Issue 50

J. Papuga et alii, Frattura ed Integrità Strutturale, 50 (2019) 163-183; DOI: 10.3221/IGF-ESIS.50.15 163 Focused on New Trends in Fatigue and Fracture Differences in the response to in-phase and out-of-phase multiaxial high-cycle fatigue loading Jan Papuga, Martin Nesládek, Jiří Kuželka, Josef Jurenka Dept. of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Czech Rep. jan.papuga@fs.cvut.cz, papuga@pragtic.com , http://orcid.org/0000-0001-9569-4997 martin.nesladek@fs.cvut.cz, http://orcid.org/0000-0003-4606-5849 jiri.kuzelka@fs.cvut.cz , http://orcid.org/0000-0002-2864-9683 josef.jurenka@fs.cvut.cz A BSTRACT . This paper discusses the phase shift effect occurring between two and more load channels of multiaxially loaded specimens. The discussion concludes that there is an extreme shortage of good experimental data that would prove the existence and the trend of the phase shift effect in the high- cycle fatigue region. It is no wonder that there are so many fatigue strength estimation criteria that use quite different computational concepts, because the response to the phase shift effect in the experimental base is often hidden in a conglomeration of other interacting effects. The paper presents results of a sensitivity study that compares the fatigue strength estimation results for various such criteria for the same stress amplitudes, but for different phase shifts between the push-pull and torsion load channels. These results show that, with the exception of criteria that assume a zero phase shift effect, the phase shift affects the results of each studied fatigue strength estimation criterion in a different way. A proposal for an experimental setup that would show the real trend unambiguously, and that would enable researchers to check the multiaxial fatigue strength criteria is provided in the paper. K EYWORDS . Proportional loading; Non-proportional loading; Out-of-phase loading; Phase shift; Multiaxial fatigue; Fatigue strength. Citation: Papuga, J., Nesládek, M., Kuželka, J., Jurenka, J., Differences in the response to in-phase and out-of-phase multiaxial high- cycle fatigue loading, Frattura ed Integrità Strutturale, 50 (2019) 163-183. Received: 30.11.2018 Accepted: 24.07.2019 Published: 01.10.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION hat basic conditions must be met before any multiaxial fatigue strength criterion can be classified as good enough? The use of multiaxial criteria is a response to any loading that causes stress/strain tensors to have more than one dominant component. If the loading is proportional, various effective stress/strain values can be chosen to express the overall load effect (see e.g. Tab. 8 in [1]). Non-proportional loading is a more demanding load case. It can be caused by several load channels acting simultaneously, but not in the same phase, not in the same mutual proportion or not with the same load wave shape. The FKM-Guideline [2] defines a separate load class of synchronous loading, where only W