Effect of surface treatment upon the pull-out behaviour of aramid fibres from epoxy resins

A detailed study has been undertaken of the pull-out behaviour of aramid fibres with different surface characteristics from blocks of an epoxy resin matrix. The fibres employed had either no surface treatment (HM), a standard surface finish (HMF) or had been treated with a special epoxy-based adhesion-activating finish (HMA). The point-to-point variation of axial fibre strain along the fibres both inside and outside of the resin matrix has been determined from stress-induced Raman band shifts. This has enabled the distribution of interfacial shear stress along the fibre/matrix interface to be determined and, in combination with scanning electron microscope analysis of the specimens following pull-out testing, the failure mechanisms to be elucidated. It is found that pull out of the HM fibre takes place by a debond propagating along the fibre/matrix interface at a low level of interfacial shear stress. The HMF fibre showed better adhesion to the epoxy matrix with pull out occurring in a complex manner through both separation of the fibre skin and failure at the fibre/finish interface. No evidence of debonding was found for the HMA fibre and failure occurred by fracture of the fibre at the point where it entered the resin block. (C) 2000 Kluwer Academic Publishers.