Influence of Anodic Layers on Fatigue-Crack Initiation in Aluminium

Abstract Polycrystal1ine 1100 and high-purity single-crystal aluminium samples were anodized to give oxide thicknesses between 200 and 1500 A, then subjected to low-cycle fatigue in high-humidity and vacuum environments. An ultrasonic method was used to identify crack initiation. Fatigue in a vacuum produces oxide cracks that are wider and fewer in number and results in an increase in fatigue life. Although the mode of fracture of both oxide and matrix is strongly dependent upon oxide thickness, it was found that neither the cycles to crack initiation nor the total fatigue lives were dependent upon oxide thickness.