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Title: Approach to consider welding residual stresses in fatigue analysis using numerical simulations
Language: English
Authors: Friedrich, Nils 
Keywords: welding simulation; initiation of macroscopic cracks; digital image correlation; multilayer K-butt weld; longitudinal stiffener; stress ratio
Issue Date: 2020
Examination Date: 14-Sep-2020
Source: Technische Universität Hamburg (2020)
Abstract (german): 
Der Einfluss von Schweißeigenspannungen auf die Schwingfestigkeit wird mittels numerischer Simulationen und experimenteller Versuche untersucht. Mithilfe numerischer Simulationen werden Schweißeigenspannungen und Spannungen unter Last ermittelt. In Schwingfestigkeitsversuchen an zwei Schweißgeometrien wird der Eigenspannungseinfluss auf den makroskopischen Anriss, Rissfortschritt und die Gesamtlebensdauer ermittelt. Aus der Korrelation der Versuchsergebnisse und der berechneten Spannungen wird ein Ansatz zur Berücksichtigung des Eigenspannungseinflusses auf die Schwingfestigkeit entwickelt.
Abstract (english): 
Although it is known that residual stresses may influence the fatigue strength of welded structures, they are usually not included explicitly in fatigue assessments. In this thesis the influence of welding residual stresses on fatigue is investigated using numerical simulations and experimental tests to develop an approach to consider welding residual stresses in fatigue analysis. A numerical welding simulation approach using a prescribed temperature heat source is described and the influence of various simulation parameters on the resulting residual stresses is assessed. The simulations are used to design small-scale specimens containing a multilayer K-butt weld and a longitudinal stiffener with tensile transversal residual stresses at the weld toe. Residual stresses are measured by X-ray diffraction and hole drilling on both specimen geometries and the simulation results are verified. Fatigue tests at different load ratios are conducted on both specimen geometries. The initiation of macroscopic cracks is detected using digital image correlation. The influence on crack initiation and propagation show differences for both investigated weld geometries. A correlation between the fatigue test results and the calculated stresses is found. Based on these findings an approach to predict S-N curves depending on the residual stress condition and stress ratio is developed. The approach is based on the presented numerical welding simulations and allows to consider the influence of welding residual stresses in fatigue analysis.
DOI: 10.15480/882.2971
Institute: Konstruktion und Festigkeit von Schiffen M-10 
Document Type: Thesis
Thesis Type: Doctoral Thesis
Advisor: Ehlers, Sören 
Referee: Sheikhi, Shahram 
Al-Emrani, Mohammad 
Project: Ansatz zur Berücksichtigung von Schweißeigenspannungen bei der Ermüdungsfestigkeitsbewertung mittels direkter numerischer Simulation 
More Funding information: Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) DFG – EH 485/4-1
License: In Copyright In Copyright
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