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Effects of Mean Stress and Stress Concentration on Fatigue Behavior of Ductile Iron

Meyer, Nicholas
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418332368

Abstract Details

2014, Master of Science, University of Toledo, Mechanical Engineering.
Cast iron tends to be more economical to manufacture than steel, but its microstructure is riddled with internal defects. With improvements in casting technology, cast iron can compete with steel in some applications due to the ability to maintain similar strength. One objective of this study was to analyze data obtained from literature and make predictive correlations between tensile, microstructural, and fatigue properties. Another objective of this study was to evaluate tensile and compressive mean stress effects on smooth and notched fatigue behavior of 120-90-02 ductile cast iron experimentally, as well as analytically by using predictive models. The relationship between these two objectives is such that with successful correlations of fatigue limit with mechanical properties, fewer experiments could be performed to verify analytical results. This grade of cast iron was selected by Eaton Corporation, who helped fund this study. The material, 120-90-02 ductile cast iron, was machined and heat-treated as provided by Eaton Corporation. Neuber’s rule, strain energy density, and finite element methods were used to obtain stresses and strains at the notch. Modified Goodman, Smith- iv Watson-Topper, FKM and the Fatemi-Socie mean stress parameters were used to account for mean stress effect on fatigue life of both smooth and notched specimens. Mean stress levels were chosen such that the R-ratios in load-controlled tests were -8, -7, -3, -1, 0, 1/3, 0.5, and 0.75. By understanding the fatigue behavior of material under varying degrees of mean stress, design safety can be improved by properly accounting for the effect of mean stress that a component may be subjected to. The Smith-Watson-Topper mean stress parameter proved to be the best method for life prediction for both smooth and notched specimens, based on the nominal stress approach. Using the local approach, which considers notch root stresses and strains, the Fatemi-Socie fatigue parameter used with the strain energy density rule provided better results compared to the Smith-Watson-Topper mean stress parameter.
Ali Fatemi, Dr. (Advisor)
Efstratios Nikolaidis, Dr. (Committee Member)
Lesley Berhan, Dr. (Committee Member)
207 p.
Engineering; Mechanical Engineering
fatigue; notch effect; mean stress; ductile iron; FKM; Fatemi-Socie; Smith-Watson-Topper; SWT; Modified Goodman

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Citations

  • Meyer, N. (2014). Effects of Mean Stress and Stress Concentration on Fatigue Behavior of Ductile Iron [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418332368

    APA Style (7th edition)

  • Meyer, Nicholas. Effects of Mean Stress and Stress Concentration on Fatigue Behavior of Ductile Iron. 2014. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418332368.

    MLA Style (8th edition)

  • Meyer, Nicholas. "Effects of Mean Stress and Stress Concentration on Fatigue Behavior of Ductile Iron." Master's thesis, University of Toledo, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418332368

    Chicago Manual of Style (17th edition)

toledo1418332368
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This open access ETD is published by University of Toledo and OhioLINK.