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Improvement of service life estimation for multiaxially loaded safety components made of forged steel and cast aluminium by selecting appropriate calculation algorithms FKM 2013
Issue number 319
Project no. 291

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Abstract:
There is currently no
standardized approach to service life estimation for multiaxial loading. Depending on the respective design situation
(load characteristics, material, available input data,...), the
existing calculation methods differ in terms of their applicability and the quality of their results.
In the present research project, extensive fatigue strength tests and
material investigations were carried out and evaluated on the ductile quenched and tempered steel 50CrMo4 V and the rather brittle
cast aluminum alloy G-AlSi7Mg0.3 T6 in order to investigate material-dependent
effects in their impact on the service life under multiaxial loading
in more detail. In addition, various calculation methods were evaluated using selected test results
from the literature.
For the cases of multiaxial loading considered here, none of the
calculation methods investigated showed any general superiority with regard to the quality of the results. Methods contained in
standard software show accurate
results for certain applications, but exhibit greater inaccuracies for other cases. The more complex methods used here
did not show a generally better reliability of the calculated
lifetimes. A method further developed within this project (SSCH stress
space curve hypothesis) showed the comparatively greatest accuracy, but it is not yet
generally applicable for random stresses and stresses with different frequencies
. As part of the project, characteristic values were derived with
which can be used to characterize multi-axial stress states with regard to the degree of non-proportionality
. The
lifetimes calculated with different hypotheses were summarized and evaluated and a decision aid for the selection
of a suitable calculation method for the respective design situation
was created. This helps the engineer in practice to assess the expected accuracy of computational
multiaxiality hypotheses.
The objective of the research project has been achieved.