as beneficial to improve the out-of-plane fracture properties of laminated composites. However, the effect of nanofiller alignment on the traction-separation behavior of multiscale FRPs is still unknown. In this study, we investigated the effect of carbon nanofiber (CNF) alignment on the mode-I interlaminar fracture toughness (ILFT) and cohesive parameters of unidirectional glass fiber reinforced polymer (GFRP) laminates. Double cantilever beam (DCB) specimens of control GFRP and electric field-aligned CNF-doped GFRP were fabricated, and the aligned CNFs enhanced both the initiation and steady-state ILFT by 80.4% and 21.1%, respectively. Scanning electron microscopy of fracture surfaces indicated the multiscale fiber bridging as one of the key toughening mechanisms in aligned specimens. The cohesive parameters (traction separation law, TSL) were extracted using a DIC-based direct method and the peak traction of aligned CNF-doped GFRP specimens increased by 93.8% compared to that of control specimens. The experimentally obtained traction separation laws were utilized in numerical modeling (as tri-linear cohesive zone model) and the numerically predicted load–displacement responses of different specimens matched satisfactorily with experimental findings. The experimental identification of cohesive parameters considering effect of nanofiller alignment would certainly help in better failure prediction and safe design of laminated composites.