Enhanced extreme temperature bending and delamination resistance of GFRP composites through z-directional aligned nano-reinforcement: Emphasizing the effects of CNT functionalization

Abstract

Laminated FRP composites' weak out-of-plane mechanical performance prevents their usage in structural applications where homogeneous load bearing qualities are required. In this regard, a z-directional nano-reinforcement approach was implemented to mitigate the poor in-plane shear and out-of-plane response of laminated glass fiber epoxy (GE) composites under extreme in-service temperature conditions. CNT and functionalized CNT (FCNT) were dispersed separately in the GE composites' epoxy matrix and subjected to a z-direction electric field alignment treatment. Flexural and short beam shear tests of GE composites with random and aligned CNT/FCNT were performed at room temperature, in-situ cryogenic and elevated temperature conditions (RT, CT and ET, respectively). GE composite with aligned FCNT (A-FCNT-GE) consistently outperformed other composites at all considered temperatures with remarkable improvements, specifically ∼39%, ∼41% and ∼47% in flexural strength, and ∼30%, ∼30%, and ∼24% in interlaminar shear strength (ILSS) over the control GE composite at RT, CT and ET, respectively. Dynamic mechanical thermal analysis suggested that the synergetic impact of functionalization and alignment of FCNT improved the viscoelastic properties of the A-FCNT-GE composite across a range of temperature conditions. Fractography analysis provided insight into the interfacial and interlayer mechanisms that improved the extreme temperature condition mechanical performance. The reliability of electric field aligned FCNT as a z-directional nano-reinforcement in laminated composites at extreme temperature conditions was established in this study.