Application of raman microscopy to the analysis of high modulus polymer fibres and composites

Raman microscopy has been used to study the deformation of carbon fibres and an experimental grade carbon-fibre/PEEK composite prepreg. It has been found that the peak position of the Raman-active bands in the fibres are sensitive to the level of applied strain. Examination of the peak positions from the carbon fibres near the surface of the prepreg shows that the fibres are subjected to a residual compressive strain. The application of a tensile stress to the composite causes the fibre strain to become tensile although significant scatter is found in the measurements. The scatter is thought to be due to variations in the local carbon-fibre strain at the 1 μm level. It is demonstrated that residual compressive strain is expected from differential shrinkage between the fibres and matrix on cooling the composite from the processing temperature to room temperature.