The interfacial properties of aramid/epoxy model composites

Many attempts have been made to measure, evaluate and improve the level of interfacial adhesion in aramid/epoxy composites. Different surface treatments have been developed in order to promote chemical bonding between the fibre and the matrix but it is found that most of the surface treatments developed have shown little or no improvement in the level of interfacial adhesion. The interfacial properties of a model composite are often determined by measuring the interfacial shear strength using micromechanical test methods that employ different loading configurations. However, the values of interfacial shear strength determined using different test methods are found to be dependent upon the variation of localized stress in the samples due to the different loading configurations and often give different results. Using Raman spectroscopy it is shown that the strain-dependent shift of the 1610 cm^–1 aramid Raman band can be used to determine the point-to-point variation of axial fibre strain along aramid fibres embedded in epoxy resin matrices from which the interfacial properties can be derived. The interfacial properties of aramid/epoxy model composites have been determined using Raman spectroscopy where the properties of the fibre, including different surface treatments, and the matrix have been changed systematically. The results are reviewed here and compared to those obtained using conventional micromechanical test methods. It is also demonstrated that the Raman technique can be used to characterize the interfacial properties of aramid/epoxy model composites deformed using different micromechanical test methods. In this way the interfacial properties can be determined at different loading levels enabling the progressive failure of the fibre/matrix interface to be monitored and defined accurately.