Avoiding free edge delamination in quasi-isotropic pseudo-ductile hybrid laminates - by material dispersion or layer angle dispersion?

Hybridisation is one of the approaches to introduce pseudo-ductility to brittle composite materials. In this approach, two or more different types of fibre are combined and if the configuration and material constituents are well selected, the tensile response shows a gradual failure and a metal-like stress-strain curve with a pseudo-yeild point. Different types of hybrid composites with continuous layers have been studied to produce pseudo-ductile tensile behaviour. However, most hybrid material studies to date have been focused on Uni-Directional (UD) laminates which are not usually applied in industry due to poor transverse mechanical properties. To make a multi-directional hybrid laminate, different approaches can be selected to mix different fibre types with different fibre orientations. In this paper, two approaches are presented and compared: (i) UD hybrid sublaminates used as the building blocks of hybrid laminates and (ii) dispersed orientation in which non-hybrid multi-directional sublaminates with different fibre types are stacked up. It is shown that the method of dispersed orientation significantly helps to reduce interlaminar stresses at the free edges of the tensile samples and therefore supresses free-edge delamination.