Fatigue behaviour and residual stresses of thin laser-beam-welded magnesium-alloys under multiaxial loading

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The aim of the research project is to develop fatigue strength hypothesis appropriate for thin walled laser-beam magnesium welds subjected to multiaxial loading with constant and variable amplitudes and constant and varying principal stress directions. In the first project phase fatigue strength hypothesis for constant amplitudes were identified successfully. In the second phase suitable hypothesis for variable amplitude loading should be provided. As there is no knowledge about the fatigue behavior of magnesium welds under multiaxial and variable loading, besides analytic work on fatigue strength hypothesis, experimental work has also to be done.The determination of the entire residual stress condition is a fundamental part of the project. With experimental methods the residual stresses of the tubular specimens can only be determined up to a limited depth which is insufficient with regard to the detected crack initiation sites. Nev-ertheless the experiments are required to assess the accuracy of the calculated residual stresses. The FE-calculations have shown that the residual stress condition cannot be described easily with the existing evaluation models. The target of the upcoming work period is the investigation of the influence of the anisotropy of the magnesium on the residual stress generation and their stability. Furthermore investigations of the relaxation behaviour of the residual stress under different loads shall be carried.The results of the project close a gap of knowledge concerning magnesium welds and therefore reduce the relative deficit of magnesium compared to aluminum and steel. Hence, this could be the basis for better exploiting the lightweight potential of magnesium in the future and conserving energy and resources.