Fibre-hybrid composites are composed of two or more fibre types in a matrix. Such composites offer more design freedom than non-hybrid composites. The aim is often to alleviate the drawbacks of one of the fibre types while keeping the benefits of the other. The hybridisation can also lead to synergetic effects or to properties that neither of the constituents possess. Even though fibre-hybrid composites are attractive, they also pose more challenges in terms of materials selection than conventional, single fibre type composites. This review analyses the mechanisms for synergetic effects provides guidance on the fibre and matrix selection and describes recent opportunities and trends. It finishes by describing the current applications, and by contrasting how the industrial use is different from the academic research.

Experimental results are presented which allow the hybrid effect to be evaluated accurately for thin ply carbon/epoxy-glass/epoxy interlayer hybrid composites. It is shown that there is an enhancement in strain at failure of up to 20% for very thin plies, but no significant effect for thicker plies. Hybrid specimens with thick carbon plies can therefore be used to measure the reference carbon/epoxy failure strain. The latter is significantly higher than the strain from all-carbon specimens in which there is an effect due to stress concentrations at the load introduction. Models are presented which illustrate the mechanisms responsible for the hybrid effect due to the constraint on failure at both the fibre and ply level. These results give a good understanding of how variability in the carbon fibre strengths can translate into hybrid effects in composite laminates.status: accepte