Micro-Raman study of the fatigue and fracture behaviour of single PA66 fibres: Comparison with single PET and PP fibres

The micro/nano-structural evolution before and after tensile loading, fatigue and ultimately, failure has been studied by Raman microspectroscopy for PA66, PP, PBO and PET single fibres and precursors, using two probes: low wavenumber collective modes at <150 cm−1 as representative of the crystalline and amorphous chains and stretching and bending modes, as representative of the C–C bond local behaviour. Wavenumber and bandwidth distributions across fibre/precursors diameters reveal different types of skin/core heterogeneity. The in situ analysis at different strain levels shows that amorphous chains in the fibre accommodate the stress differently. Slight tensile straining is observed for crystalline PA 66 chains, and compression for PP and PET chains indicating different local chain architectures. The post mortem analysis of a series of fibres failed in fatigue tests shows that amorphous domains are highly stressed during the failure and a remnant stress can be measured.