Numerische Einführung von Schädigungswirkung der Eigenspannungen in die mehrachsige Festigkeitskonzepte für Schweißbauteile und -Strukturen
Zusammenfassung der Projektergebnisse
The present study focused on the development of a comprehensive fatigue damage prediction procedure for welded joints under constant amplitude multiaxial loading conditions, considering the best known conventional and advanced multiaxial fatigue life prediction methods. Evaluations were performed using the equivalent stress/strain approach and critical plane-based damage parameters, and then compared with experimental fatigue life data from HT and AW specimens. In addition, complementary analyses were performed/developed to investigate the role of some influencing parameters such as load non-proportionality, weld-induced microstructures, weld residual stresses, transient softening, and crack growth fraction. Some key observations and findings regarding the analysis results can be summarized as follows: 1) Local equivalent stress/strain approaches resulted in decent correlation of weld specimen fatigue data for all loading conditions except for the non-proportional loading condition. The results for HT specimens were better than those of the AW specimens, and that is due to the drawback of such methods to accommodate the residual stress effect in the evaluation. 2) Fatigue life prediction based on the FS parameter was found to be more accurate than the invariant counterparts when correlating fatigue data from weld specimens. 3) Having σy term be replaced by GΔγ, the Mod-FS parameter resulted in slightly improved AW data correlation without adding any new material constants for damage calculation. Additionally, the parameter improved the correlation of fatigue data for HT specimens as well. 4) The FE-based methodology applied to account for the effect of welding residual stresses into the multiaxial fatigue assessment of welds, seems to work well thanks to the advanced critical plane-based parameter. 5) Welding thermal cycle induced intense microstructural transformations in the material in the weld region and the HAZ. Consideration of the realistic transitions of material properties into the FE model have determinant effect on the accuracy of lifetime predictions. 6) Though the application of critical plane approach improved the fatigue life predictions under OP loading condition, however the level of improvement was not satisfactory enough. The proposed so-called integral approach in conjunction with the Mod-FS parameter enhanced firmly well the correlation of the OP fatigue data. 7) For the LCF tests, where local plastic deformation may occur to some extent at the notch, incorporation of the material transient softening effect through the varying CSSC led to the enhancement of fatigue life predictions for the studied cases. 8) Implementation of the discrete crack growth approach based on the microstructural characteristics into the FE model, to simultaneously account for the crack initiation and crack growth in welded specimens, successfully improved the fatigue life predictions.
Projektbezogene Publikationen (Auswahl)
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Application of the Critical Plane Approach to the Torsional Fatigue Assessment of Welds Considering the Effect of Residual Stresses, International Journal of Fatigue, vol. 101, pp 271-281, 2017
Hemmesi K., Farajian M., Fatemi A.
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Numerical Studies of Welding Residual Stresses in Tubular Joints and Experimental Validations by means of X-ray and Neutron Diffraction Analysis, Materials and Design, vol. 126, pp 339-350, 2017
Hemmesi K., Farajian M., Boin M.
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Numerical Welding Simulation as a Basis for Structural Integrity Assessment of Structures: Microstructure and Residual Stresses, In book: Residual Stress Analysis on Welded Joints by Means of Numerical Simulation and Experiments, 2018
Hemmesi K., Farajian M.
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Numerical Evaluation of Surface Welding Residual Stress Behaviour under Multiaxial Mechanical Loading and Experimental Validations, Int. J. Mechanical Sciences, vol. 168, pp 105-127, 2019
Hemmesi K., Mallet P., Farajian M.
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Modelling and experimental validation of material deformation at different zones of welded structural-steel under multiaxial loading, Materials Science and Engineering: A, vol. 824, pp 1-15, 2021
Hemmesi K., Holey H., Elmoghazy A., Böhm R., Farajian M., Schulze V.
