A Comparison of Constitutive Equations for the Energy-Based Lifing Method

Abstract

A Comparison of Constitutive Equations for the Energy-Based Lifing iVIethodAlternatives to quasi-static and dynamic constitutive relationships have been investigated with respect to a previously developed energy-based fatigue lifing method for various load profiles, which states: the total strain energy dissipated during both a quasi-static 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 energy-based framework and were compared to the lifing method originally developed by Stowell. Extensive experimentation performed on Titanium 6AI-4V (Ti-64) combined with experimental data generated for Aluminum (Al) 6061-T6 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 modified-Halford approach. Additionally, the relative equality in predictive accuracy between the modified-Stowell approach the modified-Ramberg-Osgood approach was demonstrated. Journal of Engineering lUlateriais and Technoiogy

Correlation Between Solder Joint Fatigue Life and Accumulated Work in Isothermal Cycling

“…Thus, work dissipated as heat would not contribute to the nucleation, multiplication, and accumulation of dislocations, and the evolution of dislocation structures associated with damage. In addition, materials subject to an endurance limit will obviously disseminate an increasing fraction of the overall work without doing damage as amplitudes are reduced [2], [3]. Chang et al [3] showed how accounting for this would allow for scaling of results for steel up to tens of millions of cycles.…”