Seawater effects on interlaminar fracture toughness of glass fiber/epoxy laminates modified with multiwall carbon nanotubes

Abstract

In this work, the effect of seawater ageing on mode I and mode II interlaminar fracture toughness ( $G_{IC}$ and $G_{\mathit{IIC}}$ ) of prepreg-based woven glass fiber/epoxy laminates with and without multiwall carbon nanotubes (MWCNTs) has been investigated. The first part of the investigation reports the moisture absorption behavior of multiscale composite laminates exposed to seawater ageing for ∼3912 h at 70 °C. Then, the results of mode I and mode II fracture tests are presented and a comparison of $G_{IC}$ and $G_{\mathit{IIC}}$ for each type of material group and condition is made. Experimental results showed the significant effect of seawater ageing on $G_{IC}$ of multiscale composite laminates due to matrix plasticization and fiber bridging. The improvement in $G_{IC}$ of the wet glass fiber/epoxy laminate was about 50% higher than that of the neat laminate (without MWCNTs) under dry condition. It was also found that the presence of MWCNTs into composite laminates promotes a moderate increase (8%) in their $G_{\mathit{IIC}}$ as a result of the additional toughening mechanisms induced by CNTs during the delamination process. Scanning electron microscopy analysis conducted on fracture surface of specimens reveals the transition from brittle (smooth surface) to ductile (rough surface) in the morphology of composite laminates due to the influence of seawater ageing on the polymeric matrix and fiber/matrix interface.