Un-notched and notched tensile response and damage accumulation of quasi-isotropic carbon/epoxy hybrid laminates made of ultra-high modulus and intermediate modulus carbon fibre/epoxy thin-ply prepregs were studied. It was confirmed that the ply fragmentation demonstrated previously in unidirectional hybrids as a successful pseudo-ductility mechanism can be transferred to multi-directional laminates. Furthermore, reduced notch sensitivity was demonstrated in quasi-isotropic specimens for both open holes and sharp notches as a result of local ply fragmentation around the notch

Mode II fracture energy, GIIC, is a critical parameter for determining the propagation of delamination in composite laminates. Its value can be affected by Through-Thickness Compression (TTC) stress acting on the crack tip and here this effect has been studied using IM7/8552 carbon/epoxy laminates with cut central plies. External TTC loads were applied through bi-axial testing. Unidirectional (UD) cut-ply specimens were used to determine the TTC enhancement factor, ηG, for GIIC. A similar enhancement effect was also found in Quasi-isotropic (QI) specimens with 2 extra cut central 0° plies inserted into the layup. The TTC enhancement factor was implemented in a Finite Element Analysis (FEA) framework using cohesive interface elements, showing that the determined ηG can be successfully used to model the effect of TTC on delamination.

A novel, purpose-designed, thin interlayer glass/carbon-epoxy hybrid composite sensor concept is presented here that can be used for structural health monitoring (SHM), offering potential for safer operation in service. The hybrid composite sensors indicate the overload of a structure by exhibiting a change in their appearance when loaded in tension over a predefined strain value. The sensors can be attached to a component either as a structural sensing layer or integrated locally as demonstrated in this study through real-life applications. Furthermore, various test methods have been utilised to characterise the bonded-on sensors including mechanical testing, Digital Image Correlation (DIC) and Acoustic Emission (AE) measurements. An optimal configuration has been identified with the utilised materials that 2 can potentially be used in applications such as sporting goods, civil engineering structures (e.g. truss and bridge elements) as well as pressure vessels.

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