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TECHNICAL PAPERS

Fatigue Analysis of Load-Carrying Fillet Welds

[+] Author and Article Information
John Dalsgaard Sørensen

 Aalborg University, Sohngaardsholmsvej 57, DK-9000, Aalborg, Denmarkjds@civil.auc.dk

Jesper Tychsen

 Maersk Oil and Gas AS, Kanalen 1, DK-6700 Esbjerg, Denmarkjpt@maerskoil.dk

Jens Ulfkjær Andersen

 Det Norske Veritas, Tuborg Parkvej 8, DK-2900 Hellerup, DenmarkJens.ulfkjaer.andersen@dnv.com

Ronnie D. Brandstrup

 COWI A/S, Stormgade 2, DK-6700 Esbjerg, Denmarkrdb@cowi.dk

J. Offshore Mech. Arct. Eng 128(1), 65-74 (Sep 23, 2005) (10 pages) doi:10.1115/1.2163876 History: Received January 21, 2005; Revised September 23, 2005

The fatigue strength of load-carrying fillet welds is, in most codes of practice, performed neglecting the influence of bending in the weld throat section. However, some commonly applied structural details give rise to significant bending in the weld throat section. An example of such a detail is a doubler plate connection, which is often applied in connection with modifications of offshore structures. As a part of the present work, fatigue tests have been performed with test specimens fabricated by the current industry standard for welded offshore steel structures. The fatigue tests show that the degree of bending (DOB) has an influence on the fatigue lifetime. The fatigue lifetime decreases significantly when increasing the bending stress. In order to take into account the effect of the bending, a new fatigue stress definition applicable for fillet welds failing through the weld is presented. Using the test results, it is shown that the new definition of fatigue stress can be used for a wide range of DOB with a low standard deviation of the resulting SN curve.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Jacket structure, with doubler-plate connection

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Figure 2

Cruciform and doubler-plate joint

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Figure 3

Typical stress distribution in doubler-plate joint

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Figure 4

Importance of degree of bending (DOB)

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Figure 5

Test setup and procedure

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Figure 6

Tests specimens (measurements are in millimeters). The nominal value of a is 5mm.

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Figure 7

Test results (series 1) for transverse fillet weld connection and characteristic SN curve (maximum-likelihood estimate)

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Figure 8

Comparison to test results for test results for cruciform joints from literature (1) (maximum-likelihood estimates)

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Figure 9

Nominal test specimen geometry (measured in millimeters)

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Figure 10

Test results for doubler plate together with stress definition from Eq. 1 (maximum-likelihood estimates)

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Figure 11

Stress extrapolation points for SCF4 and SCF5 (SEXP: extrapolated stress)

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Figure 12

Alternative fatigue stress parameter SCF4

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Figure 13

Test results and characteristic SN curve with alternative stress parameter SCF4 (maximum-likelihood estimates)

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Figure 14

Test results and characteristic SN curve with alternative stress parameter SCF4 (maximum-likelihood estimates); fixed m=3

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Figure 15

Alternative stress parameter 2-SCF5

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Figure 16

Test results and characteristic SN curve with alternative stress parameter SCF5 (maximum-likelihood estimates)

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Figure 17

Test results and characteristic SN curve with alternative stress parameter SCF5 (maximum-likelihood estimates); fixed m=3

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Figure 18

Bending moment in doubler-plate specimen as function of support stiffness: (a) stiff rotational support and (b) soft rotational support

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Figure 19

Mesh size requirements in FEM analysis

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