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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

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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