Energy Absorption Performance of Meso-Scale Discontinuous Carbon Fibre Composites

Discontinuous carbon fibre composites are increasingly being considered for use in automotive crash energy management structures. Discontinuous fibres represent a route to high speed, low cost automated manufacture, either in the form of moulding compound, advanced moulding compound or directed fibre preforming approaches. In this work 40 discontinuous 6K high strength carbon / epoxy tubes have been preformed and manufactured for testing. Variables were fibre length (30mm, 60mm, and 90mm), specimen shape (circular or square) and thickness (2.54mm and 5.08mm). Mouldings were cut into 4 specimens and tested both quasi-statically at 1.6e-4m/s and dynamically at 5m/s. Average specific energy absorption (SEA) was 62.5kJ/kg for static and 43kJ/kg for dynamic. The optimum fibre architecture was a circular tube profile with 30mm long fibres and 5mm wall thickness which gave SEA values of 80.2kJ/kg and 48.4kJ/kg. In-plane mechanical testing was also performed on planar versions of the same fibre architectures to determine whether mesoscopic homogeneity effects which dominate tensile testing affect the energy absorption levels, but poor correlation was observed between tensile and energy absorption results.