Ermüdungsverhalten von Aluminium-Schweißverbindungen im Bereich sehr hoher Lastspielzahlen

In the present thesis the Very High Cycle Fatigue (VHCF) behaviour of welded aluminium alloy joints is investigated. In this context the geometrical and microstructural notch as well as process-related defects play a significant role. A systematical separation of these notch effects is realized by means of high-frequency fatigue tests using welded samples with different weld qualities with and without trimmed weld reinforcement as well as unwelded, heat-treated smooth and notched samples. The study is able to prove that the influence of the microstructure on the fatigue behaviour of the welded seams increases with increasing number of load cycles. The cyclic strength as well as the failure mechanism of the base material differs sig-nificantly from the overaged heat-affected zone. Process-related defects like pores and incomplete fusions lead to VHCF-failure depending on the weld seam quality. The investiga-tions show that the geometrical notch is no longer the sole criterion for a reliable life assess-ment of welded seams in the VHCF-regime. Finally, an existing fracture mechanical and a notch stress concept are verified for the assessment of the fatigue strength of welded samples for very high numbers of loading cycles.