Prediction of the creep properties of discontinuous fibre composites from the matrix creep law

Existing theories for predicting the creep properties of discontinuous fibre composites with non-creeping fibres from matrix creep properties, originally based on a power law, are extended to include an exponential law, and in principle a general matrix law. An analysis shows that the composite creep curve can be obtained by a simple displacement of the matrix creep curve in a log a vs. log t diagram. This principle, that each point on the matrix curve has a corresponding point on the composite curve, is given a physical interpretation. The direction of displacement is such that the transition from a power law to an exponential law occurs at lower strain rate for the composite than for the unreinforced matrix. This emphasizes the importance of the exponential creep range in the creep of fibre composites. The combined use of matrix and composite data may allow the creep phenomenon to be studied over a larger range of train rates than would otherwise be possible. A method for constructing generalized composite creep diagrams is suggested. Creep properties predicted from matrix data by the present analysis are compared with experimental data from the literature.