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Structures and Safety Reliability

Fatigue of Tubular Joints: Hot Spot Stress Method Revisited

[+] Author and Article Information
Pingsha Dong

School of Naval Architecture and Marine Engineering,  The University of New Orleans, New Orleans, LA 70148pdong@uno.edu

Jeong K. Hong

 Center for Welded Structures Research, BATTELLE Columbus, OH 43201

This assumes that shear locking in element formulation used is not present.

J. Offshore Mech. Arct. Eng 134(3), 031602 (Feb 02, 2012) (12 pages) doi:10.1115/1.4005188 History: Received May 10, 2009; Revised August 21, 2011; Published February 02, 2012; Online February 02, 2012

A series of well-known tubular joints tested in UKSORP II have been re-evaluated using the mesh-insensitive structural stress method as a part of the on-going Battelle Structural Stress JIP efforts. In this report, the structural stress based analysis procedure is first presented for applications in tubular joints varying from simple T joints, double T Joints, YT joints with overlap, and K joints with various internal stiffening configurations. The structural stress based SCFs are then compared with those obtained using traditional surface extrapolation based hot spot stress methods. Their abilities in effectively correlating the fatigue data collected from these tubular joints are demonstrated. These tests are also compared with the T curve typically used for fatigue design of tubular joints as well as the structural stress based master S-N curve adopted by ASME Section VIII Div 2. Finally, some of the implications on fracture mechanics based remaining life assessment for tubular joints are discussed in light of the results obtained in this investigation.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Traction-based structural stress definition with respect to chord wall in a tubular joint: (a) 2D equilibrium-equivalent stress definition with respect to line A-A and (b) 3D equilibrium-equivalent stress definition on a hypothetical cut surface (local x′-z′ plane) encompassing line A-A

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Figure 2

Illustration of the structural stress calculation procedure for a curved weld at brace to chord intersection using shell/plate element model

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Figure 3

Structural stress (normal component) results for a tubular T joint used by Zerbst [9]: (a) joint geometry and loading conditions; (b) four FE models with different element sizes; and (c) comparison of structural stress distributions along weld toe on chord (normalized by brace nominal stress) from four models of different element sizes

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Figure 4

Membrane and bending normal structural stress calculated from the 1t × 1t mesh–weld toe cracking on chord (see Fig. 3 for details)

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Figure 5

Three structural stress components (normal, in-plane shear, and transverse shear) using the 1t × 1t mesh–weld toe cracking on chord (see Fig. 3 for details)

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Figure 6

Geometric dimensions and loading conditions of the tubular joints from UKSORP II

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Figure 7

Comparison of structural stress results with HSS results for T-joint (UKSORP II)–weld cracking into chord

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Figure 8

Comparison of the structural stress based degree of bending (r) results with HSS-based results for T joint (UKSORP II) –weld cracking into chord under axial tension, in-plane bending, and out-of-plane bending

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Figure 9

Comparison of structural stress results with HSS results for double T joint (UKSORP II) loaded under in-plane bending–weld toe cracking into chord

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Figure 10

Comparison of structural stress results with HSS results for YT joint (UKSORP II) loaded under balanced compression/tension–weld toe cracking into brace

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Figure 11

Structural stress results K joint (K0) without internal stiffeners (UKSORP II) loaded under unbalanced out-of-plane bending–weld toe cracking into brace

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Figure 12

K joints with internal stiffeners (UKSORP II) analyzed in this investigation using the structural stress method loaded under unbalanced out-of-plane bending

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Figure 13

Structural stress results along weld toe on brace for three K joints with internal stiffeners (UKSORP II) under unbalanced out-of-plane bending

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Figure 14

Comparison of the structural stress results among K joints with and without internal stiffeners and HSS estimates using parametric equations under unbalanced out-of-plane bending

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Figure 15

Correlation of actual test data (in air) documented in UKSORP II: (a) measured HSS range with thickness correction; (b) calculated HSS range with thickness correction; and (c) the equivalent structural stress range

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Figure 16

Dimensional life integral I(r) as a function of both bending ratio r and relative initial crack size li=ai/t

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