Prüfung und Bewertung der Schwingfestigkeit von dünnwandigen Strukturen bei sehr hohen Schwingspielzahlen

Translated title of the contribution: Fatigue testing and assessment of thin-walled structures at very high number of cycles

Florian Himmelbauer

Research output: ThesisDoctoral Thesis


Digitalisation helps to improve the performance and robustness of large engines for sustainable energy and transport systems, but it places the highest demands on measurement and control technology. In general, a trend towards miniaturisation is observed here, small and thin components play a decisive role. Therefore, this work investigates and assesses the deformation behaviour and the fatigue strength in the Very High Cycle Fatigue (VHCF) regime, i. e. number of cycles N > 10^7 cycles, of component-like structures with a minimum wall thickness of 100 µm at room temperature (RT) and 350°C. New, innovative testing techniques for specimens and components operating at test frequencies in the range of 1 kHz enable VHCF tests to be carried out within one to two weeks. The characterisation of the high-strength steel X5CrNiCuNb16-4 on a specimen basis reveals noticeable differences between RT and 350°C in terms of deformation behaviour, notch sensitivity and VHCF properties. While unnotched specimens show a reduced fatigue strength along with internal cracking at 350°C, notched specimens exhibit a higher fatigue strength for 10^7 cycles at 350°C compared to RT. The VHCF behaviour of notched specimens is characterised by a predominant surface crack initiation and a low fatigue strength decrease between 10^7 cycles and 10^9 cycles, which is more pronounced at 350°C (-10 %) than at RT (-5 %). The evaluation of existing material modelling and fatigue strength assessment concepts confirms the transferability of specimen data to 100 µm thin structures made of X5CrNiCuNb16-4. A combined hardening approach leads to significant improvements in the simulation process, but geometric influences prove to be dominant. Regarding the fatigue strength assessment, the application of support factor concepts based on the relative stress gradient is recommended. However, established approaches show deficiencies in taking elevated temperature and the VHCF behaviour into account. Hence, a new engineering applicable VHCF assessment concept for thin-walled notched structures is presented. The experimental validation reveals a significantly increased fatigue strength of the structure at 350°C compared to RT. The model correctly predicts this fact. All estimates of the fatigue strength in the VHCF regime are on the conservative side, with a maximum deviation of approximately 6 %. The new testing techniques, the findings on transferability and the new assessment concept provide a valuable contribution to the future dimensioning of thin-walled components in the VHCF regime.
Translated title of the contributionFatigue testing and assessment of thin-walled structures at very high number of cycles
Original languageGerman
Awarding Institution
  • Montanuniversität
  • Brand, Clemens, Co-Supervisor (internal)
  • Stoschka, Michael, Assessor A (internal)
  • Leitner, Martin, Assessor B (external)
  • Grün, Florian, Supervisor (internal)
Publication statusPublished - 2023

Bibliographical note

no embargo


  • High-frequency fatigue testing
  • Fatigue strength assessment
  • Thin-walled structures
  • 17-4PH
  • Very High Cycle Fatigue
  • High temperature fatigue

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