Evaluation of composite interfaces using Raman spectroscopy

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. The three main test methods that are generally used for the analysis of micromechanics in polymer-based composites systems are the fragmentation, pull-out and microbond tests. The values of interfacial shear strength determined using different test methods are found to be dependent upon the variation of localised 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 Raman bands in both aramid and carbon fibres can be used to determine the point-to-point variation of axial fibre strain along such fibres embedded in epoxy resin matrices from which the interfacial properties can be derived. 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 characterise the interfacial properties of model epoxy composites deformed using different micromechanical test methods. It is demonstrated how this technique has the capability of revolutionising our interpretation of composite micromechanics and the different micromechanical test methods.