Mode I and II interlaminar critical energy release rates in all-carbon interlayer unidirectional fibre-hybrids based on ultrahigh-modulus and high-strength fibres

Delamination resistance governs the damage mode in interlayer hybrid composites. The interlaminar critical energy release rates (CERR) G(Ic) and G(IIc) are for the first time reported for the different interfaces in hybrids composed of ultrahigh-modulus, low-elongation (LE) carbon fibre layers and high-strength, high-elongation (HE) carbon fibre layers in an epoxy matrix. The G(Ic) and G(IIc), values at the LE/LE interface were several times lower than for the HE/HE. The G(Ic) of the LE/HE interface was0 close to that of the HE/HE interface, whereas its G(IIc) was significantly higher than the average of those of the LE/LE and HE/HE interfaces, and 1.5 times higher than LE/LE value. This synergy should be taken into account for the design of LE/HE carbon fibre UD hybrids featuring stable pseudo-ductile behaviour.