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RESEARCH PAPERS

Increased Temperature Margins Due to Constraint Loss

[+] Author and Article Information
Bostjan Bezensek

Faculty of Mechanical Engineering,  University of Maribor, Smetanova 17, SI-2000 Maribor, Sloveniabostjan.bezensek@uni-mb.si

John W. Hancock

Department of Mechanical Engineering, University of Glasgow, Glasgow G12 8QQ, UKj.hancock@eng.gla.ac.uk

J. Pressure Vessel Technol 127(2), 173-178 (Jan 10, 2005) (6 pages) doi:10.1115/1.1903004 History: Received November 12, 2003; Revised January 10, 2005

Enhanced levels of toughness due to loss of crack tip constraint have been related to temperature shifts in the ductile–brittle transition curve. An argument to quantify the temperature shift is developed using the self-similarity of near-tip stress fields under contained yielding combined with scaling techniques developed by Dodds and co-workers (1-2) for cleavage. This allows the temperature changes which give the same stress field at failure in constrained and unconstrained fields to be determined. The procedure is illustrated using the data of Sherry (3) for an A533B pressure vessel steel. The results are consistent with empirical expressions proposed by Wallin (4), and enable a discussion of the micromechanics of cleavage.

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Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Toughness as a function of temperature for an A533B steel from Sherry, Lidbury, and Beardsmore (3,24)

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Figure 2

Constraint at failure as a function of temperature for an A533B steel from Sherry, Lidbury, and Beardsmore (3,24)

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Figure 3

The hoop stress directly ahead of the crack for constrained (T=0) and unconstrained (T<0) fields at a fixed value of J

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Figure 4

Plots of the hoop stress ahead of the crack, showing the unconstrained field (T=−0.61σoT<0) matched to the constrained (T=+0.1σoT>0) field by a change in the yield stress at a fixed fracture stress. Fields are determined at a fixed J and normalized with a constant.

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Figure 5

Stress contours for the hoop stress at three times yield stress of a constrained field, showing the unconstrained field (T=−0.61σoT<0) matched with the constrained (T=+0.1σoT>0) field by a change in the yield stress. Fields are determined at a fixed J and normalized with a constant.

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Figure 6

Temperature shift due to constraint loss by matching fields at a local fracture stress directly ahead of the crack for an A533B steel data from (3,24)

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Figure 7

Temperature shift due to constraint loss by matching fields using the Weibull stress model on an A533B steel data from (3,24)

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Figure 8

Temperature shift due to constraint loss by matching fields at a local fracture stress and by using the Master Curve approach of Wallin (4) on an A533B steel

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Figure 9

Underprediction of cleavage toughness at the upper end of the ductile-brittle transition using the RKR model; a∕w=0.5, σf=2300MPa, and rc=120μm

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Figure 10

Temperature dependent critical microstructural distance for deep and shallow cracked data, normalized with the individual lower shelf (LS) values

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