Fretting behavior of Ti-6Al-4V under combined high cycle and low cycle fatigue loading

The fretting-fatigue behavior of titanium alloy Ti-6Al-4V under variable-amplitude (V-A) loading was investigated. This involved a two-level block of low-frequency (1 Hz) large-amplitude cycles and high-frequency (200 Hz) low-amplitude cycles, which represented the low- and high-cycle components of the turbine engine mission loading. The measured fretting-fatigue lives were compared with the predicted lives obtained from the Palmgren–Miner linear damage rule as well as from a nonlinear damage rule. These comparisons showed that there is a reasonable agreement between the predicted life from linear rule and the experimental data under variable loading conditions when conventional fatigue life relationships on the semi-logarithmic scales are employed and when the ratio of HCF and LCF cycles is large. However, the Palmgren–Miner linear prediction differs significantly from experimental data when these were compared based on the damage fraction induced by LCF and HCF components of combined cycling, and thus a non-linear method of damage accumulation is more appropriate for estimating the fretting-fatigue life under the V-A loading.