ANALYSIS OF THE SINGLE-FIBER PULL-OUT TEST BY THE USE OF RAMAN-SPECTROSCOPY .1. PULL-OUT OF ARAMID FIBERS FROM AN EPOXY-RESIN

Raman spectroscopy has been used to analyse the distribution of fibre strain in the single-fibre pull-out test by mapping the variation of s train along an aramid fibre undergoing pull-out from an epoxy resin ma trix. Both sized and de-sized aramid fibres have been used in room-tem perature and high-temperature cured resins. At low strains the behavio ur follows conventional shear-lag analysis but as the fibre strain is increased yielding can take place in the matrix at the fibre/matrix in terface. It is found that failure eventually takes place by either fib re/matrix de-bonding or fibre fracture outside the resin matrix. The p resence of radial stresses at the interface has been found to be impor tant. They are induced by thermal shrinkage upon cooling the hot-cured resin to room temperature and can also be caused by Poisson contracti on during the pull-out process. They result in the measured values of interfacial shear stress being significantly different from those foun d for fully-embedded fibres.