Flexural Properties of Epoxy and Epoxy-Based CFRP Filled with Carbon Nanotubes

The aim of this work was to determine the effect of carbon nanotubes (CNTs) on elastic and viscoelastic properties of epoxy resin used in CFRP in the matrix-dominated flexural testing mode. Two different compositions of RTM6 epoxy resin and CNTs (0 and 1% wt.) were prepared by ultrasonication method. Neat and CNTs containing CFRP specimens [0/45/90/-45](2) were prepared by resin transfer moulding. Three point bending tests were carried out for nanocomposite (NC) and CFRP specimens at room temperature in quasistatic and cyclic creep regimes. Four cycles of gradually increasing stress equal to app. 25, 50, 75, and 90% of flexural strength were used for loading during 30 min followed by 30 min of unloading. The main effect of CNTs was observed for the reduction of creep compliance of epoxy (40%) and CFRP (30%), especially at higher stress levels. Furthermore the results obtained for NC showed an increase in flexural modulus by 11%, reduction of strain at break and flexural strength by 28 and 20%, accordingly, in relation to CNTs content. CFRP with 1% of CNTs showed slight improvement in flexural modulus (by 9%) and strength (16%) in comparison with the neat CFRP.