Untersuchung und Modellierung der Lebensdauer unter nichtproportionaler mehrachsiger Wechselbeanspruchung

Abstract

The behavior of high-alloy chromium-nickel steel 1.4909 (AISI 316 L(N)) was studied under multiaxial non-proportional fatigue loading with a fixed principal axis system. Particular attention was paid to the effects of various phase shifts on the material behavior. The experiments were performed using a test facility described in detail in Section 3. Due to its conception, this test facility guarantees a temporarily invariant principal axis system even in case of non-proportional experiments. In the facility, non-proportional multiaxial fatigue tests were performed with variable load horizons and variable phase shifts. Depending on the phase position, considerable differences in lifetime were obtained at the same equivalent plastic strain range. Considering the hydrostatic part of loading, the different number of cycles to failure at the same equivalent strain load were explained by additional or reduced hardening due to non-proportional multiaxial loading. Two parameters characteristic of these two effects have been defined, which are combined in the newly established multiaxiality factor f m . This multiaxiality factor expresses the difference of the individual experiments as compared to the uniaxial case. Using this parameter, a modified Manson-Coffin model was formulated. In addition and based on the work of McDowell and Bennet, a micro fracture mechanics crack propagation model has been developed, the micro crack propagation assumptions of which are in very good agreement with the test results obtained. By implementing the above-mentioned multiaxiality factor in this model, accuracy of the latter was improved considerably. After this, the models developed were compared with several approaches to lifetime prediction under multiaxial fatigue loading known from literature. As far as accuracy was concerned, the models developed were found to be of high quality.