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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measurement and testing. S-N lines are constructed from laboratory fatigue test data using statistical evaluation. Service stress spectra are obtained by analyzing measured data during operation. If service spectra are not available so-called design stress spectra can be used. Representative information about the service loading of the assessed structural nodes of the bodywork can only be obtained on the basis of long-term measurement. For this purpose, a system for online monitoring of the service loading of structures is being developed Stress spectra are converted to fatigue damage using cumulative damage rules which have been proposed by various authors for instance Palmgren (1924), Miner (1945) and Haibach (1970). 2. S-N lines of welded bus bodywork nodes 2.1. Past approach There are databases of S-N lines that were collected in the past during cooperation with various former (IKARUS, KAROSA) and current (SKODA) bus manufacturers. The basis was exclusively experimental research, i.e. the realization of laboratory fatigue tests of various structural-technological versions of welded body joints. The concept of nominal stresses was preferred. An example of experimentally determined sets of S-N curves (S-N lines) is shown in Fig. 1. Case studies based on these results were recently presented by Kepka and Kepka jr. (2021).

Fig. 1. The sets of S-N curves from past projects.

2.2. Current approach It is usually difficult to measure the nominal stress on the finished vehicle bodywork. That is why current projects (e.g. in cooperation with manufacturers SOR and SOLARIS) already include detailed FEM analysis and detailed experimental stress analysis during laboratory tests of welded bodywork nodes. Three typical design nodes were investigated in detail during the development of the new SOR articulated electric bus. The research on their strength and fatigue life was carried out at the Laboratory of Strength and Fatigue Life of the Regional Technological Institute (the research center of the Faculty of Mechanical Engineering at the University of West Bohemia in Pilsen).