Entwicklung eines Prüfstandes zur Charakterisierung der Betriebsfestigkeit unter multiaxialer Beanspruchung

Due to a great variety in loading conditions during operation, components are relatively rare subjected to a purely uniaxial local stress state. In most cases, complex stress situations occur by a superposition of different loading types or due to the component geometry, such as geometric notches. The first part of the thesis deals with a classification of multiaxial stress states, as well as with the categorization of superimposed loads in regard to periodicity, proportionality and synchronicity. Furthermore, an overview of current methods for determining fatigue strength under multiaxial stresses is presented. The second part deals with the development of a test rig for characterizing the fatigue strength properties of round specimens, manufactured out of large crankshafts, under typical stress types such as bending, torsion and combined bending-torsion. An essential requirement to the test rig is an experimental test procedure under realistic conditions, so that the experimentally determined results can be transferred to the real operating situation. Under the application of finite element analysis and based on local strength assessments, the test rig was dimensioned and endurably designed. In the final part, experiments were conducted on representative notched round specimens of 50MnCr4. Considering the support effect and the highly-stressed volume, the statistically evaluated local fatigue strength shows a good agreement to existing results on small specimens of the same base material. This validation demonstrates the qualification of the developed test rig for the experimental characterization of multiaxial fatigue strength of round specimens and proofs the applicability for further investigations.