This paper discusses quantitative results from fatigue delamination tests (MMB) at unidirectional and cross-ply ply interfaces in carbon-fibre/epoxy-matrix laminates at three different mixed-mode loading conditions. The implications for material characterisation, structural design and certification are addressed. The results indicate the critical design parameter for delamination in thermoset-matrix composites under cyclic loading is the strain energy release rate threshold, G_(threshold). The results suggest that a design optimised for static loading with an appropriate safety factor would be approximately optimised for fatigue loading. This would significantly reduce the number of expensive time-consuming fatigue tests required for certification. The cost of fatigue testing may also be reduced by using accelerated test programmes at appropriate low-load cut-off levels, providing careful consideration is given to creep and environmental effects. There is scope for further optimesation by taking a stochastic approach to represent the local variations in toughness in delamination modelling.
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