Recently, several studies have concluded that the variational method of Nairn is the best among the available analytical models for predicting the stress fields in and around an isolated short fibre embedded in a polymer matrix. However, the variational method is not exact and has several limitations for its application as a data reduction tool for the fragmentation test. The main limitations of the variational model arise because matrix plasticity, debonding and frictional effects which are observed during fragmentation cannot be included. A comprehensive model, known as the plasticity effect model, has been developed which incorporates these aspects into the variational model. It has been argued that the interfacial debonding and shear yielding of the matrix can co-exist in a single fibre composite, thereby, requiring a three zone stress transfer model which can predict the stresses in the bonded and debonded regions along with the shear yielded region of the matrix at and near the fibre-end. Thus, the plasticity effect model is an improvement over the partial debonding model of Piggott which considers stress transfer in the bonded and debonded region; ignoring shear yielding of the matrix at the end of the fibre. The predictions of the plasticity effect model are compared with those from an elastic-plastic finite element model. A glass fibre/epoxy system is used to evaluate the features of the model. The plasticity effect model can be used to analyse the results of laser Raman spectroscopy on single short or continuous-fibre model composites and to develop a data reduction technique to measure fibre-matrix adhesion from the fragmentation test.
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