Influence of hygrothermal ageing on the mechanical properties of unidirectional carbon fibre reinforced powder epoxy composites

A systematic investigation was carried out in this work to evaluate the effect of seawater ageing on the mechanical properties of different composites manufactured with three types of unidirectional carbon fibres, based on a novel powder epoxy system. The flexural behaviour of the samples with and without accelerated seawater ageing was evaluated. A significant strength reduction due to seawater ageing was observed in the composites. Changes within the materials are also evaluated by interlaminar fracture toughness testing and dynamic mechanical thermal analysis. Interlaminar fracture toughness mode-I testing using the Double Cantilever Beam (DCB) test, revealed that the interfacial adhesion differences in combination with the moisture uptake could alter the fracture resistance of the composites, hence emphasising the importance of the interfacial bonding strength. A Finite Element analysis was carried out to gain insight on the important modelling parameters, for mode I dominated failure, and compared with the experimental results. Fracture surface examination by scanning electron microscopy revealed delamination, fibre debonding/bridging and plasticising of resin due to seawater effect.