Modeling of Fatigue Damage

K. Sadananda¹, D. Kujawski², N. Iyyer¹, M. Nani Babu³

¹Technical Data Analysis, Inc., Falls Church, VA, (USA)
²Department of Mechanical and Aerospace Engineering, Western Michigan University, Kalamazoo, MI 49008-5343, (USA)
³Metallurgy and Material Group, Indira Gandhi Center for Atomic Energy, HBNI, Kalpakkam, 603 102, (INDIA)

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ABSTRACT – DOI: https://dx.doi.org/10.47204/EMSR.4.2.2023.079-088

We have shown before that representation of the fatigue damage for all materials requires two load parameters Dσ and σmax for S-N fatigue, and DK and Kmax for fatigue crack growth. The intrinsic two-parametric nature of S-N fatigue is traditionally known in terms of mean stress effects. The two-parametric nature is ignored for fatigue crack growth since Elber, by considering the load-ratio effects due to an extrinsic factor called crack closure. When represented in terms of the two parameters, both S-N data and crack growth rate data show a hyperbolic behavior for all materials. In this paper, the Microsoft Excel program is used to solve and arrive at limiting values Dσ* and σmax* for the selected number of cycles for failure, NF, and DK* and Kmax* for selected crack growth rates, da/dN. The approach is valid for characterizing fatigue damage for any material. The predictions based on optimization using the Excel program correlate well with the experimental data. The procedure is considered a step towards developing predictive codes for both S-N fatigue and fatigue crack growth in structural materials in service.