Fatigue analysis of ship's balcony opening corner
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Journal Title
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Volume Title
Insinööritieteiden korkeakoulu |
Master's thesis
Authors
Date
2019-06-17
Department
Major/Subject
Mcode
Degree programme
Master's Programme in Mechanical Engineering (MEC)
Language
en
Pages
55+1
Series
Abstract
Fatigue strength has yet remained a major limiting factor in the application of high strength steels in ship structures, despite research showing increased resistance to crack initiation in comparison to mild steels. This indicates potential benefits to be achieved in terms of fatigue strength, with the implementation of the material. One example, where the issue is relevant, are the balcony opening corners on cruise ships, which feature large number of fatigue critical details. Utilization of higher strength steels there would allow for notable economical gains through reduced material thicknesses. In the current thesis, novel strain-based approach for fatigue assessment combined with non-linear finite element method for load analysis is used to evaluate fatigue strength of these details. This methodology allows to make clear distinction between fatigue crack initiation and propagation mechanisms and consider more explicitly the influence of material properties and loading response of the structure. The objective of the thesis is to determine, whether significant advantages could be made in terms of fatigue strength by using higher strength steel and how it is affected by production quality of the structure. The results obtained prove the potential applicability of high strength steels in fatigue critical details. Fatigue strength of the analyzed detail is can be greatly increased in comparison to rule values, if the effect of notches due to surface defects is minimized. Calculations also show the increased dependence on the notch effect, with increase of material yield strength. The method of assessment is validated by analyzing crack growth behavior parameters, which are in good agreement with experimental studies conducted by others. In the thesis, the results are obtained by numerical calculations, using material properties largely based on values presented in existing research and empirical formulae obtained by experimental studies. Therefore, in order to validate the results, experimental work in terms of fatigue tests are required together with material property assessment from full-scale specimens.Description
Supervisor
Remes, HeikkiThesis advisor
Parmasto, OliverKeywords
fatigue, ship structures, high strength steel, finite element method, crack initiation, strain-based approach