The fatigue crack propagation of high strength aluminum alloys subjected to variable amplitude loading is strongly influenced by sequence effects. For a reliable evaluation of the sequence effects, an exact knowledge of the changes in the mechanical and physical conditions of the material surrounding the crack becomes necessary. To allow greater understanding of these processes, two aspects which are based on recent crack propagation investigations are considered in the present study.

First, a verification of a new detailed stress and displacement analysis based on continuum mechanics is attempted by displacement measurements using a special grid technique. The experimental results coincide well with the analysis predictions. That means, that the mechanical processes are a predominant cause of the sequence effects.

Secondly, a systematic variation of the microstructural crack propagation mechanism of aluminum alloys is used for an evaluation of the influence of the microstructural mechanisms on the sequence effects. The results show that there is an essential influence, which can lead to significant deviations in the crack propagation behavior from that as predicted by continuum mechanics.