Study of LCF behaviour and life estimation based on modified SWT model and enhanced strain energy density of Ti–6Al–4V ELI

Among various types of Titanium alloy, Ti–6Al–4V ELI is the most extensively used alloy. This particular type of alloy is officially termed as Bio-material owing to its high strength, bio-compatibility, low density and good formability characteristics of titanium. Hence, it becomes necessary to evaluate its fatigue properties and low cycle fatigue behaviour for the bio-medical applications such as implants which is subjected to cyclic loading because of various physical movements performed by individual like walking, jumping or running. In this study, completely reversible strain controlled fatigue tests were carried out for various strain amplitudes at an ambient environment. The experimental data was evaluated to describe the cyclic deformation behaviour, Strain-Life plot, maximum stress variation, cyclic softening behaviour and massing behaviour. Finally, two different methods are proposed to estimate the fatigue life of Ti–6Al–4V ELI on the basis of experimental data. First is SWT model which was originally proposed by Swift, Watson and Topper to account the mean stress effect on Fatigue life is further modified in this study by replacing stress amplitude determined at the half-life with the stress amplitude determined at the first cycle. And second is estimation of Fatigue life on the basis of the Accumulated Plastic Strain Energy Density (PSED). The fatigue life estimation carried out based on above two approaches demonstrated very well agreement with experimental life.