Overcoming Limitations of the Conventional Strain-Life Fatigue Damage Model

[+] Author and Article Information
T. E. Langlais, J. H. Vogel

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455

J. Eng. Mater. Technol 118(1), 103-108 (Jan 01, 1996) (6 pages) doi:10.1115/1.2805921 History: Received April 13, 1994; Revised December 10, 1994; Online November 27, 2007


The strain-based approach to fatigue life prediction usually relies on the conventional strain-life equation which correlates the elastic and plastic strain to the life. The correlation is based on separate log-linear curve fits of the elastic and plastic components of the strain data versus the life. It is well known, however, that these linear relationships may be valid only within a specific interval of stress or strain. When material behavior approaches elastic-perfectly plastic, for instance, it is not uncommon for the test data to deviate from linearity at both very high and very low strains. For such materials a separate fit of each curve is likely to give material constants significantly inconsistent with the fit of the cyclic stress-strain curve, especially if a good local fit over a restricted interval is obtained. In this work, some of the errors that arise as a result of this inconsistency are described, and recommended methods are developed for treating these errors. Numerical concerns are also addressed, and sample results are included.

Copyright © 1996 by The American Society of Mechanical Engineers
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