Prediction of the longitudinal tensile strength of polymer matrix composites

A micromechanical model is presented for predicting the longitudinal tensile strength of polymer matrix composites. The model assumes strength is determined by fibre breaks within a representative volume element (RVE). Its length is equal to the so-called ineffective length, associated with the stress transfer to a broken fibre. An elastic-plastic stress transfer model is used to determine the ineffective length, while fibre strength is described by a Weibull distribution. The longitudinal tensile strength is then obtained by solving numerically an equation for the maximum load supported by the RVE. A closed-form expression was also obtained by neglecting elastic stress transfer and the contribution of broken fibres. The closed-form solution was found to be in very good agreement with the base model. In spite of the high level of uncertainty on model input data, model predictions agreed quite well with experimental strengths of carbon fibre composites.