Quasi-Static and Cyclic Interlaminar Cracking Behavior of Glass Fiber/MWCNT/Epoxy Hybrid Composites

The objective of this investigation is to evaluate the effect of multi-walled carbon nanotubes (MWCNTs) on the interlaminar cracking behavior of S-2 Glass fiber reinforced composites made with two different carbon nanotube modified epoxy matrix materials in quasi-static and cyclic loadings. Two types of MWCNTs were used: pristine long CNTs and carboxyl-functionalized short CNTs (COOH-CNTs). COOH-CNTs were also mixed into epoxy at 2 weight % and applied as a discrete interlayer between fiber reinforced plies. The mode I and mode II interlaminar cracking behaviors in quasi-static and cyclic loadings were characterized by the double cantilever beam (DCB) specimens and the end-notched flexure (ENF) tests, respectively. The quasi-static test results showed improvement in mode I onset fracture toughness by adding either type of CNTs and improvement in mode II onset fracture toughness by adding COOH-CNTs. The cyclic test results showed slower crack growth rate in both mode I and mode II cyclic loading for the COOH-CNT reinforced composite. Microscope analysis of the fracture surfaces showed better dispersion of the COOH-CNTs than the pristine CNTs in the epoxy resin.