Measurement of thermal strains during compressive fragmentation in single-fibre composites by Raman spectroscopy

Raman spectroscopy has been used to evaluate thermal strains before, during and after the manufacture of single-fibre composites. The fragmentation of high-modulus carbon fibres embedded in polycarbonate is found to relieve strains in the fibres although the strain profile along the length is unaffected by the breaks, in agreement with a recently proposed compressive fragmentation model. Deviations from linearity on a weakest link theorem/Weibull statistics plot are considered to reflect both this strain-relieving mechanism and the efficiency of stress transfer across the interface. The lower residual strain in PTFE coated fibres with respect to the unmodified fibres is explained by this competitive mechanism.