| ABSTRACT |
Fatigue tests under rotating bending fatigue machine has been carried out to estimate the size effect on strength of structural steel materials in high-humidity enviroment. The size and geometry of the specimens were in accordance with specifications of ASTM E-466. The specimens contains a shallow notch to observe crack initation. The specimen surface and shallow notch were ground with grade 1200 emery paper and then were buff finished. The tests were carried out a variation of diameter size specimen from 8 mm, 2 mm, and 1 mm in humidity enviroment with 60 pct Relative Humidity, 70 pct Relative Humidity, 80 pct Relative Humidity, and 90 pct Relative Humidity. The result show that the fatigue strength increases with decreasing specimen size from diameter of 2 mm and 1 mm of SS400 and S45C steels in high ¿ humidity environment. Ion-exchanged water remarkably reduces the fatigue strength of these steels. The initation propogation behaviors of micro cracks were investigated on the specimen surface. Cracks were observed by a scanning electron microscope(SEM)
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