High modulus carbon fibre composites: Correlation between transverse tensile and mode I interlaminar fracture properties

This paper presents test results from mode I interlaminar fracture and transverse tensile tests on unidirectional carbon/epoxy composites used in racing yacht construction. Fibre modulus has been varied from 380 to 640 GPa. PAN fibre reinforced composite properties, delamination resistance (GIc and GIp) and transverse strain to failure, decrease as fibre modulus increases. Composites based on the highest modulus pitch fibres show higher transverse failure strains than the highest modulus PAN fibre composites. A distinct failure mechanism, crack propagation within the fibres, was observed for the pitch based reinforcement. The transverse tensile tests allowed transverse fibre modulus to be estimated as 11.5 GPa for the PAN and 9 GPa for the pitch fibres. These results indicate that more detailed study is needed if pitch based composites are to be optimised.