Modelling the stress–transfer efficiency of carbon–epoxy interfaces

This study involved the investigation of the micromechanics of reinforcement of model carbon fibre–epoxy composites using the technique of remote laser Raman microscopy. The technique allows in situ axial stress monitoring in highly crystalline fibres, such as carbon or Kevlar®. Model composites were subjected to incremental tensile loading, while the stress in the fibre was monitored at each level of applied strain. The stress–transfer regime was studied in the elastic domain using a model single–fibre composite, where a fibre of finite length (i.e. of a length smaller than the coupon gauge length) was embedded along a resin coupon. A shear lag approach was employed to model the stress–transfer efficiency of the interface through the use of the shear–lag parameter β. The stress build–up in the fibre in the presence of energy dissipation mechanisms such as fibre fractures was modelled, and the stress–transfer efficiency was quantified at different levels of applied composite strain. Parallels between the interfacial efficiency of single–fibre systems and practical composites are drawn.