multiaxial fatigue in welded structural details in ship ... source pictures: google.com . 3 metocean...
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Multiaxial fatigue in welded structural details in ship and offshore structures Delft University of Technology Maritieme Innovatie Markt 2015 Paula van Lieshout MSc
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Cyclic loading
Fluctuating stresses/strains
Crack initiation
Crack growth/ propagation
Failure/Costs of
maintenance
Multiaxial fatigue Phenomenon description of fatigue
Low Cycle Fatigue
High Cycle Fatigue
Source pictures: Google.com
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Metocean analyses
Hydrodynamic analyses
Global structural response
Local structural response
Fatigue analyses
General overview General approach of fatigue problems
Source pictures: Google.com
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• Principal stresses change size and direction during a load cycle
• Structural geometry or loading induced
• The process of welding introduces additional uncertainties
• Weld material, Base material, Heat Affected Zone (HAZ)
• Nominal stress, Hot spot Stress, Notch Stress
• Mean/Residual stress
Multiaxial fatigue Multiaxiallity in welded structures
Sources: Maddox, S.J., 2010; SBM Offshore; Google.com; DNV –RP-C203, 2012
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Multiaxial fatigue in welded structures What is the problem?
Source: Sonsino, 2009
Overestimation 1:15!?
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• Uniaxial fatigue approaches provide non-conservative results for multiaxial fatigue
problems
• Multiaxial fatigue methods are mainly developed by the automotive and aerospace
industry
• Thin plated structures
• Different material types
• Often non-welded or different weld types and welding techniques are applied
• Existing multiaxial fatigue approaches require complex calculations and it is difficult to
make a physical interpretation of them
Multiaxial fatigue in welded structures What is the problem?
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• The results obtained with existing multiaxial fatigue methods show large variations in their
fatigue lifetime estimates
• There is no consensus on which method(s) should be used
• There is insufficient validation with experimental data for marine structures
Multiaxial fatigue in welded structures What is the current state-of-the-art?
Sources: pictures Backstrom & Marquis, 2004; Google.com
? Predicted mean life (cycles)
Experim
enta
l lif
e (
cycl
es)
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• Identify details sensitive to non-proportional multiaxial fatigue in a ship/offshore structure
• Make a selection of models for multiaxial fatigue analyses
• Carry out their experimental validation with a specimen which is representative for the
maritime industry (e.g. dimensions, material type, configuration)
• Recommend an approach for the assessment of non-proportional multiaxial fatigue in
ship/offshore structures
• Improve
• Develop a simplified approach for practical application
Multiaxial fatigue in welded structures Research goals and objectives
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Scope of work
Source pictures: Carpinteri & Spagnoli, 2009; Dong, 2009; FGB, 2015; Google.com
Project content
Scope of work
Fundamental Experimental Numerical
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Involvement of industrial practice
• The project obtains governmental STW funding (which is supported by 10 Dutch
industrial partners) and additionally as a Joint Industry Project (JIP) by international
industrial partners
My PhD research in a wider context