Deformation micromechanics in high-performance polymer fibres and composites

Abstract

The use of Raman spectroscopy to study both the deformation micromechanicsls of high-performance polymer fibres and of these fibres in model, single-fibre epoxy resin matrix composites is reviewed. The behaviour of aromatic polyamide (aramid) fibres is described as an example, although the technique can be applied to a wide variety of high-performance fibres. It is found that the peak position of the 1610 cm −1 raman band in aramid fibres shifts to lower frequency under the action of tensile stress or strain owing to the macroscopic deformation leading to direct stretching of the polymer molecules. These strain-induced band shifts can be used to map the distribution of stress or strain along a discontinuous, aramid fibre inside an epoxy resin matrix, and this allows the interfacial shear stress to be calculated. It is shown that the behaviour is consistent qualitatively with that predicted by the classical Cox-type shear-lag analysis. The power of the Raman technique is demonstrated by showing that it can be used to follow the effect of matrix yielding, fibre fracture and changes in fibre-matrix adhesion upon the micromechanics of deformation as such phenomena cannot be predicted using classical shear-lag analysis.