Fatigue Response and Characterization of 350WT Steel Under Semi-Random Loading

[+] Author and Article Information
Philip A. Rushton

 Martec Limted, Halifax NS, B3J 3J8, Canada

Farid Taheri1

Department of Civil Engineering, Dalhousie University, Halifax NS, B3J 1Z1, Canadafarid.taheri@dal.ca

David C. Stredulinsky

Structural Acoustics and Strength Division, The Defence R&D Canada-Atlantic, Dartmouth NS, B2Y 3Z7, Canada


Corresponding author.

J. Pressure Vessel Technol 129(3), 525-534 (Mar 09, 2006) (10 pages) doi:10.1115/1.2748835 History: Received November 28, 2005; Revised March 09, 2006

Novel data obtained through experimental investigation into the fatigue response of 350WT steel, subjected to semi-random loading, comprised of various combinations of intermittent tensile overloads and compressive underloads are presented. An effective model for predicting the fatigue response is also introduced. For that, the capabilities of some of the currently available models are investigated and then an exponential delay model, being capable of accounting for the effects of not only overload ratio, but also stress ratio and overload/underload ratio is introduced. Since most variable amplitude models are based on a constant amplitude model, efforts were also expended to identify a constant amplitude fatigue crack growth model that would be easy to use, requiring the calibration of few (if any) empirical curve-fitting parameters. The integrity of a selected model is examined and results are presented.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Sequence effects of (a) tension OL, (b) compression-tension OL, (c) tension-compression OL, and (d) compression UL (4)

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Figure 2

Schematic of terms defining Wheeler’s retardation model (from Sheu (9))

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Figure 3

(a) Fatigue crack growth emanating from an initial EDM starter notch, (b) formation of crack tip plastic zone (at OLR=1.67)

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Figure 4

Schematic representation and relationships for the assumed overload and underload terminologies

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Figure 5

Fatigue life comparison using Zheng and Hirt and Paris models

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Figure 6

Effect of stress ratio (R) on the A versus N curve

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Figure 7

Effects of OLR on the a versus N curve at R=0.1

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Figure 8

Effect of variation in OL/UL ratio on the a versus N curve (at R=0.1 and OLR=1.67)

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Figure 9

Effect of OLR and OL/UL on (normalized) minimum crack growth rate

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Figure 10

Preliminary evaluation of revised delay model

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Figure 11

Incorporation of stress ratio (R) into revised delay model

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Figure 12

Prediction of the proposed delay model illustrating influence of R and OL/UN ratio on ND



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