Abstract
This work considers the strength of the carbon fibre in unidirectional composites containing a mixture of glass and carbon fibres, commonly termed Hybrid Composites. It has confirmed earlier reports of enhancement of the failure strain of the carbon fibre in hybrids with respect to similar composites which contain only carbon fibre. The main objective has been to investigate the relationship between the mechanical properties and the ratio of the two reinforcing fibres and their state of dispersion. Hybrid-composites covering a wide range of dispersion and ratio have been fabricated and tested. The strength of the carbon fibre reinforced plastic phase (cfrp) in the hybrid composites can be explained by a model which considers the statistical probability that the individual (micro) fractures which occur at flaws in the carbon fibres will lead to a gross fracture. This model allows the strength of the cfrp to be related to the strength of single fibres, and predicts the trend of decreasing strength as the volume of the individual cfrp component is increased. Laminates of equivalent size, but containing carbon fibre alone are weaker, and do not follow this trend. This behaviour is not fully understood but is thought to be governed by defects introduced during fabrication. The work has also investigated the microscopic and macroscopic mechanisms of failure, with an emphasis on the redistribution of load when fractures occur in the cfrp components of the hybrids. This is important in understanding their overall load/extension behaviour and in determining whether failure is progressive and controlled as opposed to catastrophic.