DEFORMATION MICROMECHANICS IN HIGH-PERFORMANCE POLYMER FIBERS AND COMPOSITES

The use of Raman spectroscopy to study both the deformation micromecha nics 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, alth ough the technique can be applied to a wide variety of high-performanc e fibres. It is found that the peak position of the 1610 cm-1 Raman ba nd in aramid fibres shifts to lower frequency under the action of tens ile stress or strain owing to the macroscopic deformation leading to d irect stretching of the polymer molecules. These strain-induced band s hifts can be used to map the distribution of stress or strain along a discontinuous, aramid fibre inside an epoxy resin matrix, and this all ows the interfacial shear stress to be calculated. It is shown that th e behaviour is consistent qualitatively with that predicted by the cla ssical Cox-type shear-lag analysis. The power of the Raman technique i s demonstrated by showing that it can be used to follow the effect of matrix yielding, fibre fracture and changes in fibre-matrix adhesion u pon the micromechanics of deformation as such phenomena cannot be pred icted using classical shear-lag analysis.