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Research Papers

An Elasto-Plastic Reformulation of the Theory of Critical Distances to Estimate Lifetime of Notched Components Failing in the Low/Medium-Cycle Fatigue Regime

[+] Author and Article Information
Luca Susmel

Department of Engineering, University of Ferrara, Ferrara 44100, Italy

David Taylor

Department of Mechanical Engineering, Trinity College, Dublin 2, Ireland

J. Eng. Mater. Technol 132(2), 021002 (Feb 16, 2010) (8 pages) doi:10.1115/1.4000667 History: Received October 08, 2008; Revised October 23, 2009; Published February 16, 2010; Online February 16, 2010

This paper is concerned with a novel elasto-plastic reformulation of the Theory of Critical Distances (TCD) specifically devised to estimate lifetime of notched metallic materials (ferrous and nonferrous) failing in the low/medium-cycle fatigue regime. We used the classic Manson–Coffin and Smith–Topper–Watson approaches, but applied in conjunction with the TCD. We assumed that the material’s critical distance is a constant whose value does not depend on either the sharpness of the notch or on the number of cycles to failure. The accuracy and reliability of the proposed approach was checked by using a number of experimental results generated by testing cylindrical specimens made of En3B, which is a commercial low-carbon steel, and Al6082, which is a conventional aluminum alloy, containing different geometrical features and tested at applied load ratios of R=1 and R=0. The resulting predictions of fatigue life were highly accurate, giving estimates falling within an error factor (in lifetime) of about 2. This result is undoubtedly encouraging, especially in light of the fact that the pieces of experimental information needed to calibrate our method can easily be generated by using standard testing equipment, and the necessary stress/strain fields acting on the fatigue process zone can be determined by directly postprocessing elasto-plastic finite element results.

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Copyright © 2010 by American Society of Mechanical Engineers
Topics: Fatigue , Stress , Cycles , Failure , Testing
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Figures

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Figure 1

Notched specimen subjected to nominal uniaxial fatigue loading: (a) Effective value of the strain amplitude according to the (b) PM and to the (c) LM under Rε=−1 and of the stress amplitude according to the (d) PM and to the (e) LM under Rε>−1

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Figure 2

Proposed procedure for the determination of the critical distance values to be used to apply the TCD in terms of the PM and the LM

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Figure 3

Plain fatigue properties of the investigated En3B

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Figure 4

Plain material fatigue properties of the investigated Al6082

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Figure 5

PM and LM accuracies in estimating the fatigue results generated by testing the Al6082 notched samples

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Figure 6

PM and LM accuracies in estimating the fatigue results generated by testing the En3B notched samples

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Figure 7

PM and LM accuracies in estimating fatigue results generated by testing cylindrical and flat notched specimens of AISI 1141 (data taken from Ref. 17)

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