Micromechanical phenomena during hygrothermal ageing of model composites investigated by Raman spectroscopy. Part II: comparison of the behaviour of PBO and M5 fibres compared with Twaron

Raman spectroscopy combined with gravimetry has been used to investigate hygrothermal aging in model composites based on an epoxy resin containing a single filament of a polymeric fibre. Two fibres have been studied-PBO and M5-using two specimen configurations: The diffusion slab (DS) and the double fibre pull-out (DFPO). Time evolutions of the Raman strain profiles ε(x,t) and the water uptake M(t) have been determined for specimens immersed in liquid water. Simple micromechanical models developed for rationalising data obtained for Twaron are used to process measurements for PBO and M5 (PIPD). In this manner, a direct comparison of the time evolutions of the moisture uptake M(t), mid-fibre strain ε(x=0,t), the dimensionless Raman shear lag-parameter n and a debond length Ld allows conclusions to be drawn on the aspects of hygrothermal ageing such as durability of a fibre/matrix interface and fibre swelling.