In this work carbon fiber/epoxy composites and MWCNT (multiwalled carbon nanotube)/carbon fiber/epoxy hybrid composites with 0.1, 0.3, 0.5 and 1 weight% nanotube filling of the matrix have been prepared and compared in terms of interlaminar properties. For the dispersion of the carbon nanotubes in the epoxy resin three roll milling has been utilized. The mechanical characterization has been carried out using standard DCB (double cantilever beam) tests assisted by acoustic emission. The test results have been evaluated by the conventional method provided by the standard and a novel method implementing acoustic emission signal localization for crack propagation tracing. According to the tests carbon nanotube filling of the matrix of the composites has a beneficial effect on their interlaminar properties: the interlaminar fracture toughness values of the composites have increased by a maximum of 13 and 33% at a 0.3 weight% carbon nanotube content of the matrix according to the conventional and AE based evaluation method respectively

The aim of this research was the investigation of the effect of carbon nanotube addition on the mode I interlaminar fatigue properties of carbon fiber reinforced composites. The authors developed a localization methodology to track the interlaminar fatigue crack front using the acoustic emission (AE) technique. According to the test evaluation the carbon nanotube reinforcement decreased the crack propagation rate by 69% compared to the composite containing no nanotubes. Besides that, the fatigue life also increased significantly, the nanotube reinforced composite could withstand 3.8-times more cycles to failure than the unfilled matrix composite