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Fatigue Life Calculation with Loads Varying in Magnitude and Direction
Technical Paper
2013-01-0999
ISSN: 0148-7191, e-ISSN: 2688-3627
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English
Abstract
In fatigue life prediction, it is common to analyze a component
subjected to a load-versus-time history that varies in magnitude
over time. In established methods, it is assumed that the
directions of the applied loads do not change, so stresses along
the same reference plane can be compared as unidimensional
quantities. Put differently, these methods require that the
principal stress orientation remains the same throughout the load
history.
This work aims to determine the fatigue life of a component
experiencing a load-versus-time history that produces stresses
varying in both magnitude and principal stress orientation. To
accomplish this, all six components of the stress tensor are
required throughout the loading history. By choosing a cut plane
defined by the normal direction n, the normal stresses can be
determined. The application of the rainflow counting method can
then be used to convert the normal stresses into equivalent fatigue
cycles. The Goodman method can compare these cycles against an S-N
or Wohler curve, while Miner's rule calculates the life Lⁿ
corresponding to the plane n.
It is necessary to find the cut plane that minimizes Lⁿ while
ensuring that n remains a unit normal. The search for min Lⁿ is
completed using the Nelder and Mead optimization. The method
presented in this paper can evaluate the minimum life and the plane
on which a crack will initiate.
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Citation
Altobelli, J. and Chandrupatla, T., "Fatigue Life Calculation with Loads Varying in Magnitude and Direction," SAE Technical Paper 2013-01-0999, 2013, https://doi.org/10.4271/2013-01-0999.Also In
References
- ASTM E1049 - 85(Reapproved 2005) Standard Practices for Cycle Counting in Fatigue Analysis 15 Aug. 2012 http://www.astm.org/Standards/E1049.htm
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- Goodman J. Mechanics Applied to Engineering Longman, Green & Company London 1899 1 9th 1930
- Basquin , O. H. The Exponential Law of Endurance Tests American Society for Testing and Materials Proceedings 10 1910 625 30
- Miner , M. A. 1945 Cumulative Damage in Fatigue J. Applied Mechanics 12 A159 A164
- Nelder J. A. and Mead R. A simplex method for function minimization Computer Journal 7 308 313 1965
- Findley , W. N. A Theory for the Effect of Mean Stress on Fatigue of Metals Under Combined Torsion and Axial Load or Bending Journal of Engineering for Industry Nov. 1959 301 306