Synopsis :The effect of stress ratio on giga-cycle fatigue properties was investigated for three heats of 900-MPa-class Ti-6Al-4V alloy. Fatigue tests were carried out using ultrasonic fatigue testing at 20 kHz and conventional fatigue testing at 120 Hz. The ultrasonic and conventional fatigue testing used 3 and 6 mm specimens, respectively. These fatigue tests were conducted under stress ratio of Rϭ0 and 0.3 and under the condition fixing the maximum stress at the yield stress. As the result, internal fracture occurred in all heats, and in that case, frequency effects were negligible. This result meant that the specimen size effect was also negligible. In these tests, no specimen failed at over 10 9 cycles, which meant that the Ti-6Al-4V alloy probably revealed fatigue limits in a giga-cycle region in spite of occurrence of internal fracture. The fracture sites of the internal fracture revealed no inclusion but a cluster of several facets. The size of a facet was almost equal to the a grain size and the size of the cluster was 100ϳ300 m m. In comparison with steels, the Ti-6Al-4V alloy revealed lower fatigue strength under Rϭ0 in spite of almost equal under RϭϪ1. Hence, the fatigue limits determined at 10 10 cycles were below a modified Goodman line under Rϭ0 and 0.3. In comparing the fatigue limits with D K th , the dependency of the fatigue limits on the stress ratios was similar to that of D K th .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.