2.2.2 Fatigue testing
Data on long-life fatigue fracture of LZ91 were obtained by the fatigue
tests, which were conducted on an ultrasonic fatigue test system
(Shimadzu USF-2000) at room temperature in the air. The resonance
interval was 100 ms per 300 ms, and the stress ratio R = -1, up to a
limit of 109 cycles except for failure. Fatigue test
specimens were performed on hourglass-shaped specimens, and the length
of the specimen was designed to give it a resonance of 20 kHz. The
detailed specimen configurations is shown in Figure 3 . Before
fatigue testing, surfaces of specimens were polished in advance by
different grades of abrasive papers and cloths to eliminate the effect
of surface roughness on fatigue behavior. Temperature increment caused
by cyclic loadings used in this work was measured to be no more than 5 ℃
during fatigue tests by an infrared camera (NEC-Avio R500EX). Besides,
compressed cold air was adopted to cool the specimens during fatigue
tests.