Mean stress sensitivity in fatigue of α, (αβ) and β titanium alloys

The effect of the stress ratio on high cycle fatigue (HCF) strength has been investigated on α, (αβ) and β titanium alloys. While α and β titanium alloys show a normal mean stress sensitivity, (αβ) alloys can behave anomalously, i.e. their HCF strength at low tensile mean stresses can be much lower than expected from a linear interpolation between fully reversed HCF strength (R = −1) and tensile strength. This anomalous mean stress dependence of the HCF strength is discussed in terms of fatigue crack nucleation mechanisms.