Influence of resin properties on interlaminar shear strength of glass/epoxy/MWNT hybrid composites

Samples of glass fiber epoxy composites made with resin containing 0.5 wt.% multiwall carbon nanotubes (MWNTs) have shown enhanced interlaminar shear strength relative to unmodified epoxy when evaluated using compression shear test. Improvement in the interlaminar shear strength (ILSS) of the composites can be due to an increase in the matrix shear strength or an increase in the fiber–matrix interface strength or both. In this work, we conducted tests to assess the relative contributions of the matrix shear properties and the glass fiber–epoxy interface to the ILSS enhancement. Samples of reinforced matrix were prepared by dispersing 0.5% MWNT by weight in epoxy. Both the reinforced resin and neat resin control samples were subjected to identical ultrasonic agitation. Shear properties of the neat epoxy film and the MWNT reinforced epoxy film were investigated using a shear punch tests on miniature specimens (6.4 mm diameter, 0.5 mm thick). The strength of the fiber–matrix interface for both modified and unmodified matrix was also characterized using the microdroplet test. The results show that the change in ILSS is primarily due to the contribution from the strengthening of the fiber matrix interface and not from a change in the matrix shear strength.