Shear lag models for discontinuous composites: fibre end stresses and weak interface layers

A new shear lag (SL) type model for stress transfer in a composite with cylindrical fibres is derived. It accounts for fibre end stresses in an approximate yet realistic manner, and leads to a new formula for predicting the Young’s modulus of the composites. The predictions of this model were found to agree well with data for metal matrix composites (MMCs) with fibres of various aspect ratios. The accuracy and relative simplicity of the new model have been exploited in the development of an approximate analytical model for the stress transfer and macroscopic yield stress of a composite that contains a weak layer in the matrix adjacent to the reinforcement. With the aid of the latter model, the proof stress of MMCs which contain a precipitate free zone (PFZ) around the reinforcement, can be studied; experimental data obtained for aged 8090 MMCs is consistent with the model predictions.