This work reviews the effects of z-Pins used in composite laminates as through-the-thickness reinforcement to increase the composite’s properties in the out-of-plane direction. The paper presents the manufacture and microstructure of this reinforcement type while also incorporating the impact of z-Pins on the mechanical properties of the composite. Mechanical properties include tensile, compression, flexure properties in static, dynamic and fatigue loads. Additionally, mode I and mode II properties in both static and fatigue loading are presented, as well as hygrothermal, impact and compression after impact properties.

Carbon nanotubes (CNTs) because of their properties are alleged to be the key candidate additives for improving the mechanical properties of polymers and carbon fibre reinforced polymers (CFRPs). Nevertheless in order for the reinforcing effect of the nanotubes to be of practical use, the CNTs have to be mixed with the matrix material. In the current work an effort was made to chemically graft Multi-Wall Carbon Nanotubes (MWCNTs) on the actual reinforcing Carbon Fibres (CFs) in order to skip the sometimes complex mixing stage. Two different solutions were used in order to treat/prepare the CNTs; a) an acid solution of H ₂ SO ₄ /HNO ₃ and, b) a toluene solution. The treated CFs were added to each solution, sonic bathed with deionised water and then dried in an oven. The resulting CFs were examined under SEM and both the solutions used proved to be reasonable successful with further investigation/optimisation to be necessary.

Microcapsule-based carbon fiber reinforced composites were manufactured by wet layup, in order to assess their mechanical properties and determine their healing efficiency. Microcapsules at 10%wt. containing bisphenol-A epoxy, encapsulated in a urea formaldehyde (UF) shell, were employed with Scandium (III) Triflate (Sc (OTf)3) as the catalyst. The investigation was deployed with two main directions. The first monitored changes to the mechanical performance due to the presence of the healing agent within the composite. More precisely, a minor decrease in interlaminar fracture toughness (G_IIC) (−14%), flexural strength (−12%) and modulus (−4%) compared to the reference material was reported. The second direction evaluated the healing efficiency. The experimental results showed significant recovery in fracture toughness up to 84% after the healing process, while flexural strength and modulus healing rates reached up to 14% and 23%, respectively. The Acoustic Emission technique was used to support the experimental results by the onsite monitoring.