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.