Manufacturing and characterisation of ultra-stiff composite material

Abstract

Lighter materials are needed to decrease fuel consumption in the transport industry. Conventional carbon fibre reinforced polymer composites have excellent stiffness-to-weight ratio, but are often discarded due to brittleness. This Master’s thesis work investigates a new concept of carbon fibre reinforced polymer composite material, which can prove to be lightweight, ultra-stiff, exceptionally strong and easy to mass-produce. The new material consists of chopped ultra-thin tapes of very stiff carbon fibres held together by polymer. The tape pieces are randomly distributed to give in-plane isotropy through uniform orientation distribution. To allow for characterisation of this concept, the composite material was manufactured by tapes falling randomly through a channel onto a step-wise rotating substrate to build preforms, which were formed and cured by a heat press into plates. The plates were dissected and characterised through thermal and chemical analysis, cross-section microscopy, mechanical testing and fractography. The manufactured material shows great potential with a near isotropic behaviour, average stiffness of around 65GPa and some measured tensile strengths in the vicinity of 500MPa. The high tensile strength is found to depend on two competing fracture modes: tape pullout and fibre tension failure. In conclusion, the material concept is promising and with a refined manufacturing method we can soon see a new field of composite materials.