Creep of discontinuous fibre composites II. Theory for the steady-state

Abstract

A simple theory is developed to explain the results of paper I, for the steady-state creep of a fibre composite containing alined discontinuous fibres. Rigid and creeping fibres are considered and also the effect of sliding at the interface. The physical basis of the theory is that due to the presence of the fibres the rate of shearing of the matrix is increased. An assumption is made that this increase is inversely proportional to the fibre separation. It is shown that the assumption is not critical for large values of the exponent relating strain rate and stress of the matrix. The theory accounts for the experimental results in paper I, predicts how the strain rate sensitivity of the composite will depend on those of fibre and matrix and reduces to a known form for a Newtonian fluid.