PSI - Issue 57

J. Baumgartner et al. / Procedia Structural Integrity 57 (2024) 618–624

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J. Baumgartner et al. / Structural Integrity Procedia 00 (2023) 000–000

3. Conclusions and outlook

As it becomes aware in the list of improvements and additions, the new version of the IIW-recommendations continues to be the one leading guideline for the fatigue assessment of welded joints and structures. Especially the consideration of welded thin sheets and the possibility to better assess post-weld treated structures (weld profiling and HFMI) broadens substantially the application range and exceeds other standards and guidelines. Even though a huge step was made, future research work is still necessary. Following main topics are still under investigation for which no generalized recommendations can be given: • The worst-case assumption of high tensile residual stresses is still the basis for the assessment and S-N data for the R -ratioof R = 0 . 5 is recommended for use. This assumption is still valid, since the numerical determination of residual stress states in complex structures needs currently a high numerical e ff ort or is even in the most cases impossible. So, no information on the residual stress state can be given during the design state. However, an approach could be set up that considers the (local) yielding of the material and subsequently a decrease in residual stress. • Some quality aspects of welds are currently indirectly considered by di ff erent FAT-classes, for example the weld profile at butt joints. Even though a first good attempt was made to correlate quality and fatigue [10, 11], the correlation is designated to one material thickness of t = 10 mm and the nominal stress approach. A more generalized approach would be helpful, as well as recommendations for the assessment of quality with structural and notch stresses. • The majority of post-weld treated specimens was tested at normal stresses in literature. Information on the applicability for shear stresses are lacking. This addresses the improvements factors as well as the resulting slopes. • Non-proportionality at multiaxial loading is considered by the CV-factor that is set to CV = 0 . 5 in case of chang ing principal stress direction. This pragmatic approach leads to conservative results. However, a more di ff eren tiated approach should be used that is able better represent cases with a ”small amount” of non-proportionality. • The assessment of thin sheets is right now only captured by the notch stress approach. Recommendations are missing how thin welded joints can be evaluated by nominal or structural stresses. These and additional topics will be addressed in future work within Commission XIII of the International Institute of Welding.

Acknowledgements

Many thanks to all members of IIW-commission XIII for the hard work and valuable discussions.

References

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