Stress corrosion cracking, and corrosion fatigue in aluminium alloy 7017 with and without residual stresses

Hermann, Reinhold (1986). Stress corrosion cracking, and corrosion fatigue in aluminium alloy 7017 with and without residual stresses. MPhil thesis The Open University.



This thesis presents recent work on the stress corrosion cracking of aluminium alloy 7017 with and without residual stresses, and some results on corrosion fatigue.

Chapter I contains a literature review of the stress-corrosion cracking (SCC) and corrosion fatigue (CF) cracking mechanisms. It explains techniques, practices and the conclusions reached when Al-Zn-Mg-(Cu) are employed in such tests. The latter part of the review is devoted to recent work in aluminium alloys containing residual stresses when subjected to cyclic loading.

In Chapter II a description is given of the properties of the alloy, followed by specimen design, environmental aspects of testing, tensile loading of specimens and the deliberate introduction of residual stresses to test pieces for both stress corrosion and corrosion fatigue studies.

Chapter III outlines the experimental results of SCC without residual stress. Here the kinetics of sub-critical crack growth are assessed by analysing the v-K curves of the alloy when stress-corroded in various moist air environments. The effects of pre-exposure to salt solution prior to loading is described in the light of these experiments.

Also in Chapter III corrosion behaviour is discussed where specimens are deliberately pre-loaded in compression prior to SCC testing. It is shown that crack growth can be achieved without bolt-loading. The effects of environment and morphology of fractures are described and compared with those of Chapter III.

Chapter IV examines the corrosion fatigue behaviour of the alloy under the influence of residual stresses and cyclic loading, with reference to crack -growth rates under compressive loading, frequency and pre-exposure effects. A model for assessing the residual stress ahead of the crack tip is suggested, using data from crack closure measurements.

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