Effect of pre-strain on the fatigue life of 7050-T7451 aluminium alloy

The effect of pre-straining of 1%, 3%, 5%, and 7% on fatigue life of 7050-T7451 aluminium alloy has been evaluated. Using dogbone unnotched flat specimens, axial fatigue tests were conducted under a constant amplitude sinusoidal wave loading at stress ratio of 0.1 in air at room temperature. The results demonstrate a tendency of fatigue life reduction with the pre-straining level. Optical microscopy analysis revealed that the pre-straining anticipates some microstructural changes occurring during fatigue testing, such as slipped grains and persistent slip bands (PSBs) formation, which are commonly related to fatigue life reduction. However, heterogeneities observed in the material make this reduction less prominent. Statistical analysis using a bootstrap method suggests also a reduction in fatigue life with increasing the pre-strain level.