Deformation micromechanics in high-volume-fraction aramid/epoxy composites

Abstract

It is shown that Raman spectroscopy is an excellent technique for analysis of the relationship between structure and deformation processes in both high-performance fibres and fibre-reinforced composites. It is demonstrated that Raman spectroscopy can be used to follow molecular deformation processes in Kevlar 49 aramid fibres through stress-induced band shifts. The shift of Raman bands in a high-volume-fraction unidirectional composite is analysed and it is found that there are significant variations in local fibre strain due to imperfections in the composite microstructure. Furthermore, it is shown that it is possible to map the local fibre strain distributions around a hole in the composite. The distributions of axial fibre strain have also been mapped in both a plain weave and a four-harness satin weave Kevlar 49/epoxy composite. Complex distributions of local fibre strain that follow the pattern of the repeat units of the woven structures are found. The power of the Raman technique to follow composite micromechanics is therefore demonstrated.