A model relating grain size to the endurance limit and non-propagating crack behaviour

A model is presented for determining the endurance limit and depth of non-propagating cracks in smooth aluminum specimens. The approach is based on the non-uniformity of surface strains and crack closure development. The model is used to explain the effect of decreasing endurance limit stress with increase in grain size for commercially pure aluminum. The predicted limits are in very good agreement with reported values. Likewise, the agreement is also very good for an aluminum alloy with pancake-shaped grains, provided that the smallest grain size is considered. At stresses below the endurance limit but above the nominal threshold stress non-propagating cracks form whose lengths may be predicted by the model.