Mixed experimental-numerical method for quantitative measurement of mode II fibre/matrix interface debonding and comparison of fibre sizings in single short fibre composites

In short fibre composites, debonding cracks usually initiate from fibre tips and their growth is governed by the properties of the fibre/matrix interface. These properties are ideally acquired from a model test similar to the real composite, while excluding the effects of fibre fractures and the induced debonding interactions. Therefore, in this study, debonding growth was examined in detail, using novel single short fibre specimens, which were fabricated using a new methodology. These experiments were further complemented with a continuous fibre case study, where the established single fibre fragmentation specimens were evaluated. The progression of debonding and pull-out damages versus remote stress was studied for two fibre sizings utilizing real-time in-situ polarized light microscopy. A finite element model was built to obtain the fibre/matrix interfacial fracture toughness considering thermal residual stresses, friction and matrix plasticity, and a very good correlation was obtained between the model and the experiments.