The Fatigue Behaviour of Aluminium and the Effects of Surface Damage.

Available from UMI in association with The British Library. Both single and polycrystalline specimens of aluminium (Al) have been fatigued at a range of total strain amplitudes, both with and without prior surface indentation. Specimen surfaces have been studied by optical microscopy and scanning electron microscopy (SEM) for the formation of fatigue slip bands. Transmission electron microscopy (TEM) has been used to study the dislocation configurations resulting from fatigue and indentation. It is shown that close to unannealed indentations either a stable cell structure is formed or a very dense quasi-homogeneous dislocation distribution; PSBs do not form in these regions during fatigue in the range of amplitudes investigated. PSBs are formed in regions of moderate dislocation density which are found near annealed indentations, and at larger distances from both annealed and unannealed indentations. In addition to room temperature studies of Al, the dislocation configurations produced by fatigue at 77 K have been studied by TEM. The observed configurations after low strain amplitude fatigue at low temperature show considerable similarity to those found in other f.c.c. metals, such as copper (Cu) and nickel (Ni), after room temperature low amplitude fatigue. These configurations are quite different from those observed in Al after room temperature fatigue. A type of lattice dislocation configuration has been observed for the first time in Al fatigued at 77 K, and this can be related to multiple slip.