Fatigue-damage analysis under various loading conditions

Chapter Seven Fatigue-damage analysis under various loading conditions A. Varvani-Farahani Department of Mechanical Engineering, Ryerson University, Toronto, Canada Abstract A fatigue-damage parameter for in-phase and out-of-phase loading is proposed. A proposed fatigue-damage parameter has been developed to assess the various materials fatigue lives for (i) constant-amplitude fatigue stressing where the stresses are at the same and different frequencies, and (ii) variable-amplitude loading conditions. In this parameter, the normal and shear stress and strain ranges have been calculated from the largest stress and strain Mohr’s circles. The total damage accumulation in a block-loading history has been calculated from the summation of the normal and shear energies on the basis of a cycle-by-cycle analysis. The normal and shear energies used in this parameter are divided by the tensile and shear-fatigue properties, respectively, and the proposed parameter, unlike many other parameters, does not use an empirical fitting factor. The proposed parameter successfully correlates fatigue lives of several materials for: a) various in-phase and out-of phase fatigue-loading conditions, b) tests in which a mean stress was applied normal to the maximum shear plane, and c) out-of- phase tests in which there was additional hardening. Keywords: Varvani fatigue-damage model, in-phase and out-of-phase strain paths, shear and normal energies, critical plane, mean stress effect, loading frequency, strain hardening, constant and variable loading WIT Transactions on State of the Art in Science and Engineering, Vol 1, © 2005 WIT Press www.witpress.com, ISSN 1755-8336 (on-line) doi:10.2495/1-85312-836-8/07

Fatigue-damage analysis under various loading conditions

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varvani fatiguedamage

inphase and outofphase

shear and normal energies

critical plane

mean stress effect

loading frequency

strain hardening

constant and variable