PSI - Issue 42

Miloslav Kepka et al. / Procedia Structural Integrity 42 (2022) 687–693 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Different rules for fatigue damage calculation are used for different boundary conditions. A schematic representation of this boundary conditions is shown in Fig. 5. The approach according to Haibach, i.e. the use of a bilinear S-N curve, is preferred. Damage caused by cycles with small amplitudes, which occur very often, is taken into account. Only damage caused by cycles with very small amplitudes that are less than the considered threshold is neglected.

Fig. 5. Boundary conditions for calculating cumulative fatigue damage: a - Palmgren-Miner original, b - Palmgren-Miner elementar, c – Haibach.

3.2. Current approach Hultgren et al. (2021) published a comparison of two large-scale questionnaire surveys (from 2000 and from the present), which clearly showed that insufficient data about loading represents the biggest problem for the correct assessment of welded structures, see Fig. 6.

Fig. 6. Survey on challenges in fatigue design: (a) European Pressure Equipment Research Council in the year 2000, (b) Hultgren et al. (2021).

Their refinement represents the current biggest research challenge in this area. The authors of this article try to respond to this challenge as well. Together with other researchers are developing systems for on-line measurement and analysis of the operational loading of structures. The so-called OLIN measuring systems are based on the National Instruments CDaq modules. Software applications for recording, preprocessing and sending data are processed in the LabView programming interface environment. The functional sample OLIN_1, see Fig. 7, was successfully tested during the measurement of the SOR articulated electric bus prototype. Stress spectra representing the operation of an empty and fully loaded bus on standard public transport lines in Prague were measured and evaluated.