DEFORMATION MICROMECHANICS IN MODEL CARBON-FIBER-REINFORCED COMPOSITES .1. THE SINGLE-FIBER PULL-OUT TEST

Raman spectroscopy has been used to study the deformation micromechani cs of the single-fibre pull-out test for a carbon fibre/epoxy resin sy stem using surface-treated and untreated versions of the same type of PAN-based fibre. It has been possible to determine the detailed strain distribution along embedded fibres and it has been found that it vari es with the level of strain in the fibre outside the resin block. The variation of interfacial shear stress along the fibre/matrix interface has been determined using the balance of forces equilibrium and this has been compared with the single values of interfacial shear strength determined from conventional pull-out analyses. It has been demonstra ted that it is possible to identify situations where the interface is well-bonded, partially debonded or fully debonded and also to follow t he failure mechanisms in detail. It has been found that the level of i nterfacial adhesion is better for the surface-treated fibre and that, for the untreated fibre, interfacial failure takes place by the cohesi ve failure of a weakly-bonded surface skin that appears to be removed by the surface pretreatment process.