A Comparison of Constitutive Equations for the Energy Based Lifing Method

Abstract

Alternatives to quasistatic and dynamic constitutive relationships have been investigated with respect to a previously developed energybased fatigue lifing method for various load profiles, which states: the total strain energy dissipated during both a quasistatic process and a dynamic process are equivalent and a fundamental material property. Specifically, constitutive relationships developed by Ramberg–Osgood and Halford were modified for application to the existing energybased framework and were compared to the lifing method originally developed by Stowell. Extensive experimentation performed on Titanium 6Al4V (Ti64) combined with experimental data generated for Aluminum (Al) 6061T6 at various temperatures were utilized in support of this investigation. This effort resulted in considerable improvements to the accuracy of the lifing prediction for materials with an endurance limit through application of a modifiedHalford approach. Additionally, the relative equality in predictive accuracy between the modifiedStowell approach the modifiedRamberg–Osgood approach was demonstrated.