An experimental investigation of multi-functional z-pinned carbon-epoxy composites

Carbon fibre reinforced epoxy composites have high specific strength, stiffness and fatigue resistance whilst being durable and corrosion resistant, and these properties make them suitable for light-weight aerospace structures. Despite the many advantages, there are some factors that limit the use of composites in aircraft structures. Carbon-epoxy laminates are susceptible to delamination cracking due to the low strength and toughness properties of the epoxy matrix and the fibre-matrix interface. Delamination cracks can grow under relatively low interlaminar loads resulting in a potential threat to the structural integrity and safety of composite structures. Other problems with using carbon-epoxy composites in aircraft structures are their low electrical and thermal conductivities.<br><br> This PhD project aims to experimentally characterise a multi-functional carbon fibre-epoxy laminate that combines high delamination resistance with increased thermal and electrical conductivities. These properties are controllably improved using z-pins, which are thin composite or metal rods inserted in the through-thickness direction of the laminate. The effects of the volume content, diameter, length and material properties of z-pins on the delamination fracture toughness, fatigue resistance, impact damage tolerance, and interlaminar strengthening mechanisms are systematically investigated. In addition, the influence of the material properties and concentration of z-pins on the through-thickness electrical and thermal conductivities of carbon-epoxy laminates is determined. Using this information, it is possible to design multi-functional composites with tailored damage tolerant and electrical/thermal properties.