Interfacial failure mechanisms in aramid/epoxy model composites

By monitoring the peak position of strain-sensitive Raman bands, Raman spectroscopy can be used to study the distribution of stress or strain along discontinuous aramid fibres fully embedded in an epoxy resin matrix from which the interfacial shear stress can be calculated. The technique has been used to study the effect of fibre tensile properties and applied surface treatments upon the efficiency of stress transfer from the matrix to the fibre. At low levels of matrix strain the distribution of stress or strain along the fibre can be defined using classical shear lag theory from which the effect of fibre modulus can be distinguished. Values of interfacial shear stress were found to be higher for those fibres pretreated with an epoxy solution. This may be attributed to changes in the matrix properties in the vicinity of the fibre/matrix region. In the case of the untreated fibre samples interfacial failure was initiated by yielding of the fibre/matrix interface followed by debonding at the fibre ends. The behaviour was modelled using a modified shear lag analysis.