Analysis of SiC fibres and composites using Raman microscopy

The application of Raman spectroscopy in the analysis of the microstructure of SCS-6 silicon carbide fibres using a Renishaw Raman microscope is descr ibed. It is demonstrated that the technique allows a detailed study to be m ade of the point-to-point variation in microstructure across a fibre sectio n. It has been possible to monitor the variation of the concentration of SI C and carbon in the fibre microstructure and to detect differences in the f orms of carbon present. It is also shown that Raman spectroscopy can be use d to follow the micromechanics of both the deformation of silicon carbide f ibres and of the fibres within a model composite. Well-defined Raman spectr a have been obtained from a variety of Nicalon and Tyranno fibres and the p ositions of the Raman bands shown to shift on the application of stress or strain. From such stress-induced Raman band shifts, the point-to-point vari ation of axial fibre stress or strain along an individual fibre in an epoxy matrix can be determined. An example is given of the use of the technique to map the distributions of axial fibre strain in a Nicalon/epoxy fragmenta tion test specimen and to model the failure processes at the fibre/matrix i nterface.