2. Fatigue Crack Growth Behaviour of Epoxy Nanocomposites—Influence of Particle Geometry

In this study, surface-modified spherical nano-silica and K-fluoro hectorites (O/K-hect), characterised by large lateral extensions and aspect ratios, were employed to analyse the effect of geometrical appearance on the fatigue crack growth (FCP) behaviour of an epoxy resin. The addition of nano-silica improved the FCP behaviour by nanoparticle debonding and subsequent plastic void growth. The number of particles contributing to toughening increases remarkably with rising stress intensity factor due to plastic zone enlargement. The improvement in crack propagation resistance by the use of the large O/K-hect, even at very low amounts (2.2 vol%) has to be highlighted. The main toughening mechanism is crack deflection due to the large lateral extension being in the range of the plastic zone size. Especially in the region of crack initiation and stable crack propagation, the clay tactoids reduce the propagation of the damage zone in front of the crack tip remarkably, resulting in a hugely enhanced crack resistance of the nanocomposites.