Research Papers: Structures and Safety Reliability

Bi-Linear Fatigue and Fracture Approach for Safety Analysis of an Offshore Structure

[+] Author and Article Information
Rizwan A. Khan

Assistant Professor
Department of Civil Engineering,
National Institute of Technology,
Jalandhar, Punjab 144011, India
e-mail: rizwan_iitd@yahoo.co.in

Suhail Ahmad

Department of Applied Mechanics,
Indian Institute of Technology,
Delhi, New Delhi 110016, India

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received March 26, 2012; final manuscript received January 30, 2014; published online March 18, 2014. Assoc. Editor: Bernt J. Leira.

J. Offshore Mech. Arct. Eng 136(2), 021602 (Mar 18, 2014) (7 pages) Paper No: OMAE-12-1029; doi: 10.1115/1.4026669 History: Received March 26, 2012; Revised January 30, 2014

The design of welded structures for the fatigue limit state is normally carried out by means of either linear or bilinear S-N curves, which have been found adequate to predict crack initiation only. To properly assess the effects of the design, fabrication, inspection, and repair strategy for structure degradation due to crack growth, fracture mechanics (FM) models need to be applied. In this paper, alternative S-N and FM formulations of fatigue are investigated. The probabilistic fracture mechanics approach predicts the fatigue life of welded steel structures in the presence of cracks under random spectrum loading. It is based on a recently proposed bi-linear relationship to model fatigue crack growth. Uncertainty modeling, especially on fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bilinear crack growth relationship. Results pertaining to the fatigue reliability and fatigue crack size evolution are presented using the Monte Carlo simulation technique and the emphasis is placed on a comparison between the linear and bilinear crack growth models. Variations in the system configuration, service life, and coefficients of crack growth laws have been studied on the parametric basis

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Fig. 1

Two stage crack growth relationship

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Fig. 2

Typical marine riser

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Fig. 3

Reliability levels against variations in the number of joints

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Fig. 4

Reliability levels against variations in the number of joints

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Fig. 5

Reliability levels against the variation in the initial crack length (mm)

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Fig. 6

Reliability levels against the variation in the Paris exponent (m)

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Fig. 7

Reliability levels against the variation in the Paris coefficient (A1)

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Fig. 8

Reliability levels against the variation in the Miner–Palmgren damage index (ΔF)

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Fig. 9

Reliability levels against the fatigue strength coefficient (C1)



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