ABSTRACT
Low Cycle Fatigue (LCF, 103 ≤ N≤ 105) and High Cycle Fatigue (HCF, 105 ≤ N≤ 105) are based on different failure mechanisms. LCF is characterized by local plastic deformations whereas HCF failure is the result of linear elastic deformations. This is not considered in respective standards yet. In addition, no clearly defined intersection between static and fatigue design as well as between LCF and HCF design is given. In the Eurocode 9 (DIN EN 1999-1-3) LCF- and HCF-design checks are both carried out with nominal stresses, whereby mean stresses are taken into account by a bonus factor. Within a two-year research project at TUM the objective was, to analyze and improve the available EN-Fatigue Concepts for aluminum details and to explore the intersection between static and HCF as well as between LCF and HCF. In a first step, the databank ALFABET (Aluminum Fatigue Behavior Evaluation Task), developed in 1996 was reconstructed, verified with old testing reports and completely revised. In a second step, fatigue tests were carried with specimen made of aluminum alloys EN AW-5083 O/H111, EN AW-6063 T66 and EN AW-7020 T6. Next to parent material, also butt welded and cruciform joints were tested. Since welded details are categorized in dependence of weld geometry and weld quality, they were investigated by means of laser scanning and evaluated in respect to imperfections. The results were finally compared with EN design lines and fatigue data from ALFABET. For the intersection between static and fatigue design, a load cycle number Np considering the alloy type was derived. Furthermore, it was observed, that material characteristics and stress ratio significantly influence the LCF performance.
