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Materials Technology

Fatigue Assessment of Welded Joints Taking Into Account Effects of Residual Stress

[+] Author and Article Information
Nur Syahroni

Department of Marine Technology,  Norwegian University of Science and Technology, Otto Nielsens v.10, NO-7491 Trondheim, Norwaynur.syahroni@ntnu.no

Stig Berge

Department of Marine Technology,  Norwegian University of Science and Technology, Otto Nielsens v.10, NO-7491 Trondheim, Norwaystig.berge@ntnu.no

J. Offshore Mech. Arct. Eng 134(2), 021405 (Dec 06, 2011) (10 pages) doi:10.1115/1.4004519 History: Received July 22, 2010; Revised March 03, 2011; Published December 06, 2011; Online December 06, 2011

Residual stress may have a significant effect on the fatigue strength of welded joints. As a nonfluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers and bulk carriers. The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gauges. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shakedown effect of residual stress, testing was performed for several preload conditions, which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards a better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.

Copyright © 2012 by American Society of Mechanical Engineers
Topics: Stress , Welded joints
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References

Figures

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Figure 1

Stress-strain curve from tensile test

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Figure 2

Geometry and main dimensions of the specimen

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Figure 3

Arrangement of strain gauges to measure the initial distribution of residual stress (plan view)

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Figure 4

Signal amplifier and data acquisition system

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Figure 5

Residual stress distributions for two welds, calculated from biaxial and axial strain, respectively

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Figure 6

The 500 kN hydraulic actuator and the testing rig

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Figure 7

Shell element model

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Figure 8

Solid element model

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Figure 9

Structural hot spot stress by linear extrapolation method

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Figure 10

Experimental method for measuring hot spot stress

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Figure 11

Normalized residual stress distributions along the centerline in front of the weld toe

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Figure 12

Normalized residual stress distributions in transverse section

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Figure 13

Residual stress distributions after preloads

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Figure 14

Stress distributions towards the weld toe, by FEA and experimentally, at 100 MPa nominal stress

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Figure 15

SN data based on nominal stress

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Figure 16

SN data based on hot-spot stress

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Figure 17

SN data according to the original bulk-carrier procedure

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Figure 18

SN curves according to the bulk-carrier procedure with modification of residual stress

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Figure 19

SN curves according to tanker procedure with coefficient of compressive part of 0.6

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Figure 20

SN curves according to tanker procedure with coefficient of compressive part modified into 0.8

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