Fatigue life prediction of biomedical titanium alloys under tensile/torsional stress

In order to contribute for designing the implant devices with appropriate mechanical properties, fatigue properties of biomedical Ti-6Al-7Nb alloy, were evaluated through the tensile/torsional fatigue test. Fatigue properties for the tensile/torsional fatigue, the tensile fatigue, and the torsional fatigue were compared directly using equivalent stress defined by von Mises' yield condition. In the S-N plots, there were two regions showing different gradients in data and they are corresponded to the boundary of the low cycle fatigue and the high cycle fatigue. By the approximation with Basquin relation of the S-N data, elastic strain, sigma(a), and elastic shear strain, tau(a), showed good linearity to the fatigue life. Fatigue coefficients and fatigue exponents of Basquin relation obtained by the least square method might be useful to examine fatigue life of these alloys under tensile stress, torsional stress and tensile/torsional stress.