Large scale deformation of fibre reinforced composites (Mg alloy/Al2O3 fibres) has been observed after creep in bending at 310°C. The deformation is considered in terms of the continuum theory of fibre reinforced materials in which only elastic deformation occurs in the fibres but the matrix is allowed to deform in shear. It is shown that the continuum theory is capable of accounting for time-dependent microcracking or fracture when creep is allowed for. However, the continuum theory does not predict two stage creep or the shear cracking which was observed in the experiments. It is necessary to consider microstructural features in order to explain many aspects of the observations and some of these are considered. In particular, damage accumulates at the fibre-matrix interface and this is thought to lead to an increase in the creep rate after a critical deformation.
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