Large versus Small Grain Sizes on Fatigue Life of Aluminum Aircraft Wheels

The high cycle fatigue behavior of an aluminum alloy of small and large grains was investigated. Samples of small and large grains were provided as rotating bending fatigue test specimens. The samples were tested at eight different stress levels from 103 MPa (15 ksi) to 345 MPa (50 ksi) with a 34 MPa (5 ksi) increase at each level. As-received samples were evaluated for optical microstructural analysis. Scanning electron microscopy (SEM) images were used to evaluate the fractured surface of several samples. High cycle fatigue S-N curves were generated. The fatigue test results showed that grain size has a strong influence on the fatigue life. The high cycle fatigue S-N curves of small grains showed better fatigue life as compared to large grains in the lower stress levels. At higher stresses, the situation was reversed.